Thermoelastic properties of ice VII and its high-pressure polymorphs: Implications for dynamics of cold slab subduction in the lower mantle

Asahara, Yuki; Hirose, Kei; Ohishi, Yasuo; Hirao, Naohisa; Murakami, Motohiko

doi:10.1016/j.epsl.2010.09.037

Cited by 27 publications

(44 citation statements)

References 65 publications

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“…Above ≈30 GPa the x-ray volumes appear to be on average below our EoS, a fact which hardly can be ascribed to the ice VII-ice X transition [12,13] which occurs between 60 and 70 GPa [8]. What is clear, on the contrary, it that for pressures >85 GPa, the agreement with the x-ray data becomes better and this holds to 160 GPa (not shown in Fig.…”

Section: Ice VIImentioning

confidence: 58%

“…Although hydrogen-bonded systems were not investigated there, it is unquestionable that a similar relation holds for ice phases, i.e., one would expect B 0 (Ih) < B 0 (VI) < B 0 (VII). A B 0 value for ice VII smaller than that of ice Ih [11][12][13] between 4 and 7. Again, our B 0 = 5.7-6.2 is physically reasonable, given the value for ice Ih which ranges between 5.4 and 6.6, determined from ultrasonic and neutron diffraction measurement, see Ref.…”

Section: Discussionmentioning

confidence: 99%

“…But, although these equations of state all give acceptable fits to the data over the considered pressure range, the extracted parameters scatter strongly between different measurements. The reported bulk moduli of ice VII, for example, scatter between 4-5 GPa [11][12][13] and 24 GPa [3], and even in the most recent work vary between 13 GPa [14] and 21 GPa [15]. It hence appears that most of the reported equations of state are merely fits to V (P ) data with little physical significance concerning B 0 , B 0 , and V 0 .…”

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confidence: 87%

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Bulk moduli and equations of state of ice VII and ice VIII

et al. 2017

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Section: Ice VIImentioning

confidence: 58%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 87%

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Bulk moduli and equations of state of ice VII and ice VIII

et al. 2017

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“…A transition from the trigonal to the tetragonal phase is likely to be marked by an enhancement in both P-and S-wave velocity. Under further compression, as tetragonal Mg(OH) 2 decomposes to a mixture of MgO and H 2 O (ice) around 30 GPa, the P-wave velocity is likely to enhance whereas the S-wave velocity is likely to decrease, owing to significantly lower S-wave velocity for ice-VII at high pressure (50). In combination (Fig.…”

Section: Discussionmentioning

confidence: 97%

High-pressure phase of brucite stable at Earth’s mantle transition zone and lower mantle conditions

Hermann

Mookherjee

2016

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

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We investigate the high-pressure phase diagram of the hydrous mineral brucite, Mg(OH) 2 , using structure search algorithms and ab initio simulations. We predict a high-pressure phase stable at pressure and temperature conditions found in cold subducting slabs in Earth's mantle transition zone and lower mantle. This prediction implies that brucite can play a much more important role in water transport and storage in Earth's interior than hitherto thought. The predicted high-pressure phase, stable in calculations between 20 and 35 GPa and up to 800 K, features MgO 6 octahedral units arranged in the anatase-TiO 2 structure. Our findings suggest that brucite will transform from a layered to a compact 3D network structure before eventual decomposition into periclase and ice. We show that the high-pressure phase has unique spectroscopic fingerprints that should allow for straightforward detection in experiments. The phase also has distinct elastic properties that might make its direct detection in the deep Earth possible with geophysical methods.brucite | pressure | phase transition | electronic structure calculations W ater plays an important role in sustaining geological activity. For instance, water helps in lowering the mantle's melting temperature, enhancing diffusion and creep thus affecting rheology of rocks, and also influences mineral phase boundaries. Current estimates suggest that the Earth's mantle is likely to contain a mass of water equivalent to the mass of the world's oceans (1, 2). The exchange of water between the surface and deep mantle reservoirs is vital for the sustenance of surface water over geological time scales (3). Hydrous minerals stable in the hydrated oceanic crust and mantle play an important role in transporting water into the Earth's interior. Hydrated peridotite, the major mantle rock type, can be understood by considering mineral phases stable in the ternary system of MgO-SiO 2 -H 2 O (MSH). Brucite, Mg(OH) 2 , is arguably the simplest hydrous mineral in the MSH system. Brucite is also the most important MgO-H 2 O binary and the most water-rich phase within the MSH ternary system.The crystal structure of brucite consists of Mg 2+ cations and OH − anions arranged in layers, in an overall trigonal structure (space group symmetry P 3m1); Fig. 1. The common ionic compound CdI 2 is the archetype crystal structure for brucite as well as for portlandite [Ca(OH) 2 )] and several other transition metal hydroxides M(OH) 2 where M = Mn, Ni, Co, Fe, Cd,. In brucite, the crystal structure comprises layers of edge-sharing MgO 6 polyhedra. The interaction between the layers is weak at ambient conditions, where each upward-pointing OH group is surrounded by three downward-pointing OH groups in the adjacent layer and vice versa. Under compression the H-H repulsive interactions lead to positional disordering of the protons, which are displaced from the 2d Wyckoff site into one of three equivalent 6i sites as documented from neutron diffraction studies (11,12). Vibrational spectroscopic studies incl...

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“…4,5,11,[20][21][22][23] The HB symmetrization is described as a centering of a proton between O-O. This transition occurs over a pressure range through intermediate phases that are dynamically disordered ice VII (ice VII ) and dynamically disordered ice X (ice X ), 24 in both of which the protons constantly changes positions along doublewell potential minima in between O-O either by quantum tunneling (ice VII ) or by thermal fluctuation induced by a very low potential barrier between the two minima (ice X ).…”

Section: Introductionmentioning

confidence: 99%

Experimental evidence of superionic conduction in H2O ice

Sugimura

Komabayashi

Ohta

et al. 2012

The Journal of Chemical Physics

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Ionic conductivity and molar volume measurements were performed on H(2)O ice at high pressure (P) and temperature (T) in a resistive-heated diamond anvil cell. The conductivity data obtained at P = 20-62 GPa, T = 304-930 K are well fitted with a single Arrhenius equation. Isothermal volume measurements at T = 873 K, P = 30-101 GPa indicate that H(2)O ice undergoes phase transitions at P = 50 GPa and 53 GPa due to hydrogen-bond symmetrization. Combining these results, we suggest that the conduction mechanism does not change with pressure-induced hydrogen-bond symmetrization. Along the Arrhenius behavior of conductivity data, the experimental evidence for superionic conduction (>10(-1) S/cm) was found at T = 739 K, P = 56 GPa and T = 749 K, P = 62 GPa, which is significantly low temperature compared with earlier theoretical estimates resorted to the observation of a drastic rise of the melting curve. We infer that the sudden increase of the melting temperature is not related to the onset of superionic conduction, but is attributed to the phase change regarding to the symmetrization.

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Thermoelastic properties of ice VII and its high-pressure polymorphs: Implications for dynamics of cold slab subduction in the lower mantle

Cited by 27 publications

References 65 publications

Bulk moduli and equations of state of ice VII and ice VIII

Bulk moduli and equations of state of ice VII and ice VIII

High-pressure phase of brucite stable at Earth’s mantle transition zone and lower mantle conditions

Experimental evidence of superionic conduction in H2O ice

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