INFLUENCE OF REOXIDATION ON SILICA-CONTAINING BARIUM TITANATE CERAMICS FOR PTCR THERMISTORS PREPARED BY TAPE CASTING

Silica-containing barium-rich BaTiO 3 ceramics for thermistors with a positive temperature coefficient of resistance are prepared by a tape-casting technique. The ceramics are sintered in a reducing atmosphere at low temperatures of 1175 -1225C. The influences of reoxidation are investigated after the reduced ceramics are reoxidized in air at 700 -900C. An anomalous correlation is illustrated between room temperature resistivity and reoxidation temperature. The anomaly results from the ferroelectricity rebuilding mechanism, which includes the spontaneous polarization theory and the ferroelectricity degradation caused by oxygen vacancies. The acceptor-state densities are estimated from the temperature-dependent resistivity. A critical temperature of 750 -800C is concluded for the grain boundary reoxidation.