| Piezoelectric ceramics are a kind of function materials that can realize transformation between electric energy and mechanical energy,thus widely used in information technology,electronic communications,transportation hub,aerospace,energy acquisition,health care and other fields.Barium titanate(BaTiO3,abbreviated as BT)is a lead-free piezoelectric material with perovskite lattice structure,and has drawn intensiveattentions due to its low cost and superior electrical performance.The only problem is that the piezoelectric performance of BT still cannot match that of state-of arts lead-based materials(PbZrO3-PbTiO3,abbreviated as PZT).Fortunately,researchers discovered in 2009 that the pseudo-binary ceramics of Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3(abbreviated as BCZT)exhibited excellent piezoelectric properties near morphotropicphase boundary(MPB),almost as good as that of state-of-arts PZT.However,BCZT synthesis with traditional solid-state method needs extremely high sintering temperature(approximately 1440 ?),thus cannot be applied in large-scale commercial production in the aspect of energy cost.We,therefore,utilize molten salt method and co-precipitation method to synthesize BCZT ceramics in this thesis,for the purpose of decreasing the sintering temperature,tuning the microstructure,studying the microstructure-propertiesinter-relationship,and eventually achieving enhanced electrical properties.The main results are concluded as follows:1.We successfully prepared(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 powders and ceramics by the molten salt method,and systematically studiedthe effect of molten salt species,molten salt ratio,calcination temperature and sintering temperature on the phase structure,microstructure,piezoelectric-ferroelectric properties and energy storage performance.The optimum preparation conditions of BCZT ceramics by molten salt method are as follows:specie of molten salt is KCl-NaCl,ratio of molten salt is 50%,calcination temperature is 1100 ?,and sintering temperature is 1360 ?.Electrical properties of the BCZT ceramics synthesized under optimal conditions are as follows:Pr = 9.98 ?C/cm2,Ec = 2.58kV/cm,?max= 15872,tan? = 0.013,kp=0.57,d33 = 604pC/N,Wrec = 0.15 J/cm3,? = 47%.These results exhibit a significant enhancement over that by solid state method.In addition,a reasonable reaction mechanism of BCZT powders synthesis was proposed.2.We successfully prepared(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 materials by the co-precipitation method,and systematically studied the effects of different precursor conditions on the morphology of powders and the effects of sintering process on the properties of ceramics.The results showed that powders are with uniform grain size and sphericity.The precursor conditions are as follows:(Ba+Ca)/(Zr+Ti)(A/B)ratio is 1.3,reactant concentration is 0.20 mol/L,NaOH concentration is 8 mol/L,and the best order of addition is first B-sites(Zr+Ti),then A-sites(Ba+Ca);optimal sintering processes of compact ceramics:calcination temperature is 900 ?,sintering temperature is 1400 ?.The electrical properties of the BCZT ceramic sample prepared under optimal experimental conditions are as follows:Pr= 6.65 ?C/cm2,Ec = 1.83 kV/cm,?max = 11592,tan? = 0.019,kp=0.33,d33 = 350 pC/N,Wrec = 0.29 J/cm3,? = 69%.In particular,the energy storage density was significantly improved over that by solid-state method and molten salt method.The reaction mechanism of BCZT powders prepared by co-precipitation method was also proposed in this section.3.Phase structure,microstructure,ferroelectric properties,dielectric properties,piezoelectric properties,and energy storage performance of(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics prepared by solid-state method,molten salt method and co-precipitation method were systematically compared.We demonstrate that the molten salt method and the co-precipitation method can significantly reduce the phase formation temperature of BCZT by 200 ? and 400 ? individually.In addition,BCZT ceramics prepared by the molten salt method exhibits best electrical properties which can be ascribed to compact microstructure and large crystal grains,while BCZT ceramics prepared by the co-precipitation method own superior energy storage properties mainly due to their compact microstructure and small crystal grains.4.We introduced Ba0.3Sr0.7TiO3 into(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 in order to optimize its electrical properties using molten salt method.The effect of BST doping content and sintering temperature on the electrical properties of(1-x)BCZT-xBST ceramics were studied systematically.The optimal doping content of BST and sintering temperature are 15%and 1380 ?,respectively;and the corresponding electrical properties are as follows:Pr = 9.5 ?C/cm2,Ec = 2.40 kV/cm,d33 = 470 pC/N,kp = 50%,?m = 14904,?r=3701,tan? = 0.016,Tc = 81 ?,BDS = 70 kV/cm,Wrec= 0.18 J/cm3,? = 65%.It is remarkable that the energy storage density of 0.85BCZT-0.15BST was increased by 20%as compared with pure BCZT prepared by molten salt method. |
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