Effect of Sb and MnO2-Doping on Phase Transitions, Crystal Structure, Thermal, Dielectric, Ferroelectric and Piezoelectric Properties of Na0.5K0.5NbO3 Ceramics

Lead-free ceramics of Na_0.5 K_0.5 Nb_1-x Sb_x O₃ (NKNS) and Na_0.5 K_0.5 Nb_1-x Sb_x O₃ + 0.5 mol%MnO₂ (NKNS + 0.5 mol%MnO₂) (0 < x < 0.06) ceramics were prepared by a conventional solid-state hot pressing method. The ceramics possess a single-phase perovskite structure with orthorhombic symmetry. Microstructural examination revealed that Mn doping of NKNS leads to improvement of densification. The cubic-tetragonal and tetragonal-orthorhombic phase transitions of NKNS shifted to higher and lower temperature, respectively after introduction of Mn ion. Besides, ferroelectric and piezoelectric properties were improved. The results were discussed in term of difference in both ionic size and electronegativity of Nb⁵⁺ and Sb⁵⁺ and improvement of densification after Mn ion doping.