Electrochromism in anodic WO3 films I: Preparation and physicochemical properties of films in the virgin and coloured states
Résumé
WO3 films grown by anodic oxidation have been studied by different optical and structural techniques. Their growth kinetics have been investigated by multichannel optical analysis; a very fast initial growth step must be responsible for their particular (hexagonal) crystallographic structure. Reflection high energy electron diffraction and Raman spectroscopy allowed us to follow the structural changes related to the coloration of the oxide by different intercalated ions: H+, Na+ and above all Li+. In fact, no changes in WO3 composition (stoichiometry) or in the crystalline order can be detected: the main effect is a profound chemical perturbation of the lattice leading to the formation of W=O in place of the initial WO bonds.