24 research outputs found
Pressure-induced structural changes in α-MoO3 probed by X-ray absorption spectroscopy
The authors are grateful to Prof. Alain Polian for providing NDAC cell. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. The work was supported by philanthropist MikroTik and administrated by the University of Latvia Foundation.Energy-dispersive X-ray absorption spectroscopy at the Mo K-edge was used to study pressure-induced (up to 36 GPa) changes in the local atomic structure of 2D layered oxide α-MoO3. A linear combination analysis based on the low and high-pressure X-ray absorption near edge structure (XANES) spectra shows clear evidence of two high-pressure phases, existing at 18-25 GPa and above 32 GPa. The first transition is due to gradual decrease of the interlayer gap, whereas the second one - to its collapse and oxide structure reconstruction. The local atomic structure around molybdenum atoms at 0.2, 18.5 and 35.6 GPa was determined from the extended X-ray absorption fine structure (EXAFS) using reverse Monte Carlo calculations.Project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART
XMCD under pressure at the Fe K edge on the energy dispersive beamline of the ESRF
The present paper demonstrates the feasibility of X-ray Absorption
Spectroscopy (XAS) and X-ray Magnetic Circular Dichroism (XMCD) at high
pressure at the Fe-K edge on the ID24 energy dispersive beamline of the ESRF.
In 3d transition metals, performing experiments at the hard X-ray K-edge rather
than at the magnetically interesting soft X-ray L-edges represents, the only
way to access the high pressure regime obtainable with Diamond Anvil Cells. The
simultaneous availability of a local structure (XAS) and of a magnetic (XMCD)
probe on the sample in identical thermodynamical conditions is essential to
study correlations between local structural and magnetic properties. We briefly
summarize the state of the art theoretical understanding of K-edge XMCD data,
then illustrate the setup of beamline ID24 for high pressure XMCD experiments
and underline the conditions required to perform measurements at the K-edges of
3d transition metals. Finally, we present two examples of recent high pressure
results at the Fe-K edge in pure Fe and Fe3O4 powder
Emergence of ferromagnetism and Jahn-Teller distortion in low Cr-substituted LaMnO3
The emergence of a ferromagnetic component in with low Cr-for-Mn
substitution has been studied by x-ray absorption spectroscopy and x-ray
magnetic circular dichroism at the Mn and Cr K edges. The local magnetic moment
strength for the Mn and Cr are proportional to each other and follows the
macroscopic magnetization. The net ferromagnetic components of and
are found antiferromagnetically coupled. Unlike hole doping by La
site substitution, the inclusion of ions up to x = 0.15 does not
decrease the Jahn-Teller (JT) distortion and consequently does not
significantly affect the orbital ordering. This demonstrates that the emergence
of the ferromagnetism is not related to JT weakening and likely arises from a
complex orbital mixing.Comment: 5 figure
Structures cristallographique et magnetique des superreseaux metalliques par dichroisme lineaire et circulaire des rayons X
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Electronic and magnetic properties of iron hydride under pressure: An experimental and computational study using x-ray absorption spectroscopy and x-ray magnetic circular dichroism at the Fe K edge
International audienceThe application of a 3.5 GPa pressure on Fe in a H 2 environment leads to the formation of iron hydride FeH. Using a combination of high pressure x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at the Fe K edge, we have investigated the modification of electronic and magnetic properties induced (i) by the transition from bcc-Fe to dhcp (double hexagonal)-FeH under pressure and (ii) by the compression of FeH up to 28 GPa. XAS and XMCD spectra under pressure have been computed in bcc-Fe and dhcp-FeH within a monoelectronic framework. Our approach is based on a semirelativistic density-functional theory (DFT) calculation of the electron density in the presence of a core hole using plane waves and pseudopotentials. Our method has been successful to reproduce the experimental spectra and to interpret the magnetic and electronic structure of FeH. In addition, we have identified a transition around 28 GPa, which is a purely magnetic transition from a ferromagnetic state to a paramagnetic state
Influence of Monomer Feeding on a Fast Gold Nanoparticles Synthesis: Time-Resolved XANES and SAXS Experiments
International audienc
Ce/Al correlation in aluminosilicate glasses and optical silica fiber preforms
International audienc
Cerium redox state in silicate glasses and melts: implications for property changes and structural roles
International audienc
Development of a high temperature diamond anvil cell for x ray absorption experiments under extreme conditions
X-ray absorption spectroscopy (XAS) is presently a powerful and established tool to investigate solid and liquid matter at high pressure and high temperature (HP-HT). HP-HT XAS experiments rely on high pressure technology whose continuous development has extended the achievable range up to 100 GPa and more. In high pressure devices, high temperature conditions are typically obtained by using internal and external resistive heaters or by laser heating. We have recently developed a novel design for an internally heated diamond anvil cell (DAC) allowing XAS measurements under controlled high temperature conditions (tested up to about 1300 K). The sample in the new device can be rapidly heated or cooled (seconds or less) so the cell is suitable for studying melting/crystallization dynamics when coupled with a time-resolved XAS setup (second and sub-second ranges). Here we describe the internally heated DAC device which has been realized and tested in experiments on pure selenium at the energy dispersive ODE beamline of Synchrotron SOLEIL. We also present results obtained in XAS experiments of elemental Se using a large volume Paris-Edinburgh press, as an example of the relevance of structural studies of matter under extreme conditions