A new polymorph of MgSiO3 more stable than the Pbnm -perovskite phase has been identified by first-principles computations. It has the CaIrO3 structure with Cmcm symmetry and consists of SiO3 layers intercalated by eightfold-coordinated Mg ions. High-temperature calculations within the quasiharmonic approximation give a volume change of ∼1.5% and a Clapeyron slope of ∼7.5±0.3 MPa/K at ∼2750 K and ∼125 GPa. These pressure-temperature (P-T) conditions are close to those in which a phase transition in MgSiO3-perovskite has been observed by in situ angle dispersive X-ray diffraction measurements. This transition appears to be associated with the D″ discontinuity.
Bibliographical noteFunding Information:
The authors thank K. Hirose and M. Murakami for supplying experimental data and D. Yuen, M. Akaogi, K. Fujino, E. Ito, and K. Takemura for helpful comments. This research was supported by NSF/EAR 0135533 and 0230319. T.T. and J.T. acknowledge the Japan Society for the Promotion of Science (JSPS) for research fellowships. [SK]
Copyright 2011 Elsevier B.V., All rights reserved.
- Core-mantle boundary
- D″ layer
- First principle