W0024

In situ X-ray Scattering Studies of the Passive Oxide Film Formed on Iron. Michael Toney, Mary P. Ryan, Lucy J. Oblonsky and Alison J. Davenport, IBM Almaden Research Center, San Jose, CA 95120 USA

The atomic structure of the passive oxide film on iron has been the subject of decades of research, but there is still little consensus on questions as basic as whether the film is amorphous or crystalline. To address these issues, we have used in situ X-ray scattering to study the passive film formed on Fe(110) and Fe(001). We find that the oxide is crystalline with a very small lateral particle size of about 5 nm. The oxide structure is similar to the spinel Fe₃O₄, but with vacancies on cation octahedral and tetrahedral sites and with cations occupying octahedral interstitial sites. The oxygen anion lattice is fully occupied. There is also a high concentration of anti-phase boundaries and stacking faults. This new structural information has implications for the interpretation of the semiconducting properties of these films, and understanding their susceptibility to dissolution, and hence corrosion of iron.