EVOLUTION OF PHASE FORMATION, MICROSTRUCTURE, AND ELECTRICAL PROPERTIES OF BaTi0.91Sn0.09O3 LEAD-FREE CERAMICS FOR DIFFERENT CALCINATION AND SINTERING TEMPERATURES

Lead-free BaTi0.91Sn0.09O3 (BTS) ceramics were fabricated by the conventional solid-state reaction method. The evolution of phase, microstructure, dielectric, and ferroelectric properties of BTS powders and ceramics was examined at different calcination (1175-1250°C for 4 h.) and sintering (1375-1450°C for 2 h.) temperatures. X-ray diffraction (XRD) revealed that the calcined powders had perovskite structures, with a secondary BaSnO3 impurity phase when calcined below 1200°C. The BTS ceramics displayed a secondary Ti0.85​Sn0.15​O2 phase at a sintering temperature of 1375°C, while no impurity phases were detected at 1400-1450°C. Rietveld refinement indicated coexisting orthorhombic (O), tetragonal (T), and cubic (C) phases in all samples. The O phase increased with sintering temperatures up to 1425°C before decreasing, while the T and C phases decreased for sintering temperatures up to 1425°C before increasing. When the sintering temperature increased from 1375°C to 1425°C, the density, dielectric constant at the Curie temperature (εC), and maximum polarization (Pmax) increased from 5.90 to 5.98 g/cm3, 9,533 to 12,538 and 15.07 to 15.36 μC/cm2, respectively, before decreasing. In contrast, the dielectric loss (tan δ), remanent polarization (Pr), and coercive electric field (Ec) decreased from 0.036 to 0.020, 8.42 to 7.48 μC/cm2, and 3.49 to 1.86 kV/cm, respectively, when the sintering temperature increased from 1375°C to 1425°C, before slightly increasing. The BTS ceramic sintered at 1425°C showed the highest density, a well-packed microstructure, superior dielectric properties, and high Pmax. The increased orthorhombic phase content reduced Pr and Ec, making this ceramic suitable for dielectric capacitor applications.