Additive-free alkoxide–water–alcohol solutions as precursors for crystalline titania thin films

When titanium alkoxides are hydrolyzed for preparing coating solutions for titania thin film deposition, chelating and peptizing agents such as acetylacetone and hydrochloric acid, respectively, are employed in order to suppress the formation of precipitates and obtain homogeneous sols. The present work demonstrates that precipitation can be avoided when 2-methoxyethanol is used as solvent for hydrolyzing titanium isopropoxide even without using chelating or peptizing agents. A sol obtained from a simple solution of molar compositions, Ti(OC₃H₇ⁱ)₄:H₂O:CH₃OC₂H₄OH = 1:1:25, was demonstrated to be stable in viscosity at least for >1 month. The stability and long pot life of the sol were evidenced in the identical characters including thickness, crystallite size and refractive index and the similar microstructure of the films prepared from the sols aged for 1 and 30 days at room temperature. The formation of homogeneous sol and its long-period stability were thought to result from chelation of the titanium atoms by 2-methoxyethanol molecules.