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

(K(0.5)Na(0.5))(1-3x)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 Bi(3+) significantly improves electrical properties of (K(0.5)Na(0.5))NbO(3) ceramics while keeping the tetragonal-orthorhombic phase transition temperature above 170 degrees C. The KNBN (x=0.01) ceramics show the optimum electrical properties (d(33)=164 pC/N, k(p)=0.47, Q(m)=120, T(C)=403 degrees C, T(O-T)=174 degrees C, P(r)=30.1 mu C/cm(2), and E(c)=6.18 kV/cm). Take into account electrical properties and the polymorphic phase transition temperature (T(O-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. (C) 2007 American Institute of Physics.