CROSS EFFECT BETWEEN HEAT AND MATTER FLUXES IN MIXED CONDUCTING SOLIDS - DEFINITION OF THE HEATS OF TRANSPORT

Matter fluxes are always coupled to heat fluxes, so that temperature g radients not only cause heat fluxes but also induce matter fluxes. In the framework of irreversible thermodynamics, this coupling is express ed by the definition of so-called heats of transport of the mobile com ponents. In mixed conducting solids, the measurable fluxes of ions and electrons are in general composed of contributions of various mobile point defects (structure elements). Thus, the measurable transport coe fficients and heats of transport are necessarily a combination of seve ral independent defect properties. For the case of mixed conducting so lids with Frenkel and electronic disorder we present a formal analysis of the coupling on the basis of a distinction between structure eleme nts and building units of the crystal. The relations between the measu rable transport properties and the a priori not measurable point defec t properties are derived and discussed. Experimental results for two d ifferent systems (low-temperature phases alpha-Ag2+deltaS, alpha-Ag2+d eltaSe) are analysed on the basis of our formal results.