First-principles investigations on the anisotropic elasticity and thermodynamic properties of U₃Si₂-Al

U₃Si₂ has been tested as a new type of nuclear fuel, and Al has been proven to improve its oxidation resistance. However, there is no research on its anisotropic mechanical and thermal properties. The mechanical and thermal properties of Al-alloyed U₃Si₂ nuclear fuel are calculated on the basis of first principles. Through the phonon dispersion curves, two kinetic stable structures sub-U₃Si_1.5Al_0.5 and sub-U_2.5Si₂Al_0.5(I) are screened out. It is found that the toughness of these two compounds after alloying are significantly improved compared to U₃Si₂. The three-dimensional Young's modulus shows that, the sub-U₃Si_1.5Al_0.5 formed by Al alloying in U₃Si₂ maintains a higher mechanical isotropy, while sub-U_2.5Si₂Al_0.5(I) shows higher mechanical anisotropy, which is consistent with the value of A ^u. The calculation result shows that the lattice thermal conductivity of sub-U₃Si_1.5Al_0.5 and sub-U_2.5Si₂Al_0.5(I) after alloying exhibits high isotropy as the temperature increases.