JPS6312324B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to nonlinear dielectric elements, and particularly
The present invention relates to a nonlinear dielectric element made of BaTiO ₃ -based polycrystalline material and having excellent nonlinearity characteristics and breakdown voltage. In general, the application fields of ABO ₃ -based ferroelectrics, which have a perovskite structure centered on BaTiO ₃ -based porcelain, include the use of high permittivity and piezoelectric properties, as well as the application of nonlinearity of ferroelectrics. Are known.
In other words, if BaTiO ₃ single crystal is used for nonlinear (saturable) elements that utilize the fact that the dielectric constant changes depending on the strength of the electric field, memory storage elements that utilize hysteresis characteristics, logical operation elements, etc., the operating frequency This applied research is already being carried out at Bell Laboratories, as it is expected to have great effects, such as raising the limits of energy consumption and making it easier to create small, large-capacity devices with very low power consumption.
Published by Andreson et al. However, drawbacks such as fatigue and the absence of a threshold electric field have become apparent, and it has not been put into practical use. Recently, as a new application example, nonlinear (saturable) elements have been used in discharge lamps and non-contact starting devices for fluorescent lamps, mercury lamps, and sodium discharge lamps.
-28726, and that a nonlinear element with a good saturability curve can be obtained by mirror-finishing and etching the surface of a ferroelectric element is disclosed in JP-A-52-28726.
It is known as 146069 etc. However, D-
The slope of the E hysteresis curve is steep, the dielectric constant is high and the nonlinearity characteristics are stable with respect to temperature, and the temperature characteristics of the D-E hysteresis are good, that is, the voltage V and charge Q
The D-E hysteresis curve as shown in FIG. 1A has a rectangular characteristic and is required to be stable with respect to temperature. BaTiO ₃ single crystal is effective as a nonlinear dielectric element because its curve exhibits square characteristics, but its nonlinear characteristics are unstable with respect to temperature changes. or
Flux methods, melting methods, etc. are known for growing BaTiO ₃ single crystals. However, the manufacturing method itself is still in the research stage and has not yet been put into practical use. Therefore, conventional BaTiO ₃ -based polycrystals generally exhibit a certain degree of saturation characteristics in the DE hysteresis curve shown in Figure 1B, but the residual polarization varies widely and the dielectric constant is unstable with respect to temperature. However, the slope of the DE hysteresis curve is slow, and at present it has not been put to practical use as a nonlinear dielectric element. Therefore, the present inventors conducted extensive research with the aim of creating a BaTiO ₃ -based polycrystalline body that has properties similar to BaTiO ₃ single crystals and _can be stably manufactured industrially. Polycrystals, particularly good ones include solid solutions in which part of the Ti in BaTiO ₃ is replaced with Zr.
As a result of conducting experiments by selecting a solid solution of BaO−TiO ₂ −ZrO ₂ in which the Curie point shifted to the lower temperature side depending on the amount of Zr added, the results showed that the optimal capacitance-voltage characteristic showed nonlinearity. BaO−TiO ₂ − as a region
ZrO ₂ system with BaO……63.39~65.62% by weight, TiO ₂
......26.42 ~ 33.85 wt%, ZrO ₂ ...0.53 ~ 10.19
It was confirmed that the basic composition consisting of a range of weight % (the sum of these is 100.00 weight %) is very good. Furthermore, 0.01 to 0.40% by weight of at least one of Mn oxide, Cr oxide, Mn carbonate, and Cr carbonate is added as an additive to 100% of the basic composition.
(Total value in case of combined addition) By adding BaTiO ₃ , it prevents reduction or improves sinterability during porcelain sintering without impairing the inherent hysteresis characteristics of BaTiO 3, resulting in more dense and homogeneous sintering. It was found that an excellent polycrystalline material was obtained (see FIG. 7 and Table 2). In addition, so-called impurities such as Al ₂ O ₃ and SiO ₂ that are usually mixed into raw materials or mixed in the manufacturing process, and oxides that are sometimes intentionally added are also added by weight of 0.15 to 100 of the basic composition. It became clear that it had to be kept below %. These allowable amounts are extremely small and unique compared to the amounts of additives and impurities used when manufacturing dielectrics for capacitors. As a result of these results, the nonlinear dielectric element of the present invention is novel, has a steep slope of the D-E hysteresis curve, has a high dielectric constant, and has temperature characteristics compared to BaTiO ₃ single crystal. However, it is extremely stable and has extremely excellent characteristics of low dielectric loss, making it possible to put it to practical use as a nonlinear dielectric element in pulse generators, discharge lamps, lighting devices, etc. The present invention will be explained in detail below with reference to Examples.
