The Study Of Textured (1-x)PMN–xPT Ceramics And Their Strain Hysteresis Regulation

Piezo-actuators can output fast and ultrahigh-precision mechanical displacement and plays an indispensable role in the fields of microelectronics,optoelectronics,aeronautics,precision manufacturing.However,piezoelectric ceramics show hysteresis and nonlinearity in deformation because of their structure.The change of output displacement is unable to catch up with the input voltage,which causes the hysteresis and limits the precision and bandwidth of piezo-actuators.The strain hysteresis of commercial PZT piezo-ceramics falls in the range of 10%–15%.In view of the above problem,textured(1-x)Pb(Mg_1/2Nb_2/3)O₃–xPbTiO₃(PMN–xPT)ceramics used in actuators are prepared in this paper.The physical mechanism of strain hysteresis in textured PMN–x PT ceramics has been studied.Multiple regulation methods including composition optimization,doping and injected charges are employed to reduce the strain hysteresis and nonlinearity.Regulation mechanisms have been deeply studied.The main achievements are as follows:The influences of some key factors including template morphology,B-site valance mismatch and the grain size on the templated grain growth(TGG)have been studied.Three kinds of precursors Bi₄Ti₃O₁₂,conventional BaBi₄Ti₄O₁₅ and modified BaBi₄Ti₄O₁₅precursors are submitted to the topo-chemical microcrystal conversion(TMC)reaction to synthetize BaTiO₃ templates.Among them,the modified BaBi₄Ti₄O₁₅ precursor is more stable than the other precursors.TMC reaction can copy the shape of the modified BaBi₄Ti₄O₁₅ precursor well and the obtained BaTiO₃ templates are regular and uniform in shape.Their dimension is about 10×10×0.5?m.On the above basis,the influence of B-site valance mismatch between the BaTiO₃ template and complex perovskite Pb(B'_1/3B''_2/3)_1-xTixO₃ on the TGG has been studied.The results indicate that Ti⁴⁺content x of complex perovskite Pb(B'_1/3B''_2/3)_1-xTixO₃ has to be higher than 9%so as to epitaxiallly grow on BaTiO₃ templates.The influence of grain size on the kinetics of TGG has been studied.The results indicate that Lotgering(LOT)factor can be elevated by increasing the grain size.When the grain size reaches 20?m,LOT factor exceeds 99.5%.The influence of composition of textured PMN–x PT ceramics on the strain hysteresis has been studied.The results indicate that the strain hysteresis of MPB and tetragonal textured PMN–x PT ceramics are 24%and 50%.Compared to MPB and tetragonal PMN–x PT ceramics,rhombohedral textured PMN–24%PT ceramic shows a lower strain hysteresis which is only 9%.Its high field piezoelectric coefficientd₃₃^*is 500 pm/V and it exhibits a quasi-linear piezoelectric strain behaviour.The results of chemical etching and phase field simulation demonstrate that a stable multi-domain state is obtained in<001>poled rhombohedral PMN–24%PT.Under this fixed domain configuration,piezoelectric strain is mainly contributed from lattice stretching and it is characterized by high linearity and low hysteresis.On the above basis,the influences of MnCO₃,Ga₂O₃ and Sm₂O₃ dopants on the strain hysteresis,piezoelectric and dielectric properties of<001>textured PMN–24%PT(<001>PMN–24%PT)ceramics have been studied.The results indicate that the strain hysteresis of<001>PMN–24%PT ceramics is decreased from 9%to 7%after doping 1mol%MnCO₃,while the high field piezoelectric coefficientd₃₃^*is basically unchanged.d₃₃^*is increased up to 630 pm/V after doping 1%Sm on A sites,and the strain hysteresis is a bit increased.The results of high-temperature impedance spectroscopy and high-field dielectric loss indicate that the electric conduction of<001>PMN–24%PT ceramics is reduced by two order of magnitudes after doping 1%Mn²⁺ions on B sites and the mechanical loss is significantly reduced too.Comprehensive analysis shows that compared to Ga and Sm dopants,Mn²⁺dopants and associated oxygen vacancies can pin the domain walls and stabilize the domain structure,as a result,the strain hysteresis is reduced.Furtherly,the method of injecting charges is employed to reduce the strain hysteresis of<001>PMN–24%PT ceramics.The generation mechanism of injected charges is analyzed.Phase field simulation indicates that when the injected charges are adequate the inner offset field can pre-tighten the domain structure of<001>PMN–24%PT ceramics so domains change to be unswitchable.Based on the above principle,a ceramic/metal/ceramic multi-layer structure and a 0–3 type composite structure have been designed.The results indicate that seting silver in series connection with<001>PMN–24%PT can help to inject more charges and the inner offset field is increased.Compared with the single-layer structure,the strain hysteresis of multi-layer structure is much lower.xvol%Pt+<001>PMN–24%PT composite ceramics with 0–3 type structure have been prepared.The influence of micro Pt grains on the strain hysteresis of<001>PMN–24%PT ceramics has been studied.The results indicate that compared to multi-layer structure,0–3type structure can substantially increase the contacting area between the metal phase and the ceramic phase,which will increase the injected charges.1vol%Pt+<001>PMN–24%PT composite ceramic exhibits a linear strain behavior and the strain hysteresis is nearly zero.Its offset field is 6.4 kV/cm.The inner offset field of 1%Sm doped composite ceramic is 8kV/cm which is five times as high in the simple ceramics.d₃₃^*is still 420 pm/V and the strain hysteresis is nearly zero.The overall results indicate that when the domain structure has been pre-tightened by the inner offset field,external unipolar field which adds on the inner offset field can only induce lattice stretching so the strain hysteresis is nearly zero.Finally,the piezo-stacks actuator based on 0–3 type composite ceramics is fabricated.It is demonstrated that the piezo-stacks actuator is able to output a linear and non-hysteretic displacement.