Nickel oxide-based thin films were deposited onto ITO-coated glass substrates by chemical bath deposition using an aqueous solution of nickel nitrate and urea. The as-deposited precursor films, identified as the turbostratic alpha-Ni(OH)(2) phase. were transformed into hydrated NiO after annealing in air at 300 degrees C. The electrochromic behavior of the annealed films was tested by cyclic voltammetry, chronoamperometry and single wavelength transmittance. Ex situ transmittance spectra showed high optical contrast between colored and bleached states. Structural transformations were studied by Raman and infrared reflectance spectroscopy, and showed that the colored phase is Ni2O3 center dot xH(2)O. (C) 2008 Elsevier B.V. All rights reserved.