Rapid low-temperature hopping of hydrogen in a pure metal: TheScHxsystem

Abstract

The localized motion of hydrogen in scandium has been studied by quasielastic neutron scattering. The results reveal that the quasielastic linewidth has a pronounced minimum near 100 K and rises at lower temperature with approximate ${\mathit{T}}^{\mathrm{-}1}$ dependence, indicative of nonadiabatic behavior that can be associated with weak coupling of hydrogen to the metal conduction electrons. This is the first such observation in a pure-metal–hydrogen system. The simultaneous determination of the elastic incoherent structure factor is interpreted in terms of labile and nonlabile hydrogen configurations in a manner consistent with recent estimates of pairing and activation energies in the rare-earth–hydrogen systems.