HR: 11:14h
AN: MR22A-05    [Abstracts]
TI: The Electronic Structure of Iron in (Mg,Fe)SiO3 Perovskite and Post-Perovskite Under Megabar Pressures
AU: * Jackson, J M
EM: jackson@gps.caltech.edu
AF: Seismological Laboratory, Caltech, 1200 E. California Blvd. M/C 252-21, Pasadena, CA 91125, United States
AU: Tschauner, O
EM: olivert@physics.unlv.edu
AF: Department of Physics, University of Nevada, Box 454002, 4505 Maryland Parkway, Las Vegas, NV 89154, United States
AU: Fei, Y
EM: y.fei@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington DC, DC 20015, United States
AU: Sturhahn, W
EM: sturhahn@aps.anl.gov
AF: Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Ave., Argonne, IL 60439, United States
AU: Lerche, M
EM: lerche@aps.anl.gov
AF: Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Ave., Argonne, IL 60439, United States
AU: Zhao, J
EM: jzhao@aps.anl.gov
AF: Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Ave., Argonne, IL 60439, United States
AB: The bottom few hundred kilometers of Earth's mantle, termed the D" layer, represents one of the most extreme compositional and thermal boundary layers within our planet, where the solid silicate and (Mg,Fe)O dominant mantle is in contact with with the iron-dominant outer core. Knowledge of iron's electronic structure in this material, which in turn may influence elastic and transport properties, provides important constraints on our understanding of this boundary layer. (Mg,Fe)SiO₃ has been suggested to crystallize in the post-perovskite structure under the pressures and temperatures of Earth's D" layer, and is therefore the focus of many current experimental and theoretical investigations. We have determined the electronic structure of iron in (Mg,⁵⁷Fe)SiO₃ perovskite and post-perovskite at megabar pressures through direct measurements of iron's hyperfine fields using synchrotron Mössbauer spectroscopy at Sector 3 ID-B of the Advanced Photon Source at Argonne National Laboratory. We compressed orthoenstatite-structured (Mg,⁵⁷Fe)SiO₃ in diamond anvil cells to over one megabar and then used a CO₂ laser to synthesize the material off-line into a post-perovskite structure. Evaluation of the synchrotron Mössbauer data provides the electric field gradient (quadrupole splitting) and s-electron density (isomer shift) of the iron sites, which in turn provides constraints on the valence and spin state of iron in these materials. We will discuss the implications of our results to Earth's D" layer.
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3924 High-pressure behavior
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting