Effect of calcination temperature of precursor powders on the structure and electrical properties of Na0.52Bi0.48TiO3-δ

The effect of calcination temperature (600–850 °C) on the structure and electrical properties of Na_0.52Bi_0.48TiO_3-δ (NBT) synthesized via solid-state reaction has been systematically investigated. The structure, morphology, and electrical properties of the samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS), respectively. Perovskite phase formation initiates above 700 °C, with complete transformation occurring at higher temperatures. SEM analysis demonstrates grain size reduction and impurity emergence at temperatures exceeding 700 °C. Grain boundary conductivity (σ_gb) exhibits a non-monotonic dependence on calcination temperature: peak conductivity (2.1 × 10⁻³ S/cm at 500 °C) was achieved at 650 °C, and minimum conductivity was observed at 850 °C. Activation energy dominates conductivity behavior rather than oxygen vacancy concentration. Maximum grain boundary conductivity occurs at 600 °C. Impurity coverage ratio emerges as the primary factor governing grain boundary conduction. Our work establishes calcination temperature as a critical process parameter for NBT-based materials, providing fundamental insights into conduction mechanisms in bismuth titanate systems. And it offers practical guidelines for optimizing solid-state synthesis of oxygen ion conductors. These findings advance the understanding of structure–property relationships in NBT materials and demonstrate the importance of thermal processing control for developing high-performance electrolytes in solid oxide fuel cells and related electrochemical devices. The work particularly highlights the competitive conductivity achievable through optimized calcination conditions without requiring compositional modification.