Transmission electron microscopy study of a semiconducting SrTiO3 ceramic condenser

(Sr0.94Ba0.01Ca0.05)(0.99)TiO3 ceramic condensers, activated with Pi, Cu, and Pb, were produced by sintering at an oxygen partial pressure of P-O2 = 10(-8) Pa and by reoxidization at 1200 degrees C in air. The ceramics are composed of well-developed crystalline grains whose boundaries have a facet structure. A layer as thin as a few tens of nanometres has been found around the boundary, having more Bi, Pb, and Cu atoms and less Ti and Sr atoms than the grain inside. During the sintering, O vacancies are formed in the grain. During reoxidization, the O vacancies in the boundary layer are replaced with O atoms diffused along with Bi, Pb, and Cu atoms from the surface, while the grain inside has more O vacancies. Consequently, the combination of the very thin dielectric boundary layers and the semiconducting grains inside makes a condenser ceramic with a high capacitance. High-resolution transmission electron microscopy has revealed superstructures ascribed to the O vacancies in the grain inside.