科研之友
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摘要
The La0.8-x a- (x) Ca0.2MnO3 compounds were prepared by the solid-state reaction with 0.00a parts per thousand currency signxa parts per thousand currency sign 0.20. Morphologic, X-ray diffraction (XRD), magnetic, and electrical measurements were performed to examine the effect of the lanthanum deficiency on the physical properties of these materials. The scanning electron microscopy shown the existence of a secondary phase attributed to the Mn3O4 oxide. The XRD data have been analyzed by the Rietveld refinement technique. We have found that all samples crystallize in an orthorhombic symmetry with Pnma space group and the unit cell volume decreases with lanthanum deficiency. A magnetization versus temperature study has shown that all samples exhibit a magnetic transition from ferromagnetic (FM) to paramagnetic (PM) phase with increasing temperature. The Curie temperature T (C) increases with the lanthanum deficiency from 236 K to 247 K for the samples x=0.00 and x=0.20, respectively. Moreover, the temperature dependence of electrical resistivity shows a metal-insulator transition at T (rho) for all samples which increase with vacancy rate. The electrical resistivity is fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. Thus, show that the conduction mechanist was explained by the electron-electron and electron-phonon scattering process at low temperature and by small polaron hopping at high temperature. Furthermore, we found that the estimated results are in good agreement with experimental data.
- 出版日期2014-1
