Thickness Dependent And Doping Modification Of BiScO₃-PbTiO₃ Piezoelectric Ceramics

Perovskite BiScO₃-PbTiO₃ ceramics have high Curie temperature and excellent dielectric,ferroelectric and piezoelectric properties near the morphotropic phase boundary（MPB）,which has strong competitiveness in the application of piezoelectric devices.However,the high dielectric loss tanδand low mechanical quality factor Q_m of BS-PT ceramics limit its application in high-power piezoelectric devices.In practical application,the working frequency can be controlled by adjusting the thickness of the piezoelectric element,and the requirements of working frequency are different in different application scenarios.In this paper,0.365BiScO₃-0.635PbTiO₃ ceramics were prepared by solid state reaction.The thickness effect,phase structure and domain change were studied.The structure and properties of BS-PT ceramics doped with Mn/Fe/Ni/Co were compared.The structure and properties of BS-PT ceramics doped with different elements were compared.The phase structure,dielectric and piezoelectric properties of BS-PT ceramics with different Co content were studied,and the conductive mechanism was analyzed.The dielectric constant（ε_r）,dielectric loss（tanδ）,Curie temperature（T_c）,piezoelectric coefficient(d₃₃)and mechanical quality factor（Q_m）of BS-0.635PT were1258,5.0%,421 ^oC,458 p C/N and 23,respectively.With the increase of BS-0.635PT ceramics thickness,the content of rhombohedral phase and the degree of domain reversal increased,the dielectric and piezoelectric properties of the ceramics were improved.When the thickness increased from 0.2 mm to 1.0 mm,the and d₃₃ of BS-0.635PT ceramics increased and then stabilized（>1.0 mm）,ε_r increased by 39%from 1240 to 1720,and d₃₃ increased by 36%from 330 p C/N to 450 p C/N.The resonant frequency range of BS-0.635PT ceramics decreased from 9.3 MHz（0.2 mm）to 2.0 MHz（1.0 mm）with increasing thickness.When Mn/Fe/Ni/Co was introduced into BS-PT ceramics,the grain size of the ceramics varied greatly,which were 8.73,1.26,16.93 and 17.12μm,respectively.BS-PT ceramics doped with Mn/Ni had smalle dielectric loss and high Curie temperature,which were 0.95%0.86%and 439 ^oC 437 ^oC,but their d₃₃ and Q_m were small,which were 195 p C/N 187 p C/N and 71 78,respectively.Fe doped BS-PT ceramics had high Curie temperature and excellent piezoelectric property,but tanδand Q_m were small,T_c,d₃₃,tanδ,Q_m were 440 ^oC,290 p C/N,3.8%and 21.With the increase of Co content,tetragonal phase increased,tetragonal distortion and grain size first increased and then decreased,dielectric loss first decreased and then increased,mechanical quality factor increased.The piezoelectric coefficient and Curie temperature had no obvious change of 0.365BiScO₃-0.635Pb(Ti_1-xCo_x)O₃（x=0.01、0.02、0.03 and 0.04）ceramics.0.365BiScO₃-0.635Pb(Ti_0.97Co_0.03)O₃ ceramics had superior comprehensive properties,tanδ,T_c,d₃₃ and Q_m were 3.0%,437 ^oC,240p C/N and 151,respectively.Impedance analysis showed that the BS-PT ceramics doped with Co had negative temperature coefficient,and the macro resistance was mainly contributed by the grain size.The conductive carriers in the ceramics were mainly oxygen vacancies.