Alternative Nb2O5-TiO2 thin films for electrochromic devices

Thin films of mixed oxides of Nb2O5-TiO2 with molar ratio Nb/Ti = 3, have b een prepared by sol-gel sonocatalytic method. The precursor sols consist of a mixture of niobium salt NbCl5, titanium alkoxide Ti(OPri)(4), isopropano l and acetic acid. After addition of all components the mixture was sonicat ed. The films were deposited by dip-coating technique on ITO-Asahi Glass an d then submitted to a final heat treatment at 560 degreesC during 3 h in at mosphere of oxygen. The electrochromic properties of the films were investi gated using in situ spectroelectrochemical method. The films exhibit a blue -gray coloration under lithium ions insertion with a reversible variation o f the transmittance in the visible and near infrared range between 90% and 20%. The xerogels of Nb2O5-TiO2 also were characterized by X-ray diffractio n, thermal analysis (DTA/TGA) and IR measurements. The morphology of the fi lms was observed by scanning electron microscopy (SEM) and the topography b y atomic force microscopy (AFM). These films appear suitable for architectu ral applications, where a minimum performance in depth color is required. ( C) 2001 Kluwer Academic Publishers.