High-efficiency X-ray emission spectroscopy of cold-compressed Fe2O3 and laser-heated pressurized FeCO3 using a von Hámos spectrometer

Abstract

X-ray spectroscopy of iron-bearing compounds under high pressure and high temperature is an important tool to understand geological processes in the deep Earth. However, the sample environment using a diamond anvil cell complicates spectroscopic measurements and leads to long data acquisition times. We present a setup for resonant and non-resonant X-ray emission spectroscopy and showcase its capabilities for in situ studies at high pressure and high temperature. Spin-state imaging of laser-heated FeCO₃ at 75 GPa via Kβ_1,3 emission spectroscopy demonstrates the great potential of this setup with measurement times within seconds for robust spin-state analysis results. The results of Kβ_1,3 emission spectroscopy of cold-compressed Fe₂O₃ reveal a two-step spin transition with the ζ-phase between 57 GPa and 64 GPa, having iron in different spin states at the different iron sites. The phase transition via ζ- to Θ-phase causes a delocalization of the electronic states, which is supported by 1s2p resonant X-ray emission spectroscopy.