Quinary High‐Entropy‐Alloy@Graphite Nanocapsules with Tunable Interfacial Impedance Matching for Optimizing Microwave Absorption

Abstract

Designing heterogeneous interfaces and components at the nanoscale is proven effective for optimizing electromagnetic wave absorption and shielding properties, which can achieve desirable dielectric polarization and ferromagnetic resonances. However, it remains a challenge for the precise control of components and microstructures via an efficient synthesis approach. Here, the arc‐discharged plasma method is proposed to synthesize core@shell structural high‐entropy‐alloy@graphite nanocapsules (HEA@C‐NPs), in which the HEA nanoparticles are in situ encapsulated within a few layers of graphite through the decomposition of methane. In particular, the HEA cores can be designed via combinations of various transition elements, presenting the optimized interfacial impedance matching. As an example, the FeCoNiTiMn HEA@C‐NPs obtain the minimum reflection loss (RLmin) of −33.4 dB at 7.0 GHz (3.34 mm) and the efficient absorption bandwidth (≤−10 dB) of 5.45 GHz ranging from 12.55 to 18.00 GHz with an absorber thickness of 1.9 mm. The present approach can be extended to other carbon‐coated complex components systems for various applications.

Sub‐Nanometer Fe Clusters Confined in Carbon Nanocages for Boosting Dielectric Polarization and Broadband Electromagnetic Wave Absorption

“…The phase structures of all the composites were measured by X‐ray diffraction (XRD, Figure 2c), in which a broad peak at ≈24° could be observed, corresponding to the (002) plane of graphitic carbon. [ 7 ] Meanwhile, several additional peaks at 31°, 36°, 44°, 55°, and 65° could be detected in Fe@NCNs‐10 and Fe@NCNs‐11 composites, attributed to the formation of Fe 3 O 4 nanoparticles by the aggregation of FePc molecular via the Kirkendall effect. [ 28,36 ] The detailed characteristics of graphitic layers were evaluated by the Raman spectra, as exhibited in Figure 2d.…”

“…The RL values of −10 and −20 dB represent that 90% and 99% incident EM energy was attenuated. [ 7,12,23 ] The Fe@NCNs‐7 exhibit the lowest RL min values of −18.92 dB (18 GHz, 2.5 mm) among all the samples, and their effective absorption bandwidth (EAB ≤ −10 dB ) is 6.6 GHz at 3.1 mm. For the Fe@NCNs‐8, the RL min value of −26.18 dB was achieved at 17.3 GHz (2.3 mm), while the EAB ≤ −10 dB is 6.6 GHz at 2.8 mm.…”

“…[ 29,31 ] Consequently, such subnanometer clusters can create a 3Dconductive network for conducting the free charges, which could achieve the interaction and polarization in the nanocages and thus result in the energy transformation between permeability and permittivity at 10 GHz. The improvement is larger than that of the electric dipole polarization [ 12,17 ] and interfacial polarization [ 7,13 ] behavior contributed by the heteroatom Fe substitutions and Fe 3 O 4 nanoparticles.…”

“…[ 1–5 ] The EM wave absorption performances are strictly related to the complex permittivity (ε r ) and permeability (μ r ) and their impedance matching, which are mainly associated with dielectric and magnetic loss properties of materials. [ 6–8 ] Thus, various dielectric‐magnetic composited absorbers have been reported, in which the EM wave absorption properties can be significantly optimized through the integrated loss capacities and the constructed interfacial polarization. [ 1,4,9–11 ] For example, Li et al reported that the core@shell structural Fe@C and high‐entropy‐alloy@C nanocapsules can improve the EM wave absorption properties ascribed to the prober matching between the hetero‐components.…”

Microstructure Design of High-Entropy Alloys Through a Multistage Mechanical Alloying Strategy for Temperature-Stable Megahertz Electromagnetic Absorption

“…This facilitates the improvement of the permeability and its temperature stability over a wide temperature range. Moreover, mechanical alloying method has the advantages of room-temperature processing, homogenous element distribution, energy saving, and high efficiency [ 29 – 31 ], as compared with the complicated process commonly used for HEAs, such as carbothermal shock synthesis [ 32 ], ultrafast-cooling arc-discharged approach [ 33 , 34 ], atomization [ 31 ], and melting-strip casting–milling [ 26 ].…”