Electronic structures, mechanical properties and defect formation energies of U3Si5 from density functional theory calculations

Abstract

The uranium silicide U3Si5 has been utilized as the second phase in the UN-U3Si5 composite fuel. However, there have thus far been few theoretical investigations on its microscopic structure and mechanical behaviors. In this work, the electronic structures, elastic mechanical properties, Debye temperature and defect formation energies of U3Si5 are systematically studied by density functional theory. The crystalline structure of U3Si5 is determined to be a defective β-USi2 with a distorted lattice, in good agreement with the experimental observations. The theoretical results indicate that the U3Si5 is a metallic and brittle material and the chemical bonds in U3Si5 are found similar with those of U3Si2. We have also calculated formation energies of different types of point defects: vacancies, interstitials, and Frenkel pairs in U3Si5. The smaller Si atoms exhibit lower defect formation energies than U atoms with an isolated Si or U atom as the reference. Besides, the silicon vacancies are not prone to cluster. The volumes of supercells with interstitial and Frenkel pair defects are found to increase but single vacancies cause an opposite trend. This work may provide theoretical insights into the behavior of uranium silicide materials under irradiation.