Anisotropic Diffusion of Cadmium and Gold Tracers in Zinc Single Crystals

The anisotropic diffusion coefficients of the radioactive tracers cadmium ($115m$) and gold (198) in single crystals of high-purity zinc, in directions parallel and perpendicular to the hexagonal axis, were measured by the standard sectioning technique. Cadmium diffused at a rate faster than that of self-diffusion and with D_⊥>DII. Gold diffused at a rate slower than that of self-diffusion and with DII>D_⊥. The results of the measurements are as follows: For cadimum ($115m$), DII=(0.11±0.01)exp[-(20.54±0.09)×10³RT] cm²/sec, D_⊥=(0.12±0.01)exp[-(20.42±0.03)×10³RT] cm²/sec; for gold (198), ${D}II=(0.97±{}0.22)×{}exp[{-}{(29.73±{}0.26)×{}{10}³}{RT}]$ ${cm}²$/sec, ${D}_{{⊥}}=(0.29±{}0.12)exp[{-}{(29.72±{}0.45)×{}{10}³}{RT}]$ ${cm}²$/sec. On the basis of the vacancy mechanism one can interpret the fast diffusion of cadmium in terms of an appreciable binding between the vacancy and the diffusing ion; conversely the slow diffusion of gold in terms of a repulsion between the vacancy and the diffusing ion.