Anisotropic Diffusion of Hydrogen in Niobium Single Crystals

Quasielastic neutron scattering experiments on hydrogen in niobium single crystals have been performed in the $\overrightarrow{\mathrm{K}}$ range from 1.7 to 4.3 ${\mathrm{\AA }}^{-1\mathrm{}}$ in the three directions [100], [110], and [111]. The experimental width functions show a significant anisotropy. The results are not in agreement with the theoretical half-widths calculated for tetrahedral and octahedral positions of the hydrogen.