Grain boundary layer dielectric ceramic compositions

BACKGROUND OF THE INVENTION
The present invention relates to materials for capacitors; that is, grain boundary layer dielectric ceramic compositions in which diffusing agents mainly consisting of Bi.sub.2 O.sub.3, Cu.sub.2 O, MnO.sub.2, B.sub.2 O.sub.3, La.sub.2 O.sub.3 and TiO.sub.2 are thermally diffused into the grain boundaries of a semiconductive ceramic mainly consisting of SrTiO.sub.3 or the solid solution of Sr.sub.1-x Ca.sub.x TiO.sub.3 so that the dielectric layers are formed in the grain boundaries.
The grain boundary layer dielectric ceramic compositions which are used for the manufacture of capacitors comprise a semiconductive ceramic composition and a diffusing composition which forms dielectric layers in the grain boundaries of the semiconductive ceramic composition to form a composition having high resistance. The characteristics of capacitors, therefore, are dependent upon the selection of the semiconductive ceramic compositions and the diffusing compositions.
The semiconductive ceramic compositions in accordance with the present invention mainly consisting of SrTiO.sub.3 containing Nb.sub.2 O.sub.5 or a solid solution of Sr.sub.1-x Ca.sub.x TiO.sub.3 and containing Nb.sub.2 O.sub.5. The semiconductive ceramic compositions consisting of SrTiO.sub.3 containing Nb.sub.2 O.sub.5 are well known in the art as disclosed in Japanese Laid-Open Patent Application Ser. Nos. 129896/1974 and 8099/1975, but as the diffusing agents or compositions which are diffused into the grain boundaries of such semiconductive ceramic compositions so as to form the dielectric layers, only Bi.sub.2 O.sub.3 (as disclosed in Japanese Laid-Open Patent Application Ser. No. 129896/1974) and the compositions consisting of Nb.sub.2 O.sub.5 and ZnO (as disclosed in Japanese Laid-Open Patent Application Ser. No. 8099/1975) are known. The diffusing agents or compositions in accordance with the present invention are characterized by consisting of five constituents of Bi.sub.2 O.sub.3, Cu.sub.2 O, MnO.sub.2, B.sub.2 O.sub.3 and La.sub.2 O.sub.3 or consisting of six constituents of the above-described compounds plus TiO.sub.2. Meanwhile, the diffusing agents or compositions containing Bi.sub.2 O.sub.3 and Cu.sub.2 O and MnO.sub.2 are disclosed in Japanese Laid-Open Patent Application Ser. No. 78494/1974, but the combinations consisting of the five or six constituents in accordance with the present invention had not been disclosed. The semiconductive ceramic composition disclosed in the abovedescribed Patent Application consists of SrTiO.sub.3 containing MnO.sub.2 and Nb.sub.2 O.sub.5 or the solid solution thereof and is different from the semiconductive ceramic compositions in accordance with the present invention.
Based on the variations in electrostatic capacitance due to temperature variations, grain boundary layer dielectric ceramic capacitor elements are rated as YR, YB and YA. That is, the capacitor elements which have a temperature coefficient of capacitance of .+-.15% between +85.degree. C. and -25.degree. C. based on a capacitance at 20.degree. C. are rated as YR. Those which have the temperature coefficient of .+-.10% are rated as YB and those which have the temperature coefficient of .+-.5% are rated as YA. Regardless of their ratings, all the capacitor elements preferably have a high dielectric constant .epsilon..sub.a, a high dielectric breakdown voltage V.sub.b and a low dielectric loss tan .delta.. In practice, the YR rated capacitor elements must have dielectric constant .epsilon..sub.a higher than 35,000, a dielectric breakdown voltage V.sub.b higher than 500 V/mm and a dielectric loss tan .delta. of less than 0.01. The YB rated capacitor elements must have a dielectric constant .epsilon..sub.a higher than 20,000, a dielectric breakdown voltage V.sub.b higher than 700 V/mm and a dielectric loss tan .delta. of less than 0.01. The YA rated capacitor elements must have a dielectric constant .epsilon..sub.a higher than 5000, a dielectric breakdown voltage V.sub.b higher than 700 V/mm and a dielectric loss tan .delta. of less than 0.01.
