Changhai Zhang

Enhanced dielectric performance of amorphous calcium copper titanate/polyimide hybrid film

We report the preparation of amorphous CaCu3Ti4O12/polyimide (a-CCTO/PI) hybrid films for the first time. It was found that a relatively high dielectric permittivity, low loss and low conductivity were simultaneously achieved in the a-CCTO/PI films. Compared with the PI matrix and the CCTO/PI film with a 10 vol% concentration of CCTO, the dielectric permittivity of the a-CCTO/PI film with a 3 vol% concentration of a-CCTO increased by 29% and 16%, respectively. Interfacial polarization relaxation mainly determines the properties of a-CCTO/PI films, and this can guide the future preparation of ceramic–polymer composites. All the above-mentioned properties are beneficial for the use of a-CCTO/PI hybrid films in the electronics industry, for applications such as printed circuit boards (PCBs).

Enhanced dielectric properties of poly(vinylidene fluoride) composites filled with nano iron oxide-deposited barium titanate hybrid particles.

We report enhancement of the dielectric permittivity of poly(vinylidene fluoride) (PVDF) generated by depositing magnetic iron oxide (Fe3O4) nanoparticles on the surface of barium titanate (BT) to fabricate BT–Fe3O4/PVDF composites. This process introduced an external magnetic field and the influences of external magnetic field on dielectric properties of composites were investigated systematically. The composites subjected to magnetic field treatment for 30 min at 60 °C exhibited the largest dielectric permittivity (385 at 100 Hz) when the BT–Fe3O4 concentration is approximately 33 vol.%. The BT–Fe3O4 suppressed the formation of a conducting path in the composite and induced low dielectric loss (0.3) and low conductivity (4.12 × 10−9 S/cm) in the composite. Series-parallel model suggested that the enhanced dielectric permittivity of BT–Fe3O4/PVDF composites should arise from the ultrahigh permittivity of BT–Fe3O4 hybrid particles. However, the experimental results of the BT–Fe3O4/PVDF composites treated by magnetic field agree with percolation theory, which indicates that the enhanced dielectric properties of the BT–Fe3O4/PVDF composites originate from the interfacial polarization induced by the external magnetic field. This work provides a simple and effective way for preparing nanocomposites with enhanced dielectric properties for use in the electronics industry.

Significantly enhanced energy storage density for poly(vinylidene fluoride) composites by induced PDA-coated 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 nanofibers

In this study, high aspect ratio TiO2 nanofibers (TiO2 NFs), BaTiO3 nanofibers (BT NFs), CaCu3Ti4O12 nanofibers (CCTO NFs) and 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 nanofibers (BZT-BCT NFs) were prepared via an electrospinning technique. The nanofibers have been modified with polydopamine (PDA), which exhibited excellent dispersion and good compatibility with the polymer matrix. The effects of the structure and morphology of the fillers on the dielectric properties, leakage current density and energy densities of the composites have been also discussed systematically. On comparing the five different poly(vinylidene fluoride) (PVDF) composites, we discovered that the BZT-BCT NFs/PVDF composite displayed low loss, small leakage current and excellent storage performance. On this basis, BZT-BCT NFs/PVDF composites with different volume contents were also fabricated. It can be found that the 7 vol% BZT-BCT NFs/PVDF nanocomposite possessed an excellent dielectric constant (e ∼ 17.6 at 100 Hz). Nevertheless, the 3 vol% BZT-BCT NFs/PVDF nanocomposite demonstrated higher energy storage density (Ue ∼ 7.86 J cm−3) and greater efficiency (η ∼ 58%) at 310 kV mm−1. This study may provide a new direction to enhance the energy density of inorganic/PVDF composites.

