Transmission electron microscopy study of a semiconducting SrTiO3 ceramic condenser

(Sr0.94Ba0.01Ca0.05)(0.99)TiO3 ceramic condensers, activated with Pi, Cu, a nd Pb, were produced by sintering at an oxygen partial pressure of P-O2 = 1 0(-8) Pa and by reoxidization at 1200 degrees C in air. The ceramics are co mposed of well-developed crystalline grains whose boundaries have a facet s tructure. 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 th an the grain inside. During the sintering, O vacancies are formed in the gr ain. During reoxidization, the O vacancies in the boundary layer are replac ed 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 i nside makes a condenser ceramic with a high capacitance. High-resolution tr ansmission electron microscopy has revealed superstructures ascribed to the O vacancies in the grain inside.