Dielectric ceramic compositions

Abstract

Dielectric ceramic composition consisting essentially of substance selected from those represented by the following formulas:(1) Pb.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a(2) Pb.sub.a Ca.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b(3) Pb.sub.a Ba.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b(4) Pb.sub.a Sr.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+bwherein x+y+z=1.00, and a or a+b.gtoreq.1.001.These compositions can be sintered below 1080.degree. C. in low partial pressure of oxygen of about 1.times.10.sup.-8, and exhibit a high dielectric constant and a high electrical resistivity.

Description

BACKGROUND OF THE INVENTION

The present invention relates to dielectric ceramic compositions allowing sintering at low temperature and at low partial pressure of oxygen, and exhibiting a high dielectric constant, high electrical resistivity, low temperature coefficient of the dielectric constant, and low dielectric loss, whereby they are suitable for use as dielectric material for fabricating multi-layer ceramic capacitors having copper metal internal electrodes.

Recently, multi-layer ceramic capacitors have been used widely in electrical circuits of various electrical products, because such capacitance are small and have large capasitance and high reliability.

In general, multi-layer ceramic capacitors especially exhibiting large capacitance have been manufactured by cofiring barium titanate based ceramics as dielectric materials and internal electrode metals in an oxidizing atmosphere at a temperature above 1200.degree. C. However, firing under these conditions necessitates a highly expensive internal electrode metal such as platinum or palladium, because the electrode material used in such a system must not melt and must not be oxidized in the atmosphere at the firing temperature.

Therefore there have still been two demands for dielectric ceramic materials. One demand is to be able to be sintered at a temperature below 1100.degree. C. for enabling the use of relatively cheap metals such as silver-30% palladium for internal electrodes. The other demand is to be able to be sintered in reducing atmospheres and exhibit high specific resistivity for enabling the use of base metals such as nickel or copper.

U.S. Pat. No. 4,115,493 discloses non-reducing dielectric ceramic compositions of [(Ba.sub.1-x Ca.sub.x)O].sub.m (Ti.sub.1-y Zr.sub.y)O.sub.2, which can be sintered at a temperature range of 1300.degree. C. to 1400.degree. C. in an atmosphere of low partial pressure of oxygen, and which exhibit a high electrical resistivity. Since sintering temperature of this system is above 1100.degree. C., nickel metal can be used for an internal electrode in the multi-layer ceramic capacitors employing this composition as dielectric materials, but copper metal cannot be used for that. The electrical conductivity of nickel metal is lower than copper, silver, platinum and palladium, so that when nickel metal is employed as internal electrode, loss factor of the capacitor becomes large especially in high frequency.

U.S. Pat. No. 4,450,240 discloses low temperature sintering ceramic compositions of PbTiO.sub.3 -Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 -Pb(Mg.sub.1/2 W.sub.1/2)O.sub.3, which can be sintered at a temperature range of 900.degree. C. to 1050.degree. C. in an oxidizing atmosphere. This patent teaches that some complex perovskite compositions containing lead can be sintered at low temperature below 1100.degree. C., and exhibit a high dielectric constant and a high electrical resistivity.

Although silver or silver-palladium metals can be used for internal electrodes in the multi-layer ceramic capacitors employing this composition as dielectric materials, copper metal cannot be used, because this composition can not be sintered in a reducing atmosphere.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a dielectric ceramic composition which can be sintered at a temperature below 1080.degree. C. and in low partial pressure of oxygen, and exhibits a high dielectric constant and a high specific resistivity.

To attain this object, a dielectric ceramic composition according to the present invention essentially consists of a substance selected from those represented by the following formulas:

(1) Pb.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a (2) Pb.sub.a Ca.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2 +a+b (3) Pb.sub.a Ba.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b (4) Pb.sub.a Sr.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b wherein subscripts a, b, x, y and z represent molar fractions of the respective components, x+y+z=1.00, and a or a+b.gtoreq.1.001.

