Study On Structure And Piezoelectric Properties Of Bismuth Sodium Titanate Based Porous Ceramics

Environmentl-friendly Na_0.5Bi_0.5TiO₃（NBT）-based ceramics have excellent dielectric,piezoelectric properties and good electromechanical coupling properties.It is the main method for the development and application of functional materials to improve material properties and expand its application fields by regulating the grain size and morphology of materials.Porous piezoelectric ceramics help to reduce the acoustic impedance,modulate the piezoelectric harmonic response,and improve the electro-mechanical coupling conversion characteristics.It is expected to expand the application of porous piezoelectric ceramics in electro-mechanical coupling devices such as underwater acoustic transducers.In this paper,0.94Na_0.5Bi_0.5TiO₃-0.06BaTiO₃（NBT-BT）porous ceramics were prepared by pore-forming agent,and the effects of porous structure on micro structure,dielectric and piezoelectric properties were investigated.Firstly,pollen and dextrin were selected as pore-forming agents to prepare NBT-BT porous ceramics with micro-nano porous structure characteristics in this paper.Porous ceramics with long spherical pore structure were prepared by using pollen as pore-forming agent with porosity of 10.3～43.6%.Porous ceramics with ellipsoidal pore structure were prepared with dextrin as pore-forming agent,and the porosity was 5.4～13.3%.The effect of long spherical pore structure on the properties of NBT-BT porous piezoelectric ceramics is more obvious than that of ellipsoidal pore structure.The dielectric constant and piezoelectric coefficient are significantly reduced,and the acoustic performance is significantly improved.The hydrostatic optimal value of porous ceramics is larger,and the acoustic impedance is smaller.Secondly,rare earth Sm was selected as dopant and porous[Smx(Bi_0.5Na_0.5)_1-3x/2]_0.94Ba_0.06TiO₃（BNBT6-xSm）piezoelectric ceramics were prepared by solid-state reaction method.The effects of Sm doping on the grain size,dielectric and piezoelectric properties and harmonic response characteristics of NBT-BT piezoelectric ceramics were studied.It is found that appropriate Sm3+doping can reduce the coercive field of NBT-BT ceramics,increase the residual polarization strength,field-induced strain and piezoelectric constant,and increase the degree of ferroelectric relaxation behavior.The geometrical configuration（thickness h=0.6 mm,diameter d=13.2～14.1 mm）of the thin circular resonator is optimized by using porous BNBT6-xSm piezoelectric ceramics,which can excite the length stretching vibration mode（LE mode）perpendicular to the excitation electric field and can be used as the main material of piezoelectric resonant devices in complex vibration environment.Finally,the direct-hole NBT-BT piezoelectric ceramics were prepared by sodium alginate ion gel method,and the influence of the direct-hole structure on the piezoelectric properties and piezoelectric harmonic response characteristics was studied.In order to further predict the mechanical and electrical parameters of porous materials and devices and explore the basic resonance characteristics in the coupling process,the geometric modeling and vibration modal optimization analysis of piezoelectric vibrator are carried out based on finite element method.The measurement results of piezoelectric parameters are basically consistent with the prediction results of the model,which can further optimize,predict and evaluate the macroscopic properties of the system materials,and provide guidance for the application and development of porous lead-free piezoelectric ceramics in the fields of electro-mechanical coupling devices.