Defect Induced Polarization Loss in Multi‐Shelled Spinel Hollow Spheres for Electromagnetic Wave Absorption Application

Defect engineering is an effective approach to manipulate electromagnetic (EM) parameters and enhance absorption ability, but defect induced dielectric loss dominant mechanism has not been completely clarified. Here the defect induced dielectric loss dominant mechanism in virtue of multi-shelled spinel hollow sphere for the first time is demonstrated. The unique but identical morphology design as well as suitable composition modulation for serial spinels can exclude the disturbance of EM wave dissipation from dipolar/interfacial polarization and conduction loss. In temperature-regulated defect in NiCo₂O₄ serial materials, two kinds of defects, defect in spinel structure and oxygen vacancy are detected. Defect in spinel structure played more profound role on determining materials' EM wave dissipation than that of oxygen vacancy. When evaluated serial Co-based materials as absorbers, defect induced polarization loss is responsible for the superior absorption performance of NiCo₂O₄-based material due to its more defect sites in spinel structure. It is discovered that electron spin resonance test may be adopted as a novel approach to directly probe EM wave absorption capacities of materials. This work not only provides a strategy to prepare lightweight, efficient EM wave absorber but also illustrates the importance of defect engineering on regulation of materials' dielectric loss capacity.