A pulsed field gradient nuclear magnetic resonance spin-echo technique was used to measure diffusivities. The activation energy increased with increasing H concentration, whereas the pre-exponential factor was not greatly concentration-dependent (table 84). The results were not consistent with the random occupation of tetrahedral sites, and it was suggested that repulsive interactions existed between H atoms on nearest-neighbor sites.

P.E.Mauger, W.D.Williams, R.M.Cotts: Journal of the Physics and Chemistry of Solids, 1981, 42[9], 821-6