Diffusion of 51Cr Tracer in Cr2O3 and the Growth of Cr2O3 Films
The tracer self diffusion coefficient of Cr in Cr2O3 single crystals has been measured at temperatures of 1100 and 1300°C and for oxygen activities ranging from the Cr/Cr2O3 equilibrium to air. The dependence of D*(Cr) on a(O2) is consistent with diffusion by vacancies at high a(O2) and by interstitials at low a(O2). The activation energy of D*(Cr) in the vacancy region at constant a(O2) is 6.0 eV.
All the tracer penetration profiles show a strong contribution from diffusion along dislocations, probably in the form of low angle boundaries. The effective radius of the dislocation is determined to be ~ 0.4 nm and the dependence of the dislocation diffusion coefficient on a(O2) is similar to that observed for lattice diffusion which suggests that similar defects are involved. The present lattice diffusion coefficients are several orders of magnitude smaller than those of earlier studies which suggests that the earlier measurements were mainly controlled by short-circuit diffusion.
The lattice diffusion coefficients are far too low to account for the rate of oxidation of Cr and it is concluded that grain boundary diffusion must be responsible for Cr2O3 film growth.
KeywordsOxygen Activity Lattice Diffusion Diffusion Data Tracer Diffusion Diffusion Anneal
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- 1.P. Kofstad, “Nonstoichiometry Diffusion and Electrical Conductivity in Binary Metal Oxides”, ( Wiley, New York ) (1972).Google Scholar
- 9.F.A. Kröger in: “High Temperature Corrosion”, Ed. R.A. Rapp, (NACE 6, Houston), p. 89 (1983).Google Scholar
- 10.C. Greskovitch, to be published.Google Scholar
- 12.R. Dieckmann and H. Schmalzried, Ber. Bunsenges. Phys. Chem., 81:414 (1977).Google Scholar
- 13.C. Wagner, Z. Phvs. Chem., B21:25 (1933).Google Scholar