Abstract
Electrochromic cobalt oxide thin films were prepared by chemical vapor deposition. The source material was cobalt(II) acetylacetonate. Tricobalto tetraoxide 
thin films were obtained at a substrate temperature 250°C. Oxidation and reduction of the films in a 0.1 M KOH solution resulted in changes in optical absorption. The transmittance of the reduced film was higher and that of the oxidized film was lower than that of the as‐deposited 
film. The infrared reflection‐absorption spectra showed that the structural changes were attributable to the Co(III)/Co(II) redox process in a hydrated 
. Coulometry indicated that the coloration efficiency was 
.