Brillouin Scattering With Simultaneous X-Ray Diffraction at GSECARS, Advanced Photon Source: Toward Determination of Absolute Pressure Scales Jay Bass 1 Stanislav Sinogeikin 1,2 Dmitry Lakshtanov 1 Carmen Sanchez-Valle 1 Vitali Prakapenka 2, Guoyin Shen 2,3 Jean-Philippe Perrillat 1 Jingyun Wang 1 Bin Chen 1 1 University of Illinois at UC, Geology Dept. 2 GSECARS, The University of Chicago 3 HPCAT, Advanced Photon Sourse, Argonne National Laboratory 4 Carnegie Institution of Washington, Geophysical Laboratory Fall AGU 2006

Isothermal bulk modulus (volume measurements) Adiabatic elastic moduli (velocity measurements) Brillouin Scattering with synchrotron X-rays at the APS Elasticity Grand Challenge COMPRES Infrastructure Development Project Measure sound velocities and density simultaneously “ Absolute” or internally consistent Pressure Scales Zha et al., Brillouin on MgO (PNAS, 2000)

Phase Transitions: Stishovite - CaCl 2

Stishovite - CaCl 2 : Brillouin scattering velocities

Brillouin scattering  Acoustic waves present in a solid due to thermal motion of atoms  Laser light interacts with phonons (or density / refractive index fluctuations) and is scattered with Doppler shifted frequency   Brillouin shift is proportional to acoustic velocity V i =  / 2n*sin (  /2) V i =  / 2sin (  */2) Platelet (symmetric) geometry

Schematic diagram of the Brillouin system installed at sector 13-BMD (GSECARS) at APS Sinogeikin et al.,Rev. Sci. Instr. 77, 2006

Schematic diagram of the Brillouin system installed at sector 13-BMD at APS (Lower Tier) Motorized translation components (controllable from outside the hatch, blue boxes): HMTS - horizontal motorized translation stage; VMTS - vertical motorized translation stage; MLFA - motorized laser focusing assembly; MSCA - motorized signal collecting assembly; SPOA - sample positioning and orientation assembly; SL-LB - sample light / light block. Observation / feedback elements (red boxes): VC - video camera; BT - beam target. X-ray components: MAR - MAR Imaging plate; XBS - X-ray beam stop; CS - cleanup slit.

Mobile focusing/collecting part of the Brillouin system at 13-BMD GSECARS

X-ray image and integrated spectrum of single-crystal NaCl at ambient conditions

Single crystal NaCl (B1) at ~30 GPa in DAC in Ne pressure medium Au+Pt+NaCl NaCl Single crystal Ruby 100 μm Au+Pt+NaCl Schematic view of simultaneous Brillouin scattering and X-ray diffraction in DAC

X-ray image and spectrum of single-crystal NaCl in Ne at 30 GPa NaCl (B1) (200) Ne

Single crystal Brillouin spectrum of NaCl (B1) and velocity distribution in (100) plane at 30.5 GPa

Single crystal and aggregate elastic moduli of NaCl (B1) as a function of density

Anisotropy of NaCl (B1) to 30 GPa

Aggregate velocities of NaCl (B1) as a function of density

“Absolute” equations of state / pressure scale Isothermal bulk modulus (volume measurements) Adiabatic elastic moduli (velocity measurements) We measure Ks as a function of volume directly. The problem is to convert K S to K T at high pressure, e.g. we need to know volume dependence of   and . Possible models/assumptions:

Conclusions  We simultaneously measured single crystal (and aggregate) elastic moduli of NaCl (B1) with Brillouin spectroscopy and density with angle dispersive X-ray diffraction to 30.5 GPa.  At high pressure NaCl exhibits extreme elastic anisotropy, which is >3 times higher than that at ambient conditions.  Above ~17 GPa on approaching B1-B2 phase transition NaCl exhibits acoustic mode softening.  Above ~17 GPa the density – velocity relations deviate from linearity and violate Birch’s law.  Acoustic softening indicates that B1-B2 phase transition in NaCl may be multi-step and of more complicated nature than it was previously thought.  Pressure calculated from measured bulk modulus and density is higher than that calculated from Decker EOS by ~ 3-5% at 30 GPa.

Acknowledgments NSF: Elasticity Grand Challenge COMPRES: Infrastructure development project GSECARS: Sector 13, Advanced Photon Source