Unusual continuous dual absorption peaks in Ca-doped BiFeO3 nanostructures for broadened microwave absorption

Metal-Organic Gel Leading to Customized Magnetic-Coupling Engineering in Carbon Aerogels for Excellent Radar Stealth and Thermal Insulation Performances

Metal-organic gel (MOG) derived composites are promising multi-functional materials due to their alterable composition, identifiable chemical homogeneity, tunable shape, and porous structure. Herein, stable metal-organic hydrogels are prepared by regulating the complexation effect, solution polarity and curing speed. Meanwhile, collagen peptide is used to facilitate the fabrication of a porous aerogel with excellent physical properties as well as the homogeneous dispersion of magnetic particles during calcination. Subsequently, two kinds of heterometallic magnetic coupling systems are obtained through the application of Kirkendall effect. FeCo/nitrogen-doped carbon (NC) aerogel demonstrates an ultra-strong microwave absorption of - 85 dB at an ultra-low loading of 5%. After reducing the time taken by atom shifting, a FeCo/Fe3O4/NC aerogel containing virus-shaped particles is obtained, which achieves an ultra-broad absorption of 7.44 GHz at an ultra-thin thickness of 1.59 mm due to the coupling effect offered by dual-soft-magnetic particles. Furthermore, both aerogels show excellent thermal insulation property, and their outstanding radar stealth performances in J-20 aircraft are confirmed by computer simulation technology. The formation mechanism of MOG is also discussed along with the thermal insulation and electromagnetic wave absorption mechanism of the aerogels, which will enable the development and application of novel and lightweight stealth coatings.

Nano Ag/Co3O4 Catalyzed Rapid Decomposition of Robinia pseudoacacia Bark for Production Biofuels and Biochemicals

Biomass energy has attracted widespread attention due to its renewable, storage, huge production and clean and pollution-free advantages. Using Robinia pseudoacacia bark (RPB) as raw material, biogas and bio-oil produced by pyrolysis of RPB were detected and analyzed by TG-DTG, TG-FTIR and PY-GC-MS under the action of nanocatalysis. TG results showed that CH₄ and CO flammable gases were produced by pyrolysis. PY-GC-MS results showed that RPB was rapidly pyrolyzed to obtain alcohols, ketones, aldehydes and acids bio-oil. The content of phenolic substances was the highest, accounting for 32.18% of all substances.Nanocatalysis has a certain effect on RPB, accelerating the precipitation of pyrolysis products and improving the over-oxidation of bio-oil. In addition, the extracts of RPB were identified and analyzed by FTIR, NMR, GC-MS and LC-Q-TOF-MS, and more than 100 active ingredients, such as Betaine, Epicathin and β-sitosterol, were detected. Their applications as additive energy in other fields were explored. Therefore, Robinia pseudoacacia bark constitutes a fine biofeedstock for biofuels and biochemicals.

High-Performance Ferroelectric Electromagnetic Attenuation Materials with Multiple Polar Units Based on Nanodomain Engineering

The multirelaxation behavior is promising for high-performance dielectric materials based on polarization-controllable high-efficiency electromagnetic attenuation. However, a single polar unit is the main problem that restricts the development of dielectric materials in the field. Herein, by constructing multiple polar units based on nanodomain engineering, enhanced electromagnetic attenuation properties are achieved in La doping BiFeO₃ ferroelectric ceramics. A dual-band attenuation with a maximum reflection loss of -43.4 dB together with a wide effective bandwidth (<-10 dB) of 3.3 GHz in X-band, is acquired in Bi_0.85 La_0.15 FeO₃ which just has a thickness of 1.54 mm. A systematic experimental analysis coupled with potential well modeling suggests that the miniaturization of the ferroelectric domain, from micron to nanoscale, induces an additional interface polarization that is capable of responding to microwave frequency, leading to the formation of dual dielectric relaxation. The way that intrinsic polar unit induces another polar unit through size effect to obtain multiple contributions of electromagnetic loss provides a feasible and universal strategy to design high-performance electromagnetic attenuation materials based on the ferroelectric family.

