Theoretical Modeling and Experimental Verification of Electrochemical Equilibria in the Ba−Ti−C−H2O System

The thermodynamic principles controlling the electrochemical synthesis of barium titanate (BaTiO 3 ) films are discussed and explored. a variety of E h −pH diagrams were generated for the Ba−Ti−C−H 2 O system as a function of temperature and whether CO 2 was in the system. Barium titanate is predicted to form at 25 °C and higher temperatures under alkaline conditions. It is demosnstrated that the phase field for BaTiO 3 enlarges as a function of pH with increasing temperature in the absence of CO 2 . The role of CO 2, although still important in controlling the phase stability of BaTiO 3 via the formation of BaCO 3, becomes less important under solution pH conditions greater than pH ∼13 and temperatures greater than 100 °C. The theoretical E h −pH predictions compare favorably with experimentally determined regimes, where BaTiO 3 and films in the Ba−Ti−C−H 2 O system form through electrochemical reactions.