He-vacancy interaction and multiple He trapping in small void of silicon carbide

In fusion environment, large amounts of helium (He) atoms are produced by transmutation along with structural damage in the structural materials, causing material swelling and degrading of physical properties. To understand the microscopic mechanism of He trapping in vacancies and voids, we explored He-vacancy interactions in He(n)Va(m) (Va for vacancy) clusters (n, m = 1-4) and multiple He trapping in a 7atom void of silicon carbide (SiC) by first-principles calculations. The binding energy between He and the HenVam clusters increases with the number of vacancies, while the vacancy binding energy gradually increases with the number of He atoms. Furthermore, a small cavity of about 0.55 nm in diameter can accommodate up to 14 He atoms energetically and the corresponding internal pressure is estimated to be 2.5 GPa. The tendency of He trapping in small voids provides an explanation for the experimentally observed He bubble formation at vacancy defects in SiC materials. (C) 2014 Elsevier B. V. All rights reserved.