Structure evolution and enhanced piezoelectric properties of (K0.5Na0.5)NbO3-0.06LiTaO3-SrZrO3 lead-free ceramics

(K0.5Na0.5)NbO3-0.06LiTaO(3)-xSrZrO(3) (KNN-LT-xST) lead-free piezoelectric ceramics with rhombohedraletetragonal (R-T) phase boundary have been designed and prepared by the conventional solid-state reaction method, the phase transitional behavior and composition-dependent piezoelectric properties of KNN-LT-xST lead-free system were investigated. The R-T phase boundary is identified in the KNN-LT-xST ceramics with a composition of 0.04 <= x <= 0.06. The ceramics in the vicinity of the R-T phase coexistence zone exhibit a strong compositional dependence and significantly enhanced piezoelectric properties. A comprehensive performance of d(33) (222-254 pC/N) and T-c (282-312 degrees C) could be obtained in the KNN-LT-xSZ ceramics with 0.04 <= x <= 0.06 by tailoring the SrZrO3 content. The ceramic with x = 0.045 shows the optimum electrical properties: d(33) = 254 pC/N, k(p) = 28%, epsilon(r) = 758, tan delta = 1.7%, P-r = 8.98 mu C/cm(2) and T-c = 300 degrees C. The existence of an R-T phase boundary and therefore the involvement of the more polarization states should be responsible for the enhanced piezoelectric properties of the KNN-LT-xSZ ceramics. The good piezoelectric properties together with a high cubic-tetragonal phase transition temperatures (T-c) make the KNN-LT-xSZ ceramics showing the promising lead-free piezoelectric material system for the practical applications. (C) 2015 Elsevier B.V. All rights reserved.