Preparation And Properties Of Self-poled Bi₁₂TiO₂₀ Based Ceramics

As a kind of functional material which can convert mechanical energy and electric energy,piezoelectric material is very important in all fields of industry and science.For solid piezoelectric materials,When the temperature is higher than the Curie temperature of the material itself,the piezoelectric properties will disappear.Therefore,for traditional piezoelectric ceramics,the application of materials at high temperature will be greatly limited.However,the piezoelectric properties of the flexural piezoelectric materials designed by using the flexoelectric effect are not affected by temperature,so this problem can be avoided.The self-poled piezoelectric ceramics can have certain piezoelectric properties only by sintering and without applying electric field polarization by using the flexural electric effect.In this work,this new type of self-poled piezoelectric ceramic material is studied.The self-poled ceramic material is prepared by choosing different materials and Bi₁₂TiO₂₀ phase composite.Controlling the content of Bi₁₂Ti O₂₀phase in the composite ceramic and controlling the sintering temperature of the ceramic,this kind of self-poled ceramic is studied systematically.The piezoelectric properties of this kind of natural polar ceramics are improved by optimizing the material design.Conventional solid state method was used to prepare BCZT-x%Bi₁₂Ti O₂₀ceramics,the results of xrd show that the micro-addition of different Bi₁₂Ti O₂₀has no effect on the main crystal structure of the ceramics and all the samples are single tetragonal BaTiO₃ structure.The maximum dielectric constant of the samples is obtained at x=0.05.At 1 kHz,the dielectric loss is 1.5%.The x=0.5sample exhibits a high dielectric breakdown strength of 8 kV·mm^-1,a high maximum polarization of 17.79?C·cm^-2,and has a high energy-storage density of 0.388 J·cm^-3.The microaddition of Bi₁₂TiO₂₀ to BCZT does not exhibit macroscopic piezoelectric properties.Bi₁₂TiO₂₀-BaTiO₃ self-poled ceramic composites were prepared by conventional solid-state method.It was found from the Raman spectra that the position and half-width of the BaTi O₃ Raman peaks were not changed obviously.The decrease of Bi₁₂Ti O₂₀0 Raman peak,the broadening and the shift to low wavelength indicate that there are a large number of amorphous phases in Bi₁₂Ti O₂₀,and the BiO₅ polyhedron has obvious distortion in the material.It is inferred that the natural polarity may be related to the distortion of BiO₅polyhedron inside the material.The non-uniform deformation of ceramics is related to the strain gradient caused by temperature gradient during sintering.It can be concluded that the distortion of BiO₅ polyhedron changes gradually along the thickness direction.When the sintering temperature is 870°C,the samples of x=0.5 have the highest density,the highest piezoelectric constant,d₃₃=13 pC/N.Bi₁₂Ti O₂₀ plays a decisive role in determining the depolarization temperature.The piezoelectric constant can be kept stable and unchanged when the temperature does not exceed 800°C.Bi₁₂TiO₂₀-BCZT self-poled ceramic composites were prepared by traditional solid state method.The morphology of amorphous Bi₁₂TiO₂₀ in ceramics is irregular,amorphous Bi₁₂TiO₂₀,BCZT grains and Bi₁₂TiO₂₀ grains are distributed randomly in the ceramics.It was found from Raman spectra that the peaks of some Bi₁₂TiO₂₀ were obviously weakened and widened,indicating that there were a large number of amorphous phases in Bi₁₂TiO₂₀.The peak at224 cm^-1 weakens and moves to a lower wavelength,which indicates that the Bi O₅ polyhedron has obvious distortion in this material.The Raman peaks at 262and 320 cm^-1 shifted to higher wavelengths,indicating that the material was affected by stress and the material was deformed under compression at the test point.The stress to which the material is subjected originates from the interface between the phases in the material.It is inferred that the macroscopic stress at the interface between the distorted BiO₅ polyhedron and the solid-liquid interface affects the occurrence of the macroscopic polarity in the self-poled ceramics.When the sintering temperature is 880°C,the samples of x=0.5 have the highest density,the highest piezoelectric constant,d₃₃=14 pC/N.When the temperature is no more than 850°C,the piezoelectric constant can be kept unchanged.At high temperature,the two different components of ceramic wafer diffused with each other.With the prolongation of the holding time,the arched structure arched higher.The ceramic sample with arched structure was compared with the normal prepared ceramic sample.Under the action of external force,the piezoelectric properties is obviously higher.The self-poled ceramic sample of arch shape produces strain under the action of low frequency alternating force,and the ceramic interior produces strain gradient.The ceramic is affected by the flexural electric effect,which produces a large number of induced charges,which makes the device exhibit large macroscopic piezoelectric properties.