Phase Transitions and Structural Stability of Binary Uranium Intermetallics Under High Pressure: A Review

Structure, elastic characteristic, ideal strengths, and phonon stability of binary uranium intermetallic UGe3 of AuCu3-type

Crystallographic characterization, energy band structure, densities of states and charge density, elastic properties, ideal tensile and shear strengths, lattice dynamics and thermophysical characteristics of UGe3 of AuCu3-type have been studied by employing the first principles method based on Density Functional Theory (DFT). The optimized lattice parameters, such as lattice constant a, equilibrium cell volume V0, U-Ge distance and U-U distance of UGe3, are in favorable agreement with the available experimental results. Three single-crystalline elastic constants of C11, C12, and C44 have been obtained using the "energy-strain" technique by increasingly varying small strains. The polycrystalline elastic moduli including volume modulus B, Young's modulus E, and shear modulus G, Poisson's ratio v, brittle/ductile nature, Debye temperature θD, and the integration of elastic wave velocities over different crystallographic directions have also been successfully calculated. The anisotropy of the three-directional bulk modulus and Young's modulus is systematically explored and analyzed. The calculations indicate that UGe3 of AuCu3-type should be stabilized mechanically, and the system possesses insignificant elastic anisotropy. In particular, the vibrational spectrum, phonon densities of states and the infrared-active and inactive vibration modes at the center of the Brillouin zone are determined using Density Functional Perturbation Theory (DFPT) and group theory for the first time. This study reveals that UGe3 of AuCu3-type is also stable dynamically. Finally, within the calculated phonon densities of states and the quasi-harmonic Debye model, the constant volume heat capacity Cv and the vibration entropy S in the temperature range of 0-1000 K are predicted and analyzed comprehensively. The present investigations are expected to provide some valuable references for further exploring the properties of uranium compounds.