Elasticity and Raman and infrared spectra of MgAl2O4 spinel from density functional perturbation theory

We determine the elastic constants and the Raman spectra of spinel under pressure using density functional perturbation theory. Like other spinels, MgAl2O4shows an increasing bulk modulus and a weakly varying shear modulus under pressure. The Raman spectrum is dominated by two mains peaks whose intensities decrease under pressure. The theoretical Raman spectra of disordered spinel shows a better agreement with measurements on natural samples than the ordered one. We also investigate the high-pressure stability of different structures and find the calcium titanate type to be the stable phase beyond 45 GPa.