| Oxygen self diffusion coefficients were determined in single crystal (alpha)-Al(,2)O(,3) using the gas exchange technique. The samples were semi-infinite slabs cut from five different boules with varying background impurities. The diffusion direction was parallel to the c-axis. The tracer profiles were determined by two techniques, Single Spectrum Proton Activation and Secondary Ion Mass Spectrometry. The SIMS proved to be a more useful tool. The determined diffusion coefficients, which were insensitive to impurity levels and oxygen partial pressure, could be described by D = 1.51 x 10('-3) exp (-527 kJ/RT) m('2)/s. The insensitivities are discussed in terms of point defect clustering. Two independent models are consistent with the findings, the first considers the clusters as immobile point defect traps which buffer changes in the defect chemistry. The second considers clusters to be mobile and oxygen diffusion to be intrinsic behavior, the mechanism for oxygen transport involving neutral clusters of Schotlky quintuplets, (3V(,O)2V(,AI))('x).;Contamination of the near surface region of the samples was observed and attributated to the furnace tubes. Appendices discuss tracer studies of the thermal oxidation of silicon and silicon carbide. |
