The thermoelectric power of ionic crystals I. Theoretical

Abstract

The theory of the thermoelectric power of solid ionic conductors has been considered thermodynamically by Holtan, Mazur & de Groot (1953) and kinetically by Howard & Lidiard (1957 a, b ). In the thermodynamic treatment the defective structure of the solid was ignored and consequently the gradient of chemical potential of the salt components was equated to zero. In the kinetic treatment, the existence of defects was recognized, but vacancies were treated as species of effective unit charge moving in a uniform dielectric. In this paper the theory of the homogeneous thermoelectric power of an ionic crystal is re-formulated in a rigorous manner, vacancies being treated as separate thermodynamic species with zero charge and mass. The equation for entropy production is derived for the case of an ionic crystal containing defects. The theory requires expressions for the chemical potentials of ions and defects; inaccuracies in previous discussions are pointed out and the correct expressions for the chemical potentials are given. A new theory of the heterogeneous thermoelectric power is developed and a possible experimental test of this indicated.