Microwave sintering of PTCR ceramics and their electrical properties

Sintering behavior and electrical properties of semiconducting oxides, including (Sr/sub 0.2/Ba/sub 0.8/)TiO/sub 3/ (SBT), (Sr/sub 0.4/Pb/sub 0.6/)TiO/sub 3/ (SPT), (Ba/sub 0.7/Pb/sub 0.3/)TiO/sub 3/ (BPT) materials, processed by a microwave sintering technique were examined. Sintering temperature needed in this process is generally /spl sim/150/spl deg/C lower than and soaking time required is generally 80% shorter than those commonly used in the conventional sintering process. For SBT materials, post-annealing after sintering insignificantly modified the samples' microstructure, but substantially alter their resistivity-temperature (/spl rho/-T) characteristics. The re-oxidation which occurred at the grain boundary region is proposed as the mechanism of modification. Unique single high-T/sub c/ behavior and double-T/sub c/ characteristics in /spl rho/-T curve were obtained for as-microwave sintered SPT and BPT materials, respectively. It is attributed to the formation of the "core-shell" microstructure, which, in turn, presumably resulted from the preferential reaction of liquid phase sintering aids, SiO/sub 2/, with the Pb-species. Post-annealing restored the single low-T/sub c/ /spl rho/-T property, that is induced by the homogenization of the microstructure.