It was recalled that a strong argument had been advanced to the effect that self-diffusion in the solid metal was effectively governed by a direct exchange mechanism rather than by a vacancy exchange process. Attention was restricted here to the very pronounced curvature that was observed in the self-diffusion data for this metal. The curvature that was observed, at high temperatures, in the tracer self-diffusivity was attributed here to a mono-vacancy contribution that was superposed on the predominantly direct exchange mechanism. A comparison of the measured mono-vacancy parameters and the self-diffusivity data led to reasonable values for the mono-vacancy migration enthalpy and the entropy.

R.B.McLellan, Y.C.Angel: Scripta Metallurgica et Materialia, 1995, 33[6], 945-8