DIELECTRIC CERAMIC MATERIALS WITH INSULATED BOUNDARIES BETWEEN CRYSTAL GRAINS, AND PROCESS FOR PREPARATION

Abstract: A dielectric ceramic material composed of primary and secondary ingredients forming in combination a poly­ crystalline ceramic proper, and of insulating substances diffused throughout the intergranular boundaries of the ceramic proper for an increase in apparent relative dielectric constant. The primary ingredients comprise, in relative proportions, 90.68-99.80 wt. % SrTiO₃, 0.07-5.32 wt. % of at least one of Nb₂O₅, WO₃ and Ta₂O₅ and 0.02-4.00 wt. % of at least one of GeO₂, ZnO and CuO. The secondary ingredients comprise 0.02-0.10 wt. part SiO₂ and 0.01-0.03 wt. part Al₂O₃ with respect to 100 wt. parts of the primary ingredients, with the weight ratio of SiO₂ to Al₂O₃ being from 1.5 to 5.0. The insulating substances comprise 0.02-2.90 wt. % PbO, 0.10-­ 4.38 wt. % Bi₂O₃, and 0.001-0.18 wt. % B₂O₃ with respect to the total weight of the primary and the secondary ingre­ dients. In the fabrication of bodies of the ceramic the mixture of the insulating substances is coated or otherwise layered on polycrystalline ceramic bodies prepared from the primary and secondary ingredients. The coated ceramic bodies are then heated to cause diffusion of the insulating substances throughout their intergranular boundaries.

Description: Dielectric ceramic materials with insulated boundaries between crystal grains, and process for preparation Our invention relates to ceramic materials in general and, in particular, to those composed principally of strontium titanate (SrTiO3) and especially well suited for use as dielectrics of capacitors. Still more particularly, our invention pertains to ceramic materials of polycrystalline structure having electrically insulated boundaries between the crystal grains with a view to an increase in apparent relative dielectric constant. The invention also particularly concerns a process for the fabrication of coherent bodies of such ceramic materials. The polycrystalline ceramics having insulated intergranular boundaries are generally referred to as the boundary layer ceramics11 in the art. An example is described and claimed in United States Patent 3,933,668 issued to Takahashi et al. on January 20, 1976. The boundary layer ceramic according to this U.S. patent consists essentially of a major proportion of SrTiO3, a minor proportion of niobium oxide (Nb205) or tantalum oxide (Ta205), and a minor proportion of germanium dioxide (GeO2) or zinc oxide (ZnO). The polycrystalline ceramic of this fundamental composition has further diffused therein bismuth trioxide (Bi203) or its admixture with litharge (PbO) and boric oxide (B203) for the insulation of the boundaries between its crystal grains. An objection to this known boundary layer ceramic is that its crystal grains average in diameter only from about 40 to 60 micrometers. Its apparent relative dielectric constant is therefore up to 75,000 or so. Although this value is satisfactory for most intended applications of the material, there are strong demands today for ceramics with still higher relative dielectric constants. Our invention meets the present day demands for ceramics with such extremely high relative dielectric constants by making the crystal grains of boundary layer ceramis much greater in size than in the prior art. The invention may be summarized as a boundary layer ceramic having insulated boundaries between its constituent crystal grains, composed of primary and secondary ingredients forming in combination a polycrystalline ceramic proper, and insulating substances dispersed in the intergranular boundaries of the ceramic proper. The primary ingredients comprise approximately 90.68 to 99.88 percent by weight SrTiO3, approximately 0.07 to 5.32 percent by weight of at least one of Nb205, tungstic oxide (W03) and Ta205, and approximately 0.02 to 4.00 percent by weight of at least one of GeOZ, ZnO and black copper oxide (CuO), the percentages of these primary ingredients being relative to each other. The secondary ingredients comprise approximately 0.02 to 0.10 part by weight silica (SiO2) and approximately 0.01 to 0.03 part by weight aluminum oxide (Al 0 ) with respect to 100 parts by 23 weight of the listed primary ingredients, the ratio in weight of SiO2 to Al203 being approximately from 1.5 to 5.0. The insulating substances comprise approximately 0.02 to 2.90 percent by weight PbO, approximately 0.10 to 4.38 percent by weight Bi203, and approximately 0.001 to 0.18 percent by weight B203. The percentages of the insulating substances are all with respect to the total weight of the noted primary and secondary ingredients in use. Of the above ingredients of the boundary layer ceramics in accordance with our invention, the group of metal oxides, Nb205, WO and Ta205, function principally to make the ceramics semiconductive. The other group of oxides, GeO2, ZnO and CuO, are effective primarily to accelerate the growth of the crystal grains. Used in the above specified ranges of proportions, the secondary ingredients SiO2 and A1203 both serve to make the crystal grains of the ceramics greater in size than hitherto, namely from 60 to 120 micrometers in diameter. Generally, the greater the crystal grains of ceramics in size, the higher are their relative dielectric constants. The apparent relative dielectric constants of the ceramics in accordance with our invention are well over 80.000. As has been ascertained by experiment, moreover, the dielectric loss tangents (the tangents of the dielectric loss angles) of the ceramics in accordance with our invention are less than one percent (1 x 10 ), , and their resistivities are 11 over 1.0 x 10 1 ohm-centimeters. The ceramics with these characteristics are admirably well suited for use as dielectrics of capacitors. It will of course be understood that the listed ingredients of the ceramics in accordance with our invention perform not just the above recited functions by themselves. They intricately interact to make up the ceramics of the highly favorable electrical properties. Our invention also provides a method of fabricating coherent bodies of the above ceramic compositions. The method dictates the preparation, first of all, of uninsulated ceramic bodies composed of the primary and secondary ingredients set forth previously. Then the three insulating substances, PbO, Bi203 and B203, are suitably layered on the uninsulated ceramic bodies, which are then heated to cause diffusion of the insulating substances throughout the intergranular boundaries of the ceramic bodies. Preferably, the uninsulated ceramic bodies are prepared by firing moldings of the primary and secondary ingredients in a reductive atmosphere. On these uninsulated ceramic bodies are then coated a paste of the insulating substances. Then the coated bodies are heated in an oxidative atmosphere to cause diffusion of the insulating substances. The use of a rubber-lined bowl mill is recommended for blending together the primary and secondary ingredients as it makes possible the accurate proportioning of SiO2 and A1203, which is essential to increase the size of the crystal grains to a desired degree. The above and other features and advantages of this invention and the manner of attaining them will become more apparent, and the invention itself will best be understood, from a study of the following description taken together with the attached drawings, in which: Figure 1 is a highly diagrammatic section through a body of insulated boundary layer ceramic material in accordance with our invention, the ceramic body being shown electroded for use as a capacitor; and Figure 2 is a graphic representation of the temperature dependencies of the relative dielectric constants of test pieces of various ceramic compositions in accordance with our invention. Although the showing of Figure 1 is highly diagrammatic, it will nevertheless be seen that the boundary layer ceramic body 10 of our invention is of polycrystalline structure, composed of an aggregate of semiconductive crystal grains 11 isolated from one another by boundary layers 12, Diffused throughout these boundary layers are PbO, Bi203 and B203 which serve to insulate the crystal grains 11 from one another. The ceramic body 1Q can be converted into a capacitor by being electroded as at 13. These electrodes may be formed by coating a commercial silver paste on the opposite faces of the ceramic body 10 and then by firing the coatings. Presented hereinbelow are Examples dealing with specific compositions of the insulated boundary layer ceramics, method of their preparation, and electrical properties of capacitors made with use of the ceramics. As will be specifically pointed out in the course of the description of these Examples, some of them fall outside the purview of our invention. Such noninventive Examples are given to clearly distinguish the advantages of our invention and to give support to the claimed numerical limitations. Hereinafter in this specification all percentages and parts are by weight unless otherwise specified. Examples 1-48 SrTiO3 of the industrial grade (containing practically negligible amounts of impurities such as barium, iron, manganese, calcium, sodium and potassium) was admixed with two other primary ingredients Nub 205 and GeO2 and the secondary ingredients SiO2 and Awl 203 in various sets of proportions specified in Table 1. In order to avoid intrusion of foreign matter, these admixtures were blended wet in a rubber-lined bowl mill. After being dried, the admixtures were pasted with polyvinyl alcohol, an organic binder, and the pastes were molded under pressure into test discs. Then the test discs were heated to and held at 1000o C. for one hour thereby removing the binder therefrom by evaporation. Then the test discs were fired in a temperature range of 13500 C. to 14500 C. for two to four hours in a weakly reductive atmosphere of 99 percent by capacity of molecular nitrogen (N2) and one percent by capacity of molecular hydrogen (H2). Thus were prepared the semiconductive ceramic test discs each having a diameter of approximately eight millimeters and a thickness of approximately 0.4 millimeter. The test discs are polycrystalline, comprising a myriad of crystal grains 11 as in Figure 1. These crystal grains are, however, not yet insulated from one another, so that we will refer to the discs at this stage as the uninsulated ceramic test discs. It will be appreciated that the use of the rubber-lined bowl mill serves to prevent the introduction of impurities, as from a ceramic-made bowl, into the ceramic materials, making possible the precise proportioning of SiO2 and A1203 which are both used in extremely small quantities. Then, in order to insulate the crystal grains of the uninsulated ceramic test discs from each other, there was prepared a mixture of 50 wt. % PbO, 45 wt. % Bi203, and five wt. a B203, all in finely divided form. The mixture was pasted with nitrocellulose and butyl "Carbitol" (trademark for diethylene glycol mono-n-butyl ether). This paste was screen-printed on one face of each uninsulated ceramic test disc, at a rate of 10 milligrams (10 percent) for each 100 milligrams of the uninsulated ceramic test discs. Then the coated test discs were heated to and held at a constant temperature in the range from 11500 C. to 13000 C. for two hours in a oxidizing atmosphere. This heat treatment caused diffusion of PbO, Bi2O3 and B2O3 throughout the intergranular boundaries of the ceramic test discs. The insulated boundary layers thus formed are indicated at 12 in Figure 1. Thus was completed the fabrication of the insulated boundary layer ceramic test discs in accordance with our invention. For testing the electrical properties of the test discs, these were further processed into test capacitors by coating a commercial silver paste on their opposite faces and by firing them. Figure 1 shows at 13 the pair of electrodes thus formed on each test disc. In the foregoing process of the fabrication of the insulated boundary layer ceramic test discs, the secondary ingredients SiO2 and A1203 are both wholly retained in the completed products in the initial proportions. However, the insulating substances PbO, Bi203 and B203 partly evaporate on being heated after having been coated on the uninsulated ceramic test discs, the remainders of the substances being diffused in the intergranular boundaries of the test discs. The remaining (actually diffused) percentages of the insulating substances are subject to change depending upon the substances themselves and on the compositions of the test discs. In these particular Examples the PbO remained at rates ranging from 0.27 to 0.86 milligram (0.27 to 0.86 percent), the Bi203 at rates ranging from 0.51 to 1.60 milligrams (0.51 to 1.60 percent), and the B203 at rates ranging from 0.01 to 0.06 milligram (0.01 to 0.06 percent), for each 100 milligrams of the test discs. The boundary layer ceramic test capacitors prepared as above were tested as to apparent relative dielectric constants (E), dielectric loss tangents (tan 6), and resistivities (p). Table 1 gives the results. In this and all the following tables each listed value is the average of 30 samples. Also, in all the tables given herein, relative dielectric constants and dielectric loss tangents were both measured at one kilohertz, and resistivities were measured upon lapse of one minute after application of a direct current at 50 volts. The dielectric loss tangents in the tables are expressed in percent; therefore, for the actual values, the tabulated figures should be multiplied by 10 It will also be noted from Table 1 that the percentages of the three primary ingredients, SrTiO3, Nb205 and GeO2, sum up to 100 in each Example. The same holds true with the various combinations of three principal ingredients employed in all the Examples given in the subsequent tables. Further, in this and all the following tables, the proportions of the secondary ingredients SiO2 and A1203 are expressed in parts 3 with respect to 100 parts of the three primary ingredients combined. TABLE 1 Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Nb2O5, GeO2, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 1 97.67 1.33 1.00 ...................... 