HR: 13:40h
AN: MR13A-01 INVITED     [Abstracts]
TI: Nuclear Resonant Scattering Studies Under High Pressure and HighTtemperature
AU: * Sturhahn, W
EM: sturhahn@anl.gov
AF: Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Ave, Argonne, IL 60439 United States
AU: Lin, J
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington DC, DC 20015 United States
AU: Shen, G
AF: Consortium for Advanced Radiation Sources, University of Chicago, 5640 South Ellis Ave, Chicago, IL 60637 United States
AU: Jackson, J M
AF: Department of Geology, University of Illinois at Urbana-Champaign, 1301 W Green St, Urbana, IL 61801 United States
AU: Zhao, J
AF: Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Ave, Argonne, IL 60439 United States
AU: Prakapenka, V
AF: Consortium for Advanced Radiation Sources, University of Chicago, 5640 South Ellis Ave, Chicago, IL 60637 United States
AU: Lerche, M
AF: Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Ave, Argonne, IL 60439 United States
AU: Lerche, M
AF: Department of Geology, University of Illinois at Urbana-Champaign, 1301 W Green St, Urbana, IL 61801 United States
AU: Bass, J D
AF: Department of Geology, University of Illinois at Urbana-Champaign, 1301 W Green St, Urbana, IL 61801 United States
AU: Mao, H
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington DC, DC 20015 United States
AB: Nuclear resonant scattering techniques have been applied very successfully to iron-bearing alloys [1-3] and silicates [4] under pressures in the Mbar regime using diamond anvil cells. The two main methods, nuclear resonant inelastic x-ray scattering (NRIXS) and synchrotron M\"ossbauer spectroscopy (SMS), will be discussed in their potential for the geophysical problem area. In general, NRIXS provides the phonon density of states [5] and sound velocities [6], whereas SMS gives access to the abundance of ferric iron and the spin state of iron in minerals and their polymorphs. % The introduction of Laser heating in combination with NRIXS and SMS at sector 3-ID of the Advanced Photon Source permits us now to conduct these studies under high pressure \textit{and} high temperature. Here we will address two examples of this powerful, new opportunity. The reduction of sound velocities with increasing temperature, in particular for the shear wave, observed from NRIXS on hot, compressed iron metal in a pressure range of 40\,GPa to 60\,GPa. We find that the sound velocities do not depend on density alone but show an explicit temperature dependence. In a second experiment, we analyzed valence and spin state of iron in magnesium silicates. The starting material, orthoenstatite $^{57}$Fe$_{0.1}$Mg$_{0.9}$SiO$_3$, was compressed in several steps up to 31\,GPa in a diamond anvil cell. Each step involved laser annealing and the collection of SMS spectra at several temperatures. With x-ray diffraction we confirmed the creation of high-clinoenstatite, ringwoodite, ilmenite, and perovskite structures. Unique data on the iron behavior in each polymorph was obtained. % This work is supported by the U.S. DOE-BES, Office of Science, under Contract No. W-31-109-Eng-38 and by NSF through COMPRESS. % {}[1] H.K.Mao et al., Science \textbf{292}, 914 (2001) [1mm] % {}[2] J.-F.Lin et al., Geophysical Research Letters \textbf{30}, 2112 (2003) [1mm] % {}[3] W.L.Mao et al., Geophysical Research Letters \textbf{31}, L15618 (2004) [1mm] % {}[4] J.M.Jackson et al., American Mineralogist, (in press) [1mm] % {}[5] W.Sturhahn et al., Phys.Rev.Lett. \textbf{79}, 3832 (1995) [1mm] % {}[6] M.Y.Hu et al., Phys.Rev. B \textbf{67}, 094304 (2003)
DE: 3909 Elasticity and anelasticity
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
DE: 3994 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting