Theoretical research on structural, electronic, mechanical, lattice dynamical and thermodynamic properties of layered ternary nitrides Ti2AN (A = Si, Ge and Sn)

Abstract

First-principles density functional theory (DFT) calculations within generalized gradient approximation (GGA) are carried out to investigate the structural, electronic, mechanical, lattice dynamical and thermodynamic properties of Ti(2)AN (A = Si, Ge and Sn) MAX phases. The optimized geometrical parameters such as lattice constants (a, c) and the internal coordinates have been calculated. Electronic band structure and corresponding density of states (DOS) have been obtained. The analysis of the band structures and density of states have shown that these compounds are electrical conductors. The elastic constants have been ascertained using the stress-strain method. The isotropic elastic moduli, known as bulk modulus (B), shear modulus (G), young's modulus (E), poisson's ratio (nu), vickers hardness (H-nu) and linear compressibility coefficients (alpha) have been studied within framework of the Voigt-Reuss-Hill approximation for ideal polycrystalline Ti(2)AN (A = Si, Ge and Sn) MAX aggregates. Furthermore, the phonon dispersion curves as well as accompanying phonon density of states have been comprehensively computed. And also raman and infrared modes at the G point have been obtained. Within the thermodynamic properties, specific heat capacity, entropy, helmholtz free energy and internal energy changes were analyzed depending on the temperature of Ti(2)AN (A = Si, Ge and Sn) compounds. The obtained results are presented in comparison with present theoretical data for Ti2SiN. This is the first quantitative theoretical study of the electronic properties and other properties for Ti2GeN and Ti2SnN compounds and therefore theoretical results for these compounds need to be verified experimentally. (C) 2018 Elsevier B.V. All rights reserved.