Electrochromic properties of Nb2O5 and Nb2O5:X sol-gel coatings (X = Sn, Zr, Li, Ti, Mo)

Two-layer coatings of Nb2O5 and niobia doped with tin (up to 15 at %), zirconium (up to 15 at %), lithium (up to 15 at %), titanium (up to 30 at %) and molybdenum (up to 30 at %) have been prepared by the sol-gel process and deposited by dip-coating on conductive ITO coated glass (R-square = 10 Omega(square)). They have been sintered in air between 450 degrees C and 600 degrees C. Their structure, morphology, electrochemical and optical properties (measured in a liquid electrolyte (1M LiClO4 in PC)) are reported. All systems exhibit electrochromic properties. Those are essentially determined by the structure and the morphology of the layers which can be changed in a controlled manner by the amount of doping and the sintering temperature. After Li+-insertion all amorphous coatings present a brown color, a blue one when the structure is hexagonal and a gray one when the structure is orthorhombic (pure, titanium or molybdenum doped niobia) or monoclinic (Li-doped niobia). Samples with two different structures color either blue or gray.