These novel composition of the present invention can be sintered below 1080.degree. C. in low partial pressure of oxygen about 1.times.10.sup.-8, and have a high dielectric constant and further have a high electrical resistivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a composition diagram of Pb.sub.a TiO.sub.2+a -Pb.sub.a (Mg.sub.1/3 -Nb.sub.2/3)O.sub.2+a -Pb.sub.a (Ni.sub.1/2 /W.sub.1/2)O.sub.2+a ternary system composition in accordance with the present invention;

FIG. 2 is a composition diagram of Pb.sub.a Ca.sub.b TiO.sub.2+a+b -Pb.sub.a Ca.sub.b -(Mg.sub.1/3 Nb.sub.2/3)O.sub.2+a+b -Pb.sub.a Ca.sub.b (Ni.sub.1/2 W.sub.1/2)O.sub.2+a+b ternary system composition in accordance with the present invention;

FIG. 3 is a composition diagram of Pb.sub.a Ba.sub.b TiO.sub.2+a+b -Pb.sub.a Ba.sub.b -(Mg.sub.1/3 Nb.sub.2/3)O.sub.2+a+b -Pb.sub.a Ba.sub.b (Ni.sub.1/2 W.sub.1/2)O.sub.2+a+b ternary system composition in accordance with the present invention; and

FIG. 4 is a composition diagram of Pb.sub.a Sr.sub.b TiO.sub.2+a+b -Pb.sub.a Sr.sub.b -(Mg.sub.1/3 Nb.sub.2/3)O.sub.2+a+b -Pb.sub.a Sr.sub.b (Ni.sub.1/2W.sub.1/2) O.sub.2+a+b ternary system composition in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The composition herein may be prepared in accordance with various well-known ceramic procedures.

EXAMPLE 1

The starting materials, viz. lead oxide (PbO), titanium oxide (TiO.sub.2), niobium oxide (Nb.sub.2 O.sub.5), magnesium oxide (MgO), nickel oxide (NiO), and tungsten oxide (WO.sub.3), all relatively pure grade, were initially mixed in a ball mill with distilled water and agate balls for 17 hours. Thereafter the mixture was dried and then pressed into columns, and calcined at a temperature in the range of 750.degree. C. to 880.degree. C. for 2 hours in an aluminum crucible. The substance thus obtained was wet ground in a ball mill, dried, mixed with polyvinyl alcohol as a binder solution, and then pressed into disks of about 13 mm in diameter and about 0.8 mm in thickness at a pressure of 1000 Kg/cm.sup.2, and then the binder was burned out at about 700.degree. C. in air.

The burned out disks were put into a magnesia crucible. Initially about 1/3 of volume fraction of this crucible was filled with calcined powder as mentioned above, at the bottom of the crucible, and coarse zirconia powder was laid upon the calcined powder with about 1 mm thickness. The burned out disks were put upon the coarse zirconia layer. Then a magnesia cover was put on the crucible. This crucible containing specimens was inserted into an aluminum tube in a furnace. After the air in the aluminum tube was exhausted by a rotary pump, N.sub.2 --H.sub.2 --H.sub.2 O mixture gas was flowed into the tubes. The partial pressure of H.sub.2 O in an initial mixture gas was 3.2.times.10.sup.-3 atm, and the partial pressure of H.sub.2 in an initial mixture gas was 2.2.times.10.sup.-4 atm, and the partial pressure of O.sub.2 in a initial mixture gas was 1.0.times.10.sup.-4 atm.

The specimens were sintered at a temperature in the range of 850.degree. C. to 1100.degree. C. for 2 hours. The partial pressure of oxygen of the atmosphere in the sintering process was measured with yttrium oxide stabilized zirconia O.sub.2 sensor which was inserted on to the magnesia crucible in the aluminium tube. The partial pressure of oxygen of the atmosphere at the sintering temperature was 1.0.times.10.sup.-8 to 1.0.times.10.sup.-12 atm, which was decreased in accordance with lowering of the sintering temperature.

The sintered bodies were measured for densities. The sintering temperature is selected so that the density of the sintered disks becomes maximum. After measuring the densities Cr-Au electrodes were attached on both surfaces of the disks by a method of vacuum evaporation.

