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[Display omitted] • Controlling the load of Co-CoFe 2 O 4 can receive exceptional impedance matching. • The minimum reflection loss is −65.31 dB at 2.1 mm. • The maximum effective absorption bandwidth is 8.48 GHz at 2.4 mm. Carbon nanomaterials have attracted a great deal of attention in various fields especially in electromagnetic wave absorption due to unique physical and chemical properties. Herein, a novel Co-CoFe 2 O 4 @mesoporous hollow carbon spheres (PCHMs) nanocomposites were prepared by two-facile steps, which included synthesizing three-dimensional mesoporous hollow carbon nanospheres (3D PCHMs) by hard template method, pyrolysis and etching process and in-situ growth of ultra-small Co-CoFe 2 O 4 nanoparticles on PCHMs. The microscopic morphology and electromagnetic wave absorption mechanisms were discussed in depth. The synthesized Co-CoFe 2 O 4 @PCHMs maintained a stable hollow and mesoporous structure and the Co-CoFe 2 O 4 nanoparticles are uniformly distributed on the PCHMs. The complex permittivity and complex permeability could be effortlessly controlled by the content of Co-CoFe 2 O 4 nanoparticles. Benefitting from the remarkable impedance matching under the influence of moderate complex permittivity and complex permeability, the minimum reflection loss (RL min) of S2 exhibited −65.31 dB at 2.1 mm. The maximum effective absorption bandwidth (EAB) reached up to 8.48 GHz. The Co-CoFe 2 O 4 @PCHMs nanocomposites will have great potential application in electromagnetic wave absorption. [ABSTRACT FROM AUTHOR]

[Display omitted] • The 2D MXene-based accordion-like hybrid structure was obtained. • Controlling the addition of Ti 3 C 2 T x can effectively control the dielectric parameters. • The effective bandwidth is up to 4.24 GHz with a matched thickness of 1.5 mm. Owing to their unique structure and high dielectric loss, two-dimensional transition metal carbides and nitrides (MXenes) are widely used in electromagnetic wave absorption. The novel Co 9 S 8 /C/Ti 3 C 2 T x hybrid material with a multilayer structure was successfully fabricated by hydrothermal and annealing processes. The unique multilayered hybrid material is assembled from Ti 3 C 2 T x film layers, Co 9 S 8 particles, and carbon flakes. The Co 9 S 8 particles were uniformly anchored on Ti 3 C 2 T x and carbon flakes. The Co 9 S 8 /C/Ti 3 C 2 T x -100 hybrid material has demonstrated impressive electromagnetic absorption performance after the multi-component introduction and interface design were optimized. Besides, the hybrid material exhibits the maximum reflection loss of −50.07 dB at 7.6 GHz under a matched thickness of 2.51 mm, and the effective absorption bandwidth (RL ≤ -10 dB) is covered 4.24 GHz. The synergistic effect of dielectric and magnetic loss, interfacial polarization, and multilayer structure was beneficial to the improvement of electromagnetic wave absorption performance. This research provides a simple demonstration of the design and synthesis of high-performance MXenes-based absorbing materials. [ABSTRACT FROM AUTHOR]

• Ruddlesden-Popper type polycrystals La 3 Ni 2 O 7 /LaNiO 3 and La 2 NiO 4 /La 2 O 3 were synthesized. • The structural and electromagnetic properties were analyzed. • The interstitial O2– and V O in polycrystals were studied based on XPS and XRD. • The RL of La 3 Ni 2 O 7 /LaNiO 3 and La 2 NiO 4 /La 2 O 3 reached –22.63 and −50.06 dB in S-band. Given the remarkable performances of Ruddlesden-Popper (RP) type oxides in electronic devices, the study of their intrinsic dielectric, magnetic and electromagnetic microwave (EMW) absorption properties are still missing. Herein, two kinds of Lead-free relaxor-ferroelectric BNT-based ceramic hierarchical polycrystalline alloys (La 3 Ni 2 O 7 /LaNiO 3 , La 2 NiO 4 /La 2 O 3) were prepared via a facile solvothermal and high-temperature annealing technique as high-performance EMW absorption materials (MAMs). By a means of adjustment of solvothermal time in the precursor systems, Nickel salt layers precipitation declined gradually. The phase and crystal state of the powders were characterized by X-ray diffraction (XRD) with refinement treatment (Rietveld analysis). XPS was utilized on the determination of interstitial O2– quantitatively in La 3 Ni 2 O 7+δ (δ = 1.95) and La 2 NiO 4+δ (δ = 0.75). Responsible to the synergistic effect of dielectric and magnetic response and well-matched impedance, the as-fabricated MAMs performed excellent wave absorbability, especially in low frequency (S-band). In details, La 3 Ni 2 O 7 /LaNiO 3 achieved optimal effective absorption band (f E) 3.36 GHz at 9.52–12.80 GHz and a minimum reflection loss (RL min) −43.30 dB with a thickness of 2.2 mm. Moreover, La 3 Ni 2 O 7 /LaNiO 3 and La 2 NiO 4 /La 2 O 3 overcame the challenge of absorbers' thickness in S-band, of which the RL reached –22.63 and −29.90 dB at 0.7 mm, respectively. Noteworthily, La 3 Ni 2 O 7 /LaNiO 3 obtained RL value of −50.06 dB at 10.72 GHz with a device thickness of 2.8 mm. It is emphasized that this report has interpreted the EMW absorption capacity and mechanism exhaustively, which will initiate simultaneous enhancement of recoverable energy density and efficiency application of RPs. [ABSTRACT FROM AUTHOR]