JPS63281406A - Voltage non-linear resistance material - Google Patents

Abstract

PURPOSE:To realize a varister of very high stability with excellent nonlinearity but without any deterioration with time, by containing a predetermined amount of bismuth and antimonium with relations between barium and bismuth and between tantalum and bismuth in an admixture being respectively in a predetermined range. CONSTITUTION:A sintered material, which consists mainly of zinc oxide containing at least barium, bismuth, tantalum and antimonium as an admixture, is formed by containing 0.05-1.0 mol% of bismuth expressed in terms of Bi2O3 and 0.05-3.0 mol% of antimonium expressed in terms of Sb2O3 with relations between barium and bismuth and between tantalum and bismuth being respectively in ranges of Ba/Bi=0.05-0.5 and Ta/Bi=0.2-2.0 in said admixture, and at a grain boundary segregation part of crystal grains composed mainly of zinc oxide in the sintered material, constitutes 50% or more of all the bismuth in the said sintered material so as to be a pyrochlore type compound.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to a zinc oxide-based voltage nonlinear resistor (hereinafter referred to as a varistor) containing bismuth, which has excellent stability against thermal history. related to).

(Prior art) In recent years, there has been a remarkable development of various varistors, and among them, zinc oxide-based varistors containing bismuth have been recognized for their excellent stability in nonlinearity, surge absorption, and constant voltage performance. Widely used as a protective varistor or constant voltage varistor against lightning surges and abnormal voltages. However, this type of varistor uses zinc oxide as the main component and bismuth and cobalt as additives.

Several to ten kinds of manganese, nickel, chromium, etc. are added and mixed, and the sintered body is granulated and sintered. Silver paste is coated on both sides of the sintered body, and the electrode metal is metallized. Electrodes are formed through various means and put into practical use.

Therefore, the varistor used in this way has a small idling current (leakage current) under normal (normal) voltage conditions, and has a large absorption capacity when absorbing normal voltage and lightning surges. It is required that there be very little change in physical characteristics. Conventionally, as a technique to meet such demands, Japanese Patent Publication No. 53-21509,
Alternatively, there is one disclosed in Japanese Patent Publication No. 60-38841.

The technology disclosed in Japanese Patent Publication No. 53-21509 (hereinafter referred to as the song title) is stable against DC loads by including 10% or more of the BiO contained in the sintered body as γ-Bi203. Furthermore, the varistor exhibits stable and excellent varistor characteristics even with pulsed current.

In addition, the technology disclosed in Japanese Patent Publication No. 6.0-38841 (hereinafter referred to as the latter) is that bismuth borosilicate glass containing silver is added, and more than 90% by weight of Bi2O3 in the sintered body is converted into a body-centered cubic product. Bismuth oxide (γ-B i 203
), this invention relates to a varistor that has characteristics such that the change in leakage current over a long period of time is extremely small even under extremely severe energizing conditions, and furthermore, the leakage current decreases over time.

That is, in the former case, the α-Bi203 phase is formed in the sintered body depending on the type of additives, calcination conditions, firing conditions, etc.

In addition to β-Bi O phase and γ-Bi2O3 phase, β-Bi2
03 phase is generated, and at the time of firing, γ-Bi2O
Even if the sintered body does not contain three phases, α-Bi203 phase, β-B
It has been found that a stable varistor can be obtained when the γ-Bi2O3 phase is 10% or more when the i203 phase and the δ-BiO phase are transformed into the γ-Bi2O3 phase. The latter is obtained by adding silver-containing bismuth borosilicate glass.The bismuth oxide constituting the sintered body containing bismuth oxide usually starts to react at 800 to 900°C, once forming a pyrochlore crystal phase, and then β-3i203 phase, which is decomposed to produce a spinel crystal phase and a liquid phase of bismuth oxide (I[[), and is formed in the process of progressing sintering of zinc oxide;
The sintered body containing the δ-Bi203 phase was published in Journal of Absorbed Physics (Japan), Vol. 15 (197
6) According to the method described on page 1847, 90% or more of the bismuth oxide (I[I) in the sintered body is changed to the γ-Bi2O3 phase by re-firing at 700°C in the atmosphere. It was discovered that a stable varistor can be obtained by using this method.

As a result of various studies based on the above-mentioned technology, the present inventors found that α contained in the sintered body in both the former and the latter disclosed as the above-mentioned prior art.

