Study On The Abnormal Increase Of Tunability In P(VDF-TrFE) Based Ferroelectric/Dielectric Composite Films

In the field of microwave tuning,the permittivity and loss tangent of ferroelectric materials are usually relatively large.Generally,adding dielectric materials to ferroelectric materials is used to reduce the permittivity and loss tangent of the material,but this will lead to the reduction of the tunability.In recent years,studies have found that in BST-Mg₂Ti O₄composite ceramics,the tunability of composite materials increases abnormally with the increase of Mg₂Ti O₄content.Due to the simultaneous presence of doping and composite effects in ferroelectric/dielectric composites,and the doping effect will lead to the decrease of the tunability,so it is speculated that the composite effect caused the abnormal increase of the tunability.There is no doping effect in organic ferroelectric materials and inorganic dielectric materials.Therefore,organic ferroelectric/inorganic linear dielectric composite materials can be used to study the mechanism of abnormally increased tunability.P(VDF-Tr FE)/Mg₂Si O₄ composite films with different mass fractions were prepared by the solvent evaporation method.When the concentration of Mg₂Si O₄ increased from 0wt%to 50wt%,the permittivity of the composite film decreased from 18.9 to 13.3,the tunability under 20k V/mm increases from 2.7%to 6.1%;when the concentration of Mg₂Si O₄increases to 60wt%,the permittivity decreases to 12.6,and the tunability drops to 4.4%.P(VDF-Tr FE)/Ce O₂ composite films with different mass fractions were prepared by the solvent evaporation method.When Ce O₂ content increased from 0wt%to 50wt%,the permittivity of the composite film increased from 18.9 to 21.9,the tunability under20k V/mm increased from 2.7%to 5.9%;when the Ce O₂ content increased to 60wt%,the permittivity increased to 23.1 and the tunability dropped to 4.4%.The P(VDF-Tr FE)/Sr Ti O₃ composite films with different mass fractions were prepared by the solvent evaporation method,and their dielectric properties were studied.The results show that as the frequency increases,the permittivity of the composite film gradually decreases,and the loss tangent gradually increases.When the concentration of Sr Ti O₃increases from 0wt%to 50wt%,the permittivity of the composite film increases from 18.9 to39.8,the tunability under 20k V/mm increases from 2.7%to 9.8%;when the concentration of Sr Ti O₃ increases to 60wt%,the permittivity increases to 53.3,and the tunability drops to6.4%.The P(VDF-Tr FE)-based ferroelectric/dielectric composite film model was constructed using finite element analysis software.It was found that the electric field in the composite film would be redistributed after adding the dielectric material,so that the electric field strength applied on some P(VDF-Tr FE)was locally enhanced.This caused the abnormal increase tunability of the composite film.In the P(VDF-Tr FE)/Mg₂Si O₄ composite model,the average electric field intensity applied on P(VDF-Tr FE)is lower than the applied electric field intensity,but electric field intensity applied on part of P(VDF-Tr FE)is higher than the applied electric field intensity;futhermore,the average electric field intensity increases with the increase of Mg₂Si O₄ content;In the P(VDF-Tr FE)/Sr Ti O₃ and P(VDF-Tr FE)/Ce O₂composite models,the average electric field intensity applied on P(VDF-Tr FE)is higher than the applied electric field intensity.The simulation results verify the experimental data,indicating that the abnormal increase in tunability is caused by the compound effect.