High-entropy Rare-earth Ferrite "Cool Pigments" with High Near-infrared Reflectance and Infrared Emissivity

The utilization of near-infrared (NIR) reflective pigments has been proven effective in mitigating the heat island effect induced by building surfaces and decreasing energy consumption from air conditioning. In this particular research, (Y_0.2Sm_0.2Eu_0.2Er_0.2Gd_0.2)₃Fe₅O₁₂ and (Y_0.2Sm_0.2Eu_0.2Er_0.2Bi_0.2)₃Fe₅O₁₂ high-entropy ceramic powders were synthesized using the sol-gel method. The pigments were subjected to characterization through X-ray diffraction (XRD), scanning electron microscopy (SEM), colorimeter, and UV-vis-NIR spectrophotometer analysis. The results exhibited a garnet-like structure and a porous network morphology for both (Y_0.2Sm_0.2Eu_0.2Er_0.2Gd_0.2)₃Fe₅O₁₂ and (Y_0.2Sm_0.2Eu_0.2Er_0.2Bi_0.2)₃Fe₅O₁₂. The samples displayed a yellow-green color and were found to possess exceptional acid and alkali resistance. Furthermore, the average near-infrared reflectance of the pigments within the 700 nm~2500 nm wavelength range exceeded 95%, while showcasing high emissivity in the 8 μm~14 μm wavelength range. As a result, it is anticipated that pigments fabricated utilizing this methodology will find valuable applications as " cool" pigments in coatings designed for building insulation and other related purposes.