Dimensional Design and Core-Shell Engineering of Nanomaterials for Electromagnetic Wave Absorption

Electromagnetic (EM) wave absorption materials possess exceptionally high EM energy loss efficiency. With vigorous developments in nanotechnology, such materials have exhibited numerous advanced EM functions, including radiation prevention and antiradar stealth. To achieve improved EM performance and multifunctionality, the elaborate control of microstructures has become an attractive research direction. By designing them as core-shell structures with different dimensions, the combined effects, such as interfacial polarization, conduction networks, magnetic coupling, and magnetic-dielectric synergy, can significantly enhance the EM wave absorption performance. Herein, the advances in low-dimensional core-shell EM wave absorption materials are outlined and a selection of the most remarkable examples is discussed. The derived key information regarding dimensional design, structural engineering, performance, and structure-function relationship are comprehensively summarized. Moreover, the investigation of the cutting-edge mechanisms is given particular attention. Additional applications, such as oxidation resistance and self-cleaning functions, are also introduced. Finally, insight into what may be expected from this rapidly expanding field and future challenges are presented.

Heterointerface Engineering in Electromagnetic Absorbers: New Insights and Opportunities

Electromagnetic (EM) absorbers play an increasingly essential role in the electronic information age, even toward the coming "intelligent era". The remarkable merits of heterointerface engineering and its peculiar EM characteristics inject a fresh and infinite vitality for designing high-efficiency and stimuli-responsive EM absorbers. However, there still exist huge challenges in understanding and reinforcing these interface effects from the micro and macro perspectives. Herein, EM response mechanisms of interfacial effects are dissected in depth, and with a focus on advanced characterization as well as theoretical techniques. Then, the representative optimization strategies are systematically discussed with emphasis on component selection and structural design. More importantly, the most cutting-edge smart EM functional devices based on heterointerface engineering are reported. Finally, current challenges and concrete suggestions are proposed, and future perspectives on this promising field are also predicted.

Strain Engineering in Electrochemical Activity and Stability of BiFeO3 Perovskites

Strain engineering is widely employed to manipulate the intrinsic relationship of activity and the crystal structure, while the mechanism and rational strategy toward high-performance devices are still under investigation. Here straining engineering is utilized to manipulate a series of a typical perovskite structures via introducing different types of heteroions (Bi_1-xM_xFeO₃, M = Ca²⁺ or Y³⁺ ion). The space group R3c in BiFeO₃ perovskites is found to be maintained with substituting a certain amount of heteroions at Bi³⁺ sites (<5%), while it would shift into either space groups P4mm (with Ca²⁺ substitute) or Pnma (with Y³⁺ substitute) beyond some critical doping amounts (>5%). Such a transformation is linked with the mismatched crystal strain induced by the heteroions substituted at Bi³⁺ sites, while the activity, stability, and energy storage capability of Bi_1-xM_xFeO₃ have been essentially varied. The results offer a strategy for manipulating stability and activity of perovskites in electrochemical energy conversion and storage.

Ultra-broadband and covalently linked core-shell CoFe2O4@PPy nanoparticles with reduced graphene oxide for microwave absorption

Covalent bond usually ensures a stable connection between nonmetallic atoms. However, the traditional reflux method usually requires the construction of complex instruments and equipment with tedious steps to ensure airtightness and reaction stability. In this work, an advanced method is adopted to bind core-shell CoFe₂O₄@PPy and rGO tightly via the aid of 2-(1H-pyrrol-1-yl)ethanamine (PyEA), dispense with a high-temperature environment or protective gas. Cobalt ferrite core and polypyrrole shell collaborate to approach suitable magnetic and conduction loss, while reduced graphene oxide usually provides a stable sheet structure for interface multiple reflections, and replenish the insufficient dielectric loss. The filled biscuit-shaped covalently bond CoFe₂O₄@PPy-rGO has a fantastically broad absorption bandwidth of 13.12 GHz under the thickness of 3.6 mm, together with a minimum reflection loss of -50.1 dB at 6.56 GHz, achieving both impedance matching and attenuation matching, and effectively responding to all electromagnetic waves in the X and Ku bands. Thus, the covalently bonded CoFe₂O₄@PPy-rGO has potential application in broadband absorption.

