Microstructure evolution during BaTiO3 formation by solid-state reactions on rutile single crystal surfaces

To study the modified phase formation sequence observed during sintering of TiO2–BaCO3 core-shell powders, model experiments on phase formation and microstructure evolution during BaTiO3 genesis were performed. Reaction products between BaO vapour and TiO2 (rutile) single crystals with different orientations, obtained at different temperatures, were investigated by XRD texture analysis, HRTEM and EELS. BaTiO3 was found in reactions performed at temperatures between 700 and 900 °C. Using Pt markers, in-diffusion of Ba ions was detected at 800 and 850 °C. Ti-rich phases were found after the reaction at 850 °C. At 900 °C, BaTiO3 forms at the surface of the reaction layer with a well-defined orientation to the rutile substrate. In addition, pores and Ti-rich phases were identified at the BaTiO3–TiO2 interface. The pore formation is explained by an out-diffusion of titanium and oxygen ions from the BaTiO3–TiO2 interface through the reaction layer to the surface.