Ab initio calculations based on density functional theory were performed to determine the relative stabilities and migration of H and He atoms in hexagonal close-packed Sc. The results showed that the formation energy of an interstitial H or He atom was smaller than that of a corresponding substitutional atom. The tetrahedral interstitial position was more stable than an octahedral position for both He and H interstitials. The nudged elastic band method was used to study the migration of interstitial H and He atoms in hexagonal close-packed Sc. It was found that the migration energy barriers for H interstitials in hexagonal close-packed Sc were significantly different from those for He interstitials, but their migration mechanisms were similar. In addition, the formation energies of five different configurations of a H–H pair were determined, revealing that the most stable configuration consists of two H atoms located at the second-neighbor tetrahedral interstitial sites along the hexagonal direction. The formation and relative stabilities of some small He clusters have also been investigated.

Ab initio Study of Stability and Migration of H and He in HCP-Sc. L.Yang, S.M.Peng, X.G.Long, F.Gao, H.L.Heinisch, R.J.Kurtz, X.T.Zu: Journal of Physics - Condensed Matter, 2011, 23[3], 035701