V-shaped PTCR properties of (Pb,Sr)TiO/sub 3/ materials prepared by conventional, rapid thermal and microwave sintering processes

(Pb/sub 0.6/Sr/sub 0.4/)TiO/sub 3/ materials containing Y/sup 3+/ as donors and TiO/sub 2//SiO/sub 2/ 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/sub c/=220/spl deg/C were obtained by conventional sintering at 1270-1300/spl deg/C for 30 min. Double-T/sub c/ PTCR behaviors with T/sub c1/=260/spl deg/C and T/sub c2/=430/spl deg/C were resulted by rapid-thermal sintering at 1250-1300/spl deg/C for 30 min. By contrast, a single high-T/sub c/ resistivity-temperature (/spl rho/-T) properties with T/sub c/-value as high as 460/spl deg/C was observed by microwave sintering of these materials at 1100/spl deg/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/sub 0.9/Sr/sub 0.1/)TiO/sub 3/. A conduction model was proposed based on these observations.