JPH0126169B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a voltage-sensitive current limiting element, that is, a polycrystalline ferroelectric ceramic having a square hysteresis characteristic whose impedance changes depending on an applied electric field. The device according to the invention contains BaTiO ₃ or a part thereof.
The main component is substituted with Sr, Zr, Sn or Pb. The present invention maximizes and emphasizes the ferroelectricity of BaTiO _3- based porcelain to provide an impedance element with low loss for alternating current by utilizing the change in apparent dielectric constant with respect to alternating electric field. . Normally used as an electric power source for both household and industrial purposes.
50 cycles or 60 cycles of 100V or
A 200V single-phase or three-phase power supply is used, and LCR can be considered as a passive element for current regulation function for low-impedance loads that use these power supplies as energy. Among these, resistance elements are the cheapest and easiest to use, but they generate a lot of heat during use, and all of that heat is lost, resulting in not only poor power usage efficiency, but also deterioration of the entire device due to the heat generated. Due to reliability issues, it is currently only used to limit minute currents. Currently, the most commonly used method is L, or inductance, and specifically, a chiyoke coil is used (for example, as a ballast in a discharge lamp). This is because even when a large current is passed through it, there is little loss and therefore no heat generation, which does not impair the reliability of the device itself. Another advantage is that when a large current is passed, the inductance is low and the number of windings can be reduced. On the other hand, if a large current is to flow, a wire with a thick winding must be used, which increases the size and weight, making it difficult to use in small equipment or equipment that needs to be lightweight. On the other hand, a method using C, that is, the capacitance of a capacitor, can be considered, but as a current adjustment function at low frequencies such as 50 cycles or 60 cycles, a large capacitance is required, which is very expensive. In particular, in order to flow a large current, it is necessary to reduce the reactance, so conventional capacitors are large.As for the large capacitance capacitors currently used, for example, aluminum electrolytic capacitors, etc. There was a problem that it was difficult to use because the reliability was not sufficient. Therefore, there has been a need for a small, high-capacity, high-voltage, high-heat-resistant, and inexpensive impedance element. Traditionally, ceramic capacitors containing BaTiO ₃ as the main component were thought to be the most likely to meet these difficult conditions. The reason for this is that other capacitors such as mica,
While paper and film-based materials have a dielectric constant ε _S of about 3 to 15, BaTiO ₃ has a practical dielectric constant ε _S of about 20,000, which is much higher than other materials. This is because a high capacitance value can be obtained despite the small size and simple structure. In addition, porcelain is fired at 1300 to 1400°C, so it has high heat resistance and good reliability. However, since BaTiO ₃ -based porcelain is porcelain (pottery), it is difficult to roll or bend it, and capacitors using it do not necessarily have a large capacitance per volume. Generally, the capacitance C of a capacitor having parallel plate electrodes is given by: C=ε _O ×ε _S ×S/t where C is the capacitance F, ε _O is the permittivity of vacuum, ε _S
is the relative permittivity of the dielectric material, and S is the overlapping area of the electrodes.
m ² , t is the thickness m of the dielectric material. Therefore, in order to increase the capacitance, it is necessary to reduce the thickness t, use a dielectric material with a large relative dielectric constant ε _S , and increase the overlapping area S of the electrodes. Figures A and B show conventional capacitors using barium titanate, where 1 is the dielectric constant, 2 and 3 are the electrodes,
4 and 5 are lead wires, and 6 is composed of insulating resin. A ceramic capacitor with this structure has a practical capacitance of about 0.05 μF at most in terms of mechanical strength and area occupied. When a laminated electrode structure as shown in FIGS. 2A and 2B is used, the overlapping area of the electrodes increases depending on the number of stacked electrodes, and a large capacitance can be obtained. In FIGS. 2A and 2B, 1 is a dielectric, 2 is an internal electrode, and 2a is an external electrode. However, the laminated electrode structure has a low withstand voltage because the dielectric is thin, and the electrode materials include Pt, Au, etc.
Since noble metals such as Pd and Ag are used, it has the disadvantage of being expensive. SUMMARY OF THE INVENTION Accordingly, the present invention aims to improve the above-mentioned drawbacks of the prior art and provides a current limiting element (impedance element) for an AC circuit that is small, inexpensive, and has low loss. The present invention utilizes the rectangular hysteresis characteristic of a ferroelectric element for current limiting, and uses the impedance value calculated back from the current value measured in an AC electric field of 5V/mm as a reference.
