Structural, electronic and mechanical properties of (NbxTi1−x)2SC and (NbxZr1−x)2SC (0 ⩽ x ⩽ 1) from first-principles investigations

Abstract

MAX phase materials are one of the research hotspots for years due to their various potential applications. In this work, the structural, electronic and mechanical properties of the (NbxTi1−x)2SC and (NbxZr1−x)2SC (0⩽x⩽1) solid solutions are investigated by first-principles density functional theory. The analyses of electronic band structures and density of states suggest good electric conductivities of the solid solutions, and the bands near the Fermi level are mainly contributed by Nb 4d and Ti 3d (Zr 4d) orbitals. Strong bonding interactions between M (M=Ti, Zr, Nb) and S or C atoms can be identified by the theoretical predictions, illuminating the phase stabilities of the solid solutions. The calculated mechanical properties including bulk modulus, shear modulus, Young′s modulus, Poisson′s ratio and Debye temperature of the solid solutions lead to the conclusion that Nb atom substitution of Ti2SC or Zr2SC enhances the mechanical strength. The highly correlation between surface energies and substitution contents of the solid solutions provides new insight into the structural stability of MAX phases against fracture and fabrication of substituted MXenes.