Hollow Zn<sub>1-x</sub>Co<sub>2-y</sub>Ni<sub>x</sub>Fe<sub>y</sub>O<sub>4</sub> spinel via multi-metal ion doping: ultralight and broadband microwave absorber

Hollow architectures offer significant advantages in achieving simultaneous weight reduction and efficient electromagnetic (EM) wave absorption; however, their practical application is often constrained by inherent structural limitations. In this study, Zn<sub>1-x</sub>Co<sub>2-y</sub>-Ni<sub>x</sub>Fe<sub>y</sub>O<sub>4</sub> composites were synthesized through an integrated self-sacrificing templating and ion-doping approach. Specifically, mixed zeolitic imidazolate frameworks (ZIFs) were utilized as sacrificial templates to fabricate hollow dodecahedral nanocages. Subsequent ion doping was facilitated by the chelating effect of tannic acid,…