| In order to satisfy the requirements of high-power multilayered piezoelectric transformers for practical applications, the properties of piezoelectric ceramics should combine a high mechanical quality factor (Qm) a high electromechanical coupling factor (Kp), a high piezoelectric constant (d33) with a low dielectric loss (tan δ) and a low resonant resistance (r). From the aspects of powders preparation, composition designing, dopants addition and sintering aids addition, the quaternary piezoelectric ceramics of Pb(Zr0.52Ti0.48)O3-Pb(Mn1/3Sb2/3)O3-Pb(Zn1/3Nb2/3)O3 (PZT-PMS-PZN) were investigated in this work.Piezoelectric powders and ceramics with the composition of PZT-PMS-PZN were prepared successfully by Molten Salt Synthesis (MSS) method. The calcining temperature of pure perovskite phase powders was reduced from 800 ℃ to 750 ℃. The results of scanning electron microscope (SEM) photographs showed that the powders prepared by MSS method had higher activity and relatively homogeneous microstructure. In addition, the ceramics obtained by MSS method exhibited higher density and better electrical properties than those of samples obtained by conventional mixed-oxide (CMO) method. The solid-state reaction mechanism by MSS was also proposed in this work.The influence of PZN content on the phase structure, microstructure, dielectric and piezoelectric properties of PZT-PMS-PZN system was investigated in detail. The XRD analysis results showed that the phase structure of ceramics transformed from rhombohedral phase to tetragonal phase with the increasing of PZN content. The morphotropic phase boundary (MPB) of composition existed in the range of 0.02 mol< x ≤ 0.07 mol. The SEM results showed that the grain size markedly decreased with the increasing of PZN content. As PZN content increased, Qm gradually dropped. Kp increased and then decreased, and d33 sharply increased. Meanwhile, tan S and r decreased, and then increased. Ceramics sintered at 1150 ℃ with 0.05 mol PZN achieved better properties, which were as follows: Qm=1381, Kp=0.64, d33=369 pC/N, tan δ=0.0044 and r=1.576 Ω. The 0.90PZT-0.05PMS-0.05PZN composition waschosen as a basic material for high-power multilayered piezoelectric transformer applications.To further improve the electrical properties of the ceramics, especially for Qm, the 0.90PZT-0.05PMS-0.05PZN ceramic was investigated by doping MnO2 and WO3. The influence of MnO2 content on the phase structure, microstructure, dielectric and piezoelectric properties of the ceramics was investigated in detail. The XRD analysis results showed that all the ceramics were the rhombohedral phase. With the increasing of MnO2 content, the grain size of ceramics increased. Kp and dy$ kept decreasing all the time, Qm and tan S firstly increased and then decreased, while r showed an increase trend. As MnO2 was 0.2 wt.%, the ceramics sintered at 1150 °C showed better electrical properties.The influence of WO3 content on the phase structure, microstructure, dielectric and piezoelectric properties of the ceramics was also investigated in detail. The XRD analysis results showed that all the ceramics were tetragonal phase, indicated by the splitting of (002)T and (200}r peaks. The WO3 addition significantly inhibited the grain growth. With increasing the amount of WO3, Qm increased slowly, Kp and ^33 increased at first and then decreased, whereas, tan S decreased firstly, then increased and r decreased all the time. The PZT-PMS-PZN ceramics with 0.6 wt.% WO3 addition and sintered at 1150 "C showed the optimized electrical properties. Taking into account the addition of WO3 and MnO2, the PZT-PMS-PZN ceramics sintered at 1150 °C co-doped with 0.6 wt.%WO3 and 0.2 wt.%MnO2 showed the optimum properties: Qm=\ 852, A:p=0.58,the ceramics had better electrical properties. It was also found that the 0.1 wt.% ZnO addition reduced the sintering temperature of the ceramics from 1150 °C to 1120 °C. Meanwhile, the ceramics exhibited good properties, which were Qm=lS99, Kp=0.55, d33=300 pC/N, tan |
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