Evolution of phase structure and enhancement of piezoelectric properties in (K0.5Na0.5)0.94Li0.06NbO3–SrZrO3 lead-free ceramics

Abstract

(Na0.5K0.5)0.94Li0.06NbO3–xSrZrO3 (NKLN–xSZ) lead-free piezoelectric ceramics with a composition near the rhombohedral–tetragonal (R–T) phase boundary and high Curie temperature Tc have been designed and prepared by conventional solid-state sintering. The phase transition behavior and composition-dependent piezoelectric properties of NKLN–xSZ lead-free system are investigated systematically. The R–T phase boundary is identified to lie in the composition range of 0.04 < x < 0.06 in NKLN–xSZ ceramics by XRD and temperature-dependent dielectric spectroscopy. The ceramics in the vicinity of the R–T phase boundary exhibit a strong composition dependent and significantly enhanced piezoelectric properties. A comprehensive study of d33 (197–220 pC/N) and Tc (310–349 °C) were conducted in the NKLN–xSZ ceramics with 0.04 < x < 0.06. The ceramic with x ~ 0.05 shows the optimum electrical properties: d33 ~ 220 pC/N, kp ~ 30%, er ~ 778, tan δ ~ 0.024, and Tc ~ 331 °C. The good piezoelectric properties together with high Tc of the NKLN–xSZ ceramics make NKLN–xSZ a promising environmental friendly lead-free material system for a wide range of electromechanical transducer applications.