9.4 LIU Jin
Hydrogen-bearing iron peroxide at the core-mantle boundary
Knowledge of water in the Earth's interior, presumably at least several times the size of the world’s oceans, is fundamental importance to understanding the dynamics, structure, and evolution of Earth. In particular, the presence of trace amount of water (or hydrogen) can dramatically affect many physical and chemical properties of Earth materials, such as changing phase stability fields, reducing viscosity, and decreasing thermal conductivity. Here, we report that the reaction between water and iron change unexpectedly from FeO to pyrite-structured FeO2Hx (with x = 0 to 1) under the pressure-temperature conditions relevant to the Earth’s deep lower mantle. Combined with theoretical calculations and high-pressure experiments (i.e., nuclear resonant inelastic x-ray scattering spectroscopy, X-ray absorption spectroscopy, and X-ray diffraction coupled with laser-heated diamond-anvil cell techniques), we find that this oxygen-rich form of iron oxide possesses potential impacts on the evolution of Earth’s interior and the global oxygen and hydrogen cycles.