7.5 0.4 3.5 2 97.67 1.33 1.00 0.020 0.020 1.0 7.8 0.5 1.3 3 93.10 4.80 2.10 0.022 0.017 1.3 7.8 0.5 1.3 4 97.67 1.33 1.00 0.040 0.030 1.3 7.9 0.7 1.4 5 99.70 0.14 0.16 0.035 0.025 1.4 7.8 0.6 1.7 6 97.67 1.33 1.00 0.015 0.010 1.5 7.7 0.4 2.6 7 97.67 1.33 1.00 0.030 0.020 1.5 11.6 0.6 1.8 8 95.53 1.47 3.00 0.045 0.030 1.5 11.8 0.5 1.4 9 97.67 1.33 1.00 0.060 0.040 1.5 7.9 0.5 1.3 10 97.47 0.53 2.00 0.050 0.030 1.7 11.6 0.5 1.4 11 97.67 1.33 1.00 0.050 0.030 1.7 12.0 0.6 1.3 12 90.68 5.32 4.00 0.040 0.020 2.0 9.7 0.4 2.0 13 93.10 4.80 2.10 0.020 0.010 2.0 10.8 0.6 1.2 14 95.53 1.47 3.00 0.020 0.010 2.0 10.8 0.5 1.5 15 97.67 1.33 1.00 0.020 0.010 2.0 9.7 0.4 2.0 16 97.67 1.33 1.00 0.050 0.025 2.0 11.8 0.6 1.5 TABLE 1 - Continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Nb2O5, GeO2, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 17 98.03 1.47 0.50 0.040 0.020 2.0 11.2 0.5 1.2 18 99.83 0.07 0.05 0.040 0.020 2.0 10.9 0.4 1.4 19 99.83 0.07 0.05 0.040 0.020 2.0 9.6 0.5 1.7 20 99.70 0.14 0.16 0.080 0.040 2.0 7.8 0.6 1.5 21 97.67 1.33 1.00 0.030 0.012 2.5 10.1 0.5 1.8 22 93.19 4.80 2.01 0.080 0.030 2.7 11.0 0.5 1.3 23 93.40 2.80 3.80 0.080 0.030 2.7 10.2 0.5 1.3 24 99.88 0.07 0.05 0.080 0.030 2.7 10.1 0.4 1.5 25 95.53 1.47 3.00 0.030 0.010 3.0 10.6 0.4 1.5 26 98.03 1.47 0.50 0.060 0.030 3.0 10.5 0.4 1.3 27 93.40 2.80 3.80 0.060 0.020 3.0 11.0 0.6 1.3 28 97.67 1.33 1.00 0.060 0.020 3.0 12.9 0.5 1.5 29 97.67 1.33 1.00 0.090 0.028 3.2 12.2 0.5 1.3 30 97.67 1.33 1.00 0.100 0.030 3.3 11.2 0.6 1.8 31 97.47 0.53 2.00 0.100 0.030 3.3 12.3 0.6 1.3 32 94.63 5.32 0.05 0.100 0.030 3.3 10.4 0.6 1.4 TABLE 1 - Continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Nb2O5, GeO2, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 33 97.67 1.33 1.00 0.020 0.005 4.0 7.9 0.4 2.2 34 94.63 5.32 0.05 0.040 0.010 4.0 10.9 0.4 1.4 35 90.68 5.32 4.00 0.080 0.020 4.0 11.3 0.4 1.9 36 97.67 1.33 1.00 0.080 0.020 4.0 12.6 0.5 1.7 37 97.67 1.33 1.00 0.120 0.030 4.0 7.9 0.5 1.3 38 97.67 1.33 1.00 0.050 0.010 5.0 15.3 0.8 1.0 39 95.53 1.47 3.00 0.075 0.015 5.0 13.5 0.6 1.0 40 93.40 2.80 3.80 0.075 0.015 5.0 13.4 0.6 1.2 41 97.67 1.33 1.00 0.100 0.020 5.0 11.6 0.5 1.8 42 95.93 0.07 4.00 0.100 0.020 5.0 11.2 0.4 1.7 43 99.88 0.07 0.05 0.090 0.017 5.3 13.7 0.6 0.3 44 97.67 1.33 1.00 0.055 0.010 5.5 18.4 1.5 0.1 45 93.40 2.80 3.80 0.080 0.014 5.7 14.1 0.8 0.3 46 97.67 1.33 1.00 0.060 0.010 6.0 19.3 2.0 0.1 47 91.20 5.32 3.48 0.120 0.020 6.0 7.4 0.6 1.6 48 95.53 1.47 3.00 0.090 0.012 7.5 12.0 0.7 0.5 Of the forty-eight Examples of Table 1, Examples 7, 8, 10-19, 21-32, 34-36, and 38-42 represent ceramic compositions complying with the teachings of our invention. The relative proportions of the three primary ingredients in use, SrTiO3, Nb205 and Ge02, of these Examples are from 90.68 to 99.88 percent, from 0.07 to 5.32 percent, and from 0.05 to 4.00 respectively. Their SiO2 and A1203 contents are from 0.02 to 0.10 part, and from 0.01 to 0.03 part, respectively, with respect to 100 parts of the primary ingredients. The ratios in weight of SiO2 to Al203 are from 1.5 to 5.0. The crystal grains of the ceramic test discs of the above inventive Examples averaged from 60 to 120 micrometers in diameter. As is seen from Table 1, the boundary layer ceramic test capacitors of the inventive Examples have apparent relative dielectric constants ranging from 77,000 to as high as 153,000, dielectric loss tangents of as small as 0.4 to 0.8 percent, and resistivities of one to 2 x 1011 ohm-centimeters. The ceramic compositions of Examples 1-6, 9, 20, 33, 37, and 43-48, on the other hand, do not conform to the principles of our invention. A consideration of Table 1 will show that if the weight ratio of SiO2 to A1203 is not more than 1.5, the apparent relative dielectric constants of the resulting capacitors fall short of 80,000. If this weight ratio exceeds 5.0, on the other hand, then the resulting capacitors have dielectric loss tangents of over 1.0 percent or resistivities of less than 1.0 x 1011 ohm-centimeters. Also, if the proportion of SiO2 is less than about 0.02 part or more than about 0.10 part with respect to 100 parts of the primary ingredients, the apparent relative dielectric constants of the resulting capacitors become less than 80,000. The apparent relative dielectric constants do not exceed 80,000, either, if the proportion of Al2O3 is less than about 0.01 part or more than about 0.03 part. We conclude from the above tabulated results that, for the boundary layer ceramics composed principally of SrTiO3, Nub 205 and GeO2 in accordance with our invention, the contents of the secondary ingredients SiO2 and Al203 should be from about 0.02 to about 0.10 part, and from about 0.01 to about 0.03 part, respectively, with respect to 100 parts of the primary ingredients. Further the weight ratio of SiO2 to A1203 should be from about 1.5 to about 5.0. Experiment has proved that capacitors of no favorable electrical properties are obtainable from boundary layer ceramics whose proportions of the three primary ingredients fall outside the ranges of our invention, even if their SiO2 and Awl 203 contents and the weight ratios thereof are within the ranges of our invention. We measured the temperature dependencies of the apparent relative dielectric constants of the above inventive Examples. The results were as graphically represented in Figure 2. With the apparent relative dielectric constants at 200 C. taken as a criterion, the percent variations of the dielectric constants of all the tested Examples with temperatures fell within the hatched regions of the graph. That is, the percent variations of the dielectric constants were plus or minus 15 in the temperature range of -25 C. to +850 C. Examples 49-79 Uninsulated ceramic test discs were fabricated by use of the same ingredients, and in the same proportions, as in Examples 8, 18, 22, 31, 35, 36 and 42, and through the same procedure as in Examples 1-48. Then the three insulating substances, PbO, Bi203 and B203, in the various sets of proportions given in Table 2 were thermally diffused throughout the intergranular boundaries of the test discs through the same procedure as in Examples 1-48. The thus insulated boundary layer ceramic test discs were then processed into test capacitors through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the three electrical properties in question of the above prepared test capacitors were as given in Table 2. In this table the column labelled "Ceramic" represents, of course, the uninsulated ceramics composed only of the primary ingredients SrTiO3, Nb205 and GeO2 and the secondary ingredients SiO2 and A1203. TABLE 2 Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 49 Example 8 32 59 10 11.0 0.5 1.5 50 Example 8 52 36 12 13.3 1.1 1.0 51 Example 8 35 64 1 10.5 0.8 0.5 52 Example 8 61 37 2 12.8 0.7 1.4 53 Example 18 59 40 1 11.0 1.1 0.2 54 Example 18 48 50 2 10.3 0.4 1.4 55 Example 18 35 63 2 10.2 0.4 1.5 56 Example 22 45 50 5 10.5 0.4 1.5 57 Example 22 34 64 2 10.2 0.5 1.6 58 Example 22 60 30 10 12.6 1.1 0.1 59 Example 31 45 53 2 12.4 0.4 1.6 60 Example 31 59 31 10 11.9 0.5 1.5 61 Example 31 61 31 8 12.0 0.6 1.2 62 Example 35 45 53 2 10.6 0.5 1.4 63 Example 35 61 34 5 11.8 0.6 1.3 64 Example 35 55 37 8 11.4 0.5 1.4 TABLE 2 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011#-cm Same as: 65 Example 35 34 56 10 10.8 0.6 1.5 66 Example 36 32 65 3 9.6 1.2 1.0 67 Example 36 45 54 1 11.7 0.8 0.3 68 Example 36 30 60 10 7.8 1.1 1.6 69 Example 36 45 45 10 12.0 0.5 1.6 70 Example 36 45 43 12 13.5 1.2 1.0 71 Example 36 34 64 2 10.5 0.5 1.4 72 Example 36 32 58 10 11.4 0.5 1.3 73 Example 36 38 57 5 11.5 0.4 1.3 74 Example 36 62 31 7 12.9 1.2 0.4 75 Example 36 61 34 5 12.4 0.8 1.0 76 Example 36 63 35 2 11.3 1.5 0.05 77 Example 42 32 64 4 10.6 0.6 1.7 78 Example 42 45 53 2 11.1 0.4 1.5 79 Example 42 61 37 2 12.1 0.6 1.2 Consider Examples 49, 52, 54-57, 59, 62-66, 69, 71-73, 75, and 77-79 of Table 2. The relative proportions of the in sulating substances PbO, By203 and B203 in these Examples 23 23 all fall within the ranges from 32 to 61 percent, from 34 to 64 percent, and from two to 10 percent, respectively. The apparent relative dielectric constants of all these inventive Examples are sufficiently high, and their dielectric loss tangents and resistivities are also favorable. In Examples 50, 51, 53, 58, 60, 61, 67, 68, 70, 74 and 76, on the other hand, the relative proportions of PbO, Bi 203 and B203 all fall outside the above ranges. All these noninventive Examples are unsatisfactory in one or more of the three electrical properties. We conclude from the results of Table 2 that the ranges of the relative proportions of the three insulating substances PbO, Bi203 and B203 should be from about 32 to about 61 percent, from about 34 to about 64 percent, and from about two to about 10 percent, respectively, for the ceramic compositions now under consideration. We measured the percentages of the insulating substances remaining diffused in the ceramic test discs of the above inventive Examples after the heat treatment. PbO remained at rates ranging from 0.06 to 1.45 percent, Bi203 at rates ranging from 0.23 to 2.17 percent, and B203 at rates ranging from 0.002 to 0.09 percent. Example 80 In this Example it was intended to ascertain the percentages of the three insulating substances to remain diffused in the boundary layer ceramics composed principally of SrTiO3, Nb205 and GeO2, for the provision of capacitors of favorable properties. The relative proportions of the insulating substances in use were within the ranges specified in connection with Examples 49-79. The pasted mixture of the insulating substances was coated on uninsulated ceramic test discs (prepared through the same procedure as in Examples 1-48, with the proportions of the ingredients in conformity with our invention) in various amounts ranging from one to 15 percent of the weight of the test discs. The coated discs were heated at various temperatures ranging from 11500 C. to 13000 C. for various lengths of time ranging from one to four hours, thereby preparing a number of insulated boundary layer ceramic test discs containing various amounts of the insulating substances. Then the test discs were processed into test capacitors through the same procedure as in Examples 1-48. Of the thus fabricated test capacitors, those having an apparent relative dielectric constant of over 80,000, a dielectric loss tangent of not more than one percent, and a resistivity of not less than 1.0 x 1011 ohm-centimeters were picked up. The PbO, Bi2O3 and B2O3 contents of these test capacitors with the favorable electrical properties ranged from 0.03 to 2.90 percent, from 0.11 to 4.34 percent, and from 0.001 to 0.18 percent, respectively, with respect to the weight of the uninsulated ceramic discs (i.e., those composed of the primary ingredients SrTiO3, Nub 205 and GeO2 and the secondary ingredients SiO2 and Al203). Examples 81-114 As the primary ingredients there were employed SrTiO3, W03 and ZnO. Insulated boundary layer ceramic test capacitors were prepared by use of these primary ingredients and the secondary ingredients Si02 and A1203, in various sets of proportions given in Table 3, and of the insulating substances PbO. Bi2O3 and B2O3, through the same procedure as in Examples 1-48. The electrical properties of these test capacitors, measured by the same methods as in Examples 1-48, were as set forth also in Table 3. As has been stated, the percentages of the insulating substances remaining diffused in the ceramic test discs are subject to change depending upon the ceramic compositions. In these Examples, using SrTiO3, W03 and ZnO as the main ingredients, PbO, Bi203 and B203 remained at percentages ranging from 0.31 to 0.80, from 0.57 to 1.48, and from 0.01 to 0.06, respectively, relative to the weight of the ceramic test discs in the uninsulated state. TABLE 3 Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, WO3, ZnO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 81 98.20 1.00 0.80 ...................... 6.4 0.3 1.8 82 95.20 2.30 2.50 0.024 0.028 0.9 5.9 0.7 1.8 83 99.80 0.15 0.05 0.020 0.020 1.0 5.8 0.5 1.8 84 98.25 0.35 1.40 0.040 0.030 1.3 6.4 0.6 1.7 85 99.20 0.50 0.30 0.024 0.018 1.3 6.3 0.5 1.7 86 97.65 2.30 0.05 0.034 0.025 1.4 6.2 0.6 1.7 87 97.35 0.15 2.50 0.015 0.010 1.5 5.9 0.4 1.7 88 98.55 1.35 0.10 0.021 0.014 1.5 8.5 0.5 1.6 89 97.35 0.15 2.50 0.030 0.020 1.5 8.9 0.5 1.5 90 97.65 2.30 0.05 0.045 0.030 1.5 9.1 0.6 1.6 91 98.20 1.00 0.80 0.040 0.025 1.6 9.7 0.5 1.5 TABLE 3 - Continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, WO3, ZnO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011#-cm 92 95.20 2.30 2.50 0.060 0.035 1.7 5.9 0.6 1.7 93 99.80 0.15 2.50 0.052 0.028 1.9 8.7 0.6 1.6 94 99.20 0.50 0.30 0.020 0.010 2.0 8.1 0.4 1.6 95 98.25 0.35 1.40 0.043 0.020 2.2 9.8 0.5 1.5 96 97.35 0.15 2.50 0.070 0.030 2.3 9.3 0.6 1.5 97 99.67 0.18 0.15 0.078 0.031 2.5 6.0 0.6 1.5 98 97.65 2.30 0.05 0.032 0.012 2.7 8.1 0.4 1.5 99 96.20 2.00 1.80 0.095 0.035 2.7 6.0 0.7 1.7 100 98.55 1.35 0.10 0.060 0.020 3.0 10.6 0.5 1.5 101 99.80 0.15 0.05 0.090 0.028 3.2 9.1 0.6 1.5 102 98.25 0.35 1.40 0.100 0.030 3.3 9.1 0.6 1.5 TABLE 3 - continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, WO3, ZnO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 103 97.65 2.30 0.05 0.102 0.026 3.9 6.2 0.7 1.6 104 98.20 1.00 0.80 0.020 0.005 4.0 6.5 0.3 1.7 105 96.20 2.00 1.80 0.040 0.010 4.0 9.4 0.4 1.5 106 99.20 0.50 0.30 0.080 0.020 4.0 10.2 0.5 1.5 107 95.20 2.30 2.50 0.070 0.015 4.7 11.7 0.6 1.3 108 97.35 0.15 2.50 0.040 0.008 5.0 6.0 0.4 1.8 109 99.67 0.18 0.15 0.050 0.010 5.0 11.6 0.5 1.4 110 97.65 2.30 0.05 0.100 0.020 5.0 9.2 0.5 1.5 111 98.55 1.35 0.10 0.080 0.015 5.3 11.5 1.2 0.1 112 97.35 0.15 2.50 0.055 0.010 5.5 14.3 1.0 0.1 113 96.20 2.00 1.80 0.090 0.010 6.0 9.6 0.9 0.4 114 99.80 0.15 0.05 0.095 0.012 7.9 7.5 0.9 0.6 As is seen from Table 3, Examples 88-91, 93-96, 98, 100102, 105-107, 109 and 110 have ceramic compositions within the scope of our invention. The SrTiO3, W03 and ZnO contents of all these Examples fall within the ranges from 95.20 to 99.80 percent, from 0.15 to 2.30 percent, and from 0.05 to 2.50 percent, respectively. The SiO2 and A1203 contents of the Examples range from 0.02 to 0.10 part, and from 0.01 to 0.03 part, respectively, with respect to 100 parts of the primary ingredients, and the ratios in weight of SiO2 to Al203 are in the range from 1.5 to 5.0. The crystal grains of the above inventive Examples were from 60 to 120 micrometers in diameter. The apparent relative dielectric constants of the Examples range from 81,000 to 117,000, their dielectric loss tangents from 0.4 to 0.6 percent, and their resistivities from 1.3 to 1.6 x 1011 ohm-centimeters. Let us consider the other, noninventive Examples 81-87, 92, 97, 99, 103, 104, 108, and 111-114. In those Examples whose weight ratio of SiO2 to Al2O3 is less than 1.5, the apparent relative dielectric constant becomes less than 80,000. If the weight ratio of SiO2 to Awl203 exceeds 5.0, on the other hand, then the dielectric loss tangent becomes more than 1.0 percent, or the resistivity becomes less than 1.0 x 1011 ohm-centimeters. Examples containing less than 0.02 part SiO2 with respect to 100 parts of the primary ingredients have apparent relative dielectric constants of less than 80,000. The apparent relative dielectric constant also becomes poor if the SiO2 content exceeds 0.1 part with respect to 100 parts of the primary ingredients. Examples containing less than 0.01 part, or more than 0.03 part, A1203 with respect to 100 parts of the primary ingredients also have apparent relative dielectric constants of not more than 80,000. From the foregoing results we conclude that the proportions of SiO2 and A1203 in the boundary layer ceramics composed principally of SrTiO3, WO3 and ZnO should be from about 0.02 to about 0.10 part, and from about 0.01 to about 0.03 part, respectively, with respect to 100 parts of the principal ingredients, and that the weight ratio of the SiO2 content to that of A1203 should be from about 1.5 to about 5.0. These conclusions presuppose, of course, that the proportions of the three primary ingredients are within the ranges of the invention set forth previously. We measured the temperature dependencies of the apparent relative dielectric constants of the above inventive Examples. The results were the same as those in the graph of Figure 2, with the percent variations of the dielectric constants of all the inventive Examples with temperatures falling within the hatched areas of the graph. Examples 115-152 Uninsulated ceramic test discs were fabricated by use of the same ingredients, and in the same proportions, as in Examples 88, 91, 93, 96, 100, 102, 107, 109 and 110, and through the same procedure as in Examples 1-48. Then the three insulating substances, PbO, Bi203 and B203, in the various sets of proportions specified in Table 4 were diffused throughout the intergranular boundaries of the test discs by the same method as in Examples 1-48. The insulated boundary layer ceramic test discs were then processed into test capacitors also through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the three electrical properties in question of the thus prepared test capacitors were as set forth in Table 4. In this table the column labelled "Ceramic" represents the uninsulated ceramics composed of the main ingredients SrTiO , WO and ZnO and the 3' 3 auxiliary ingredients SiO2 and A1203. TABLE 4 Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011#-cm Same as: 115 Example 88 35 55 10 8.1 0.6 1.7 116 Example 88 45 52 3 8.0 0.5 1.7 117 Example 88 54 36 10 8.9 0.6 1.6 118 Example 91 34 59 7 8.8 1.2 1.6 119 Example 91 39 52 9 9.3 0.6 1.5 120 Example 91 50 40 10 9.9 0.6 1.5 121 Example 91 54 44 2 9.2 0.5 1.5 122 Example 93 35 55 10 8.3 0.7 1.6 123 Example 93 45 52 3 8.1 0.6 1.5 124 Example 93 54 44 2 8.6 0.6 1.5 TABLE 4 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011#-cm Same as: 125 Example 96 38 57 5 8.6 0.5 1.6 126 Example 96 45 45 10 9.1 0.6 1.6 127 Example 96 55 43 2 8.3 0.8 0.2 128 Example 96 54 40 6 9.2 0.5 1.5 129 Example 100 35 58 7 9.9 0.5 1.5 130 Example 100 40 58 2 9.9 0.5 1.4 131 Example 100 45 47 8 10.2 0.6 1.5 132 Example 100 53 38 9 10.5 0.6 1.5 133 Example 100 55 35 10 11.3 0.7 0.1 134 Example 102 34 55 11 7.9 1.2 1.3 135 Example 102 39 52 9 8.7 0.5 1.6 136 Example 102 45 52 3 8.5 0.5 1.6 137 Example 102 50 40 10 9.3 0.5 1.5 TABLE 4 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011#-cm Same as: 138 Example 107 35 58 7 10.9 0.7 1.4 139 Example 107 40 58 2 10.8 0.7 1.3 140 Example 107 53 38 9 11.6 0.6 1.3 141 Example 107 54 45 1 10.6 0.6 0.3 142 Example 109 38 57 5 10.8 0.5 1.3 143 Example 109 41 58 1 9.4 1.3 1.4 144 Example 109 45 45 10 11.4 0.5 1.4 145 Example 109 50 38 12 12.5 1.5 1.2 146 Example 109 54 44 2 11.0 0.6 1.4 147 Example 110 35 55 10 8.7 0.5 1.6 148 Example 110 40 58 2 8.6 0.4 1.6 149 Example 110 40 49 11 8.0 1.2 1.6 150 Example 110 45 52 3 8.5 0.4 1.6 151 Example 110 50 40 10 9.4 0.5 1.5 152 Example 110 54 36 10 9.7 0.5 1.5 In Examples 115-117, 119-126, 128-132, 135-140, 142, 144, 146-148, and 150-152, the relative proportions of PbO, Bi203 and B203 range from 