Fabrication of Lead-Free Piezoelectric KNbO3 Ceramics by Modified Solid State Reaction Method

Potassium niobate (KNbO 3 ) fine powder has been successfully synthesized at a low temperature of 500 °C through a modified solid state reaction, in which urea [CO(NH 2 ) 2 ] plays an important role. High-density KNbO 3 ceramics can be obtained by the conventional sintering of the synthesized KNbO 3 fine powder with the addition of 1 mol % Co 3 O 4 , which is a sintering additive. Their crystal structure, microstructure, and dielectric and piezoelectric properties were characterized. The KNbO 3 ceramics show a comparatively saturated P – E hysteresis loop. The remnant polarization and coercive field are 14 µC/cm 2 and 16 kV/cm, respectively. The KNbO 3 ceramics also show piezoelectricity with a planar electromechanical coupling factor, k p , of 16%.