Altered chemistry of oxygen and iron under deep Earth conditions

Jin Liu; Qingyang Hu; Wenli Bi; Liuxiang Yang; Yuming Xiao; Paul Chow; Yue Meng; Vitali B Prakapenka; Ho-Kwang Mao; Wendy L Mao

doi:10.1038/s41467-018-08071-3

Altered chemistry of oxygen and iron under deep Earth conditions

Nat Commun. 2019 Jan 11;10(1):153. doi: 10.1038/s41467-018-08071-3.

Authors

Jin Liu^{1

2}, Qingyang Hu³, Wenli Bi^{4

5}, Liuxiang Yang^{1

6}, Yuming Xiao⁷, Paul Chow⁷, Yue Meng⁷, Vitali B Prakapenka⁸, Ho-Kwang Mao^{9

10}, Wendy L Mao^{11

12}

Affiliations

¹ Center for High Pressure Science and Technology Advanced Research, Beijing, 100094, China.
² Department of Geological Sciences, Stanford University, Stanford, CA, 94305, USA.
³ Center for High Pressure Science and Technology Advanced Research, Beijing, 100094, China. qingyang.hu@hpstar.ac.cn.
⁴ Advanced Photon Source, Argonne National Laboratory, Argonne, IL, 60439, USA.
⁵ Department of Geology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
⁶ Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC, 20015, USA.
⁷ HPCAT, X-Ray Science Division, Argonne National Laboratory, Argonne, IL, 60439, USA.
⁸ Center for Advanced Radiation Sources, University of Chicago, Chicago, IL, 60439, USA.
⁹ Center for High Pressure Science and Technology Advanced Research, Beijing, 100094, China. hmao@gl.ciw.edu.
¹⁰ Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC, 20015, USA. hmao@gl.ciw.edu.
¹¹ Department of Geological Sciences, Stanford University, Stanford, CA, 94305, USA. wmao@stanford.edu.
¹² Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA. wmao@stanford.edu.

Abstract

A drastically altered chemistry was recently discovered in the Fe-O-H system under deep Earth conditions, involving the formation of iron superoxide (FeO₂Hx with x = 0 to 1), but the puzzling crystal chemistry of this system at high pressures is largely unknown. Here we present evidence that despite the high O/Fe ratio in FeO₂Hx, iron remains in the ferrous, spin-paired and non-magnetic state at 60-133 GPa, while the presence of hydrogen has minimal effects on the valence of iron. The reduced iron is accompanied by oxidized oxygen due to oxygen-oxygen interactions. The valence of oxygen is not -2 as in all other major mantle minerals, instead it varies around -1. This result indicates that like iron, oxygen may have multiple valence states in our planet's interior. Our study suggests a possible change in the chemical paradigm of how oxygen, iron, and hydrogen behave under deep Earth conditions.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.
Research Support, Non-U.S. Gov't