O-K and Co-L XANES Study on Oxygen Intercalation in Perovskite SrCoO_3-δ

Abstract

Evolution of the O-K and Co-L edge XANES spectra for SrCoO3-δ upon increasing oxygen content from 2.50 to 2.82 reveals that superoxide (O2 −) related features are overwhelmingly strong in the surface region of highly oxygen-deficient samples. Moreover, should it be always present in the bulk, octahedrally coordinated cobalt is unobservable in the surface region of highly oxygen-deficient samples. On the other hand, the surface region hosts square-pyramidally coordinated cobalt even in brownmillerite SrCoO2.50. Observations in the present work support an oxygen-intercalation mechanism in which (i) O2 is first absorbed on the surface as O2 −, (ii) then reductively split into O x- associated with square-pyramidally coordinated cobalt, and (iii) finally in the bulk eventually reoxidized to O z- (0 < z < x) being attached to octahedrally coordinated cobalt. The fact that only minute chemical shifts of the Co-L edge branches are seen indicates that electron transfer mostly takes place between oxygen atoms.

Topotactic Phase Transformation of the Brownmillerite SrCoO2.5 to the Perovskite SrCoO3–δ

“…[24,25] As expected, the overall trend represents that the P-SCO film has a higher valence state of Co ions than that of BM-SCO. We further compared O K-edge XAS data for both BM-SCO and P-SCO films.…”

“…the pre-peak intensity increases substantially as the Co valence state changes from 3+ toward 4+. [24] As shown in Figure 3b, the pre-peak is distinctively visible near 527 eV in P-SCO, while it is highly suppressed in case of BM-SCO. This clearly indicates that both oxygen intercalation into BM-SCO and subsequent change in the Co valence state were successful.…”

Electronic structure of RuSr2EuCu2O8studied by x-ray absorption and photoemission spectroscopies

“…These features provide detailed information about unoccupied O 2p-derived states or hole concentration of O 2p character commonly observed in perovskite oxides and ruthenocuprates. [17][18][19][20][21][22] The general line shapes of the features a 1 -c 1 of RuEu-1212 differ significantly from those of reference SRO, all of which are magnified in Ru e g band. The energy separation between the Ru t 2g band (∼528 eV) and the center of the e g band (∼531 eV) (with a crystal field splitting, = 10 D q ) is approximately 3 eV in agreement with that obtained from the Ru L 3 -edge XANES spectra to be shown later.…”

Strain Control of Oxygen Vacancies in Epitaxial Strontium Cobaltite Films

“…[26] Supporting Information Supporting Information is available from the Wiley Online Library or from the author. [29,30,34,37] From this combined data set, x is found to range from just below 3 to 2.75 as tensile strain increases from ε = 1% to ε = 4.2% , and e) while those of annealed P-SCO are displayed on the right panels in b), d), and e). We note that the growth in highly oxidizing ambient using ozone could improve the oxygen stoichiometry.…”

“…Quantification of the oxygen non-stoichiometry is given in Figure 3. The estimates of oxygen deficiency were obtained from comparing structural data (unit cell volume) [29,30] and spectroscopic peak shifts (O-K and Co-L edges) [34,37] to previous studies.…”