Microstructure, Piezoelectric, and Ferroelectric Properties of Bi₂O₃-Added (K_0.5Na_0.5)NbO₃ Lead-Free Ceramics

Lead-free piezoelectric (K0.5Na0.5)NbO3-x wt% Bi2O3 ceramics have been synthesized by an ordinary sintering technique. The addition of Bi2O3 increases the melting point of the system and improves the sintering temperature of (K0.5Na0.5)NbO3 ceramics. All samples show a pure perovskite phase with a typical orthorhombic symmetry when the Bi2O3 content < 0.7 wt%. The phase transition temperature of orthorhombic-tetragonal (TO-T) and tetragonal-cubic (T-C) slightly decreased when a small amount of Bi2O3 was added. The remnant polarization P-r increased and the coercive field E-c decreased with increasing addition of Bi2O3. The piezoelectric properties of (K0.5Na0.5)NbO3 ceramics increased when a small amount of Bi2O3 was added. The optimum piezoelectric properties are d(33)=140 pC/N, k(p)=0.46, Q(m)=167, and T-C=410 degrees C for (K0.5Na0.5)NbO3-0.5 wt% Bi2O3 ceramics.