IET Nanodielectrics最新文献

The significant progresses of polymer-based nanocomposites with improved dielectric performances are urgently calling for an effect way to realise commercial production. Up to now, the biaxial stretching technology is still a powerful method to produce the high-performance dielectric films applied in the film capacitors due to its full-blown applications. In this work, a classical composite system of BaTiO₃/polypropylene was applied to reveal the connection between the microstructure changes and dielectric properties of the corresponding nanocomposite films in the biaxial stretching process. The permittivity of BT-30 wt% nanocomposite reached 2.8 at 10³ Hz after stretching, and its breakdown strength reached 340 MV/m. In addition, the breakdown strength of BT-10 wt% nanocomposite could even be promoted to 452 MV/m, which was 1.3 times higher than that before stretching. The microstructure test demonstrated that the rearrangement of nanofillers, high crystallinity and the oriented polypropylene crystals were advantageous to the improvement of breakdown strength for the stretched nanocomposite films. Therefore, the application of biaxial stretching technology into the preparation of nanocomposite dielectric film is an enormous potential way for the energy storage film capacitors.

Dielectric energy storage capacitors with excellent high temperature resistance are essential in fields such as aerospace and pulse power. However, common high-temperature resistant polymers such as polyimide (PI) and polyether sulfone have low energy storage densities and energy efficiencies at high temperature, which are greatly limited in practical applications. The polymer nanocomposites prepared by doping modification can regulate the charge injection and transport process, and improve the high-temperature energy storage performance. However, the quantitative relationship between charge injection and charge trapping and the energy storage performance of linear polymer nanocomposites still needs further study. An energy storage and release model considering the charge trapping effects is constructed by the authors. We simulate the high-temperature energy storage properties of polyimide nanocomposite dielectrics (PI PNCs) with different charge injection barriers and trap parameters at 150°C. A triangular voltage is applied to the electrodes at both sides of the PI PNCs, the electric displacement-electric field loop is simulated, and the discharged energy densities and energy efficiencies are calculated. The simulation results are consistent with the experimental results. Increasing the charge injection barrier, deep trap energy and deep trap density can effectively reduce the charge injection and the carrier mobility, thereby improving the discharged energy densities and energy efficiencies of dielectric capacitors. In the case of low charge injection barrier (1.3 eV), with the increase of deep trap energy (0.7–1.5 eV) and deep trap density (1 × 10²¹–1 × 10²⁵ m⁻³), the discharged energy density changes from 0.20 to 1.44 Jcm⁻³, the energy efficiency changes from 9.0% to 99.9%, and the high-temperature energy storage performance improves significantly. This research provides theoretical and model support for the improvement of the high-temperature energy storage performance of nanocomposites.

High-performance dielectric capacitors are essential components of advanced electronic and pulsed power systems for energy storage. Because of their high breakdown strength and excellent flexibility, polymer-based capacitors are regarded as auspicious energy storage material. However, the energy storage capacity of polymer-based capacitors is severely limited due to their low polarisation and low dielectric permittivity. The modified Stöber method was used to construct two types of CNT@SiO₂ (CS) one-dimensional core-shell structured nanowires with different shell thicknesses. By integrating the procedures of solution mixing, melt blending, hot-stretching orientation and hot pressing, sandwich-structured poly (vinylidene fluoride) (PVDF)-based composites were fabricated. The CS core-shell nanowires dispersed in the inter-layer serve as electron donors, leading to a high permittivity, while two PVDF outer layers provide the favourable overall breakdown strength. The insulating SiO₂ shell can effectively limit the migration of carriers and keep the dielectric loss at a relatively low level in the composites. The CS/PVDF composite exhibited an enhanced discharged density (~6.1 J/cm³) and breakdown strength (~241 kV/mm) when the interlayer filled with as small as 1 wt% CS nanowires with the SiO₂ shell thickness of 8 nm, which is 203% and 18.7 % higher than pure PVDF (~2.01 J/cm³ at 203 kV/mm), respectively. This research presents a practical strategy for designing and fabricating advanced polymer film capacitor energy storage devices.

Barium titanate (BaTiO₃, BT) was co-doped by solid-state sintering with niobium pentoxide (Nb₂O₅) and cobalt trioxide (Co₃O₄) as dopants. The modified barium titanate containing Nb and Co (BTNC) with larger particle size (0.5–1 μm) and silver powder (Ag) with smaller particle size (25 nm) were co-filled with polyvinylidene fluoride (PVDF) to prepare (BTNC-Ag)/PVDF three-phase composites. The morphology and crystal structure of composites were characterised by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. SEM shows that when the volume ratio of BTNC and Ag in the composite is 4:1, the two fillers have good dispersion in polymer matrix and could intersperse with each other to reduce voids. XRD patterns display that the filling of BTNC and Ag powders was conducive to promoting the enhancement of the diffraction peaks of β phase and γ phase in PVDF. The dielectric properties of the composites are effectively enhanced through the synergistic effect of the micro-nano bicomponent ceramic BTNC and conductive particles Ag co-filled polymer PVDF. When the volume ratio of filler (BTNC:Ag = 4:1) to matrix PVDF is 2/1, the dielectric properties of the composite are the best, the dielectric constant reaches 134.1 at 10² Hz and the dielectric loss is 0.04.

