The effects of vacancies and fission products on the structures and properties of β-SiC: a first-principles study

Understanding the interaction between fission products (FPs) from nuclear fuel nuclear and SiC is important for SiCf/SiC composites as an accident tolerance fuel cladding (ATFC). Thus, the effects of vacancies and FPs (I/Pd/Xe) on the structure, mechanical and thermal properties of β-SiC were investigated by DFT calculations in this work. The formation of defects (vacancies, FPs) could result in the distortion of SiC lattice and the loss of symmetry. The calculated binding energies indicated that most vacancies and FPs atoms could attract each other to form complex defects (vacancies clusters or FPs on vacancy sites). Mechanical calculations indicated that the formation of defects inside SiC led to the degradation of its mechanical properties. The more vacancies, the lower elastic moduli and tensile strength. While the effects of FPs on the elastic moduli were complex. Further tensile calculations indicated that Xe led to tensile strength degrade most significantly because of its weak interaction with surrounding atoms. For thermal properties, considering the vacancies only, isobaric heat capacity and thermal conductivity of SiC reduced while thermal expansion increased. In addition, the I/Pd/Xe could lead to an increase in thermal expansion and heat capacity but a decrease in thermal conductivity. In most case, Xe had the greatest effect on thermal properties.