X-Ray Absorption Fine Structure Spectroscopy of Iron Compounds at High-Energy-Density Conditions
David Chin, University of Rochester
A critical next step in understanding high-energy-density (HED) matter is characterizing both the temperature and complex chemistry of materials at HED conditions. Temperature is historically difficult to measure at low-temperature HED conditions above 100 GPa and below 5000 K. In this region of phase space, the temperature of the material is often not measured but must be estimated from the thermodynamic compression path and equation of state of the material. Furthermore, when we compress matter to these extreme conditions, electron orbitals can be distorted, leading to new chemistry. X-ray absorption fine structure (XAFS) spectroscopy is a unique technique capable of simultaneously constraining in situ both the temperature and chemistry of compressed materials. At the Omega Laser Facility, multiple iron compounds were quasi-ramp compressed to above 500 GPa and probed with a broadband x-ray source. A new x-ray spectrometer with improved spectral resolution and energy calibration was used to measure the x-ray absorption spectrum. This improved resolution allowed x-ray absorption near edge spectroscopy (XANES) features of Fe2O3 to be measured for the first time at the Omega Laser Facility and these data indicate continued electron orbital distortion with increasing pressure. Moreover, the modulations in the extended x-ray absorption fine structure (EXAFS) region of the spectrum were fit using a FEFF1-based Bayesian inference routine to characterize the ion positions and ultimately the temperature through analytical models of the phonon spectrum and lattice potential wells.
This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856, the University of Rochester, and the New York State Energy Research and Development Authority.
[1] J. J. Rehr et al., Phys. Chem. Chem. Phys. 12, 5503 (2010).
Abstract Author(s): D. A. Chin,1 P. M. Nilson,1 J. J. Ruby,3 D. T. Bishel,1 A. Amouretti,4 A. Coleman,3 F. Coppari,3 M. K. Ginnane,1 X. Gong,1 M. Harmand,4 B. J. Henderson,1 S. X. Hu,1 O. Mathon,5 R. Paul,1 D. N. Polsin,1 E. Smith,1 R. Torchio,5 D. Trail,2 Y. Ping,3 J. R. Rygg,1 and G. W. Collins11Laboratory for Laser Energetics, University of Rochester, USA2Department of Earth and Environmental Sciences, University of Rochester, USA3Lawrence Livermore National Laboratory, USA4Sorbonne University, France5European Synchrotron Radiation Facility, France