Fe@C nanocapsules with substitutional sulfur heteroatoms in graphitic shells for improving microwave absorption at gigahertz frequencies

Microwave absorption materials are usually designed to integrate multiple heterogeneous components containing magnetic and dielectric loss abilities, solving the electromagnetic impedance matching. We herein report a simple strategy to further improve the dielectric loss capacity of magnetic/dielectric-composed Fe@C nanocapsules absorbents by incorporating substitutional sulfur atoms into highly defective graphitic shells. Moreover, by optimizing the sulfur contents, the microwave absorption efficiency could be effectively adjusted. Experimental results coupled with the theoretical calculations evidence that the dielectric enhancement is originated from the atomic-scale symmetry breaking at the sulfur-substituted sites, resulting in the charge separation of localized microstructures. The present work has important implications in understanding the structural origin of electromagnetic phenomena, and meanwhile could be widely extended to exploit high-performance carbon-based microwave absorbents. [Display omitted]