Polarization Relaxation Research Articles

Study on the change of the oil-paper insulation’s AC conductivity characteristics based on dielectric response in frequency domain

Oil-immersed power equipment (transformers and high voltage bushings) are key components of power systems. Oil-paper insulation has endured complex and harsh operating conditions when used as a primary insulation system, so it is essential to determine the insulation state of oil-paper insulation system to ensure a stable operation for the power grid. The oil-paper insulation’s conductivity behavior can effectively characterize the degree of insulation deterioration. However, the relationship between the alternating current (AC) and direct current (DC) conductivity behavior for oil-paper insulation systems is still unclear in current research, resulting in limitations in the traditional evaluation model’s application. Therefore, this paper uses oil-paper insulation materials under different aging to carry out relevant research about the changing features of the complex AC conductivity under different test temperature environments. The influence of oil-paper insulation aging, test temperature, and excitation frequency on the complex AC conductivity is verified. Considering the correlation between low-frequency AC conductivity and DC conductivity, the frequency range of AC conductivity is extended by means of frequency temperature and conductance double translation. The temperature dependence of the AC conductivity behavior is defined over a wide frequency test range. The relaxation polarization process dominated the AC conductivity variation law is obtained. The impact of experimental temperature and insulation aging on the cumulative characteristic parameters of AC ionic mobility is clarified. This study theoretically corrects the traditional calculation model for AC conductivity of oil-paper insulation. The bias in conductivity calculations caused by only considering a single relaxation polarization process is eliminated. The conductivity model that can characterize multiple relaxation polarization processes in the dielectric is established. This model provides theoretical support for the later assessment of oil-paper insulation state depending on conductance behavior.

Correlating Ionic Conductivity to Structure and Dynamics of Li-Ion Battery Electrolyte Systems: Raman Spectroscopy, Dielectric Relaxation Measurements, and Streak Camera Solvation Data Analysis.

A correlation between ionic conductivity and electrolyte solution structure and dynamics was explored by performing electrolyte concentration- and temperature-dependent measurements of conductivity, viscosity, and dielectric relaxation (DR) in solutions of lithium bis(trifluoromethane)sulfonimide (LiTFSI) in triethylene glycol dimethyl ether (also known as triglyme, G3). In addition, an electrolyte concentration-dependent Raman spectroscopic study and ultrafast dynamic fluorescence Stokes shift measurements of solvation of a dissolved solute by employing a streak camera detection technique were carried out. Measured conductivities (σ) and the average DR times (⟨τDR⟩) were found to be partially decoupled from the solution viscosities (η) and obeyed the relation, σ or ⟨τDR⟩-1 ∝(η/T)-p, with p = 0.6-0.75 for σ and p = 0.2-0.45 for ⟨τDR⟩-1. Raman data indicated the formation of ion pairs and ionic aggregates in these solutions, while the measured glass transition temperature increased with LiTFSI concentration. Conductivities (σ) showed a nonlinear concentration dependence but increased linearly with the solution static dielectric constants (εs). The latter may be explained by considering the temperature effects on complex electrolyte species and the subsequent solution dielectric behavior. Interestingly, an inverse power-law dependence of σ on the measured DR or solvation time scales, σ ∝ (τx)-m, with m = 1.2-1.9, was observed. This dependence may be explained by considering that the same environmental friction regulates both the ion diffusion and the medium polarization relaxation. The control of a slow process (ion translation) by relatively faster medium dynamics (dipolar rotation), although quite fascinating for the present system, warrants further experimental scrutiny for other electrolyte systems relevant to battery applications.

Achieving excellent microwave absorption performance in ultralight Ti3C2Tx MXene with M−O bonds (M = Fe, Co, Ni) as surface terminating groups

