Revealing Site Selectivity and Clustering in the Compositionally Complex (Cr,Mn,Fe,Mg,Ni)₃O₄

Area of Science:

• Materials Science
• Solid-State Chemistry
• Nanotechnology

Background:

• High-entropy oxides with cubic spinel structures are multifunctional materials with tunable properties.
• These materials show promise in catalysis and Li-ion battery anodes.
• Understanding cation distribution is key to optimizing their performance but is challenging due to compositional complexity.

Purpose of the Study:

• To determine the cation distribution in the Co-free (Cr,Mn,Fe,Mg,Ni)3O4 high-entropy oxide.
• To demonstrate the utility of resonant X-ray diffraction (ReXRD) for this purpose.
• To correlate cation distribution with atomic and electronic structures.

Main Methods:

• Resonant X-ray Diffraction (ReXRD) was employed to probe cation site occupancy.
• X-ray absorption spectroscopy and neutron total scattering were used to investigate local structures and cation clustering.

Main Results:

• ReXRD revealed significant cation site selectivity in (Cr,Mn,Fe,Mg,Ni)3O4.
• Nickel (Ni) and Chromium (Cr) preferentially occupy octahedral sites.
• Magnesium (Mg) is predominantly found in tetrahedral sites.
• X-ray absorption spectroscopy and neutron scattering indicated Ni cation clustering and local lattice distortions.

Conclusions:

• Cation distribution in cubic spinel high-entropy oxides can be precisely determined using ReXRD.
• The observed site selectivity provides fundamental insights into the structure-property relationships of these materials.
• Understanding cation distribution and local distortions is essential for designing next-generation energy materials.