Effects of Bi_0.5Na_0.5HfO₃ addition on the phase structure and piezoelectric properties of (K, Na)NbO₃‐based ceramics

Abstract

Lead‐free perovskite (1‐x)(K0.48Na0.48Li0.04)Nb0.95Sb0.05O3‐x(Bi0.5Na0.5)HfO3 piezoelectric ceramics were prepared by a traditional ceramic fabrication method. An investigation was conducted to assess the effects of (Bi0.5Na0.5)HfO3 content on the crystal structure, microstructure, phase‐transition temperatures, and piezoelectric properties of the ceramics. The X‐ray diffraction results, combined with the temperature dependence of dielectric properties, revealed that the ceramics experienced a structural transition from an orthorhombic phase to a tetragonal phase with the addition of (Bi0.5Na0.5)HfO3, and a coexistence of orthorhombic and tetragonal phases was identified in the composition range of 0.005≤x≤0.015. An obviously improved piezoelectric activity was obtained for the ceramics with compositions near the orthorhombic‐tetragonal phase boundary, among which the composition x=0.005 exhibited the maximum values of piezoelectric constant d33, and planar and thickness electromechanical coupling coefficients (kp and kt) of 246 pC/N, 0.435, and 0.554, respectively. Furthermore, the Curie temperature of the ceramics was found decreasing with the increase in (Bi0.5Na0.5)HfO3 content, but still maintaining above 300°C for the phase boundary compositions. These results indicate that the ceramics are promising lead‐free candidate materials for piezoelectric applications.