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Polymer dielectrics for electrostatic capacitors possess well-recognized advantages, including ultrahigh power density, excellent processability, and unique self-healing capability. Nevertheless, the negative coupling relationship between dielectric permittivity and breakdown strength in dielectrics always constrains the enhancement of energy density, which cannot satisfy the ever-increasing requirements for integrated and miniaturized technologies. Here, a kind of C/SiO2@TiO2 triphase nanoparticle (CST NP) with a hybrid-core satellite structure is prepared and introduced into nonlinear poly(vinylidene fluoride-co-hexafluoropylene) [P(VDF-HFP)] matrix to improve permittivity and polarization. Benefited from the intensified interfacial polarization induced by CST NPs, a high permittivity of ∼18.8, which is approximately 219% that of pure P(VDF-HFP) (∼8.6), is obtained at 10 kHz. Meanwhile, a linear PEI film with high breakdown strength is stacked with the CST/P(VDF-HFP) composites, forming linear/nonlinear CST/P(VDF-HFP)-PEI bilayer composites. Eventually, a high breakdown strength of ∼503.9 kV/mm, a high energy density of ∼4.26 J/cm3, and a high efficiency of ∼91% are simultaneously achieved in the bilayer composite with merely 0.75 wt. % nanoparticles. The linear/nonlinear bilayer structure incorporated with hybrid-core satellite nanofillers offers an effective strategy to design high-performance dielectric energy storage materials. [ABSTRACT FROM AUTHOR]

With the rapid development of miniaturization and high integration of electronic devices, increasing attention has been paid to the exploration of dielectric composites with further improved dielectric permittivities. Herein, a unique design of high dielectric permittivity composites consisting of three-dimensional porous W-WO3/BaTiO3 foams hosted in epoxy matrix is proposed. It is demonstrated that the introduction of W-WO3/BaTiO3 foams into the epoxy matrix results in substantially improved dielectric permittivities in comparison with the epoxy matrix. Meanwhile, low loss which is comparable to that of the epoxy matrix is well maintained. Interestingly, obviously enhanced dielectric permittivities and greatly depressed loss are concurrently achieved via increasing the oxidation temperature. In particular, the composite with 53.1 wt% W-WO3/BaTiO3 foam oxidized at 1300 °C exhibits a high dielectric permittivity of ~ 536 and a low loss tangent of ~ 0.05@10 kHz which are about 149 and 1.5 times those of the epoxy matrix, respectively. It is believed that the strong interfacial polarization and the numerous equivalent micro-capacitors result in the significantly improved dielectric permittivities. The finite element simulation results reveal that the formation of the WO3 shell on the surface of W can effectively weaken the leakage current density, yielding the sharply depressed loss. This work provides a new strategy to design polymer composites with simultaneous high dielectric permittivity and low loss, and the strategy could also be applicable to the exploration of other high-performance dielectric composites. [ABSTRACT FROM AUTHOR]

Aerogels with negative parameters have become a research hotspot since the discovery of negative Poisson's ratio and negative thermal expansion coefficient in aerogels. The negative parameters are originally brought up and studied in electromagnetic metamaterials, leaving a question that whether aerogels can be used to construct metamaterials with negative electromagnetic parameters. Here, the authors show that negative permittivity (epsilon‐negative) property can be achieved in carbon aerogels, and its value is adjusted continuously by changing the composition of carbon aerogels but keeping their microstructure unchanged. This is a novel strategy different from the typical array‐structure‐containing metamaterials. Moreover, a physical state transition is found when increasing the carbonization temperature, where the initial low‐loss dielectric state evolves into a high‐loss one upon increasing the temperature from 400 to 700 °C followed by a final degenerate semiconductor state when increasing the temperature to 800 °C and above. This work can provide a new method toward the design of electromagnetic metamaterials, starting by choosing the component materials with optimal composition. [ABSTRACT FROM AUTHOR]

Negative capacitance in ferroelectrics has seem remarkable progress in recent years. However, direct measurement of negative capacitance has so far been a challenge due to its instable characteristic in the electrostatic field. An ingenious method to design stable negative capacitance by dielectric resonance under high‐frequency alternating electric fields is demonstrated. The well‐pronounced dielectric resonance and electrical property in BaTiO3/SrTiO3 (BT/ST) bulk ceramics consisted of epitaxial core–shell particles are studied. As the negative capacitance can be considered as an inductive behavior, the dielectric resonance of permittivity induced by a LC resonance can be occurred. The dielectric resonance can be described by the Lorentz model and explained by Fano‐like resonance of TO2 phonon in BT. In addition, lowest resonant frequency is observed at effective Curie temperature. Benefiting from negative capacitance in the BT/ST ceramics, both high permittivity and negative permittivity are accompanied with low losses around the resonant frequency, which is useful for developing capacitors and metamaterials. Significantly, this work will provide an initiative avenue to obtain explicit negative capacitance of ferroelectrics in the frequency spectrum. [ABSTRACT FROM AUTHOR]

