LATTICE DYNAMICAL ASPECTS OF H IN V, NB, TA AND PD

We have calculated the local frequency spectrum and the mean thermal displacement of H in the transition metals Nb, V, Ta, and Pd by the Green's function method. The force constant model includes changes in the surrounding host lattice which are fitted to the experimentally observed localized frequencies, to the dipole force tensor and to the changes of the elastic constants. For all materials the calculated frequency spectra show within the band modes a strong resonant like peak which yields a strongly temperature dependent contribution to the thermal displacements. We argue that the band modes of the H are also very important for the diffusional properties: a rough estimate shows the possibility of a classical jump diffusion process which is dominated by the band modes of the H and nearly isotope independent. © by Akademische Verlagsgesellschaft