Contact

Porträt Prof. Dr. Kvashnina, Kristina; FWOS

Prof. Dr. Kristina Kvashnina

Head of Department "Molecular Structures"
Responsible for the BM20 (ROBL) beamline at ESRF
k.kvashnina@hzdr.de
Phone: +33 476 88 2367

Dr. habil. Andreas Scheinost

Head
Molecular Structures

Phone: +33 476 88 2462
+33 6 340 358 18

Department of Molecular Structures

Research

Synchrotron-based research on the short-range structure, oxidation state and bonding of actinides, using the following methods:
EXAFS: Extended X-ray absorption fine-structure spectroscopy to determine the short-range structure of a target element, i.e. the elemental identity, number and radial distance of atoms in its coordination shell and beyond (typically to radial distances of up to 5 A, in well ordered systems even to 10 A).
HERFD-XANES: High-energy-resolution fluoresence-detected X-ray absorption near-edge structure spectroscopy to derive oxidation states of the target element
XES and RIXS: X-ray emission and resonant inelastic X-ray spectroscopy to derive information on the bonding character (covalent <-> ionic)
P-XRD: Powder X-ray diffraction offering much higher resolution or faster speed (in-situ/in-operando) than with lab sources
SX-XRD: Single-crystal diffraction
Surface-sensitive techniques like CTR (crystal truncation rods) and RAXR (resonant anomalous X-ray reflectivity)
EXAFS, HERFD-XANES, XES and RIXS is not restricted to crystalline solids, but can be applied to a wide range of samples, to derive
information on e.g. aqueous speciation, complexation with dissolved inorganic ligands like chloride, sulfate or nitrate, complexation with organic ligands like acetate or humic acid, interaction with bacteria and plants, sorption to mineral and rock surfaces for actinides an other metals and metalloids.
Due to the high penetration depth of the employed hard X-rays, the methods are suited to study chemical reactions in-situ/in-operando, for instance at very low or high temperatures, under special atmospheres, or under electrochemical potentials.

Latest Publication

Effect of carbon content on electronic structure of uranium carbides

Butorin, S. M.; Bauters, S.; Amidani, L.; Beck, A.; Rossberg, A.; Weiss, S.; Vitova, T.; Kvashnina, K.; Tougait, O.

The electronic structure of UC (x = 0.9, 1.0, 1.1, 2.0) was studied by means of x-ray absorption spectroscopy (XAS) at the C K edge and measurements in the high energy resolution fluorescence detection (HERFD) mode at the U and edges. The full-relativistic density functional theory calculations taking into account the Coulomb interaction U and spin-orbit coupling (DFT+U+SOC) were also performed for UC and UC. While the U HERFD-XAS spectra of the studied samples reveal little difference, the U HERFD-XAS spectra show certain sensitivity to the varying carbon content in uranium carbides. The observed gradual changes in the U HERFD spectra suggest an increase in the C 2p-U 5f charge transfer, which is supported by the orbital population analysis in the DFT+U+SOC calculations, indicating an increase in the U 5f occupancy in UC as compared to that in UC. On the other hand, the density of states at the Fermi level were found to be significantly lower in UC, thus affecting the thermodynamic properties. Both the x-ray spectroscopic data (in particular, the C K XAS measurements) and results of the DFT+U+SOC calculations indicate the importance of taking into account U and SOC for the description of the electronic structure of actinide carbides.

Related publications

DOI: 10.1107/S1600577520014265 is cited by this (Id 37950) publication

Scientific Reports 13(2023), 20434
DOI: 10.1038/s41598-023-47579-7

Publications

Equipment

Experiments are performed at the Rossendorf Beamline (BM20-ROBL), at the European Synchrotron Radiation Facility in Grenoble, France

Team

Most team members are permanently at the ESRF in Grenoble (France).

ROBL Group Picture 2017/12 ©Copyright: HZDR/Denis Morel — ROBL Group Picture 2017/12

Foto: HZDR/Denis Morel

Download

Name	Bld./Office	+49 351 260	Email
Head
Prof. Dr. Kristina Kvashnina	ROBL/21.6.01	+33 476 88 2367	k.kvashnina@hzdr.de
Employees
Name	Bld./Office	+49 351 260	Email
Dr. Lucia Amidani	ROBL/14.1.04	+33 476 88 1982	l.amidanihzdr.de
Dr. Nils Baumann	ROBL/21.6.03	+33 476 88 2849	n.baumannhzdr.de
Jörg Exner	ROBL/BM20	+33 476 88 2372
Dr. Christoph Hennig	ROBL/21.6.02a	+33 476 88 2005
Damien Naudet	ROBL/BM20	+33 476 88 1941	d.naudethzdr.de
Dr. Damien Prieur	ROBL/21.6.04	+33 476 88 2849	d.prieurhzdr.de
Dr. André Roßberg	801/P316	2758
Dr. habil. Andreas Scheinost	ROBL/21.6.04	+33 476 88 2462 +33 6 340 358 18
Thomas Zimmermann	801/P254	3487	t.zimmermannhzdr.de