| In recent years,lead-based piezoelectric ceramics have been widely used in electronic components and communication technology.However,the lead element in lead-based piezoelectric ceramics has harmful effects on the natural environment and human health.Hence,it is necessary to consider the development of lead-free high-performance piezoelectric ceramics.Bi0.5Na0.5TiO3(BNT)and BaTiO3(BT)-based ceramics are two candidate materials that are expected to replace lead-based piezoelectric ceramics in lead-free piezoelectric ceramics.BNT based ceramics generally have high strain performance in high field,but its coercive field is relatively high.BT based ceramics have excellent piezoelectric properties in weak field.Based on this,the main research objects of this paper are BNT and BaSn0.11Ti0.89O3(BST)-based lead-free piezoelectric ceramics.The microstructures and electrical properties of the ceramics were studied.The main contents and results were as follows:(1)BNT-xBT(x=0,0.06,0.07,0.075,0.08 and 0.088)ceramics were prepared by traditional solid-phase synthesis method.The XRD and Raman spectra showed that structures of the ceramics changed from pseudo cubic phase(x=0)to tetragonal phase(x>0.075)at room temperature,and there was two-phase coexistence of rhombohedral and tetragonal phase structures in the range of 0.06<x<0.07.The grain size of ceramics decreased with the increase of x at x ≤0.07 and increased at x>0.07.In the analysis of dielectric properties,as Curie temperatures of ceramics moved to low temperatures with increasing BT content,the maximum dielectric constants of ceramics increased and the degrees of dielectric dispersion increased.The highest value of remnant polarization was 42.6 μC/cm2 at x=0.06.The best piezoelectric properties were obtained at x=0.07:high piezoelectric coefficient d33*=～20534 pm/V in the initial cyclic electric field;the maximum in-situ piezoelectric coefficient and the maximum room temperature piezoelectric coefficient of ceramics were 223 pC/N and 160 pC/N,respectively.Rayleigh law analysed that the coexistence of two-phases structure enhanced extrinsic contributions on piezoelectric properties of ceramics,and the intrinsic contribution of the piezoelectric properties of the piezoelectric ceramics with tetragonal phase structure was relatively large.(2)Co-doped BST+xCo2O3(BST+xCo,x=0,0.1%,0.3%,0.5%,0.7%and 0.9%)ceramics were prepared by traditional solid-phase synthesis.XRD and Raman spectra showed that structures of the ceramics transformed from pseudo cubic phase(x=0)to tetragonal phase(0.1%≤x≤0.3%),and finally to pseudo cubic phase(0.5%≤x≤0.9%)at room temperature.The grain sizes of ceramics increased first and then decreased with the increased of Co content,and the maximum average grain size was 253.64 μm at x=0.1%.The best electrical properties were obtained at BST+0.1%Co ceramics:the maximum dielectric constant of 4.49×104,the highest value of polarization was 19.1μm/cm2,the maximum unipolar inverse piezoelectric coefficient of 1570 pm/V(E=1.4 kV/cm),the maximum in-situ and ex-situ piezoelectric coefficients were 726 pC/N and 670 pC/N,respectively,the maximum bias electric field inverse piezoelectric coefficient of 1158 pm/V.In addition,the electrostrictive coefficient of BST+xCo ceramics increases first and then decreases with the increase of Co content(maximum Q33=0.0336 m4C-2).With the increased of Co content,the mechanical quality factor of ceramics first decreased and then increased(maximum Qm=426)and the dispersion indexs of ceramics decreased first and then increased.(3)Cu-doped BST+xCuO(BST+xCu,x=0.1%,0.3%,0.5%,0.7%and 0.9%)ceramics were prepared by traditional solid-phase synthesis.The XRD patterns showed that all ceramics are tetragonal phase perovskite structures.The SEM indicated that the growth of ceramic grains was inhibited with the increase of Cu content.Excessive Cu content would cause pores between ceramic grains.With the increased of Cu content,the dielectric dispersion of BST+xCuO ceramics decreased and the dielectric properties of ceramics were improved.The best electrical properties were obtained at BST+0.8%CuO ceramics:the maximum permittivity εmax=5.23×104,the maximum residual polarization Pr=10.53 μC/cm2,the minimum coercive electric field Ec=1.01 kV/cm,the maximum strains of bipolar and unipole were 0.114%and 0.116%,respectively,the maximum reverse piezoelectric coefficients of bipolar and unipole were 676 pm/V and 808 pm/V(E=10 kV/cm),respectively,the maximum piezoelectric coefficient d33=878 pC/N and kp=0.562,respectively.The effect of intrinsic and extrinsic contributions on unipolar strain of ceramics was analyzed by Rayleigh law,and it was found that the high strain of ceramics at x=0.8%was mainly dominated by intrinsic contributions.(4)In this paper,BNT and BST-based lead-free ceramics were selected to illustrate the relationship between structure and electrical properties.The two-phase coexistence structure of the BNT-based ceramics resulted in excellent electrical properties of the ceramics.The large size grain structure of the BST-based ceramics made it easy to switch the domains and cause sensitivity to low electric fields.BST-based ceramics showed excellent piezoelectric performance in weak field.Therefore,we proposed a new idea for the design of high-performance lead-free piezoelectric ceramics based on the characteristics of the two ceramic systems. |
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