DESCRIPTION OF THE INVENTION
The grain boundary layer dielectric ceramic capacitors in accordance with the present invention can satisfy all the characteristics required in practice. The semiconductive ceramic compositions which are especially recommended for the fabrication of YR rated ceramic capacitor elements consist of from 50.23 to 49.47 mol% of SrO, from 49.72 to 50.23 mol% of TiO.sub.2 and from 0.05 to 0.3 mol% of Nb.sub.2 O.sub.5 or consist essentially of the above-described constituents and contains less than 0.2 mol parts of SiO.sub.2 based on 100 mol parts of the main constituents. The semiconductive ceramic compositions for YB rated ceramic capacitor elements consist of from 50.23 to 34.47 mol% of SrO and less than 15 moL% of CaO, the contents of the constituents SrO and CaO being from 50.23 to 49.47 mol%, from 49.72 to 50.23 mol% of TiO.sub.2 and from 0.05 to 0.3 mol% of Nb.sub.2 O.sub.5 or mainly consist of the above-described constituents. The semiconductive ceramic compositions for YA rated capacitor elements consist of from 35.23 to 26.87 mol% of SrO, from 15 to 22.6 mol% of CaO, the contents of the constituents SrO and CaO being from 50.23 to 49.47 mol%, from 49.72 to 50.23 mol% of TiO.sub.2 and from 0.05 to 0.3 mol% of Nb.sub.2 O.sub.5, or mainly consist of the above-described constituents and further contain less than 2 mol parts of SiO.sub.2 based on 100 mol parts of the main constituents.
The semiconductive ceramic compositions in accordance with the present invention for YR, YB and YA rated capacitor elements contain from 0.05 to 0.3 mol% of Nb.sub.2 O.sub.5. Nb.sub.2 O.sub.5 is the constituent needed, based upon the principle of the valence control, to render SrTiO.sub.3 consisting of SrO and TiO.sub.2 or of the solid solution of Sr.sub.1-x Ca.sub.x TiO.sub.3 consisting of SrO, CaO and TiO.sub.2 semiconductive. However, when the contents of Nb.sub.2 O.sub.5 is less than 0.05 mol% (about 0.02 mol% based on the contents of SrTiO.sub.3 or Sr.sub.1-x Ca.sub.x TiO.sub.3), sufficient semiconductive properties cannot be attained in SrTiO.sub.3 or the solid solution of Sr.sub.1-x Ca.sub.x TiO.sub.3. On the other hand, when Nb.sub.2 O.sub.5 exceeds 0.3 mol% (about 0.6 mol% based on the contents of SrTiO.sub.3 or Sr.sub.1-x Ca.sub.x TiO.sub.3), the grain growth of SrTiO.sub.3 or Sr.sub.1-x Ca.sub.x TiO.sub. 3 is inhibited. In addition, the semiconductive ceramic compositions will have a high specific resistance. Thus, the addition of Nb.sub.2 O.sub.5 in excess of 0.3 mol% is not preferable. When the SrO constituent is substituted by the CaO constituent in SrTiO.sub.3 which is the main constituent of semiconductive ceramic, the temperature coefficient of capacitance will be decreased with increase in contents of the CaO constituent and the grain sizes are in general reduced after sintering. When the CaO constituent exceeds 22.6 mol% (this corresponds almost to Sr.sub.0.55 Ca.sub.0.45 TiO.sub.3) the grain size after sintering becomes less than 5 .mu.m so that a minimum apparent dielectric constant .epsilon..sub.a of 5000 cannot be attained. When the combined contents of SrO and CaO exceeds 50.23 mol% or when the TiO.sub.2 constituent is less than 49.72 mol%, the grain size after sintering will become small, so that a minimum apparent dielectric constant .epsilon..sub.a of 5000 cannot be attained. Furthermore, when the contents of SrO and CaO is less than 49.47 mol% or when TiO.sub.2 exceeds 50.23 mol%, the grain size will become small, so that a minimum apparent dielectric constant .epsilon..sub.a of 5000 cannot be attained. The reason is that when the SrO, CaO and TiO.sub.2 constituents are present in excess of certain contents in SrTiO.sub.3 or Sr.sub.1-x Ca.sub.x TiO.sub.3, the grain growth is inhibited during sintering.
The SiO.sub.2 constituent has the effect of not only facilitating the formation of the semiconductive ceramic of SrTiO.sub.3 or Sr.sub.1-x Ca.sub.x TiO.sub.3 (so that the main sintering temperatures can be lowered) but also slightly lowering the dielectric loss tan .delta.. However, when the SiO.sub.2 constituent exceeds 2 mol parts based on 100 mol parts of the main composition consisting of three or four constituents of SrO, CaO, TiO.sub.2 and Nb.sub.2 O.sub.5, the grain growth is considerably inhibited, so that the average grain size of greater than 5 .mu.m cannot be obtained. (That is, a minimum apparent dielectric constant .epsilon..sub.a of 5000 cannot be attained.)
