Stability and crystal structure of MgSiO₃ perovskite to the core‐mantle boundary

Abstract

We report in situ angle‐dispersive X‐ray diffraction measurements for MgSiO 3 at 90–118 and 135–144 GPa and 300–2900 K. At 90–144 GPa, we observed a new diffraction peak at 2.57–2.62 Å as reported in Shim et al. [2001] . The pressure‐induced position shift of the new peak is consistent with those of MgSiO 3 perovskite (Mg‐Pv), supporting that the new peak is associated with a modification in crystal structure of Mg‐Pv at 88 GPa. During laser heating above 2500 K at 144 ± 10 GPa, in addition to peaks of Mg‐Pv, we observed new peaks as well as peak splittings and intensity changes of some peaks. The major features in the diffraction patterns can be explained by the modified Mg‐Pv proposed by Shim et al. [2001] together with the post‐perovskite phase proposed by Murakami et al. [2004] . This supports the existence of a major phase transition in MgSiO 3 under conditions close to those at the base of Earth's mantle.