Quasielastic neutron scattering study of hydrogen motion in C15-type YMn2Hx

Abstract

In order to study the mechanism and parameters of hydrogendiffusion in the cubic (C15-type) Laves phase YMn2,we have performed quasielastic neutron scattering measurements in YMn2Hx(x = 0.4,0.65 and 1.26) over the temperature range 30–395 K. It is found that thediffusive motion of hydrogen in this system can be described in terms of twojump processes: the fast localized H motion with the jump rate τl−1and the slower process with the rate τd−1associated with H jumps leading to long-range diffusion. The ratio τd /τl at room temperatureis close to 102.Our results suggest that the localized H motion in YMn2Hxcorresponds to back-and-forth jumps of hydrogen atoms within pairs of interstitial g (Y2Mn2)sites. The parameters of the long-range diffusion of hydrogen in thesamples with different H content are found to be close to each other.In the range 210–395 K, the temperature dependences of τd−1and the hydrogen diffusivity are reasonably described by the Arrhenius law withactivation energies 0.18–0.22 eV.