The first model-independent measurements of H diffusion in LaHx, where x was between 2 and 3, were carried out by means of pulsed-field gradient nuclear magnetic resonance techniques. At x-values of up to 2.92, the diffusivity exhibited an Arrhenius behavior over wide temperature ranges. The activation enthalpy decreased with increasing x-value; from 0.55eV at x = 2.00 to 0.17eV at x = 2.92 (table 71), thus leading to a sharp increase in diffusivity. The formation of a H superstructure, that was associated with the semiconductor-to-metal transition, resulted in a marked reduction in the diffusivity. It was noted for the first time that, in the stoichiometric limit, the diffusivity depended upon the thermal history of the sample.

G.Majer, U.Kaess, R.G.Barnes: Physical Review Letters, 1999, 83[2], 340-3