Pressure-Induced Landau-Type Transition in Stishovite

A Rietveld structural analysis of stishovite, with angle-dispersive x-ray diffraction synchrotron source at the European Synchrotron Radiation Facility, confirmed a CaCl$_2$ form of stishovite distortion at 54 ± 1 gigapascals but confirmed no further phase transformation up to 120 gigapascals. The d...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 1998-10, Vol.282 (5389), p.720-724
Main Authors: Andrault, Denis, Fiquet, Guillaume, Guyot, François, Hanfland, Michael
Format: Article
Language:English
Subjects:
Climate
Cosmic microwave background radiation
Crystals
Data Processing
Earth sciences
Earth, ocean, space
Entropy
Equations of state
Exact sciences and technology
Grade Point Average
Heat
Lasers
Lower mantle
Metallic composites
Mineralogy
Minerals
Octahedrons
Oxygen
Pressure
Rutile
Scientific Concepts
Silicates
Spectroscopy
Stishovite
Structural Analysis (Linguistics)
Structural Analysis (Science)
Transition pressure
Wave diffraction
X ray diffraction
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Summary:A Rietveld structural analysis of stishovite, with angle-dispersive x-ray diffraction synchrotron source at the European Synchrotron Radiation Facility, confirmed a CaCl$_2$ form of stishovite distortion at 54 ± 1 gigapascals but confirmed no further phase transformation up to 120 gigapascals. The deviatoric stress that is usually encountered at such pressures was relaxed after yttrium-aluminum-garnet-laser heating. A single Birch-Murnaghan equation of state fits volumes of stishovite and a CaCl$_2$ form, showing that the tetragonal distortion occurs without a substantial change in volume. At the 54-gigapascal transition, the pressure-induced lattice modifications were similar to those found in a Landau-type temperature-induced transition. It is proposed that, above the transition pressure, the critical temperature increases above 300 kelvin, so that the lower entropy form becomes stable.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.282.5389.720