Site Change of Hydrogen in Nb due to Interaction with Oxygen

To locate hydrogen in Nb alloyed with 0.3 at. % oxygen, which is the alloy system for the tunnelling motion of hydrogen to be observed, channelling experiments have been performed at room temperature utilizing a nuclear reaction 1 H( 11 B,α)αα with a 11 B beam of about 2 MeV. It has been demonstrated that for a hydrogen concentration of C H = 0.003 ( C H = [ H ]/[ M ]; hydrogen-to-metal-atom ratio), H atoms are located at sites displaced by 0.5–0.6 A from tetrahedral ( T ) sites towards their nearest-neighbour lattice points, while for C H = 0.019, most of the H atoms are located at T sites and the remains are at the same sites as those observed for C H = 0.003. This result indicates the trapping of hydrogen by oxygen and the formation of O–H pairs. The number of H atoms trapped by one O atom is approximately unity. As locations of the trapped hydrogen involved in the tunnelling motion, three types of displaced sites, which are described above, with the same separation of about 0.82 A between neighbouring...