Optical and Electrochemical Properties of Sol-gel Spin Coated CeO₂-TiO₂ Films

The optical and electrochemical properties of sol-gel spin coated Ce0₂-TiO₂ (50% CeO₂) films were investigated for electrochrornic applications. The coating solutions were prepared by using mixed organic-inorganic | Ti(OC₂H₅)₄ and Ce(NH₄)₂ (NO₃)₆ | precursors. X-ray diffraction studies showed the sol-gel spin-coated films were composed of an amorphous matrix of titanium oxide containing nanocrystallites of cerium oxide. The coating solar transmission value was T_s=0.8 (250 nm thick). The refractive index and the extinction coefficient were derived from transmittance measurements in the UV-VIS-NIR regions. These films had refractive index value of n=2.18 and extinction coefficient value of k=8x10^-4 at λ=550 nm. Cyclic voltametric measurements showed reversible electrochemical insertion of lithium ions in a CeO₂-TiO₂/LiClO₄-propylene carbonate electrochemical cell. During cycling the films maintain high optical transmittance. Spectrophotometric and electrochemical investigations performed on CeO₂-TiO₂ films revealed that these films are suitable as an optically passive counter-electrode in lithium electrochromic devices.