Entropy-mediated defect engineering in spinel high entropy oxide / CNT composites for superior microwave absorption

Metal oxides, with their abundant polarization loss mechanisms and tunable microstructures, constitute a significant portion of electromagnetic wave absorption materials. Nevertheless, their high dielectric constant tends to cause strong surface reflection, posing a challenge in simultaneously achieving high loss capacity and favorable impedance matching. High-entropy oxides, leveraging their unique entropy effect, offer a new approach to reconcile this contradiction. In this study, a high-efficiency and straightforward microwave-assisted combustion method was employed to synthesize in-situ high-entropy absorbing materials composed of spinel-type transition metal oxides and carbon nanotubes (CNTs). Through the incorporation of a high mixing entropy design, a high-entropy oxide (HEO)/CNT composite (denoted as HECNT) absorbing system with abundant heterointerfaces and defect structures was successfully constructed. Entropy regulation not only facilitates the synergistic enhancement of multiple polarization mechanisms, encompassing defect polarization and interface/dipole polarization, but also effectively refines the impedance matching properties of the material. The HECNT composite material exhibits an exceptionally strong reflection loss (RL) of −69.9 dB with a mere 20 wt% filler content and a thin layer thickness of 1.6 mm, while effectively absorption bandwidth (EAB) of 3.76 GHz, thereby meeting the electromagnetic wave absorption demands of the C and X bands. The absorber system also has good high-temperature stability and corrosion resistance, which expands its weather resistance in complex application environments. This research achieves a harmonious balance between loss and impedance matching through a high-entropy strategy, offering a viable pathway for the advancement of high-performance, lightweight, and thin next-generation absorbing materials.