Think locally – linking structure, thermodynamics and transport in grossly non-stoichiometric compounds and solid solutions

Abstract

We highlight the crucial influence of the local environment of individual cations or of oxygen vacancies on the structure and energetics of grossly non-stoichiometric compounds and solid solutions. Consideration of the average structure is not sufficient. In solid solutions non-ideality is strongly linked to the local environment, and our results question the use of models which assume entirely random distributions of particular ions or vacancies over particular lattice sites. We consider three examples: (i) the oxide Ba₂In₂O₅, representative of a family of oxygen-deficient perovskites; (ii) the superionic conductor α-CuI; (iii) the pyrope–grossular garnet solid solution. We emphasise the different insights gained into the solid state chemistry of these systems and the consequences for thermodynamic and transport properties.