High pressure and high temperature in situ X-ray diffraction studies in the Paris-Edinburgh cell using a laboratory X-ray source

International audienceWe have developed a new laboratory experimental set-up to study in situ the pressure-temperature phase diagram of a given pure element or compound, its associated phase transitions, or the chemical reactions involved at high pressure and high temperature (HP-HT) between different solids and liquids. This new tool allows laboratory studies before conducting further detailed experiments using more brilliant synchrotron X-ray sources or before kinetic studies. This device uses the diffraction of X-rays produced by a quasi-monochromatic micro-beam source operating at the silver radiation (λ(Ag)Kα1,2 ≈ 0.56Å). The experimental set-up is based on a VX Paris-Edinburgh cell equipped with tungsten carbide or sintered diamond anvils and uses standard B-epoxy 5 or 7mm gaskets. The diffracted signal coming from the compressed (and heated) sample is collected on an image plate. The pressure and temperature calibrations were performed by diffraction, using conventional calibrants (BN, NaCl and MgO) for determination of the pressure, and by crossing isochores of BN, NaCl, Cu or Au for the determination of the temperature. The first examples of studies performed with this new laboratory set-up are presented in the article: determination of the melting point of germanium and magnesium under HP-HT, synthesis of MgB2 or C-diamond and partial study of the P, T phase diagram of MgH2

Strategy for the management of diabetic macular edema: the European Vitreo-Retinal Society macular edema study

Objective. To compare the efficacy of different therapies in the treatment of diabetic macular edema (DME). Design. Nonrandomized, multicenter clinical study. Participants. 86 retina specialists from 29 countries provided clinical information on 2,603 patients with macular edema including 870 patients with DME. Methods. Reported data included the type and number of treatment(s) performed, the pre-and posttreatment visual acuities, and other clinical findings.The results were analyzed by the French INSEE (National Institute of Statistics and Economic Studies). Main Outcome Measures. Mean change of visual acuity and mean number of treatments performed. Results.The change in visual acuity over time in response to each treatment was plotted in second order polynomial regression trend lines. Intravitreal triamcinolone monotherapy resulted in some improvement in vision. Treatmentwith threshold or subthreshold grid laser also resulted in minimal vision gain. Anti-VEGF therapy resulted in more significant visual improvement. Treatment with pars plana vitrectomy and internal limiting membrane (ILM) peeling alone resulted in an improvement in vision greater than that observed with anti-VEGF injection alone. In our DME study, treatment with vitrectomy and ILM peeling alone resulted in the better visual improvement compared to other therapies

ETUDE DE CHALCOGENURES ET OXYCHALCOGENURES DE TERRES RARES ET METAUX DE TRANSITION A STRUCTURATION BIDIMENSIONNELLE (CRISTALLOCHIMIE, MAGNETISME ET INCOMMENSURABILITE)

NANTES-BU Sciences (441092104) / SudocSudocFranceF

RX & Matière (2015)

Comité d'organisatio

Unidirectional charge-density-wave sliding in two-dimensional rare-earth tritellurides

Nonlinear transport properties in the layered TbTe3 and GdTe3 rare-earth tritellurides with a charge- density-wave( CDW) transition above room temperature have been studied along different crystal- lographic orientations.The pronounced effect of collective CDW motion is observed along c-axis andi s absent completely in the perpendicular direction demonstrating the unidirectional character of the CDW.In contrast to one-dimensiona lCDWs the threshold electric field for CDW sliding is linearly temperature dependent in a wide range of temperature

Differences and Similarities between Lanthanum and Rare-Earth Iodate Anhydrous Polymorphs: Structures, Thermal Behaviors, and Luminescent Properties

