Theoretical Modeling and Experimental Verification of Electrochemical Equilibria in the Ba−Ti−C−H<INF>2</INF>O System

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