Source: http://www.google.com/patents/US4541974?dq=5,758,352
Timestamp: 2013-12-10 16:13:44
Document Index: 763101616

Matched Legal Cases: ['in fine', 'in fine', 'in fine', 'in fine', 'in fine', 'in fine', 'in fine', 'in fine', 'in fine', 'in fine']

Patent US4541974 - Semiconductive ceramic compositions with a nonlinear volt-ampere ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Advanced Patent Search | Sign inAdvanced Patent SearchPatentsCeramic materials suitable for use in varistors, enabling the same to function both as such and as capacitors. The ceramic compositions comprise a major proportion of SrTiO.sub.3, the balance being (1) one or more of Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, WO.sub.3, La.sub.2 O.sub.3, CeO.sub.2, Nd.sub.2...http://www.google.com/patents/US4541974?utm_source=gb-gplus-sharePatent US4541974 - Semiconductive ceramic compositions with a nonlinear volt-ampere characteristic, and process for preparing coherent bodies of such compositionsPublication numberUS4541974 APublication typeGrantApplication numberUS 06/526,446Publication dateSep 17, 1985Filing dateAug 25, 1983Priority dateJul 30, 1980Fee statusLapsedAlso published asDE3168765D1, EP0044981A2, EP0044981A3, EP0044981B1, US4519942Publication number06526446, 526446, US 4541974 A, US 4541974A, US-A-4541974, US4541974 A, US4541974AInventorsKazuo Sasazawa, Akira Tsukada, Nobutatsu YamaokaOriginal AssigneeTaiyo Yuden Co., Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (8), Referenced by (11), Classifications (13), Legal Events (6) External Links: USPTO, USPTO Assignment, EspacenetSemiconductive ceramic compositions with a nonlinear volt-ampere characteristic, and process for preparing coherent bodies of such compositionsUS 4541974 AAbstract Ceramic materials suitable for use in varistors, enabling the same to function both as such and as capacitors. The ceramic compositions comprise a major proportion of SrTiO.sub.3, the balance being (1) one or more of Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, WO.sub.3, La.sub.2 O.sub.3, CeO.sub.2, Nd.sub.2 O.sub.3, Pr.sub.6 O.sub.11, Dy.sub.2 O.sub.3, Y.sub.2 O.sub.3, and Sm.sub.2 O.sub.3, for making the compositions semiconductive, and (2) one or more of V.sub.2 O.sub.5, Cr.sub.2 O.sub.3, CuO, Cu.sub.2 O, MoO.sub.3, and MnO.sub.2, for improving the nonlinear volt-ampere characteristic of the compositions. If desired, for improving the coherency of bodies molded from the composition, there can be added one or more of GeO.sub.2, ZnO, B.sub.2 O.sub.3, and PbO. For use as varistors the mixture of the above ingredients, all in finely divided form and made coherent with a binder, is molded into desired shape under pressure. The moldings are first fired in a nonoxidative atmosphere and then further heated in an oxidative atmosphere. Electrodes can be formed as by silver painting.
What is claimed is: 1. A process for the fabrication of coherent bonded bodies of a semiconductive ceramic composition with a nonlinear volt-ampere characteristic, particularly well suited for use in varistors, which comprises:(a) providing a mixture of: SrTiO.sub.3 in finely divided form;(2) from about 0.001 to about 5.000% of at least one metal oxide in finely divided form, for making the composition semiconductive, selected from the group consisting of Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, WO.sub.3, La.sub.2 O.sub.3, CeO.sub.2, Nd.sub.2 O.sub.3, Pr.sub.6 O.sub.11, Dy.sub.2 O.sub.3, Y.sub.2 O.sub.3, and Sm.sub.2 O.sub.3 ; (3) from about 0.010 to about 5.000% of at least one other metal oxide in finely divided form, for improving the nonlinear volt-ampere characteristic of the composition, selected from the group consisting of V.sub.2 O.sub.5, Cr.sub.2 O.sub.3, CuO, Cu.sub.2 O, MoO.sub.3, and MnO.sub.2 ; and (4) a binder; (b) molding the mixture into bodies of desired shape under pressure; (c) firing the bodies in a temperature range of from about 1300 about 1500 (d) heating the fired bodies in a temperature range of from about 800 2. A process for the fabrication of coherent bonded bodies of a semiconductive ceramic composition with a nonlinear volt-ampere characteristic, particularly well suited for use in varistors, which comprises:(a) providing a mixture of:(1) from about 86.000 to about 99.979% SrTiO.sub.3 in finely divided form; (2) from about 0.001 to about 5.000% of at least one metal oxide in finely divided form, for making the composition semiconductive, selected from the group consisting of Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, WO.sub.3, La.sub.2 O.sub.3, CeO.sub.2, Nd.sub.2 O.sub.3, Pr.sub.6 O.sub.11, Dy.sub.2 O.sub.3, Y.sub.2 O.sub.3, and Sm.sub.2 O.sub.3 ; (3) from about 0.010 to about 5.000% of at least one other metal oxide in finely divided form, for improving the nonlinear volt-ampere characteristic of the composition, selected from the group consisting of V.sub.2 O.sub.5, Cr.sub.2 O.sub.3, CuO, Cu.sub.2 O, MoO.sub.3, and MnO.sub.2 ; (4) from about 0.010 to about 4.000% of at least one still other metal oxide in finely divided form, for improving the coherency of the bodies of the composition, selected from the group consisting of GeO.sub.2, ZnO, B.sub.2 O.sub.3, and PbO; and (5) a binder; (b) molding the mixture into bodies of desired shape under pressure; (c) firing the bodies in a temperature range of from about 1300 about 1500 (d) heating the fired bodies in a temperature range of from about 900 3. A process according to claims 1 or 2, wherein the mixture is molded at pressures ranging from about 500 to about 2000 kg/cm.sup.2.
4. A process according to claims 1 or 2, wherein the molded bodies are fired in a reductive atmosphere.
5. A process according to claim 4, wherein the atmosphere is about 95 volume % molecular nitrogen and about five volume % molecular hydrogen.
6. A process according to claims 1 or 2, wherein the binder is polyvinyl alcohol.
This is a division of application Ser. No. 280,801, filed July 6, 1981.
BACKGROUND OF THE INVENTION This invention relates to ceramic materials particularly well suited for use in semiconductor devices having a nonlinear volt-ampere characteristic. The invention also concerns a process for the fabrication of coherent bonded bodies of such materials.
Semiconductor devices with a nonlinear volt-ampere characteristic find extensive use in electric circuits for the absorption of abnormal voltages, suppression of noise, and elimination of sparks. Commonly referred to as varistors, as hereinafter so called in this specification, such semiconductor devices have been fabricated typically from silicon (using the pn-junctions of silicon semiconductors), silicon carbide (SiC), zinc oxide (ZnO), stannic oxide (SnO.sub.2), and titanium dioxide (TiO.sub.2).
The pn-junction silicon varistors make use of forward voltage rises, so that they offer a varistor voltage of as low as 0.6 volt (V) or so per pn-junction. For higher varistor voltages, therefore, a plurality of pn-junction silicon chips must be interconnected in series. As regards the SiC varistors, the nonlinearity coefficient α of their volt-ampere characteristic is as low as two or three in a voltage range of 3-20 V. Another disadvantage is that SiC cannot possibly be sintered into annular or other more or less complex shape with sufficient coherency. The ZnO varistors have a high nonlinearity coefficient in a voltage range of over 30 V, but it becomes as low as about two in a low voltage range of 3-20 V. The nonlinearity coefficient of the SnO.sub.2 varistors is higher, being up to about five, in the voltage range of 3-20 V. This advantage is offset, however, by the poor sinterability, expensiveness, and low moisture-withstanding ability of the material. Moreover, since the SnO.sub.2 varistors function as such by making use of the PN-junctions at the interfaces between the electrodes and the semiconductor bodies, their physical properties tend to deteriorate from voltage pulses. The TiO.sub.2 varistors can be molded and sintered into any desired shape, but their nonlinearity coefficient is only two to four in a voltage range of 20-30 V. Additionally, their varistor voltage varies with temperature (temperature characteristic) at a rate ranging from -0.5 to 0.7% per Another known varistor material being studied is barium titanate (BaTiO.sub.3). The BaTiO.sub.3 varistors utilize the PN-junctions at the interfaces between the electrodes and the semiconductor bodies, just like the SnO.sub.2 varistors, so that they possess drawbacks similar to those pointed out in connection with the SnO.sub.2 varistors.
For the purposes of the absorption of abnormal voltages and the elimination of noise and sparks, the parallel connections of varistors and capacitors have hitherto served better than varistors only, as is well known to the specialists. No ceramic composition having both functions has so far been discovered, as far as the applicant is aware. Such a material will significantly contribute to the miniaturization and cost reduction of electrical equipment.
U.S. Pat. No. 3,933,668 issued to Takahashi et al. on Jan. 20, 1976, describes and claims a ferroelectric ceramic compound in a perovskite structure, composed principally of strontium titanate (SrTiO.sub.3). This known ceramic material is well suited for use in capacitors. The high resistance offered by the particles constituting the ceramic, however, practically inhibits its use in varistors. Another disadvantage of the known SrTiO.sub.3 ceramic is easy deterioration of electrical properties due to voltage pulses.
SUMMARY OF THE INVENTION The present invention seeks to combine both varistor and capacitor functions in a single class of semiconductive ceramic compositions, and to provide such compositions themselves and a process for the fabrication of coherent bonded bodies of such compositions.
The invention also seeks to provide semiconductive ceramic materials which are capable of providing such a low range of varistor voltages as, say, from three to 100 V, which are little affected physically by voltage pulses in their use in semiconductor devices, and which, manufactured by the inventive method, hardly fluctuate in electrical properties.
Briefly, the invention provides a semiconductive ceramic composition comprising: (1) from about 90.000 to about 99.989 mole percent SrTiO.sub.3 (hereinafter referred to as the first or main ingredient); (2) from about 0.001 to about 5.000 mole percent of at least one metal oxide (the second ingredient), for improving the semiconductivity of the composition, which is selected from the group of niobium oxide (Nb.sub.2 O.sub.5), tantalum oxide (Ta.sub.2 O.sub.5), tungstic oxide (WO.sub.3), lanthanum oxide (La.sub.2 O.sub.3), ceric oxide (CeO.sub.2), neodymium oxide (Nd.sub.2 O.sub.3), praseodymia (Pr.sub.6 O.sub.11), dysprosium oxide (Dy.sub.2 O.sub.3), yttrium oxide (Y.sub.2 O.sub.3), and samarium oxide (Sm.sub.2 O.sub.3); and (3) from about 0.010 to about 5.000 mole percent of at least one other metal oxide (the third ingredient), for improving the nonlinear volt-ampere characteristic of the composition, which is selected from the group of vanadium pentoxide (V.sub.2 O.sub.5), chromic oxide (Cr.sub.2 O.sub.3), black copper oxide (CuO), red copper oxide (Cu.sub.2 O), molybdenum trioxide (MoO.sub.3), and manganese dioxide (MnO.sub.2).
Hereinafter in this specification and in the claims appended thereto, all percentages are molar unless otherwise specified.
The exact proportion of each of the at least three ingredients of the ceramic composition according to the invention depends on those of the others. Preferably, the main ingredient is used in a range of about 97.7-99.1%, the second ingredient in a range of about 0.3-1.0%, and the third ingredient in a range of about 0.1-0.3%, in proportions.
In the above described ceramic composition according to the invention, the addition of at least one of the third group of ingredients (V.sub.2 O.sub.5, Cr.sub.2 O.sub.3, CuO, Cu.sub.2 O, MoO.sub.3, and MnO.sub.2) to the first and second ingredients serves to give the material a markedly nonlinear volt-ampere characteristic, or voltage-dependent nonlinear resistance. The crystal system of the material is in a ferroelectric perovskite structure, so that it offers a high electrostatic capacitance, making it possible to provide semiconductor devices integrally combining the functions of both varistor and capacitor.
It is reasoned that the ceramic materials formulated in accordance with the invention derive their varistor-like characteristics from the PN-junctions between their constituent particles, with the N-type semiconductor particles of, principally, the first and second ingredients surrounded by the third ingredient of P type or of substantially P type. Consequently, compared with the known varistors having the PN-junctions formed between the ceramic bodies and the electrodes, the varistors incorporating the ceramic materials of this invention will suffer less from voltage pulses. A further advantage of the ceramic compositions according to the invention is the inexpensiveness of their main ingredient, SrTiO.sub.3, making possible the provision of high-quality varistor ceramics at low costs.
According to another aspect of the invention the above compositions of at least three ingredients are admixed with at least one still other metal oxide (hereinafter referred to as the fourth ingredient) with a view to higher coherency of the ceramic bodies prepared from the compositions. The fourth ingredient is selected from the group of germanium dioxide (GeO.sub.2), zinc oxide (ZnO), boric oxide (B.sub.2 O.sub.3), and litharge (PbO). The fourth ingredient serves to make the particles of the sintered ceramic bodies from about 20 to 40 microns in size, and further to improve the voltage rises of their V-I curves and to reduce fluctuations in the nonlinearity coefficient. The proportion of the fourth ingredient, dependent on those of the other ingredients, normally ranges from about 0.010 to about 4.000%, preferably from about 0.5 to about 1.0%. When a ceramic composition contains from about 0.010 to about 4.000% of the fourth ingredient, the amount of the first ingredient is correspondingly reduced to a range of about 86.000-99.979%.
For the fabrication of coherent bonded bodies of the first described composition (having no fourth ingredient) by the method of this invention, SrTiO.sub.3 and at least two selected metal oxides of the prescribed proportions, all in finely divided form, are blended together and admixed with an organic binder. The blended mixture is molded into desired shape, such as that of a disc, at pressures ranging from about 500 to about 2000 kg/cm.sup.2. The molding is first fired in a temperature range of about 1300 neutral) atmosphere and then further heated in a temperature range of about 800
If the composition includes a fourth ingredient or ingredients, the temperature of the oxidative heat treatment of the fired molding is selected from a range of about 900 respects, coherent bodies of this four-ingredient composition can be formed by the same method as are those of the three-ingredient composition.
The ceramic bodies manufactured by the methods of this invention are remarkably well suited for varistors, besides being notable for their high abilities of absorbing abnormal voltages in use. Subsequently electroded, the ceramic bodies find use as varistors.
The above and other features and advantages of this invention will become more apparent, and the invention itself will best be understood, from the following description and appended claims taken together with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view of a varistor incorporating a ceramic body formulated in accordance with the invention;
FIG. 2 is a graphic representation of the volt-ampere characteristic of an SrTiO.sub.3 --CeO.sub.2 --V.sub.2 O.sub.5 varistor fabricated in EXAMPLE 1 of the invention;
FIG. 3 is a graph representing the degrees of attenuation of various megahertz frequencies by the SrTiO.sub.3 --CeO.sub.2 --V.sub.2 O.sub.5 varistor, in comparison with the attenuation characteristic of a known ZnO varistor, as tested in EXAMPLE 1 of the invention;
FIG. 4 is a graph plotting the curve of the varistor voltage E.sub.10 of SrTiO.sub.3 --Nb.sub.2 O.sub.5 --CuO varistors against the varying percentages of their CuO content, with their Nb.sub.2 O.sub.5 content fixed at 0.1%, as tested in EXAMPLE 3 of the invention;
FIG. 5 is a graph plotting the curve of the varistor voltage E.sub.10 of SrTiO.sub.3 --Nb.sub.2 O.sub.5 --CuO varistors against the varying percentages of their Nb.sub.2 O.sub.5 content, with their CuO content fixed at 0.01%, also as tested in EXAMPLE 3 of the invention;
FIG. 6 is a graph plotting the curve of the volt-ampere nonlinearity coefficient α of SrTiO.sub.3 --Nb.sub.2 O.sub.5 --CuO varistors against the temperatures at which they were subjected to oxidative heat treatment in manufacture, as tested in EXAMPLE 13 of the invention;
FIG. 7 is a graph plotting the curve of the α of SrTiO.sub.3 --Nb.sub.2 O.sub.5 --CuO--GeO.sub.2 varistors against the temperatures at which they were subjected to oxidative heat treatment in manufacture, as tested in EXAMPLE 23 of the invention;
FIG. 8 is a graph plotting the curve of the E.sub.10 of the SrTiO.sub.3 --Nb.sub.2 O.sub.5 --CuO--GeO.sub.2 varistors against the temperatures at which they were subjected to oxidative heat treatment in manufacture, in comparison with the curve representing similar relationship in the case of the SrTiO.sub.3 --Nb.sub.2 O.sub.5 --CuO varistors, also as tested in EXAMPLE 23 of the invention; and
FIG. 9 is a graph plotting the curves of the rates of change in the E.sub.10 of SrTiO.sub.3 --Nb.sub.2 O.sub.5 --CuO--GeO.sub.2 and SrTiO.sub.3 --Nb.sub.2 O.sub.5 --MoO.sub.3 --GeO.sub.2 varistors with the temperatures at which they were put to use, as tested in EXAMPLE 25 of the invention.