This review provides a comprehensive understanding of polymeric dielectric capacitors, from the fundamental theories at the dielectric material level to the latest developments for constructing prototypical capacitors, with an emphasis on synergetic strategies for enhancing dielectric and energy storage properties. [Display omitted] The evolutionary success in advanced electronics and electrical systems has been sustained by the rapid development of energy storage technologies. Among various energy storage techniques, polymeric dielectric capacitors are gaining attention for their advantages such as high power density, fast discharge speed, cost-effectiveness, ease of processability, capability of self-healing, and tailorable functional properties. Great advances have been made in this field over the past decade, involving the discovery of new dielectric polymers, innovation of basic processing technologies, as well as the extension toward up-and-coming material computations and design strategies. This review provides a comprehensive understanding of polymeric dielectric capacitors, from the fundamental theories at the dielectric material level to the latest developments for constructing prototypical capacitors, with an emphasis on synergetic strategies for enhancing dielectric and energy storage properties. To begin with a brief introduction and description of the fundamentals, the subsequent sections cover intrinsic polymers, blended polymers, polymer nanocomposites, multilayer polymers, metacapacitors, and their properties. Then, we discuss corresponding fabrication techniques and highlight the challenges of commercialization, from polymer dielectric materials to film capacitors in developing commercial prototypes. Finally, we comment on the current state and future requirements for the development of polymer dielectric capacitors to high-performance devices. [ABSTRACT FROM AUTHOR]

Ferroelectric ceramic materials are receiving increasing attention due to their extensive applications in electrical systems. In this work, three-layer BaTiO 3 /SrTiO 3 ceramic composites consisting of one Ba 1-x TiO 3 -Sr x TiO 3 (at x = 5, 10, 20 and 30) composite interlayer sandwiched by two BaTiO 3 outer layers were fabricated. And the effects of SrTiO 3 modification on their phase structures, microstructures and dielectric performance were studied in detail. A pure perovskite phase was observed in the Ba 1-x TiO 3 -Sr x TiO 3 ceramic composites. The BaTiO 3 ceramic doping by SrTiO 3 exhibited refined grain size. With increased SrTiO 3 content, both the permittivity and dielectric loss have increased. Furthermore, a layered structure was designed to enhance the dielectric properties. Consequently, a high permittivity of 7118 and low loss of 0.028 were achieved at 10 kHz in BaTiO 3 -30 w% SrTiO 3 –BaTiO 3 three-layer ceramic composites. In summary, the introduction of SrTiO 3 is believed to reduce the BaTiO 3 Curie temperature and greatly improve its permittivity at room temperature. Furthermore, the accumulation of charge carriers at the interface significantly increases the permittivity, while preventing the transport of the charge carriers and reducing the loss. The ultrahigh permittivity and low loss make these composites promising candidates for microwave antennas, field effect transistors and dielectric capacitors. [ABSTRACT FROM AUTHOR]

In this work, dielectric behaviors of dielectric resonance, relaxation, and plasma-like negative permittivity are observed in percolative copper/rutile cermets. Transition for permittivity changing from positive to negative is associated with composition and determined by percolation. The resonance and relaxation responses are related to isolated metallic particles or clusters. Negative permittivity is induced by the plasmonic state of electrons within percolating pathways and dielectric loss of epsilon-negative composites is dominated by conduction loss. Besides, the percolative cermets change from electrical capacitive to inductive with the permittivity transition. Epsilon-negative cermets are expected to be used for electromagnetic shielding and coil-less electrical inductors. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• The subtractive manufacturing was firstly used to construct the epsilon-negative material. • Negative permittivity value was effectively adjusted by chemical corrosion. • The conductivity mechanism changed from metal-type conductivity to the hopping conductivity. Epsilon-negative materials are usually prepared by additive manufacturing, while a reverse design method needs to be developed to construct the epsilon-negative materials by subtractive manufacturing. Here the Nickel-Network/Epoxy composites were prepared via a chemical corrosion and curing process. The connectivity of nickel network was weakened by chemical corrosion, which was companied with a change of conductivity mechanism from metal-type conductivity to the hopping conductivity. The negative permittivity value could be effectively adjusted by corroding the nickel network, which was attributed to low-frequency plasmonic state of nickel network. The reverse design method provided a novel and more flexible method to construct the desired the epsilon-negative materials. [ABSTRACT FROM AUTHOR]

