Study On Preparation And Dielectric Properties Of Ceramic/PVDF Composites

The integration and miniaturization of electronic devices require the capacitors to have higher energy density,thereby placing higher requirements on the dielectric constant,dielectric loss,and processing performance of the dielectric materials.The preparation of ceramic/polymer composites by mixing high-dielectric ceramics with flexible polymers is one of the ways to solve the difficulties.Ceramic/polymer composites can achieve high dielectric constants at high ceramic loadings.But the high filling amount will reduce the processing performance of the composite material,thus cannot meet the practical application.In this paper,ceramic/polymer composites with high dielectric constant,low dielectric loss and good processability were prepared under low ceramic filling.The main research contents and conclusions are as follows:1.CaCu3Ti4O12(CCTO)gels were prepared by sol-gel method and were calcined at different temperatures to obtain CCTO ceramic powders.Subsequently,CCTO was mixed with polyvinylidene fluoride(PVDF)and CCTO/PVDF composites were prepared by hot-pressing.It was found that CCTO grains gradually increase with the calcination temperature.At various calcination temperatures,particle size distribution of the CCTO is not concentrated.The dielectric constant and dielectric loss of CCTO/PVDF composites decrease with the calcination temperature of CCTO.The dielectric constant and dielectric loss of CCTO/PVDF composites were 60 and 0.225 at 65 Hz,respectively,when the CCTO content calcined at 700? were 60wt%.2.In order to improve the dielectric properties of CCTO/PVDF composites,Na0.5La0.5Cu3Ti4O12(NLCTO)ceramic powders were prepared by replacing Ca with Na and La in this study.The obtained NLCTO ceramic powder was added into PVDF to prepare NLCTO/PVDF composites.It was found that the NLCTO grains gradually increased with the increase of the calcination temperature,and the particle size distribution of the NLCTO was not concentrated at each calcining temperature.When the NLCTO content is fixed,the dielectric constant of NLCTO/PVDF composites increases first and then decreases with the calcination temperature of ceramic powders increasing.However,the change trend of dielectric loss is on the opposite.When the calcination temperature of NLCTO is 900?,the NLCTO/PVDF composite achieves both high dielectric constant and low dielectric loss.The dielectric constant and dielectric loss of NLCTO/PVDF composites are 62 and 0.08 at 65 Hz when the NLCTO loading is 60wt%,respectively.Compared to the dielectric loss of CCTO/PVDF composites,the dielectric loss of the NLCTO/PVDF is significantly lower.3.Copper-coated NLCTO ceramic powders were prepared by redox precipitation method and Cu@NLCTO/PVDF composites with good dielectric properties were prepared at lower Cu@NLCTO loadings.Results of XRD and TEM characterization show that the copper was successfully coated on the surface of NLCTO.The study on the dielectric properties of composites found that when the amount of copper coated is 100%of NLCTO content,dielectric constant and dielectric loss of Cu@NLCTO/PVDF composite were 120 and 2 at 65 Hz,respectively,at 25wt%Cu@NLCTO and that when the amount of copper coated is 50%of NLCTO content,PVDF composites with 25wt%Cu@NLCTO achieved a high dielectric constant(55)and low dielectric loss(0.1)at 65Hz and excellent frequency stability over the entire test frequency range.4.Cu@NLCTO/PVDF composites were prepared with high dielectric constant,low dielectric loss and good processability when the amount of copper coated is 50%of NLCTO content.Therefore,the Cu@NLCTO/PVDF composites prepared in this study are expected to be widely used in embedded capacitors.