Progress and Perspectives on Aurivillius-Type Layered Ferroelectric Oxides in Binary Bi4Ti3O12-BiFeO3 System for Multifunctional Applications

Driven by potentially photo-electro-magnetic functionality, Bi-containing Aurivillius-type oxides of binary Bi4Ti3O12-BiFeO3 system with a general formula of Bin+1Fen−3Ti3O3n+3, typically in a naturally layered perovskite-related structure, have attracted increasing research interest, especially in the last twenty years. Benefiting from highly structural tolerance and simultaneous electric dipole and magnetic ordering at room temperature, these Aurivillius-phase oxides as potentially single-phase and room-temperature multiferroic materials can accommodate many different cations and exhibit a rich spectrum of properties. In this review, firstly, we discussed the characteristics of Aurivillius-phase layered structure and recent progress in the field of synthesis of such materials with various architectures. Secondly, we summarized recent strategies to improve ferroelectric and magnetic properties, consisting of chemical modification, interface engineering, oxyhalide derivatives and morphology controlling. Thirdly, we highlighted some research hotspots on magnetoelectric effect, catalytic activity, microwave absorption, and photovoltaic effect for promising applications. Finally, we provided an updated overview on the understanding and also highlighting of the existing issues that hinder further development of the multifunctional Bin+1Fen−3Ti3O3n+3 materials.

Constructing Ni12P5/Ni2P Heterostructures to Boost Interfacial Polarization for Enhanced Microwave Absorption Performance

Heterostructures with a rich phase boundary are attractive for surface-mediated microwave absorption (MA) materials. However, understanding the MA mechanisms behind the heterogeneous interface remains a challenge. Herein, a phosphine (PH₃) vapor-assisted phase and structure engineering strategy was proposed to construct three-dimensional (3D) porous Ni₁₂P₅/Ni₂P heterostructures as microwave absorbers and explore the role of the heterointerface in MA performance. The results indicated that the heterogeneous interface between Ni₁₂P₅ and Ni₂P not only creates sufficient lattice defects for inducing dipolar polarization but also triggers uneven spatial charge distribution for enhancing interface polarization. Furthermore, the porous structure and proper component could provide an abundant heterogeneous interface to strengthen the above polarization relaxation process, thereby greatly optimizing the electromagnetic parameters and improving the MA performance. Profited by 3D porous heterostructure design, P400 could achieve the maximum reflection loss of -50.06 dB and an absorption bandwidth of 3.30 GHz with an ultrathin thickness of 1.20 mm. Furthermore, simulation results confirmed its superior ability (14.97 dB m² at 90°) to reduce the radar cross section in practical applications. This finding may shed light on the understanding and design of advanced heterogeneous MA materials.

Ho and Ti Co-Substitution Tailored Structural Phase Transition and Enhanced Magnetic Properties of BiFeO3 Thin Films

The polycrystalline thin films of BiFeO₃ (BFO) and Bi_0.90Ho_0.10Fe_1-xTi_xO (x = 0, 0.025, 0.05, 0.10, 0.15, and 0.20) were successfully synthesized by the simple sol-gel method. X-ray diffraction and Raman spectra revealed the substitution of Bi and Fe by Ho and Ti, respectively, and correspondingly a structural phase transition from the rhombohedral phase to orthorhombic phase. The field-emission scanning electron microscopy and transmission electron microscopy images indicated that the average size of the particles was decreased and the surface homogeneous agglomeration was enhanced with the increased concentration of Ti to x = 0.05. The X-ray photoelectron spectroscopy measurements illustrated that Fe³⁺ and O^2- ions tended to increase with the Ti concentration increase, which accounted for the enhanced super-exchange interaction between Fe³⁺ and O^2-. Because of the reduced concentration of oxygen vacancies, Ho and Ti ions with a smaller ionic radius and denser surface structure, the Ho and Ti co-substituted films with an appropriate concentration of Ti (x = 0.05) showed an optimal saturation magnetization (M _s) of 44.23 emu/cm³ and remanent magnetization (M _r) of 4.62 emu/cm³, which were approximately 1.8 times and 1.9 times than that of the pure BFO, respectively. This work opened up an effective way to modulate the structure and properties of BFO-based materials.

Synthesis of sandwich-like Co15Fe85@C/RGO multicomponent composites with tunable electromagnetic parameters and microwave absorption performance

Magnetic particle/carbon hybrid structures are promising candidates for high performance microwave absorbing materials with light weight and strong absorption. However, it remains a great challenge to balance the permittivity and permeability to realize impedance matching and further improve their absorption bandwidth. Herein, an effective strategy is designed to fabricate sandwich-like Co₁₅Fe₈₅@C/RGO composites. By introducing RGO sheets in the hybrid structures, the electromagnetic parameters, impedance matching and microwave absorption properties of the final materials can be well controlled. The optimized Co₁₅Fe₈₅@C/RGO composite shows an excellent microwave absorption performance, the strongest reflection loss (RL) of the sample is up to -33.38 dB at 10.72 GHz with a matching thickness of 2.5 mm, and the effective bandwidth (RL < -10 dB) can reach 9.2 GHz (8.64-17.84 GHz). With a single thickness, such a wide absorption band is rarely reported. Their excellent performance can be ascribed to the synergetic effect of the chemical composition and unique sandwich-like structures, which will improve impendence matching and strong microwave attenuation constants of the composites. Our results provide a facile strategy for tuning the electromagnetic parameters and microwave absorption properties of magnetic metal/carbon hybrid structures.

