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要旨:
A layered Sr2Co0.5Ir0.5O4 (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 A suggestina high-spin state of the Co3+ ion in Sr2Co0.5Ir0.5O4. 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 Sr2Co0.5Ir0.5O4 structure. High-pressure synchrotron powder diffraction studies showed stability of the Sr2Co0.5Ir0.5O4 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.
