Energy and long-range disorder in simple spinels

Interionic potential calculations conducted on simple spinels in the framework of the Born model indicate that, within experimental uncertainties, observed control of P, T intensive variables on long-range disorder may be completely due to static effects. Parameterization of repulsive potentials allows us to rationalize the existing experimental data and quantify the variation of static energy, configuration entropy and static Gibbs free energy with temperature. The static energy of the investigated phases cannot be expressed in simple quadratic terms of the inversion parameter, as commonly assumed, but requires higher order terms. Knowledge of the longrange disorder at various temperatures allows us to express configurational entropy as a Maier-Kelley type polynomial expansion on temperature. As configurational entropy simply depends on the static part of the internal energy, the integration of the obtained functions in d T allows rapid evaluation of the effect of long-range disorder on the static part of energy.