Preparation And Performance Control Mechanism Of High Performance Lead Zirconate Titanate Based Piezoelectric Ceramics

Piezoelectric materials are extensively used in aviation,communication,medical treatment and other fields because they can realize the mutual conversion between electrical energy and mechanical energy.Lead zirconate titanate(PZT)based piezoelectric ceramics are the most popular piezoelectric materials at present.With excellent piezoelectric performance and electromechanical coupling performance,low preparation cost and adjustable performance,they have dominated the piezoelectric material market for decades.Based on the actual demand of high-power applications such as underwater acoustic transducers and ultrasonic actuators,this work focuses on the two main objectives,including the synergetic enhancement of electrical properties and the mechanism exploration of softening and hardening effect in PZT-based piezoelectric ceramics.The relationship between microstructure and macroscopic electrical properties of PZT-based piezoelectric ceramics was investigated and a new strategy was proposed to optimize the comprehensive performances of PZT-based piezoelectric ceramics.Firstly,by analyzing the solid-state sintering mechanism of PZTbased piezoelectric ceramics,the advantages and disadvantages of traditional solid-state sintering processes were summarized,revealing that the origin of problems such as the compositional heterogeneity and the low density of PZT-based piezoelectric ceramics is the lead volatilization at high temperatures.Therefore,a modified solid-state sintering process was proposed,which ensures high lead partial pressure during the sintering process by spreading lead powder and nesting double layer crucibles,thereby suppressing the lead volatilization at high temperatures.The proposed modified solid-state sintering process was compared with the traditional solid-state sintering process through experimental design.The results showed that this sintering process can significantly improve the compositional homogeneity and the density of PZT-based piezoelectric ceramics,and has low cost and simple operation.It is suitable for scientific research and large-scale production in factories,and also provides an experimental basis for subsequent research.Secondly,(Pb0.92Sr0.08)(Zr0.533Ti0.443Nb0.024)O3(PSZTN-xMn)piezoelectric ceramics doped with different mass fractions of MnCO3 were prepared by solid-state sintering process,and the influence of Mn doping on the microstructure and electrical properties of PSZTN piezoelectric ceramics was systematically studied.It was found that when the doping amount of MnCO3 is less than 1 wt.%,Mn ions promoted the grain growth in PSZTN piezoelectric ceramics and produced a significant hardening effect,while the piezoelectric response only suffered slight losses.A optimal performance combination was achieved in coarse-grain PSZTN ceramic samples with 0.4～0.5 wt.%MnCO3 doping amount:piezoelectric constant d33＝510～460 pC/N,mechanical quality factor Qm=614～750,electromechanical coupling coefficient kp=0.63～0.59,dielectric loss tanδ=0.002～0.004,Curie temperature Tc=278℃.Based on the classical defect models and the hardening effect models,a defects-domain walls-grain boundaries interaction model related to grain size was proposed.This work successfully solved the performance bottleneck that PZT-based piezoelectric ceramics cannot achieve high d33 and Qm simultaneously,and creatively proposed that grain size engineering is an effective strategy for synergistically optimizing the comprehensive performance of piezoelectric ceramics.Finally,a series of tetragonal PbZr0.48Ti0.52O3(PZT48/52)and rhombohedral PbZr0.55Ti0.45O3(PZT55/45)piezoelectric ceramic samples with different grain sizes were prepared by controlling the sintering temperatures and holding times.The grain size effect and physical mechanism in tetragonal and rhombic PZT piezoelectric ceramics were systematically studied.The experimental results indicate that the reduction of grain size in PZT piezoelectric ceramics with different phase structures can lead to a decrease in macroscopic piezoelectric properties and changes in microscopic domain morphology.In tetragonal PZT ceramics,it was observed that the decrease in grain size caused the destruction of longrange ordering of ferroelectric domains,whereas in rhombohedral PZT ceramics,grain size reduction significantly suppresses the non-180°ferroelectric domain formation.It was proved through piezoelectric microscopy that the influence of grain size reduction on domain morphology comes from the increase of residual stress inside grains.On the contrary,the increase in grain size produced a significant softening effect in both phase structure PZT ceramics,and even a hardening effect was observed in rhombohedral PZT ceramics at the same time.The switching behavior of local ferroelectric domains was characterized by the piezoelectric microscopy,demonstrating that increasing grain size is beneficial for enhancing the contribution of bulk effects,resulting in macroscopic hardening effects.This result further validates the proposed grain size-dependent defects-domain walls-grain boundaries interaction model.