| Nano-ferroelectric ceramics as fillers can effectively improve the dielectric and energy storage properties of polymer dielectric materials.However,with the development of research,the properties brought by zero-dimensional granular nano-fillers gradually fail to meet the requirements of material applications,and the type of fillers and the preparation process of materials need to be innovated.According to the relevant research:1.Compared to zero dimension particle packing,the composite material containing one-dimensional nanowire filler gives low percolation threshold 2.Compared with the random order one dimensional nano filler,orderly arrangement with one dimensional nano filler composites have better energy storage performance 3.Targeted surface modification of one-dimension nanowire can not only enhance the compatibility between filler and matrix,reduce the occurrence of defects,but also bring higher saturation polarization to composite materials by introducing new interface polarization,resulting in improving the dielectric and energy storage performance of composite materials.However,how to effectively construct a core-shell structure of nanowires and how to realize the directional alignment of the nanowires is the issue.To solve these difficulties,in this paper,Ti O2@Hf O2 nanowires were prepared by hydrothermal method and sol-gel method.And synthesized Ti O2@Hf O2 nanowire arrays were fabricated by hydrothermal method and atomic layer deposition.The thickness of the shell Hf O2 was controlled by adjusting the cycles to study the effects of nanowires arrangement and shell thickness on dielectric behavior and energy storage performance of PVDF matrix composites.Main research content is as follows:?1?In order to study the influence of the surface modification layer of ceramic nanofiller on the dielectric and energy storage performance of PVDF-based nanocomposites,Ti O2 nanowires were synthesized by hydrothermal method,and the core-shell Ti O2@Hf O2 nanowires were synthesized by sol-gel method by coating Hf O2 on the surface of Ti O2 nanowires.Ti O2@Hf O2 NWs/PVDF nanocomposite thin film was prepared by solution casting method.The microstructure,dielectric and energy storage properties of the composite were characterized in detail by scanning electron microscope,impedance analyzer and ferroelectric analyzer.The experimental results show that,although the dispersion of Ti O2 nanowires coated with hafnium oxide is not as good as that of uncoated Ti O2 nanowires in PVDF,the Ti O2@Hf O2NWs/PVDF composite has higher dielectric and energy storage properties.Among all composite materials prepared,Ti O2@Hf O2 NWs/PVDF with 10%mass fraction had the highest permittivity,which was 12.65 at 1000Hz and 172.1%of pure PVDF.The energy storage density of Ti O2@Hf O2 NWs/PVDF with 2.5%mass fraction is 6.38J/cm3 in the 400kv/mm,which is 250%of the energy storage density of PVDF in the same electric field,suggesting that the modification of hafnium oxide layer can improve the dielectric and storage performance of PVDF-based Ti O2 nanowires composite.However,titanium dioxide nanowires are more likely to aggregate in the composite material after surface modification,leading to that the modified composite material with high filler ratio shows poor energy storage performance.?2?In order to study the effect of the ordered arrangement and shell thickness of the core-shell structure nano-ceramic filler on the dielectric and energy storage properties of nano-arrays/PVDF composite,highly ordered Ti O2 nanowire arrays were synthesized by hydrothermal method.Atomic layer deposition?ALD?was used to coat Hf O2 with controllable and uniform thickness on the surface of Ti O2 nanowire arrays,and the core-shell structure and the thickness of coating layer were characterized in detail.The experimental results showed that when the number of deposition cycles increased from 13 to 50,the thickness of shell Hf O2 increased from2.4?±0.1?nm to 5.4?±0.1?nm.PVDF was rotated onto the surface of the array using the spinning coating method,and Ti O2@Hf O2 NWs array/PVDF composite material with different coating thickness was obtained.The microstructure of the composite material was characterized by scanning electron microscopy.PVDF was well combined with nanowires array without obvious defects.The frequency dependence of dielectric constant and energy storage performance of composite were studied by impedance analyzer and ferroelectric analyzer.Experimental results show that with the increase of Hf O2 coated layer thickness,the dielectric constant,breakdown strength,saturation polarization value and energy storage density of composite also increase.When the number of deposition cycles reaches 50,the dielectric constant of the composite reaches its maximum value at 1000Hz??r=27.1?,which is 203.8%of that of the uncoated composite,and the energy storage density reaches 2.91J/cm3 at140KV/mm,which is 140%of that of the uncoated composite under the same electric field.This suggests that in the case of composite interface is fairly,the energy storage properties of the composite increase with the coating layer thickness.Through the comparison with the first part,the ordered packing can more effectively raise the energy storage performance of materials.Therefore,this study proposes a new method to prepare high-performance composite dielectric energy storage materials,and further illustrates the influence of the modified layer thickness of packing on the dielectric energy storage performance of composite materials. |
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