PREPARATION OF VANADIUM TITANIUM-OXIDE THIN-FILMS BY SOL-GEL METHOD AND THEIR ELECTROCHROMIC PROPERTIES

Vanadium-titanium oxide thin films were prepared by sol-gel method. Spin-coating solutions containing VO(O-i-C3H7)3 and Ti(O-i-C3H7)4 in isopropanol could be stabilized properly with the addition of acetylacetone and excess acetic acid. Electrochromic properties of the coated films were strongly dependent both on the atomic ratio of titanium and vanadium, i.e., Ti/(V+Ti) (x) in the coating solutions of alkoxides and on the calcination temperatures. In the case of calcination at 400-degrees-C, the films having x = 0-0.17 gave the two-step electrochromism, that is , blue<-- -->green<-- -->yellow, while the titanium-rich films, especially those having x=0.60-0.67, exhibited new coloration of reddish-brown at a cathodic potential of -0.8 V vs. SCE. On the other hand, the electrochromism of the films calcined at 500-degrees-C was similar to that of a pure V2O5 film. No crystalline phases but poorly crystalline TiO2 (anatase) were detected in the 400-degrees-C-calcined films having x greater-than-or-equal-to 0.60 by XRD, indicating that vanadium oxide should be amorphous. The formation of V3+ in the cathodically polarized films was observed by XPS measurement, which seems to cause the reddish-brown coloration.