A first principles investigation of the mechanical properties of g-ZnO: The graphene-like hexagonal zinc oxide monolayer

We investigate the mechanical properties, including high order elastic constants, of the graphene-like hexagonal zinc oxide monolayer (g-ZnO) using first-principles calculations based on density-functional theory. Compared to the graphene-like hexagonal boron nitride monolayer (g-BN), g-ZnO is much softer, with 17% in-plane stiffness and 36%, 33%, and 33% ultimate strengths in armchair, zigzag, and biaxial strains respectively. However, g-ZnO has a larger Poisson’s ratio, 0.667, about three times that of g-BN. It was found that the g-ZnO also sustains much smaller strains before the rupture. We obtained the second, third, fourth, and fifth order elastic constants for a rigorous continuum description of the elastic response of g-ZnO. The second order elastic constants, including in-plane stiffness, are predicted to monotonically increase with pressure while the Poisson’s ratio monotonically decreases with increasing pressure.