The microstructure and ferroelectric properties of (K0.5Na0.5)NbO3–LiNbO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)(K0.5Na0.5)NbO3–xLiNbO3 have been synthesized by traditional ceramics process without cold-isostatic pressing. Effect of the amount of LiNbO3 on the phase structure, microstructure, ferroelectric and piezoelectric properties of (1 − x)(K0.5Na0.5)NbO3–xLiNbO3 ceramics were investigated. Results show that the pure perovskite phase is in all ceramics specimens (x < 0.08). With the content of LiNbO3 increases, remnant polarization Pr, coercive field Ec and mechanical quality factor Qm decrease. Pr and Ec show their minimum in this system when the amount of LiNbO3 is 0.06 mol, respectively. However, 0.94(K0.5Na0.5)NbO3–0.06LiNbO3 ceramics show the optimum piezoelectric properties. The optimum piezoelectric, dielectric and ferroelectric properties for 0.94(K0.5Na0.5)NbO3–0.06LiNbO3 ceramics are piezoelectric constant d33 = 215pC/N, planar electromechanical coupling factor kp = 0.41, thickness electromechanical coupling factor kt = 0.48, Qm = 80, Pr = 20.0 μC/cm2, Ec = 13.4 kV/cm, relative dielectric constant ɛr = 530, dielectric loss tan δ = 0.034, Curie temperature Tc = 450 °C. Compared with other KNN-based piezoelectric ceramics, it can be concluded that 0.94(K0.5Na0.5)NbO3–0.06LiNbO3 piezoelectric ceramics is a promising candidate for high temperature lead-free piezoelectric ceramics.