Design and electrical properties' investigation of (K0.5Na0.5)NbO3-BiMeO3 lead-free piezoelectric ceramics

Based on the discussion on the "origin" of the high piezoelectric properties of Pb-based piezoelectric ceramics, it was predicted that (K0.5Na0.5)NbO3-BiMeO3 solid solutions (where Me3+=Sc, Al, Ga, Y, In, etc.) should possess high piezoelectric properties because of the formation of the morphotropic phase boundary and the hybridization between the Bi 6p and O 2p orbits. (1-x)(K0.5Na0.5)NbO3-xBiScO(3) [(1-x)KNN-xBS] ceramics were selected as an example to verify this prediction. (1-x)KNN-xBS ceramics were synthesized by conventional solid-state sintering. The phase structure, microstructure, and dielectric and piezoelectric properties of (1-x)KNN-xBS ceramics were investigated. At room temperature, the polymorphic phase transition (PPT) (from the orthorhombic to the tetragonal phase) in (1-x)KNN-xBS ceramics is identified at x=0.0175 by the analysis of x-ray diffraction patterns and dielectric spectroscopy. The ceramics (x=0.0175) with PPT near room temperature exhibit excellent electrical properties (d(33)=similar to 253 pC/N, k(p)=0.48, k(t)=0.49, and T-C=351 degrees C). The related mechanisms for the high piezoelectric properties in (1-x)KNN-xBS (x=0.0175) ceramics are also systematically discussed. Compared to the other KNN-based ceramics and hard Pb(Zr,Ti)O-3 ceramics, it is concluded that the (1-x)KNN-xBS (x=0.0175) ceramic is a promising lead-free piezoelectric candidate material. In addition, this article could provide an alternative approach for the development of lead-free piezoelectric ceramics. (c) 2008 American Institute of Physics.