COMPOSITION OF PORCELAIN FOR VOLTAGE-DEPENDENT, NON-LINEAR RESISTOR

Abstract: The composition of a porcelain for a voltage-dependent, non-linear resistor includes SrTiO₃ as a main component, and Dy₂O₃ or Dy₂O₃ and Nb₂O₅, Ta₂O₅, or Ta₂O₆ and Nb₂O₅ as accelerators for making the crystals thereof semiconduc­ tive, so that the resistance of the crystals is lowered but additional components added thereto are segregated at the grain boundaries to increase the resistance thereof. When Dy₂O₃, or Dy₂O₃ and Nb₂O₅ are employed as the acceler­ ators, at least one component selected from the group consisting of Na, K, Ca, Cd, In, Ba, Pb, Ag, Ce, La, Sc, Y, Cs, Au, Mg, Zr, Sn, Sb, W, Bi, Ni, Fe, Ga, Pt, Tl, Al, Si, Be, Li, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os, Hf and Ru is used as an additional component. When Ta₂O₅, or Ta₂O₅ and Nb₂O₅ are employed as the accelerators, on the other hand, at least one compo­ nent selected from the group consisting of Na, K, Ca, Cd, In, Ba, Pb, Mg, Zr, Sn, Sb, W, Bi, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os, Hf, Ru, Ga, Pt, Tl, La, Sc, Y, Cs and Au is used as the additional component. As a result, varistor properties can be obtained by the high-resistance layers at the grain bound­ aries, and capacitor properties can be obtained between each grain - grain boundary - grain. This means that it is possible to obtain a single element which has the functions of both a varistor and a capacitor. Such an element is effective for the absorption of abnormally high voltages and the removal of noise.

Description: TECHNICAL FIELD The present invention relates to a voltage dependent non-linear resistance ceramic composition for use in surge absorbing and noise elimination in various electric apparatuses and electronic apparatuses. BACKGROUND ART Heretofore, in various electric apparatuses and electronic apparatuses, in order to absorb extraordinary high voltage, elimination of noise, elimination of arc, and the like, SiC varistors or varistors of the ZnO system having a voltage-dependent non-linear resistance characteristics are used. Voltage-current characteristic of such varistors can be approximately represented by the following equation: I = ( V/C ) α , wherein I is current, V is voltage, C is a constant proper for the varistor, and α is a voltage non-linearity exponent. The α of the SiC varistor is about 2-7, and for the ZnO system varistor there are some reaching an value of 50. Though such varistors have superior characteristics for absorbing relatively high voltage called surge, for voltages lower than varistor voltage (for instance, absorption of noise) almost no effect is observed, since its dielectric constant is low and its inherent capacitance is small, and their dielectric loss angles tan δ are as large as 5-10%. On the other hand, for elimination of low voltage noise, static electricity, or the like, by appropriately. selecting composition and firing condition, semiconductor ceramic capacitors having an apparent dielectric constant of about 5 x 10⁴ -6 x 10⁴ and tan δ of about 1% are utilized. However, these semiconductor ceramic capacitors are liable to be destroyed or to become non-functional as capacitors when extraordinary high voltage such as surge is impressed thereon or a current above a certain limit is impressed on the element. For such reason, in the electric apparatuses or electronic apparatuses, for the purpose of both the absorbing of high voltage surge and the elimination of low voltage noise, the varistors are used in combination with capacitors and other components (for instance, coil), and for instance, a noise filter has such a configuration. FIG. 1 shows a general noise filter circuit, FIG. 2 shows a conventional noise filter circuit constituted by combining a varistor, capacitors and a coil, wherein 1 is the coil, 2 are the capacitors and 3 is the varistor. When a noise input A as shown in FIG. 5 is impressed on these circuits, the output characteristic from general noise filter circuit of FIG. 1 is such as C of FIG. 5, and noise is not eliminated sufficiently. The output characteristic from the conventional noise filter circuit including a varistor shown in FIG. 2 is such as B of FIG. 5, and though noise is eliminated, such configuration has the shortcoming that it has a large number of components in the inside of the apparatus and besides is contrary to the tendency of miniaturization of the apparatus. Accordingly, an electronic component which absorbs extraordinaryly high voltage, can eliminate low voltage, such as noise, has a small number of components and is capable of miniaturization, is demanded. EP-A-0 070 and EP-A-0 044 981 both disclose non-linear resistance compositions which contain SrTiO₃ as the main component along with one or more further oxides. DISCLOSURE OF THE INVENTION The voltage-dependent non-linear resistance ceramic composition according to the present invention is characterized by comprising 80.000 - 99.990 mol% of SrTiO₃ and 0.005-10.000 mol% of Dy₂O₃ and at least one kind of compound selected from the group consisting of A said A consists of 