HR: 0800h
AN: MR31A-0114    [Abstracts]
TI: Aggregate Elastic Moduli and Equation of State of B2 Phase of NaCl to 73 GPa by Simultaneous Synchrotron X-ray Diffraction and Brillouin Scattering Measurements.
AU: * Lakshtanov, D L
EM: lakshtan@uiuc.edu
AF: University of Illinois at Urbana-Champaign, 1301 W Green St., Urbana, il 61801 United States
AU: Sinogeikin, S V
EM: sinogeik@uiuc.edu
AF: University of Illinois at Urbana-Champaign, 1301 W Green St., Urbana, il 61801 United States
AU: Sanchez-Valle, C
EM: csanchez@ens-lyon.fr
AF: University of Illinois at Urbana-Champaign, 1301 W Green St., Urbana, il 61801 United States
AU: Prakapenka, V
EM: prakapenka@cars.uchicago.edu
AF: GSECARS, University of Chicago, University of Chicago, Chicago, il 60637 United States
AU: Shen, G
EM: gshen@hpcat.aps.anl.gov
AF: HPCAT, Advanced Photon Source, Argonne National Lab, Argonne, IL 60439 United States
AU: Gregoryanz, E
EM: e.gregoryanz@gl.ciw.edu
AF: Carnegie Institution of Washington, Geophysical Lab, 5251 Broad Branch Rd NW, Washington, DC 20015 United States
AU: Bass, J D
EM: jaybass@uiuc.edu
AF: University of Illinois at Urbana-Champaign, 1301 W Green St., Urbana, il 61801 United States
AB: NaCl is not only the most studied ionic compound in nature, it is also a widely used quasi-hydrostatic pressure medium and pressure calibrant in high-pressure experiments up to the Megabar range. At pressures of about 30 GPa NaCl undergoes a reconstructive phase transition from the rocksalt (B1) structure to CsCl (B2) structure with more than a 4% increase in density. There have been several attempts to constrain the EOS of NaCl B2 phase by cross calibration of the NaCl unit cell volume with other pressure standards such as Au and MgO (Sata et al., 2002) or ruby fluorescence (Heinz and Jeanloz, 1984). While the resulting equations of state adequately describe the data within the pressure range of direct measurements, extrapolation of the data to higher pressures can lead to serious errors in pressure determination. This is due to the significant trade-off between the inferred bulk modulus (K_T) and its pressure derivative (K_T'), as well as the inability to directly measure the zero-pressure volume (V₀). Thus, finite strain extrapolations of the P-V data beyond the experimental pressure range are rather uncertain. We have recently installed a Brillouin spectrometer on station 13-BM-D at GSECARS, APS. This allowed us to simultaneously measure isotropic acoustic velocities by Brillouin spectroscopy and unit cell volumes by angle-dispersive x-ray diffraction on a polycrystalline sample of the B2 phase of NaCl. A plate of NaCl was loaded into a DAC with Ne as a pressure medium. Ruby chips,Au,and Pt were also in the sample chamber for pressure measurement and cross-calibration. Simultaneous velocity and density measurements were performed at pressures from 35 to 73 GPa. Thus, at each pressure we directly obtained the isotropic adiabatic bulk and shear moduli of NaCl (B2). Direct knowledge of the bulk modulus as a function of pressure allows us to extrapolate the unit cell parameters of NaCl to ambient pressure with a high degree of accuracy, and to tightly constrain the P-V EOS of NaCl (B2). Our data extends the usage of NaCl as an independent pressure marker in high-pressure experiments, providing a consistent pressure scale as a reference for comparing results obtained by various experimental techniques in the megabar pressure range.
DE: 3909 Elasticity and anelasticity
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3934 Optical, infrared, and Raman spectroscopy
DE: 3994 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005