Structural properties and electrical resistivity of Na-substituted lanthanum manganites: La 1− xNa xMnO 3+ y ( x = 0.1, 0.125 and 0.15)

Abstract

The structural properties and electrical resistivity of the polycrystalline La 1− x Na x MnO 3+ y ( x = 0.1, 0.125 and 0.15) are investigated. The result of the Rietveld refinement of X-ray powder diffraction following the FullProf refinement program indicates that these compounds having a rhombohedrally distorted structure with space group R 3 ¯ C . Both the lattice parameter and unit-cell volume decreases with increased Na content. There is a systematic change in both the Mn–O–Mn bond angle and the tolerance factor with Na content. The temperature dependence of resistivity shows that all samples undergo a metal–insulator transition at well-defined transition temperature T mi . The metallic resistivity for temperatures T < T mi , is theoretically analysed with electron–phonon, electron–electron and electron–magnon scattering. For temperatures, T > T mi , the semiconducting nature is discussed with small polaron conduction (SPC) model. The resistivity shows an upturn at low temperatures that has been explained by considering both the enhanced electron–electron interactions attributed to Coulomb interaction (CI) between carriers and the Kondo-like spin dependent scattering.