Experimental data for proton nuclear spin relaxation and diffusion in HfTi2Hx were analyzed by simultaneously fitting the temperature-dependent relaxation and diffusion data using a common set of parameters. The HfTi2Hx had a C15 structure, with H occupying inequivalent interstitial sites. Fitting of the relaxation data used a rigorous theory of nuclear spin relaxation between inequivalent sites and made no assumptions concerning which types of H jump were significant for relaxation. The diffusion data were  fitted by developing the theory of diffusion between inequivalent interstitial sites. This permitted the diffusivity to be calculated rigorously as a function of temperature from the H jump rates in the low-concentration limit. Monte Carlo simulations were used to estimate the effect of diffusion correlation effects at higher H concentrations. Models for diffusion between inequivalent sites involved a large number of parameters, and density functional theory calculations were used to provide constraints. Good fits to both relaxation and diffusion data were obtained for energy parameters that were close to those found from density functional theory calculations. A complete set of jump parameters for H between interstitial sites was deduced which provided a detailed microscopic description of the diffusion as a function of temperature.

Diffusion of Hydrogen in Cubic Laves Phase HfTi2Hx. B.Bhatia, X.Luo, C.A.Sholl, D.S.Sholl: Journal of Physics - Condensed Matter, 2004, 16[49], 8891-903