Microstructure, dielectric, and piezoelectric properties of (Li, Ag, Ta) modified (K0.50Na0.50)NbO3 lead-free ceramics with high Curie temperature

(1-x)[(K0.4725Na0.4725Li0.055)NbO3]-xAgTaO(3) [(1-x)KNNL-xAT] lead-free ceramics have been prepared by the conventional mixed oxide method. Effect of the AgTaO3 (AT) content on the microstructure and electrical properties of (1-x)KNNL-xAT ceramics were systematically investigated. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal phases was identified in the composition range of 0.015 < x < 0.025. The materials near the MPB exhibit a strong compositional dependence and enhanced electrical properties along with high Curie temperature. It is found that the samples with 2 mol % AT exhibit relatively good electrical properties along with high Curie temperature: the piezoelectric constant d(33) and Curie temperature T-C reach 237 pC/N and 470 degrees C, respectively; the electromechanical coupling coefficient of the planar mode k(p) reaches 39%; and the remnant polarization (P-r) is 29.4 mu C/cm(2) with a coercive field (E-c) of 13.6 kV/cm. These results show that (1-x)KNNL-xAT is a promising candidate material for high temperature lead-free piezoelectric ceramics. (C) 2007 American Institute of Physics.