First principles prediction of a new high-pressure phase of dense hydrous magnesium silicates in the lower mantle

Abstract

First principles calculations have shown that the high-pressure phase transition of phase D MgSi2O6H2 to the new high-pressure hydrous phase MgSiO4H2 plus stishovite occurs at about 40 GPa. The crystal structure of the new phase is very similar to that of CaCl2-type SiO2 and has monoclinic symmetry with space group P2/m. This new hydrous phase is stable up to about 52 GPa and then dissociates into MgSiO3 perovskite and H2O (ice VIII) at static 0 K conditions. The Clapeyron slope between phase D and the new phase + SiO2 is positive; about 6.4 MPa/K at 1000 K. This new hydrous phase further extends the stability field of dense hydrous magnesium silicates and also opens the pathway toward the existence of a high-pressure phase of ice at the lower mantle conditions. Key Points High pressure phase of phase D has been predicted This new phase dissociate into PV and H2O at higher pressure conditions There is a possibility of the existence of high pressure ice in the Earth ©2013. American Geophysical Union. All Rights Reserved.