Ti3C2Tx MXenes as thin broadband absorbers

Atomically multilayered two-dimensional transition-metal carbides have abundant interfaces, and are very promising as outstanding electromagnetic absorbing materials at thin thickness. Here, a Ti₃C₂T_x MXene was prepared by hydrofluoric acid etching method, and has typical multilayered morphology with stacks of nanosheets. The microwave dielectric behaviours of the Ti₃C₂T_x with efficient microwave absorption were investigated. The Ti₃C₂T_x presents good impedance matching, achieved with effective absorption bandwidth covering from 12.4 GHz to 17.1 GHz, with thickness of only 1.5 mm, which nearly covers the whole Ku band. The microwave absorption performance was adjusted, and the Ti₃C₂T_x has a minimum reflection loss of -34.4 dB at 12 GHz at only 1.7 mm. This study demonstrates the real potential of Ti₃C₂T_x MXene materials as electromagnetic wave thin broadband absorbers.

Facile Synthesis of Sandwich-Like rGO/CuS/Polypyrrole Nanoarchitectures for Efficient Electromagnetic Absorption

Currently, electromagnetic pollution management has gained much attention due to the various harmful effects on wildlife and human beings. Electromagnetic absorbers can convert energy from electromagnetic waves into thermal energy. Previous reports have demonstrated that reduced graphene oxide (rGO) makes progress in the electromagnetic absorption (EA) field. But the high value of permittivity of rGO always mismatches the impedance which results in more electromagnetic wave reflection on the surface. In this work, sandwich-like rGO/CuS/polypyrrole (PPy) nanoarchitectures have been synthesized by a facile two-step method. The experimental result has shown that a paraffin composite containing 10 wt.% of rGO/CuS/PPy could achieve an enhanced EA performance both in bandwidth and intensity. The minimum reflection loss (RL) value of −49.11 dB can be reached. Furthermore, the effective bandwidth can cover 4.88 GHz. The result shows that the as-prepared rGO/CuS/PPy nanoarchitectures will be a promising EA material.

Investigation of the structural, optical and electrical properties of Ca2+ doped CuCoO2 nanosheets

In this work, we present the hydrothermal synthesis of delafossite oxide Ca-doped CuCoO2 (CCCaO) nanosheets at a low temperature of 100 °C. The crystal phase, morphology and chemical composition of these CuCoO2 (CCO) based samples were comprehensively characterized by powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The size of CCCaO nanosheets decreased with increasing Ca dopant concentration, and the optimized CCCaO nanosheets (∼490 nm in lateral size and ∼15 nm in thickness) were much smaller than CCO nanocrystals (∼540 nm in lateral size and 85 nm in thickness). The specific surface area of these CCO based samples increased with increasing Ca content, and the optimized CCCaO nanosheets present a high BET surface area of 28 m2 g-1. XPS and Raman spectroscopy analyses indicate Ca2+ dopant substitution on the Cu+ site in CCCaO nanosheets. Moreover, the effects of Ca2+ doping on the optical and electrical properties of these CCO based samples were further studied. The optical properties measured at room temperature show high absorbability (up to 90%) in the ultraviolet-visible-near infrared (UV-VIS-NIR) region, and the indirect band gap shows a significant blue-shift with increasing Ca2+ concentration. The CCO nanocrystals possess a higher electrical conductivity than the CCCaO nanosheets, and present good conductivities of around 12.81, 4.47 and 0.69 s m-1 for the CCO and CCCaO samples at room temperature. The facile fabrication process, tunable crystallite sizes, and excellent optical absorption and electrical properties of these CCO based nanomaterials are encouraging for the development of future applications in photoelectric devices.

