The WO3 films were grown in 0.1M HClO4 aqueous solution, at different formation potentials (Ef) in the range of 2.0–7.0VSCE, on a W electrode. The anion diffusion coefficient (DO••) of WO3 films was calculated from electrochemical impedance spectra, following the surface charge approach (at high-field limit approximation), the point defect model and the Mott–Shottky analysis. Among the parameters necessary to evaluate DO••, the half-jump distance (a) was very relevant, given that a small variation in a had a great impact in the calculation of DO••. It was proposed here that the half-jump distance should be evaluated from spectroscopic data available in the literature. The value of a (≈1.9Å) was taken from the lattice constants of amorphous WO3, with various values of the coordination number, and the lattice constants of monoclinic WO3. The calculated value of DO•• was about 3 x 10−17cm2/s.

Diffusivity of Anion Vacancies in WO3 Passive Films. G.Vázquez, I.González: Electrochimica Acta, 2007, 52[24], 6771-7