Perovskite-type MgSiO ₃ ; single-crystal X-ray diffraction study

The crystal structure of orthorhombic perovskite-type MgSiO₃ has been refined by means of X-ray diffraction analysis using a single crystal synthesized at 27 GPa and 1830°C. In the structure, SiO₆ is close to an ideal octahedron in which the Si-O distances and O-Si-O angles are nearly equal; their values range from 1.783 to 1.801 Å and from 88.49 to 91.51°, respectively. On the other hand, the position of the Mg atom deviates from the center of the MgO₁₂ polyhedron. As a result, the Mg-O distances and O-Mg-O angles range widely from 2.014 to 3.120 Å and from 50.05 to 70.89°, respectively. As a result, rotation and tilting of cation octahedra govern the structure, as suggested in other orthorhombic perovskite-structure compounds.