Study On Dielectric Property Of PVDF/Ceramic Composites

Polyvinylidene fluoride(PVDF) is an organic piezoelectric polymer with excellent chemical stability, high dielectric strength, low density, good flexibility, and easy to be processed to large films, but the low dielectric constant limits its application in the storage capacitor. Piezoelectric ceramics such as barium titanate(Ba TiO3) having a high dielectric constant, when it is incorporated into PVDF, a higher dielectric constant of PVDF-based composites can be obtained.In this paper, different volume fraction of BaTiO3/PVDF composites were prepared by solution mixing method, and their microstructure and dielectric properties were studied. The results showed that: the incorporation of a high dielectric constant ceramic BaTiO3 can improve the dielectric constant of the composite effectively. When the volume fraction of BaTiO3 reaches to 40%, at room temperature, 1 kHz conditions, the dielectric constant of the composite increased to 24, which is three times of the dielectric constant of PVDF(εr = 7), and the dielectric loss of the composite is 0.034.To further enhance the dielectric constant of the composite, solid state reaction method and sol- gel method were used to prepare high dielectric ceramic barium zirconate titanate(BZT). Ba(ZrxTi1-x)O3(x = 0.13,0.20,0.25,0.30) ceramic were prepared by solid state reaction method and their dielectric constant and loss were tested.the results showed that, at room temperature, 1 kHz conditions, Ba(Zr0.25Ti0.75)O3 has the best dielectric properties. Different sizes of nano Ba(Zr0.25Ti0.75)O3 ceramic powder were prepared by sol- gel method, and their microstructure was characterized by XRD and SEM. The SEM images show that the particle sizes of BZT ceramic powder calcined at 900 ℃, 1000 ℃, 1100 ℃ were 30 nm, 50 nm, 60 ~ 300 nm, respectively.Different volume fraction of 30 nm BZT/PVDF composites were prepared by solution mixing method, and their microstructure and dielectric properties were studied.The XRD data shows that BZT ceramic particles reduce the crystallinity of PVDF; SEM figure shows that compared with BT/PVDF composite, the density of the BZT/PVDF composite is greatly improved.The dielectric properties of the composite with different size(30 nm, 50 nm, 60 ~300 nm) of BZT were stutied. The test results show that the 50 nm BZT/PVDF composite has the highest dielectric constant. At room temperature, 1kHz conditions,the dielectric constant of 30 vol% BZT/PVDF composite reaches to 33, and the dielectric loss is 0.0291.To further improve the compatibility of the inorganic phase and organic phase,silane coupling agent KH550 was used to modified the surface of the BZT(30 nm), and the M-BZT/PVDF composite was prepared. SEM images shows that the adding of KH550 improve the dispersion of nano powders.. At room temperature, 1 kHz conditions, the dielectric constant of the composite with the coupling agent increase from 17 to 24 when the volume fraction is 30%.