The thermal and elastic properties of U₃Si₅ and their variations induced by incorporated aluminum

Uranium silicide compounds have attracted intensive attention as candidate alternative fuels in commercial light water reactors (LWRs). In this work, the electronic, thermal, mechanical and elastic properties of U₃Si₅ are comprehensively investigated based on first-principles density functional calculations and semi-classical Boltzmann transport theory. U₃Si₅ is determined to be a brittle and magnetic metal, and thermal conductivity is dominated by its electronic contribution at high temperature. The ratio between the bulk and shear moduli is 1.205. In addition, the elastic ideal strength is strongly anisotropic, with the minimum value only 6.831 GPa at a uniaxial tensile strain of 0.07. This low strength is mainly caused by an emerged structural transition forming silicon-silicon bonds to absorb strain energy. Moreover, the influences of aluminum incorporation on the structural and elastic properties, and thermal conductivities of U₃Si₅ are further studied. The aluminum atom prefers to replace the silicon atom at the vertex shared by the silicon triangles and pentagons. The incorporated atom impedes the structural transition, and enhances the toughness of U₃Si₅. The results from this work may provide useful clue for the improvement in the application of U₃Si₅.