Structure and elastic anisotropy of uranium under pressure up to 100 GPa

Abstract

The pressure-induced structural and elastic evolutions of uranium with orthorhombic Cmcm structure up to 100 GPa are investigated by performing ab initio density functional calculations using the projector augmented wave (PAW) method. The calculated lattice parameters a, b, c, and internal coordinate y, as well as the atomic volume V of the orthorhombic uranium at zero pressure and high pressure are in favorable agreement with the available experimental data and other theoretical values. The nine different elastic constants under high pressure, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, the brittle/ductile characteristics, Debye temperature and the integration of elastic wave velocities over different directions dependences on pressure are also successfully obtained. Especially, the anisotropy of the directional linear compressibility and the Young’s modulus under high pressure up to 100 GPa is obtained and analyzed systematically for the first time. It turns out that Cmcm uranium should be stabilized mechanically at least up to 100 GPa, this accords with angle-dispersive X-ray diffraction experimental findings in diamond anvil cells of Le Bihan et al. [Phys. Rev. B 67, 134102 (2003)]. The calculated various elastic anisotropic factors, directional Young’s modulus and linear compressibility demonstrate that Cmcm uranium possesses high elastic anisotropy.