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Abstract Polycarbosilane-derived SiC (PCS-derived SiC) has been suggested as a promising candidate for particularly effective microwave absorption materials. To optimize the microwave absorption properties, while retaining the crystallinity of SiC, PCS-derived SiC ceramics were prepared by a combination of dehydrogenation, appropriate oxidation, and pyrolysis. This study investigated microstructures, dielectric properties, and microwave absorption properties of as-prepared PCS-derived SiC. Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results demonstrate that dehydrogenation effectively prevented the breakage of Si C bonds during the following oxidation. Furthermore, PCS-derived SiC with a similar core-shell structure was obtained after oxidation, the surface of which showed fewer SiC nanocrystals and shorter graphene-like carbon compared to the inner microstructure. Due to this unique microstructure, the oxidized PCS-derived SiC shows both better attenuation capability and impedance match than as-received PCS-derived SiC. Moreover, with extended oxidation time, the average ε ′ and ε ″ of PCS-derived SiC decreased from 13.0 to 5.2 to 10.5 and 4.4, respectively, which could be attributed to weakened polarization and decreased electrical conductivity. The minimum reflection loss of PCS-derived SiC could be significantly improved from −18 to −27 dB after oxidation, which indicates strong improvement in microwave absorption properties. Highlights • Microwave absorption properties of PCS-derived SiC were improved by oxidation. • Oxidized SiC particles with core-shell structure exhibits better impedance match. • The minimum RL for SiC is obviously decreased from −18 to −27 dB after oxidation. • The bandwidth below −10 dB extends to 3.4 GHz in X-band with a thickness of 2.3 mm. [ABSTRACT FROM AUTHOR]

Highlights • Ti 3 SiC 2 encapsulated by magnetic Ni 0.5 Zn 0.5 Fe 2 O 4 shell were successfully prepared. • Moderated complex permittivity for the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 was achieved. • Desirable higher complex permeability for the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 was realized. • The Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 coating with wide bandwidth (RL <-10 dB) of 5.3 GHz. Abstract Ti 3 SiC 2 particles encapsulated by Ni 0.5 Zn 0.5 Fe 2 O 4 shell were in-situ synthesized via a facile sol-gel method. Effects of Ni 0.5 Zn 0.5 Fe 2 O 4 shell on electromagnetic properties of Ti 3 SiC 2 were investigated in 2–18 GHz. Moderated complex permittivity and desirable higher complex permeability presented for the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 composite, resulting in strong microwave attenuation ability and good impedance matching property. The measured effective absorbing bandwidth (RL < −10 dB) of 5.3 GHz and corresponding maximum RL of −38.6 dB were obtained for the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 absorbing coating of 1.2 mm thickness. These results indicate that the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 composite may become a new type of microwave absorbent. [ABSTRACT FROM AUTHOR]

• Magnetic CoNi-wrapped Ti 3 SiC 2 composites were successfully prepared. • Obvious regulated electromagnetic parameters for the composites can be realized. • The EAB of 4.88 GHz and optimal RL value of −41.41 dB were achieved. The magnetic–dielectric composites with synergetic magnetic and dielectric losses have exhibited great potential in the practical applications of microwave absorbing material. This paper reports a simple low-temperature in situ hydrothermal approach for synthesizing novel composites composed of the dielectric Ti 3 SiC 2 wrapped with magnetic CoNi nanoparticles. The microstructure, morphology, electromagnetic properties, and microwave absorption performance of as-synthesized samples were investigated. By adjusting the content of formed magnetic CoNi nanoparticles on the surface of Ti 3 SiC 2 , obvious regulated frequency-dependence of electromagnetic parameters for the proposed CoNi/Ti 3 SiC 2 composites can be realized. Consequently, the effective absorption bandwidth (RL < −10 dB) and optimal reflection loss value of CoNi/Ti 3 SiC 2 -40 composites under thinner thickness of 1.55 mm can reach up to 4.88 GHz and −41.41 dB, respectively. Exceptional microwave absorption performance of the CoNi/Ti 3 SiC 2 composites is attributed to its simultaneously improved attenuation characteristics and optimized impedance matching, and thus can be undoubtedly identified as high-efficiency microwave absorbing material. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal carbides (MXenes) exhibit great potential application in the microwave absorption (MA) field due to their layered structure, excellent dielectric loss and adjustable layer spacing. Herein, Nb 2 O 5 with different morphologies (columnar and irregular granular) was successfully synthesized in situ and implanted between the layers of a Nb 2 CT x MXene through a rapid microwave-assisted hydrothermal method. Newly formed Nb 2 O 5 and Nb 2 CT x from an incomplete reaction composed the Nb 2 O 5 /Nb 2 CT x hybrids. Compared with that for the pure Nb 2 CT x , the Nb 2 O 5 /Nb 2 CT x composites showed enhanced MA performance, especially the Nb 2 O 5 /Nb 2 CT x composites with columnar Nb 2 O 5 (c-Nb 2 O 5 /Nb 2 CT x). The minimum reflection loss (RL) value reached −44.1 dB at 2.8 GHz with a thickness of 5 mm, indicating that approximately 99.99% of the incident microwaves were absorbed. The special morphology of the columnar Nb 2 O 5 , the increased lamellar spacing of the Nb 2 CT x , and the optimized impedance matching characteristic are all important factors that contributed to the enhanced MA performance. • Controllable morphology regulation of Nb 2 O 5 was achieved through oxidation of Nb 2 CT x. • Nb 2 O 5 with a columnar structure could supply expanded spacing between Nb 2 CT x layers. • Impedance matching and multiple scattering were enhanced for Nb 2 O 5 /Nb 2 CT x composites. [ABSTRACT FROM AUTHOR]

• Magnetic CoFe 2 O 4 -decorated Ti 3 C 2 MXene were successfully prepared. • Tunable electromagnetic properties were observed in the CoFe 2 O 4 -Ti 3 C 2 MXene. • A broad effective bandwidth of 8.5 GHz was achieved. Ti 3 C 2 MXene has demonstrated to be a potential microwave absorber if some difficulties, e.g., poor impedance matching and lack of magnetic loss, can be well-solved. In this paper, laminated Ti 3 C 2 MXene was synthesized using the HF etching method. CoFe 2 O 4 nanoparticles-decorated Ti 3 C 2 MXene (CoFe 2 O 4 -Ti 3 C 2) composites were then fabricated via a novel in-situ solvothermal process. The incorporation of CoFe 2 O 4 nanoparticles on the electromagnetic (EM) and microwave absorption properties of Ti 3 C 2 MXene were systematically studied over 2–18 GHz. Interestingly, increased percolation threshold and controlled complex permittivity were well-observed in the CoFe 2 O 4 -Ti 3 C 2 composites. Furthermore, additional magnetic loss due to the existence of magnetic CoFe 2 O 4 was easily obtained. Benefiting from tunable electromagnetic properties, the minimum reflection loss (RL) value of the CoFe 2 O 4 -Ti 3 C 2 -filled absorbing coating achieved −30.9 dB with a matching thickness of only 1.5 mm. A wide effective absorption bandwidth (RL < −10 dB) of 8.5 GHz was correspondingly realized. These results demonstrated that the CoFe 2 O 4 -Ti 3 C 2 composites are favorable as a broadband microwave absorbent. [ABSTRACT FROM AUTHOR]