DETAILED DESCRIPTION The compositions of the semiconductive ceramic materials according to this invention are as set forth in the foregoing summary of the invention. The fabrication of coherent bonded bodies of such compositions, as in the form of discs for use in varistors, starts with the preparation of SrTiO.sub.3, the main ingredient, which occupies a major proportion in all the possible combinations of ingredients in accordance with the invention. This main ingredient is usually prepared from strontium carbonate (SrCO.sub.3) and titanium dioxide (TiO.sub.2), proportioned to unite into SrTiO.sub.3. SrCO.sub.3 and TiO.sub.2 do so by being fired at temperatures ranging from 1050
If the composition is to include no fourth ingredient, from about 90.000 to about 99.989% SrTiO.sub.3, prepared as above, is combined with about 0.001-5.000% of at least one metal oxide (second ingredient) selected from the group of Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, WO.sub.3, La.sub.2 O.sub.3, CeO.sub.2, Nd.sub.2 O.sub.3, Pr.sub.6 O.sub.11, Dy.sub.2 O.sub.3, Y.sub.2 O.sub.3, and Sm.sub.2 O.sub.3, and with about 0.010-5.000% of at least one other metal oxide (third ingredient) selected from the group of V.sub.2 O.sub.5, CrO.sub.3, CuO, Cu.sub.2 O, MoO.sub.3, and MnO.sub.2. The combination of at least three ingredient is pulverized and intimately intermingled by being placed in a ball mill for 10 hours or so. The blended mixture of finely divided form is then admixed with 5-10 percent by weight of an organic binder, normally polyvinyl alcohol. This admixture is molded into disc-like or other desired shape by pressing at about 500-2000 kg/cm.sup.2.
Then the moldings are fired in a temperature range of about 1300 C., for 1-6 hours in a nonoxidative atmosphere. The total firing time, inclusive of the time for the buildup and drop of the firing temperature in the furnace, may be from 24 to 48 hours. The firing atmosphere is reductive for the better results, consisting for example of 95 percent by volume of molecular nitrogen (N.sub.2) and five percent by volume of molecular hydrogen (H.sub.2). The fired moldings are put to oxidative heat treatment (reoxidizing treatment), by being heated in a temperature range of about 800 800 The total time of such oxidative heat treatment, inclusive of the time for the buildup and drop of the heating temperature in the furnace, may range from four to eight hours. Thus are completed the desired ceramic bodies, which can be put to use as varistors on being electroded, as by silver painting and baking.
In the EXAMPLES of the invention presented subsequently, all but CrO.sub.3 of the listed metal oxides are used as such as starting materials. All that is required for the attainment of the purposes of this invention, however, is that the completed ceramic bodies contain the selected metal oxides. The starting materials may therefore be not necessarily in the form of metal oxides but of, for example, metallic elements, carbonates, hydroxides, oxalates, etc. To give more specific examples, the first ingredient may be formed from starting substances of strontium and titanium; the second ingredient from such starting substances as Nb(HC.sub.2 O.sub.4).sub.5, La.sub.2 (C.sub.2 O.sub.4).sub.3, La.sub.2 (CO.sub.3).sub.3, Ce.sub.2 (C.sub.3 O.sub.4).sub.3, Ce.sub.2 (CO.sub.3).sub.3, Pr.sub.2 (C.sub.2 O.sub.4).sub.3, Nd.sub.2 (C.sub.2 O.sub.4).sub.3, Nd.sub.2 (CO.sub.3).sub.3, Sm.sub.2 (C.sub.2 O.sub.4).sub.3, Sm.sub.2 (CO.sub.3).sub.3, Dy.sub.2 (C.sub.2 O.sub.4).sub.3, Dy.sub.2 (CO.sub.3).sub.3, and Y.sub.2 (CO.sub.3).sub.3 ; and the third ingredient from such starting substances as CuCO.sub.3, CuC.sub.2 O.sub.4, CuCN, Cu.sub.2 S, Cr.sub.2 (CH.sub.3 COO).sub.3, Cr.sub.2 (SO.sub.3).sub.3, V.sub.2 S.sub.3, Mo(OH).sub.3, Mo(OH).sub.5, MnCO.sub.3, and MoC.sub.2 O.sub.4.
The invention also dictates the use, in combination with the first, second and third ingredients, of at least one additional metal oxide selected from the group of GeO.sub.2, ZnO, B.sub.2 O.sub.3, and PbO. The metal oxide chosen as the fourth ingredient is also required to exist as such in the completed ceramics, so that it may be formed from such starting substances as Ge(OH).sub.2, ZnC.sub.2 O.sub.4, 5ZnO.sub.2 CO.sub.3 4H.sub.2 O, PbC.sub.2 O.sub.4, and (PbCO.sub.3).sub.2 Pb(OH).sub.2.
The following EXAMPLES will provide further details of the compositions and manufacturing methods of the ceramic materials in accordance with the invention, as well as the characteristics of varistors incorporating the ceramic materials.
EXAMPLE 1 SrCO.sub.3 and TiO.sub.2, proportioned to combine into SrTiO.sub.3, were fired in a temperature range of 1050 hours. The fired substances were pulverized by means of a crusher, thus providing SrTiO.sub.3 as the first ingredient of the desired ceramic materials. This first ingredient was combined with CeO.sub.2 as the second ingredient and V.sub.2 O.sub.5 as the third ingredient, in various proportions set forth in TABLE 1, wherein the Test Numbers refer to the combinations of the three ingredients in various proportions.
Each combination of the three ingredients, which were all in finely divided form, was then admixed with 5-10 wt. % polyvinyl alcohol, an organic binder. The admixtures were molded at pressures ranging from 500 to 2000 kg/cm.sup.2 into the form of discs each sized to have a diameter of 5 millimeters (mm) and a thickness of 0.8 mm on firing.
Then the moldings were fired for three hours at a temperature of 1390 in a reductive atmosphere of 95 vol. % N.sub.2 and five vol. % H.sub.2. The firing temperatures could be anywhere between about 1300 about 1500 depending upon the firing temperature selected. Then, in order to control the varistor voltage (rising voltage of the voltage-current curve) of the end products, the fired moldings were treated at a temperature of 900 placed within a furnace for a total of six hours. This oxidizing heat treatment could be effected in a temperature range of about 800 to 6.0 hours depending upon the temperature.
Then, as illustrated in FIG. 1, each disc-like ceramic body 1 composed and fabricated in accordance with the invention had its opposite faces coated with silver paint to be processed into a varistor. The silver coatings were baked in a temperature range of 400 pair of electrodes 2 and 3, thus completing the desired varistor. The varistor according to this invention derives its intended functions from the interior of the sintered body itself, so that the electrodes 2 and 3 could be made from other materials such as indium-gallium alloy, and by other methods such as evaporation or plating.
The ceramic body 1 of the varistor prepared as above comprises fine, conductive crystal grains 4 dispersed in a resistive oxide region 5, just like the ZnO varistor ceramic. The nonlinearity of its volt-ampere characteristic results as the first ingredient, SrTiO.sub.3, is acted upon by the second, CeO.sub.2, and third, V.sub.2 O.sub.5, ingredients. Although the exact reason for this is not necessarily clear, a fairly reasonable theory would be that the second ingredient acts on the minute crystal particles 4 of the first ingredient to provide N-type semiconductors, whereas the oxide region 5, composed principally of the third ingredient, provides a P-type semiconductor.
Polyvinyl alcohol was used to bind the three pulverized ingredients in molding them into disc-like shape. This organic binder evaporates or is burnt out by the subsequent heat treatments of the moldings. Consequently the composition of the completed ceramic body 1 essentially corresponds to the starting substances only.
The characteristics of the varistors of this class might be evaluated from α and K in the volt-ampere characteristic formula of varistors in general, I=(V/K).sup.α, where I is the varistor current, V the applied voltage, K a constant, and α a coefficient indicative of the voltage-current nonlinearity. Exact measurement of K is difficult, however, so that the characteristics of the above prepared varistors were ascertained from the varistor voltage E.sub.10 when a current of 10 mA was flowing, and from α=1/log (E.sub.10 /E.sub.1), where E.sub.1 is the varistor voltage corresponding to the current of 1 mA. The following TABLE 1 represents the various sets of proportions of the three noted ingredients used to produce the varistors in this EXAMPLE 1, together with their varistor voltage E.sub.10, nonlinearity coefficient α, and electrostatic capacity C. The electrostatic capacities of the varistors were measured at a frequency of 1 kHz.
TABLE 1______________________________________Test  Composition in percent                    PropertiesNo.   SrTiO.sub.3          CeO.sub.2                   V.sub.2 O.sub.5                          E.sub.10, V                                 &#945;                                      C, nF______________________________________1     99.98    0.01     0.01   13     6    492     99.94    0.05     0.01   5      5    513     99.89    0.10     0.01   4      4    634     98.99    1.00     0.01   7      5    575     94.99    5.00     0.01   12     6    506     99.94    0.01     0.05   20     7    527     99.90    0.05     0.05   7      6    668     99.85    0.10     0.05   6      5    769     98.95    1.00     0.05   11     6    6210    94.95    5.00     0.05   18     7    5311    99.89    0.01     0.10   32     11   4612    99.85    0.05     0.10   12     6    5713    99.80    0.10     0.10   10     6    6114    98.90    1.00     0.10   17     7    5615    94.90    5.00     0.10   29     9    4716    99.49    0.01     0.50   64     20   3717    99.45    0.05     0.50   25     8    5018    99.40    0.10     0.50   20     7    5119    98.50    1.00     0.50   36     11   4620    94.50    5.00     0.50   61     20   3321    98.99    0.01     1.00   106    35   2622    98.95    0.05     1.00   45     13   4123    98.90    0.10     1.00   36     12   3924    98.00    1.00     1.00   63     21   3125    94.00    5.00     1.00   101    34   21______________________________________
FIG. 2 graphically represents by way of example the volt-ampere characteristic of the varistor of Test No. 13 given in TABLE 1.
The varistor of Test No. 13 was also evaluated as to the attenuation of various megahertz frequencies, by connecting the varistor in parallel with a signal generator and with a spectrum analyzer. The curve A in the graph of FIG. 3 represents the results. The curve B in the same graph indicates, by way of comparison, the damping characteristic (measured by the same method as above) of a varistor having its ceramic body composed principally of ZnO. A comparison of the curves A and B will reveal that the varistor according to this invention has a higher damping ability over a wide frequency range, thus exhibiting a capacitor-like property. The inventive material is therefore capable of absorbing voltage surges, noise, etc., by acting as both varistor and capacitor.
Although only the varistor of Test No. 13 was experimented as to its capacitor-like property, it is obvious that all the other varistors fabricated in this EXAMPLE 1 have a similar property, for their varistor voltages E.sub.10 all fall between four and 106 V, their voltage-current nonlinearity coefficients α between four and 35, and their electrostatic capacity C between 21 and 76 nF.
In thus producing the SrTiO.sub.3 --CeO.sub.2 --V.sub.2 O.sub.5 varistors proportioned as in TABLE 1, it has proved that if the proportion of the third ingredient, V.sub.2 O.sub.5, is less than about 0.01%, the material introduces considerable fluctuations in the varistor voltage E.sub.10 and nonlinearity coefficient α of the resulting products, making it difficult to provide varistors of desired properties. If the proportion of V.sub.2 O.sub.5 exceeds about 1%, on the other hand, the resistive oxide region 5 of FIG. 5 has proved to occupy an unduly large space, with the V.sub.2 O.sub.5 present at the surfaces causing fusion of the adjacent ceramic bodies to each other.
EXAMPLE 2 Ceramic bodies were fabricated from a combination of SrTiO.sub.3 as the first ingredient, WO.sub.3 as the second ingredient, and CrO.sub.3 as the third ingredient, and were processed into varistors, through exactly the same procedure as in EXAMPLE 1. TABLE 2 indicates the various sets of proportions of the three ingredients used to produce the ceramic bodies, together with the varistor voltage E.sub.10, voltage-current nonlinearity coefficient α, and electrostatic capacity C of the corresponding varistors. These properties of the varistors were also measured by the same method as in EXAMPLE 1.
TABLE 2______________________________________Test  Composition in percent                    PropertiesNo.   SrTiO.sub.3          WO.sub.3 CrO.sub.3                          E.sub.10, V                                 &#945;                                      C, nF______________________________________1     99.98    0.01     0.01   7      4    642     99.94    0.05     0.01   4      4    713     99.89    0.10     0.01   2      4    844     98.99    1.00     0.01   5      4    805     97.49    2.50     0.01   9      5    766     99.94    0.01     0.05   11     6    727     99.90    0.05     0.05   7      5    858     99.85    0.10     0.05   3      4    1019     98.95    1.00     0.05   9      5    9210    97.45    2.50     0.05   15     7    9011    99.89    0.01     0.10   17     7    6612    99.85    0.05     0.10   9      5    8013    99.80    0.10     0.10   5      4    10814    98.90    1.00     0.10   13     6    9915    97.40    2.50     0.10   22     8    8116    98.99    0.01     1.00   43     13   5317    98.95    0.05     1.00   25     8    6618    98.90    0.10     1.00   13     6    7319    98.00    1.00     1.00   33     10   6220    96.50    2.50     1.00   55     16   7021    97.99    0.01     2.00   55     15   4622    97.95    0.05     2.00   32     10   5923    97.90    0.10     2.00   15     7    6424    97.00    1.00     2.00   41     12   5925    95.50    2.50     2.00   74     22   57______________________________________
In the preparation of the ceramic bodies according to EXAMPLE 2 the oxidative heat treatment of the fired moldings converted the CrO.sub.3 into Cr.sub.2 O.sub.3. When the proportion of CrO.sub.3 was made less than about 0.01% the E.sub.10 and α of the resulting varistors fluctuated considerably. Also, when its proportion was made greater than about 2%, the relative space occupied by the resistive oxide region 5 became too large, and the Cr.sub.2 O.sub.3 at the surfaces of the moldings caused their adhesion to each other.
EXAMPLE 3 SrTiO.sub.3 was employed as the first ingredient, Nb.sub.2 O.sub.5 as the second ingredient, and Cuo as the third ingredient. Combined in various sets of proportions listed in TABLE 3, these ingredients were treated into ceramic bodies, and further into varistors, through exactly the same procedure as in EXAMPLE 1. TABLE 3 also shows the E.sub.10, and C of the varistors, as ascertained by the same method as in EXAMPLE 1.
