Elastic properties and electronic structure of the lanthanum sulfides MLa ₂ S ₄ (M = Ca, Sr, Ba)

Abstract CaLa 2 S 4 sulfides are promising transparent ceramics for infrared windows application in harsh environment conditions, but the theoretical studies on the mechanical properties of this material are limited. Using density functional theory calculations, we performed a systematic theoretical study on the structural, electronic, bonding, and elastic properties of cubic CaLa 2 S 4 . A comparison was made with the cubic SrLa 2 S 4 and BaLa 2 S 4 compounds. The investigations were accomplished by employing the full potential augmented plane wave and the projector augmented wave methods as, respectively, implemented in the WIEN2k and VASP packages. The independent elastic constants and the most important elastic properties (including the bulk modulus B , shear modulus G, Young's modulus E , and Poisson's ratio ν ) were determined by precise calculations under normal and different pressures. The degree of elastic anisotropy has been evaluated from 3D curved surface representations of several elastic constants. Experimental values were also performed through ultrasonic velocity and a normal compression testing for CaLa 2 S 4 . A comparison with experimental studies was done.