Hydrogen local modes and phonon dispersion inLuD0.19and Lu

The phonon dispersion of both pure Lu and α-${\mathrm{LuD}}_{0.19}$ is determined along the symmetry directions Γ-A and Γ-K-M. The phonon energies are partly found to increase due to hydrogen absorption. At low temperatures no influence of deuterium ordering on the phonon frequencies can be detected. Furthermore, the hydrogen local-mode properties are investigated in α-${\mathrm{LuD}}_{0.19}$. In accordance with recent results on α-YH(D${)}_{0.18}$, the potential at the hydrogen site is found to be very anisotropic.