It was recalled that the weak concentration dependence of Ni diffusion in this material had been interpreted as being evidence for Ni diffusion via next-nearest neighbour jumps. This seemed to be reasonable, in view of the comparatively high enthalpy of formation in this alloy. Quasi-elastic neutron scattering and back-scattering spectrometry were used to study the elementary diffusion jumps of Ni in NiGa single crystals which contained 50at%Ni, and in polycrystals which contained 57 or 62at%Ni. The weak concentration-dependence of the Ni diffusion coefficient was confirmed over a wide concentration range on the Ni-rich site of the phase diagram (table 26, figure 20). The diffusive jumps of Ni atoms were proved to involve jumps via nearest-neighbour (antistructure) sites. In the case of the near-stoichiometric compositions, it was possible to determine directly the residence times of Ni atoms, at antistructure sites, from quasi-elastic neutron scattering data. The results were concluded to indicate the existence of very high defect concentrations near to the melting point.

Nickel Diffusion in B2-NiGa Studied with Quasielastic Neutron Scattering. M.Kaisermayr, J.Combet, H.Ipser, H.Schicketanz, B.Sepiol, G.Vogl: Physical Review B, 2000, 61[18], 12038-44

Figure 20

Diffusion of Ni in NiGa

Table 26

Diffusivity of Ni in NiGa