Valence‐to‐core X‐ray emission spectroscopy of titanium compounds using energy dispersive detectors

Abstract

X-ray emission spectroscopy (XES) of transition metal compounds is a powerful tool for investigating the spin and oxidation state of the metal centers. Valence-to-core (vtc) XES is of special interest, as it contains information on the ligand nature, hybridization, and protonation. To date, most vtc-XES studies have been performed with high-brightness sources, such as synchrotrons, due to the weak fluorescence lines from vtc transitions. Here, we present a systematic study of the vtc-XES for different titanium compounds in a laboratory setting using an X-ray tube source and energy dispersive microcalorimeter sensors. With a full-width at half-maximum energy resolution of approximately 4 eV at the Ti Kβ lines, we measure the XES features of different titanium compounds and compare our results for the vtc line shapes and energies to previously published and newly acquired synchrotron data as well as to new theoretical calculations. Finally, we report simulations of the feasibility of performing time-resolved vtc-XES studies with a laser-based plasma source in a laboratory setting. Our results show that microcalorimeter sensors can already perform high-quality measurements of vtc-XES features in a laboratory setting under static conditions and that dynamic measurements will be possible in the future after reasonable technological developments. 1 | INTRODUCTION Non-resonant X-ray emission spectroscopy (XES) is a powerful technique for the study of occupied electron orbitals in the valence shell with elemental selectivity and under in situ conditions. 1-8 In XES, X-ray photons with energy greater than the binding energy of an innershell electron produce core-hole vacancies. These core holes are quickly filled by the relaxation of less tightly bound electrons with concomitant X-ray fluorescence or

Sensitivity of the Kβ″ X-ray Emission Line to Coordination Changes in GeO2 and TiO2

“…Our calculated vtc XES spectrum of rutile-TiO 2 is in reasonable agreement with experimental data (see, e.g., refs and ) and shows the Kβ 1,3 , Kβ″, and Kβ 2,5 lines separated from each other (Figure a). The simulated spectra of the three TiO 2 polymorphs of the rutile-, ZrO 2 -, and PbCl 2 -type with 6-, 7-, and 9-fold coordination (and of metallic titanium as reference) are shown in Figure b, normalized to the area of the Kβ 1,3 line.…”

“…It is known to allow for insight into several aspects of the first ligand coordination shell around the probed atom, such as chemical sensitivity, cation–ligand bond length, and—the target of this study—CN. 8 , 9 , 11 − 25 …”

“…Ti, V, Mn, Fe, Cr, Cu, and Nb. 8 , 9 , 11 − 25 The sensitivity of the Kβ″ line with respect to cation–ligand bond length has been demonstrated in e.g. Mn, V, Ti, and Ge systems 5 , 12 − 14 , 23 and results from the variable extent of overlap between the ligands’ n s orbitals with the valence orbitals of the cation: When the bond length shortens, the overlap increases, leading to a higher “crossover” transition probability and therefore to a more intense Kβ″ line.…”

“…It reflects the valence orbital hybridization with the 2s orbitals of the coordinating ligands, as evidenced in projected electronic density-of-states (pDOS) calculations. ,− The Kβ″ line is also termed “crossover” transition and is absent in any vtc XES spectrum of a cation in its elemental form. It is known to allow for insight into several aspects of the first ligand coordination shell around the probed atom, such as chemical sensitivity, cation–ligand bond length, andthe target of this studyCN. ,,− …”

“…The chemical sensitivity of the Kβ″ line with respect to the type of ligand results from differences in binding energy of the n s electrons of the ligands, e.g., about 5 eV between nitrogen and oxygen, and has been demonstrated in a variety of studies on e.g. Ti, V, Mn, Fe, Cr, Cu, and Nb. ,,− The sensitivity of the Kβ″ line with respect to cation–ligand bond length has been demonstrated in e.g. Mn, V, Ti, and Ge systems ,− , and results from the variable extent of overlap between the ligands’ n s orbitals with the valence orbitals of the cation: When the bond length shortens, the overlap increases, leading to a higher “crossover” transition probability and therefore to a more intense Kβ″ line .…”