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Compressional behavior and spin state of delta -(Al,Fe)OOH at high pressures

Itaru Ohira, Jennifer M. Jackson, Natalia V. Solomatova, Wolfgang Sturhahn, Gregory J. Finkelstein, Seiji Kamada, Takaaki Kawazoe, Fumiya Maeda, Naohisa Hirao, Satoshi Nakano, Thomas S. Toellner, Akio Suzuki and Eiji Ohtani
Compressional behavior and spin state of delta -(Al,Fe)OOH at high pressures
American Mineralogist (September 2019) 104 (9): 1273-1284


Hydrogen transport from the surface to the deep interior and distribution in the mantle are important in the evolution and dynamics of the Earth. An aluminum oxy-hydroxide, delta -AlOOH, might influence hydrogen transport in the deep mantle because of its high stability extending to lower mantle conditions. The compressional behavior and spin states of delta -(Al,Fe3+)OOH phases were investigated with synchrotron X-ray diffraction and Moessbauer spectroscopy under high pressure and room temperature. Pressure-volume (P-V) profiles of the delta -(Al0.908(9)57Fe0.045(1))OOH1.14(3) [Fe/(Al+Fe) = 0.047(10), delta -Fe5] and the delta -(Al0.832(5)57Fe0.117(1))OOH1.15(3) [Fe/(Al+Fe) = 0.123(2), delta -Fe12] show that these hydrous phases undergo two distinct structural transitions involving changes in hydrogen bonding environments and a high- to low-spin crossover in Fe3+. A change of axial compressibility accompanied by a transition from an ordered (P21nm) to disordered hydrogen bond (Pnnm) occurs near 10 GPa for both delta -Fe5 and delta -Fe12 samples. Through this transition, the crystallographic a and b axes become stiffer, whereas the c axis does not show such a change, as observed in pure delta -AlOOH. A volume collapse due to a transition from high- to low-spin states in the Fe3+ ions is complete below 32-40 GPa in delta -Fe5 and delta -Fe12, which i ~10 GPa lower than that reported for pure epsilon -FeOOH. Evaluation of the Moessbauer spectra of delta -(Al0.824(10)57Fe0.126(4))OOH1.15(4) [Fe/(Al+Fe) = 0.133(3), delta -Fe13] also indicate a spin transition between 32-45 GPa. Phases in the delta -(Al,Fe)OOH solid solution with similar iron concentrations as those studied here could cause an anomalously high rho /nu Phi ratio (bulk sound velocity, defined as K/rho at depths corresponding to the spin crossover region (~900 to ~1000 km depth), whereas outside the spin crossover region a low rho /nu Phi anomaly would be expected. These results suggest that the delta -(Al,Fe)OOH solid solution may play an important role in understanding the heterogeneous structure of the deep Earth.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 104
Serial Issue: 9
Title: Compressional behavior and spin state of delta -(Al,Fe)OOH at high pressures
Affiliation: Tohoku University, Department of Earth Science, Sendai, Japan
Pages: 1273-1284
Published: 201909
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 78
Accession Number: 2019-082818
Categories: Geophysics of minerals and rocks
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
Secondary Affiliation: California Institute of Technology, USA, United StatesUniversity of Hawaii at Manoa, USA, United StatesUniversity of Bayreuth, DEU, GermanyHiroshima University, JPN, JapanJapan Synchrotron Radiation Research Institute, JPN, JapanNational Institute for Materials Science, JPN, JapanArgonne National Laboratory, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201944
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