MODIFICATION ON PTCR BEHAVIOR OF (SR0.2BA0.8)TIO3 MATERIALS BY POST-HEAT TREATMENT AFTER MICROWAVE SINTERING

Effect of post-sintering treatment on PTCR behavior of (Sr0.2Ba0.8) Ti O3 materials prepared by microwave-sintering (ms) process was compared to that prepared by rapid thermal sintering (RTS) process. The microw ave-sintering process needed only 1130 degrees C-40 min to effectively densify (Sr0.2Ba0.8) TiO3 materials. The grain size was around 6 mu m and PTCR characteristics was around rho(max)/rho(min) approximate to 10(1.75), with T-c = 50 degrees C. Lowering the cooling rate after sin tering substantially increases the resistivity jump (rho(max)/rho(min) ) from 10(2) to 10(3.4) without altering the microstructure. The annea ling at 1250 degrees C for 2 h markedly increased the resistivity jump to (rho(max)/rho(min))approximate to 10(6). On the other hand, the ra pid thermal sintering (RTS) process required 1320 degrees C-30 min to fully develop the good microstructure (similar to 15 mu m) and PTCR pr operty (rho(max)/rho(min) similar to 10(3.0)). Post-sintering process, including cooling rate control and annealing, did not improve the ele ctrical properties of these samples, that is ascribed to the slow-cool ing rate characteristics of RTS-process for a temperature lower than 8 00 degrees C.