Method for manufacturing a ceramic capacitor having varistor characteristics

TECHNICAL FIELD
This invention relates to a method for manufacturing a ceramic capacitor having varistor characteristics used in electronic devices or the like.
BACKGROUND ART
It is known that a capacitor element body with a very large apparent dielectric constant compared with a conventional ceramic dielectric can be obtained by insulating the crystal grain boundaries in a ceramic oxide semiconductor such as SrTiO.sub.3. It is also known that in a varistor where the current rises suddenly at threshold voltage can be obtained by forming electrodes on the element body. These elements are widely used for the circuits in electronic devices or the like to absorb noises. That is, low noise level of the element is advantageous in the application of it as a circuit element mounted with a capacitor while it can be used as a varistor to absorb large surge current.
For example, materials with large apparent dielectric constant of 2,000 to 100,000 are used as materials for a ceramic capacitor of grain boundary barrier type obtained by the following steps; diffusing cupric oxide (CuO) and bismuth trioxide (Bi.sub.2 O.sub.3) from the surface of the sintered body into a grain boundary of polycristalline ceramic semiconductor composed of SrTiO.sub.3 as a main component formed by adding Nb.sub.2 O.sub.5 and TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 compound and sintered in a reducing atmosphere, and forming a resistance layer in a grain boundary by forming a depletion layer in the crystal grain boundaries. The functions of CuO and Bi.sub.2 O.sub.3 as are often used as diffusion materials in a conventional manufacturing method are as follows: CuO containing sufficient oxygen forms a electron trap center in an crystal grain boundaries of the sintered body and traps electrons existing near the crystal grain boundaries of n-type semiconductor SrTiO.sub.3, thereby forming a depletion layer near the grain boundary where electrons do not exist. A capacitor is composed of the materials for a ceramic capacitor of grain boundary barrier type, charging electric loads on both sides of the insulated depletion layer thus formed.
On the other hand, it is known that varistor characteristics which raise the current suddenly at the threshold voltage or more appear when Na oxide or the like is added to a diffused material, Bi.sub.2 O.sub.3. This threshold voltage is also called the varistor voltage and is defined as the voltage that the current of 1 mA flows through varistor elements when a voltage is applied.
In the materials for the aforementioned ceramic capacitor of grain boundary barrier type, the apparent dielectric constant of the sintered body is approximately the value that the dielectric constant of SrTiO.sub.3 (approximately 200) is multiplied by the ratio of the grain diameter of SrTiO.sub.3 in the sintered body to the thickness of said grain boundary depletion layer (grain diameter / the thickness of grain boundary depletion layer). A typical thickness of the grain boundary depletion layer of the SrTiO.sub.3 sintered body is about 0.2 .mu.m. The standards of apparent dielectric constant are 2,000, 20,000, 200,000 corresponding to the grain diameters of the SrTiO.sub.3 sintered body of 2 .mu.m, 20 .mu.m, and 200 .mu.m, respectively.
Bi.sub.2 O.sub.3 which is added to form a barrier in a grain boundary is known as a good conductor of oxygen when Bi.sub.2 O.sub.3 is a .beta.-Bi.sub.2 O.sub.3 and .delta.-Bi.sub.2 O.sub.3 phase. When the surface of the sintered body is coated with Bi.sub.2 O.sub.3 and heat-treated, Bi.sub.2 O.sub.3 is first diffused along the grain boundary of the sintered body and then oxygen is transported by diffusion from outside to the inner portion of the sintered body along Bi.sub.2 O.sub.3 existing in the grain boundary. Bi.sub.2 O.sub.3 works to supply necessary oxygen to form the grain boundary depletion layer. This grain boundary barrier type of ceramic varistor having a high electrostatic capacitance displays excellent electrostatic capacitance and temperature characteristics and provides wide application fields in the industrial fields.
The aforementioned ceramic varistor having a high electrostatic capacitance of grain boundary barrier type is manufactured by the following steps; generally sintering is carried out at a high temperature so as to make the crystal grains in the sintered body as large as possible, by coating the sintered body with pasted cupric oxide and bismuth trioxide, etc. containing sodium oxide, followed by the heat treatment so as to diffuse such oxides as Bi.sub.2 O.sub.3, CuO, NaO into the inner portion of the sintered body and oxidize it.
When a ceramic capacitor with varistor characteristics having a high capacitance is manufactured by the method mentioned above it is required to uniformly diffuse Bi.sub.2 O.sub.3, Na.sub.2 O and CuO or the like from the surface of the sintered body into the inner portion thereof during the process. Nonuniform coating of diffused materials or the like is prone to cause variation in characteristics and, further, it is difficult to diffuse enough Bi.sub.2 O.sub.3, Na.sub.2 O and CuO or the like into the inner portion of the sintered body when it is thick, which causes problems such as limitation of the element size.
In addition, in a grain boundary barrier type ceramic varistor with large electrostatic capacitance, it is electrically required to have uniform characteristics and stability of characteristics against high voltage pulses, therefore a uniform material composition is required.
The present invention has an objective to provide a ceramic capacitor having varistor characteristics which solves these problems.
DISCLOSURE OF THE INVENTION
A ceramic capacitor having varistor characteristics of the present invention, which solved the aforementioned problems, is manufactured by the steps comprising; adding a sintering accelerant, a semiconducting accelerant, a control agent, and a forming agent to perovskite type oxides powder made of SrTiO.sub.3 as a main component, mixing and forming followed by sintering to a porous body; being made semiconductive by reduction and diffusing oxygen and oxidizing the forming agent to form a grain boundary depletion layer in the oxidizing atmosphere so as to form a barrier in the grain boundary and electrodes, wherein said sintering accelerant mainly forms a liquid phase at a high temperature, said semiconducting accelerant can form a solid solution with perovskite type oxides, said control agent controls the grain growth for porous sintering, and said forming agent forms a grain boundary depletion layer which also functions as a control agent to control the grain growth.
As mentioned above, in a conventional method, a capacitor was manufactured by coating the outer surface of the sintered body which was made semiconductive with Bi.sub.2 O.sub.3 or the like, and heat-treating the sintered body in the oxidizing atmosphere so as to diffuse Bi.sub.2 O.sub.3 and oxygen in the whole body, oxidize the crystal grain boundaries to form the depletion layer in the grain boundary. However, the feature of the present invention is to manufacture a capacitor by a special sintering method to form fine porosities along a triple point of crystallite in the sintered body and diffuse oxygen along the porosities in the heat treatment in the oxidizing atmosphere so as to oxidize the grain boundary and form the depletion layer.
One of the important points of the present invention is to form fine porosities along the triple point of crystallite, which is made possible by a sensitive interaction between the sintering accelerant and the a control agent to control the grain growth.
As mentioned above, according to the manufacturing method of the present invention, a uniform porous body can be obtained without complicated processes of coating and diffusing Bi.sub.2 O.sub.3 or the like, and, moreover, the size of the porous body is not subject to any particular restriction.

BRIEF DESCRIPTIONS OF THE DRAWINGS
FIG. 1 is a schematic diagram showing a laminated ceramic capacitor having varistor characteristics according to an example of the present invention and
FIG. 2 is a schematic diagram of a ceramic capacitor having varistor characteristics according to another example of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION
The outline of the present invention will now be described.
A sintering accelerant mainly forming a liquid phase at a high temperature, a semiconducting accelerant which can form a solid solution with perovskite type oxides, a control agent to control the grain growth for porous sintering, and a forming agent to form a grain boundary depletion layer which also functions as a control agent to control the grain growth are added to and mixed with perovskite type oxides powder made of the materials of SrTiO.sub.3 as a main component followed by the pressure molding. When they are calcinated to reduce in the air, or sintered in the reducing atmosphere at a high temperature, the sintering accelerant mainly forming a liquid phase at a high temperature accelerates the reaction between the forming agent to form a grain boundary depletion layer which also functions as a control agent to control the grain growth, the semiconducting accelerant and perovskite type oxides powder made of SrTiO.sub.3 as a main component so as to form the solid solution therebetween. The control agent to control the grain growth controls the growth of crystals and make the sintered body porous. The SrTiO.sub.3 main component phase loses some oxygen by the reduction and becomes a n-type semiconducting substance, reacting with a semiconducting accelerant.
When the sintered body thus obtained is heat-treated in the oxidizing atmosphere, oxygen freely diffuses in the fine porosities formed at the tripple grain junctions in the grain boundary. Oxides including copper, manganese, cobalt or the like deposited in the crystal grain boundaries are further oxidized by oxygen reached thereto. Consequently, electron trap centers composed of cupric oxide, manganese oxide, cobalt oxide or the like as a main component are formed in the grain boundary. These electron trap centers trap electrons from the grains in the low resistant n-type SrTiO.sub.3 semiconductors formed by the reduction, therefore forming the depletion layer of carriers along the grain boundary. The depletion layer thus obtained has an excellent insulating characteristic and a capacitor with varistor characteristics having high capacitance is obtained when the voltage is applied to the sintered body and electric loads are charged on both sides of the insulated depletion. This manufacturing method does not require the processes to coat and diffuse CuO, Bi.sub.2 O.sub.3 or the like after the sintered body is made semiconductive and a ceramic capacitor having varistor characteristic is readily provided.
FIG. 1 is a schematic diagram showing a laminated ceramic capacitor having varistor characteristics according to an example of the present invention comprising a ceramic capacitor having varistor characteristics 1, inner electrodes 2, an outer electrode 3. FIG. 2 is a schematic diagram of a ceramic capacitor having varistor characteristics according to another example of the present invention comprising a ceramic 4 with varistor characteristics having high capacitance, an electrode 5, and a lead line 6.
The specific examples of the present invention will be described hereinafter.
EXAMPLE 1
A sintering accelerant TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 (ratio of 20:30:45 wt %) of 0.05 to 6.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.02 to 3.0 wt % which can form a solid solution with perovskite type oxides, a good oxygen conductive solid electrolyte ZrO.sub.2 of 0.05 to 12.0 wt % which functions as a control agent to control the grain growth, and a forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.1 to 6.0 wt %) to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to strontium titanat (SrTiO.sub.3) obtained by pyrolyzing titanyl strontium oxalate (SrTio(C.sub.2 O.sub.4).sub.2 .multidot.4H.sub.2 O) and mixed well followed by calcination at 900.degree. C. Then it was ground in a wet state followed by drying, making the grain, and molding, sintering at 1300.degree. C. in the air. It was re-ground in a wet state, made into paste using resin and organic solutions so as to form a sheet, printed platinum paste for inner electrodes were laminated thereon, sintered at 1400.degree. C. in the air followed by the hydrogen reduction at 1300.degree. C., and heat-treated at 950.degree. C. in the air. Finally, electrodes were adjusted so as to connect inner electrodes with outer electrodes, thereby completing the manufacture of a laminated ceramic capacitor having grain boundary varistor characteristics of FIG. 1. Electric characteristics of the laminated ceramic capacitor were measured and the results are shown in Table 1. The sintering accelerant TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 (ratio of 20:30:45 wt %) was obtained by weighing commercial TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 powder according to the predetermined weight ratio, mixing, calcinating at 1200.degree. C., and grinding. The forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 to form a grain boundary depletion layer which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, Nb.sub.2 O.sub.5, CuO or the like, calcinating at 1000.degree. C., and grinding.
The size of the varistor after sintering was approximately 4 mm square and about 0.6 mm in thickness and composed of 8 layers of the dielectrics each of which was about 70 .mu.m in thickness. The apparent dielectric constant .epsilon. was calculated from the value of the capacitance (measurement 1 kHz) of the laminated varistor. The grain diameter in the sintered body was obtained by examining a cross section after polishing under an optical microscope, to the surface of which Bi.sub.2 O.sub.3 series metallic soap was applied and heat-treated at 1000.degree. C. to make the grain boundary clear.
TABLE 1__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 growth ZrO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 2.5 3200 9.5 440 4.50.1 0.2 0.5 0.8 6.5 7300 1.7 450 120.5 0.2 0.5 0.8 7.0 7500 0.9 400 121.0 0.2 0.5 0.8 7.5 8300 0.9 3800 113.0 0.2 0.5 0.8 6.5 7400 1.0 430 115.0 0.2 0.5 0.8 7.5 8200 0.9 360 116.0 0.2 0.5 0.8 7.5 8100 0.8 350 121.0 0.02 0.5 0.8 6.0 7200 35.0 230 4.51.0 0.05 0.5 0.8 7.0 7600 1.6 430 111.0 0.5 0.5 0.8 7.0 7500 0.7 390 121.0 2.0 0.5 0.8 6.5 7200 1.8 450 111.0 3.0 0.5 0.8 4.0 6200 15.0 380 4.01.0 0.2 0.1 0.8 5.0 6900 9.9 250 3.01.0 0.2 0.2 0.8 7.5 8100 1.3 380 121.0 0.2 0.5 0.8 7.5 8400 0.6 350 111.0 0.2 2.0 0.8 8.0 8800 0.8 350 111.0 0.2 4.0 0.8 7.5 8300 1.9 370 121.0 0.2 6.0 0.8 7.0 7500 14.1 210 4.01.0 0.2 0.5 0.05 7.0 4100 26.5 270 4.51.0 0.2 0.5 0.1 7.5 8300 1.8 380 121.0 0.2 0.5 1.0 8.0 8600 0.9 340 121.0 0.2 0.5 5.0 8.0 8700 1.1 370 111.0 0.2 0.5 10.0 6.5 7300 1.6 430 111.0 0.2 0.5 12.0 5.5 6400 7.7 270 4.0__________________________________________________________________________
As is apparent from the results in Table 1, the present material obtained by adding to SrTiO.sub.3 a sintering accelerant TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 0.1 to 10.0 wt %, and a forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 of 0.2 to 4.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high electrostatic capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body was uniform and approximately 7 .mu.m in thickness and the dielectric loss was 2.0% or less and the apparent dielectric constant was 7,000 or more. The rising voltage V.sub.1 mA of the materials as a varistor was 300 to 500 V/mm and the resistance nonlinear exponent .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as withstanding-surge-current as a varistor, the ratio of limited voltage representing the resistance nonlinear exponent in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained. When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 2)
A sintering accelerant of 1.0 wt % selected from TiO.sub.2 --MgO--SiO.sub.2 series (for example, ratio of 30:30:40 wt %), TiO.sub.2 --MnO--SiO.sub.2 series (for example, ratio of 10:50:40 wt %), TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 series (for example, ratio of 20:35:45 wt %) mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.04 wt % which can form a solid solution with perovskite type oxides, a good oxygen conductive solid electrolyte ZrO.sub.2 of 0.2 to 8.0 wt % which functions as a control agent to control the grain growth, and a forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 of 0.4 to 3.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to commercial industrial strontium titanat (SrTiO.sub.3) and mixed well followed by calcination at 900.degree. C. Then it was ground in a wet state followed by drying, making grain, and molded into like a disk shape, sintered at 1380.degree. C. in the reducing atmosphere composed of 95% of nitrogen and 5% of hydrogen. It was heat-treated at 950.degree. C. in the air and silver electrodes were formed on both sides of the disk, thereby completing the manufacture of a ceramic capacitor having grain boundary varistor characteristics of FIG. 2. Electric characteristics of the laminated ceramic capacitor were measured and the results are shown in Table 2.
The sintering accelerant TiO.sub.2 -MgO-SiO.sub.2 series (for example, ratio of 30:30:40 wt %) was obtained by weighing commercial TiO.sub.2, MgO, SiO.sub.2 powder according to the predetermined weight ratio, mixing, calcinating at 1200.degree. C., and grinding. The forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 to form a grain boundary depletion layer which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, Nb.sub.2 O.sub.5 and CuO, calcinating at 900.degree. C., and grinding.
TABLE 2__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 growth ZrO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 2.0 7.5 8400 1.6 380 131.0 0.4 3.0 2.0 6.5 7300 1.2 450 121.0 0.4 1.0 0.2 7.5 8100 1.5 400 111.0 0.4 1.0 8.0 7.5 8300 0.9 370 12TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 2.0 7.0 7500 1.4 380 131.0 0.4 3.0 2.0 6.5 7200 1.1 470 131.0 0.4 1.0 0.2 7.0 7600 1.5 420 111.0 0.4 1.0 8.0 6.5 7400 0.9 440 12TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 2.0 8.0 8600 1.7 360 111.0 0.4 3.0 2.0 8.5 9200 1.3 320 131.0 0.4 1.0 0.2 8.5 9300 1.2 340 111.0 0.4 1.0 8.0 8.0 8700 0.9 350 11__________________________________________________________________________
As is apparent from the results in Table 2, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a good oxygen conductive electrolyte ZrO.sub.2 of 0.2 to 8.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 3.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 1.
EXAMPLE 3
A sintering accelerant of 3.0 wt % of TiO.sub.2 --MgO--SiO.sub.2 series (for example, ratio of 0:30:40 wt %) mainly forming a liquid phase at a high temperature, semiconducting accelerants WO.sub.3, Nb.sub.2 O.sub.5, La.sub.2 O.sub.3 and Y.sub.2 O.sub.3 of 0.05 to 2.0 wt %, a good oxygen conductive solid electrolyte ZrO.sub.2 of 1.5 wt % which functions as a control agent to control the grain growth, and a forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to commercial industrial strontium titanat (SrTiO.sub.3) and mixed well followed by calcination at 900.degree. C. Then it was ground in a wet state followed by drying, making grain, and molding, sintered at 380.degree. C. in the reducing atmosphere composed of 95% of nitrogen and 5% of hydrogen. It was heat-treated at 1050.degree. C. in the air and electrodes were formed, thereby completing the manufacture of a ceramic capacitor having grain boundary varistor characteristics of FIG. 2. Electric characteristics of the laminated ceramic capacitor were measured and the results are shown in Table 3.