Modulating surface terminating groups has been recognized as an effective approach for regulating the electrical properties of MXene. Nevertheless, achieving the simultaneous majorization of electrical and magnetic properties of MXene through terminating groups modulation remains an essential challenge. Herein, we present an innovative series of M−Ti3C2Tx (M = Fe, Co, Ni) with M−O bonds as partial terminating groups. First principles calculations are employed to investigate the impact of M−O bonds on electrical properties of M−Ti3C2Tx. The M−O bonds introduce magnetic loss mechanisms while increasing polarization relaxation and conductivity, resulting in a synergistic optimization of dielectric and magnetic loss. Consequently, the Fe–Ti3C2Tx achieves a favorable minimum reflection loss (RLmin) of − 53.01 dB at 2.47 mm and an effective absorption bandwidth (EAB) of 4.20 GHz at 1.34 mm. The RLmin of Co–Ti3C2Tx reaches − 54.90 dB at 1.43 mm with an EAB of 3.94 GHz at 1.35 mm. The Ni–Ti3C2Tx attains a RLmin of − 47.66 dB and a remarkable EAB of 4.90 GHz at 1.58 mm and 1.63 mm, respectively. Notably, these excellent MA performances are accomplished with an exceptionally low filling ratio of merely 2 wt%, completely satisfying lightweight requirements of absorbers. This research presents a novel method for designing efficient absorbers with simultaneous optimized electromagnetic properties by terminating groups modulation.

Comprehensive properties analysis of epoxy composites synergistically toughened with liquid nitrile rubber and polyethersulfone

In this paper, epoxy resin (EP) composites with different phase structures were prepared by introducing hydroxyl-terminated liquid nitrile rubber (HTBN) and hydroxyl-terminated polyethersulfone (PES) individually or simultaneously into the resin matrix. The results revealed that the rational distribution of phase structure of rigid PES and flexible HTBN can effectively contributed to the enhancement in their mechanical and electrical insulation strengths. The synergistic effect of the two reinforcing fillers granted the optimized ternary composite a tougher structural network, leading to significant improvements of 73.13 % and 18.98 % in mechanical impact strength and electrical breakdown strength, respectively, compared to the pristine EP. Furthermore, compared to HTBN, PES exhibited inhibited HTBN dielectric interfacial polarization and EP molecular chain segment relaxation, resulting in decreased dielectric constant and loss in the composites. This study provide insights into the dielectric properties and design strategies for the development of resin-based dielectric materials, ensuring their broader applicability.

Effects of La3+ doping on the structural, vibrational, elemental, and dielectric characteristics of Sr-Ba-Zr2 R-type hexaferrite

Hexagonal ferrites possess physicochemical and dielectric features that make them highly favorable for absorption purposes. Due to its excellent characteristics at high frequencies, R-type hexagonal ferrite is specifically designed for efficient microwave absorption. Samples of R-type hexaferrite were prepared using the sol-gel auto-combustion process. The samples had the chemical composition Sr0.7Ba0.3Zr2Fe4-xLaxO11, where x ranged from 0.00 to 0.09 in increments of 0.03. This replacement seeks to enhance the understanding of how the La3+ ions affect the physicochemical characteristics of these ferrites, such as their structure, dielectric properties, XPS, and FTIR properties. The single phase of R-type hexaferrite is confirmed by the FTIR and XRD methods. The crystallite size of the samples of R-type hexaferrite doped with La was determined using three different methods. The crystallite size, determined using Sherrer's formula, ranged from 25.865 to 41.393 nm. Meanwhile, the size calculated using Williamson's method was between 36.084 nm and 62.32 nm. The Size-strain analysis revealed a size range of 24.26 nm to 27.31 nm. The FTIR spectra exhibit two intrinsic vibrational bands, labelled as υ1 and υ2, in the wavenumber range of 400 to 600 cm-1. The XPS examination verifies the elemental composition of a representative specimen that has been swapped with La. As the La3+ content increases, additional semicircles are formed, suggesting the existence of more mechanisms for polarization relaxation and a greater capacity for polarization loss. Out of all the compositions that were created, the material with a composition of x = 0.09 exhibits the highest absorption capabilities. This is because of its minimal reflection loss. By replacing the La3+ element in R-type hexaferrites, the peak of the sample moves towards the higher frequency range, indicating excellent microwave absorption properties. R-type hexaferrites are utilized in transformers to reduce eddy current losses and in microwave absorption devices.

