Phase structure and electrical properties of (Li,Ta)-doped (K,Na)NbO3 lead-free piezoceramics in the vicinity of Na/K = 50/50
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The phase structure and electrical properties of (K,Na)NbO3 (KNN)-based lead-free piezoelectric ceramics with nominal composition Li0.03 (NaxK1−x)0.97Nb0.8Ta0.2O3 (LKNNT, x = 0.50−0.55) were investigated with an emphasis on the influence of Na/K ratio. By XRD and Raman measurements, it was revealed that the phase transition from the co-existence of O1 and T1 to the co-existence of O2 and T2 occurs when x = 0.52. At this Na/K ratio, a peak of dielectric constants was obtained, which also corresponds to a morphotropic phase boundary between T1 and T2 besides that between O1 and O2 in LKNNT ceramics. All the Li0.03 (NaxK1−x)0.97Nb0.8Ta0.2O3 ceramics with x = 0.50 − 0.55 show excellent piezoelectric performance, and the piezoelectric coefficient d*33 can reach as high as 335 pm/V. The room-temperature piezoelectric properties in the present LKNNT ceramics are not sensitive to the change of Na/K ratio, indicating that the orthorhombic to tetragonal phase co-existence dominates the enhancement of piezoelectric properties. However, the results on the piezoelectricity measurement at elevated temperature showed possible to further enhance piezoelectric properties by adjusting Na/K ratio in the tetragonal LKNNT ceramics.
KeywordsPiezoelectric Property Orthorhombic Phase Morphotropic Phase Boundary Electromechanical Coupling Coefficient Sodium Niobate
This study was supported by the National Nature Science Foundation of China (Grant nos. 50772050 and 50921061) and the Ministry of Science and Technology of China under the Grant 2009CB623304, as well as by the Tsinghua University Initiative Scientific Research Program.
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