HR: 09:00h
AN: MR21A-05    [Abstracts]
TI: Novel melting investigations of iron at high-pressure using synchrotron Mossbauer spectroscopy
AU: * Jackson, J M
EM: jjackson@aps.anl.gov
AF: Advanced Photon Source, XFD, High-resolution x-ray scattering group, 9700 S. Cass Ave., Argonne, IL 60439 United States
AU: Sturhahn, W
EM: sturhahn@aps.anl.gov
AF: Advanced Photon Source, XFD, High-resolution x-ray scattering group, 9700 S. Cass Ave., Argonne, IL 60439 United States
AU: Lerche, M
EM: lerche@aps.anl.gov
AF: Advanced Photon Source, XFD, High-resolution x-ray scattering group, 9700 S. Cass Ave., Argonne, IL 60439 United States
AU: Zhao, J
EM: jzhao@aps.anl.gov
AF: Advanced Photon Source, XFD, High-resolution x-ray scattering group, 9700 S. Cass Ave., Argonne, IL 60439 United States
AU: Sinogeikin, S V
EM: sinogeik@uiuc.edu
AF: Department of Geology, University of Illinois, 245 NHB, 1301 W. GReen St., Urbana, IL 61801 United States
AU: Lakshtanov, D L
EM: lakshtan@hercules.geology.uiuc.edu
AF: Department of Geology, University of Illinois, 245 NHB, 1301 W. GReen St., Urbana, IL 61801 United States
AU: Bass, J D
EM: jaybass@uiuc.edu
AF: Department of Geology, University of Illinois, 245 NHB, 1301 W. GReen St., Urbana, IL 61801 United States
AU: Murakami, M
EM: mmurakam@geo.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, 152-8551 Japan
AB: Seismological observations show that Earth's iron-dominated core consists of a solid inner region surrounded by a liquid outer core. The melting temperature of iron at high-pressure therefore provides a bound on the temperature regime of the core. Previously, melting studies of iron metal at high-pressures were performed by shock-compression, resistive- and laser-heating in diamond anvil cells using visual observations or synchrotron x-ray diffraction, and theoretical methods. However, the melting curve of iron is still controversial, especially at very high pressures. Here we present a novel method of detecting the solid-liquid phase boundary of iron at high-pressure using ⁵⁷Fe synchrotron Mössbauer spectroscopy (SMS). Focused synchrotron radiation with 1 meV bandwidth passes through a laser-heated sample inside a diamond anvil cell. The characteristic SMS time signature is observed by fast detectors and vanishes suddenly when melting occurs. This process is described by the Lamb-Mössbauer factor f = exp(-k²<x²>), where k is the wave number of the resonant x-rays and <x²> is the mean-square displacement of the iron atoms. We will discuss our melting results in comparison with previous data and also discuss future applications of this method to the study of melting of Earth materials under pressure. In addition to the detection of melt, the Lamb-Mössbauer factor is related to the phonon density of states (PDOS) of the material investigated. Results thus far indicate that the phonon density of states of fcc-structured iron softens with increasing temperature at high-pressure. We propose that the softening of the PDOS is related to a reduction of the shear modulus. This behavior that occurs at high-pressure near the melting point of iron should be considered when extrapolating the behavior of iron to the outermost inner core conditions.
DE: 3909 Elasticity and anelasticity
DE: 3924 High-pressure behavior
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
DE: 3939 Physical thermodynamics
DE: 7207 Core (1212, 1213, 8124)
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005