DFT study of hydrogen and helium defects at the (112̄1) twin boundary in hcp scandium

Abstract

We have investigated the grain boundary energy of ([Formula: see text]) twin boundaries, the formation energies of hydrogen (H) and helium (He) defects in tetrahedral (T) and octahedral (O) interstitial sites at the ([Formula: see text]) twin boundary in hcp scandium (Sc) by first-principles calculations based on density functional theory. It is found that the formation energies of the tetrahedral and octahedral interstices H, and tetrahedral interstice He increase significantly towards the ([Formula: see text]) twin boundary plane, while the formation energy of the octahedral interstice He atom near the ([Formula: see text]) twin boundary plane decreases. To analyze these results, we present the electronic densities of states (DOSs) of H, He and their nearest-neighbor Sc (NN-Sc) atoms in several tetrahedral and octahedral configurations. We have also calculated the formation energies of He-vacancy clusters (He[Formula: see text]V) in the Sc grain boundary, which indicates the stabilities of He[Formula: see text]V clusters depend on the variations of the relaxed vacancy volume near the ([Formula: see text]) twin boundary plane.