Entropy‐Driven Multiphase Engineering Enables Superior Broadband Infrared Emissivity in High‐Entropy Oxides

Efficient infrared (IR) thermal management is crucial for advanced industrial and aerospace heat management. However, achieving stable, broadband emissivity across 0.78-16 µm, particularly at high temperatures, remains challenging. Herein, an entropy-driven phase-engineering strategy is presented that enables synergistic enhancement of broadband IR emissivity in high-entropy spinel oxides. By systematically tuning La doping, controlled coexistence of three intimately coupled crystalline phases is achieved. Multi-scale structural and atomic-level analyses reveal dense phase boundaries, abundant defects, and pronounced lattice strains, which together induce bandgap narrowing and facilitate efficient free carrier transitions in the short-wavelength IR regime. Simultaneously, the intricate network of phase interfaces and local lattice disorders intensifies phonon vibrations, resulting in enhanced lattice vibration absorption in the mid-to-long wavelength region. Consequently, the multiphase oxide achieves a robust emissivity of 0.91 across 0.78-16 µm and retains high performance after prolonged exposure to 900 °C. When applied as coatings, even higher emissivity (up to 0.95) and excellent mechanical durability are achieved. Compared to state-of-the-art emitters, these entropy-stabilized ceramics uniquely integrate broadband high emissivity, thermal stability, and mechanical robustness. The findings provide fundamental insights into entropy-enabled multiphase synergy and establish a framework for next-generation radiative thermal management materials in extreme environments.