0.005-10.000 mol% in the form of oxide of at least one kind of element selected from the group consisting of K, Ca, Cd, In, Ba, Pb, Ag, Ce, La, Sc, Y, Cs, Au, Mg, Zr, Sn, Sb, W, Bi, Ni, Fe, Pt, Tl, Be, Li, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os, Hf and Ru, and the mol percentages of all stated ingredients adding up to 100 mol%. According to another embodiment of the invention there is envisaged a voltage-dependent non-linear resistance ceramic composition characterized by comprising 79.800--99.989 mol% of Sr TiO₃, 0.005--10.000 mol% of Dy₂O₃, 0.001--0.200 mol% of Nb₂O₅ and 0.005--10.000 mol% in the form of oxide(s) of one or more element selected from the group consisting of K, Ca, Cd, In, Ba, Pb, Ag, Ce, La, Sc, Y, Cs, Au, Mg, Zr, Sn, Sb, W, Bi, Ni, Fe, Pt, Tl, Al, Si, Be, Li, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os, Hf and Ru, and the mol percentages of all stated ingredients adding up to 100 mol%. In a third embodiment of the invention the voltage-dependent non-linear resistance ceramic composition is characterized by comprising 80.000--99.990 mol% of SrTiO₃, 0.005--10.000 mol% of Dy₂O₃, 0.001--0.200 mol% of Nb₂O₅ and 0.005--10.000 mol% in the form of oxide(s) of one or more element selected from the group consisting of Ca, Ba, Ce, La, Y, Zr, Ni, Si and Gd, and the mol percentages of all stated ingredients adding up to 100 mol%. In a preferred embodiment this type of ceramic composition comprises 79.800--99.989 mol% of TiO₃, 0.005--10.000 mol% of Dy₂O₃, 0.001--0.200 mol% of Nb₂O₅ and 0.005--10.000 mol% in the form of oxide(s) of one or more element selected from the group consisting of Ca, Ba, Ce, La, Y, Zr, Ni, Si and Gd, the mol percentages of all stated ingredients adding up to 100 mol%. In a fourth embodiment of the invention the voltage-dependent non-linear resistance ceramic composition is characterized by comprising 80.000 - 99.990 mol% of SrTiO₃ and 0.005 - 10.000 mol% of Ta₂O₅ and 0.005 - 10.000 mol% in the form of oxide of at least one kind of element selected from the group consisting of K, Ca, Cd, In, Ba, Pb, Mg, Zr, Sn, Sb, W, Bi, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os, Hf, Ru, Pt, Tl, La, Sc, Y, Cs and Au, and the mol percentages of all stated ingredients adding up to 100 mol%. In a preferred embodiment this type of ceramic composition comprises 80.000 - 99.990 mol% of SrTiO₃, 0.005 - 10.000 mol% of Ta₂O₅, and 0,005 - 10.000 mol% in the form of oxide(s) of one or more element selected from the group consisting of Cd, Ba, Zr, Gd, La and Y, and the mol percentages of all stated ingredients adding up to 100 mol%. In a fifth embodiment of the invention the voltage-dependent non-linear resistance ceramic composition is characterized by comprising 79.800 to 99.989 mol% of SrTiO₃, 0.005 - 10.000 Mol% of Ta₂O₅, 0.001 - 0.200 Mol% of Nb₂O₅ and 0.005 - 10.000 Mol% in the form of oxide(s) of one or more element selected from the group consisting of K, Ca, Cd, In, Ba, Pb, Mg, Zr, Sn, Sb, W, Bi, La, Sc, Y, Cs, Au, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os, Hf and Ru, and the mol percentages of all stated ingredients adding up to 100 mol%. In a preferred embodiment this type of ceramic composition is characterized in that it comprises 79.800 - 99.989 mol% of SrTiO₃, 0.005 to 10.000 mol% of Ta₂O₅, 0.001 - 0.200 mol% of Nb₂O₅ and 0.005 - 10.000 mol% in the form of oxide(s) of one or more element selected from the group consisting of Cd, Ba, Ce, La, Y, Zr, Ni, Si and Gd, and the mol percentages of all stated ingredients adding up to 100 mol%. There are known ceramic materials with a voltage-dependent non-linear resistance, having however another composition both as regards the components regarded as essential and as regards their concentration. EP-A1-0 070 540 discloses ceramic compositions that must contain as essential surge-proofing component Na₂O in amounts of 0.02 to 2.50 mol parts. Additionally systems comprising Nb₂O₅ have a rather high content of this component, that is always greater than 0.2 mol percent. EP-A1-0 044 981 discloses ceramic materials which are even more different from those of the present invention in that they must comprise as important ingredients one or more of the following components: V₂O₅, Cr₂O₃, CuO, Cu₂O, MoO₃, MnO₂, the necessary amounts being 0.001 - 5 mol percent. The compositions according to the invention as heretofore defined do not contain such oxides. "Chemical Abstracts", Vol 86(1977), 86132232n, describes a ceramic material made from SrCO₃, TiO₂ and Dy₂O₃ using additionally 0.05 to 0.5 % by weight of kaolin as a binder material. This clay material comprises chemically bound water and, therefore, the concentrations of oxides of Al and Si, on a molar basis, are very low. For the receipt disclosed, comprising 0.15% by weight of kaolin a calculation demonstrates that the ceramic material comprises 0.025 to 0.261 mol% Al₂O₃ and 0.051 to 0.523 mol% SiO₂. BRIEF EXPLANATION OF THE DRAWING FIG.1 is a circuit diagram of a general noise filter, FIG.2 is a circuit diagram of a noise filter using the conventional varistors and capacitors, FIG.3 is a