35 to 54 percent, from 36 to 58 percent, and from two to 10 percent, respectively. The apparent relative dielectric constants of all these Examples are sufficiently high, and their dielectric loss tangents and resistivities are also favorable. In Examples 118, 127, 133, 134, 141, 143, 145 and 149, on the other hand, the relative proportions of PbO, Bi203 and B203 all fall outside the above ranges. The electrical properties of these noninventive Examples are unsatisfactory. Thus, for the ceramics composed principally of SrTiO3, W03 and ZnO, the relative proportions of the insulating substances PbO, Bi203 and B203 should be in the ranges from about 35 to about 54 percent, from about 36 to about 58 percent, and from about two to about 10 percent, respectively. We measured the percentages of the insulating substances remaining diffused in the ceramic test discs of the inventive Examples after the heat treatment. PbO remained at rates ranging from 0.07 to 1.54 percent, Bi203 at rates ranging from 0.22 to 2.37 percent, and B203 at rates ranging from 0.002 to 0.10 percent. Example 153 In this Example there were ascertained the percentages of the three insulating substances to remain diffused in the boundary layer ceramics composed principally of SrTiO3, W03 and ZnO, for the provision of capacitors of favorable electrical properties. The relative proportions of the insulating substances in use were within the desired ranges specified in connection with Examples 115-152. The pasted mixture of PbO, Bi203 and B203 was coated on uninsulated ceramic test discs in various amounts ranging from one to 15 wt. % of the test discs. The uninsulated test discs were composed principally of SrTiO3, W03 and ZnO, with their proportions within the ranges of our invention set forth in connection with Examples 81-114, and were prepared through the same procedure as in Examples 1-48. The above coated discs were heated at various temperatures ranging from 11500 C. to 13000 C. for various lengths of time ranging from one to four hours. Thus were fabricated a number of insulated boundary layer ceramic test discs having the three insulating substances remaining diffused throughout their intergranular boundaries in various percentages. Then the test discs were processed into test capacitors through the same procedure as in Examples 1-48. From among the thus prepared test capacitors we picked up those having an apparent relative dielectric constant of over 80,000, a dielectric loss tangent of not more than one 11 percent, and a resistivity of not less than 1.0 x 10 ohm- centimeters. The PbO, Bi203 and B203 contents of these test capacitors with the favorable electrical properties ranged from 0.03 to 2.75 percent, from 0.11 to 4.23 percent, and from 0.001 to 0.18 percent, respectively, with respect to the weight of the uninsulated test discs. Examples 154-187 As the primary ingredients there was employed a combination of SrTiO3, Ta205 and CuO. Insulated boundary layer ceramic test capacitors were prepared by use of these principal ingredients and the secondary ingredients SiO2 and Awl203, in various sets of proportions represented in Table 5, and of the insulating substances PbO, Bi203 and B203, through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the electrical properties of these test capacitors were as set forth also in Table 5. We measured the percentages of the three insulating substances actually remaining diffused in the boundary layer ceramic test discs of the above compositions consisting primarily of SrTiO3, Ta2O5 and CuO. PbO, Bi2O3 and B2O3 remained at percentages ranging from 0.28 to 0.86, from 0.49 to 1.50. and from 0.01 to 0.06, respectively, relative to the weight of the ceramic test discs in the uninsulated state. TABLE 5 Primary ingredients (100 wt. pars) Secondary inredients Elecrical properties SiO2, Al2O3, SiO2 SrTiO3, Ta2O5, CuO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 154 98.30 1.20 0.50 ...................... 6.2 0.6 1.5 155 95.20 3.30 1.50 0.024 0.028 0.9 5.9 0.8 1.5 156 99.65 0.33 0.02 0.020 0.020 1.0 6.2 0.7 1.5 157 97.40 2.50 0.10 0.040 0.030 1.3 6.3 0.7 1.5 158 98.17 0.33 1.50 0.024 0.018 1.3 6.1 0.6 1.5 159 96.68 3.30 0.02 0.034 0.025 1.4 6.0 0.7 1.5 160 96.60 2.00 1.40 0.015 0.010 1.5 5.9 0.6 1.5 161 98.30 1.20 0.50 0.021 0.014 1.5 8.4 0.6 1.4 162 98.17 0.33 1.50 0.030 0.020 1.5 9.1 0.6 1.4 163 95.20 3.30 1.50 0.045 0.030 1.5 8.6 0.7 1.5 164 99.30 0.50 0.20 0.040 0.025 1.6 9.4 0.6 1.3 TABLE 5 - Continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Ta2O5, CuO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 165 99.65 0.33 0.02 0.060 0.035 1.7 6.3 0.7 1.5 166 96.60 2.00 1.40 0.052 0.028 1.9 9.0 0.6 1.4 167 98.30 1.20 0.50 0.020 0.010 2.0 8.5 0.5 1.4 168 96.68 3.30 0.02 0.043 0.020 2.2 9.2 0.5 1.4 169 99.35 0.80 0.65 0.070 0.030 2.3 9.7 0.6 1.3 170 97.40 2.50 0.10 0.078 0.031 2.5 6.3 0.6 1.5 171 95.20 3.30 1.50 0.032 0.012 2.7 8.2 0.5 1.5 172 99.35 0.80 0.65 0.095 0.035 2.7 6.3 0.7 1.4 173 99.65 0.33 0.02 0.060 0.020 3.0 10.6 0.5 1.3 174 96.60 2.00 1.40 0.090 0.028 3.2 9.4 0.6 1.4 175 98.17 0.33 1.50 0.100 0.030 3.3 8.7 0.6 1.3 TABLE 5 - Continued Pimary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Ta2O5, CuO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 176 97.40 2.50 0.10 0.102 0.026 3.9 6.3 0.7 1.4 177 98.30 1.20 0.50 0.020 0.005 4.0 6.3 0.6 1.5 178 97.40 2.50 0.10 0.040 0.010 4.0 9.9 0.6 1.4 179 96.68 3.30 0.02 0.080 0.020 4.0 9.7 0.6 1.4 180 99.65 0.33 0.02 0.070 0.015 4.7 12.9 0.7 1.1 181 98.30 1.20 0.50 0.040 0.008 5.0 6.4 0.6 1.5 182 99.35 0.80 0.65 0.050 0.010 5.0 13.6 0.6 1.0 183 99.30 0.50 0.20 0.100 0.020 5.0 9.4 0.6 1.3 184 96.60 2.00 1.40 0.080 0.015 5.3 13.7 1.5 0.05 185 97.40 2.50 0.10 0.055 0.010 5.5 15.1 1.4 0.05 186 98.17 0.33 1.50 0.090 0.15 6.0 10.3 1.2 0.2 187 96.68 3.30 0.02 0.095 0.12 7.9 7.8 1.2 0.9 Examples 161-164, 166-169, 171, 173-175, 178-180, 182 and 183 are in conformity with the principles of our invention. The relative proportions of the three primary ingredients, SrTiO3, Ta205 and CuO in all these Examples are in the ranges from 95.18 to 99.65 percent, from 0.33 to 3.32 percent, and from 0.02 to 1.50 percent, respectively. The SiO2 and Awl 203 contents of the Examples range from 0.02 to 0.10 part, and from 0.01 to 0.03 part, respectively, with respect to 100 parts of the primary ingredients. The ratios in weight of SiO2 to Awl203 range from 1.5 to 5.0. The crystal grains of these inventive Examples averaged from 60 to 120 micrometers in diameter. The apparent relative dielectric constants of the Examples were in the range from 82,000 to 136,000, their dielectric loss tangents from 0.5 to 0.7 percent, and their resistivities over 1.0 x i011 ohm-centimeters. The other Examples, 154-160, 165, 170, 172, 176, 177, 181, and 184-187, are not in conformity with the principles of our invention. As will be noted from these noninventive Examples, the apparent relative dielectric constant becomes less than 80,000 if the weight ratio of SiO2 to Al203 falls short of 1.5. If the weight ratio of SiO2 to A1203 exceeds 5.0, on the other hand, then the dielectric loss tangent becomes more than 1.0 percent, or the resistivity becomes less than 1.0 x 10 ohm-centimeters. Also the apparent relative dielectric constant does not become greater than 80,000 if the proportion of SiO2 is less than 0.02 part or more than 0.10 part with respect to 100 parts of the primary ingredients. Similarly the apparent relative dielectric constant becomes low if the proportion of A1203 is less than 0.01 part or more than 0.03 part with respect to 100 parts of the primary ingredients. Consequently, for the boundary layer ceramics composed prin cipally of SrTiO3, Ta205 and CuO in accordance with our invention, the proportions of SiO2 and A1203 should be from about 0.02 to about 0.10 part, and from about 0.01 to about 0.03 part, respectively, with respect to 100 parts of the principal ingredients. Further the weight ratio of SiO2 to Al2O3 shuld be from about 1.5 to about 5.0. In drawing thse conclusions we presuppose, of course, that the proportions of the three principal ingredients are within the ranges of our invention. We measured the temperature dependencies of the apparent relative dielectric constants of the above inventive Examples. The results were the same as those in the graph of Figure 2, with the percent variations of the dielectric constants of all the inventive Examples with temperatures falling within the hatched areas of the graph. Examples 188-227 Uninsulated ceramic test discs were fabricated by use of the same ingredients, in the same proportions, as in Examples 163, 167, 169, 173, 175, 179, 182 and 183, and through the same procedure as in Examples 1-48. Then the three insulating substances in the various sets of proportions set forth in Table 6 were diffused throughout the intergranular boundaries of the test discs by the same method as in Examples 148. The insulated boundary layer ceramic test discs were then processed into test capacitors through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the electrical properties in question of the thus prepared test capacitors were as given in Table 6. In this table the column labelled "Ceramic" indicates the uninsulated ceramics composed of the primary ingredients SrTiO3, Ta205 and CuO and the secondary ingredients SiO2 and Awl203. TABLE6 Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 188 Example 163 34 56 10 7.9 0.7 1.5 189 Example 163 35 55 10 8.2 0.6 1.4 190 Example 163 45 52 3 8.0 0.6 1.4 191 Example 163 50 40 10 8.8 0.7 1.4 192 Example 167 38 57 5 8.0 0.6 1.4 193 Example 167 45 47 8 8.2 0.6 1.4 194 Example 167 53 38 9 8.4 0.7 1.4 195 Example 169 34 59 7 8.8 1.1 1.4 196 Example 169 35 58 7 9.0 0.7 1.4 197 Example 169 40 58 2 9.0 0.7 1.4 TABLE 6 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x104 % x 1011 #-cm Same as: 198 Example 169 45 45 10 9.5 0.6 1.3 199 Example 169 54 44 2 9.2 0.6 1.3 200 Example 173 35 58 7 9.9 0.7 1.3 201 Example 173 39 52 9 10.2 0.7 1.3 202 Example 173 47 52 1 9.3 0.7 0.2 203 Example 173 50 40 10 10.8 0.6 1.3 204 Example 173 55 40 5 10.4 0.8 0.6 205 Example 175 39 52 9 8.4 0.7 1.4 206 Example 175 40 49 11 8.5 1.2 1.5 207 Example 175 53 38 9 8.6 0.7 1.4 TABLE 6 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 208 Example 175 38 57 5 8.1 0.7 1.4 209 Example 175 45 52 3 8.1 0.6 1.3 210 Example 175 50 40 10 8.9 0.6 1.3 211 Example 179 40 58 2 9.0 0.7 1.5 212 Example 179 45 45 10 9.5 0.6 1.4 213 Example 179 54 44 2 9.2 0.6 1.4 214 Example 179 54 40 6 9.6 0.6 1.4 215 Example 179 35 55 10 9.2 0.7 1.4 216 Example 179 45 52 3 9.0 0.6 1.4 217 Example 179 50 40 10 9.9 0.6 1.5 TABLE 6 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 218 Example 179 54 36 10 10.2 0.7 0.5 219 Example 182 38 57 5 12.6 0.6 1.3 220 Example 182 45 45 10 13.3 0.6 1.3 221 Example 182 54 45 1 12.1 0.8 0.3 222 Example 182 54 44 2 12.9 0.6 1.3 223 Example 183 40 58 2 8.7 0.6 1.4 224 Example 183 39 52 9 7.0 0.6 1.4 225 Example 183 45 52 3 8.7 0.6 1.4 226 Example 183 50 40 10 9.6 0.6 1.4 227 Example 183 50 38 12 10.2 1.1 1.1 In Examples 189-194, 196-201, 203, 205, 207-217, 219, 220, and 222-226 the relative proportions of PbO, Bi203 and B203 range from 35-54 percent, from 37 to 58 percent, and from two to 10 percent, respectively. The apparent relative dielectric constants of all these inventive Examples are sufficiently high, and their dielectric loss tangents and resistivities are also favorable. In Examples 188, 195, 202, 204, 206, 218, 221 and 227, on the other hand, the relative proportions of the insulating substances all fall outside the above ranges. The electrical properties of these noninventive Examples are unsatisfactory. Thus, for the boundary layer ceramics composed primarily of SrTiO3, Ta205 and CuO, the relative proportions of the three insulating substances, PbO, Bi203 and B203, should be in the ranges from about 35 to about 54 percent, from about 37 to about 58 percent, and from about two to about 10 percent, respectively. We measured the percentages of the insulating substances remaining diffused in the ceramic test discs of the above inventive Examples after the heat treatment. PbO remained at rates ranging from 0.07 to 1.65 percent, Bi203 at rates ranging from 0.23 to 2.53 percent, and B 203 at rates ranging from 0.002 to 0.11 percent. Example 228 This Example was intended to ascertain the percentages of the three insulating substances to remain diffused in the boundary layer ceramics composed mainly of SrTiO3, Ta205 and CuO, for the provision of capacitors of favorable electrical properties. The relative proportions of the insulating substances in use were within the desired ranges set forth in connection with Examples 188-227. The pasted mixture of the insulating substances was coated on uninsulated test discs in various amounts ranging from one to 15 wt. % of the test discs. The uninsulated ceramic test discs were composed principally of SrTiO3, Tea 205 and CuO, with their relative proportions within the desired ranges set forth in connection with Examples 154-187, and were prepared through the same procedure as in Examples 1-48. The above coated discs were heated at various temperatures ranging from 11500 C. to 13000 C. for various lengths of time ranging from one to four hours. Thus were prepared a number of insulated boundary layer ceramic test discs having the three insulating substances remaining diffused in their intergranular boundaries at various percentages. Then the test discs were processed into test capacitors through the same procedure as in Examples 1-48. From among the thus prepared test capacitors we chose those having an apparent relative dielectric constant of over 80, 000, a dielectric loss tangent of not more than one percent, and a resistivity of not less than 1.0 x 1011 ohm-centimeters. The PbO, Bi203 and B203 contents of these test capacitors with the favorable electrical properties ranged from 0.03 to 2.75 percent, from 0.11 to 4.22 percent, and from 0.001 to 0.18 percent, respectively, with respect to the weight of the uninsulated test discs composed of the primary ingredients SrTiO3, Ta205 and CuO and the secondary ingredients SiO2 and Awl203 Examples 229-262 In these Examples we tested a combination of SrTiO3, W03 and GeO2 as the primary ingredients. Insulated boundary layer ceramic test capacitors were prepared by use of these primary ingredients and the secondary ingredients SiO2 and Al203, in various sets of proportions represented in Table 7, and of the insulating substances PbO, Bi203 and B203, through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the electrical properties of these test capacitors were as represented also in Table 7. We also measured the percentages of the three insulating substances actually remaining diffused in the boundary layer ceramic test discs of the above compositions consisting primarily of SrTiO3 W03 and GeO2. PbO, Bi203 and B203 remained at percentages ranging from 0.31 to 0.86, from 0.57 to 1.61, and from 0.01 to 0.06, respectively, relative to the weight of the ceramic discs in the uninsulated state. TABLE 7 Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, WO3, GeO2, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 229 98.65 1.25 0.10 ...................... 