Medium-range structure motifs of complex iron oxides

Abstract

Natural occurring iron oxides, such as Fe2O3, Fe3O4, and FeO, are abundant on Earth's surface and feature many implications in our daily life since the Iron Age, the final epoch of the prehistory of humanity. The physics of iron oxides is at the frontier of physical research due to their complicated magnetic and electronic properties. What makes it even more intriguing is the introduction of pressure, which not only regulates the crystal structures and physical properties, but also creates new iron-oxide stoichiometry. Recent studies discovered several novel iron-oxygen compounds under various pressure–temperature conditions. Despite different Fe/O ratios, those iron oxides are built upon similar structural units including FeO6 octahedra and trigonal prisms. Complex stoichiometry of pressurized iron oxides is built up by stacking layers of those FeO6 units, and in the medium-range, they are organized by certain structural motifs. In this perspective, we go beyond conventional iron-oxygen binary compounds and reveal the general formation mechanism of complex iron oxide crystals under high-pressure conditions. The results will be helpful for summarizing literary works of iron oxides and exploring novel stoichiometry with optimal physical properties.

Evolution of electrical conductivity and semiconductor to metal transition of iron oxides at extreme conditions

“…[11,12] Our previous work has discussed the medium-range structural properties of the Fe-O system under high pressure. [13] Here in this work, we narrow down the scope to the electrical property of iron oxides, with a focus on its bandgap width under the influence of extreme conditions. While iron is a conventional metal, the other end-member of the Fe-O binary, oxygen also closes its bandgap at 96 GPa [14,15] and even becomes a superconductor at above megabar pressures.…”