Study On The Dielectric Tunable Properties Of Composite Films Based On P (VDF-TrFE)

Ferroelectric materials usually have the high permittivity and large loss tangent,their application in microwave tuning equipment has been greatly restricted.Therefore,dielectric materials are usually added to ferroelectric materials to reduce permittivity and loss tangent,but it will also reduce the tunability of the material.Generally,dielectric materials are usually added to ferroelectric materials to form composite materials to reduce permittivity and loss tangent of the materials.However,the addition of dielectric materials will also reduce the tunability of the materials.In the study of BST-Mg₂Ti O₄ composite ceramics,researchers have found that as the content of dielectric materials increases,the tunability of composite ceramics increased abnormally.There are two main mechanisms that affect the tunability in ferroelectric/dielectric composite materials:doping and composite effects.Since there is no doping effect between the organic materials and inorganic materials,the organic ferroelectric materials and inorganic linear dielectric materials can be prepared into composite materials to study the mechanism of the increased of the tunability.In this paper,P(VDF-TrFE)/BaWO₄ composite films were prepared by solvent evaporation method.Under the same electric field strength,the tunability of the composite films first increases and then decreases with the increase of the mass fractions.,the permittivity of the P(VDF-TrFE)/Ba WO₄ decreased from 16.06 to 11.94 with the mass fractions of Ba WO₄ increased from 0 wt%to 30 wt%;the tunability increases from 1.36%to3.65%under the 20 k V/mm;when the mass fractions of Ba WO₄increases to 40 wt%,the tunability decreases rapidly.P(VDF-TrFE)/ZrO₂ composite films were prepared by solvent evaporation method.Under the same electric field strength,the tunability of the composite films first increases with the increase of the mass fractions.When the tunable of Zr O₂ increased from 0 wt%to50 wt%,the permittivity of P(VDF-TrFE)/Zr O₂ decreased from 16.06 to 21.14;the tunability increases from 1.36%to 8.23%under the 20 k V/mm.As the content of Zr O₂ continues to increase,the tunability decreases rapidly.P(VDF-TrFE)/TiO₂ composite films were prepared by the same method,experiment result shows that under the same electric field strength,the tunability of the composite material first increases with the increase of the dielectric material content.When the mass fractions of Ti O₂ increased from 0 wt%to 40 wt%,the permittivity of P(VDF-TrFE)/Ti O₂decreased from 16.06 to 28.35;the tunability increases from 1.36%to 7.36%under the 20k V/mm;when the mass fractions of Ti O₂increases to 50 wt%,the tunability decreases rapidly.The P(VDF-TrFE)/BaWO₄composite models,P(VDF-TrFE)/Zr O₂ composite models and P(VDF-TrFE)/Ti O₂ composite models were constructed by using finite element analysis software.After applying the same electric field strength to the three models,the internal electric fields of the three composite models all present an uneven distribution.In the P(VDF-TrFE)/Ba WO₄ composite models,the electric field strength of P(VDF-TrFE)nearing the Ba WO₄ were higher than the applied electric field strength.The tunability of this P(VDF-TrFE)will increase due to the increase of electric field strength,this leads to an increase in tunability of P(VDF-TrFE)/Ba WO₄ composite models;In P(VDF-TrFE)/Zr O₂ and P(VDF-TrFE)/Ti O₂ composite models,the average electric field strength of P(VDF-TrFE)were much more higher than the applied electric field strength in these models.Therefore,the tunability of P(VDF-TrFE)/Zr O₂ and P(VDF-TrFE)/Ti O₂ are higher than P(VDF-TrFE)/Ba WO₄under the same content of dielectric materials.The simulation results of the three models are consistent with the experimental results,which proves the main reason for the increase of the tunability in the composite material is composite effects.