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

( 1 − x ) [ ( K 0.4725 Na 0.4725 Li 0.055 ) NbO 3 ] − x AgTaO 3 [ ( 1 − x ) KNNL − x AT ] 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 d33 and Curie temperature TC reach 237 pC/N and 470 °C, respectively; the electromechanical coupling coefficient of the planar mode kp reaches 39%; and the remnant polarization (Pr) is 29.4 μC∕cm2 with a coercive field (Ec) 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.