Structure and charge transport mechanism in hydrothermally synthesized (La0.5Ba0.5MnO3) cubic perovskite manganite

Abstract

Perovskite manganites with chemical formula La0.5Ba0.5MnO3 (LBMO) samples were synthesized though the hydrothermal process by heating suitable reactants at 270 °C in an autoclave for 25 h. After washing with de-ionized water several times, the as prepared samples were then calcined at different temperatures, ranging from 120 to 1000 °C to remove the impurities. Final sintering of the sample was carried out at 1350 °C for 24 h. Subsequent X-ray diffraction (XRD) measurements were also carried out. Rietveld refinement of XRD data for the sample sintered at 1350 °C confirmed single phase cubic structure with lattice parameter a = 3.9057Ǻ and space group P m −3 m. The dc electrical measurements were performed in a broad range of temperatures from 77 to 870 K on this sample. The focal point of this study was to obtain microscopic parameters and characteristic length in order to discuss the relationship between magnetic, electric and phonon excitations. The electrical resistivity measurements revealed a metallic/ferromagnetic to semiconductor/paramagnetic phase transition (TC) at 339 K. In the metallic region the experimental data best fitted the resistivity equation $$\uprho (\text{T})={\uprho _{o}}+{\uprho _2}{\text{T}^2}+{\uprho _{2.5}}{\text{T}^{2.5}}+{\uprho _{4.5}}{\text{T}^{4.5}}$$ showing that the resistivity effect arises due to residual impurities, grain boundaries, electron–electron (e–e), electron–magnon (e–mag) and electron–phonon (e–ph) scattering. The analysis of the resistivity data above TC has shown a transformation in conduction mechanism from Mott’s variable range hopping (MVRH) to small polaron hopping (SPH), around 585 K. Hopping of carriers to larger distances with multiplying values of activation energies are analyzed through MVRH below 585 K. Above 585 K, the carriers were found to be trapped by several scattering centers through small polaron, this behavior having been interpreted in the light of SPH model.