JPH0440853B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a nonlinear dielectric element having excellent nonlinearity and made of a BaTiO ₃ polycrystal. [Prior art] In general, ABO ₃ -based ferroelectrics with a perovskite structure, mainly BaTiO ₃ -based ceramics, are applied in fields that make use of their high dielectric constant and piezoelectric properties, as well as applications of ferroelectric materials that utilize their high permittivity and piezoelectric properties. Fields that utilize nonlinearity are known. In recent years, as a new example of application, the use of such ferroelectric materials as high-voltage pulse generating elements for non-contact starting devices for discharge lamps such as fluorescent lamps, mercury discharge lamps, and sodium discharge lamps has been reported in Japanese Patent Publication No. 48-28726. Disclosed in, etc. By the way, nonlinear dielectric elements used for such applications must have a steep DE hysteresis curve and good temperature characteristics, and have a high dielectric constant and good temperature characteristics. ,
That is, the relationship between the voltage V and the charge Q is required to have a square characteristic as shown in FIG. 8, and to be stable with respect to temperature. BaTiO ₃ single crystal is effective as a nonlinear dielectric element because its hysteresis curve exhibits square characteristics, but its nonlinear characteristics are unstable with respect to temperature changes, and its manufacturing method is still in the research stage. However, it has not yet been put into practical use. Therefore, conventionally, it has been considered to use a nonlinear dielectric element using BaTiO ₃ polycrystalline material, but this BaTiO ₃ polycrystalline material generally has a D-E structure as shown in FIG. Although the hysteresis curve shows some saturation characteristics, the residual polarization varies widely, the dielectric constant is unstable with respect to temperature, and the slope of the D-E hysteresis curve is slow, resulting in nonlinear dielectric properties. As a physical element, one with good characteristics has not yet been put into practical use. In order to improve this point, Japanese Patent Application Laid-Open No. 128019/1983 proposes a method using BaO−TiO ₂ −SnO ₂ as the main component.
A nonlinear dielectric element made of BaTiO ₃ -based polycrystalline material has been proposed. A nonlinear dielectric element with this composition has a steeper D-E hysteresis curve, a higher dielectric constant, and a higher dielectric loss than a conventional nonlinear dielectric element made of BaTiO ₃ polycrystalline material. It has a small and excellent feature. [Problems to be solved by the invention] However, when BaO−TiO ₂ −SnO ₂ is the main component,
As mentioned above, nonlinear dielectric elements made of BaTiO ₃ -based polycrystals have considerably improved characteristics compared to conventional ones, but when used in pulse generators, the pulse generation voltage is low; Moreover, it has the problem of poor temperature characteristics, particularly poor pulse generation characteristics in the high temperature range (50 to 60° C.). This high-temperature region is the temperature near the starter when a high-intensity discharge lamp such as a high-pressure sodium lamp with a built-in starter is restarted, and a decrease in pulse generation characteristics in this temperature region is a major drawback. The present invention has been made in order to improve the above-mentioned problems in the non-linear dielectric element proposed above. The purpose is to provide an element. [Means and effects for solving the problem] In order to solve the above problem, the present inventors
As a result of various experiments and studies, we found that the crystal structure of BaTiO ₃ does not exhibit good nonlinear characteristics in the tetragonal and cubic systems, but does show good nonlinear characteristics in the rhombohedral and orthorhombic systems. I found out. In general, the change in crystal structure of pure BaTiO ₃ with respect to temperature is as shown in Figure 1. Above the Curie point T _CP , _the crystal structure changes;
Tetragonal system between transformation point T _C2 and second transformation point T _C2
It is known that between and the third transformation point T _C3 , it becomes an orthorhombic system, and below the third transformation point T _C3 , it becomes a rhombohedral system (Kiyoshi Okazaki, "Ceramic Dielectric Engineering")
Published by Gakukensha on September 15, 1969, see page 21). Therefore, the rhombohedral and orthorhombic crystal systems exhibiting good nonlinear characteristics are in the temperature range below the second transformation point T _C2 . In order to improve the nonlinear characteristics on the high temperature side, that is, the pulse generation characteristics, it is necessary to reduce the second transformation point T _C2 as much as possible.
It is necessary to shift to the high temperature side. As shown in Figure 2, by replacing Ti in BaTiO ₃ with Sn, Zr, or Hf, the second transformation point T _C2 shifts to the high temperature side (Bernard Jaffe et al., “Piezoelectric Ceramics”, Academic Press).
Published in 1971, see page 94). As is clear from Fig. 2, by substituting Ti with Zr or Hf rather than Sn, the second transformation point T _C2 shifts to the higher temperature side, and therefore the pulse generation characteristics on the high temperature side become better. It can be seen that a good improvement effect can be obtained. Therefore, in the present invention, BaO−TiO ₂ −ZrO ₂
The combination of -HfO ₂ forms a BaTiO ₃ -based polycrystalline body and constitutes a nonlinear dielectric element.
In particular, TiO ₂ is 85.25 to 96.75 mol%, ZrO ₂ is 3 to 9.75 mol%, HfO ₂ is 0.25 to 5 mol%, and the mol ratio of BaO and (TiO ₂ + ZrO ₂ + HfO ₂ ) is in the range of 0.98 to 1.02. It consists of a polycrystalline body with a basic composition of Mn,
The nonlinear dielectric material contains one or more Cr oxides in an amount of 0.004 to 0.04% by weight. This improves nonlinearity and increases the relative pulse generation voltage, particularly improves the pulse generation characteristics on the high temperature side, and also improves the reduction prevention effect and sinterability during porcelain sintering.
A nonlinear dielectric element made of dense, homogeneous, and excellent polycrystalline material can be obtained. [Example] Examples will be described below. ○ First Example Raw material powders TiO ₂ , ZrO ₂ , and HfO ₂ were made into composition ratios shown in Table 1, and raw material powders BaO and (TiO ₂ + ZrO ₂ +
The molar ratio of HfO ₂ ) is in the range of 0.98 to 1.02, and further,
0.01% by weight of MnO ₂ and 0.015% by weight of Cr ₂ O ₃ were added and wet mixed using a polyethylene pot and an agate ball. After dehydration and drying, the mixture was calcined at 1150° C. for 2 hours, and then pulverized again using a polyethylene pot and an agate ball. Next, after the water was evaporated, an appropriate amount of binder was added thereto, and the mixture was pressure-molded into a disc of 18.5 mm and 0.75 mm using a 10-ton press. Next, a ceramic element was formed by firing at 1300 to 1400°C for 2 hours, and a silver electrode was baked onto this to create a nonlinear dielectric element. Note that the first
In the table, Samples Nos. 1, 2, 8, and 11 are elements outside the scope of the present invention that were prepared for comparison. The pulse generation voltage of the thus obtained nonlinear dielectric element was measured using the pulse generation circuit and pulse measurement circuit shown in Fig. 3 while changing the surrounding temperature. The results are shown in Fig. 4. The following results were obtained. As shown in FIG. 3, the pulse generation circuit includes each nonlinear dielectric element 1 having the above configuration.
Connect the series circuit of ballast 2 for 125W mercury lamp to 200V, 50
The device was configured to be connected to a Hz AC power source 3, and the generated pulse voltage was measured with an oscilloscope 4 connected between the terminals of the nonlinear dielectric element 1.

