Novel microwave dielectric response of Ni/Co-doped manganese dioxides and their microwave absorbing properties

Abstract

A facile redox reaction between KMnO₄ and MnSO₄ was carried out to investigate the dielectric response and microwave absorbing properties of Ni/Co-doped MnO₂. The samples were characterized by X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM), and vector network analysis. The analysis results revealed that the powders were α-MnO₂ with one-dimensional nanostructure. The doping of Ni/Co had a certain effect on the dielectric properties: the relative complex permittivity showed a more distinct dielectric response characteristic, and the imaginary part exhibited a great enhancement of 2–18 GHz, which resulted in controllable wave-absorbing properties. The microwave absorbing bandwidth (RL < −10 dB) for Co-doped MnO₂ was located at 10.96–16.13 GHz with a thickness of 2 mm. Furthermore, the Debye equation was introduced to explain the novel microwave dielectric response of doped MnO₂. Some other properties derived from dielectric performances were also investigated, such as dielectric loss tangent and dielectric conductivity. In particular, first-principles calculations based on density functional theory (DFT) were used to uncover the relationship of electronic structure and dielectric properties on the microscopic scale.