Influence of stoichiometry on electrochromic cerium-titanium oxide compounds

CeO2-TiO2 finds use as passive counter-electrode in electrochromic devices. Thin films were produced by de-sputtering in a wide range of compositions. Influence of total pressure and oxygen partial pressure on the optical constants of TiO2 was investigated. Slightly substoichiometric TiO2 films exhibit a red-shift of the bandgap. The TiO2 content in the compound essentially determines the degree of cathodical coloring upon Li+ intercalation [1] [von Rottkay, K., Richardson, T., Rubin, M., Slack, I., Masetti, E., Dautzenberg, G., 1997. SPIE Proceedings 3138 9]. However, pure TiO2 films with comparable visible transmittance in the clear state behave differently during electrochemical cycling depending on oxygen stoichiometry. Films that are deposited at higher total pressure are more oxygen rich and require initial formatting until current voltage cycles become stable. CeO2-TiO2 films of intermediate compositions have the relatively highest charge capacity. Comparison with atomic force microscopy indicates a correlation of small grain size with high charge capacity. (C) 1998 Published by Elsevier Science B.V. All rights reserved.