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Cordierite under hydrostatic compression; anomalous elastic behavior as a precursor for a pressure-induced phase transition

Ronald Miletich, G. Diego Gatta, Thomas Willi, Peter W. Mirwald, Paolo Lotti, Marco Merlini, Nicola Rotiroti and Thomas Loerting
Cordierite under hydrostatic compression; anomalous elastic behavior as a precursor for a pressure-induced phase transition
American Mineralogist (February 2014) 99 (2-3): 479-493

Abstract

The high-pressure behavior of cordierite was investigated by means of in situ experiments using piston-cylinder press and diamond-anvil cell. Static compression in diamond-anvil cells was conducted with various penetrating and non-penetrating pressure media (H (sub 2) O up to 2 GPa, argon and 4:1-methanol-ethanol up to 7 GPa). The measurement of lattice parameters revealed neither a significant influence on the elasticity nor any indication for effects in analogy to over-hydration within the experimental pressure ranges. Volumetric compression experiments at constant rates up to 1.2 GPa in a piston-cylinder apparatus insinuate subtle irregularities in the low-pressure range at around approximately 0.35 and approximately 0.85 GPa. The Delta V/V contribution related to the anomalous compression behavior in that pressure range is of the order of 5 X 10 (super -4) . The results obtained from single-crystal X-ray diffraction between 10 (super -4) and 7 GPa revealed an unexpected and anomalous linear volume decrease, corresponding to K (sub T,298) = 131+ or -1 GPa for the bulk modulus and K' = -0.4+ or -0.3 for its pressure derivative for a third-order Birch-Murnaghan equation of state. The compressional behavior of the main axis directions is anisotropic with beta (sub a) (super -1) nearly equal beta (sub b) (super -1) > beta (sub c) (super -1) for an initial pressure regime up to approximately 3 GPa. At pressures above approximately 4 GPa, the compression of the a- and b-axis starts to differ significantly, with the b-axis showing elastic softening as indicated by negative values for theta (beta (sub b) (super -1) )/theta P. The diversification between the a- and b-axis is also expressed by the pressure-depending increase of the distortion parameter Delta . The pronounced elastic softening in both the b-axis and c-axis directions theta (beta (sub b) (super -1) )/theta P = -4.3+ or -0.9, theta (beta (sub c) (super -1) )/theta P = -1.2+ or -0.8) are responsible for the apparent linear bulk compression, which indicates the structural instability and precedes a so far not reported ferroelastic phase transition to a triclinic polymorph, following a primitive lattice above the critical transition at approximately 6.1 GPa.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 99
Serial Issue: 2-3
Title: Cordierite under hydrostatic compression; anomalous elastic behavior as a precursor for a pressure-induced phase transition
Affiliation: Universitaet Wien, Institut fuer Mineralogie und Kristallographie, Vienna, Austria
Pages: 479-493
Published: 201402
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 79
Accession Number: 2014-101585
Categories: Geophysics of minerals and rocks
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables
Secondary Affiliation: Universita degli Studi di Milano, ITA, ItalyUniversitaet Heidelberg, DEU, GermanyUniversitaet Innsbruck, AUT, Austria
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: 201451
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