Displaced-T Site Occupancy of Hydrogen in Nb Alloyed with a High Concentration of Mo

Abstract

The site occupancy of hydrogen in 52 at. % Nb–48 at. % Mo alloys is investigated at room temperature for hydrogen concentrations 0.028 and 0.055 in the hydrogen–metal-atom ratio (C_H=[H]⁄[M]) by the channelling method utilizing a nuclear reaction ¹H(¹¹B,α)αα with a ¹¹B beam. A large portion of H atoms are located at sites displaced from tetrahedral (T) sites towards their nearest neighbour octahedral (O) sites by about 0.3 Å (displaced-T sites; d-T), which are similar to the sites observed in V under uniaxial stress and completely different from the sites observed in the Nb alloys containing undersized Mo atoms up to 26 at. %. For C_H=0.028 and 0.055, 30–40% and 15–25% of H atoms are located at T sites, respectively.