Influence of sintering temperature on resistivity, magnetoresistance and thermopower of La0.67Ca0.33MnO3

A systematic investigation of La0.67Ca0.33MnO3 manganites has been undertaken, mainly to understand the influence of varying crystallite size (nanometer range) on electrical resistivity, magnetic susceptibility and thermoelectric power. The materials were prepared by the sol-gel method of sintering at four different temperatures between 800 and 1100 degrees C. The samples were characterized by X-ray diffraction and data were analyzed using Rietveld refinement. The metal-insulator transition temperatures (TP) are found to increase with increasing sintering temperatures, while the magnetic transition temperatures (TC) decrease. The electrical resistivity and thermoelectric power data at low temperatures (T < TP) have been analyzed by considering various scattering phenomena, while the high temperature (T > TP) data were analyzed with Mott's small polaron hopping conduction mechanisms. PACS Codes: 73.50.Lw, 75.47.Gk, 75.47.Lx