Preparation And Dielectric Properties Of Sodium Bismuth Titanate/Polyvinylidene Fluoride Composites

With the development of electronic science and technology,flexible dielectric materials have been widely used in the fields of pulse power system,hybrid electric vehicles,communication equipment and portable electronic equipment due to their advantages of miniaturization and integration.Therefore,higher requirements have been put forward for all aspects of dielectric materials.Among them,nanofillers/polymer matrix composites have become a research hotspot in recent years due to their superior dielectric properties.In this paper,sodium bismuth titanate(Na_0.5Bi_0.5Ti O₃,NBT)ceramic particles with different morphologies were prepared by hydrothermal method and molten salt method,respectively.After modification by silane coupling agent KH550,they were combined with polyvinylidene fluoride(PVDF)to prepare PVDF-based composite films.The effects of different process parameters on the microstructure and morphology of ceramic particles,and the effects of filler content and filler morphology on the microstructure,dielectric and energy storage properties of PVDF-based composite films were investigated.The spherical NBT ceramic particles were prepared by hydrothermal method,and the preparation conditions were adjusted to obtain NBT ceramic particles with regular shape and uniform size.Then this obtained spherical NBT particles were doped into PVDF to prepare the composites.XRD test results show that the addition of spherical NBT ceramic particles can effectively induce the?phase to?phase transition of PVDF with better dielectric properties.With the increase of NBT contents,the dielectric constant of the NBT/PVDF composite film gradually increases,and the dielectric loss remains at a relatively low level.At 200 k V/mm,the discharge energy density of the composite film is 2.58 J/cm~3,which is 1.4 times of that of the pure PVDF film,and the charge-discharge efficiency is about 52%.The rod-like NBT ceramic particles were prepared by molten salt method,and they were combined with PVDF matrix by solution casting method.The rod-like NBT ceramic particles showed good dispersion in PVDF matrix,and the introduction of rod-like NBT ceramic particles effectively improved the dielectric properties of the composites.When the filler content was 15 wt.%,the dielectric constant of rod-like NBT/PVDF composite film was 12,which was 31.58%higher than that of pure PVDF film.At 210 k V/mm,the discharge energy density is 2.95 J/cm~3,which is 41.2%higher than that of pure PVDF membrane.Compared with the spherical NBT/PVDF composite film with the same filling amount,the discharge energy density increased by 14.34%.This increase should be attributed to the larger aspect ratio and larger dipole moment of rod-like NBT ceramic particles,so the polarization ability is stronger,and the dielectric properties of the composite film are better.