It is characterized by ferroelectric polycrystalline porcelain whose main component is barium titanate (BaTiO ₃ ), which has square hysteresis such that the impedance in an AC electric field of 500 V/mm or less is 1/10 or less. In order to improve the above impedance characteristics,
Part of Ba in BaTiO ₃ is replaced with Sr, Pb, and Ti
It is effective to replace a part of with Zr or Sn. Furthermore, it is preferable to add at least one of 0.005 to 0.3% by weight of Cr and 0.005 to 0.3% by weight of Mn as a mineralizing agent in order to improve the impedance characteristics. More preferably, it is effective to limit the content of impurities other than the main component and mineralizer to 0.5% by weight or less. The present invention will be explained in detail below. Generally, when current limiting in an AC circuit is implemented using a ferroelectric material, it is necessary to consider the reactance determined by capacitance and the resistance inserted in series with the reactance (equivalent series resistance). The equivalent series resistance component causes energy loss, so it must be kept to a value as small as possible, but in reality it is closely related to the actance due to capacitance, so it is difficult to manipulate both characteristics separately. Therefore, the present invention was accomplished not only by obtaining a large capacity by using a composition system with a high relative permittivity ε _S in order to simply lower the reactance, but also by focusing on the AC voltage dependence of the relative permittivity ε _S of BaTiO ₃ -based porcelain. There is. Regarding BaTiO ₃ based high dielectric constant ceramic compositions,
As stated in Japanese Patent Publication No. 52-44440, it is known that the apparent ε _S increases by about 100 to 140% by applying an alternating current voltage. The fact that the relative permittivity changes depending on the applied voltage is considered to mean that the relative permittivity, that is, the dielectric polarization phenomenon, has voltage dependence. In normal dielectrics, the voltage dependence of the relative permittivity ε _S is negligibly small. Incidentally, the electric flux density D in the dielectric is given by the following equation. D=εE=ε _O ε _S E where D ; Electric flux density (C/m ² ) ε ; Dielectric constant ε _O ; Vacuum permittivity ε _S ; Capacity increase rate of dielectric E ; Applied electric field (V/m ) As a means of observing the above relationship, the Sawyer
It is common to observe DE hysteresis characteristics in tower circuits. Figure 3 shows D of a normal dielectric.
- Indicates E characteristics. From this figure, in a normal dielectric material, D
-E characteristic is linear. Figure 4 shows the D of conventional BaTiO ₃ based high permittivity porcelain.
- It is suggested that there is no linear relationship with the E characteristic, and that ε changes depending on E (in this example, ε _S =18000).
When a capacitor was made using the sample shown in Figure 4 and its capacitance-voltage characteristics were measured using a Schering bridge, the characteristics were almost the same as those shown in Figure 4, but it was found that the impedance itself had little voltage dependence. Ivy. By the way, the fact that the DE hysteresis characteristic is not in a linear relationship indicates that ε changes as a function of the AC electric field, and the fact that the rise of the DE characteristic is sudden means that ε changes as a function of the applied electric field. On the other hand, this shows that ε is rapidly increasing. Further, the area surrounded by the hysteresis loop corresponds to the equivalent resistance (loss). Conventionally, the application fields of ABO ₃ type ferroelectric porcelain, which has a perovskite crystal structure centered on BaTiO ₃ type porcelain, have been applied to the use of high dielectric constant, piezoelectric properties,
Although it is known that the DE hysteresis phenomenon is utilized, studies on the DE hysteresis phenomenon have not yet been completed because materials that provide good squareness characteristics have not yet been developed. The present inventor has developed a dielectric ceramic having a sudden rise and good square hysteresis characteristics, and by utilizing the property that its capacitance and impedance greatly depend on the applied alternating current electric field, the present inventor has developed a dielectric ceramic that has a rapid rise and good square hysteresis characteristics, and by utilizing the property that its capacitance and impedance greatly depend on the applied alternating current electric field, the current limiting element in an alternating current circuit. Alternatively, we developed a variable impedance element. As described above, in order to increase the sensitivity as a voltage-sensitive current limiting element, the present inventors have conducted extensive research on ferroelectric ceramic compositions, and as a result, we have developed BaTiO ₃ alone or with Sn, Zr, etc. as _{subcomponents} . of
Partial replacement of Ti or Ba with Sr and Pb
Good results were obtained using a basic composition in which a portion of . For materials other than BaTiO ₃ , impedance cannot be lowered unless the capacitance increase rate is low or a very high alternating current electric field is applied, making them impractical due to the relationship with the withstand voltage of porcelain. Furthermore, by adding a small amount of Mn and Cr coordination as additives to such a basic composition, reduction can be prevented during porcelain sintering without impairing the properties, and the sinterability can be improved, resulting in more dense and homogeneous porcelain. It has been found that a polycrystalline body can be obtained. Characteristics are additives (mineralizers)