TABLE 3______________________________________Test  Composition in percent                    PropertiesNo.   SrTiO.sub.3          Nb.sub.2 O.sub.5                   CuO    E.sub.10, V                                 &#945;                                      C, nF______________________________________1     99.98    0.01     0.01   10     5    802     99.94    0.05     0.01   5      5    813     99.89    0.10     0.01   3      4    964     98.99    1.00     0.01   6      5    625     97.49    2.50     0.01   13     6    766     99.94    0.01     0.05   11     6    997     99.90    0.05     0.05   6      5    1098     99.85    0.10     0.05   3      4    1169     98.95    1.00     0.05   7      5    10210    97.45    2.50     0.05   14     6    8911    99.89    0.01     0.10   12     6    7912    99.85    0.05     0.10   6      5    9313    99.80    0.10     0.10   4      4    10714    98.90    1.00     0.10   8      5    9315    97.40    2.50     0.10   16     7    8016    98.99    0.01     1.00   36     18   6617    98.95    0.05     1.00   18     8    7218    98.90    0.10     1.00   11     6    9019    98.00    1.00     1.00   22     9    8120    96.50    2.50     1.00   47     21   7721    94.99    0.01     5.00   73     30   5222    94.95    0.05     5.00   36     17   6123    94.90    0.10     5.00   23     9    7324    94.00    1.00     5.00   45     20   6225    92.50    2.50     5.00   95     37   61______________________________________
An inspection of TABLE 3 will show that the percentage of Nb.sub.2 O.sub.5 is fixed at 0.1 in some tests, while in others the percentage of CuO is fixed at 0.01. FIG. 4 graphically represents the curve of the E.sub.10 of those varistors whose Nb.sub.2 O.sub.5 content is fixed at 0.1%, plotted against the varying percentages of their CuO content. FIG. 5, on the other hand, plots the curve of the E.sub.10 of those varistors whose CuO content is fixed at 0.01%, against the varying percentages of their Nb.sub.2 O content.
A decrease of the CuO content to less than about 0.01% caused substantial fluctuations in the E.sub.10 and α of the resulting varistors. The CuO content of over 5%, on the other hand, made too large the relative space occupied by the resistive oxide region 5 of each varistor, and caused mutual adhesion of the adjacent ceramic moldings through the CuO lying at their surfaces.
EXAMPLE 4 Disc-like ceramic bodies were fabricated from SrTiO.sub.3 as the first ingredient, Dy.sub.2 O.sub.3 as the second ingredient, and Cu.sub.2 O as the third ingredient, in various sets of proportions, and were processed into varistors, through exactly the same procedure as in EXAMPLE 1. TABLE 4 represents the proportions of the three ingredients, as well as the E.sub.10, α, and C of the resulting varistors, as measured by the same method as in EXAMPLE 1.
TABLE 4______________________________________Test  Composition in percent                    PropertiesNo.   SrTiO.sub.3          Dy.sub.2 O.sub.3                   Cu.sub.2 O                          E.sub.10, V                                 &#945;                                      C, nF______________________________________1     99.98    0.01     0.01   7      4    572     99.94    0.05     0.01   4      4    633     99.89    0.10     0.01   2      4    734     98.99    1.00     0.01   5      4    705     97.49    2.50     0.01   9      5    516     99.94    0.01     0.05   11     6    687     99.90    0.05     0.05   7      5    748     99.85    0.10     0.05   3      4    899     98.95    1.00     0.05   9      5    6910    97.45    2.50     0.05   15     7    5811    99.89    0.01     0.10   17     7    5112    99.85    0.05     0.10   9      5    6713    99.80    0.10     0.10   5      4    7114    98.90    1.00     0.10   13     6    6315    97.40    2.50     0.10   22     8    5316    98.99    0.01     1.00   43     13   4717    98.95    0.05     1.00   25     8    5918    98.90    0.10     1.00   13     6    6319    98.00    1.00     1.00   33     10   5420    96.50    2.50     1.00   55     16   4721    97.99    0.01     2.00   55     15   3622    97.95    0.05     2.00   32     10   4823    97.90    0.10     2.00   15     7    5124    97.00    1.00     2.00   41     12   4225    95.50    2.50     2.00   73     22   30______________________________________
A decrease of the Cu.sub.2 O content to less than about 0.01% in the above combination caused substantial fluctuations in the E.sub.10 and α of the resulting varistors. When the Cu.sub.2 O content was made greater than about 2.5%, on the other hand, the resistive oxide region 5 occupied too large a space, causing the thermal fusion to each other of the adjacent ceramic moldings through the Cu.sub.2 O at their surfaces.
EXAMPLE 5 Ceramic discs were fabricated from SrTiO.sub.3 as the first ingredient, La.sub.2 O.sub.3 as the second ingredient, and MoO.sub.3 as the third ingredient, in various sets of proportions, and were processed into varistors, through exactly the same procedure as in EXAMPLE 1. TABLE 5 lists the proportions of the three ingredients, together with the E.sub.10, α, and C of the varistors made therefrom, as measured by the same method as in EXAMPLE 1. Experiment has proved that the MoO.sub.3 content of the ceramic materials in the above combination should be from about 0.01 to about 5.00%, for falling outside this range, MoO.sub.3 gave rise to the same difficulties as those pointed out in the foregoing EXAMPLES.
TABLE 5______________________________________Test  Composition in percent                    PropertiesNo.   SrTiO.sub.3          La.sub.2 O.sub.3                   MoO.sub.3                          E.sub.10, V                                 &#945;                                      C, nF______________________________________1     99.98    0.01     0.01   8      4    542     99.94    0.05     0.01   4      3    613     99.89    0.10     0.01   3      3    764     98.99    1.00     0.01   5      4    695     97.49    2.50     0.01   7      4    506     99.94    0.01     0.05   22     7    637     99.90    0.05     0.05   11     5    738     99.85    0.10     0.05   9      5    819     98.95    1.00     0.05   14     6    7010    97.45    2.50     0.05   20     7    5611    99.89    0.01     0.10   53     15   4912    99.85    0.05     0.10   28     9    6713    99.80    0.10     0.10   19     7    7014    98.90    1.00     0.10   36     11   5815    97.40    2.50     0.10   47     13   4816    98.99    0.01     1.00   53     15   4317    98.95    0.05     1.00   28     9    5118    98.90    0.10     1.00   19     7    6119    98.00    1.00     1.00   36     11   5420    96.50    2.50     1.00   47     13   4121    94.99    0.01     5.00   89     30   3022    94.95    0.05     5.00   46     13   4223    94.90    0.10     5.00   34     10   4824    94.00    1.00     5.00   57     17   4025    92.50    2.50     5.00   79     25   27______________________________________
EXAMPLE 6 Ceramic discs were fabricated from SrTiO.sub.3 as the first ingredient, Ta.sub.2 O.sub.5 as the second ingredient, and MnO.sub.2 as the third ingredient, in various combinations of proportions, and were processed into varistors, through exactly the same procedure as in EXAMPLE 1. TABLE 6 gives the proportions of the above three ingredients, together with the E.sub.10, and C of the varistors made therefrom, as measured by the same method as in EXAMPLE 1. It has also been found that the MnO.sub.2 content of the ceramic discs in the above combination, if outside the range of about 0.01-2.50%, gives rise to the difficulties mentioned previously.
TABLE 6______________________________________Test  Composition in percent                    PropertiesNo.   SrTiO.sub.3          Ta.sub.2 O.sub.5                   MnO.sub.2                          E.sub.10, V                                 &#945;                                      C, nF______________________________________1      99.985  0.005    0.01   9      5    632     99.94    0.05     0.01   4      4    713     99.49    0.50     0.01   2      3    814     98.99    1.00     0.01   5      4    735     97.49    2.50     0.01   8      5    616      99.945  0.005    0.05   16     7    687     99.90    0.05     0.05   7      5    798     99.45    0.50     0.05   4      4    969     98.95    1.00     0.05   9      5    8210    97.45    2.50     0.05   14     6    7711     99.895  0.005    0.10   23     8    7012    99.85    0.05     0.10   11     5    8613    99.40    0.50     0.10   7      5    10114    98.90    1.00     0.10   14     6    6015    97.40    2.50     0.10   21     7    5816     98.995  0.005    1.00   59     17   5417    98.95    0.05     1.00   27     10   7618    98.50    0.50     1.00   13     6    9019    98.00    1.00     1.00   34     10   6120    96.50    2.50     1.00   51     15   4921     97.495  0.005    2.50   91     32   4922    97.45    0.05     2.50   42     13   6123    97.00    0.50     2.50   21     8    7324    96.50    1.00     2.50   53     16   5425    95.00    2.50     2.50   83     27   44______________________________________
EXAMPLE 7 Ceramic discs were fabricated from SrTiO.sub.3 as the first ingredient, Sm.sub.2 O.sub.3 as the second ingredient, and CuO as the third ingredient, in various combinations of proportions, and were processed into varistors, through exactly the same procedure as in EXAMPLE 1. TABLE 7 lists the proportions of the above three ingredients, together with the E.sub.10, α, and C of the varistors made therefrom, as measured by the same method as in EXAMPLE 1.
TABLE 7______________________________________Test  Composition in percent                    PropertiesNo.   SrTiO.sub.3          Sm.sub.2 O.sub.3                   CuO    E.sub.10, V                                 &#945;                                      C, nF______________________________________1     99.98    0.01     0.01   8      5    542     99.94    0.05     0.01   4      4    633     99.89    0.10     0.01   3      4    724     98.99    1.00     0.01   6      4    695     96.99    3.00     0.01   10     5    606     99.94    0.01     0.05   12     6    467     99.90    0.05     0.05   6      5    728     99.85    0.10     0.05   4      4    819     98.95    1.00     0.05   9      5    8610    96.95    3.00     0.05   14     6    6311    99.89    0.01     0.10   18     7    4112    99.85    0.05     0.10   9      5    6513    99.80    0.10     0.10   7      5    7314    98.90    1.00     0.10   13     6    7015    96.90    3.00     0.10   22     8    5916    98.99    0.01     1.00   43     12   3717    98.95    0.05     1.00   19     7    5318    98.90    0.10     1.00   16     7    6119    98.00    1.00     1.00   29     8    7220    96.00    3.00     1.00   48     13   4221    94.99    0.01     5.00   71     23   4022    94.95    0.05     5.00   35     11   4923    94.90    0.10     5.00   28     9    6024    94.00    1.00     5.00   51     15   5425    92.00    3.00     5.00   93     31   39______________________________________
EXAMPLE 8 Ceramic discs were fabricated from SrTiO.sub.3 as the first ingredient, Pr.sub.6 O.sub.11 as the second ingredient, and MnO.sub.2 as the third ingredient, in various combinations of proportions, and were processed into varistors, through exactly the same procedure as in EXAMPLE 1. TABLE 8 lists the proportions of the above three ingredients, together with the E.sub.10, α, and C of the varistors made therefrom, as measured by the same method as in EXAMPLE 1.
TABLE 8______________________________________Test  Composition in percent                    PropertiesNo.   SrTiO.sub.3          Pr.sub.6 O.sub.11                   MnO.sub.2                          E.sub.10, V                                 &#945;                                      C, nF______________________________________1      99.989  0.001    0.01   10     5    682     99.98    0.01     0.01   5      4    713     99.89    0.10     0.01   2      4    844     98.99    1.00     0.01   6      5    765     97.49    2.50     0.01   11     6    706      99.949  0.001    0.05   15     6    747     99.94    0.01     0.05   7      5    778     99.85    0.10     0.05   3      4    919     98.95    1.00     0.05   9      5    8310    97.45    2.50     0.05   17     7    7711     99.899  0.001    0.10   22     8    6012    99.89    0.01     0.10   11     6    6813    99.80    0.10     0.10   5      5    8214    98.90    1.00     0.10   13     6    7115    97.40    2.50     0.10   24     8    6916     98.999  0.001    1.00   48     12   5117    98.99    0.01     1.00   24     8    5318    98.90    0.10     1.00   9      5    7619    98.00    1.00     1.00   29     9    6320    96.50    2.50     1.00   52     15   6121     97.499  0.001    2.50   88     24   2922    97.49    0.01     2.50   43     11   4423    97.40    0.10     2.50   17     7    5424    96.50    1.00     2.50   43     13   5025    95.00    2.50     2.50   97     31   42______________________________________
EXAMPLE 9 Ceramic discs were fabricated from SrTiO.sub.2 as the first ingredient, Nd.sub.2 O.sub.3 as the second ingredient, and CrO.sub.3 as the third ingredient, in various combinations of proportions, and were processed into varistors, through exactly the same procedure as in EXAMPLE 1. TABLE 9 lists the proportions of the above three ingredients, together with the E.sub.10, α, and C of the varistors made therefrom, as measured by the same method as in EXAMPLE 1. In the preparation of of the ceramic discs according to this EXAMPLE 9 the oxidative heat treatment of the fired moldings converted the CrO.sub.3 into Cr.sub.2 O.sub.3.
TABLE 9______________________________________Test  Composition in percent                    PropertiesNo.   SrTiO.sub.3          Nd.sub.2 O.sub.3                   CrO.sub.3                          E.sub.10, V                                 &#945;                                      C, nF______________________________________1     99.98    0.01     0.01   7      5    662     99.94    0.05     0.01   3      4    693     99.89    0.10     0.01   2      4    774     98.99    1.00     0.01   5      5    715     95.99    4.00     0.01   11     6    636     99.94    0.01     0.05   10     6    697     99.90    0.05     0.05   4      4    788     99.85    0.10     0.05   4      4    889     98.95    1.00     0.05   7      5    7610    95.95    4.00     0.05   17     7    6911    99.89    0.01     0.10   15     7    6512    99.85    0.05     0.10   7      5    7113    99.80    0.10     0.10   5      4    7614    98.90    1.00     0.10   12     6    7015    95.90    4.00     0.10   23     8    6116    98.99    0.01     1.00   34     10   6017    98.95    0.05     1.00   15     6    6218    98.90    0.10     1.00   10     5    6119    98.00    1.00     1.00   25     8    6020    95.00    4.00     1.00   54     15   5921    97.99    0.01     2.00   60     18   5122    97.95    0.05     2.00   25     8    5123    97.90    0.10     2.00   17     7    5224    97.00    1.00     2.00   43     12   5125    94.00    4.00     2.00   94     30   50______________________________________
EXAMPLE 10 Ceramic discs were fabricated from SrTiO.sub.3 as the first ingredient, Y.sub.2 O.sub.3 as the second ingredient, and MoO.sub.3 as the third ingredient, in various combinations of proportions, and were processed into varistors, through exactly the same procedure as in EXAMPLE 1. TABLE 10 lists the proportions of the above three ingredients, together with the E.sub.10, α, and C of the varistors made therefrom, as measured by the same method as in EXAMPLE 1.
TABLE 10______________________________________Test  Composition in percent                    PropertiesNo.   SrTiO.sub.3          Y.sub.2 O.sub.3                   MoO.sub.3                          E.sub.10, V                                 &#945;                                      C, nF______________________________________1     99.98    0.01     0.01   8      5    422     99.94    0.05     0.01   3      4    503     99.89    0.10     0.01   2      4    614     98.99    1.00     0.01   5      4    525     95.99    4.00     0.01   12     6    466     99.94    0.01     0.05   12     6    467     99.90    0.05     0.05   4      4    638     99.85    0.10     0.05   3      4    749     98.95    1.00     0.05   7      5    6610    95.95    4.00     0.05   18     7    5211    99.89    0.01     0.10   18     7    4112    99.85    0.05     0.10   7      5    5113    99.80    0.10     0.10   5      4    6314    98.90    1.00     0.10   11     6    5715    95.90    4.00     0.10   25     8    4116    98.99    0.01     1.00   38     11   3317    98.95    0.05     1.00   15     7    4918    98.90    0.10     1.00   9      6    6119    98.00    1.00     1.00   24     8    4120    95.00    4.00     1.00   57     16   3621    94.99    0.01     5.00   70     21   1922    94.95    0.05     5.00   27     8    3223    94.90    0.10     5.00   17     7    4324    94.00    1.00     5.00   43     13   3325    91.00    4.00     5.00   99     29   21______________________________________
EXAMPLE 11 This EXAMPLE is intended for the confirmation of the fact that the use of two different metal oxides as the second set of ingredients, in combination with the first and third ingredients chosen in accordance with the invention, makes the resulting ceramic materials as suitable for varistors as those containing but one second ingredient. The following combinations of two different metal oxides were tested as the second sets of ingredients, together with SrTiO.sub.3 as the first ingredient and CuO as the third ingredient: Nb.sub.2 O.sub.5 and Ta.sub.2 O.sub.5, Nb.sub.2 O.sub.5 and WO.sub.3, Nb.sub.2 O.sub.5 and La.sub.2 O.sub.3, Nb.sub.2 O.sub.5 and CeO.sub.2, Nb.sub.2 O.sub.5 and Dy.sub.2 O.sub.3, La.sub.2 O.sub.5 and Ta.sub.2 O.sub.5, La.sub.2 O.sub.3 and WO.sub.3, La.sub.2 O.sub.3 and CeO.sub.2, La.sub.2 O.sub.3 and Nd.sub.2 O.sub.3, and La.sub.2 O.sub.3 and Sm.sub.2 O.sub.3.
