JPS5815078A - High dielectric constant ceramic dielectric composition - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-permittivity ceramic dielectric composition, in particular a ceramic dielectric composition having an extremely high dielectric constant and a small temperature change rate of the dielectric constant.
The present invention relates to a ceramic dielectric composition suitable for use in multilayer capacitors.

Conventionally, porcelain dielectrics with flat permittivity-temperature characteristics have been mainly composed of barium titanate (BaTi03) and bismuth oxide (Bi2O3), with tin oxide (
8n02) or those with added titanium oxide (TiO2) or zirconium oxide (ZrO2),
In either case, if the temperature change rate of the dielectric constant is within 110% in the temperature range of -30℃ to +85℃, the dielectric constant will be 20%.
00 or less, and for those with a dielectric constant of 2000 or more, the temperature change rate of the dielectric constant is ± within the above temperature range.
Only more than 10% was obtained.

On the other hand, as a porcelain dielectric composition that solves this problem,
BaTiO3 and Bi2O3 with Nb2O5.

By adding Ce 02 or L a 203 , the dielectric constant temperature change rate is within 110%, and the temperature change rate is 30%.
The one that achieves a dielectric constant of 00 to 8500 is
This is disclosed in Publication No.-21402.

However, the B r 20 contained in such compositions
3. If a high firing temperature is used to make a multilayer capacitor, there is a problem that it will evaporate and thereby damage the electrodes. Therefore, compositions containing component i such as Bi2O3 are not suitable for multilayer capacitors. It was appropriate.

Here, as a result of various studies on such porcelain dielectric compositions, the present inventors discovered that the main component, BaTiO
In the formation process of 3, strontium oxide (S
rO) and calcium oxide (CaO) have a negative effect on the electrical properties such as the dielectric constant, and therefore their content is below a certain value so that high-purity BaTiO3 is formed.

By combining this with cobal oxide (00203), niobium oxide (Nb205), and cerium oxide (CeO2), it has a flat dielectric constant temperature characteristic and a high dielectric constant for multilayer capacitors. They discovered that a suitable porcelain dielectric material can be obtained, and the present invention was achieved.

That is, the high permittivity ceramic dielectric composition according to the present invention contains high-purity BaTi0-395 to 99% by weight in which the total content of SrO and CaO is 0.5% by weight or less, and Co2.
030.05~0.5% by weight and Nb2050.5~2
According to the barrel porcelain dielectric composition with 0.05% to 0.5% by weight of Ce 02, a flat dielectric constant temperature characteristic is achieved, especially within the temperature range of -30°C to +80'C. When using the dielectric constant of +25°C as a standard, it is easy to obtain a dielectric constant whose temperature change rate is within ±10%, and at the same time, the dielectric constant can be easily increased to 8000.
In particular, a value as high as 4000I to 4500 can be obtained.

Furthermore, since the porcelain dielectric composition according to the present invention does not contain evaporable components such as Bi203 and PbO, the electrode will not be damaged at all even if a high firing temperature is employed. It can be suitably used for dispersed multilayer capacitors.

Furthermore, as shown in the Examples below, the ceramic dielectric of the present composition has excellent characteristics in various performances after applying a voltage of 10 KV/+nm for 8000 hours, and this shows that This is proof that it has a voltage resistance of K V/mm or more, and it also has a considerably higher voltage resistance than other compositions of barium titanate-based high permittivity porcelain dielectrics 1 to 7/InIn. Therefore, the ceramic composition according to the present invention is also suitable for use in medium- and high-voltage ceramic capacitors.

In addition, in the present invention, first, high-purity BaTiO3
It is necessary to contain 95 to 99% by weight, preferably 97 to 99% by weight, in the composition. If the content is too high or low, the dielectric constant may decrease significantly or This may cause problems such as significant humidity changes. This high-purity BaTiO3 must be formed so as to contain SrO and CaO in a total amount of 0.5% by weight or less;
O.

Containing CaO lowers the dielectric constant and increases the temperature change rate of the dielectric constant. In particular, such 8rO, CaO
is easily mixed in from BaCO3, which is the starting material for BaTiO3, so 8rO and Ca are used as Ba003.
B
It is recommended to use a BaCO3 raw material of 9% or more, preferably 99.5% or more.

In addition, TiO, which is another starting material for BaTiO3,
2, it is possible to use a TiO2 raw material with a purity of about 98 to 99%, but preferably a TiO2 raw material with a purity of 99% or more, more preferably 99.5% or more can be advantageously used. It is.

