Nanocrystalline structure of WO3 thin films prepared by the sol-gel technique

Using high-resolution transmission electron microscopy, it was established that WO3 thin films (d = 190 nm) prepared by the sol-gel method exhibit a nanocrystalline ReO3-type structure already at curing temperatures not exceeding 180°C. Electron diffraction studies showed no additional crystalline or amorphous hydrated phases WO3·nH2O in samples obtained at this temperature. This result is important with respect to the kinetic behavior and aging properties of electrochromic devices. As detected by X-ray diffraction, a crystalline phase appeared when the thin films were heated at 325°C for 1 h. A comparison of the electron diffraction pattern of the latter with the one of the materials cured at 180°C showed growth of the crystals in size, but no changes in structure or ordering.