The sintering accelerant TiO.sub.2 --MgO--SiO.sub.2 series (ratio of 30:30:40 wt %) was obtained by weighing commercial TiO.sub.2, MgO, SiO.sub.2 powder according to the predetermined weight ratio, mixing, calcinating at 1200.degree. C., and grinding. The forming agent to form a grain boundary depletion layer which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, Nb.sub.2 O.sub.5 and CuO, calcinating at 900.degree. C., and grinding.
TABLE 3__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth ZrO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 7.5 8300 1.2 380 12 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 7.0 7300 1.5 410 13 0.05 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 6.5 7200 1.1 430 12 0.05 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 7.0 7400 1.2 420 13 0.05 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 7.5 8400 1.4 370 13 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 7.5 8300 1.0 390 13 0.50 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 7.5 8200 1.4 380 13 0.50 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 7.5 8400 1.1 390 12 0.50 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.3 Ba.sub.0.1 Ca.sub.0.1 1.5 7.0 7500 1.7 400 11 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 6.5 7100 1.8 450 12 2.0 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 6.5 7300 1.6 420 11 2.0 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 7.0 7300 1.7 410 11 2.0 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 3, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 series of 3.0 wt %, a semiconducting accelerant of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 1.
EXAMPLE 4
A capacitor was manufactured according to the method in Example 1 including the manufacturing method for other materials, sintering accelerant or the like, except that the forming agent Sr(Cu.sub.1/3 Ta.sub.2/3)O.sub.3 (0.1 to 0.6 wt %) was used instead of the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.1 to 0.6 wt %) to form a grain boundary depletion and electric characteristics thereof were measured in the same method as Example 1 and the results are shown in Table 4.
The forming agent Sr(Cu.sub.1/3 Ta.sub.2/3)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, Ta.sub.2 O.sub.5, and CuO, sintering at 1000.degree. C. and grinding.
TABLE 4__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Cu.sub.1/3 Ta.sub.2/3)O.sub.3 growth ZrO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 2.5 3100 7.4 370 7.50.1 0.2 0.5 0.8 6.0 7100 1.7 490 120.5 0.2 0.5 0.8 6.5 7300 1.8 460 111.0 0.2 0.5 0.8 6.5 7400 1.1 440 123.0 0.2 0.5 0.8 6.5 7300 0.8 450 115.0 0.2 0.5 0.8 7.0 7500 1.6 420 126.0 0.2 0.5 0.8 7.5 8200 1.4 380 121.0 0.02 0.5 0.8 7.5 5500 28.0 250 6.51.0 0.05 0.5 0.8 6.5 7300 1.8 470 111.0 0.5 0.5 0.8 7.5 8100 0.9 370 121.0 2.0 0.5 0.8 7.0 7600 1.7 430 111.0 3.0 0.5 0.8 4.5 5800 25.9 320 7.01.0 0.2 0.1 0.8 5.0 6000 8.4 310 6.01.0 0.2 0.2 0.8 6.5 7200 1.5 470 121.0 0.2 1.0 0.8 7.5 8300 0.7 380 121.0 0.2 2.0 0.8 7.0 7400 0.6 390 121.0 0.2 5.0 0.8 6.5 7400 1.6 430 111.0 0.2 6.0 0.8 6.0 6100 18.1 290 6.01.0 0.2 0.5 0.05 4.5 3500 31.4 200 4.51.0 0.2 0.5 0.1 6.5 7200 1.5 450 111.0 0.2 0.5 1.0 7.0 7700 0.7 420 111.0 0.2 0.5 3.0 7.0 7500 1.0 390 121.0 0.2 0.5 10.0 6.5 7800 1.8 440 11.01.0 0.2 0.5 12.0 5.5 6200 14.5 270 7.5__________________________________________________________________________
As is apparent from the results in Table 4, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 0.1 to 10.0 wt %, and a forming agent Sr(Cu.sub.1/3 Ta.sub.2/3)O.sub.3 of 0.2 to 5.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high electrostatic capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 6.0 to 7.0 .mu.m and the dielectric loss was 20% or less and the apparent dielectric constant was 7000 or more.
The riser voltage V.sub.1 mA of the materials as a varistor was 350 to 500 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the resistance non-linearity coeffecient in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained.
When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 5
A capacitor was manufactured according to the method in Example 2 including the manufacturing method for other materials, sintering accelerant or the like, except that the forming agent Sr(Cu.sub.1/3 Ta.sub.2/3)O.sub.3 (0.4 to 4.0 wt %) was used instead of the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.4 to 3.0 wt %) to form a grain boundary depletion and electric characteristics thereof were measured by the same method as Example 2 and the results are shown in Table 5. The forming agent Sr(Cu.sub.1/3 Ta.sub.2/3)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, Ta.sub.2 O.sub.5, and CuO, sintering at 900.degree. C. and grinding.
TABLE 5__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Cu.sub.1/3 Ta.sub.2/3)O.sub.3 growth ZrO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 2.0 6.0 7100 1.8 480 131.0 0.4 4.0 2.0 6.0 7200 1.1 490 121.0 0.4 1.0 0.2 6.0 7200 1.7 490 121.0 0.4 1.0 8.0 6.5 7300 1.0 470 11TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 2.0 6.0 7100 1.7 490 131.0 0.4 4.0 2.0 6.5 7100 1.2 450 121.0 0.4 1.0 0.2 6.5 7300 1.9 440 131.0 0.4 1.0 8.0 7.0 7500 1.2 420 12TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 2.0 6.5 7200 1.8 460 131.0 0.4 4.0 2.0 7.0 7400 1.2 400 121.0 0.4 1.0 0.2 7.0 7600 1.8 410 111.0 0.4 1.0 8.0 6.5 7400 0.9 450 12__________________________________________________________________________
As is apparent from the results in Table 5, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a good oxygen conductive solid electrolyte ZrO.sub.2 of 0.2 to 8.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 4.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 4.
EXAMPLE 6
The forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 of 2.0 wt % was added instead of the forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 of 2.0 wt % to form a grain boundary depletion of Example 3. The forming agent to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, Ta.sub.2 O.sub.5, and CuO, sintering at 900.degree. C. and grinding.
The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 3 and electric characteristics thereof were measured in the same method as Example 3 and the results are shown in Table 6.
TABLE 6__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth ZrO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 7.5 8300 0.8 380 11 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 6.5 7300 0.9 470 12 0.05 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 6.0 7100 1.0 490 12 0.05 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 6.5 7300 1.1 460 11 0.05 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 7.0 7500 1.8 420 13 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 6.5 7200 1.0 440 12 0.50 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 6.5 7400 1.3 460 13 0.50 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 6.5 7200 1.1 470 13 0.50 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 7.0 7600 1.6 410 11 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 6.5 7300 1.7 460 11 2.0 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 6.0 7100 1.8 480 12 2.0 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 6.0 7200 1.8 490 11 2.0 (Cu.sub.1/3 Ta.sub.2/3)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 6, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 -MgO-SiO.sub.2 series of 3.0 wt %, a semiconducting accelerant of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 of 2.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 4.
EXAMPLE 7
The forming agent Sr(Co.sub.1/3 Nb.sub.2/3)O.sub.3 (0.1 to 8.0 wt %) was added instead of the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.1 to 6.0 wt %) to form a grain boundary depletion of Example 1. The manufacturing method for other materials, sintering accelerant or the like, was same as Example 1 and electric characteristics thereof were measured in the same method as Example 1 and the results are shown in Table 7. The forming agent to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, Nb.sub.2 O.sub.5, and CuO, sintering at 1000.degree. C. and grinding.
TABLE 7__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Co.sub.1/3 Nb.sub.2/3)O.sub.3 growth ZrO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 2.5 3500 23.0 230 4.50.1 0.2 0.5 0.8 8.0 8700 2.3 320 110.5 0.2 0.5 0.8 8.5 9200 2.4 310 121.0 0.2 0.5 0.8 8.5 9100 2.1 320 123.0 0.2 0.5 0.8 8.0 8600 2.3 340 125.0 0.2 0.5 0.8 8.0 8700 2.1 340 116.0 0.2 0.5 0.8 8.5 9200 2.8 310 121.0 0.02 0.5 0.8 5.0 6100 31.0 170 3.01.0 0.05 0.5 0.8 7.5 8300 2.2 360 121.0 0.5 0.5 0.8 8.0 8700 2.6 350 111.0 2.0 0.5 0.8 8.5 9300 2.4 330 111.0 3.0 0.5 0.8 6.5 6100 22.5 190 3.51.0 0.2 0.1 0.8 7.0 6300 18.5 180 4.01.0 0.2 0.2 0.8 7.5 8400 2.3 370 111.0 0.2 0.5 0.8 8.0 8800 2.5 330 121.0 0.2 2.0 0.8 8.5 9200 2.4 320 121.0 0.2 6.0 0.8 8.0 8600 2.2 340 121.0 0.2 8.0 0.8 6.0 6200 12.5 220 4.51.0 0.2 0.5 0.05 6.5 6700 17.5 210 5.01.0 0.2 0.5 0.1 7.5 8200 2.5 350 121.0 0.2 0.5 1.0 8.5 9400 2.4 310 121.0 0.2 0.5 5.0 8.5 9600 2.6 320 121.0 0.2 0.5 10.0 8.0 8700 2.3 340 111.0 0.2 0.5 12.0 6.0 6600 18.0 230 6.5__________________________________________________________________________
As is apparent from the results in Table 7, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.3 of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 0.1 to 10.0 wt %, and a forming agent Sr(Co.sub.1/3 Nb.sub.2/3)O.sub.3 of 0.2 to 6.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high electrostatic capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 8 .mu.m and the dielectric loss was 3.0% or less and the apparent dielectric constant was 800,000 or more. The riser voltage V.sub.1 mA of the materials as a varistor was 300 to 400 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the non-linearity resistive characteristics in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained.
When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 8
The forming agent Sr(Co.sub.1/3 Nb.sub.2/3)O.sub.3 (0.4 to 4.0 wt %) was added instead of the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.4 to 3.0 wt %) to form a grain boundary depletion of Example 2. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 2 and electric characteristics thereof were measured by the same method as Example 2. The results are shown in Table 8.
The forming agent Sr(Co.sub.1/3 Nb.sub.2/3)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, Nb.sub.2 O.sub.5, and CoO, sintering at 900.degree. C. and grinding.
TABLE 8__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Co.sub.1/3 Nb.sub.2/3)O.sub.3 growth ZrO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 2.0 8.5 9000 2.5 320 111.0 0.4 4.0 2.0 8.0 8600 2.3 340 111.0 0.4 1.0 0.2 8.5 9400 2.4 330 121.0 0.4 1.0 8.0 8.0 8800 2.2 350 12TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 2.0 8.5 9300 2.6 320 111.0 0.4 4.0 2.0 7.5 8400 2.5 360 121.0 0.4 1.0 0.2 8.5 9300 2.6 310 111.0 0.4 1.0 8.0 8.0 8700 2.5 340 11TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 2.0 8.0 8600 2.4 330 121.0 0.4 4.0 2.0 7.5 8300 2.4 370 111.0 0.4 1.0 0.2 8.5 9400 2.3 320 111.0 0.4 1.0 8.0 8.0 8800 2.6 350 12__________________________________________________________________________
As is apparent from the results in Table 8, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a good oxygen conductive solid electrolyte ZrO of 0.2 to 8.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 4.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high electrostatic capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 7.
EXAMPLE 9
The forming agent Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 or Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 of 2.0 wt % was added instead of the forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 of 2.0 wt % to form a grain boundary depletion of Example 3. The forming agent to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, Nb.sub.2 O.sub.5, and CoO, sintering at 900.degree. C. and grinding. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 3 and electric characteristics thereof were measured by the same method as Example 3. The results are shown in Table 9.
TABLE 9__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth ZrO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 8.0 8600 2.3 330 12 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 8.0 8800 2.1 340 11 0.05 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 7.5 8400 2.5 360 12 0.05 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 8.5 9000 2.8 310 11 0.05 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 8.0 8500 2.4 330 12 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 8.5 9200 2.4 310 12 0.50 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 8.5 9100 2.2 320 12 0.50 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 8.0 8800 2.3 350 11 0.50 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 7.5 8300 2.5 350 12 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 8.0 8700 2.5 320 12 2.0 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 7.5 8200 2.7 340 11 2.0 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 8.0 8800 2.6 330 11 2.0 (Co.sub.1/3 Nb.sub.2/3)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 9, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 series of 3.0 wt %, a semiconducting accelerant of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high electrostatic capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 7.
EXAMPLE 10
The forming agent Sr(Co.sub.1/3 Ta.sub.2/3)O.sub.3 (.sub.0.1 to 8.0 wt %) was added instead of the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.1 to 6.0 wt %) to form a grain boundary depletion of Example 1. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 1 and electric characteristics thereof were measured by the same method as Example 1. The results are shown in Table 10.
The forming agent Sr(CO.sub.1/3 Ta.sub.2/3)O to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, Ta.sub.2 O.sub.5, and CoO, sintering at 1000.degree. C. and grinding.
TABLE 10__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Co.sub.1/3 Ta.sub.2/3)O.sub.3 growth ZrO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 3.0 3400 15.0 160 4.50.1 0.2 0.5 0.8 7.0 7600 1.2 380 130.5 0.2 0.5 0.8 7.5 8300 1.3 340 121.0 0.2 0.5 0.8 8.0 8700 1.1 310 123.0 0.2 0.5 0.8 8.0 8600 1.4 320 125.0 0.2 0.5 0.8 8.5 9100 1.8 310 136.0 0.2 0.5 0.8 8.5 9300 1.6 320 131.0 0.02 0.5 0.8 4.0 4800 45.0 150 4.01.0 0.05 0.5 0.8 7.0 7300 1.5 360 131.0 0.5 0.5 0.8 7.5 8400 1.6 340 121.0 2.0 0.5 0.8 8.0 8800 1.5 310 121.0 3.0 0.5 0.8 3.5 4000 18.5 240 5.51.0 0.2 0.1 0.8 9.0 6200 32.0 250 5.01.0 0.2 0.2 0.8 7.5 8100 1.4 360 131.0 0.2 0.5 0.8 8.0 8700 1.2 330 121.0 0.2 2.0 0.8 8.0 8900 1.8 320 131.0 0.2 7.0 0.8 8.5 9200 1.2 310 131.0 0.2 8.0 0.8 4.5 5200 12.5 180 5.51.0 0.2 0.5 0.05 7.5 6500 18.0 220 7.01.0 0.2 0.5 0.1 7.5 8300 1.8 350 131.0 0.2 0.5 1.0 8.0 8300 1.4 330 121.0 0.2 0.5 5.0 7.5 8200 1.0 340 121.0 0.2 0.5 10.0 7.0 7500 1.5 360 131.0 0.2 0.5 12.0 6.0 6100 22.0 210 6.0__________________________________________________________________________
As is apparent from the results in Table 10, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 0.1 to 10.0 wt%, and a forming agent Sr(Co.sub.1/3 Ta.sub.2/3)O.sub.3 of 0.2 to 7.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high electrostatic capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 7.0 to 8.0 .mu.m and the dielectric loss was 2.0% or less and the apparent dielectric constant was 7,000 or more. The riser voltage V.sub. 1 mA of the materials as a varistor was 300 to 400 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the resistance non-linearity coeffecient in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained.
When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 11
The forming agent Sr(Co.sub.1/3 Ta.sub.2/3)O.sub.3 (0.4 to 6.0 wt %) was added instead of the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.4 to 3.0 wt %) to form a grain boundary depletion of Example 2. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 2 and electric characteristics thereof were measured by the same method as Example 2. The results are shown in Table 11.
The forming agent Sr(Co.sub.1/3 Ta.sub.2/3)O.sub.3 to form a grain boundary depletion was obtained by mixing commercial SrCO.sub.3, Ta.sub.2 O.sub.5 and CoO sintering at 900.degree. C. and grinding.
TABLE 11__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Co.sub.1/3 Ta.sub.2/3)O.sub.3 growth ZrO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 2.0 8.5 9500 1.4 320 131.0 0.4 6.0 2.0 7.5 8300 1.5 360 121.0 0.4 1.0 0.2 8.0 8500 1.4 340 121.0 0.4 1.0 8.0 8.0 8700 1.7 330 13TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 2.0 8.5 9100 1.4 320 121.0 0.4 6.0 2.0 8.0 8600 1.6 360 121.0 0.4 1.0 0.2 8.0 8800 1.5 330 131.0 0.4 1.0 8.0 7.5 8400 1.3 350 12TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 2.0 8.5 9400 1.8 310 121.0 0.4 6.0 2.0 8.0 8600 1.6 340 121.0 0.4 1.0 0.2 8.5 9300 1.3 310 131.0 0.4 1.0 8.0 7.5 8100 1.7 350 12__________________________________________________________________________
As is apparent from the results in Table 11, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a good oxygen conductive solid electrolyte ZrO.sub.2 of 0.2 to 8.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 6.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high electrostatic capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 10.
