Self-diffusion was measured in single crystals of -phase yttria-doped material, at temperatures ranging from 1110 to 1630C, using 18O2 and secondary ion mass spectrometry. It was found that the diffusion involved a bulk mechanism and a sub-boundary mechanism. At high temperatures, both of these were observed while, at lower temperatures, only bulk diffusion was observed. It was shown that the bulk and sub-boundary diffusion data (tables 3 and 4) could be described by:

D(cm2/s) = 67 exp[-590(kJ/mol)/RT]

and

D(cm2/s) = 1017exp[-980(kJ/mol)/RT]

respectively. Upon comparing these results with those obtained using undoped samples that had been prepared from the same powder, it was deduced that Y slightly enhanced the bulk and sub-boundary O diffusivities. It was concluded that an extrinsic diffusion mechanism which involved O interstitials or defect complexes could explain the results for bulk undoped material, while the diffusion enhancement in doped material was attributed to the donor effect of Y. The latter slightly increased the defect concentration. In the case of sub-boundaries, this was attributed to an enhancement of the dislocation density in dislocation walls. This, in turn, arose from the doping and processing method.

M.Le Gall, A.M.Huntz, B.Lesage, C.Monty: Philosophical Magazine A, 1996, 73[4], 919-34

Table 3

Bulk Diffusivity of O in Monocrystals of -Al2O3

(doped with 135ppm[mol] of Y2O3)

Table 4

Diffusivity of O in Sub-Boundaries of -Al2O3

(doped with 135ppm[mol] of Y2O3)