sectional view of an element using the voltage dependent non-linear resistance ceramic composition in accordance with the present invention, FIG.4 is a circuit diagram of a noise filter using the voltage dependent non-linear resistance ceramic composition in accordance with the present invention, FIG.5 is a characteristic chart showing the situation in respect of input noise and output in accordance with the circuit of noise filters of the present invention and the prior art. THE BEST MODE FOR EMBODYING THE INVENTION As a result of accumulating various experiments the inventors propose a voltage dependent non-linear resistance ceramic composition in a system different from the conventional composition by using strontium-titanate (SrTiO₃) as host material, and adding either Dy₂O₃ or Ta₂O₅ as semi-conductorization accelerating agent, and by further adding, depending on necessity, appropriate amounts of additives; hereafter the present invention is described with respect to the different embodiments as heretofore defined. Examples Nos. 1 to 8 are using Dy₂O₃ as addition, examples Nos. 9 to 15 are using Dy₂O₃ + Nb₂O₅ as addition. In examples Nos. 16 to 21 Ta₂O₅ is used instead of Dy₂O₃ and in examples Nos. 22 to 27 Ta₂O₅ in combination with Nb₂O₅ is added. EXAMPLE 1 SrTiO₃ and Dy₂O₃ and BaO are used in amounts to give the composition ratios as shown in the below-mentioned Table 1, they are blended for 6 hours by a wet method in a ball-mill or the like, and after drying the mixture is calcinated for 1 to 5 hours at 1000 - 1250°C in air. After grinding for 4 hours with the wet method in a ball mill or the like and subsequently drying, the mixture is granulated by adding 8 wt % of an organic binder (for instance polyvinyl alcohol), and then press-formed to the size of 8.0(mm) Ø x 1.0(mm) t with a pressing force of 1.0 t/cm². The granulated body is fired in a reducing atmosphere (e.g. N₂ : H₂ = 10 : 1) at 1300 - 1450°C for 1 - 6 hours. The fired body thus obtained has a specific resistance of 0.1 - 0.8 Ω.cm and an average granular size of 20 to 50 µm. The fired body is further fired in air at 1000 - 1300°C for 0.5 - 5 hours to obtain the fired body 4 of FIG.3. Both faces of the fired body 4 are ground with an abrasive, such as SiC. The diameters of the above-mentioned electrodes 5, 6 are selected to be 5.0(mm). The characteristics of the elements thus obtained are shown in TABLE 1. Eveluation of the characteristics of the elements as varistor can be made by α and C in a voltage-current characteristic equation: I = (V/C) α (wherein I is the current, V is the voltage, C is a constant proper to the varistor and α is a non-linearity exponent). Since the accurate measurement of C is difficult, in the present invention the characteristic assessment as a varistor is made by the value of varistor voltage for unit thickness when 1 mA of varistor current has flown (hereinafter expressed as V₁mA/mm) and by a value of α = 1/log (V₁₀mA/V₁mA) (wherein V₁₀mA is a varistor voltage when a varistor current of 10 mA has flown and V₁mA is a varistor voltage when a varistor current of 1 mA has flown). Characteristic assessment as capacitors are made by the dielectric constant and by the dielectric loss tan δ at a measurement frequency of 1 KHz. The above-mentioned data are those for a firing temperature of 1400°C and a firing time in the reducing atmosphere of 2 hours, respectively, and a firing temperature of 1200°C and a firing time in air of 3 hours, respectively. EXAMPLE 2 SrTiO₃, Dy₂O₃ and CeO₂ are used in composition ratios as shown in the below-mentioned TABLE 2, and mixing, forming and firings are carried out in a similar operation as in the above-mentioned EXAMPLE 1, and the measurements are made under similar conditions, results are shown in TABLE 2. EXAMPLE 3 SrTiO₃, Dy₂O₃ and La₂O₃ are used in composition ratios shown in the below-mentioned TABLE 3, and mixing, forming and firings are carried out in a similar operation as in the above-mentioned EXAMPLE 1, and measurements are made under similar conditions. Results are shown in TABLE 3. EXAMPLE 4 SrTiO₃, Dy₂O₃ and Y₂O₃ are used in composition ratios as shown in the below-mentioned TABLE 4, and mixing, forming and firings are carried out in a similar operation as in the above-mentioned EXAMPLE 1, and the measurements are made under similar conditions. Results are shown in TABLE 4. EXAMPLE 5 SrTiO₃, Dy₂O₄ and ZrO₂ are used in composition ratios shown in the below-mentioned TABLE 5, and mixing, forming and firings are carried out in a similar operation as in the above-mentioned EXAMPLE 1, and the measurements are made under similar conditions; Results are shown in TABLE 5. EXAMPLE 6 SrTiO₃, Dy₂O₃ and NiO are used in composition ratios as shown in the below-mentioned TABLE 6, and mixing, forming and firings are carried out in a similar operation as in the above-mentioned EXAMPLE 1, and the measurements are made under similar conditions. Results are shown in TABLE 6. EXAMPLE 7 SrTiO₃, Dy₂O₃ and Gd₂O₃ are used in composition ratios as shown in the below-mentioned TABLE 7 and mixing, forming and firings are carried