<title>Preparation and optical properties of sol-gel-deposited electrochromic iron oxide films</title>

Abstract

The preparation and optical properties of sol-gel deposited iron oxide films are investigated in this study. The films are deposited on glass by spin-coating from polymeric sol-gel solutions. The coating solutions were prepared from Fe(OCH₃H₇)₃ and isopropanol. Fe₂O₃ films were obtained at a firing temperature 180 degrees Celsius. The films were characterized by x-ray diffractometry (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and UV-Vis spectroscopy. The electrochemical properties of the films were studied in 0.5 M LiClO₄/propylene carbonate (PC) solution. The CV results showed reversibility of the Li⁺/e^- insertion/extraction process in the Fe₂O₃ films up to 200 cycles. Reduction and oxidation of the amorphous films in 0.5 M LiClO₄-PC solution caused noticeable changes in optical absorption. XRD of the films showed that they had an amorphous structure. Fourier transform infrared spectroscopy (FTIR) measurements showed that the composition of the film is Fe₂O₃. In-situ spectrophotometric measurements indicated that these films show weak electrochromism in the spectral range of 350 - 800 nm. The optical band gap is estimated to be 1.92 eV for the amorphous film. The spectroelectrochemical properties clearly indicated that cyclic stability of the iron oxide films deteriorated above 200 cycles.