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.