Rare-Earth Oxide–Induced interfacial Engineering for tailoring dielectric response in NiCo₂O₄/CeO₂ composites toward high-performance Electromagnetic wave absorbers

Comprehensively understanding the role of interfacial engineering in tailoring dielectric response is essential for the development of next-generation electromagnetic wave (EMW) absorbers. Rare-earth oxides, with their flexible valence states and localized 4f orbitals, hold great potential to mediate interfacial charge transfer and polarization, yet the electromagnetic loss mechanisms underlying such effects remain unclear. Here, we demonstrate a rare-earth oxide–regulated interfacial engineering strategy, where the incorporation of CeO₂ into NiCo₂O₄ constructs abundant heterointerfaces with dynamic valence states. Such CeO₂-induced interfacial polarization markedly strengthens dielectric response and facilitates impedance matching, thereby surpassing the limitations of single-phase components. Dielectric analysis reveals that polarization loss dominates (>88 %) within the absorption band, while conduction loss plays a secondary role. The results show that interfacial charge redistribution driven by Ce³⁺/Ce⁴⁺ redox flexibility, which creates abundant interfacial polarization centers and enhances relaxation. As a result, the optimized NiCo₂O₄/CeO₂–T3 delivers outstanding EMW absorption, achieving a broad effective absorption bandwidth of 6.37 GHz at 2.00 mm and reflection loss of −60.09 dB at 2.20 mm (>99.99 % attenuation). This study establishes rare-earth oxide–enabled interfacial engineering as a powerful paradigm for amplifying interfacial polarization and guides the rational design of high-performance, lightweight EMW absorbers.