| Summary: | 碩士 === 國立成功大學 === 電機工程學系碩博士班 === 101 === In this study, the development of lead-free (1-x)(Na0.535K0.48)NbO3－xLiNbO3 (NKLN) ceramics were investigated and the phase transition behavior of material, sintering temperature and poling condition were discussed. In NKLN ceramics, it was observed that the morphotropic phase boundary (MPB) not only contented the orthorhombic and tetragonal phases, but also had the formation of monoclinic phase. The best piezoelectric properties of NKLN ceramics with kp = 42%、kt = 52% were obtained at x = 0.05. In 0.95NKN-0.05LN ceramics, the sintering temperature was reduced from 1050oC to 900oC and the excellent piezoelectric properties were obtained under sintering at 950oC. Moreover, the 0.95NKN-0.05LN ceramics sintered at 950oC for different soak times was also investigated. The maximum values of kp (48%) and kt (52 %) were obtained at the optimum soak time of 4 h. In the present study, the electric properties of ceramics were significantly by the poling conditions, including poling temperature and poling electric field. The optimum poling conditions obtained were under the poling temperature of 90oC and poling electric field of 3 kV/mm.
Based on the properties of ceramics above, the ceramics with high kp and kt values were chose for fabrication of single-element ultrasound transducers. The acoustic impedances of the ceramics and backing layer were calculated. The pulse/echo response of the ultrasound transducers fabricated using the (Na0.5K0.5)NbO3 and 0.95(Na0.535K0.48)NbO3- 0.05LiNbO3 ceramics were examined and the performances of these two ultrasound transducers were compared. Effects of piezoelectric properties of ceramics on the performances of ultrasound transducer were also investigated.
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