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Title: New insights into the high-pressure polymorphism of SiO[subscript 2] cristobalite

Abstract

Single-crystal X-ray diffraction experiments with SiO{sub 2} {alpha}-cristobalite reveal that the well-known reversible displacive phase transition to cristobalite-II, which occurs at approximately 1.8 GPa, can be suppressed by rapid pressure increase, leading to an overpressurized metastable state, persisting to pressure as high as 10 GPa. In another, slow pressure increase experiment, the monoclinic high-pressure phase-II was observed to form at {approx}1.8 GPa, in agreement with earlier in situ studies, and its crystal structure has been unambiguously determined. Single-crystal data have been used to refine the structure models of both phases over the range of pressure up to the threshold of formation of cristobalite X-I at {approx}12 GPa, providing important constraints on the feasibility of the two competing silica densification models proposed in the literature, based on quantum mechanical calculations. Preliminary diffraction data obtained for cristobalite X-I reveal a monoclinic unit cell that contradicts the currently assumed model.

Authors:
; ; ; ;  [1];  [2]
  1. (UC)
  2. (
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
DOE - BASIC ENERGY SCIENCESNSF
OSTI Identifier:
1022271
Resource Type:
Journal Article
Resource Relation:
Journal Name: Phys. Chem. Miner.; Journal Volume: 38; Journal Issue: (7) ; 04, 2011
Country of Publication:
United States
Language:
ENGLISH

Citation Formats

Dera, Przemyslaw, Lazarz, John D., Prakapenka, Vitali B., Barkley, Madison, Downs, Robert T., and Ariz). New insights into the high-pressure polymorphism of SiO[subscript 2] cristobalite. United States: N. p., 2016. Web. doi:10.1007/s00269-011-0424-5.
Dera, Przemyslaw, Lazarz, John D., Prakapenka, Vitali B., Barkley, Madison, Downs, Robert T., & Ariz). New insights into the high-pressure polymorphism of SiO[subscript 2] cristobalite. United States. doi:10.1007/s00269-011-0424-5.
Dera, Przemyslaw, Lazarz, John D., Prakapenka, Vitali B., Barkley, Madison, Downs, Robert T., and Ariz). 2016. "New insights into the high-pressure polymorphism of SiO[subscript 2] cristobalite". United States. doi:10.1007/s00269-011-0424-5.
@article{osti_1022271,
title = {New insights into the high-pressure polymorphism of SiO[subscript 2] cristobalite},
author = {Dera, Przemyslaw and Lazarz, John D. and Prakapenka, Vitali B. and Barkley, Madison and Downs, Robert T. and Ariz)},
abstractNote = {Single-crystal X-ray diffraction experiments with SiO{sub 2} {alpha}-cristobalite reveal that the well-known reversible displacive phase transition to cristobalite-II, which occurs at approximately 1.8 GPa, can be suppressed by rapid pressure increase, leading to an overpressurized metastable state, persisting to pressure as high as 10 GPa. In another, slow pressure increase experiment, the monoclinic high-pressure phase-II was observed to form at {approx}1.8 GPa, in agreement with earlier in situ studies, and its crystal structure has been unambiguously determined. Single-crystal data have been used to refine the structure models of both phases over the range of pressure up to the threshold of formation of cristobalite X-I at {approx}12 GPa, providing important constraints on the feasibility of the two competing silica densification models proposed in the literature, based on quantum mechanical calculations. Preliminary diffraction data obtained for cristobalite X-I reveal a monoclinic unit cell that contradicts the currently assumed model.},
doi = {10.1007/s00269-011-0424-5},
journal = {Phys. Chem. Miner.},
number = (7) ; 04, 2011,
volume = 38,
place = {United States},
year = 2016,
month = 7
}
  • Three isotypic crystals, SiO 2 (α-cristobalite), ε-Zn(OH) 2 (wülfingite), and Be(OH) 2 (β-behoite), with topologically identical frameworks of corner-connected tetrahedra, undergo displacive compression drivenphase transitions at similar pressures (1.5–2.0 GPa), but each transition is characterized by a different mechanism resulting in different structural modifications. In this study, we report the crystal structure of the high pressure γ-phase of beryllium hydroxide and compare it with the high pressure structures of the other two minerals. In Be(OH) 2, the transition from the ambient β-behoite phase with the orthorhombic space group P2 12 12 1 and ambient unit cell parameters a = 4.5403(4)more » Å, b = 4.6253(5) Å, c = 7.0599(7) Å, to the high pressure orthorhombic γ-polymorph with space group Fdd2 and unit cell parameters (at 5.3(1) GPa) a = 5.738(2) Å, b = 6.260(3) Å, c = 7.200(4) Å takes place between 1.7 and 3.6 GPa. This transition is essentially second order, is accompanied by a negligible volume discontinuity, and exhibits both displacive and reversible character. The mechanism of the phase transition results in a change to the hydrogen bond connectivities and rotation of the BeO 4 tetrahedra.« less
  • Three isotypic crystals, SiO 2 (α-cristobalite), ε-Zn(OH) 2 (wülfingite), and Be(OH) 2 (β-behoite), with topologically identical frameworks of corner-connected tetrahedra, undergo displacive compression-driven phase transitions at similar pressures (1.5–2.0 GPa), but each transition is characterized by a different mechanism resulting in different structural modifications. In this study, we report the crystal structure of the high-pressure γ-phase of beryllium hydroxide and compare it with the high-pressure structures of the other two minerals. In Be(OH) 2, the transition from the ambient β-behoite phase with the orthorhombic space group P2 12 12 1 and ambient unit cell parameters a = 4.5403(4) Å, bmore » = 4.6253(5) Å, c = 7.0599(7) Å, to the high-pressure orthorhombic γ-polymorph with space group Fdd2 and unit cell parameters (at 5.3(1) GPa) a = 5.738(2) Å, b = 6.260(3) Å, c = 7.200(4) Å takes place between 1.7 and 3.6 GPa. This transition is essentially second order, is accompanied by a negligible volume discontinuity, and exhibits both displacive and reversible character. The mechanism of the phase transition results in a change to the hydrogen bond connectivities and rotation of the BeO 4 tetrahedra.« less
  • Minerals with composition (Fe,Ni){sub 2}P, are rare, though important accessory phases in iron and chondritic meteorites. The occurrence of these minerals in meteorites is believed to originate either from the equilibrium condensation of protoplanetary materials in solar nebulae or from the later accretion and condensation processes in the cores of parent bodies. Fe-Ni phosphides are considered a possible candidate for a minor phase present in the Earth's core, and at least partially responsible for the observed density deficit with respect to pure iron. We report results of high-pressure high-temperature X-ray diffraction experiments with synthetic barringerite (Fe{sub 2}P) up to 40more » GPa and 1400 K. A new phase transition to the Co{sub 2}Si-type structure has been found at 8.0 GPa, upon heating. The high-pressure phase can be metastably quenched to ambient conditions at room temperature, and then, if heated again, transforms back to barringerite, providing an important constraint on the thermodynamic history of meteorite.« less