The diffusing compositions in accordance with the present invention which are thermally diffused into the grain boundaries of the semiconductive ceramic are characterized by consisting of five or six constituents of from 93.5 to 8.5 mol% of Bi.sub.2 O.sub.3, from 4.5 to 45 mol% of Cu.sub.2 O, from 0.5 to 4 mol% of MnO.sub.2, from 1 to 8.5 mol% of B.sub.2 O.sub.3, from 0.5 to 17 mol% of La.sub.2 O.sub.3 and less than 17 mol% of TiO.sub.2. The results of experiments conducted by the inventors show that when the content of the Bi.sub.2 O.sub.3 constituent is high in the grain boundaries after thermal diffusion, the dielectric constant .epsilon..sub.a becomes high, but the dielectric breakdown voltage V.sub.b becomes low and the temperature coefficient of capacitance (between 85.degree. C. and -25.degree. C.) becomes high. On the other hand, when the Cu.sub.2 O constituent is increased, the temperature coefficient of capacitance becomes low, the dielectric breakdown voltage V.sub.b becomes high and the dielectric constant .epsilon..sub.a becomes low. The Bi.sub.2 O.sub.3 constituent in excess of 93.5 mol% or the Cu.sub.2 O constituent less than 4.5 mol% is not preferable because a minimum dielectric breakdown voltage V.sub.b of 500 V/mm cannot be attained. Furthermore, the Cu.sub.2 O constituent in excess of 45 mol% or the Bi.sub.2 O.sub.3 constituent less than 8.5 mol% is not preferable because the dielectric constant of higher than 5000 cannot be obtained. (This minimum dielectric constant cannot be attained even when semiconductive ceramic has a relatively large average grain size of greater than about 20 .mu.m.)
The addition of the MnO.sub.2 constituent results in the increase in dielectric breakdown voltage V.sub.b, slight decrease in dielectric circuit .epsilon..sub.a and an increase in dielectric loss tan .delta.. It is preferable that the contents of the MnO.sub.2 constituent is less than 4 mol% because when the MnO.sub.2 constituent exceeds 4 mol%, the dielectric loss tan .delta. of less than 0.01 cannot be obtained. Furthermore, the MnO.sub.2 constituent less than 0.5 mol% will not contribute to the increase in the dielectric breakdown voltage V.sub.b.
The presence of the B.sub.2 O.sub.3 constituent has the effect of decreasing the dielectric loss tan .delta.. The contents of the B.sub.2 O.sub.3 constituent is preferably less than 8.5 mol% because when the contents is in excess of 8.5 mol%, the breakdown voltage V.sub.b higher than 500 V/mm cannot be attained. On the other hand, when the B.sub.2 O.sub.3 constituent is less than 1 mol%, the dielectric loss tan .delta. cannot be reduced to a satisfactory level.
The La.sub.2 O.sub.3 constituent has the effect of reducing the temperature coefficient of capacitance, but when the La.sub.2 O.sub.3 constituent exceeds a certain amount, the dielectric constant .epsilon..sub.a will be drastically lowered and the dielectric breakdown voltage V.sub.b will also be decreased. When the La.sub.2 O.sub.3 constituent exceeds 17 mol%, the YR rating requirements that the breakdown voltage V.sub.b is higher than 500 V/mm and the dielectric constant .epsilon..sub.a be higher than 35,000 as well as the YB rating requirements that the breakdown voltage V.sub.b be higher than 700 V/mm and the dielectric constant .epsilon..sub.a be higher than 20,000 cannot be met. On the other hand, when the La.sub.2 O.sub.3 constituent is less than 0.5 mol%, there is no effect at all of lowering the temperature coefficient of capacitance.
When the TiO.sub.2 constituent is present with the La.sub.2 O.sub.3 constituent, the temperature coefficient of capacitance can be further decreased, but when the TiO.sub.2 constituent exceeds 17 mol%, both the dielectric constant .epsilon..sub.a and the dielectric breakdown voltage V.sub.b are lowered. Thus, the TiO.sub.2 constituent in excess of 17 mol% is not preferable.
As described above, the grain boundary layer dielectric ceramic compositions in accordance with the present invention can completely satisfy the YR, YB and YA requirements. For instance, the present invention provides a YR rated capacitor element which has a temperature coefficient of capacitance of less than .+-.15%, a dielectric constant .epsilon..sub.a of between 40,000 and 60,000, a dielectric breakdown voltage V.sub.b of between 600 and 1300 and a dielectric loss tan .delta. of between 0.003 and 0.005. The present invention can also provide a YB rated capacitor element which has a temperature coefficient of capacitance of less than .+-.10%, a dielectric constant .epsilon..sub.a of between 20,000 and 35,000, a dielectric breakdown voltage V.sub.b of between 1,000 and 2,000 V/mm, and a dielectric loss tan .delta. of between 0.003 and 0.005. The present invention can further provide a YA rated capacitor element which has a temperature coefficient of capacitance of less than .+-.5%, a dielectric constant .epsilon..sub.a of between 7,000 and 20,000, a dielectric breakdown voltage V.sub.b of between 2,000 and 4,000 V/mm and a dielectric loss tan .delta. of between 0.003 and 0.005.

Next some examples will be described.