Ceramic discs were fabricated from the combinations of the above enumerated components, in various sets of proportions, and were processed into varistors, through exactly the same procedure as in EXAMPLE 1. TABLES 11A through 11J represent the proportions of the respective combinations of components, as well as the E.sub.10, α, and C of the varistors prepared therefrom, as measured by the same method as in EXAMPLE 1. It will be noted from these tables that the ceramic compositions of this EXAMPLE 11 are as suitable for varistors as those of EXAMPLES 1 through 10.
TABLE 11A______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 Ta.sub.2 O.sub.5                       CuO   E.sub.10, V                                   &#945;                                        C, nF______________________________________1     99.4    0.02    0.08  0.5   12    5    712     99.4    0.05    0.05  0.5   13    6    683     99.4    0.08    0.02  0.5   13    6    67______________________________________
TABLE 11B______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 WO.sub.3                       CuO   E.sub.10, V                                   &#945;                                        C, nF______________________________________4     99.4    0.02    0.08  0.5   14    6    665     99.4    0.05    0.05  0.5   13    6    656     99.4    0.08    0.02  0.5   14    6    67______________________________________
TABLE 11C______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 La.sub.2 O.sub.3                       CuO   E.sub.10, V                                   &#945;                                        C, nF______________________________________7     99.4    0.02    0.08  0.5   9     5    798     99.4    0.05    0.05  0.5   8     5    839     99.4    0.08    0.02  0.5   8     5    86______________________________________
TABLE 11D______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 CeO.sub.2                       CuO   E.sub.10, V                                   &#945;                                        C, nF______________________________________10    99.4    0.02    0.08  0.5   7     5    8911    99.4    0.05    0.05  0.5   8     5    9112    99.4    0.08    0.02  0.5   7     5    90______________________________________
TABLE 11E______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 Dy.sub.2 O.sub.3                       CuO   E.sub.10, V                                   &#945;                                        C, nF______________________________________13    99.4    0.02    0.08  0.5   7     5    8714    99.4    0.05    0.05  0.5   7     5    8915    99.4    0.08    0.02  0.5   6     4    93______________________________________
TABLE 11F______________________________________ Test Composition in percent                     PropertiesNo.   SrTiO.sub.3         La.sub.2 O.sub.3                 Ta.sub.2 O.sub.5                       CuO   E.sub.10, V                                   &#945;                                        C, nF______________________________________16    99.4    0.02    0.08  0.5   10    5    7617    99.4    0.05    0.05  0.5   11    5    7318    99.4    0.08    0.02  0.5   10    5    77______________________________________
TABLE 11G______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         La.sub.2 O.sub.3                 WO.sub.3                       CuO   E.sub.10, V                                   &#945;                                        C, nF______________________________________19    99.4    0.02    0.08  0.5   11    5    7020    99.4    0.05    0.05  0.5   12    5    6521    99.4    0.08    0.02  0.5   10    5    74______________________________________
TABLE 11H______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         La.sub.2 O.sub.3                 CeO.sub.2                       CuO   E.sub.10, V                                   &#945;                                        C, nF______________________________________22    99.4    0.02    0.08  0.5   7     4    8423    99.4    0.05    0.05  0.5   7     5    8324    99.4    0.08    0.02  0.5   8     5    79______________________________________
TABLE 11I______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         La.sub.2 O.sub.3                 Nd.sub.2 O.sub.3                       CuO   E.sub.10, V                                   &#945;                                        C, nF______________________________________25    99.4    0.02    0.08  0.5   6     4    9226    99.4    0.05    0.05  0.5   7     4    8627    99.4    0.08    0.02  0.5   7     4    83______________________________________
TABLE 11J______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         La.sub.2 O.sub.3                 Sm.sub.2 O.sub.3                       CuO   E.sub.10, V                                   &#945;                                        C, nF______________________________________28    99.4    0.02    0.08  0.5   8     5    8329    99.4    0.05    0.05  0.5   7     4    9030    99.4    0.08    0.02  0.5   7     5    87______________________________________
EXAMPLE 12 This EXAMPLE is intended to prove that ceramic materials suitable for varistors can be fabricated with the use of two different metal oxides as the third set of ingredients, in combination with the first and second ingredients chosen in accordance with the invention. The following combinations of two different metal oxides were tested as the second sets of ingredients, together with SrTiO.sub.3 as the first ingredient and Nb.sub.2 O.sub.5, WO.sub.3 or La.sub.2 O.sub.3 as the second ingredient: CuO and Cu.sub.2 O, CuO and MoO.sub.3, MoO.sub.3 and V.sub.2 O.sub.5, V.sub.2 O.sub.5 and CrO.sub.3, and CrO.sub.3 and Cu.sub.2 O.
Ceramic bodies were fabricated from the various combinations of four of the listed ingredients, in various sets of proportions, and were processed into varistors, through exactly the same procedure as in EXAMPLE 1. TABLES 12A through 12-O represent the proportions of such combinations of ingredients, as well as the E.sub.10, α, and C of the varistors prepared therefrom, as measured by the same method as in EXAMPLE 1. The tabulated results indicate that the ceramic composition of this EXAMPLE 12 are as suitable for varistors as those of EXAMPLES 1 through 10.
TABLE 12A______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 CuO   Cu.sub.2 O                             E.sub.10, V                                   &#945;                                        C, nF______________________________________1     99.4    0.1     0.1   0.4   11    5    692     99.4    0.1     0.25  0.25  10    5    723     99.4    0.1     0.4   0.1   11    5    68______________________________________
TABLE 12B______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 CuO   MoO.sub.3                             E.sub.10, V                                   &#945;                                        C, nF______________________________________4     99.4    0.1     0.1   0.4   12    5    685     99.4    0.1     0.25  0.25  11    5    706     99.4    0.1     0.4   0.1   10    5    73______________________________________
TABLE 12C______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 MoO.sub.3                       V.sub.2 O.sub.5                             E.sub.10, V                                   &#945;                                        C, nF______________________________________7     99.4    0.1     0.1   0.4   13    5    628     99.4    0.1     0.25  0.25  15    6    599     99.4    0.1     0.4   0.1   15    6    59______________________________________
TABLE 12D______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 V.sub.2 O.sub.5                       CrO.sub.3                             E.sub.10, V                                   &#945;                                        C, nF______________________________________10    99.4    0.1     0.1   0.4   15    6    6011    99.4    0.1     0.25  0.25  14    5    6212    99.4    0.1     0.4   0.1   13    5    67______________________________________
TABLE 12E______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 CrO.sub.3                       Cu.sub.2 O                             E.sub.10, V                                   &#945;                                        C, nF______________________________________13    99.4    0.1     0.1   0.4   10    5    7214    99.4    0.1     0.25  0.25   9    5    7615    99.4    0.1     0.4   0.1   12    5    67______________________________________
TABLE 12F______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         WO.sub.3                 CuO   Cu.sub.2 O                             E.sub.10, V                                   &#945;                                        C, nF______________________________________16    99.4    0.1     0.1   0.4   12    5    6517    99.4    0.1     0.25  0.25  13    6    6218    99.4    0.1     0.4   0.1   13    5    63______________________________________
TABLE 12G______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         WO.sub.3                 CuO   MoO.sub.3                             E.sub.10, V                                   &#945;                                        C, nF______________________________________19    99.4    0.1     0.1   0.4   13    5    6220    99.4    0.1     0.25  0.25  15    5    5921    99.4    0.1     0.4   0.1   15    6    57______________________________________
TABLE 12H______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         WO.sub.3                 MoO.sub.3                       V.sub.2 O.sub.5                             E.sub.10, V                                   &#945;                                        C, nF______________________________________22    99.4    0.1     0.1   0.4   14    5    6023    99.4    0.1     0.25  0.25  16    6    5524    99.4    0.1     0.4   0.1   15    6    59______________________________________
TABLE 12I______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         WO.sub.3                 V.sub.2 O.sub.5                       CrO.sub.3                             E.sub.10, V                                   &#945;                                        C, nF______________________________________25    99.4    0.1     0.1   0.4   16    6    5526    99.4    0.1     0.25  0.25  16    6    5427    99.4    0.1     0.4   0.1   13    5    62______________________________________
TABLE 12J______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         WO.sub.3                 CrO.sub.3                       Cu.sub.2 O                             E.sub.10, V                                   &#945;                                        C, nF______________________________________28    99.4    0.1     0.1   0.4   10    5    7129    99.4    0.1     0.25  0.25  12    5    6630    99.4    0.1     0.4   0.1   12    5    65______________________________________
TABLE 12K______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         La.sub.2 O.sub.3                 CuO   Cu.sub.2 O                             E.sub.10, V                                   &#945;                                        C, nF______________________________________31    99.4    0.1     0.1   0.4   8     5    7732    99.4    0.1     0.25  0.25  7     5    8133    99.4    0.1     0.4   0.1   7     5    82______________________________________
TABLE 12L______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         La.sub.2 O.sub.3                 CuO   MoO.sub.3                             E.sub.10, V                                   &#945;                                        C, nF______________________________________34    99.4    0.1     0.1   0.4   7     5    8235    99.4    0.1     0.25  0.25  7     5    8336    99.4    0.1     0.4   0.1   8     5    80______________________________________
TABLE 12M______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         La.sub.2 O.sub.3                 MoO.sub.3                       V.sub.2 O.sub.5                             E.sub.10, V                                   &#945;                                        C, nF______________________________________37    99.4    0.1     0.1   0.4   9     5    7638    99.4    0.1     0.25  0.25  9     5    7239    99.4    0.1     0.4   0.1   10    5    69______________________________________
TABLE 12N______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         La.sub.2 O.sub.3                 V.sub.2 O.sub.5                       CrO.sub.3                             E.sub.10, V                                   &#945;                                        C, nF______________________________________40    99.4    0.1     0.1   0.4   10    5    6841    99.4    0.1     0.25  0.25  9     5    7242    99.4    0.1     0.4   0.1   8     5    81______________________________________
TABLE 12-O______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         La.sub.2 O.sub.3                 CrO.sub.3                       Cu.sub.2 O                             E.sub.10, V                                   &#945;                                        C, nF______________________________________43    99.4    0.1     0.1   0.4   7     4    8244    99.4    0.1     0.25  0.25  6     4    8545    99.4    0.1     0.4   0.1   7     5    83______________________________________
EXAMPLE 13 In order to ascertain the relationship between the temperatures of the oxidative heat treatment during the fabrication of ceramic materials and the properties of the varistors made therefrom, the temperature of the oxidative heat treatment was set in this EXAMPLE at various values from 700 combinations of SrTiO.sub.3, Nb.sub.2 O.sub.5 and CuO, of SrTiO.sub.3, Dy.sub.2 O.sub.3 and Cu.sub.2 O, of SrTiO.sub.3, CeO and V.sub.2 O.sub.5, of SrTiO.sub.3, WO.sub.3 and CrO.sub.3, of SrTiO.sub.3, Y.sub.2 O.sub.3 and MoO.sub.3, and of SrTiO.sub.3, Ta.sub.2 O.sub.5 and MnO.sub.2, in various sets of proportions, and were processed into varistors in a manner identical in other respects with that of EXAMPLE 1. TABLES 13A through 13F give the proportions of such combinations of ingredients, as well as the temperatures of the oxidative heat treatment, the resistivities of the ceramic bodies, and of the varistors made therefrom. The resistivity was measured by the four-probe method at a temperature of 25
TABLE 13A______________________________________          Temperature of                    PropertiesTest Composition in percent                oxidative heat                            Resistivity,No.  SrTiO.sub.3        Nb.sub.2 O.sub.5                CuO   treatment,                                 ohm-cm  &#945;______________________________________1    99.0    0.5     0.5    700      .sup. 5                                          12    99.0    0.5     0.5    800      3                                          23    99.0    0.5     0.5    900      1                                          44    99.0    0.5     0.5   1000      5                                         135    99.0    0.5     0.5   1100      8                                         266    99.0    0.5     0.5   1170      2                                         61______________________________________
TABLE 13B______________________________________          Temperature of                    PropertiesTest Composition in percent                oxidative heat                            Resistivity,No.  SrTiO.sub.3        Dy.sub.2 O.sub.3                Cu.sub.2 O                      treatment,                                 ohm-cm  &#945;______________________________________ 7   99.0    0.5     0.5    700      .sup. 6                                          1 8   99.0    0.5     0.5    800      4                                          2 9   99.0    0.5     0.5    900      1                                          410   99.0    0.5     0.5   1000      5                                         1211   99.0    0.5     0.5   1100      9                                         2912   99.0    0.5     0.5   1170      3                                         69______________________________________
TABLE 13C______________________________________          Temperature of                    PropertiesTest Position in percent                oxidative heat                            Resistivity,No.  SrTiO.sub.3        CeO.sub.2                V.sub.2 O.sub.5                      treatment,                                 ohm-cm  &#945;______________________________________13   99.0    0.5     0.5    700      .sup. 8                                          114   99.0    0.5     0.5    800      6                                          215   99.0    0.5     0.5    900      2                                          416   99.0    0.5     0.5   1000      7                                         1517   99.0    0.5     0.5   1100      10                                         3118   99.0    0.5     0.5   1170      5                                         84______________________________________
TABLE 13D______________________________________          Temperature of                    PropertiesTest Composition in percent                oxidative heat                            Resistivity,No.  SrTiO.sub.3        WO.sub.3                CrO.sub.3                      treatment,                                 ohm-cm  &#945;______________________________________19   99.0    0.5     0.5    700      .sup. 6                                          120   99.0    0.5     0.5    800      6                                          221   99.0    0.5     0.5    900      1                                          422   99.0    0.5     0.5   1000      6                                         1323   99.0    0.5     0.5   1100      8                                         3024   99.0    0.5     0.5   1170      3                                         70______________________________________
TABLE 13E______________________________________          Temperature of                    PropertiesTest Composition in percent                oxidative heat                            Resistivity,No.  SrTiO.sub.3        Y.sub.2 O.sub.3                MoO.sub.3                      treatment,                                 ohm-cm  &#945;______________________________________25   99.0    0.5     0.5    700      .sup. 7                                          126   99.0    0.5     0.5    800      7                                          227   99.0    0.5     0.5    900      2                                          428   99.0    0.5     0.5   1000      7                                         1629   99.0    0.5     0.5   1100      11                                         3330   99.0    0.5     0.5   1170      5                                         86______________________________________
TABLE 13F______________________________________          Temperature of                    PropertiesTest Composition in percent                oxidative heat                            Resistivity,No.  SrTiO.sub.3        Ta.sub.2 O.sub.5                MnO.sub.2                      treatment,                                 ohm-cm  &#945;______________________________________31   99.0    0.5     0.5    700      .sup. 6                                          132   99.0    0.5     0.5    800      4                                          233   99.0    0.5     0.5    900      1                                          434   99.0    0.5     0.5   1000      6                                         1235   99.0    0.5     0.5   1100      9                                         3136   99.0    0.5     0.5   1170      3                                         63______________________________________
On the basis of the data given in TABLE 13A, FIG. 6 plots the curve of the α of the SrTiO.sub.3 --Nb.sub.2 O.sub.5 --CuO varistors against the temperature of the oxidative heat treatment. This graph makes clear that the α of the varistors can be controlled by the temperature of the oxidative heat treatment during the fabrication of the ceramic bodies. It will also be seen from TABLES 13A through 13F that the resistivity of the ceramic bodies varies with the temperature of the oxidative heat treatment. For the provision of varistors of the desired characteristics, therefore, the oxidative heat treatment should be conducted in a temperature range of about 800 temperature be less than about 800 bodies would become too small for varistors. If the temperature were made higher than about 1300 of the ceramic bodies would become too high for varistors.
EXAMPLE 14 Ceramic discs were fabricated from various combinations of three possible ingredients set forth in TABLE 14, in like proportions, and were processed into varistors, through a procedure similar to that of EXAMPLE 1. In order to evaluate the pulse-withstanding abilities of these varistors, 10 voltage pulses of 100 V were successively applied to each varistor, and a rate of change in E.sub.10 before and after the pulse application was calculated. TABLE 14 summarizes the results.
