Direct Observation of Pressure-Driven Valence Electron Transfer in Ba ₃ BiRu ₂ O ₉ , Ba ₃ BiIr ₂ O ₉ , and Ba ₄ BiIr ₃ O ₁₂

Journal Article · Mon Jun 06 00:00:00 EDT 2016 · Inorganic Chemistry

DOI:https://doi.org/10.1021/acs.inorgchem.6b00718· OSTI ID:1391758

Blanchard, Peter E. R.; Chapman, Karena W.; Heald, Steve M.; Zbiri, Mohamed; Johnson, Mark R.; Kennedy, Brendan J.; Ling, Chris D.

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).

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: Australian Research Council; Australian Synchrotron - International Synchrotron Access Program (ISAP); USDOE Office of Science - Office of Basic Energy Sciences - Chemical Sciences, Geosciences, and Biosciences Division; National Science Foundation (NSF) - Directorate for Geosciences Division of Earth Sciences (GEO/EAR); USDOE Office of Science - Office of Basic Energy Sciences - Scientific User Facilities Division
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1391758
• Journal Information: Inorganic Chemistry, Vol. 55, Issue 11; ISSN 0020-1669
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English