Composition dependence of phase structure and piezoelectric properties in (0.98 − x)(K0.4Na0.6)NbO3–0.02CaZrO3–xBi0.5Na0.5HfO3 ternary ceramics

Abstract

Lead-free perovskite (0.98 − x)(K0.4Na0.6)NbO3–0.02CaZrO3–xBi0.5Na0.5HfO3 (KNN–CZ–xBNH) ceramics were prepared by a conventional solid-state reaction method, and the connections between their composition, phase structure, and electrical properties were investigated. The X-ray diffraction results, together with the temperature dependence of dielectric properties, showed that a rhombohedral–tetragonal (R–T) phase boundary was successfully constructed in the composition range of 0.04 ≤ x ≤ 0.045. An enhancing effect of R–T phase boundary on the piezoelectric activity was observed, and the ceramics with the composition x = 0.045 exhibited the highest piezoelectric properties, possessing a piezoelectric constant d 33 of 320 pC/N and a planar electromechanical coupling coefficient of 0.40. In addition, it was found that while adding a small amount of Bi0.5Na0.5HfO3 could result in very large grain sizes in the (K,Na)NbO3-based ceramics, adding too much of it would lead to extremely fine grain sizes. In general, our experimental results indicate that the KNN–CZ–xBNH ceramics are promising candidate materials for lead-free piezoelectric applications.