Oxygen self-diffusion in single-crystal MgO: secondary-ion mass spectrometric analysis with comparison of results from gas-solid and solid-solid exchange

摘要

Self-diffusion coefficients for O-18 in single-crystal MgO have been determined from a novel specimen comprising an epitaxial layer of high-purity (MgO)-O-18 upon a single crystal substrate of normal MgO. Heating the specimen in air produced a gas-solid exchange gradient at the sample surface as O-18 in the epitaxial layer exchanged with O-16 in air. A solid-solid interdiffusion gradient was produced between the substrate crystal and the O-18-enriched epitaxial layer. SIMS analysis of gas solid exchange gradients prepared in the temperature range 1000-1650 degreesC provided diffusion coefficients that could be described as D/(m(2)s(-1)) = (1.8(-1.1)(+2.9)) x 10(-10)exp[-(3.24+/-0.13)eV/kT]. Interdiffusion gradients produced by annealing at 1100 and 1200 degreesC yielded the self-diffusion coefficients that were comparable to those obtained from gas-solid exchange, indicating that the surface exchange reaction is fast enough. The results are interpreted in terms of a defect model in which oxygen diffusion occurs by an interstitial type of defect as a result of suppression of anion vacancy concentration by large concentrations of extrinsic cation vacancies. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 25]