The Inorganic/organic Composites In Which BaTiO₃ Based Ferroelectric Powders As Fillers And Their Dielectricities

The inorganic/organic composites in which BaTiO3 based ferroelectric powders as fillers received extensive attentions and deep study due to the functional characteristics of the ferroelectric powders and lightness and flexibility of organics.The functionality of the composites decreased quickly with the introduction of the organics,such as the dielectric constant reduced rapidly,and thus the application of them is much restricted.Our study is based on the analysis of the composites of different BT powders(grain size,ingredients and semiconducting of ferroelectrics)and different organic base,study on the relationship among the different processing,the characteristics of the powders,and the organic bases,and finally optimized a certain composite material with high performant dielectric properties.Epoxy Resin(EP)is a universal organic/inorganic composite matrix,which is widely used as binder in electronic circuits and has good compatibility with electronic circuit system.Therefore,First,EP is selected as the matrix of the composite material.However,the dielectric properties of the composites are greatly decreased because of the non-ferroelectricity of EP.The dielectric constant of omposites is no more than 100 at room temperature and low frequency.In order to further improve the dielectric performance of composite,diisopropylammonium bromide(DIPAB),an organic macromolecular salt with ferroelectric properties,is added to the EP,which not only maintains the lightness and flexibility of the composite material,but also improves the dielectric property of the matrix material.For example,when the mass fraction EP and DIPAB is 1:1,the dielectric constant is 34.6,which is about 10 times that of epoxy resin and is half that of DIPAB(400Hz,～85).On this basis,the EP/DIPAB/BT three-phase composites were prepared by solution blending method and cold-pressing molding process by using the functional body with mass ratio as 1:1EP/DIPAB as the matrix,and the BT ceramic nano-powders prepared by wet spherical mill at room temperature and pre-treatment of BT at different temperature were introduced as the third component.The results show that the dielectric properties of the composites are not only related to the content of inorganic ceramics with high dielectric constants,but also to the Pre-sintering temperature of BT.Compared with the dielectric properties of two-phase composites EP/DIPAB and EP/BT,EP/DIPAB/BT three-phase composites significantly improved the dielectric properties of the materials,such as 1100℃ BT/EP/DIPAB composite,the dielectric constant of the material reached 2200,and loss is only 2.This is attributed to the introduction of a new interface in the ternary system to form a space charge layer,which greatly improves the dielectric properties of the composite.BT is the most basic ceramic material,a ferroelectric barium titanate(BST)powder was prepared by introducing Sr to lower the Curie temperature using the peak shift effect.We used BST instead of BT to prepare and study the dielectric properties of EP/DIPAB/BST composites.The results show that the introduction of BST does improve the dielectric constant of composites,and the dielectric constant of 950℃ BST/EP/DIPAB composites～2040 is 5 times that of 950℃ BT/EP/DIPAB～420.Epoxy resin is difficult to clean in the preparation process of composites,and as a substrate,its dielectric constant is low and the curing process inevitably produces pores that are difficult to discharge,resulting in the decrease of dielectric constant and the increase of loss.Therefore,we try to prepare two-phase and three-phase composites by using the flexible organic material polyvinylidene fluoride PVDF with ferroelectric and easy to process instead of epoxy resin.The dielectric constant of PVDF/DIPAB com posites with a mass ratio of 1:1 is 10.Preparation of three-phase composites with mass ratio 1:1PVDF/DIPAB as matrix.The results show that the dielectric constant of PVDF/DIPAB/BT is greatly improved compared with the dielectric constant of DIPAR/PVDF,PVDF/BT two-phase materials and EP/BT/DIPAB,whether it is as-prepared BT or pre-treatment BT in the composites,the dielectric constant of composite material is>105 And the dielectric loss of 950℃ and 1100℃BT composites is<5.The composite material was prepared by adding EST instead of BT to PVDF/DIPAB with ratio of 1:1.The magnitude of dielectric constant is equivalent to that of BT three-phase composite.The dielectric constant reaches 105 and the dielectric loss is<10 at room temperature and 20Hz.The dielectric constant of the optimized BT/PVDF/DIPAB composite is>105.This is attributed to the fact that both the organic and inorganic components in the composite material are ferroelectrics,the interaction between ferroelectric domains and space charges,and the transfer of ferroelectrics to the applied electric field,so that the dielectric constant of the composite material is greatly improved.