YU Zudeng, JIANG Xiangping ,YANG Qing ,TU Na ,CHEN Chao

(Department of Material Science and Engineering, Jingdezhen Ceramic Institute, Jingdezhen 333001)

Abstract: In this paper, Lead-free piezoelectric ceramics K_0.5Na_0.5NbO₃-xmol%La₂O₃ (abbreviated as KNN-xLa) were prepared by traditional solid state reaction. The phase structure, microstructure, piezoelectric properties and dielectric properties were studied for KNN-xLa samples with different La₂O₃ content (x = 0.0, 0.05, 0.15, 0.25, 0.35, 0.5, 1.0). It was found that the Asite substitution of La³⁺ does not change the crystal structure within the studied doping level and all the ceramics possess a single-phase perovskite structure with orthorhombic symmetry. The piezoelectric constant (d₃₃), mechanical quality factor (Q_m), planar electromechanical coupling coefficient (k_p) and the density of all the samples increased firstly and decreased subsequently with increasing x, while the dielectric loss (tan_δ) decreased firstly and then increased at the same time. And the sintering temperature increased with increasing x. The ceramic (x=0.15) displayed the optimum properties (d₃₃=120pC/N,Q_m=130, k_p =0.41, tan_δ =0.021, ρ =4.52 g/cm3). Moreover, increasing x caused the increase of Tc and after reaching the maximum value (404℃) at x=0.15, Tc began to decrease, which was opposite to the variation of the T_o-t (189℃) at x=0.15.

Keywords: K_0.5Na_0.5NbO₃K0.5Na0.5NbO3, La₂O₃, lead-free piezoelectric ceramics, piezoelectric pr