Preparation of WO₃-MoO₃ Mixed Thin Films by the Sol-Gel Method and Its Electrochromic Properties

Abstract

Mixed oxide films of WO₃-MoO₃ with an electrochromic property have been cathodically deposited onto an electroconductive glass (NESA) from a colloidal solution of tungstic and molybdic acid mixture. The colloidal tungstic and molybdic acid solution was prepared as follows: at first a mixture of sodium tungstate and molybdate solution was filtered off through a cation-exchanger colunm. Then the isolated acid mixture was kept at a constant temperature for more than 70h to promote the polymerization of the acid mixture for aging.
As the aging of the solution proceeded, the specific conductivity of the solutio n decreased and attained a constant value.
The absorption spectrum of the deposited mixed oxide film showed a peak shift of the absorption maximum toward a shorter wavelength than that of the pure tungsten trioxide film, as was already reported by Shirmer et al. or by Faughnan et al. In the present experiment, the largest peak shift of this absorption spectrum was observed for the 7 : 3 mixture of WO₃ and MoO₃.
The molar ratio of WO₃, to MoO₃ in the deposited film was almost proportional to that of the electrolytic solution.