Depending on the element and amount of
It was 0.005-0.3% by weight. Moreover, there is no particular problem even if both are added and contained as a mixture. Basically, Sr, Sn, Zr, and Pb enter BaTiO ₃ crystals to form a solid solution and have the effect of controlling the properties of the ferroelectricity within the crystal grains without impairing them.
Mn and Cr mainly precipitate at grain boundaries and play the role of mineralizing agents that promote sintering of porcelain and prevent reduction. It is itself a paraelectric material, and its electrical properties are significantly different from those of the crystal grains themselves. Essentially, this device needs to maximize the AC voltage dependence of the dielectric constant, which is a feature of ferroelectricity, and the fewer grain boundaries that form this paraelectric layer, the better the characteristics. This was also confirmed in experiments in which the amount of mineralizing agent was varied. However, impurities contained in raw materials and impurities mixed in during the manufacturing process, such as Al ₂ O ₃ and SiO ₂ , precipitate at grain boundaries during sintering to form a paraelectric substance, or BaTiO ₃
It was found that the ferroelectricity was weakened by forming a solid solution with ferroelectricity, and that only a small amount was allowed. this is,
The types and amounts of additives are significantly limited compared to the amount of additives used in general high-permittivity ceramic dielectrics, and the raw materials and manufacturing processes used are much more rigorous than those for conventional ceramic capacitors. It is necessary to carefully control impurities, which is unique compared to conventional high dielectric constant polycrystalline porcelain. As a result, the voltage-sensitive current-limiting element of the present invention has an extremely sensitive impedance dependence on voltage, and the impedance reduction rate is at most 1/100 in an AC electric field of 500 V/mm or less when 5 V/mm is the standard. We were able to complete an alternating current limiting element based on a completely new concept. For this reason, it is small, lightweight, highly reliable, and low cost, and has a wide range of applications, making it an extremely important contribution to the electrical industry. Example 1 Raw material powder BaTiO ₃ , TiO ₂ , SnO ₂ , ZrO ₂ ,
SrO ₂ , PbO, MnCO ₃ with the desired composition shown in Table 1 (sample
No. 1 to No. 15) polyethylene pots,
Wet mixing was performed using an agate ball. After dehydration and drying
Temporarily fired by holding at 1150℃ for 2 hours, then using a polyethylene pot and agate ball again.
I did the crushing. After the water was evaporated, an appropriate amount of binder was added to this, and the mixture was pressure-molded into a 16.5φ0.50mm disc using a 10-ton press. Then, it was baked at 1300 to 1400°C for 2 hours. Silver electrodes were baked onto the thus obtained ceramic element, the lead wires were then fixed with solder, washed and coated with insulating paint, and the effective current flowing through the circuit was measured using the measurement circuit shown in Figure 6 by varying the 50Hz AC voltage. Then, impedance Z was calculated. In Fig. 6, 10 is the sample,
12 is an AC ammeter, 14 is an AC voltmeter, 16 is a 50
Indicates Hz AC power supply. The measurement results are shown in Table 1, FIG. 7, and FIG. 5. Note that Samples No. 14 and No. 15 are samples that do not belong to the present invention and are merely for comparison with the present invention samples. From Table 1, the ratio of impedance Z ₁ at 5V/mm (rms) to impedance Z ₂ at 500V/mm (Z ₂ /Z ₁ ) is 1/20 to 1/ for samples No. 1 to No. 13. 108, which fully satisfies the practical value of 1/10 as a current limiting element. Figure 7 shows the relationship between impedance and applied electric field V/mm (rms).In the samples belonging to Group P, which belongs to the present invention, as the electric field increases, the impedance gradually decreases; When the electric field becomes higher than mm, the impedance rises again. Although the theoretical reason why the impedance rises again is not necessarily clear, a sufficiently reduced impedance can be obtained for practical use up to about 500 V/mm. Note that the impedance in FIG. 7 is a value for a sample having a diameter of 16.5 mm and a thickness of 0.50 mm and having electrodes attached thereto as described above. FIG. 5 shows an example of actually measured DE hysteresis characteristics of a sample according to the present invention, which shows the characteristics of sample No. 3 in Table 1, and it can be seen that it exhibits excellent hysteresis characteristics. In the experiment shown in Figure 5, the sample thickness was 0.5 mm.
The applied electric field is 280V (rms). Therefore 560V/mm
This means that an electric field of . As described above, the impedance drop when a high electric field is applied is remarkable for those containing BaTiO ₃ as the main component, indicating that BaTiO ₃ has unique properties compared to ferroelectric ceramics of other compositions.

