Phase transition in ABi4Ti4O15 (A=Ca,Sr,Ba) Aurivillius oxides prepared through a soft chemical route

A series of compounds, CaBi4Ti4O15 (CBT), SrBi4Ti4O15 (SBT), and BaBi4Ti4O(15) (BBT), belonging to the Aurivillus-type structure (four layers) has been prepared by a modified chemical route. Different oxalates were precipitated from their respective nitrate solution onto the surface of TiO2 powders. The room temperature x-ray diffraction study reveled that the compounds were having orthorhombic symmetry. Considering the tolerance factor, a significant deformation of the perovskite block is observed and that decreases with increase in ionic radius of A site atom. Temperature dependent dielectric study showed normal ferroelectric to paraelectric transition well above the room temperature except for BBT. The BBT ceramic showed a relaxorlike behavior near phase transition. The quantitative characterization and comparison of relaxor behavior were based on empirical parameters gamma and Delta T-res. The dielectric relaxation rate follows the Vogel-Fulcher relation with activation energy=0.02 eV and freezing temperature=362 degrees C. All these measurements confirmed its relaxorlike phase transition.