Fluffy microrods to heighten the microwave absorption properties through tuning the electronic state of Co/CoO

In this work, we fabricated unique fluffy Co/CoO micro-rod composites with various weight ratios between Co and CoO. The microwave absorption properties of the Co/CoO micro-rod composites were significantly affected by the Co content. With increasing Co content, due to the high conductive loss, the microwave absorption properties were improved, correspondingly. The fluffy Co/CoO micro-rod composite (Co57) prepared at 700 degrees C under nitrogen flow after its precursor was annealed at 500 degrees C exhibited outstanding microwave absorption properties. The optimal reflection loss (RL) was -21.7 dB with a thickness of 2.3 mm and the effective absorption bandwidth (RL is lower than -10 dB) can reach more than 6.1 GHz. In addition, the microwave absorption properties of paraffin/Co57 composites with different Co57 amounts were also investigated, and the paraffin-based composite containing 40 wt% Co57 shows excellent microwave absorption properties. Furthermore, density functional theory (DFT) calculations were used to evaluate the electronic structure of different Co/CoO composites to describe the microwave absorption variation. When the Co amount is gradually increased, the electrical conductivity is enhanced, affecting the dielectric properties of the products. Thus, the difference of the microwave absorbing properties of the experimentally obtained sample was explained from the viewpoint of the electronic structure. We paved a new avenue to use the electronic structure of absorbers to forecast the microwave absorption performance.