EXAMPLE 12
The forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 of 2.0 wt % was added instead of the forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 or Sr.sub.0.60 Ba.sub.0.2 Ca.sub.0.2 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 of 2.0 wt % to form a grain boundary depletion of Example 3. The forming agent to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, Ta.sub.2 O.sub.5, and CoO sintering at 900.degree. C. and grinding.
The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 3 and electric characteristics thereof were measured by the same method as Example 3 and the results are shown in Table 12.
TABLE 12__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth ZrO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 8.5 9300 1.3 310 12 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 8.0 8800 1.2 330 13 0.05 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 7.5 8500 1.3 350 12 0.05 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 8.0 8700 1.3 320 13 0.05 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 8.0 8900 1.6 320 13 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 8.0 8800 1.5 330 12 0.50 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 8.5 9200 1.6 320 12 0.50 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 7.5 8200 1.4 370 13 0.50 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 8.0 8700 1.4 330 12 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 8.5 9100 1.5 310 11 2.0 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 7.5 8300 1.6 360 11 2.0 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 7.5 8400 1.6 370 13 2.0 (Co.sub.1/3 Ta.sub.2/3)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 12, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 -MgO-SiO.sub.2 series of 3.0 wt %, a semiconducting accelerant of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high electrostatic capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 10.
EXAMPLE 13
The forming agent Sr(Cu.sub.1/3 W.sub.2/3)O.sub.3 (0.1 to 6.0 wt %) was added instead of the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.1 to 6.0 wt %) to form a grain boundary depletion of Example 1. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 1 and electric characteristics thereof were measured by the same method as Example 1. The results are shown in Table 13. The forming agent Sr(Cu.sub.1/2 W.sub.1/2)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, WO.sub.3, and CoO, sintering at 1000.degree. C. and grinding.
TABLE 13__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Cu.sub.1/2 W.sub.1/2)O.sub.3 growth ZrO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 2.5 3300 19.5 190 4.00.1 0.2 0.5 0.8 5.0 6200 1.6 610 120.5 0.2 0.5 0.8 5.0 5800 1.6 580 121.0 0.2 0.5 0.8 5.5 6300 1.3 540 113.0 0.2 0.5 0.8 6.0 6500 1.7 480 125.0 0.2 0.5 0.8 6.0 6800 1.4 500 116.0 0.2 0.5 0.8 6.0 6700 1.8 480 121.0 0.02 0.5 0.8 3.5 4200 26.5 180 4.51.0 0.05 0.5 0.8 5.0 6100 1.7 630 121.0 0.5 0.5 0.8 5.0 5800 1.8 590 111.0 2.0 0.5 0.8 5.5 6200 1.9 570 121.0 3.0 0.5 0.8 4.5 5100 24.0 220 5.51.0 0.2 0.1 0.8 5.0 5900 15.5 240 5.01.0 0.2 0.2 0.8 5.5 6300 1.8 550 111.0 0.2 0.5 0.8 6.0 6600 1.6 530 121.0 0.2 2.0 0.8 6.0 6700 1.6 490 121.0 0.2 5.0 0.8 5.5 6400 1.8 540 111.0 0.2 6.0 0.8 5.0 6000 10.5 180 5.01.0 0.2 0.5 0.05 5.5 6400 14.0 150 6.01.0 0.2 0.5 0.1 5.5 6200 1.9 580 121.0 0.2 0.5 1.0 5.0 6100 1.9 600 111.0 0.2 0.5 5.0 5.5 6400 1.6 550 121.0 0.2 0.5 10.0 5.0 5800 1.8 620 121.0 0.2 0.5 12.0 4.0 4700 12.0 190 4.0__________________________________________________________________________
As is apparent from the results in Table 13, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 0.1 to 10.0 wt %, and a forming agent Sr(Cu.sub.1/2 W.sub.1/2)O.sub.3 of 0.2 to 5.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high electrostatic capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 5.0 to 6.0 .mu.m and the dielectric loss was 2.0% or less and the apparent dielectric constant was 5500 or more. The riser voltage V.sub.1 mA of the materials as a varistor was 450 to 650 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the nonlinearity resistive charac-teristics in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained.
When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 14
The forming agent Sr(Cu.sub.1/2 W.sub.1/2)O.sub.3 (0.4 to 4.0 wt %) was added instead of the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.4 to 3.0 wt %) to form a grain boundary depletion of Example 2. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 2 and electric characteristics thereof were measured by the same method as Example 2. The results are shown in Table 14.
The forming agent Sr(Cu.sub.1/2 W.sub.1/2)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, WO.sub.3 and CoO sintering at 900.degree. C. and grinding.
TABLE 14__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Cu.sub.1/2 W.sub.1/2)O.sub.3 growth ZrO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 2.0 6.0 6500 1.6 480 131.0 0.4 4.0 2.0 5.5 6200 1.5 560 121.0 0.4 1.0 0.2 6.0 6600 1.6 520 121.0 0.4 1.0 8.0 5.5 6400 1.5 530 11TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 2.0 5.5 6400 1.4 550 121.0 0.4 4.0 2.0 5.0 6000 1.4 620 131.0 0.4 1.0 0.2 6.0 6700 1.3 530 121.0 0.4 1.0 8.0 5.5 6200 1.6 580 11TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 2.0 5.5 6300 1.5 530 121.0 0.4 4.0 2.0 5.0 5900 1.3 580 121.0 0.4 1.0 0.2 6.0 6600 1.4 500 131.0 0.4 1.0 8.0 5.5 6100 1.2 540 13__________________________________________________________________________
As is apparent from the results in Table 14, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 -MgO-SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a solid electrolyte ZrO.sub.2 of 0.2 to 8.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 4.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 13.
EXAMPLE 15
The forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Cu.sub.1/2 W.sub.1/2) O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Cu.sub.1/2 W.sub.1/2)O.sub.3 of 2.0 wt % was added instead of the forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 of 2.0 wt % to form a grain boundary depletion of Example 3. The forming agent to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, WO.sub.2, and CuO, sintering at 900.degree. C. and grinding.
The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 3 and electric characteristics thereof were measured by the same method as Example 3. The results are shown in Table 15.
TABLE 15__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth ZrO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 5.5 6600 1.9 530 12 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 5.0 6300 1.8 580 11 0.05 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 5.5 6500 1.5 580 12 0.05 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 5.0 6100 1.8 630 11 0.05 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 5.0 6200 1.7 610 13 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 5.5 6400 1.7 560 12 0.50 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 5.5 6300 1.9 540 13 0.50 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 5.0 6200 1.8 590 12 0.50 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 6.0 6700 1.8 520 11 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 5.0 6300 1.7 600 11 2.0 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 5.5 6300 1.6 570 11 2.0 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 6.0 6600 1.7 510 12 2.0 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 15, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 -MgO-SiO.sub.2 series of 3.0 wt %, a semiconducting accelerant of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 13.
EXAMPLE 16
The forming agent Sr(Co.sub.1/2 W.sub.1/2)O.sub.3 (0.1 to 7.0 wt %) was added instead of the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.1 to 6.0 wt %) to form a grain boundary depletion of Example 1. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 1 and electric characteristics thereof were measured by the same method as Example 1. The results are shown in Table 16. The forming agent Sr(Co.sub.1/2 W.sub.1/2)O.sub.3 to form a grain boundary depletion was obtained by mixing commercial SrCO.sub.3, WO.sub.3, and CoO, sintering at 1000.degree. C. and grinding.
TABLE 16__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Co.sub.1/2 W.sub.1/2)O.sub.3 growth ZrO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 2.0 2200 35.0 190 3.00.1 0.2 0.5 0.8 4.5 5500 1.9 650 120.5 0.2 0.5 0.8 5.0 5700 1.5 680 121.0 0.2 0.5 0.8 5.0 5700 1.5 620 143.0 0.2 0.5 0.8 5.0 5600 1.7 600 125.0 0.2 0.5 0.8 5.5 5900 1.6 560 136.0 0.2 0.5 0.8 5.5 5800 1.6 540 121.0 0.02 0.5 0.8 4.5 5300 28.0 150 4.01.0 0.05 0.5 0.8 4.5 5600 1.8 660 111.0 0.5 0.5 0.8 5.0 5800 1.5 630 111.0 2.0 0.5 0.8 5.5 5700 1.5 540 131.0 3.0 0.5 0.8 4.5 5000 15.5 140 3.51.0 0.2 0.1 0.8 5.5 6300 21.5 130 4.51.0 0.2 0.2 0.8 4.5 5400 1.6 660 131.0 0.2 0.5 0.8 5.0 5600 1.4 590 131.0 0.2 2.0 0.8 5.5 5900 1.6 530 141.0 0.2 5.0 0.8 5.0 5800 1.8 610 131.0 0.2 7.0 0.8 4.5 5500 14.5 200 4.01.0 0.2 0.5 0.05 6.0 6900 35.0 190 3.51.0 0.2 0.5 0.1 5.0 5700 1.7 590 121.0 0.2 0.5 1.0 5.5 6100 1.6 570 121.0 0.2 0.5 5.0 5.5 6200 1.6 560 131.0 0.2 0.5 10.0 4.5 5600 1.5 640 121.0 0.2 0.5 12.0 4.0 4600 12.0 220 5.5__________________________________________________________________________
As is apparent from the results in Table 16, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 0.1 to 10.0 wt %, and a forming agent Sr(Co.sub.1/2 W.sub.1/2)O.sub.3 of 0.2 to 5.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 4.5 to 5.5 .mu.m and the dielectric loss was 2.0% or less and the apparent dielectric constant was 5000 or more. The riser voltage V.sub.1 mA of the materials as a varistor was 500 to 700 V/mm and the resistance non-linearity coeffecient o is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the nonlinearity resistive charac-teristics in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained.
When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 17
The forming agent Sr(Co.sub.178 W.sub.1/2)O.sub.3 (0.4 to 4.0 wt %) was added instead of the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.4 to 3.0 wt %) to form a grain boundary depletion of Example 2. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 2 and electric characteristics thereof were measured by the same method as Example 2. The results are shown in Table 17.
The forming agent Sr(Co.sub.1/3 W.sub.2/3)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, WO.sub.3 and CoO sintering at 900.degree. C. and grinding.
TABLE 17__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Co.sub.1/2 W.sub.1/2)O.sub.3 growth ZrO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 2.0 5.0 5800 1.5 590 111.0 0.4 4.0 2.0 4.5 5400 1.3 640 121.0 0.4 1.0 0.2 5.5 6100 1.4 530 131.0 0.4 1.0 8.0 5.0 5600 1.2 610 12TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 2.0 5.5 6000 1.6 560 111.0 0.4 4.0 2.0 5.0 5700 1.5 620 131.0 0.4 1.0 0.2 5.5 6100 1.6 550 111.0 0.4 1.0 8.0 5.0 5600 1.5 590 12TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 2.0 5.5 5900 1.4 580 131.0 0.4 4.0 2.0 4.5 5500 1.4 650 121.0 0.4 1.0 0.2 5.5 6000 1.3 560 121.0 0.4 1.0 8.0 5.0 5700 1.6 620 11__________________________________________________________________________
As is apparent from the results in Table 17, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 -MgO-SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a solid electrolyte ZrO.sub.2 of 0.2 to 8.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 4.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 16.
EXAMPLE 18
The forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Co.sub.1/2 W.sub.1/2) O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Co.sub.1/2 W.sub.1/2)O.sub.3 of 2.0 wt % was added instead of the forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.O.1 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.1/3 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 of 2.0 wt % to form a grain boundary depletion of Example 3. The forming agent to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, WO.sub.3, and CoO, sintering at 900.degree. C. and grinding.
The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 3 and electric characteristics thereof were measured by the same method as Example 3. The results are shown in Table 18.
TABLE 18__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth ZrO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.5 5600 1.3 630 12 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.5 5600 1.2 650 13 0.05 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 5.0 5900 1.2 590 13 0.05 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 5.0 6200 1.4 610 12 0.05 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 4.5 5700 1.3 670 13 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 5.0 6100 1.4 600 13 0.50 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 4.5 5800 1.3 660 11 0.50 (co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 5.0 6000 1.3 620 13 0.50 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.5 5700 1.3 670 12 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.5 5800 1.3 650 12 2.0 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 5.0 6000 1.4 620 11 2.0 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.5 5600 1.5 660 11 2.0 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 18, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 -MgO-SiO.sub.2 series of 3.0 wt %, a semiconducting accelerant of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 16.
EXAMPLE 19
The forming agent Sr(Co.sub.1/2 Mo.sub.1/2)O.sub.3 (0.1 to 6.0 wt %) was added instead of the forming agent Sr(Cu.sub.1/2 Nb.sub.2/3)O.sub.3 (0.1 to 6.0 wt %) to form a grain boundary depletion of Example 1. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 1 and electric characteristics thereof were measured by the same method as Example 1. The results are shown in Table 19.
The forming agent Sr(Co.sub.1/2 Mo.sub.1/2)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, MoO.sub.3, and CoO, sintering at 1000.degree. C. and grinding.
TABLE 19__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Co.sub.1/2 Mo.sub.1/2)O.sub.3 growth ZrO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 4.0 4400 17.0 170 5.50.1 0.2 0.5 0.8 9.0 10500 4.8 320 120.5 0.2 0.5 0.8 10.0 11200 4.5 310 141.0 0.2 0.5 0.8 10.0 11300 4.4 300 123.0 0.2 0.5 0.8 10.0 11500 4.6 280 135.0 0.2 0.5 0.8 11.0 12200 4.3 270 126.0 0.2 0.5 0.8 11.0 12300 4.5 260 121.0 0.02 0.5 0.8 9.0 10300 23.0 140 6.01.0 0.05 0.5 0.8 9.5 10800 4.3 290 141.0 0.5 0.5 0.8 10.0 11200 4.5 290 131.0 2.0 0.5 0.8 11.0 12000 4.4 280 141.0 3.0 0.5 0.8 9.0 9500 17.5 110 4.51.0 0.2 0.1 0.8 8.0 8300 17.5 150 6.51.0 0.2 0.2 0.8 9.5 10700 4.6 320 121.0 0.2 0.5 0.8 10.5 11100 4.1 300 131.0 0.2 2.0 0.8 11.0 12200 4.6 270 131.0 0.2 5.0 0.8 10.0 11300 4.8 290 141.0 0.2 6.0 0.8 9.0 10300 12.5 170 4.51.0 0.2 0.5 0.05 12.0 13500 21.0 160 5.01.0 0.2 0.5 0.1 10.0 11300 4.7 290 121.0 0.2 0.5 1.0 11.0 12200 4.6 270 141.0 0.2 0.5 5.0 11.0 12400 4.6 260 141.0 0.2 0.5 10.0 9.0 10200 4.5 310 111.0 0.2 0.5 12.0 9.0 9200 16.0 210 6.5__________________________________________________________________________
As is apparent from the results in Table 19, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 0.1 to 10.0 wt %, and a forming agent Sr(Co.sub.1/2 Mo.sub.1/2)O.sub.3 of 0.2 to 5.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering, has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 9.0 to 10 .mu.m and the dielectric loss was 5.0% or less and the apparent dielectric constant was 10000 or more. The riser voltage V.sub.1 mA of the materials as a varistor was 250 to 350 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the resistance non-linearity coeffecient in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained.
When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 20
The forming agent Sr(Co.sub.1/2 Mo.sub.1/2)O.sub.3 (0.4 to 4.0 wt %) was added instead of the forming agent Sr(Cu.sub.1/3 Nb.sub.1/2)O.sub.3 (0.4 to 3.0 wt %) to form a grain boundary depletion of Example 2. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 2 and electric characteristics thereof were measured by the same method as Example 2. The results are shown in Table 20. The forming agent Sr(Co.sub.1/2 Mo.sub.1/2)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, MoO.sub.3 and CoO sintering at 900.degree. C. and grinding.
TABLE 20__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Co.sub.1/2 Mo.sub.1/2)O.sub.3 growth ZrO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 2.0 10.0 11200 4.5 310 121.0 0.4 4.0 2.0 9.5 10800 4.2 320 121.0 0.4 1.0 0.2 11.0 12200 4.4 280 131.0 0.4 1.0 8.0 10.0 11100 4.1 290 13TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 2.0 11.0 12000 4.3 260 121.0 0.4 4.0 2.0 10.0 11400 4.5 300 141.0 0.4 1.0 0.2 11.0 12100 4.5 270 121.0 0.4 1.0 8.0 10.5 11700 4.5 290 12TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 2.0 10.5 11800 4.4 280 141.0 0.4 4.0 2.0 10.5 11600 4.1 270 121.0 0.4 1.0 0.2 11.0 12000 4.3 270 131.0 0.4 1.0 8.0 10.0 11300 4.3 300 12__________________________________________________________________________
As is apparent from the results in Table 20, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 -MgO-SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a solid electrolyte ZrO.sub.2 of 0.2 to 8.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 4.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 19.
