Preparation And Modification Of PMT-PMS-PZT High Power Piezoelectric Ceramics

Piezoelectric ceramic is a key component in ultrasonic motors that converts electrical energy to mechanical energy and is necessary to have high mechanical quality factor (Q_m), high piezoelectric coefficient (d₃₃) and electromechanical coupling factor (k_p), low loss factor(tanδ) and good high power properties. However, the"soft"and"hard"properties of ordinary PZT ceramics are contradictory to each other, Pb(Mn_1/2Sb_2/3)O₃-Pb(Zr,Ti)O₃ (PMS-PZT)based ceramics is a good candidate for high power applications due to its high Q_m and k_p. In our previous work, the relaxor ferroelectrics Pb(Mg_1/3Ta_2/3)O₃ was introduced into PMS-PZT to form a quaternary system Pb(Mg_1/3Ta_2/3)O₃-Pb(Mn1/3Sb2/3)O3-Pb(Zr,Ti)O₃(PMT-PMS-PZT) and good properties were obtained. However, many superior characteristics of PMT-PMS-PZT have not been discovered. Therefore, the effects of composition, process and doping effects on the crystal structure, microstructure and high power properties of PMT-PMS-PZT were studied to improve the properties of this system.Firstly, the effects of PMT content on the properties of PMT-PMS-PZT ceramics have been investigated and the optimized content of PMT is 0.05 mol in this system; secondly, the morphotropic phase boundary (MPB) in 0.05PMT-0.05PMS-0.9PZT ceramics was found near Zr/Ti = 48/52 by changing the Zr/Ti ratio, the ceramics of this composition possess good properties:ε_r = 1296,d₃₃ = 308 pC/N, Q_m = 1557, k_p = 0.55, tanδ= 0.46%, T_c = 302 oC, the P-E loops presented pinched shapes at low electric fields because of the pinning effect of defect dipoles, the dielectric study revealed a diffuse phase transition behavior in the ceramics andγhad the maximum value near the MPB; the calcined temperature, sintering temperature and poling process to the piezoelectric properties of the ceramics were also investigated, the proper processing procedure of the ceramics is calcined at 850 oC, intering at 1240 oC and poled at a electric field of 4.1 kV/mm in 110 oC silicon oil for 20 minutes.La₂O₃ and Yb₂O₃ were doped into the ceramics to investigate their effcts on the electrical and high power properties. La₂O₃ improved the"soft"properties of the ceramics evidently, the properties of the ceramics with 0.4 wt.% doped La₂O₃ are:ε_r = 1418,d₃₃ = 336 pC/N,Q_m = 975,k_p = 0.571, tanδ= 0.42%。Yb₂O₃also improved the"soft"properties of the ceramics, the ceramics with 0.5 at.% Yb₂O₃ show optimium properties:ε_r = 1164, d₃₃ = 278 pC/N, Q_m = 1243, k_p = 0.547, tanδ= 0.42%, the high power test show that the maximum vibration velocity was as high as 0.78 m/s for this composition.