THE MECHANISM OF FAST NI DIFFUSION IN THE HIGH-TEMPERATURE PHASE OF NI3SB STUDIED WITH QUASI-ELASTIC NEUTRON-SCATTERING

Nickel diffusion in Ni3Sb (D0(3) structure, four sublattices) is so fa st that an unusual jump mechanism might be suspected. This suspicion i s nourished by the recent discovery of high concentrations of ordered vacancies, i.e. vacancies on two of the nickel sublattices, the alpha- sublattices. Quasielastic neutron scattering (QNS) can be used to dete rmine the elementary diffusion jump. Using this method we have found t hat the elementary diffusion jump is unambiguously a jump into a neare st-neighbour site, i.e. between sites on alpha- and gamma-sublattices. In spite of the very high vacancy concentration on the alpha-sites (w hich certainly supports the fast jumping) it is-interestingly enough-n ot a jump directly between alpha-sites.