Electrochemical, hydrothermal, and electrochemical-hydrothermal synthesis of barium titanate thin films on titanium substrates

Well-crystallized polycrystalline films of cubic BaTiO₃ have been synthesized on Ti metal substrates by electrochemical, hydrothermal, and electrochemical-hydrothermal reaction of a Ti metal with a saturated solution of Ba(OH)₂ in the temperature range 80 °C−200 °C. The films can be produced in the electrochemical process by the anodization of a Ti substrate in Ba(OH)₂ solution at pH = 13 and current densities of the order of 10–50 mA/cm². The films can also be synthesized by the hydrothermal reaction of Ba(OH)₂ and a Ti substrate without electrical bias. A combination of these two techniques reduces the reaction time to 30–45 min. The films were found to have good adherence on the substrate and films of thickness up to 2 μm could be formed within a reaction time of 45 min. Capacitance measurements have yielded a dielectric constant of 300. The films prepared by the three different techniques have been compared for crystallinity and microstructure. The thickness of the films increased with temperature and time of reaction. The crystallinity decreased with extended time of reaction for a given temperature. It is likely that a reactive intermediate such as Ti(OH)₄ (aq.) is formed in all the three cases which leads to the formation of crystalline BaTiO₃.