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

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

doi:10.1038/s41598-017-03950-z

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-L3 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.

Highlights

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
As shown in previous studies, the presence of the low-energy shoulder S1 at the Co3+ L3 edge is characteristic for the high-spin state, while the high-energy shoulder S2 is indicative for the low-spin state[24, 29]
We have studied the valence state and spin state transition of Co ion under external pressures in a hybrid 3d-5d transition metals solid-state oxide Sr2Co0.5Ir0.5O4 using hard X-ray absorption and Co-Kβ emission spectroscopies

Summary

Introduction

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 Kβ 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 have drawn a phase diagram of the spin state of a Co3+ ion as a function of the anisotropic Co-O bond lengths

Methods

Results

Discussion

Conclusion