Formation of Hydrogen-Associated Vacancy Clusters in Nb as Investigated from Site Occupancy Change of Hydrogen

Abstract

In order to study hydrogen-defect interactions, the effects of ion irradiation and annealing on the site occupancy of hydrogen dissolved in Nb, NbH 0.023 , have been investigated at room temperature by the channelling method utilizing a nuclear reaction 1 H( 11 B,α)αα with a 2 MeV 11 B + beam. By irradiation at room temperature up to a dose of 1.4×10 16 /cm 2 of 2 MeV 11 B ions, the lattice location of hydrogen changes from the original tetrahedral ( T ) site ( T -1 state) to the T tr site, which is displaced from a T site by 0.45–0.55 A towards its nearest-neighbour lattice point. This site occupancy remains the same even for an approximately three times higher irradiation dose. On the subsequent annealing at 523 K for 1 h, the state of hydrogen changes from the T tr -site occupancy to the occupancies of (55–70)% of H atoms at T sites ( T -2 state) and (30–45)% at random ( R ) sites. The irradiation-induced site change from the T site to the T tr site is due to the trapping of hydrogen by vacancies, i.e....