| Zusammenfassung |
X-ray spectrometry, enhanced by advanced theoretical models, has become indispensable for probing the electronic structure of materials at the atomic level, offering essential insights into their elemental and electronic environments. Yet, validating these
models poses significant challenges, including the risk of circular conclusions, where models are tailored to fit the experimental data they aim to predict. This thesis addresses these challenges through the use of independent measurements coupled with
calibrated instrumentation, thereby enhancing the accuracy and reliability of quantitative X-ray spectroscopy for diverse material systems, including transition metals like titanium and its oxides, complex mixed covalent and ionic crystals such as cyanates
and thiocyanates, and lithium-ion battery cathode materials. Methodologically, the study employs a multi-edge approach that combines complementary measurements across both K and L edges using X-ray absorption spectroscopy, X-ray emission spectroscopy, and resonant inelastic X-ray scattering. These measurements are compared with theoretical predictions from the ocean code, utilizing a consistent set of input parameters for each material. The calibration of energy scales ensures transferability from the beamline to detector systems, significantly improving the reliability of spectroscopic measurements, reducing systematic errors, and supporting an objective evaluation of theoretical model accuracy. The findings extend the validation of the ocean code, demonstrating its broad applicability and precision by conducting multi-edge studies of Ti and its oxides. Specific areas for improvement are identified, such as discrepancies in spectroscopic features of metal-ligand systems at transition metal L edges and oxygen K edge, which arise from oversimplifications in modeling electron interactions. Extending the scope to light elements
in mixed covalent and ionic bonds, the thesis validates theoretical calculations in predicting effects of interchanging atoms within a class of inorganic salts. An innovative, slit-less design for a wavelength-dispersive spectrometer is developed, significantly
enhancing measurement efficiency and flexibility for material characterization. Combining the learning from the validation studies and enhanced spectroscopy methods to quantify oxidation state changes, a critical question in battery material research
regarding the effect of increasing the Ni content on the oxidation state of Co in NMC cathodes is answered. This research bridges gaps in our understanding of material properties through the integration of calibrated instrumentation and advanced computational methods, laying a foundation for future scientific exploration and technological innovation in materials science. |
