X-ray free electron laser heating of water and gold at high static pressure

The study of water at high pressure and temperature is essential for understanding planetary interiors but is hampered by the high reactivity of water at extreme conditions. Here, indirect X-ray laser heating of water in a diamond anvil cell is realized via a gold absorber, showing no evidence of reactivity

ÉTUDE PAR DIFFRACTION X DES DÉFAUTS PLANAIRES MIS EN ÉVIDENCE DANS LES PHASES AnBnO3n+2 DES SYSTÈMES La2Ti2O7-CaTiO3, Nd2Ti2O7-CaTiO3, ET Ca2Nb2O7-CaTiO3 (A = La, Nd, Ca ; B = Ti, Nb)

Les phases AnBnO3n+2 mises en évidence dans les systèmes La2Ti2O7-CaTiO3, Nd2Ti2O7-CaTiO3 et Ca2Nb2O7-CaTiO3 possèdent une structure qui dérive de celle de la perovskite par des cisaillements périodiques délimitant des feuillets de n octaèdres d'épaisseur. Chaque feuillet est constitué de couches X et Y alternant régulièrement suivant la direction [100]. Deux types d'arrangement ont été observés XY (I) et XX (II), suivant la direction [010]*. Ceux-ci présentent le plus souvent des fautes d'empilement réparties au hasard qui entrainent dans le spectre de diffraction X un allongement selon [010]* des taches hkl avec h impair. Un calcul de l'intensité diffusée en fonction de la probabilité de défauts est proposé. Intensités observées et calculées sont comparées.The AnBnO3n+2 phases observed in the systems La2Ti2O7-CaTiO3, Nd2Ti2O7-CaTiO3 and CanNb2O7-CaTiO3 have a structure derived from the perovskite structure by periodic crystallographic shears that delimitate n octahedron thick sheets. Each sheet consists of regularly alternate X and Y slabs in the [100] direction. Two types of arrangement can be observed in the [010]* direction : XY (I) and XX (II) : They most often show random stacking faults that draw out, along [010]* direction, all the reflections with odd h. A calculation of the diffuse intensity versus the probability of faults is proposed. The observed intensities will be compared to calculated intensities

Photothermal characterization of refractories for the steel industry

The companion paper ("Non-destructive Characterisation of Refractories by Mirage Effect and Photothermal Microscopy", by G. Savignat, P. Boch, L. Pottier, D. Vandembroucq, and D. Fournier, in the same EUROMAT meeting) has explained the potential of photothermal techniques for the non-destructive evaluation of refractories. The present study gives photothermal data for three sorts of refractories: carbon bonded alumina, aluminium nitride / boron nitride bonded alumina, and carbon-bonded magnesia. The mirage effect and the photothermal microscopy are shown to be complementary methods, able to bring information about both macroscopic and microscopic thermal diffusivity

Structure of liquid carbon dioxide at pressures up to 10 GPa

The short-range structure of liquid carbon dioxide is investigated at pressures (P) up to 10 GPa and temperatures (T) from 300 to 709 K by means of x-ray diffraction experiments in a diamond anvil cell (DAC) and classical molecular dynamics (MD) simulations. The molecular x-ray structure factor could be measured up to 90 nm(-1) thanks to the use of a multichannel collimator which filters out the large x-ray scattered signal from the diamond anvils. The experimental data show that the short-range structure of fluid CO2 is anisotropic and continuously changes from a low density to a high density form. The MD simulations are used to extract a detailed three-dimensional analysis of the short-range structure over the same P-T range as the experiment. This reveals that upon compression, a fraction of the molecules in the first-neighbor shell change orientation from the (distorted) T shape to the slipped parallel configuration, accounting for the observed structural changes. The local arrangement is found similar to that of the Pa (3) over bar solid at low density and to that of the Cmca crystal at high density. The comparison with other simple quadrupolar liquids, either diatomic (I-2) or triatomic (CS2), suggests that this structural evolution with density is a general one for these systems.Funding Agencies|ESRF [HD-463]; Agence Nationale de la Recherche [ANR 13-BS04-0015]; Grand Equipement National de Calcul Intensif French National Supercomputing Facility [x2013091387]</p

Topologically frustrated ionisation in a water-ammonia ice mixture

Water and ammonia are major constituents of icy planet interiors, however their phase behaviour under extreme conditions remain relatively unknown. Here, the authors show that ammonia monohydrate transforms under pressure into an alloy composed of molecules as well as ions, owing to a topological frustration