Preparation And Properties Research Of Inorganic Powder/PVDF High Dielectric Permittivity Composite Thin Films

With the rapid development of the electronic industry and the urgent need of solving environmental problems,increasing energy efficiency of electronic systems is becoming more and more important.This demand promotes the emerging of new materials with high permittivity,and these materials can store more electrical energy.Ceramics possess high dielectric constant and good thermal stability,there is a limitation of their applications because of their high density,brittleness and difficulty to process.The dielectric constant of polymer materials is usually low,but they have high breakdown strength,and are light weight and easy processing,which is complementary to ceramic materials.In recent years,it has become a research frontier in the field of energy storage to prepare high dielectric composite materials with excellent over-all performance through ceramic/polymer compounding route.As a new type of ceramic,the dielectric constant of SiCN precursor ceramics is several orders of magnitude higher than that of traditional ceramics.In this paper,high dielectric composites are obtained from SiCN ceramic which is used as filler and polymer which is matrix.The results are compared with the composites prepared by ferroelectric barium titanate fillers,which have been studied more in our field.PVDF thin films,Ba TiO₃/PVDF and SiCN/PVDF composite thin films were prepared via both tape casting and vacuum hot pressing.By measuring their dielectric constant,dielectric loss and breakdown voltage,the effects of different fillers,different film-making processes,and different filler amounts on the electrical properties of the films were studied.The internal microstructure,polymer morphology and thermal stability of the films were studied by FR-IR,SEM and TG.The results are as follows:?1?The dielectric constants of these Ba TiO₃ and SiCN composite films increased with the rising of the filler volume.At room temperature,the dielectric constants of films via the tape casting method with BaTiO₃ filler contents 10%,20%,30%and 40%are 11,14.1,23.4and 31.9,respectively.In case of SiCN filler,dielectric constants of the films with corresponding filler contents are 13.3,19.7,36.2 and 52.4,respectively.Meanwhile the dielectric loss of those Si CN/PVDF composite films increases slightly.At the same time,it is found that the dielectric constants of SiCN/PVDF composite films increase dramatically at low frequencies.In the 40vol%SiCN/PVDF thin films prepared via hot pressing,the dielectric constant under 0.1Hz is 2810,which is 25 times higher than that of BaTiO₃/PVDF composite film with the same volume fraction.?2?At room temperature,the dielectric constant of the PVDF,40vol%Ba Ti O₃/PVDF and 40vol%SiCN/PVDF composite films prepared via the tape casting method is 9.34,31.9and 52.4 under 100Hz,respectively.However,dielectric constant of the films that prepared via hot pressing is improved compared with their counterparts from tape casting method.The dielectric constant of PVDF film rises to 11.9,and when the filler content is 40vol%,the dielectric constants of BaTiO₃/PVDF and SiCN/PVDF composite films prepared via hot pressing go up to 53 and 65.8.The dielectric loss of thin films prepared via hot pressing decreases to varying degrees.Through the microstructure characterization,the internal structure of the films prepared via hot pressing is more smooth and consistent,the particles distribute homogeneously,the porosity is low,and the two phases combine closely,which is believed to be the reason for better dielectric property.The experimental results also show that different film processing methods have no obvious effect on the breakdown strength.?3?The theoretical energy storage density of the composite films were calculated,and the results show that in the BaTiO₃ composite films,the energy storage density of30vol%BaTiO₃/PVDF prepared via hot pressing is the best under 100Hz,which is0.462J/cm³.In the SiCN/PVDF composite films,the energy storage density under low frequency?0.1Hz?exhibits large advantage.When filler is 40vol%,the energy density of SiCN/PVDF film is up to 13J/cm³,which is over 20 times of the Ba TiO₃/PVDF film.