Abstract
In the previous paper, the authors confirmed that addition of glass powders rich in BaO and TiO2 to BaTiO3 crystal powders was effective to extend the firing range of the pressed mixture and to obtain BaTiO3 ceramics with dielectric properties little influenced by sintering temperature (J. Ceram. Assoc. Japan 75, 278 (1967)). In the present study, temperature characteristics in dielectric properties were measured at 1 kc/sec (applied voltage, 2V) by means of Bridge method in the cooling process of the specimens from 160°C to -60°C. On the same specimens, observation of microstructure by electron microscope was made in order to investigate structure dependency of the temperature characteristics.
The results obtained are summarized as follows: 1) By addition of glass powders of a BaO-Mg(Ca)O-TiO2-SiO2-Al2O3 system, the BaTiO3 ceramics with temperature characteristics of dielectric properties little affected by sintering temperature were able to be prepared. 2) The temperature characteristics in dielectric properties of the BaTiO3 ceramics thus prepared are much influenced by the composition of the glass powders added. The MgO component is especially effective in decreasing the temperature changes of their dielectric properties. 3) Addition of the MgF2 crystal powders together with the BaO-TiO2-SiO2-Al2O3 glass powders (glass 7.5, MgF2 2.5 by wt%) to BaTiO3 powders is effective in decreasing temperature changes of dielectric properties and also in raising dielectric constant near room temperature of the BaTiO3 ceramics. 4) Effects of addition of the glass powders on temperature characteristics of dielectric properties can be reasonably explained on the basis of the electron microscopic observation of the microstructure of the specimens.
