Phase stability, ductility, electronic, elastic and thermo-physical properties of TMNs (TM = V, Nb and Ta): An ab initio high pressure study

The structural, electronic, mechanical and thermo-physical properties of transition-metal ceramics VN, NbN and TaN have been analyzed in the B1 and high pressure B2 phases by first-principles approach. Two different pseudo-and full-potential based formalisms have been used for present calculations. In both the approaches, generalized gradient approximation is chosen as exchange-correlation function. The electronic structure and DOS show mixed covalent and metallic bonding in both the phases while charge density plots show some ionic contribution too. Under very high pressures, these materials undergo first-order phase transition from B1 to B2 phase and show small volume collapse of about 3%-5% at transition pressure. The calculated second-order elastic constants illustrate the mechanical stability of these nitrides in B1 and B2 phases. These nitrides show ductile nature in B1 phase while brittle in B2 phase. The anisotropy is observed in both B1 and B2 phases with increased anisotropy in B2 phase. The calculated longitudinal and shear wave velocities are used to determine the Debye temperature in two structures. The structural properties, elastic moduli and other related properties show a reasonable agreement with experimental data in rock-salt structure. The study in high pressure B2 phase needs experimental validation. (C) 2014 Elsevier B. V. All rights reserved.