Extended Data Fig. 7: Atom probe tomography results assessing the extent of Ni redissolution into FeOx.
a, The 3D reconstructed atom distribution map for Fe, Ni, and O. This APT sample was taken from a pellet synthesized using 20 °C/min heating rate where noticeable FeOx is remained (see Extended Data Fig. 2c for the SXRD results). b, Fe, Ni, and O content acquired within a cylindrical area of interest (AOI) shown in a. The maximum amount of Ni in the FeOx barely exceeds ~3 at. %, confirming the subtle role of Ni redissolution, which validates the kinetic proposition discussed in main text Fig. 4b. We note that the Fe-O stoichiometry ratio is not rigorously unity, which is mostly due to the oxygen loss during APT measurement. The O content measured for the FeOx phase is consistent with similar analysis in the literature61.
