Diffusion of Pd in Pb at high pressures

The diffusion of ${}_{}{}^{109}{}_{}{}^{}\mathrm{Pd}$ in Pb has been found to be very rapid with $D=(3.4\mathrm{}\pm 0.6)\times {10}^{-3\mathrm{}}\exp (-0.367\mathrm{}\pm 0.009 \frac{\mathrm{eV}}{\mathrm{kT}})$ ${\mathrm{cm}}^2$/sec. The activation volume for diffusion is only 0.04 ± 0.02 atomic volumes, indicating a very small effect of pressure on this diffusion. The pressure and temperature derivatives of the activation volume, $\frac{\Delta V}{V_0}$, are (2.6 ± 0.5) × ${10}^{-3\mathrm{}}$ ${\mathrm{kbar}}^{-1\mathrm{}}$ and (0.9 ± 0.4) × ${10}^{-4\mathrm{}}$ ${\mathrm{K}}^{-1\mathrm{}}$, respectively. These results, coupled with those from seven other tracers diffusing in Pb, have been analyzed in terms of an equilibrium model of interstitial, substitutional, and interstitial-vacancy pair defects. The analysis predicts the defects of Cu and Au in Pb to be primarily interstitial, Ni and Pd primarily interstitial-vacancy pairs, and Cd and Hg primarily substitutional.