out in a similar operation as in the above-mentioned EXAMPLE 1, and the measurements are made under similar conditions. Results are shown in TABLE 7. As shown by EXAMPLEs 1 through 7, Dy₂O₃ when added in amounts in a range of 0.005-10.000 mol %, contributes to reduce specific resistance of the reduced fired body, and by re-firing in air it shows varistor characteristics. This is because the granules and grain boundaries of the fired body obtained by the reduced firing have low resistances, and by re-firing in air only the crystal boundaries are gaining a high resistance thereby forming electric barriers. However, when only Dy₂O₃ is added, the electric barrier formed at the grain boundaries is small, and the varistor characteristics are relatively small. Accordingly, by adding additives such as BaO, CeO₂, La₂O₃, Y₂O₃, ZrO₂, NiO, SiO₂ or Gd₂O₃ , the additive is segregated at the grain boundaries during the reduced firing, and by re-firing in air such additives form large electric barriers at the grain boundary, thereby making the varistor characteristics large. By making only the crystal grain boundary high in resistance, capacitance characteristics are present between crystal granule-crystal grain boundaries-crystal granules. Accordingly, by adding Dy₂O₃ and still another additive, such as BaO, CeO₂, La₂O₃, Y₂O₃, ZrO₂, NiO, SiO₂, Gd₂O₃ to SrTiO₃, it is possible to provide characteristics which combine the varistor characteristics and the capacitance characteristics. Though in the above-mentioned EXAMPLES 1-8, the elucidation was made for the cases where only one other additive was added besides Dy₂O₃, it was confirmed that the same effect was obtained even when two kinds or more oxides of elements of the group consisting of K, Ca, Cd, In, Ba, Pb, Ag, Ce, La, Sc, Y, Cs, Au, Mg, Zr, Sn, Sb, W, Bi, Ni, Fe, Pt, Tl, Al, Si, Be, Li, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os, Hf and Ru were used in a manner that the total added amount is within the above-mentioned range. EXAMPLE 8 SrTiO₃, an extremely small amount of Nb₂O₅ which was existing from the initial stage of material (Nb₂O₅ content in the material used in the present example was 0.050 mol %), Dy₂O₃ as a metal oxide for acceleration of semiconductorization and CaO as element to improve non-linearity were used in amounts necessary to give the composition ratios shown in the below-mentioned TABLE 8. They were mixed and ground and dried, and thereafter calcinated at 1000°C for 4 hours. This mixture was then ground by a wet method in a ball mill or the like for 4 hours, and dried, subsequently, the mixture was granulated by adding 8 wt % of an organic binder (e.g. polyvinylalcohol) and pressformed into a shape of disc of 8.0 Ø (mm) x 1.0 t (mm) with a forming pressure of about 1.0 t/cm². The formed body was fired for 4 hours in a reducing atmosphere (e.g. N₂:H₂= 1:1, flow rate is 1.0ℓ/min) and at 1350°C. The specific resistance of the fired body thus obtained was averagely 0.3 Ω.cm and the average granule size was 30 µm. The above-mentioned fired body was fired in air for 2 hours at 1300°C to obtain a sintered body 4 of FIG.3. Both faces of the above-mentioned sintered body 4 are ground by using an abrasive such as SiC or the like, and the electrodes 5, 6 are formed by using a conductive metal such as Ag on the ground faces. Sizes of electrodes 5, 6 are circles of 5.0 Ø (mm) each. The characteristics of the devices thus obtained are shown in TABLE 8. EXAMPLE 9 SrTiO₃, a very small amount of Nb₂O₅ which was existing from the initial stage of the material (contents of Nb₂O₅ of the material used in the present example was 0.050 mol %), Dy₂O₃ as a metal oxide for accelerating semiconductorization and CeO₂ as an element to improve non-linearity are mixed, formed, reduced, fired and oxidated in a similar operation as that of the above-mentioned EXAMPLE 8. Results obtained by measuring the characteristics of the devices thus obtained under similar conditions as in the above-mentioned examples are shown in TABLE 9. EXAMPLE 10 SrTiO₃, a very small amount of Nb₂O₅ which was existing from the initial stage of a material (contents of Nb₂O₅ of the material used in the present example was 0.050 mol %), Dy₂O₃ as metal oxide for accelerating semiconductorization and ZrO₂ as an element to improve non-linearity are mixed, formed, reduced, fired and oxidated in a similar operation as that of the above-mentioned EXAMPLE 8. Results obtained by measuring the characteristics of devices thus obtained under similar conditions as in the above-mentioned examples are shown in TABLE 10. EXAMPLE 11 SrTiO₃, a very small amount of Nb₂O₅ which was existing from the initial stage of material (contents of Nb₂O₅ of the material used in the present example was 0.050 mol %), Dy₂O₃ as metal oxide for accelerating semiconductorization and NiO as an element to improve non-linearity are mixed, formed, reduced, fired and oxidated in a similar operation as that of the above-mentioned EXAMPLE 8. Results obtained by measuring the characteristics of the devices thus obtained under similar conditions as in the above-mentioned