Self-diffusion in α‒Al2O3. III. Oxygen diffusion in single crystals doped with Y2O3

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Abstract
Oxygen self-diffusion has been measured in single crystals of α-alumina (α‒Al2O3) doped with yttria (Y2O3) in the temperature range 1110–1630°C, using 18O2 and secondary-ion mass spectrometry. Two diffusion mechanisms are involved a bulk diffusion mechanism and a subboundary mechanism. At high temperatures, both these two mechanisms are observed while, at lower temperatures, only bulk diffusion is observed. Bulk and subboundary diffusion coefficients obey the equations D′o (cm2s−1) = 67exp[-590(kJ mol−1)/RT] and D′o (cm2 s−1) = 1017exp [-980(kJmol−1)/RT] respectively. On comparison with results obtained for ‘undoped’ α‒Al2O3 single crystals produced from the same powder, it appears that yttrium slightly enhances oxygen bulk and subboundary diffusion. An extrinsic diffusion mechanism by oxygen interstitials or by defect complexes can explain these results in the bulk of ‘undoped’ Al2O3, and the enhancement of D o in α‒Al2O3: Y2O3 is due to the donor effect of yttrium which slightly increases the defect concentration. In subboundaries this phenomenon is attributed to an enhancement of the dislocation density in the dislocation walls which results from the doping and the method of crystal production.

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