Various properties of the ceramic disks thus obtained are shown in TABLE 1. The dielectric constant (.epsilon.) and the dielectric loss (tan .delta.) were measured at a frequency of 1 KHz and a voltage of 1 V at 20.degree. C. The temperature coefficients of the dielectric constants were obtained by measuring the dielectric constants at temperatures in the range of -25.degree. C. to 85.degree. C. and calculating the dielectric constant at 20.degree. C. The electrical resistivity is measured at 20.degree. C. under application of a D.C voltage of 1000 V.

From TABLE 1 it is obvious that ceramic compositions which fall within the polygon ABCDE in the ternary system composition diagram of FIG. 1 and in which 1.001.ltoreq.a.ltoreq.1.110 provide a high dielectric constant (.epsilon.=21,350 to 7520), high electrical resistivity up to 1.0.times.10.sup.11 .OMEGA..cm, low dielectric loss, low temperature coefficient of the dielectric constant, and can be sintered below 1080.degree. C.

TABLE 1__________________________________________________________________________ Change of Specific Sintering .epsilon. tan .delta. resistivityComposition temperature .epsilon. (-25.degree. C.) (85.degree. C.) (20.degree. C.) .times. (20.degree. C.) DensityNo. a x y z (.degree.C.) (20.degree. C.) % % 10.sup.-4 .OMEGA. .multidot. cm g/cm.sup.3__________________________________________________________________________ 101* 1.000 0.850 0.100 0.050 1080 16860 -45.2 -61.8 266 1.0 .times. 10.sup.+9 7.653102 1.001 0.850 0.100 0.050 1020 16980 -44.9 -61.0 112 1.5 .times. 10.sup.+11 7.998103 1.025 0.850 0.100 0.050 950 15870 -44.6 -60.8 56 2.6 .times. 10.sup.+12 8.153104 1.110 0.850 0.100 0.050 860 10690 -40.8 -54.6 102 1.0 .times. 10.sup.+12 8.223 105* 1.180 0.850 0.100 0.050 830 6830 -39.5 -42.3 305 8.5 .times. 10.sup. 8.159 106* 1.000 0.700 0.200 0.100 1050 20390 -60.0 -54.0 622 7.5 .times. 10.sup.+9 7.865107 1.001 0.700 0.200 0.100 1020 21340 -60.0 -53.4 422 5.0 .times. 10.sup.+11 7.963108 1.025 0.700 0.200 0.100 920 20630 -60.0 -52.6 432 1.6 .times. 10.sup.+12 8.122109 1.110 0.700 0.200 0.100 890 15630 -58.4 -50.2 622 4.5 .times. 10.sup.+11 8.103 110* 1.180 0.700 0.200 0.100 820 6230 -45.3 -40.6 553 2.6 .times. 10.sup.+9 8.096111 1.025 0.950 0.025 0.025 1020 10520 -5.2 -34.0 358 5.2 .times. 10.sup.+11 8.169112 1.025 0.850 0.125 0.025 1020 16090 -65.4 -26.3 420 5.0 .times. 10.sup.+11 8.115113 1.025 0.100 0.600 0.300 880 7860 -32.6 -51.3 265 1.5 .times. 10.sup.+11 8.065114 1.025 0.100 0.400 0.500 860 7520 +8.6 -60.3 24 2.5 .times. 10.sup.+11 8.066115 1.025 0.900 0.025 0.075 950 10890 -10.6 -60.2 36 1.0 .times. 10.sup.+11 8.104 116* 1.025 0.400 0.500 0.100 900 3220 -82.5 +40.2 558 1.0 .times. 10.sup.+11 8.100 117* 1.025 0.400 0.200 0.400 820 2150 +25.3 -50.3 123 1.0 .times. 10.sup.+11 8.114__________________________________________________________________________ (1) Basic compositions: Pb.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a (2) Compositions of the Nos. with asterisk (*) are outside of the scope o the present invention.

