Electronic properties of passive films from the multi-frequency Mott–Schottky and power-law coupled approach

• Semi-conductive properties of passive films of pure chromium grown under potentiostatic conditions in acidic sulfate solution.
• Determination of the space charge capacitance by using the power-law model
• Mott-Schottky theory used to estimate the electronic properties from point defect model.

The electronic properties of the passive film formed on pure chromium in an acidic sulfate medium at 30 °C was studied by using the multi-frequency Mott–Schottky approach and the point defect model. Conversely to common Mott–Schottky experiments, the relevance of the multi-frequency Mott–Schottky analysis relies on the determination of the space charge capacitance from a large frequency range impedance diagram. To analyze the Constant-Phase-Element behavior commonly observed for the impedance diagrams which characterize the passive film, the power-law model was used and allowed to determine the space charge capacitance. The consistency of the results showed that it was relevant to combine the power-law model to the predictive point defect model. The aim of this study is to extract the semi-conductive parameters of a passive film from impedance measurements using a sensitive analytical method.