Structure,Properties And Multilayer Devices Of PZT-based Piezoelectric Ceramics

PZT-based piezoelectric ceramics exhibit high Curie temperature,excellent piezoelectric properties,good temperature stability and simple preparation process,which makes them useful in a wide range of applications,including transducers,high-voltage generators,actuators and sensors.Although commercial PZT-based ceramics have achieved excellent comprehensive performance at present,the applications and basic research for PZT can not be well combined.There are still many important phenomena in PZT-based piezoelectric ceramics to be explained and understood.For instance,the difference between relaxor and diffused phase transition and influencing factors have not been lucubrated.The defect dipoles affecting the dielectric and piezoelectric properties is not well understood.In addition,PZT based piezoelectric ceramics,the fabrication of device prototypes and the optimization of technological process still need to be further explored after basic studying.Thus,it is important to investigate the relationship between structure and performance of PZT-based piezoelectric ceramics and develop the application research of multi-layer structures.In this paper,the phase structure,microstructure and electrical properties of PZnTe-PZT and PMW-PZT ternary piezoelectric ceramics were studied.We discuss the influence factors on diffused phase transition behavior and explain dielectric and piezoelectric abnormal phenomena by defect dipoles.Furthermore,we obtain the optimum ceramics composition through the regulation of ceramic components,fabricate multilayer piezoelectric ceramic devices by stacking process and casting process,and then study their structure and properties.In the xPZnTe-（1-x）PZT system,it is found that the crystal structure gradually change from the tetragonal phase to the rhombohedral phase as the increase of x content.The c-axis decreases while the a-axis increases,and the lattice volume decreases.MPB is located in x=0.08 composition.With the addition of PZnTe,the grain size of ceramics decreases obviously,but it remains unchanged with the increase of x content.MPB composition has the best ferroelectric and piezoelectric properties,and P_r,d₃₃ and k_p reach the maximum value.The T_m decreases linearly with the increase of x content,and the decline is much larger than that of other PZT-based ceramics.The permittivity peak becomes broaden when PZnTe is added into in permittivity-temperature curves.The"brick wall"model is introduced to explain the dielectric diffusion phenomenon.The results show that the smaller the ceramics grain size,the higher the diffusion degree of the permittivity peak.The element distribution of the grain and the grain boundary is analyzed by EDS,which proves the rationality of the"brick-wall"model.The dielectric diffusion is also related to the doping effect of PZnTe.The fitting of the empirical formula shows that the diffusion characteristic is more remarkable when PZnTe content is higher.The permittivity diffusion of PZnTe-PZT system does not exhibit the frequency dispersion effect,so it is not a relaxor.Diffused phase transition in PZnTe-PZT system is also found in thermal expansion properties.In the PMW-PZT system,the rhombohedral-tetragonal phase boundary is located in the composition of Zr/Ti=47.5/52.5.Different dopants have different doping effects on the properties.Fe doping shows the hard doping effect and Nb doping shows the soft doping effect,as the normal doping effect for PZT system,while Mn doping shows the both hard and soft doping effect and its comprehensive performance is the best.Different Mn doping content in PMW-PZT system are studied in detail.It is found that the addition of Mn can incerase P_r,decrease E_c,and improve strain and reverse current.When the Mn content is 0.5 at%,ceramics have the best electrical properties,including T_c²34℃,ε_r（1 kHz）¹958,tanδ（1 kHz）⁰.92%,P_r³4.5μC/cm²,E_c¹3.8 kV/cm,S（40 kV/cm）⁰.216%,d₃₃⁵62 pC/N,k_p⁰.70,Q_m¹89.The Mn doped PMW-PZT ceramics poled samples show a small peaks ofε_r,tanδ,k_p and d₃₁ at 80℃¹00℃.XRD tests with different temperature show the phase structure does not change during the heating process.The dielectric and piezoelectric peaks disappear after aging treatment,which indicate that the phenomenon is related to the movement of defect dipoles.The state of defect dipoles in unpoled,poled,testing and aging treatment is described and it explains successfully the dielectric and piezoelectric abnormal phenomenon.The TSDC results also prove the defect dipoles.In the study of stacking process of multilayer ceramics,it is found that the S,f_r,k_p,Q_m and d₃₁ of PMW-PZT-Mn system have good temperature stability.Twenty layers of multilayer ceramics are prepared by stacking process.The thermal expansion coefficient of multilayer ceramics is larger than that of single ceramics.The displacement of multilayer structure can reach 3.55 um under 320 V voltage and 20 N preload force,and the displacement decreases slightly with the increase of preload force.The vibration velocity of multilayer ceramics is 1.86 mm/s when the applied voltage is 320 V and the voltage frequency is 100 Hz.In the study of tape casting process of multilayer ceramics,the modification of PMW-PZT-Mn system by low temperature sintering is studied firstly.The optimum low-temperature sintering aids composition is 1 wt%LiBiO₂+0.2 wt%CuO,which can make the ceramics sintered at 900℃⁹80℃.Twenty layers of multilayer ceramic films are prepared by tape casting process and laminated process.The particle size of ceramic powders is measured and its D50 is 0.439 um.The viscosity of slurry is tested and it is 1200 mPa s when the shear rate is 25 s^-1.The displacement of the multilayer ceramic film is 1.75 um at 320 V applied voltage,and the hysteresis of displacement is 6%.