MR23B-2648
Discovery of New Iron Oxide Fe7O9 and its Solid Solution, (Mg,Fe2+)3Fe3+4O9
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Ryosuke Sinmyo1,2, Elena Bykova1, Sergey V Ovsyannikov1, Catherine A McCammon1, Ilya Kupenko3, Leyla Ismailova1 and Leonid S Dubrovinsky4, (1)University of Bayreuth, Bayreuth, Germany, (2)Tokyo Institute of Technology, Tokyo, Japan, (3)ESRF European Synchrotron Radiation Facility, Grenoble, France, (4)Bayerisches Geoinsitut, Bayreuth, Germany
Abstract:
Iron oxides are fundamentally important compounds for Earth science. Particularly, the stability and properties of iron oxides are essential information to understand the structure and chemistry of the mantle. Here we report new high-pressure polymorphs of iron oxide Fe7O9 (Fe3+/Fe2+ = 4/3) and its Fe2+-Mg solid solution (Mg,Fe2+)3Fe3+4O9 that can be recovered at ambient conditions. We synthesized single crystals of the both compounds at about 24-26 GPa using a multi-anvil press. Single crystal X-ray diffraction (XRD) studies showed that the crystal structures of both Fe7O9 and (Mg,Fe2+)3Fe3+4O9 have monoclinic C2/m space groups, that differ from any other known lattices of iron oxides. Mössbauer spectra are in agreement with the crystal structure refined from single crystal XRD. This newly found Fe7O9 polymorph suggests that iron oxides may have more variable mixed valence state under high-pressure condition than previously thought. Based on analogy with Fe2+1+nFe3+2O4+n group, a Fe2+3±nFe3+4O9±n group might be also stable at certain high pressures and temperatures and oxygen fugacity.
