Study Of Synthesis And Microwave Electromagnetic Property Of Ni-doped And Cube-shaped MnO₂

To further study the effects of the doping Ni on the microwave electromagnetic property, Ni-doped MnO2 with different doping amount was prepared among (NH4)2S2O8, MnSO4 and NiSO4 by hydrothermal synthesis methods. Besides, under hydrothermal conditions, cube-shaped β-MnO2 was preared through redox reaction between MnCl2 and KClO3. The phase structure, morphology, chemical composition and electromagnetic properties were characterized by X-ray diffraction diffractometer (XRD), X-ray fluorescence spectrometry (XRF), scanning electron microscope (SEM), transmission electron microscope (TEM) and vector network analyzer. Moreover, first-principles calculation was employed to study the electronic density of state, electromagnetic properties of α-MnO2 with craystal defects.Results showed that the Ni-doped MnO2 with different morphology was prepared by hydrothermal synthesis method, including urchin-shaped spheres and hollow structure. The crystal type of products were all the mixture of α-MnO2 and γ-MnO2, which were not affected by the Ni doping amount. When the reaction temperature was higher than 120 ℃, the product became a single phase of α-MnO2. With the increase of Ni doping amount, the morphology changed from regular urchin-shaped spheres to flocculent shape; with the increase of temperature, the morphology changed from regular urchin-shaped spheres to hollow spheres. Manganese dioxide is a dielectric loss type of electromagnetic wave absorbtion materials. The peak of reflection loss curve peak moved towards the high frequency gradually with the increase of doping amount, and moved in the direction of low frequency with the increase of the thickness of the absorbing body. Besides, in high frequency range, Ni-doped samples had a better reflection loss performance.The theoretical calculation results of the manganese dioxide mode with different defects showed that the introduction of crystal defects made the displacement relaxation of surrounding atomic happened, which was helpful for magnetic loss. The presence of the new defect mode with the introduction of crystal defects made the relaxation polarization occurs, resulting in enhance of the dielectric loss ability of the material. Moreover, the bond strength and covalency of Mn-O were weakened because of crystal defects, which meaned that the dielectric loss of material is improved.A novel morphology of microncube with rectangular pyramid of β-MnO2 was synthesized via a simple aqueous chemical route between MnCl2 and KClO3 for the first time under hydrothermal conditions without any templates. When the reaction temperature was 180 ℃, with the extension of reaction time, the crystal type changed from γ-MnO2 to β-MnO2 and the morphology changed from an urchin-like shape to a microncube with rectangular pyramid, which can be explained by the "intrinsic crystal structural growth" mechanism. With the increase of reaction time, the real part and imaginary part of complex permittivity were increased and decreased, respectively, and the dielectric loss tangent value significantly decreased, and with the increase of reaction tempreture, the complex permittivity and the dielectric loss tangent value were both decreased. In addition, the manganese dioxide with urchin-shaped spheres had better performance of reflection loss. Overall, the results showed that the morphology of manganese dioxide has great influence on the electromagnetic properties.