Neutron inelastic scattering spectra were measured as a function of temperature and scattering angle for α‐TaH0.15 and for Ta2H in its α and β1 phases. The widths of the quasi-elastic peaks vs momentum transfer were derived. The results suggested a predominance of tetrahedral jumps in the diffusion process, although no completely satisfactory theoretical fit was obtained. Residence times between 1.6 (340C) and 4.0 (148C) psec for TaH0.15 and between 2.4 (300C) and 7 (153C) psec for Ta2H were deduced from a fit of the observed widths to the tetrahedral model. The results indicated a significant concentration-dependence of the diffusion rates in α‐TaHx, with activation energies for diffusion of 10.4kJ/mol in TaH0.15 and 15kJ/mol for Ta2H. Effective mean-square amplitudes of proton vibration, of 0.02 to 0.04Å2 were obtained from the momentum transfer dependence of the quasi-elastic peak intensities. The results were compared with previous neutron results on VHx and NbHx. On the basis of this comparison, it was tentatively concluded that the very high Debye‐Waller factors obtained for VHx and other hydrides were related to high hydrogen diffusion rates.

Study of Hydrogen Diffusion in Tantalum Hydrides by Inelastic Neutron Scattering. J.J.Rush, R.C.Livingston, L.A.De Graaf, H.E.Flotow, J.M.Rowe: Journal of Chemical Physics, 1973, 59, 6570-6

Table 162

Diffusivity of H in TaH0.52