Room-temperature synthesis of crystalline barium titanate thin films by high-concentration sol–gel method

We have succeeded in single-step synthesis of polycrystalline BaTiO3 thin film on glass substrate with the thickness of 500 nm at 50°C by newly established sol–gel method starting from high-concentration Ba- and Ti-alkoxide precursor solutions. The film was in good quality with a crack-free, smooth surface. The key process of crystallization of BaTiO3 at low temperature was the aging of gel film in a mist of water and alcohol in a sealed cell. The water mist may slow hydrolysis and the alcohol mist may stabilize the reactive Ti-alkoxide to associate the reaction rate with that of Ba-alkoxide. Both effects may lead the alkoxides to crystallize into BaTiO3 perovskite instead of being hydrolyzed separately. The dried and fired films showed optical transmission spectra in the wavelength range of 350–2600 nm with sharp absorption edge at 350 nm and the refractive index n=2.0 in the visible light region was estimated from the interference fringes.