| In this dissertation, binary system piezoelectric ceramics of the Pb(ZrxTi1-x)O3(PZT) and(1-x)PMN-x PT(PMN-PT) were synthesized by the conventional solid-state reaction method, and their phase structure, microstructure and piezoelectric properties were investigated in order to identify the MPB compositions in these systems. The results of X-ray diffraction(XRD) reveal that all ceramic samples exhibit a typical ABO3 perovskite structure without any other impurity phase. The favorable performance of d33=192 p C/N, εr=2416 were obtained for Pb(ZrxTi1-x)O3 ceramics with x=0.52 near MPB region. However, the piezoelectric properties of relaxor-ferroelctric 0.65PMN-0.35 PT ceramics are better than those of normal-ferroelectric Pb(Zr0.52Ti0.48)O3 sample, and the corresponding values of piezoelectric constant(d33) and relative dielectric constant(εr) are 412 p C/N, εr=3225, respectively.Based on two systems of PZT and PMN-PT binary ceramics, 0.25Pb(Mg1/3Nb2/3)O3-0.75Pb(ZryTi1-y)O3(PMN-y PZT, y=0.30~0.45), 0.3Pb(Zn1/3Nb2/3)O3-0.7Pb(Zrxi1-x)O3(PZN-x PZT, x=0.45~0.51) and 0.55Pb(Ni1/3Nb2/3)O3-0.45Pb(ZrxTi1-x)O3(PNN-x PZT, x=0.20~0.35) ternary piezoelectric ceramics have been fabricated by conventional sintering technique with sintering temperature at1200℃. The effect of Zr/Ti ratio on phase transition, microstructure, piezoelectric, dielectric and ferroelectric properties were systematically investigated. With these data, the results demonstrated that all samples possess a pure perovskite structure, and the optimal electrical properties were verified closed to MPB between tetragonal and rhombohedral phase. By comparing the properties of these three series of ceramics, the most impressive results are the excellent piezoelectric properties(eg. d33=810 p C/N, εr=6371 and kp=0.54) in PNN-x PZT system with x=0.30, and the composition exhibits superior electrical properties than those in PMN-y PZT system with y=0.35(d33=346 p C/N, εr=1513 and kp=0.47) and PZN-x PZT system with x=0.49(d33=477 p C/N, εr=2127 and kp=0.69). In addition, the 0.55Pb(Ni1/3Nb2/3)O3- 0.45Pb(Zr0.3Ti0.7)O3(PNN-PZT) ternary piezoelectric ceramics was selected as research object, the effect of sintering temperature(Ts=1175~1300 ℃) on microstructure, piezoelectric, dielectric and ferroelectric properties of PNN-PZT ceramics was investigated. Both XRD and Raman scattering spectra analysis showed that these samples possess a typical perovskite host phase with rhombohedral symmetry. The d33 and εr increase initially and then decrease with increasing sintering temperature, which can be ascribed to both the grain growth and density decrease. The maximum piezoelectric properties of d33=1070 p C/N, kp=0.69, εr=8170 and tanδ=2.6% were achieved for the sample sintered at 1250℃ for 2 h.In order to enhance piezoelectric properties and improve sinterability of PNN-PZT ceramics, Cu O and Fe2O3 were respectively doped into the ceramics to investigate their effects on the microstructure and properties. The addition of Cu O has almost no influence on the phase structure of PNN-PZT ceramics, but it was effective for improving piezoelectric and dielectric properties. The enhanced properties of d33=777 p C/N and kp=0.55 were obtained for the 0.4 wt% Cu O-added sample sintered at 1125℃. Fe2O3 doped PNN-PZT ceramics were prepared and sintered at 1200℃for 2 h, using the normal sintering(NS) and microwave sintering(MS) methods, respectively. It was found that excellent piezoelectric and dielectric properties of d33=956 p C/N, kp=0.74, εr=6095 and tanδ=2.6% for the sample with 1.2 mol% Fe2O3 doping prepared by normal sintering method. However, the piezoelectric properties of Fe2O3 doped PNN-PZT ceramics with NS were lower than those of samples with MS, which can be attributed to the inhomogeneous grain size and lower density.Temperature stability and electrical properties of quaternary piezoelectric ceramics PNN-PFN-PZT system were adjusted by doping with Li2CO3 and Zn O. The phase transition, temperature dependence of dielectric and piezoelectric properties were investigated in detail. The results revealed that the Li2CO3 doping could improve temperature stability of dielectric constant(γ), but deteriorate piezoelectric properties for the PFN-PNN-PZT-x Li ceramics. The favorable properties of d33=820 p C/N, kp=0.63, εr=6628, tanδ=2.8%, Ec=4.48 k V/cm and γ=17% for the sample doped with 1.5% Li2CO3. Furthermore, Zn O doping could not only significantly improve the temperature stability(Δd31/d31 30°C) and the coercive field(Ec), but also increase Curie temperature(Tm) of PNN-PFN-PZT-x Zn system. The optimized electrical properties of d33=810 p C/N, εr=6243, Ec=4.7 k V/cm, Tm=136 ℃ and Δd31/d31 30°C=21% were obtained for the PFN-PNN-PZT-x Zn sample with x=0.04.Raw materials of 0.55PNN-0.45 PZT and PNN-PFZT ceramics were synthesized by solid phase method, and then the piezoelectric ceramic fibers with platinum(Pt) metal core(PFC) were successfully fabricated by an extruding technique. Based on our previous research works, the relationship between sintering process, material structure and electrical properties was further discussed in present study. It was found that with the proper sintering temperature and sintering time can contribute to the improvement of electrical properties for these piezoelectric ceramic fibers. Especially, the fine morphology and enhanced electrical properties were achieved for the PNN-PFZT fibers sintered at 1200℃ for 2 h, the main parameters: d31=-197.4 p C/N, kp=0.29, εr=3683 and tanδ=2.7%. For the special geometry and small dimension, PFC as a novel function device has good applications in structure health monitoring, vibration control, sensor and actuator. X... |
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