CHROMIC MECHANISM IN AMORPHOUS WO3 FILMS

We propose a new model for the chromic mechanism in amorphous tungsten oxide films (WO3-y. nH(2)O). This model not only explains a variety o f seemingly conflicting experimental results reported in the literatur e that cannot be explained by existing models, it also has practical i mplications with respect to improving the coloring efficiency and dura bility of electrochromic devices. According to this model, a typical a s-deposited tungsten oxide film has tungsten mainly in W6+ and W4+ sta tes and can be represented as W1-y6+Wy4+O3-y. nH(2)O. The proposed chr omic mechanism is based on the small polaron transition between the ch arge-induced W5+ state and the original W4+ state instead of the W5+ a nd W6+ states as suggested in previous models. The correlation between the electrochromic and photochromic behavior in amorphous tungsten ox ide films is also discussed.