EXAMPLE 21
The forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Co.sub.1/2 Wo.sub.1/2) O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Co.sub.1/2 Wo.sub.1/2)O.sub.3 of 2.0 wt % was added instead of the forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Cu.sub.1/3 Nb.sub.2/3 or Sr.sub.0.2 Ba.sub.0.2 Ca.sub.0.2 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 of 2.0 wt % to form a grain boundary depletion of Example 3. The forming agent to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, Mo.sub.3, and CoO, sintering at 900.degree. C. and grinding.
The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 3 and electric characteristics thereof were measured by the same method as Example 3. The results are shown in Table 21.
TABLE 21__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth ZrO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 9.0 10100 4.3 330 13 (Co.sub.1/2 Mo.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 9.5 10800 4.2 320 12 0.05 (Co.sub.1/2 Mo.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 10.0 11300 3.9 300 12 0.05 (Co.sub.1/2 Mo.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 10.0 11100 4.0 290 13 0.05 (Co.sub.1/2 Mo.sub.1/2)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 10.0 11400 4.0 300 12 (Co.sub.1/2 Mo.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 10.5 12200 3.5 280 12 0.50 (Co.sub.1/2 Mo.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 10.0 11000 4.1 300 13 0.50 (Co.sub.1/2 Mo.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 10.5 11800 4.0 270 12 0.50 (Co.sub.1/2 Mo.sub.1/2)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 9.5 10700 4.3 310 12 (Co.sub.1/2 Mo.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 10.0 11200 3.8 290 12 2.0 (Co.sub.1/2 Mo.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 9.5 10600 4.0 290 13 2.0 (Co.sub. 1/2 Mo.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 10.5 12000 4.3 280 12 2.0 (Co.sub.1/2 Mo.sub.1/2)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 21,
the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 -MgO-SiO.sub.2 series of 3.0 wt %, a semiconducting accelerant of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 19.
EXAMPLE 22
The forming agent SrO.multidot.1/3Mn.sub.2 O.sub.3 .multidot.1/3MoO.sub.3 (0.1 to 10.0 wt %) was added instead of the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.1 to 6.0 wt %) to form a grain boundary depletion of Example 1. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 1 and electric characteristics thereof were measured by the same method as Example 1. The results are shown in Table 22.
The forming agent SrO.multidot.1/3Mn.sub.2 O.sub.3 .multidot.1/3MoO.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, MoO.sub.3, and MnCO.sub.3, sintering at 1000.degree. C. and grinding.
TABLE 22__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 SrO.1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 growth ZrO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 6.5 5500 9.2 220 5.50.1 0.2 0.5 0.8 9.5 10200 2.4 320 120.5 0.2 0.5 0.8 9.5 10300 2.6 310 111.0 0.2 0.5 0.8 9.5 10100 2.3 310 133.0 0.2 0.5 0.8 10.0 10700 2.3 320 125.0 0.2 0.5 0.8 9.5 10500 2.4 310 126.0 0.2 0.5 0.8 10.0 10900 2.8 340 121.0 0.02 0.5 0.8 7.0 5400 11.0 190 4.51.0 0.05 0.5 0.8 9.0 9800 2.6 340 111.0 0.5 0.5 0.8 9.5 10200 2.5 320 131.0 2.0 0.5 0.8 9.5 10100 2.3 320 131.0 3.0 0.5 0.8 6.0 5500 14.5 180 3.41.0 0.2 0.1 0.8 10.5 5400 10.5 170 5.01.0 0.2 0.2 0.8 10.5 11000 2.7 310 131.0 0.2 1.0 0.8 10.0 10500 2.5 330 121.0 0.2 2.0 0.8 9.5 10100 2.7 310 141.0 0.2 8.0 0.8 9.0 9700 2.4 320 121.0 0.2 10.0 0.8 7.5 7100 11.5 150 3.51.0 0.2 0.5 0.05 12.0 7700 17.5 130 4.51.0 0.2 0.5 0.1 10.0 11000 2.7 310 121.0 0.2 0.5 1.0 9.5 10400 2.2 330 121.0 0.2 0.5 3.0 9.0 9600 2.3 310 131.0 0.2 0.5 10.0 9.5 10200 2.9 340 141.0 0.2 0.5 12.0 7.0 6400 12.0 170 4.5__________________________________________________________________________
As is apparent from the results in Table 22, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 0.1 to 10.0 wt %, and a forming agent SrO.multidot.1/3Mn.sub.2 O.sub.3 .multidot.1/3MoO.sub.3 of 0.2 to 8.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 9.0 to 10.5 .mu.m and the dielectric loss was 3.0% or less and the apparent dielectric constant was 10000 or more. The riser voltage V.sub. 1 mA of the materials as a varistor was 300 to 400 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the resistance non-linearity coeffecient in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained.
When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 23
The forming agent SrO.multidot.1/3Mn.sub.2 O.sub.3 .multidot.1/3MoO.sub.3 (0.4 to 6.0 wt %) was added instead of the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.4 to 3.0 wt %) to form a grain boundary depletion of Example 2. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 2 and electric characteristics thereof were measured by the same method as Example 2. The results are shown in Table 23.
The forming agent SrO.multidot.1/3Mn.sub.2 O.sub.3 .multidot.1/3MoO.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, MoO.sub.3, and MnCO.sub.3, sintering at 900.degree. C. and grinding.
TABLE 23__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 SrO.1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 growth ZrO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 2.0 9.5 9800 2.5 340 131.0 0.4 6.0 2.0 10.0 10400 2.3 320 121.0 0.4 1.0 0.2 10.0 10700 2.4 310 131.0 0.4 1.0 8.0 9.5 10100 2.1 340 11TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 2.0 10.0 10500 2.4 330 121.0 0.4 6.0 2.0 10.0 10500 2.3 310 121.0 0.4 1.0 0.2 9.5 10100 2.7 330 131.0 0.4 1.0 8.0 10.0 10600 2.4 320 13TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 2.0 9.5 10000 2.5 310 121.0 0.4 6.0 2.0 9.5 9900 2.8 340 131.0 0.4 1.0 0.2 10.0 10500 2.7 310 131.0 0.4 1.0 8.0 9.5 10300 2.8 330 12__________________________________________________________________________
As is apparent from the results in Table 23, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 -MgO-SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a good oxygen conductive solid electrolyte ZrO.sub.2 of 0.2 to 8.0 wt %, and a forming agent of 0.4 to 6.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 22.
EXAMPLE 24
The forming agent 0.8SrO.multidot.0.1BaO.multidot.0.1CaO.multidot.1/3Mn.sub.2 O.sub.3 .multidot.1/3MoO.sub.3 or 0.6SrO.multidot.0.2BaO.multidot.0.2CaO.multidot.1/3Mn.sub.2 O.sub.3 .multidot.1/3MoO.sub.3 of 2.0 wt % was added instead of the forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 or Sr.sub.0.6 boundary depletion of Example 3. The forming agent to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, MoO.sub.3, and MnCO.sub.3, sintering at 900.degree. C. and grinding.
The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 3 and electric characteristics thereof were measured by the same method as Example 3. The results are shown in Table 24.
TABLE 24__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth ZrO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 0.8SrO.9.1CaO.0.1BaO 1.5 9.5 9800 2.3 340 13 .1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 2.03.0 Nb.sub.2 O.sub.5 0.8SrO.0.1CaO.0.1BaO 1.5 9.5 10000 2.4 340 12 0.05 .1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 2.03.0 La.sub.2 O.sub.3 0.8SrO.0.1CaO.0.1BaO 1.5 9.5 10100 2.1 340 12 0.05 .1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 2.03.0 Y.sub.2 O.sub.3 0.8SrO.0.1CaO.0.1BaO 1.5 10.0 10500 2.3 310 11 0.05 .1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 2.03.0 WO.sub.3 0.50 0.6SrO.0.2CaO.0.2BaO 1.5 9.5 9900 2.3 340 12 .1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 2.03.0 Nb.sub.2 O.sub.5 0.6 SrO.0.2CaO.0.2BaO 1.5 10.0 10300 2.2 310 13 0.50 .1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 2.03.0 La.sub.2 O.sub.3 0.6SrO.0.2CaO.0.2BaO 1.5 9.5 9800 2.3 340 12 0.50 .1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 2.03.0 Y.sub.2 O.sub.3 0.6SrO.0.2CaO.0.2BaO 1.5 10.0 10300 2.9 320 12 0.50 .1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 2.03.0 WO.sub.3 2.0 0.8SrO.0.1CaO.0.1BaO 1.5 10.0 10400 2.5 310 13 .1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 2.03.0 Nb.sub.2 O.sub.5 0.8SrO.0.1CaO.0.1BaO 1.5 10.0 10500 2.3 310 12 2.0 .1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 2.03.0 La.sub.2 O.sub.3 0.8SrO.0.1CaO.0.1BaO 1.5 9.5 9800 2.0 340 12 2.0 .1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 2.03.0 Y.sub.2 O.sub.3 0.8SrO.0.1CaO.0.1BaO 1.5 9.5 10000 2.4 340 11 2.0 .1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 24, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 -MgO-SiO.sub.2 series of 3.0 wt %, a semiconducting accelerant of 0.05 to 2.0 wt %, a solid electrolyte ZrO.sub.2 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent 0.8SrO.multidot.0.1BaO.multidot.0.1CaO.multidot.1/3Mn.sub.2 O.sub.3 MoO.sub.3 or 0.6SrO.multidot.0.2BaO.multidot.0.2CaO.multidot.1/3Mn.sub.2 O.sub.3 .multidot.1/3MoO.sub.2 of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 22.
EXAMPLE 25
A sintering accelerant TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 (ratio of 20:35:45 wt %) of 0.05 to 6.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.02 to 3.0 wt % which can form a solid solution with perovskite type oxides, a good oxygen conductive solid electrolyte CeO.sub.2 of 0.05 to 4.0 wt % which functions as a control agent to control the grain growth, and a forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 (0.1 to 12.0 wt %) to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to strontium titanat (SrTiO.sub.3) obtained by pyrolyzing titanyl strontium oxalate (SrTiO(C.sub.2 O.sub.4).sub.2 .multidot.4H.sub.2 O) and mixed well followed by calcination at 900.degree. C. Then it was ground in a wet state followed by drying, making grain, and molding, sintering at 1300.degree. C. in the air. It was reground in a wet state, made into a paste using resin and organic solutions so as to form a sheet, printed platinum paste for inner electrodes were laminated thereon, sintered at 1400.degree. C. in the air followed by the hydrogen reduction at 1300.degree. C., and heat-treated at 950.degree. C. in the air. Finally, electrodes were adjusted so as to connect inner electrodes with outer electrodes, thereby completing the manufacture of a laminated ceramic capacitor having grain boundary varistor characteristics of FIG. 1. Electric characteristics of the laminated ceramic capacitor were measured and the results are shown in Table 25. The sintering accelerant TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 (ratio of 20:35:45 wt %) was obtained by weighing commercial TiO.sub.2, Al.sub.2 O.sub.3 and SiO.sub.2 powder according to the predetermined weight ratio, mixing, calcinating at 1200.degree. C., and grinding. The forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 to form a grain boundary depletion layer which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, Nb.sub.2 O.sub.5, MnCO.sub.3 or the like, calcinating at 1000.degree. C., and grinding. The size of the varistor after sintering was approximately 4 mm square and about 0.6 mm in thickness and composed of 8 layers of the dielectrics, each of which was about 70 pm in thickness. The apparent dielectric constant was calculated from the value of the capacitance (measurement 1 kHz) of the laminated varistor. The grain diameter in the sintered body was obtained by examining a cross section after polishing under an optical microscope, to the surface of which Bi.sub.2 O.sub.3 series metallic soap was applied and heat-treated at 1000.degree. C. to make the grain boundary clear.
TABLE 25__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 growth CeO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 2.0 2400 11.0 330 4.50.1 0.2 0.5 0.8 3.0 3400 1.2 960 140.5 0.2 0.5 0.8 3.5 4400 0.9 860 131.0 0.2 0.5 0.8 3.5 3800 1.0 910 123.0 0.2 0.5 0.8 3.0 3600 1.1 1040 135.0 0.2 0.5 0.8 3.0 3200 1.0 980 146.0 0.2 0.5 0.8 3.0 3300 1.2 1020 131.0 0.02 0.5 0.8 3.5 2100 19.0 850 3.01.0 0.05 0.5 0.8 3.0 3500 1.3 970 141.0 0.5 0.5 0.8 3.0 3100 0.9 1130 131.0 2.0 0.5 0.8 3.5 4000 1.0 880 141.0 3.0 0.5 0.8 3.0 2100 18.0 1030 6.01.0 0.2 0.1 0.8 3.0 2400 12.5 1010 3.51.0 0.2 0.2 0.8 3.5 3900 1.2 860 141.0 0.2 1.0 0.8 3.0 3100 1.1 1140 121.0 0.2 3.0 0.8 3.5 4100 1.0 870 111.0 0.2 10.0 0.8 3.0 3600 1.1 970 121.0 0.2 12.0 0.8 2.0 1300 5.5 350 6.01.0 0.2 0.5 0.05 2.5 1800 12.5 320 4.01.0 0.2 0.5 0.1 3.0 3200 1.4 990 131.0 0.2 0.5 0.5 3.5 4400 1.1 910 131.0 0.2 0.5 1.0 3.0 3400 1.0 930 121.0 0.2 0.5 3.0 3.0 3100 1.0 1130 131.0 0.2 0.5 4.0 2.0 2100 12.5 350 5.0__________________________________________________________________________
As is apparent from the results in Table 25, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte CeO.sub.2 0.1 to 3.0 wt %, and a forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 of 0.2 to 10.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 3.0 to 3.5 .mu.m and the dielectric loss was 2.0% or less and the apparent dielectric constant was 3,000 or more. The riser voltage V.sub.1 mA of the materials as a varistor was 850 to 1150 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the resistance non-linearity coeffecient in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained. When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 26
A sintering accelerant of 1.0 wt % selected from TiO.sub.2 -MgO-SiO.sub.02 series (for example, ratio of 30:30:40 wt %), TiO.sub.2 -MnO-SiO.sub.2 series (for example, ratio of 10:50:40 wt %), TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 series (for example, ratio of 20:35:45 wt %) mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.04 wt % which can form a solid solution with perovskite type oxides, a good oxygen conductive solid electrolyte CeO.sub.2 of 0.2 to 2.0 wt % which functions as a control agent to control the grain growth, and a forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 of 0.4 to 8.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to commercial industrial strontium titanat (SrTiO.sub.3) and mixed well followed by calcination at 900.degree. C. Then it was ground in a wet state followed by drying, making grain, and molded like a disk shape, sintered at 1380.degree. C. in a reducing atmosphere composed of 95% of nitrogen and 5% of hydrogen. It was heat-treated at 950.degree. C. in the air and silver electrodes were formed on both sides of the disk, thereby completing the manufacture of a ceramic capacitor having grain boundary varistor characteristics of FIG. 2. Electric characteristics of the laminated ceramic capacitor were measured and the results are shown in Table 26.
The sintering accelerant, for example TiO.sub.2 -MgO-SiO.sub.2 series (for example, ratio of 30:30:40 wt %), was obtained by weighing commercial TiO.sub.2, MgO and SiO.sub.2 powder according to the predetermined weight ratio, mixing, calcinating at 1200.degree. C., and grinding. The forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 to form a grain boundary depletion layer which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, Nb.sub.2 O.sub.5 and MnCO.sub.3, calcinating at 900.degree. C., and grinding.
TABLE 26__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 SrO(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 growth CeO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 1.0 3.0 3100 1.2 1120 131.0 0.4 8.0 1.0 3.0 3300 1.4 950 121.0 0.4 1.0 0.2 3.0 3200 1.1 1050 131.0 0.4 1.0 2.0 3.0 3500 1.1 990 14TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 1.0 3.5 3800 1.3 890 121.0 0.4 8.0 1.0 3.0 3400 1.2 1020 111.0 0.4 1.0 0.2 3.5 4000 1.2 910 121.0 0.4 1.0 2.0 3.0 3300 1.0 930 12TIO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 1.0 3.0 3400 0.9 960 131.0 0.4 8.0 1.0 3.5 3900 1.1 880 121.0 0.4 1.0 0.2 3.5 4200 0.9 860 131.0 0.4 1.0 2.0 3.0 3300 1.2 930 12__________________________________________________________________________
As is apparent from the results in Table 26, the present material obtained by adding SrTiO.sub.2 to a sintering accelerant such as TiO.sub.2 -MgO-SiO.sub.2 of 1.0 wt %, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a good oxygen conductive solid electrolyte CeO.sub.2 of 0.2 to 2.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 3.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 25.
EXAMPLE 27
A sintering accelerant of 3.0 wt % of TiO.sub.2 -MgO-SiO.sub.2 series (for example, ratio of 30:30:40 wt %) mainly forming a liquid phase at a high temperature, semiconducting accelerants WO.sub.3, Nb.sub.2 O.sub.5, La.sub.2 O.sub.3 and Y.sub.2 O.sub.3 of 0.05 to 2.0 wt %, a good oxygen conductive solid electrolyte CeO.sub.2 of 1.5 wt % which functions as a control agent to control the grain growth, and a forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to commercial industrial strontium titanat (SrTiO.sub.3) and mixed well followed by calcination at 900.degree. C. Then it was ground in a wet state followed by drying, making grain, and molding, sintering at 1380.degree. C. in the reducing atmosphere composed of 95% of nitrogen and 5% of hydrogen. It was heat-treated at 950.degree. C. in the air and electrodes were formed, thereby completing the manufacture of a ceramic capacitor having grain boundary varistor characteristics of FIG. 2. Electric characteristics of the laminated ceramic capacitor were measured and the results are shown in Table 27.
