Study On Preparation And Electromechanical Coupling Properties Of 1-3 PZT/P(VDF-TrFE) Composities

The 1-3 piezoelectric composites based on ceramic/polymer have a wide application prospect in the fields of ultrasonic probes and hydroacoustic transducers,etc.The electrical properties of polymer matrix are of great significance to improve the electromechanical coupling properties of piezoelectric vibrators of composite materials.However,in the traditional 1-3 type piezoelectric composites,non-piezoelectric epoxy resin base is used as the polymer filling phase.From the perspective of microscopic mechanism,there is no synergistic effect between the polymer phase and ceramic piezoelectric phase,which cannot further enhance the overall piezoelectric effect of 1-3 composite materials.Therefore,in this paper,the piezoelectric polymer polyvinylidene-trifluoroethylene（P（VDF-TrFE）and Epoxy resin as the matrix,lead zirconate titanate（PZT）ceramics as the piezoelectric body.Type 1-3 PZT/P（VDF-TrFE）and PZT/Epoxy9holes（16.5%volume of piezoelectric phase）piezoelectric composites were prepared by hot pressing and casting methods respectively.Then,the PZT/P（VDF-TrFE）13-holes（23.83%）and 17-holes（31.168%）composite wafer were prepared by changing the volume of piezoelectric phase,and the thickness were 0.6 mm,0.9 mm,1.2 mm,1.5 mm,1.8 mm,respectively.On this basis,the effects of two different polymer phase matrix and three different piezoelectric phase volumes on the dielectric,ferroelectric,piezoelectric and electromechanical coupling properties of the composite were studied.The main research work is as follows:1）The stress,displacement and strain distribution maps of 1-3 type 9-holes PZT/P（VDFTrFe）and PZT/Epoxy piezoelectric composites were analyzed by COMSOL simulation software.The results show that the stress distribution in the piezoelectric phase is much larger than that in the polymer phase,and the stress can be transferred between the two phases and increases with the increase of the thickness.The displacement of piezoelectric phase PZT is larger than that of polymer phase.The strain distribution diagram shows that the strain of the 1-3 type piezoelectric composite is concentrated in the thickness direction.2)The structure and morphology of PZT and P（VDF-TrFE）piezoelectric ceramics were studied by XRD and SEM.The results show that PZT has a compact texture and typical perovskite structure.The P（VDF-TrFE）powder crystal region is dominated by β phase.SEM images showed that there were no obvious cracks at the interface of piezoelectric phase and polymer phase,and no obvious bubbles and defects on the sample surface.This result lays a foundation for the subsequent performance experiments.3)The electrical properties of 1-3 type 9-holes PZT/P（VDF-TrFE）and PZT/Epoxy piezoelectric composites were studied.The results show that the dielectric properties of the composite have good frequency stability,and the dielectric loss（tanδ）is less than 0.15.The piezoelectric constant(d₃₃)of 1-3 PZT/P（VDF-TrFE）piezoelectric composite decreases slightly after the polarization of 80℃ at 5 MV/m electric field.The electric hysteresis loop（P-E）shows that the residual polarization strength（Pr）of samples with thickness of 0.9 mm,1.2 mm and 1.5 mm decreases by 0.21 μC/cm²,0.36 μC/cm² and 0.5 μC/cm²,respectively,under the electric field of 3.5 MV/m According to the impedance spectrum,the mechanical and electrical coupling coefficients（kt）of the polarized materials are increased by 0.034,0.014 and 0.045,respectively.Compared with PZT/Epoxy 1-3,kt of 0.9 mm,1.2 mm,and 1.5 mm thickened was 0.04,0.017,and 0.014 higher,respectively.These results indicate that P（VDF-TrFE）polar polymer matrix can improve the mechanical and electrical coupling properties of composites.4)The electrical properties of 1-3 type PZT/P（VDF-TrFE）piezoelectric composites with 13 and 17-holes were systematically studied.It is found that P_r and d₃₃ increase with increasing volume fraction of piezoelectric phase.When the sample thickness is the same,the k_t value of 17-holes sample is higher than that of 13-holes sample,and the k_t value of 0.9 mm sample is 0.687 and 0.444,1.2 mm sample is 0.601 and 0.592,1.5 mm sample is 0.725 and 0.707,respectively.The results show that the electro-mechanical coupling properties of the composites can be improved by increasing the volume of piezoelectric phase and the electric-field polarized polymer phase P（VDF-TrFE）.In addition,the acoustic impedance of the sample is up to 14.16 MRayls,which is significantly lower than that of pure ceramics.The above studies show that the use of piezoelectric P（VDF-TrFE）instead of the traditional epoxy resin as the matrix phase of 1-3 composite material is beneficial to improve the electromechanical coupling performance of the sample,effectively reduce the acoustic impedance value,improve the receiving sensitivity,reduce the energy loss during the working process,and better realize the transmission and reception between the instrument and the human body.This study can provide reference for the application of PZT/P（VDF-TrFE）1-3 piezoelectric composite in the field of medical transducer.