Inelastic x-ray scattering from high pressure fluids in a diamond anvil cell

Gorelli, Federico A.; Santoro, Mario; Scopigno, T.; Krisch, M.; Bryk, Taras; Ruocco, G.; Ballerini, R.

doi:10.1063/1.3076123

Cited by 15 publications

(13 citation statements)

References 22 publications

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“…Isothermal, experimental and molecular dynamics simulation data on argon are reported in pink inside a rectangle. The extra point on argon outside the rectangle has been obtained in another experiment at room temperature 20 . Open points represent cases where the positive dispersion of the sound velocity exhibits low values, full points cases where there is a clear signature of high positive dispersion.…”

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confidence: 87%

The Widom line as the crossover between liquid-like and gas-like behaviour in supercritical fluids

Simeoni

Bryk

Gorelli³

et al. 2010

Nature Phys

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According to textbook definitions 1 , there exists no physical observable able to distinguish a liquid from a gas beyond the critical point, and hence only a single fluid phase is defined. There are, however, some thermophysical quantities, having maxima that define a line emanating from the critical point, named 'the Widom line' 2 in the case of the constant-pressure specific heat. We determined the velocity of nanometric acoustic waves in supercritical fluid argon at high pressures by inelastic X-ray scattering and molecular dynamics simulations. Our study reveals a sharp transition on crossing the Widom line demonstrating how the supercritical region is actually divided into two regions that, although not connected by a first-order singularity, can be identified by different dynamical regimes: gas-like and liquid-like, reminiscent of the subcritical domains. These findings will pave the way to a deeper understanding of hot dense fluids, which are of paramount importance in fundamental and applied sciences. Throughout the past century great effort was devoted to the investigation of the physics of fluid systems: all of their thermodynamical properties in the phase diagram below the critical point are nowadays well known 3. On the other hand, experimental studies in the supercritical region have been limited so far, owing to technical difficulties. The fluid pressure-temperature (P-T) phase diagram includes a subcritical region with two different phases (liquid and gas, separated by the liquid-vapour coexistence line) and a single-phase supercritical region. Structural and dynamical investigations, aiming to extend the study of the fluid phase diagram well beyond the critical point play a crucial role in many fundamental and applied research fields, such as condensedmatter physics, Earth and planetary science, nanotechnology and waste management 4-8. From an experimental point of view, the challenge is to close the gap between studies on fluid and solid phases using diamond anvil cell (DAC) techniques 9-12 and studies on hot dense fluids by shock waves 13,14. As this gap typically overlaps with the supercritical fluid region, it is crucial to track the evolution of transport properties of fluids beyond the critical point. In the specific case of acoustic waves, most of the liquids show the so-called positive dispersion. This is an increase of the speed of sound as a function of wavelength from the continuum limit (λ → ∞)-in which the acoustic waves propagate adiabatically-to the short-wavelength limit, that is, on approaching the interparticle distances 15-17. The ultimate origin of this effect can be traced back to the presence of one (or more)

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confidence: 87%

The Widom line as the crossover between liquid-like and gas-like behaviour in supercritical fluids

Simeoni

Bryk

Gorelli³

et al. 2010

Nature Phys

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460

328

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“…More recently, it has been discovered that subtle but remarkable changes in supercritical fluids do occur in the positive sound dispersion (PSD)345. These changes posses the potential to part the phase diagram in a gas like and a liquid like region.…”

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confidence: 99%

Dynamics and Thermodynamics beyond the critical point

Gorelli¹,

Bryk

Krisch

et al. 2013

Sci Rep

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Sudden changes in the dynamical properties of a supercritical fluid model have been found as a function of pressure and temperature (T/Tc = 2–5 and P/Pc = 10–103), striving with the notion of a single phase beyond the critical point established by thermodynamics. The sound propagation in the Terahertz frequency region reveals a sharp dynamic crossover between the gas like and the liquid like regimes along several isotherms, which involves, at sufficiently low densities, the interplay between purely acoustic waves and heat waves. Such a crossover allows one to determine a dynamic line in the phase diagram which exhibits a very tight correlation with a number of thermodynamic observables, showing that the supercritical state is remarkably more complex than thought so far.

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“…The DAC was placed inside a vacuum chamber especially designed for IXS experiments on fluids [31]. The dynamic structure factor was simultaneously measured at nine different momentum transfer values in the range 2 − 15 nm −1 .…”

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confidence: 99%

Dynamical Crossover at the Liquid-Liquid Transformation of a Compressed Molten Alkali Metal

et al. 2013

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Density-driven phase transformations are a known phenomenon in liquids. Pressure-driven transitions from an open low-density to a higher-density close-packed structure were observed for a number of systems. Here, we show a less intuitive, inverse behavior. We investigated the electronic, atomic, and dynamic structures of liquid Rb along an isothermal line at 573 K, at 1.2-27.4 GPa, by means of ab initio molecular dynamics simulations and inelastic x-ray scattering experiments. The excellent agreement of the simulations with experimental data performed up to 6.6 GPa validates the overall approach. Above 12.5 GPa, the breakdown of the nearly-free-electron model drives a transition of the pure liquid metal towards a less metallic, denser liquid, whose first coordination shell is less compact. Our study unveils the interplay between electronic, structural, and dynamic degrees of freedom along this liquid-liquid phase transition. In view of its electronic nature, we believe that this behavior is general for the first group elements, thus shedding new light into the high-pressure properties of alkali metals.

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Inelastic x-ray scattering from high pressure fluids in a diamond anvil cell

Cited by 15 publications

References 22 publications

The Widom line as the crossover between liquid-like and gas-like behaviour in supercritical fluids

The Widom line as the crossover between liquid-like and gas-like behaviour in supercritical fluids

Dynamics and Thermodynamics beyond the critical point

Dynamical Crossover at the Liquid-Liquid Transformation of a Compressed Molten Alkali Metal

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