Doping strategy to boost electromagnetic property and gigahertz tunable electromagnetic attenuation of hetero-structured manganese dioxide

Abstract

A facile and simple chemical route has been used to synthesize novel three-dimensional (3D) architectures of nickel-doped ε-MnO₂ without the addition of any surfactant or organic template. Nickel salt is used directly as the reagent rather than as an additive to produce doped manganese dioxide, which is different from the overwhelming majority of previous synthetic methods for doped MnO₂ for use as an electromagnetic wave absorption material. This method overcomes the shortcomings of the previously reported approaches of doping with a slight amount of metallic ion, which is sometimes hard to detect. The chemical composition of the samples is analyzed by electron-probe micro-analysis (EPMA) and energy dispersive spectroscopy (EDS). The chemical state of the elements in the composites is demonstrated with X-ray photoelectron spectroscopy (XPS). The structures of the micro-spheres are detected by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the self-organized crystals are made up of walnut-like spheres and are arrays of polycrystals. The nickel ion is certified to have been successfully doped into the crystal based on the results of EPMA, EDS, and XPS as well as dark field scanning TEM. Thus, a multiple heterojunction structure is constructed. After nickel doping, the crystalline phase remains ε type and the morphology turns into a walnut-like structure. Electromagnetic performances also exhibit significant variation with the introduction of nickel ions. Nickel-doped MnO₂ has a decreased dielectric constant compared with that of commercial MnO₂, while the nickel-doped MnO₂ appears to have fascinating magnetic properties with a maximum magnetic loss tangent value of 0.37, which is 7 times greater than that of the dielectric loss tangent. Likewise, it is further presented that the optimized electromagnetic capacities are related to the mass fraction of the walnut-like MnO₂ spheres in the composite. When the mass fraction is as high as 50%, the magnetic loss tangent goes up with a distinct increase in mutations as well as in relaxation times and in the real part and the imaginary part of the relative complex permeability. Furthermore, the mechanisms of the highlighted electromagnetic attenuation are explored in detail.