TABLE 14______________________________________Composition First      Second     Third    Rate ofTest  ingredient ingredient ingredient                                change inNo.   99.4%      0.1%       0.5%     E.sub.10, %______________________________________1     SrTiO.sub.3            Nb.sub.2 O.sub.5                       CuO      0.032     SrTiO.sub.3            WO.sub.3   CrO.sub.3                                0.023     SrTiO.sub.3            Ta.sub.2 O.sub.5                       MnO.sub.2                                0.034     SrTiO.sub.3            Y.sub.2 O.sub.3                       MoO.sub.3                                0.065     SrTiO.sub.3            Sm.sub.2 O.sub.3                       CuO      0.046     SrTiO.sub.3            CeO.sub.2  V.sub.2 O.sub.5                                0.047     SrTiO.sub.3            Pr.sub.6 O.sub.11                       MnO.sub.2                                0.068     SrTiO.sub.3            Nd.sub.2 O.sub.3                       CrO.sub.3                                0.059     SrTiO.sub.3            Dy.sub.2 O.sub.3                       Cu.sub.2 O                                0.0510    SrTiO.sub.3            La.sub.2 O.sub.3                       MoO.sub.3                                0.06______________________________________
It will be observed from TABLE 14 that the E.sub.10 of the various varistors in accordance with the invention varies only from 0.02 to 0.06% before and after the application of ten 100-volt pulses in succession. The rate of change in E.sub.10 of the conventional ZnO varistors, measured by a like method by way of comparison, was in the range of 15-20%. The little change in E.sub.10 of the varistors in accordance with the invention evidences that they hardly suffer from voltage surges in use.
The above presented EXAMPLES 1 through 14 prove that the second ingredient should be used in a proportion of about 0.001-5.000% in any combination with first and second ingredients in the manufacture of ceramic materials in accordance with the invention. Intended as an additive for making the materials semiconductive, the second ingredient when used in that range makes the size of the crystal grains from about 20 to 40 micrometers in diameter and does not make the E.sub.10 too high. Should the content of the second ingredient fall outside the specified range, the grain size would become too large, and the E.sub.10 too high, to provide favorable semiconductor materials and favorable varistors. The proportion of the second ingredient should be in a range of 0.05-1.00% to obtain appropriate values of E.sub.10.
Intended as an additive for improving the nonlinear volt-ampere characteristic of the ceramic materials, the third ingredient should be used in an amount ranging from about 0.01 to about 5.00%. If the content of the third ingredient were less than about 0.01%, the E.sub.10, α, etc., of ceramic bodies would fluctuate considerably, making it difficult to provide varistors of desired performance characteristics. If it were greater than about 5.00%, on the other hand, then the resistive oxide region 5, in FIG. 1, of each ceramic body would occupy too large a space in relation to the crystal grains 4, and the third ingredient at the surfaces of the ceramic bodies would cause their mutual adhesion during firing or would flow over the surfaces. Too great a proportion of the third ingredient would also result in an unduly high value of E.sub.10. A preferred range of the proportion of the third ingredient is from about 0.05 to about 1.00%.
EXAMPLE 15 While all the foregoing EXAMPLES dealt with the ceramic compositions of the first, second and third ingredients, the present EXAMPLE introduces a fourth ingredient with a view to the higher coherency of the ceramic bodies. The particular fourth ingredient herein employed was GeO.sub.2, in combination with SrTiO.sub.3 as the first ingredient, Nb.sub.2 O.sub.5 as the second ingredient, and CuO as the third ingredient, and in various sets of proportions presented in TABLE 15. These ingredients were processed into ceramic discs, and further into varistors, through the same procedure as in EXAMPLE 1 except that GeO.sub.2 was used as the fourth ingredient and that the oxidative heat treatment of the fired bodies was performed at a temperature of 1000 E.sub.10, α, and C of the varistors manufactured as above.
As is apparent from the tabulated results, the varistors containing the fourth ingredient have properties similar to those of the varistors having no fourth ingredient. The addition of GeO.sub.2 as the fourth ingredient, however, made more uniform the size of the ceramic particles, which ranged from 20 to 40 micrometers, thereby serving to reduce fluctuations in the E.sub.10 and α of the varistors.
TABLE 15______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 CuO   GeO.sub.2                             E.sub.10, V                                   &#945;                                        C, nF______________________________________1     99.48   0.01    0.01  0.5   8     5    1012     99.44   0.05    0.01  0.5   3     4    1073     99.39   0.10    0.01  0.5   2     4    1204     98.49   1.00    0.01  0.5   6     5    1015     96.99   2.50    0.01  0.5   11    5    966     99.44   0.01    0.05  0.5   9     5    977     99.40   0.05    0.05  0.5   3     4    1018     99.35   0.10    0.05  0.5   2     4    1169     98.45   1.00    0.05  0.5   7     5    9910    96.95   2.50    0.05  0.5   12    5    9511    99.39   0.01    0.10  0.5   10    6    8912    99.35   0.05    0.10  0.5   4     4    10013    99.30   0.10    0.10  0.5   3     4    11714    98.40   1.00    0.10  0.5   8     6    9215    96.90   2.50    0.10  0.5   14    7    8616    98.49   0.01    1.00  0.5   18    8    8217    98.45   0.05    1.00  0.5   10    6    9218    98.40   0.10    1.00  0.5   7     6    10519    97.50   1.00    1.00  0.5   14    8    8520    96.00   2.50    1.00  0.5   33    11   6121    94.49   0.01    5.00  0.5   35    12   6622    94.45   0.05    5.00  0.5   24    9    7923    94.40   0.10    5.00  0.5   16    8    9124    93.50   1.00    5.00  0.5   26    10   7625    92.00   2.50    5.00  0.5   89    32   33______________________________________
EXAMPLE 16 SrTiO.sub.3 as the first ingredient was combined with Nb.sub.2 O.sub.5 as the second ingredient, Cu.sub.2 O as the third ingredient, and GeO.sub.2 as the fourth ingredient. In various sets of proportions these ingredients were processed into ceramic discs, and further into varistors, through the same procedure as in EXAMPLE 1 except that the temperature of the oxidative heat treatment was 1000 proportions of the above four ingredients, together with the E.sub.10, α, and C of the varistors made therefrom, as measured by the same method as in EXAMPLE 1.
TABLE 16______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 Cu.sub.2 O.sub.5                       GeO.sub.2                             E.sub.10, V                                   &#945;                                        C, nF______________________________________1     99.48   0.01    0.01  0.5   9     4    762     99.44   0.05    0.01  0.5   4     4    873     99.39   0.10    0.01  0.5   2     4    984     98.49   1.00    0.01  0.5   5     4    865     96.99   2.50    0.01  0.5   14    6    716     99.44   0.01    0.05  0.5   10    5    757     99.40   0.05    0.05  0.5   4     4    838     99.35   0.10    0.05  0.5   2     4    1009     98.45   1.00    0.05  0.5   6     4    8110    96.95   2.50    0.05  0.5   16    7    7311    99.39   0.01    0.10  0.5   12    6    7212    99.35   0.05    0.10  0.5   5     5    8113    99.30   0.10    0.10  0.5   3     4    9214    98.40   1.00    0.10  0.5   6     4    8215    96.90   2.50    0.10  0.5   17    8    6216    98.49   0.01    1.00  0.5   33    11   6117    98.45   0.05    1.00  0.5   14    7    7418    98.40   0.10    1.00  0.5   7     5    8219    97.50   1.00    1.00  0.5   18    8    6320    96.00   2.50    1.00  0.5   49    15   4321    96.99   0.01    2.50  0.5   65    21   3622    96.95   0.05    2.50  0.5   29    10   5123    96.90   0.10    2.50  0.5   15    7    7724    96.00   1.00    2.50  0.5   36    10   5125    94.50   2.50    2.50  0.5   95    34   39______________________________________
EXAMPLE 17 SrTiO.sub.3 as the first ingredient was combined with Nb.sub.2 O.sub.5 as the second ingredient, V.sub.2 O.sub.5 as the third ingredient, and GeO.sub.2 as the fourth ingredient. In various sets of of proportions these ingredients were processed into ceramic disc, and further into varistors, through the same procedure as in EXAMPLE 1 except that the temperature of the oxidative heat treatment was 1000 lists the proportions of the above four ingredients, together with the E.sub.10, α, and C of the varistors made therefrom, as measured by the same method as in EXAMPLE 1.
TABLE 17______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 V.sub.2 O.sub.5                       GeO.sub.2                             E.sub.10, V                                   &#945;                                        C, nF______________________________________1     99.48   0.01    0.01  0.5   4     4    882     99.44   0.05    0.01  0.5   2     4    933     99.39   0.10    0.01  0.5   2     4    914     98.49   1.00    0.01  0.5   4     4    875     96.99   2.50    0.01  0.5   8     5    726     99.44   0.01    0.05  0.5   5     4    837     99.40   0.05    0.05  0.5   3     4    828     99.35   0.10    0.05  0.5   2     4    899     98.45   1.00    0.05  0.5   5     4    7910    96.95   2.50    0.05  0.5   10    5    6311    99.39   0.01    0.1   0.5   6     5    8112    99.35   0.05    0.1   0.5   3     4    8013    99.30   0.10    0.1   0.5   3     4    8114    98.40   1.00    0.1   0.5   7     4    6615    96.90   2.50    0.1   0.5   13    6    5116    98.99   0.01    0.50  0.5   12    6    7017    98.95   0.05    0.50  0.5   6     4    7618    98.90   0.10    0.50  0.5   5     4    8219    98.00   1.00    0.50  0.5   13    6    4920    96.50   2.50    0.50  0.5   25    8    4221    98.49   0.01    1.00  0.5   17    8    5022    98.45   0.05    1.00  0.5   9     5    7523    98.40   0.10    1.00  0.5   7     4    8024    97.50   1.00    1.00  0.5   19    8    4425    96.00   2.50    1.00  0.5   38    13   26______________________________________
EXAMPLE 18 SrTiO.sub.3 as the first ingredient was combined with Nb.sub.2 O.sub.5 as the second ingredient, CrO.sub.3 as the third ingredient, and GeO.sub.2 as the fourth ingredient. In various sets of proportions these ingredients were processed into ceramic discs, and further into varistors, through the same procedure as in EXAMPLE 1 except that the temperature of the oxidative heat treatment was 1000 proportions of the above four ingredients, together with the E.sub.10, α, and C of the varistors made therefrom, as measured by the same method as in EXAMPLE 1.
TABLE 18______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 CrO.sub.3                       GeO.sub.2                             E.sub.10, V                                   &#945;                                        C, nF______________________________________1     99.48   0.01    0.01  0.5   8     5    612     99.44   0.05    0.01  0.5   3     4    773     99.39   0.10    0.01  0.5   2     4    764     98.49   1.00    0.01  0.5   7     5    605     96.99   2.50    0.01  0.5   14    6    526     99.44   0.01    0.05  0.5   9     5    607     99.40   0.05    0.05  0.5   3     4    768     99.35   0.10    0.05  0.5   2     4    719     98.45   1.00    0.05  0.5   8     5    6110    96.95   2.50    0.05  0.5   15    7    5011    99.39   0.01    0.10  0.5   10    6    6112    99.35   0.05    0.10  0.5   4     4    7213    99.30   0.10    0.10  0.5   3     4    7314    98.40   1.00    0.10  0.5   9     6    5215    96.90   2.50    0.10  0.5   18    7    4316    98.49   0.01    1.00  0.5   32    11   3517    98.45   0.05    1.00  0.5   12    5    6218    98.40   0.10    1.00  0.5   8     5    6419    97.50   1.00    1.00  0.5   28    10   3620    96.00   2.50    1.00  0.5   57    17   3221    97.49   0.01    2.00  0.5   48    15   2822    97.45   0.05    2.00  0.5   18    7    4223    97.40   0.10    2.00  0.5   12    6    6124    96.50   1.00    2.00  0.5   45    14   2925    95.00   2.50    2.00  0.5   91    33   21______________________________________
EXAMPLE 19 SrTiO.sub.3 as the first ingredient was combined with Nb.sub.2 O.sub.5 as the second ingredient, MoO.sub.3 as the third ingredient, and GeO.sub.2 as the fourth ingredient. In various sets of proportions these ingredients were processed into ceramic discs, and further into varistors, through the same procedure as in EXAMPLE 1 except that the temperature of the oxidative heat treatment was 1000 proportions of the above four ingredients, together with the E.sub.10, α, and C of the varistors made therefrom, as measured by the same method as in EXAMPLE 1.
TABLE 19______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 MoO.sub.3                       GeO.sub.2                             E.sub.10, V                                   &#945;                                        C, nF______________________________________1     99.48   0.01    0.01  0.5   5     4    1312     99.44   0.05    0.01  0.5   3     4    1433     99.39   0.10    0.01  0.5   2     4    1544     98.49   1.00    0.01  0.5   5     4    1305     96.99   2.50    0.01  0.5   12    6    1106     99.44   0.01    0.05  0.5   7     5    1237     99.40   0.05    0.05  0.5   3     4    1458     99.35   0.10    0.05  0.5   2     4    1619     98.45   1.00    0.05  0.5   6     5    12910    96.95   2.50    0.05  0.5   14    7    10511    99.39   0.01    0.10  0.5   8     5    11612    99.35   0.05    0.10  0.5   4     4    13913    99.30   0.10    0.10  0.5   3     4    14414    98.40   1.00    0.10  0.5   7     6    12115    96.90   2.50    0.10  0.5   16    8    10116    98.49   0.01    1.00  0.5   21    9     9317    98.45   0.05    1.00  0.5   11    6    10618    98.40   0.10    1.00  0.5   5     4    13719    97.50   1.00    1.00  0.5   18    8     9920    96.00   2.50    1.00  0.5   42    14    6321    94.49   0.01    5.00  0.5   39    12    7222    94.45   0.05    5.00  0.5   20    9     9623    94.40   0.10    5.00  0.5   13    7    10624    93.50   1.00    5.00  0.5   33    11    7925    92.00   2.50    5.00  0.5   78    27    46______________________________________
EXAMPLE 20 SrTiO.sub.3 as the first ingredient was combined with Nb.sub.2 O.sub.5 as the second ingredient, MnO.sub.2 as the third ingredient, and GeO.sub.2 as the fourth ingredient. In various sets of proportions these ingredients were processed into ceramic discs, and further into varistors, through the same procedure as in EXAMPLE 1 except that the temperature of the oxidative heat treatment was 1000 proportions of the above four ingredients, together with the E.sub.10, α, and C of the varistors made therefrom, as measured by the same method as in EXAMPLE 1.
TABLE 20______________________________________Test  Composition in percent                     PropertiesNo.   SrTiO.sub.3         Nb.sub.2 O.sub.5                 MnO.sub.2                       GeO.sub.2                             E.sub.10, V                                   &#945;                                        C, nF______________________________________1     99.48   0.01    0.01  0.5   9     5    1212     99.44   0.05    0.01  0.5   5     4    1303     99.39   0.10    0.01  0.5   2     4    1414     98.49   1.00    0.01  0.5   6     5    1255     96.99   2.50    0.01  0.5   11    5    1156     99.44   0.01    0.05  0.5   12    6    1097     99.40   0.05    0.05  0.5   6     4    1238     99.35   0.10    0.05  0.5   3     4    1359     98.45   1.00    0.05  0.5   8     5    11510    96.95   2.50    0.05  0.5   13    6    10511    99.39   0.01    0.10  0.5   14    7    10312    99.35   0.05    0.10  0.5   8     5    11313    99.30   0.10    0.10  0.5   3     4    13914    98.40   1.00    0.10  0.5   10    5    11015    96.90   2.50    0.10  0.5   18    7     9616    98.49   0.01    1.00  0.5   42    15    7117    98.45   0.05    1.00  0.5   24    8     8918    98.40   0.10    1.00  0.5   9     5    12019    97.50   1.00    1.00  0.5   28    10    8920    96.00   2.50    1.00  0.5   52    19    6621    96.99   0.01    2.50  0.5   72    30    4822    96.95   0.05    2.50  0.5   41    14    6223    96.90   0.10    2.50  0.5   17    7     9624    96.00   1.00    2.50  0.5   47    16    5925    94.50   2.50    2.50  0.5   90    36    33______________________________________
EXAMPLE 21 SrTiO.sub.3 as the first ingredient and CuO as the third ingredient were variously combined with a second ingredient selected from the group of Ta.sub.2 O.sub.5, WO.sub.3, La.sub.2 O.sub.3, Dy.sub.2 O.sub.3, Y.sub.2 O.sub.3, CeO.sub.2, Nb.sub.2 O.sub.5, Pr.sub.6 O.sub.11, Nd.sub.2 O.sub.3, and Sm.sub.2 O.sub.3, and with a fourth ingredient selected from the group of B.sub.2 O.sub.3, ZnO, PbO, and GeO.sub.2. This EXAMPLE was intended to prove that B.sub.2 O.sub.3, ZnO and PbO could each be used as the fourth ingredient, in place of GeO.sub.2 tested in some foregoing EXAMPLES. It was also intended to ascertain the allowable range of percentages in which the fourth ingredient might be used to provide ceramic materials suitable for varistors.