Interface-driven microwave absorption enhancement in Mn-optimized Co2FeAl1-xMnx Heusler alloys

To address the urgent need for efficient and stable electromagnetic wave absorbing materials for electromagnetic interference (EMI) protection, we synthesized Co2FeAl1−xMnx Heusler soft magnetic alloys using a high-energy planetary ball milling method. We comprehensively analyzed their structural characteristics, surface morphology, magnetic properties, and electromagnetic parameters to explore their potential in electromagnetic wave absorption. The results show that incorporating manganese (Mn) significantly changes the alloys' crystal structure, surface morphology, and magnetic properties, greatly enhancing their wave absorption performance. The Mn doping specifically alters the surface morphology, which plays a crucial role in influencing the wave absorption characteristics of the Heusler alloys. When the Mn content increased to 25 %, the sample exhibits superior wave absorption, achieving the maximum reflection loss of −44.83 dB at 13.68 GHz with a thickness of 1.5 mm and an effective absorption bandwidth of 5.52 GHz. With a significant increase in the aspect ratio and noticeable changes in surface morphology, the sample with 75 % Mn content shows exceptional performance with an effective absorption bandwidth of 5.68 GHz, representing the highest effective absorption bandwidth in single-phase Heusler alloys. The Mn doping strategy effectively improves the material's impedance matching by adjusting its permittivity and permeability, facilitating multiple polarization relaxation mechanisms and significantly enhancing the alloys' electromagnetic wave absorption efficiency. Our study provides detailed experimental data for optimizing the electromagnetic wave absorption characteristics of Heusler alloys, verifies their practical application potential, and paves the way for developing new high-performance electromagnetic wave absorbing materials.

Electromagnetic wave absorbing behavior of nano-Fe1Co0.8Ni1@C single-layer core-shell and nano-Fe1Co0.8Ni1@SiO2 @C double-layer core-shell composite particles

To effectively explore the influence of nano core-shell structure on the absorption properties of Fe1Co0.8Ni1@X composite particles, three groups of Fe1Co0.8Ni1@C single-layer core-shell structures with varying C coating layer thicknesses and Fe1Co0.8Ni1@SiO2@C double-layer core-shell structure magnetic composite particles were prepared via chemical liquid phase deposition and high-temperature carbonization, and corresponding electromagnetic absorption properties were investigated. The study revealed that the prepared nano core-shell Fe1Co0.8Ni1@X composite particles exhibited a near-spherical shape with particle size of approximately 100 nanometers. The core of the FeCoNi alloy particles was FCC polycrystalline with C coating layer thicknesses ranging from 2 to 3 nm, 10–20 nm, to 30–50 nm, while Fe1Co0.8Ni1@SiO2@C composite particles with SiO2 coating layer thicknesses of 5–10 nm and C coating layer thicknesses of 2–3 nm. As the C coating layer thickness increased, the specific saturation magnetization intensity showed a decreasing trend while the coercivity exhibited an increasing trend, all composite particles presented soft magnetic properties. With the increase of the C coating layer thickness, the real and imaginary parts of the dielectric constant of composite particles continued to rise, while real part of the permeability showed minimal change and imaginary part of permeability exhibited significant variation. Polarization relaxation and electric conduction were observed as C layer thickness increased and magnetic loss primarily including eddy current loss and resonance loss. Additionally, the peak of the dielectric loss of the composite particles demonstrated a shift towards higher frequency with increasing C coating layer thickness, and the dielectric loss of the Fe1Co0.8Ni1@SiO2@C double-layer coating structure sample was lower than that of the Fe1Co0.8Ni1@C. The attenuation constant of Fe1Co0.8Ni1@C composite particles increased with C coating layer thickness and rising continuously with the electromagnetic wave frequency. The double-layer coating structure exhibited a lower attenuation constant than single-layer coating structure and FeCoNi alloy particles, which presented the best impedance matching. Compared with the Fe1Co0.8Ni1 alloy particles, the electromagnetic wave absorption performance of the Fe1Co0.8Ni1@C composite particles was enhanced in both high and low frequency bands, and with the increase of the C coating layer thickness the main absorption frequency band of the samples with the same thickness shifted towards lower frequency. Furthermore, the thickness of sample decreased from 1.5mm to 2.0 mm to 1–1.5 mm as the C coating layer thickness increased. Maximum reflection loss |RLmax| of 61.76 dB and effectively absorbed bandwidth of 4.64 GHz was obtained for Fe1Co0.8Ni1@C composite particle.

Low-Cost Purpose-Built Ultra-Low-Field NMR Spectrometer.

