Tungsten oxide is the most widely studied electrochromic (EC) oxide due to his mixed oxidation states; V₂O₅ is a good candidate to form counter electrodes in EC devices, having high ion storage capacity and providing a coloration complementary to the tungsten oxide. Nanocrystalline oxides are expected to show improved EC performances during the optical switching process. In order to develop low-cost and low-environmental impact synthesis routes, macro-porous vanadium and tungsten oxides films were produced by sol–gel method with the addition of different structure-directing agents.Micro-Raman spectroscopy was employed for the determination of the phases and XAS measurements were performed to study the local order. SEM was used to study the films morphology.A first series of samples was deposited directly on soda-lime glass substrates using polyethylenglycol (PEG) as templating agent. At low temperatures spherical shaped mesostructure (in tungsten oxide) and ribbons (in vanadium oxide) are observed. After heating, many different phases arise, due to the interaction with the soda lime substrate: together with minor stoichometric V₂O₅ and WO₃, hydrous phases and bronzes are obtained, not suitable for EC applications. The structure of the sodium vanadate Na₂V₂O₆ is refined from the EXAFS data. A second series of films was deposited on glass substrates covered with ITO (indium tin oxide) in order to avoid the diffusion of alkali ions, using four different surfactants. In the new series the heating treatments from 250 to 500 °C give pure orthorhombic V₂O₅ or monoclinic WO₃, with very good homogeneity of the films.In vanadium oxide the strong anisotropy of the crystalline network leads to unidirectional growth: nanorods and nanobelts are observed. In tungsten oxide the effect of the surfactant gives mesostructures composed by micro-sphere aggregated to give a network of filaments. All the obtained structures are well suitable for EC applications.

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1. Surfactant-based synthesis and characterization of nanostructured V₂O₅ thin films
2. Surfactant-based nanostructured tungsten oxide thin films by sol-gel