Dielectric Polarization Mode Evolution-Induced Band-Tunable Microwave Absorption of Hollow Ni/C Microtubes

1D hollow Ni/C microtubes with tunable carbon shell coating were fabricated through a three-step method with carbon fiber templating, polydopamine coating and carbothermal reduction. The competitive behavior between NiO reduction and Ni-catalyzed graphitization dominates the evolution of carbon structure and interface state. Adjusting dopamine content achieves the dielectric polarization mode evolution from NiO/Ni Schottky junction to Ni/C interfacial and intrinsic dipole polarization, realizing band-tunable microwave absorption. With favorable modulation of the carbon shell, the absorber thickness required for efficient absorption declines substantially, while the absorbing bands shift from the X-Ku boundary toward high-frequency Ku and low-frequency S-C band. NC-3 with the thickest carbon coating delivers the strongest absorption of −49.58 dB at merely 1 mm, and its absorbing band can also be tuned to the S band at 6.6 mm. This work offers a concise interfacial strategy for lightweight and band-tunable microwave absorbers.