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Manganese dioxide (MnO 2) has been widely utilized in the electromagnetic wave (EMW) absorption field because it exhibits numerous crystal types including α-MnO 2 , β-MnO 2 , γ-MnO 2 , and δ-MnO 2 , and is environmentally friendly. To enhance the EMW absorption performance of this material, we combined the precipitation method and calcination process to obtain γ-MnO 2 microspheres, and developed a core-shell structure of γ-MnO 2 @SiO 2 and γ-MnO 2 @SiO 2 @TiO 2 microspheres via the sol-gel process. Based on the synergistic effects between the core-shell structure and dielectric loss, γ-MnO 2 @SiO 2 with a thickness of 2.85 mm achieved the minimum reflection loss of −60.2 dB, demonstrating that these microspheres are excellent candidates for EMW absorbers. [ABSTRACT FROM AUTHOR]

The hierarchical SiOC/SiCnws/CF composites (A/B/C structure) were designed via precursor infiltration and pyrolysis process. The SiOC ceramics served as the wave‐transparent characteristic materials to adjust the impedance matching. Herein, the in situ growth of SiCnws not only was used for the absorber but served as the reinforcement of SiOC matrix composites. In detail, the SiOC/SiCnws/CF‐1200°C‐2 exhibits excellent electromagnetic absorption performance with minimum reflection loss of −46 dB at 14.4 GHz with the thickness of 1.6 mm, and its effective absorption band reaches 4.3 GHz. Its compressive strength reaches 8.69 and 16.41 MPa in z and x/y directions, separately. This contribution has a guidance for the application of carbon fiber/ceramics matrix composites in harsh environment. [ABSTRACT FROM AUTHOR]

The development of electromagnetic wave (EMW) absorption materials with lightweight, wide absorption bandwidth, thin thickness, and strong EMW absorption performance has become a hotspot. Herein, the morphology‐controlled preparation of α‐manganese dioxide (α‐MnO2) was successfully obtained via a facile hydrothermal method, and the EMW absorption performance of α‐MnO2 was investigated in detail. The results indicated the as‐obtained Mn‐1.0‐120 possessed the best EMW absorption performance with minimum reflection loss of −53.43 dB at about 5.2 GHz with a thickness of 4.1 mm originated from the synergistic effects of multiply scattering, dielectric loss, and magnetic loss. This contribution demonstrates that the MnO2 has promising candidates with a tunable EMW absorption performance for applications in the electromagnetic field in the future. [ABSTRACT FROM AUTHOR]

The development of lightweight electromagnetic wave absorbers with strong absorption performance, and broad absorption bands has garnered significant attention toward electromagnetic protection. In this study, 3D hierarchically porous (Zn 1/2 Ni 1/2)Co 2 O 4 spinel clusters were synthesized via a straightforward hydrothermal reaction followed by calcination. Notably, the (Zn 1/2 Ni 1/2)Co 2 O 4 spinel calcined at 500 ℃, the hierarchically porous (Zn 1/2 Ni 1/2)Co 2 O 4 spinel clusters achieved the minimum reflection loss value and effective absorption band of −66.6 dB and 6.45 GHz at a matching thickness of 2.47 mm and 2.35 mm, respectively. These outcomes were due to the synergistic effects induced by dielectric loss, magnetic loss, and the unique hierarchical porous structure of the prepared spinel. Our findings will promote the development of electromagnetic protection technologies and inspire the design and fabrication of high-performance electromagnetic wave absorbing materials. • 3D hierarchically porous (Zn 1/2 Ni 1/2)Co 2 O 4 spinel clusters were successfully fabricated by a simple hydrothermal reaction and calcination. • The (Zn 1/2 Ni 1/2)Co 2 O 4 spinel obtained at the temperature of 500 ℃ exhibited a RL min of −66.6 dB and an EAB of 6.45 GHz. • The excellent electromagnetic wave absorption performance was attributed to the synergistic effect of dielectric loss, magnetic loss, and the unique hierarchical porous structure of the prepared spinel. [ABSTRACT FROM AUTHOR]

