Hydrogen dynamics in Laves-phase hydride YFe2H2.6: Inelastic and quasielastic neutron scattering studies

• H jump rates in YFe2H2.6 are determined from quasielastic neutron scattering.
• Temperature dependence of the H jump rate is non-Arrhenius.
• Fast two-site localized H motion within pairs of closely-spaced g sites.
• Local lattice distortions resulting from hydrogenation of YFe2.

The vibrational spectrum of hydrogen and the parameters of H jump motion in the C15-type compound YFe2H2.6 have been studied by means of inelastic and quasielastic neutron scattering. It is found that hydrogen atoms occupying tetrahedral interstitial g (Y2Fe2) sites participate in the fast localized jump motion. The behavior of the elastic incoherent structure factor as a function of momentum transfer (measured up to Qmax ≈ 4 Å−1) is consistent with the two-site motion of H atoms within pairs of closely spaced g sites. In the studied T range of 140–390 K, the temperature dependence of the jump rate of this localized motion is found to be non-Arrhenius; however, it can be described by two Arrhenius-like terms with the activation energies of 42 and 10 meV in the ranges 295–390 K and 140–240 K, respectively. Our results also indicate that hydrogen dynamics in YFe2H2.6 is affected by considerable local lattice distortions resulting from hydrogenation of YFe2.