CA-ACCEPTORS IN DIELECTRIC CERAMICS SINTERED IN REDUCIVE ATMOSPHERES

Dielectric ceramics of the system (Ba, Ca) (Ti,Zr)O-3 (BCTZ) have been fired with BaO-excess in reducive atmosphere. By the influence of BaO-excess the Ca2+-ions are shifted from the Ba- to the Ti-sites of the perovskite lattice. The solubility of Ca2+ on Ti-sites is largely independent of the firing atmosphere, but shows a pronounced temperature dependence. At 1400 degrees C congruent to 2 at.% Ca can be dissolved on the Ti-sites. Ca-ions on Ti-sites are strong electron acceptors. Highly insulating materials can be thus prepared in reducive atmospheres. The Ca-acceptors are electrically compensated by large numbers of ionized oxygen vacancies. Electromigration of the oxygen vacancies gives rise to ionic conductivity, resulting in low life stability of multilayer capacitors, sintered in reducive atmosphere.