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Showing papers on "Dielectric loss published in 2021"


Journal ArticleDOI
TL;DR: In this paper, the authors designed heterostructure NiCo-LDHs@ZnO nanorod and then subsequent heat treating to derive NiCo@C/ZnOs composites, where the synergy of excellent dielectric loss and magnetic loss was achieved with the reflection loss of 60.97 dB at the matching thickness of 2.3mm.
Abstract: Layered double hydroxides (LDHs) have a special structure and atom composition, which are expected to be an excellent electromagnetic wave (EMW) absorber. However, it is still a problem that obtaining excellent EMW-absorbing materials from LDHs. Herein, we designed heterostructure NiCo-LDHs@ZnO nanorod and then subsequent heat treating to derive NiCo@C/ZnO composites. Finally, with the synergy of excellent dielectric loss and magnetic loss, an outstanding absorption performance could be achieved with the reflection loss of − 60.97 dB at the matching thickness of 2.3 mm, and the widest absorption bandwidth of 6.08 GHz was realized at 2.0 mm. Moreover, this research work provides a reference for the development and utilization of LDHs materials in the field of microwave absorption materials and can also provide ideas for the design of layered structural absorbers.

205 citations


Journal ArticleDOI
TL;DR: In this article, the defect induced dielectric loss dominant mechanism in virtue of multi-shelled spinel hollow sphere for the first time is demonstrated, and the unique but identical morphology design as well as suitable composition modulation for serial spinels can exclude the disturbance of EM wave dissipation from dipolar/interfacial polarization and conduction loss.
Abstract: Defect engineering is an effective approach to manipulate electromagnetic (EM) parameters and enhance absorption ability, but defect induced dielectric loss dominant mechanism has not been completely clarified. Here the defect induced dielectric loss dominant mechanism in virtue of multi-shelled spinel hollow sphere for the first time is demonstrated. The unique but identical morphology design as well as suitable composition modulation for serial spinels can exclude the disturbance of EM wave dissipation from dipolar/interfacial polarization and conduction loss. In temperature-regulated defect in NiCo2O4 serial materials, two kinds of defects, defect in spinel structure and oxygen vacancy are detected. Defect in spinel structure played more profound role on determining materials' EM wave dissipation than that of oxygen vacancy. When evaluated serial Co-based materials as absorbers, defect induced polarization loss is responsible for the superior absorption performance of NiCo2O4-based material due to its more defect sites in spinel structure. It is discovered that electron spin resonance test may be adopted as a novel approach to directly probe EM wave absorption capacities of materials. This work not only provides a strategy to prepare lightweight, efficient EM wave absorber but also illustrates the importance of defect engineering on regulation of materials' dielectric loss capacity.

148 citations


Journal ArticleDOI
TL;DR: In this paper, the Co9S8/C/Ti3C2Tx-100 hybrid material with a multilayer structure was successfully fabricated by hydrothermal and annealing processes.

148 citations


Journal ArticleDOI
01 May 2021-Carbon
TL;DR: In this article, hybrid graphene aerogels with decoration of 1D CoNi chains and CNTs (GA-CNT-CoNi) were fabricated via a facile freeze-drying method and followed by thermal reduction.

142 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated polymer nanocomposites containing a series of Al@Al2O3 nanofillers with different shell thicknesses and showed that the high dielectric constant of percolative composites is contributed by a fast intra-particle polarization and a slow interparticle polarization.