【table】

[Table] Example 2 Regarding the samples that showed a good capacity increase rate in Example 1, that is, samples with BaTiO ₃ as the main component (Samples No. 1 to No.
13) We investigated the types of additives and the range of their additive amounts. Examples of the most average among them are shown in Table 2 and FIG. i.e. BaTiO ₃ 94 mol%, BaSnO ₃ 6 mol%
Measurements were made in the same manner as in Example 1 by adding one or a combination of MnCO ₃ and Cr ₂ O ₃ as additives as shown in Table 2. Table 2 shows that the addition of additives prevented reduction during porcelain sintering or improved the sinterability without impairing the properties, resulting in an excellent polycrystalline body that was denser and more homogeneous. When adding these additives, for example, MnCO ₃ and Cr are
Although it was added as Cr ₂ O ₃ , it is not limited to this, and the same effect can be seen even if it is used as other compounds, and the amount added should also take into account the condition of the compound to be added, but the main for the ingredients
A content of 0.005 to 0.3% by weight of Cr ₂ O ₃ is considered to be within a practical range, but a content of 0.5% by weight or more is not preferable because the impedance decreases less. Figure 8 is a graph showing the degree of impedance reduction and the amount added. From this figure, it can be seen that an additive content of 0.05 to 0.3% by weight is sufficient to reduce electrical properties, especially impedance. It can be said that it is a range (group P). In this case, if the amount is less than 0.005% by weight, no effect will be observed at all. On the other hand, similarly
Regarding MnCO ₃ , 0.005 to 0.3% by weight is considered to be a practical range, and no effect was observed below 0.005% by weight.

【table】

[Table] Furthermore, the addition of MnCO ₃ and Cr ₂ O ₃ prevents reduction of the porcelain during sintering or promotes more dense sintering. Note that Samples No. 6 and No. 12 are outside the scope of the present invention. Example 3 To the materials shown in Example 1 and Example 2 which showed good characteristics, as shown in Table 3, impurities, etc., especially elements that are easily included in the raw materials or mixed during the material manufacturing process, were added. As a result of measurement in the same manner as in Example 1, as shown in Table 3 and FIG. Compared to the permissible amount of the ceramic dielectric material or the amount of the added element other than Examples 1 and 2 belonging to the present invention, which is about 0.6 to 1.0% by weight, the difference is very small. This is because, as mentioned above, additives and impurities that do not dissolve in BaTiO ₃ precipitate at grain boundaries and form a paraelectric layer, weakening the ferroelectricity of the entire porcelain. This is why the amount of

[Table] In Table 3, samples No. 4 and No. 8 have magnification (Z ₂ /Z ₁ )
is insufficient and is outside the scope of the present invention. Also the 9th
In the figure, curve a is the characteristic of a sample containing 0 wt% of impurity Al ₂ O ₃ . As described above, the current limiting element according to the present invention is sensitive to alternating current voltage, and the impedance decreases by 1/10 to 1/100 depending on the applied electric field. Furthermore, since it is a fired product, its properties do not deteriorate even at high temperatures. Therefore, it is possible to apply it to a small current limiting element having an appropriate impedance value, and ballasts for discharge lamps are one example of the application, and it is also promising for applications in other electronic industries.

[Brief explanation of drawings]

Figures 1A and B are configuration examples of conventional ferroelectric ceramic capacitors, Figures 2A and B are other configuration examples of conventional ferroelectric ceramic capacitors, and Figure 3 is D-E in a general dielectric material. Figure 4 shows the characteristics of the conventional
FIG. ₅ is a diagram showing the DE characteristics of the current limiting element according to the present invention. FIG. 6 is a block diagram of the characteristic measuring device according to the present invention. FIGS. 9 and 9 are diagrams showing the experimental results of the relationship between the applied electric field and the impedance of the current limiting element according to the present invention. 10... Sample (current limiting element), 12... AC ammeter, 14... AC voltmeter, 16... AC power supply.

Claims (1)

[Claims] 1 The main component is barium titanate (BaTiO ₃ ), with some of the Ba replaced by Sr or Pb, and some of the Ti
Ferroelectric polycrystalline porcelain substituted with Zr or Sn,
As mineralizers, 0.005~0.3 wt% Cr and 0.005~
At least one of 0.3% by weight of Mn is added, and the ratio of impurities other than the main component and mineralizer is 0.5%.
% or less by weight.