Abstract: Heterogeneous interfaces can significantly improve interface polarization loss, promote multiple reflections or scatter of incident electromagnetic waves; simultaneously, the mutual diffusion of constituent elements introduces interface states and defects, which results in the asymmetric localized electric field effect and dipole polarization effect, promoting electromagnetic wave (EW) absorption performance. Various cobalt sulfides (Co_xS_y) with heterogeneous interfaces formed by the variable stoichiometric ratios of cobalt and sulfide, producing high dielectric loss, which has received considerable attention in the microwave absorption (MA) field. Nevertheless, preparation of Co_xS_y EW absorbers with a broadened effective absorption bandwidth (EAB) is still a challenge. Herein, the heterophasic cobalt sulfide (CoS, Co₉S₈, Co₃S₄)/carbon nanospheres rich in heterogeneous interfaces were synthesized. Numerous heterogeneous interfaces in prepared composites enhanced the interfacial polarizability, which plays an important role in optimizing the electromagnetic parameters and absorption performance. An EAB value of 5.44 GHz at 1.8 mm, which essentially covers the entire Ku band, and an excellent minimum reflection loss (RL_min) of -62.68 dB at 2.8 mm was achieved. Furthermore, the dissipation capability of the absorber in practical applications was verified by radar scattering cross-sectional (RCS) simulation results. Besides, the high thermal insulation performance of the prepared composites was achieved, which proves its possible application under extreme conditions.

Key words: Heterophasic cobalt sulfide, Heterogeneous interfaces, Microwave absorption, Radar cross-sectional simulation, Thermal insulation