International audienceThe Ln(IO)(HIO) (y = 1 or 1.33) compounds are isostructural with the La(IO)(HIO) phases, but thermal studies reveal different behaviors. On the one hand, the partial thermal decompositions of these lanthanide compounds lead to the Ln(IO) formulation, with a room temperature structure different from the β-La(IO) obtained from La(IO)(HIO). On the other hand, the partial thermal decompositions of the LaLn(IO)(HIO) compounds prepared with lanthanides ions (Ce, Pr, Nd, Sm, Eu, Gd, and Yb) lead to acentric β-LaLn(IO). As for β-La(IO), reversible structural transitions from β-LaLn(IO) to centrosymmetric γ-LaLn(IO) are observed. Differential scanning calorimetry analyses of LaLn(IO) solid solutions show that the transition temperatures vary with the lanthanide concentration in the solid solution. A transition is observed only up to a certain fraction of lanthanide-ion substitution; this substitution limit decreases with the cationic radius of the lanthanide ion. Finally, the β-LaNd(IO) and β-LaYb(IO) phases are investigated by luminescence spectroscopy

Elastic anomalies at the magnetic phase transitions of TBTe3

International audienceWe report sound velocity and ultrasonic attenuation measurements in the vicinity of the successive magnetic phase transitions Tmag1~6.5 K,Tmag2~5.8 K and Tmag3~5.3 K in the charge density wave TbTe3 compound. A detailed investigation of the critical contributions to the temperature dependences of the sound velocity and ultrasonic attenuation is presented. Anisotropic stress dependences Tmag1/dp found at the antiferromagnetic phase transition Tmag1 is associated with the layered structure of this compound. An abrupt step-like increase in the velocity and a sharp peak in the attenuation are observed with the longitudinal and shear modes at the lock-in magnetic phase transition Tmag3=5.3 K. The critical velocity and attenuation behaviors in the high temperature paramagnetic state above Tmag1 are described in terms of a phenomenological dynamic scaling expression

Evidence of reaction intermediates in microwave-assisted synthesis of SHG active α-La(IO 3 ) 3 nanocrystals

International audienceWe explore here how, under microwave assisted hydrothermal process, various synthesis conditions influence the formation of different lanthanum iodate compounds: α-La(IO3)3, La(IO3)3(H2O), La(IO3)3(HIO3) and La(IO3)2.66(OH)0.66. Whatever the intial [La 3+ ]:[IO3-] ratio, α-La(IO3)3 crystallizes if the synthesis temperature exceeds 220°C. Phase transformations in solid state or under hydrothermal synthesis are also discussed. Interestingly, we evidence the full phase transformation under hydrothermal synthesis from the new hydrate form La(IO3)3(H2O) into stable and optically active α-La(IO3)3 through an appropriate hydrothermal process. This evolution can be explained by structural rearrangements of the coordination sphere of lanthanum atoms, stabilizing the structure

First evidence of a phase transition in a high-pressure metal iodate. Structural and thermal studies of AgIO3 polymorphs

International audienceA new phase of silver iodate, β-AgIO3, was obtained at 2.7 GPa by heating the α-AgIO3 precursor above 240 °C. β- AgIO3 is the first iodate obtained at high pressure that stabilizes under normal conditions. The crystal structure was determined by X-ray powder diffraction and Rietveld refinement. In comparison to α-AgIO3, which crystallizes in the Pbc21 acentric orthorhombic space group with the lattice parameters a = 7.265(2) Å, b = 15.17(4) Å, c = 5.786(2) Å, and V = 638(2) Å3, β-AgIO3 crystallizes in the Pbca centric orthorhombic space group, with the following parameters: a = 6.137(2) Å, b = 16.980(4) Å, c = 5.827(1) Å, and V = 607.3(3) Å3. Differential thermal analysis under high pressure (2.7 GPa) and structural studies showed an endothermic transformation at 260 °C corresponding to a first-order reconstructive phase transition from α-AgIO3 to β-AgIO3. The thermal behaviors of α-AgIO3 and β-AgIO3 were studied by differential scanning calorimetry at ambient pressure and in situ temperature-dependent X-ray powder diffraction

Les rayons X au service de l’art pariétal australien : identification des matières picturales et des phases d’altération

International audienc