6.5 0.5 2.0 230 94.50 2.50 3.00 0.024 0.028 0.9 6.0 0.7 2.0 231 99.82 0.13 0.05 0.020 0.020 1.0 6.1 0.6 2.0 232 99.10 0.50 0.40 0.040 0.030 1.3 6.4 0.6 2.0 233 96,87 0.13 3.00 0.024 0.018 1.3 6.0 0.5 2.0 234 97.45 2.50 0.05 0.034 0.025 1.4 6.1 0.6 2.0 235 96.70 2.00 1.30 0.015 0.010 1.5 6.2 0.5 1.8 236 99.63 0.22 0.15 0.021 0.014 1.5 8.4 0.5 1.8 237 96.87 0.13 3.00 0.030 0.020 1.5 8.9 0.5 1.8 238 94.50 2.50 3.00 0.045 0.030 1.5 8.8 0.5 1.8 239 98.65 1.25 0.10 0.040 0.025 1.6 9.9 0.5 1.7 TABLE 7 - Continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, WO3, GeO2, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 240 99.82 0.13 0.05 0.060 0.035 1.7 6.1 0.6 1.6 241 96.70 2.00 1.30 0.052 0.028 1.9 9.5 0.5 1.7 242 99.82 0.13 0.05 0.020 0.010 2.0 8.5 0.4 1.8 243 97.45 2.50 0.05 0.043 0.020 2.2 9.4 0.5 1.7 244 98.53 0.17 1.30 0.070 0.030 2.3 9.9 0.5 1.6 245 99.10 0.50 0.40 0.078 0.031 2.5 6.4 0.6 2.0 246 94.50 2.50 3.00 0.032 0.012 2.7 8.4 0.4 1.8 247 98.53 0.17 1.30 0.095 0.035 2.7 6.4 0.6 1.8 248 99.63 0.22 0.15 0.060 0.020 3.0 10.2 0.4 1.6 249 96.70 2.00 1.30 0.090 0.028 3.2 9.9 0.6 1.6 250 98.53 0.17 1.30 0.100 0.030 3.3 8.6 0.6 1.7 TABLE 7 - Continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, WO3, GeO2, , tan , , wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 251 99.10 0.50 0.40 0.102 0.026 3.9 6.4 0.6 1.8 252 99.63 0.22 0.15 0.020 0.005 4.0 6.2 0.5 2.0 253 99.10 0.50 0.40 0.040 0.010 4.0 10.0 0.5 1.6 254 97.45 2.50 0.05 0.080 0.020 4.0 9.8 0.5 1.6 255 99.82 0.13 0.05 0.070 0.015 4.7 12.7 0.5 1.3 256 99.63 0.22 0.15 0.040 0.008 5.0 6.2 0.5 2.0 257 98.53 0.17 1.30 0.050 0.010 5.0 13.9 0.5 1.1 258 98.65 1.25 0.10 0.100 0.020 5.0 9.8 0.6 1.6 259 96.70 2.00 1.30 0.080 0.015 5.3 14.3 1.2 0.1 260 99.10 0.50 0.40 0.055 0.010 5.5 15.3 1.3 0.1 261 96.87 0.13 3.00 0.090 0.015 6.0 10.1 1.0 0.7 262 97.45 2.50 0.05 0.095 0.012 7.9 7.9 0.9 0.8 Examples 236-239, 241-244, 246, 248-250, 253-255, 257, and 258 comply with the principles of our invention The relative proportions of the three primary ingredients, SrTiO3, W03 and GeO2, in all these inventive Examples are in the ranges from 94.50 to 99.82 percent, from 0.13 to 2.50 percent, and from 0.05 to 3.00 percent, respectively. The SiO2 and Awl 203 contents of the inventive Examples range from 0.02 to 0.10 part, and from 0.01 to 0.03 part, respectively, with respect to 100 parts of the primary ingredients, and the ratios in weight of SiO2 to Al203 range from 1.5 to 5.0. The crystal grains of the above inventive Examples averaged from 60 to 120 micrometers in diameter. The apparent relative dielectric constants of the Examples were in the range from 84,000 to 139,000, their dielectric loss tangents from 0.4 to 0.6 percent, and their resistivities over 1.1 x 1011 ohm-centimeters. The remaining Examples, 229-235, 240, 245, 247, 251, 252, 256, and 259-262, fall outside the purview of our invention. As will be noted from these noninventive Examples, the apparent relative dielectric constant becomes less than 80,000 if the weight ratio of SiO2 to A1203 is less than 1.5. If the weight ratio of SiO2 to Al203 exceeds 5.0, on the other hand, then either the dielectric loss tangent becomes more than 1.0 percent, or the resistivity becomes less than 1.0 x 1011 ohm-centimeters. Also the apparent relative dielectric constant does not become greater than 80,000 if the proportion of SiO2 is less than 0.02 part or more than 0.10 part with respect to 100 parts of the primary ingredients. Similarly the apparent relative dielectric constant becomes low if the proportion of A1203 is less than 0.01 part or more than 0.03 part with respect to 100 parts of the primary ingredients. We conclude from the foregoing results of Table 7 that, for the boundary layer ceramics composed principally of SrTiO3, WO3 and GeO2 in accordance with our invention, the proportions of SiO@ and Al@O@ should be from about 0.02 to about 23 0.10 part, and from about 0.01 to about 0.03 part, respectively, with respect to 100 parts of the primary ingredients. Further the weight ratio of SiO2 to Al203 should be from about 1.5 to about 5.0. These conclusions presuppose, of course, that the relative proportions of the three primary ingredients are within the ranges of our invention. We measured the temperature dependencies of the apparent relative dielectric constants of the above inventive Examples. The results were also as in the graph of Figure 2, with the percent variations of the dielectric constants of all the inventive Examples with temperatures falling within the hatched areas of the graph. Examples 263-297 Uninsulated ceramic test discs were fabricated by use of the same ingredients, and in the same proportions , as in Examples 238, 242, 244, 248, 250, 254, 257 and 258, and through the same procedure as in Examples 1-48. Then, in the various sets of proportions set forth in Table 8, the three insulating substances were diffused throughout the intergranular boundaries of the test discs by the same method as in Examples 1-48. The insulated ceramic test discs were then processed into test capacitors through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the electrical properties of the thus prepared test capacitors were as given in Table 8. In this table the column labelled "Ceramic" indicates the uninsulated ceramics composed of the primary ingredients SrTiO3, W03 and Ge02 and the secondary ingredients SiO2 and Al203. TABLE 8 Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 263 Example 238 31 59 10 8.2 1.2 1.8 264 Example 238 35 60 5 8.2 0.8 1.8 265 Example 238 39 52 9 8.4 0.6 1.8 266 Example 238 54 44 2 8.4 0.5 1.7 267 Example 238 61 34 5 8.5 0.6 1.7 268 Example 242 32 58 10 8.0 0.9 1.8 269 Example 242 40 59 1 8.0 0.9 0.8 270 Example 242 45 47 8 8.2 0.6 1.8 271 Example 242 54 40 6 8.4 0.5 1.8 272 Example 242 61 37 2 8.1 0.6 1.7 273 Example 244 34 59 7 9.0 0.6 1.6 274 Example 244 45 52 3 9.2 0.5 1.6 TABLE 8 - Contimied Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 275 Example 244 54 45 1 8.8 0.6 0.5 276 Example 244 58 32 10 10.7 0.5 1.5 277 Example 248 40 58 2 9.5 0.7 1.6 278 Example 248 40 49 11 8.6 1.2 1.1 279 Example 248 50 40 10 10.4 0.5 1.5 280 Example 248 55 40 5 10.0 0.5 1.5 281 Example 250 35 55 10 8.2 0.7 1.7 282 Example 250 37 61 2 8.1 1.1 1.6 283 Example 250 54 36 10 9.0 0.6 1.6 284 Example 250 61 37 2 8.2 0.6 1.6 285 Example 254 38 57 5 9.1 0.7 1.7 286 Example 254 45 45 10 9.6 0.6 1.6 TABLE 8 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 287 Example 254 55 40 5 9.6 0.6 1.6 288 Example 254 59 31 10 10.7 0.6 0.5 289 Example 254 61 34 5 9.5 0.7 1.5 290 Example 257 32 58 10 12.9 0.6 1.2 291 Example 257 40 58 2 12.9 0.6 1.2 292 Example 257 53 38 9 13.8 0.5 1.0 293 Example 257 61 31 8 15.4 0.6 0.2 294 Example 258 35 60 5 9.1 0.7 1.7 295 Example 258 39 52 9 9.4 0.6 1.6 296 Example 258 54 44 2 9.3 0.6 1.6 297 Example 258 63 35 2 9.5 0.8 0.6 In Examples 264-268, 270-274, 276, 277, 279-281, 283-292, and 294-296 the relative proportions of PbO, By 203 and B203 are in the ranges from 32 to 61 percent, from 32 to 60 percent, and from two to 10 percent, respectively. The apparent relative dielectric constants of all these inventive Examples are sufficiently high, and their dielectric loss tangents and resistivities are also favorable. In Examples 263, 269, 275, 278, 282, 293 and 297, on the other hand, the relative proportions of PbO, Bi203 and B203 all fall outside the above ranges. The electrical properties of these noninventive Examples are unsatisfactory. Thus, for the boundary layer ceramics composed primarily of SrTiO3, W03 and GeO2, the relative proportions of the three insulating substances, PbO, Bi203 and B203, should be in the ranges from about 32 to about 61 percent, from about 32 to about 60 percent, and from about two to about 10 percent, respectively. We measured the percentages of the insulating substances remaining diffused in the ceramic test discs of the above inventive Examples after the heat treatment. PbO remained at rates ranging from 0.06 to 1.45 percent, Bi203 at rates ranging from 0.21 to 2.14 percent, and B203 at rates ranging from 0.002 to 0.10 percent. Example 298 This Example was intended to ascertain the percentages of the three insulating substances to remain diffused in the boundary layer ceramics composed principally of SrTiO3, W03 and Ge02, for the provision of capacitors of favorable electrical properties. The relative proportions of the insulating substances in use were within the desired ranges set forth in connection with Examples 263-297. The pasted mixture of PbO, Bi 203 and B203 was coated on uninsulated test discs in various amounts ranging from one to 15 wt. % of the test discs. The uninsulated ceramic test discs were composed primarily of SrTiO3, W03 and Ge02, with their relative proportions within the desired ranges specified in connection with Examples 229-262, and were prepared through the same procedure as in Examples 1-48. The above coated discs were heated at various temperatures ranging from 11500 C. to 13000 C. for various lengths of time ranging from one to four hours. Thus were prepared a number of insulated boundary layer ceramic test discs having the three insulating substances remaining diffused throughout their intergranular boundaries at various percentages. Then the test discs were processed into test capacitors through the same procedure as in Examples 1-48. From among the thus prepared test capacitors we picked up those having an apparent relative dielectric constant of over 80,000, a dielectric loss tangent of not more than one percent, and a resistivity of not less than 1.0 x 1011 ohmcentimeters. The PbO, Bi 203 and B203 contents of these test capacitors with the favorable electrical properties ranged from 0.03 to 2.90 percent, from 0.10 to 4.28 percent, and from 0.001 to 0.18 percent, respectively, with respect to the weight of the uninsulated test discs composed of the primary ingredients SrTi03, W03 and GeO2 and the secondary ingredients SiO2 and Al203. Examples 299-332 As the primary ingredients there was tried a combination of SrTiO3, Nb205 and ZnO. Insulated boundary layer ceramic test capacitors were prepared by use of these primary ingredients and the secondary ingredients SiO2 and Al203, in various sets of proportions specified in Table 9, and of the insulating substances PbO, Bi203 and B203, through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the electrical properties of these test capacitors were as represented also in Table 9. We also measured the percentages of the three insulating substances remaining diffused in the boundary layer ceramic test discs of the above compositions consisting primarily of SrTiO3, Nb205 and ZnO. PbO, By 203 and B203 remained at percentages ranging from 0.27 to 0.79, from 0.51 to 1.48, and from 0.01 to 0.04, respectively, with respect to the weight of the ceramic discs in the uninsulated state. TABLE 9 Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Nb2O5, ZnO #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 299 98.45 1.05 0.50 ...................... 6.3 0.7 1.5 300 91.20 5.30 3.50 0.024 0.028 0.9 5.8 0.8 1.5 301 99.82 0.13 0.05 0.020 0.020 1.0 6.1 0.7 1.5 302 93.50 4.50 2.00 0.040 0.030 1,3 6.1 0.7 1.5 303 97.35 2.50 0.15 0.024 0.018 1.3 6.3 0.5 1.5 304 94.65 5.30 0.05 0.034 0.025 1.4 6.0 0.7 1.5 305 96.37 0.13 3.50 0.015 0.010 1.5 5.8 0.7 1.5 306 99.75 0.20 0.05 0.021 0.014 1.5 8.5 0.6 1.5 307 96.37 0.13 3.50 0.030 0.020 1.5 8.8 0.6 1.5 308 94.65 5.30 0.05 0.045 0.030 1.5 8.8 0.6 1.5 309 98.45 1.05 0.50 0.040 0.025 1.6 9.6 0.6 1.4 TABLE 9 - Continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Nb2O5, ZnO #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 310 91.20 5.30 3.50 0.060 0.035 1.7 5.8 0.8 1.4 311 99.82 0.13 0.05 0.052 0.028 1.9 9.2 0.6 1.4 312 97.35 2.50 0.15 0.020 0.010 2.0 8.7 0.6 1.5 313 93.50 4.50 2.00 0.043 0.020 2.2 9.4 0.5 1.4 314 96.37 0.13 3.50 0.070 0.030 2.3 9.1 0.6 1.4 315 98.10 0.40 1.50 0.078 0.031 2.5 6.2 0.7 1.4 316 94.65 5.30 0.05 0.032 0.012 2.7 8.4 0.6 1.5 317 98.45 1.05 0.50 0.095 0.035 2.7 6.4 0.7 1.4 318 93.50 4.50 2.00 0.060 0.020 3.0 10.1 0.5 1.4 319 91.20 5.30 3.50 0.090 0.028 3.2 9.1 0.6 1.4 320 97.35 2.50 0.15 0.100 0.030 3.3 9.0 0.7 1.4 TABLE 9 - Continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Nb2O5, ZnO #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 321 98.45 1.05 0.50 0.102 0.026 3.9 6.4 0.7 1.5 322 97.35 2.50 0.15 0.020 0.005 4.0 6.3 0.7 1.5 323 98.10 0.40 1.50 0.040 0.010 4.0 9.7 0.6 1.4 324 99.82 0.13 0.05 0.080 0.020 4.0 9.8 0.6 1.4 325 98.45 1.05 0.50 0.070 0.015 4.7 13.3 0.7 1.2 326 93.50 4.50 2.00 0.040 0.008 5.0 6.1 0.7 1.5 327 91.20 5.30 3.50 0.050 0.010 5.0 12.5 0.6 1.0 328 99.75 0.20 0.05 0.100 0.020 5.0 9.4 0.6 1.4 329 97.35 2.50 0.15 0.080 0.015 5.3 14.3 1.4 0.1 330 96.37 0.13 3.50 0.055 0.010 5.5 14.1 1.4 0.1 331 98.45 1.05 0.50 0.090 0.015 6.0 10.8 1.2 0.7 332 98.10 0.40 1.50 0.095 0.012 7.9 8.1 1.0 0.8 Examples 306-309, 311-314, 316, 318-320, 323-325, 327, and 328 are in conformity with the principles of our invention. The relative proportions of the primary ingredients SrTiO3, Nb2O5 and ZnO in all these inventive Examples are in the ranges from 91.18 to 99.82 percent, from 0.13 to 5.32 percent, and from 0.05 to 3.50 percent, respectively. The SiO2 and Awl 203 contents of the inventive Examples range from 0.02 to 0.10 part, and from 0.01 to 0.03 part, respectively, with respect to 100 parts of the primary ingredients, and the ratios in weight of Si02 to Al203 range from 1.5 to 5.0. The crystal grains of these inventive Examples averaged from 60 to 120 micrometers in diameter. The apparent relative dielectric constants of the Examples were in the range from 84,000 to 133,000, their dielectric loss tangents from 0.5 to 0.7 percent, and their resistivities over 1.0 x 1O11 ohm-centimeters. The e other Examples, 299-305, 310, 315, 317, 321, 322, 326, and 329-332, are noninventive. As will be noted from these noninventive Examples, the apparent relative dielectric constant becomes less than 80,000 if the weight ratio of SiO2 to Al2O3 is less than 1.5. If the weight ratio exceeds 5,0, on the other hand, then either the dielectric loss tangent becomes more than 1.0 percent, or the resistivity becomes less than 1.0 x 1011 ohm-centimeters. Also the apparent relative dielectric constant does not become greater than 80,ooo if the proportion of SiO2 is less than 0.02 part or more than 0.10 part with respect to 100 parts of the primary ingredients. Similarly the apparent relative dielectric constant becomes low if the proportion of A1203 is less than 0.01 part or more than 0.03 part with respect to 100 parts of the primary ingredients. We conclude from the foregoing results of Table 9 that, for the boundary layer ceramics composed principally of SrTiO3, Nb2O5 and ZnO in accordance with our invention, the proportions of SiO2 and Al2O3 should be from about 0.02 to 0.10 part, and from about 0.01 to about 0.03 part, respectively, with respect to 100 parts of the primary ingredients. Further the weight ratio of SiO2 to Al2O3 should be from about 1.5 to about 5.0. These conclusions presuppose, of course, that the relative proportions of the primary ingredients are within the ranges of our invention. We measured the temperature dependencies of the apparent relative dielectric constants of the above inventive Examples. The results were also as in the graph of Figure 2, with the percent variations of the dielectric constants of all the inventive Examples with temperatures falling within the hatched areas of the graph. Examples 333-366 Uninsulated ceramic test discs were fabricated by use of the same ingredients, in the same proportions, as in Examples 308, 312, 313, 314, 320, 324, 327 and 328, and through the same procedure as in Examples 1-48. Then, in the various sets of proportions given in Table 10, the insulating substances PbO, Bi203 and B203 were diffused in the intergranular boundaries of the test discs by the same method as in Examples 1-48. The insulated ceramic test discs were then processed into test capacitors through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the electrical properties in question of the thus prepared test capacitors were as represented in Table 10. In this table the column labelled "Ceramic" indicates the uninsulated ceramics composed of the primary ingredients SrTiO3, Nb205 and ZnO and the auxiliary ingredients SiO2 and Al2O3. TABLE 10 Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 333 Examples 308 30 60 10 8.0 0.7 1.6 334 Examples 308 38 57 5 8.2 0.6 1.6 335 Examples 308 50 38 12 9.5 1.2 1.2 336 Examples 308 61 37 2 8.4 0.7 1.5 337 Examples 312 35 58 7 8.1 0.6 1.5 338 Examples 312 45 52 3 8.1 0.6 1.5 339 Examples 312 50 40 10 8.9 0.6 1.5 340 Examples 312 61 34 5 8.4 0.8 0.7 341 Examples 313 35 55 10 8.9 0.6 1.5 342 Examples 313 45 47 8 9.0 0.6 1.5 343 Examples 313 54 40 6 9.3 0.6 1.4 344 Examples 313 54 45 1 8.4 0.7 0.5 TABLE 10 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 345 Example 314 34 56 10 8.4 0.6 1.5 346 Example 314 45 52 3 8.5 0.6 1.5 347 Example 314 61 37 2 8.6 0.8 1.4 348 Example 314 62 36 2 8.2 0.9 0.6 349 Example 320 29 61 10 7.8 1.5 1.6 350 Example 320 35 60 5 8.2 0.8 1.5 351 Example 320 45 45 10 8.8 0.6 1.5 352 Example 320 60 35 5 8.8 0.7 1.4 353 Example 324 30 60 10 8.9 0.7 1.4 354 Example 324 40 58 2 9.1 0.7 1.4 355 Example 324 40 49 11 8.2 1.2 1.4 TABLE 10 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 356 Example 324 61 34 5 9.3 0.7 0.6 357 Example 324 61 37 2 9.3 0.8 1.3 358 Example 327 34 59 7 11.4 0.7 1.1 359 Example 327 38 61 1 10.4 1.2 0.6 360 Example 327 45 47 8 12.0 0.6 1.1 361 Example 327 54 40 6 12.4 0.7 1.0 362 Example 328 35 55 10 8.9 0.7 1.5 363 Example 328 47 52 1 8.3 0.7 0.7 364 Example 328 53 38 9 9.3 0.6 1.4 365 Example 328 55 40 5 9.2 0.6 1.4 366 Example 328 61 37 2 8.9 0.7 1.4 In Examples 333, 334, 336-339, 341-343, 345-347, 350-354, 357, 358, 360-362, and 364-366 of Table 10 the relative proportions of PbO, Bi203 and B203 are in the ranges from 30 to 61 percent, from 35 to 60 percent, and from two to 10 percent, respectively. The apparent relative dielectric constants of all these inventive Examples are sufficiently high, and their dielectric loss tangents and resistivities are also