Electrically insulated C@MnxOy foams with engineered defects and heterointerfaces toward superior microwave absorption, Radar wave stealth, and thermal dissipation

To address the severe electromagnetic (EM) pollution and thermal exhaustion issues in modern electronics, C@Mn_xO_y foams were first reported as an advanced multifunctional filler with superior microwave absorption, Radar wave stealth, and thermal dissipation. They were synthesized using a simple one-step annealing route, in which PVP and in-situ generated gas bubbles play a crucial role in the foam formation. Our results show that the C@Mn_xO_y foams possess excellent electrical insulation and a large thermal conductivity of 3.58 W (m K)^–1 at a low load of 5 wt.%. Also, they exhibit prominent microwave absorption capabilities (MWACs) with a strong absorption (–46.03 dB) and a wide bandwidth (11.04 GHz) in a low load (30 wt.%). When they are then used as a patch, the wideband Radar cross-section can be effectively reduced by up to 41.34 dB m². This performance outperforms most other heterostructures. Furthermore, the mechanism of dielectric loss and thermal transfer at the atomic level is revealed by the First-principle calculations of the density of states (DOS) and the phonon density of states (PDOS). The combination of C, MnO, and Mn₃O₄ disrupts local microstructure symmetry and induces extra electrical dipoles at the heterointerfaces, benefiting the enhanced MWACs of C@Mn_xO_y foams along with defect polarization and multiple scattering. Their enhanced TC could be credited to the co-transmission of low phonon-boundary/phonon-defect scattering and multiple-frequency phonons from C, MnO, and Mn₃O₄. Overall, the C@Mn_xO_y foams are highly promising for application in EM protection, absorption, and thermal management. What is more, this study provides a theoretical guide for designing heterostructures as effective microwave absorbing and thermally conductive materials used in modern electronics.