Activation in the rate of oxygen release of Sr_0.8Ca_0.2FeO_3-<i>δ</i> through removal of secondary surface species with thermal treatment in a CO₂-free atmosphere.

6a , a clear trend was observed, i.e. an increase in the shoulder feature at ∼131.2 eV and a decrease in the intensity of the secondary peak at ∼134.3 eV with cycle number; the features at 131.2 eV and 134.3 eV correspond to surface- and lattice-Sr, respectively. 39,46,48,61–63 Similarly, the O 1s spectra ( Fig. 6b ) showed a change in the distribution of oxygen species with cycle number, specifically, the intensity of the feature at ∼528.8 eV (lattice oxygen 64,65 ) increased with cycle number, while the intensity of the feature at ∼531.3 eV (surface oxygen species 64–66 ) decreased.

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