Facile synthesis of hierarchical chrysanthemum-like copper cobaltate-copper oxide composites for enhanced microwave absorption performance

Hierarchical chrysanthemum-like CuCo₂O₄-CuO composites were successfully synthesized by a facile one-pot hydrothermal method after calcination at 500 °C. Based on the results of X-ray diffraction (XRD), Raman spectra, thermogravimetric analysis (TGA) and transmission electron microscope (TEM), we found that not only the morphology (from 2 dimensional to 3 dimensional) but also the crystalline structure (Cu⁰ + Cu₂O + CoO_x → CuO + CuCo₂O₄) of the samples could be tuned by the calcination temperature. The existed interfaces of CuCo₂O₄-CuCo₂O₄, CuCo₂O₄-CuO, and CuO-CuO played a key role on the attenuation of electromagnetic waves. The effective absorption frequency bandwidth is up to 4.02 GHz with a matched thickness of 2.8 mm. The CuCo₂O₄-CuO/paraffin composites can even exhibit bigger effective frequency bandwidth (from 4.02 to 4.65 GHz) if we turn the incident angle of electromagnetic (EM) wave to a proper value (i.e., 45°). We believe that the hierarchical chrysanthemum-like CuCo₂O₄-CuO composites can be a good candidate for the high-performance Co-based spinel microwave absorbers.