A, B, C, D and E of FIG. 1 are represented by the values of x, y, and z as follows:

______________________________________x y z______________________________________A: 0.950 0.025 0.025B: 0.850 0.125 0.025C: 0.100 0.600 0.300D: 0.100 0.400 0.500E: 0.900 0.025 0.075______________________________________

The reasons for the limitations of values in TABLE 1 and value <a> are as follows:

In case of the compositions wherein proportions x, y and z are out of the polygon ABCDE such as sample Nos. 116 and 117, the dielectric constant is lower than 3500 and the temperature coefficient of the dielectric constant is large. In case of the compositions wherein a is smaller than 1.001 such as samples Nos. 101 and 106, the electrical resistivity is lower than 1.0.times.10.sup.10 .OMEGA..cm. In case of the compositions wherein a is larger than 1.110 such as sample Nos. 105 and 110, the dielectric loss are increased.

EXAMPLE 2

The starting materials, viz. lead oxide (PbO), titanium oxide (TiO.sub.2), niobium oxide (Nb.sub.2 O.sub.5), magnesium oxide (MgO), nickel oxide (NiO), tungsten oxide (WO.sub.3), and calcium carbonate (CaCO.sub.3), all relatively pure grade, were initially mixed in a ball mill with distilled water and calcium oxide stabilised zirconia balls for 17 hours. The following powder process, sintered process and measuring of properties of sintering body were the same as those in Example 1.

Various properties of the ceramic disks thus obtained are shown in TABLE 2.

From TABLE 2 it is obvious that ceramic compositions which fall within the polygon FGHIJ in the ternary system composition diagram of FIG. 2 and in which 0.001.ltoreq.b.ltoreq.0.225 and 1.001.ltoreq.a+b.ltoreq.1.225 provide a high dielectric constant (.epsilon.=21540 to 4030), high electrical resistivity up to 1.0.times.10.sup.10 .OMEGA..cm, low dielectric loss, low temperature coefficient of the dielectric constant, and can be sintered below 1080.degree. C.

F, G, H, I and J of FIG. 2 are represented by the values of x, y and z as follows:

______________________________________x y z______________________________________F: 0.950 0.049 0.001G: 0.750 0.249 0.001H: 0.010 0.800 0.190I: 0.010 0.450 0.540J: 0.900 0.050 0.050______________________________________ TABLE 2__________________________________________________________________________ Change of Specific Sintering .epsilon. tan .delta. resistivityComposition temperature .epsilon. (-25.degree. C.) (85.degree. C.) (20.degree. C.) (20.degree. C.) DensityNo. a b x y z (.degree.C.) (20.degree. C.) % % 10.sup.-4 .OMEGA. .multidot. g/cm.sup.3__________________________________________________________________________ 201* 1.000 0.000 0.700 0.250 0.050 1120 15390 -72.6 -50.1 412 1.5 .times. 10.sup.+9 7.661202 1.000 0.001 0.700 0.250 0.050 1050 16320 -70.2 -50.1 442 2.0 .times. 10.sup.+11 7.891203 1.000 0.025 0.700 0.250 0.050 980 21540 -52.3 -58.6 215 8.0 .times. 10.sup.+13 8.112204 1.000 0.225 0.700 0.250 0.050 920 14260 -23.5 -65.3 42 1.5 .times. 10.sup.+13 8.023 205* 1.000 0.400 0.700 0.250 0.050 950 8500 + 10.3 -48.6 125 4.5 .times. 10.sup.+12 7.756 206* 0.950 0.030 0.700 0.250 0.050 1150 15230 -58.6 -47.6 321 5.5 .times. 10.sup.+9 7.752207 0.950 0.070 0.700 0.250 0.050 980 16840 -32.1 -65.3 32 1.0 .times. 10.sup.+14 8.116 208* 0.950 0.350 0.700 0.250 0.050 950 4860 -63.2 -32.1 421 1.6 .times. 10.sup.+12 7.985209 1.035 0.025 0.700 0.250 0.050 920 20650 -50.6 -50.3 215 8.5 .times. 10.sup.+13 8.154 210* 1.035 0.250 0.700 0.250 0.050 880 4180 +21.3 -42.5 23 4.0 .times. 10.sup.+12 7.798 211* 1.000 0.000 0.450 0.400 0.150 1080 9520 -85.4 -15.2 542 2.0 .times. 10.sup.+9 7.554212 1.015 0.001 0.450 0.400 0.150 1000 10230 -78.3 -22.4 512 3.5 .times. 10.sup.+12 7.985213 1.015 0.025 0.450 0.400 0.150 920 11560 -56.3 -41.3 224 1.5 .times. 10.sup.+13 8.087214 1.000 0.075 0.450 0.400 0.150 900 11650 -41.3 -52.3 42 4.5 .times. 10.sup.+13 8.102 215* 1.000 0.275 0.450 0.400 0.150 880 2350 +12.0 -42.3 145 1.5 .times. 10.sup.+12 7.795216 1.015 0.025 0.950 0.049 0.001 920 11860 -22.3 -82.5 163 5.0 .times. 10.sup.+12 7.858217 1.015 0.025 0.750 0.249 0.001 920 8560 -85.3 -12.6 482 3.5 .times. 10.sup.+12 7.985218 1.015 0.025 0.010 0.800 0.190 880 4030 -52.1 -5.3 662 2.5 .times. 10.sup.+12 7.854219 1.015 0.025 0.010 0.450 0.540 850 4250 +0.8 -41.3 88 5.0 .times. 10.sup.+12 7.965220 1.015 0.025 0.900 0.050 0.050 900 11280 -22.3 -82.9 41 4.5 .times. 10.sup.+12 8.085 221* 1.015 0.025 0.300 0.650 0.050 950 1950 -32.5 +15.3 253 1.5 .times. 10.sup.+12 8.025 222* 1.015 0.025 0.300 0.250 0.450 900 1480 +12.3 -45.6 554 2.5 .times. 10.sup.+12 8.152__________________________________________________________________________ (1) Basic compositions: Pb.sub.a Ca.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b (2) Compositions of the Nos. with asterisk (*) are outside of the scope o the present invention.

