Deuterium diffusion in niobium: The influence of coherency stresses

We studied the influence of coherency stresses on deuterium diffusion in a NbD0.33 crystal by quasielastic neutron scattering, discriminating coherent from incoherent scattering by neutron spin analysis (454 less than or equa l to T less than or equal to 504 K). The diffusion coefficient D of the deu terium interstitials, describing collective diffusion according to Fick's l aw, was derived from the coherent quasielastic scattering. The values of D exceed published Gorsky effect results for the same quantity by factors of up to 30. We demonstrate quantitatively that the large differences in D ref lect the dissimilar influence of coherency stresses on the deuterium fluctu ations respectively probed by neutron scattering and Gorsky effect.