First-principles study of hydrogen-vacancy complexes in Be12Ti

Abstract

First-principles calculations have been conducted to gain insight into the vacancy trapping mechanism of H atoms produced by neutron induced transmutation in Be12Ti, which is a promising candidate for the plasma facing materials in fusion reactors. The microscopic mechanisms for H trapping by four kinds of vacancies, namely, Be1, Be2, Be3, and Ti vacancy have been studied by calculating the solution energies and the trapping energies of hydrogen-vacancy complexes. We have included a zero-point energy correction that generally leads to a higher trapping energy, but the energy tendency remains unchanged. Vacancies serve as trapping centers to induce H atoms to segregate on their internal surface by providing an optimal H-embedding isosurface of charge density. The Ti vacancies exhibit a stronger H trapping ability than the Be vacancies. A Ti vacancy can capture up to ten H atoms, while the maximal number of H atoms that a Be vacancy can accommodate is four. But a Be1 vacancy can only capture two H atoms if the zero-point energy correction is included in the simulation. Among all HnVBe1 (n = 1–5) complexes, the configuration of H2 VBe1 has the lowest H solution energy. The H2 molecules are not formed in the most stable hydrogen-vacancy complexes explored. The present results provide a fundamental image of vacancy trapping mechanism for H atoms as well as H bubble formation in solid Be12Ti, which is extremely important for the reduction of radioactive tritium inventory within fusion reactor and appropriate handling of radioactive nuclear wastes during the decommissioning of the fusion blanket.