Pressure induced bandgap variation for the optical and photo-catalytic properties of MgA2X4 (A = Sc, Y; X = S, Se) spinel compounds

Abstract

Spinels possess excellent properties for use in advanced applications. Here in this study, using density functional theory (DFT) calculations, we have studied the structural, electronic and optical properties (dielectric function, electron energy loss, extinction coefficient, reflectivity and refractive index, absorption coefficient, optical conductivity) of spinel compounds of the form MgA₂X₄ (A = Sc/Y; X = S, Se) under the effect of applied pressure. Interesting physical variations were observed in these materials under the application of pressure. The generalised gradient approximation (GGA) method was performed to figure out structure optimisation. By adopting the modified Becke–Johnson (mBJ) exact exchange technique, electronic and optical properties were computed. The energy band gap is shrunken from 2.9 to 1.6 eV and 0.736 to 0.084 eV for MgA₂X₄ (A = Sc/Y; X = S, Se) compounds under the effect of pressure. A noticeable variation was seen in the lattice parameters, band gap, electronic and optical properties via exceeding the pressure from 0 to 20 GPa, featuring a prominent absorption coefficient and higher optical conductivity in the visible and UV region, showing greater potential for their use in high-frequency devices. The compounds have the appropriate band gaps for water splitting through redox reactions.