Atomic Structure of the Passive Oxide Film Formed on Iron

We have used x-ray scattering to measure the structure of the passive oxide film formed at high anodic potentials on Fe(110) and Fe(001). The crystalline film has a small crystallite size ({approx}50 {Angstrom}) and is oriented with the substrate. The film structure is based on Fe{sub 3}O{sub 4}, but with cation vacancies on octahedral and tetrahedral sites (80{percent} and 66{percent} occupancies, respectively) and with cations occupying octahedral interstitial sites (12{percent} occupancy). These results resolve the long-standing controversy surrounding the film structure and provide a basis for understanding and modeling film properties important for corrosion resistance. {copyright} {ital 1997 } {ital The American Physical Society}