To increase our understanding of the formation and evolution of the Earth and iron-rich exoplanets, x-ray absorption fine structure (XAFS) spectroscopy was used to characterize iron oxides dynamically compressed to core Earth and super-Earth conditions. XAFS spectroscopy is a unique technique capable of simultaneously constraining in situ both the temperature and electron structure of compressed materials. At the Omega Laser Facility, Fe2O3 was compressed to above 700 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 absorption spectrum, where this improved resolution allowed x-ray absorption near edge spectroscopy (XANES) features of Fe2O3 to be measured at these extreme conditions. Analysis of the XANES spectrum, indicates that the iron 3d orbitals split in energy with increasing density due to interactions with neighboring oxygen atoms. Furthermore, Fe2O3 undergoes a crystal structure and magnetic transition when compressed to above 150 GPa, resulting in a negative shift in the K-edge absorption energy. Lastly, the persistence of the 1s to 3d transition peak is an indication that the iron remains bonded to oxygen above 700 GPa.
Authors: D. A. Chin1, P.M. Nilson1, R. Paul2, M. Signor1, A. Amouretti3, M. Harmand3, D.N. Polsin1, J.J. Ruby1, D.T. Bishel1, E.A. Smith1, X. Gong1, M.K. Ginnane1, F. Coppari1, Y. Ping1, J.R. Rygg1 and G.W. Collins1
1Laboratory for Laser Energetics, University of Rochester, USA
2Lawrence Livermore National Laboratory, USA
3Sorbonne University, France
