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

Abstract

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(open square) = 10 Ω (open square)). They have been sintered in air between 450°C and 600°C. Their structure, morphology, electrochemical and optical properties (measured in a liquid electrolyte (1 M 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.