Influence of amorphicity on properties of Ce-Ti mixed oxide films for electrochromic devices

Abstract

Alcohol based sols of cerium chloride and titanium propoxide mixed in 1:1 and 1:3 mole ratios have yielded mixed oxide films with excellent chemical as well as mechanical stability on densification at 500ºC. The 1:1 films are more transparent due to their highly porous structure. Electrochemical studies have revealed the significant role of TiO₂ in controlling the ion storage capacity of the films, as it induces amorphicity in them. Although both the films are found to be amorphous to X-rays, the 1:1 composition however, is characterized by the presence of CeO₂ nanocrystallites of about 5 nm dimension. XPS studies have shown the presence of both Ce³⁺ and Ce⁴⁺ states in the films. Scanning electron microscopic study has shown the presence of CeO₂ and TiO₂ agglomerates respectively in the 1:1 and 1:3 films. The faster coloration-bleaching kinetics for the primary electrochromic electrode working in combination with Ce/Ti (1:1) electrode indicates the better utility of the latter in electrochromic windows. Appreciable optical modulation of the electrochromic devices comprising both the Ce/Ti compositions of the counter electrodes over the visible spectral region displays their potential as the ion storage layer for the electrochromic windows.