FIG. 1A is an example of a DE hysteresis curve of a BaTiO ₃ single crystal, and FIG. 1B is an example of a DE hysteresis curve of a conventional BaTiO ₃ polycrystal. FIG. 2 is an example of a DE hysteresis curve of a nonlinear dielectric element according to an embodiment of the present invention. FIG. 3 is a circuit diagram of a discharge lamp/non-contact starting device using the nonlinear dielectric element of the present invention. 4 and 5 are circuits and operation waveform diagrams showing the operating principle of the circuit shown in FIG. 3. FIG. Figures 6 to 10 relate to embodiments of the present invention, and Figure 6 shows a BaTiO ₃ polycrystalline body according to the present invention.
The temperature characteristics of the pulse voltage according to the BaO−TiO ₂ −ZrO ₂ system composition ratio are shown. FIG. 7 shows the additive-pulse voltage relationship. FIG. 8 shows the impurity-pulse voltage relationship. FIG. 9 shows the relationship between the amount of impurities and the crystal structure, and is a microscopic photograph of the crystal structure of this crystal. FIG. 10 shows the relationship between the time course and the pulse voltage for each impurity amount in the device of the present invention. Example 1 Raw material powders BaCO ₃ , TiO ₂ , ZrO ₂ , MnCO ₃ as the first
Wet mixing was performed using a polyethylene pot and an agate ball to obtain the composition shown in the table. 1150 after dehydration and drying
The mixture was kept at ℃ for 2 hours to undergo temporary calcination, and then pulverized again using a polyethylene pot and an agate ball. After evaporating the water, add an appropriate amount of binder to it and make it with a diameter of 16.5mmφ and a thickness of 0.45mm.
It was press-molded into a 10-ton press into a disc of mm. Then
It was baked at 1300-1400°C for 2 hours. A silver electrode was baked on the thus obtained ceramic element, and then the pulse voltage characteristics and pulse voltage temperature characteristics were
Measurements were made using the circuit shown in the figure, and then its DE hysteresis curve was measured. An example diagram is shown in FIG. In addition, the dielectric constant (ε _s ), dielectric loss tan δ (%), and insulation resistance IR were measured. The measured values of the above electrical characteristics are summarized in Table 1. Regarding the simple operating principle of the above pulse generation,
The operating principle and operating waveform diagrams are shown in FIGS. 4 and 5. In FIG. 3, Cn is a nonlinear dielectric element whose characteristics are as shown in FIG. In FIG. 5, A is the characteristic of a normal capacitor, and Q is proportional to E. However, B is a characteristic of the device according to the present invention, and Q becomes approximately constant above E ₀ . Since Q<C>=C(F)×V(V), the characteristic shown in B in the same diagram is that when the voltage exceeds _E0 , the apparent volume decreases rapidly, the accumulated charge saturates, and the result is As a result, the charging current decreases rapidly. For this reason, in the ballast, as shown in Figure 4,
A back electromotive force proportional to di/dt is generated, generating a trigger (pulse) voltage that starts the discharge lamp FL. L is the inductance of the ballast and di/dt is the change in the charging current of the nonlinear dielectric element. di／
In order to increase dt, E ₀ (V) in Figure 5
The larger the difference between the slope of the charging current below and the slope of the saturated charging current above E ₀ (V), the higher the trigger (pulse) voltage becomes, allowing stable activation. Therefore, the DE hysteresis of the Cn element needs to be close to the square characteristic. Although it is not easy to express this hysteresis form quantitatively, in this experiment, the pulse voltage from the circuit shown in FIG. 3 was used as a quantitative measure of this hysteresis form. In Fig. 4, for example, when an AC voltage with E ₀ (V) set to an appropriate value is applied to the Cn element, the charging current changes rapidly at E ₀ as shown in Fig. 5. As described above, a pulse due to a back electromotive force proportional to the inductance L of the ballast is superimposed on the AC voltage E ₀ .
