Ultrahigh concentration surface oxygen vacancies in ferrite foams for broadened electromagnetic absorption bandwidth

Currently, the absorbing bandwidth of the Ferrites is enormously limited at X-band and Ku-band by the poor intrinsic dielectric properties. Thus, there are few reports about the pure Ferrites' application at 8-18 GHz. In this paper, the Ferrites composite foams (NFC) with a high surficial oxygen vacancy concentration (48.1%) were prepared by the NH4NO3 assisted solution-combustion strategy and solid phase sintering. Noteworthily, the concentration of surficial oxygen vacancy can be effectively regulated by the NH4NO3. This is facilitated to achieve balanced impedance matching. Therefore, the effective absorption bandwidth (EAB) of the NFC covered the whole X-band and Ku-band. Conduction loss and defect polarization relaxation realized by surficial oxygen vacancies were confirmed to be the key to such wide EAB for the NFC at 8-18 GHz. This work explores the important role of surficial oxygen vacancy engineering in regulating the dielectric parameters of the Ferrites, and provides a feasible strategy of surficial oxygen vacancy engineering for wide EAB electromagnetic performance at the high-frequency.