The effect of irradiation-induced point defects on energetics and kinetics of hydrogen in 3C-SiC in a fusion environment

Abstract

3C-SiC is a promising candidate for structural material of nuclear fusion reactors, and H, T, and D irradiation often causes undesired volume swelling, bubble formation, and degradation of the mechanical properties of the material. However, the underlying mechanisms of these processes are still not well understood. We thereby carried out systematical first-principles calculations to investigate the interaction of H with irradiation-induced point defects in 3C-SiC. Our results show that both self-interstitial atoms and vacancies can act as trap sites for H, which can effectively influence the retention of H and its isotopes in 3C-SiC. Self-interstitial C and Si atoms can trap up to six and five H atoms, respectively. A C vacancy can trap up to eight H atoms with two H2 molecules formed, while a Si vacancy can trap only four H atoms with no H2 molecule formation. The accumulation of H atoms in vacancy forming vacancy-hydrogen clusters may act as the nucleation site for bubbles or blisters in 3C-SiC. The accumulation of H in a vacancy can result in the instability of atoms around the vacancy, which may result in the growth of vacancy-hydrogen clusters to blisters or bubbles. Both Si and C vacancies can significantly slow down the diffusion of H, and energy barriers of H diffusion from the Si and C vacancies reach respectively up to 3.40 and 2.13 eV, which are much higher than that in bulk. These results explain why the calculated diffusion activation energy of H in perfect 3C-SiC is much smaller than experimental values. Our results are helpful for understanding the micro-mechanism of H retention and bubble formation experimentally observed in 3C-SiC.