Color impedance and electrochemical impedance studies of WO3 thin films: Behavior of thinner films in non-aqueous electrolyte

The electrochemical and color impedance behavior of thin (0.25 mu m) amorphous WO3 films was examined. In general, the two types of behavior match rather well over most of the frequency range, but deviations were observed at high and low frequencies. The high frequency deviation involved a phase shift of greater than 90 degrees due to a non-faradaic capacitance, which most likely involves either ClO4- insertion or an ion exchange process in which Li+ adsorbs on the surface of the film and displaces protons, which then jump into lattice sires associated with coloring. The low frequency deviation probably involves a similar but much slower ion exchange process involving the bulk of the amorphous WO, structure. (C) 1997 Elsevier Science S.A.