Anomalous behavior at the I2/a to Imab phase transition in SiO 2 -moganite: An analysis using hard-mode Raman spectroscopy

Peter J. Heaney, David A. McKeown, Jeffrey E. Post

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

The silica polymorph moganite is commonly intergrown with quartz in microcrystalline silica varieties that are less than ∼100 Ma in age. Synchrotron X-ray diffraction suggests that a displacive phase transition occurs when moganite is heated above ∼570 K, with an increase in symmetry from I2/a to Imab. In the present study, we employed hard-mode Raman spectroscopy to confirm the existence of the α-β moganite transformation and to offer complementary insight into the transition mechanism. Our analysis of the displacement of the 501 Δcm -1 symmetric stretching-bending vibration (B 3g mode) with changing temperature strongly supports the existence of a monoclinic-to-orthorhombic phase transition between 570 and 590 K. Between 593 and 723 K, however, the mode remained fixed at 496 Δcm -1 . This behavior was repeated on cooling, but with a hysteresis of over 100 K. We offer three hypotheses that may explain this observation: (1) the intergrowth of nanoscale quartz lamellae within moganite may exert a strain that inhibits the transition; (2) the transition may exhibit a martensitic character marked by the co-existence of α- and β-moganite over a finite temperature interval; and (3) the α- and β-moganite transition may occur via an intermediate phase.

Original languageEnglish (US)
Pages (from-to)631-639
Number of pages9
JournalAmerican Mineralogist
Volume92
Issue number4
DOIs
StatePublished - Apr 1 2007

Fingerprint

Quartz
Raman spectroscopy
phase transition
Silicon Dioxide
silica
Phase transitions
quartz
Polymorphism
Synchrotrons
hysteresis
coexistence
Stretching
symmetry
Hysteresis
vibration
temperature
X-ray diffraction
Cooling
cooling
X ray diffraction

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

Cite this

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abstract = "The silica polymorph moganite is commonly intergrown with quartz in microcrystalline silica varieties that are less than ∼100 Ma in age. Synchrotron X-ray diffraction suggests that a displacive phase transition occurs when moganite is heated above ∼570 K, with an increase in symmetry from I2/a to Imab. In the present study, we employed hard-mode Raman spectroscopy to confirm the existence of the α-β moganite transformation and to offer complementary insight into the transition mechanism. Our analysis of the displacement of the 501 Δcm -1 symmetric stretching-bending vibration (B 3g mode) with changing temperature strongly supports the existence of a monoclinic-to-orthorhombic phase transition between 570 and 590 K. Between 593 and 723 K, however, the mode remained fixed at 496 Δcm -1 . This behavior was repeated on cooling, but with a hysteresis of over 100 K. We offer three hypotheses that may explain this observation: (1) the intergrowth of nanoscale quartz lamellae within moganite may exert a strain that inhibits the transition; (2) the transition may exhibit a martensitic character marked by the co-existence of α- and β-moganite over a finite temperature interval; and (3) the α- and β-moganite transition may occur via an intermediate phase.",
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Anomalous behavior at the I2/a to Imab phase transition in SiO 2 -moganite : An analysis using hard-mode Raman spectroscopy. / Heaney, Peter J.; McKeown, David A.; Post, Jeffrey E.

In: American Mineralogist, Vol. 92, No. 4, 01.04.2007, p. 631-639.

Research output: Contribution to journalArticle

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AB - The silica polymorph moganite is commonly intergrown with quartz in microcrystalline silica varieties that are less than ∼100 Ma in age. Synchrotron X-ray diffraction suggests that a displacive phase transition occurs when moganite is heated above ∼570 K, with an increase in symmetry from I2/a to Imab. In the present study, we employed hard-mode Raman spectroscopy to confirm the existence of the α-β moganite transformation and to offer complementary insight into the transition mechanism. Our analysis of the displacement of the 501 Δcm -1 symmetric stretching-bending vibration (B 3g mode) with changing temperature strongly supports the existence of a monoclinic-to-orthorhombic phase transition between 570 and 590 K. Between 593 and 723 K, however, the mode remained fixed at 496 Δcm -1 . This behavior was repeated on cooling, but with a hysteresis of over 100 K. We offer three hypotheses that may explain this observation: (1) the intergrowth of nanoscale quartz lamellae within moganite may exert a strain that inhibits the transition; (2) the transition may exhibit a martensitic character marked by the co-existence of α- and β-moganite over a finite temperature interval; and (3) the α- and β-moganite transition may occur via an intermediate phase.

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