A number of cubic C15 Laves phase intermetallic compounds were able to absorb large amounts of hydrogen. At low solute concentrations, the protons occupy tetrahedral interstitial sites, which form a network of hexagons. It was believed that the motion of hydrogen occurred on two distinct time-scales; a rapid localized motion around the hexagons, coupled with a slower long-range diffusion between hexagons. Results from Monte Carlo simulations of hydrogen diffusion in a Laves phase compound were presented. It was demonstrated that the incoherent quasielastic neutron scattering function, obtained from the simulations, could be interpreted in terms of a broad and a narrow Lorentzian component, emanating from hydrogen motion on the two time scales. The narrower component followed a Chudley-Elliot model, indicative of long-range diffusion, whilst the broader component could be interpreted in terms of localized motion. The calculated effective jump length for long-range diffusion was significantly in excess of the actual jump-length, in agreement with experimental observation. The model was briefly discussed in relation to hydrogen diffusion in ZrV2H1.1.

Monte Carlo Simulation of Quasielastic Neutron Scattering from Localised and Long-Range Hydrogen Motion in C15 Laves Phase Intermetallic Compounds. D.J.Bull, D.P.Broom, D.K.Ross: Chemical Physics, 2003, 292[2-3], 153-60