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

(K0.5 Na0.5) 1-3x Bix NbO3 (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 (K0.5 Na0.5) 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 pCN, kp =0.47, Qm =120, TC =403 °C, TO-T =174 °C, Pr =30.1 μC cm2, and Ec =6.18 kVcm). 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.