Equations of state and phase boundary for stishovite and CaCl2-type SiO2

Fischer, R. A.; Campbell, A. J.; Chidester, B.; Reaman, D. M.; Thompson, E. C.; Pigott, J. S.; Prakapenka, Vitali B.; Smith, Jesse S.

doi:10.2138/am-2018-6267

Cited by 36 publications

(68 citation statements)

References 104 publications

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“…The differences between the EOS for laser‐annealed stishovite powder compressed in NaCl or without pressure‐transmitting medium (Andrault et al, ) and the EOS for stishovite powder compressed in helium (Nisr et al, ) may arise from different stress environments such as deviations from hydrostaticity imposed by the different pressure‐transmitting media. Taking into account their uncertainties, both EOS for stishovite powder in Table are consistent with the range of bulk moduli and their pressure derivatives of earlier studies as compiled by Fischer et al ().…”

Section: Eos Of Sintered Polycrystalline Stishovitesupporting

confidence: 88%

Equation of State of Polycrystalline Stishovite Across the Tetragonal‐Orthorhombic Phase Transition

et al. 2018

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High‐pressure silica polymorphs may contribute to lithologies in Earth's lower mantle. Stishovite, the tetragonal rutile‐type polymorph of SiO2, distorts to an orthorhombic CaCl2‐type structure at pressures and temperatures of the lower mantle. We compressed sintered polycrystalline stishovite and determined the unit cell parameters as a function of pressure using synchrotron X‐ray diffraction. The compression behavior of sintered polycrystalline stishovite deviates systematically from previous results on stishovite powder and single crystals. Following an initial stiffening, the bulk modulus of sintered polycrystalline stishovite drops at the ferroelastic phase transition. We analyzed the observed spontaneous strains using Landau theory to predict the complete elastic behavior of sintered polycrystalline silica across the phase transition. The reduction in bulk modulus at the phase transition as derived here from the compression curve of sintered polycrystalline silica may have implications for the seismic detection of silica‐rich materials in Earth's lower mantle.

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Section: Eos Of Sintered Polycrystalline Stishovitesupporting

confidence: 88%

Equation of State of Polycrystalline Stishovite Across the Tetragonal‐Orthorhombic Phase Transition

et al. 2018

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“…(b) Phase boundary between Stv and CaCl 2 -type SiO 2 . Solid gray line: phase boundary in Nomura et al (2010); dashed gray line: phase boundary in Fischer et al (2018). (c) Phase boundary between CaCl 2 -type SiO 2 and seifertite.…”

Section: Resultsmentioning

confidence: 99%

High Pressure‐Temperature Study on the Thermal Equations of State of Seifertite andCaCl₂‐Type SiO₂

et al. 2019

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In this study, we have determined the thermal equations of state (EoS) of CaCl2‐type SiO2 and seifertite (α‐PbO2‐type SiO2) from 55 to 147 GPa up to 3500 K using X‐ray diffraction in laser‐heated diamond anvil cells. The phase transition from stishovite to CaCl2‐type SiO2 is in good agreement with previous experimental results, whereas the transition from CaCl2‐type SiO2 to seifertite was observed to strongly rely on the starting material. For CaCl2‐type SiO2, we obtained a bulk modulus, KT0 = 245(7) GPa with a fixed KT′ = 4, V0 = 48.1(2) Å3, γ0 = 1.3(3), q = 1(fixed), and θD0 = 1100(400) K. Seifertite has a greater KT0 = 290(10) GPa (KT′ = 4 fixed) than CaCl2‐type SiO2. Other thermoelastic parameters of seifertite are V0 = 92.3(5) Å3, γ0 = 1.6(2), q = 1 (fixed), and θD0 = 1600(200) K. Using the obtained results and phase boundary in previous studies, we have found that the phase transition from stishovite to CaCl2‐type SiO2 cannot cause a noticeable change in density but can lower the bulk sound velocity (VФ) by ~10%. This phase transition in the subducted oceanic crust with 20 vol.% SiO2 was estimated to generate a ~2% discontinuity in VФ, which could be related to the observed seismic velocity anomalies at depths of 1,400–1,800 km. At the bottom of the lower mantle, CaCl2‐type SiO2 to seifertite phase transition can lead to a 0.3% jump in ρ and a 0.8% jump in VΦ considering 20 vol.% SiO2 in the subducted mid‐ocean ridge basalt, which may contribute to the formation of the D″ discontinuity above the core‐mantle boundary.

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“…Stishovite is known to undergo a ferro-elastic phase transition to the orthorhombic CaCl 2 -type structure above 50 GPa (Fischer et al, 2018;Tsuchida & Yagi, 1989). Stishovite is known to undergo a ferro-elastic phase transition to the orthorhombic CaCl 2 -type structure above 50 GPa (Fischer et al, 2018;Tsuchida & Yagi, 1989).…”

Section: Discussionmentioning

confidence: 99%

“…Under static compression, SiO 2 adopts the CaCl 2 -type structure (Pnnm) at ∼50-80 GPa (Fischer et al, 2018;Tsuchida & Yagi, 1989). When shock compressed above ∼70 GPa and 4,500 K, pyrometry measurements record a drop in temperature with increasing stress (Boslough, 1988;Lyzenga et al, 1983;Millot et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Sound Velocities in Shock‐Synthesized Stishovite to 72 GPa

Berryman

Winey

Gupta

et al. 2019

Geophysical Research Letters

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Stishovite (rutile-type SiO 2 ) is the archetype of dense silicates and may occur in postgarnet eclogitic rocks at lower-mantle conditions. Sound velocities in stishovite are fundamental to understanding its mechanical and thermodynamic behavior at high pressure and temperature. Here, we use plate-impact experiments combined with velocity interferometry to determine the stress, density, and longitudinal sound speed in stishovite formed during shock compression of fused silica at 44 GPa and above. The measured sound speeds range from 12.3(8) km/s at 43.8(8) GPa to 9.8(4) km/s at 72.7(11) GPa. The decrease observed at 64 GPa reflects a decrease in the shear modulus of stishovite, likely due to the onset of melting. By 72 GPa, the measured sound speed agrees with the theoretical bulk sound speed indicating loss of all shear stiffness due to complete melting. Our sound velocity results provide direct evidence for shock-induced melting, in agreement with previous pyrometry data.

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Equations of state and phase boundary for stishovite and CaCl2-type SiO2

Cited by 36 publications

References 104 publications

Equation of State of Polycrystalline Stishovite Across the Tetragonal‐Orthorhombic Phase Transition

Equation of State of Polycrystalline Stishovite Across the Tetragonal‐Orthorhombic Phase Transition

High Pressure‐Temperature Study on the Thermal Equations of State of Seifertite andCaCl₂‐Type SiO₂

Sound Velocities in Shock‐Synthesized Stishovite to 72 GPa

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Equations of state and phase boundary for stishovite and CaCl2-type SiO2

Cited by 36 publications

References 104 publications

Equation of State of Polycrystalline Stishovite Across the Tetragonal‐Orthorhombic Phase Transition

Equation of State of Polycrystalline Stishovite Across the Tetragonal‐Orthorhombic Phase Transition

High Pressure‐Temperature Study on the Thermal Equations of State of Seifertite andCaCl2‐Type SiO2

Sound Velocities in Shock‐Synthesized Stishovite to 72 GPa

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High Pressure‐Temperature Study on the Thermal Equations of State of Seifertite andCaCl₂‐Type SiO₂