Modification of growth parameters of Ti anodic films by fluoride ion insertion

The potentiostatic growth of Ti anodic films formed in 0.1 M HClO ₄/xM HF (0.05 M≤x≤0.50 M) media was studied by electrochemical impedance spectroscopy, EIS. The obtained EIS spectra were analyzed by using the surface charge approach model, which showed oxide growth parameters being modified as the HF concentration increased. While the electric field through the film decreased, oxide growth rate and atomic half jump distance increased, evidencing that fluoride ions are inserted into the oxide through oxygen vacancies, thereby modifying the lattice structure and electric properties of the oxide. Additionally, the experimental data obtained for the pseudocapacitance C ₀, appearing at low-frequency domain, allowed the interpretation commonly given for this element (modulation of film thickness) to be discarded; instead, the F ^- ion diffusion coefficient was estimated, casting with variation of electric properties with HF concentration and E _F.