Phase stability, electronic structure and mechanical properties of ternary-layered carbide Nb4AlC3:: An ab initio study

In this paper we calculated the phase stability, electronic structure and mechanical properties of Nb4AlC3 by means of a first-principles pseudopotential total energy method. Based on thermodynamical calculations of the two possible crystal structures of Nb4AlC3, alpha-type Nb4AlC3 is confirmed to be the preferred equilibrium phase at ambient conditions. The chemical bonding displays layered characteristics that have commonly been reported for MAX ceramics. The equation of state and compressibility of alpha-Nb4AlC3 were investigated. The material exhibits anisotropic elasticity under hydrostatic pressure: it is more compressible along the c direction than along the a and b directions. The second-order elastic coefficients, bulk modulus, shear modulus and Young's moduli were reported and compared with those of Nb2AlC. Since the salt-rock-type Nb-C slab is thicker in Nb4AlC3 than that in Nb2AlC, the former material shows higher elastic stiffness than the latter one; at the same time, Nb4AlC3 may display quasi-ductility, which has been well documented for MAX ceramics. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.