Structural and optical characterization of amorphous and crystalline evaporated WO3 layers

Amorphous and crystalline WO3 films show electrochromic properties by means of double injection of cations and electrons. At low substrate temperature thermal evaporation technique produces an amorphous material mixed to a na nocrystalline phase. When this material is annealed at temperatures higher than 400 degrees C a fully crystalline structure is obtained. Different abs orption mechanisms are responsible for colored amorphous and crystalline WO 3 layers, small polaron transitions and Drude-like free electron scattering , respectively. Furthermore, both O/W ratio and crystalline structure affec t electrochromic efficiency of a WO3 film. It has been confirmed that a hyd rogen tungsten bronze structure appears when the material is colored. Final ly, a self-bleaching process occurs when a colored WO3 film is exposed to a n oxidative environment. (C) 1999 Elsevier Science S.A. All rights reserved .