Authors: Nyrow, Alexander
Title: Iron containing compounds of the inner earth: X-ray Raman scattering from ambient to extreme conditions
Language (ISO): en
Abstract: Iron is one of the most abundant elements inside the deep Earth. Numerous geologically relevant iron bearing materials are well characterized utilizing minerals obtained e.g. from volcano eruptions. Here, typical geophysical and geochemical properties of iron, especially the oxidation state, local coordination and spin state, are subject of extensive research in order to understand the structural and electronic properties of minerals as well as the mechanism of chemical reactions at extreme conditions. The local chemical and physical properties of iron in minerals can be studied by core-level spectroscopy using sensitive techniques like x-ray absorption or electron energy loss spectroscopy, which are routinely applied to measure absorption edges of elements in compounds. However, these tools cannot be applied at extreme conditions when diamond anvil cells in combinations with external or laser heating are utilized. X-ray Raman scattering, a non-resonant inelastic X-ray scattering technique, can be used for bulk sensitive studies of low energy absorption edges by hard x-rays. In contrast to x-ray absorption spectroscopy or electron energy loss spectroscopy, X-ray Raman scattering can be applied also using highly absorbing sample environments being a perfect alternative for high pressure high temperature applications. On the way towards extreme conditions, novel measurements of the Fe L2/3- and M2/3-are performed on pre-characterized geologically relevant materials to prove the capability of such a study as well the sensitivity of the Fe M2/3-edge on the oxidation state and the local coordination of iron in compounds. In addition, the momentum transfer dependence of the spectra, which is a special feature of inelastic X-ray scattering, is discussed. The results are subsequently used to obtain quantitative results about the oxidation state of iron in glasses and to study the impact of the local coordination. Furthermore, first in-situ study of the Fe M2/3-edge is presented to track the high-spin to low-spin transition in FeS at pressures up to 10 GPa. In combination with atomic multiplet crystal field calculations, in-situ measurements of the Fe M2/3-edge can be used to extract quantitative information about the crystal field splitting, the main component of the spin cross-over process. To simulate the conditions of the inner Earth a portable double-sided laser heating setup optimized for inelastic X-ray scattering is designed and constructed in order to provide a possibility to perform high temperature experiments.
Subject Headings: X-ray absorption spectroscopy
X-ray Raman scattering
Iron speciation
High pressure
Laser heating
Issue Date: 2014-07-29
Appears in Collections:Experimentelle Physik I

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