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Anomalous behavior at the I2/a to Imab phase transition in SiO (sub 2) -moganite; an analysis using hard-mode Raman spectroscopy

Peter J. Heaney, David A. McKeown and Jeffrey E. Post
Anomalous behavior at the I2/a to Imab phase transition in SiO (sub 2) -moganite; an analysis using hard-mode Raman spectroscopy
American Mineralogist (April 2007) 92 (4): 631-639

Abstract

The silica polymorph moganite is commonly intergrown with quartz in microcrystalline silica varieties that are less than approximately 100 Ma in age. Synchrotron X-ray diffraction suggests that a displacive phase transition occurs when moganite is heated above approximately 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 alpha -beta moganite transformation and to offer complementary insight into the transition mechanism. Our analysis of the displacement of the 501 Delta cm (super -1) symmetric stretching-bending vibration (B (sub 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 Delta cm (super -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 alpha - and beta -moganite over a finite temperature interval; and (3) the alpha - and beta -moganite transition may occur via an intermediate phase.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 92
Serial Issue: 4
Title: Anomalous behavior at the I2/a to Imab phase transition in SiO (sub 2) -moganite; an analysis using hard-mode Raman spectroscopy
Affiliation: Pennylvania State University, Department of Geosciences, University Park, PA, United States
Pages: 631-639
Published: 200704
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 53
Accession Number: 2007-047385
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Catholic University of America, USA, United StatesSmithsonian Institution, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200725
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