EXAMPLE 1
SrCO.sub.3 powder (with a purity higher than 97.5%), CaCO.sub.3 powder (with a purity higher than 98%), TiO.sub.2 (anatase type, with a purity higher than 98.5%) and Nb.sub.2 O.sub.5 powder (with a purity higher than 98%), all of which are for industrial use and available in the market), were proportioned as shown in TABLE 1 and mixed by a wet mixing process. After being dried, the semiconductive ceramic compositions were pre-sintered at 1200.degree. C. and then crushed into the powder with an average grain size of 2.5 .mu.m. An aqueous solution of polyvinyl alcohol was added as a binder. After being passed through a sieve of 32 mesh, the compositions were pressed under a pressure of about one ton/cm.sup.2 into disks 15 mm in diameter and 0.5 mm in thickness. The disks were heat-treated in the air at 1000.degree. C. and then sintered at 1,390.degree. C. for four hours in the flow of a gas mixture consisting of 95% of N.sub.2 and 5% of H.sub.2, whereby semiconductive ceramic disks about 12.5 mm in diameter and about 0.4 mm in thickness were obtained. The disk was then fractured and the fractured surface was polished and etched for observation through a microscope so as to measure the grain size. The results were shown also in TABLE 1. Even when the sintering temperature was varied between 1,380.degree. and 1,400.degree. C., the average grain size remained unchanged.
TABLE 1______________________________________ Compositions (in mol %) Average of grainSpecimen semiconductive ceramic size inNo. SrO CaO TiO.sub.2 Nb.sub.2 O.sub.3 .mu.m______________________________________11* 49.99 -- 49.99 0.02 6.813* 50.30 -- 49.65 0.05 3.314 50.23 -- 49.72 0.05 7.416 49.87 -- 50.08 0.05 2221* 50.15 -- 49.65 0.20 3.422 50.08 -- 49.72 0.20 7.724 49.80 -- 50.00 0.20 3025 49.75 -- 50.05 0.20 2427 49.57 -- 50.23 0.20 7.528* 49.50 -- 50.30 0.20 4.231 49.75 -- 49.95 0.30 2434 49.47 -- 50.23 0.30 6.335* 49.40 -- 50.30 0.30 3.744* 49.60 -- 50.00 0.40 4.765 47.25 2.5 50.05 0.20 2381* 44.99 5.0 49.99 0.02 6.186 44.87 5.0 50.08 0.05 1991* 45.15 5.0 49.65 0.20 3.292 45.08 5.0 49.72 0.20 6.995 44.75 5.0 50.05 0.20 2196 44.70 5.0 50.10 0.20 1597 44.57 5.0 50.23 0.20 7.098* 44.50 5.0 50.30 0.20 3.8101 44.75 5.0 49.95 0.30 20104 44.47 5.0 50.23 0.30 6.9105* 44.40 5.0 50.30 0.30 3.6114* 44.70 5.0 50.00 0.40 4.4134 39.80 10.0 50.00 0.20 23135 39.75 10.0 50.05 0.20 18154 34.80 15.0 50.00 0.20 17155 34.75 15.0 50.05 0.20 12171* 32.49 17.5 49.99 0.02 3.8176 32.37 17.5 50.08 0.05 10184 32.30 17.5 50.00 0.20 12185 32.75 17.5 50.05 0.20 7.2191 32.25 17.5 49.95 0.30 8.6204* 32.20 17.5 49.90 0.40 2.8224 27.20 22.6 50.00 0.20 6.1254* 25.00 25.0 50.00 0.20 4.2______________________________________ *specimens used for comparison.
Except the specimen Nos. 11 and 171, the specific resistance measured at 20.degree. C. with In-Ga electrodes was between 0.2 and 0.5 ohm.cm. Specimen Nos. 11 and 171 showed high specific resistance of 3.5 and 8.5 ohm.cm, respectively, which means that the valance-controlled semiconductive properties are not sufficient. The grain growth of specimen Nos. 44, 114 and 204 whose Nb.sub.2 O.sub.5 contents were in excess of 0.30 mol% was inhibited, so that the average grain size was small and less than 5 .mu.m.
Further, the grain growth of specimen No. 13 whose SrO content was in excess of 50.23 mol%, specimen Nos. 35 and 105 whose SrO and TiO.sub.2 contents were less than 49.47 mol%, specimen Nos. 13, 21 and 91 whose TiO.sub.2 content was less than 49.72 mol%, specimen Nos. 35, 98 and 105 whose TiO.sub.2 content was in excess of 50.23 mol% was inhibited, so that the average grain size was small and less than 5 .mu.m.
The fact that the CaO contents in excess of 22.6 mol% is not preferable was proved by the specimen No. 264 whose grain size was less than 5 .mu.m. Except the specimen Nos. 13, 21, 28, 35, 44, 91, 98, 105, 114, 171, 204 and 254, the average grain sizes were greater than 5 .mu.m.
