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¯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 Tmi. The metallic resistivity for temperatures T < Tmi, is theoretically analysed with electron–phonon, electron–electron and electron–magnon scattering. For temperatures, T > Tmi, 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.

► Unit-cell volume decreases and tolerance factor increases on enhancing Na doping at La site in La1–xNaxMnO3.
► Below 50 K resistivity upturn is due to Coulomb interaction and Kondo-like spin dependent scattering.
► Transport mechanism in doped manganites is dominated by Electron/phonon/magnon scattering (50 ≤ T ≤ Tmi).
► The product kFl ∼ 1 as well ɛFτ > 1 favors the metallic conduction and validate Bloch–Gruneisen model.
► Role of two-magnon scattering in resistivity behavior is prominent above 175 K with essential T4.5 dependence.
► For T > Tmi small polaron conduction mechanism in La1–xNaxMnO3 is viable and Ep gradually decreases with doping.