Single-crystal X-ray diffraction study of Fe2SiO4 fayalite up to 31 GPa

Zhang, Jin S.; Hu, Yi; Shelton, Hannah; Kung, Jennifer; Dera, Przemysław

doi:10.1007/s00269-016-0846-1

Cited by 16 publications

(20 citation statements)

References 50 publications

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“…If Fo metastably exists in the cold oceanic slab at the depths >~410 km, it should provide strong positive buoyancy force at least partially suppressing further subduction of the slab: its density at 900 K (the GGA result) is lower than the ambient mantle by~10.5-18.3% in the depth range of~450-720 km (Figure 17a). Both a lower T in the slab (an unlikely and extremely low T of 600 K for example) and some substitution of Fe for the Mg in the Fo phase (the typical upper mantle Ol of (Mg 0.89 Fe 0.11 ) 2 SiO 4 for example) elevate the density-depth profile somewhat, but never alter the density contrast between the metastable Fo (or Ol) and the warm ambient mantle [101]. This observation is therefore in agreement with all existing studies such as Schmeling et al [102], Tetzlaff and Schmeling [8], and Zhang et al [101].…”

Section: Fo-iii In the Subduction Zonementioning

confidence: 99%

A Metastable Fo-III Wedge in Cold Slabs Subducted to the Lower Part of the Mantle Transition Zone: A Hypothesis Based on First-Principles Simulations

Zhang

Liu

et al. 2019

Minerals

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The metastable olivine (Ol) wedge hypothesis assumes that Ol may exist as a metastable phase at the P conditions of the mantle transition zone (MTZ) and even deeper regions due to inhibition of the phase transitions from Ol to wadsleyite and ringwoodite caused by low T in the cold subducting slabs. It is commonly invoked to account for the stagnation of the descending slabs, deep focus earthquakes and other geophysical observations. In the last few years, several new structures with the forsterite (Fo) composition, namely Fo-II, Fo-III and Fo-IV, were either experimentally observed or theoretically predicted at very low T conditions. They may have important impacts on the metastable Ol wedge hypothesis. By performing first-principles calculations, we have systematically examined their crystallographic characteristics, elastic properties and dynamic stabilities from 0 to 100 GPa, and identified the Fo-III phase as the most likely metastable phase to occur in the cold slabs subducted to the depths equivalent to the lower part of the MTZ (below the ~600 km depth) and even the lower mantle. As disclosed by our theoretical simulations, the Fo-III phase is a post-spinel phase (space group Cmc21), has all cations in sixfold coordination at P < ~60 GPa, and shows dynamic stability for the entire P range from 0 to 100 GPa. Further, our static enthalpy calculations have suggested that the Fo-III phase may directly form from the Fo material at ~22 GPa (0 K), and our high-T phase relation calculations have located the Fo/Fo-III phase boundary at ~23.75 GPa (room T) with an averaged Clapeyron slope of ~−1.1 MPa/K for the T interval from 300 to 1800 K. All these calculated phase transition pressures are likely overestimated by ~3 GPa because of the GGA method used in this study. The discrepancy between our predicted phase transition P and the experimental observation (~58 GPa at 300 K) can be explained by slow reaction rate and short experimental durations. Taking into account the P-T conditions in the cold downgoing slabs, we therefore propose that the Fo-III phase, rather than the Ol, highly possibly occurs as the metastable phase in the cold slabs subducted to the P conditions of the lower part of the MTZ (below the ~600 km depth) and even the lower mantle. In addition, our calculation has showed that the Fo-III phase has higher bulk seismic velocity, and thus may make important contributions to the high seismic speeds observed in the cold slabs stagnated near the upper mantle-lower mantle boundary. Future seismic studies may discriminate the effects of the Fo-III phase and the low T. Surprisingly, the Fo-III phase will speed up, rather than slow down, the subducting process of the cold slabs, if it metastably forms from the Ol. In general, the Fo-III phase has a higher density than the warm MTZ, but has a lower density than the lower mantle, as suggested by our calculations.

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Section: Fo-iii In the Subduction Zonementioning

confidence: 99%

A Metastable Fo-III Wedge in Cold Slabs Subducted to the Lower Part of the Mantle Transition Zone: A Hypothesis Based on First-Principles Simulations

Zhang

Liu

et al. 2019

Minerals

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“…However, when considering the associated uncertainties, the observed differences of β between Fo 100 and Fo 62 are negligible over the large compositional range. The polyhedral volume of the unique tetrahedral site does not present any significant variations over the pressure range investigated for all compositions, indicating that the Si tetrahedron is a rigid unit, as commonly observed in silicate minerals (e.g., [20]).…”

