Melting of ice under pressure

Schwegler, Eric; Sharma, Manu; Gygi, François; Galli, Giulia

doi:10.1073/pnas.0808137105

Cited by 122 publications

(88 citation statements)

References 38 publications

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“…When increasing T from 1,000 to 2,000 K along an isobar, e ∞ decreases slightly by 0.1-0.2, but overall in the P-T range studied here, it does not substantially change. This result is not surprising, as the fluid and the solid are both molecular in this regime (24,25,33).…”

Section: Equation Ofmentioning

confidence: 74%

“…As a first step of our investigation, we validated the description of the equation of state of water under pressure provided by density functional theory (DFT) with the Perdew-Burke-Ernzerhof (PBE) exchangecorrelation functional (18). We previously used the same level of theory to investigate dissociation of water under pressure (17,23,24) and the ice-melting line (25). Details of our calculations are given in Methods.…”

Section: Equation Ofmentioning

confidence: 99%

See 1 more Smart Citation

Dielectric properties of water under extreme conditions and transport of carbonates in the deep Earth

Pan¹,

Spanu²,

Harrison

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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179

150

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Water is a major component of fluids in the Earth's mantle, where its properties are substantially different from those at ambient conditions. At the pressures and temperatures of the mantle, experiments on aqueous fluids are challenging, and several fundamental properties of water are poorly known; e.g., its dielectric constant has not been measured. This lack of knowledge of water dielectric properties greatly limits our ability to model water-rock interactions and, in general, our understanding of aqueous fluids below the Earth's crust. Using ab initio molecular dynamics, we computed the dielectric constant of water under the conditions of the Earth's upper mantle, and we predicted the solubility products of carbonate minerals. We found that MgCO 3 (magnesite)-insoluble in water under ambient conditions-becomes at least slightly soluble at the bottom of the upper mantle, suggesting that water may transport significant quantities of oxidized carbon. Our results suggest that aqueous carbonates could leave the subducting lithosphere during dehydration reactions and could be injected into the overlying lithosphere. The Earth's deep carbon could possibly be recycled through aqueous transport on a large scale through subduction zones.water solvation properties | carbon cycle | ab initio simulations | supercritical water W ater, a major component of fluids in the Earth's mantle (1, 2), is expected to play a substantial role in hydrothermal reactions occurring in the deep Earth at supercritical conditions (3, 4). Pressure (P) and temperature (T) increase with increasing depth (5) and at ∼400 km, where seismic discontinuities define the bottom boundary of the upper mantle, the pressure can reach ∼13 GPa and the temperature can be as high as 1,700 K (6-8). In this regime the properties of water and thus of aqueous fluids are remarkably different from those at ambient conditions. For example, water has an unusually large static dielectric constant e 0 ∼ 78 at ambient conditions; however, at the vapor-liquid critical point at 647 K, e 0 deceases to less than 10 (9), implying that ionwater interactions in solution are greatly modified. In turn these changes affect the solubility of minerals and hence chemical reactions occurring in aqueous solutions under pressure (10, 11).Measurements of the dielectric constant of water date back to the 1890s (12), but they are still limited to P < 0.5 GPa and T < 900 K, corresponding to crustal metamorphic conditions. Indeed, it is challenging to measure e 0 at high P and T because water becomes highly corrosive (11). Several models correlating experimental data suggested extrapolations of e 0 to ∼1 GPa and ∼1,300 K (e.g., refs. 13-15), which corresponds to only very shallow mantle conditions under the oceans; however, deeper mantle conditions relevant to plate tectonic processes could not be reached and different extrapolations showed poor agreement with each other (1). The current lack of knowledge of the dielectric constant of water under the P and T of the mantle hampers our ability...

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Section: Equation Ofmentioning

confidence: 74%

Section: Equation Ofmentioning

confidence: 99%

Dielectric properties of water under extreme conditions and transport of carbonates in the deep Earth

Pan¹,

Spanu²,

Harrison

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

179

150

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“…The existence of interstitial protons in ice VII has important implications for the structures of the higher pressure phases. In particular, superionicity in ice at higher P-T conditions has been suggested and proposed as a source of magnetic field generation in Neptune and Uranus (34)(35)(36). Protonic density on interstitial sites and potential transport via these provides a framework to model this unusual phase and could even facilitate superionicity at more modest P-T conditions.…”

