To obtain an excellent electromagnetic wave (EMW) absorption material, a strategy was proposed in this study with the aid of in-situ growth of carbon nanotubes (CNTs) on the surface of a metal–organic framework (MOF)-derived FeCoNiMnMg high-entropy alloy (HEA). The HEA@CNT composite was successfully prepared via a solvothermal method combined with a one-step pyrolysis process. With the pyrolysis temperature increasing from 600 °C to 800 °C, the length of CNTs grew from 200 nm to about 600 nm approximately, while the defect density of CNTs was enhanced. This structural evolution significantly improved the dielectric properties and impedance matching. Consequently, the sample prepared at 800 °C (HEA@CNT-800) exhibited outstanding microwave absorption performances, achieving a minimum reflection loss (RL_min) of −57.52 dB at a matched thickness of 2.3 mm and an effective absorption bandwidth (EAB) of 4.4 GHz at a thinner thickness of 1.9 mm. This work provides a novel perspective for designing high-performance MOF-derived absorption materials.

In this study, the core–shell structured BaCe _0.8 Gd _0.2 O _{3− δ} @Ce _0.8 Gd _0.2 O _{2− δ} (BCG@GDC) powders were synthesized by co-precipitation method, and the corresponding core–shell BCG@GDC ceramics were prepared through conventional sintering at 1400 °C, 1500 °C and 1600 °C. XRD and SEM analyses confirm that the synthesized BCG@GDC powders and ceramics are only composed of BCG and GDC phases. A TEM analysis on the BCG@GDC powders demonstrates that a layer of GDC shell with a thickness of about 9.4 nm is wrapped on the surface of BCG core with an average size of 49 nm. Compared with core–shell structured Ce _0.8 Gd _0.2 O _{2− δ} @BaCe _0.8 Gd _0.2 O _{3− δ} (GDC@BCG) ceramics, in which the BCG phase is wrapped by GDC phase, the relative density of BCG@GDC ceramics sintered at 1600 °C in this study rises by 4%. This leads to an enhancement of the electrical conductivity of BCG@GDC (1.9 × 10 ⁻² S cm ⁻¹ at 600 °C in air), significantly higher than that of GDC@BCG (1.0 × 10 ⁻² S cm ⁻¹ at 600 °C in air). The rise in sintering temperatures can contribute to the improvement of the relative density as well as the electrical conductivity of the core–shell structured BCG@GDC ceramics.