Structural properties and electrical resistivity of Na-substituted lanthanum manganites: La1-xNaxMnO3+y (x=0.1, 0.125 and 0.15)

The structural properties and electrical resistivity of the polycrystalline La1-xNaxMnO3+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) over barC. 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. (C) 2011 Elsevier B.V. All rights reserved.