Relation between the Co-O bond lengths and the spin state of Co in layered Cobaltates: A high-pressure study

Yi Ying Chin, Hong Ji Lin*, Zhiwei Hu, Chang Yang Kuo, Daria Mikhailova, Jenn Min Lee, Shu Chih Haw, Shin An Chen, Walter Schnelle, Hirofumi Ishii, Nozomu Hiraoka, Yen Fa Liao, Ku Ding Tsuei, Arata Tanaka, Liu Hao Tjeng, Chien Te Chen, Jin Ming Chen

*Corresponding author for this work

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15 Scopus citations

Abstract

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 Kβ emission spectra, on the other hand, revealed a gradual spin state transition of Co3+ ions from a high-spin (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 Å) as well as a very large ratio of Co-Oapex/Co-Oin-plane is needed to stabilize the IS Co3+, a situation which is rarely met in reality.

Original languageEnglish
Article number3656
JournalScientific reports
Volume7
Issue number1
DOIs
StatePublished - 1 Dec 2017

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