Modulating Magnetic/Dielectric Loss of Fe-Based Core-Shell Microspheres by Controlling Tetrabutyl Titanate Dosage for...

Optimizing loss components by phase engineering is crucial for enhancing the microwave absorption performance of magnetic core-dielectric shell composites. In this work, a series of core-shell structured composites (FTR) were elaborately synthesized by high-temperature hydrogen reduction of Fe₃O₄@TiO₂ precursors and the TiO₂ shell content was effectively regulated by varying the dosage of tetrabutyl titanate (TBOT). With the increase of TBOT dosage, the phase composition of FTR composites gradually evolves from Fe/Fe₂O₃@TiO₂ (FTR-2.0) to Fe@TiO₂ (FTR-2.5) and Fe@FeTiO₃/TiO₂ (FTR-3.0, FTR-3.5). FTR-2.5 has the highest Fe content (86.24 wt %) and saturation magnetization (141.7 emu·g^-1). Low TBOT dosage leads to TiO₂ cracks around the magnetic core after hydrogen reduction, but the remaining shell still encapsulates the magnetic core. In contrast, high TBOT dosage promotes the solid-state reaction between Fe and TiO₂ shells, generating thick and dense FeTiO₃ shells and abundant hollow spheres. Regarding loss components, FTR-2.5 is dominated by magnetic loss due to its highest metallic Fe content, whereas dielectric loss plays a more prominent role in other FTR composites. Notably, polarization loss prevails in the high-frequency range, including interfacial polarization at the heterogeneous interfaces among Fe, Fe₂O₃, TiO₂, and FeTiO₃ and dipole polarization enhanced by abundant oxygen vacancies. Benefiting from the synergistic effects of strong magnetic loss, enhanced multiple polarization, and a continuous impedance matching region, FTR-2.5 achieves a maximum effective absorption bandwidth of 5.92 GHz at a thickness of 1.95 mm. This work provides insights into the phase evolution mechanism of Fe₃O₄@TiO₂ during H₂ reduction and a reference for improving broadband microwave absorption.