Low-field NMR has emerged as a new analytical technique for the investigation of molecular structure and dynamics. Here, we introduce a highly integrated ultralow-frequency NMR spectrometer designed for the purpose of ultralow-field NMR polarimetry of hyperpolarized contrast media. The device measures 10 cm × 10 cm × 2.0 cm and weighs only 370 g. The spectrometer's aluminum enclosure contains all components, including an RF amplifier. The device has four ports for connecting to a high-impedance RF transmit-receive coil, a trigger input, a USB port for connectivity to a PC computer, and an auxiliary RS-485/24VDC port for system integration with other devices. The NMR spectrometer is configured for a pulse-wait-acquire-recover pulse sequence, and key sequence parameters are readily controlled by a graphical user interface (GUI) of a Windows-based PC computer. The GUI also displays the time-domain and Fourier-transformed NMR signal and allows autosaving of NMR data as a CSV file. Alternatively, the RS485 communication line allows for operating the device with sequence parameter control and data processing directly on the spectrometer board in a fully automated and integrated manner. The NMR spectrometer, equipped with a 250 ksamples/s 17-bit analog-to-digital signal converter, can perform acquisition in the 1-125 kHz frequency range. The utility of the device is demonstrated for NMR polarimetry of hyperpolarized 129Xe gas and [1-13C]pyruvate contrast media (which was compared to the 13C polarimetry using a more established technology of benchtop 13C NMR spectroscopy, and yielded similar results), allowing reproducible quantification of polarization values and relaxation dynamics. The cost of the device components is only ∼$200, offering a low-cost integrated NMR spectrometer that can be deployed as a plug-and-play device for a wide range of applications in hyperpolarized contrast media production─and beyond.

Hierarchical Engineering on Built‐In Electric Field of Bimetallic Zeolitic Imidazolate Derivatives Towards Amplified Dielectric Loss

AbstractConstruction of built‐in electric field (BIEF) in nanohybrids has been demonstrated as an efficacious strategy to boost the dielectric loss by facilitating oriented transfer and transition of charges, thus optimizing the electromagnetic wave absorption property. However, the specific influence of BIEF on interface polarization needs to explore thoroughly and the BIEF strength should be further augmented. Herein, several dielectric systems incorporated Mott–Schottky heterojunctions and hollow structures are designed and constructed, where bimetallic zeolitic imidazolate framework are employed to derive Cu‐ZnO Mott–Schottky heterojunctions, and hierarchical structures and BIEF are further enriched by introducing hollow structure and reduced graphene oxide. The well‐established “double” BIEF verified by theoretical calculation and hollow engineering can regulate the conductivity, and enhance the polarization relaxation effectively. Especially, there always coexisted both enhanced charge separation and reversed charge distribution in this “double” BIEF, boosting the interface polarization. Attributing to the synergy of well‐matched impedance and amplified dielectric loss, the obtained hybrids exhibited superior absorption (reflection loss of −46.29 dB and an ultra‐wide effective absorption bandwidth of 7.6 GHz at only 1.6 mm). This work proves an innovative model for dissecting dielectric loss mechanisms and pioneers a novel strategy to explore advanced absorbers through enhancing BIEF.

Dielectric behavior and defects of nitrogen-containing single crystal diamond films

Single crystal diamond (SCD) film, as a new substrate material, has attracted growing attention because of its low dielectric loss. The nitrogen was usually introduced into microwave plasma chemical vapor deposition (MPCVD) process in order to enhance the growth rate of SCD films. So SCD films with nitrogen were prepared by MPCVD compared with the undoped film. The impurities and defects of diamond films were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and photoluminescence spectroscopy (PL). The dielectric behavior of SCD films was measured using the LCR measurement in the frequency range of 1 kHz to 110 MHz. The results indicate that the primary dielectric loss in SCD films is conductivity loss and space charge polarization below 1 MHz, while the main dielectric loss is dipole orientation polarization and electronic relaxation polarization in the frequency range of 1 MHz to 110 MHz. Point defects like substitutional N+, NV− and SiV− exert a significant influence on polarization loss. This is essential to improve the growth of SCD with excellent dielectric properties.

