The diffusion of Fe in chromia was studied in both polycrystals, and in oxide films formed by the oxidation of Ni–30Cr alloy at 700 to 1100C at an O pressure of 10−4atm. An Fe film of about 80nm thick was deposited onto the chromia surface and, after diffusion annealing, the Fe depth profiles were determined by secondary ion mass spectrometry. Two diffusion domains appeared whatever the form of the chromia: polycrystal or film. In the first domain, effective or bulk diffusion coefficients were determined using a solution of Fick’s second law for diffusion from a thick film. For the second domain, LeClaire’s and Hart’s models permitted both the bulk diffusion coefficient and the grain-boundary diffusion parameter (αDgbδ) to be obtained. The bulk and grain-boundary Fe diffusion did not vary significantly as a function of the microstructure of the chromia (tables 2 to 5). The activation energy for grain-boundary diffusion was at least equal to, or even greater than, the activation energy for bulk diffusion. This was attributed to segregation.

Diffusion of Iron in Cr2O3 - Polycrystals and Thin Films. A.C.S.Sabioni, A.M.Huntz, F.Silva, F.Jomard: Materials Science and Engineering A, 2005, 392[1-2], 254-61