Effect Of Composite Effect On Tunability In Ferroelectric-Dielectric Composites

It is found that the tunability of BST based ferroelectric-dielectric composites increases abnormally with the increase of dielectric content.The mechanisms is unclear because there are two kind of main effect:i.e.doping effect and composite effect.Suppressing the doping effect can be used to explore the reasons.As there is no doping effect between organic material and inorganic material,organic ferroelectric material P（VDF-TrFE）can be combined with inorganic linear dielectric materials to form ferroelectric-dielectric composites,which can be used to explore the reasons for the abnormal increase of tunability of ferroelectric-dielectric composites.The dielectric constant of P（VDF-TrFE）-MgO composite films prepared by spin-coating method decreases with the increase of frequency,while the dielectric loss increases with the increase of frequency and is about 0.1 at 10kHz.When the content of MgO increases from 0wt%to 30wt%,the dielectric constant of the composite film decreases from 20.4 to 14.2,while the tunability increases from 4.7%to 7.5%at 10kV/mm.When the content of MgO continues to increase,the dielectric constant of the composite film continues to decrease and the tunability rapidly decreases.Therefore,it can be concluded that the composite effect leads to the increase of tunability.Two kinds of P（VDF-TrFE）-Mg₂TiO₄ compiosite films were prepared by using Mg₂TiO₄ and calcined Mg₂TiO₄.The dielectric constant of the two kinds of composite films is basically the same and the dielectric loss is about 0.1.With the increase of dielectric content,the tunability increases first and then decreases.The tunability of the composite film formed by Mg₂TiO₄ is little higher than that of the composite film formed by calcined Mg₂TiO₄.The dielectric constant of P（VDF-TrFE）-CaTiO₃ composite films prepared by spin-coating method increases from 20.4 to 57.8 when CaTiO₃ content increases from 0wt%to 40wt%,and the tunability of the composite films increases from 4.7%to 8.8%at10kV/mm.The tunability of the the composite films is also higher than that of pure P（VDF-TrFE）,and that of P（VDF-TrFE）-MgO and P（VDF-TrFE）-Mg₂TiO₄ composite films.Because only P（VDF-TrFE）in composite film has tunability,and its tunability increases with the increase of electric field intensity.Therefore,it can be inferred that the local electric field intensity on P（VDF-TrFE）increases when the tunability of composite films increases abnormally.The model of P（VDF-TrFE）-MgO and P（VDF-TrFE）-CaTiO₃ composites was constructed by finite element analysis software.The results show that the average electric field strength applied on P（VDF-TrFE）in P（VDF-TrFE）-MgO composite films is lower than that of the applied electric field strength,but the average electric field strength in the enhanced region increases with the increase of MgO content,resulting in an increase in tunability.In P（VDF-TrFE）-CaTiO₃ composite films,the average electric field strength applied on P（VDF-TrFE）is higher than that of the applied electric field strength,and increases with the increase of CaTiO₃ content,resulting in an increase in the tunability.