Section: Discussionmentioning

confidence: 99%

Neutron diffraction observations of interstitial protons in dense ice

Guthrie

Boehler

Tulk

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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The motif of distinct H 2 O molecules in H-bonded networks is believed to persist up to the densest molecular phase of ice. At even higher pressures, where the molecule dissociates, it is generally assumed that the proton remains localized within these same networks. We report neutron-diffraction measurements on D 2 O that reveal the location of the D atoms directly up to 52 GPa, a pressure regime not previously accessible to this technique. The data show the onset of a structural change at ∼13 GPa and cannot be described by the conventional network structure of ice VII above ∼26 GPa. Our measurements are consistent with substantial deuteron density in the octahedral, interstitial voids of the oxygen lattice. The observation of this "interstitial" ice VII form provides a framework for understanding the evolution of hydrogen bonding in ice that contrasts with the conventional picture. It may also be a precursor for the superionic phase reported at even higher pressure with important consequences for our understanding of dense matter and planetary interiors.crystallography | high pressure | water A ll of the some 16 phases of crystalline ice documented to date exhibit a tetrahedrally coordinated structure in which each molecule is H-bonded to four neighbors in an extended network. Above ∼2 GPa, the phase diagram contains just two, closely related, molecular phases: orientationally disordered ice VII and its ordered low-temperature analog ice VIII (1). Both phases have body-centered, close-packed oxygen sublattices with cubic and tetragonal symmetry, respectively. Infrared spectroscopy has provided evidence for bond symmetrization in ice VII-meaning covalent and H-bonds become geometrically equivalent, and ice becomes a simple oxide-starting around 60 GPa (2-4). Meanwhile, X-ray diffraction indicates the persistence of a closely body-centered cubic (bcc) oxygen sublattice up to at least 210 GPa (5-9). At the highest pressures, this system has been studied extensively by numerous experimental techniques [including infrared (3-4, 10) and Raman spectroscopy (2, 11), Brillouin scattering (12), and other optical techniques (13) as well as computational theory (e.g., refs. 14-18 and references therein)]. These efforts, spanning almost 50 years, have led to a consensus view that ice VII moves gradually toward a symmetric H-bonded phase (ice X) across a broad pressure range with protons essentially localized between neighboring O-atoms on network sites. However, the positions of the hydrogen nuclei have not been determined directly at pressures sufficient to significantly change the molecular geometry from that found in common ice Ih (19). In addition, the nature of the proposed intermediate states between ices VII and X remains uncertain (11,20), and changes in ices VII and VIII themselves have been suggested by anomalies in X-ray (5,7,8,21,22) and spectroscopic (12,22,23) data beginning as low as 13-14 GPa.In contrast to other techniques, neutron diffraction can resolve the location of deuterons (D) directly within the l...

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“…These states of matter of ice are of great astrophysical interest because of the presence of H 2 O, one of the thermodynamic sinks of all worlds, 7 in the interior of giant gas planets. [8][9][10][11][12] However, the corresponding environments usually combine high pressures with very high temperatures, and this hot, or near-classical, melting of ice is quite different from the cold, or even quantum, melting associated purely with zero point vibrational excursions and which is of especial interest here.…”

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confidence: 99%

Isotopic differentiation and sublattice melting in dense dynamic ice

2013

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The isotopes of hydrogen provide a unique exploratory laboratory for examining the role of zero point energy (ZPE) in determining the structural and dynamic features of the crystalline ices of water. There are two critical regions of high pressure: (i) near 1 TPa and (ii) near the predicted onset of metallization at around 5 TPa. At the lower pressure of the two, we see the expected small isotopic effects on phase transitions. Near metallization, however, the effects are much greater, leading to a situation where tritiated ice could skip almost entirely a phase available to the other isotopomers. For the higher pressure ices, we investigate in some detail the enthalpics of a dynamic proton sublattice, with the corresponding structures being quite ionic. The resistance toward diffusion of single protons in the ground state structures of high-pressure H 2 O is found to be large, in fact to the point that the ZPE reservoir cannot overcome these. However, the barriers toward a three-dimensional coherent or concerted motion of protons can be much lower, and the ensuing consequences are explored.

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Melting of ice under pressure

Cited by 122 publications

References 38 publications

Dielectric properties of water under extreme conditions and transport of carbonates in the deep Earth

Dielectric properties of water under extreme conditions and transport of carbonates in the deep Earth

Neutron diffraction observations of interstitial protons in dense ice

Isotopic differentiation and sublattice melting in dense dynamic ice

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