Barrier and semiconducting properties of thin anodic films on chromium in an acid solution

The study of barrier and semiconducting properties of anodically formed oxide films on chromium in an acid solution was carried out using the Cr-quartz crystal electrode. The oxide film formation and growth occur through an anion vacancies transport via a low-field-assisted mechanism (H = 10⁶ V cm⁻¹). The anion diffusion coefficient, which quantitatively describes the transport of point defects within the growing film, was calculated from capacitance data using the Nernst-Planck equation for low-field limit approximation and Mott-Schottky analysis. The depletion region in the passive film, close to the film|electrolyte interface, dominates the semiconducting properties. The passive film on Cr in an acid solution behaves as an n-type semiconductor. An energy-band structure model of the passive film is given.