Proton nuclear magnetic resonance was measured in two Nb–H samples prepared so as to introduce vacancy–H clusters and a reference sample containing no vac–H clusters. A motionally narrowed signal persisting to very low temperatures was observed only in the former samples, and was assigned to protons executing a cage motion in Nb-atom vacancies. From the temperature dependence of the line-width between 7 and 30K, an apparent activation energy of 3.8meV was deduced.

NMR Studies of Hydrogen Motion in Vacancies in Nb–H Alloys. T.Imai, A.Kayanuma, Y.Fukai, S.Masubuchi: Journal of Physics - Condensed Matter, 2004, 16[46], 8191-200