Electronic properties and pressure effect on the structural behaviour of M2AC (M = V, Nb and A = P, As)

Using first principles calculations, we have investigated the pressure effect on the structural properties of unexplored M2AC compounds, relevant to the so called MAX phases, with M = V or Nb and A = P or As. Band structure and bonding properties of these compounds were studied at 0 GPa. Our results for the lattice parameters a, c and the equilibrium volume v are in good agreement with the available experimental data. Relative change of the volumes, lattice parameters, M–C and M–A bonds length are studied up to 40 GPa. The bulk modulus was deduced from the Birch–Murnaghan equation of state. A systematic study on the effect of both M and A elements on the bulk modulus B, shows that the bulk modulus is more affected by the substitution of A atoms (P → As) than by the substitution of M atoms (V → Nb). We have also found that the band structure shows a metallic character of the investigated compounds. From the total and partial density of states, we could notice that the conductivity is mostly assured by the d electrons of the transition metal (M = V, Nb). The charge densities are presented and the chemical bonding are discussed and compared to the available data in the literature.