Preparation and properties of aluminum-containing high-entropy spinel oxides in Co-Mn-Fe-Cr-Ni-Al-O system

Two quinary aluminum-containing spinel high-entropy oxides, (Co,Mn,Fe,Cr,Al) 3 O 4 (CMFCAO) and (Mn,Fe,Cr,Ni,Al) 3 O 4 (MFCNAO), together with one senary counterpart, (Co,Mn,Fe,Cr,Ni,Al) 3 O 4 (CMFCNAO), were synthesized from Co-Mn-Fe-Cr-Ni-Al-O system via solid-state reaction using in-situ formed flaky alumina as the aluminum source, and their infrared radiation and mechanical properties and thermal expansion coefficients were investigated. Compared with reactive micro-alumina and nano-alumina, the in-situ formed flaky alumina facilitated the formation of single-phase aluminum-containing spinel high-entropy oxides. Among the synthesized compositions, CMFCNAO exhibited the highest near-infrared emissivity (0.802), which is related with its relatively narrow bandgap (1.24 eV). Notably, the near-infrared emissivity of the synthesized spinel high-entropy oxides increased after high-temperature treatment, demonstrating their excellent thermal stability and potential for application as energy-saving materials in high-temperature furnaces. CMFCNAO also exhibited the higher hardness (989.0 HV) and compressive strength (139.3 MPa) than those of CMFCAO and MFCNAO, which can be attributed to the greater lattice distortion induced by higher configurational complexity. This work provides an effective strategy for the synthesis of aluminum-containing spinel HEOs and offers valuable insights into their infrared radiation and mechanical properties.