Polymorphs of Alumina Predicted by First Principles:
Putting Pressure on the Ruby Pressure Scale
Kendall T. Thomson,
*
Renata M. Wentzcovitch,
Mark S. T. Bukowinski
Fully optimized quantum mechanical calculations indicate that
Al2O3 transforms from the corundum structure to
the as yet unobserved Rh2O3 (II) structure at
about 78 gigapascals, and it further transforms to
Pbnm-perovskite structure at 223 gigapascals. The predicted x-ray spectrum of the Rh2O3 (II) structure is
similar to that of the corundum structure, suggesting that the
Rh2O3 (II) structure could go undetected in
high-pressure x-ray measurements. It is therefore possible that the
ruby (Cr3+-doped corundum) fluorescence pressure scale is
sensitive to the thermal history of the ruby chips in a given
experiment.
K. T. Thomson, Department of Chemical Engineering and Materials
Science, and Minnesota Supercomputer Institute, University of
Minnesota, Minneapolis, MN 55455, USA.
R. M. Wentzcovitch, Department of Chemical Engineering and Materials
Science, and Minnesota Supercomputer Institute, University of
Minnesota, Minneapolis, MN 55455, USA, and Instituto de Fisica,
Universidade de Sao Paulo, CP 66318, 0 5389-970, Sao Paulo, SP, Brazil.
M. S. T. Bukowinski, Department of Geology and Geophysics, University
of California, Berkeley, CA 94720, USA.
*
To whom correspondence should be addressed.
