Enhancement of temperature coefficient of resistivity in La0.67Ca0.33MnO3 polycrystalline ceramics

La0.67Ca0.33MnO3 polycrystalline ceramics with high temperature coefficient of resistivity (TCR) have been synthesized by the sol–gel method at the sintering temperature of 1450 °C and in a sintering time range of 2 h–24 h. The micrographs of the ceramics reveal that the grains grow up from 2 μm to about 10 μm with increasing the sintering time. The optimization of the sintering time is found to be a simple and effective way to largely enhance the TCR values of the ceramics. The highest metal–insulator transition temperature Tp (272.5 K) and the largest TCR (21.4%) were obtained in the ceramic sintered for 12 h. The reduction of grain boundary and resistivity contributes to the enhancement of Tp and TCR values.