Irradiation-Induced Site Change of Hydrogen in Niobium

The effect of ion-irradiation on the state of hydrogen in Nb doped with hydrogen of a concentration of [H]/[M] = 0.023 (hydrogen-to-metal-atom ratio) from the gas phase has been investigated at room temperature by the channelling method utilizing a nuclear reaction 1 H( 11 B,α)αα with a 11 B beam of an energy of about 2 MeV. It has been demonstrated that, before irradiation, hydrogen is located at a tetrahedral ( T ) site, while, after irradiation at room temperature with the 11 B beam in the off-channelling direction up to a dose of about 1.4 ×10 16 /cm 2 , hydrogen is displaced from a T site by 0.45–0.55 A towards its nearest neighbour lattice point. It is concluded that this irradiation-induced site change of hydrogen is due to trapping of hydrogen by irradiation-introduced monovacancies. Hydrogen is located at a site displaced from one of the nearest neighbour T sites of a vacancy by 0.45–0.55 A towards that vacancy.