Elasticity, lattice dynamics and ideal strengths of USi3 and U3Si via first principles calculations

Abstract

We have investigated the structure, elastic anisotropy, lattice dynamics, ideal tensile and shear strengths of USi3 and U3Si using first-principles method of density functional theory (DFT). The present fully relaxed structural parameters, equilibrium volumes as well as the single crystal elastic constants agree well with the available experimental data and other theoretical results. Also, the polycrystalline properties such as bulk modulus, Young's modulus, and shear modulus, Poisson's ratio and brittle/ductile properties have been evaluated using Voigt-Reuss-Hill model. The elastic anisotropy of Fmmm U3Si has been characterized by different anisotropic factors. It is concluded that Pm-3m USi3, Pm-3m U3Si, and Fmmm U3Si should be stabilized mechanically, and Pm-3m USi3 should be stabilized mechanically up to 80 GPa. The dynamical properties of U3Si and USi3 have been investigated using density functional perturbation theory (DFPT) method. The present calculations mean that both Pm-3m USi3 and Fmmm U3Si are dynamically stable, and Pm-3m USi3 should be stabilized dynamically up to 80 GPa. However, Pm-3m U3Si is not dynamically stable. Additionally, the ideal tensile strengths along typical crystallographic directions, and the ideal shear strengths in the (010)[101] slip system of Pm-3m USi3 and Fmmm U3Si have been explored using first principles total energy method. These calculated results provide useful information for the applications of uranium silicides as potential nuclear fuels.