Evidence for an 12/a to Imab phase transition in the silica polymorph moganite at ∼570 K

Peter J. Heaney, J. E. Post

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

Rietveld analysis of synchrotron X-ray powder diffraction data for the silica mineral moganite from 100 K to 1354 K has revealed a reversible phase transition from space group 12/a to Imab at approximately 570 K. The thermal expansion behavior of the lattice parameters alters sharply at the transition point, and the monoclinic β angle decreases to 90°. The displacive transition from α- to β- moganite is effected by the rotation of apparently rigid tetrahedra about the [010] axis, and the linear temperature dependence of the volume strain and of the non-symmetry-breaking e11 and e22 strains indicates that the character of the transition is second-order. The continuous increase in the b axis over the entire temperature range reveals a concomitant rotation of tetrahedra about [100] that does not affect the overall symmetry. In addition, we present a refinement without structural constraints for α-moganite at room temperature using time-of-flight neutron diffraction data.

Original languageEnglish (US)
Pages (from-to)1358-1366
Number of pages9
JournalAmerican Mineralogist
Volume86
Issue number11-12
DOIs
StatePublished - Jan 1 2001

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phase transition
Polymorphism
Silicon Dioxide
silica
Phase transitions
silicon dioxide
tetrahedrons
Rietveld analysis
silica mineral
neutron diffraction
temperature
thermal expansion
Neutron diffraction
transition points
Synchrotrons
X ray powder diffraction
Temperature
Lattice constants
Thermal expansion
Minerals

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

Cite this

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title = "Evidence for an 12/a to Imab phase transition in the silica polymorph moganite at ∼570 K",
abstract = "Rietveld analysis of synchrotron X-ray powder diffraction data for the silica mineral moganite from 100 K to 1354 K has revealed a reversible phase transition from space group 12/a to Imab at approximately 570 K. The thermal expansion behavior of the lattice parameters alters sharply at the transition point, and the monoclinic β angle decreases to 90°. The displacive transition from α- to β- moganite is effected by the rotation of apparently rigid tetrahedra about the [010] axis, and the linear temperature dependence of the volume strain and of the non-symmetry-breaking e11 and e22 strains indicates that the character of the transition is second-order. The continuous increase in the b axis over the entire temperature range reveals a concomitant rotation of tetrahedra about [100] that does not affect the overall symmetry. In addition, we present a refinement without structural constraints for α-moganite at room temperature using time-of-flight neutron diffraction data.",
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Evidence for an 12/a to Imab phase transition in the silica polymorph moganite at ∼570 K. / Heaney, Peter J.; Post, J. E.

In: American Mineralogist, Vol. 86, No. 11-12, 01.01.2001, p. 1358-1366.

Research output: Contribution to journalArticle

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T1 - Evidence for an 12/a to Imab phase transition in the silica polymorph moganite at ∼570 K

AU - Heaney, Peter J.

AU - Post, J. E.

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N2 - Rietveld analysis of synchrotron X-ray powder diffraction data for the silica mineral moganite from 100 K to 1354 K has revealed a reversible phase transition from space group 12/a to Imab at approximately 570 K. The thermal expansion behavior of the lattice parameters alters sharply at the transition point, and the monoclinic β angle decreases to 90°. The displacive transition from α- to β- moganite is effected by the rotation of apparently rigid tetrahedra about the [010] axis, and the linear temperature dependence of the volume strain and of the non-symmetry-breaking e11 and e22 strains indicates that the character of the transition is second-order. The continuous increase in the b axis over the entire temperature range reveals a concomitant rotation of tetrahedra about [100] that does not affect the overall symmetry. In addition, we present a refinement without structural constraints for α-moganite at room temperature using time-of-flight neutron diffraction data.

AB - Rietveld analysis of synchrotron X-ray powder diffraction data for the silica mineral moganite from 100 K to 1354 K has revealed a reversible phase transition from space group 12/a to Imab at approximately 570 K. The thermal expansion behavior of the lattice parameters alters sharply at the transition point, and the monoclinic β angle decreases to 90°. The displacive transition from α- to β- moganite is effected by the rotation of apparently rigid tetrahedra about the [010] axis, and the linear temperature dependence of the volume strain and of the non-symmetry-breaking e11 and e22 strains indicates that the character of the transition is second-order. The continuous increase in the b axis over the entire temperature range reveals a concomitant rotation of tetrahedra about [100] that does not affect the overall symmetry. In addition, we present a refinement without structural constraints for α-moganite at room temperature using time-of-flight neutron diffraction data.

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