The thermal history of bismuth oxide exhibiting the Bi2O3 phase of β and δ during the manufacturing process, that is, the cumulative thermal history of electrical energy during practical use even in the case of plating and metallicon that do not have a thermal history during baking of saw electrodes or electrode formation. It was found that the γ-B i 203 phase transforms (phase change) and the voltage-current (V-I) characteristics deteriorate in the low current region.

However, the present inventors have discovered that B, which constitutes the grain boundary segregation region, is produced by producing a thermally stable bismuth compound in the grain boundary segregation region of the crystal grains mainly composed of zinc oxide that constitute the sintered body.
Focusing on the fact that the phase change due to heat in the i2O3 phase can be reduced, various developments were carried out, leading to the present invention.

(Problems to be Solved by the Invention) As described above, in order to obtain a stable varistor, varistors are formed at grain boundary segregation areas of crystal grains in a sintered body depending on the type of additives, calcination conditions, firing conditions, etc. γ of desired gradient in Bi2O3 phase
- Even if the Bi2O3 phase is obtained, the remaining α, β, and δ Bi2O3 phases undergo a phase change due to subsequent thermal history, that is, electrode baking and electrical energy during use, resulting in V-1 characteristics in the low current region. It is not possible to prevent the decline in

An object of the present invention is to provide an extremely stable varistor with excellent nonlinearity and no change over time by reducing the Bi2O3 phase present in grain boundary segregation areas in a sintered body.

[Constitution of the Invention (Means for Solving Problems) The varistor of the present invention contains zinc oxide as a main component, and contains at least barium and bismuth as additives.

Contains tantalum and antimony, and the relationship between barium and bismuth, tantalum, and bismuth in the additive is Ba/B i ~0. 05~0. 5゜Ta/B
In the range of i=0.2 to 2.0, bismuth is converted to Bi2O3 from 0.05 to
1.0 mol%, 0.0% when antimony is converted to Sb2O3.
In the sintered body containing 05 to 3.0 mol%, 50% or more of the total mass in the sintered body is contained in a pyrochlore type compound in the grain boundary segregation part of the crystal grains mainly composed of zinc oxide. It is constructed in a certain way.

(Function) According to the varistor configured as described above, by making 50% or more of the total bismuth into a pyrochlore type compound as a segregated substance intervening in the grain boundary segregation area of crystal grains in the sintered body, the varistor can be heated to about 1000°C. It can be formed as a thermally stable material that does not undergo any transformation up to
The deterioration of the -I characteristics is extremely small, and excellent nonlinear characteristics that cannot be obtained conventionally can be obtained.

(Example) Examples of the present invention will be described in detail below.

Bismuth oxide (Bi203), barium oxide (Bad), M
Tantalum oxide (Ta205).

Antimony oxide (Sb203), cobalt oxide (Co
o), chromium oxide (Cr203), nickel oxide (Nt
O), contains at least barium oxide, bismuth oxide, tantalum oxide, and antimony oxide from the oxides of manganese oxide (MrlO), and the relationship between barium and bismuth and tantalum and bismuth in the additive is Ba/B i ~0 Bi2O3 in the range of .05~0.5゜Ta/B i ~0.2~2.0
0.05-1.0 mol%.

3b Ceramic powder containing 0.05 to 3.0 mol% O is granulated and fired at a temperature of 1000 to 1300°C, and both sides of the obtained plate-shaped sintered body are coated with silver baking, plating, or metallicon to form electrodes. It is formed by forming.

The table shows the difference between ZnO crystal grains determined from the main peak intensity ratio of X-ray diffraction of a sintered body heat-treated at 700°C under the same conditions as for forming a silver baked electrode, depending on the type and amount (mol%) of additives added. In order to understand the amount of bismuth contained in the pyrochlore type compound as a component of the grain boundary segregation part that constitutes the sintered body, and the electrical characteristics of the sintered body itself, Vloo was measured by forming an aluminum metallicon electrode without thermal history. μA−Vl mA(7)α, Vloo uA− measured by silver baked electrode formation with thermal history
It shows α of Vl mA and further Vl mA/lry.

The size of the sintered body used as a sample was 14mm in diameter.
, the thickness is 1 mm, and the electrode diameter is 13.4 mm.

Next, in order to understand the results shown in the table above, T < 7, an explanation will be given with reference to FIGS. 1 to 9.

Figures 1 and 3 are BayB; or Ding a/B1 and non-linear 'r! It shows the relationship between I-α (Vloo μA-V 1 mA), and Figures 2 and 4 show the amount of bismuth contained in Ba/Bi or Ta/Bi and pyrochlore type compounds. In Figures and Figure 2 (PuruT
a/Bi is 1. 13a in O1 Figures 3 and 4
/Bi is 0.25. Furthermore, Figure 5 shows the relationship between the amount of bismuth contained in the pyrochlore type compound and the LC fluctuation due to annealing at 700°C, and Figure 6 shows the relationship between the amount of bismuth contained in the pyrochlore type compound and the high temperature charging (1
05°C, DC 2mA.

