Diffusion of ${\mathrm{Sb}}^{124}$, ${\mathrm{Cd}}^{109}$, ${\mathrm{Sn}}^{113}$, and ${\mathrm{Zn}}^{65}$ in tin

The anisotropic diffusion coefficients of ${\mathrm{Sb}}^{124}$, ${\mathrm{Cd}}^{109}$, and ${\mathrm{Zn}}^{65}$ in single crystals of tin have been measured by the tracer-sectioning method. The results of the measurements are for Sb, $D_{\parallel }=71\mathrm{}\exp [-\frac{(29.0\mathrm{}\pm 0.03 \frac{\mathrm{kcal}}{\mathrm{mol}})}{RT}]$, $D_{\perp }=73\mathrm{}\exp [-\frac{(29.4\mathrm{}\pm 0.4 \frac{\mathrm{kcal}}{\mathrm{mol}})}{RT}]$; for Cd, $D_{\parallel }=220\mathrm{}\exp [-\frac{(28.2\mathrm{}\pm 0.6 \frac{\mathrm{kcal}}{\mathrm{mol}})}{RT}]$, $D_{\perp }=120\mathrm{}\exp [-\frac{(27.6\mathrm{}\pm 0.5 \frac{\mathrm{kcal}}{\mathrm{mol}})}{RT}]$; for Zn, $D_{\parallel }=1.1\mathrm{}\exp [-\frac{(12.0\mathrm{}\pm 0.4 \frac{\mathrm{kcal}}{\mathrm{mol}})}{RT}]$, $D_{\perp }=8.4\mathrm{}\exp [-\frac{(21.3\mathrm{}\pm 0.2 \frac{\mathrm{kcal}}{\mathrm{mol}})}{RT}]$, all in ${\mathrm{cm}}^2$/sec. The literature values for self-diffusion in tin were also checked by a separate experiment. Considerable persistence was needed to find an effective electroplating procedure for zinc diffusion in tin. The low values of diffusivity of Sb and Cd strongly indicate a substitutional-vacancy mechanism. Divalent zinc has the same valence as cadmium but diffuses fairly fast, somewhat like the noble-metal solutes. In contrast with monovalent and most divalent solvents, there appears to be no systematic variation of activation energy for the impurity diffusion in tin with the valence of the diffusion ion. Substitutional and interstitial mechanisms for impurity diffusion in tin are discussed. A revision in method for the calculation of the migration energy for impurity diffusion is indicated.