FTIR investigations of tungsten oxide electrochromic films derived from organically modified peroxotungstic acid precursors

Alcoholic solutions of acetylated peroxotungstic acid (APTA) and oxylated APTA (ox-APTA) precursors are used for casting films by a spin coating technique. Fourier transform infrared (diffuse reflectance mode) spectroscopy is used to investigate the linkages prevalent in the constituents of the films in the as-deposited as well as annealed states. The modes of association of peroxo and acetate/oxalate in the form of bidentate, chelating or bridging ligands is highlighted. The spectra clearly reveal the gradual decomposition of peroxo and organic ligands and also the hydrated state of film at various stages of the annealing treatment. Films based on ox-APTA precursor exhibit better electrochromic performance in contrast to films based on APTA alone. This feature of ox-APTA films which is of enormous practical importance, has been established by spectral studies, as heat-treated ox-APTA films have a microstructure which is entirely different from that of heat-treated APTA films. (C) 2001 Elsevier Science B.V. All rights reserved.