Strain-induced defects suppress conductivity to enhance microwave absorption in high-entropy hollow microspheres

Carbon-based materials are extensively utilized for electromagnetic wave (EMW) absorption due to their low density and high stability. However, their absorption capacity is often hindered by impedance mismatch originating from high intrinsic conductivity. Here, we synthesize high-entropy carbide nanoparticles with in-situ growth on hollow carbon spheres (HECs@HCSs) to form core-shell composites via entropy engineering. The results show that the high configurational entropy in the carbides leads to an expansion of the HEC lattice constant from 4.309 Å to 4.401 Å, yielding a great lattice strain from 3.55% to 13.45%. The atomic-scale strain field promotes defect formation and suppresses the long-range ordering of the carbon matrix, leading to the disruption of the conductive carbon network. Together with enhanced carrier scattering and interfacial transport barriers, the electrical conductivity decreases from 20.46 S/m to 0.27 S/m. As a result, the HECs@HCSs composites exhibit outstanding microwave absorption with an effective absorption bandwidth of 7.24 GHz at 1.81 mm and a minimum reflection loss of -45.28 dB at 1.89 mm. Furthermore, radar cross-section simulations demonstrate that the HEC5 coating reduces the monostatic RCS by 18.85 dB·m² relative to the bare PEC plate at normal incidence, confirming its excellent radar stealth capability. The superior EMW absorption properties are attributed to the enhanced impedance matching and the mechanistic transition from conduction loss to polarization relaxation. This work provides novel design insights and theoretical criteria for developing lightweight, wideband, and high-efficiency EMW absorbing protection materials.