title: Vacancy trapping mechanism for multiple hydrogen and helium in beryllium: a first-principles study.
abstract: The microscopic mechanism for H and He trapping by vacancy defects and bubble formation in a Be host lattice is investigated using first-principles calculations. A single He atom prefers to occupy a vacancy centre while H does not. He can segregate towards the vacancy from the interstitial site much more easily than H. Both H and He exhibit lower diffusion barriers from a remote interstitial to a vacancy with regard to their diffusion barriers inside a perfect Be solid. Up to five H or 12 He atoms can be accommodated into the monovacancy space, and the Be-He interaction is much weaker than Be-H. The physical origin for aggregation of multiple H or He atoms in a vacancy is further discussed. The strong tendency of H and He trapping at vacancies provides an explanation for why H and He bubbles were experimentally observed at vacancy defects in materials. We therefore argue that vacancies provide a primary nucleation site for bubbles of H and He gases inside Be materials.
authors.affiliation: Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Dalian University of Technology), Ministry of Education, Dalian 116024, People's Republic of China.
authors.forename: Pengbo
authors.initials: P
authors.lastname: Zhang
authors.forename: Jijun
authors.initials: J
authors.lastname: Zhao
authors.forename: Bin
authors.initials: B
authors.lastname: Wen
mesh_terms: D001608:Beryllium / Q000737:chemistry*; D004058:Diffusion; D006371:Helium / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D008956:Models, Chemical
chemical_list: D006371:Helium; D006859:Hydrogen; D001608:Beryllium