Elastic, phonon and thermodynamic properties of ZnAl2O4 and ZnAl2S4 compounds from first–principles calculations

Abstract

First–principles calculations are performed to investigate the elastic, phonon and thermodynamic properties of ZnAl2O4 and ZnAl2S4 structures. The equations of state are fitted by a four–parameter Birch–Murnaghan equation upon the first–principles energy vs. volume data. Three independent elastic constants c11, c12 and c44 at zero pressure are determined by strain energy vs. strain relationships, and the two structures are both mechanically stable. Elastic properties including bulk moduli, shear moduli, Young's moduli, Poisson's ratios and anisotropy values for both phases are estimated by Voigt–Reuss–Hill averaging scheme. The mechanical properties such as ductility and brittleness are further analyzed. The density functional perturbation theory is utilized to calculate the phonon properties and both phases are found to be dynamically stable. The phonon and Debye models are used to predict the thermodynamic properties such as the Gibbs free energies, entropies and specific heats at constant pressure for ZnAl2O4 and ZnAl2S4 compounds.