Dielectric bi-layer model for electrochemical impedance spectroscopy characterisation of oxide film

Abstract

In this study, the impedance response of a passive material is investigated, attributing it to a normal time constant distribution caused by resistivity variations within the passive film. Two models, namely the Power Law Model (PLM) and the recently developed Dielectric Bi-Layer Model (DBLM), are employed to express the impedance data. The PLM considers an oxide film as a single layer with a power-law distribution of resistivity, while the DBLM incorporates two distinct layers: an inner layer with constant resistivity (ρ0) and an outer layer with resistivity following Young's theory. Application of both models to 316L stainless steel immersed in a borate buffer solution exhibit that PLM and DBLM fitting results are in good agreement with experimental data. While the models differ mainly in resistivity profiles at the vicinity of the outer interface, the results suggest that deviations in regressed parameters indicate similar ranges for resistivity profiles calculated by both models. DBLM, in particular, is highlighted as promising for interpreting impedance data of passive materials due to its reliance on physical concepts.