Preparation of meta-stable phases of barium titanate by Sol-hydrothermal method

Two low-cost chemical methods of sol-gel and the hydrothermal process have been strategically combined to fabricate barium titanate (BaTiO₃) nanopowders. This method was tested for various synthesis temperatures (100°C to 250°C) employing barium dichloride (BaCl₂) and titanium tetrachloride (TiCl₄) as precursors and sodium hydroxide (NaOH) as mineralizer for synthesis of BaTiO₃ nanopowders. The as-prepared BaTiO₃ powders were investigated for structural characteristics using x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The overall analysis indicates that the hydrothermal conditions create a gentle environment to promote the formation of crystalline phase directly from amorphous phase at the very low processing temperatures investigated. XRD analysis showed phase transitions from cubic - tetragonal - orthorhombic - rhombohedral with increasing synthesis temperature and calculated grain sizes were 34-38 nm (using the Scherrer formula). SEM and TEM analysis verified that the BaTiO₃ nanopowders synthesized by this method were spherical in shape and about 114-170 nm in size. The particle distribution in both SEM and TEM shows that as the reaction temperature increases from 100°C to 250°C, the particles agglomerate. Selective area electron diffraction (SAED) shows that the particles are crystalline in nature. The study shows that choosing suitable precursor and optimizing pressure and temperature; different meta-stable (ferroelectric) phases of undoped BaTiO₃ nanopowders can be stabilized by the sol-hydrothermal method.