Polaron hopping conduction mechanism and magnetic properties of Pb‐doped LaMnO3

Abstract

AbstractIn the present work, we have synthesized La1‐xPbxMno3 (0 ≤ x ≤ 0.20) perovskites through a conventional solid‐state reaction route. The powder x‐ray diffraction data analyzed through the Rietveld refinement program confirm monophase rhombohedral distorted structure (R‐3c space group). Fourier transform infrared spectra exhibit strong and well‐defined absorption bands of a typical perovskite structure. The x‐ray photoelectron spectroscopy studies confirm the elemental composition and oxidation state of various elements in the samples. Low temperature resistivity measurements do not reveal metal–semiconductor transition (MST) in the pristine sample while Pb‐doped samples show MST. The metallic region of the temperature‐dependent resistivity data is well fitted with ρ(T) = ρο + ρ2.5T2.5, which reveals the significance of electron–magnon interaction. Moreover, the semiconducting behavior of all the samples follows the Mott's variable range hopping conduction process. Additionally, the semiconducting part is also fitted with the small‐polaron hopping (SPH) model that establishes the non‐adiabatic SPH mechanism obeyed for the lower doping, whereas adiabatic mechanism for the higher Pb concentration. Magnetic studies clearly indicate a paramagnetic to weak ferromagnetic transition associated with the Pb doping that may be due to the double‐exchange mechanism between the manganese ions via oxygen orbitals. The outcomes are elucidated on the basis of substitution effect induced by Pb2+ ions.