113 citations


Journal ArticleDOI
TL;DR: In this paper, the mesoporous polydopamine (CoMOF@MPDA) composites with a core-shell structure are prepared by the bottom-up monomicelle assembly.
Abstract: Electromagnetic wave absorbents with hierarchically porous and core–shell structures have significantly positive influence on the electromagnetic wave absorption because of the enhanced interfacial polarization. Furthermore, the core–shell structure also introduces components with strong dielectric loss and good resistance to chemical corrosion. Herein, the cobalt–metal–organic frameworks @mesoporous polydopamine (Co–MOF@MPDA) composites with a core–shell structure are prepared by the bottom-up monomicelle assembly. After calcination, the Co@S-doped carbon core and mesoporous N-doped carbon shell (Co@SC@MNC) were obtained. Through adjusting the calcination temperature, the dielectric and magnetic loss can be tuned, resulting in the strong absorption capability for the electromagnetic wave. The minimum reflection loss reaches −72.3 dB, while the effective absorption bandwidth is as broad as 6.0 GHz. The unique structure and the formation of internal cavity between Co@SC and MNC contribute to the interfacial polarization. The enhancement of the dipole polarization loss and conduction loss are ascribed to the S, N-doped hierarchically porous carbon. Importantly, the presence of Co nanoparticles facilitates the magnetic–dielectric synergy to improve the impedance matching due to the introduction of magnetic loss. The novel structural design has potential application in the electromagnetic wave absorption field.

112 citations


Journal ArticleDOI
01 Mar 2021-Carbon
TL;DR: In this paper, a hydrangea-like Ni/NiO/C composites have been successfully synthesized by in-situ pyrolysis stemmed from Ni-MOFs.

109 citations


Journal ArticleDOI
01 May 2021-Carbon
TL;DR: In this paper, a novel porous ZnO/ZnFe2O4/C@PG composites are synthesized using metal organic framework and micro-sized porous graphene network as precursors via a synchronous reflux strategy for sufficient microwave absorption performance.

88 citations


Journal ArticleDOI
TL;DR: The role of synergistic effect and interface on through-plane thermal conductivity and dielectric properties by intercalating the hybrid fillers of the alumina and boron nitride nanosheets (BNNs) into epoxy resin was reported in this paper.
Abstract: Dielectric materials with good thermal transport performance and desirable dielectric properties have significant potential to address the critical challenges of heat dissipation for microelectronic devices and power equipment under high electric field. This work reported the role of synergistic effect and interface on through-plane thermal conductivity and dielectric properties by intercalating the hybrid fillers of the alumina and boron nitride nanosheets (BNNs) into epoxy resin. For instance, epoxy composite with hybrid fillers at a relatively low loading shows an increase of around 3 times in through-plane thermal conductivity and maintains a close dielectric breakdown strength compared to pure epoxy. Meanwhile, the epoxy composite shows extremely low dielectric loss of 0.0024 at room temperature and 0.022 at 100 ℃ and 10-1 Hz. And covalent bonding and hydrogen-bond interaction models were presented for analyzing the thermal conductivity and dielectric properties.

84 citations


Journal ArticleDOI
TL;DR: In this paper, spiny globose like NiCo2X4 (X = O, S, Se, Te) are successfully prepared through hydrothermal and subsequent oxidation, sulfidation, selenization and tellurization methods, respectively.

84 citations


Journal ArticleDOI
TL;DR: In this article, a review of microwave dielectric ceramics (MWDCs) sintered higher than 1000 from 2010 up to now, °C is presented.
Abstract: The explosive process of 5G communication evokes the urgent demand of miniaturized and integrated dielectric ceramics filter. It is a pressing need to advance the development of dielectric ceramics utilization of emerging technology to design new materials and understand the polarization mechanism. This review provides the summary of the study of microwave dielectric ceramics (MWDCs) sintered higher than 1000 from 2010 up to now, °C with the purpose of taking a broad and historical view of these ceramics and illustrating research directions. To date, researchers endeavor to explain the structure-property relationship of ceramics with multitude of approaches and design a new formula or strategy to obtain excellent microwave dielectric properties. There are variety of factors that impact the permittivity, dielectric loss, and temperature stability of dielectric materials, covering intrinsic and extrinsic factors. Many of these factors are often intertwined, which can complicate new dielectric material discovery and the mechanism investigation. Because of the various ceramics systems, pseudo phase diagram was used to classify the dielectric materials based on the composition. In this review, the ceramics were firstly divided into ternary systems, and then brief description of the experimental probes and complementary theoretical methods that have been used to discern the intrinsic polarization mechanisms and the origin of intrinsic loss was mentioned. Finally, some perspectives on the future outlook for high-temperature MWDCs were offered based on the synthesis method, characterization techniques, and significant theory developments.

