Tungsten films on ITO glass were anodized into a porous amorphous WO3 film morphology at 60 V. The follow-up acidic treatment of the anodized WO3 films in H2SO4 solution transformed the morphology into plate-like WO3 center dot 2H(2)O. Glancing incident X-ray diffraction and Raman scattering spectra indicated that the growth of plate-like WO3 center dot 2H(2)O films was caused by a dissolution-precipitation reaction in H2SO4 solution. The plate-like WO3 center dot 2H(2)O transformed into monoclinic WO3 by dehydration at 400 degrees C, and it collapsed into a dense particle-like one at 500 degrees C due to the strain of dehydration. Due to its highly porous plate-like morphology, the 400 degrees C-annealed WO3 film has the highest optical modulation of 52% and coloration efficiency of 71 cm(2)/C at 633 nm. (C) 2013 Elsevier Ltd. All rights reserved.