Influence of the forming electrolyte on the electrical properties of tantalum and niobium oxide films: an EIS comparative study

The electrochemical oxidation of Ta and Nb and the dielectric behaviour of the oxide films thus formed were investigated in the following electrolytes: H2SO4, HNO3, H3PO4 and NaOH. Characterization of the films was carried out by means of potentiodynamic current–potential profiles (in the range 0–8V) and electrochemical impedance spectra (in the range 0.1Hz–100kHz). The a.c. response of the oxide films was modelled as a single layer structure on the basis of an equivalent circuit with constant phase elements (CPE). The dependence of the oxide resistance and oxide capacitance with potential is also reported.