Self-diffusion was studied, at 1460 to 1720C, in polycrystalline samples of the -phase which were undoped, or doped with 225ppm[mol] of yttria. This was done by using secondary-ion mass spectrometry and 18O2. It was found that the O grain-boundary diffusivity obeyed:

D(cm2/s) = 1.6 x 1016exp[-219(kcal/mol)/RT]

in the case of undoped samples, and:

D(cm2/s) = 7.0 x 1010exp[-191(kcal/mol)/RT]

in the case of yttrium-doped samples. A comparison of the results suggested that yttrium additions decreased the O grain-boundary diffusivity.

D.Prot, M.Le Gall, B.Lesage, A.M.Huntz, C.Monty: Philosophical Magazine A, 1996, 73[4], 935-49