Structure of densified vitreous silica: Silicon and oxygen XANES spectra and multiple scattering calculations

Davoli, I.; Paris, Eleonora; Stizza, S.; Benfatto, M.; Fanfoni, M.; Gargano, A.; Bianconi, A.; Seifert, F.

doi:10.1007/bf00202105

Cited by 57 publications

(46 citation statements)

References 23 publications

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“…This approach is particularly helpful because the connection between x-ray Raman features and the local oxygen electronic bonding environment has not been fully understood in these materials. The x-ray Raman spectra for amorphous SiO 2 glass at 1 atm and MgSiO 3 glass are similar and consist of a broad peak at Ϸ538 eV, consistent with previous studies of the oxygen K-edge spectra of SiO 2 glasses at 1 atm (27,33,34) (Fig. 2 A).…”

Section: Resultssupporting

confidence: 75%

“…The low energy feature for pyroxene is probably associated with Mg-O- [4] Si (41). The 538 eV feature in quartz arises from the transition of the core electrons from 1s states to unoccupied oxygen 2p states hybridized with the silicon 3s and 3p states in two nearby [4] Si and that at Ϸ546 eV apparently originates from its long-range periodicity as it becomes prevalent for the larger clusters with several coordination shells in full multiple-scattering simulations (33). (D) Oxygen K-edge spectra for amorphous MgSiO 3 at 1 atm and perovskite.…”

Section: Resultsmentioning

confidence: 99%

“…2B). At Ϸ538 eV, the oxygen K-edge spectrum for quartz shows a distinct feature because of [4] Si-O- [4] Si (Ref (27,33,34).). The spectrum for ilmenite-type MgSiO 3 shows distinctive features at 537 and 541 eV.…”

Section: Resultsmentioning

confidence: 99%

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X-ray Raman scattering study of MgSiO ₃ glass at high pressure: Implication for triclustered MgSiO ₃ melt in Earth's mantle

Lee

Lin

Cai

et al. 2008

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

127

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Silicate melts at the top of the transition zone and the core-mantle boundary have significant influences on the dynamics and properties of Earth's interior. MgSiO 3-rich silicate melts were among the primary components of the magma ocean and thus played essential roles in the chemical differentiation of the early Earth. Diverse macroscopic properties of silicate melts in Earth's interior, such as density, viscosity, and crystal-melt partitioning, depend on their electronic and short-range local structures at high pressures and temperatures. Despite essential roles of silicate melts in many geophysical and geodynamic problems, little is known about their nature under the conditions of Earth's interior, including the densification mechanisms and the atomistic origins of the macroscopic properties at high pressures. Here, we have probed local electronic structures of MgSiO 3 glass (as a precursor to Mg-silicate melts), using high-pressure x-ray Raman spectroscopy up to 39 GPa, in which high-pressure oxygen K-edge features suggest the formation of tricluster oxygens (oxygen coordinated with three Si frameworks; [3] O) between 12 and 20 GPa. Our results indicate that the densification in MgSiO 3 melt is thus likely to be accompanied with the formation of triculster, in addition to a reduction in nonbridging oxygens. The pressure-induced increase in the fraction of oxygen triclusters >20 GPa would result in enhanced density, viscosity, and crystal-melt partitioning, and reduced element diffusivity in the MgSiO 3 melt toward deeper part of the Earth's lower mantle.silicate melts at high pressure ͉ tricluster oxygen T he nature of silicate melts at high pressure and temperature governs magmatic processes in the Earth's interior and it probably dominated the differentiation of Earth in the Hadean magma ocean where significant fractions of the Earth were melts (1-3). It has been suggested that the potential presence of silicate melts, primarily in MgSiO 3 composition, at the top of the transition zone (4-6) and in the core-mantle boundary (7,8) significantly contributes to the seismic heterogeneity of the regions. Pressure-induced structural changes in the silicate melts play an important role in the macroscopic thermodynamic, transport, and electronic properties at high pressure (e.g., refs. 9-13). Despite their importance and implications for global geophysical processes in the Earth's interior as precursors to crystalline MgSiO 3 phases, including perovskite and postperovskite (14, 15), the high-pressure structures of MgSiO 3 glass and melt remain enigmatic because of their inherent structural disorder and the lack of suitable experimental probes at high pressures. In other binary alkali and ternary aluminosilicate glasses, the densification mechanism is mostly associated with an increase, either gradual or abrupt, in the coordination number of the framework cations, such as Si and Al from 4 to 5 and 6 at the expense of the nonbridging oxygen (NBO) (11,12,(16)(17)(18)(19)(20). However, pressure dependence of the coord...

