Thermodynamics and Defect Chemistry of Some Oxide Solid Solutions Part II: Pair Interactions

Abstract

AbstractThis paper is concerned with solid solutions of two isostructural ionic oxides. Relations are derived between activities and composition on the assumptions that interactions between nearest and next‐nearest neighbours are involved, and that the distribution of the cations present in any sublattice is random.Proof is given that such solutions will be regular if they show no substitutional disorder. A comparison is made with some experimental data given in the literature. The available data show that binary systems of halides, silicates, oxides with rock‐salt structure and oxides with spinel structure are indeed regular, if there is no substitutional disorder. The energy of interactions between next‐nearest neighbours could be evaluated and varied from – 3 to +4 kcal/mol. The nature of these interactions is discussed. It is shown that the „interaction”︁ energy originates from Coulomb energy, crystal‐field stabilization and deviations from stoichiometry with respect to the oxygen content and that further the chemical binding between next‐nearest neighbours is negligibly small except in solid solutions of Fe3O4 and inverse ferrites with other spinels.