The reasons for limitations of values in TABLE 2 and values <a> and <a+b> are as follows:

In case of the compositions wherein proportion x, y and z are out of the polygon FGHIJ such as sample Nos. 221 and 222, the dielectric constant is lower than 3500 and the temperature coefficient of the dielectric constant is large. In case of the compositions wherein b is smaller than 0.001 and a+b is smaller than 1.00 such as sample Nos. 201, 206, and 211, the electrical resistivity are lower than 1.0.times.10.sup.10 .OMEGA..cm. In case of the composition wherein b is larger than 0.225 and a+b is larger than 1.250 such as sample No. 205, 208, 210, 215, the dielectric constants is decreased or dielectric loss are increased.

EXAMPLE 3

The starting materials, viz. lead oxide (PbO), titanium oxide (TiO.sub.2), niobium oxide (Nb.sub.2 O.sub.5), magnesium oxide (MgO), and nickel oxide (NiO) were initially mixed in a ball mill with distilled water and calcium oxide stabilised zirconia balls for 17 hours. The following power process, sintering process and measuring of properties of sintering body were the same as those in Example 1.

Various properties of the ceramic disks thus obtained are shown in Table 3.

TABLE 3__________________________________________________________________________ Change of Specific Sintering .epsilon. tan .delta. resistivityComposition temperature .epsilon. (-25.degree. C.) (85.degree. C.) (20.degree. C.) (20.degree. C.) DensityNo. a b x y z (.degree.C.) (20.degree. C.) % % 10.sup.-4 .OMEGA. .multidot. g/cm.sup.3__________________________________________________________________________ 301* 1.000 0.000 0.700 0.250 0.050 1120 15390 -72.6 -50.1 412 1.5 .times. 10.sup.+9 7.661302 1.000 0.001 0.700 0.250 0.050 1050 16410 -70.3 -50.5 412 1.5 .times. 10.sup.+11 7.891303 1.000 0.025 0.700 0.250 0.050 990 18660 -41.3 -61.2 111 5.0 .times. 10.sup.+13 8.005304 1.000 0.200 0.700 0.250 0.050 920 12260 -11.2 -78.6 52 1.0 .times. 10.sup.+13 7.923 305* 1.000 0.400 0.700 0.250 0.050 950 4250 + 25.3 -98.3 585 1.2 .times. 10.sup.+11 7.655 306* 0.950 0.030 0.700 0.250 0.050 1180 13200 -54.6 -92.6 445 1.5 .times. 10.sup.+8 7.521307 0.950 0.070 0.700 0.250 0.050 1020 14150 -41.8 -72.2 25 1.5.times. 10.sup.+13 8.008 308* 0.950 0.350 0.700 0.250 0.050 980 3820 -70.0 -41.2 552 1.0 .times. 10.sup.+11 7.885309 1.035 0.025 0.700 0.250 0.050 950 17450 -45.3 -51.2 125 6.0 .times. 10.sup.+13 8.022 310* 1.035 0.200 0.700 0.250 0.050 880 3820 +11.7 -78.6 42 1.0 .times. 10.sup.+11 7.665 311* 1.000 0.000 0.450 0.400 0.150 1080 9520 -85.4 -15.2 542 2.0 .times. 10.sup.+9 7.554312 1.015 0.001 0.450 0.400 0.150 1000 10450 -76.2 -21.4 458 3.5 .times. 10.sup.