DFT prediction of the stability and physical properties of M2GaB (M = Sc, V, Nb, Ta)

Abstract

This study explored the physical properties of MAX phase borides, M2GaB (M = Sc, V, Nb, Ta), aided by the density functional theory (DFT) for the first time. The optimized lattice constants were obtained by minimizing the total energy. We checked the thermodynamic stability by computing the formation energies. We calculated the electronic band structure, density of states (DOS), and charge density mapping to reveal the electronic ground state and bonding nature. The computed stiffness constants (Cij) confirmed the mechanical stability of the investigated compounds. Young's modulus, shear modulus, bulk modulus, and Poison's ratio have been computed using Cij. We calculated the Pugh's ratio, Poisson's ratio, and Cauchy pressure to judge the ductility/brittleness. The Vickers hardness values were calculated. The anisotropic properties of M2GaB compounds were studied by the elastic moduli's directional projections and the anisotropy indices' calculations. We have discussed the acoustic behavior of the M2GaB phases. We have also investigated the Grüneisen parameter, the Debye temperature ϴD, the thermal expansion coefficient, the specific heat, the Helmholtz free energy, the entropy, the internal energy, and the lattice thermal conductivity (Kph) of these borides. To determine the suitability as thermal barrier coating (TBC) materials or whether the compounds are appropriate for high-temperature applications, the minimum thermal conductivity (Kmin) and melting temperature (Tm) have also been calculated. The compounds' dynamical stability was examined using the phonon dispersion curves. The optical parameters have been studied, and it has been found that these compounds are compatible as coating materials to reduce solar heating.