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

Abstract

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 θ_D, 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 C_v 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.