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Nat Commun. 2016 Feb 11;7:10661. doi: 10.1038/ncomms10661.

Structural complexity of simple Fe2O3 at high pressures and temperatures.

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Bayerisches Geoinstitut, University of Bayreuth, Universitaetsstrasse 30, D-95447 Bayreuth, Germany.
Laboratory of Crystallography, University of Bayreuth, Universitaetsstrasse 30, D-95447 Bayreuth, Germany.
Photon Sciences, Deutsches Elektronen-Synchrotron, Notkestrasse 85, D-22607 Hamburg, Germany.
European Synchrotron Radiation Facility, 71 avenue des Martyrs, Grenoble F-38000, France.
Center for Advanced Radiation Sources, University of Chicago, 9700 South Cass Avenue, Illinois, Argonne 60437, USA.


Although chemically very simple, Fe2O3 is known to undergo a series of enigmatic structural, electronic and magnetic transformations at high pressures and high temperatures. So far, these transformations have neither been correctly described nor understood because of the lack of structural data. Here we report a systematic investigation of the behaviour of Fe2O3 at pressures over 100 GPa and temperatures above 2,500 K employing single crystal X-ray diffraction and synchrotron Mössbauer source spectroscopy. Crystal chemical analysis of structures presented here and known Fe(II, III) oxides shows their fundamental relationships and that they can be described by the homologous series nFeO·mFe2O3. Decomposition of Fe2O3 and Fe3O4 observed at pressures above 60 GPa and temperatures of 2,000 K leads to crystallization of unusual Fe5O7 and Fe25O32 phases with release of oxygen. Our findings suggest that mixed-valence iron oxides may play a significant role in oxygen cycling between earth reservoirs.

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