Vacancies in NiGa

Abstract

Vacancy concentrations and vacancy mobility are studied in stoichiometric NiGa. The thermal vacancy content, which is determined from density and thermal expansion experiments amounts to some percents. The activation energy for vacancy formation for the temperature interval in which the experiments are carried out is 0.20 eV. During the thermal expansion measurements an after‐effect in the macroscopic length is measured simultaneously. The annealing curves are well described by first‐order kinetics and from the temperature dependence of the time constants an activation energy for vacancy migration of (1.34 ± 0.04) eV is derived. On the basis of the present after‐effect measurements and tracer self‐diffusion measurements a diffusion mechanism is proposed for NiGa: nickel and gallium migration via nearest‐neighbour jumps and through single as well as divacancies.

Nickel diffusion inB2−NiGastudied with quasielastic neutron scattering

“…By doing so, we obtain ␣ϭ0.037 (20) at 990°C and ␣ϭ0.091(20) at 1130°C. These results are in agreement with the extrapolation of the values obtained by Ho et al 22 and Van Ommen, 23 both using dilatometric methods.…”