Optical, Structural and Electrochemical Properties of CeO$_2$--Al$_2$O$_3$--SiO$_2$ Thin Films

CeO$_2$ thin films can be used as counter-electrodes in electrochromic devices, but have the disadvantage of slow reaction kinetics. Thus research has shifted to composite CeO$_2$ films as more promising ion-storage candidates. In this work, we examine the sol-gel coating and characterization of CeO$_2$--Al$_2$O$_3$--SiO$_2$ transparent thin films deposited onto glass microslides and indium-tin-oxide-coated conducting glass. We investigate the evolution of the surface morphology, and the optical, structural and electrochemical properties of the films with varying Si-Al-Ce mol ratios. In particular we find the formation of novel complex phase-segregated structures at the surface, which have the potential for enhancing Li ion insertion/extraction.