Structure and phase engineering afforded gradient manganese dioxide composites for impedance matching toward electromagnetic wave absorption.

Impedance mismatch severely limits the performance of electromagnetic (EM) microwave absorber materials. Aiming at addressing this issue, this study proposes a strategy combining structure and phase engineering to design gradient manganese dioxide (MnO) core@shell composites. The core of the composites comprises cadmium (Cd)-doped α-MnO nanowires, synthesized via a self-assembly process achieved using the hydrothermal method, which possess remarkable dielectric attenuation capability that can effectively consume EM energy. The shell comprised α-MnO nanosheets, which serve as a matching layer and introduce interfaces and defects that further enhance EM energy attenuation; notably, these α-MnO nanosheets are formed through calcination-induced phase transition of δ-MnO nanosheets grown on the core nanowire surface. The uniform growth of nanosheets on nanowires is facilitated by the low lattice mismatch between α-MnO and δ-MnO. The resulting Cd-doped α-MnO nanowire@α-MnO nanosheet composites deliver remarkable absorption performance; the minimum reflection loss can reach - 50.50 dB and effective absorption bandwidth reaches 5.44 GHz in the Ku band, which are attributed to optimized synergy between attenuation and impedance matching, dipole polarization enhancement through heteroatom doping, and interfacial polarization at the core-shell interface. This study provides a novel approach to designing advanced EM absorption materials.