The self-diffusion of O was measured (using 18O and secondary ion mass spectroscopy) in monocrystals and polycrystals of -Al2O3, doped with Y2O3, at temperatures ranging from 1110 to 1630C. In the case of the monocrystals, 2 mechanisms were involved. These were a bulk diffusion mechanism and a sub-boundary one. Both mechanisms were observed at high temperatures while, at lower temperatures, bulk diffusion predominated. The lattice and sub-boundary diffusion coefficients could be described by:

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

and

D (cm2/s) = 1017exp[-977(kJ/mol)/RT]

respectively. In the case of the polycrystals, the grain boundary diffusivity could be

described by:

D (cm2/s) = 5 x 1011exp[-835(kJ/mol)/RT]

It was concluded that Y slightly increased O bulk diffusion, and decreased grain boundary diffusion.

M.Le Gall, B.Lesage, N.Brun, A.M.Huntz, M.Miloche, C.Monty: Materials Science Forum, 1993, 126-128, 411-4

Table 8

Bulk Diffusivity of O in Monocrystals of -Al2O3

(doped with 135ppm[mol] of Y2O3)