Lattice dynamical and thermo-elastic properties of M₂AlB (M = V, Nb, Ta) MAX phase borides

Abstract

The structural, electronic, dynamic, and thermo-elastic properties of M2AlB (X = V, Nb, Ta) MAX phase borides were investigated using first principle calculations as implemented in the Vienna Ab-initio Simulation Package (VASP) with the generalized gradient approximation (GGA). The obtained structural properties and formation energies showed the thermodynamic stability and synthesizability of M2AlB. The electronic band structures were determined and they revealed that these compounds had a metallic character. The dynamic stability of M2AlB compounds were investigated with phonon dispersion curves and these compounds were found to be dynamically stable. The elastic constants were also calculated to determine the mechanical stability and to obtain the polycrystalline properties such as bulk modulus, shear modulus, etc. The thermo-elastic properties (thermal expansion coefficient, heat capacity, entropy, and free energy) were studied in a temperature range in between 0 and 1000 K and a pressure range in between 0 and 30 GPa. In addition, the direction dependent sound wave velocities were studied in three dimensions. Moreover, the minimum thermal conductivities and the diffusion thermal conductivities of these compounds were determined. This work is the processor study for the investigation of the main physical properties of M2AlB (M = V, Nb, Ta) ceramic compounds to date. (C) 2019 Elsevier B.V. All rights reserved.