Herein, the SiC‐coated carbon fiber decorated with SiC nanowire (SiCnw/CF) composites are successfully prepared by one‐step chemical vapor infiltration (CVI) process. Microstructures, the formation mechanism of SiCnws, thermal stability performance, and electromagnetic wave (EMW) absorption performance of the composites are investigated in detail. In particularly, benefiting the dielectric loss and conductive loss, the SiCnw/CF composites obtained at 1500 °C exhibit superior EMW absorption property with the minimum reflection loss (RL) of −36.5 dB with the effective absorption band of 5.5 GHz at a thickness of 1.88 mm. This work provides a simple way to obtain and design the CF‐based materials with good microwave absorption. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) is expected to be the new-generation electromagnetic wave (EMW) absorber. In this context, the SiC/C composites were first prepared through a hydrothermal method using glucose as the carbon source. Then SiC/MnO 2 composites were fabricated by a second hydrothermal reaction using potassium permanganate (KMnO 4) as raw material. With glucose content increased to 10 wt%, the composition exhibited outstanding EMW absorption performance with the minimum reflection loss value of − 55.7 dB at the frequency of 2.1 GHz, and effective absorption bandwidth can cover the entire S-band by adjusting sample thickness. Therefore, the SiC/MnO 2 composites present a promising EMW-absorbing material for low-frequency applications. • The impedance matching of composites was optimized by MnO 2 , and the RL min value of SiC-10HTC-MnO 2 was up to − 55.7 dB at the frequency of 2.1 GHz. • The EAB can cover the entire S-band by adjusting the sample thickness owing to the synergistic effect of dielectric loss and single-crystal volume polarization of SiC and MnO 2. • The SiC/MnO 2 composites present a promising EMW-absorbing material for loe-frequency application. [ABSTRACT FROM AUTHOR]

Herein, the SiC nanowires were successfully fabricated via chemical vapor infiltration (CVI) into carbon fiber felts (CFs) and then the SiOC/SiCnws/CFs composites were synthesized by precursor infiltration and pyrolysis (PIP) processes. Results indicated that the lightweight composites possessed enhanced mechanical performance, low thermal conductivity, and excellent electromagnetic wave absorption properties. Detailedly, the compressive strength reached to 22.0 MPa and 9.6 MPa after two PIP processes cycles in z and x/y directions, respectively. Meanwhile, the composites exhibited tailored electromagnetic wave absorption performance with the effective absorption bandwidth of 3.06 GHz, and the minimum reflection loss (RL min) was -48.2 dB with a thickness of 3.6 mm. The present work has a guidance to prepare and design multifunction properties for application in harsh environment. [ABSTRACT FROM AUTHOR]

Polymer‐derived ceramics (PDCs), such as SiOC, SiCN, SiBCN, and SiC are considered the best candidates for designing high‐performance microwave absorber due to their controllable structure, homogeneous element composition at atom level, tunable electromagnetic and electrochemical properties. Herein, Fe ions doped silicon oxycarbide (Fe ions‐SiOC) ceramics have been successfully fabricated via solvothermal method. The electromagnetic absorption performances of the nanocomposites prove to be controllable via tailoring Fe ion contents. The Fe ions effectively enhance both the interfacial polarization of amorphous SiOC, and the dielectric properties of the nanocomposites but barely effect magnetic properties of the nanocomposite. As for 0.16 mol/L‐SiOC ceramics annealed at 1450°C, the effective absorption bandwidth as high as 2.00 GHz and reflection loss of −59.60 dB at 5.40 GHz with the thickness of 4.55 mm are obtained. Such work opens up a novel and simple route to scale up the PDC‐based materials with broadband and excellent microwave absorbing performances. [ABSTRACT FROM AUTHOR]

