Hydrogen relaxation in lutetium

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Abstract
The internal friction and the dynamic modulus have been measured between 4.2 and 470 K in the system α-LuH(D)x, with x = 0 to 0.2. In well annealed specimens, an (H)-peak is observed at 215-225 K, which has a linearly x-dependent amplitude and exhibits an isotope effect on its activation energy and relaxation time. It is attributed to a Snoek-like relaxation of H-H pairs reorienting in the Lu-lattice. The isotope effect is interpreted in a model of tunnelling from different excited levels for LuHx and LuDx. Deformation introduces a (d-H)-peak at 250-260 K in H(D)-containing samples only, also exhibiting an isotope effect; it is attributed to a Snoek-Köster type relaxation of H(D) trapped on dislocations. Two (d1,2)-peaks at 160 and 215 K, which occur in the pure metal only, and a (d)-peak centred near 350 K in all deformed specimens are ascribed to geometrical kink migration and to double-kink generation on a screw dislocation network, respectively