Discrepancies between infrared and dc resistivities of La0.7Ca0.3MnO3 samples

Abstract

Infrared (IR) reflectivity spectra were measured in temperatures between 160 K and 290 K for polycrystalline ${\mathrm{La}}_{0.7}$ ${\mathrm{Ca}}_{0.3}$ ${\mathrm{MnO}}_3$ (LCMO) samples. Though all the samples showed nearly the same reflectivities, their dc resistivities were varied by more than one order of magnitude. Their resistivities predicted by the Hagen-Rubens relation from the IR spectra were much lower than the values from dc measurements, but they were very close to those of epitaxially grown LCMO films. Our results suggest that dc transport properties of LCMO might be strongly influenced by intergranular resistance, but that the IR responses reflect intrinsic properties of the LCMO grains.