The sintering accelerant TiO.sub.2 -MgO.sub.SiO.sub.2 series (ratio of 30:30:40 wt %) was obtained by weighing commercial TiO.sub.2, MgO, SiO.sub.2 powder according to the predetermined weight ratio, mixing, calcinating at 1200.degree. C., and grinding. The forming agent to form a grain boundary depletion layer which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, Nb.sub.2 O.sub.5 and MnCO.sub.3, calcinating at 900.degree. C., and grinding.
TABLE 27__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth CeO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4100 1.0 880 14 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3200 1.2 960 13 0.05 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3300 1.2 1010 13 0.05 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub. 0.1 1.5 3.5 3800 1.4 860 12 0.05 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.0 3400 1.3 970 13 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.6 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.5 4000 1.2 870 12 0.50 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.0 3600 1.2 950 14 0.50 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.0 3300 1.0 1020 13 0.50 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4200 1.0 900 14 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3500 1.2 980 14 2.0 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3200 1.2 910 13 2.0 (Mn.sub. 1/2 Nb.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 3900 1.4 680 12 2.0 (MN.sub.1/2 Nb.sub.1/2)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 27, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 series of 3.0 wt %, semiconducting accelerants WO.sub.3, Nb.sub.2 O.sub.5, La.sub.2 O.sub.3 and Y.sub.2 O.sub.3 of 0.05 to 2.0 wt %, a solid electrolyte CeO.sub.2 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 25.
EXAMPLE 28
A capacitor was manufactured according to the method in Example 25 including the manufacturing method for other materials, sintering accelerant or the like, except that the forming agent Sr(Mn.sub.1/2 Ta.sub.1/2)O.sub.3 (0.1 to 12.0 wt %) was used instead of the forming agent Sr(Mn.sub.1/2 Nb.sub.1/2) (0.1 to 12.0 wt %) to form a grain boundary depletion both of which also function as a control agent to control the grain growth and electric characteristics thereof were measured by the same method as Example 25.
The results are shown in Table 28.
The forming agent Sr(Mn.sub.1/2 Ta.sub.1/2)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, Ta.sub.2 O.sub.5, MnCO.sub.3 or the like, sintering at 1000.degree. C. and grinding.
TABLE 28__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Mn.sub.1/2 Ta.sub.1/2)O.sub.3 growth CeO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 2.0 3500 23.0 350 3.50.1 0.2 0.5 0.8 3.5 3600 1.8 910 110.5 0.2 0.5 0.8 3.0 3300 1.7 960 121.0 0.2 0.5 0.8 3.5 3900 0.5 830 133.0 0.2 0.5 0.8 3.5 4200 1.4 880 125.0 0.2 0.5 0.8 4.0 4600 1.1 800 126.0 0.2 0.5 0.8 4.0 4700 1.3 760 121.0 0.02 0.5 0.8 2.0 2500 33.0 420 6.01.0 0.05 0.5 0.8 3.5 4300 1.6 890 111.0 0.5 0.5 0.8 3.0 3600 1.3 980 121.0 2.0 0.5 0.8 3.5 3700 1.7 860 111.0 3.0 0.5 0.8 2.0 2200 18.5 260 5.51.0 0.2 0.1 0.8 3.0 2700 25.5 310 4.51.0 0.2 0.2 0.8 3.0 3300 1.9 940 111.0 0.2 1.0 0.8 3.5 3900 1.4 810 121.0 0.2 3.0 0.8 4.0 5100 1.3 770 131.0 0.2 10.0 0.8 3.5 4100 1.8 870 131.0 0.2 12.0 0.8 2.5 2700 20.5 400 4.51.0 0.2 0.5 0.05 4.0 2500 17.7 280 5.01.0 0.2 0.5 0.1 3.5 4400 1.7 830 121.0 0.2 0.5 0.5 3.5 3800 1.7 890 121.0 0.2 0.5 1.0 3.5 4200 1.4 810 131.0 0.2 0.5 3.0 3.0 3400 1.3 980 111.0 0.2 0.5 4.0 2.5 2500 18.8 320 4.0__________________________________________________________________________
As is apparent from the results in Table 28, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte CeO.sub.2 0.1 to 3.0 wt % which also functions as a control agent to control the grain growth, and a forming agent Sr(Mn.sub.1/2 Ta.sub.1/2)O.sub.3 of 0.2 to 10.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 3.0 to 3.5 .mu.m and the dielectric loss was 2.0% or less and the apparent dielectric constant was 3000 or more. The riser voltage V.sub.1 mA of the materials as a varistor was 750 to 1000 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the non-linearity resistive charac-teristics in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained.
When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 29
A capacitor was manufactured according to the method in Example 26 including the manufacturing method for other materials, sintering accelerant or the like, except that the forming agent Sr(Mn.sub.1/2 Ta.sub.1/2)O.sub.3 (0.4 to 8.0 wt %) was used instead of the forming agent Sr(Mn.sub.1/2 Nb.sub.1/2) (0.4 to 8.0 wt %) to form a grain boundary depletion both of which also function as control agents to control grain growth and electric characteristics thereof was measured by the same method as Example 26. The results are shown in Table 29. The forming agent Sr(Mn.sub.1/2 Ta.sub.1/2)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control grain growth was obtained by mixing commercial SrCO.sub.3, Ta.sub.2 O.sub.5, MnCO.sub.3 or the like, sintering at 900.degree. C. and grinding.
TABLE 29__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Mn.sub.1/2 Ta.sub.1/2)O.sub.3 growth CeO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 1.0 3.5 4200 1.4 850 121.0 0.4 8.0 1.0 3.5 4000 1.5 890 121.0 0.4 1.0 0.2 4.0 4900 1.6 790 111.0 0.4 1.0 2.0 3.0 3400 1.3 920 11TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 1.0 3.5 3800 1.7 830 121.0 0.4 8.0 1.0 3.5 4100 1.4 880 111.0 0.4 1.0 0.2 3.5 4200 1.4 900 111.0 0.4 1.0 2.0 3.5 3900 1.6 830 11TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 1.0 4.0 4800 1.3 800 121.0 0.4 8.0 1.0 3.5 3700 1.6 850 121.0 0.4 1.0 0.2 4.0 5000 1.7 780 111.0 0.4 1.0 2.0 3.5 4200 1.7 870 12__________________________________________________________________________
As is apparent from the results in Table 29, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a good oxygen conductive solid electrolyte CeO.sub.2 of 0.2 to 2.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 8.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 28.
EXAMPLE 30
The forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Mn.sub.1/2 Ta.sub.1/2) O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 of 2.0 wt % was added instead of the forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Mn.sub.1/2 Nb.sub.1/2) or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 of 2.0 wt % to form a grain boundary depletion of Example 27. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 27 and electric characteristics thereof were measured by the same method as Example 27. The forming agent to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, Ta.sub.2 O.sub.5, and MnCO.sub.3 sintering at 900.degree. C. and grinding.
TABLE 30__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth CeO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.0 5000 1.2 790 12 (Mn.sub.1/2 Ta.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4200 1.2 820 13 0.05 (Mn.sub.1/2 Ta.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 3800 1.3 870 13 0.05 (Mn.sub.1/2 Ta.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3400 1.4 940 12 0.05 (Mn.sub.1/2 Ta.sub.1/2)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 4.0 4800 1.3 800 11 (Mn.sub.1/2 Ta.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.6 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.5 4100 1.3 840 13 0.50 (Mn.sub.1/2 Ta.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.5 3700 1.6 810 11 0.50 (Mn.sub.1/2 Ta.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 4.0 4900 1.5 790 12 0.50 (Mn.sub.1/2 Ta.sub.1/2)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4300 1.2 830 12 (Mn.sub.1/2 Ta.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.0 4700 1.2 770 13 2.0 (Mn.sub.1/2 Ta.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 3800 1.3 870 13 2.0 (Mn.sub.1/2 Ta.sub.1/2 )O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3500 1.4 920 12 2.0 (Mn.sub.1/2 Ta.sub.1/2)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 30, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 series of 3.0 wt %, semiconducting accelerants WO.sub.3, Nb.sub.2 O.sub.5, La.sub.2 O.sub.3 and Y.sub.2 O.sub.3 of 0.05 to 2.0 wt %, a solid electrolyte CeO.sub.2 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 28.
EXAMPLE 31
A capacitor was manufactured according to the method in Example 25 including the manufacturing method for other materials, sintering accelerant or the like, except that the forming agent Sr(Cu.sub.1/2 W.sub.1/2)O.sub.3 (0.1 to 6.0 wt %) was used instead of the forming agent Sr(Mn.sub.1/2 Nb.sub.1/2) (0.1 to 12.0 wt %) to form a grain boundary depletion and electric characteristics thereof were measured by the same method as Example 25. The results are shown in Table 31. The forming agent Sr(Cu.sub.1/2 W.sub.1/2)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, WO.sub.3, CuO or the like, sintering at 1000.degree. C. and grinding.
TABLE 31__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Cu.sub.1/2 W.sub.1/2)O.sub.3 growth CeO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 2.5 1800 18.0 460 2.50.1 0.2 0.5 0.8 3.5 4200 1.9 880 120.5 0.2 0.5 0.8 3.5 4000 0.5 900 121.0 0.2 0.5 0.8 3.0 3600 0.5 940 133.0 0.2 0.5 0.8 3.5 4100 1.7 900 135.0 0.2 0.5 0.8 3.5 4100 1.6 850 126.0 0.2 0.5 0.8 3.5 3800 1.8 870 121.0 0.02 0.5 0.8 3.0 2500 25.0 340 3.51.0 0.05 0.5 0.8 3.0 3300 1.8 910 131.0 0.5 0.5 0.8 3.0 3100 0.5 950 131.0 2.0 0.5 0.8 3.5 3900 0.5 830 121.0 3.0 0.5 0.8 3.5 2500 17.0 330 4.51.0 0.2 0.1 0.8 3.5 2200 22.0 430 4.01.0 0.2 0.2 0.8 3.5 4200 1.6 870 111.0 0.2 0.5 0.8 3.0 3500 1.4 970 121.0 0.2 2.0 0.8 3.5 4100 1.6 850 121.0 0.2 5.0 0.8 3.0 3500 1.8 980 131.0 0.2 6.0 0.8 3.0 2400 18.0 530 4.51.0 0.2 0.5 0.05 3.5 2800 17.0 310 2.51.0 0.2 0.5 0.1 3.5 4000 1.8 890 111.0 0.2 0.5 0.5 3.0 3200 1.7 980 121.0 0.2 0.5 1.0 3.0 3500 1.7 930 121.0 0.2 0.5 3.0 3.0 3300 0.5 910 111.0 0.2 0.5 4.0 2.5 2700 10.0 280 3.5__________________________________________________________________________
As is apparent from the results in Table 31, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte CeO.sub.2 0.1 to 3.0 wt %, and a forming agent Sr(Cu.sub.1/2 W.sub.1/2)O.sub.3 of 0.2 to 5.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 3.0 to 3.5 .mu.m and the dielectric loss was 2.0% or less and the apparent dielectric constant was 3,000 or more. The riser voltage V.sub.1 mA of the materials as a varistor was 800 to 1000 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.2 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the resistance non-linearity coeffecient in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained. When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 32
A capacitor was manufactured according to the method in Example 26 including the manufacturing method for other materials, sintering accelerant or the like, except that the forming agent Sr(Cu.sub.1/2 W.sub.1/2)O.sub.3 (0.4 to 4.0 wt %) was used instead of the forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 (0.4 to 8.0 wt %) to form a grain boundary depletion and electric characteristics thereof were measured by the same method as Example 26. The results are shown in Table 32. The forming agent Sr(Cu.sub.1/2 W.sub.1/2)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, WO.sub.3 and CuO, sintering at 900.degree. C. and grinding.
TABLE 32__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Cu.sub.1/2 W.sub.1/2)O.sub.3 growth CeO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 2.0 3.0 3500 1.6 920 121.0 0.4 4.0 2.0 3.5 4200 0.5 840 121.0 0.4 1.0 0.2 3.5 4100 1.4 870 131.0 0.4 1.0 1.0 3.0 3600 0.5 940 12TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 2.0 3.5 3800 1.4 890 121.0 0.4 4.0 2.0 3.0 3300 1.4 990 131.0 0.4 1.0 0.2 3.5 4000 1.3 820 121.0 0.4 1.0 1.0 3.0 3400 1.6 980 12TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 2.0 3.5 4100 0.5 850 131.0 0.4 4.0 2.0 3.5 4400 1.3 880 121.0 0.4 1.0 0.2 3.5 3900 1.4 900 121.0 0.4 1.0 1.0 3.0 3600 1.2 950 12__________________________________________________________________________
As is apparent from the results in Table 32, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a good oxygen conductive solid electrolyte CeO.sub.2 of 0.2 to 2.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 4.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 31.
EXAMPLE 33
The forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Cu.sub.1/2 W.sub.1/2) O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Cu.sub.1/2 W.sub.1/2)03 of 2.0 wt % was added instead of the forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Mn.sub.1/2 Nb.sub.1/2) or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 of 2.0 wt % to form a grain boundary depletion of Example 27. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 27 and electric characteristics thereof were measured by the same method as Example 27. The forming agent to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, WO.sub.3 and CuO, sintering at 900.degree. C. and grinding. The results are shown in Table 33.
TABLE 33__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth CeO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3400 1.3 930 12 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3600 1.6 970 12 0.05 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 3900 0.5 890 11 0.05 9Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3500 1.2 910 12 0.05 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.5 4300 1.2 870 13 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.0 3300 1.2 950 11 0.50 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.0 3600 1.1 930 13 0.50 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.5 4000 1.3 860 12 0.50 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3400 1.3 970 13 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3500 1.6 930 13 2.0 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4100 0.5 890 11 2.0 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3300 1.2 910 12 2.0 (Cu.sub.1/2 W.sub.1/2)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 33, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 series of 3.0 wt %, semiconducting accelerants WO.sub.3, Nb.sub.2 O.sub.5, La.sub.2 O.sub.3 and Y.sub.2 O.sub.3 of 0.05 to 2.0 wt %, a solid electrolyte CeO.sub.2 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 31.
EXAMPLE 34
A capacitor was manufactured according to the method in Example 25 including the manufacturing method for other materials, sintering accelerant or the like, except that the forming agent Sr(Co.sub.1/2 W.sub.1/2)O.sub.3 (0.1 to 6.0 wt %) was used instead of the forming agent Sr(Mn.sub.1/2 Nb.sub.1/2) (0.1 to 12.0 wt %) to form a grain boundary depletion both of which also function as control agents to control the grain growth and electric characteristics thereof were measured by the same method as Example 25. The results are shown in Table 34.
The forming agent Sr(Co.sub.1/2 W.sub.1/2)O.sub.3 to form grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, WO.sub.3, CoO or the like, sintering at 1000.degree. C. and grinding.
TABLE 34__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Co.sub.1/2 W.sub.1/2)O.sub.3 growth CeO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 1.0 1300 27.5 330 3.50.1 0.2 0.5 0.8 3.0 3200 1.7 950 110.5 0.2 0.5 0.8 3.5 3800 1.6 910 121.0 0.2 0.5 0.8 3.5 4000 0.5 870 113.0 0.2 0.5 0.8 3.5 4100 1.7 860 125.0 0.2 0.5 0.8 3.5 4100 1.7 890 116.0 0.2 0.5 0.8 3.5 4300 1.4 900 121.0 0.02 0.5 0.8 3.5 3300 24.0 240 2.51.0 0.05 0.5 0.8 3.5 3900 1.7 890 111.0 0.5 0.5 0.8 3.0 3400 1.6 980 121.0 2.0 0.5 0.8 3.5 4200 1.6 870 121.0 3.0 0.5 0.8 3.5 3100 20.5 270 3.51.0 0.2 0.1 0.8 3.5 3200 17.5 330 5.51.0 0.2 0.2 0.8 3.5 4200 1.7 860 111.0 0.2 0.5 0.8 3.0 3600 0.5 960 121.0 0.2 2.0 0.8 3.0 3500 1.6 990 111.0 0.2 5.0 0.8 3.0 3400 1.7 920 121.0 0.2 6.0 0.8 2.5 2800 12.5 550 5.51.0 0.2 0.5 0.05 3.5 3100 17.0 490 4.01.0 0.2 0.5 0.1 3.5 4400 1.6 870 111.0 0.2 0.5 0.5 3.5 4100 1.6 910 121.0 0.2 0.5 1.0 3.5 4300 1.7 900 111.0 0.2 0.5 3.0 3.0 3600 1.6 960 111.0 0.2 0.5 4.0 2.0 2200 15.0 460 6.5__________________________________________________________________________
As is apparent from the results in Table 34, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte CeO.sub.2 0.1 to 3.0 wt % which also functions as a control agent to control the grain growth, and a forming agent Sr(Co.sub.1/2 W.sub.1/2)O of 0.2 to 5.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 3.0 to 3.5 .mu.m and the dielectric loss was 2.0% or less and the apparent dielectric constant was 3,000 or more. The riser voltage V.sub.1 mA of the materials as a varistor was 850 to 1000 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the resistance non-linearity coeffecient in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained.
