Morphology-Controlled Synthesis And Microwave Electromagnetic Properties Of Novel MnO₂ Powder

Novel morphology-controlled MnO2 powder was synthesized via three simple methods, which were the synthesis under a high magnetic field, doping Fe and doping Fe under a high magnetic field. The synthesized samples were characterized by XRD, SEM, TEM, EPMA and vector network analysis.The morphology of MnO2 synthesized under a high magnetic field is sea urchin ball chain shape. And the permittivity and its loss tangent clearly decrease under a high magnetic field. The magnetic loss tangent and the imaginary part of the permeability increase substantially. With 0.5 mm,1 mm and 2 mm thickness, the sample 3 T performs the best reflection loss in 2-10 GHz. But in 10-18 GHz, the sample 5 T shows the best with 0.5 mm thickness, and the sample 0 T shows the best with 1 mm and 2 mm thickness.Fe-doped MnO2 have hollow sea urchin ball-like shape morphology. With doping Fe, the permittivity and its loss tangent clearly decrease, but the permeability and its loss tangent increase evidently. Due to doping Fe, the better magnetic property, the better absorption property in the low frequency is. With 0.5 mm and 1 mm thickness, the reflection loss of Fe-doped sample is markedly better than that of pure sample in 2-14 GHz, but in 14-18 GHz, the pure sample displays the better. For 2 mm, the reflection loss of Fe-doped sample is relatively better in 2-10 GHz, but in 10-18 GHz it is not as good as that in the low frequency.The morphology of Fe-doped MnO2 under a high magnetic field is hollow sea urchin ball-like chain shape. The variation of electromagnetic and reflection loss properties are similar to that without a high magnetic field. However, comparing to the sanmples without a high magnetic field, the dielectric loss tangent, magnetic loss tangent and reflection loss are enhanced evidently under a high magnetic field, mainly due to the interaction of the polarization loss (the chain anisotropy) and the electromagnetic wave loss with doping Fe.The calcination has an effect on MnO2 properties. When the calcination temperature is 500℃, a-MnO2 changes to Mn2O3 completely. Moreover, with increasing the calcination temperature properly (<500℃), the dielectric loss tangent, magnetic loss tangent and reflection loss can be improved effectively.