Thermal and electronic transport in La0.7Sr0.3-xAgxMnO3 compounds between 50 and 450 K

Temperature dependence of electrical and thermal conductivity of nanocrystalline LaO0.7Sr0.3-xAgxMnO3 (x = 0.05, 0.10, 0.20, 0.25) pellets prepared by pyrophoric method is reported between 20 and 300 K. Silver doping in LSMO influences strongly both the electrical and thermal conductivity. The metal-insulator transition temperature shows significant enhancement from 303 K (x = 0.05) to 363 K (x = 0.25). Electrical conduction in La0.7Sr0.3-xAgxMnO3 above T-C is consistent with adiabatic small polaron hopping, while, in the ferromagnetic region (T < T-C) the resistivity data shows a nearly perfect fit for all the samples to an expression containing, the residual resistivity, two-magnon scattering term and the term associated with small-polaron metallic conduction, which involves a relaxation time due to a soft optical phonon mode. Heat conduction in this compound is dominated by phonons and electronic part is only similar to 1% of the total lambda. Lattice thermal conductivity (lambda(ph)) between 20 and 250 K, estimated using relaxation time approach gives an excellent agreement (within 2%) with the measured values, only when Umklapp scattering and scattering by two-level states are included along with phonon scattering by grain boundaries, sheet-like faults and point defects in the phonon relaxation time expression. Strengths of these phonon scattering rates are also estimated individually. Two-dimensional sheet-like faults appear to be the most important phonon scatterer in La0.7Sr0.3-xAgxMnO3 compounds. (c) 2005 Elsevier B.V. All rights reserved.