When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 35
A capacitor was manufactured according to the method in Example 26 including the manufacturing method for other materials, sintering accelerant or the like, except that the forming agent Sr(Co.sub.1/2 W.sub.1/2)O.sub.3 (0.4 to 4.0 wt %) was used instead of the forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 (0.4 to 8.0 wt %) to form a grain boundary depletion both of which function as control agents to control the grain growth and electric characteristics thereof were measured by the same method as Example 26. The results are shown in Table 35.
The forming agent Sr(Co.sub.1/2 W.sub.1/2)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, WO.sub.3 and CoO, sintering at 900.degree. C. and grinding.
TABLE 35__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Co.sub.1/2 W.sub.1/2)O.sub.3 growth CeO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 2.0 3.0 3400 1.4 940 111.0 0.4 4.0 2.0 3.5 3900 0.5 910 121.0 0.4 1.0 0.2 3.5 4100 1.7 880 111.0 0.4 1.0 1.0 3.0 3600 0.5 920 12TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 2.0 3.5 4000 1.6 860 111.0 0.4 4.0 2.0 3.0 3400 1.7 930 111.0 0.4 1.0 0.2 3.5 4200 1.7 840 121.0 0.4 1.0 1.0 3.0 3600 1.8 990 12TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 2.0 3.5 3800 0.5 890 121.0 0.4 4.0 2.0 3.5 4200 1.6 910 111.0 0.4 1.0 0.2 3.5 4000 1.8 860 111.0 0.4 1.0 1.0 3.0 3500 1.8 970 11__________________________________________________________________________
As is apparent from the results in Table 35, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a solid electrolyte CeO.sub.2 of 0.2 to 2.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 4.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 34.
EXAMPLE 36
The forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Co.sub.1/2 W.sub.1/2) O.sub.3 or Sr.sub.0.8 Ba.sub.0.2 Ca.sub.0.2 (Co.sub.1/2 W.sub.1/2)O.sub.3 of 2.0 wt % was added instead of the forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (M.sub.1/2 Nb.sub.1/2)O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 of 2.0 wt % to form a grain boundary depletion all of which function as control agents to control the grain growth of Example 27. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 27 and electric characteristics thereof were measured by the same method as Example 27.
The forming agent to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, WO.sub.3 and CoO, sintering at 900.degree. C. and grinding.
The results are shown in Table 36.
TABLE 36__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth CeO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4100 1.2 870 12 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 3900 1.1 900 13 0.05 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3600 1.2 960 13 0.05 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub. 0.1 1.5 3.0 3500 1.3 920 12 0.05 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.5 4000 0.5 870 13 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.0 3400 1.6 990 13 0.50 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.5 4300 0.5 890 11 0.50 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.5 4200 1.6 870 13 0.50 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4100 1.2 900 12 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 3900 1.1 880 13 2.0 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3600 1.2 940 13 2.0 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3500 1.3 950 12 2.0 (Co.sub.1/2 W.sub.1/2)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 36, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 series of 3.0 wt %, semiconducting accelerants WO.sub.3, Nb.sub.2 O.sub.5, La.sub.2 O.sub.3 and Y.sub.2 O.sub.3 of 0.05 to 2.0 wt %, a solid electrolyte CeO.sub.2 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 34.
EXAMPLE 37
A capacitor was manufactured according to the method in Example 25 including the manufacturing method for other materials, sintering accelerant or the like, except that the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.1 to 5.0 wt %) was used instead of the forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 (0.1 to 12.0 wt %) to form a grain boundary depletion both of which function as control agents to control the grain growth and electric characteristics thereof were measured by the same method as Example 25. The results are shown in Table 37. The forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, Nb.sub.2 O.sub.5, CuO or the like, sintering at 1000.degree. C. and grinding.
TABLE 37__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 growth CeO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 2.0 2200 15.0 220 3.00.1 0.2 0.5 0.8 3.5 3800 1.6 860 110.5 0.2 0.5 0.8 4.0 4700 1.4 730 121.0 0.2 0.5 0.8 3.5 3900 1.0 840 123.0 0.2 0.5 0.8 4.0 4800 0.8 780 115.0 0.2 0.5 0.8 4.0 5200 1.0 790 116.0 0.2 0.5 0.8 4.0 5100 1.2 770 121.0 0.02 0.5 0.8 2.5 2300 26.0 150 4.01.0 0.05 0.5 0.8 3.5 4100 0.5 810 111.0 0.5 0.5 0.8 4.0 4800 0.7 750 121.0 2.0 0.5 0.8 3.5 4400 1.2 890 121.0 3.0 0.5 0.8 2.0 2000 19.0 320 6.51.0 0.2 0.1 0.8 2.5 2300 17.5 300 4.01.0 0.2 0.2 0.8 3.5 4100 1.7 890 121.0 0.2 0.5 0.8 4.0 4600 0.9 770 131.0 0.2 2.0 0.8 3.5 4400 1.0 870 121.0 0.2 4.0 0.8 4.0 4800 1.6 780 121.0 0.2 6.0 0.8 2.5 2400 18.5 550 3.01.0 0.2 0.5 0.05 3.0 3100 22.0 330 4.51.0 0.2 0.5 0.1 4.0 4700 1.7 770 111.0 0.2 0.5 0.5 3.5 4100 1.0 860 121.0 0.2 0.5 1.0 3.5 4200 1.2 830 111.0 0.2 0.5 3.0 3.5 3800 1.8 810 111.0 0.2 0.5 4.0 2.5 2200 17.0 250 5.0__________________________________________________________________________
As is apparent from the results in Table 37, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte CeO.sub.2 0.1 to 3.0 wt % which also functions as a control agent to control the grain growth, and a forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 of 0.2 to 4.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 3.5 to 4.0 .mu.m and the dielectric loss was 2.0% or less and the apparent dielectric constant was 3500 or more. The riser voltage V.sub.1 mA of the materials as a varistor was 700 to 900 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the resistance non-linearity coeffecient in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained.
When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 38
A capacitor was manufactured according to the method in Example 26 including the manufacturing method for other materials, sintering accelerant or the like, except that the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.4 to 3.0 wt %) was used instead of the forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 (0.4 to 3.0 wt %) to form a grain boundary depletion both of which function as control agents to control the grain growth and electric characteristics thereof were measured by the same method as Example 26. The results are shown in Table 38.
The forming agent Sr(Cu Nb )O to form a grain boundary depletion was obtained by mixing commercial SrCO , Nb O , and CuO, sintering at 900.degree. C. and grinding.
TABLE 38__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Co.sub.1/3 Nb.sub.2/3)O.sub.3 growth CeO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 1.0 4.0 4800 1.2 770 121.0 0.4 3.0 1.0 4.0 4700 1.4 760 111.0 0.4 1.0 0.2 3.5 4400 1.3 830 121.0 0.4 1.0 2.0 4.0 4600 1.6 730 11TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 1.0 4.0 5100 1.1 770 121.0 0.4 3.0 1.0 3.5 4100 1.3 810 131.0 0.4 1.0 0.2 3.5 4300 1.4 820 121.0 0.4 1.0 2.0 4.0 4800 1.2 790 12TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 1.0 3.5 4200 1.0 820 111.0 0.4 3.0 1.0 4.0 4800 1.5 780 121.0 0.4 1.0 0.2 4.0 5000 1.4 740 111.0 0.4 1.0 2.0 4.0 5100 1.2 770 12__________________________________________________________________________
As is apparent from the results in Table 38, the present material obtained by adding SrTiO.sub.2 to a sintering accelerant such as TiO.sub.2 -MgO-SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a good oxygen conductive solid electrolyte CeO.sub.2 of 0.2 to 2.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 3.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 37.
EXAMPLE 39
The forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Cu.sub.1/3 Nb.sub.2/3) O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 of 2.0 wt % was added instead of the forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Mn.sub.178 Nb.sub.1/2)O.sub.3 or Sr.sub.0.6 Ba.sub.0.1 Ca.sub.0.1 (Mn.sub.1/2 Nb.sub.2/3)O.sub.3 of 2.0 wt % to form a grain boundary depletion all of which function as control agents to control the grain growth of Example 27. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 27 and electric characteristics thereof were measured by the same method as Example 27.
The forming agent to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, Nb.sub.2 O.sub.5, and CuO, sintering at 900.degree. C. and grinding.
The results are shown in Table 39.
TABLE 39__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth CeO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.0 4800 1.2 750 12 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4300 1.2 810 12 0.05 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.0 4900 1.2 760 13 0.05 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub. 0.1 1.5 4.0 4700 1.1 790 13 0.05 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.5 4100 1.3 830 11 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 4.0 4600 1.3 790 12 0.50 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 4.0 4700 1.6 770 12 0.50 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 4.0 4600 1.5 790 11 0.50 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.0 4800 1.2 750 13 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4200 1.2 810 12 2.0 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.0 4900 1.2 760 12 2.0 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4400 1.1 850 13 2.0 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 39, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 -MgO-SiO.sub.2 series of 3.0 wt %, semiconducting accelerants WO.sub.3, Nb.sub.2 O.sub.5, La.sub.2 O.sub.3 and Y.sub.2 O.sub.3 of 0.05 to 2.0 wt %, a solid electrolyte CeO.sub.2 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 37.
A sintering accelerant TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 (ratio of 20:30:45 wt %) of 0.05 to 6.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.02 to 3.0 wt % which can form a solid solution with perovskite type oxides, a good oxygen conductive solid electrolyte Pr.sub.6 O.sub.11 of 0.05 to 5.0 wt % which functions as a control agent to control the grain growth, and a forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 (0.1 to 12.0 wt %) to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to strontium titanat (SrTiO.sub.3) obtained by pyrolyzing titanyl strontium oxalate (SrTiO(C.sub.2 O.sub.4).sub.2 .multidot.4H.sub.2 O) and mixed well followed by calcination at 900.degree. C. Then it was ground in a wet state followed by drying, making grain, and molding, sintering at 1300.degree. C. in the air. It was reground in a wet state, made paste using resin and organic solutions so as to form a sheet, printed platinum paste for inner electrodes were laminated theron, sintered at 1400.degree. C. in the air followed by the hydrogen reduction at 1300.degree. C., and heat-treated at 950.degree. C. in the air. Finally, electrodes were adjusted so as to connect inner electrodes with outer electrodes, thereby completing the manufacture of a laminated ceramic capacitor having grain boundary varistor characteristics of FIG. 1. Electric characteristics of the laminated ceramic capacitor were measured and the results are shown in Table 40. The sintering accelerant TiO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 (ratio of 20:30:45 wt %) was obtained by weighing commercial TiO.sub.2, Al.sub.2 O.sub.3 and SiO.sub.2 powder according to the predetermined weight ratio, mixing, calcinating at 1200.degree. C., and grinding. The forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 to form a grain boundary depletion layer which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, Nb.sub.2 O.sub.5, MnCO.sub.3 or the like, calcinating at 1000.degree. C., and grinding. The size of the varistor after sintering was approximately 4 mm square and about 0.6 mm in thickness and composed of 8 layers of the dielectrics each of which was about 70 .mu.m in thickness. The apparent dielectric constant .epsilon. was calculated from the value of the capacitance (measurement 1 kHz) of the laminated varistor. The grain diameter in the sintered body was obtained by examining a cross section after polishing under an optical microscope, to the surface of which Bi.sub.2 O.sub.3 series metallic soap was applied and heat-treated at 1000.degree. C. to make the grain boundary clear.
TABLE 40__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 growth Pr.sub.6 O.sub.11 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 1.5 2800 28.0 220 3.00.1 0.2 0.5 0.8 3.5 4400 2.9 820 110.5 0.2 0.5 0.8 3.5 4500 2.4 840 111.0 0.2 0.5 0.8 3.5 4200 2.6 820 123.0 0.2 0.5 0.8 4.0 4900 2.2 770 125.0 0.2 0.5 0.8 4.0 4800 2.5 780 116.0 0.2 0.5 0.8 4.0 4800 2.5 760 111.0 0.02 0.5 0.8 3.5 4300 31.0 270 5.01.0 0.05 0.5 0.8 3.5 4200 2.3 820 121.0 0.5 0.5 0.8 4.0 4600 2.6 770 121.0 2.0 0.5 0.8 3.5 4400 2.1 800 111.0 3.0 0.5 0.8 2.0 3700 22.4 270 4.01.0 0.2 0.1 0.8 3.5 4500 17.4 250 3.51.0 0.2 0.2 0.8 4.0 4700 2.8 760 121.0 0.2 1.0 0.8 4.0 4800 2.4 750 111.0 0.2 3.0 0.8 3.5 4400 2.3 810 111.0 0.2 10.0 0.8 3.5 4200 2.5 830 121.0 0.2 12.0 0.8 2.5 2800 19.2 280 4.51.0 0.2 0.5 0.05 3.5 4200 24.3 810 6.51.0 0.2 0.5 0.1 4.0 4800 2.3 790 111.0 0.2 0.5 0.5 4.0 4800 2.2 780 121.0 0.2 0.5 2.0 3.5 4200 2.7 820 121.0 0.2 0.5 4.0 3.5 4100 2.4 800 111.0 0.2 0.5 5.0 2.0 3200 14.2 320 4.5__________________________________________________________________________
As is apparent from the results in Table 40, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.3 -Al.sub.2 O.sub.3 -SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte Pr.sub.6 O.sub.11 0.1 to 4.0 wt %, and a forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 of 0.2 to 10.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 3.5 to 4.0 .mu.m and the dielectric loss was 3.0% or less and the apparent dielectric constant was 4,000 or more. The riser voltage V.sub. 1 mA of the materials as a varistor was 750 to 850 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between v.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the resistance non-linearity coeffecient in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained. When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it not practical.
EXAMPLE 41
A sintering accelerant of 1.0 wt % selected from TiO.sub.2 --MgO--SiO.sub.2 series (for example, ratio of 30:30:40 wt %), TiO.sub.2 --MnO--SiO.sub.2 series (for example, ratio of 10:50:40 wt %), TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 series (for example, ratio of 20:35:45 wt %) mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.04 wt % which can form a solid solution with perovskite type oxides, a good oxygen conductive solid electrolyte Pr.sub.6 O.sub.11 of 0.2 to 3.0 wt % which functions as a control agent to control the grain growth, and a forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 of 0.4 to 0.8 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth, and a forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 of 0.4 to 0.8 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to commercial industrial strontium titanat (SrTiO.sub.3) and mixed well followed by calcination at 900.degree. C. Then it was ground in a wet state followed by drying, making grain, and molded into a disk shape, sintered at 1380.degree. C. in the reducing atmosphere composed of 95% of nitrogen and 5% of hydrogen. It was heat-treated at 950.degree. C. in the air and silver electrodes were formed on both sides of the disk, thereby completing the manufacture of a ceramic capacitor having grain boundary varistor characteristics of FIG. 2. Electric characteristics of the laminated ceramic capacitor were measured and the results are shown in Table 41. The sintering accelerant, for example, TiO.sub.2 --MgO--SiO.sub.2 series (for example, ratio of 30:30:40 wt %) was obtained by weighing commercial TiO.sub.2, MgO and SiO.sub.2 powder according to the predetermined weight ratio, mixing, calcinating at 120.degree. C., and grinding. The forming agent Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 to form a grain boundary depletion layer which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, Nb.sub.2 O.sub.5 and MnCO.sub.3, calcinating at 900.degree. C., and grinding.
TABLE 41__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Mn.sub.1/2 Nb.sub.1/2)O.sub.3 growth Pr.sub.6 O.sub.11 mean grain(wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 1.0 3.5 4300 2.7 800 121.0 0.4 8.0 1.0 3.5 4200 2.4 810 121.0 0.4 1.0 0.2 4.0 4800 2.7 760 111.0 0.4 1.0 3.0 3.5 4500 2.1 830 12TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 1.0 4.0 4800 2.3 780 111.0 0.4 8.0 1.0 3.5 4300 2.5 840 121.0 0.4 1.0 0.2 4.0 4600 2.2 780 111.0 0.4 1.0 3.0 3.5 4300 2.2 820 11TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 1.0 4.0 4700 2.3 790 121.0 0.4 8.0 1.0 4.0 4600 2.7 760 111.0 0.4 1.0 0.2 4.0 4700 2.5 770 121.0 0.4 1.0 3.0 3.5 4400 2.3 830 11__________________________________________________________________________
As is apparent from the results in Table 41, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a good oxygen conductive solid electrolyte Pr.sub.6 O.sub.11 of 0.2 to 3.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 8.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 40.
