Reinvestigation of the MgSiO3 perovskite structure at high pressure

Abstract

High-pressure single-crystal X-ray diffraction experiments of MgSiO 3 perovskite have been carried out up to 15 GPa in a diamond-anvil cell using synchrotron radiation. Precise crystal structural parameters, including the anisotropic displacement parameters of every atom in MgSiO 3 , are determined under high pressure. In the pressure range up to 15 GPa, the most important responses of the structure are the compressions of SiO 6 and MgO 8 polyhedra and an increase in tilting of SiO 6 octahedra represented by the decrease in angles between octahedra (both Si-O2-Si angle in the a-b plane and Si-O1-Si angle in the b-c plane decrease). The degree of the change in both angles in the a-b and b-c planes is the same. The amplitude of mean square displacement for the Mg atom has the largest value in the structures and its thermal vibration is significantly anisotropic at ambient pressure. Under high pressure, all atoms in the structure have obvious anisotropy of thermal vibration and the largest amplitudes of thermal vibration for Mg, Si, and O2 atoms are directed toward vacant space in the structure. Anisotropy of the structure increases with pressure.