Various combinations of four selected ingredients, each in various sets of proportions, were processed into ceramic discs through the same procedure as in EXAMPLE 1 except that the temperature of the oxidative heat treatment was 1000 combinations and proportions of the above ingredients, as well as the resistivities of the corresponding ceramic bodies, as measured by the four-probe method.
The resistivity of each ceramic body serves as a measure of its utility as a semiconductor. Conventional SrTiO.sub.3 ceramic materials, for use in capacitors, had a resistivity of more than 10.sup.10 ohm-cm in general. Contrastively, as will be noted from TABLES 21A through 21S, the ceramic bodies of this invention have all a resistivity of less than 10.sup.6 ohm-cm and thus are sufficiently semiconductive and suitable for varistors.
Experiment has also proved that if the content of the fourth ingredient in each composition is less than about 0.01%, it hardly serves the purpose of improving the coherency of the ceramic bodies prepared therefrom. Should the proportion of the fourth ingredient exceed about 4.00%, on the other hand, the resistivity of the ceramic bodies will become too high, making them unsuitable for varistors. Thus the proportion of the fourth ingredient should range from about 0.01 to about 4.00%, preferably from about 0.5 to about 1.0%.
TABLE 21A______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          Ta.sub.2 O.sub.5                   CuO    B.sub.2 O.sub.3                                 ohm-cm______________________________________1     99.485   0.005    0.5    0.01   6 2     98.995   0.005    0.5    0.50   13 3     95.495   0.005    0.5    4.00   19 4     98.99    0.50     0.5    0.01   2 5     98.50    0.50     0.5    0.50   5 6     95.00    0.50     0.5    4.00   7 7     96.99    2.50     0.5    0.01   9 8     96.50    2.50     0.5    0.50   20 9     93.00    2.50     0.5    4.00   31 ______________________________________
TABLE 21B______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          WO.sub.3 CuO    B.sub.2 O.sub.3                                 ohm-cm______________________________________10    99.48    0.01     0.5    0.01   6 11    98.99    0.01     0.5    0.50   13 12    95.49    0.01     0.5    4.00   19 13    98.99    0.50     0.5    0.01   2 14    98.50    0.50     0.5    0.50   5 15    95.00    0.50     0.5    4.00   7 16    94.49    5.00     0.5    0.01   9 17    94.00    5.00     0.5    0.50   20 18    95.50    5.00     0.5    4.00   31 ______________________________________
TABLE 21C______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          La.sub.2 O.sub.3                   CuO    B.sub.2 O.sub.3                                 ohm-cm______________________________________19    99.48    0.01     0.5    0.01   5 20    98.99    0.01     0.5    0.50   7 21    95.49    0.01     0.5    4.00   17 22    98.99    0.50     0.5    0.01   2 23    98.50    0.50     0.5    0.50   4 24    95.00    0.50     0.5    4.00   6 25    96.99    2.50     0.5    0.01   4 26    96.50    2.50     0.5    0.50   6 27    93.00    2.50     0.5    4.00   13 ______________________________________
TABLE 21D______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          Dy.sub.2 O.sub.3                   CuO    B.sub.2 O.sub.3                                 ohm-cm______________________________________28    99.48    0.01     0.5    0.01    7 29    98.99    0.01     0.5    0.50   13 30    95.49    0.01     0.5    4.00   23 31    98.99    0.50     0.5    0.01    3 32    98.50    0.50     0.5    0.50    5 33    95.00    0.50     0.5    4.00   11 34    96.99    2.50     0.5    0.01    6 35    96.50    2.50     0.5    0.50   11 36    93.00    2.50     0.5    4.00   20 ______________________________________
TABLE 21E______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          Y.sub.2 O.sub.3                   CuO    B.sub.2 O.sub.3                                 ohm-cm______________________________________37    99.48    0.01     0.5    0.01   7 38    98.99    0.01     0.5    0.50   12 39    95.49    0.01     0.5    4.00   24 40    98.99    0.50     0.5    0.01   2 41    98.50    0.50     0.5    0.50   3 42    95.00    0.50     0.5    4.00   7 43    95.49    4.00     0.5    0.01   7 44    95.00    4.00     0.5    0.50   12 45    91.50    4.00     0.5    4.00   25 ______________________________________
TABLE 21F______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          CeO.sub.2                   CuO    ZnO    ohm-cm______________________________________46    99.48    0.01     0.5    0.01    8 47    98.99    0.01     0.5    0.50   15 48    95.49    0.01     0.5    4.00   33 49    98.99    0.50     0.5    0.01    5 50    98.50    0.50     0.5    0.50   10 51    95.00    0.50     0.5    4.00   21 52    95.49    4.00     0.5    0.01    9 53    95.00    4.00     0.5    0.50   17 54    91.50    4.00     0.5    4.00   35 ______________________________________
TABLE 21G______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          La.sub.2 O.sub.3                   CuO    ZnO    ohm-cm______________________________________55    99.48    0.01     0.5    0.01    7 56    98.99    0.01     0.5    0.50   13 57    95.49    0.01     0.5    4.00   27 58    98.99    0.50     0.5    0.01    4 59    98.50    0.50     0.5    0.50    9 60    95.00    0.50     0.5    4.00   16 61    96.99    2.50     0.5    0.01    6 62    96.50    2.50     0.5    0.50   12 63    93.00    2.50     0.5    4.00   25 ______________________________________
TABLE 21H______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          WO.sub.3 CuO    ZnO    ohm-cm______________________________________64    99.48    0.01     0.5    0.01   5 65    98.99    0.01     0.5    0.50   9 66    95.49    0.01     0.5    4.00   20 67    98.99    0.50     0.5    0.01   2 68    98.50    0.50     0.5    0.50   4 69    95.00    0.50     0.5    4.00   8 70    94.49    5.00     0.5    0.01   4 71    94.00    5.00     0.5    0.50   8 72    90.50    5.00     0.5    4.00   16 ______________________________________
TABLE 21I______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          Ta.sub.2 O.sub.5                   CuO    ZnO    ohm-cm______________________________________73    99.485   0.005    0.5    0.01    9 74    98.995   0.005    0.5    0.50   17 75    95.495   0.005    0.5    4.00   36 76    99.44    0.05     0.5    0.01    4 77    98.95    0.05     0.5    0.50    8 78    95.45    0.05     0.5    4.00   15 79    96.99    2.50     0.5    0.01   13 80    96.50    2.50     0.5    0.50   24 81    93.00    2.50     0.5    4.00   48 ______________________________________
TABLE 21J______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          Ta.sub.2 O.sub.5                   CuO    PbO    ohm-cm______________________________________82    99.485   0.005    0.5    0.01    7 83    98.995   0.005    0.5    0.50   15 84    95.495   0.005    0.5    4.00   31 85    98.99    0.50     0.5    0.01    4 86    98.50    0.50     0.5    0.50    8 87    95.00    0.50     0.5    4.00   18 88    96.99    2.50     0.5    0.01   10 89    96.50    2.50     0.5    0.50   21 90    93.00    2.50     0.5    4.00   45 ______________________________________
TABLE 21K______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          Nb.sub.2 O.sub.5                   CuO    PbO    ohm-cm______________________________________91    99.48    0.01     0.5    0.01   21 92    98.99    0.01     0.5    0.50   44 93    95.49    0.01     0.5    4.00   96 94    98.99    0.50     0.5    0.01    7 95    98.50    0.50     0.5    0.50   15 96    95.00    0.50     0.5    4.00   30 97    94.49    5.00     0.5    0.01   18 98    94.00    5.00     0.5    0.50   39 99    90.50    5.00     0.5    4.00   81 ______________________________________
TABLE 21L______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          Pr.sub.6 O.sub.11                   CuO    PbO    ohm-cm______________________________________100   99.489   0.001    0.5    0.01    8 101   98.999   0.001    0.5    0.50   17 102   95.499   0.001    0.5    4.00   39 103   98.99    0.50     0.5    0.01    4 104   98.50    0.50     0.5    0.50    9 105   95.00    0.50     0.5    4.00   18 106   96.99    2.50     0.5    0.01    7 107   96.50    2.50     0.5    0.50   16 108   93.00    2.50     0.5    4.00   32 ______________________________________
TABLE 21M______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          Nd.sub.2 O.sub.3                   CuO    PbO    ohm-cm______________________________________109   99.48    0.01     0.5    0.01    8 110   98.99    0.01     0.5    0.50   16 111   95.49    0.01     0.5    4.00   36 112   98.99    0.50     0.5    0.01    3 113   98.50    0.50     0.5    0.50    6 114   95.00    0.50     0.5    4.00   13 115   95.49    4.00     0.5    0.01    7 116   95.00    4.00     0.5    0.50   15 117   91.50    4.00     0.5    4.00   33 ______________________________________
TABLE 21N______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          Sm.sub.2 O.sub.3                   CuO    PbO    ohm-cm______________________________________118   99.48    0.01     0.5    0.01    9 119   98.99    0.01     0.5    0.50   20 120   95.49    0.01     0.5    4.00   41 121   98.99    0.50     0.5    0.01    3 122   98.50    0.50     0.5    0.50    6 123   95.00    0.50     0.5    4.00   11 124   96.49    3.00     0.5    0.01   10 125   96.00    3.00     0.5    0.50   23 126   92.50    3.00     0.5    4.00   46 ______________________________________
TABLE 21-O______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          Ta.sub.2 O.sub.5                   CuO    GeO.sub.2                                 ohm-cm______________________________________127   99.485   0.005    0.5    0.01    8 128   98.995   0.005    0.5    0.50   17 129   95.495   0.005    0.5    4.00   33 130   98.99    0.50     0.5    0.01    4 131   98.50    0.50     0.5    0.50    9 132   95.00    0.50     0.5    4.00   18 133   96.99    2.50     0.5    0.01   11 134   96.50    2.50     0.5    0.50   25 135   93.00    2.50     0.5    4.00   45 ______________________________________
TABLE 21P______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          Nb.sub.2 O.sub.5                   CuO    GeO.sub.2                                 ohm-cm______________________________________136   99.48    0.01     0.5    0.01   29 137   98.99    0.01     0.5    0.50   57 138   95.49    0.01     0.5    4.00   122 139   98.99    0.50     0.5    0.01   10 140   98.50    0.50     0.5    0.50   24 141   95.00    0.50     0.5    4.00   46 142   94.49    5.00     0.5    0.01   24 143   94.00    5.00     0.5    0.50   53 144   90.50    5.00     0.5    4.00   103 ______________________________________
TABLE 21Q______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          CeO.sub.2                   CuO    GeO.sub.2                                 ohm-cm______________________________________145   99.48    0.01     0.5    0.01    9 146   98.99    0.01     0.5    0.50   21 147   95.49    0.01     0.5    4.00   40 148   98.99    0.50     0.5    0.01    6 149   98.50    0.50     0.5    0.50   13 150   95.00    0.50     0.5    4.00   27 151   95.49    4.00     0.5    0.01    8 152   95.00    4.00     0.5    0.50   18 153   91.50    4.00     0.5    4.00   35 ______________________________________
TABLE 21R______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          Nd.sub.2 O.sub.3                   CuO    GeO.sub.2                                 ohm-cm______________________________________154   99.48    0.01     0.5    0.01   10 155   98.99    0.01     0.5    0.50   23 156   95.49    0.01     0.5    4.00   46 157   98.99    0.50     0.5    0.01    5 158   98.50    0.50     0.5    0.50   11 159   95.00    0.50     0.5    4.00   22 160   95.49    4.00     0.5    0.01    9 161   95.00    4.00     0.5    0.50   23 162   91.50    4.00     0.5    4.00   44 ______________________________________
TABLE 21S______________________________________Test  Composition in percent  Resistivity,No.   SrTiO.sub.3          Y.sub.2 O.sub.3                   CuO    GeO.sub.2                                 ohm-cm______________________________________163   99.48    0.01     0.5    0.01    8 164   98.99    0.01     0.5    0.50   20 165   95.49    0.01     0.5    4.00   37 166   98.99    0.50     0.5    0.01    5 167   98.50    0.50     0.5    0.50   12 168   95.00    0.50     0.5    4.00   24 169   95.49    4.00     0.5    0.01   11 170   95.00    4.00     0.5    0.50   23 171   91.50    4.00     0.5    4.00   41 ______________________________________
EXAMPLE 22 Fifteen different combinations of ingredients in accordance with the invention were prepared as in TABLES 22A through 22-O, in order to make sure that two or more different metal oxides could be employed as the second, third, or fourth set of ingredients, in combination with SrTiO.sub.3 as the first ingredient. The various combinations of ingredients, each in several different sets of proportions, were processed into ceramic discs through the same procedure as in EXAMPLE 1 except that the temperature of the oxidative heat treatment was 1000 resistivities of these ceramic bodies, measured by the same method as in EXAMPLE 21, were as given in TABLES 22A through 22-O. The tabulated results demonstrate that the ceramic bodies made with the use of two or more different metal oxides as the second, third, or fourth set of ingredients are all sufficiently semiconductive.
