High-entropy rare-earth hexaborides with high infrared emissivity for high-temperature thermal management

Infrared radiative materials are pivotal for thermal management in aerospace, industrial furnaces, and refractory linings, yet conventional ceramics often struggle to combine high infrared emissivity with high melting temperature. This work employs a high-entropy strategy to tailor the properties of hexaborides. Compared to LaB 6 , the designed high-entropy hexaborides (Sr 0.2 La 0.2 Ce 0.2 Eu 0.2 Yb 0.2 )B 6 and (Ba 0.2 La 0.2 Pr 0.2 Eu 0.2 Dy 0.2 )B 6 exhibit a significant increase in the infrared emissivity (from 81.40% to 83.82% and 85.49% over 1.28–25 μm respectively). Both samples exhibit a dramatic decrease in the electrical conductivity (11501.5 and 13016.3 S cm −1 respectively), approximately an order of magnitude lower than that of LaB 6 (112359.6 S cm −1 ). The pronounced lattice distortion intensifies electron scattering, which lowers both electrical conductivity and electronic thermal conductivity. The accompanying reduction in the relaxation time further alters the intraband dielectric function. These combined effects synergistically enhance the infrared emissivity of the hexaborides. The study thus demonstrates a novel and effective approach for designing advanced thermal management materials.