EXAMPLE 42
A sintering accelerant of 3.0 wt % of TiO.sub.2 --MgO--SiO.sub.2 series (for example, ratio of 30:30:40 wt %) mainly forming a liquid phase at a high temperature, semiconducting accelerants WO.sub.3, Nb.sub.2 O.sub.5, La.sub.2 O.sub.3 and Y.sub.2 O.sub.3 of 0.05 to 2.0 wt %, a good oxygen conductive solid electrolyte Pr.sub.6 O.sub.11 of 1.5 wt % which functions as a control agent to control the grain growth, and a forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 of to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to commercial industrial strontium titanat (SrTiO.sub.3) and mixed well followed by calcination at 900.degree. C. Then it was ground in a wet state followed by drying, making grain, and molding, sintering at 1380.degree. C. in the reducing atmosphere composed of 95% of nitrogen and 5% of hydrogen. It was heat-treated at 950.degree. C. in the air and electrodes were formed, thereby completing the manufacture of a ceramic capacitor having grain boundary varistor characteristics of FIG. 2. Electric characteristics of the laminated ceramic capacitor were measured and the results are shown in Table 42.
The sintering accelerant TiO.sub.2 --MgO--SiO.sub.2 series (ratio of 30:30:40 wt %) was obtained by weighing commercial TiO.sub.2, MgO, SiO.sub.2 powder according to the predetermined weight ratio, mixing, calcinating at 1200.degree. C., and grinding. The forming agent to form a grain boundary depletion layer which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, Nb.sub.2 O.sub.5 and MnCO.sub.3, calcinating at 900.degree. C., and grinding.
TABLE 42__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth Pr.sub.6 O.sub.11 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.0 4700 2.8 780 12 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4300 2.7 810 12 0.05 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.0 4800 2.7 790 13 0.05 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub. 0.1 Ca.sub.0.1 1.5 3.5 4300 2.6 840 11 0.05 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 4.0 4800 2.3 790 12 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.6 Ba.sub.0.2 ca.sub.0.2 1.5 3.5 4500 2.4 830 11 0.50 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.5 4400 2.5 820 12 0.50 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.5 4400 2.4 810 11 0.50 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4300 2.4 830 12 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4400 2.3 810 13 2.0 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.0 4600 2.6 790 13 2.0 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4300 2.4 820 11 2.0 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 42, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 series of 3.0 wt %, semiconducting accelerants WO.sub.3, Nb.sub.2 O.sub.5, La.sub.2 O.sub.3 and Y.sub.2 O.sub.3 of 0.05 to 2.0 wt %, a solid electrolyte Pr.sub.6 O.sub.11 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 40.
EXAMPLE 43
A capacitor was manufactured according to the method in Example 40 including the manufacturing method for other materials, sintering accelerant or the like, except that the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.1 to 6.0 wt %) was used instead of the forming agent Sr(Mn.sub.1/2 Nb.sub.1/2) (0.1 to 12.0 wt %) to form a grain boundary depletion both of which also function as control agents to control the grain growth and electric characteristics thereof were measured by the same method as Example 40. The results are shown in Table 43. The forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 to form a grain boundary depletion was obtained by mixing commercial SrCO.sub.3, Nb.sub.2 O.sub.5, CuO or the like, sintering at 1000.degree. C. and grinding.
TABLE 43__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 growth Pr.sub.6 O.sub.11 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 0.5 0.8 1.2 1500 55.0 250 5.00.1 0.2 0.5 0.8 3.0 3600 2.6 940 120.5 0.2 0.5 0.8 3.0 3600 2.2 920 131.0 0.2 0.5 0.8 3.5 3900 1.8 860 133.0 0.2 0.5 0.8 3.5 3700 1.8 830 125.0 0.2 0.5 0.8 3.5 3800 1.7 860 136.0 0.2 0.5 0.8 3.5 3700 1.7 840 131.0 0.02 0.5 0.8 1.2 2500 25.0 310 5.01.0 0.05 0.5 0.8 3.0 3600 2.2 920 121.0 0.5 0.5 0.8 3.5 3900 1.8 850 131.0 2.0 0.5 0.8 3.5 3800 1.7 870 121.0 3.0 0.5 0.8 3.0 3400 25.0 400 4.51.0 0.2 0.1 0.8 3.0 3100 32.5 380 3.51.0 0.2 0.2 0.8 3.5 3900 2.8 880 111.0 0.2 1.0 0.8 3.0 3600 1.1 900 121.0 0.2 3.0 0.8 3.5 3800 1.9 890 131.0 0.2 5.0 0.8 3.5 3900 1.8 860 111.0 0.2 6.0 0.8 3.5 2700 17.0 320 5.51.0 0.2 0.5 0.05 3.0 3300 17.7 430 4.01.0 0.2 0.5 0.1 3.5 3700 2.2 850 131.0 0.2 0.5 0.5 3.5 3800 1.7 880 121.0 0.2 0.5 2.0 3.5 3700 1.9 830 131.0 0.2 0.5 4.0 3.0 3600 1.1 900 111.0 0.2 0.5 5.0 2.0 2700 12.5 330 5.0__________________________________________________________________________
As is apparent from the results in Table 43, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 --Al.sub.2 O.sub.3 --SiO of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte Pr.sub.6 O.sub.11 0.1 to 4.0 wt % which also functions as a control agent to control the grain growth, and a forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 of 0.2 to 5.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 3 0 to 3.5 .mu.m and the dielectric loss was 3.0% or less and the apparent dielectric constant was 3,500 or more. The riser voltage V.sub.1 mA of the materials as a varistor was 800 to 950 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the resistance non-linearity coeffecient in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained. When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 44
A capacitor was manufactured according to the method in Example 41 including the manufacturing method for other materials, sintering accelerant or the like, except that the forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 (0.4 to 4.0 wt %) was used instead of the forming agent Sr(Mn.sub.1/2 Nb.sub.1/2) (0.4 to 8.0 wt %) to form a grain boundary depletion both of which also function as control agents to control the grain growth and electric characteristics thereof were measured by the same method as Example 41. The results are shown in Table 44. The forming agent Sr(Cu.sub.1/3 Nb.sub.2/3)O.sub.3 to form a grain boundary depletion was obtained by mixing commercial SrCO.sub.3, Nb.sub.2 O.sub.5 and CuO, sintering at 900.degree. C. and grinding.
TABLE 44__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Co.sub.1/3 Nb.sub.2/3)O.sub.3 growth Pr.sub.6 O.sub.11 mean grain(wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 1.0 3.5 3800 1.2 890 121.0 0.4 4.0 1.0 3.0 3600 1.4 950 121.0 0.4 1.0 0.2 3.5 3800 1.2 840 121.0 0.4 1.0 3.0 3.0 3500 1.0 930 11TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 1.0 3.5 3900 1.8 870 131.0 0.4 4.0 1.0 3.5 3700 1.8 880 121.0 0.4 1.0 0.2 3.5 3800 1.9 880 121.0 0.4 1.0 3.0 3.0 3500 1.7 910 13TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 1.0 3.5 3800 0.8 890 131.0 0.4 4.0 1.0 3.5 3700 0.8 880 121.0 0.4 1.0 0.2 3.5 3600 0.9 850 111.0 0.4 1.0 3.0 3.0 3500 0.9 900 12__________________________________________________________________________
As is apparent from the results in Table 44, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a good oxygen conductive solid electrolyte Pr.sub.6 O.sub.11 of 0.2 to 3.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 4.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 43.
EXAMPLE 45
The forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Cu.sub.1/3 Nb.sub.2/3) O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 of 2.0 wt % was added instead of the forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 Mn.sub.1/2 Nb.sub.1/2)O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Mn.sub.1/2 Nb.sub.1/2)O.sub.3 of 2.0 wt % to form a grain boundary depletion all of which also function as control agents to control the grain growth of Example 42. The manufacturing method for other materials, sintering accelerant or the like, was the same as Example 42 and electric characteristics thereof were measured by the same method as Example 42. The forming agent to form a grain boundary depletion was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, Mb.sub.2 O.sub.5, and CuO, sintering at 900.degree. C. and grinding
The results are shown in Table 45.
TABLE 45__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth Pr.sub.6 O.sub.11 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 3800 1.9 880 13 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3500 1.4 920 12 0.05 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3600 1.8 910 13 0.05 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub. 0.1 Ca.sub.0.1 1.5 3.0 3500 1.9 920 12 0.05 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.5 3700 1.8 890 11 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.0 3600 1.2 900 12 0.50 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.0 3400 2.8 910 13 0.50 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.0 3500 1.7 920 13 0.50 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 3800 1.9 890 13 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 3700 1.3 870 13 2.0 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3600 1.8 910 12 2.0 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.0 3500 1.9 920 13 2.0 (Cu.sub.1/3 Nb.sub.2/3)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 45, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 series of 3.0 wt %, semiconducting accelerants WO.sub.3, Nb O.sub.2, .sub.5 La.sub.2 O.sub.3 and Y.sub.2 O.sub.3 of 0.05 to 2.0 wt %, a solid electrolyte Pr.sub.6 O.sub.11 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 43.
EXAMPLE 46
A sintering accelerant TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 (ratio of 20:30:45 wt %) of 0.05 to 5.0 wt % mainly forming a liquid phase at a high temperature, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.02 to 3.0 wt % which can form a solid solution with perovskite type oxides, a good oxygen conductive solid electrolyte CeO.sub.2 of 0.05 to 4.0 wt % which functions as a control agent to control the grain growth, and a forming agent Sr(Mn.sub.2/3 W.sub.1/3)O.sub.3 (0.1 to 8.0 wt %) to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to strontium titanat (SrTiO.sub.3) obtained by pyrolyzing titanyl strontium oxalate (SrTio(C.sub.2 O.sub.4).sub.2 .multidot.4H.sub.2 O) and mixed well followed by calcination at 900.degree. C. Then it was ground in a wet state followed by drying, making grain, and molding, sintering at 1300.degree. C. in the air. It was reground in a wet state, made into paste using resin and organic solutions so as to form a sheet, printed platinum paste for inner electrodes were laminated theron, sintered at 1400.degree. C. in the air followed by the hydrogen reduction at 1300.degree. C., and heat-treated at 950.degree. C. in the air. Finally, electrodes were adjusted so as to connect inner electrodes with outer electrodes, thereby completing the manufacture of a laminated ceramic capacitor having grain boundary varistor characteristics of FIG. 1. Electric characteristics of the laminated ceramic capacitor were measured and the results are shown in Table 46. The sintering accelerant TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 (ratio of 20:35:45 wt %) was obtained by weighing commercial TiO.sub.2, Al.sub.2 O.sub.3 and SiO.sub.2 powder according to the predetermined weight ratio, mixing, calcinating at 1200.degree. C., and grinding. The forming agent Sr(Mn.sub.2/3 W.sub.1/3)O.sub.3 to form a grain boundary depletion layer which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, WO.sub.3, MnCO.sub.3 or the like, calcinating at 1000.degree. C., and grinding. The size of the varistor after sintering was approximately 4 mm square and about 0.6 mm in thickness and composed of 8 layers of the dielectrics, each of which was about 70 pm in thickness. The apparent dielectric constant was calculated from the value of the capacitance (measurement 1 kHz) of the laminated varistor. The grain diameter in the sintered body was obtained by examining a cross section after polishing under an optical microscope, to the surface of which Bi.sub.2 O.sub.3 series metallic soap was applied and heat-treated at 1000.degree. C. to make the grain boundary clear.
TABLE 46__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 Sr(Mn.sub.2/3 W.sub.1/3)O.sub.3 growth CeO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 1.5 1.0 1.5 2400 25.0 430 6.50.1 0.2 1.5 1.0 3.5 4100 4.2 840 130.5 0.2 1.5 1.0 4.0 4800 2.9 750 141.0 0.2 1.5 1.0 3.5 4300 2.5 820 133.0 0.2 1.5 1.0 3.5 4100 3.1 840 135.0 0.2 1.5 1.0 4.0 4800 2.0 760 141.0 0.02 1.5 1.0 4.0 3100 35.0 450 5.01.0 0.05 1.5 1.0 4.0 4800 4.3 720 131.0 0.5 1.5 1.0 3.5 4200 2.9 820 141.0 2.0 1.5 1.0 4.0 5300 3.0 750 131.0 3.0 1.5 1.0 3.5 2500 22.0 480 4.01.0 0.2 0.1 1.0 3.5 3400 18.5 510 4.01.0 0.2 0.2 1.0 4.0 5200 2.2 760 121.0 0.2 1.0 1.0 3.5 4300 2.1 820 131.0 0.2 3.0 1.0 4.0 4900 3.0 720 131.0 0.2 6.0 1.0 3.5 4200 2.1 820 131.0 0.2 8.0 1.0 1.5 2800 5.5 450 6.01.0 0.2 1.5 0.05 2.5 2200 17.5 420 3.51.0 0.2 1.5 0.1 3.5 4200 2.4 830 131.0 0.2 1.5 0.3 4.0 5000 2.1 710 141.0 0.2 1.5 1.0 3.5 4100 2.0 880 131.0 0.2 1.5 3.0 3.5 4200 3.0 810 131.0 0.2 1.5 4.0 1.5 2500 15.5 380 4.0__________________________________________________________________________
As is apparent from the results in Table 46, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 --Al.sub.2 O.sub.3 --SiO of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte CeO.sub.2 0.1 to 3.0 wt %, and a forming agent Sr(Mn.sub.2/3 W.sub.1/3)O.sub.3 of 0.2 to 6.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a varistor with high capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and approximately 3.5 to 4.0 .mu.m and the dielectric loss was 5.0% or less and the apparent dielectric constant was 4000 or more. The riser voltage V.sub.1 mA of the materials as a varistor was 700 to 900 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the resistance non-linearity coeffecient in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained. When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 47
A sintering accelerant of 1.0 wt % selected from TiO.sub.2 --MgO--SiO.sub.2 series (for example, ratio of 30:30:40 wt %), TiO.sub.2 --MnO--SiO.sub.2 series (for example, ratio of 10:50:40 wt %), TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 series (for example, ratio of 20:35:45 wt %) mainly forming a liquid phase at a high temperature, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt % which can form a solid solution with perovskite type oxides, a good oxygen conductive solid electrolyte CeO.sub.2 of 0.2 to 2.0 wt % which functions as a control agent to control the grain growth, and a forming agent Sr(Mn.sub.2/3 W.sub.1/3)O.sub.3 of 0.4 to 4.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to commercial industrial strontium titanat (SrTiO.sub.3) and mixed well followed by calcination at 900.degree. C. Then it was ground in a wet state followed by drying, making grain, and molded into a disk shape, sintered at 1380.degree. C. in the reducing atmosphere composed of 95% of nitrogen and 5% of hydrogen. It was heat-treated at 950.degree. C. in the air and silver electrodes were formed on both sides of the disk, thereby completing the manufacture of a ceramic capacitor having grain boundary varistor characteristics of FIG. 2. Electric characteristics of the laminated ceramic capacitor were measured and the results are shown in Table 47. The sintering accelerant TiO.sub.2 --MgO--SiO.sub.2 series (for example, ratio of 30:30:40 wt %) was obtained by weighing commercial TiO.sub.2, MgO and SiO.sub.2 powder according to the predetermined weight ratio, mixing, calcinating at 1200.degree. C., and grinding. The forming agent Sr(Mn.sub.2/3 W.sub.1/3) O.sub.3 to form a grain boundary depletion layer which also function as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, WO.sub.3 and MnCO.sub.3, calcinating at 900.degree. C., and grinding.
TABLE 47__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 Sr(Mn.sub.2/3 W.sub.1/3)O.sub.3 growth CeO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 1.0 3.5 4100 3.2 830 131.0 0.4 4.0 1.0 3.5 4200 3.4 850 121.0 0.4 1.0 0.2 4.0 4500 2.9 750 131.0 0.4 1.0 2.0 3.5 4300 3.7 810 14TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 1.0 3.7 4800 3.3 820 121.0 0.4 4.0 1.0 3.7 4500 3.2 810 111.0 0.4 1.0 0.2 3.4 5000 3.2 850 111.0 0.4 1.0 2.0 4.0 4800 3.0 740 14TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 1.0 4.0 5100 3.9 770 131.0 0.4 4.0 1.0 3.7 4600 2.9 800 111.0 0.4 1.0 0.2 3.7 4500 3.9 780 131.0 0.4 1.0 2.0 3.5 4100 3.2 860 12__________________________________________________________________________
As is apparent from the results in Table 47, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 of 1.0 wt %, a semiconducting accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a good oxygen conductive solid electrolyte CeO.sub.2 of 0.2 to 2.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 4.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 46.
EXAMPLE 48
A sintering accelerant of 30 wt % of TiO.sub.2 --MgO--SiO.sub.2 series (for example, ratio of 30:30:40 wt %) mainly forming a liquid phase at a high temperature, semiconducting accelerants WO.sub.3 .multidot.Nb.sub.2 O.sub.5, La.sub.2 O.sub.3 and Y.sub.2 O.sub.3 of 0.05 to 2.0 wt %, a good oxygen conductive solid electrolyte CeO.sub.2 of 1.5 wt % which functions as a control agent to control the grain growth, and a forming agent Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 (Mn.sub.2/3 W.sub.1/3)O.sub.3 or Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 (Mn.sub.2/3 W.sub.1/3)O.sub.3 of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to commercial industrial strontium titanat (SrTiO.sub.3) and mixed well followed by calcination at 900.degree. C. Then it was ground in a wet state followed by drying, making grain, and molding, sintering at 1380.degree. C. in the reducing atmosphere composed of 95% of nitrogen and 5% of hydrogen. It was heat-treated at 950.degree. C. in the air and electrodes were formed, thereby completing the manufacture of a ceramic capacitor having grain boundary varistor characteristics of FIG. 2. Electric characteristics of the laminated ceramic capacitor were measured and the results are shown in Table 48. The sintering accelerant TiO.sub.2 --MgO--SiO.sub.2 series (ratio of 30:30:40 wt %) was obtained by weighing commercial TiO.sub.2, MgO, SiO.sub.2 powder according to the predetermined weight ratio, mixing, calcinating at 1200.degree. C., and grinding. The forming agent to form a grain boundary depletion layer which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, BaCO.sub.3, CaCO.sub.3, WO.sub.3 and MnCO.sub.3, calcinating at 900.degree. C., and grinding.