favorable. In Examples 335, 340, 344, 348, 349, 355, 356, 359 and 363, on the other hand, the relative proportions of PbO, Bi203 and B203 all fall outside the above ranges. The electrical properties of these noninventive Examples are unsatisfactory. Thus, for the boundary layer ceramics composed primarily of SrTiO3, Nb 205 and ZnO, the relative proportions of the insulating substances PbO, Bi203 and B203 should be in the ranges from about 30 to about 61 percent, from about 35 to about 60 percent, and from about two to about 10 percent, respectively. We measured the percentages of the insulating substances remaining diffused in the ceramic test discs of the above inventive Examples after the heat treatment. PbO remained at rates ranging from 0.06 to 1.45 percent, Bi203 at rates ranging from 0.23 to 2.14 percent, and B2O3 at rates ranging from 0.002 to 0.09 percent. Example 367 This Example was intended to ascertain the percentages of the three insulating substances to remain diffused in the boundary layer ceramics composed principally of SrTiO3, Nub 205 and ZnO, for the provision of capacitors of favorable electrical properties. The relative proportions of the three insulating substances in use were within the desired ranges set forth in connection with Examples 333-366. The pasted mixture of PbO, Bi203 and B203 was coated on uninsulated test discs in various amounts ranging from one to 15 wt. % of the test discs. The uninsulated ceramic test discs were composed principally of SrTi03, Nb205 and ZnO, with their relative proportions within the desired ranges specified in connection with Examples 299-332, and were prepared through the same procedure as in Examples 1-48. The above coated discs were heated at various temperatures ranging from 11500 C to 13000 C. for various lengths of time ranging from one to four hours. Thus were prepared a number of insulated boundary layer ceramic test discs having the three insulating substances remaining diffused throughout their intergranular boundaries at various percentages. Then the test discs were processed into test capacitors through the same procedure as in Examples 1-48. From among the thus prepared test capacitors there were chosen those having an apparent relative dielectric constant of over 80,ooo, a dielectric loss tangent of not more than one percent, and a resistivity of not less than 1.0 x 1O11 ohm-centimeters. The PbO, Bi203 and B203 contents of these test capacitors with the favorable electrical properties ranged from 0.03 to 2.90 percent, from 0.11 to 4.28 percent, and from 0.001 to 0.18 percent, respectively, with respect to the weight of the uninsulated test discs composed of the primary ingredients SrTiO3, Nb205 and ZnO and the secondary ingredients Si02 and Al203. Examples 368-401 SrTiO3, Ta205 and ZnO were used in combination as the primary ingredients. Insulated boundary layer ceramic test capacitors were fabricated by use of these primary ingredients and the secondary ingredients SiO2 and Al203, in various sets of proportions given in Table 11, and of the insulating substances PbO, Bi203 and B203, through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the electrical properties of these test capacitors were as represented in Table 11. We also measured the percentages of the three insulating substances remaining diffused in the boundary layer ceramic test discs of the above compositions consisting primarily of SrTiO3, Ta205 and ZnO. PbO, Bi203 and B203 remained at percentages ranging from 0.27 to 0.79, from 0.51 to 1.50, and from 0.01 to 0.05, respectively, with respect to the weight of the ceramic discs in the uninsulated state. TABLE 11 Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Ta2O5, ZnO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt.% part part x 104 % x 1011 #-cm 368 98.50 1.20 0.30 ................ 6.7 0.6 2.0 369 94.50 3.00 2.50 0.024 0.028 0.9 6.0 0.8 2.0 370 99.62 0.33 0.05 0.020 0.020 1.0 6.3 0.6 2.0 371 98.14 1.80 0.06 0.040 0.030 1.3 6.5 0.8 2.0 372 97.17 0.33 2.50 0.024 0.018 1.3 6.1 0.6 2.0 373 96.95 3.00 0.05 0.034 0.025 1.4 6.3 0.6 2.0 374 96.25 1.75 2.00 0.015 0.010 1.5 6.4 0.6 2.0 375 98.50 1.20 0.30 0.021 0.014 1.5 9.2 0.5 1.7 376 97.17 0.33 2.50 0.030 0.020 1.5 9.1 0.6 1.7 377 94.50 3.00 2.50 0.045 0.030 1.5 8.8 0.6 1.8 378 99.40 0.50 0.10 0.040 0.025 1.6 9.9 0.6 1.6 TABLE 11 - Continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Ta2O5, ZnO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt.% part part x 104 % x 1011 #-cm 379 99.62 0.33 0.05 0.060 0.035 1.7 6.3 0.8 2.0 380 96.25 1.75 2.00 0.052 0.028 1.9 9.8 0.6 1.6 381 99.62 0.33 0.05 0.020 0.010 2.0 8.7 0.5 1.8 382 96.95 3.00 0.05 0.043 0.020 2.2 9.7 0.5 1.7 383 97.80 0.70 1.50 0,070 0.030 2.3 10.2 0.6 1.6 384 98.14 1.80 0.06 0.078 0.031 2.5 6.5 0.6 2.0 385 94.50 3.00 2.50 0.032 0.012 2.7 8.4 0.5 1.8 386 97.80 0.70 1.50 0.095 0.035 2.7 6.5 0.7 2.0 387 98.50 1.20 0.30 0.060 0.020 3.0 11.3 0.5 1.5 388 96.25 1.75 2.00 0.090 0.028 3.2 10.2 0.5 1.6 389 97.17 0.33 2.50 0.100 0.030 3.3 8.7 0.6 1.8 TABLE 11 - Continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Ta2O5, ZnO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt.% part part x 104 % x 1011#-cm 390 98.14 1.80 0.06 0.102 0.026 3.9 6.5 0.6 2.0 391 98.50 1.20 0.30 0.020 0.005 4.0 6.8 0.6 2.0 392 98.14 1.80 0.06 0.040 0.010 4.0 10.2 0.5 1.7 393 96.95 3.00 0.05 0.080 0.020 4.0 10.2 0.6 1.6 394 99.62 0.33 0.05 0.070 0.015 4.7 13.1 0.6 1.2 395 98.50 1.20 0.30 0.040 0.008 5.0 6.8 0.6 2.0 396 97.80 0.70 1.50 0.050 0.010 5.0 14.3 0.5 1.1 397 99.40 0.50 0.10 0.100 0.020 5.0 9.8 0.6 1.6 398 96.25 1.75 2.00 0.080 0.015 5.3 14.8 1.3 0.1 399 98.14 1.80 0.06 0.055 0.010 5.5 15.6 1.5 0.1 400 97.17 0.33 2.50 0.090 0.015 6.0 10.3 1.1 0.9 401 96.95 3.00 0.05 0.095 0.012 7.9 8.2 1.0 0.8 Examples 375-378, 380-383, 385, 387-389, 392-394, 396, and 397 comply with the teachings of our invention. The relative proportions of the three primary ingredients, SrTiO3, Ta205 and ZnO, in all these inventive Examples are in the ranges from 94.50 to 99.62 percent, from 0.33 to 3.00 percent, and from 0.05 to 2.50 percent, respectively. The SiO2 and Awl 203 contents of the inventive Examples range from 0.02 to 0.10 part, and from 0.01 to 0.03 part, respectively, with respect to 100 parts of the primary ingredients, and the ratios in weight of SiO2 to Al 203 are in the range from 1.5 to 5.0. The crystal grains of the above inventive Examples averaged in the range from 60 to 120 micrometers in diameter. The apparent relative dielectric constants of the Examples were in the range from 84,000 to 143,000, their dielectric loss tangents not more than 0.6 percent, and their resistivities over 1.1 x 1011 ohm-centimeters. The other Examples, 368-374, 379, 384, 386, 390, 391, 395, and 398-401, fall outside the purview of our-invention. As will be noted from these noninventive Examples, the apparent relative dielectric constant becomes less than 80,000 if the weight ratio of SiO2 to A1203 is less than 1.5. If the weight ratio of SiO2 to A1203 exceeds 5.0, on the other hand, then either the dielectric loss tangent becomes more than 1.0 percent, or the resistivity becomes less than 1.0 x 10 ohmcentimeters. Also the apparent relative dielectric constant does not become greater than 80,000 if the proportion of SiO2 is less than 0.02 part or more than 0.10 part with respect to 100 parts of the primary ingredients. Similarly the apparent relative dielectric constant becomes low if the proportion of A1203 is less than 0.01 part or more than 0.03 part with respect to 100 parts of the primary ingredients. We conclude from the foregoing results of Table 11 that, for the boundary layer ceramics comprising SrTiO3, Tea 205 and ZnO in accordance with our invention, the proportions of SiO2 and Awl 203 should be from about 0.02 to about 0.10 part, and from about 0.01 to about 0.03 part, respectively, with respect to 100 parts of the primary ingredients. Further the weight ratio of SiO2 to A1203 should be from about 1.5 to about 5.0. These conclusions presuppose, of course that the relative proportions of the three primary ingredients are within the ranges of our invention. We measured the temperature dependencies of the apparent relative dielectric constants of the above inventive Examples. The results were also as in the graph of Figure 2, with the percent variations of the dielectric constants of all the inventive Examples with temperatures falling within the hatched areas of the graph. Examples 402-435 Uninsulated ceramic test discs were fabricated by use of the same ingredients, in the same proportions, as in Examples 377, 381, 383, 387, 389, 393, 396 and 397, and through the same procedure as in Examples 1-48. Then, in the various sets of proportions given in Table 12, the three insulating substances, PbO, Bi203 and B203, were diffused in the intergranular boundaries of the test discs by the same method as in Examples 1-48. The insulated boundary layer ceramic test discs were then processed into test capacitors through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the three electrical properties in question of the thus prepared test capacitors were as set forth in Table 12. The column labelled "Ceramic" in this table represents the uninsulated ceramics composed of the primary ingredients SrTiO3, Ta205 and ZnO and the auxiliary ingredients SiO2 and Al 203 TABLE 12 Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 402 Example 377 30 60 10 7.8 0.7 1.9 403 Example 377 34 64 2 8.1 0.7 1.9 404 Example 377 45 45 10 8.6 0.6 1.8 405 Example 377 56 42 2 8.8 0.6 1.8 406 Example 381 31 66 3 8.0 0.8 1.9 407 Example 381 39 52 9 8.4 0.5 1.8 408 Example 381 54 45 1 8.1 0.6 0.3 409 Example 381 54 40 6 8.2 0.5 1.8 410 Example 383 34 56 10 9.5 0.6 1.6 411 Example 383 47 52 1 9.0 0.6 0.4 412 Example 383 54 36 10 10.7 0.6 1.6 TABLE 12 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 413 Example 383 57 41 2 10.4 0.7 0.6 414 Example 387 31 59 10 10.3 0.7 1.6 415 Example 387 40 58 2 10.5 0.7 1.6 416 Example 387 40 49 11 9.5 1.2 1.5 417 Example 387 54 44 2 11.1 0.5 1.5 418 Example 387 57 33 10 12.1 0.6 0.5 419 Example 389 31 67 2 8.0 1.1 1.9 420 Example 389 35 58 7 8.1 0.7 1.9 421 Example 389 45 52 3 8.0 0.7 1.8 422 Example 389 56 34 10 9.1 0.6 1.8 423 Example 393 32 66 2 9.2 0.7 1.7 TABLE 12 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 424 Example 393 45 47 8 9.8 0.6 1.6 425 Example 393 50 40 10 10.4 0.6 1.6 426 Example 393 55 40 5 10.0 0.6 1.6 427 Example 396 32 64 4 12.7 0.7 1.3 428 Example 396 38 57 5 13.3 0.6 1.2 429 Example 396 50 38 12 15.4 1.3 1.0 430 Example 396 53 38 9 14.2 0.6 1.1 431 Example 397 31 62 7 8.8 0.7 1.7 432 Example 397 35 55 10 9.3 0.6 1.6 433 Example 397 45 52 3 9.1 0.6 1.6 434 Example 396 56 42 2 9.8 0.6 1.6 435 Example 397 56 34 10 10.3 0.6 1.6 In Examples 403-407, 409, 410, 412, 414, 415, 427, 420-428, and 430-435 the relative proportions of the insulating sub stances PbO, By203 and B203 are in the ranges from 31 to 56 23 23 percent, from 34 to 66 percent, and from two to 10 percent, respectively. The apparent relative dielectric constants of all these inventive Examples are sufficiently high, and their dielectric loss tangents and resistivities are also favorable. In Examples 402, 408, 411, 413, 416, 418, 419 and 429, on the other hand, the relative proportions of the insulating substances all fall outside the above ranges. The electrical properties of these noninventive Examples are unsatisfactory. Thus, for the boundary layer ceramics composed principally of SrTiO3, Ta205 and ZnO, the relative proportions of the three insulating substances, PbO, Bi203 and B203, should be in the ranges from about 31 to 56 percent, from about 34 to about 66 percent, and from about two to about 10 percent, respectively. We measured the percentages of the insulating substances remaining diffused in the ceramic test discs of the above inventive Examples after the heat treatment. PbO remained at rates ranging from 0.06 to 1.79 percent, Bi203 at rates ranging from 0.23 to 2.80 percent, and B203 at rates ranging from 0.002 to 0.12 percent. Example 436 We examined in this Example the percentages of the three insulating substances to remain diffused in the boundary layer ceramics composed primarily of SrTiO3, Ta205 and ZnO, for the provision of capacitors of favorable electrical properties. The relative proportions of the insulating substances in use were within the desired ranges set forth in connection with Examples 402-435. The pasted mixture of the insulating substances was coated on uninsulated ceramic test discs in various amounts ranging from one to 15 wt. % of the test discs. The uninsulated ceramic test discs were composed principally of SrTiO2, Ta205 and ZnO, with their relative proportions within the desired ranges specified in connection with Examples 368-401, and were prepared through the same procedure as in Examples 1-48. The above coated discs were then heated at various temperatures ranging from 11500 C. to 13000 C. for various lengths of time ranging from one to four hours. Thus were prepared a number of insulated boundary layer ceramic test discs having the three insulating substances remaining diffused throughout their intergranular boundaries at various percentages. Then the test discs were processed into test capacitors through the same procedure as in Examples 1-48 From among the thus prepared test capacitors we picked up those having an apparent relative dielectric constant of over 80,000, a dielectric loss tangent of not more than one 11 percent, and a resistivity of not less than 1.0 x 10 1 ohm- centimeters. The PbO, Bi203 and B203 contents of these test capacitors with the favorable electrical properties ranged from 0.03 to 2.80 percent, from 0.11 to 4.38 percent, and from 0.001 to 0.18 percent, respectively, with respect to the weight of the uninsulated test discs composed of the primary ingredients SrTiO3, Ta205 and ZnO and the secondary ingredients SiO2 and A1203. Examples 437-470 We employed SrTiO3, W03 and CuO as the three primary ingredients in these Examples. Insulated boundary layer ceramic test capacitors were fabricated by use of these primary ingredients and the secondary ingredients SiO2 and Al203, in various sets of proportions specified in Table 13, and of the insulating substances PbO, Bi203 and B203, through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the electrical properties of these test capacitors were as represented also in Table 13. We also measured the percentages of the three insulating substances remaining diffused in the boundary layer ceramic test discs of the above compositions consisting primarily of SrTiO3, W03 and CuO. PbO, Bi203 and B203 remained at percentages ranging from 0.31 to 0.86, from 0.57 to 1.61, and from 0.01 to 0.06, respectively, with respect to the weight of the ceramic discs in the uninsulated state. TABLE 13 Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, WO3, CuO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt.% part part x 104 % x 1011 #-cm 437 99.30 0.50 0.20 ...................... 6.5 0.6 1.8 438 96.70 2.30 1.00 0.024 0.028 0.9 5.9 0.8 1.8 439 99.83 0.15 0.02 0.020 0.020 1.0 6.2 0.7 1.8 440 97.15 2.00 0.85 0.040 0.030 1.3 6.2 0.7 1.8 441 98.20 1.70 0.10 0.024 0.018 1.3 6.2 0.6 1.8 442 98.68 2.30 0.02 0.034 0.025 1.4 6.1 0.6 1.8 443 98.85 0.15 1.00 0.015 0.010 1.5 5.8 0.6 1.8 444 99.30 0.50 0.20 0.021 0.014 1.5 8.9 0.5 1.7 445 96.70 2.30 1.00 0.030 0.020 1.5 8.8 0.6 1.7 446 98.20 1.70 0.10 0.045 0.030 1.5 9.1 0.6 1.6 447 98.68 2.30 0.02 0.040 0.025 1.6 9.1 0.6 1.6 TABLE 12 - Continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, WO3, CuO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt.% part part x 104 % x 1011 #-cm 448 99.14 0.26 0.60 0.060 0.035 1.7 6.3 0.7 1.8 449 99.69 0.26 0.05 0.052 0.028 1.9 9.6 0.6 1.6 450 99.83 0.15 0.02 0.020 0.010 2.0 8.6 0.5 1.7 451 97.15 2.00 0.85 0.043 0.020 2.2 9.5 0.5 1.6 452 98.85 0.15 1.00 0.070 0.030 2.3 9.1 0.6 1.6 453 98.68 2.30 0.02 0.078 0.031 2.5 6.1 0.6 1.8 454 96.70 2.30 1.00 0.032 0.012 2.7 8.7 0.5 1.7 455 99.30 0.50 0.20 0.095 0.035 2.7 6.6 0.7 1.8 456 98.20 1.70 0.10 0.060 0.020 3.0 10.3 0.5 1.5 457 99.14 0.26 0.60 0.090 0.028 3.2 9.9 0.6 1.6 458 99.69 0.26 0.05 0.100 0.030 3.3 9.2 0.6 1.6 TABLE 13 - Continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, WO3, CuO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt.