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

A new synchrotron X-ray diffraction study of MgSiO3 perovskite at high-pres sure and high-temperature has been carried out-in a laser-heated diamond-an vil cell to 94 GPa and temperatures above 2500 K. MgSiO3 perovskite is show n to be stable in this P-T rang and adopts an orthorhombic structure (space group Pbnm), thus ruling out any phase transition or decomposition to an a ssemblage of denser oxides. Structural refinements show an increase of the orthorhombic distortion with increasing pressure, counterbalanced by a decr ease of this distortion at high temperature, as evidenced by the Si-O-Si an gle evolution. In addition, thermoelastic parameters identified from this n ew pressure-volume-temperature data set indicate that a significant amount of magnesiowustite is required to match PREM bulk modulus profile, thus mak ing a pure perovskite lower mantle unlikely.