Alcoholysis of NbCI, in EtOH gives a viscous solution of NbCI,(OEt),-, which may be used to spin-coat optically transparent electrodes (indium tin oxide, ITO). The electrode is converted to Nb205 by immersion in 1 mol dm-3 H2S04. Electron microscopic examination of the resulting 5-10 pm thick films revealed extensive shrinkage and cracking on gel drying. These films proved to be electrochromic (A,,, ca. 800 nm) but unstable to voltammetric cycling in MeCN-(0.5 mol dm-3)LiCI04. Greater stability (>30 cycles) was achieved with a composite Nb205/ silicone electrode, prepared from a solution containing Nb : Si : H20 in the molar ratio 5 : 13 : 82. This increase in durability was achieved with no sacrifice in electrochromic efficiency. The electrochromic colouration efficiency (6 cm2 C-') compares favourably with that for sputtered Nb205 films. The colouration-bleaching cycle of the composite is complete in <40s, and the electrochromical kinetics of colouration and bleaching follow a diffusional model with DLi = 6 x lo-' cm2 s-' for Nb20, and 3.2 x lo-' cm2 s-' for the composite. The mechanism of the electrochromic response and its decay are discussed.

High‐temperature superconductors, ferroelectric materials, electrochromic films, and semiconductors are just some of the materials which can be produced from transition‐metal alkoxides using the sol–gel method. The method itself is outlined, the control of the various parameters, such as choice of precursor and medium, and stabilizing ligands, is discussed, and applications over a broad area of materials science are presented.