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

Cubic spinel high-entropy oxides are compositionally complex, multifunctional materials that continue to garner incredible research interest. They offer tunable magnetic properties, enhanced catalytic activity, and structural stability in oxygen evolution reactions. They have shown improved cyclability as anodes in Li-ion battery research when compared to their binary counterparts. However, due to the high number of elements in spinel high-entropy oxides, a systematic study that links the improved physical properties to the atomic and electronic structures of these materials is challenging. Atomic and electronic structures are heavily tied to the cation distribution in cubic spinel oxides. Yet very little research is focused on determining the cation distribution in cubic spinel high-entropy oxides. This work seeks to bridge this gap and demonstrates the power of resonant X-ray diffraction (ReXRD) in determining the cation distribution in the Co-free (Cr,Mn,Fe,Mg,Ni)₃O₄ composition. Results from ReXRD showed pronounced cation site selectivity in (Cr,Mn,Fe,Mg,Ni)₃O₄. Ni and Cr were found to prefer the octahedral site, while Mg was predominantly found in the tetrahedral site of the cubic spinel structure. X-ray absorption spectroscopy and neutron total scattering revealed Ni cation clustering and local lattice distortions that were averaged on long length scales.