Fig. 5: Phase evolution, structural and chemical characterization, and elemental homogeneity in the six-cation MgCoNiZnMnFeO parent high-entropy oxide.

a X-ray diffraction patterns of the 6-component high-entropy composition Mg_1/6Co_1/6Ni_1/6Zn_1/6Mn_1/6Fe_1/6O (MgCoNiZnMnFeO) sintered for 5 h under 100SCCM of Ar at different temperatures, suggesting that the transition to single phase occurs between 850–900 °C with the disappearance of the wurtzite peaks. ‘RS’ denotes peaks from the rock salt structure, and ‘W’ indicates the wurtzite structure. b X-ray diffraction patterns of MgCoNiZnMnFeO sintered at 1100 °C under varying oxygen partial pressures. A single-phase rock salt structure forms after 5 h under a 100 SCCM Ar flow. In contrast, sintering in air results in the emergence of a spinel phase, while introducing a small percentage of H₂ leads to the formation of a reduced metallic phase. ‘RS’ denotes peaks from the rock salt structure, ‘S’ denotes those from the cubic spinel structure, and ‘FCC’ indicates the face-centered cubic metal structure. c–e are obtained by characterizing the parent composition MgCoNiZnMnFeO sintered for 5 h under 100SCCM Ar. c Selected area electron diffraction (SAED) along the [110] zone axis of MgCoNiZnMnFeO sintered for 5 h under 100SCCM Ar, with the inset showing the selected area (yellow circle ~700 nm in radius) corresponding to the diffraction pattern. The electron diffraction pattern is consistent with the rock salt crystal structure. d Energy-dispersive spectroscopy (EDS) maps showing a homogeneous distribution of elements at the 50 nm scale. e Mn K-edge and Fe K-edge photon energy vs valence state with best-fit line confirming a predominance of Mn²⁺ and Fe²⁺ within MgCoNiZnMnFeO composition, with the 2+ reference values are indicated by orange stars. Source data for (a), (b) and (e) are provided as a Source Data file.