<title>Electrochromism of dip-coated Fe-oxide, Fe/Ti-oxide and Fe/Si-oxide films prepared by the sol-gel route</title>

Abstract

Iron oxide films which were synthesized via the sol-gel route from the iron (III) chloride precursor exhibit electrochromism (T<SUB>b</SUB> - T<SUB>c</SUB> equals 55% at 400 nm) in LiOH (0.01 M) electrolyte. The structure of the XRD amorphous films was identified with the help of near- normal reflection absorption (6 degree(s)) (IRRA) and near-grazing incidence angle (NGIA) FT-IR spectroscopy to correspond to the nano-crystalline (gamma) -Fe<SUB>2</SUB>O<SUB>3</SUB>. Ex-situ NGIA FT-IR spectra of bleached and re-colored films were measured and it was found that the Fe-oxide films irreversibly change to the new phase in which `amorphous iron oxide' is admixed with the characteristic LO mode at 545 cm<SUP>-1</SUP>. Electrochemical stability of the Fe-oxide film was modified by admixing other non-absorbing Ti and Si-oxides. The structure of the mixed oxide films was identified from the corresponding IR spectra and was described as translatory disordered solid solution in which the phonon modes exhibit one mode (Fe/Ti-oxide) and two-mode (Fe/Si-oxide) behavior. Electrochemical investigations revealed that the films are able to uptake reversibly Li<SUP>+</SUP>, Na<SUP>+</SUP>, K<SUP>+</SUP> ions with Q/d values in the range 0.1 - 0.31 mQ/cm<SUP>2</SUP>nm. The electrochromic properties of the films investigated were established from the measured in-situ UV-VIS spectroelectrochemical measurements which revealed that the electrochromic efficiencies ((Delta) OD/Q<SUB>(de</SUB>int)) are in the range of 6 - 14 cm<SUP>2</SUP>/C. The nature of the electrochromic process is discussed and correlated to the absorption edges of the various iron oxygenated compounds.