Search

Ab initio calculations based on density functional theory have been performed to determine the properties of self-interstitial atoms (SIAs), vacancies, and single H and He atoms in hcp-Er. The results show that the most stable configuration for a SIA is a basal octahedral configuration, while the octahedral (O), basal split, and crowdion (C) interstitial configurations are less stable, followed by the split <0001> dumbbell and tetrahedral configurations. For both H and He defects, the formation energy of an interstitial atom is less than that of a substitutional atom in hcp-Er. Furthermore, the tetrahedral interstitial position is more stable than an octahedral position for both He and H interstitials. The hybridization of the He and H defects with Er atoms has been used to explain the relative stabilities of these defects in hcp-Er. [ABSTRACT FROM AUTHOR]

The interactions of He and vacancy defects with 〈111〉 screw dislocations in alpha-Fe were modeled using molecular statics, molecular dynamics and transition state energy determinations. The formation energies and binding energies of interstitial He atoms, vacancies and He-vacancy clusters near and within dislocations in alpha-Fe were determined at various locations relative to the dislocation core. Using the dimer transition state method, the migration energies and trajectories of the He and vacancy defects near and within the screw dislocation were also determined. Both interstitial He atoms and single vacancies are attracted to and trapped in the dislocation core region, and they both migrate along the dislocation line with a migration energy of about 0.4 eV, which is about half the migration energy of vacancies in the perfect crystal and about five times the migration energy for interstitial He in the perfect crystal. Divacancies and He-divacancy complexes have migration properties within the dislocation core that are similar to those in the perfect crystal, although the stability of these defects within the dislocation may be somewhat less than in the perfect crystal. [ABSTRACT FROM AUTHOR]