Optimized energy storage performances via high-entropy design in KNN-based relaxor ferroelectric ceramics

Dielectric capacitors play an irreplaceable role in complex and integrated electronic systems. However, attaining ultrahigh recoverable energy storage density (Wrec) alongside energy storage efficiency (η) poses a formidable challenge, impeding the advance towards the miniaturization and integration of cutting-edge energy storage devices. In this work, a high-entropy strategy with a viscous polymer process is adopted, bringing about ultrafine grains and polar nanoregions (PNRs) accompanied by enhanced electrical homogeneity and polarization relaxation characteristics. As a result, an ultrahigh Wrec ∼ 7.51 J/cm3 is achieved in a high-entropy KNN-based energy storage ceramic with a high η ∼ 88.4% at 750 kV/cm. Moreover, the ceramic capacitor exhibits a colossal power density reaching approximately 420 MW/cm3 and a discharge energy density of approximately 4.85 J/cm3 at 160 ℃. Impressively, it maintains low variation rates of less than 4% across a broad temperature range from 20 ℃ to 160 ℃. The new approach opens avenues for the design and development of superior dielectric materials used in next-generation high-power pulse devices.

Single and double quantum transitions in spin-mixed states under photo-excitation

Electronic spins associated with the Nitrogen-Vacancy (NV) center in diamond offer an opportunity to study spin-related phenomena with extremely high sensitivity owing to their high degree of optical polarization. Here, we study both single- and double-quantum transitions (SQT and DQT) in NV centers between spin-mixed states, which arise from magnetic fields that are non-collinear to the NV axis. We demonstrate the amplification of the ESR signal from both these types of transition under laser illumination. We obtain hyperfine-resolved X-band ESR signal as a function of both excitation laser power and misalignment of static magnetic field with the NV axis. This, combined with our analysis using a seven-level model that incorporates thermal polarization and double quantum relaxation, allows us to comprehensively analyze the polarization of NV spins under off-axis fields. Such detailed understanding of spin-mixed states in NV centers under photo-excitation can help greatly in realizing NV-diamond platform’s potential in sensing correlated magnets and biological samples, as well as other emerging applications, such as masing and nuclear hyperpolarization.

A Hybrid Perovskite-Based Electromagnetic Wave Absorber with Enhanced Conduction Loss and Interfacial Polarization through Carbon Sphere Embedding.

Electronic equipment brings great convenience to daily life but also causes a lot of electromagnetic radiation pollution. Therefore, there is an urgent demand for electromagnetic wave-absorbing materials with a low thickness, wide bandwidth, and strong absorption. This work obtained a high-performance electromagnetic wave absorption system by adding conductive carbon spheres (CSs) to the CH3NH3PbI3 (MAPbI3) absorber. In this system, MAPbI3, with strong dipole and relaxation polarization, acts dominant to the wave absorber. The carbon spheres provide a free electron transport channel between MAPbI3 lattices and constructs interfacial polarization loss in MAPbI3/CS. By regulating the content of CSs, we speculate that this increased effective absorption bandwidth and reflection loss intensity are attributed to the conductive channel of the carbon sphere and the interfacial polarization. As a result, when the mass ratio of the carbon sphere is 7.7%, the reflection loss intensity of MAPbI3/CS reaches -54 dB at 12 GHz, the corresponding effective absorption bandwidth is 4 GHz (10.24-14.24 GHz), and the absorber thickness is 2.96 mm. This work proves that enhancing conduction loss and interfacial polarization loss is an effective strategy for regulating the properties of dielectric loss-type absorbing materials. It also indicates that organic-inorganic hybrid perovskites have great potential in the field of electromagnetic wave absorption.

Interfacial and Defective Construction from Diverse CuxSy Quantum Dots toward Broadband Carbon-Based Microwave Absorber.

In this study, highly monodisperse copper sulfide (CuxSy) quantum dots (QDs) have been successfully obtained using a ligand-chemistry strategy, and then a variety of S-deficient CuxSy/nitrogen-doped carbon (NC) heterointerfaces are constructed by compositional fine-tuning (Cu9S5 → Cu1.96S → Cu). First-principles calculations show that the S-deficient domains of CuxSy QDs and N-doped domains of carbon synergistically enhance the electron transfer from CuxSy to NC. In addition, the finite element simulations demonstrate that the diverse CuxSy QDs exhibit their intrinsic size and dielectric confinement effects to precisely manipulate the electric field distortion and improve the relaxation polarization. Consequently, CuxSy@NC achieves excellent impedance matching and a strong loss mode dominated by dielectric polarization. Among them, CuxSy@NC-650 has a maximum effective absorption bandwidth of 7.7 GHz at 2.5 mm, while CuxSy@NC-700 features a minimum reflection loss of -66.7 dB at 13.7 GHz, respectively. Furthermore, the simulations of radar cross-sections have confirmed that the CuxSy@NC series is promising in the field of radar stealth.

