Extended Data Fig. 1: Volumes of Py-FeO2 and Py-FeO2Hx under pressure and room temperature.
From: Superionic iron oxide–hydroxide in Earth’s deep mantle
Open circles are experimental volumes in literature. Measurement uncertainties from XRD are generally less than the symbol size. Dash curves are volumes of FeO2Hx with x=0, 0.25, 0.5, 0.75 and 1.0 from theoretical calculation (see Methods). The stability and stoichiometry of FeO2-FeO2H in pyrite structure. In eight different experiments converting FeO2H to the Py-phase at 86.0–133.5 GPa and 1500–2500 K, Hu et al. observed a wide variation of the unit-cell volume, that was attributed to the variation of x from 0.43 to 0.81 in Py-FeO2Hx due to the difference in the P–T of their synthesis. The set of curves for the volume dependence on x and P as shown in Fig. S1. Nishi. et al. conducted a set of experiments with all P–V data correspond to the maximum of Hu’s volume. Subsequent investigations by Yuan et al. from Tohoku University synthesized a Py-FeO2Hx with unit-cell volumes 2% larger than Nishi. et al. approaching the full hydrogenation of x = 1. Many additional publications in 2017–2019 further showed variation of volume and thus H. Most importantly, all experiments of four different groups consistently demonstrated that Py-FeO2Hx (x≤1) is stable under DLM pressures and is at least thermodynamically stable up to 2500–2600 K at 110 GPa. While the exact stoichiometry of the H and its relation to P, T, and hydrogen fugacity remain interesting, it is not the subject of the present work which focuses on the superionization behavior in hydrogen in the Py phase regardless of its stoichiometry. Therefore, our FPMD simulation chose x = 0.5 and 1.0 because they mainly cover the range of x obtained from XRD experiments.
