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

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.

First-principles study of hydrogen diffusion in transition metal palladium

By adopting the first-principles total energy calculations based on density functional theory (DFT), the diffuse pattern and path of hydrogen in bulk palladium are investigated by calculating the system energy of hydrogen atom occupying different positions in palladium crystal lattice. The results indicate that the most stable position of hydrogen atom in palladium crystal lattice locates at the octahedral interstice, and the tetrahedral interstice is the second stable site. Hydrogen diffusion along the indirect octahedral–tetrahedral–octahedral (O–T–O) path is energetically most favorable in transition metal palladium, and the activation energy is 0.5245 eV.

Lattice Site of Helium Implanted in Si and Diamond

ABSTRACTSingle crystals of silicon and diamond were implanted at 300K with 70 keV 3He. Ion channeling analyses were executed by application of Rutherford backscattering spectrometry and nuclear reaction analysis. Helium exhibits a non-random lattice site in the channeling angular distributions for silicon and diamond. A major fraction of the implanted 3He was qualitatively identified to be near to the tetrahedral interstice in both materials.