The effect of the isotopic mass (195Au, 198Au) upon diffusion in these alloys was studied (table 129) by using a tracer/sectioning technique. It was found that the isotope effect amounted to 0.18 in pure Pb, with a negligible temperature dependence. The result was consistent with previous isotope effect measurements of so-called fast diffusers in polyvalent materials. The magnitude of the isotope effect increased with increasing In concentration, and reached 0.4 at 2at%In. The variation with temperature was again less than the experimental error. Since the anticipated value of the isotope mass was near to unity in the case of a simple interstitial mechanism for pure Pb, it was concluded that the diffusion mechanism for Au in Pb-In alloys could not be accounted for by this mechanism.

J.Shi, R.J.Healy, H.B.Huntington: Journal of the Physics and Chemistry of Solids, 1994, 55[6], 487-91

Table 129

Isotope Effect for Au in Pb-In Alloys