Jiufeng Dong

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.

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.

Effects of magnetic field treatment on dielectric properties of CCTO@Ni/PVDF composite with low concentration of ceramic fillers

Using melt mixing, we produced a ceramic/polymer composite with a matrix of polyvinylidene fluoride (PVDF) and a filler of 5 vol.% Ni-deposited CaCu3Ti4O12 core-shell ceramic particles (CCTO@Ni), and studied its prominent dielectric characteristics for the first. Its phase composition and morphology were analyzed by X-ray diffraction and scanning electron microscopy, respectively. After treating the composite films with various durations of a magnetic field treatment, we compared their dielectric properties. We found that the CCTO@Ni ceramic had a typical urchin-like core-shell structure, and that different durations of the magnetic field treatment produced different distributions of ceramic particles in the PVDF matrix. The dielectric permittivity of the untreated CCTO@Ni/PVDF composite was 20% higher than that of neat PVDF, and it had a low loss tangent. However, only the composite treated for 30 min in the magnetic field had an ultra-high dielectric permittivity of 1.41 × 104 at 10 Hz, three orders of ...

Enhanced energy density of PVDF-HFP/CCTO nanocomposites induced by aspect ratio fillers

Dielectric materials with high energy density have a wide range of applications in high-performance capacitors, sensors, brakes, spacecraft, and electric stress control devices. Adding inorganic filler in the polymer matrix is an effective way to increase the energy density of the polymer materials, the characteristics of composites and inorganic filler with high dielectric constant and high breakdown strength of polymer materials. However, the aggregation and phase separation of inorganic fillers in the polymer matrix is still the key obstacle to the practical application of the composites. Here, we develop a novel strategy for the growth of high aspect ratio calcium copper tianate nanofibers (CCTO-NFs) with electrospinning method, and then the high energy density nanofiber composites materials are fabricated using polydopamine (PDA) modify high aspect ratio CCTO-NFs in a poly(vinylidene fluoride-co hexafluoropropylene) (PVDF-HFP) matrix. The microstructure, dielectric properties, and energy storage density of the composites were studied. It was found that the two types of fillers were dispersed homogeneously in the PVDF-HFP matrix. The dielectric constant of the composites filled by CCTO nanofiber is large than CCTO nanoparticles at the same content. Stronger interfacial polarization mainly determined the dielectric properties that we observed on PVDF-HFP/CCTO-NFs composites. Moreover, a relatively low dielectric loss and a low conductivity achieved is attributed to the high aspect ratio of fillers and excellent compatibility of the CCTO nanofiber and PVDF-HFP matrix. Furthermore, when the content of filler was 10 wt.%, the discharged energy density of PVDF-HFP/CCTO NFs composites (1.508 J/cm3) is 4.17 times higher than that of PVDF-HFP/CCTO NPs composites (0.214 J/cm3). Such significant enhancement could be attributed to the combined effects of the surface modification and large aspect ratio of the CCTO-NFs. This work may provide a route for using the surface modified CCTO nanofibers to enhance the dielectric energy density in ceramic-polymer nanocomposites.

Improving dielectric properties of PVDF composites by obtaining the BT-Ni particles

In the rapid development of modern science and technology, the dielectric materials with more extraordinary performance were extremely demanded in the electronic system fields. Nowadays, outstanding-performance polymers, which possess a high dielectric constant and flexibility but low dielectric loss have attracted great attention owing to their potential application in many cutting-edge industries, including microelectronics, aerospace, and aviation. In general, the polymers possess excellent flexibility and high breakdown strength, but their applications was limited by the low dielectric permittivity. Numerous efforts have been made to improve the dielectric permittivity of dielectrics by incorporating ceramic additives into polymer matrix. Unfortunately, the high dielectric permittivity needs high filler loading, which causes them to lose their flexibility and decreased breakdown strengths. Herein, the Ni nanoparticles was deposited on the surface of the BT particles to obtain the BT-Ni particles by electroless plating method. The phase composition and morphology were analyzed by X-ray diffraction and scanning electron microscopy, and the effects of BT-Ni filler on the dielectric properties of the composites were investigated in detail. It can be found that the high dielectric permittivity of the composites increased to 61 at 100 Hz when the content of BT-Ni filler was 20vol.%, which is 2.54 times higher than that of 20vol.% BT/PVDF (24) and even greater than that of 40vol.% BT/PVDF (56). The Ni nanoparticles was strong interaction deposited on BT particles, and this structure can effectively suppress the probability of the Ni nanoparticles to form a conductive networks in the PVDF polymer matrix, which can greatly depress the increase of dielectric loss tangent and conductivity of the BT-Ni/PVDF composites. These results indicated that the dielectric constant of the composites can be significantly improved by incorporating Ni conducting particles into the polymer matrix and that the interfacial polarization effect is an important feature of BT-Ni/PVDF composites. This work provides a simple and effective way for preparing nanocomposites with enhanced dielectric properties for use in the electronics industry.