+12 7.885313 1.015 0.025 0.450 0.400 0.150 940 10060 -43.5 -31.2 123 1.0 .times. 10.sup.+12 8.002314 1.000 0.075 0.450 0.400 0.150 920 10020 -32.2 -62.3 33 1.0 .times. 10.sup.+13 8.025 315* 1.000 0.220 0.450 0.400 0.150 900 1890 +11.2 -52.3 285 5.0 .times. 10.sup.+11 7.662316 1.015 0.025 0.950 0.049 0.001 950 12100 -22.5 -75.5 102 4.0 .times. 10.sup.+12 7.855317 1.015 0.025 0.750 0.249 0.001 950 7250 -80.2 -11.2 552 1.2 .times. 10.sup.+12 7.855318 1.015 0.025 0.010 0.800 0.190 900 3880 -54.2 -9.6 452 1.5 .times. 10.sup.+12 7.885319 1.015 0.025 0.010 0.450 0.540 880 3860 +12.2 -51.2 11 2.2 .times. 10.sup.+12 7.585320 1.015 0.025 0.900 0.050 0.050 920 10220 -20.2 -79.3 22 3.0 .times. 10.sup.+12 7.951 321* 1.015 0.025 0.300 0.650 0.050 980 1560 -21.2 +11.2 452 6.0 .times. 10.sup.+10 8.001 322* 1.015 0.025 0.300 0.250 0.450 920 1120 +22.3 -51.2 455 1.2 .times. 10.sup.+11 8.055__________________________________________________________________________ (1) Basic compositions: Pb.sub.a Ba.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub. 1/2).sub.z O.sub.2+a+b (2) Compositions of the Nos. with asterisk (*) are outside of the scope o the present invention.

From TABLE 3 it is obvious that ceramic compositions which fall within the polygon KLMNO in the ternary system composition diagram of FIG. 3 and in which 0.001.ltoreq.b.ltoreq.0.200 and 1.001.ltoreq.a+b.ltoreq.1.200 provide a high dielectric constant (.epsilon.=18660 to 3860), and high electrical resistivity up to 1.0.times.10.sup.10 .OMEGA..cm, low dielectric loss and low temperature coefficient of the dielectric constant, and can be sintered below 1080.degree. C.

K, L, M, N and O of FIG. 3. are represented by the values of x, y and z as follows:

______________________________________x y z______________________________________K: 0.950 0.049 0.001L: 0.750 0.249 0.001M: 0.010 0.800 0.190N: 0.010 0.045 0.540O: 0.900 0.050 0.050______________________________________

The reasons for limitations of values in TABLE 3 and values <a> and <a+b> are as follows:

In case of the compositions wherein proportion x, y and z are out of the polygon FGHIJ such as sample Nos. 321 and 322, the dielectric constant is lower than 3500 and the temperature coefficient of the dielectric constant is large. In case of the compositions wherein b is smaller than 0.001 and a+b is smaller than 1.00 such as sample Nos. 301, 306 and 311, the electrical resistivity is lower than 1.0.times.10.sup.10 .OMEGA..cm. In case of the composition wherein b is larger than 0.250 and a+b is larger than 1.200 such as sample Nos. 305, 308, 310 and 315, the dielectric constants are decreased or dielectric loss is increased.

