High entropy design enhances the high temperature infrared emissivity of La-based perovskite oxides

La-based perovskite oxides with configurational entropy increasing from low to high, namely LaMnO 3 , La(Mn 0.5 Fe 0.5 )O 3 , La(Mn 1/3 Fe 1/3 Co 1/3 )O 3 , La(Mn 0.25 Fe 0.25 Co 0.25 Ni 0.25 )O 3 , and La(Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )O 3 , were synthesized by a solid-state reaction method, and their phase evolution, microstructure, and infrared (IR) radiation properties were systematically investigated. X-ray diffraction and transmission electron microscopy reveal that increasing configurational entropy at the B-site induces a structural transformation from R-3c to Pm-3m and eventually back to a stabilized R-3c phase in the five-component system, accompanied by lattice distortion and suppressed elemental segregation. Room-temperature spectral emissivity measurements show that the R-3c phase exhibits superior IR emission compared to the Pm-3m phase in the 2-8 μm range. Notably, at elevated temperatures (600-900 °C), the emissivity of LMFCNCO increases with temperature, reaching 0.910 at 900 °C, while the binary oxide LaMnO 3 exhibits a marked decline. X-ray photoelectron spectroscopy indicates that the high entropy design promotes mixed-valence states of B-site cations and a high concentration of oxygen vacancies, which enhance small-polaron hopping and carrier absorption at high temperatures. This work demonstrates that entropy engineering is an effective strategy for tailoring the high temperature infrared radiation performance of perovskite ceramics, offering promising candidates for thermal management and energy conversion applications.