Elastic anisotropies, thermal conductivities and tensile properties of MAX phases Zr2AlC and Zr2AlN: A first-principles calculation

In this study, the mechanical stability, elastic properties, including single-crystal elastic constants, polycrystalline elastic modulus and elastic anisotropy, Debye temperatures, electronic properties, minimum thermal conductivities and tensile character of Zr2AlC and Zr2AlN were calculated by first-principles calculations based on density functional theory. The results showed that Zr2AlX (X = C, N) are mechanically stable and anisotropic in elastic properties, and the degree of elastic anisotropy of Zr2AlN is slightly greater than Zr2AlC, and the sound velocities and minimum thermal conductivities of Zr2AlC and Zr2AlN along the [001] and [100] directions are also anisotropic. Moreover, the density of states (DOS) and charge density difference distributions showed that these Zr2AlX have metallic-covalent-ionic mixed bonds. Finally, the calculated tensile properties along the [001] and [110] directions of these MAX phases showed that the tensile strength along the [110] direction is greater than that along the [001] direction.