The semiconductive ceramic disks which had average grain sizes greater than 12 .mu.m were coated with a diffusing agent or composition in a paste form and were subjected to heat-treatment at 1150.degree. C. for two hours, so that dielectric layers were formed in the grain boundaries. In like manner, the semiconductor ceramic specimens which had an average grain size of less than 12 .mu.m were coated with a diffusing agent or composition in the form of paste and were subjected to heat-treatment at 1000.degree. C. for two hours, so that dielectric layers were formed in the grain boundaries. The diffusing agent or composition used was a six-constituent composition consisting of 67.6 mol% of Bi.sub.2 O.sub.3, 12.0 mol% of Cu.sub.2 O, 2.4 mol% of MnO.sub.2, 6.0 mol% of B.sub.2 O.sub.3, 4.0 mol% of La.sub.2 O.sub.3 and 8.0 mol% of TiO.sub.2. These constituents are all available in the market and of the special grade for tests. 1.9 mg of the diffusing agent or composition paste was applied to each specimen of 250 mg. Care was taken during thermal diffusion so that the diffusing agent or composition would not leave the specimens by evaporation or diffusion. On both major surfaces of the grain boundary layer dielectric ceramic disks, Ag electrodes were formed by a pyrolytic process, whereby the capacitor elements were provided. The dielectric constant .epsilon..sub.a and the dielectric loss tan .delta. were measured both at 1 KHz. The results were shown in TABLE 2.
TABLE 2______________________________________ Capacitor characteristics Composition Temper- of atureSpeci- semiconductive coefficientmen ceramic V.sub.b of capaci-No. (Specimen No.) .epsilon..sub.a tan .delta. (V/mm) tance in %______________________________________1011* 11* 6500 0.0180 2600 4.61013* 13* 3400 0.0044 3900 4.41014 14 6800 0.0035 2800 3.81016 16 43000 0.0058 1200 13.51021* 21* 3600 0.0041 3800 4.11022 22 7100 0.0038 3000 4.31024 24 61000 0.0047 510 14.81025 25 47000 0.0036 1100 13.31027 27 7000 0.0030 3200 4.31028* 28* 4200 0.0027 3800 3.51031 31 46000 0.0033 1150 13.01034 34 6100 0.0029 3200 3.31035* 35* 3800 0.0027 4100 3.41044* 44* 4600 0.0037 3500 3.01065 65 45000 0.0031 1250 12.91081* 81* 5900 0.0200 2900 3.91086 86 35000 0.0029 1400 11.71091* 91* 3500 0.0046 3900 3.81092 92 6600 0.0040 3200 4.01095 95 41000 0.0033 1300 12.61096 96 27000 0.0033 2000 8.51097 97 6600 0.0031 3300 3.91098* 98* 4000 0.0036 3700 3.71101 101 38000 0.0036 1350 12.21104 104 6500 0.0034 3400 3.01105* 105* 3700 0.0030 4200 3.11114* 114* 4400 0.0041 3600 2.81134 134 45000 0.0052 1200 11.41135 135 32000 0.0035 1450 9.61154 154 30000 0.0054 1500 8.91155 155 23000 0.0040 1600 5.71171* 171* 3900 0.0220 3100 3.01176 176 11000 0.0041 4000 2.11184 184 19000 0.0045 2500 4.61185 185 6700 0.0043 3300 1.71191 191 8500 0.0045 3200 1.61204* 204* 3100 0.0052 4300 1.31224 224 6200 0.0057 3500 2.91254* 254* 4500 0.0062 3800 3.4______________________________________ *Specimens for the sake of comparison.
Specimen Nos. 1011, 1081 and 1171 had a dielectric loss tan .delta. in excess of 0.01, so that they have no practical value and consequently are excluded from the present invention.
Specimen Nos. 1013, 1021, 1028, 1035, 1044, 1091, 1098, 1105, 1114, 1171, 1204 and 1254 had a dielectric constant .epsilon..sub.a of less than 5,000 so that they have no practical value as a large-capacity capacitor and consequently are excluded from the present invention. Specimen Nos. 1016, 1024, 1025, 1031, 1065, 1086, 1095, 1101 and 1134 showed a dielectric constant .epsilon..sub.a of higher than 35,000, a dielectric loss tan .delta. of less than 0.01, a dielectric breakdown voltage V.sub.b of higher than 500 V/mm and a temperature coefficient of capacitance of less than .+-.15% (YR rating) which are all satisfactory in practical use. Specimen Nos. 1096, 1135, 1154 and 1155 showed a dielectric constant .epsilon..sub.a of higher than 20,000, a dielectric loss tan .delta. of less than 0.01, the dielectric breakdown voltage V.sub.b of higher than 700 V/mm and a temperature coefficient of capacitance of less than .+-.10% (YB rating). The specimens 1014, 1022, 1027, 1034, 1092, 1097, 1104, 1176, 1184, 1185, 1191 and 1224 satisfied the YA ratings of dielectric constant .epsilon..sub.a of higher than 5,000, a dielectric loss tan .delta. of less than 0.01, a dielectric breakdown voltage V.sub.b of higher than 700 V/mm and a temperature coefficient of capacitance of less than .+-.5%.
