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Prediction of a new phase transition in Al 2 O 3 at high pressures
Author(s) -
Caracas R.,
Cohen R. E.
Publication year - 2005
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2004gl022204
Subject(s) - perovskite (structure) , metastability , corundum , phase transition , post perovskite , materials science , phase (matter) , high pressure , thermodynamics , crystallography , mineralogy , mantle (geology) , chemistry , geology , physics , geochemistry , organic chemistry
We use density functional theory to investigate several high‐pressure polymorphs of Al 2 O 3 and predict a new stable polymorph at high pressures with post‐perovskite structure. The ambient pressure Rc corundum phase transforms to the Pbcn Rh 2 O 3 (II) structure at about 104 GPa. At about 156 GPa, the Rh 2 O 3 (II) structure transforms further to the Cmcm post‐perovskite structure. The Al 2 O 3 Pbnm perovskite structure is metastable at all pressures with respect to corundum, Rh 2 O 3 (II) and post‐perovskite. The metastable perovskite to post‐perovskite transition takes place at about 120 GPa, which is above the same transition in MgSiO 3 . Thus the presence of Al 2 O 3 in the lower mantle, dissolved in MgSiO 3 perovskite, will increase the transition pressure to post‐perovskite. Our calculations also show that Al 2 O 3 is most likely dissolved in the post‐perovskite phase of MgSiO 3 , increasing its stability at high pressures.