Fe-Doped MnO 2 Nanostructures for Attenuation–Impedance Balance-Boosted Microwave Absorption

The attenuation–impedance property plays the key role in the microwave absorption process. In this work, the phenomenon of Fe inducing the gradient phase and morphology transition of MnO 2 has been well explored. As the Fe doping content increases, the phase evolution from δ-MnO 2 to α-MnO 2 and the morphology transition from nanosheets to nanowires occur. Based on this, the multiphase MnO 2 nanostructures composed by δ-MnO 2 nanosheets and α-MnO 2 nanowires are controllably synthesized, in which the former has a high impedance matching characteristic and the latter owns an excellent attenuation ability. By adjusting the Fe 3+ doping content, the multiphase MnO 2 can realize the balance between attenuation and impedance. When the doping ratio (Fe/Mn) is 7.14 mol %, in the frequency range of 2–18 GHz, the attenuation coefficient of the MnO 2 composite is 14.77–194.35, the intrinsic impedance coefficient is 0.29–0.40, and the effective absorption bandwidth (reflection loss < −10 dB) can reach 5.44 GHz when the thickness of the absorbing layer is only 2 mm. This work provides an effective method for designing broadband microwave absorption materials.