Ab initio high-pressure thermodynamics of cationic disordered MgAl2O4 spinel

Ab initio calculations are per-formed in the framework of density functional theory and the local density approximation, to evaluate structural, thermodynamic and vibrational behaviour of MgAl2O4 spinel with cationic disorder under pressure. An effective thermodynamic model using both a regular solution and a quadratic form for the internal energy is parametrized to describe the non-convergent cationic disordering. The evolution of cationic disorder rate with temperature and isostatic pressure is deduced from this model. Relative density and heat capacity excess evolution are simulated as a function of cationic disorder. Infrared modes are calculated in the Brillouin zone centre for several disordered spinels. Good agreement is found with available experimental data.