Ultrathin Topological Insulator Absorber: Unique Dielectric Behavior of Bi2Te3 Nanosheets Based on Conducting Surface States

Topological insulators exhibit great potential in the fields of electronics and semiconductors for their gapless surface states. Intriguingly, most topological insulators are possibly excellent microwave-absorbing materials because of easy adjustment of electrical transport based on conducting surface states in the nanostructure. Herein, topological insulator Bi₂Te₃ nanosheets are synthesized by a simple solvothermal method. The material demonstrates a unique dielectric behavior based on conducting surface states, resulting in excellent microwave-absorbing performance. Benefiting from the outstanding impedance matching, Bi₂Te₃ nanosheets exhibit an ultrathin microwave absorption with the qualified frequency bandwidth of 3.0 GHz at only 0.77 mm thickness, which is thinner than other absorbers in reported references. Moreover, a strong reflection loss of -41 dB at 0.8 mm is achieved. The result provides a new approach for developing ultrathin microwave absorption materials at the submillimeter scale.

A neoteric sandwich-configurational composite film offering synchronous conductive aeolotropy, superparamagnetism and dual-color fluorescence

A new type of two-dimensional (2D) sandwich-configurational composite film offering electrically conductive aeolotropism, superparamagnetism and dual-color fluorescence was successfully fabricated via electrospinning. The composite film consists of a [polyaniline (PANI)/polymethylmethacrylate (PMMA)]//[Eu(BA)₃phen/PMMA] Janus nanobelt array aeolotropic conductive-fluorescent layer (first layer), a Fe₃O₄/polyvinylpyrrolidone (PVP) superparamagnetic nanofibers layer (second layer) and a Tb(BA)₃phen/polyacrylonitrile (PAN) fluorescent nanofiber layer (third layer), which have been tightly bonded together to form a sandwich-configurational composite film with trifunctionality. Because of the exceptive sandwich-like structure, electrically conductive, superparamagnetic, and fluorescent substances are mutually and efficaciously segregated. Thus, reciprocally pernicious interferences among them can be thoroughly avoided; thus, the sandwich-configurational composite film coinstantaneously possesses superior conductive aeolotropism, fluorescence and magnetism tri-functionality. Thus, the aeolotropic conductive-fluorescent layer and fluorescent layer respectively exhibit excellent red and green fluorescence properties. Further, the conductive aeolotropism and superparamagnetism of the composite film can be severally adjusted via regulating the contents of PANI and Fe₃O₄ NPs. Owing to the peculiar nanostructure made of Janus nanobelts in the aeolotropic conductive-fluorescent layer, the conduction ratio reaches 10⁸ times between conductive and insulating directions of the sandwich-configurational composite film. Under the excitation of 290 nm ultraviolet light, prominent red emission at 615 nm can be clearly observed in the aeolotropic conductive-fluorescent layer. Additionally, major green emission at 545 nm can be observed in the fluorescent layer under 314 nm light excitation. Furthermore, due to the exceptional sandwich structure, the properties of each layer of the whole film are relatively independent, the fluorescence intensities of the aeolotropic conductive-fluorescent layer and the fluorescent layer are hardly affected by the magnetic variation of the superparamagnetic layer, and the fluorescence intensity of the fluorescent layer is not influenced by the modulation of the PANI content of the aeolotropic conductive-fluorescent layer. The neoteric sandwich-configurational composite film with concurrent trifunctionality constructed by a facile method has potential applications in many fields. Overall, the academic design and manufacturing means will provide support for the design and construction of new-typed aeolotropic conductive films with multifunctionality.

Interface Modulating CNTs@PANi Hybrids by Controlled Unzipping of the Walls of CNTs To Achieve Tunable High-Performance Microwave Absorption

Making full use of the interface modulation-induced interface polarization is an effective strategy to achieve excellent microwave absorption (MA). In this study, we develop an interfacial modulation strategy for achieving this goal in the commonly reported dielectric carbon nanotubes@polyaniline (CNTs@PANi) hybrid microwave absorber by optimizing the CNT nanocore structure. The heterogeneous interfaces from PANi and CNTs can be well regulated by longitudinal unzipping of the walls of CNTs to form 1D CNT- and 3D CNT-bridged graphene nanoribbons and 2D graphene nanoribbons. By controlling the oxidation peeling degree of CNTs, their interface area and defects are enhanced, thus producing more polarization centers to generate interfacial polarization and polarization relaxation, and also introducing more PANi loadings. Furthermore, more interface contact area can be produced between CNTs and PANi. This could induce a strong dielectric resonant and further improve the impedance matching, leading to significant enhancement of MA performance. With filler loading of only 10 wt % and a thinner coating thickness of 2.4 mm, the optimized CNTs@PANi exhibits excellent MA performance with the minimum reflection loss (RL_min) value of -45.7 dB at 12.0 GHz and the effective bandwidth is from 10.2 to 14.8 GHz. Meanwhile, the broadest effective bandwidth reaches 5.6 GHz, covering the range of 12.4-18.0 GHz with a thin thickness of 2.0 mm and its RL_min reaches -29.0 dB at 14.6 GHz. It is believed that the proposed interfacial modulation strategy can provide new opportunities for designing efficient MA absorbers.