EXAMPLE 2
Powders of Bi.sub.2 O.sub.3, Cu.sub.2 O, MnO.sub.2, B.sub.2 O.sub.3, La.sub.2 O.sub.3 and TiO.sub.2, all of which are available in the market and of the special grade for testing purposes or the like, were proportioned as shown in TABLE 3, wet mixed and added with a suitable amount of terepintine oil or pine resin, whereby the diffusing agents or compositions in the form of paste were prepared.
TABLE 3__________________________________________________________________________ Capacitor characteristics Compositions of TemperatureSpeci- diffusing agents coefficientmen in mol % V.sub.b of capaci-No. Bi.sub.2 O.sub.3 Cu.sub.2 O MnO.sub.2 B.sub.2 O.sub.3 La.sub.2 O.sub.3 TiO.sub.2 .epsilon..sub.a tan .delta. (V/mm) tance in %__________________________________________________________________________2111* 95.0 3.0 0.5 1.0 0.5 -- 67000 0.0056 350 15.02112 93.5 4.5 0.5 1.0 0.5 -- 62000 0.0045 600 14.82114 80.0 18.0 0.5 1.0 0.5 -- 53000 0.0041 800 14.32117 67.6 30.4 0.5 1.0 0.5 -- 47000 0.0035 1000 14.02120 53.0 45.0 0.5 1.0 0.5 -- 36000 0.0032 1300 13.72122* 48.0 50.0 0.5 1.0 0.5 -- 28000 0.0031 1500 13.52311 69.3 12.2 0.5 6.0 4.0 8.0 51000 0.0021 700 13.52313 68.7 12.1 1.2 6.0 4.0 8.0 49000 0.0030 900 13.32315 67.6 12.0 2.4 6.0 4.0 8.0 47000 0.0036 1100 13.32317 66.3 11.7 4.0 6.0 4.0 8.0 44000 0.0083 1200 13.22318* 65.9 11.6 4.5 6.0 4.0 8.0 42000 0.0121 1300 13.12321 71.9 12.7 2.4 1.0 4.0 8.0 49000 0.0061 1300 13.62323 70.6 12.5 2.4 2.5 4.0 8.0 48000 0.0052 1250 13.52325 69.4 12.2 2.4 4.0 4.0 8.0 47000 0.0045 1200 13.32328 65.5 11.6 2.4 8.5 4.0 8.0 45000 0.0027 700 13.22329* 63.4 11.2 2.4 11.0 4.0 8.0 43000 0.0021 400 13.02331* 71.1 12.5 2.4 6.0 -- 8.0 57000 0.0041 1350 15.22332* 70.9 12.5 2.4 6.0 0.2 8.0 56000 0.0040 1350 15.12333 70.6 12.5 2.4 6.0 0.5 8.0 54000 0.0039 1300 14.72334 70.2 12.4 2.4 6.0 1.2 8.0 51000 0.0037 1300 14.32336 69.4 12.2 2.4 6.0 2.0 8.0 49000 0.0036 1200 13.82340 64.3 11.3 2.4 6.0 8.0 8.0 39000 0.0035 900 12.02343 56.6 10.0 2.4 6.0 17.0 8.0 31000 0.0034 700 9.72344* 52.4 9.2 2.4 6.0 22.0 8.0 24000 0.0032 500 7.52351 74.5 13.1 2.4 6.0 4.0 -- 49000 0.0033 1300 14.32354 71.1 12.5 2.4 6.0 4.0 4.0 48000 0.0034 1200 13.82357 60.0 10.6 2.4 6.0 4.0 17.0 37000 0.0037 800 12.62358* 55.8 9.8 2.4 6.0 4.0 22.0 26000 0.0039 500 11.92825 45.5 8.0 4.0 8.5 17.0 17.0 39000 0.0045 800 12.92827 37.5 16.0 4.0 8.5 17.0 17.0 35000 0.0042 900 11.32829 29.5 24.0 4.0 8.5 17.0 17.0 30000 0.0046 1000 9.62831 8.5 45.0 4.0 8.5 17.0 17.0 23000 0.0049 1200 8.32832* 3.5 50.0 4.0 8.5 17.0 17.0 19000 0.0055 1300 7.5__________________________________________________________________________ *Specimens used for the sake of comparison.
Thus prepared diffusing pastes were applied to the disks, Specimen No. 25 shown in TABLE 1, which had an average grain size of 24 .mu.m. The amount of the diffusing paste applied to each disk (250 mg) was 1.9 mg in terms of the oxide powder. The semiconductive ceramic disks were then heat-treated at 1150.degree. C. for two hours. Care was taken so that the applied diffusing agents or compositions would not leave the disks by evaporation, diffusion or melting. Ag electrodes were formed on both major surfaces of the grain boundary layer dielectric ceramic disks, whereby capacitor elements were prepared. The dielectric constant .epsilon..sub.a, the dielectric loss tan .delta., the dielectric breakdown voltage V.sub.b and the temperature coefficient of capacitance were measured at 1 KHz at between 85.degree. C. and -25.degree. C. The results were shown also in TABLE 3.
