Scrutinizing Detailed Structure Conditions for the Stabilization of the Intermediate-spin Co3+ Ground State
Yi-Ying Chin1*, Zhiwei Hu2, Y. Tsujimoto3, A. Tanaka4, C. T. Chen5
1Department of Physics, National Chung Cheng University, Chiayi county, Taiwan
2Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
3Research Center for Functional Materials, National Institute for Materials Science, Ibaraki, Japan
4Department of Quantum Matter, Hiroshima University, Higashi-Hiroshima, Japan
5National Synchrotron Radiation Research Center, Hsinchu, Taiwan
* Presenter:Yi-Ying Chin,
Different from other 3d transition-metal elements, cobalt has a spin state degree of freedom: for example, Co3+ can be in low-spin (LS), high-spin (HS), and even intermediate-spin (IS) states. Cobaltates with distinct spin states would have different transport and magnetic properties; for example, an IS-Co3+ state with eg1 was predicted to be the highest-performing Co oxide catalyst [Science 334, 1383 (2011)].
Band structure calculations proposed that Sr1.7Ca0.3CoO3F should have an IS-Co3+ ground state [Appl. Phys. Lett. 108, 092402 (2016)]. To study the possible IS state, we prepared samples of this compound, but only discovered that the Co3+ ions are actually in an HS ground state using Co-L2,3 and O-K X-ray absorption spectra. The HS ground state was also confirmed via theoretical simulation of the Co-L2,3 spectra with the configuration-interaction cluster calculations. Then, we employed theoretically-calculated energy diagrams to investigate whether an IS state could be stabilized by external pressure and to scrutinize structural conditions for the stabilization of the IS state of Co3+.

Keywords: spin state, X-ray absorption , Cobaltates