This study focussed on determining the electric field distribution formed by asymmetric agglomerates in order to elucidate the mechanism by which large agglomerates reduce the dielectric breakdown strength of nanocomposites. Epoxy nanocomposite sample was prepared by adding 2.5 vol% of TiO₂ nanoparticles with a primary particle size ranging from 30 to 50 nm. The three-dimensional (3D) structure of the epoxy nanocomposites with a thickness of 5 μm was analysed via focussed ion beam and scanning electron microscopy. The 3D reconstruction was performed using 250 observation images, and a 3D model of the particle in the observational range was obtained. The electric field distribution for the 3D model of the agglomerate with the largest size was determined using the finite element method. In addition, we constructed a calculation model that effectively accommodate changes in the direction of the applied electric field. Subsequently, we examined the changes in the maximum electric field intensity around the agglomerate.

Vibrational energy harvesters, which can convert mechanical energy distributed widely in the surrounding environment to electrical energy in a convenient, eco-friendly and sustainable way, have attracted great attention in both academia and industry. In this study, a resilient electret film-based vibrational energy harvester with a V-shaped counter electrode is introduced, simulated and constructed. A negatively charged fluorinated polyethylene propylene (FEP) electret film with a wavy shape was adopted in the devices, achieving simultaneously a stable embedded biased voltage and a large tensile deformation during vibration. The influences of the factors on the performance of the device, including the initial stretching state of the resilient electret film, seismic mass and depth of the V-shape counter electrode, were analyzed comprehensively with finite element simulation and compared to experiments. Further, the structure of the device was optimised for generating a high output power, and a good agreement between the simulation and experimental data was achieved. Additionally, the resonant frequency of the device can be easily tuned between 28 and 68 Hz by merely adjusting the initial stretching state of the wavy FEP electret film, guaranteeing great superiority for broad bandwidth energy harvesting applications. For an optimised energy harvester with a volume of only 15 × 5 × 1.7 mm³ and a tiny seismic mass of 25 mg, and a normalized output power referring to 1 × g (g is the gravity of the Earth) up to 547 μW was obtained at its resonant frequency of 28 Hz. These results demonstrate that such a miniaturised vibrational energy harvester is a promising electrical energy supplier for low-power-consumption electronic devices, in particular in wireless sensor networks.

A series of high-performance linear and cross-linked polyimide (PI) aerogels with different molecular structures have been successfully synthesised using the freeze-drying process. In this study, the comprehensive regulation of microstructure, thermodynamic, thermal insulation and dielectric properties of PI aerogels are achieved by controlling the rigid/flexible structure and composition of polymerised monomers. The increase in rigidity of PI molecular structure could promote the formation of denser pores, which is beneficial to improve the thermodynamic and thermal insulation properties of aerogels. Notably, the cross-linked PI aerogel prepared by introducing cross-linking agent (tris(4-aminophenyl) amine, [TPA]) into linear PI exhibits high thermal stability (T_d5% > 560°C), excellent ultralow permittivity (ε_r = 1.31, f = 10⁶ Hz) and good thermal insulation property (k = 0.056 W/m · K). This innovative strategy promotes the wider application of the cross-linked polyimide aerogel in the field of integrated circuits and aerospace exploration.

Piezoelectric polymers have been widely used in a variety of applications, including tactile sensors, energy harvesting, polymer actuators, and biological devices. In this investigation, we fabricated the PLLA (poly(L-lactic Acid)-based bimorph structures for piezoelectric motor applications. First, a strain measurement setup was established to measure the strain of the PLLA and PDLA film at different temperatures. The effective piezoelectric constants d₁₄ calculated for the PLLA and PDLA films were 10.2 pC/N and 9.4 pC/N, respectively. Furthermore, the PLLA films showed a strong thermostability of piezoelectricity at 130°C. The PLLA bimorph minimotor showed the maximum load of 1.2 g and the maximum torque of 0.019 cN·m. The minimotors were capable of rotating a plastic hemisphere container in the clockwise and counterclockwise directions at 65 V voltage. Due to the light weight, low driving voltage, and thermal stability, the PLLA/PDLA motors show a great promise in future Braille display, robots, and mini-digital camera applications.

Ferroelectrets (also called piezoelectrets) are relatively young members in the family of piezo-, pyro- and ferroelectric materials. They exhibit ferroic behaviour phenomenologically undistinguishable from that of traditional ferroelectrics, although the materials per se are essentially non-polar space-charge electrets with artificial macroscopic dipoles (i.e. internally charged cavities). Since ferroelectrets not only represent a scientific curiosity but also have great application potential, they have attracted tremendous attention from science and industry. The research and development of ferroelectrets has witnessed significant progress in the past few years. New ferroelectrets with large transverse piezoelectric activity, biodegradable ferroelectrets as well as 3-D printed ferroelectrets are reported. Charging methods of high efficiency are proposed based on better understanding of the physico-chemical processes during charging. New insights into the piezoelectricity of ferroelectrets are provided. The development of ferroelectret-based piezoelectric-magnetic multimodal transducer films opens up new avenues for the research of ferroelectrets. Particularly, more and more novel applications of ferroelectrets in flexible pressure sensors, health monitoring, energy harvesting, air-coupled ultrasonic non-destructive testing etc. are reported. Here, these exciting recent advancements in the field of ferroelectret research are reviewed and discussed.

Al electrodes with different thickness (sheet resistance 2–100 Ω/□) were deposited onto the films of polypropylene (PP), polyester (PET) and polyimide (PI) by vacuum evaporation. The root-mean-square (RMS) and peak-to-valley roughness of Al electrodes were characterised by atomic force microscopy (AFM). It was found that the PET and PI substrates showed the reduced threshold thickness of the continuous growth of Al electrodes compared with the PP substrate. The sheet resistance of Al electrodes decreases with the increase of peak-to-valley roughness. The current surge capability of the Al electrode decreases with the increase of RMS roughness. The Al electrode deposited on the PET film has higher sheet resistance and better current carrying capability, and the self-healing performance of metallised film is also excellent among three kinds of films.