Sol-gel derived tungsten oxide based electrochromic coatings

Işık, Dilek
The microstructural, electrochemical and optical properties of sol-gel derived tungsten oxide electrochromic coatings have been investigated. Coatings were formed by spinning of tungsten metal based aqueous sol on glass with native ITO layer. Three sol formulations; acetylated peroxotungstic acid (APTA), peroxotungstic acid (PTA) and titanium-doped peroxotungstic acid (Ti-PTA) were employed to obtain 200-300 nm thick multi-layered coatings. Material and electrochromic characterization of the coatings have been performed by DSC, XRD, SEM, cyclic voltammetry and UV-Vis spectroscopy. The electrochromic performance of the WO3 coatings was influenced by calcination temperature, by sol chemistry and by the adsorbed water content. For all sol formulations the coatings calcined at 250 °C were amorphous and have shown better performance compared to crystalline counterparts calcined at 400 °C. High calcination temperature also leads to formation of WO3 nanocrystals for APTA and PTA derived coatings, titanium doping retards crystallization. Presence of acetic acid as in APTA sol improved the electrochromic and electrochemical performance. This was related to removal of organics- acetic acid and peroxo ligands- during calcination, which results in an open W-O network providing more ion insertion sites. The water adsorption affected the electrochromic performance in different ways for the coatings calcined at 250 °C and 400 ºC. The amorphous coatings with limited structural water removal and excessive hydroxyl groups tend to crystallize by condensation of W-OH groups upon storage in open atmosphere, therefore exhibiting degrading electrochromic activity with aging. Conversely, hydroxyl groups enhanced Li+ ion insertion for the stable crystalline coatings calcined at 400 °C.


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This thesis aims to examine the possibility of using Magnetic Barkhausen Noise technique in characterizing the ferritic-martensitic microstructure of hypoeutectoid steels quenched from the intercritical temperature range. For this purpose, rectangular specimens were prepared from SAE 1020, 1040 and 1060 steels. The specimens were heated at different temperatures within the intercritical temperature range and then quenched into water. Microstructures of the specimens were characterized by metallographic exam...
Citation Formats
D. Işık, “Sol-gel derived tungsten oxide based electrochromic coatings,” M.S. - Master of Science, Middle East Technical University, 2008.