% part part x 104 % x 1011#-cm 459 99.83 0.15 0.02 0.102 0.026 3.9 6.2 0.7 1.8 460 97.15 2.00 0.85 0.020 0.005 4.0 6.1 0.6 1.8 461 98.85 0.15 1.00 0.040 0.010 4.0 9.3 0.6 1.6 462 98.68 2.30 0.02 0.080 0.020 4.0 9.9 0.6 1.6 463 99.30 0.50 0.20 0.070 0.015 4.7 14.0 0.6 1.1 464 98.20 1.70 0.10 0.040 0.008 5.0 6.3 0.6 1.8 465 99.83 0.15 0.02 0.050 0.010 5.0 13.8 0.6 1.1 466 99.14 0.26 0.60 0.100 0.020 5.0 9.6 0.6 1.6 467 98.85 0.15 1.00 0.080 0.015 5.3 14.1 1.2 0.1 468 96.70 2.30 1.00 0.055 0.010 5.5 14.9 1.2 0.1 469 98.68 2.30 0.02 0.090 0.015 6.0 10.8 1.1 0.6 470 99.69 0.26 0.05 0.095 0.012 7.9 8.3 1.0 0.9 Examples 444-447, 449-452, 454, 456-458, 461-463, 465 and 466 comply with the principles of our invention. The relative proportions of the primary ingredients SrTiO3, W03 and CuO in all these inventive Examples are in the ranges from 96.70 to 99.83 percent, from 0.15 to 2.30 percent, and from 0.02 to 1.00 percent, respectively. The SiO2 and A1203 contents of the inventive Examples range from 0.02 to 0.10 part, and from 0.01 to 0.03 part, respectively, with respect to 100 parts of the primary ingredients, and the ratios in weight of SiO2 to A1203 are in the range from 1.5 to 5.0. The crystal grains of the above inventive Examples averaged in the range from 60 to 120 micrometers in diameter. The apparent relative dielectric constants of the Examples were in the range from 86,ooo to 140,000, their dielectric loss tangents not more than 0.6 percent, and their resistivities 11 over 1.1 x 10 ohm-centimeters. Examples 437-443, 448, 453, 455, 459, 460, 464, and 467-470, on the other hand, fall outside the purview of our invention. As will be observed from these noninventive Examples, the apparent relative dielectric constant becomes less than 80,000 if the weight ratio of SiO2 to A1203 is less than 1.5. If the weight ratio of SiO2 to A1203 exceeds 5.0, on the other hand, then either the dielectric loss tangent becomes more than 1.0 percent, or the resistivity becomes less than 1.0 x 1011 ohm-centimeters. Also the apparent relative dielectric constant does not become greater than 80,000 if the proportion of SiO2 is less than 0.02 part or more than 0.10 part with respect to 100 parts of the primary ingredients. Similarly the apparent relative dielectric constant becomes low if the proportion of Al2O3 is less than 0.01 part or more than 0.03 part with respect to 100 parts of the primary ingredients. We conclude from the foregoing results of Table 13 that, for the boundary layer ceramics composed principally of SrTiO3, W03 and CuO in accordance with our invention, the proportions of SiO2 and A1203 should be from about 0.02 to about 0.10 part, and from about 0.01 to 0.03 part, respectively, with respect to 100 parts of the primary ingredients. Further the weight ratio of SiO2 to A1203 should be from about 1.5 to about 5.0. These conclusions presuppose, of course, that the relative proportions of the three primary ingredients in use are within the ranges of our invention. We measured the temperature dependencies of the apparent relative dielectric constants of the above inventive Examples. The results were also as in the graph of Figure 2, with the percent variations of the dielectric constants of all the inventive Examples with temperatures falling within the hatched areas of the graph. Examples 471-504 Uninsulated ceramic test discs were fabricated by use of the same ingredients, in the same proportions, as in Examples 446, 450, 452, 454, 458, 462, 465 and 466, and through the same procedure as in Examples 1-48. Then, in the various sets of proportions specified in Table 14, the three insulating substances were diffused throughout the intergranular boundaries of the test discs by the same method as in Examples 1-48. The insulated boundary layer ceramic test discs were then processed into test capacitors through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the three electrical properties in question of the thus prepared test capacitors were as set forth in Table 14. The column labelled "Ceramic't in this table represents the uninsulated ceramics composed of the primary ingredients SrTiO3, WO and CuO and 3 the secondary ingredients SiO2 and Al2O3. TABLE 14 Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 471 Example 446 30 60 10 7.9 0.8 1.7 472 Example 446 36 62 2 8.4 0.8 1.7 473 Example 446 45 47 8 8.5 0.6 1.6 474 Example 446 58 40 2 9.3 0.6 1.6 475 Example 450 34 56 10 8.1 0.6 1.6 476 Example 450 39 52 9 8.3 0.6 1.6 477 Example 450 54 44 2 8.4 0.6 1.6 478 Example 450 59 31 10 9.4 0.6 0.2 479 Example 452 34 56 10 8.6 0.7 1.7 480 Example 452 45 52 3 8.5 0.6 1.6 481 Example 452 54 36 10 9.6 0.6 1.6 TABLE 14 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 482 Example 452 59 39 2 9.6 0.6 0.6 483 Example 454 34 59 7 8.1 0.7 1.7 484 Example 454 47 52 1 7.6 0.7 0.3 485 Example 454 50 40 10 8.9 0.6 1.6 486 Example 454 54 45 1 7.7 0.6 0.2 487 Example 458 35 63 2 8.5 1.1 1.7 488 Example 458 40 58 2 8.6 0.7 1.7 489 Example 458 45 45 10 9.0 0.6 1.6 490 Example 458 55 40 5 9.0 0.6 1.6 491 Example 462 31 62 7 8.9 0.7 1.7 492 Example 462 40 49 11 8.3 1.1 1.5 TABLE 14 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 493 Example 462 53 38 9 9.8 0.6 1.6 494 Example 462 58 40 2 10.1 0.6 1.6 495 Example 462 58 32 10 10.7 0.7 1.6 496 Example 465 31 59 10 12.6 0.7 1.3 497 Example 465 45 52 3 12.8 0.6 1.2 498 Example 465 54 36 10 14.5 0.6 1.1 499 Example 465 58 31 11 15.2 1.5 0.8 500 Example 466 38 57 5 8.9 0.7 1.6 501 Example 466 45 45 10 9.4 0.6 1.6 502 Example 466 50 38 12 10.4 1.2 1.2 503 Example 466 58 40 2 9.8 0.6 1.6 504 Example 466 58 32 10 10.4 0.6 1.6 In Examples 472-477, 479-481, 483, 485, 488-491, 493-498, 500, 501, 503 and 504 of Table 14 the relative proportions of the insulating substances PbO, Bi203 and B203 are in the ranges from 31 to 58 percent, from 32 to 62 percent, and from two to 10 percent, respectively. The apparent relative dielectric constants of all these inventive Examples are sufficiently high, and their dielectric loss tangents and resistivities are also favorable. In examples 471, 478, 482, 484, 486, 487, 492, 499 and 502, on the other hand, the relative proportions of'PbO, By 203 and B203 all fall outside the above ranges. The electrical properties of these noninventive Examples are unsatisfactory. Thus, for the boundary layer ceramics composed principally of SrTiO3, W03 and CuO in accordance with our invention, the relative proportions of the three insulating substances, PbO, Bi203 and B203, should be in the ranges from about 31 to about 58 percent, from about 32 to about 62 percent, and from about two to 10 percent, respectively. We measured the percentages of the insulating substances remaining diffused in the ceramic test discs of the above inventive Examples after the heat treatment. PbO remained at rates ranging from 0.06 to 1.81 percent, Bi203 at rates ranging from 0.21 to 2.74 percent, and B203 at rates ranging from 0.002 to 0.12 percent. Example 505 We sought to determine in this Example the percentages of the three insulating substances to remain diffused in the boundary layer ceramics composed principally of SrTiO3, W03 and CuO, for the provision of capacitors of favorable electrical properties. The relative proportions of the insulating substances in use were within the desired ranges set forth in connection with Examples 471-504. The pasted mixture of the insulating substances was coated on uninsulated ceramic test discs in various amounts ranging from one to 15 wt. vv of the test discs. The uninsulated ceramic test discs were composed mainly of SrTiO3, W03 and CuO, with their relative proportions within the desired ranges specified in connection with Examples 437-470, and were prepared through the same procedure as in Examples 1-48. The above coated discs were heated at various temperatures ranging from 1150O C. to 13000 C. for various lengths of time ranging from one to four hours. Thus were prepared a number of insulated boundary layer ceramic test discs having the three insulating substances remaining diffused throughout their intergranular boundaries at various percentages. Then the test discs were processed into test capacitors through the same procedure as in Examples 1-48. From among the thus prepared test capacitors we picked up those having an apparent relative dielectric constant of over 80,000, a dielectric loss tangent of not more than one percent, and a resistivity of not less than 1.0 x 101l ohmcentimeters. The PbO, Bi203 and B203 contents of these test capacitors with the favorable electrical properties ranged from 0.03 to 2.83 percent, from 0.10 to 4.30 percent, and from 0.001 to 0.18 percent, respectively, with respect to the weight of the uninsulated test discs composed of the primary ingredients SrTi03, W03 and CuO and the secondary ingredients Si02 and Al 203 Examples 506-539 In these Examples we tested a combination of SrTiO3, Ta205 and GeO2 as the primary ingredients. Insulated boundary layer ceramic test capacitors were fabricated by use of these primary ingredients and the secondary ingredients Si02 and A1203, in various sets of proportions specified in Table 15, and of the insulating substances PbO, Bi203 and B203, through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the electrical properties of these test capacitors were as represented also in Table 15 We also measured the percentages of the three insulating substances remaining diffused in the boundary layer ceramic test discs of the above compositions primarily comprising SrTiO3, Ta205 and GeO2. PbO, Bi203 and B203 remained at percentages ranging from 0.28 to 0.86, from 0.49 to i.6i, and from 0.01 to 0.06, respectively, with respect to the weight of the ceramic discs in the uninsulated state. TABLE 15 Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Ta2O5, GeO2, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 506 96.40 1.60 2.00 ...................... 7.0 0.7 2.0 507 95.67 0.33 4.00 0.024 0.028 0.9 6.6 0.9 2.0 508 95.87 4.08 0.05 0.020 0.020 1.0 6.4 0.8 2.0 509 94.40 2.50 0.10 0.040 0.030 1.3 7.0 0.8 2.0 510 96.52 2.10 1.38 0.024 0.018 1.3 6.8 0.8 2.0 511 99.62 0.33 0.05 0.034 0.025 1.4 6.9 0.8 2.0 512 91.92 4.08 4.00 0.015 0.010 1.5 6.8 0.7 2.0 513 97.40 2.50 0.10 0.021 0.014 1.5 9.5 0.7 1.8 514 91.92 4.08 4.00 0.030 0.020 1.5 9.1 0.7 1.9 515 95.67 0.33 4.00 0.045 0.030 1.5 9.7 0.7 1.8 516 97.60 0.40 2.00 0.040 0.025 1.6 10.4 0.7 1.8 TABLE 15 - Continued Primary ingredients (100 wt. parts) Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Ta2O5, GeO2, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 517 99.62 0.33 0.05 0.060 0.035 1.7 6.9 0.8 2.0 518 96.40 1.60 2.00 0.052 0.028 1.9 10.9 0.7 1.7 519 99.30 0.55 0.15 0.020 0.010 2.0 9.9 0.6 1.8 520 95.87 4.08 0.05 0.043 0.020 2.2 9.8 0.6 1.8 521 99.62 0.33 0.05 0.070 0.030 2.3 10.7 0.7 1.7 522 96.40 1.60 2.00 0.078 0.031 2.5 7.1 0.8 1.9 523 95.67 0.33 4.00 0.032 0.012 2.7 9.4 0.6 1.8 524 99.30 0.55 0.15 0.095 0.035 2.7 6.9 0.8 2.0 525 91.92 4.08 4.00 0.060 0.020 3.0 10.1 0.6 1.7 526 95.52 2.10 1.38 0.090 0.028 3.2 10.7 0.7 1.7 527 97.40 2.50 0.10 0.100 0.030 3.3 10.0 0.7 1.7 TABLE 15 - Continued Primary ingredients Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Ta2O5, GeO2, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 528 95.67 0.33 4.00 0.102 0.026 3.9 6.6 0.7 2.0 529 96.52 2.10 1.38 0.020 0.005 4.0 6.8 0.7 2.0 530 95.87 4.08 0.05 0.040 0.010 4.0 10.0 0.6 1.7 531 99.62 0.33 0.05 0.080 0.020 4.0 11.2 0.6 1.5 532 96.40 1.60 2.00 0.070 0.015 4.7 15.5 0.6 1.2 533 99.30 0.55 0.15 0.040 0.008 5.0 6.8 0.6 2.0 534 97.60 0.40 2.00 0.050 0.010 5.0 15.7 0.6 2.0 535 96.52 2.10 1.38 0.100 0.020 5.0 10.4 0.7 1.7 536 97.40 2.50 0.10 0.080 0.015 5.3 16.8 1.1 0.1 537 97.60 0.40 2.00 0.055 0.010 5.5 17.3 1.2 0.1 538 91.92 4.08 4.00 0.090 0.015 6.0 10.5 1.1 0.2 539 95.87 4.08 0.05 0.095 0.012 7.9 8.4 1.0 0.9 Examples 513-516, 518-521, 523, 525-527, 530-532, 534 and 535 comply with the principles of our invention. The relative proportions of the three primary ingredients, SrTiO3, Ta2O5 and GeO2, in all these inventive Examples are in the ranges from 91.92 to 99.62 percent, from 0.33 to 4.08 percent, and from 0.05 to 4.00 percent, respectively. The SiO2 and Awl 203 contents of the inventive Examples range from 0.02 to 0.10 part, and from 0.01 to 0.03 part, respectively, with respect to 100 parts of the primary iongredients, and the ratios in weight of SiO2 to Al203 are in the range from 1.5 to 5.0 The crystal grains of the above inventive Examples averaged in the range from 60 to 120 micrometers in diameter. The apparent relative dielectric constants of the Examples were in the range from 91,000 to 157,000, their dielectric loss tangents not more than 0.7 percent, and their resistivities over 1.1 x 1011 ohm-centimeters. Examples 506-512, 517, 522, 524, 528, 529, 533, and 536-539, on the other hand, fall outside the scope of our invention As will be seen from these noninventive Examples , the apparent relative dielectric constant becomes less than 80,000 if the weight ratio of SiO2 to A1203 is less than 1.5. If the weight ratio exceeds 5.0, on the other hand, then either the dielectric loss tangent becomes more than 1.0 percent, or the resistivity becomes less than 1.0 x 1011 ohm-centimeters. Also the apparent relative dielectric constant does not become greater than 80,000 if the proportion of SiO2 is less than 0.02 part or more than 0.10 part with respect to 100 parts of the primary ingredients. Similarly the apparent relative dielectric constant becomes low if the proportion of Awl 203 is less than 0.01 part or more than 0.03 part with respect to 100 parts of the primary ingredients. We conclude from the above summarized results of Table 15 that, for the boundary layer ceramics composed principally of SrTiO3, Ta205 and GeO2 in accordance with our invention, the proportions of Si02 and A1203 should be from about 0.02 to about 0.10 part, and from about 0.01 to about 0.03 part, respectively, with respect to 100 parts of the primary ingredients. Further the weight ratio of SiO2 to Awl 203 should be from about 1.5 to about 5.0. These conclusions presuppose, of course, that the relative proportions of the three primary ingredients are within the ranges of our invention. We measured the temperature dependencies of the apparent relative dielectric constants of the above inventive Examples. The results were also as in the graph of Figure 2, with the percent variations of the dielectric constants of all the inventive Examples with temperatures falling within the hatched areas of the graph. Examples 540-575 Uninsulated ceramic test discs were fabricated by use of the same ingredients, in the same proportions, as in Examples 515, 519, 521, 525, 527, 530, 534 and 535, and through the same procedure as in Examples 1-48. Then, in the various sets of proportions specified in Table 16, the insulating substances PbO, Bi203 and B203 were diffused throughout the intergranular boundaries of the test discs by the same method as in Examples 1-48. The insulated boundary layer ceramic test discs were then processed into test capacitors through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the three electrical properties in question of the thus prepared test capacitors were as set forth in Table 16. The column labelled "Ceramic" in this table represents the uninsulated ceramics composed of the primary ingredients SrTiO3, Ta205 and GeO2 and the secondary ingredients SiO2 and A1203. TABLE 16 Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 540 Example 515 26 64 10 7.9 1.1 2.0 541 Example 515 35 63 2 8.9 0.8 1.9 542 Example 515 45 47 8 9.3 0.7 1.8 543 Example 515 58 40 2 9.9 0.7 1.8 544 Example 519 27 63 10 8.8 0.9 1.9 545 Example 519 40 58 2 9.2 0.7 1.8 546 Example 519 56 34 10 10.5 0.6 1.7 547 Example 519 59 39 2 10.4 0.6 1.7 548 Example 521 34 64 2 9.6 1.1 1.8 549 Example 521 39 52 9 10.3 0.7 1.7 550 Example 521 45 52 3 10.0 0.7 1.7 551 Example 521 50 40 10 10.9 0.7 1.7 TABLE 16 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 552 Example 521 58 34 8 11.4 0.7 1.7 553 Example 525 30 60 10 9.2 0.7 1.8 554 Example 525 38 57 5 9.4 0.6 1.7 555 Example 525 40 59 1 8.2 0.7 0.3 556 Example 525 54 36 10 10.6 0.6 1.7 557 Example 525 59 34 7 10.9 0.6 0.7 558 Example 527 27 63 10 8.5 0.8 1.8 559 Example 527 35 58 7 9.3 0.7 1.7 560 Example 527 54 44 2 9.8 0.7 1.7 561 Example 527 57 33 10 10.8 0.7 0.5 562 Example 530 34 59 7 9.1 0.7 1.7 563 Example 530 40 49 11 8.4 1.2 1.7 TABLE 16 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm. Same as: 564 Example 530 53 38 9 9.9 0.6 1.7 565 Example 530 58 40 2 10.2 0.6 1.7 566 Example 534 35 55 10 14.9 0.6 1.2 567 Example 534 45 52 3 14.6 0.6 1.1 568 Example 534 45 45 10 15.4 0.6 1.1 569 Example 534 50 38 12 17.0 1.3 1.0 570 Example 534 55 40 5 15.4 0.6 1.1 571 Example 535 35 63 2 9.6 0.8 1.8 572 Example 535 38 57 5 9.7 0.7 1.7 573 Example 535 50 40 10 10.6 0.7 1.7 574 Example 535 54 45 1 9.3 0.7 0.3 575 Example 535 56 34 10 11.0 0.7 1.6 In Examples 541-546, 549-554, 556, 558-560, 562, 564-568, 570-573 and 575 of Table 16 the relative proportions of PbO, By 203 and B203 are in the ranges from 27 to 58 percent, from 34 to 63 percent, and