Abstract
In this paper we calculated the phase stability, electronic structure and mechanical properties of Nb 4AlC 3 by means of a first-principles pseudopotential total energy method. Based on thermodynamical calculations of the two possible crystal structures of Nb 4AlC 3, α-type Nb 4AlC 3 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 α-Nb 4AlC 3 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 Nb 2AlC. Since the salt-rock-type Nb–C slab is thicker in Nb 4AlC 3 than that in Nb 2AlC, the former material shows higher elastic stiffness than the latter one; at the same time, Nb 4AlC 3 may display quasi-ductility, which has been well documented for MAX ceramics.
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