Study On Microstructure Design And Dielectric Properties Of Potassium Tantalate Niobate/Polyvinylidene Fluoride Nanocomposites

The polymer-based composites are more preponderant than single phase dielectric materials in terms of performance,and are able to combine advantages of inorganic fillers and polymer materials to satisfy application in the electric and electronic field.To obtain polymer-based composites with high dielectric constant,previous researchers took the method of introducing ceramic particles or conductive particles into the polymer.The results turned out to be that it is little possible to prepare the polymer-based composites with excellent dielectric performance by simply changing the kind of the filler or polymer matrix.Besides,new problems may be given rise to by doing so,such as the increase of dielectric loss,the degradation of breakdown strength and mechanical properties.This paper,based on the previous researches,designed different structures and surfaces of KTa0.5Nb0.5O3(KTN)nanofillers and studied the influences of their introduction on the polarization mechanism and electric properties of PVDFbased nanocomposites.According to the results of our study,we then prepared polymer-based composites with excellent dielectric performance.To further study how the structure and surface of nanoparticles influence the dielectric properties and microstructure of polymer-based composites,four major factors in the hydrothermal method(namely reaction temperature,KOH concentration,reaction time and the volume of solution)are observed through the range analysis and variance analysis of orthogonal experiment,aiming to achieve the control on KTN particles' size and shape.Besides,we made it operable to adjust the dielectric propertie of polymerbased composites by controlling the size and shape of fillers.There is –OH group on the surface of KTN nanoparticles(H-KTN)prepared by hydrothermal method,which can be combined with PVDF molecular chains to form hydrogen bond.And the formation of hydrogen bonds enables the PVDF matrix to better coat the H-KTN nanoparticles,reduce defects in the composites and inhibit the migration of carriers,and therefore to restrain dielectric loss and improve dielectric strength.Compared with the cube KTN nanofillers(NC-KTN),the rod KTN nanofillers(NR-KTN)owns a larger BET specific surface area which leads to the larger nonbond energy between NR-KTN and PVDF and thus decreases defects in composites.Especially when the doping concentration is lower than 10 vol%,the NR-KTN/PVDF composite films possess more outstanding dielectric properties.Finally,we designed the core-shell structured KTN@Ag nanoparticles as filler,with an attempt to realize outstanding performances of PVDF-based composite(high dielectric constant and low dielectric loss)and reduce the doping concentration of fillers in composites at one time.However,the breakdown strength of composites may be reduced when KTN@Ag nanoparticles are excessively doped.In order to solve this problem and optimize performances like improving the dispersity of nanoparticles in polymer matrix,inhibiting the oxidation of Ag shell and restraining dielectric loss,we designed and synthesized core@double-shell structured KTN@Ag@c PS nanoparticles by covering the surface of KTN@Ag nanoparticles with cross-linked polystyrene(c PS).