examples are shown in TABLE 11. EXAMPLE 12 SrTiO₃, a very small amount of Nb₂O₅ which was existing from the initial stage of material (contents of Nb₂O₅ of the material used in the present example was 0.050 mol %), Dy₂O₃ as metal oxide for accelerating semiconductorization and La₂O₃ as an element to improve non-linearity are mixed, formed, reduced , fired and oxidated in a similar operation as that of the above-mentioned EXAMPLE 8. Results obtained by measuring the characteristics of the devices thus obtained under similar conditions as in the above-mentioned examples are shown in TABLE 12. EXAMPLE 13 SrTiO₃, a very small amount of Nb₂O₅ which was existing from the initial stage of material (contents of Nb₂O₅ of the material used in the present example was 0.050 mol %), Dy₂O₃ as metal oxide for accelerating semiconductorization and Y₂O₃ as an element to improve non-linearity are mixed, formed, reduced, fired and oxidated in a similar operation as that of the above-mentioned EXAMPLE 8. Results obtained by measuring the characteristics of the devices thus obtained under similar conditions as in the above-mentioned examples are shown in TABLE 13. EXAMPLE 14 SrTiO₃, a very small amount of Nb₂O₅ which was existing from the initial stage of the material (contents of Nb₂O₅ of the material used in the present example was 0.050 mol %), Dy₂O₃ as metal oxide for accelerating semiconductorization and Gd₂O₃ as an element to improve non-linearity are mixed, formed, reduced, fired and oxidated in a similar operation as that of the above-mentioned EXAMPLE 8. Results obtained by measuring the characteristics of the devices thus obtained under similar conditions as that in the above-mentioned examples are shown in TABLE 14. As shown by EXAMPLES 9 through 15, in a case where Dy₂O₃ is added in amounts of 0.005 - 10.000 mol % together with a small amount of Nb₂O₅, this contributes to reduce the specific resistance of the reduced fired body, and by refiring in air it shows varistor characteristics. Herein, the amount of Nb₂O₅ is that of an impurity naturally included in the starting material TiO₂, and its concentration is in a range of 0.001 - 0.200 mol % (result of analysis). The effect of Dy₂O₃ for semiconductorization of SrTiO₃ is not damaged even in the case when Nb₂O₅ is present at the same time. Accordingly, even when Dy₂O₃ and Nb₂O₅ are used at the same time as accelerating agent for semiconductorization, it is possible to produce the varistor characteristics. However, in the case when only Dy₂O₃ and Nb₂O₅ are added, the electric barrier formed at the grain boundaries is low, and the varistor characteristics are relatively small. However, when an additive such as CaO, CeO₂, ZrO₂, NiO, La₂O₃, Y₂O₃, Gd₂O₃ or the like is added, the added substance is segregated at the crystal granule boundaries during the reducing firing, and by re-firing in air these additives contribute to give the crystal grain boundaries a high resistance, and the varistor characteristics become greater. Besides, since only the crystal grain boundaries are given high resistance, the capacitance characteristic is present between crystal grain-crystal grain boundary-crystal grain. Accordingly, by adding Dy₂O₃, Nb₂O₅ and such additives as CaO, CeO₂, ZrO₂, NiO, La₂O₃, Y₂O₃ or Gd₂O₃ to SrTiO₃, it is possible to provide characteristics combining the varistor characteristics and the capacitance characteristics. Though in the above-mentioned EXAMPLEs 8 - 14 only one other additive was added besides Dy₂O₃ and Nb₂O₅, it was confirmed that the same effect was obtained even when two kinds or more of oxides of elements of the group consisting of K, Ca, Cd, In, Ba, Pb, Ag, Ce, La, Sc, Y, Cs, Au, Mg, Zr, Sn, Sb, W, Bi, Ni, Fe, Pt, Tl, Al, Si, Be, Li, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os, Hf and Ru were used in a manner that the total amount is within the above-mentioned range. By using elements 7 made by providing electrodes of conductive material such as Ag on the sintered body obtained as above and a coil B, a noise filter shown in FIG.4 is constituted, and by impressing a noise input A shown in FIG.5 thereon, a noise output B was obtained. As is obvious from this, the noise is satisfactorily eliminated, and besides, the number of components is decreased by the combination of the element unit and the coil, enabling this miniaturization. EXAMPLE 15 SrTiO₃, Ta₂O₅ and CdO are used in amounts to give the composition ratios shown in the below-mentioned TABLE 15, they were mixed by a wet method in a ball mill or the like for 6 hours, dried and thereafter calcinated at 1000-1250°C in air for 1-5 hours. Thereafter the mixture was ground by a wet method in a ball mill or the like for 4 hours, dried, subsequently granulated by adding 8 wt % of an organic binder (for instance, polyvinylalcohol)and press-formed into the shape of a disc of 8.0 (mm) Ø x 1.0 (mm)t with a forming pressure of about 1.0 t/cm² . The formed body was fired for 1-6 hours in a reducing atmosphere (for instance, N₂ : H₂ = 10 : 1) at 1300-1450°C. The specific resistance of the fired body thus obtained was averagely 0.1-0.8 