Diffusivity of point defects (DO) in the passive film formed on Fe in deaerated pH 8.5 buffer solution at ambient temperature was estimated by the Mott-Schottky analysis based on the Point Defect Model and surface charge approach assuming that donors are oxygen vacancies and/or iron interstitials. From the exponential decay of the concentration of donors with film formation potential, Do was calculated to be 1.69 x 10(-20) cm(2) s(-1). (c) 2005 Elsevier B.V. All rights reserved.