from two to 10 percent, respectively. The apparent relative dielectric constants of all these inventive Examples are sufficiently high, and their dielectric loss tangents and resistivities are also favorable. In Examples 540, 547, 548, 555, 557, 561, 563, 569 and 574, on the other hand, the relative proportions of PbO, Bi203 and B203 all fall outside the above ranges. the electrical properties of these noninventive Examples are unsatisfactory. Thus, for the boundary layer ceramics composed principally of SrTiO3, Ta205 and GeO2, the relative proportions of the three insulating substances, PbO, Bi203 and B203, should be in the ranges from about 27 to about 58 percent, from about 34 to about 63 percent, and from about two to about 10 percent, respectively. We measured the percentages of the insulating substances remaining diffused in the ceramic test discs of the above inventive Examples after the heat treatment. PbO remained at rates ranging from 0.05 to 1.76 percent, Bi203 at rates ranging from 0.23 to 2.69 percent, and B203 at rates ranging from 0.002 to 0.12 percent. Example 576 In this Example we ascertained the percentages of the three insulating substances to remain diffused in the boundary layer ceramics composed principally of SrTiO3, Ta205 and GeO2, for the provision of capacitors of favorable electrical properties. The relative proportions of the insulating substances in use were within the desired ranges set forth in connection with Examples 540-575. The pasted mixture of the insulating substances was coated on uninsulated ceramic test discs in various amounts ranging from one to 15 wt. % of the test discs. The uninsulated ceramic test discs were composed primarily of SrTiO3, Ta205 and GeO2, with their relative proportions within the desired ranges specified in connection with Examples 506-539, and were prepared through the same procedure as in Examples 1-48. The above coated discs were heated at various temperatures ranging from 11500 C. to 13000 C. for various lengths of time ranging from one to four hours. Thus were prepared a number of insulated boundary layer ceramic test discs having the three insulating substances remaining diffused throughout their intergranular boundaries at various percentages. Then the test discs were processed into test capacitors through the same procedure as in Examples 1-48. From among the thus fabricated test capacitors we picked up those having an apparent relative dielectric constant of over 80,000, a dielectric loss tangent of not more than one percent, and a resistivity of not less than 1.0 x 1011 ohmcentimeters. The PbO, By 203 and B203 contents of these test capacitors with the favorable electrical properties ranged from 0.02 to 2.83 percent, from 0.11 to 4.33 percent, and from 0.001 to 0.18 percent, respectively, with respect to the weight of the uninsulated test discs composed of the primary ingredients SrTiO3, Ta205 and GeO2 and the secondary ingredients SiO2 and A1203. Examples 577-610 In these Examples we tried a combination of SrTiO3, Nb205 and CuO as the primary ingredients. Insulated boundary layer ceramic test capacitors were fabricated by use of these primary ingredients and the auxiliary ingredients SiO2 and Awl203, in various sets of proportions specified in Table 17, and of the insulating substances PbO, Bi203 and B203, through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the electrical properties of these test capacitors were as represented also in Table 17. We also measured the percentages of the three insulating substances remaining diffused in the boundary layer ceramic test discs of the above compositions primarily comprising SrTiO3, Nb205 and CuO. PbO, Bi203 and B203 remained at percentages ranging from 0.28 to 0.86, from 0.49 to 1.50, and from 0.01 to 0.06, respectively, with respect to the weight of the ceramic discs in the uninsulated state. TABLE 17 Primary ingredients Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Nb2O5, CuO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 577 98.80 0.70 0.50 ...................... 6.4 0.3 1.7 578 98.37 0.13 1.50 0.024 0.028 0.9 6.0 0.6 1.7 579 97.25 2.70 0.05 0.020 0.020 1.0 6.3 0.5 1.7 580 99.85 0.13 0.02 0.040 0.030 1.3 5.9 0.6 1.7 581 94.66 5.32 0.02 0.024 0.018 1.3 6.0 0.5 1.7 582 98.30 0.30 1.40 0.034 0.025 1.4 6.1 0.5 1.7 583 93.18 5.32 1.50 0.015 0.010 1.5 6.0 0.3 1.7 584 99.70 0.25 0.05 0.021 0.014 1.5 8.2 0.3 1.6 585 98.37 0.13 1.50 0.030 0.020 1.5 8.6 0.4 1.6 586 94.66 5.32 0.02 0.045 0.020 1.5 8.3 0.5 1.6 587 98.80 0.70 0.50 0.040 0.025 1.6 9.7 0.5 1.5 TABLE 17 - Continued Primary ingredients Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Nb2O5, CuO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 588 94.75 4.50 0.75 0.060 0.035 1.7 6.4 0.6 1.7 589 99.85 0.13 0.02 0.052 0.028 1.9 8.9 0.5 1.6 590 93.18 5.32 1.50 0.020 0.010 2.0 8.4 0.3 1.6 591 94.75 4.50 0.75 0.043 0.020 2.2 9.8 0.3 1.5 592 97.25 2.70 0.05 0.070 0.030 2.3 9.7 0.4 1.5 593 93.37 0.13 1.50 0.078 0.031 2.5 5.7 0.6 1.7 594 94.66 5.32 0.02 0.032 0.012 2.7 8.4 0.4 1.6 595 93.18 5.32 1.50 0.095 0.035 2.7 5.9 0.6 1.7 596 99.70 0.25 0.05 0.060 0.020 3.0 10.1 0.4 1.5 597 99.85 0.13 0.02 0.090 0.028 3.2 9.3 0.5 1.5 598 94.75 4.50 0.75 0.100 0.030 3.3 9.1 0.5 1.5 TABLE 17 - Continued Primary ingredients Secondary ingredients Electrical properties SiO2, Al2O3, SiO2 SrTiO3, Nb2O5, CuO, #, tan #, #, wt. wt. Al2O3 Examples wt. % wt. % wt. % part part x 104 % x 1011 #-cm 599 94.66 5.32 0.02 0.102 0.26 3.9 6.0 0.6 1.7 600 98.80 0.70 0.50 0.020 0.005 4.0 6.5 0.4 1.7 601 97.25 2.70 0.05 0.040 0.010 4.0 9.9 0.4 1.5 602 93.18 5.32 1.50 0.080 0.020 4.0 9.5 0.5 1.5 603 98.37 0.13 1.50 0.070 0.015 4.7 12.3 0.5 1.3 604 97.25 2.70 0.05 0.040 0.008 5.0 6.3 0.4 1.7 605 98.30 0.30 1.40 0.050 0.010 5.0 13.2 0.5 1.5 606 98.80 0.70 0.50 0.100 0.020 5.0 9.7 0.5 1.5 607 99.70 0.25 0.05 0.080 0.015 5.3 14.6 1.1 0.1 608 93.18 5.32 1.50 0.055 0.010 5.5 14.1 1.2 0.1 609 94.66 5.32 0.02 0.090 0.015 6.0 10.1 1.9 0.7 610 94.75 4.50 0.75 0.095 0.012 7.9 8.3 0.9 0.8 Examples 584-587, 589-592, 594, 596-598, 601-603, 605 and 606 comply with the teachings of our invention. The relative proportions of the three primary ingredients, SrTiO3, Nb 0 and CuO, in all these inventive Examples are in the 25 ranges from 93.18 to 99.85 percent, from 0.13 to 5.32 percent, and from 0.12 to 1.50 percent, respectively. The SiO2 and Al 203 contents of the inventive Examples range from 0.02 to 0.10 part, and from 0.01 to 0.03 part, respectively, with respect to 100 parts of the primary ingredients, and the ratios in weight of Si02 to Al 203 are in the range from 1.5 to 5.0 The crystal grains of these inventive Examples averaged in the range from 60 to 120 micrometers in diameter. The apparent relative dielectric constants of the Examples were in the range from 82,000 to 132,000, their dielectric loss tangents not more than 0.5 percent, and their resistivities over 1.3 x 1011 ohm-centimeters. Examples 577-583, 588, 593, 595, 599, 600, 604, and 607-610, on the other hand, fall outside the scope of our invention. As will be noted from these noninventive Examples, the apparent relative dielectric constant does not exceed 80,000 if the weight ratio of SiO2 to Awl 03 is less than 1.5. If the weight ratio of Si02 to A1203 is greater than 5.0, on the other hand, then either the dielectric loss tangent becomes more than 1.0 percent, or the resistivity becomes less than 1.0 x 101l ohm-centimeters. Also the apparent relative dielectric constant does not become greater than 80,000 if the proportion of SiO2 is less than 0.02 part or more than 0.10 part with respect to 100 parts of the primary ingredients. Similarly the apparent relative dielectric constant becomes low if the proportion of Al203 is less than 0.01 part or more than 0.03 part with respect to 100 parts of the primary ingredients. We conclude from the above summzrized results of Table 17 that, for the boundary layer ceramics composed primarily of SrTiO3, Nub 205 and CuO in accordance with our invention, the proportions of SiO2 and Al2O3 should be from about 0.02 to about 0.10 part, and from about 0.01 to about 0.03 part, respectively, with respect to 100 parts of the primary ingredients. Further the ratio in weight of SiO2 to A1203 should be from about 1.5 to about 5.0. These conclusions presuppose, of course, that the relative proportions of the three primary ingredients are within the ranges of our invention. We measured the temperature dependencies of the apparent relative dielectric constants of the above inventive Examples. The results were also as in the graph of Figure 2, with the percent variations of the dielectric constants of all the inventive Examples with temperatures falling within the hatched areas of the graph. Examples 611-646 Uninsulated ceramic test discs were fabricated by use of the same ingredients, in the same proportions, as in Examples 585, 586, 590, 596, 597, 598, 605 and 606, and through the same procedure as in Examples 1-48. Then, in the various sets of proportions specified in Table 18, the three insulating sub stances PbO, By203 and B20 were diffused throughout the 23 23 intergranular boundaries of the test discs by the same method as in Examples 1-48. The insulated ceramic test discs were then processed into test capacitors through the same procedure as in Examples 1-48. Measured by the same methods as in Examples 1-48, the electrical properties of the thus prepared test capacitors were as given in Table 18. The column labelled "Ceramic" in this table represents the uninsulated ceramics composed of the primary ingredients SrTiO3, Nb205 and CuO and the secondary ingredients SiO2 and A1203. TABLE 18 Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 611 Example 585 34 56 10 7.9 0.6 1.7 612 Example 585 38 57 5 8.0 0.6 1.7 613 Example 585 45 45 10 9.0 0.5 1.6 614 Example 585 54 44 2 9.9 0.5 1.6 615 Example 586 35 58 7 8.0 0.7 1.7 616 Example 586 39 52 9 8.2 0.6 1.7 617 Example 586 47 52 1 8.5 0.7 0.5 618 Example 586 50 40 10 8.6 0.6 1.6 619 Example 590 35 55 10 8.0 0.6 1.7 620 Example 590 40 59 1 8.0 1.1 0.6 621 Example 590 45 47 8 8.1 0.5 1.6 622 Example 590 54 40 6 8.3 0.4 1.6 TABLE 18 -Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 623 Example 596 35 58 7 9.4 0.5 1.6 624 Example 596 45 52 3 10.2 0.5 1.5 625 Example 596 50 40 10 10.4 0.4 1.5 626 Example 596 52 43 5 9.9 0.4 1.5 627 Example 596 55 40 5 10.1 0.5 0.8 628 Example 597 34 59 7 7.9 1.1 1.7 629 Example 597 40 58 2 8.6 0.6 1.6 630 Example 597 45 45 10 9.6 0.5 1.5 631 Example 597 54 44 2 8.8 0.6 1.6 632 Example 598 38 57 5 8.5 0.7 1.7 633 Example 598 40 49 11 9.3 1.2 1.3 634 Example 598 45 52 3 8.5 0.1 1.6 TABLE 18 - Continued Insulating substances Electrical properties PbO, Bi2O3, B2O3, #, tan #, #, Examples Ceramic wt. % wt. % wt. % x 104 % x 1011 #-cm Same as: 635 Example 598 50 40 10 8.6 0.5 1.6 636 Example 598 54 40 6 9.0 0.5 1.5 637 Example 605 35 55 10 12.5 0.6 1.6 638 Example 605 40 58 2 12.3 0.7 1.6 639 Example 605 45 47 8 12.7 0.5 1.5 640 Example 605 52 43 5 12.9 0.5 1.5 641 Example 605 54 45 1 11.7 0.8 0.3 642 Example 606 35 59 6 8.8 1.3 1.5 643 Example 606 35 55 10 9.2 0.6 1.5 644 Example 606 45 52 3 9.0 0.5 1.5 645 Example 606 52 43 5 9.5 0.5 1.5 646 Example 606 51 39 10 9.6 0.6 0.6 In Examples 612-616, 618, 619, 621-626, 629-632, 634-640, and 643-645 of Table 18 the relative proportions of PbO, Bi203 and B20 are in the ranges from 35 to 54 percent, from 40 to 58 percent, and from two to 10 percent, respectively. The apparent relative dielectric constants of all these inventive Examples are sufficiently high, and their dielectric loss tangents and resistivities are also favorable. In Examples 611, 617, 620, 627, 628, 633, 641, 642 and 646, on the other hand, the relative proportions of PbO, Bi 203 and B 203 all fall outside the above ranges. The electrical properties of these noninventive Examples are unsatisfactory. Thus, for the boundary layer ceramics composed principally of SrTiO3, Nb205 and CuO in accordance with our invention, the relative proportions of the insulating substances PbO, Bi203 and B203 should be in the ranges from about 35 to about 54 percent, from about 40 to about 58 percent, and from about two to about 10 percent, respectively. We measured the percentages of the insulating substances remaining diffused in the ceramic test discs of the above inventive Examples after the heat treatment. PbO remained at rates ranging from 0.07 to 1.76 percent, By 203 at rates ranging from 0.24 to 2.70 percent, and B203 at rates ranging from 0.002 to 0.12 percent. Example 647 We sought to determine in this Example the percentages of the three insulating substances to remain diffused in the boundary layer ceramics composed primarily of SrTiO3, Nb205 and CuO, for the provision of capacitors of favorable electrical properties. The relative proportions of the insulating substances in use were within the desired ranges set forth in connection with Examples 611-646. The pasted mixture of the insulating substances was coated on uninsulated ceramic test discs in various amounts ranging from one to 15 wt. % of the test discs. The uninsulated ceramic test discs were composed principally of SrTiO3, Nub 205 and CuO, with their relative proportions within the desired ranges specified in connection with Examples 577-610, and were prepared through the same procedure as in Examples 1-48. The above coated discs were heated at various temperatures from 11500 C. to 13000 C. for various lengths of time from one to four hours. Thus were prepared a number of insulated boundary layer ceramic test discs having the three insulating substances remaining diffused throughout their intergranular boundaries at various percentages. These test discs were then processed into test capacitors through the same procedure as in Examples 1-48. From among the thus prepared test capacitors we picked up those having an apparent relative dielectric constant of over 80,000, a dielectric loss tangent of not more than one percent, and a resistivity of not less than 1.0 x 1011 ohmcentimeters. The PbO, Bi203 and B203 contents of these test capacitors with the favorable electrical properties ranged from 0.03 to 2.75 percent, from 0.12 to 4.23 percent, and from 0.001 to 0.18 percent, respectively, with respect to the weight of the uninsulated test discs composed of the primary ingredients SrTiO3, Nb205 and CuO and the secondary ingredients SiO2 and Al2O3. Although we have disclosed the boundary layer ceramics of our invention and the method of their preparation in terms of specific Examples, we understand that these are meant purely to illustrate or explain and not to impose limitations upon the invention, since a variety of modifications or variations will readily occur to the ceramics specialist on the basis of this disclosure. The following is a brief list of such modifications and variations: 1. The insulating substances PbO, Bi203 and B203 may not necessarily be used as starting substances in the manufacture of the boundary layer ceramics in accordance with our invention, all that is required being that they exist as such in the intergranular boundaries of the completed ceramics. Other substances may therefore be adopted as well, only if they become PbO, Bi203 and B203 on being heated for diffusion in the intergranular boundaries. Examples include red lead oxide (Pb304), lead fluoride (PbF2), lead borate (Pb(BO2)2-H20), and bismuth trifluoride (BiF3). 2. As another method of diffusing the insulating substances in the intergranular boundaries, there may be prepared a mixture of substances that will be thermally converted into PbO, Bi203 and B2O3 in the desired ranges of proportions. This mixture may be fired at, for instance, 1000o C. to provide the required insulating substances, then pulverized, pasted, and coated on uninsulated ceramic bodies. 3. The insulating substances may not necessarily be coated on uninsulated ceramic bodies but may be otherwise layered thereon as by vacuum deposition or by immersion of the bodies therein. 4. The primary ingredients SrTiO3, Nb205, W03, Ta205, GeO2, ZnO and CuO and the auxiliary ingredients SiO2 and A1203 are also required to exist as such only in the completed ceramics; starting substances may be different. Thus, for example, strontium carbonate and titanium oxide may be used as starting substances to provide SrTiO3 in the completed ceramics. 5. Not only one but two or all of Nb2O5, WO3 and Ta2O5 may be used in a total amount ranging from about 0.07 to about 5.32 percent. 6. Not only one but two or all of GeO2, ZnO and CuO may be used in a total amount ranging from about 0.02 to about 4.00 percent. Additional modifications and variations of our invention may be resorted to without departing from the scope of the appended claims.