TABLE 22A__________________________________________________________________________Composition in percent   First Second  Third FourthTest   ingredient    ingredients            ingredient                  ingredients                             Resistivity,No.   SrTiO.sub.3    Nb.sub.2 O.sub.5        Ta.sub.2 O.sub.5            CuO   GeO.sub.2                      PbO                         ZnO ohm-cm__________________________________________________________________________1  98.90 0.02        0.08            0.5   0.5 0  0   5 2  98.90 0.05        0.05            0.5   0.5 0  0   7 3  98.90 0.08        0.02            0.5   0.5 0  0   6 4  98.90 0.02        0.08            0.5   0   0.5                         0   7 5  98.90 0.05        0.05            0.5   0   0.5                         0   3 6  98.90 0.08        0.02            0.5   0   0.5                         0   4 7  98.90 0.02        0.08            0.5   0   0  0.5 9 8  98.90 0.05        0.05            0.5   0   0  0.5 11 9  98.90 0 08        0.02            0.5   0   0  0.5 7 __________________________________________________________________________
TABLE 22B__________________________________________________________________________Composition in percent   First Second  Third FourthTest   ingredient    ingredients            ingredient                  ingredients                             Resistivity,No.   SrTiO.sub.3    Nb.sub.2 O.sub.5        WO.sub.3            CuO   GeO.sub.2                      PbO                         ZnO ohm-cm__________________________________________________________________________10 98.90 0.02        0.08            0.5   0.5 0  0   7 11 98.90 0.05        0.05            0.5   0.5 0  0   9 12 98.90 0.08        0.02            0.5   0.5 0  0   6 13 98.90 0.02        0.08            0.5   0   0.5                         0   4 14 98.90 0.05        0.05            0.5   0   0.5                         0   5 15 98.90 0.08        0.02            0.5   0   0.5                         0   4 16 98.90 0.02        0.08            0.5   0   0  0.5 6 17 98.90 0.05        0.05            0.5   0   0  0.5 7 18 98.90 0.08        0.02            0.5   0   0  0.5 3 __________________________________________________________________________
TABLE 22C__________________________________________________________________________Composition in percent   First Second  Third FourthTest   ingredient    ingredients            ingredient                  ingredients                             Resistivity,No.   SrTiO.sub.3    Nb.sub.2 O.sub.5        La.sub.2 O.sub.3            CuO   GeO.sub.2                      PbO                         ZnO ohm-cm__________________________________________________________________________19 98.90 0.02        0.08            0.5   0.5 0  0    8 20 98.90 0.05        0.05            0.5   0.5 0  0   13 21 98.90 0.08        0.02            0.5   0.5 0  0   15 22 98.90 0.02        0.08            0.5   0   0.5                         0   10 23 98.90 0.05        0.05            0.5   0   0.5                         0   16 24 98.90 0.08        0.02            0.5   0   0.5                         0   21 25 98.90 0.02        0.08            0.5   0   0  0.5 14 26 98.90 0.05        0.05            0.5   0   0  0.5 15 27 98.90 0.08        0.02            0.5   0   0  0.5 20 __________________________________________________________________________
TABLE 22D__________________________________________________________________________Composition in percent   First Second  Third FourthTest   ingredient    ingredients            ingredient                  ingredients                             Resistivity,No.   SrTiO.sub.3    Nb.sub.2 O.sub.5        CeO.sub.2            CuO   GeO.sub.2                      PbO                         ZnO ohm-cm__________________________________________________________________________28 98.90 0.02        0.08            0.5   0.5 0  0   14 29 98.90 0.05        0.05            0.5   0.5 0  0   19 30 98.90 0.08        0.02            0.5   0.5 0  0   11 31 98.90 0.02        0.08            0.5   0   0.5                         0   23 32 98.90 0.05        0.05            0.5   0   0.5                         0   21 33 98.90 0.08        0.02            0.5   0   0.5                         0   13 34 98.90 0.02        0.08            0.5   0   0  0.5 16 35 98.90 0.05        0.05            0.5   0   0  0.5 29 36 98.90 0.08        0.02            0.5   0   0  0.5 21 __________________________________________________________________________
TABLE 22E__________________________________________________________________________Composition in percent   First Second  Third FourthTest   ingredient    ingredients            ingredient                  ingredients                             Resistivity,No.   SrTiO.sub.3    Nb.sub.2 O.sub.5        Dy.sub.2 O.sub.3            CuO   GeO.sub.2                      PbO                         ZnO ohm-cm__________________________________________________________________________37 98.90 0.02        0.08            0.5   0.5 0  0   8 38 98.90 0.05        0.05            0.5   0.5 0  0   11 39 98.90 0.08        0.02            0.5   0.5 0  0   10 40 98.90 0.02        0.08            0.5   0   0.5                         0   7 41 98.90 0.05        0.05            0.5   0   0.5                         0   9 42 98.90 0.08        0.02            0.5   0   0.5                         0   6 43 98.90 0.02        0.08            0.5   0   0  0.5 6 44 98.90 0.05        0.05            0.5   0   0  0.5 13 45 98.90 0.08        0.02            0.5   0   0  0.5 9 __________________________________________________________________________
TABLE 22F__________________________________________________________________________Composition in percent   First Second  Third FourthTest   ingredient    ingredients            ingredient                  ingredients                             Resistivity,No.   SrTiO.sub.3    La.sub.2 O.sub.3        Ta.sub.2 O.sub.5            CuO   GeO.sub.2                      ZnO                         B.sub.2 O.sub.3                             ohm-cm__________________________________________________________________________46 98.90 0.02        0.08            0.5   0.5 0  0   11 47 98.90 0.05        0.05            0.5   0.5 0  0   13 48 98.90 0.08        0.02            0.5   0.5 0  0   15 49 98.90 0.02        0.08            0.5   0   0.5                         0   13 50 98.90 0.05        0.05            0.5   0   0.5                         0   16 51 98.90 0.08        0.02            0.5   0   0.5                         0   17 52 98.90 0.02        0.08            0.5   0   0  0.5 13 53 98.90 0.05        0.05            0.5   0   0  0.5 14 54 98.90 0.08        0.02            0.5   0   0  0.5 16 __________________________________________________________________________
TABLE 22G__________________________________________________________________________Composition in percent   First Second  Third FourthTest   ingredient    ingredients            ingredient                  ingredients                             Resistivity,No.   SrTiO.sub.3    La.sub.2 O.sub.3        WO.sub.3            CuO   GeO.sub.2                      ZnO                         B.sub.2 O.sub.3                             ohm-cm__________________________________________________________________________55 98.90 0.02        0.08            0.5   0.5 0  0   12 56 98.90 0.05        0.05            0.5   0.5 0  0   16 57 98.90 0.08        0.02            0.5   0.5 0  0   21 58 98.90 0.02        0.08            0.5   0   0.5                         0   23 59 98.90 0.05        0.05            0.5   0   0.5                         0   24 60 98.90 0.08        0.02            0.5   0   0.5                         0   23 61 98.90 0.02        0.08            0.5   0   0  0.5 29 62 98.90 0.05        0.05            0.5   0   0  0.5 31 63 98.90 0.08        0.02            0.5   0   0  0.5 30 __________________________________________________________________________
TABLE 22H__________________________________________________________________________Composition in percent   First Second  Third FourthTest   ingredient    ingredients            ingredient                  ingredients                             Resistivity,No.   SrTiO.sub.3    La.sub.2 O.sub.3        CeO.sub.2            CuO   GeO.sub.2                      ZnO                         B.sub.2 O.sub.3                             ohm-cm__________________________________________________________________________64 98.90 0.02        0.08            0.5   0.5 0  0   26 65 98.90 0.05        0.05            0.5   0.5 0  0   23 66 98.90 0.08        0.02            0.5   0.5 0  0   25 67 98.90 0.02        0.08            0.5   0   0.5                         0   31 68 98.90 0.05        0.05            0.5   0   0.5                         0   30 69 98.90 0.08        0.02            0.5   0   0.5                         0   29 70 98.90 0.02        0.08            0.5   0   0  0.5 29 71 98.90 0.05        0.05            0.5   0   0  0.5 36 72 98.90 0.08        0.02            0.5   0   0  0.5 35 __________________________________________________________________________
TABLE 22I__________________________________________________________________________Composition in percent   First Second  Third FourthTest   ingredient    ingredients            ingredient                  ingredients                             Resistivity,No.   SrTiO.sub.3    La.sub.2 O.sub.3        Nd.sub.2 O.sub.3            CuO   GeO.sub.2                      ZnO                         B.sub.2 O.sub.3                             ohm-cm__________________________________________________________________________73 98.90 0.02        0.08            0.5   0.5 0  0   21 74 98.90 0.05        0.05            0.5   0.5 0  0   20 75 98.90 0.08        0.02            0.5   0.5 0  0   18 76 98.90 0.02        0.08            0.5   0   0.5                         0   17 77 98.90 0.05        0.05            0.5   0   0.5                         0   19 78 98.90 0.08        0.02            0.5   0   0.5                         0   13 79 98.90 0.02        0.08            0.5   0   0  0.5 22 80 98.90 0.05        0.05            0.5   0   0  0.5 21 81 98.90 0.08        0.02            0.5   0   0  0.5 19 __________________________________________________________________________
TABLE 22J__________________________________________________________________________Composition in percent   First Second  Third FourthTest   ingredient    ingredients            ingredient                  ingredients                             Resistivity,No.   SrTiO.sub.3    La.sub.2 O.sub.3        Sm.sub.2 O.sub.3            CuO   GeO.sub.2                      ZnO                         B.sub.2 O.sub.3                             ohm-cm__________________________________________________________________________82 98.90 0.02        0.08            0.5   0.5 0  0   29 83 98.90 0.05        0.05            0.5   0.5 0  0   30 84 98.90 0.08        0.02            0.5   0.5 0  0   33 85 98.90 0.02        0.08            0.5   0   0.5                         0   28 86 98.90 0.05        0.05            0.5   0   0.5                         0   32 87 98.90 0.08        0.02            0.5   0   0.5                         0   35 88 89.90 0.02        0.08            0.5   0   0  0.5 34 89 89.90 0.05        0.05            0.5   0   0  0.5 36 90 89.90 0.08        0.02            0.5   0   0  0.5 39 __________________________________________________________________________
TABLE 22K__________________________________________________________________________Composition in percent   First Second     Third  FourthTest   ingredient    ingredients               ingredients                      ingredient                            Resistivity,No.   SrTiO.sub.3    Nb.sub.2 O.sub.5        WO.sub.3           La.sub.2 O.sub.3               CuO                  Cu.sub.2 O                      GeO.sub.2                            ohm-cm__________________________________________________________________________91 98.90 0.1 0  0   0.1                  0.4 0.5   9 92 98.90 0.1 0  0   0.25                  0.25                      0.5   12 93 98.90 0.1 0  0   0.4                  0.1 0.5   6 94 98.90 0   0.1           0   0.1                  0.4 0.5   11 95 98.90 0   0.1           0   0.25                  0.25                      0.5   13 96 98.90 0   0.1           0   0.4                  0.1 0.5   8 97 98.90 0   0  0.1 0.1                  0.4 0.5   9 98 98.90 0   0  0.1 0.25                  0.25                      0.5   9 99 98.90 0   0  0.1 0.4                  0.1 0.5   7 __________________________________________________________________________
TABLE 22L__________________________________________________________________________Composition in percent   First Second     Third  FourthTest   ingredient    ingredients               ingredients                      ingredient                            Resistivity,No.   SrTiO.sub.3    Nb.sub.2 O.sub.5        WO.sub.3           La.sub.2 O.sub.3               CuO                  MoO.sub.3                      GeO.sub.2                            ohm-cm__________________________________________________________________________100   98.90 0.1 0  0   0.1                  0.4 0.5   6 101   98.90 0.1 0  0   0.25                  0.25                      0.5   7 102   98.90 0.1 0  0   0.4                  0.1 0.5   5 103   98.90 0   0.1           0   0.1                  0.4 0.5   7 104   98.90 0   0.1           0   0.25                  0.25                      0.5   6 105   98.90 0   0.1           0   0.4                  0.1 0.5   7 106   98.90 0   0  0.1 0.1                  0.4 0.5   6 107   98.90 0   0  0.1 0.25                  0.25                      0.5   8 108   98.90 0   0  0.1 0.4                  0.1 0.5   11 __________________________________________________________________________
TABLE 22M__________________________________________________________________________Composition in percent   First Second     Third  FourthTest   ingredient    ingredients               ingredients                      ingredient                            Resistivity,No.   SrTiO.sub.3    Nb.sub.2 O.sub.5        WO.sub.3           La.sub.2 O.sub.3               MoO.sub.3                  V.sub.2 O.sub.5                      GeO.sub.2                            ohm-cm__________________________________________________________________________109   98.90 0.1 0  0   0.1                  0.4 0.5   11 110   98.90 0.1 0  0   0.25                  0.25                      0.5   13 111   98.90 0.1 0  0   0.4                  0.1 0.5   14 112   98.90 0   0.1           0   0.1                  0.4 0.5   15 113   98.90 0   0.1           0   0.25                  0.25                      0.5   10 114   98.90 0   0.1           0   0.4                  0.1 0.5   11 115   98.90 0   0  0.1 0.1                  0.4 0.5   17 116   98.90 0   0  0.1 0.25                  0.25                      0.5   14 117   98.90 0   0  0.1 0.4                  0.1 0.5   15 __________________________________________________________________________
TABLE 22N__________________________________________________________________________Composition in percent   First Second     Third  FourthTest   ingredient    ingredients               ingredients                      ingredient                            Resistivity,No.   SrTiO.sub.3    Nb.sub.2 O.sub.5        WO.sub.3           La.sub.2 O.sub.3               V.sub.2 O.sub.5                  CrO.sub.3                      GeO.sub.2                            ohm-cm__________________________________________________________________________118   98.90 0.1 0  0   0.1                  0.4 0.5   7 119   98.90 0.1 0  0   0.25                  0.25                      0.5   9 120   98.90 0.1 0  0   0.4                  0.1 0.5   8 121   98.90 0   0.1           0   0.1                  0.4 0.5   3 122   98.90 0   0.1           0   0.25                  0.25                      0.5   6 123   98.90 0   0.1           0   0.4                  0.1 0.5   9 124   98.90 0   0  0.1 0.1                  0.4 0.5   8 125   98.90 0   0  0.1 0.25                  0.25                      0.5   9 126   98.90 0   0  0.1 0.4                  0.1 0.5   9 __________________________________________________________________________
TABLE 22-O__________________________________________________________________________Composition in percent   First Second     Third  FourthTest   ingredient    ingredients               ingredients                      ingredient                            Resistivity,No.   SrTiO.sub.3    Nb.sub.2 O.sub.5        WO.sub.3           La.sub.2 O.sub.3               CrO.sub.3                  Cu.sub.2 O                      GeO.sub.2                            ohm-cm__________________________________________________________________________127   98.90 0.1 0  0   0.1                  0.4 0.5   10 128   98.90 0.1 0  0   0.25                  0.25                      0.5    9 129   98.90 0.1 0  0   0.4                  0.1 0.5    7 130   98.90 0   0.1           0   0.1                  0.4 0.5   11 131   98.90 0   0.1           0   0.25                  0.25                      0.5   12 132   98.90 0   0.1           0   0.4                  0.1 0.5   11 133   98.90 0   0  0.1 0.1                  0.4 0.5   13 134   98.90 0   0  0.1 0.25                  0.25                      0.5   11 135   98.90 0   0  0.1 0.4                  0.1 0.5    9 __________________________________________________________________________
EXAMPLE 23 Six different combinations of four ingredients chosen in accordance with the invention, each in a fixed set of proportions, were prepared as in TABLES 23A through 23F, in order to to study the relationship between the temperatures of the oxidative heat treatment and the characteristics of the resulting ceramic bodies and varistors. The tabulated combinations of ingredients were processed into ceramic discs, and further into varistors, through the same procedure as in EXAMPLE 1 except that the temperature of the oxidative heat treatment was set at various values from 700 1170 α, and resistivity of the thus-fabricated ceramic bodies and varistors. The E.sub.10 of the varistors oxidatively heat-treated at 700
TABLE 23A__________________________________________________________________________              Temperature of                      PropertiesTest   Composition in percent              oxidative heat Resistivity,No.   SrTiO.sub.3  Nb.sub.2 O.sub.5      CuO GeO.sub.2              treatment,                       E.sub.10, V                          &#945;                             ohm-cm__________________________________________________________________________1  98.9  0.1 0.5 0.5 700     --  1  6 2  98.9  0.1 0.5 0.5 800     --  1  23  98.9  0.1 0.5 0.5 900      4  4  4 4  98.9  0.1 0.5 0.5 1000    14  6  1 5  98.9  0.1 0.5 0.5 1100    36  17 4 6  98.9  0.1 0.5 0.5 1170    68  26 7 __________________________________________________________________________
TABLE 23B__________________________________________________________________________              Temperature of                      PropertiesTest   Composition in percent              oxidative heat Resistivity,No.   SrTiO.sub.3  Nb.sub.2 O.sub.5      Cu.sub.2 O          GeO.sub.2              treatment,                       E.sub.10, V                          &#945;                             ohm-cm__________________________________________________________________________ 7 98.9  0.1 0.5 0.5  700    --  1  7  8 98.9  0.1 0.5 0.5  800    --  1  5 9 98.9  0.1 0.5 0.5  900     4  4  3 10 98.9  0.1 0.5 0.5 1000    17  8  2 11 98.9  0.1 0.5 0.5 1100    44  21 4 12 98.9  0.1 0.5 0.5 1170    99  35 1 __________________________________________________________________________
TABLE 23C__________________________________________________________________________              Temperature of                      PropertiesTest   Composition in percent              oxidative heat Resistivity,No.   SrTiO.sub.3  Nb.sub.2 O.sub.5      V.sub.2 O.sub.5          GeO.sub.2              treatment,                       E.sub.10, V                          &#945;                             ohm-cm__________________________________________________________________________13 98.9  0.1 0.5 0.5  700    --  1  9 14 98.9  0.1 0.5 0.5  800    --  1  615 98.9  0.1 0.5 0.5  900     5  4  4 16 98.9  0.1 0.5 0.5 1000    14  6  2 17 98.9  0.1 0.5 0.5 1100    35  16 3 18 98.9  0.1 0.5 0.5 1170    67  29 7 __________________________________________________________________________
TABLE 23D__________________________________________________________________________              Temperature of                      PropertiesTest   Composition in percent              oxidative heat Resistivity,No.   SrTiO.sub.3  Nb.sub.2 O.sub.5      CrO.sub.3          GeO.sub.2              treatment,                       E.sub.10, V                          &#945;                             ohm-cm__________________________________________________________________________19 98.9  0.1 0.5 0.5  700    --  1  8 20 98.9  0.1 0.5 0.5  800    --  1  521 98.9  0.1 0.5 0.5  900     6  4  5 22 98.9  0.1 0.5 0.5 1000    15  7  2 23 98.9  0.1 0.5 0.5 1100    40  20 4 24 98.9  0.1 0.5 0.5 1170    82  33 8 __________________________________________________________________________
TABLE 23E__________________________________________________________________________              Temperature of                      PropertiesTest   Composition in percent              oxidative heat Resistivity,No.   SrTiO.sub.3  Nb.sub.2 O.sub.5      MoO.sub.3          GeO.sub.2              treatment,                       E.sub.10, V                          &#945;                             ohm-cm__________________________________________________________________________25 98.9  0.1 0.5 0.5  700    --  1  6 26 98.9  0.1 0.5 0.5  800    --  1  327 98.9  0.1 0.5 0.5  900     3  4  5 28 98.9  0.1 0.5 0.5 1000    13  6  1 29 98.9  0.1 0.5 0.5 1100    41  21 4 30 98.9  0.1 0.5 0.5 1170    82  31 9 __________________________________________________________________________
TABLE 23F__________________________________________________________________________              Temperature of                      PropertiesTest   Composition in percent              oxidative heat Resistivity,No.   SrTiO.sub.3  Nb.sub.2 O.sub.5      MnO.sub.2          GeO.sub.2              treatment,                       E.sub.10, V                          &#945;                             ohm-cm__________________________________________________________________________31 98.9  0.1 0.5 0.5  700    --  1  .sup. 8 32 98.9  0.1 0.5 0.5  800    --  2  333 98.9  0.1 0.5 0.5  900     4  4  4 34 98.9  0.1 0.5 0.5 1000    14  6  2 35 98.9  0.1 0.5 0.5 1100    39  18 4 36 98.9  0.1 0.5 0.5 1170    89  31 8 __________________________________________________________________________
Based on the data given in TABLE 23A, FIG. 7 graphically represents the curve of the α of the SrTiO.sub.3 --Nb.sub.2 O.sub.5 --CuO--GeO.sub.2 varistors against the temperature of the oxidative heat treatment. The graph exhibits some proportionality between the two factors, making clear that the α of the varistors can be controlled by the temperature of the oxidative heat treatment during the fabrication of the ceramic bodies. A comparison of this graph with that of FIG. 6, which plots a similar curve in the case where the ceramic composition contains no fourth ingredient, will reveal that the α of the varistors including the fourth ingredient varies less with the temperature and so is easier to control.
