The thermodynamics of cation distributions in simple spinels

The cation distribution in binary spinels has been treated as a simple chemical equilibrium. If the entropy change associated with the disordering of an initially normal spinel is equated to the configurational entropy alone, the molar enthalpy of interchange of ions on tetrahedral sites with ions on octahedral sites may be calculated from cation distribution data known at a single temperature for each spinel. These interchange enthalpies have been calculated for a series of 2–3 spinels, and have been used to obtain empirical site preference energies for a series of divalent and trivalent ions in the spinel structure. Results are presented of a calorimetric study of the disordering enthalpy in a sample of natural spinel (MgAl2O4).