Nonreducible Mechanism of {(Ba1-xCax)O}mTiO2 (m > 1) ceramics

The nonreducible mechanism of {(Ba1-xCax)O}(m)TiO2 (m > 1) ceramics fired in a reducing atmosphere was investigated by measuring the electrical conduction under various atmospheres at elevated temperatures. The high insulation resistance of the Ca-doped BaTiO3 ceramics can be explained by the following three factors; (1) the decrease of electron concentration in the lattice by the substitution of Ca2+ ions for the Ti4+ site, (2) the high enthalpy change of the reduction reaction by the substitution of Ca2+ ions for the Ba2+ site, and (3) the low freezing temperature of the equilibrium reaction due to high concentration of the extrinsic oxygen vacancies developed by Ca2+ ions on the Ti4+ site.