The curve C in the graph of FIG. 8 represents the E.sub.10 of the SrTiO.sub.3 --Nb.sub.2 O.sub.5 --CuO--GeO.sub.2 varistors plotted against the temperature of the oxidative heat treatment, on the basis of the data also given in TABLE 23A. The curve indicates that the E.sub.10 of the varistors can likewise be controlled by the temperature of the oxidative heat treatment.
By way of comparison several ceramic bodies were prepared from 99.4% SrTiO.sub.3, 0.1% Nb.sub.2 O.sub.5, and 0.5% CuO, with no fourth ingredient added, by progressively varying the temperature of the oxidative heat treatment. The curve D in FIG. 8 represents the E.sub.10 of the varistors made from these ceramic bodies, plotted agaist the temperature of the oxidative heat treatment. As will be understood upon comparison of the curves C and D, the addition of the fourth ingredient makes less the change of E.sub.10 with temperature. When 10 SrTiO.sub.3 --Nb.sub.2 O.sub.5 --CuO varistors were produced, with the temperature of the oxidative heat treatment set at 1000 between 33 and 53 V, averaging 44 V. There was thus a difference of as much as 20 V between the maximum and minimum values. Constrastively, when another ten varistors were prepared by adding GeO.sub.2 as the fourth ingredient to the above composition, with the temperature of the oxidative heat treatment also set at 1000 between 12 and 16 V, averaging 14 V. Thus the addition of the fourth ingredient greatly reduces fluctuations in E.sub.10. Such reduction of fluctuations in E.sub.10 and α results, obviously, from the higher coherency of the ceramic bodies and greater uniformity of particle size, brought about by the introduction of the fourth ingredient.
When the temperature of the oxidative heat treatment was below 900 C., the resistivity of the ceramic bodies became too low, and when the temperature was above 1300 varistors. The oxidative heat treatment should therefore be conducted in a temperature range of about 900 900
EXAMPLE 24 Varistors incorporating a fourth ingredient were tested as to their pulse-withstanding abilities in this EXAMPLE. Ceramic discs were prepared from six different combinations of four possible ingredients given in TABLE 24, in like proportions, and were processed into varistors, through the same procedure as in EXAMPLE 1 except that the temperature of the oxidative heat treatment was 1000 pulses of 100 V were successively applied to each varistor, and a rate of change in E.sub.10 before and after the pulse application was computed. TABLE 24 shows the results.
TABLE 24______________________________________CompositionFirst     Second    Third   Fourth  ChangeTest ingredient          ingredient                    ingredient                            ingredient                                    inNo.  (98.9%)   (0.1%)    (0.5%)  (0.5%)  E.sub.10, %______________________________________1    SrTiO.sub.3          Nb.sub.2 O.sub.5                    V.sub.2 O.sub.5                            GeO.sub.2                                    -0.052    SrTiO.sub.3          Nb.sub.2 O.sub.5                    CrO.sub.3                            GeO.sub.2                                    -0.033    SrTiO.sub.3          Nb.sub.2 O.sub.2                    CuO     GeO.sub.2                                    -0.014    SrTiO.sub.3          Nb.sub.2 O.sub.5                    Cu.sub.2 O                            GeO.sub.2                                    -0.035    SrTiO.sub.3          Nb.sub.2 O.sub.5                    MoO.sub.3                            GeO.sub.2                                    -0.066    SrTiO.sub.3          Nb.sub.2 O.sub.5                    MnO.sub.2                            GeO.sub.2                                    -0.05______________________________________
EXAMPLE 25 Six different combinations of four possible ingredients in accordance with the invention, each in different sets of proportions, were prepared as in TABLES 25A through 25F. The various combinations of ingredients were processed into ceramic discs, and further into varistors, through the same procedure as in EXAMPLE 1 except that the temperature of the oxidative heat treatment was 1000 variations in the E.sub.10 of the varistors with temperatures at which they are put to use, the temperature change Tc.sub.25-50 of the E.sub.10 of each varistor was computed from the equation, Tc.sub.25-50 =(A-B)100/A, where A is the value of E.sub.10 at 25 E.sub.10 at 50
TABLE 25A______________________________________                        TemperatureTest Composition in percent  change Tc.sub.25-50No.  SrTiO.sub.3         Nb.sub.2 O.sub.5                  CuO    GeO.sub.2                                of E.sub.10, %______________________________________1    99.48    0.01     0.01   0.5    -0.072    98.99    0.01     0.50   0.5    -0.073    94.49    0.01     5.00   0.5    -0.064    99.39    0.10     0.01   0.5    -0.065    98.90    0.10     0.50   0.5    -0.056    94.40    0.10     5.00   0.5    -0.057    96.99    2.5      0.01   0.5    -0.068    96.50    2.5      0.50   0.5    -0.059    92.00    2.5      5.00   0.5    -0.05______________________________________
TABLE 25B______________________________________                        TemperatureTest Composition in percent  change Tc.sub.25-50No.  SrTiO.sub.3         Nb.sub.2 O.sub.5                  Cu.sub.2 O                         GeO.sub.2                                of E.sub.10, %______________________________________10   99.48    0.01     0.01   0.5    -0.0711   98.99    0.01     0.50   0.5    -0.0612   96.99    0.01     2.50   0.5    -0.0513   99.39    0.10     0.01   0.5    -0.0614   98.90    0.10     0.50   0.5    -0.0615   96.90    0.10     2.50   0.5    -0.0516   96.99    2.5      0.01   0.5    -0.0617   96.50    2.5      0.50   0.5    -0.0518   94.50    2.5      2.50   0.5    -0.05______________________________________
TABLE 25C______________________________________                        TemperatureTest Composition in percent  change Tc.sub.25-50No.  SrTiO.sub.3         Nb.sub.2 O.sub.5                  V.sub.2 O.sub.5                         GeO.sub.2                                of E.sub.10, %______________________________________19   99.48    0.01     0.01   0.5    -0.0620   98.99    0.01     0.50   0.5    -0.0621   98.49    0.01     1.00   0.5    -0.0522   99.39    0.10     0.01   0.5    -0.0523   98.90    0.10     0.50   0.5    -0.0624   98.40    0.10     1.00   0.5    -0.0725   96.99    2.5      0.01   0.5    -0.0626   96.50    2.5      0.50   0.5    -0.0627   96.00    2.5      1.00   0.5    -0.05______________________________________
TABLE 25D______________________________________                        TemperatureTest Composition in percent  change Tc.sub.25-50No.  SrTiO.sub.3         Nb.sub.2 O.sub.5                  CrO.sub.3                         GeO.sub.2                                of E.sub.10, %______________________________________28   99.48    0.01     0.01   0.5    -0.0729   98.99    0.01     0.50   0.5    -0.0630   97.49    0.01     2.00   0.5    -0.0631   99.39    0.10     0.01   0.5    -0.0732   98.90    0.10     0.50   0.5    -0.0733   97.40    0.10     2.00   0.5    -0.0534   96.99    2.5      0.01   0.5    -0.0635   96.50    2.5      0.50   0.5    -0.0736   95.00    2.5      2.00   0.5    -0.05______________________________________
TABLE 25E______________________________________                        TemperatureTest Composition in percent  change Tc.sub.25-50No.  SrTiO.sub.3         Nb.sub.2 O.sub.5                  MoO.sub.3                         GeO.sub.2                                of E.sub.10, %______________________________________37   99.48    0.01     0.01   0.5    -0.0738   98.99    0.01     0.50   0.5    -0.0639   94.49    0.01     5.00   0.5    -0.0640   99.39    0.10     0.01   0.5    -0.0741   98.90    0.10     0.50   0.5    -0.0742   94.40    0.10     5.00   0.5    -0.0643   96.99    2.50     0.01   0.5    -0.0644   96.50    2.50     0.50   0.5    -0.0545   92.00    2.50     5.00   0.5    -0.05______________________________________
TABLE 25F______________________________________                        TemperatureTest Composition in percent  change Tc.sub.25-50No.  SrTiO.sub.3         Nb.sub.2 O.sub.5                  MnO.sub.2                         GeO.sub.2                                of E.sub.10, %______________________________________46   99.48    0.01     0.01   0.5    -0.0747   98.99    0.01     0.50   0.5    -0.0648   96.99    0.01     2.50   0.5    -0.0649   99.39    0.10     0.01   0.5    -0.0650   98.90    0.10     0.50   0.5    -0.0651   96.90    0.10     2.50   0.5    -0.0552   96.99    2.50     0.01   0.5    -0.0553   96.50    2.50     0.50   0.5    -0.0554   94.50    2.50     2.50   0.5    -0.05______________________________________
The tabulated results all indicate little changes in the E.sub.10 of the varistors with the temperatures at which they operate. It can be concluded from this that the operating temperatures of the varistors prepared in accordance with the invention hardly affect their performance.
By way of example the E.sub.10 of the varistor of Test No. 5 in TABLE 25A was further measured at temperatures of -20 +80 represents the relation, (A-C)100/A, of this varistor, where A is as defined above and C is the value of E.sub.10 at each of the other temperatures. The curve F in the same graph plots a similar relation of the varistor of Test No. 41 in TABLE 25E. The curves show little changes in the E.sub.10 of the exemplified varistors over a wide temperature range. Obviously, the same holds true with the other varistors manufactured in accordance with the invention.
It is to be understood that the foregoing EXAMPLES are meant purely to illustrate or explain and not to impose limitations upon the invention. Experiment has proved, for example, that alumina, silica and other additives might be used insofar as they do not impair the desired properties of the ceramic materials in accordance with the invention. It has also been confirmed that the addition of up to 1.5% bismuth trioxide, with a view to the control of particle size, firing temperature, etc., does not adversely affect the desired properties of the ceramic materials. The appended claims should therefore be construed to specify only the fundamental ingredients of the inventive ceramics.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS3933668 *Jul 10, 1974Jan 20, 1976Sony CorporationIntergranular insulation type polycrystalline ceramic semiconductive compositionUS4073846 *Feb 3, 1976Feb 14, 1978Tdk Electronics Co., Ltd.Reduction-reoxidation type semiconducting ceramic capacitorUS4191665 *Sep 13, 1978Mar 4, 1980Murata Manufacturing Co., Ltd.Barium titanate semiconductor ceramic compositionsUS4283753 *Sep 28, 1979Aug 11, 1981Sprague Electric CompanyLow firing monolithic ceramic capacitor with high dielectric constantUS4292209 *May 2, 1979Sep 29, 1981The United States Of America As Represented By The United States Department Of EnergyCeramic component for MHD electrodeUS4347167 *Oct 1, 1980Aug 31, 1982University Of Illinois FoundationFine-grain semiconducting ceramic compositionsUS4362637 *Apr 1, 1981Dec 7, 1982Matsushita Electric Industrial Co. Ltd.Grain boundary layer dielectric ceramic compositionsUS4419310 *May 6, 1981Dec 6, 1983Sprague Electric CompanySrTiO.sub.3 barrier layer capacitor* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS4692289 *Jul 11, 1985Sep 8, 1987U.S. Philips CorporationMethod of manufacturing voltage-dependent resistorUS4746483 *Sep 9, 1986May 24, 1988Didier Engineering GmbhProcess for the manufacture of catalyst moldingUS4811164 *Mar 28, 1988Mar 7, 1989American Telephone And Telegraph Company, At&T Bell LaboratoriesMonolithic capacitor-varistorUS4839097 *Feb 9, 1987Jun 13, 1989Matsushita Electric Industrial Co., Ltd.Voltage-dependent non-linear resistance ceramic compositionUS5006957 *Jun 7, 1990Apr 9, 1991Canon Kabushiki KaishaSemiconductor porcelain substrate, dielectric porcelain substrate and capacitor employing the compositionUS5166759 *Mar 14, 1990Nov 24, 1992Matsushita Electric Industrial Co., Ltd.Semiconductor-type laminated ceramic capacitor with a grain boundary-insulated structureUS5166859 *Dec 20, 1991Nov 24, 1992Matsushita Electric Industrial Co., Ltd.Laminated semiconductor ceramic capacitor with a grain boundary-insulated structure and a method for producing the sameUS5225126 *Oct 3, 1991Jul 6, 1993Alfred UniversityPiezoresistive sensorUS5268006 *Jul 28, 1992Dec 7, 1993Matsushita Electric Industrial Co., Ltd.Ceramic capacitor with a grain boundary-insulated structureUS5294374 *Mar 20, 1992Mar 15, 1994Leviton Manufacturing Co., Inc.Electrical overstress materials and method of manufactureUS6030681 *Jul 10, 1997Feb 29, 2000Raychem CorporationMagnetic disk comprising a substrate with a cermet layer on a porcelain* Cited by examinerClassifications U.S. Classification264/617, 252/520.21, 252/519.5, 264/620, 252/519.33International ClassificationH01C7/10, H01G4/12, H01C7/115, C04B35/47Cooperative ClassificationC04B35/47, H01C7/115European ClassificationC04B35/47, H01C7/115Legal EventsDateCodeEventDescriptionNov 25, 1997FPExpired due to failure to pay maintenance feeEffective date: 19970917Sep 14, 1997LAPSLapse for failure to pay maintenance feesApr 22, 1997REMIMaintenance fee reminder mailedFeb 1, 1993FPAYFee paymentYear of fee payment: 8Dec 30, 1988FPAYFee paymentYear of fee payment: 4Sep 22, 1987CCCertificate of correctionRotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google