SPECTROELECTROCHEMICAL AND STRUCTURAL-PROPERTIES OF ELECTROCHROMIC CO(AL)-OXIDE AND CO(AL,SI)-OXIDE FILMS PREPARED BY THE SOL-GEL ROUTE

New electrochromic spinel-type Co(Al)-oxide and Co(Al,Si)-oxide films exhibiting coloring/bleaching changes Delta T=T-colored-T-bleached =75 %-25%=50% (where T is transmittance) with a coloring efficiency of 22c m(2) C-1 were deposited by a dip-coating method from aqueous colloidal solutions made by thermal hydrolysis of Co(II)-acetate, Al(III)-sulph ate, citric acid and 3-aminopropyltriethoxysilane precursors. The nano composite spinel structure of the films and powders was determined usi ng X-ray diffraction, thermogravimetry, visible and infrared transmiss ion and reflection-absorption spectroscopy performed at near-grazing i ncidence angle conditions (80 degrees) using p-polarized light The exi stence of spinel lattice modes in the IR spectra of cycled films prove d that the spinel structure of Co(Al,Si)-oxide films is preserved at l east on the scale of short-range interactions detected with IR spectro scopy, In addition to this, sulphate (SO42-) ions are retained in the structure of cycled films heat-treated at 500 degrees C. The role of o rder-disorder transitions of sulphate ions present in cycled films is discussed with respect to their influence in enhancing the speed and d egree of coloring/bleaching changes of electrochromic Co(Al,Si)-oxide spinel films.