High pressure behavior of CsC8 graphite intercalation compound

International audienceThe high pressure phase diagram of CsC8 graphite intercalated compound has been investigated at ambient temperature up to 32 GPa. Combining X-ray and neutron diffraction, Raman and X- ray absorption spectroscopies, we report for the first time that CsC8, when pressurized, undergoes phase transitions around 2.0, 4.8 and 8 GPa. Possible candidate lattice structures and the transition mechanism involved are proposed. We show that the observed transitions involve the structural re- arrangement in the Cs sub-network while the distance between the graphitic layers is continuously reduced at least up to 8.9 GPa. Around 8 GPa, important modifications of signatures of the electronic structure measured by Raman and X-ray absorption spectroscopies evidence the onset of a new transition

Application du rayonnement synchrotron à l'étude des transitions de phases sous haute pression des zéolites. Exemple de la scolécite

Le phénomène d'amorphisation sous haute pression a déjà été observé dans le cas de certains tectosilicates comme le quartz ou les feldspaths. L'objet de cette étude concerne le comportement sous haute pression des zéolites et plus particulièrement de la scolécite. Le phénomène d'amorphisation est mis en évidence par diffraction des rayons X et par microspectrométrie Raman. Cette transformation d'un cristal en un solide hautement désordonné est précédée par des transitions polymorphiques et se produit au-dessous de 10 GPa. La transition cristal-solide amorphe est irréversible et les échantillons ramenés à la pression ambiante présentent en particulier des spectres de diffusion Raman proches de ceux des verres alumino-silicatés obtenus par trempe d'un liquide. Dans certains cas cependant, la décompression s'accompagne d'une WQ de recristallisation. Le comportement hydrostatique ou non-hydrostatique du milieu transmetteur de pression est à prendre en compte dans l'apparition d'un tel phénomène.Pressure-induced amorphization has already been observed in some framework silicates like quartz and feldspars. A similar crystal to highly disordered solid transition is reported in this study for a zeolite named scolecite, which is the calcium end-member of the natrolite group. Pressure-induced amorphization is demonstrated using in-situ X-ray diffraction and Raman spectroscopy. This transformation is preceded by polymorphic transitions and occurs below 10 GPa. The crystal-amorphous transition is irreversible and the pressure quenched samples exhibit Raman specua which bear slrong resemblance with alumino-silicate glasses obtained by quenching a liquid. In some cases however, decompression is accompanied by a rim recrystallisation of the sample. The role of shear stresses seems thus to be crucial during the decompression of the samples

EXAFS Evidence of a Phase Transition in Icosahedral AlLiCu Quasicrystals under High Pressure

In situ EXAFS studies, performed at the Cu K absorption edge, are reported for icosahedral Al6Li3Cu quasicrystals frorn ambient pressure up to 33 GPa. The increase in the average distance of first neighbours around Cu atoms above 20 GPa is interpreted as the finger-print of a phase transition, while the evolution of the disorder parameter could be the signature of phason disorder

Bromine metallization studied by X-ray absorption spectroscopy

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Ultrasonic and Brillouin scattering measurements under pressure near the structural phase transition of strontium titanate

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X-ray absorption spectroscopy on solid krypton np to 20 GPa

International audienceHigh-pressure properties of krypton were investigated by energy-dispersive extended x-ray absorption fine-structure spectroscopy in a diamond anvil cell at room temperature. The equation of state agrees very well with x-ray diffraction data. The pressure dependence of the Debye-Wailer factor was determined and compared with calculations using pair potentials. The analysis of the xray absorption near-edge structure part of the spectrum shows the possibility of measuring the pressure in bubbles of krypton implanted in metallic matrices

Ultrasonic and Brillouin scattering measurements under pressure near the structural phase transition of strontium titanate

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High pressure x-ray absorption spectroscopy at lower energy in the dispersive mode: application to Ce and FePO4.

X-ray absorption spectroscopy (XAS) using a diamond anvil cell has been extended to lower energies (below 6 keV) thanks to smaller diamond anvils and to a new acquisition set-up on the energy dispersive x-ray absorption beamline of LURE. The valence change of Ce with pressure is followed at the LIII edge of cerium up to 8 GPa together with the bond length variation during the same experiment. The pressure induced coordination change around the Fe atom in FePO4 is determined at the Fe K edge through the pre-edge feature behaviour, the XANES modification and the Fe–O bond length increase

Elastic properties of SrTiO/sub 3/ under extreme conditions: a new high pressure ultrasonic measurement set-up

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