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

In the present work, we have synthesized La(1-)(x)Pb(x)Mno(3) (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 rho(T) = rho(omicron )+ rho T-2(.)5(2).(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.