Claims: Claims: 1. An insulated boundary layer ceramic having primary and secondary ingredients forming in combination a polycrystalline ceramic proper, and insulating substances dispersed throughout the intergranular boundaries of the ceramic proper, the primary ingredients comprising, in relative proportions, from about 90.68 to about 99.88 percent by weight SrTiO3, from about 0.07 to about 5.32 percent by weight of at least one of Nub205, W03 and Ta205, and from about 0.02 to about 4.00 percent by weight of at least one of GeO2, ZnO and CuO, the secondary ingredients comprising from about 0.02 to about 0.10 part by weight SiO2 and from about 0.01 to about 0.03 part by weight A1203 with respect to 100 parts by weight of the primary ingredients, the ratio in weight of SiO2 to A1203 being from about 1.5 to about 5.0, and the insulating substances comprising from about 0.02 to about 2.90 percent by weight PbO, from about 0.10 to about 4.38 percent by weight Bi203, and from about 0.001 to about 0.18 percent by weight B203, the percentages of the insulating substances being all with respect to the total weight of the primary and the secondary ingredients. 2. An insulated boundary layer ceramic as claimed in claim 1, wherein the primary ingredients comprise, in relative proportions, from about 90.68 to about 99.88 percent by weight SrTiO3, from about 0.07 to about 5.32 percent by weight Nb205, and from about 0.05 to about 4.00 percent by weight GeO2, and wherein the insulating substances comprise from about 0.03 to about 2.90 percent by weight PbO, from about 0.11 to about 4.34 percent by weight BiO3, and from about 0.001 to about 0.18 percent by weight B203, with respect to the total weight of the primary and the secondary ingredients. 3. An insulated boundary layer ceramic as claimed in claim 1, wherein the primary ingredients comprise, in relative proportions, from about 95.20 to about 99.80 percent by weight SrTiO3, from about 0.15 to about 2.30 percent by weight W03, and from about 0.05 to about 2.50 percent by weight ZnO , and wherein the insulating substances comprise from about 0.03 to about 2.75 percent by weight PbO, from about 0.11 to about 4.23 percent by weight Bi203, and from about 0.001 to about 0.18 percent by weight B203, with respect to the total weight of the primary and the secondary ingredients. 4. An insulated boundary layer ceramic as claimed in claim 1, wherein the primary ingredients comprise, in relative proportions, from about 95.18 to about 99.65 percent by weight SrTiO3, from about 0.33 to about 3.32 percent by weight Tea205, and from about 0.02 to about 1.50 by weight CuO, and wherein the insulating substances comprise from about 0.03 to about 2.75 percent by weight PbO, from about 0.11 to about 4.22 percent by weight Bi203, and from about 0.001 to about 0.18 percent by weight B203, with respect to the total weight of the primary and the secondary ingredients. 5. An insulated boundary layer ceramic as claimed in claim 1, wherein the primary ingredients comprise, in relative proportions, from about 94.50 to about 99.82 percent by weight SrTiO3, from about 0.13 to about 2.50 percent by weight W03, and from about 0.05 to about 3.00 percent by weight GeO2, and wherein the insulating substances comprise from about 0.03 to about 2.90 percent by weight PbO, from about 0.10 to about 4.28 percent by weight Bi203, and from about 0.001 to about 0.18 percent by weight B203, with respect to the total weight of the primary and the secondary ingredients. 6. An insulated boundary layer ceramic as claimed in claim 1, wherein the primary ingredients comprise, in relative proportions, from about 91.18 to about 99.82 percent by weight SrTiO3, from about 0.13 to about 5.32 percent by weight Nb205, and from about 0.05 to about 3.50 percent by weight ZnO, and wherein the insulating substances comprise from about 0.03 to about 2.90 percent by weight PbO, from about 0.11 to about 4.28 percent by weight Bi203, and from about 0.001 to about 0.18 percent by weight B203, with respect to the total weight of the primary and the secondary ingredients. 7. An insulated boundary layer ceramic as claimed in claim 1, wherein the primary ingredients comprise, in relative proportions, from about 94.50 to about 99.62 percent by weight SrTiO3, from about 0.33 to about 3.00 percent by weight Ta205, and from about 0.05 to about 2.50 percent by weight ZnO, and wherein the insulating substances comprise from about 0.03 to about 2.80 percent by weight PbO, from about 0.11 to about 4.38 percent by weight Bi203, and from about 0.001 to about 0.18 percent by weight B203, with respect to the total weight of the primary and the secondary ingredients. 8. An insulated boundary layer ceramic as claimed in claim 1, wherein the primary ingredients comprise, in relative proportions, from about 96.70 to about 99.83 percent by weight SrTiO3, from about 0.15 to about 2.30 percent by weight W03, and from about 0.02 to about 1.00 percent by weight CuO, and wherein the insulating substances comprise from about 0.03 to about 2.83 percent by weight PbO, from about 0.10 to about 4.30 percent by weight BiO2, and from about 0.001 to about 0.18 percent by weight B203, with respect to the total weight of the primary and the secondary ingredients. 9. An insulated boundary layer ceramic as claimed in claim 1, wherein the primary ingredients comprise, in relative proportions, from about 91.92 to about 99.62 percent by weight SrTiO3, from about 0.33 to about 4.08 percent by weight Ta2O5, and from about 0.05 to about 4.00 percent by weight GeO2, and wherein the insulating substances comprise from about 0.02 to about 2.83 percent by weight PbO, from about 0.11 to about 4.33 percent by weight Bi203, and from about 0.001 to about 0.18 percent by weight B203, with respect to the total weight of the primary and the secondary ingredients. 10. An insulated boundary layer ceramic as claimed in claim 1, wherein the primary ingredients comprise, in relative proportions, from about 93.18 to about 99.85 percent by weight SrTiO3, from about 0.13 to about 5.32 percent by weight Nb205, and from about 0.02 to about 1.50 percent by weight CuO, and wherein the insulating substances comprise from about 0.03 to about 2.75 percent by weight PbO, from about 0.12 to about 4.23 percent by weight Bi203, and from about 0.001 to about 0.18 percent by weight B203, with respect to the total weight of the primary and the secondary ingredients. 11. A process for the fabrication of insulated boundary layer ceramic bodies which comprises the steps of preparing uninsulated, polycrystalline ceramic bodies composed of primary and secondary ingredients , the primary ingredients comprising, in relative proportions, from about 90.68 to about 99.88 percent by weight SrTiO3, from about 0.07 to about 5.32 percent by weight of at least one of Nb205, W03 and Ta205, and from about 0.02 to about 4.00 percent by weight of at least one of GeO2, ZnO and CuO, and the secondary ingredients comprising from about 0.02 to about 0.10 part by weight SiO2 and from about 0.01 to about 0.03 part by weight Awl 203 with respect to 100 parts by weight of the primary ingredients, the ratio in weight of SiO2 to A1203 being from about 1.5 to about 5.0, forming on the uninsulated ceramic bodies layers of insulating substances essentially comprising PbO, Bi2O3 and B2O3 in relative proportions of from about 27 to about 61 percent by weight, from about 32 to about 66 percent by weight, and from about two to about 10 percent by weight, respectively, the layers of insulating substances being from about one to about 15 parts by weight with respect to 100 parts of the uninsulated ceramic bodies, and heating the ceramic bodies, together with the layers of insulating substances thereon, thereby causing diffusion of the insulating substances throughout the intergranular boundaries of the ceramic bodies. 12. A process for the fabrication of insulated boundary layer ceramic bodies as claimed in claim 11, wherein the uninsulated, polycrystalline ceramic bodies are prepared by firing moldings of a mixture of the primary and secondary ingredients in a reductive atmosphere. 13. A process for the fabrication of insulated boundary layer ceramic bodies as claimed in claim 11 or 12, wherein the primary ingredients comprise, in relative proportions, from about 90.68 to about 99.88 percent by weight SrTiO3, from about 0.07 to about 5.32 percent by weight Nb205, and from about 0.05 to about 4.00 percent by weight GeO2, and wherein the insulating substances layered on the uninsulated ceramic bodies comprise, in relative proportions, from about 32 to about 61 percent by weight PbO, from about 34 to about 64 percent by weight Bi203, and from about two to about 10 percent by weight B203. 14. A process for the fabrication of insulated boundary layer ceramic bodies as claimed in claim 11 or 12, wherein the primary ingredients comprise, in relative proportions , from about 95.20 to about 99.80 percent by weight SrTiO3, from about 0.15 to about 2.30 percent by weight W03, and from about 0.05 to about 2.50 percent by weight ZnO, and wherein the insulating substances layered on the uninsulated ceramic bodies comprise, in relative proportions, from about 35 to about 54 percent by weight PbO, from about 36 to about 58 percent by weight Bi203, and from about two to about 10 percent by weight B203. 15. A process for the fabrication of insulated boundary layer ceramic bodies as claimed in claim 11 or 12, wherein the primary ingredients comprise, in relative proportions, from about 95.18 to about 99.65 percent by weight SrTiO3, from about 0.33 to about 3.32 percent by weight Ta205, and from about 0.02 to about 1.50 percent by weight CuO, and wherein the insulating substances layered on the uninsulated ceramic bodies comprise, in relative proportions, from about 35 to about 54 percent by weight PbO, from about 37 to about 58 percent by weight Bi203, and from about two to about 10 percent by weight B203. 16. A process for the fabrication of insulated boundary layer ceramic bodies as claimed in claim 11 or 12, wherein the primary ingredients comprise, in relative proportions, from about 94.50 to about 99.82 percent by weight SrTiO3, from about 0.13 to about 2.50 percent by weight W03, and from about 0.05 to about 3.00 percent by weight GeO2, and wherein the insulating substances layered on the uninsulated ceramic bodies comprise, in relative proportions, from about 32 to about 61 percent by weight PbO, from about 32 to about 60 percent by weight Bi203, and from about two to about 10 percent by weight B203. 17. A process for the fabrication of insulated boundary layer ceramic bodies as claimed in claim 11 or 12, wherein the primary ingredients comprise, in relative proportions, from about 91.18 to about 99.82 percent by weight SrTiO3, from about 0.13 to about 5.32 percent by weight Nb205, and from about 0.05 to about 3.50 percent by weight ZnO, and wherein the insulating substances layered on the uninsulated ceramic bodies comprise, in relative proportions, from about 30 to about 61 percent by weight PbO, from about 35 to about 60 percent by weight Bi203, and from about two to about 10 percent by weight B203. 18. A process for the fabrication of insulated boundary layer ceramic bodies as claimed in claim 11 or 12, wherein the primary ingredients comprise, in relative proportions, from about 94.50 to about 99.62 percent by weight SrTiO3, from about 0.33 to about 3.00 percent by weight Ta205, and from about 0.05 to about 2.50 percent by weight ZnO, and wherein the insulating substances layered on the uninsulated ceramic bodies comprise, in relative proportions, from about 31 to about 56 percent by weight PbO, from about 34 to about 66 percent by weight Bi203, and from about two to about 10 percent by weight B203. 19. A process for the fabrication of insulated boundary layer ceramic bodies as claimed in claim 11 or 12, wherein the primary ingredients comprise, in relative proportions, from about 96.70 to about 99.83 percent by weight SrTiO3, from about 0.15 to about 2.30 percent by weight W03, and from about 0.02 to about 1.00 percent by weight CuO, and wherein the insulating substances layered on the uninsulated ceramic bodies comprise, in relative proportions, from about 31 to about 58 percent by weight PbO, from about 32 to about 62 percent by weight Bi203, and from about two to about 10 percent by weight B203. 20. A process for the fabrication of insulated boundary layer ceramic bodies as claimed in claim 11 or 12, wherein the primary ingredients comprise, in relative proportions, from about 91.92 to about 99.62 percent by weight SrTiO3, from about 0.33 to about 4.08 percent by weight Ta205, and from about 0.05 to about 4.00 percent by weight GeO2, and wherein the insulating substances layered on the uninsulated ceramic bodies comprise, in relative proportions, from about 27 to about 58 percent by weight PbO, from about 34 to about 63 percent by weight Bi203, and from about two to about 10 percent by weight B2O3. 23 21. A process for the fabrication of insulated boundary layer ceramic bodies as claimed in claim 11 or 12, wherein the primary ingredients comprise, in relative proportions, rom about 93.18 to about 99.85 percent by weight SrTiO3, from about 0.13 to about 5.32 percent by weight Nb2O5, and from about 0.02 to about 1.50 percent by weight CuO, and wherein the insulating substances layered on the uninsulated ceramic bodies comprise, in relative proportions, from about 35 to about 54 percent by weight PbO, from about 40 to about 58 percent by weight Bi203, and from about two to about 10 percent by weight B203

Inventors: KAZUJI, ONIGATA, KIYOSHI, MURASE, MASAYUKI, FUJIMOTO, NOBUTATSU, YAMAOKA
Applicants: TAIYO YUDEN CO., LTD.
Application year: 1982
Main classification: C04B35
IPC codes: C04B35, H01G4