Tailoring the Shape, Size, Crystal Structure, and Preferential Growth Orientation of BaTiO3 Plates Synthesized through a Topochemical Conversion Process

The conditions for the topochemical transformation of variously sized Bi4Ti3O12 template plates into BaTiO3 particles were studied in order to control their morphology, crystal structure, and preferential orientation. In the transformation from sub-200 nm- and μm-sized template plates in the presence of surplus BaCO3 (Bi4Ti3O12/BaCO3 = 1:10), the final BaTiO3 particles retained a memory of the precursor size when the conversion reaction in the molten salt (NaCl/KCl) occurred at 660 and 900 °C, respectively. In both cases the side length of the template was well preserved, while the thicknesses of the final BaTiO3 plates were larger compared to those of the templates. The morphology of the BaTiO3 particles formed from micrometer-sized Bi4Ti3O12 plates at 660 °C did not closely resemble the template shape because of the exfoliation and disintegration processes. Through the transformation of sub-200 nm Bi4Ti3O12 plates at 900 °C the formed BaTiO3 particles grew by Ostwald ripening, and thus also the shape of the final perovskite particles did not retain a memory of the template. We confirmed by Raman spectroscopy and X-ray diffraction that the BaTiO3 plates formed at 900 °C exhibited a higher tetragonality than those prepared at 660 °C. Ferroelectric hysteresis and piezoelectric butterfly curves, as obtained using a piezo-force microscope, indicated the significant ferroelectric response of [001] preferentially oriented micrometer-sized and sub-micrometer-sized BaTiO3 plates.