This pulse voltage serves as a starting pulse or trigger for the discharge lamp in FIG. As can be seen from Table 1, the pulse voltage characteristics within the range of the present invention exhibit high values of 450 to 900V. Note that Samples Nos. 1 and 7 are outside the scope of the present invention. Furthermore, as shown in Fig. 6, when BaO is 63.39 to 65.62% by weight and ZrO ₂ is 0.53 to 10.19% by weight, -
It was confirmed that high voltage pulses of 470 to 900V were generated at temperatures of 30 to +60°C, and that it was sufficiently practical. According to Table 1 and FIG. 6 above, in the present invention,
BaO in the basic composition of BaO−TiO ₂ −ZrO ₂
63.39-65.62 wt%, _TiO2 26.42-33.85 wt%,
ZrO ₂ is limited to 0.53 to 10.19% by weight.

[Table] Example 2 As an additive (mineralizer) to the BaO-TiO ₂ -ZrO ₂ composition (not containing MnCO ₃ ) containing 92 mol% of BaTiO ₃ and 8 mol% of BaZrO ₃ shown in Table 1. _MnCO3 ,
One or both of Cr ₂ O ₃ (combined addition) were added as shown in Table 2 and FIG. 7, and the pulse voltage was determined in the same manner as in Example 1. In Table 2 (Samples Nos. 1 to 18), the pulse voltage was significantly improved depending on the amount of the additive added. When adding these additives, for example
Although Mn is added as MnCO ₃ and Cr is added as Cr ₂ O ₃ , the present invention is not limited to these. Similar effects can be observed even when other forms of compounds are used, and the amount of addition also depends on the compound added. However, 0.01 to 0.4% by weight based on 100% of the main component is considered to be within the practical range, and if it exceeds 0.4% by weight, the electrical characteristics will deteriorate significantly, which is not preferable. Figure 7 is a graph showing the relationship between the amount of addition and the pulse voltage. From this figure, it can be seen that the range of the amount of addition of 0.01 to 0.4% by weight is the electrical property.
In particular, it can be said that this is a range that satisfies the pulse voltage. In this case, if the amount is less than 0.01% by weight, no effect will be observed at all. Furthermore, the addition of MnCO ₃ and Cr ₂ O ₃ has the effect of preventing reduction of the porcelain or promoting denser sintering during sintering. In addition, sample No. 1, 6, 7, which is not marked with 〇
8, 13, 14, 17, and 18 are outside the scope of the present invention.

[Table] Example 3 In addition to the sticky additives used in Example 2, SiO ₂ , Al ₂ O ₃ and the like are added in an amount of 0.3 to 1.0% by weight as sintering accelerators in a typical dielectric composition. Often added. In addition, they may be contained as impurities in the raw materials or mixed in during the manufacturing process, and these are considered impurities, but in any case, as a normal dielectric material, about 1.0% by weight is It is allowed. Therefore, in order to investigate the influence of the amount of impurities on the non-linear capacitance element, Al ₂ O ₃ and B ₂ O were added to a composition containing BaTiO ₃ 92.0 mol% BaZrO ₃ 8.0 mol% MnO 0.05 wt%. ₃ , impurities such as MgO, SiO ₂ etc.
It was added as shown in the figure, and the pulse voltage was measured in the same manner as in Example 1. The results are shown in Figure 8 and 2.
The results are summarized in the table (Sample Nos. 19 and 20). As shown in FIG. 8, there is a clear correlation between the amount of impurities and the pulse voltage. In particular, when the amount of impurities exceeded 0.15% by weight based on 100% of the above composition, a rapid decrease in pulse voltage was observed. This is also supported by the photograph shown in Figure 9. That is, the impurity (SiO ₂ ) is 0.1 to 0.15% by weight.
