In situ investigation of chemical reactions between BaCO₃ and anatase or rutile TiO₂

The most popular method of preparation of BaTiO₃, which is one of the most widely used ferroelectric materials for multi-layered ceramic capacitors, is the solid-state reaction process between powdered barium carbonate (BaCO₃) and titanium dioxide (TiO₂) at high temperature. The influence of the different structural forms of TiO₂ used (i.e. rutile or anatase) on the reaction process and on the crystallinity of synthesized BaTiO₃ is only known on empirical grounds. The solid-state reaction between BaCO₃ and either TiO₂ anatase or TiO₂ rutile was investigated by in situ by X-ray diffraction and micro Raman scattering measurements. The formation of both barium oxycarbonate BaO_x(CO₃)_1−x and of a very small amount of Ba₂TiO₄ were detected in the samples as intermediate phase before the formation of BaTiO₃. The Raman spectra of the final product obtained in each case is essentially the tetragonal BaTiO₃ containing small amounts of non-reacting BaCO₃ and of hexagonal barium titanate. The tetragonality of the final product was found to be slightly better for BaTiO₃ synthesized from rutile and BaCO₃ than from anatase and BaCO₃, whereas the average particle sizes are essentially the same for both products.