Phase structure, microstructure, and electrical properties of bismuth modified potassium-sodium niobium lead-free ceramics

( K 0.5 Na 0.5 ) 1 − 3 x Bi x NbO 3 (KNBN) ceramics were prepared by conventional solid-state sintering without cold-isostatic pressing. The phase structure, microstructure, and electrical properties of KNBN ceramics are studied. The phase structure of KNBN ceramics (x=0.01) is pure perovskite phase with orthorhombic symmetry at room temperature. The addition of Bi3+ significantly improves electrical properties of (K0.5Na0.5)NbO3 ceramics while keeping the tetragonal-orthorhombic phase transition temperature above 170 °C. The KNBN (x=0.01) ceramics show the optimum electrical properties (d33=164 pC∕N, kp=0.47, Qm=120, TC=403 °C, TO-T=174 °C, Pr=30.1 μC∕cm2, and Ec=6.18 kV∕cm). Take into account electrical properties and the polymorphic phase transition temperature (TO-T), it can be concluded that the KNBN (x=0.01) ceramic is a promising lead-free piezoelectric candidate material for practical application. The related mechanisms for high piezoelectric properties in KNBN (x=0.01) ceramics are also discussed.