On the effect of polarization relaxation on dielectric breakdown

On the effect of polarization relaxation on dielectric breakdown

Multi-heterogeneous interfaces boost dielectric polarization in PBA-derived Co/MnO@NC ternary composites for electromagnetic wave absorption

The elaborate construction of multi-component composites has been deemed as a promising strategy to enhance dielectric polarization response capability in the preparation of highly efficient microwave absorbers. However, the rational design and integration of homogeneous composites with diverse components continues to pose a great challenge. Herein, we propose a straightforward self-assembly-carbonization strategy for fabricating Co/MnO@NC ternary composites derived from CoMn-Prussian Blue Analogous precursors, featuring enriched heterogeneous interfaces and balanced magneto-electric coupling synergy. The ternary composites effectively introduce diverse dissipation mechanisms, including interfacial polarization behavior originated from the constructed heterogeneous interfaces, dipole polarization relaxation triggered by atomic defects, and optimized magnetic loss ability from well-dispersed metallic Co species. Benefiting from these advantages, the Co/MnO@NC composites demonstrate superior electromagnetic wave absorption performances, with a minimum reflection loss value of −61.37 dB at the thickness of 3.5 mm and effective frequency absorption bandwidth of 6.32 GHz, covering the full Ku-band. Furthermore, power loss density and radar cross-section simulations validate that the Co/MnO@NC ternary composites possess exceptional microwave signal attenuation abilities, with a maximum radar cross-section reduction value of up to 27.98 dBm2 at 0°. Such outstanding absorption properties exceed those of most currently reported ternary composites and exhibit significant potential to replace conventional ferromagnetic-based absorbers. This work offers a straightforward strategy to fabricate ternary composites with excellent electromagnetic wave attenuation properties and sheds novel insights into the dissipation mechanisms.

Optical, AC conductivity and antibacterial activity enhancement of chitosan-silver nanocomposites for optoelectronic and biomedical applications

This study is aimed to prepare and investigate the optical, electrical and antibacterial activity of the environmentally friendly (green) chitosan (Cs)/silver nanocomposites. TEM demonstrated that AgNPs have a spherical shape with particle size ranged from 3 nm to 25 nm. UV analysis spectra of Cs and Cs/Ag nanocomposites showed that, increasing the content of AgNPs led to a noticeable increase in the values of Urbach energy (E U ) and a dramatic decrease in both the indirect (E ig ) and direct (E dg ) optical bandgap energies. It is found that (E ig ) and (E dg ) are decreased from (4.72/5.31 eV) to (2.47/4.19 eV). The formation of the AgNPs is verified by the existence of surface plasmon resonance (SPR) peak at ∼ (421–450) nm. Wemple-DiDomenico and Sellmeier oscillator models are employed and displayed a clear enrichment in the dispersion energy (E d ) and oscillator energy (E 0) as well as the linear and nonlinear optical parameters of Cs. It is observed that the linear (χ(1)) and nonlinear (χ(3) and n2) parameters are enhanced from 0.083, 0.868 × 10−14 and 1.584 × 10−12 to 0.153, 9.762 × 10−14 and 4.088 × 10−12. The novel results in our study nominate Cs/Ag nanocomposites for applications in linear/nonlinear optical devices. AC conductivity behavior of Cs and Cs/Ag nanocomposites is analyzed based on Jonscher’s law and the analysis showed that the overlapping large polaron tunneling (OLPT) is the dominant conduction mechanism for our samples. It is clear that the values of dielectric constant (ε′) of Cs and Cs/Ag nanocomposites are higher confirming the presence of interface polarization (IP) relaxation. Moreover, it is found that the antibacterial activity of Cs against Gram-negative (P. aeruginosa) and Gram-positive (B. thuringiensis) bacteria is found to be enhanced with increasing the content of Ag NPs. These results suggested that Cs/Ag nanocomposites will be good source for preparing bio-nanocomposites for use in many biomedical and industrial applications.

