| With the coming of 5G,communication technology is developing towards higher frequency and lower time delay,which puts forward higher requirements for the electronic and electrical properties of various energy storage materials and antenna materials.Dielectric composites with excellent dielectric properties as an important branch of materials and electrical engineering,which have attracted the attention of scientists and relevant industry personages and have been widely used in capacitors and storage batteries.Using the advantages of easy processing,easy molding and low cost of the polymer,high dielectric composites are prepared by mixing with high dielectric permittivity ceramic fillers.Compared with traditional single materials,they have better dielectric properties,thermal stability,and mechanical properties to meet the requirements of electronic equipment's performance in the future.In this paper,the BTNC(modified barium titanate with Co3O4 and Nb2O5)and CCTO(copper calcium titanate)were used as fillers with PVDF to prepare BTNC/PVDF composites and CCTO/PVDF composites firstly.Then,respectively comparing the dielectric properties,SEM photos and XRD patterns of composites the frequency range(10-1 Hz?107 Hz)under two preparation methods.Choose the best method to prepare better dielectric properties BTNC/CCTO/PVDF three-phase composite,which dielectric properties and ac conductivity of the two-ceramic-fillers composites with different filling ratio were studied to research the best filler ratio.1.Different filler contents of BTNC/PVDF composites were prepared by chemical solution method and melt hot pressing method respectively.The effets of BTNC filler content and frequency range(10-1 Hz?107 Hz)on the microstructure,crystal phase,dielectric property and ac conductivity of the composites were studied by SEM,XRD and dielectric impedance spectroscopy.SEM images show that BTNC fillers are more compatible with PVDF than Ba Ti O3;XRD diffraction pattern shows that Ba Ti O3 doped with Nb and Co changes the crystal structure of the composites,which is beneficial to improve the dielectric properties.The dielectric properties of the composites prepared by solution method are better than melt method,and the ultrasonic process in the solution method can effectively improve the dispersion of the fillers in the polymer,also improved the stability of the dielectric properties of the composite material in the range 10-1?107 Hz.At the low frequency f=10-1 Hz and the filler content 75 wt%,the dielectric permittivity is as high as 476.77 and the ac conductivity is4.10×10-11 S/m;at the medium and high frequency 105 Hz and 107 Hz,the dielectric permittivity is 86.99 and 59.96,about 7 times that of pure PVDF material,and the dielectric loss hardly increases.2.Different filler contents of CCTO/PVDF composites were prepared by chemical solution method and melt hot pressing method respectively.SEM photos show that chemical solution method is beneficial to the dispersion of CCTO filler in PVDF matrix,CCTO/PVDF composite with 70 wt%filler content is the most evenly dispersed in PVDF,with small interspace between particles and regular arrangement.The XRD diffraction pattern shows that after adding CCTO,CCTO filler and PVDF matrix can be better compounded,the change of CCTO mass fraction has no effect on the crystal structure of the composite,and the physical and chemical properties of CCTO/PVDF composite are stable.At low frequency f=10-1 Hz,the maximum dielectric permittivity of the composite with 70 wt%filler content is 212.06,and the ac conductivity is 1.27×10-11 S/m,so the composite has better adjustability at low frequency,which has potential application prospect.3.BTNC/CCTO/PVDF three-phase composites with a mass fraction addition is 70 wt% of two-fillers were prepared by the solution method,and the BTNC and CCTO ratios were continuously adjusted,compared with BTNC/PVDF composite and CCTO/PVDF composite,the dielectric loss of three-phase composite is lower and more stable;The dielectric loss of 10wt%CCTO content BTNC/CCTO/PVDF composite at f=104 Hz is the smallest,which value is 0.113.Adding a small amount of CCTO and BTNC can effectively improve the dielectric permittivity of PVDF.When the mass ratio of m CCTO/m BTNC=2:3,the dielectric permittivity is the largest,the low frequency f=10-1 Hz,and the CCTO content of composite is 40 wt%which dielectric permittivity is 27.24,meanwhile the ac conductivity is 6.08×10-14 S/m. |
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