Hydrogen jump diffusion in C14-typeZrMn2H3: Quasielastic neutron scattering study

Abstract

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.