Journal ArticleDOI
Zhen Xiang1, Xiaojie Zhu1, Yanyan Dong1, Xiang Zhang1, Yuyang Shi1, Wei Lu1 
TL;DR: In this paper, the authors demonstrated the multifunctional electromagnetic absorbing characteristics of magnetic cobalt nanoparticles suspended in carbon nanotubes/expanded graphite (Co/CNTs/EG) porous composites.
Abstract: High-performance electromagnetic wave absorbing materials have aroused widespread interest, but their synthesis is still a tremendous challenge. Here, we demonstrated the multifunctional electromagnetic absorbing characteristics of magnetic cobalt nanoparticles suspended in carbon nanotubes/expanded graphite (Co/CNTs/EG) porous composites. The well-designed multi-component and novel nano-micro porous structure endowed Co/CNTs/EG porous composites with an enhanced electromagnetic wave absorption performance. As expected, a high reflection loss of −67.2 dB, an ultrathin thickness of 1.4 mm, a broad effect absorption bandwidth of 5.1 GHz, and an ultra-low filler loading of 3 wt% were achieved. The underlying microwave absorption mechanism was synergistic effects between conduction loss caused by electron transmission in the 3D conductive network, dielectric loss attributed to dipole and interface polarization in the porous structure, magnetic loss originating from the magnetic resonance of Co nanoparticles, and multiple reflections in the porous framework. In addition, the Co/CNTs/EG porous composites exhibited favorable waterproof, flame retardant, thermal insulation, and infrared shielding functions. Therefore, we report a flexible development strategy of novel porous composites with multifunctional and efficient electromagnetic wave absorption performances.

Journal ArticleDOI
30 Apr 2021-Carbon
TL;DR: In this paper, the effect of the multi-shell hollow structure of carbon sub-microspheres on the microwave absorption properties was investigated. And the results revealed that the improved complex permittivity and tangent loss of hollow CSs were mainly related to their unique structure.

Journal ArticleDOI
TL;DR: In this article, the main physical mechanisms of polarization, breakdown and energy storage in multilayer structure dielectric are introduced, the theoretical simulation and experimental results are systematically summarized, and the preparation methods and design ideas of multi-layer structure energy storage dielectrics are mainly described.
Abstract: An electrostatic capacitor has been widely used in many fields (such as high pulsed power technology, new energy vehicles, etc.) due to its ultrahigh discharge power density. Remarkable progress has been made over the past 10 years by doping ferroelectric ceramics into polymers because the dielectric constant is positively correlated with the energy storage density. However, this method often leads to an increase in dielectric loss and a decrease in energy storage efficiency. Therefore, the way of using a multilayer structure to improve the energy storage density of the dielectric has attracted the attention of researchers. Although research on energy storage properties using multilayer dielectric is just beginning, it shows the excellent effect and huge potential. In this review, the main physical mechanisms of polarization, breakdown and energy storage in multilayer structure dielectric are introduced, the theoretical simulation and experimental results are systematically summarized, and the preparation methods and design ideas of multilayer structure dielectrics are mainly described. This article covers not only an overview of the state-of-the-art advances of multilayer structure energy storage dielectric but also the prospects that may open another window to tune the electrical performance of the electrostatic capacitor via designing a multilayer structure.

Journal ArticleDOI
TL;DR: In this article, double-shell hollow glass microspheres (HGMs) coated with cobalt silicate (Co2SiO4) were synthesized by hydrothermal method with a further calcination process.

Journal ArticleDOI
TL;DR: In this article, a review of 2D filler-reinforced polymer nanocomposite dielectrics (PNDs) is presented, including carbon materials, MXenes, oxide ceramics, clays, boron nitride and so on.