Interfacial polarizations induced by incorporating traditional perovskites into reduced graphene oxide (RGO) for strong microwave response

The as-prepared La_0.7Sr_0.3MnO₃/RGO nanocomposites were synthesized via a simple hydrothermal method to provide excellent microwave absorbing performance resulting from good electrical conductivity and high impedance matching.

Direct Growth of a Polypyrrole Aerogel on Hollow CuS Hierarchical Microspheres Yields Particles with Excellent Electromagnetic Wave Properties

A current hot topic in polymer science is the development of electromagnetic wave-absorbing materials with desired properties (i.e., proper impedance matching and strong attenuation capability), but it presents a considerable challenge. In this work, solvothermal, and self-assembled polymerization were employed for the controlled fabrication of a uniform polypyrrole (PPy) aerogel coated on hollow CuS hierarchical microspheres (CuS@PPy). The PPy coating thickness of the heterostructure could be tuned by varying the feeding weight ratios of CuS/pyrrole monomer. The electromagnetic wave absorption properties of the CuS@PPy composites were estimated to be in the frequency range 2–18 GHz. The as-prepared Sample B (fabricated by the addition of 35 mg CuS) showed a maximum reflection loss (RL) of −52.85 dB at a thickness of 2.5 mm. Moreover, an ultra-wide effective bandwidth (RL ≤ −10 dB) from 9.78 to 17.80 GHz (8.02 GHz) was achieved. Analysis of the electromagnetic properties demonstrated that the CuS@PPy had a remarkable enhancement compared to pure CuS platelet-based spheres and pure PPy, which can be attributed to the increased relatively complex permittivity and the promoted dielectric loss by the intense interfacial dielectric polarizations. We believe that the as-fabricated CuS@PPy can be a good reference for the fabrication of lightweight and optimal broadband absorbers.

Enhanced Low-Frequency Electromagnetic Properties of MOF-Derived Cobalt through Interface Design

It is still a formidable challenge to ameliorate the low-frequency electromagnetic property of conventional microwave-absorbing materials, which may be conquered by the coexistence of both strong dielectric and magnetic loss ability in low-frequency range and the perfect balance between complex permittivity and permeability with the help of structural design. Herein, by virtue of appropriate composition and structure of Co₃[HCOO]₆·dimethylformamide parallelepipeds, one-dimensional spongelike metallic Co can be directly synthesized for the first time with strong magnetic loss in the low-frequency range. Furthermore, attenuation ability and impedance matching condition have been improved through the construction of interfacial structures between inner cobalt and surface carbon. With the structure of carbon changed from fragments to vertically aligned nanoflakes and eventually to a thick layer with extra fragments, the dielectric loss would be continuously strengthened, while the magnetic loss maintains well, followed by a remarkable decline. A perfect balance between dielectric and magnetic loss has been achieved by sample S-Co/C-0.3 with minimum reflection loss value around -20 dB and effective absorption frequency range about 3.84 GHz in the C band. Excellent microwave absorption performance can also be realized in X and Ku bands. In addition, as-prepared Co and Co/C composites can also be potentially applied in electromagnetic shielding. The findings may pave the way for the manufacture of metal-based metal-organic framework derivatives and the design of lightweight low-frequency electromagnetic materials.