Investigation of the Effect of Alloying Element Equilibrium Relationship on the Electromagnetic Microwave Absorption Properties of Nano FeNi Magnetic Particles

AbstractIn order to effectively comprehend the impact of alloying element equilibrium relationship of binary nano‐magnetic particles on their electromagnetic wave absorption performance, four sets of binary nano FeNi magnetic particles with Fe:Ni alloy ratios of 2:8, 4:6, 6:4, and 8:2 were prepared with liquid‐phase reduction and the microstructure, static magnetic properties, and electromagnetic wave absorption performance of the particles were studied. The results show that the nano FeNi magnetic particles exhibit a spherical geometric structure, with a decrease in crystallinity as the Fe:Ni alloy ratio increases. The remanence and coercivity initially increase and then decrease with the increased Fe:Ni alloy ratio, with a 270 % decrease in saturation magnetization intensity as the alloy ratio changes from 2:8 to 8:2. With the increase in the Fe:Ni alloy ratio, the real and imaginary parts of the complex permittivity exhibit a decreasing trend, while the real part of the magnetic permeability decreases with increasing frequency. Aside from the 8:2 Fe:Ni alloy ratio, significant polarization relaxation losses were observed in the prepared magnetic particles, with eddy current losses was not the main mechanism of magnetic losses. The attenuation constant shows a peak at high frequencies, and the impedance matching performance increases with the increase in the Fe:Ni alloy ratio. When the Fe:Ni alloy ratio changes from 2:8 to 8:2, the minimum reflection loss decreased by 3340 %, and at a thickness of 2.1 mm and a frequency of 12 GHz, the FeNi alloy particles with a ratio of 2:8 exhibited a minimum reflection loss of −17.2 dB with an effective absorption bandwidth of 1.92 GHz.

Designing a Microstructure of NiCo-LDH@CNTs@Carbon Foam for Efficient Electromagnetic Wave Absorption and Excellent Environmental Tolerance.

The constantly evolving environment imposes increasingly stringent demands on the mechanical qualities of materials employed for absorbing electromagnetic waves (EMWs). Therefore, there is an urgent need for advanced materials capable of efficiently absorbing EMWs and withstanding harsh electromagnetic conditions. In this study, the electrodeposition method was effectively used to synthesize nickel-cobalt layered double hydroxides (NiCo-LDHs) in a controlled manner on a composite structure of carbon nanotubes and carbon foam, creating an exquisite construction. The manipulation of the electrodeposition time facilitated the regulation of the density of the layered structure within the composite material, thereby significantly enhancing its polarization relaxation performance. Increased defect sites and interface polarization enhance impedance matching and the attenuation constant, resulting in greatly improved absorption performance. The optimized sample demonstrated exceptional wave-absorbing performance in comparative experimental analysis, attaining a maximum reflection loss of -58.18 dB. It also has an effective absorption bandwidth of 5.36 GHz at a wavelength of 2.28 mm. The exceptional isolation effect of LDH, coupled with the outstanding insulation ability of the porous carbon skeleton, confers remarkable corrosion resistance and thermal insulation performance on the composite material. Hence, this discovery offers novel insights into designing environmentally tolerant absorbent materials.

Structural, optical, and morphological properties of PVC-BaTiO3 nanocomposite films

This work aims to fabricate barium titanate (BaTiO3) nanoparticles and study the effect of adding different contents of BaTiO3 nanoparticles on the structural, optical, and electrical properties of PVC polymer matrices. The PVC/BaTiO3 nanocomposite films were characterized by X-ray diffraction, FT-IR spectroscopy, and SEM. In addition, dielectric properties were studied within the frequency range of 0.1 KHz–6 MHZ. The XRD analysis reveals an amorphous nature of pure PVC with two characteristic peaks at 2θ = 17.09° and 2θ = 23.25°, and it reveals that BaTiO3 has sharp and narrow peaks. In PVC/BaTiO3 nanocomposite films, all XRD peaks of BaTiO3 appeared in all the samples with an increase in the average particle size from ∼46 nm to 55 nm. There is no shift of IR position in PVC bands, but the decreased intensity of some bands suggests complexation between PVC and BaTiO3. The UV–visible absorption spectrum of pure PVC has a band at λ = 278 nm. This band was shifted to 252 nm after adding BaTiO3 content. UV–visible transmission spectra demonstrate a decrease in the transmittance as an increase of BaTiO3 content from 89.23 % for pure PVC to 5.23 % for 0.1 wt% of BaTiO3. The values of the optical bandgap decrease with increasing BaTiO3 contents due to defect formation in PVC matrices. The optical parameters of the prepared nanocomposite films were also enhanced. The AC conductivity shows an increase with both frequency and BaTiO3 concentration, leading to enhanced movement of charge carriers and relaxation of interface polarization.