Journal ArticleDOI
TL;DR: In this paper, a layered polymer composites consisting of the boron nitride nanosheet/polyetherimide and TiO2 nanorod arrays/polyhetimide layers are reported.
Abstract: To reach the full potential of polymer dielectrics in advanced electronics and electrified transportation, it calls for efficient operation of high-energy-density dielectric polymers under high voltages over a wide temperature range. Here, the polymer composites consisting of the boron nitride nanosheet/polyetherimide and TiO2 nanorod arrays/polyetherimide layers are reported. The layered composite exhibits a much higher dielectric constant than the current high-temperature dielectric polymers and composites, while simultaneously retaining low dielectric loss at elevated temperatures and high applied fields. Consequently, the layered polymer composite presents much improved capacitive performance than the current dielectric polymers and composites over a temperature range of 25-150 °C. Moreover, the excellent capacitive performance of the layered composite is achieved at an applied field that is about 40% lower than the typical field strength of the current polymer composites with the discharged energy densities of >3 J cm-3 at 150 °C. Remarkable cyclability and dielectric stability are established in the layered polymer nanocomposites. This work addresses the current challenge in the enhancement of the energy densities of high-temperature dielectric polymers and demonstrates an efficient route to dielectric polymeric materials with high energy densities and low loss over a broad temperature range.

Journal ArticleDOI
TL;DR: In this paper, transition metal sulfides (MoS2, NiS) with outstanding dielectric properties are introduced to fabricate the novel system of NiS/MoS 2/Ti3C2Tx, which has a unique multilayer-scale structure.
Abstract: For the purpose of achieving excellent electromagnetic wave absorption performance, composition control and microstructure design of absorbers are crucial. Ti3C2Tx, transition metal carbides with remarkable conductivity and mechanical properties, are considered as common substrates to construct high-performance absorbers. In order to improve the impedance matching and enrich electromagnetic wave attenuation mechanism of single Ti3C2Tx substrate, transition metal sulfides (MoS2, NiS) with outstanding dielectric properties are introduced to fabricate the novel system of NiS/MoS2/Ti3C2Tx. Notably, this system has a unique multilayer-scale structure that spherical NiS particles are decorated on the multilayered Ti3C2Tx substrate and two-dimensional (2D) MoS2 nanosheets stack on the surface like scales. Under the synergistic effects of intense dielectric loss and multiple reflection, NiS/MoS2/Ti3C2Tx hybrid shows the wide effective absorption bandwidth (EAB) of 5.04 GHz at 2.1 mm and the minimum reflection loss (RLmin) of −58.48 dB at 2.4 mm. This work provides an innovative idea for the research of novel MXene-based absorbers.

Journal ArticleDOI
TL;DR: In this article, a composite absorbing material with amazing electromagnetic wave absorption is presented. But the preparation of absorbing materials with sustainable development, light weight, strong absorption and wide absorption bandwidth has become an urgent problem that should be solved.

Journal ArticleDOI
TL;DR: In this paper, a step-by-step hydrothermal method was used to texture rod-like TiO2 semiconductor with different mass ratios on the a few layers of WS2 nanosheets.

Journal ArticleDOI
TL;DR: In this article, a novel approach to development of ferrites/carbon fibers coated with polypyrrole (PPy) was revealed, and the ZnFe2O4/C@PPy composites exhibit great potential application as the materials with high-efficient absorption properties.

Journal ArticleDOI
TL;DR: In this article, dielectric properties of percolative copper/rutile cermets were studied and negative permittivity was induced by the plasmonic state of electrons within percolating pathways.

Journal ArticleDOI
TL;DR: In this article, a novel type of polymer dielectrics simultaneously exhibiting an extraordinarily high recoverable energy density of 35 J cm-3 and a low dielectric loss was reported, which is attributed to the covalent-bonding restricted ion polarization and the strong charge trapping by the zwitterions.
Abstract: Polymer dielectrics are highly desirable in capacitor applications due to their low cost, high breakdown strength, and unique self-healing capability. However, existing polymer dielectrics suffer from either a low energy density or a high dielectric loss, thereby hindering the development of compact, efficient, and reliable power electronics. Here, a novel type of polymer dielectrics simultaneously exhibiting an extraordinarily high recoverable energy density of 35 J cm-3 and a low dielectric loss is reported. It is synthesized by grafting zwitterions onto the short side chains of a poly(4-methyl-1-pentene) (PMP)-based copolymer, which increases its dielectric constant from ≈2.2 to ≈5.2 and significantly enhances its breakdown strength from ≈700 MV m-1 to ≈1300 MV m-1 while maintaining its low dielectric loss of 90%. Based on a combination of the phase-field method description of mesoscale structures, Maxwell equations, and theoretical analysis, it is demonstrated that the outstanding combination of high energy density and low dielectric loss of zwitterions-grafted copolymers is attributed to the covalent-bonding restricted ion polarization and the strong charge trapping by the zwitterions. This work represents a new strategy in polymer dielectrics for achieving simultaneous high energy density and low dielectric loss.

