Abstract
(Pb 0.6 Sr 0.4 )TiO 3 materials containing Y 3+ as donors and TiO 2 /SiO 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 c = 220 °C were obtained by conventional sintering at 1270 to approximately 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 to approximately 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 0.9 Sr 0.1 )TiO 3 . A conduction model was proposed based on these observations.