A $SrTiO_3$-based grain boundary layer capacitor is used widely because of its excellent properties such as high capacitance, low dielectric loss, and the stable temperature property of capacitance.
A $SrTiO_3$-based grain boundary layer capacitor was made by penetrating the oxide mixture (PbO, $Bi_2O_3$, $B_2O_3$) into grain boundaries of a semiconducting strontium titanate.
The effect of the 2nd heat treatment on the microstructure and dielectric properties was studied and the grain boundary phenomena were investigated by the change of dielectric properties with various conditions of heat treatment during the 2nd firing.
The following is the result with increasing the temperature of the 2nd firing from 900℃ to 1300℃: the dominant reaction in grain boundaries is the forming process of the second phase at the lower temperature region (900℃-1000℃), homogeneously distributing process of the second phase at the intermediate temperature region (1000℃-1100℃), and the diffusing process of the oxidation layer adjacent to the second phase at the higher temperature region (over 1150℃).
The influence of the 2nd firing time on the dielectric properties was similar to that of the 2nd firing temperature.
A $SrTiO_3$-based grain boundary layer capacitor is explained by a n-i-n band model with the grain boundary structure composed of the two kinds of the insulating layer.
