Evolution of phase structure and enhancement of piezoelectric properties in (K_(0.5)Na_(0.5))_(0.94)Li_(0.05)NbO_3-SrZrO_3 lead-free ceramics

摘要

(Na_(0.5)K_(0.5))_(0.94)Li_(0.06)NbO_3-xSrZrO_3 (NKLN-xSZ) lead-free piezoelectric ceramics with a composition near the rhombohedral-tetragonal (R-T) phase boundary and high Curie temperature T_c 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 d_(33) (197-220 pC/N) and T_c (310-349 ℃) were conducted in the NKLN-xSZ ceramics with 0.04 < x < 0.06. The ceramic with x ~ 0.05 shows the optimum electrical properties: d_(33) ~ 220 pC/N, k_p ~ 30%, ε_r ~ 778, tan δ ~ 0.024, and T_c ~ 331 ℃. The good piezoelectric properties together with high T_c of the NKLN-xSZ ceramics make NKLN-xSZ a promising environmental friendly lead-free material system for a wide range of electromechanical transducer applications.