Electro-magnetic transport behavior of La0.7Ca0.3MnO3/SnO2 composites

The composites of (1 - x)La{sub 0.7}Ca{sub 0.3}MnO{sub 3} (LCMO) + xSnO{sub 2} (x = 0.01, 0.05, 0.10, 0.30, 0.50, 0.60, 0.65 and 0.70) were synthesized by conventional solid-state reaction method. The results of X-ray diffraction (XRD) and scanning electronic microscopy (SEM) indicate that SnO{sub 2} and LCMO coexist in the composites and SnO{sub 2} mainly segregates at the grain boundaries of LCMO, which are in accordance with the results of the magnetic measurements. The detailed electrical characterizations for all the samples showed that a new metal-insulator (M-I) transition temperature (T{sub P2}) appeared at a lower temperature compared with the intrinsic metal-insulator (M-I) transition temperature (T{sub P1}) when x T{sub P2}). When x > 0.50, T{sub P1} disappeared, leaving only T{sub P2}. The resistivity percolation threshold of the composites occurred at x = 0.60. Corresponding to the two M-I transition peaks, the curves of magnetoresistance against temperature also showed two peaks for all composites. These phenomena can be explained by the segregation of a new phase related to SnO{sub 2} at the grain boundaries or surfaces of the LCMO grains.