Preparation And Application Of Lead Zirconate Titanate And Potassium Sodium Niobate Based Piezoelectric Materials

Piezoelectric materials can realize the conversion of mechanical energy and electrical energy that have been widely used in industry,information communication,military,medical and so on.Among them,piezoelectric energy harvesters（PEHs）based on the principle of piezoelectric effect can convert vibration energy widely existing in life into electrical energy,and power a variety of self-powered microelectronic devices,which has been favored by researchers.On the other hand,the multilayer ceramic actuator（MLCA）based on the inverse piezoelectric effect can output higher displacement at lower driving voltage.MLCA has widely used in the field of precision instruments due to its light,thin and small size advantages.However,the research process also exists a lot of problems,such as the deterioration of piezoelectric properties of piezoelectric composites and the high production cost of precious metal electrodes apply in MLCA.In order to solve these problems,improving the fabrication process and doping modification was applied that prepared the lead zirconate titanate（PZT）-based piezoelectric composite energy harvester with high piezoelectric properties and the potassium sodium niobate（KNN）-based piezoelectric ceramic with good anti-reduction properties and the multilayer ceramic driver with base metal inner electrode.The microstructure,crystal structure,element distribution,piezoelectric,ferroelectric and dielectric properties of the samples were measured and analyzed.The main contents of this thesis are as follows:With the rapid development of electronic information technology,only by continuously improving the performance of piezoelectric materials can we better meet the application requirements and let piezoelectric materials burst into new vitality.In this paper,the PEHs,MLCA and the reducing-sintered potassium-sodium niobate（KNN）based piezoelectric ceramics were obtained by improving the preparation process and doping modification that with excellent performance.The improving mechanisms of the performance are described by testing and analyzing their micro-morphology,crystal structure,element distribution,piezoelectric,ferroelectric and dielectric properties.The works of this paper are as following:（1）The lead zirconate titanate（PZT）based piezoelectric composites with three dimensional（3D）vertically aligned microchannel structure and dense microscopy was constructed by the phase-inversion method.The polymer polyvinylidene fluoride（PVDF）and carbon nanotubes（CNTs）were mixed as the fillers and injected into the microchannels to fabricate the PZT/PVDF&CNTs composites.On the one hand,the 3D vertically aligned microchannel skeleton and uniformly distributed CNTs network could enhance the polarization and thus improve the piezoelectric coefficient d₃₃.On the other hand,the PVDF filler could effectively reduce the dielectric constantε_r.As a consequence,the excellent piezoelectric properties(d₃₃=595 p C/N,(9₃₃^*=881 pm/V)and relative low dielectric properties（ε_r=1603）were obtained in the PZT/PVDF&CNTs piezoelectric composites,which generated the ultra-high d₃₃×g₃₃(～24942×10^-15m²/N).Therefore,the PEHs assembled by PZT/PVDF&CNTs piezoelectric composite achieved the excellent energy harvesting performance（output voltage:66 V;short current:39.2μA;peak power:129.4μW）,and could easily light up 44 commercial LEDs.（2）K_0.48Na_0.52Nb_0.8Ta_0.2O₃+x mol%Cu O lead-free piezoelectric ceramics were prepared by traditional solid-state method,and their low-temperature sintering in reduction atmosphere was studied in detail.Cu O as the additive could not enter KNN perovskite lattice,so that the phase structure of KNN-based piezoelectric ceramics is unaffected.In addition,with the increase of the amount of Cu O doping,the liquid phase appears during the sintering process,which could promote the sintering of the ceramics and reduce the sintering temperature,this process also accompanies the increasement of the number of smaller grains.Furthermore,the reduction atmosphere sintering can reduce the average grain size and domain size,thus reduce the activation energy of domain wall switch.As a result,the domain switch faster under the applied electric field and the piezoelectric properties can improve.KNN-based piezoelectric ceramics doped with 2 mol%Cu O obtained excellent piezoelectric properties(d₃₃=166 p C/N,k_p=43.01%)and ferroelectric properties(P_max=27.42μC/cm²,P_r=19.01μC/cm²,(9₃₃^*=231pm/V@4 k V/mm),especially it could be sintered at a lower temperature（1060°C）in reducing atmosphere.（3）Prepared the KNN/Ni inner electrode co-fired MLCA by tape casting process,the micro-morphology and crystal structure of ceramic/electrode interface were analysed in detail.On the one hand,the low diffusion coefficient of Ni electrode ensured the stability of the ceramic/electrode interface,which led to excellent electrical stability of MLCA.On the other hand,different cations occupied the A/B position in the ceramic perovskite of MLCA samples by multi-element doping strategy,the differences between ion charge and size made the MLCA sample exhibit obvious relaxation behavior.As a result,the domain switch was promoted and the piezoelectric properties of the samples were improved.Finally,the 9-layer MLCA sample achieved ultra-high piezoelectric properties(d₃₃=3157 p C/N),nearly nine times as high as the bulk ceramics,and generated a displacement of 1.8μm at a low applied voltage of 200 V（the same displacement requires a voltage as high as 3700 V for～1 mm–thick bulk ceramic）.