Ω.cm, and the average granule size was 20-50 µm. The above-mentioned fired body was then baked in air for 0.5-5 hours at 1000-1300°C to obtain a sintered body 4 of FIG. 3. Both faces of the above-mentioned sintered body 4 were ground by using an abrasive such as SiC, and electrodes 5, 6 were formed by using a conductive metal such as Ag thereon. The electrodes 5, 6 are circles of 5.0 (mm)Ø each. The characteristics of the devices thus obtained are shown in TABLE 15. With respect to assessments of the varistor elements thus obtained, they were made under the same conditions as in EXAMPLE 1. EXAMPLE 16 SrTiO₃, Ta₂O₅ and BaO are used in composition ratios as shown in Table 16 and mixing, forming und firing are carried out in a similar operation as in the above-mentioned EXAMPLE 15 the measurements are made under similar conditions, too, and results are shown in Table 16. EXAMPLE 17 SrTiO₃, Ta₂O₅ and ZrO₂ are used in composition ratios as shown in Table 17 and mixing, forming and firing are carried out in a similar operation as in the above-mentioned EXAMPLE 15 the measurments are made under similar conditions, too, and results are shown in Table 17. EXAMPLE 18 SrTiO₃, Ta₂O₅ and La₂O₃ are used in composition ratios as shown in Table 18 and mixing, forming and firing are carried out in a similar operation as in the above-mentioned EXAMPLE 15 measurements are made under similar conditions, too, and results are shown in Table 18. EXAMPLE 19 SrTiO₃, Ta₂O₅ and Y₂O₃ are used in composition ratios as shown in Table 19 and mixing, forming and firing are carried out in a similar operation as in the above-mentioned EXAMPLE 15, measurements are made under similar conditions, too, and results are shown in Table 19. EXAMPLE 20 SrTiO₃, Ta₂O₅ and Gd₂O₃ are used in composition ratios shown in Table 20 and mixing, forming and firing are carried out in a similar operation as in the above-mentioned EXAMPLE 15; measurements are made under similar conditions, too, and results are shown in Table 20. As shown by EXAMPLEs 15 through 20 Ta₂O₅ when added in amounts in a range of 0.005-10.000 mol %, contributes to reduce the specific resistance of the reduced fired body, and by re-firing in air it shows varistor characteristics. This is because the granules and grain boundaries of the fired body obtained by the reduced firing have low resistances, and by re-firing in air only the crystal boundaries are gaining a high resistance thereby forming electric barriers. However, when only Ta₂O₅ is added, the electric barrier formed at the grain boundaries is small, and the varistor characteristics are relatively small. Accordingly, by adding additives such as CdO, BaO, ZrO₂, La₂O₃, Y₂O₃ or Gd₂O₃, the additive is segregated at the grain boundaries during the reduced firing, and by re-firing in air such additives form large electric barriers at the grain boundary, thereby making the varistor characteristics large. By making only the crystal grain boundary high in resistance, capacitance characteristics are present between crystal granule-crystal grain boundaries-crystal granules. Accordingly, by adding Ta₂O₅ and another additive, such as CdO, BaO, ZrO₂, La₂O₃, Y₂O₃ or Gd₂O₃ to SrTiO₃, it is possible to provide characteristics which combine the varistor characteristics and the capacitance characteristics. Though in the above-mentioned EXAMPLES 15 - 20 the elucidation was made for the cases where one additive was added besides Ta₂O₅, it was confirmed that the same effect was obtained even when two kinds or more of oxides of elements of the group consisting cf K, Ca, Cd, In, Ba, Pb, La, Sc, Y, Cs, Au, Mg, Zr, Sn, Sb, W, Bi, Pt, Tl, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os, Hf and Ru were used so that the total added amount is within the above-mentioned range. EXAMPLE 21 SrTiO₃, an extremely small amount of Nb₂O₅ which existed from the initial stage of the material (Nb₂O₅ content in the material used in the present example was 0.050 mol %), Ta₂O₅ as metal oxide for acceleration of semiconductorization and CdO as element to improve non-linearity are used in amounts to give the composition ratios shown in the below-mentioned TABLE 21 They were mixed, ground, dried and thereafter calcinated at 1000°C for 4 hours. This mixture was ground again by a wet method in a ball mill or the like for 4 hours, then dried, subsequently granulated by adding 8 wt % of an organic binder (for instance polyvinylalcohol), and pressformed into the shape of a disc of 8.0 Ø (mm) x 1.0 t (mm) with a forming pressure of about 1.0 t/cm². The formed body was fired for 4 hours in a reducing atmosphere (e.g. N₂ :H₂ = 1:1, flow rate is 1.0 1/min) at 1350°C. The specific resistance of the fired body thus obtained was averagely 0.3 Ω.cm, and the average granule size was 30 µm. The above-mentioned fired body was then baked in air for 2 hours at 1300°C to obtain a sintered body 4 of FIG.3. Both faces of the above-mentioned sintered body 4 were ground by using an abrasive such as SiC or the like, and electrodes 5, 6 were formed by using a conductive metal, such as Ag on the ground faces. The electrodes 5, 