A semiempirical model of the Seebeck coefficient for a small polaron hopping conductor is presented. The population of small polarons is allowed to change as a function of temperature via the mechanism of charge disproportionation. The energy required for polaron formation by the disproportionation mechanism is modeled as screened by a Coulomb interaction with nearby small polarons. The charge carrier site occupancies generated by the model are used to successfully predict the electrical conductivity and Seebeck coefficient for compositions in the ${\mathrm{La}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{CoO}}_3$ system. Cobalt ion valence populations predicted by the model are used to calculate effective paramagnetic moments for ${\mathrm{LaCoO}}_3$, which are favorably compared to those found experimentally.

• Received 10 April 1995

DOI:https://doi.org/10.1103/PhysRevB.52.11681