Design And Study Of Molecular Ferroelectrics/polyvinylidene Fluoride Trifluoroethylene(P(VDF-TrFE))composite Pyroelectric Materials

Composite materials have many advantages,such as excellent electrical properties,large area preparation,light weight and high strength,and have a wide application prospect.Among them,composite pyroelectric materials are suitable for thermal imaging,thermal sensing,infrared detection and other fields due to their advantages of spontaneous polarization,simple structure,thermoelectric conversion and low cost.As all known,composite pyroelectric materials,which are widely used at present,are mostly prepared by ceramics and polymer organic polymers.However,this kind of composite pyroelectric materials need a large proportion of doped ceramics.The defects will affect the electrical breakdown performance and limit its application in high temperature environment.The results show that the molecular ferroelectrics have low dielectric constant,simple preparation process,and can be soluble in deionized water and some organic solutions,which brings innovative progress in the research of composite pyroelectric materials.In order to break through the limitations of the current composite pyroelectric materials,this paper selects hydrogen bonded multipolar molecular ferroelectric[Hdabco]BF₄（[D]BF₄）as the doping functional phase and flexible polymer P（VDF-TrFE）as the matrix.Aiming at the variety innovation and performance expansion of composite materials,based on the application of finite element analysis in physical field,the material is designed by COMSOL software The simulation provides theoretical support for the follow-up experiments.The hydrogen bond of the molecular ferroelectrics interacts with fluorine ions in dimer to induce P（VDF-TrFE）to formβphase,and a flexible composite pyroelectric film with high pyroelectric coefficient and low dielectric constant was prepared.Firstly,the geometric models of[D]BF₄/P（VDF-TrFE）thin films with different doping ratios were established during COMSOL numerical modeling.On the one hand,the electrostatic physical interface of electromagnetic field module is used to simulate the electric field distribution of composite materials.The results show that with the increase of[D]BF₄mass fraction,the maximum field strength of the composite film increases to about 111 MV/m,which makes[D]BF₄fully polarized,which provides a theoretical explanation for the enhancement of electrical properties and polarization experiment.On the other hand,the pyroelectric current density of[D]BF₄/P（VDF-TrFE）is simulated by coupling heat transfer and current fields by thermoelectric module.Simulation results show that the pyroelectric performance of8wt%[D]BF₄/P（VDF-TrFE）is the best,which is consistent with the pyroelectric experimental results.Secondly,the[D]BF₄ferroelectrics were prepared by natural evaporation.Through the verification of crystal phase structure,it is confirmed that there is hydrogen bond in[D]BF₄crystal,and the hydrogen bond chain in[001]direction is located in the crystal plane parallel to the surface of the sample.After that,the ferroelectric,dielectric and pyroelectric properties of[D]BF₄crystal were characterized.The results show that the Curie temperature of[D]BF₄crystal is about 101℃,and the higher Curie temperature makes the material have a wider application prospect.At Curie temperature,the polarization intensity is 5.8μC/cm²,the coercive field is 13.6 k V/cm,the dielectric constant and loss are about 35 and 0.15 respectively,and the pyroelectric coefficient is 400.81*10^-4C/m²K.Finally,[D]BF₄/P（VDF-TrFE）composite pyroelectric thin films were prepared.Through the analysis of phase structure and morphology,[D]BF₄is evenly distributed in the polymer,and the particle shape and particle size are uniform,which effectively reduces the porosity of the composite.The results of XRD and FTIR show that the introduction of[D]BF₄can induce the increase of theβphase contents of P（VDF-TrFE）,and the maximum content ofβphase is 83.52%when the mass fraction is 8wt%,which is 23.62%higher than that of pure P（VDF-TrFE）film.Then,the electrical properties of the films were characterized.The polarization strength,dielectric constant and pyroelectric coefficient of the films reached their maximum at8wt%[D]BF₄/P（VDF-TrFE）.Among them,the polarization intensity is 9.86μC/cm²,which is 1.89 times higher than that of pure P（VDF-TrFE）film;at 20℃,the pyroelectric coefficient is about 0.139*10^-4C/m²K,which is increased by about 7.72times.