Microstructure evolution during BaTiO 3 formation by solid-state reactions on rutile single crystal surfaces

Abstract

To study the modified phase formation sequence observed during sintering of TiO 2–BaCO 3 core-shell powders, model experiments on phase formation and microstructure evolution during BaTiO 3 genesis were performed. Reaction products between BaO vapour and TiO 2 (rutile) single crystals with different orientations, obtained at different temperatures, were investigated by XRD texture analysis, HRTEM and EELS. BaTiO 3 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, BaTiO 3 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 BaTiO 3–TiO 2 interface. The pore formation is explained by an out-diffusion of titanium and oxygen ions from the BaTiO 3–TiO 2 interface through the reaction layer to the surface.