Localized motion of hydrogen in C15-type TaV₂: A quasielastic neutron scattering study

In order to clarify the nature of the unusual low-temperature hydrogen motion in TaV₂, we have performed high-resolution quasielastic neutron scattering measurements on TaV₂H_0.6 in the temperature range 10-300 K. The results confirm the existence of localized H motion with the hopping rate of the order of 10⁹ s^-1 at 90 K. The temperature dependence of the hopping rate appears to be non-Arrhenius. The behaviour of the elastic incoherent structure factor is consistent with the models of H jumps between three or six sites on a circle with radius r ≈ 1.1 Å.