Localized hydrogen motion in C15-typeTaV2H0.65: temperature dependence of the H jump rate

Abstract

In order to study the temperature dependence of the jump rateτl−1 for the fast localized motion of hydrogen in cubic (C15-type) Laves-phaseTaV2, we have performed time-of-flight quasielastic neutron scattering measurements forTaV2H0.65 over the temperature range 12–290 K. The quasielastic line broadening corresponding to thelocalized H motion has been observed down to 70 K; the observability of the quasielastic line atlower temperatures is limited by the decrease in the fraction of H atoms participating inthe fast localized motion. In the range 70–290 K the temperature dependence ofτl−1 is found to deviate from the Arrhenius behaviour. This temperaturedependence can be reasonably well described by the exponential functionexp(T/T0) withT0 = 220 K. The samefunction with T0 of the order of 100 K also appears to describeτl−1(T) in some other metallic systems showing fast localized hydrogen motion.