DIFFUSION OF NI-63 IN THE INTERMETALLIC B82-ALLOYS IN THE SYSTEMS NI/SN AND NI/IN

The self-diffusion of Ni-63 has been investigated in single crystals of the ordered intermetallic compounds Ni61Sn39, Ni62Sn38 and Ni64In36. The activation energies for diffusion perpendicular and parallel to the hexagonal c-axis are nearly the same and the values are between 2.14 and 2.34 eV. Moreover the D0-values are direction dependent and range from 0.5 to 0.8 cm2/s for Ni/Sn and from 65 to 110 cm2/s for Ni/In. The experimental values of D(perpendicular-to)/D(parallel-to) are between 1.13 and 1.68 for Ni/Sn and between 0.87 and 0.79 for Ni/In, depending on temperature. These values are to be compared with theoretical values for the different diffusion mechanisms. The majority mechanism should be a site change of the tracer atom between the Ni-chains in c-direction and the double tetraeder interstices (DTI) with a further jump to another chain. Moreover two other mechanisms as minority mechanisms are possible. With rising temperature and filling the DTI's the part of minority mechanisms increases.