JPH0135488B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a grain boundary layer type ceramic dielectric material obtained by providing an oxide dielectric layer consisting of at least one of _{B a} and S _r and Ti at the grain boundaries of zinc oxide (ZnO), and a method for manufacturing the same. be. BACKGROUND ART Grain boundary layer type semiconductor ceramic capacitors obtained by reoxidizing or valence-compensating grain boundaries of semiconductor ceramics mainly composed of barium titanate or strontium titanate have been well known. In other words, these grain boundary layer type semiconductor ceramic capacitors are manufactured by first adding a trace amount of a valence control element to barium titanate or strontium titanate, and then firing the mixture at high temperature in a neutral or reducing atmosphere to produce semiconductor ceramic. After this, it is possible to insulate only the grain boundaries by heat treatment in air to re-oxidize the grain boundaries or compensate for valence, and the same effect as connecting thin dielectric layers in parallel can be obtained. , an apparently extremely large dielectric constant can be obtained. However, the above-mentioned semiconductor capacitors, which are mainly made of barium titanate or strontium titanate, must be fired in a hollow atmosphere or reducing atmosphere in order to produce semiconductor porcelain, so firing furnace atmosphere control is an important characteristic control factor. Therefore, particularly in mass-production furnaces, considerably advanced technology was required to set conditions in order to obtain stability of the atmosphere. In addition, it also had the disadvantage of being extremely expensive in terms of equipment compared to air firing furnaces. The present invention takes the above-mentioned drawbacks into consideration and provides a grain boundary layer type porcelain dielectric material that can be fired in air and a method for manufacturing the same. Hereinafter, the present invention will be explained based on examples. Example 1 A mixed powder consisting of 99.8 to 99.0 mol% of ZnO and 0.2 to 1.0 mol% of BaCO ₃ was molded into a size of 13.0 mmφ x 1.0 mm, and the resulting sintered body was baked at 1200 to 1400°C in the air. A mixture consisting of 20-50 mol% Bi ₂ O ₃ and 80-50 mol % TiO ₂ is attached with an organic binder,
Heat treated in air at 1200℃. After this, silver electrodes are provided on both sides of the sintered body. Table 1 below shows the characteristics of the device thus obtained.

[Table] In addition, if the firing temperature of the above sintered body is lower than 1200°C, ZnO will not be sufficiently sintered and crystal grains will not grow, which is not good. Furthermore, if the firing temperature exceeds 1400°C, abnormal grain growth will occur and the crystal grains will become non-uniform, which is not preferable. When fired in the firing temperature range of 1200 to 1400℃, the average crystal grain size becomes 50 to 100μ.
A sintered body consisting of a group of crystal grains having a size of m is obtained. As a result of X-ray microanalysis of this sintered body, Zn element was observed in the crystal grains, and Ba
Almost no elements are observed, and only Ba element is observed at the grain boundaries. In other words, since the ionic radius of Ba is significantly larger than that of Zn,
BaO is not dissolved in solid solution in the ZnO crystal lattice, and a so-called segregation layer of BaO is formed at grain boundaries. Then _{Bi2O3 and TiO2}
When attached to the surface of the sintered body and heat-treated, it forms at the grain boundaries.
Bi ₂ O ₃ and TiO ₂ diffuse, but the heat treatment temperature is
At temperatures lower than 1100°C, it is difficult to diffuse sufficiently into the interior. Further, a heat treatment temperature higher than 1200° C. is not preferable because the grain boundary layer is broken and the particles become electrically conductive. Furthermore, no Bi ₂ O ₃ is used in the deposits.
When only TiO ₂ is attached and heat treated, it is difficult to diffuse into the grain boundaries, and ZnTiO ₃ is only generated on the surface of the sintered body, but Ti is not uniformly present at the grain boundaries.
In other words, the presence of Bi ₂ O ₃ allows Bi and Ti to be uniformly diffused at the grain boundaries.
_Bi2O has a low melting point of 820-860℃ after heat treatment for several hours.
is scattered, and T _i and B _a are uniformly present.
The above results were confirmed by X-ray microanalysis. Example 2 Exactly the same treatment as in Example 1 was performed except that BaCO ₃ was replaced with SrCO ₃ . Table 2 below shows the characteristics of typical examples in this case.

[Table] Although the present invention has been described above based on Examples, the present invention is extremely significant in that it can provide a high permittivity grain boundary layer type porcelain dielectric material obtained by firing in the atmosphere.

Claims (1)

[Claims] 1. The crystal grains of the sintered body are semiconductor grains mainly composed of ZnO, and the grain boundaries of these crystal grain groups are composed of a dielectric layer of an oxide composed of Ba and Ti or Sr and Ti. grain boundary layer type porcelain dielectric. 2 Molding a mixture formed by adding at least one compound among BaCO ₃ and SrCO ₃ to ZnO powder,
Bi ₂ O ₃ and TiO ₂ are added to the sintered body obtained by firing in the atmosphere.
1. A method for producing a grain boundary layer type porcelain dielectric, characterized in that the mixture is deposited and then heat-treated in the atmosphere.