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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.