Constructing magnetic/dielectric dual loss and phonon/electron thermal carriers γ-AlO-based yolk-shell microspheres to collaboratively advance microwave absorption and heat conduction.

The severe electromagnetic (EM) interference and overheating issues in 5G/6G electric devices increasingly heighten the need for developing multifunctional materials with large heat conduction (HC) and high EM wave (EMW) absorption. Here, a series of γ-AlO-based yolk-shell microspheres (γ-AlOOH, γ-AlO, γ-AlO@C, γ-AlO@FeO@C, and γ-AlO@FeAlO@Fe@C YSMSs) as multifunctional fillers are investigated for the simultaneous improvement in the HC and EMW absorption of γ-AlO-based composites. Using γ-AlOOH YSMSs as precursors produced from a hydrothermal method, the γ-AlO-based YSMSs were synthesized an annealing route or soaking-annealing route; their phases, textures, and compositions were finely adjusted by changing the Al/Fe molar ratio () and annealing temperature (). Results show that the thermal transfers in the γ-AlO-based YSMSs are promoted by the synergic effect of phonons and electrons when they are utilized as thermally conductive fillers. Comparatively, the γ-AlO@FeAlO@Fe@C YSMSs formed at = 8 : 2 and = 700 °C exhibit a high HC of 1.84-3.29 W m K in a loading amount of 5-40%, exceeding those of not merely γ-AlO, γ-AlOOH, γ-AlO@C, and γ-AlO@FeO@C YSMSs but also most previously reported fillers. Furthermore, the γ-AlO@FeO@C YSMSs exhibit prominent EMW absorption properties with a large ABW/ of 4.49 GHz mm (just 30% loading), superior to most other AlO-based absorbers. Such excellent EMW absorption could be explained by magnetic/dielectric dual loss and significant cavity and interfacial effects caused by yolk-shell structures. In conclusion, this work inspires the development of yolk-shell structures with magnetic/dielectric dual loss and phonon/electron thermal carriers as high-performance bifunctional materials with exceptional heat conduction and EMW absorption.