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Page 8 of 15 Wang et al. J Mater Inf 2023;3:3 https://dx.doi.org/10.20517/jmi.2022.45

Table 1. Quantification results from STEM-EDX analysis of LSCF treated at 800 °C in dry air from the ROIs in Figure 4
ROI-4A (% error) ROI-4B (% error)
(atomic %) (atomic %)
O 58.01 0.17 60.30 0.03
S 0.04 13.72 0.05 13.49
Fe 3.91 0.11 17.25 0.12
Co 37.95 0.04 3.71 0.30
Sr 0.04 8.22 7.96 0.19
La 0.05 2.51 10.72 0.10

Figure 4. TEM characterization of a Co-rich region of the LSCF surface after treatment in dry air at 800 °C. (A) Dark field STEM image
of Co-rich surface nanocrystal. White circle marks the location of the SAD aperture used to acquire a diffraction pattern of the
nanocrystal, and the cyan box marks the location of the STEM EDS elemental map (C-I); (B) TEM diffraction pattern of nanocrystal; d-
spacing values match those of Co O for d ; (C-H) STEM-EDX elemental maps for Sr, S, La, Fe, Co, and O, displayed as relative
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atomic composition for each element; (I) combined elemental map for atomic fractions of Sr, S, La, Co, and Fe. ROI-4A and ROI-4B
mark the regions where atomic composition was quantified using the STEM-EDS data, shown in Table 1.
containing large Co-rich phase crystals, and the ROIs in Figure 5 and Figure 7 were chosen for containing
several tiny S-rich phase crystals. For LCSF at 800 °C in the air [Figure 4], the surface crystal (ROI-4A) only
contains Cr and O (and trace Fe), at ca 3:4 ([Co/Fe]:O) atomic ratio by STEM-EDS analysis [Table 1]. Based
on TEM diffraction of the same surface crystal [Figure 4B], the measured d-spacing values are consistent
with Co O , spinel #1, which fits the EDS composition results and agrees well with our modeling
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predictions. While the small surface crystal (ROI-5A) in Figure 5 only contains Sr, S, and O, at ca 1:1:2.5
atomic ratio by STEM-EDS analysis [Table 2]. Based on the TEM diffraction of the surface crystal, shown in
Figure 5B, the crystal’s measured d-spacing values are consistent with SrSO . Based on the STEM-EDX and
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TEM diffraction analysis of the LSCF sample treated in dry air at 800 °C, it can be concluded that the Co/O
rich phase is primarily composed of the spinel #1 phase ([Co/Fe] O ), while the small S-rich surface grains
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are SrSO , in agreement with the simulation predictions [Figure 1A].
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