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

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

Melting Curve and Isostructural Solid Transition in Superionic Ice

International audienceThe phase diagram and melting curve of water ice is investigated up to 45 GPa and 1600 K by synchrotron x-ray diffraction in the resistively and laser heated diamond anvil cell. Our melting data evidence a triple point at 14.6 GPa, 850 K. The latter is shown to be related to a first-order solid transition from the dynamically disordered form of ice VII, denoted ice VII 0 , toward a high-temperature phase with the same bcc oxygen lattice but larger volume and higher entropy. Our experiments are compared to ab initio molecular dynamics simulations, enabling us to identify the high-temperature bcc phase with the predicted superionic ice VII 00 phase [J.-A

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