Ref HAL: hal-01531002_v1
DOI: 10.1038/ncomms13538
WoS: WOS:000388991800001
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6 Citations
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Reply to 'Strongly-driven Re + CO2 redox reaction at high-pressure and high-temperature'.

Ref HAL: hal-01390130_v1
DOI: 10.1088/0022-3727/48/50/504008
WoS: 000368443100010
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2 Citations
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The results obtained by high pressure neutron powder diffraction and single-crystal x-ray diffraction for the P4mm–Pm $\bar{3}$ m phase transition in the prototype ferroelectric perovskite lead titanate are shown. Neutron diffraction is found to be strongly sensitive to the dipolar moment in the PbTiO3 unit cell due to the gradual reduction of the displacement of the Ti and O atoms from centrosymmetric positions in the cubic perovskite structure which exhibits anti-phase scattering of Pb, Ti and O atoms. From applying both techniques, the anomalously high Debye–Waller factor for the lead atoms confirms the disordered character of the cubic phase. High pressure single crystal x-ray diffraction also perfectly describes the ferroelectric–paraelectric transition and will be the technique of choice to solve higher pressure structures for PbTiO3.

Ref HAL: hal-01202111_v1
DOI: 10.1021/acs.jpcc.5b00318
WoS: WOS:000352823300025
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14 Citations
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Microporous AlPO4-54, which exhibits the largest pores among zeolites and aluminophosphates with a diameter of 12.7 Å, was investigated at high pressure by X-ray powder diffraction (XRD), mid- and far-infrared (IR) spectroscopy in diamond anvil cells. The material undergoes a phase transition beginning around 0.8 GPa. The amount of AlPO4-8 gradually increases with pressure and the phase transition is complete between 2 and 3 GPa. The closure of the (P—O—Al) angle destabilizes the structure of AlPO4-54, which drives the transition to AlPO4-8. The pressure-induced phase transformation of AlPO4-54 to AlPO4-8 is associated with a symmetry reduction from hexagonal to orthorhombic and with a change in the unidirectional ring channel parallel to the c-axes from 18 to 14 AlO4 and PO4 tetrahedra. An abrupt decrease along the b direction is linked to the formation of 4 new rings of 6 tetrahedra with significant structural reorganization. The transition is followed by irreversible amorphization beginning around 3.5 GPa due to the collapse of the pores. The amorphization of AlPO4-8 was detected from the disappearance of the XRD lines, abrupt shifts, and strong broadening of the mid-IR modes, and by changes in the pressure dependence of the mid- and far-IR modes, indicating a lower compressibility for the more dense amorphous form. Far-IR spectra indicate that the new amorphous form retains the local structure of AlPO4-8.

Ref HAL: hal-01144926_v1
DOI: 10.1021/jp5126206
WoS: 000353603500005
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4 Citations
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Gallium arsenate (GaAsO4) has the highest piezoelectric properties among α-quartz-type materials. We describe first-principles calculations of the linear and second-order nonlinear optical properties of GaAsO4 combined with measurements of its second harmonic generation (SHG). Our calculations show that GaAsO4 has a SHG efficiency between 7.1 (LDA) and 12.3 pm/V (GGA), which is in agreement with our experiments (7.5 ± 1.5 pm/V) using the technique of Maker fringes. This SHG efficiency, attributed to an electronic transition from O 2p to As 4 s states, is higher than that observed in GaPO4 due to a better polarizability of As atoms. Thus, the thermal stability of GaAsO4 (no phase transition up to its thermal decomposition at 1303 K) associated with its high laser damage threshold (0.93 GW/cm2) make this compound a promising bifunctional material for piezoelectric and nonlinear optical applications at high temperatures.

Ref HAL: hal-01573026_v1
DOI: 10.1088/1742-6596/500/2/022010
WoS: 000337722900011
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Zeolites exhibit an immense range of applications, such as those in the chemical industry, electronics and photonics among others. We used non-catalytic zeolites in an entirely new fashion. In fact, high pressure (0.5-26 GPa) chemical reactions of simple molecules in the pores of a pure SiO2 zeolite, silicalite were performed in the diamond anvil cell to obtain unique nano-composites with drastically modified properties. These materials were investigated using a combination of X-ray diffraction and optical spectroscopy. We will first show how silicalite can be easily filled by simple molecules at high pressures and how this filling deactivates pressure induced amorphization of the silica framework. We will then present a silicon carbonate phase synthesized by reacting silicalite and molecular CO2 that fills the nano-pores, at 18-26 GPa and 600-980 K; the resulting compound is slightly metastable at room pressure. On the other hand, a nano-composite, which is stable at room temperature and pressure, is obtained by photo-polymerizing ethylene at 0.5-1.5 GPa under UV (351-364 nm) irradiation in the channels of silicalite. The structure of this material is characterized by single polyethylene chains adapting very well to the confining channels, which significantly modifies the physical properties of the silicalite framework. These findings may pave the way to the high pressure synthesis of a unique generation of technological materials

Ref HAL: hal-01135023_v1
DOI: 10.1039/C4CP00186A
WoS: 000337122000039
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12 Citations
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Confined H$_2$O molecules act as local probes for depressurization phenomena during the pressure induced amorphisation of faujasite NaX at which the OH stretching frequency first decreases and then increases almost to its room pressure value upon further compression. Pair distribution function (PDF) analysis provides evidence that amorphisation corresponds to a collapse of the structure around hydrated sodium cations with strong distortion of the secondary building units (double six-membered rings, sodalite cages). Both the use of guest molecules as local probes in far- and mid-infrared spectroscopy, where we correlate intermolecular water H bonding vibrations and internal mode behaviour under confinement, and PDF analysis could be of great use to study the mechanical behaviour of other hydrated materials.

Ref HAL: hal-01084087_v1
Ref Arxiv: 1412.3536
DOI: 10.1021/ic402409f
WoS: 000334902400008
Ref. & Cit.: NASA ADS
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2 Citations
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Relaxor ferroelectric perovskites are highly polarizable and can exhibit giant coupling between elastic strain and an applied electric field. Here, we report an in situ extended X-ray absorption fine structure (EXAFS) study of a PbZn1/3Nb2/3O3 (PZN) single crystal as a function of the electric field. We show that the strong dipoles in the NbO6 octahedra bonds are aligned along the four < 011 > directions close to the orientation of the electric field, while a small reversible polar shift occurs for Zn in the direction of the electric field, i.e., positive or negative. This reversible Zn-O polar shift is proposed to play an important role in both the "easy" switching of the ferroelectric polarization and the giant piezoelectric effect in PZN.