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In this work, the x = 1 member of the Ba2In2−xIrxO5+δ family was discovered via neutron diffraction experiments to have a monoclinically distorted 6H structure (pictured) contrary to literature. Analysis of members containing low Ir content (x = 0.2−0.6) showed that, for the first time, Ir(VI) was stabilized under ambient pressure and atmosphere. Additionally, the magnetic and electrical properties of the entire Ba2In2−xIrxO5+δ family were measured and analyzed.
In this work, the solid solution series Ba2In2–xIrxO5+δ (x = 0–1.4, 2) was synthesized, and its structural, magnetic, and charge-transport properties were measured. With increasing Ir content, three transitions in the room-temperature structure were observed: orthorhombic to tetragonal to cubic to a monoclinic distortion of a hexagonal BaTiO3 structure. Neutron diffraction shows Ba2In1.6Ir0.4O5.4 to be cubic and Ba2InIrO6 to be monoclinic, the latter contrary to previously published X-ray diffraction refinements. Magnetization measurements show Curie–Weiss behavior for x = 0.2–0.6, which arises from nearly 50:50 ratio of Ir(V) and Ir(VI). To our knowledge, this is the first time Ir(VI) has been stabilized with standard solid-state methods under ambient conditions. The electrical resistivity measurements show all the compounds studied are semiconducting and that resistivity decreases with increasing Ir content, suggesting the proximity to a metal–insulator transition. A sign reversal in the high-temperature Seebeck coefficient is observed indicating both electron and hole charge transport.
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