The sub-stoichiometric halide was investigated by using incoherent quasi-elastic neutron scattering techniques. The halide had a layered structure in which H atoms occupied tetrahedral interstitial sites that were situated in Y bi-layers which were sandwiched between Br bi-layers. This arrangement impeded H transfer between Y bi-layers, but a study was made of the essentially 2-dimensional H diffusion within a given Y bilayer (figure 9). It was estimated that the H self-diffusion coefficient was 1.2 x 10-6cm2/s at 900K. The temperature dependence obeyed an Arrhenius relationship, with an activation energy of 0.48eV. A momentum-transfer dependence of the measured spectra suggested that correlation effects occurred during H diffusion.

U.Stuhr, H.Wipf, R.K.Kremer, H.Mattausch, A.Simon, J.C.Cook: Journal of Physics - Condensed Matter, 1994, 6[1], 147-58