EXAMPLE 4

The starting materials, viz. lead oxide (PbO), titanium oxide (TiO.sub.2), niobium oxide (Nb.sub.2 O.sub.5), magnesium oxide (MgO), nickel oxide (NiO), tungsten oxide (WO.sub.3), and strontium carbonate (SrCO.sub.3), all relatively pure grade, were initially mixed in a ball mill with distilled water and calcium oxide stabilised zirconia balls for 17 hours. The following powder process, the sintered process and measuring of properties of sintering body were the same as those in Example 1.

Various properties of the ceramic disks thus obtained are shown in TABLE 4.

From TABLE 4 it is obvious that ceramic compositions within the polygon PQRS in the ternary system compositions diagram of FIG. 4 and in which 0.001.ltoreq.b.ltoreq.0.225 and 1.001.ltoreq.a+b.ltoreq.1.240 provide a high dielectric constant (.epsilon.=16630 to 4010), high electrical resistivity up to 1.0.times.10.sup.10 .OMEGA..cm, low dielectric loss and low temperature coefficient of the dielectric constant, and can be sintered below 1080.degree. C.

TABLE 4__________________________________________________________________________ Change of Specific Sintering .epsilon. tan .delta. resistivityComposition temperature .epsilon. (-25.degree. C.) (85.degree. C.) (20.degree. C.) (20.degree. C.) DensityNo. a b x y z (.degree.C.) (20.degree. C.) % % 10.sup.-4 .OMEGA. .multidot. g/cm.sup.3__________________________________________________________________________ 401* 1.000 0.000 0.700 0.250 0.050 1120 15390 -72.6 -50.1 412 1.5 .times. 10.sup.+9 7.661402 1.000 0.001 0.700 0.250 0.050 1050 16630 -71.2 -51.2 402 3.0 .times. 10.sup.+11 7.884403 1.000 0.025 0.700 0.250 0.050 1000 15320 -45.3 -42.2 125 7.5 .times. 10.sup.+13 8.023404 1.000 0.225 0.700 0.250 0.050 920 8520 -15.2 -72.3 32 1.0 .times. 10.sup.+13 7.855 405* 1.000 0.400 0.700 0.250 0.050 1000 5220 + 20.3 -65.3 225 1.5 .times. 10.sup.+12 7.325 406* 0.950 0.030 0.700 0.250 0.050 1150 12350 -42.3 -35.6 225 7.5 .times. 10.sup.+10 7.215407 0.950 0.070 0.700 0.250 0.050 1000 11520 -40.2 -45.3 125 1.5 .times. 10.sup.+14 8.002 408* 0.950 0.350 0.700 0.250 0.050 1080 2560 -24.2 -75.3 542 5.2 .times. 10.sup.+13 7.252409 1.035 0.025 0.700 0.250 0.050 980 11560 -45.2 -42.3 45 9.0 .times. 10.sup.+13 8.088 410* 1.035 0.250 0.700 0.250 0.050 880 1980 +32.1 -31.2 14 7.0 .times. 10.sup.+12 7.425 411* 1.000 0.000 0.450 0.400 0.150 1080 9520 -85.4 -15.2 542 2.0 .times. 10.sup.+9 7.554412 1.015 0.001 0.450 0.400 0.150 1000 10020 -74.3 -22.5 458 7.2 .times. 10.sup.+12 7.985413 1.015 0.025 0.450 0.400 0.150 970 9520 -42.3 -38.5 114 1.0 .times. 10.sup.+13 8.002414 1.000 0.075 0.450 0.400 0.150 950 8560 -33.2 -65.2 52 3.0 .times. 10.sup.+13 7.988 415* 1.000 0.275 0.450 0.400 0.150 900 2850 +25.3 -55.9 78 2.6 .times. 10.sup.+12 7.668416 1.015 0.030 0.950 0.049 0.001 970 10580 -20.3 -79.6 88 7.0 .times. 10.sup.+12 7.756417 1.015 0.150 0.400 0.591 0.001 1050 4990 -77.3 -5.3 851 2.0 .times. 10.sup.+12 7.668418 1.015 0.200 0.001 0.900 0.099 1000 4000 -42.6 -8.9 775 1.5 .times. 10.sup.+12 7.566419 1.015 0.025 0.001 0.600 0.399 980 4010 +5.6 -22.1 115 2.5 .times. 10.sup.+12 7.558420 1.015 0.225 0.150 0.825 0.025 1000 1420 -42.1 +22.3 336 2.5 .times. 10.sup.+12 7.789 421* 1.015 0.025 0.150 0.350 0.500 980 2150 -1.23 -52.1 335 1.3 .times. 10.sup.+12 8.002__________________________________________________________________________ (1) Basic compositions: Pb.sub.a Sr.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b (2) Compositions of the Nos. with asterisk (*) are outside of the scope o the present invention.

