Building versus Structure Elements: Ionic Charge Carriers in Solids

Abstract

Abstract The contribution deals with the thermodynamics of charge carriers in crystals, in particular with the distinction between building and structure elements. In this context the use of the basic mechanistic processes (addition, elimination, substitution) usually applied for describing reactions with organic molecules proves helpful. It is shown that as far as thermodynamics is concerned, the use of building elements is to be preferred. The only advantage of structure elements is that they automatically include site exhaustibility effects, which have to be included by using Fermi-Dirac statistics in the case of building elements. A rigorous proof is given for the applicability of the structure element approach for the interaction free case. If interactions have to be considered and multinary crystals are addressed, the structure element approach becomes artificial. In the case of kinetic considerations structure elements naturally appear in the rate equation. If the rates approach zero the description has to match the building element description. How interactions behave as a function of the deviation from equilibrium is a matter of specific considerations.