Anisotropic Diffusion of Mercury in Zinc

The diffusion of mercury has been studied in high-purity zinc as a function of temperature, using the sectioning technique. The diffusion coefficients as measured in single crystals are given by DII=(0.056±0.002)×exp[-(19700±48)RT] cm²/sec, and D_⊥=(0.073±0.006)exp[-(20180±94)RT] cm²/sec, where DII and D_⊥ are the diffusion coefficients parallel and perpendicular to the hexagonal axis, respectively. Compared to the diffusion of cadmium in zinc, where D_⊥>DII, mercury diffuses with a slightly smaller activation energy, and with DII>D_⊥. The results are discussed on the basis of the basal and nonbasal vacancy mechanisms, and the influence of the ion size of the diffusing atom is examined to explain the diffusion anisotropy.