QUASI-ELASTIC NEUTRON-SCATTERING STUDY OF THE NI DIFFUSION MECHANISM IN THE INTERMETALLIC ALLOY NISB

Ni diffusion in the hexagonal NiSb intermetallic phase of approximatel y equiatomic composition is surprisingly fast, more than two orders of magnitude faster than Sb diffusion. In order to determine the atomic jump mechanism of the Ni atoms, quasielastic neutron scattering was ca rried out at two single crystals kept at 1040-degrees-C, 1080-degrees- C and 1100-degrees-C. Jumps of the Ni atoms between regular sites (oct ahedral interstices of the Sb lattice) and double tetrahedral intersti ces (DTI) and back yield very satisfactory fits on the measured data. Such jumps had been proposed by Frohberg in order to explain the diffe rence in tracer diffusivities parallel and vertical to the hexagonal c axis. Even with a 12% surplus of Ni atoms over Sb atoms in the alloy Ni53Sb47, about 4% vacancies remain on the regular Ni sites. Our measu rements permit the exclusion of jumps just between the regular sites o r just between the DTI sites.