Lattice dynamics of ZnAl2O4 and ZnGa2O4 under high pressure

Abstract

In this work we present a first-principles density functional study of the vibrational properties of ZnAl2O4 and ZnGa2O4 as function of hydrostatic pressure. Based on our previous structural characterization of these two compounds under pressure, herewith, we report the pressure dependence on both systems of the vibrational modes for the cubic spinel structure, for the CaFe2O4-type structure (Pnma) in ZnAl2O4 and for marokite (Pbcm) ZnGa2O4. Additionally we report a second order phase transition in ZnGa2O4 from the marokite towards the CaTi2O4-type structure (Cmcm), for which we also calculate the pressure dependence of the vibrational modes at the Γ point. Our calculations are complemented with Raman scattering measurements up to 12 GPa that show a good overall agreement between our calculated and measured mode frequencies.