Stability of MgAl2O4 under high-pressure conditions

A theoretical investigation of the MgAl2O4 crystal response to high-pressure conditions has been carried out to determine its stability against decomposition towards MgO and alpha-Al2O3, and towards recently observed orthorhombic phases. We have evaluated total energy versus volume curves using the density functional formalism under the non-local B3LYP approximation, as implemented in the CRYSTAL package. Numerical and analytical fittings have been carried out to determine the equilibrium unit cell geometry and equation of state parameters for all the structures and compounds involved in the phase diagram. The macroscopic compressibility of the spinel phase is interpreted considering the compressibility of its elementary MgO4 and AlO6 coordination polyhedra, and implications to understand the phase stability are suggested.