Self-diffusion coefficients for 18O in single-crystal MgO were determined from a novel specimen comprising an epitaxial layer of high-purity Mg18O upon a single crystal substrate of normal MgO. Heating the specimen in air produced a gas–solid exchange gradient at the sample surface as 18O in the epitaxial layer exchanged with 16O in air. A solid–solid interdiffusion gradient was produced between the substrate crystal and the 18O-enriched epitaxial layer. SIMS analysis of gas–solid exchange gradients prepared in at 1000 to 1650C provided diffusion coefficients that could be described by:

D(m2/s) = 1.8 x 10-10 exp[-3.24(eV)/kT]

Interdiffusion gradients produced by annealing at 1100 and 1200C yielded the self-diffusion coefficients that were comparable to those obtained from gas–solid exchange, indicating that the surface exchange reaction was fast enough. The results were interpreted in terms of a defect model in which O diffusion occurred by an interstitial type of defect as a result of suppression of anion vacancy concentration by large concentrations of extrinsic cation vacancies.

Oxygen Self-Diffusion in Single-Crystal MgO - Secondary-Ion Mass Spectrometric Analysis with Comparison of Results from Gas–Solid and Solid–Solid Exchange. H.I.Yoo, B.J.Wuensch, W.T.Petuskey: Solid State Ionics, 2002, 150[3-4], 207-21