Structures and Role of the Intermediate Phases on the Crystallization of BaTiO₃ from an Aqueous Synthesis Route

Carbonate formation is a prevailing challenge in synthesis of BaTiO₃, especially through wet chemical synthesis routes. In this work, we report the phase evolution during thermal annealing of an aqueous BaTiO₃ precursor solution, with a particular focus on the structures and role of intermediate phases forming prior to BaTiO₃ nucleation. In situ infrared spectroscopy, in situ X-ray total scattering, and transmission electron microscopy were used to reveal the decomposition, pyrolysis, and crystallization reactions occurring during thermal processing. Our results show that the intermediate phases consist of nanosized calcite-like BaCO₃ and BaTi₄O₉ phases and that the intimate mixing of these along with their metastability ensures complete decomposition to form BaTiO₃ above 600 °C. We demonstrate that the stability of the intermediate phases is dependent on the processing atmosphere, where especially enhanced CO₂ levels is detrimental for the formation of phase pure BaTiO₃.