Journal
SCIENTIFIC REPORTS
Volume 7, Issue -, Pages -Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/s41598-017-03950-z
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- Ministry of Science and Technology [MOST 102-2112-M-213 -004 -MY3, MOST 105-2113-M-213 -005 -MY3]
- Deutsche Forschungsgemeinschaft [SFB 1143]
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The pressure-response of the Co-O bond lengths and the spin state of Co ions in a hybrid 3d-5d solid-state oxide Sr2Co0.5Ir0.5O4 with a layered K2NiF4-type structure was studied by using hard X-ray absorption and emission spectroscopies. The Co-K and the Ir-L-3 X-ray absorption spectra demonstrate that the Ir5+ and the Co3+ valence states at ambient conditions are not affected by pressure. The Co Ka emission spectra, on the other hand, revealed a gradual spin state transition of Co3+ ions from a highspin (S = 2) state at ambient pressure to a complete low-spin state (S = 0) at 40 GPa without crossing the intermediate spin state (S = 1). This can be well understood from our calculated phase diagram in which we consider the energies of the low spin, intermediate spin and high spin states of Co3+ ions as a function of the anisotropic distortion of the octahedral local coordination in the layered oxide. We infer that a short in-plane Co-O bond length (<1.90 angstrom) as well as a very large ratio of Co-O-apex/Co-Oin-plane is needed to stabilize the IS Co3+, a situation which is rarely met in reality.
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