Mechanical properties of cubic Cu3N and Cu4N: A theoretical investigation

Abstract

We derive the elastic and mechanical characteristics of cubic Pm3‾m Cu3N and Cu4N via the first-principles density functional theory (DFT) calculations and elastic theory. For cubic Cu3N and Cu4N, the relaxed unit-cells match up with available data. The electronic density of states (DOS) confirms that Cu3N is a semiconductor and Cu4N is metallic. From single-crystal elastic constants, Cu3N and Cu4N are both mechanically stable. Polycrystalline properties are systematically predicted, including bulk moduli B, Lame's constants λ, and more. Cu3N and Cu4N are ductile based on Pugh criteria and Poisson's ratio. The elastic anisotropy is derived by analysis of anisotropy factors, directional elastic moduli, and Poisson's ratio σ. These demonstrate that the anisotropic degree of Cu3N is greater than that of Cu4N. We also predicted the velocities of sounds in different propagation directions, as well as the Debye temperature θD. The higher θD of Cu4N manifests that it has larger microhardness than Cu3N.