Phase relations and physical properties of iron-oxygen compounds at multimegabar pressures and high temperatures – FEOX

The structures, properties and high-pressure and high-temperature behavior of compounds in the Fe–O system remain controversial and full of surprises despite a long history of research. Over the last decade several high-pressure iron oxides with hitherto unknown stoichiometries were discovered. These materials are very important for the geosciences (and planetary sciences) as potential phases during the Earth’s accretion, as possible components of present day mantle, and for controlling oxygen fugacity in the mantle, core mantle boundary, and in the core. Moreover, novel iron oxides, their electronic and magnetic properties are of great interest for modern solid state physics, chemistry, material sciences, and even for in the industry (as elements in switching electronics and memories).
Iron oxides will be synthesized at pressures over 200 GPa and temperatures up to 3500 K and studied in situ in laser-heated diamond anvil cells (DACs) employing a range of advanced complementary techniques: X-ray diffraction (XRD), Mössbauer and Raman spectroscopy (and when applicable X-ray absorption spectroscopy and electrical resistivity measurements) and theoretical calculations. Methodological aim of the project is to extend single-crystal diffraction studies to over 200 GPa. Particular attention will be paid on studies of FeO, Fe3O4, Fe2O3, Fe4O5, Fe5O6, Fe5O7, Fe7O9, and FeO2. The ultimate goals of the project are to construct pressure-temperature-composition (P–T–X) phase diagram of Fe–O system at conditions covering entire Earth mantle and significant part of the core; analyze how pressure-temperature induced transformations in Fe–O compounds may affect geochemical processes in the Earth’s interior; reveal relations between structure, chemical bonding, and properties of different iron oxides; and formulate crystal chemical principals governing behavior of transition metal oxides at extreme conditions.
The investigations will focus on the following questions:
- Which crystal structures are adopted by FeO, Fe3O4, Fe2O3, Fe4O5, Fe5O6, Fe5O7, Fe7O9, and FeO2 at pressures up to 200 GPa and high temperatures?
- Which binary Fe–O compounds may exist at pressures over 200 GPa and temperatures up to 3500 K?
- How pressure, temperature, and oxygen fugacity affect phase equilibria in Fe–O system?
- What is oxidation and spin state of iron in different Fe–O compounds?
- What are the relationships between the magnetic, electronic and structural phase diagrams for Fe–O system?
- What are the P–T conditions of formations and stability field of FeO2Hx (0 < x = 1) compounds?
- What implications do these results have for the Earth’s lower mantle, core-mantle boundary, and core mineralogy and geochemistry?