Journal ArticleDOI
TL;DR: In this article, the synthesis of nanoparticles and doping of Cu-doped Co-Zn ferrites using the auto-combustion sol-gel synthesis technique was reported.
Abstract: Herein, we report the synthesis of nanoparticles and doping of Cu-doped Co–Zn ferrites using the auto-combustion sol–gel synthesis technique. X-ray diffraction studies confirmed the single-phase structure of the samples with space group Fd3m and crystallite size in the range of 20.57–32.69 nm. Transmission electron microscopy micrographs and selected area electron diffraction patterns confirmed the polycrystalline nature of the ferrite nanoparticles. Energy-dispersive X-ray spectroscopy revealed the elemental composition in the absence of any impurity phases. Fourier-transform infrared studies showed the presence of two prominent peaks at approximately 420 cm−1 and 580 cm−1, showing metal–oxygen stretching and the formation of ferrite composite. X-ray photoelectron spectroscopy was employed to determine the oxidation states of Fe, Co, Zn, and Cu and O vacancies based on which cationic distributions at tetrahedral and octahedral sites are proposed. Dielectric spectroscopy showed that the samples exhibit Maxwell–Wagner interfacial polarization, which decreases as the frequency of the applied field increases. The dielectric loss of the samples was less than 1, confirming that the samples can be used for the fabrication of multilayer inductor chips. The ac conductivity of the samples increased with increasing doping and with frequency, and this has been explained by the hopping model. The hysteresis loops revealed that coercivity decreases slightly with doping, while the highest saturation magnetization of 55.61 emu/g was obtained when x = 0.1. The magnetic anisotropic constant was found to be less than 0.5, which suggests that the samples exhibit uniaxial anisotropy rather than cubic anisotropy. The squareness ratio indicates that the samples are useful in high-frequency applications.

Journal ArticleDOI
TL;DR: In this article, the authors used Co-ZIF-67 self-template to grow N-doped graphene/carbon nanotube interlinked conductive networks in-situ under a one-step carbonization process with tailored microwave absorption properties.

Journal ArticleDOI
Bin Du1, Mei Cai1, Xuan Wang1, Junjie Qian1, Chao He1, Anze Shui1 
TL;DR: In this paper, the binary ZnO/NiCo2O4 nanoparticles were successfully synthesized via hydrothermal reaction and the electromagnetic wave absorption properties of the composites were investigated in detail.
Abstract: Nowadays, metal oxide-based electromagnetic wave absorbing materials have aroused widely attentions in the application of telecommunication and electronics due to their selectable mechanical and outstanding dielectric properties. Herein, the binary ZnO/NiCo2O4 nanoparticles were successfully synthesized via hydrothermal reaction and the electromagnetic wave absorption properties of the composites were investigated in detail. As a result, benefiting from the dielectric loss, the as-obtained ZnO/NiCo2O4-7 samples possessed a minimum reflection loss value of −33.49 dB at 18.0 GHz with the thickness of 4.99 mm. This work indicates that ZnO/NiCo2O4 composites have the promising candidate applications in electromagnetic wave absorption materials in the future.