[Table] As can be seen from Table 1 and Figure 4 above, the pulse generation voltage of the nonlinear dielectric element according to the present invention shows a high value of 600 to 1100 V over a temperature range of -30 to +60°C. In particular, it shows a high value of 600-900V in the high temperature range of 50-60°C, which is the restart temperature of high-intensity discharge lamps such as high-pressure sodium lamps. Based on the above data, the present invention is based on BaO−TiO ₂ −ZrO ₂
- In the basic composition of HfO ₂ , TiO ₂ is 85.25 ~
96.75mol%, _ZrO2 3-9.75mol%, _HfO2 0.25
~5 mol% of BaO and (TiO ₂ + ZrO ₂ + HfO ₂ )
The molar ratio is limited to a range of 0.98 to 1.02.
In addition, as shown in Table 2, BaO and (TiO ₂ +
If the molar ratio of ZrO ₂ + HfO ₂ ) is less than 0.98, the crystals will become enlarged and the grain boundaries will become wider, resulting in poor nonlinearity; if the molar ratio exceeds 1.02, the crystals will become too small, and the same problem will occur. It was confirmed that nonlinearity worsened.

[Table] ○ Second Example Same basic composition (TiO ₂ :
92 mol%, ZrO ₂ : 5 mol%, HfO ₂ : 3 mol%),
In a composition in which the molar ratio of BaO and (TiO ₂ +ZrO ₂ +HfO ₂ ) is 1, MnO ₂ and Cr ₂ O ₃ are added as additives.
The seeds or two seeds are added as shown in Table 3, and the first
A nonlinear dielectric element was created using the same process as in the example. When the pulse generation voltage of the device thus obtained was measured using the measuring circuit shown in FIG. 3, the results shown in Table 3 and FIG. 5 were obtained.

【table】

〔Effect of the invention〕

As explained above based on the examples, according to the present invention, in the BaTiO ₃ polycrystalline body, BaO-
Since the nonlinear dielectric element was constructed with a basic composition containing TiO ₂ −ZrO ₂ −HfO ₂ as its main component and a specific mixing ratio, it improved the nonlinearity in the high temperature region and improved the pulse generation characteristics. can be improved.

[Brief explanation of drawings]

Figure 1 shows the relative dielectric constant ε _S and changes in crystal structure with respect to temperature of BaTiO ₃ porcelain, and Figure 2 shows
Figure 3 shows the variation of the transformation point due to substitution elements in BaTiO ₃ porcelain. Figure 3 shows the pulse generation circuit and pulse measurement circuit. Figure 4 shows the generated pulse voltage versus ambient temperature for each sample with different composition ratios. 5 is a diagram showing the fluctuation of pulse voltage with respect to the amount of additive added, FIG. 6 is a diagram showing the fluctuation of pulse voltage with respect to the amount of impurity added, and FIG. Figure 8 shows the D-E hysteresis curve of BaTiO ₃ single crystal, and Figure 9 shows the variation of pulse generation voltage with respect to the amount of additive added.
It is a DE hysteresis curve diagram of _BaTiO3 polycrystalline body.

Claims (1)

[Claims] 1 BaO-TiO ₂ -ZrO ₂ -HfO ₂ as the main component,
85.25-96.75mol% _TiO2 , 3-9.75mol% _ZrO2
%, HfO ₂ 0.25-5 mol%, BaO and (TiO ₂ + ZrO ₂
It consists of a polycrystalline substance with a basic composition in which the molar ratio with +HfO ₂ ) is in the range of 0.98 to 1.02, and is characterized by containing 0.004 to 0.04% by weight of one or more oxides of Mn and Cr. Non-linear dielectric element. 2. The nonlinear dielectric element according to claim 1, characterized in that the content of elements serving as impurities is 0.2% by weight or less as an oxide. 3 One or more oxides of Ca, Pb, and Sr
3. The nonlinear dielectric element according to claim 1 or 2, wherein 0.1 to 1.0 mol% of BaO is added.