With 0.25% by weight, the grain boundary layer becomes very thick, and with 0.6% by weight, the crystal growth is extreme compared to those with less than 0.25% by weight. It is defective. The reason is that these impurities are BaO−TiO ₂
-ZrO precipitates at the grain boundaries of ₂ -based solid solution crystals, so it is thought that there is a correlation with the development of grain boundaries depending on the amount. In other words, the grain boundaries are considered to be composed of a paraelectric material with a low dielectric constant and small residual polarization that does not exhibit small hysteresis characteristics, and those with grown grain boundaries are unsuitable for use as a nonlinear dielectric element. Furthermore, it is well known that even in single crystals of BaTiO ₃ where strain remains, the hysteresis is deformed and the crystal does not take the form shown in FIG. 1A. However, due to the difference in physical properties between grain boundaries and crystals, it is easy to think that grain boundaries become a factor that imparts strain to crystals, and are thought to have a negative effect on hysteresis. It became clear from the photograph in FIG. 9 and the data in FIG. 8 that the pulse voltage would be higher if such grain boundaries were not developed as much as possible. Furthermore, it is known that when such impurities are present in large quantities, they act as inhibitors that suppress the growth of crystals, and the photograph in Figure 9 shows that the crystals are small when the impurities are 0.6% by weight, supporting this fact. . Since the device of the present invention brings out the properties of BaO- _TiO2 - _ZrO2 -based crystals, it is natural that the pulse voltage is low in the range where the crystals do not develop. Furthermore, as shown in FIG. 10, the rate of change in pulse voltage with respect to the natural standing time for each impurity amount was measured. As a result, it became clear that when the amount of impurities exceeds 0.15% by weight, not only the initial pulse voltage is low, but also the rate of change of the pulse voltage with respect to the natural standing time is large, making it impractical. As mentioned above, the impurities are limited to 0.15% by weight or less, and this is considered to be a major difference from ordinary dielectric ceramics for capacitors. As described above, the nonlinear dielectric element of the present invention has a steep DE hysteresis curve as shown in FIG. 2, a high dielectric constant, a small dielectric loss, a high pulse voltage, and It has excellent characteristics such as small and stable changes in pulse voltage over time, and the present invention has made it possible to put it into practical use for the first time as a new nonlinear dielectric element that has never existed before. It is something. Therefore, in addition to the aforementioned discharge lamps and non-contact starting devices that are used as nonlinear dielectric elements, it can be put to practical use in pulse generators, etc. In the future, applications that actively utilize this nonlinearity will be developed. It became an issue. As described above, the nonlinear dielectric element according to the present invention has great utility in the electronic industry.

[Brief explanation of the drawing]

Figure 1 A and B are related to the conventional example, and Figure A is
An example of a D-E hysteresis curve of a BaTiO ₃ single crystal, and B of the same figure is an example of a D-E hysteresis curve of a BaTiO ₃ polycrystal. FIG. 2 is an example of a DE hysteresis curve of a nonlinear dielectric element according to an embodiment of the present invention, and FIG. 3 is a circuit diagram of a discharge lamp/non-contact starting device using this element. 4 and 5 are a circuit diagram and an operation waveform diagram showing the operating principle of the circuit shown in FIG. 3, respectively. Figures 6 to 10 relate to embodiments of the present invention, and Figure 6 is
It is a graph showing the temperature characteristics of the pulse voltage according to the BaO- _TiO2 - _ZrO2 system composition ratio of the _BaTiO3 polycrystalline body.
FIG. 7 is a graph showing the relationship between the type and amount of additives and pulse voltage. FIG. 8 is a graph showing the relationship between the type and amount of impurities and pulse voltage. FIG. 9 is a micrograph showing the relationship between the amount of impurity (SiO ₂ ) and the crystal structure of the crystal. FIG. 10 is a graph showing changes in pulse voltage with respect to natural standing time for each impurity amount.

Claims (1)

[Scope of Claims] 1 BaO-TiO ₂ -ZrO ₂ as the main component, BaO 63.39 to 65.62% by weight and TiO ₂ 26.42 to 65.62% by weight in terms of oxides.
33.85% by weight, ZrO ₂ in the range of 0.53 to 10.19% by weight, a total of 0.01 to 0.40% by weight of at least one of Mn and Cr oxides and carbonates, and other impurities and additives. A nonlinear dielectric element characterized in that the amount of oxide is 0.15% by weight or less. 2. The nonlinear dielectric element according to claim 1, which is used as a nonlinear dielectric element for a pulse generator, a discharge lamp, a lighting device, etc.