Structural, electronic, elastic and thermal properties of Cr-doped U3Si2: A DFT study

Abstract

Alloying has been considered as an effective strategy to make up for the poor oxidation corrosion resistance of U3Si2. However, the theoretical studies on alloyed U3Si2 are rarely reported. In this study, the structural, electronic, elastic and thermal properties of 10at% Cr-doped U3Si2 were studied using first principles calculations and semiclassical Boltzmann transport theory. Our results show that the U3Si1.5Cr0.5 phase is determined to be thermodynamically, dynamically and elastically stable, and U2.5Si2Cr0.5 phase is dynamically and elastically stable. U3Si1.5Cr0.5 is more stable than U2.5Si2Cr0.5 from the thermodynamic calculation results. From the calculated electronic structure results, a mixture of ionic and metallic bonds dominates the bonding of Cr-doped U3Si2. They are ductile materials compared to the brittleness of U3Si2 according to the results of B/G ratio, Cauchy pressure and Poisson's ratio. Moreover, U3Si1.5Cr0.5 is a nearly elastic isotropic material, while U2.5Si2Cr0.5 exhibits strong anisotropy. The thermal conductivity of Cr-alloyed U3Si2 is dominated by the electronic contribution at high temperature, which is lower than U3Si2 but higher than UO2 at service temperature and increases with temperature. Therefore, in addition to significantly improving the resistance to oxidation and corrosion of U3Si2, Cr doping can also convert the brittleness of U3Si2 into toughness and improve its machinability, albeit at the reasonable expense of some mechanical properties and thermal conductivities, while maintaining the high uranium density of U3Si2 fuel form. The results of this work may provide useful clues for the application and improvement of uranium silicide fuels.