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Effect of Al on the sharpness of the MgSiO 3 perovskite to post‐perovskite phase transition
Author(s) -
AkberKnutson S.,
SteinleNeumann G.,
Asimow P. D.
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 - 10.1029/2005gl023192
Subject(s) - perovskite (structure) , post perovskite , phase diagram , materials science , phase transition , thermodynamics , phase (matter) , ab initio , mantle (geology) , phase boundary , chemistry , crystallography , geology , physics , organic chemistry , paleontology
By means of static ab‐initio computations we investigate the influence of Al on the recently discovered perovskite to post‐perovskite phase transition in MgSiO 3 . We examine three substitution mechanisms for Al in the two structures: MgSi → AlAl; SiSiO → AlAl□; and Si → AlH. The substitutions introducing oxygen vacancies (highly unfavorable, energetically) and water (favorable) both lower the 0 Kelvin transition pressure, whereas charge coupled substitution increases it relative to 105 GPa for pure MgSiO 3 . From the transition pressures for 0, 6.25, and 100 mol% charge coupled Al 2 O 3 incorporation and simple solution theories, we estimate the phase diagram of Al‐bearing MgSiO 3 at low Al concentrations. Assuming the Clapeyron slope is independent of Al concentration, we find the perovskite‐to‐post‐perovskite transition region to span 127–140 GPa, at 6.25 mol% Al 2 O 3 . When the upper pressure limit is bounded by the core‐mantle boundary, the phase coexistence region has width 150 km.