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Section: Resultssupporting

confidence: 75%

Section: Resultsmentioning

confidence: 99%

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X-ray Raman scattering study of MgSiO ₃ glass at high pressure: Implication for triclustered MgSiO ₃ melt in Earth's mantle

Lee

Lin

Cai

et al. 2008

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

127

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“…Therefore experiments were conducted below 1000 K. Increasing temperature resulted only in a progressive shift of feature C toward lower energy. Feature C is most likely due in a large part to the EXAFS signal associated with the Si-O pair correlation (Davoli et al, 1992). Then, we attribute the shift in feature C to the presence of a longer average Si-O bond length at higher temperatures thanks to the l/R2 dependence of the EXAFS oscillations (R is the average Si-O distance here).…”

Section: In-situ Melting Of Na2si20 5 Glass To 900 Kmentioning

confidence: 82%

Collecting XAFS spectra at soft X-ray energies in a heated loop cell up to 1600 K

Farges¹,

Flank²,

Lagarde³

et al. 1999

J Synchrotron Radiat

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“…In general the conclusion has been reached that either there is little or no coordination change, or it is unquenchable to room pressure: For example, for SiO2 glasses it is has been shown that an increase in pressure up to 30 kbar produces no changes of the Si-O bond-length of the network-forming tetrahedra but produces instead a decrease of the intertetrahedral angles (Seifert et al 1983;Davoli et al 1992). Highly sensitive NMR investigations have identified the presence of several percent of more highly coordinated Si from pressures much higher than those accessed in this work (Stebbins and McMillan 1989;Xue et al 1989).…”

Section: Discussionmentioning

confidence: 99%

Pressure-induced coordination change of Ti in silicate glass: a XANES study

et al. 1994

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Abstract. The effect of pressure on titanium coordination in glasses, with composition K2TiSi4Oll, quenched isobarically from liquids equilibrated at high pressure (5, 10, 15, 20, 25, 30 kbar respectively) and T= 1600 ~ C has been investigated by X-ray absorption spectroscopy (XAS). The XANES spectra collected at the Ti K-edge clearly show a variation with pressure that is related to changes in the geometrical environment around the Ti atoms. By comparison with spectra of standard materials, the XANES spectra of the glasses suggest a relatively low average coordination number (near 5) in samples quenched at low pressure and a higher coordination number (near 6) in samples quenched from the highest pressure. The combination of XANES data with density and compressibility measurements supports the idea that a mixture of 6-and lower coordinated (4-and/or 5-coordinated) Ti geometries are present in the 1 bar glass, and an increasing proportion of 6-coordinated Ti occurs in the glasses synthesized at progressively higher pressures.

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Structure of densified vitreous silica: Silicon and oxygen XANES spectra and multiple scattering calculations

Cited by 57 publications

References 23 publications

X-ray Raman scattering study of MgSiO ₃ glass at high pressure: Implication for triclustered MgSiO ₃ melt in Earth's mantle

X-ray Raman scattering study of MgSiO ₃ glass at high pressure: Implication for triclustered MgSiO ₃ melt in Earth's mantle

Collecting XAFS spectra at soft X-ray energies in a heated loop cell up to 1600 K

Pressure-induced coordination change of Ti in silicate glass: a XANES study

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Structure of densified vitreous silica: Silicon and oxygen XANES spectra and multiple scattering calculations

Cited by 57 publications

References 23 publications

X-ray Raman scattering study of MgSiO 3 glass at high pressure: Implication for triclustered MgSiO 3 melt in Earth's mantle

X-ray Raman scattering study of MgSiO 3 glass at high pressure: Implication for triclustered MgSiO 3 melt in Earth's mantle

Collecting XAFS spectra at soft X-ray energies in a heated loop cell up to 1600 K

Pressure-induced coordination change of Ti in silicate glass: a XANES study

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X-ray Raman scattering study of MgSiO ₃ glass at high pressure: Implication for triclustered MgSiO ₃ melt in Earth's mantle

X-ray Raman scattering study of MgSiO ₃ glass at high pressure: Implication for triclustered MgSiO ₃ melt in Earth's mantle