2 METHODS OF OBTAINING SOL-GEL NB2O5 THIN-FILMS FOR ELECTROCHROMIC DEVICES

Nb2O5 coatings prepared by the sol-gel route using the dip coating tec hnique with sols prepared from alkoxide or chloroalkoxide (two differe nt methods: sonocatalytic and conventional) precursors are a promising alternative for WO3 electrochromic coatings. The crystalline films (T T phase) sintered at 560 and 600 degrees C are transparent and present a deep blue colour under Li+ ion insertion. Electrochemical stability is excellent as these systems are fully reversible and stable and no change in colour, amount of charge exchanged and corrosion effect coul d be observed after 2000 voltammetry cycles between 2 and - 1.8 V vers us Ag. The electrochemical and optical properties of these coatings ha ve been determined as a function of sintering temperature. The superfi cial structure was visualized by atomic force microscopy (AFM) and sca nning electron microscopy (SEM) and the Li+ diffusion coefficient was determined for both kinds of coatings. (C) 1998 Chapman & Hall.