Influence of reaction-medium pH on phase evolution, microstructure, and dielectric properties of BaTiO₃ synthesized by a sonochemically activated solid-state route

Controlling phase evolution during solid-state synthesis is essential for optimizing the dielectric performance of BaTiO₃ ceramics; however, the influence of the reaction-medium pH under sonochemically activated conditions remains poorly understood. This study systematically investigates the role of pH in governing the processing–structure–property relationship of BaTiO₃ synthesized via a sonochemically activated solid-state route. Thermal analysis and the observed phase evolution are consistent with enhanced precursor reactivity that may be facilitated by sonochemical activation. Quantitative Rietveld refinement revealed that mildly acidic to near-neutral conditions (pH 5–6) favor the formation of tetragonal BaTiO₃, reaching a maximum phase fraction of 92.9%, while refined c/a ratios confirmed the preservation of tetragonal distortion. Increasing alkalinity progressively promoted BaTi₂O₅ formation, accompanied by systematic changes in particle morphology and a corresponding deterioration of the dielectric response. The highest dielectric performance was obtained for powders synthesized at pH 6, exhibiting a maximum dielectric constant of approximately 2050 at 1 kHz, whereas increasing BaTi₂O₅ content reduced the dielectric permittivity by nearly 50%. These findings demonstrate that the reaction-medium pH is a critical processing parameter governing phase formation and dielectric performance during sonochemically activated solid-state synthesis, providing mechanistic insights into phase-selective BaTiO₃ formation and a practical strategy for designing high-performance dielectric ceramics.