The vibrational spectra of hydrogen and parameters of H diffusion in the coarse-grained C15-type system ZrCr2H3 and in nanostructured ZrCr2H3 were studied by means of inelastic and quasi-elastic neutron scattering. It was found that the diffusive motion of hydrogen in coarse-grained ZrCr2H3 could be described in terms of at least two jump processes: a fast localized H motion with the jump rate τl-1 over the hexagons formed by interstitial Zr2Cr2 sites and a slower process with the rate τd-1 associated with H jumps leading to long-range diffusion. While τd-1(T) at 250 to 380K follows the Arrhenius law with the activation energy of 142meV, the temperature dependence of τl-1 deviates from Arrhenius behavior. The nanostructured ZrCr2H3 samples prepared by ball milling consist of C15-type grains and strongly distorted (amorphous-like) regions. H atoms in the strongly distorted regions were found to be immobile on the time-scale of the experiments. The microscopic picture of H jump motion in the C15-type grains of the nanostructured samples was similar to that in coarse-grained ZrCr2H3; however, the ball milling leads to a considerable decrease in the jump rate τd-1.

A Neutron Scattering Study of Hydrogen Dynamics in Coarse-Grained and Nanostructured ZrCr2H3. A.V.Skripov, T.J.Udovic, J.J.Rush, M.A.Uimin: Journal of Physics - Condensed Matter, 2011, 23[6], 065402