6 are circles of 5.0 Ø (mm) each. The characteristic of the devices thus obtained are shown in TABLE 21. EXAMPLE 22 SrTiO₃, a very small amount of Nb₂O₅ which existed from the initial stage of material (contents of Nb₂O₅ of the material used in the present example was 0.050 mol %), Ta₂O₅ as metal oxide for accelerating semiconductorization and BaO as an element to improve non-linearity are formed, reduced, fired and oxidated in a similar operation as that of the above-mentioned EXAMPLE 21. Results obtained by measuring the characteristics of the devices thus obtained under similar conditions as in the above-mentioned examples are shown in TABLE 22. EXAMPLE 23 SrTiO₃, a very small amount of Nb₂O₅ which existed from the initial stage of material (contents of Nb₂O₅ of the material used in the present example was 0.050 mol %), Ta₂O₅ as metal oxide for accelerating semiconductorization and ZrO₂ as an element to improve non-linearity are formed, reduced, fired and oxidated in a similar operation as that of the above-mentioned EXAMPLE 21. Results obtained by measuring the characteristics of the devices thus obtained under similar conditions as in the above-mentioned examples are shown in TABLE 23. EXAMPLE 24 SrTiO₃, a very small amount of Nb₂O₅ which existed from the initial stage of the material (contents of Nb₂O₅ of the material used in the present example was 0.050 mol %), Ta₂O₅ as metal oxide for accelerating semiconductorization and La₂O₃ as an element to improve non-linearity are formed, reduced, fired and oxidated in a similar operation as that of the above-mentioned EXAMPLE 21. Results obtained by measuring the characteristics of the devices thus obtained under similar conditions as in the above-mentioned examples are shown in TABLE 24. EXAMPLE 25 SrTiO₃, a very small amount of Nb₂O₅ which existed from the initial stage of the material (contents of Nb₂O₅ of the material used in the present example was 0.050 mol %), Ta₂O₅ as metal oxide for accelerating semiconductorization and Y₂O₃ as an element to improve non-linearity are formed, reduced , fired and oxidated in a similar operation as that of the above-mentioned EXAMPLE 21. Results obtained by measuring the characteristics of the devices thus obtained under similar conditions as in the above-mentioned examples are shown in TABLE 25. EXAMPLE 26 SrTiO₃, a very small amount of Nb₂O₅ which existed from the initial stage of the material (contents of Nb₂O₅ of the material used in the present example was 0.050 mol %), Ta₂O₅ as metal oxide for accelerating semiconductorization and Gd₂O₃ as an element to improve non-linearity are formed, reduced, fired and oxidated in a similar operation as that of the above-mentioned EXAMPLE 21. Results obtained by measuring the characteristics of the devices thus obtained under similar conditions as in the above-mentioned examples are shown in TABLE 26. As shown by EXAMPLEs 21 through 26 in a case where Ta₂O₅ is added in amounts of 0.005-10.000 mol % together with a small amount of Nb₂O₅ this contributes to reduce the specific resistance of the reduced fired body, and by re-firing in air it shows varistor characteristics. Herein, the amount of Nb₂O₅ was that of an impurity naturally included in the starting material TiO₂, and its concentration was in a range of 0.001-0.200 mol % Though for semiconductorization of SrTiO₃, Ta₂O₅ is more effective than Nb₂O₅, the effect of Ta₂O₅ is not damaged even in the case wherein Nb₂O₅ is present at the same time. Accordingly, even when Ta₂O₅ and Nb₂O₅ are used at the same time as accelerating agent for semiconductorization, it is possible to produce the varistor characteristics. However, in the case when only Ta₂O₅ and Nb₂O₅ are added, the electric barrier formed at the grain boundaries is low, and the varistor characteristics are relatively small. However,when such an additive as CdO, BaO, ZrO₂, La₂O₃, Y₂O₃, Gd₂O₃ or the like is added, the added substance is segregated at the crystal granule boundaries during the reducing firing, and by re-firing in air these additives contribute to give the crystal grain boundaries a high resistance, and the varistor characteristics become greater. Besides, since only the crystal grain boundaries are given high resistance, the capacitance characteristic is present between crystal grain-crystal grain boundary-crystal grain. Accordingly, by adding Ta₂O₅, Nb₂O₅ and such additive as CdO, BaO, ZrO₂, La₂O₃, Y₂O₃ or Gd₂O₃ to SrTiO₃, it is possible to provide characteristics combining the varistor characteristics and the capacitance characteristics. Though in the above-mentioned EXAMPLEs 21 - 26 only one other additive was added besides Ta₂O₅ and Nb₂O₅, it was confirmed that the same effect was obtained even when two kinds or more of oxides of elements of the group consisting of K, Ca, Cd, In, Ba, Pb, La, Sc, Y, Cs, Au, Mg, Zr, Sn, Sb, W, Bi, Pt, Tl, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os, Hf and Ru were used in a manner that the total added amount is within the above-mentioned range. When electrodes were provided by conductive material such as Ag on a thus obtained element, and a