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Crystal
structure of a high-pressure/high-temperature phase of alumina
by in situ X-ray diffraction |
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| Letters |
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Nature Materials
3,
389–393 (2004) |
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Full Text |
PDF |
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| JUNG-FU LIN1,
OLGA DEGTYAREVA1,
CHARLES T. PREWITT2,
PRZEMYSLAW DERA1,
NAGAYOSHI SATA3,
EUGENE GREGORYANZ1,
HO-KWANG MAO1 and
RUSSELL J. HEMLEY1
1 Geophysical
Laboratory, Carnegie Institution of Washington,
Washington DC 20015, USA
2 Department of Geosciences, University of
Arizona, Tucson, Arizona 85721, USA
3 Institute for Frontier Research on Earth
Evolution, Japan Marine Science and Technology Center,
Kanagawa 237-0061, Japan
Correspondence to:
JUNG-FU LIN j.lin@gl.ciw.edu
Nature Materials
AOP Published online: 16 May
2004 | doi:10.1038/nmat1121 |
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Alumina (Al2O3)
has been widely used as a pressure calibrant in static
high-pressure experiments and as a window material in
dynamic shock-wave experiments; it is also a model
material in ceramic science. So understanding its
high-pressure stability and physical properties is
crucial for interpreting such experimental data, and for
testing theoretical calculations. Here we report an
in situ X-ray diffraction study of alumina (doped
with Cr3+) up to 136 GPa and 2,350 K. We
observe a phase transformation that occurs above 96 GPa
and at high temperatures. Rietveld full-profile
refinements show that the high-pressure phase has the Rh2O3
(II) (Pbcn) structure, consistent with
theoretical predictions. This phase is structurally
related to corundum, but the AlO6 polyhedra
are highly distorted, with the interatomic bond lengths
ranging from 1.690 to 1.847 Å at 113 GPa. Ruby
luminescence spectra from Cr3+ impurities
within the quenched samples under ambient conditions
show significant red shifts and broadening, consistent
with the different local environments of chromium atoms
in the high-pressure structure inferred from
diffraction. Our results suggest that the ruby pressure
scale needs to be re-examined in the high-pressure
phase, and that shock-wave experiments using sapphire
windows need to be re-evaluated.
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