Enhanced Magnetic Properties of BiFeO₃ Thin Films by Doping: Analysis of Structure and Morphology

The improvement of ferromagnetic properties is critical for the practical application of multiferroic materials, to be exact, BiFeO₃ (BFO). Herein, we have investigated the evolution in the structure and morphology of Ho or/and Mn-doped thin films and the related diversification in ferromagnetic behavior. BFO, Bi_0.95Ho_0.05FeO₃ (BHFO), BiFe_0.95Mn_0.05O₃ (BFMO) and Bi_0.95Ho_0.05Fe_0.95Mn_0.05O₃ (BHFMO) thin films are synthesized via the conventional sol-gel method. Density, size and phase structure are crucial to optimize the ferromagnetic properties. Specifically, under the applied magnetic field of 10 kOe, BHFO and BFMO thin films can produce obvious magnetic properties during magnetization and, additionally, doping with Ho and Mn (BHFMO) can achieve better magnetic properties. This enhancement is attributed to the lattice distortions caused by the ionic sizes difference between the doping agent and the host, the generation of the new exchange interactions and the inhibition of the antiferromagnetic spiral modulated spin structure. This study provides key insights of understanding the tunable ferromagnetic properties of co-doped BFO.

Extended Working Frequency of Ferrites by Synergistic Attenuation through a Controllable Carbothermal Route Based on Prussian Blue Shell

One of the major hurdles of ferrite-based microwave absorbing materials is the limited working frequency that urgently calls for an effective modification technique. Herein, a controllable carbothermal route has been developed to ameliorate the microwave absorption performance of Fe₃O₄ nanospheres by using metal-organic frameworks (MOFs) shell as a carbon source with changing ramping rates. An enhanced synergistic attenuation induced by varied composition and tailored morphology is of great importance, which can be regarded as the superiority of the comprehensive (magnetic and dielectric), rather than unilateral (dielectric), modification technique. The drawbacks of dielectric modification can be concluded as the separated attenuation mechanisms at discrete frequencies, proven by the construction of the core-shell structured Fe₃O₄@Prussian blue composite. The advantages of magnetic modification can also be confirmed by a series of Fe-based composites with unique composition and tailored structure derived from the Fe₃O₄@Prussian blue composite at a distinct heating rate. Further, the superiority can be summarized as the rearrangement of magnetic loss by exceeding the Snoek limit and the reinforcement of dielectric loss by enhancing the electrical conductivity and introducing multiple polarization processes. Consequently, the sample obtained at 10 °C min^-1, which contains Fe and Fe₃O₄, shows an extended working frequency of 14.05 GHz, with a thickness less than 5 mm and a high reflection loss value of -48.04 dB at 1.55 mm. This work not only offers a novel carbothermal route based on MOFs coating to prepare desired magnetic composites, but also acquires deeper insights of the comprehensive modification technique, which may pave the way for designing high-performance electromagnetic devices.

Synthesis of u-channelled spherical Fex(CoyNi1-y)100-x Janus colloidal particles with excellent electromagnetic wave absorption performance

Due to their distinctive structure, inherently anisotropic properties and broad applications, Janus colloidal particles have attracted tremendous attention and it is significant to synthesize high yield Janus colloidal particles in a cost-effective and reliable way. On the other hand, due to the expanded electromagnetic interference problems, it is highly desired to develop excellent electromagnetic wave absorbing materials with an ultra-wide absorption bandwidth for practical application. Herein, a confined liquid-solid redox reaction strategy has been developed to fabricate a series of Fe_x(Co_yNi_1-y)_100-x ternary alloy particles. The as-prepared particles are in the form of u-channelled noncentrosymmetric spheres, one kind of Janus colloidal particles which have been rarely observed. Due to the combination and synergy effects of multi-magnetic metals, the polycrystalline structure and their specific morphology, the as-prepared particles possess multiple magnetic resonance and multiple dielectric relaxation processes, and therefore show excellent electromagnetic wave absorption performances. In particular, the strongest reflection loss (RL) of the Fe₁₅(Co_0.2Ni_0.8)₈₅ Janus colloidal particles is up to -36.9 dB with a thickness of 2.5 mm, and the effective absorption (RL < -10 dB) bandwidth can reach 9.2 GHz (8-17.2 GHz) with a thickness of 2 mm. Such a wide bandwidth has barely been reported for magnetic metal alloys under a single thickness. These results suggest that the Fe_x(Co_yNi_1-y)_100-x Janus particles could be a promising candidate for highly efficient electromagnetic wave absorbing materials for practical application.

Fe3O4 nanoparticles decorated on a CuS platelet-based sphere: a popcorn chicken-like heterostructure as an ideal material against electromagnetic pollution

A popcorn chicken-like CuS/Fe₃O₄ heterostructure was fabricated via the solvothermal deposition method to investigate its potential as a high electromagnetic wave absorber.

