A survey investigation on the stability, electronic and elastic properties of hexagonal ternary transition-metal borides by first-principles calculations

Abstract

The crystal structure, stability, elastic constants and electronic structures of a class of ternary transition-metal borides with the general formula of h-M2AB2 (where M is a 3d, 4d and 5d transition metal; A is Al, Ga, In; and h represents a hexagonal structure) were investigated using the first-principles calculations within the framework of density functional theory (DFT). The stability of the h-M2AB2 was assessed with the cohesive energy, formation energy and phonon dispersion curves. In general, h-M2AB2 crystallizes in a hexagonal structure, and consists of six-member boron rings (B6) and interleaved M and A layers. The h-M2AB2 containing an IVB-M and VB-M is more energetically favorable with respect to the orthorhombic MAB phase. The lattice constants and bond lengths of the ternary borides are highly dependent on their chemical composition. All the stable borides exhibit metallic transport behaviors. The solid B-B bonding is responsible to the good stability and high bulk modulus of h-M2AB2. The high ductility of late-transition-metal borides is attributed to the delocalized M d and A p electrons. The correlations between the elastic property and the electronic structure of h-M2AB2 were also discussed.