Self-diffusion in α‒Al2O3. II. Oxygen diffusion in ‘undoped’ single crystals

Oxygen self-diffusion in ‘undoped’ (i.e. unintentionally doped) alumina (Al2O3) single crystals was investigated using the gas-solid isotope exchange technique. After diffusion annealing, profiles of 18O were determined by secondary ion mass spectrometry. These showed two parts: close to the initial surface, the first part was attributed to bulk self-diffusion, while the diffusion tails were attributed to diffusion in dislocation walls. In the temperature range 1500–1720°C the bulk self-diffusion coefficients of the oxygen in Al2O3 are represented by: Do(cm2s−1) = 206 exp[-(636 kJ mol−1)/RT]. Possible diffusion mechanisms are proposed considering an extrinsic behaviour associated with silicon contamination. In the same temperature range, the oxygen diffusion coefficients in the Al2O3 subboundaries are described by: D″o(cm2 s−1) = 3.1 × 1014exp[-(896 kJ mol−1)/RT]. The high activation enthalpy observed is attributed to segregation effects on subboundaries.