Study On The Performance And Doping Effect Of PMN-PZT Ceramics

PMN ceramics exhibit high dielectric and piezoelectric properties, while the Curie temperature remains below room temperature. PZT ceramics exhibit high Curie temperature and low piezoelectric properties at lower temperature. Therefore, the introduction of PMN to PZT ceramic may obtain a new product which express mixed properties of the two ceramics. PMN-PZT ceramics could be easily tailored for desired dielectric and piezoelectric properties by changing the composition and doping with different dopants, it is an ideal material for the fabrication of multilayer piezoelectric ceramic capacitors, precision micro-displacement, sensors, actuators, medical ultrasound transducers, and other functions of the device.The piezoelectric ceramics we studied are used for preparing long strip of piezoelectric bimorph, based on the composition of PMN-PZT piezoelectric ceramic, the MgNb2O6powder and the ceramics with pure perovskite phase are successfully obtained by columbite precursor method. Firstly, we try to get the compositions with excellent properties by optimizing the PMN component content and adjusting Zr/Ti ratio. When the Zr/Ti ratio is fixed as52/48, the Curie temperature of the ceramic is significantly decreased with increasing PMN mole fraction, while the dielectric constant at room temperature is gradually increased, the excellent electrical properties are obtained for ceramic with25mol%PMN, d33=260pC/N, K31=0.36and Qm=131. The MPB compositions of the PMN-PZT systems with20mol%addition of PMN lies near the Zr/Ti ratios of48/52-52/48, while the Zr/Ti ratios of44/56-48/52when it with25mol%addition of PMN, We can conclude that:the MPB of the ceramic move to the low ratio of Ti/Zr with increasing PMN content.Secondly, the effect of Sr2+, Ba2+, La3+, Nb5+and Ni2+doping on phase compose, microstructure, piezoelectric properties and dielectric properties are systemly studied. The Curie temperature of the ceramic is significantly decreased when doping with Sr2+, the excellent electrical properties are obtained for the PMN-PZT ceramic with10mol%Sr2+,:ε=4731, tanθ=0.026, d33=530pC/N, K3i=0.42, Qm=73.5, but Tc of the samples are just154℃. The influence of multiple doping with Sr2+and Ba2+on dielectric and piezoelectric properties is investigated, the Tc of the ceramic is increased gradually with Sr2+content decreasing and Ba2+content increasing, but the electrical properties degradation because of the ceramic component deviated from MPB. The Tc of the ceramic is significantly decreased when modified with La3+, witch is used to increasing the ε at room temperature. The pyrochlore phase which deterioration in performance is produced when the doping amount of La2O3exceeds0.75wt%, the optimum piezoelectric properties is observed in0.25wt%La2O3doping PMN-PZT, d33=509pC/N, K31=0.45, Qm=82.5. The electrical properties of the ceramic are slightly improved when doping with a small amount of Nbs+or Ni2+, degenerated with excess Nb5+or Ni2+, while the Tc of the ceramic is nearly unchanged. The optimum electrical properties are obtained with0.2wt%Nb2O5(ε=3850, tanθ=0.019, d33=528pC/N, K31=0.45, Qm=57) and0.1wt%NiCO3(ε=3830, tanθ=0.017, d33=501pC/N, K31=0.43, Qm=87) respectively.