Modification of PTCR Behavior of (Sr_(0.2)Ba_(0.8))TiO_3 Materials by Post-Heat Treatment after Microwave Sintering

摘要

(Sr_(0.2)Ba_(0.8)) TiO_3 materials have been effectively densified by microwave sintering process. The grain I size (～ 6 μm) and PTCR characteristics (T_c = 50℃, ρ_(max)/ρ_(min)≈ 10~2) of the as-sintered samples wry insignificantly with sintering temperature (1100-1180℃) and soaking time (10-40 min). However, lowering the cooling rate after sintering substantially increases the resistivity jump (ρ_(max)/ρ_(min)) from 10~2 to 10~(5.3), without altering the microstructure. Subsequent annealing, on the other hand, substantially modifies the microstructure and PTCR characteristics. The resistivity jump increases monotonously with heat treatment temper-ature (T_(ht)) and reaches (ρ_(max)/ρ_(min)) = 10~7 for sam-ples heat-treated at 1300℃ for 2 h. The grain size remains nearly unchanged for T_(ht) ≤ 1200℃ and grows markedly for samples heat-treated at a higher temperature. The effective trap level is estimated to be E_s = 1.46 eV. The activation energy for the densification rate is Q_(MS) = 8.2 kcal/mol for microwave sintering and Q_(cs) = 62.5 kcal/mol for conventional sintering process.