Microwave absorbing materials with lightweight, strong absorption, broad bandwidth and thin matching thickness have gained considerable attentions in recent years. Herein, C-doped SiC ceramic nanocomposites with heterostructure were successfully fabricated via solvothermal method using renewable glucose as the carbon source. Such nanocomposites show different permittivity dependent on glucose contents. By tailoring the dielectric properties of the nanocomposites, the C-doped SiC nanocomposites using 0.50 mmol/mL glucose solution with a strong reflection loss of −76.6 dB at 16.0 GHz with the thickness of 1.66 mm were obtained. Microwave absorption mechanism indicates that dielectric loss originating from the conductive paths and dipole polarization contributes to the improvement microwave absorption properties. The results provide new strategy for designing and fabricating composites consisting of ceramic and C materials with the strong absorbing and broad bandwidth properties. Image 1 [ABSTRACT FROM AUTHOR]

In this work, Fe-containing polymer-derived silicon oxycarbide ceramic (PDC-SiOC) nanocomposites were successfully synthesized by a facile route. Electromagnetic wave absorption properties were significantly improved due to formation of SiC particles. Results indicated that Fe-containing SiOC ceramic composites showed strong electromagnetic wave absorption performance, in which the minimum reflection loss (RL min) reached −58.4 dB at 13.6 GHz at the thickness of 1.70 mm as well as a wide absorption bandwidth of 4.10 GHz (11.5–15.6 GHz) with a normalized weight fraction of iron (III) acetylacetonate at 1 wt%. This work provides a new way to fabricate and design PDC-based electromagnetic wave absorbers with strong absorbing performance. • The Fe-containing SiOC ceramics were successfully fabricated by a facile solvothermal method. • The effects of phase composition and structures on dielectric parameters of Fe-containing SiOC ceramics were studied. • The electromagnetic microwave absorption capabilities of Fe-containing SiOC ceramics were investigated. [ABSTRACT FROM AUTHOR]

Polymer-derived-ceramics (PDCs) are considered as a promising candidate for excellent microwave absorption under harsh environments due to their controllable microstructure at the molecular level. Herein, a series of silicon oxycarbide (SiOC) nanospheres are successfully fabricated through a PDC method and then pyrolyzed under argon atmosphere at different temperatures and the evolutions of microstructure and their microwave absorption properties are investigated simultaneously. It is found that the microwave absorption properties mainly depend on carbon content. With a relative carbon content of 38.13%, the carbon-rich SiOC nanospheres-1 pyrolyzed at 1400 °C possess excellent microwave absorption properties with a minimum reflection loss (RL) value of −56.28 dB at 6.8 GHz with a thickness of 2.93 mm. Electromagnetic analysis demonstrates that proper impedance matching, intrinsic attenuation ability, and the multiple reflection are responsible for the excellent RL. This work will provide a novel approach to obtain the PDCs with excellent microwave absorption properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Exploring highly efficient electromagnetic wave (EMW) absorbing materials with strong absorption and low density is a viable strategy to address the growing issue of electromagnetic pollution. A type of carbon-coated MnO (MnO@C) microspheres with enhanced EMW absorption properties was synthesized via the precipitation method, followed by a facile sol-gel process. The results demonstrate that the carbon source content is critical in determining the thickness of the carbon shell, which in turn has a great impact on impedance matching and attenuation constant. Due to the moderately complex permittivity of MnO@C microspheres, the minimum reflection loss (RL min) reaches − 43.69 dB at 15.03 GHz with an ultra-thin matching thickness of only 1.53 mm. Additionally, the corresponding effective absorption bandwidth (EAB) is 4.81 GHz. The enhanced performance can mainly be attributed to appropriate impedance matching and multiple attenuation mechanisms, including interfacial polarization, defect-induced polarization, and conduction loss. Therefore, the MnO@C microspheres are considered to be suitable for high-efficiency microwave absorbers. • The MnO@C microspheres were successfully fabricated via the precipitation method followed by the sol-gel process. • The uniform C layer was closely coated on the MnO surface and exhibited improvement in dielectric parameters. • The RL min of − 43.69 dB and EAB of 4.81 GHz can be achieved simultaneously with an ultrathin thickness of 1.53 mm. [ABSTRACT FROM AUTHOR]