Enhanced Microwave Absorption Properties by Tuning Cation Deficiency of Perovskite Oxides of Two-Dimensional LaFeO3/C Composite in X-Band

Development of microwave absorption materials with tunable thickness and bandwidth is particularly urgent for practical applications but remains a great challenge. Here, two-dimensional nanocomposites consisting of perovskite oxides (LaFeO₃) and amorphous carbon were successfully obtained through a one pot with heating treatment using sodium chloride as a hard template. The tunable absorption properties were realized by introducing A-site cation deficiency in LaFeO₃ perovskite. Among the A-site cation-deficient perovskites, La_0.62FeO₃/C (L_0.62FOC) has the best microwave absorption properties in which the maximum absorption is -26.6 dB at 9.8 GHz with a thickness of 2.94 mm and the bandwidth range almost covers all X-band. The main reason affecting the microwave absorption performance was derived from the A-site cation deficiency which induced more dipoles polarization loss. This work proposes a promising method to tune the microwave absorption performance via introducing deficiency in a crystal lattice.

Carbon Hollow Microspheres with a Designable Mesoporous Shell for High-Performance Electromagnetic Wave Absorption

In this work, mesoporous carbon hollow microspheres (PCHMs) with designable mesoporous shell and interior void are constructed by a facile in situ stöber templating approach and a pyrolysis-etching process. The PCHMs are characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectra, Raman spectroscopy, and nitrogen adsorption and desorption system. A uniform mesoporous shell (pore size 4.7 nm) with a thickness of 55 nm and a cavity size of 345 nm is realized. The composite of paraffin mixed with 20 wt % PCHMs exhibits a minimum reflection coefficient (RC_min) of -84 dB at 8.2 GHz with a sample thickness of 3.9 mm and an effective absorption bandwidth (EAB) of 4.8 GHz below -10 dB (>90% electromagnetic wave is attenuated). Moreover, the composite of phenolic resin mixed with 20 wt % PCHMs exhibits an ultrawide EAB of 8 GHz below -10 dB with a thinner thickness of 2.15 mm. Such excellent electromagnetic wave absorption properties are ascribed to the large carbon-air interface in the mesoporous shell and interior void, which is favorable for the matching of characteristic impedance as compared with carbon hollow microspheres and carbon solid microspheres. Considering the excellent performance of PCHMs, we believe the as-fabricated PCHMs can be promising candidates as highly effective microwave absorbers, and the design philosophy can be extended to other spherical absorbers.

Construction of three-dimensional graphene interfaces into carbon fiber textiles for increasing deposition of nickel nanoparticles: flexible hierarchical magnetic textile composites for strong electromagnetic shielding

Since manipulating electromagnetic waves with electromagnetic active materials for environmental and electric engineering is a significant task, here a novel prototype is reported by introducing reduced graphene oxide (RGO) interfaces in carbon fiber (CF) networks for a hierarchical carbon fiber/reduced graphene oxide/nickel (CF-RGO-Ni) composite textile. Upon charaterizations of the microscopic morphologies, electrical and magnetic properties, the presence of three-dimensional RGO interfaces and bifunctional nickel nanoparticles substantially influences the related physical properties in the resulting hierarchical composite textiles. Eletromagnetic interference (EMI) shielding performance suggests that the hierarchical composite textiles hold a strong shielding effectiveness greater than 61 dB, showing greater advantages than conventional polymeric and foamy shielding composites. As a polymer-free lightweight structure, flexible CF-RGO-Ni composites of all electromagnetic active components offer unique understanding of the multi-scale and multiple mechanisms in electromagnetic energy consumption. Such a novel prototype of shielding structures along with convenient technology highlight a strategy to achieve high-performance EMI shielding, coupled with a universal approach for preparing advanced lightweight composites with graphene interfaces.

The effect of the phase structure on physicochemical properties of TMO materials: a case of spinel to bunsenite

It is worthwhile to comprehensively investigate the relationship between different phase structures and physicochemical properties of TMO materials.

Facile synthesis of NiS2@MoS2 core–shell nanospheres for effective enhancement in microwave absorption

Core–shell structural NiS₂@MoS₂ nanospheres have been successfully fabricated and they possess enhanced microwave absorption properties as compared to single NiS₂ nanospheres or MoS₂ nanoplates due to this core–shell structure.