A study was made of the effect of coherency stresses, upon D diffusion at 454 to 504K in a NbD0.33 crystal (figure 17), by using quasi-elastic neutron scattering while discriminating coherent from incoherent scattering by means of neutron spin analysis. The diffusion coefficient of D interstitials, which described collective diffusion according to Fick’s law, was deduced from the coherent quasi-elastic scattering. The values of the diffusivity exceeded published Gorsky-effect results, for the same quantity, by a factor of up to 30. It was demonstrated quantitatively that the large differences in diffusivity reflected the dissimilar influence of coherency stresses upon the D fluctuations that were probed by neutron scattering and the Gorsky effect, respectively.

U.Stuhr, K.Cornell, H.Wipf: Physical Review Letters, 1999, 82[11], 2302-5

Figure 17

Diffusivity of D in NbD0.333

(a: self-diffusivity, b: chemical diffusivity)