One of the major applications of $SrTiO_3$ based materials is the grain boundary barrier layer capacitor (GBBLC) which consists of semiconducting $SrTiO_3$ grains and insulating layers between grains. In order to make semiconducting grains, the doping of $Nb_2O_5$ or $La_2O_3$ is usually made and the powder compact is sintered in a reducing atmosphere. For making insulating layers, oxides with low melting points, such as PbO, $Bi_2O_3$ and CuO, are infiltrated into sintered $SrTiO_3$ in an oxidizing atmosphere. The aim of the present investigation is to study the effect of sintering atmosphere on solid/liquid interface migration and resultant dielectric properties of Nb-doped $SrTiO_3$-based GBBLC. In chapter III, the effect of sintering atmosphere on the microstructure of $SrTiO_3$-0.2 mol\% $Nb_2O_5$ during the infiltration of CuO, $50PbO-45Bi_2O_3-5B_2O_3$ (wt\%), $Bi_2O_3$, or PbO was studied. The specimen sintered in air did not show any migration during oxide infiltration in air while the specimen sintered in $5H_2-95N_2$ showed appreciable migration during the infiltration. In the migrated layers of the specimen sintered in the reducing atmosphere and infiltrated in the oxidizing atmosphere, no cations of the infiltrants were detected by WDS. These results suggest that the change in charge compensation mechanism due to the atmosphere change can induce the interface migration as in the case of frequently observed migrations due to solute concentration change. The driving force for the migration has been discussed in terms of the coherency strain energy in a thin diffusional oxidized layer of receding grain. In chapter IV, another step of heat-treatment was introduced between sintering and oxides melt infiltration in order to test the charge compensation mechanism as the major cause of interface migration in chapter III. When the specimen sintered in air was reheated in a reducing atmosphere before CuO infiltration in air, interface migration was observed. In contrast, when the specimen sintered in a reducing atmosphere was reheated in air before CuO infiltration in air, no interface migration was observed. The $SrTiO_3$-based GBBLC fabricated by the latter process showed higher effective dielectric constant than that of the GBBLC made by the conventional process without post heat-treatment. In chapter V, the effect of the change in charge compensation mechanism on lattice parameter was studied. In order to compare the lattice parameter of the specimens sintered in air and in a reducing atmosphere, 80CuO-20[xCaO-(1-x)BaO] liquid was infiltrated in air. No interface migration was observed in the specimen sintered in $5H_2-95N_2$ with the liquid of x=0.3 only. In contrast, the specimen sintered in air was lattice-matched when using the liquid composition between x=0.3 and 0.5. The lattice parameter of the specimen sintered in air appears therefore to be smaller than that of the specimen sintered in a reducing atmosphere. When liquid melts of CuO, $50PbO-45Bi_2O_3-5B_2O_3$ (wt\%), $Bi_2O_3$, and PbO were infiltrated into the specimen sintered in a reducing atmosphere, the sign of the coherency strain formed in a thin diffusional oxidized layer of receding grain would be tensile.
