Electrical Properties Of Low Sintered Temperature PZT-PFW-PMN Based Piezoelectric Ceramics

In order to satisfy the requirements of high-power multilayeredpiezoelectric transformers for practical applications, the properties of piezoelectricceramics should combine a high mechanical quality factor (Q_m), a highelectromechanical coupling factor (K_p), a high piezoelectric constant (d₃₃) with a lowdielectric loss (tanδ) and a low sintering temperature. The quaternary piezoelectricceramics of Pb(Fe_2/3W_1/3)O₃-Pb(Mn_1/3Nb_2/3)O₃ -PbZrO₃-PbTiO₃ (PFW-PMN-PZT)were investigated in this work from the aspects of process, dopants addition andsintering aids addition.PFW-PMN-PZT ceramics were fabricated by the conventional mixed-oxidemethod. The density, microstructure, dielectric and piezoelectric properties ofPb(Mg_1/3Nb_2/3)O₃-Pb(Zn_1/3 Nb_2/3)O₃-Pb(Zr_0.52Ti_0.48)O₃ (PMN-PZN-PZT) ceramicsas a function of Li₂CO₃, LiSbO₃, CuO-PbO, YMnO₃, BiFeO₃ content and sinteringtemperature were investigated. The results indicated that the optimized properties ofceramics and the low sintering temperature can be hardly simultaneously obtained byadding Li₂CO₃, LiSbO₃ and CuO-PbO, respectively. Moreover, YMnO₃ and BiFeO₃addtition were added to the ceramics, which could make the sintering temperaturedecrease to 1020℃. The liquid phase was formed and the pyrochlore phase wasinhibited by YMnO₃ additive. With increasing YMnO₃ content, d₃₃, K_p and Q_mincreases at first, and then decrease. The optimal values were obtained by doping0.30 wt.% YMnO₃, which are listed as follows: d₃₃=341 pC/N, K_p=0.57, Q_m=1393,tanδ=0.0053 and T_c=304. In addition, it was found that the addition of BiFeO₃significantly improved the sinterability of PZT-PFW-PMN ceramics.The favorablepiezoelectric and dielectric properties were obtained by doping 0.20 wt.% BiFeO₃addition, which are listed as follows: d₃₃=309pC/N, K_p=0.59, Q_m=1551, tanδ=0.0056,ε_r=1723 and T_c=308℃. As comparison, the YMnO₃ doped ceramics withbetter properties was sintered at 1020℃, demonstrating that the PZT-PFW-PMN-0.20wt.% BiFeO₃ ceramics have optimal properties. Therefore, the obtainedproperties make the ceramics to be a good candidate for high power piezoelectricdevices. To further decrease the sintering temperature and improve the electrical propertiesof the ceramics, the PFW-PMN-PZT +0.2 wt.% CeO₂+2.0 wt.% Pb₃O₄+0.20 wt.%BiFeO₃ ceramic was investigated by doping ZnO. The influence of ZnO content onthe phase structure, microstructure, dielectric, piezoelectric properties and thetemperature stability on the ceramics was investigated in details. Therefore, ZnO wasselected as a sintering aid in order to further lower the sintering temperature of thePMN-PZN-PZT- 0.20 wt.% BiFeO₃. The ZnO addition influenced the phase structureand microstructure of ceramics. The ceramics transformed from tetragonal phase torhombohedral phase. Grain sizes grew with increase ZnO content and sinteringtemperature decreased. On the other hand, with the increasing of ZnO content, K_p, d₃₃and Q_m first increased and then decreased. Tanδfirst decreased and then increased,while the curie temperature (T_c) had a decrease trend. It was also found that thesintering temperature of the ceramics with adding 0.10 wt.% ZnO reduced from 1020℃to 950℃. Meanwhile, the ceramics exhibited good properties, which wered₃₃=313 pC/N, K_p=0.56, Q_m=1387,ε_r=1384, tanδ=0.0053 and T_c=295℃. Thematerial is a good candidate for high-power multilayered piezoelectric transformerapplications.