Mitigation of Thermal Instability for Electrical Properties in CaZrO3-Modified (Na, K, Li) NbO3 Lead-Free Piezoceramics

Lead-free ceramics 0.96(Na0.52K0.48)(0.95)Li0.05NbO3-0.04CaZrO(3) (NKLN-CZ) are prepared by using the solid-state procedure and two-step synthesis technique. The crystal structure and thermal stability of NKLN-CZ ceramics sintered at 1140-1180 degrees C are investigated. All the NKLN-CZ ceramics are ABO(3)-type perovskite phases without impure phases. With the increase in sintering temperature, a phase transition occurs in NKLN-CZ ceramics from the orthorhombic (O) phase to the concomitance of O-tetragonal (T) phases. Meanwhile, ceramics become dense because of the presence of liquid phases. In the vicinity of ambient temperature, an O-T phase boundary is obtained above 1160 degrees C, which triggers the improvement of electrical properties for the samples. The NKLN-CZ ceramics sintered at 1180 ffi C exhibit optimum electrical performances (d(33) = 180 pC/N, k(p) = 0.31, dS/dE = 299 pm/V, # r = 920.03, tan delta = 0.0452, Pr = 18 mu C/cm(2), Tc = 384 degrees C, E-c = 14 kV/cm). The relaxor behavior of NKLN-CZ ceramics was induced by the introduction of CaZrO3, which may lead to A-site cation disorder and show diffuse phase transition characteristics. Hence, it broadens the temperature range of phase transformation and mitigates thermal instability for piezoelectric properties in NKLN-CZ ceramics. The value of kp for NKLN-CZ ceramics is held at 27.7-31% (variance of kp < 9%) in the range from 25 to 125 degrees C. The results indicate that lead-free ceramics NKLN-CZ is one of the hopeful temperature-stable piezoceramics for practical application in electronic devices.