In addition, Co2O3 and Nb constituting the composition according to the present invention
2O5 is a component that flattens the temperature change rate of dielectric constant, and 0o203 is 0.05 to 0.5%, preferably 0.09 to 0.4%; Nb2O5 is 0.5 to 2%. ,
Preferably, it needs to be contained in a proportion of 0.9 to 1.5% (both based on weight).

In addition, C! o20. is less than 0.05%,
When the temperature change rate of the dielectric constant becomes large and exceeds 0.5%, the dielectric constant becomes low. In addition, Nb2O5 is 0.5%
When the amount is less than 2, the problem of poor sintering occurs;
When the proportion is less than 0.05%, the problem arises that the temperature change rate of the dielectric constant becomes large.Furthermore, CeO2 in the composition of the present invention has the effect of lowering the firing temperature, but when the proportion is less than 0.05%, This will result in poor sintering, and if it exceeds 0.5%, the temperature change rate of the dielectric constant will increase. Therefore, the proportion of CeO2 is 0.05~0.5J [1%, preferably 0.09~
It needs to be 0.3% by weight.

Furthermore, like CeO2, TiO2 contributes to lowering the firing temperature, but if its proportion is too large, it lowers the dielectric constant and increases dielectric loss (tan δ), so 1.5% by weight is used. It is necessary to have a content ratio of 0.2 to 1.0% by weight, in particular, to exhibit its effective effect. Note that this amount of TiO2 can be introduced by combining excess TiO2 with BaCO3 when forming the high-purity BaTiO3, as well as a necessary amount of T +
It can also be introduced by separately incorporating 02 into the composition.

In this way, according to the present invention, a predetermined proportion of BaTi
O3, Co2 o3. Nb, 205, CeO2,
The porcelain dielectric is composed of TiO2, and BaTiO
By controlling the amount of 5rO-)-CaO brought in from No. 3, it was possible to impart excellent electrical properties such as dielectric constant to the fired ceramic dielectric material of the present invention.

Examples will be given below to clarify the present invention in more detail, but it goes without saying that the present invention is not limited in any way by the description of the examples. Note that all parts and percentages in the examples are expressed on a weight basis.

Examples The raw materials for each component were wet-mixed uniformly in a ball mill so that the proportions shown in Table 1 were obtained, and then 900 to 1
After calcining at 100°C for 3 hours to carry out a chemical reaction, the mixture was ground again in a ball mill until the average particle size was about 1 micron.

In addition, in order to form a high purity BaTiO3 component, 8r
Purity is 99.0% with various total contents of O and CaO
The above Bjima C03 and TiO2 with a purity of 99.9% were used and wet-mixed with other components in the ball mill.

Next, after drying this mixture, an appropriate amount of polyvinyl alcohol was added as a binder and molded at a pressure of about 1 ton/ad to form a disc-shaped molded product with a diameter of t6 m/ms and a thickness of 0.5 m/m. was created.

Furthermore, about 1350
After performing the main firing operation for 8 hours at a temperature of ~1400°C, the obtained fired product was used as a sample by baking silver electrodes on both sides, and the properties were measured and the results are shown in Table 2. It was shown to.

As is clear from the results in Tables 1 and 2, the compositions according to the present invention, namely (a) and (b) of each sample series.
They all have a high dielectric constant (ε) of 3000 or more, a small dielectric loss (tan δ), and a small rate of change in dielectric constant with respect to temperature.

On the other hand, BaTiO3, Co2O3, Nb2O6
Even if the contents of , CeO2, and TiO2 are similar, SrO
+The total content of CaO exceeds 0.5% ((C) and (
In case d), (a) and (b) according to the invention
The dielectric constant (ε) was significantly inferior to that in the case of .

Table 1 Table 2 JP-A-58-15078 (4) (Note> i (a), (b), (C), (d) are
The total contents of SrO and OaO in BaTiO3 are 0.20%, 0.50%, 0.55%, and 0.75%, respectively.

Claims (1)

[Claims] Total content of strontium oxide and calcium oxide is 0
．． High purity titanate barium A95 with a content of 5% by weight or less
~99% by weight and 0.05-0.5% by weight of cobalt oxide
, 0.5 to 2% by weight of niobium oxide, and 0.5 to 2% by weight of niobium oxide.
A high dielectric constant ceramic dielectric composition comprising 0.05 to 0.5% by weight of titanium oxide and up to 1.5% by weight of titanium oxide.