Non-resonant and resonant X-ray emission at high pressure using a von Hámos setup: the case of FeO

Abstract

We present a setup exploiting a von Hámos spectrometer in order to study (resonant) X-ray emission of matter exposed to high pressure. The capabilities of this setup are demonstrated for the case of FeO at pressures between 13 GPa and 75 GPa. The setup provides high-quality Kβ 1,3 X-ray emission spectra at high pressures for iron spin state analysis within minutes and iron valence-to-core spectra in less than one hour. Resonant X-ray emission maps can be obtained on a timescale of one hour with 1.0 eV and in approximately 3 hours with 0.2 eV incident energy resolution. Both Kα and Kβ emission can be utilized to gain L-edge and M-edge-like information, respectively, with the option of measuring both simultaneously. The spin state results on FeO between 13 GPa and 75 GPa are in accordance with recent literature. The structural distortion is reflected in both, valence-to-core spectra and resonant X-ray emission maps, which showcase the great potential of the presented setup. The achieved data acquisition times are promising to couple pressure with temperature by laser heating.

High-efficiency X-ray emission spectroscopy of cold-compressed Fe2O3and laser-heated pressurized FeCO3using a von Hámos spectrometer

“…This might be based on a symmetry reduction of the trigonal-prismatic HS site, as seen also for FeO, which undergoes a transition from octahedral to rhombohedral distorted coordination under pressure. The resulting Kb 1,3 peak-shape change results in an IAD value of around 20% of a complete HS-LS transition 25 and, translated to this case, would perfectly t the difference of 10% to the expected value, as only half of the iron is impacted by the distortion. These ndings are in good agreement with recently published literature.…”

“…[15][16][17][18][19] Thus, a detailed understanding of the electronic structure of iron-bearing compounds in situ at extreme conditions, i.e., high temperature and high pressure, is crucial to understand and interpret the material's properties and chemistry of the interior of the Earth and other terrestrial planets. Besides Mössbauer spectroscopy [20][21][22] and X-ray absorption spectroscopy, 4,23 X-ray emission spectroscopy, resonant 24,25 and nonresonant, 5,6,[25][26][27][28][29][30] is widely used to determine spin state, covalency, oxidation state, electronic structure and structural changes.…”