Journal ArticleDOI
TL;DR: In this article, a linear dependence of the unit cell parameters is found for indium-substituted strontium hexaferrites, where the average crystallite size varies within 0.84-0.65μm.
Abstract: Indium-substituted strontium hexaferrites were prepared by the conventional solid-phase reaction method. Neutron diffraction patterns were obtained at room temperature and analyzed using the Rietveld methods. A linear dependence of the unit cell parameters is found. In3+ cations are located mainly in octahedral positions of 4fVI and 12 k. The average crystallite size varies within 0.84-0.65 μm. With increasing substitution, the TC Curie temperature decreases monotonically down to ~ 520 K. ZFC and FC measurements showed a frustrated state. Upon substitution, the average and maximum sizes of ferrimagnetic clusters change in the opposite direction. The Mr remanent magnetization decreases down to ~ 20.2 emu/g at room temperature. The Ms spontaneous magnetization and the keff effective magnetocrystalline anisotropy constant are determined. With increasing substitution, the maximum of the e/ real part of permittivity decreases in magnitude from ~ 3.3 to ~ 1.9 and shifts towards low frequencies from ~ 45.5 GHz to ~ 37.4 GHz. The maximum of the tg(α) dielectric loss tangent decreases from ~ 1.0 to ~ 0.7 and shifts towards low frequencies from ~ 40.6 GHz to ~ 37.3 GHz. The low-frequency maximum of the μ/ real part of permeability decreases from ~ 1.8 to ~ 0.9 and slightly shifts towards high frequencies up to ~ 34.7 GHz. The maximum of the tg(δ) magnetic loss tangent decreases from ~ 0.7 to ~ 0.5 and shifts slightly towards low frequencies from ~ 40.5 GHz to ~ 37.7 GHz. The discussion of microwave properties is based on the saturation magnetization, natural ferromagnetic resonance and dielectric polarization types.

Journal ArticleDOI
TL;DR: In this article, the structure and dielectric properties of Sm(Nb1−xVx)O4 (SNV-x) (0.0 ≤ x ≤ 0.9) ceramics were studied by crystal structure refinement, Raman, transmission electron microscope (TEM), far-infrared/THz reflectivity spectroscopy and microwave Dielectric tests.
Abstract: Herein, the structure and dielectric properties of Sm(Nb1−xVx)O4 (SNV-x) (0.0 ≤ x ≤ 0.9) ceramics were studied by crystal structure refinement, Raman, transmission electron microscope (TEM), far-infrared/THz reflectivity spectroscopy and microwave dielectric tests. Three kinds of ultra-low dielectric loss and temperature-stable Sm(Nb1−xVx)O4 (0.2 ≤ x ≤ 0.4) ceramics with permittivities of 18.01–16.89, Q × f values of 97 800–75 200 GHz (@∼8.6 GHz), and TCF of −5.6 (x = 0.2), to +2.3 ppm °C−1 (x = 0.3), then −6.3 (x = 0.4) ppm °C−1 were synthesized in this system. It was found that V5+ substitution can reliably induce the phase transition of monoclinic fergusonite (M-fergusonite, I2/a) to tetragonal zircon phase (T-zircon, I41/amd) (x ≈ 0.3), while effectively reducing the phase transition temperature. TEM shows that there were two different orientation domain structures in the M-fergusonite phase, and the widths of the two domain structures get closer with an increase in B-site substitution. Moreover, the variations in permittivity (er), quality factor (Q × f), and the temperature coefficient of resonance frequency (TCF) were strongly related to the crystal distortion and phase transition. Notably, a rectangular dielectric resonator antenna (RDRA) was fabricated with an Sm(Nb0.8V0.2)O4 (SNV-0.2) specimen. The antenna resonated at 27.04 GHz and had a bandwidth of ∼820 MHz (S11 < −10 dB). This system is a good candidate for 5G and future millimeter-wave applications.

Journal ArticleDOI
TL;DR: In this article, the intrinsic defect and polarization mechanism are investigated in A-site-deficient 0.66(Bi0.5Na 0.5)TiO3-0.28(BixSr1-3x/2▯x/1) relaxors where strontium vacancies (V Sr ′ ′ ) are designed to compensate the negative charge shortage when Sr2+ is substituted by Bi3+ (Bi Sr • ).

Journal ArticleDOI
TL;DR: In this article, the EMW absorbing properties of transition metal carbides TMCs (TM=Ti, Zr, Hf, Nb and Ta) and high entropy (Ti0.2Zr 0.2Hf 0.4Nb 0.6 GHz) C which belong to ultrahigh temperature ceramics, were investigated.