High-temperature thermopower ofLaMnO3and related systems

We investigate theoretically the high-temperature Seebeck coefficient in ${\mathrm{LaMnO}}_3$ and related transition-metal-oxide perovskites. Our analysis employs a model for small polaron conduction that takes into account the electronic structure of the 3d orbitals of B-site transition-metal cations, yielding expressions for systems in which conduction occurs through the ${\mathit{e}}_{\mathit{g}}$ transition-metal manifold. Limiting forms for the Seebeck coefficient as a function of carrier concentration and site degeneracy are identified for strong and weak Coulomb interactions between electrons on the same and neighboring sites. Results are applied to an analysis of experimental data for ${\mathrm{LaMnO}}_3$, the ${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ca}}_{\mathit{x}}$ ${\mathrm{MnO}}_3$ series, and the ${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{MnO}}_3$ series. © 1996 The American Physical Society.