Interactions of extrinsic interstitial atoms (H, He, O, C) with vacancies in beryllium from first-principles

We present a first-principles study of the interactions between extrinsic atoms (H, He, O, C) with vacancy defects in hexagonal close packed (HCP) beryllium (Be). Presence of a vacancy reduces solution enthalpies of O and C by about 0.60 eV and 0.80 eV, respectively, but does not change their preferential sites. In perfect Be, both OO and CC pairs are attractive, while HH and HeHe pairs exhibit weak repulsion. Out-of-plane configurations for the OO and CC pairs are always more stable than the other configurations in Be HCP lattices. Moreover, we found strong attraction between the O/C atoms and the H/He atoms, weak attraction of HHe pairs, and strong repulsion of OC pairs. Thus, we suggest that the interstitial O and C impurities provide trapping sites for H and He impurities and hinder their diffusion inside Be metal.