Computational investigations of XMgGa (X = Li, Na) half Heusler compounds for thermo-elastic and vibrational properties

Abstract

In present study, thermo-elastic and vibrational properties of XMgGa (X = Li, Na) half Heusler compounds are investigated using density functional theory implemented in WIEN2k and Quantum ESPRESSO codes. Generalized gradient approximation as an exchange correlation functional is used in Kohn-Sham equations to find three elastic constants C11, C12 and C44 for C1b type structures. First, we optimized the structures of these Heusler compounds. These three elastic constants are then used to determine different elastic modulii like bulk modulus, shear modulus, Young modulus and other mechanical parameters like Pugh's ratio, Poisson's ratio, anisotropic ratio, sound velocities, Debye temperature and melting temperature. On behalf of these mechanical parameters, the brittle/ductile nature and isotropic/anisotropic behavior of the materials are investigated. Different regions of vibrational modes in the materials are also discussed on behalf of Debye temperature calculations. The vibrational properties of the half Heusler compounds are computed using Martins-Troullier pseudo potentials implemented in Quantum ESPRESSO. The phonon dispersion curves and phonon density of states in first Brillion zone are obtained and discussed. Reststrahlen band of LiMgGa is found greater than NaMgGa.