Electron Holography of Yolk–Shell Fe3O4@mSiO2 Microspheres for Use in Microwave Absorption

Yolk–shell nanostructures are very promising alternatives as next-generation microwave absorption materials. However, it still remains a great challenge to understand structure–property relationships and develop highly efficient yolk–shell structured microwave absorbers. Herein, a series of dielectric-magnetic yolk–shell Fe3O4@mesoporous SiO2 microspheres (denoted as Fe3O4@mSiO2) were synthesized by combining a modified Stober method and hydrothermal etching process. The microwave absorption performance of the Fe3O4@mSiO2 yolk–shell microspheres could be optimized by tuning the void space and shell number easily. By increasing the average diameter of the void space from 380 to 490 nm, the maximum reflection loss (RL) value of −38.7 dB at 8 GHz was achieved with a composite thickness of 2 mm, and the effective bandwidth (RL < −10 dB) was beyond 4 GHz. Compared with the single-shelled counterparts, the double-shelled Fe3O4@mSiO2 microspheres exhibited significantly enhanced absorption properties. Importantl...