Influence of pyrolysis temperature on the low-frequency microwave absorption properties of carbon encapsulated nickel/nickel oxide composites

Owing to the urgent need of microwave absorbers in low-frequency range, herein, the core–shell nickel/nickel oxide@carbon nanocomposites with ideal low-frequency absorbing properties were fabricated via a simple solvothermal and pyrolysis approach. The Ni and NiO nanoparticles were wrapped by outer carbon shell, providing abundant defects and interfaces, which is helpful to the dipole and interfacial polarizations. Besides, the conduction loss of the carbon shell and Ni nanoparticles, magnetic losses induced by Ni nanoparticles, core–shell porous structure and proper impedance matching regulated by calcining process could accelerate the absorption of microwave. Importantly, these factors are all strongly influenced by the pyrolysis temperature, and the composite treated under 500 °C shows the maximum reflection loss of − 34.13 dB at 0.85 GHz when the thickness is 3.0 mm, also the broadest effective frequency bandwidth in low frequency range can reach 1.65 GHz at 2.0 mm. Thus, this calcination temperature depended core–shell nickel/nickel oxide@carbon composite provides a feasible way to design absorbers with high performance and thin thickness in low-frequency bands.