First-principles calculations on phase transformation and elastic properties of CuO under pressure

The crystal structure, phase transformation, and elastic properties of copper oxide (CuO) are determined using first-principles calculations. The calculated results first predict the phase transformation from monoclinic to cubic structure, which occurs at 29.32 GPa, and the high-pressure phase is identified as cubic CuO. With increasing pressure, the variations of the elastic constant C-ij, bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio upsilon, the ratio of the bulk to shear modulus B/G, and normalized primitive cell volume V/V-0 are investigated. Our results show that the pressure has a positive effect firstly and then negative effect on the ductility of monoclinic CuO, but results in the opposite of hardness. Moreover, we find that the structural abnormality of monoclinic CuO may be existing at pressures of 15 GPa.