Eur. Phys. J. B (2013) 86: 9
https://doi.org/10.1140/epjb/e2012-30584-1

Regular Article

Structural, elastic, electronic and dynamical properties of Ba₂MgWO₆ double perovskite under pressure from first principles

¹ Department of Physics, School of Sciences, China University of Mining and Technology, Xuzhou 221116, P.R. China
² Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Science, P.O. Box 912, Beijing 100083, P.R. China
³ Faculty of Science, China University of Petroleum, Qingdao 266555, P.R. China

^a e-mail: liweishi@semi.ac.cn

Received: 12 July 2012
Received in final form: 6 September 2012
Published online: 9 January 2013

Abstract

Ab initio calculations within the framework of density-functional theory employing the local density approximation have been performed to study the structural, elastic, electronic and dynamical properties for cubic double perovskite Ba₂MgWO₆ under hydrostatic pressure. The calculated ground-state properties and compression curve are in good agreement with the available experimental results. Pressure-induced enhancements of elastic constants, aggregate elastic moduli, elastic wave velocities and Debye temperature are observed, without any softening behaviors. Upon compression, the fundamental indirect energy gap E_g^Γ−X first increases slightly and then monotonically decreases. A linear-response approach is adopted to derive the full phonon-dispersion curves and phonon density of states. Evolution with pressure of the zone-center phonon frequencies for Raman- and infrared-active modes is analyzed. A pressure-induced soft optically silent T_1g phonon mode is identified near the Γ point, signifying a structural dynamical instability. Our calculated results reveal that, when the pressure is high enough, besides bond shortening, the W-O-Mg bond becomes nonlinear, resulting in octahedral tilting distortion and thus a slight departure from the ideal cubic symmetry.