Charge Transfer and Structural Anomaly in Stoichiometric Layered Perovskite Sr₂Co_0.5Ir_0.5O₄

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• 作者：Daria Mikhailova ; Zhiwei Hu ; Chang-Yang Kuo ; Steffen Oswald ; Kailash M. Mogare ; Stefano Agrestini ; Jyh-Fu Lee ; Chin-Wen Pao ; Shin-An Chen ; Jenn-Min Lee ; Shu-Chih Haw ; Jin-Ming Chen ; Yen-Fa Liao ; Hirofumi Ishii ; Ku-Ding Tsuei ; Anatoliy Senyshyn and Helmut Ehrenberg
• 刊名：European Journal of Inorganic Chemistry
• 出版年：2017
• 出版时间：January 18, 2017
• 年：2017
• 卷：2017
• 期：3
• 页码：587-595
• 全文大小：1767K
• ISSN：1099-0682c

文摘

A layered Sr₂Co_0.5Ir_0.5O₄ (space group I4/mmm) perovskite of the K₂NiF₄ structure type was synthesized as a single-phase sample. Neutron powder diffraction measurements revealed full site occupancy of oxygen atoms. The Co³⁺/Ir⁵⁺ valence states were evaluated by a combination of X-ray absorption and X-ray photoemission spectroscopy as well as by magnetization measurements, and thus the differences to the parent compounds Sr₂CoO₄ and Sr₂IrO₄ with similar structures were confirmed. Co-K edge EXAFS studies indicated a long average Co–O distance of 1.967 Å suggesting a high-spin state of the Co³⁺ ion in Sr₂Co_0.5Ir_0.5O₄. No long-range magnetic ordering down to 4 K was detected by neutron powder diffraction, probably hindered by the random distribution of Co and Ir cations in the Sr₂Co_0.5Ir_0.5O₄ structure. High-pressure synchrotron powder diffraction studies showed stability of the Sr₂Co_0.5Ir_0.5O₄ structure up to at least 27 GPa at room temperature. A maximum in the c/a ratio at 10 GPa together with an anomaly in the pressure dependence of the unit-cell volume could be a sign of a change in the spin state of the Co ions under pressure.