Effects of BaHfO3 addition on the phase transition and piezoelectric properties of (K,Na)NbO3-based ceramics

Lead-free piezoelectric ceramics based on (1-x)(K0.48Na0.48Li0.04)Nb0.95Sb0.05O3-xBaHfO3 were designed and prepared by a conventional ceramic fabrication method. An investigation was conducted to judge the effects of BaHfO3 content on the ceramics' phase structure, microstructure, phase transition temperatures, and piezoelectric properties. It was found that all the ceramics possessed a perovskite structure in the studied composition range, despite the fact that they experienced gradual transitions from orthorhombic symmetry to rhombohedral symmetry upon increases of BaHfO3 content. Furthermore, a three-phase coexistence of rhombohedral-orthorhombic-tetragonal phases was identified in the composition range of 0.05 ≤ x ≤ 0.055, based on X-ray diffraction results together with the temperature dependence of dielectric properties. In the three-phase coexistence region, the ceramics displayed effectively enhanced piezoelectric activity, with the maximum values of the piezoelectric constant d33, and planar electromechanical coupling coefficient, being 268 pC/N and 0.432 respectively. In addition, the Curie temperature of the ceramics was found to decrease in accordance with increases of BaHfO3 content. We believe that this work can provide a valuable reference for researchers to further improve the piezoelectric properties of (K,Na)NbO3-based ceramics.