P, Q, R and S of FIG. 4 are represented by the values of x, y and z as follows:

______________________________________x y z______________________________________P: 0.950 0.049 0.001Q: 0.400 0.591 0.001R: 0.001 0.900 0.099S: 0.001 0.600 0.399______________________________________

The reasons for limitations of values in FIG. 4 and values <a> and <a+b> are as follows:

In case of the compositions wherein proportion x, y and z is out of the polygon PQRS such as sample Nos. 320 and 321, the dielectric constant is lower than 3500 and the temperature coefficient of the dielectric constant is large. In case of the compositions wherein b is smaller than 0.001 and a+b is smaller than 1.00 such as sample Nos. 301, 306 and 311, the electrical resistivity is lower than 1.0.times.10.sup.10 .OMEGA..cm. In case of the composition wherein b is larger than 0.250 and a+b is larger than 1.200 such as sample Nos. 305, 308, 310 and 315, the dielectric constants are decreased or dielectric loss are increased.

As apparent from these Examples 1 to 4, the ternary ceramic compositions according to the present invention can be sintered below 1100.degree. C., and in low partial pressure of oxygen atmosphere, at which temperature and atmosphere the copper metal internal electrode is not melted and oxidized, and exhibit high dielectric constant, high electrical resistivity, low dielectric loss and low temperature coefficient of dielectric constant. Therefore copper metal can be used as internal electrodes of multi-layer ceramic capacitors, employing compositions according to this invention as dielectric materials.

It will be evident that the starting materials to be used in the present invention are not limited to those used in the above examples. Other oxides or compounds which are easily decomposed at elevated temperature may be used in place of the starting materials of the above examples.

Claims

1. A ceramic composition consisting essentially of a material represented by the formula

Pb.sub.a (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a

wherein subscripts a, x, y and z represent molar fractions of the respective components, x+y+z=1 and 1.001.ltoreq.a.ltoreq.1.110, said composition falling within a polygonal area defined by the points A, B, C, D and E in FIG. 1.

2. A ceramic composition consisting essentially of a material represented by the formula

Pb.sub.a Ca.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b

wherein subscripts a, b, x, y and z represent molar fractions of the respective components, x+y+z=1, 1.001.ltoreq.a+b.ltoreq.1.225, and 0.001.ltoreq.b.ltoreq.0.225, said composition falling within a polygonal area defined by the points F, G, H, I and J in FIG. 2.

3. A ceramic composition consisting essentially of a material represented by the formula

Pb.sub.a Ba.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b

wherein subscripts a, b, x, y and z represent molar fractions of the respective components, x+y+z=1, 1.001.ltoreq.a+b.ltoreq.1.200, and 0.001.ltoreq.b.ltoreq.0.200, said composition falling within a polygonal area defined by the points K, L, M, N and O in FIG. 3.

4. A ceramic composition consisting essentially of a material replesented by the formula

Pb.sub.a Sr.sub.b (Mg.sub.1/3 Nb.sub.2/3).sub.x Ti.sub.y (Ni.sub.1/2 W.sub.1/2).sub.z O.sub.2+a+b

wherein subscripts a, b, x, y and z represent molar fractions of the respective components, x+y+z=1, 1.001.ltoreq.a+b.ltoreq.1.240, and 0.001.ltoreq.b.ltoreq.0.225, said composition falling within a polygonal area defined by the points P, Q, R and S in FIG. 4.