Highly (100)-oriented sandwich structure of (Na0.85K0.15)0.5Bi0.5TiO3 composite films with outstanding pyroelectric properties

In this paper, by introducing a Pb0.8La0.1Ca0.1Ti0.975O3 (PLCT) seed layer between films and substrates, a dense (Na0.85K0.15)0.5Bi0.5TiO3 (NKBT)/porous NKBT/dense NKBT sandwich structure composite film with high orientation was successfully fabricated at low temperature. The effects of the heating rate on the microstructures and electrical properties of the sandwich structure composite film were investigated in detail. It is found that the porous density of the films increased with decreasing heating rates, and the dielectric constants were significantly decreased. Compared with the sandwich structure NKBT composite films, the sandwich structure NKBT composite films with a seed layer possesses high remnant polarization values and a low leakage current density due to its low-temperature crystallization and high orientation. For the sandwich structure composite film with a seed layer annealed at a heating rate of 20 °C s−1, a low dielectric constant (er = 110) and a high pyroelectric coefficient (p = 172 µC m−2 K−1) are simultaneously achieved, making great contribution to a higher pyroelectric figure of merit (Fd = 1.3 × 10−5 Pa−1/2) than those of previously reported lead-free pyroelectric films. This work establishes a facile, yet efficient approach to prepare films with a high pyroelectric figure of merit at low temperature, and it extends the possible applications of the sandwich structure films for pyroelectric devices.

Enhanced Thermal Conductivity and Dielectric Properties of Iron Oxide/Polyethylene Nanocomposites Induced by a Magnetic Field

Iron Oxide (Fe3O4) nanoparticles were deposited on the surface of low density polyethylene (LDPE) particles by solvothermal method. A magnetic field was introduced to the preparation of Fe3O4/LDPE composites, and the influences of the magnetic field on thermal conductivity and dielectric properties of composites were investigated systematically. The Fe3O4/LDPE composites treated by a vertical direction magnetic field exhibited a high thermal conductivity and a large dielectric constant at low filler loading. The enhancement of thermal conductivity and dielectric constant is attributed to the formation of the conductive chains of Fe3O4 in LDPE matrix under the action of the magnetic field, which can effectively enhance the heat flux and interfacial polarization of the Fe3O4/LDPE composites. Moreover, the relatively low dielectric loss and low conductivity achieved are attributed to the low volume fraction of fillers and excellent compatibility between Fe3O4 and LDPE. Of particular note is the dielectric properties of Fe3O4/LDPE composites induced by the magnetic field also retain good stability across a wide temperature range, and this contributes to the stability and lifespan of polymer capacitors. All the above-mentioned properties along with the simplicity and scalability of the preparation for the polymer nanocomposites make them promising for the electronics industry.

Enhanced electric polarization and breakdown strength in the all-organic sandwich-structured poly(vinylidene fluoride)-based dielectric film for high energy density capacitor

It is essential to develop the dielectric energy storage capacitor for the modern electrical and electronic equipment. Here, the all-organic sandwich-structured composite with superior breakdown strength and delayed saturation polarization is presented. Furthermore, the energy storage characteristics of the composite are enhanced by the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) fiber and the redistribution of local electric field. The dielectric permittivity of composite increases to ∼16, and the discharged energy density is high to ∼8.7 J/cm3 at 360 kV/mm, and the breakdown strength is up to ∼408 kV/mm. The excellent performance of the composite broadens the application in the field of power electronics industry.

Study on nonlinear conductivity and breakdown characteristics of zinc oxide–hexagonal boron nitride/EPDM composites

The ethylene–propylene–diene monomer (EPDM) has been widely used in HVDC cables accessories. The nonlinear conductivity of EPDM-based composites plays an important role on relieving the distortion of electric field. In this study, the zinc oxide (ZnO) particles are selected as fillers for improving the nonlinear conductivity of EPDM. The result shows that nonlinear conductivity characteristics of ZnO/EPDM becomes more and more pronounced with the increase of ZnO doping content, however, the breakdown strength of ZnO/EPDM composites has been seriously deteriorated with the increase of ZnO doping content. The excellent breakdown strength of composites is very important for ensuring the safe operation of cable accessories, so the hexagonal boron nitride (h-BN) with good electrical insulation has been employed for improving the breakdown strength of ZnO/EPDM. The results indicate that both of non-linear conductivity and good breakdown strength have been obtained in ZnO–h composite-BN/EPDM composites. This work provides a novel way for constructing the composites with excellent electrical performances which are used for cable accessories.