Given its easy-to-tailor microstructure with mixed nanodomains including amorphous and pseudo-graphitic parts, hard carbon (HC) as a type of non-graphitizable carbon promises to play a role in extended selection for novel metal/carbon microwave absorbers. Herein, we report the preparation of FeCoNi@HC composites as electromagnetic (EM) absorbers at different pyrolysis-controlled temperatures, derived from FeCoNi nanosheets (NSs)@polyimide (PI) composites. According to suitable pyrolysis treatments, FeCoNi@HC composites exhibit a wide range of mixed morphologies constituted of nanosheets and nanoparticles: original FeCoNi NSs are thermally converted into a particle-like structure as the core; the HC derived from the polyimide (PI) matrix inherits the original framework of the FeCoNi NSs for varying degrees of pyrolysis as the shell. The heat treatments also strongly influence the inner HC structural properties, including defect feature and graphitization degree. Treated by a moderate degree of pyrolysis, the optimal sample achieves decent enhancements of lossy attenuations (e.g., dielectric/magnetic losses) and promoted impedance matching for excellent EM absorption performances. The minimum reflection loss (RL) of the optimal sample is −61.12 dB, along with an effective absorption bandwidth (RL ≤ −10 dB) of 5.53 GHz. We anticipate that this work may enrich the survey of metals/carbon absorbers with non-graphitizable carbon supports.

中文翻译：

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热解控制的 FeCoNi@硬碳复合材料具有促进阻抗匹配的强电磁波响应

鉴于其具有混合纳米域（包括无定形和假石墨部分）的易于定制的微观结构，硬碳（HC）作为一种不可石墨化的碳有望在新型金属/碳微波吸收剂的扩展选择中发挥作用。在此，我们报告了 FeCoNi@HC 复合材料在不同热解控制温度下作为电磁 (EM) 吸收剂的制备，源自 FeCoNi 纳米片 (NSs)@聚酰亚胺 (PI) 复合材料。根据合适的热解处理，FeCoNi@HC复合材料呈现出由纳米片和纳米颗粒构成的广泛混合形态：原始的FeCoNi NSs被热转化为以颗粒状结构为核心；源自聚酰亚胺 (PI) 基体的 HC 继承了 FeCoNi NSs 的原始框架，用于不同程度的热解作为壳。热处理也强烈影响内部 HC 结构特性，包括缺陷特征和石墨化程度。通过中等程度的热解处理，最佳样品实现了有损衰减的适当增强（例如，介电/磁损耗）并促进阻抗匹配以获得出色的 EM 吸收性能。最佳样品的最小反射损耗 (RL) 为 −61.12 dB，有效吸收带宽 (RL ≤ −10 dB) 为 5.53 GHz。我们预计这项工作可能会丰富对具有不可石墨化碳载体的金属/碳吸收剂的调查。