Phase transitions in ε-FeOOH at high pressure and ambient temperature
- Univ. of the South, Sewanee, TN (United States); University of Illinois at Chicago
- Univ. of Chicago, IL (United States)
- Univ. of Illinois, Chicago, IL (United States)
Constraining the accommodation, distribution, and circulation of hydrogen in the Earth's interior is vital to our broader understanding of the deep Earth due to the significant influence of hydrogen on the material and rheological properties of minerals. Recently, a great deal of attention has been paid to the high-pressure polymorphs of FeOOH (space groups P21nm and Pnnm). These structures potentially form a hydrogen-bearing solid solution with AlOOH and phase H (MgSiO4H2) that may transport water (OH–) deep into the Earth's lower mantle. Additionally, the pyrite-type polymorph (space group Pa3¯ of FeOOH), and its potential dehydration have been linked to phenomena as diverse as the introduction of hydrogen into the outer core, the formation of ultralow-velocity zones (ULVZs), and the Great Oxidation Event. In this paper, the high-pressure evolution of FeOOH was re-evaluated up to ~75 GPa using a combination of synchrotron-based X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and optical absorption spectroscopy. Based on these measurements, we report three principal findings: (1) pressure-induced changes in hydrogen bonding (proton disordering or hydrogen bond symmetrization) occur at substantially lower pressures in ε-FeOOH than previously reported and are unlikely to be linked to the high-spin to low-spin transition; (2) ε-FeOOH undergoes a 10% volume collapse coincident with an isostructural Pnnm → Pnnm transition at approximately 45 GPa; and (3) a pressure-induced band gap reduction is observed in FeOOH at pressures consistent with the previously reported spin transition (40 to 50 GPa).
- Research Organization:
- Univ. of Illinois, Chicago, IL (United States)
- Sponsoring Organization:
- National Science Foundation (NSF); USDOE National Nuclear Security Administration (NNSA), Office of Defense Programs (DP); USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Contributing Organization:
- National Synchrotron Light Source-II Advanced Photon Source
- Grant/Contract Number:
- AC02-06CH11357; AC02-98CH10886; FG02-94ER14466; NA0003975
- OSTI ID:
- 1736252
- Alternate ID(s):
- OSTI ID: 1760536
OSTI ID: 1765201
- Journal Information:
- American Mineralogist, Journal Name: American Mineralogist Journal Issue: 12 Vol. 105; ISSN 0003-004X
- Publisher:
- Mineralogical Society of AmericaCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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