Revealing the Complex Nature of Bonding in the Binary High-Pressure Compound FeO2

Extreme pressures and temperatures are known to drastically affect the chemistry of iron oxides, resulting in numerous compounds forming homologous series nFeOmFe(2)O(3) and the appearance of FeO2. Here, based on the results of in situ single-crystal x-ray diffraction, Mossbauer spectroscopy, x-ray absorption spectroscopy, and density-functional theory + dynamical mean-field theory calculations, we demonstrate that iron in high-pressure cubic FeO2 and isostructural FeO2H0.5 is ferric (Fe3+), and oxygen has a formal valence less than 2. Reduction of oxygen valence from 2, common for oxides, down to 1.5 can be explained by a formation of a localized hole at oxygen sites.

Automated summary

Extreme pressures and temperatures can significantly impact the chemistry of iron oxides, resulting in the formation of various compounds. Research has shown that iron in high-pressure cubic FeO2 and isostructural FeO2H0.5 is ferric (Fe3+), with oxygen having a formal valence less than 2. The reduction of oxygen valence from 2 to 1.5 can be explained by the formation of a localized hole at oxygen sites.