Diffusion in NiGa

Abstract

Quasielastic neutron scattering (QENS) at the backscattering spectrometer IN16 at ILL has been used to study the elementary diffusion jump of Ni in NiGa single crystals near the stoichiometric composition, Ni₅₀Ga₅₀. As indicated above, B2 structures consist of two simple interpenetrating cubic sublattices and, in the NiGa case, this occurs in the unit cell of the cube structure (structure CsCl), where the corner sites of one lattice are located in the center of the second lattice or vice versa. If, for instance, one assumes that the corner sites represent Ni atoms, then a Ga atom will be located at the center of this sublattice. As such, in this B2 structure, as in the others, diffusion occurs by means of a vacancy mechanism. During a NN jump, the local order is disturbed; consider such jumps as being to antisite positions. In Ni-rich compositions, excess Ni atoms exchange positions onto Ga-sublattice sites, whereas in Ga-rich compositions, vacancies are present on the Ni-sublattice.