It shows the relationship with LC fluctuation after 1000h. Note that this sample uses an aluminum metallicon electrode. Furthermore, FIG. 7 shows the voltage-current characteristics of V1μA-VlomA of Example 9 and Conventional Example 73 shown in the table above, and FIGS. 8 and 9 show the voltage-current characteristics of the same sample used in FIG. The X-ray diffraction graphs are shown in FIG. 8 before heat treatment and FIG. 9 after heat treatment (700° C.) of the sintered body.

As is clear from the above table and FIGS. 1 to 4, Ba
The proportion of bismuth contained in the pyrochlore type compound tends to increase as /Bi and Ta/Bi increase, and Ba/Bj and Ta have the highest nonlinearity α.
It can be seen that the range of /B i is Ba/B i =0.05 to 0.5°Ta/B i =0.2 to 2.0.

In other words, an increase in the amount of bismuth contained in the pyrochlore type compound in the grain boundary segregation area of the sintered body decreases Bi2O3 and does not show excellent nonlinearity, but Ba/B i , Ta/
It is presumed that if B i becomes too large beyond the upper limit, the reaction stage of pyrochlorization becomes too rapid, impairing sinterability. Furthermore, as is clear from the table above as well as from Figures 5 and 6, pyrochlore compounds containing 50% or more of bismuth are excellent varistors with very little change in nonlinear α characteristics due to thermal history. It shows the characteristics. Furthermore, as is clear from FIG. 7, the voltage drop of the conventional example without a pyrochlore type compound is significant in the low current range, whereas the voltage drop of the present invention is slight even in the low current range of 1 μA. The results showed that the leakage current was extremely small. As shown in FIGS. 8 and 9, the reason why the present invention exhibits the above-mentioned excellent effects is that pyrochlore-type compounds are present in the grain boundary segregated areas between the crystal grains of the sintered body. This is because the pyrochlore type compound contains 50% or more of the total bismuth contained in the sintered body, thereby suppressing the Bi2O3 phase that changes in phase due to thermal history.

It is assumed that a part of bismuth exists as vitrified bismuth that does not undergo phase change.

[Effects of the Invention] As described above, according to the present invention, it has excellent nonlinearity,
Moreover, it is possible to obtain an extremely stable varistor with high practical value without characteristic deterioration due to thermal history.

[Brief explanation of the drawing]

Figure 1 is a Ba/Bi-α characteristic curve diagram, Figure 2 is Ba/B
A correlation diagram of the amount of bismuth contained in i-pyrochlore type compounds, Figure 3 is a Ta/B i-α characteristic curve diagram, and Figure 4 is a diagram of the Ta/B i-α characteristic curve.
a/Bi - Correlation diagram of the amount of bismuth contained in the pyrochlore type compound, FIG.
Figure 6 shows the amount of bismuth contained in pyrochlore type compounds.
Figure 7 is a current-voltage ratio characteristic curve diagram, Figure 8 is an X-ray diffraction graph of the sintered body before heat treatment, and Figure 9 is the sintered body after heat treatment. It is an X-ray diffraction graph of. Patent application Hito Marukon Electronics Co., Ltd. (VvL LA ~ Vn 0OLA D (%)
ulr7r29'lJ:f'G:l'lr'fbV'
1)iW&05L]), V0.40.81.21.62
．． 02.42.8Ta/B i Figure 3; Kuun 80 Kuun◇ # Tsukudakukukuchi υ 100H Kuchiheku ¥ Pyroku [Bismuth hl (%) contained in 1A-type compounds
Figure 5.〉

Claims (1)

[Claims] The main component is zinc oxide, and contains at least additives of barium, bismuth, tantalum, and antimony, and the relationship between barium and bismuth and tantalum and bismuth in the additives is Ba/Bi = 0.05 to 0.05. 0.5, in the range of Ta/Bi=0.2 to 2.0, bismuth is converted to Bi_2O_3 and is 0.0.
In a sintered body containing 5 to 1.0 mol% of antimony and 0.05 to 3.0 mol% of antimony calculated as Sb_2O_3, the total amount of bismuth in the sintered body is A voltage nonlinear resistor characterized by containing 50% or more of a pyrochlore type compound.