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

Highlights: • The superstructure of U₃Si₅ was determined to be a distortion defect β-USi₂. • Theoretical results indicate that the U₃Si₅ is a metallic and brittle material. • The chemical bonds in U₃Si₅ are found similar with those of U₃Si₂. • The silicon defects have lower formation energy and are not prone to cluster. • In addition to the single vacancy, other point defects volumes are expanding. -- 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.