Except specimen Nos. 2111, 2122, 2318, 2329, 2331, 2332, 2344, 2358 and 2832, the specimens satisfied the YR ratings of a dielectric constant .epsilon..sub.a of higher than 35,000, a dielectric loss tan .delta. of less than 0.01, a dielectric breakdown voltage V.sub.b of higher than 500 V/mm and a temperature coefficient of capacitance of less than .+-.15% or the YB rating of a dielectric constant .epsilon..sub.a higher than 20,000, a dielectric loss tan .delta. of less than 0.01, a dielectric breakdown voltage V.sub.b higher than 700 V/mm and a temperature coefficient of capacitance of less than .+-.10%.
EXAMPLE 3
Following the procedure of the EXAMPLE 2, paste-like diffusing agents or compositions were prepared and applied to the disks, specimen No. 191 shown in TABLE 1, whose average grain size was 8.6 .mu.m. The applied amount was 1.9 mg in terms of an oxide powder for each disk of 250 mg. The disks were then heat-treated at 1000.degree. C. for two hours. Care was taken so that the applied diffusing agents or compositions would not leave the disks. Silver electrodes were attached to the both major surfaces of the grain boundary layer dielectric ceramic disks and following the procedure of EXAMPLE 2, the characteristics were measured. The results were shown in TABLE 4.
TABLE 4__________________________________________________________________________ Capacitor characteristics Compositions ofSpeci- diffusing agents coefficientmen in mol % V.sub.b of capaci-No. Bi.sub.2 O.sub.3 Cu.sub.2 O MnO.sub.2 B.sub.2 O.sub.3 La.sub.2 O.sub.3 TiO.sub.2 .epsilon..sub.a tan .delta. (V/mm) tance in %__________________________________________________________________________5331* 71.1 12.5 2.4 6.0 -- 8.0 10400 0.0056 4000 5.65332* 70.9 12.5 2.4 6.0 0.2 8.0 10300 0.0055 3900 5.45333 70.6 12.5 2.4 6.0 0.5 8.0 10100 0.0053 3900 3.75334 70.2 12.4 2.4 6.0 1.0 8.0 9700 0.0050 3800 2.45336 69.4 12.2 2.4 6.0 2.0 8.0 9200 0.0047 3600 1.95338 67.6 12.0 2.4 6.0 4.0 8.0 8500 0.0045 3200 1.65340 64.3 11.3 2.4 6.0 8.0 8.0 6900 0.0043 2600 1.45343 56.6 10.0 2.4 6.0 17.0 8.0 5300 0.0041 1900 1.25344* 52.4 9.2 2.4 6.0 22.0 8.0 4200 0.0039 1100 1.15351 74.5 13.1 2.4 6.0 4.0 -- 9100 0.0040 3700 3.95354 71.1 12.5 2.4 6.0 4.0 4.0 8900 0.0043 3500 2.65357 60.0 10.6 2.4 6.0 4.0 17.0 6300 0.0048 2100 1.05358* 55.8 9.8 2.4 6.0 4.0 22.0 4500 0.0051 1200 0.75576 64.2 11.3 4.0 8.5 4.0 8.0 6800 0.0079 2400 1.55577* 61.6 10.9 4.5 11.0 4.0 8.0 5200 0.0116 1500 1.4__________________________________________________________________________ *Specimens for the sake of comparison.
Except Specimen Nos. 5331, 5332, 5344, 5358 and 5577, the specimens showed a dielectric constant .epsilon..sub.a higher than 5000, a dielectric loss tan .delta. of less than 0.01, a dielectric breakdown voltage V.sub.b higher than 700 V/mm and a temperature coefficient less than .+-.5%. Thus they satisfied the YA rating.
EXAMPLE 4
The constituents used in EXAMPLE 1 and SiO.sub.2 powder, which is available in the market and of the special grade for testing purpose or the like, were proportioned as shown in TABLE 5 and following the procedure of EXAMPLE 1, the disks or "compacts" were formed. The disks were heat-treated in the air at 1000.degree. C. and then sintered at a predetermined temperature between 1390.degree. C. and 1330.degree. C. for four hours in an atmosphere consisting of 95% of N.sub.2 and 5% of H.sub.2, whereby the semiconductive ceramic disks about 12.5 mm in diameter and about 0.4 mm in thickness were obtained. Following the procedure of EXAMPLE 1, the average grain sizes were measured. The results are also shown in TABLE 5.
