ELECTRICAL CHARACTERISTICS OF (SR0.2BA0.8)TIO3 POSITIVE TEMPERATURE-COEFFICIENT OF RESISTIVITY MATERIALS PREPARED BY MICROWAVE SINTERING

The resistivity-temperature (ρ-T) properties of the (Sr 0.2Ba0.8)TiO3 materials densified by the microwave sintering process were investigated. Neither the sintering temperature (1100-1180°C) nor the soaking time (10-40 min) in this process exert a significant influence on the positive temperature coefficient of resistivity behavior of the as-sintered samples. Contrarily, reducing the cooling rate from 154°C/min to 4°C/min or post-annealing the samples at 1250°C for 2 h would increase the maximum resistivity (ρmax) more than three orders of magnitude. Consequently, the resistivity jump with the maximum to minimum resistivity ratio ρmax/ρmin≊10 7 has been achieved. The increase in maximum resistivity by these processes is ascribed to the increase in cationic vacancies, which subsequently act as effective electronic traps. The trap level (Ese) of the cationic vacancies is estimated from the Arrhenius plots of maximum resistivity (ρmax) and temperature (Tmax) to be E se≊1.5-2.0 eV. On the other hand, the ρ-T curves in the T≳Tmax regime estimate the intrinsic trap level (Esi) of the (Sr0.2Ba0.8)TiO3 materials to be E si≊2.46-2.51 eV. © 1995 American Institute of Physics.