The structure, elastic, electronic properties and Debye temperature of M2AlC (M=V, Nb and Ta) under pressure from first-principles

With the help of first-principles generalized gradient approximation (GGA) calculation, the dependences of structure, elastic, electronic properties and Debye temperature of M2AlC (M=V, Nb and Ta) ternary compounds on pressure were investigated based on density functional theory. Our calculated structural data are in good agreement with previous experiment and other theoretical results. It is shown that all the three compounds are mechanically stable. C-M bonds are more resistant to deformation than the other bonds and the Nb2AlC is less resistant to deformation than V2AlC and Ta2AlC. The elastic properties including the isotropic bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio v of the hexagonal M2AlC ternary compounds were determined using the Voigt-Reuss-Hill (VRH) averaging scheme. The results show that the shear modulus is the principal restraining factor for the stability of hexagonal M2AlC. The B/G and Poisson's ratio under various pressures were also calculated. The band structure and density of states have been discussed, and the results indicate that with atomic number increasing, less valence electrons present in the unit cell, which leads to smaller values of Fermi level. The Debye temperatures Theta(D) of the M2AlC compounds were calculated from the elastic constants and sound velocities. It is indicated that pressure has little influence on the Theta(D) values. (C) 2011 Elsevier B.V. All rights reserved.