Direct Observation of Pressure-Driven Valence Electron Transfer in Ba3BiRu2O9, Ba3BiIr2O9, and Ba4BiIr3O12

详细信息    查看全文

• 作者：Peter E.R. Blanchard ; Karena W. Chapman ; Steve M. Heald ; Mohamed Zbiri ; Mark R. Johnson ; Brendan J. Kennedy ; Chris D. Ling
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：June 6, 2016
• 年：2016
• 卷：55
• 期：11
• 页码：5649-5654
• 全文大小：456K
• 年卷期：0
• ISSN：1520-510X

文摘

The hexagonal perovskites Ba₃BiIr₂O₉, Ba₃BiRu₂O₉, and Ba₄BiIr₃O₁₂ all undergo pressure-induced 1% volume collapses above 5 GPa. These first-order transitions have been ascribed to internal transfer of valence electrons between bismuth and iridium/ruthenium, which is driven by external applied pressure because the reduction in volume achieved by emptying the 6s shell of bismuth upon oxidation to Bi⁵⁺ is greater in magnitude than the increase in volume by reducing iridium or ruthenium. Here, we report direct observation of these valence transfers for the first time, using high-pressure X-ray absorption near-edge spectroscopy (XANES) measurements. Our data also support the highly unusual “4+” nominal oxidation state of bismuth in these compounds, although the possibility of local disproportionation into Bi³⁺/Bi⁵⁺ cannot be definitively ruled out. Ab initio calculations reproduce the transition, support its interpretation as a valence electron transfer from Bi to Ir/Ru, and suggest that the high-pressure phase may show metallic behavior (in contrast to the insulating ambient-pressure phase).