JPH0248122B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a ceramic composition for varistors having a large voltage nonlinearity index. [Prior Art] Varistor elements are used in electronic circuits for purposes such as absorbing abnormal voltage and removing noise. Conventional varistor elements use ceramic compositions containing SrTiO as a main component and various other oxides. For example, in a varistor element configured by providing a pair of silver electrodes on the surface of the above-mentioned porcelain with a diameter of 5.1 mm and a thickness of 0.8 mm, the varistor voltage (the applied voltage required to flow a current of 0.1 mA, the same applies hereinafter) is 15
~40V, wavefront length 8μs, wavetail length as shown in Figure 2
Rate of change in varistor voltage V ₁ when a 20μs surge current is applied five times at 10 second intervals and left at room temperature for one hour (hereinafter simply referred to as "rate of change in varistor voltage")
ΔV ₁ is −0.3 to −0.8% Voltage nonlinear index α is 13 to 15
It has the following characteristics, and the capacitance C is 30000
~4000PF. In Patent Application No. 27675 filed in 1982, the inventors of the present invention disclosed a ceramic composition capable of obtaining a varistor element with a smaller capacitance C than that of conventional ones without significantly changing the rate of change V ₁ of the varistor voltage. Disclosed.
Its contents are Sr _1-x Mg _x TiO ₃ (0.05≦x≦0.5)
The main component is group a of the periodic table of elements (La, Ce,
Pr, Nd, Sm, Eu, Dy, Y), group a (Nb,
This is a ceramic composition consisting of NaF and a component that acts as an atomic control material, which is an oxide of Ta) or group a (W). In a varistor element of the same shape as above made using this porcelain, the varistor voltage V ₁ is 12~
40V, the rate of change ΔV ₁ of the same voltage was −0.4 to −1.0%, the voltage nonlinearity index α was 11.1 to 13.9, and the capacitance C was 450 to 2280PF. However, in order to accommodate a wide range of uses, it is desired to develop a ceramic composition that can obtain a higher voltage nonlinearity index α. [Objective of the Invention] The present invention aims to provide a porcelain composition that allows a varistor with a large voltage nonlinearity index α, which could not be obtained with conventional varistor porcelain compositions, to be obtained without changing its shape or other mechanical properties. This is the purpose. [Structure of the invention] The porcelain composition according to the present invention has Sr _1-x Mg _x TiO ₃
(However, 0.05≦x≦0.5) (hereinafter referred to as the first component) and 100 mole parts of La ₂ O ₃ , CeO ₂ ,
Nd ₂ O ₃ , Y ₂ O ₃ , Pr ₆ O ₁₁ , Sm ₂ O ₃ , Eu ₂ O ₃ ,
0.01 to 3.00 mole parts of one or more components among Dy ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , and WO ₃ (hereinafter referred to as the second component) and 0.01 to 1.25 mole parts of NaF (hereinafter referred to as the third component) A component consisting of a molar part and one or more of Ag ₂ O, CuO, Al ₂ O ₃ , SiO ₂ , MnO ₂ (hereinafter referred to as the fourth component)
It is made by sintering porcelain raw material consisting of 0.01 to 3.00 mole parts. In this case, the third component may not be used as a starting material together with the first, second and fourth components, but may be incorporated into the porcelain by means of so-called thermal diffusion. That is, after molding and sintering the porcelain raw material excluding this third component, the powder of the third component is placed on the main surface of the obtained porcelain, and this is treated at a temperature of 800 to 1300°C. Components can be incorporated into the porcelain. As already mentioned, the varistor element is constructed by providing a pair of opposing electrodes on both sides of the above-mentioned ceramic composition formed into a plate shape. [Example] Next, this example and its comparative example will be explained. Example 1 First, SrCO ₃ , MgCO ₃ , and TiO ₂ with a purity of 97.5% were each weighed in the proportions shown in Table 1, mixed in a ball mill for 10 hours, and then desorbed.

〔Effect of the invention〕

As described above, by using the ceramic composition according to the present invention, the voltage can be increased without significantly changing the characteristics such as the varistor voltage V ₁ , its rate of change ΔV ₁ , and capacitance C while maintaining the compact size. A varistor element with a particularly large dependent nonlinearity index α is obtained.
This allows it to be used in a wider range of applications.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a lightning surge tolerance tester used in measuring the rate of change in varistor voltage due to surge current of a sample in an embodiment of the present invention;
FIG. 2 is a chart showing the waveform of a surge current applied to a sample in the same test device.

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Claims (1)

[Claims] 100 mole parts of a component consisting of 1 Sr _1-x Mg _x TiO ₃ (0.05≦x≦0.5) and La ₂ O ₃ , CeO ₂ , Nd ₂ O ₃ ,
Y ₂ O ₃ , Pr ₆ O ₁₁ , Sm ₂ O ₃ , Eu ₂ O ₃ , Dy ₂ O ₃ ,
One or more components among Nb ₂ O ₅ , Ta ₂ O ₅ , WO ₃ 0.01~
3.00 mol parts, 0.01 to 1.25 mol parts of NaF, and Ag ₂ O,
One or more components among CuO, Al ₂ O ₃ , SiO ₂ , MnO ₂
A porcelain composition for a varistor, characterized in that it is made by sintering a composition containing 0.01 to 3.00 mole parts.