Acrylic-polyurethane (APu) as one of self-adhesive materials has been widely used in various coating industries, however it has seldom caused the researchers concern on its dielectric property. In this paper, acrylic polyurethane and carbon fibers (CFs) composites with good dispersibility have been successfully prepared. The dielectric properties and ac conductivity of the CFs/APu composites as a function of frequency and volume fraction of CFs were studied. High dielectric constant about 700 (10 kHz) was observed in APu-14.7% CFs composites. The outstanding dielectric properties make CFs/APu composites as promising candidates for thin-film capacitors, electromagnetic shielding and attenuation coatings. [ABSTRACT FROM AUTHOR]

Loss materials have great potential applications in electromagnetic wave absorption and attenuation. In this paper, we report an epsilon-negative composite that has very high dielectric loss (tan δ~100@10 MHz). This percolative polymer composite is filled with spherical micron-sized copper particles. Below the percolation threshold, conductivity spectra showed obvious frequency dispersion and conformed to the Jonscher's power law, indicating hopping conduction. When composites reached up to percolated state, the conduction mechanism changed to electron-like conduction. It is suggested that the electron transfer between copper particles leads to a very high loss of the composites. [ABSTRACT FROM AUTHOR]

[Display omitted] • Drude-type negative permittivity is achieved in MWCNTs/PVDF composites. • Electric transport mechanism changes from local to non-local transport with the increase of functional phase content. • It is found that the percolation threshold of MWCNTs/PVDF composites is between 8 wt% and 10 wt% Composites with negative permittivity behavior have brought about widespread attention for their broad application prospects in electromagnetic field or being used for novel capacitance. In this work, multiwall carbon nanotubes/polyvinylidene fluoride (MWCNTs/PVDF) composites with gradually increasing MWCNT filling content were prepared by hot-pressing in order to acquire negative permittivity. The microstructure, ac conductivity, and real permittivity of the samples were elaborated. As MWCNTs content increases, the percolation phenomenon occurs accompanied by the conversion of conductive mechanism from hopping conduction to free electron conduction. It's found that negative permittivity property was obtained at a lower filler content and can be regulated by controlling MWCNTs content, which is related to the plasma oscillation state of free electrons in MWCNTs. [ABSTRACT FROM AUTHOR]

Abstract: Cement-based 0-3 type piezoelectric composites, fabricated from white cement, lead zirconate titanate (PZT) powder and small amounts of carbon black, are exploited for potential applications in civil engineering. The nature of the aging and poling behavior of the carbon black/PZT/cement composites is investigated. It is shown that the use of a conductive carbon black phase can facilitate the poling process at room temperature. The influences of the carbon black on the piezoelectric and dielectric properties are studied as well. It is demonstrated that the piezoelectric sensitivities of the composites can be dramatically enhanced by incorporation of small amounts of carbon black, due to its conductive properties. With a poling field of 4kV/mm and poling time of 20min, the d 33, ɛ r , tan δ and K t values of the composite containing 70vol.% PZT and 1.0vol.% carbon black are 28.5pC/N, 202.6, 0.19 and 12.2%, respectively. [Copyright &y& Elsevier]

• Layered polymer films consisting of stacked high- k films and linear dielectric films are prepared. • An obvious suppression of loss from 0.13 to 0.05 at 100 Hz is achieved. • A significant increase of breakdown strength from 138 kV/mm to 413 kV/mm is realized. • The energy density and efficiency of the multilayer films are higher than that of their 1-layer counterparts. High dielectric materials are widely used in electronic devices, but their applications are severely hindered by the high loss and low breakdown strength. Herein, a layered structure is designed to effectively suppress the loss and enhance the breakdown strength of high dielectric materials. In the design, the high dielectric films are stacked with linear dielectric films, which can not only form breakdown barriers between adjacent layers but also reduce the leakage conduction loss. As a result, an obvious suppression of loss from 0.13 to 0.05 at 100 Hz, along with a significant increase of breakdown strength from 138 kV/mm to 413 kV/mm, are successfully achieved. [ABSTRACT FROM AUTHOR]

• Graphene/PPS composites for negative permittivity media were realized. • Properties of negative permittivity for composites can be easily tailored. • Negative permittivity and electric percolation appeared at low content percolation. Composites with negative permittivity have drawn much attentions for novel capacitance design and electromagnetic shielding applications. Herein, polyphenylene sulfide (PPS) matrix composites filled with graphene were prepared by hot-pressing for tailorable negative permittivity media. Electrical percolation occurred as graphene content increasing and the conduction mechanism changed into free electron model. Graphene/PPS composites with tailorable negative permittivity properties were realized, resulting from the plasmonic oscillation of free electrons in composites exceeding percolation threshold. The regulation mechanism of negative permittivity in this random composite was clarified, and the obtained tailorable negative permittivity media could be novel candidates for various electromagnetic applications. [ABSTRACT FROM AUTHOR]