Thermoelastic properties and crystal structure of MgSiO₃ perovskite at lower mantle pressure and temperature conditions

A new synchrotron X‐ray diffraction study of MgSiO 3 perovskite at high‐pressure and high‐temperature has been carried out in a laser‐heated diamond‐anvil cell to 94 GPa and temperatures above 2500 K. MgSiO 3 perovskite is shown to be stable in this P–T range and adopts an orthorhombic structure (space group Pbnm ), thus ruling out any phase transition or decomposition to an assemblage of denser oxides. Structural refinements show an increase of the orthorhombic distortion with increasing pressure, counterbalanced by a decrease of this distortion at high temperature, as evidenced by the Si‐O‐Si angle evolution. In addition, thermoelastic parameters identified from this new pressure‐volume‐temperature data set indicate that a significant amount of magnesiowüstite is required to match PREM bulk modulus profile, thus making a pure perovskite lower mantle unlikely.