noise filter shown in FIG.4 was constituted therewith, and a noise input A as shown in FIG.5 was impressed thereon, an output of the same characteristics as that of the noise output B was obtained. As is apparent from this, the noise is sufficiently eliminated, and also by combining the element unit and the coil the number of components is reduced and miniaturization becomes possible. POSSIBLE UTILIZATION IN INDUSTRY As has been elucidated, according to the voltage-dependent non-linear resistance ceramic composition, absorption or surge impressed on the electric and electronic apparatuses and elimination of noise can be effected by a element, and it has many functions and can be miniaturized and is indispensable for protection of a semiconductor product in electric and electronic apparatuses, therefore the practical utility thereof is extremely great. LIST OF REFERENCE NUMERALS IN THE DRAWING 1 coil 2 capacitors 3 baristor 4 sintered body 5 electrode 6 electrode 7 element using ceramic composition of the present invention 8 coil A noise input B output characteristic of the noise filter circuit shown in FIG. 2 C output characteristic of the noise filter circuit shown in FIG. 1

Claims: A voltage-dependent non-linear resistance ceramic composition characterized by comprising 80.000 - 99.990 mol% of SrTiO₃ and 0.005 - 10.000 mol% of Dy₂O₃ and at least one kind of compound selected from the group consisting of A said A consists of 0.005 - 10.000 mol% in the form of oxide of at least one kind of element selected from the group consisting of K, Ca, Cd, In, Ba, Pb, Ag, Ce, La, Sc, Y, Cs, Au, Mg, Zr, Sn, Sb, W, Bi, Ni, Fe, Pt, Tl, Be, Li, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os, Hf and Ru, and the mol percentages of all stated ingredients adding up to 100 mol%. A voltage-dependent non-linear resistance ceramic composition characterized by comprising 79.800 - 99.989 mol% of SrTiO₃, 0.005 - 10.000 mol% of Dy₂O₃, 0.001 - 0.200 mol% of Nb₂O₅ and 0.005 - 10.000 mol% in the form of oxide(s) of one or more element selected from the group consisting of K, Ca, Cd, In, Ba, Pb, Ag, Ce, La, Sc, Y, Cs, Au, Mg, Zr, Sn, Sb, W, Bi, Ni, Fe, Pt, Tl, Al, Si, Be, Li, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os, Hf and Ru, and the mol percentages of all stated ingredients adding up to 100 mol%. A voltage-dependent non-linear resistance ceramic composition characterized by comprising 80.00 - 99.990 mol% of SrTiO₃, 0.005 - 10.000 mol% of Dy₂O₃, 0.001 - 0.200 mol% of Nb₂O₅ and 0.005 - 10.000 mol% in the form of oxide(s) of one or more element selected from the group consisting of Ca, Ba, Ce, La, Y, Zr, Ni, Si and Gd, and the mol percentages of all stated ingredients adding up to 100 mol%. A voltage-dependent non-linear resistance ceramic composition in accordance with claim 2, characterized in that it comprises 79.800 - 99.989 mol% of SrTiO₃, 0.005 - 10.000 mol% of Dy₂O₃, 0.001 - 0.200 mol% of Nb₂O₅ and 0.005 - 10.000 mol% in the form of oxide(s) of one or more element selected from the group consisting of Ca, Ba, Ce, La, Y, Zr, Ni, Si and Gd. and the mol percentages of all stated ingredients adding up to 100 mol%. A voltage-dependent non-linear resistance ceramic composition characterized by comprising 80.000 - 99.990 mol% of SrTiO₃ and 0.005 - 10.000 mol% of Ta₂O₅ and 0.005 - 10.000 mol% in the form of oxide of at least one kind of element selected from the group consisting of K, Ca, Cd, In, Ba, Pb, Mg, Zr, Sn, Sb, W, Bi, Eu, Gd, Tb, Tm, Lu, Th, Sr, Os, Hf, Ru, Pt, Tl, La, Sc, Y, Cs and Au, and the mol percentages of all stated ingredients adding up to 100 mol%. A voltage-dependent non-linear resistance ceramic composition characterized by comprising 79.800 - 99.989 mol% of SrTiO₃, 0.005 - 10.000 mol% of Ta₂O₅, 0.001 - 0.200 mol% of Nb₂O₅ and 0.005 - 10.000 mol% in the form of oxide(s) of one or more element selected from the group consisting of K, Ca, Cd, In, Ba, Pb, Mg, Zr, Sn, Sb, W, Bi, La, Sc, Y, Cs, Au, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os, Hf and Ru, and the mol perventages of all stated ingredients adding up to 100 mol%. A voltage.-dependent non-linear resistance ceramic composition in accordance with claim 5, characterized in that it comprises 80.000 - 99.990 mol% of SrTiO₃, 0.005 - 10.000 mol% of Ta₂O₅, and 0.005 - 10.000 mol% in the form of oxide(s) of one or more element selected from the group consisting of Cd, Ba, Zr, Gd, La and Y, and the mol percentages of all stated ingredients adding up to 100 mol%. A voltage-dependent non-linear resistance ceramic composition in accordance with claim 6, characterized in that it comprises 79.800 - 99.989 mol% of SrTiO₃, 0.005 - 10.000 mol-% of Ta₂O₅, 0.001 - 0.200 mol% of Nb₂O₅ and 0.005 - 10.000 mol% in the form of oxide(s) of one or more element selected from the group consisting of Cd, Ba, Ce, La, Y, Zr, Ni, Si and Gd and the mol percentages of all stated ingredients adding up to 100 mol%.

Inventors: EBINE, KAZUHIDE, KUMAZAWA, KIMIKO, NOI, KEIICHI, TAKAMI, AKIHIRO
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1984
Main classification: H01C7
IPC codes: H01C7, C04B35