New insights into the high-pressure polymorphism of SiO2 cristobalite

Przemyslaw Dera, John D. Lazarz, Vitali B. Prakapenka, Madison Barkley, Robert T. Downs

Research output: Contribution to journalArticle

44 Scopus citations

Abstract

Single-crystal X-ray diffraction experiments with SiO2 α-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 ~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 ~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.

Original languageEnglish (US)
Pages (from-to)517-529
Number of pages13
JournalPhysics and Chemistry of Minerals
Volume38
Issue number7
DOIs
StatePublished - Jul 1 2011

Keywords

  • High pressure
  • Metastability
  • Phase transitions
  • Polymorphism
  • Silica

ASJC Scopus subject areas

  • Materials Science(all)
  • Geochemistry and Petrology

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