TABLE 48__________________________________________________________________________ solid electrolyte forming agent to form a which functions semicon- grain boundary deple- as a control ducting tion layer which also agent to controlsintering accelerant accel- functions as a control the grainTiO.sub.2 --MgO--SiO.sub.2 erant agent to control the growth CeO.sub.2 mean graincompound (wt %) (wt %) grain growth (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________3.0 WO.sub.3 0.05 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.7 4500 3.8 780 14 (Mn.sub.2/3 W.sub.1/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.0 4700 3.2 740 14 0.05 (Mn.sub.2/3 W.sub.1/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.0 5100 3.3 810 13 0.05 (Mn.sub.2/3 W.sub.1/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub. 0.1 1.5 3.7 4400 3.6 810 12 0.05 (Mn.sub.2/3 W.sub.1/3)O.sub.3 2.03.0 WO.sub.3 0.50 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 4.0 4900 3.1 770 13 (Mn.sub.2/3 W.sub.1/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.7 4500 3.3 790 12 0.50 (Mn.sub.2/3 W.sub.1/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 3.5 4300 3.7 850 14 0.50 (Mn.sub.2/3 W.sub.1/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.6 Ba.sub.0.2 Ca.sub.0.2 1.5 4.0 5100 3.0 760 13 0.50 (Mn.sub.2/3 W.sub.1/3)O.sub.3 2.03.0 WO.sub.3 2.0 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.7 4500 3.9 780 14 (Mn.sub.2/3 W.sub.1/3)O.sub.3 2.03.0 Nb.sub.2 O.sub.5 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.5 4200 3.5 860 13 2.0 (Mn.sub.2/3 W.sub.1/3)O.sub.3 2.03.0 La.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 4.0 4700 3.7 740 14 2.0 (Mn.sub.2/3 W.sub.1/3)O.sub.3 2.03.0 Y.sub.2 O.sub.3 Sr.sub.0.8 Ba.sub.0.1 Ca.sub.0.1 1.5 3.7 4400 3.2 810 13 2.0 (Mn.sub.2/3 W.sub.1/3)O.sub.3 2.0__________________________________________________________________________
As is apparent from the results in Table 48, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 series of 3.0 wt %, semiconducting accelerants WO.sub.3, Nb.sub.2 O.sub.5, La.sub.2 O.sub.3 and Y.sub.2 O.sub.3 of 0.05 to 0.5 or 1.0 wt %, a solid electrolyte CeO.sub.2 of 1.5 wt % which also functions as a control agent to control the grain growth, and a forming agent of 2.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a varistor with high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 46.
EXAMPLE 49
A capacitor was manufactured according to the method in Example 46 including the manufacturing method for other materials, sintering accelerant or the like, except that a compound SrO.multidot.1/3Mn.sub.2 O.sub.3 1/3MoO.sub.3 (0.1 to 6.0 wt %) was used as a forming agent instead of the forming agent Sr(Mn.sub.2/3 W.sub.1/3)O.sub.3 (0.1 to 6.0 wt %) to form a grain boundary depletion and electric characteristics thereof were measured by the same method as Example 46. The results are shown in Table 49. The forming agent SrO.multidot.1/3Mn.sub.2 O.sub.3 .multidot.1/3MoO.sub.3 to form a grain boundary depletion which also functions as a control agent to control the grain growth was obtained by mixing commercial SrCO.sub.3, MoO.sub.3, MnCO.sub.3 or the like, sintering at 1000.degree. C. and grinding.
TABLE 49__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to controlsintering accelerant erant grain growth the grainTiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 Nb.sub.2 O.sub.5 SrO.1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 growth CeO.sub.2 mean grain rising voltagecompound (wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________0.05 0.2 1.5 1.0 2.0 3500 16.5 270 4.50.1 0.2 1.5 1.0 3.5 4200 3.4 810 110.5 0.2 1.5 1.0 4.0 4800 3.5 760 121.0 0.2 1.5 1.0 3.5 3900 3.6 830 133.0 0.2 1.5 1.0 4.0 5200 3.8 780 125.0 0.2 1.5 1.0 3.5 4300 3.1 830 121.0 0.02 1.5 1.0 2.5 2500 26.5 270 3.51.0 0.05 1.5 1.0 3.5 4300 3.9 890 111.0 0.5 1.5 1.0 3.5 4100 3.2 870 121.0 2.0 1.5 1.0 4.0 4700 3.1 760 111.0 3.0 1.5 1.0 2.5 3800 22.5 270 4.51.0 0.2 0.1 1.0 3.0 4200 38.0 260 2.51.0 0.2 0.2 1.0 4.0 4800 3.2 720 111.0 0.2 0.5 1.0 3.5 3900 3.5 850 121.0 0.2 1.0 1.0 3.5 4300 3.1 870 131.0 0.2 5.0 1.0 3.5 4100 3.1 870 131.0 0.2 6.0 1.0 2.0 3700 18.2 350 8.51.0 0.2 1.5 0.05 3.0 4300 21.3 310 7.01.0 0.2 1.5 0.1 4.0 4900 3.1 780 121.0 0.2 1.5 0.5 3.5 3900 3.4 860 121.0 0.2 1.5 1.0 3.5 4200 3.8 840 131.0 0.2 1.5 3.0 4.0 4600 3.4 790 121.0 0.2 1.5 4.0 2.0 3200 22.9 420 3.5__________________________________________________________________________
As is apparent from the results in Table 49, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2 of 0.1 to 5.0 wt %, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt %, a solid electrolyte CeO.sub.2 0.1 to 3.0 wt %, and a forming agent SrO.multidot.1/3Mn.sub.2 O.sub.3 .multidot.1/3MoO.sub.3 of 0.2 to 5.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics with uniform grain diameter and can be used as a ceramic capacitor with varistor characteristics having high capacitance. According to a microscopic examination, the grain diameters of corpuscles in the sintered body were uniform and the mean grain diameter was approximately 3.5 to 4.0 .mu.m and the dielectric loss was 4.0% or less and the apparent voltage V.sub.1 mA of the materials as a varistor was 700 to 900 V/mm and the resistance non-linearity coeffecient .alpha. is 10 or more in most cases between V.sub.1 mA to V.sub.0.1 mA. Other values such as surge durability as a varistor, the ratio of limited voltage representing the resistance non-linearity coeffecient in high current area, the temperature coefficient of the riser voltage V.sub.1 mA and capacitance were measured and sufficient values were obtained. When the amount of the sintering accelerant added exceeds 5%, the sintered body is prone to deform or adhere, therefore it is not practical.
EXAMPLE 50
A capacitor was manufactured according to the method in Example 47 including the manufacturing method for other materials, sintering accelerant or the like, except that the forming agent SrO.multidot.1/3Mn.sub.2 O.sub.3 .multidot.1/3MoO.sub.3 (0.4 to 4.0 wt %) was used instead of the forming agent Sr(Mn.sub.2/3 W.sub.1/3) (0.4 to 4.0 wt %) to form a grain boundary depletion and electric characteristics thereof were measured by the same method as Example 47. The results are shown in Table 50. The forming agent SrO.multidot.1/3Mn.sub.2 O.sub.3 .multidot.1/3MoO.sub.3 to form a grain boundary depletion which also functions as a control agent to control grain growth was obtained by mixing commercial SrCO.sub.3, MoO.sub.3, MnCO.sub.3 or the like, sintering at 1000.degree. C. and grinding. The sintering accelerant, for example, TiO.sub.2 --MgO--SiO.sub.2 series (ratio of 30:30:40 wt %) was obtained by weighing and mixing commercial TiO.sub.2, MgO, SiO.sub.2 powder according to the predetermined weight ratio, mixing, calcinating at 1200.degree. C., and grinding.
TABLE 50__________________________________________________________________________ forming agent to form a grain boundary deple- solid electrolyte semicon- tion layer which also which functions ducting functions as a control as a control accel- agent to control the agent to control erant grain growth the grainsintering accelerant Y.sub.2 O.sub.3 SrO.1/3Mn.sub.2 O.sub.3.1/3MoO.sub.3 growth CeO.sub.2 mean grain(wt %) (wt %) (wt %) (wt %) diameter (.mu.m) .epsilon. tan .delta. (%) V.sub.1 mA .alpha.__________________________________________________________________________TiO.sub.2 --Al.sub.2 O.sub.3 --SiO.sub.2compound1.0 0.4 0.4 1.0 3.7 4900 3.4 790 111.0 0.4 4.0 1.0 3.7 4700 3.5 830 111.0 0.4 1.0 0.2 4.0 5100 3.6 750 121.0 0.4 1.0 2.0 3.7 4400 3.3 770 11TiO.sub.2 --MnO--SiO.sub.2compound1.0 0.4 0.4 1.0 3.5 4200 3.7 830 111.0 0.4 4.0 1.0 3.5 4000 3.4 840 121.0 0.4 1.0 0.2 3.7 4200 3.4 810 111.0 0.4 1.0 2.0 3.5 3900 3.6 830 12TiO.sub.2 --MgO--SiO.sub.2compound1.0 0.4 0.4 1.0 4.0 5100 3.3 760 121.0 0.4 4.0 1.0 3.5 4100 3.6 850 121.0 0.4 1.0 0.2 4.0 5300 3.7 750 111.0 0.4 1.0 2.0 3.7 4600 3.7 770 12__________________________________________________________________________
As is apparent from the results in Table 50, the present material obtained by adding SrTiO.sub.3 to a sintering accelerant such as TiO.sub.2 --MgO--SiO.sub.2 of 1.0 wt % mainly forming a liquid phase at a high temperature, a sintering accelerant Y.sub.2 O.sub.3 of 0.4 wt %, a good oxygen conductive solid electrolyte CeO.sub.2 of 0.2 to 2.0 wt % which also functions as a control agent to control the grain growth, and a forming agent of 0.4 to 4.0 wt % to form a grain boundary depletion layer which also functions as a control agent to control the grain growth and sintering has excellent varistor and dielectric characteristics and can be used as a ceramic capacitor with varistor characteristics having high capacitance. The electric characteristics of the materials used in these devices are similar to those used in Example 49.
In examples 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 17, 18, 20, 21, 23 and 24, when a sintering accelerant a semiconducting accelerant, a good oxygen conductive solid electrolyte which functions as a control agent to control the grain growth, and a forming agent to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to and mixed with SrTiO.sub.3, molded under pressure, calcinated to reduce at 800.degree. to 1500.degree. C. and then heat-treated at 900.degree. to 1150.degree. C. in the oxidizing atmosphere, the same results obtained from each example were confirmed.
In examples 1, 4, 7, 10, 13, 16, 19 and 22, when a sintering accelerant, a semiconducting accelerant, a good oxygen conductive solid electrolyte which functions as a control agent to control the grain growth, and a forming agent to form a grain boundary depletion layer which also functions as a control agent to control the grain growth, were added to and mixed with SrTiO.sub.3, molded under pressure, sintered at 1200.degree. C. to 1500.degree. C. in the air, re-ground so as to laminate with metal inner electrodes alternately, and sintered at 1250.degree. C. to 1500.degree. C. in the air followed by the reduction at 800.degree. C. to 1500.degree. C. in the reducing atmosphere containing hydrogen, and heat-treated at 900.degree. C. to 1150.degree. C. in the oxidizing atmosphere, the same results obtained from each example were confirmed. In examples 26, 27, 29, 30, 32, 33, 35, 36, 38 and 39, when a sintering accelerant, a semiconducting accelerant, a good oxygen conductive solid electrolyte, which functions as a control agent to control the grain growth, and a forming agent to form a grain boundary depletion layer which also functions as a control agent to control the grain growth, were added to and mixed with SrTiO.sub.3, molded under pressure, calcinated to reduce at 1100.degree. C. to 1500.degree. C. and then heat-treated at 900.degree. C. to 1150.degree. C. in the oxidizing atmosphere, the same results obtained from each example were confirmed. In examples 25, 28, 31, 34 and 37, when a sintering accelerant, a semiconducting accelerant, a good oxygen conductive solid electrolyte which functions as a control agent to control the grain growth, and a forming agent to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to and mixed with SrTiO.sub.3, molded under pressure, sintered at 1200.degree. C. to 1500.degree. C. in the air, re-ground so as to laminate with noble metal inner electrodes alternately, and sintered at 1250.degree. C. to 1500.degree. C. in the air followed by the reduction at 900.degree. C. to 1150.degree. C. in the reducing atmosphere containing hydrogen, and heat-treated at 900.degree. C. to 1150.degree. C. in the oxidizing atmosphere, the same results obtained from each example were confirmed. In examples 41, 42, 44 and 45, when a sintering accelerant, a semiconducting accelerant, a good oxygen conductive solid electrolyte which functions as a control agent to control the grain growth, and a forming agent to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to and mixed with SrTiO.sub.3, molded under pressure, calcinated to reduce at 1100.degree. C. to 1500.degree. C. and then heat-treated at 900.degree. C. to 1150.degree. C. in the oxidizing atmosphere, the same results obtained from each example were confirmed. In examples and 43, when a sintering accelerant, a semiconducting accelerant, a good oxygen conductive solid electrolyte which functions as a control agent to control the grain growth, and a forming agent to form a grain boundary depletion layer which also functions as a control agent to control the grain growth were added to and mixed with SrTiO.sub.3, molded under pressure, sintered at 1200.degree. C. to 1500.degree. C. in the air, re-ground so as to laminate with noble metal inner electrodes alternately, and sintered at 1250.degree. C. to 1500.degree. C. in the air followed by the reduction at 900.degree. C. to 1150.degree. C. in the reducing atmosphere containing hydrogen, and heat-treated at 900.degree. C. to 1150.degree. C. in the oxidizing atmosphere, the same results obtained from each example were confirmed. In examples 47, 48 and 50, when a sintering accelerant, a semiconducting accelerant, a good oxygen conductive solid electrolyte which functions as a control agent to control the grain growth, and a forming agent to form a grain boundary depletion layer, which also functions as a control agent to control the grain growth were added to and mixed with SrTiO.sub.3, molded under pressure, calcinated to reduce at 900.degree. C. to 1500.degree. C. and then heat-treated at 900.degree. C. to 1150.degree. C. in the oxidizing atmosphere, the same results obtained from each example were confirmed. In examples 46 and 49, when a sintering accelerant, a semiconducting accelerant, a good oxygen conductive solid electrolyte which functions as a control agent to control the grain growth, and a forming agent to form a grain boundary depletion layer, which also functions as a control agent to control the grain growth were added to and mixed with SrTiO.sub.3, molded under pressure, sintered at 1100.degree. C. to 1500.degree. C. in the air, re-ground so as to laminate with noble metal inner electrodes alternately, and sintered at 1250.degree. C. to 1500.degree. C. in the air followed by the reduction at 900.degree. C. to 1500.degree. C. in the reducing atmosphere containing hydrogen, and heat-treated at 900.degree. C. to 1150.degree. C. in the oxidizing atmosphere, the same results obtained from each example were confirmed.
INDUSTRIAL APPLICABILITY
As described above, according to the present invention, a ceramic capacitor having varistor characteristics is manufactured by the steps comprising; adding a sintering accelerant of 0.1 to 5.0 wt % mainly composed of the mixture and forming a liquid phase at a high temperature, a semiconducting accelerant Nb.sub.2 O.sub.5 of 0.05 to 2.0 wt % that can form a solid solution with perovskite type oxides, and a control agent for porous sintering and a forming agent to form a grain boundary depletion layer which also functions as a control agent to control the grain growth, to perovskite type oxides powder made of the materials of strontium titanate (SrTiO.sub.3) as a main component, mixing and molding under pressure, sintering and reducing at 1250.degree. C. to 1500.degree. C., heat-treating at 900.degree. C. to 1150.degree. C. in the oxidizing atmosphere so as to form electrodes. Therefore, a uniform porous body can be obtained without complicated processes of coating and diffusing Bi.sub.2 O.sub.3 or the like, and, moreover, the size of the porous body is not subject to any particular restriction. The effects of the present application are greatly improved from the point of view of practical applications.

Number	Date	Country	Kind
1-85445	Apr 1989	JPX
1-124867	May 1989	JPX

Number	Name	Date
3872360	Sheard	Mar 1975
4403236	Mandai et al.	Sep 1983
4607314	Wada et al.	Aug 1986
5014158	Nishimura et al.	May 1991
5166859	Ueno et al.	Nov 1992

Number	Date	Country
157276	Oct 1985	EPX
0255072	Feb 1988	EPX

Method for manufacturing a ceramic capacitor having varistor characteristics

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