Single-crystal elasticity of brucite, Mg(OH)2, to 15 GPa by Brillouin scattering

Jiang, Fengxing; Speziale, S.; Duffy, Thomas S.

doi:10.2138/am.2006.2215

Cited by 61 publications

(40 citation statements)

References 49 publications

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“…Hill ) and shear (G P 3 Hill ) moduli for the trigonal phase, 46.7 and 36.4 GPa, respectively (36). The compressional (V P ) and shear (V S ) sound velocities for the tetragonal phase are also faster compared with the trigonal phase (Fig.…”

Section: Hillmentioning

confidence: 86%

“…(F) Calculated compressional/shear sound-wave velocities (circles/squares) for tetragonal Mg(OH) 2 (light-green symbol). Gray symbols refer to the experimentally determined sound velocity of brucite (36). Experimental data are given for the decomposition products periclase (MgO) (filled blue symbols) (63) and ice-VII (filled light-blue symbols: compression; white symbols: decompression) (50).…”

Section: Hillmentioning

confidence: 99%

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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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Section: Hillmentioning

confidence: 86%

Section: Hillmentioning

confidence: 99%

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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“…Firstly, we indicate here that components of the elasticity tensor evaluated on the base of the relaxed P3m1 equilibrium geometry are well consistent with those predicted by experiment. [79][80][81] Secondly, one can see that elastic stability criteria of the trigonal system 82,83 certainly hold, i.e.…”

Section: B Stability Aspectsmentioning

confidence: 92%

Materials properties of magnesium and calcium hydroxides from first-principles calculations

Pishtshev

Karazhanov

Klopov

2014

Computational Materials Science

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This work presents a study of ground state properties, electronic structure, dielectric and optical properties of magnesium and calcium hydroxides X(OH)2 (X = Mg and Ca) within PBE-GGA and range-separated hybrid functional schemes as well as by using GW approximation. The relevant HSE06 hybrid functional mixing parameters were determined from a self-consistent adjustment to the electronic dielectric constant ǫ∞. It was shown that the overall performance of our adaptation of the HSE06 functional via implementation of the modified amount of the Fock exchange is nearly best for the ground state properties as compared to other relevant HF and DFT methods. Structural stability of the crystalline X(OH)2 hydroxides has been considered in static and dynamic aspects. The most important factors describing the bonding situation have been investigated, and a crystalchemical integrity of the hydroxides has been analyzed. From electronic structure studies it was found that both materials are direct band gap insulators. Predictions for the fundamental band gaps were shown to be in the range of 7.7-8.3 eV for Mg(OH) 2 and 7.3-7.6 eV for Ca(OH) 2 . The origin of the conduction and valence band states near the band edges has been studied in terms of orbital and site projected density of states as well as by comparison with the X-ray photoelectron spectroscopy measurements. It was shown that effective masses of carriers at the Γ-point in vicinity of the band extreme are strongly anisotropic and for the electrons are similar to those in the ZnO crystal. Optical properties of the bulk X(OH)2 hydroxides have been investigated in terms of the real and imaginary parts of the optical dielectric function calculated in GW approximation. Electronic character of anisotropy of optical properties has been clarified. On the base of the obtained results the potential of applicability of the Mg(OH) 2 and Ca(OH) 2 crystalline hydroxides in semiconductor device engineering and optoelectronics has been analyzed.

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“…Moreover, C 11 and C 13 at high pressures in Zha et al (1998) are much lower than our results. To independently determine all elastic constants of minerals in the orthorhombic system, previous studies have shown that measuring velocities using platelets close to basal planes, such as (100), (010), and (001), permits reliable derivations of all elastic constants (Jiang et al, 2006;Speziale et al, 2004;Wang et al, 2014), because some of the longitudinal and/or shear moduli in such planes are not covariance with other elastic constants and can be better constrained. Even so, it is still necessary to measure the velocity in two or three different crystal planes, because single-crystal elastic moduli of a given orthorhombic mineral may not be well constrained when lacking sufficient velocity measurements (Every, 1980;Fan et al, accepted).…”

Section: Single-crystal Elasticity Of Olivine At High P-tmentioning

confidence: 99%

Elasticity of single-crystal olivine at high pressures and temperatures

Mao

Fan

Lin

et al. 2015

Earth and Planetary Science Letters

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Available online xxxx Editor: J. BrodholtKeywords: elasticity of single crystal San Carlos olivine high pressure and temperature metastable olivine wedge mantle seismic anisotropy Elasticity of single-crystal San Carlos olivine has been derived from sound velocity and density measurements at simultaneous high pressure-temperature conditions up to 20 GPa and 900 K using in situ Brillouin spectroscopy and single-crystal X-ray diffraction in externally-heated diamond anvil cells. These experimental results are used to evaluate the combined effect of pressure and temperature on full elastic constants of single-crystal olivine to better understand its velocity profiles and anisotropies in the deep mantle. Analysis of the results shows that the shear moduli display strong concave behaviors as a function of pressure at a given high temperature, while the longitudinal modulus, C 11 , and the off-diagonal moduli, C 12 and C 13 , exhibit greater temperature dependence at higher pressures than at relatively lower pressures. Using a finite-strain theory and thermal equation of state modeling for a pyrolitic mantle composition along an expected mantle geotherm, our results show that the magnitude of the V P and V S jumps at the 410-km depth are 6% and 6.4%, respectively, which are greater than that found in seismic observations, suggesting a mantle olivine content of 40-50 vol%, which is less than what is expected for the pyrolite model. Our modeled velocity profiles for a metastable olivine wedge in the subduction slabs along a representative cold slab geotherm are 6% and 10% lower than those of wadsleyite and ringwoodite, respectively, at corresponding depths of the normal mantle. Our modeled results also show that metastable olivine in the cold slabs could have strong V P and V S anisotropies. The maximum V P anisotropy is estimated to be 19-22% at transition zone depth, whereas the maximum V S splitting is 13-23% and increases with depth. As a result, the presence of a metastable olivine wedge at the transition zone depth would exhibit a seismic signature of low velocity and strong seismic anisotropy which are consistent with recent seismic observations for various locations of the slabs and can be used as mineral physics constraints for future seismic detections of the metastable olivine wedges in the deep mantle.

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Single-crystal elasticity of brucite, Mg(OH)2, to 15 GPa by Brillouin scattering

Cited by 61 publications

References 49 publications

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

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

Materials properties of magnesium and calcium hydroxides from first-principles calculations

Elasticity of single-crystal olivine at high pressures and temperatures

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