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Crystal structures and stabilities of cristobalite-helium phases at high pressures

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Published/Copyright: January 15, 2014
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American Mineralogist
From the journal American Mineralogist Volume 99 Issue 1

Abstract

First-principles calculations were used to study the structural and energetic properties of cristobalite- He I and II at high pressures, both of which were recently found in high-pressure powder X‑ray diffraction experiments of a-cristobalite with helium pressure-medium at room temperature. These calculations have revealed that both cristobalite-He I and II contain one helium atom per SiO2 with the formula SiO2He. It has also been revealed that cristobalite-He I is energetically favored above 6.4 GPa, cristobalite-He II is the stable phase at pressures between 1.7 and 6.4 GPa, and the mixture of cristobalite II and crystalline He is more stable than either cristobalite-He I or II below 1.7 GPa, in general agreement with the observation. Cristobalite-He I and II have been predicted to be monoclinic with space group P21/c, and rhombohedral with space group R3̅c, respectively. The unit-cell parameters of both cristobalite-He I and II were re-determined from the previously measured high-pressure X-ray diffraction data on the basis of these predicted cells. There is an excellent agreement between the observed (re-determined) and calculated pressure dependence of the cell parameters for the both phases. The calculated X-ray diffraction patterns for both cristobalite-He I and II are also consistent with the observed data. Cristobalite-He I and II have been predicted to have molar volumes 21% larger at 10 GPa and 23% larger at 4 GPa than cristobalite II due to the penetration of helium atoms into large voids of the structure.

Keywords : Cristobalite-helium; high pressure; stability; first-principles calculations
Published Online: 2014-01-15
Published in Print: 2014-01-01

© 2014 by Walter de Gruyter GmbH & Co.

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https://doi.org/10.2138/am.2014.4637
Keywords for this article
Cristobalite-helium; high pressure; stability; first-principles calculations

Articles in the same Issue

  1. Shedding light on bone material
  2. Weddellite from renal stones: Structure refinement and dependence of crystal chemical features on H2O content
  3. Erionite and offretite from the Killdeer Mountains, Dunn County, North Dakota, U.S.A.
  4. Molecular water in nominally unhydrated carbonated hydroxylapatite: The key to a better understanding of bone mineral
  5. Precipitation and dissolution of chromite by hydrothermal solutions in the Oman ophiolite: New behavior of Cr and chromite
  6. Phase transitions and equation of state of forsterite to 90 GPa from single-crystal X-ray diffraction and molecular modeling
  7. Weathering of cobalt arsenides: Natural assemblages and calculated stability relations among secondary Ca-Mg-Co arsenates and carbonates
  8. Alburnite, Ag8GeTe2S4, a new mineral species from the Roşia Montana Au-Ag epithermal deposit, Apuseni Mountains, Romania
  9. Cathodoluminescence of alkali feldspars and radiation effects on the luminescent properties
  10. Thermochemistry of the alkali feldspars: Calorimetric study of the entropy relations in the low albite–low microcline series
  11. Thermal equation of state and spin transition of magnesiosiderite at high pressure and temperature
  12. Thermal diffusivities of MgSiO3 and Al-bearing MgSiO3 perovskites
  13. The sound velocity measurements of Fe3S
  14. PDF analysis of ferrihydrite: Critical assessment of the under-constrained akdalaite model
  15. Aluminum ion occupancy in the structure of synthetic saponites: Effect on crystallinity
  16. DFT investigation of structural and vibrational properties of type B and mixed A-B carbonated hydroxylapatite
  17. Chlorite topography and dissolution of the interlayer studied with atomic force microscopy
  18. The effect of XPS background removing method on the appraisal of Ti and Fe: The case of phlogopites and brookite
  19. Measurement of water contents in olivine using Raman spectroscopy
  20. Perbøeite-(Ce) and alnaperbøeite-(Ce), two new members of the epidote-törnebohmite polysomatic series: Chemistry, structure, dehydrogenation, and clue for a sodian epidote end-member
  21. Crystal structure and compressibility of lead dioxide up to 140 GPa
  22. A comparative analysis of the mechanical behavior of carbon dioxide and methane hydrate-bearing sediments
  23. Crystal structures and stabilities of cristobalite-helium phases at high pressures
  24. X-ray absorption characterization of Cr in forsterite within the MacAlpine Hills 88136 EL3 chondritic meteorite
  25. Monipite, MoNiP, a new phosphide mineral in a Ca-Al-rich inclusion from the Allende meteorite
  26. Compositional zoning in dolomite from lawsonite-bearing eclogite (SW Tianshan, China): Evidence for prograde metamorphism during subduction of oceanic crust
  27. Vanadio-oxy-dravite, NaV3(Al4Mg2)(Si6O18)(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup
  28. XAS evidence for Ni sequestration by siderite in a lateritic Ni-deposit from New Caledonia
  29. Vladykinite, Na3Sr4(Fe2+Fe3+)Si8O24: A new complex sheet silicate from peralkaline rocks of the Murun complex, eastern Siberia, Russia
  30. New Mineral Names
  31. Memorial of James Burleigh Thompson, Jr., 1921–2011
  32. Book review: MANTLE CONVECTION FOR GEOLOGISTS by Geoffrey F. Davies
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