This work deals with the study of zinc self-diffusion in ZnO polycrystal of high density and of high purity. The diffusion experiments were performed using the 65Zn radioactive isotope as zinc tracer. A thin film of the tracer was deposited on the polished surface of the samples, and then diffusion annealing was performed from 1006 to 1377C, in an oxygen atmosphere. After the diffusion treatment, the 65Zn diffusion profiles were established by means of the residual activity method. From the zinc diffusion profiles were deduced the volume diffusion coefficient and the product δDgb for the grain-boundary diffusion, where δ was the grain-boundary width and Dgb was the grain-boundary diffusion coefficient. The results obtained for the volume diffusion coefficient showed good agreement with the most recent results obtained in ZnO single crystals using stable tracer and depth profiling by secondary ion mass spectrometry (Nogueira et al., 2003)

D(m2/s) = 1.6 x 10-7exp[-2.66(eV)/kT]

while, for the grain-boundary diffusion, there were no data published by other authors for comparison with the results. The zinc grain-boundary diffusion coefficients were about 4 orders of magnitude greater than the volume diffusion coefficients, in the same experimental conditions, which means that grain-boundary was a fast path for zinc diffusion in polycrystalline ZnO.

Zinc Self-Diffusion in ZnO. Nogueira, M.A.N., Sabioni, A.C.S., Ferraz, W.B.: Defect and Diffusion Forum, 2005, 237-240[1], 163-8

Figure 39

Diffusivity of Zn in Monocrystalline ZnO