Enhanced dielectric and ferroelectric properties near the morphotropic phase boundary in BNBT-BSN ceramics prepared by the solid-state combustion technique

The effect of firing temperatures on the phase structure, microstructure, and electrical properties of 0.99Bi_0.47Na_0.47Ba_0.06TiO₃-0.01BaSn_0.70Nb_0.24O₃ (abbreviated as BNBT-BSN) lead-free ceramics fabricated by the solid-state combustion technique, with glycine used as the fuel, were investigated. All BNBT-BSN samples were calcined at temperatures ranging from 750 to 850 °C for 1 to 4 h and sintered at temperatures from 1100 to 1200 °C for 2 h. A pure perovskite structure was obtained after calcination at 800 °C for 2 h. The X-ray diffraction (XRD) patterns showed the coexistence of rhombohedral and tetragonal phases in all ceramics. The average grain size tended to increase with rising sintering temperatures. The optimal condition for fabricating BNBT-BSN ceramics with a morphotropic phase boundary (MPB) was observed at a sintering temperature of 1175 °C for 2 h, where the material exhibited the highest measured density (5.50 g/cm³), maximum dielectric constant at T_m (ɛ_m = 6513), maximum polarization (P_max = 42.21 µC/cm²), the largest bulk resistivity (ρ = 1.70 × 10⁴) and the highest activation energy of conduction (E_a = 1.52 eV). These features suggest that this ceramic is a suitable material for applications in actuators, transducers, and high-performance capacitors.