The self-diffusion of O in undoped alumina monocrystals was investigated by using the gas-solid isotope exchange technique. After diffusion annealing, the profiles of 18O were determined by means of secondary ion mass spectrometry. This revealed 2 parts, in which the behavior close to the initial surface was attributed to bulk self-diffusion while the diffusion tails were attributed to migration in dislocation walls. At temperatures ranging from 1500 to 1720C (table 44), the bulk self-diffusivity of O could be described by:

D(cm2/s) = 2.06 x 102exp[-636(kJ/mol)/RT]

Possible diffusion mechanisms were proposed in terms of an extrinsic behavior that was associated with Si contamination. Within the same temperature range, the O diffusivity in sub-boundaries could be described by:

D(cm2/s) = 3.1 x 1014exp[-896(kJ/mol)/RT]

The high activation enthalpy was attributed to segregation effects at sub-boundaries.

Self-Diffusion in α-Al2O3 II. Oxygen Diffusion in ‘Undoped’ Single Crystals. D.Prot, C.Monty: Philosophical Magazine A, 1996, 73[4], 899-917

Table 44

Bulk Diffusivity of O in Undoped -Al2O3