Melting Curve and Liquid Structure of Nitrogen Probed by X-ray Diffraction to 120 GPa

Weck, Gunnar; Datchi, F.; Garbarino, Gastón; Ninet, Sandra; Queyroux, Jean-Antoine; Plisson, Thomas; Mézouar, M.; Loubeyre, P.

doi:10.1103/physrevlett.119.235701

Cited by 31 publications

(33 citation statements)

References 24 publications

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“…In dense monatomic liquids it is empirically found that the position of the maximum of the FDP, Q M is related to the density ρ through the relation Q M 4.4(4πρ/3) 1/3 [63], and thus (Q M /Q M 0 ) 3 ρ/ρ 0 where Q M 0 and ρ 0 correspond to a reference state. This relation has also been found to be verified in molecular liquids with weak orientational correlations, such as H 2 [26] and N 2 [28]. To test whether it also holds in ammonia, we plot in Fig.…”

Section: A Experimentssupporting

confidence: 56%

“…The purpose of the present study is to extend the experimental investigation to higher pressures in order to determine the structural evolution over a larger range of densities. To this end, we used recently developed techniques for the measurement of the structure of low-Z fluids in the diamond anvil cell by synchrotron x-ray diffraction [25], which have been successfully used in the recent past to study liquid hydrogen [26] and carbon dioxide [27] and allowed to determine the melting lines of liquid nitrogen [28] and ammonia [29] up to the megabar range. Here we present experimental data for liquid ammonia obtained at 690 K and 800 K up to 6.3 GPa.…”

Section: Introductionmentioning

confidence: 99%

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Structure of liquid ammonia at high pressures and temperatures

et al. 2019

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The structure of liquid ammonia (NH3) is investigated from 1 to 6.3 GPa and up to 800 K by means of synchrotron x-ray diffraction (XRD) and ab initio molecular dynamics (AIMD) simulations. The XRD data are used to extract the molecular structure factor S mol (Q), pair distribution function (PDF) g mol (r), and the density of NH3. There is an excellent agreement between present S mol (Q) and g mol (r) at our lowest density and those reported in reference neutron experiments. Our densities agree better with the equation of state of Tillner-Roth et al. [1] than with more recent equation of state (EoS) models. The experimental structure factor and PDF are well reproduced by AIMD simulations using either the BLYP or the PBE exchange-correlation functional. The shapes of S mol (Q) and g mol (r) vary little over the investigated pressure range and suggest a compact liquid with weak orientational correlations between molecules, which is corroborated by the coordination number varying from 12.7 to ∼14. The simulations are used to study the evolution of the site-site pair distribution functions, which reveals that the number of H-bonds per molecule (between 1.5 and 2) do not evolve with density, and that the distribution of H atoms around N atoms becomes more and more anisotropic with pressure.

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Section: A Experimentssupporting

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Structure of liquid ammonia at high pressures and temperatures

et al. 2019

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“…Assigning peak positions to a specific temperature would require the knowledge of the temperature distribution inside the sample, which is not trivial and beyond the scope of this study. Similarly we could not extract the structure factor of the liquid phase as in our previous work on nitrogen 39 due to the weak liquid diffuse scattering signal and poor signal-to-noise ratio.…”

Section: A X-ray Diffraction Experimentsmentioning

confidence: 91%

Melting curve and chemical stability of ammonia at high pressure: Combined x-ray diffraction and Raman study

et al. 2019

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The melting curve and stability of ammonia (NH3) is investigated up to 40 GPa and 3500 K by x-ray diffraction and Raman spectroscopy in the laser-heated diamond anvil cell. The NH3 samples were directly heated by the 10.6 µm radiation of a CO2 laser to reduce the risks of chemical reactions. Melting was unambiguously detected by the appearance of the liquid diffraction signal upon temperature increase. The melting temperature of NH3 is found to steadily increase with pressure up to 40 GPa, and the previously reported turnover is not observed. As a result, the melting line of NH3 is expected to cross the isentropes of Neptune and Uranus in the pressure range 55-65 GPa, implying the possible presence of superionic solid NH3 in these planets. Our x-ray and Raman measurements confirm the appearance of N2 and H2 upon heating the liquid phase from 6 to 40 GPa. But while the equilibrium 2N H3 N2 + 3H2 balances towards the dissociated elements at low pressure and high temperature, ammonia is found to the more stable species in the range 20-40 GPa, 300-3000 K.

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“…A 1-2 μm thick Al 2 O 3 or LiF layer was coated on the pitted anvil culets for thermal insulation. This geometry is similar to the one used for the determination of the nitrogen melting curve [21] and provides uniform heating of the sample.…”

Section: Methodsmentioning

confidence: 99%

Determination of the melting curve of gold up to 110 GPa

et al. 2020

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The melting curve of gold has been measured up to 110 GPa using laser-heated diamond anvil cells and synchrotron x-ray diffraction techniques. Accurate pyrometry temperature measurements and a homogeneous heating of the gold sample were achieved by implementing a sample assembly consisting of two boron-doped diamond cupped disks sandwiching the gold sample. In the investigated pressure range, the fcc solid gold remains stable up to melting. A clear structural signature of bulk melting is observed. Ab initio molecular dynamics simulations within the two-phase approach give a melting curve in good agreement with the experimental one. We discuss the validity of calculations based on the Lindemann criteria of melting which have been up to now used to obtain the melting line of Au in the 100 GPa range.

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Melting Curve and Liquid Structure of Nitrogen Probed by X-ray Diffraction to 120 GPa

Cited by 31 publications

References 24 publications

Structure of liquid ammonia at high pressures and temperatures

Structure of liquid ammonia at high pressures and temperatures

Melting curve and chemical stability of ammonia at high pressure: Combined x-ray diffraction and Raman study

Determination of the melting curve of gold up to 110 GPa

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