Thesis defense of Johannes Martin Kaa

A significant part of researching the interior of planets is done by recreating the pressures and temperatures, that are expected in large depths, in the laboratory. While pressures are routinely created statically with a diamond anvil cell to cover the pressure ranges in most planets of the solar system (up to ≈ 10 Mbar), simultaneous temperature increases are a more delicate topic, especially when combined with in-situ X-ray analysis with high exposure times. In this work, we introduce a novel approach of determining electronic states of matter at high pressures and temperatures by combining diamond anvil cells (DACs) with heating via ultra-short and intense X-ray pulses, which also serve as a probe of the spin state sensitive X-ray emission (XES) signal and structural sensitive X-ray diffraction (XRD). In the proof-of-concept experiment in the vacuum chamber 1 (IC1) at the HED instrument, we heated FeCO3 up to melting temperatures at 51GPa with this technique and caused a temperature-driven electronic low spin to high spin transition in the Fe. After designing, building and commissioning a dedicated von H´amos spectrometer in IC1 we measured structural and electronic spin state changes for (Fe0.5Mg0.5)O at 100GPa and FeS between 5GPa to 25GPa at high temperatures. The latter sample served as a simplified model for the Martian mantle and core, giving us unique information to expand on the just recently published seismic measurements. Additionally, the setup was tested for future time-resolved XES from a DAC and inelastic X-ray scattering techniques of free-standing samples and is available for user experiments at the European X-ray free electron laser.

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