Akber-Knutson, S. and Steinle-Neumann, G. and Asimow, P. D. (2005) Effect of Al on the sharpness of the MgSiO_3 perovskite to post-perovskite phase transition. Geophysical Research Letters, 32 (14). Art. No. L14303. ISSN 0094-8276 http://resolver.caltech.edu/CaltechAUTHORS:20120905-144353150
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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_2O_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_2O_3. When the upper pressure limit is bounded by the core-mantle boundary, the phase coexistence region has width 150 km.
|Additional Information:||© 2005 American Geophysical Union. Received 8 April 2005; revised 8 June 2005; accepted 13 June 2005; published 19 July 2005. We thank two anonymous reviewers and R. Caracas, E. J. Garnero, D. V. Helmberger, T. Lay, and L. Stixrude for helpful comments. This work is funded by ASCI (U. S. D. O. E. contract W-7405-ENG-48) and the Bayerisches Geoinstitut Visitor Program.|
|Official Citation:||Akber-Knutson, S., G. Steinle-Neumann, and P. D. Asimow (2005), Effect of Al on the sharpness of the MgSiO3 perovskite to post-perovskite phase transition, Geophys. Res. Lett., 32, L14303, doi:10.1029/2005GL023192.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||05 Sep 2012 22:19|
|Last Modified:||26 Dec 2012 16:07|
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