Section: Resultsmentioning

confidence: 57%

“…Therefore, it is crucial to understand the factors controlling its compression mechanisms. Finkelstein et al [19] and Zhang et al [20] recently Many studies have been conducted in the past four decades in order to determine the elastic properties of olivine (e.g., the bulk modulus) as a function of pressure and composition (see [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]). However, the results of these studies have shown significant scattering.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, it is crucial to understand the factors controlling its compression mechanisms. Finkelstein et al [19] and Zhang et al [20] recently investigated the crystal structure evolution of olivine end members Fo and Fa, respectively. However, a systematic study describing the structural evolution of olivine as a function of pressure and chemical composition is still lacking.…”

Section: Introductionmentioning

confidence: 99%

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The High-Pressure Structural Evolution of Olivine along the Forsterite–Fayalite Join

et al. 2019

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Structural refinements from single-crystal X-ray diffraction data are reported for olivine with a composition of Fo100 (forsterite Mg2SiO4, synthetic), Fo80 and Fo62 (~Mg1.6Fe0.4SiO4 and ~Mg1.24Fe0.76SiO4, both natural) at room temperature and high pressure to ~8 GPa. The new results, along with data from the literature on Fo0 (fayalite Fe2SiO4), were used to investigate the previously reported structural mechanisms which caused small variations of olivine bulk modulus with increasing Fe content. For all the investigated compositions, the M2 crystallographic site, with its bonding configuration and its larger polyhedral volume, was observed to control the compression mechanisms in olivine. From Fo100 to Fo0, the compression rates for M2–O and M1–O bond lengths were observed to control the relative polyhedral volumes, resulting in a less-compressible M1O6 polyhedral volume, likely causing the slight increase in bulk modulus with increasing Fe content.

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“…Even though the electronic structure of solid-state materials at room temperature can be found from many experimental techniques as demonstrated by Ono and Zhang et al [26,27] yet, it is anticipated that the DFT+U carried out in the present work, will provide more basic theoretical background and understandings of the ground and excited-state properties of the SFO spinel-type material.…”

Section: Introductionmentioning

confidence: 92%

Investigation of self-consistent site-dependent DFT + U effect on electronic band structure and optical properties of SiFe₂O₄ spinel

Idris¹,

Shaari²,

Razali³

et al. 2020

Mater. Res. Express

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The first-principle investigation of SiFe 2 O 4 (SFO) spinel was performed with the help of a plane-wave pseudopotential technique within the generalized gradient approximation (GGA) and local density approximation (LDA) as implemented in Quantum Espresso Simulation package. The Electronic band structure and optical properties of SFO spinel-type material have been investigated and discussed in this paper. The calculated band structure reveals that SFO spinel-type material is a direct bandgap semiconductor. Using GGA+U and LDA+U the band gap value so obtained is 3.52 eV and 2.96 eV respectively. The contribution to valence and conduction bands due to different bands was analyzed on the basis of the total and partial density of state. The Optical properties of SFO spinel-type material have been calculated and discussed in detail. The real, e w 1 ( ) and the imaginary, e w 2 ( ) part of the complex dielectric constants is found to be 6.52 and 5.42 at energies of 3.44 eV and 6.21 eV respectively. The refractive index n 0 ( ) and the reflectivity index w R , ( ( )) at zero energy value were found to be 1.88 and 10% respectively. We found that SFO spinel-type material has good properties for optical devices.

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Single-crystal X-ray diffraction study of Fe2SiO4 fayalite up to 31 GPa

Cited by 16 publications

References 50 publications

A Metastable Fo-III Wedge in Cold Slabs Subducted to the Lower Part of the Mantle Transition Zone: A Hypothesis Based on First-Principles Simulations

A Metastable Fo-III Wedge in Cold Slabs Subducted to the Lower Part of the Mantle Transition Zone: A Hypothesis Based on First-Principles Simulations

The High-Pressure Structural Evolution of Olivine along the Forsterite–Fayalite Join

Investigation of self-consistent site-dependent DFT + U effect on electronic band structure and optical properties of SiFe₂O₄ spinel

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Single-crystal X-ray diffraction study of Fe2SiO4 fayalite up to 31 GPa

Cited by 16 publications

References 50 publications

A Metastable Fo-III Wedge in Cold Slabs Subducted to the Lower Part of the Mantle Transition Zone: A Hypothesis Based on First-Principles Simulations

A Metastable Fo-III Wedge in Cold Slabs Subducted to the Lower Part of the Mantle Transition Zone: A Hypothesis Based on First-Principles Simulations

The High-Pressure Structural Evolution of Olivine along the Forsterite–Fayalite Join

Investigation of self-consistent site-dependent DFT + U effect on electronic band structure and optical properties of SiFe2O4 spinel

Contact Info

Product

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About

Investigation of self-consistent site-dependent DFT + U effect on electronic band structure and optical properties of SiFe₂O₄ spinel