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

This is the authors' abstract. We don't add key points for this paper.

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.