Formation, thermal stability, and infrared radiation properties of spinel-structured high-entropy oxides in Co–Mn–Fe–Cr–Ni–Zn–O system

Using a simple and scalable solid-state synthesis process, a series of spinel-structured high-entropy oxides were systematically designed and synthesized in a Co–Mn–Fe–Cr–Ni–Zn–O system. These included (Co,Mn,Fe,Cr)3O4, (Co,Mn,Fe,Ni)3O4, (Co,Mn,Fe,Cr,Ni)3O4, (Co,Mn,Fe,Zn)3O4, (Co,Mn,Fe,Cr,Zn)3O4, (Co,Mn,Fe,Ni,Zn)3O4 and (Co,Mn,Fe,Cr,Ni,Zn)3O4. The phase, microstructure and color evolution of 1/3Co3O4–1MnO-1/2Fe2O3-1/2Cr2O3–1NiO powders were studied without ZnO addition. These underwent four phase evolution processes and three color evolution processes before forming the final phase of black, octahedral (Co,Mn,Fe,Cr,Ni)3O4 powders. The formation of an intermediate phase of (Co,Mn,Fe)3O4 medium-entropy oxide powders served as the foundation for the creation of other high-entropy oxide powders. The infrared radiation properties of these synthesized medium and high-entropy oxides powders were evaluated in the near-infrared region at room temperature. Among these synthesized powders, the infrared emissivity values of (Co,Mn,Fe)3O4, (Co,Mn,Fe,Ni)3O4 and (Co,Mn,Fe,Cr,Ni)3O4 powders exceeded 0.8. All the synthesized powders exhibited excellent thermal stability after being annealed at high temperatures. Notably, after being annealed at high temperatures, the infrared emissivity values of these synthesized powders increased markedly without degradation, surpassing a value of 0.8, and displayed potential for applications in the field of high-temperature infrared energy savings.