Short positron lifetime at vacancies observed in electron-irradiated tungsten: Experiments and first-principles calculations

Abstract

A positron lifetime component of ~170 ps has been reported for irradiated tungsten (W) in some studies. This value is considerably shorter than that calculated for isolated monovacancies (~200 ps). In this study, positron annihilation lifetime spectroscopy was used to investigate the recovery behavior of the defects with a short positron lifetime of ~170 ps in electron-irradiated W. The binding energies and positron lifetimes of vacancy-impurity complexes decorated with impurity atoms were calculated. A positron lifetime of 169 ps, which was similar to the experimentally observed lifetime of 171 ± 1 ps, was calculated for defect complexes comprising a monovacancy decorated with two hydrogen atoms (V-2H complexes). In addition, a value of 1.42 eV was calculated for the dissociation energy of a hydrogen atom from the V-H and V-2H complexes, and the defects with a positron lifetime of ~170 ps were experimentally observed to migrate at 623 K. These were consistent with previously reported dissociation energy and desorption temperature of deuterium from vacancies in W studied by thermal desorption spectroscopy. These results suggested that the vacancies observed in the electron-irradiated W were hydrogen-decorated V-nH complexes.