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

Vanadium-titanium oxide thin films were prepared by sol-gel method. Sp in-coating solutions containing VO(O-i-C3H7)3 and Ti(O-i-C3H7)4 in iso propanol could be stabilized properly with the addition of acetylaceto ne and excess acetic acid. Electrochromic properties of the coated fil ms were strongly dependent both on the atomic ratio of titanium and va nadium, i.e., Ti/(V+Ti) (x) in the coating solutions of alkoxides and on the calcination temperatures. In the case of calcination at 400-deg rees-C, the films having x = 0-0.17 gave the two-step electrochromism, that is , blue<-- -->green<-- -->yellow, while the titanium-rich film s, especially those having x=0.60-0.67, exhibited new coloration of re ddish-brown at a cathodic potential of -0.8 V vs. SCE. On the other ha nd, the electrochromism of the films calcined at 500-degrees-C was sim ilar to that of a pure V2O5 film. No crystalline phases but poorly cry stalline TiO2 (anatase) were detected in the 400-degrees-C-calcined fi lms having x greater-than-or-equal-to 0.60 by XRD, indicating that van adium oxide should be amorphous. The formation of V3+ in the cathodica lly polarized films was observed by XPS measurement, which seems to ca use the reddish-brown coloration.