摘要
近年来,由于压电作动器和变压器的大规模使用,大功率压电陶瓷材料引起了广泛的研究和关注。为获得高的功率密度,多层叠片式压电陶瓷元器件也逐渐成为近期的研究热点。日前实现叠层结构更倾向采用Ag-Pd贵金属作内电极多层叠合一次烧成。若PZT压电陶瓷能在900°C以下烧成,则可采用Ag作内电极,这样不仅可以降低成本也可以抑制PbO的挥发。
目前,人们通过添加钙钛矿型弛豫铁电体发展了许多三元系、四元系的PZT基大功率压电陶瓷。PZT–PMS–PZN由于具备优异的电学性能:d_(33) = 369 pC/N, Qm = 1381, k_p = 64%, tanδ= 0.44%,ε_(33)~T = 1600,而被认为是大功率的候选材料之一。然而针对该材料的研究局限于熔盐合成法,且烧结温度偏高。为此,本课题选择PZT–PMS–PZN材料为研究对象,从成分设计、低温烧结特性、掺杂改性对材料的显微结构与电学性能的影响进行系统的研究。
采用普通固相法制备四元系0.90Pb(Zr_xTi_(1-x))O3-0.05Pb(Mn1/3Sb2/3)O3-0.05Pb(Zn1/3Nb2/3)O3陶瓷,进一步添加CuO烧结助剂降低烧结温度。研究不同Zr:Ti比和CuO添加量对陶瓷微结构、电学性能的影响规律。结果表明,Zr:Ti比对陶瓷电学性能影响显著,当Zr:Ti=48:52时,1100°C烧结后的陶瓷具有优异的电学性能:d_(33) = 355 pC/N, Qm = 1550, k_p = 60%, tanδ= 0.33%,ε_(33)~T = 1308。该配方在添加1.0 wt% CuO后,烧结温度下降到900°C,并且保持较好的电学性能:d_(33) = 306 pC/N, Qm = 997, k_p = 53.6%, tanδ= 0.50%,ε_(33)~T = 1351。通过对0.90PZT-0.05PMS-0.05PZN + 1.0 wt% CuO陶瓷原始粉体进行了差热-热失重分析,930°C左右出现的吸热峰证实了烧结过程中液相的存在。
为进一步优化0.90PZT-0.05PMS-0.05PZN + 1.0 wt% CuO陶瓷的压电性能,选择La_2O_3和Nb_2O_5分别作为A-/B-位的施主掺杂物。研究结果表明,La_2O_3掺杂可以显著提高d_(33)和k_p值,且几乎不降低Qm。当掺杂0.5 wt% La_2O_3时,陶瓷的电学性能最佳:d_(33) = 355 pC/N, Qm = 936, k_p = 58.4%, tanδ= 0.32%,ε_(33)~T= 1590。另一方面,Nb_2O_5掺杂对陶瓷压电性能的影响相对复杂,当Nb_2O_5掺杂量为0.5 wt%时,陶瓷也具有良好的电学性能:d_(33) = 300 pC/N, Qm = 971, k_p = 58.4%, tanδ= 0.36%,ε_(33)~T = 1332.。
Nowadays, high-power piezoelectric ceramics have received extensive attention and study due to their increasing applications in piezoelectric actuators and transformers. Particularly, the multilayer layer piezoelectric devices become a popular topic for their high power density. In general, co-firing process is preferred for multilayer devices. If the piezoelectric ceramics could be sintered below 900°C, pure Ag internal electrodes can be used instead of Ag-Pd alloy and the volatilization of PbO can be suppressed as well.
These days, some ternary or quaternary high-power piezoelectric ceramics were obtained by adding perovskite structure relaxors into PZT system. Among them, PZT–PMS–PZN quaternary system is a most qualified candidate for high-power applications with good electrical properties: d33 = 369 pC/N, Qm = 1381, k_p = 64%, tanδ= 0.44%, andε_(33)~T = 1600. However, previous studies used the molten salt synthesis method and the sintering temperature was as high as 1100°C. Therefore, PZT-PMS-PZN quaternary system was selected in this study, the composition design, low temperature sintering behavior and doping effects were discussed with respect to the crystal structure, micro-morphology and electrical performance.
0.90Pb(Zr_xTi_(1-x_)O_3-0.05Pb(Mn_(1/3_Sb_(2/3))O_3-0.05Pb(Zn1/3Nb_(2/3))O_3 quaternary high power piezoelectric ceramics were synthesized by using conventional solid-state sintering; to decrease the sintering temperature CuO was added as a sintering agent. The crystal structure, micro-morphology and electrical properties were studied in terms of Zr:Ti ratio and CuO content. These results indicate that the Zr:Ti ratio has a significant influence on the electrical properties; 0.90PZT-0.05PMS-0.05PZN (Zr:Ti=48:52) ceramics sintered at 1100°C with maximum tetragonality exhibit the optimal electrical properties: d33 = 355 pC/N, Qm = 1550, k_p = 60%, tanδ= 0.33%, andε_(33)~T = 1308. Moreover, 1.0 wt% CuO additive has a significant improvement in the sinterability of 0.90PZT-0.05PMS-0.05PZN ceramics, lowering the sintering temperature to 900°C and maintaining moderate electrical properties: d33 = 306 pC/N, Qm = 997, k_p = 53.6%, tanδ= 0.50%, andε_(33)~T = 1351. The low temperature sintering behavior could be explained with the formation of a transient liquid phase by CuO during sintering. Moreover, the endothermic peak at about 930°C in the differential thermal analysis (DTA) curve of the raw ceramic powder provides further evidence for amorphous phase.
To obtain more optimum piezoelectric properties, La_2O_3 and Nb_2O_5 were selected as donor doping to 0.90PZT-0.05PMS-0.05PZN + 1.0 wt% CuO system. Our study demonstrates that La_2O_3 is very effective on piezoelectric properties, remarkably increasing the d_(33) and k_p value without degrading the Qm value. Finally, 0.5 wt% La_2O_3 added 0.90PZT-0.05PMS-0.05PZN + 1.0 wt% CuO ceramics show excellent electrical properties: d_(33) = 355 pC/N, Qm = 936, k_p = 58.4%, tanδ= 0.32%, andε_(33)~T= 1590. On the other hand, the effect of Nb_2O_5 on piezoelectric properties is much complicated, 0.50 wt% Nb_2O_5 doped 0.90PZT-0.05PMS-0.05PZN + 1.0 wt% CuO ceramics have a remarkable improvement in k_p value and maintain good electrical properties: d_(33) = 300 pC/N, Qm = 971, k_p = 58.4%, tanδ= 0.36%, andε_(33)~T = 1332.
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