Quasielastic neutron scattering study of hydrogen motion in NbC0.71H0.28
In order to study the mechanism and parameters of H jump motion in the nonstoichiometric Nb carbides, we have performed quasielastic neutron scattering (QENS) measurements for NbC0.71H0.28 over the temperature range 11– 475 K. Our results indicate that about 30% of H atoms in this system participate in a fast diffusive motion. The temperature dependence of the corresponding H jump rate in the range 298–475 K follows the Arrhenius law with an activation energy of 328 ± 9 meV. The Q dependence of the QENS data suggests that the observed jump motion corresponds to long-range diffusion of H atoms along chains of the off-centre sites in carbon vacancies.
Hydrogen jump diffusion in C14-type ZrMn2H3 : Quasielastic neutron scattering study
In order to study the mechanism and parameters of hydrogen diffusion in the hexagonal (C14-type) Laves-phase $\mathrm{Zr}{\mathrm{Mn}}_{2}$, we have performed quasielastic neutron scattering measurements for $\mathrm{Zr}{\mathrm{Mn}}_{2}{\mathrm{H}}_{3}$ over the temperature range $10--390\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. It is found that the diffusive motion of hydrogen in this system can be described in terms of at least two jump processes: a fast localized H motion with the jump rate ${\ensuremath{\tau}}_{l}^{\ensuremath{-}1}$ and a slower process with the rate ${\ensuremath{\tau}}_{d}^{\ensuremath{-}1}$ associated with H jumps leading to long-range diffusion. The temperature dependence of ${\ensuremath{\tau}}_{d}^{\ensuremath{-}1}$ in the range $225--390\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ follows the Arrhenius law with the activation energy of $124\ifmmode\pm\else\textpm\fi{}4\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. In the same range, the temperature dependence of ${\ensuremath{\tau}}_{l}^{\ensuremath{-}1}$ deviates from the Arrhenius behavior and is considerably weaker than that of ${\ensuremath{\tau}}_{d}^{\ensuremath{-}1}$. The $Q$ dependence of the elastic incoherent structure factor (studied up to ${Q}_{\mathrm{max}}\ensuremath{\approx}3.8\phantom{\rule{0.3em}{0ex}}{\mathrm{\AA{}}}^{\ensuremath{-}1}$) suggests that the fast localized H motion in $\mathrm{Zr}{\mathrm{Mn}}_{2}{\mathrm{H}}_{3}$ corresponds to two-site jumps within pairs of closely spaced interstitial ${\mathrm{Zr}}_{2}{\mathrm{Mn}}_{2}$ sites.
Hydrogen location and diffusion in a two-dimensional metal: Proton magnetic resonance in metallic zirconium monohalide hydrides
Abstract Proton magnetic resonance has been studied in a new class of metal-hydrogen systems, ZrXH, based on the metallic double-layered monohalides of zirconium, ZrCl and ZrBr. The rigid lattice second moments of the proton resonance show that in the hemihydride phases hydrogen predominantly occupies alternate chains of tetrahedral sites within the double layer of close-packed Zr atoms. In the monohydrides all tetrahedral sites are occupied by hydrogen. Activation energies for hydrogen diffusion within the layers are derived from the temperature dependence of the resonance linewidth. A substantial anisotropy of the proton resonance shape is observed at high temperatures.