Microstructure, Piezoelectric, and Ferroelectric Properties of Bi ₂ O ₃ ‐Added (K _0.5 Na _0.5 )NbO ₃ Lead‐Free Ceramics

Lead‐free piezoelectric (K 0.5 Na 0.5 )NbO 3 – x wt% Bi 2 O 3 ceramics have been synthesized by an ordinary sintering technique. The addition of Bi 2 O 3 increases the melting point of the system and improves the sintering temperature of (K 0.5 Na 0.5 )NbO 3 ceramics. All samples show a pure perovskite phase with a typical orthorhombic symmetry when the Bi 2 O 3 content <0.7 wt%. The phase transition temperature of orthorhombic–tetragonal ( T O − T ) and tetragonal–cubic ( T C ) slightly decreased when a small amount of Bi 2 O 3 was added. The remnant polarization P r increased and the coercive field E c decreased with increasing addition of Bi 2 O 3 . The piezoelectric properties of (K 0.5 Na 0.5 )NbO 3 ceramics increased when a small amount of Bi 2 O 3 was added. The optimum piezoelectric properties are d 33 =140 pC/N, k p =0.46, Q m =167, and T C =410°C for (K 0.5 Na 0.5 )NbO 3 –0.5 wt% Bi 2 O 3 ceramics.