Ab initio study of the pressure dependence of mechanical and thermodynamic properties of GeB2O4 (B = Mg, Zn and Cd) spinel crystals

Abstract

Ab initio full-potential (linearized) augmented plane-wave plus local orbitals (FP-(L)APW + lo) calculations are performed to study the hydrostatic pressure dependence of the mechanical and thermodynamics properties of GeMg2O4, GeZn2O4, and GeCd2O4 cubic spinels. The calculated equilibrium structural parameters using both the local density approximation and the generalized gradient approximation are well consistent with the available theoretical and experimental data in the literature. The monocrystalline elastic constants are predictet using the energy-strain scheme. The polycrystalline elastic moduli are determined from the monocrystalline elastic constants through the Voigt-Reuss-Hill approximations. To understand the mechanical behavior of the investigated compounds, assessments of their mechanical stability, ductility/brittleness, sound velocities, elastic anisotropy, pressure-dependent elastic constants, and Debye temperature are made. Regarding thermodynamic properties, temperature dependence of the lattice parameter, bulk modulus, isochoric and isobaric heat capacities, volume thermal expansion coefficient, and Debye temperature at different fixed pressures are explored through the quasi-harmonic Debye model coupled with the FP-(L)APW + lo approach.