Study on electronic structures and mechanical properties of new predicted orthorhombic Mg2SiO4 under high pressure

Zhou, Ping; Wu, Ganggang; Zuo, Chunying; Li, Li; Zhou, Zheng; Zhang, Wei-Bin; Pan, Guobing; Wang, Feng

doi:10.1016/j.jallcom.2014.10.201

Cited by 4 publications

(13 citation statements)

References 47 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The static geometry optimization and ionic relaxation under different hydrostatic P were performed using the conjugate algorithm [53], and both the lattice parameters and the atomic positions were allowed to change during the optimization. All the initial structures used were adopted from previous studies (Fo: Hazen [54]; Wds: Horiuchi and Sawamoto [55]; Rwd: Hazen et al [56]; Brg: Horiuchi et al [57]; Aki: Horiuchi et al [58]; Pe: Hazen [59]; Fo-II and Fo-III: Finkelstein et al [37]; Fo-IV: Zhou et al [40]). The planewave cutoff energy was set as 650 eV for all these structures for consistency, and the energy convergence criterion was set as 10 −8 eV.…”

Section: Methodsmentioning

confidence: 99%

Section: Phasementioning

confidence: 99%

“…The Fo-IV phase was a theoretical discovery (space group P2 1 2 1 2; Zhou et al [40]). Our optimized lattice parameters for 0 GPa are compared in Table 3 with the results of Zhou et al [40]. Since we used the GGA method and Zhou et al [40] used the LDA method, our calculated unit-cell parameters are all slightly larger than theirs (a by 1.28%, b by 1.30%, c by 1.51% and V by 4.15%), as expected.…”

Section: Phasementioning

confidence: 99%

“…However, some new high-P polymorphs, compositionally identical to but structurally different from Ol, have been discovered in the last decade or so, which thus introduces new variables to the metastable Ol wedge hypothesis. These new metastable high-P polymorphs were discovered in meteorites [35,36], in in-situ X-ray diffraction single-crystal compression experiments [37,38], in polycrystalline shock-wave compression experiments [39] and in first-principles simulation experiments [40]. Using micro-Raman spectroscopy and high-resolution transmission electron microscopy combined with molecular dynamics simulations, Van de Moortèle et al [35] reported a new polymorph (ζ-(Mg, Fe) 2 SiO 4 ) in some shocked Ol grains of the Martian meteorites NWA 2737 and NWA 1950, but did not document the structural details.…”

Section: Introductionmentioning

confidence: 95%

“…Their meta-dynamics simulation showed a stepwise phase transition sequence from Fo to Fo-II and then to Fo-III via a shear mechanism. Using first-principles molecular dynamic calculations, Zhou et al [40] found another polymorph with the P2 1 2 1 2 space group, which had lower enthalpy than Fo at P > 43. 46 GPa and 0 K (named as Fo-IV hereafter in this study).…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

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

View full text Add to dashboard Cite

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.

show abstract

Section: Methodsmentioning

confidence: 99%

Section: Phasementioning

confidence: 99%