Microstructure and piezoelectric properties of K5.70Li4.07Nb10.23O30-added K0.5Na0.5NbO3 ceramics

Lead-free piezoelectric ceramics K0.5Na0.5NbO3-xmol% K5.70Li4.07Nb10.23O30 (x = 0-2.5, KNN-xmol%KLN) were prepared by conventional sintering technique. The phase structure and electrical properties of KNN ceramics were investigated as a function of KLN concentration. The results showed that small amount of KLN introduced into the lattice formed a single phase perovskite structure. The KLN modification lowered the phase transition temperature of orthorhombic-tetragonal (TO-T) and increased the Curie temperature (T-C). Some abnormal coarse grains were formed in a matrix when the content of KLN was relatively low (1 mol%). However, normally grown grains were only observed when the sintering aid content was increased to 2 mol%. Proper content of KLN decreased the amount of defects, thus the remanent polarization increased and the coercive field decreased markedly, and the sinterability of the KNN ceramics was simultaneously improved with significant increase of piezoelectric properties.