V-shaped PTCR properties of (Pb,Sr)TiO3 materials prepared by conventional, rapid thermal and microwave sintering processes

(Pb_0.6Sr_0.4)TiO₃ materials containing Y³⁺ as donors and TiO₂/SiO₂ as sintering aids were densified by either conventional sintering (CS), rapid thermal sintering (RTS) or microwave sintering (MS) process. V-shaped PTCR characteristics with T_c=220°C were obtained by conventional sintering at 1270-1300°C for 30 min. Double-T_c PTCR behaviors with T_c1=260°C and T_c2=430°C were resulted by rapid-thermal sintering at 1250-1300°C for 30 min. By contrast, a single high-T_c resistivity-temperature (ρ-T) properties with T_c-value as high as 460°C was observed by microwave sintering of these materials at 1100°C for 10 min. The unique properties of these materials were ascribed to the formation of core-shell microstructure, which was induced by rapid cooling rate after sintering in RTS or MS process. The core was deficient and the shell was riched in Pb-species. The composition of the shell was estimated to be around (Pb_0.9Sr _0.1)TiO₃. A conduction model was proposed based on these observations