Decentral distribution of helium in β-SiC: Studied by density functional theory

Abstract

β-SiC is an excellent material as a fuel cladding material in next generation fission reactors and structural components in the fusion reaction. The introduction of helium (He) atoms from the deuterium-tritium reaction or (n,α) reaction will inevitably affect the properties of nuclear materials. It is imperative to explore the behavior of He in β-SiC, and thus, the influence on the physical and chemical properties of materials on the atomic scale. In this work, the possible configurations of He interstitials existing in β-SiC were investigated using density functional theory (DFT). It was found that the He atom prefers to occupy Si tetrahedron interstitial (Tsi) site, surrounded by four Si atoms rather than the C tetrahedron interstitial (Tc) site, surrounded by four C atoms. The detailed analysis concerned with chemical bonding of host atoms with He has been carried out using partial density of states (PDOS) and an orbital-based descriptor (projected crystal orbital Hamilton population, pCOHP). In addition, the calculation of binding energy implies that in the absence of vacancies, He atoms tend to decentralize themselves in separated Tsi positions, and are hard to cluster through exothermal processes. This is due to the fact that in β-SiC, tetrahedral interstitials, surrounded by strong SiC bonds, act as firm cages to make helium atoms confined separately. Our results are in agreement with the experimental observation that no He bubbles are generated in a single crystal.