TABLE 5__________________________________________________________________________Semiconductive CeramicSemiconductive ceramic Sinter- Capacitor characteristicscompositions ing Average TemperatureSpeci- Major SiO.sub.2 temper- grain coefficientmen constituents in mol ature size in V.sub.b of capaci-No. (100 mol parts) parts (.degree.C.) .mu. .epsilon..sub.a tan .delta. (V/mm) tance in %__________________________________________________________________________8511 -- 1390 24 47000 0.0036 1100 13.38512 0.1 1390 21 42000 0.0034 1250 13.18521 0.2 1390 18 36000 0.0033 1300 12.08522 SrO 49.75 mol % 0.2 1370 18 37000 0.0030 1350 12.28523 0.2 1350 17.5 35000 0.0044 1100 12.18531 TiO.sub.2 55.05 mol % 0.5 1390 14 26000 0.0031 1500 9.78541 1.0 1390 10.1 15000 0.0032 1800 3.88542 Nb.sub.2 0.20 mol % 1.0 1360 10.0 16000 0.0029 1800 3.98543 1.0 1340 9.3 12000 0.0039 1600 3.68551 Total 100 mol % 1.5 1390 7.6 7100 0.0034 2200 3.28561 2.0 1390 5.4 5200 0.0037 2600 2.78571* 2.5 1290 4.7 4600 0.0040 3000 2.48811 SrO 3980 mol % -- 1390 23 45000 0.0052 1200 11.48812 0.1 1390 21 40000 0.0049 1300 11.08821 CaO 10.00 mol % 0.2 1390 17 32000 0.0047 1400 9.88831 TiO.sub.2 50.00 mol % 0.5 1390 13 23000 0.0046 1500 7.78832 0.5 1360 13 25000 0.0041 15008841 Nb.sub.2 O.sub.3 0.20 mol % 1.0 1390 8.5 8400 0.0048 1900 3.688851 Total 100 mol % 1.5 1390 6.3 6100 0.0051 2300 2.98861 2.0 1390 5.1 5100 0.0055 2700 2.38871* 1390 4.3 4400 0.0060 3100 1.9__________________________________________________________________________ *Specimens for the sake of comparison.
The specimen Nos. 8571 and 8871 had the SiO.sub.2 constituent in excess of 2 mol parts based on 100 mol parts of the main constituents or composition (consisting of three or four of SrO, CaO, TiO.sub.2 and Nb.sub.2 O.sub.5) so that the grain growth was inhibited and consequently they had the average grain size of less than 5 .mu.m. The effect of the SiO.sub.2 constituent for facilitating the sintering is clear from Specimen Nos. 8521, 8522 and 8523. That is, even when the sintering temperature was dropped from 1390.degree. C. to 1350.degree. C., the average grain size remained almost unchanged. Specimen Nos. 8541, 8542 and 8543 containing 1 mol part of SiO.sub.2 and Specimen Nos. 8831 and 8832 containing 0.5 mol parts of SiO.sub.2 showed the same tendency.
Following the procedure of EXAMPLE 1, specimens whose average grain size was in excess of 12 .mu.m were coated with the diffusion pastes and heat-treated at 1150.degree. C. for two hours. In like manner, the specimens whose average grain size was less than 12 .mu.m were coated with the diffusing pastes and heat-treated at 1000.degree. C. for two hours. Also following the procedure of EXAMPLE 1, the grain boundary layer dielectric ceramic disk elements were formed with Ag electrodes and their characteristics were measured. The results are also shown in TABLE 5.
Except Specimen Nos. 8571 and 8871, all the specimens (8511, 8512, 8521, 8522, 8523, 8811 and 8812) satisfied the YR rating of a dielectric constant .epsilon..sub.a higher than 35,000, a dielectric loss tan .delta. less than 0.01, a dielectric breakdown voltage V.sub.b higher than 500 V/mm and a temperature coefficient of capacitance less than .+-.15%. Especially Specimen Nos. 8531, 8821, 8831 and 8832 satisfied the YB rating of a dielectric constant .epsilon..sub.a higher than 20,000, a dielectric loss tan .delta. less than 0.01, a dielectric breakdown voltage V.sub.b of higher than 700 V/mm and a temperature coefficient of capacitance less than .+-.10%. Furthermore, specimen Nos. 8541, 8542, 8543, 8551, 8561, 8841, 8851 and 8861 satisfied the YA rating of a dielectric constant .epsilon..sub.a higher than 5,000, a dielectric loss tan .delta. less than 0.01, a dielectric breakdown voltage V.sub.b higher than 700 V/mm and a temperature coefficient less than .+-.5%.

Number	Name	Date
3350212	Fujiwara	Oct 1967
3666505	Hoffman et al.	May 1972
4073846	Masumura et al.	Feb 1978
4143207	Itakura et al.	Mar 1979
4237084	Payne et al.	Dec 1980

Grain boundary layer dielectric ceramic compositions

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