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

Potassium niobate (KNbO3) fine powder has been successfully synthesized at a low temperature of 500 °C through a modified solid state reaction, in which urea [CO(NH2)2] plays an important role. High-density KNbO3 ceramics can be obtained by the conventional sintering of the synthesized KNbO3 fine powder with the addition of 1 mol % Co3O4, which is a sintering additive. Their crystal structure, microstructure, and dielectric and piezoelectric properties were characterized. The KNbO3 ceramics show a comparatively saturated P–E hysteresis loop. The remnant polarization and coercive field are 14 µC/cm2 and 16 kV/cm, respectively. The KNbO3 ceramics also show piezoelectricity with a planar electromechanical coupling factor, kp, of 16%.