マグネシウム珪酸塩高圧相の構造

抄録

The structures of high-pressure phases of Mg₂SiO₄ and MgSiO₃ are summarized based on the results of X-ray diffraction method using single crystals, and the relationships among their structures are discussed with configurations of polyhedra about cations. The α→β→γ phase transformations of Mg₂SiO₄, which are not accompanied with the change in coordination number of cations, are mainly characterized by the idealization and compression of MgO₆ and _??_O₆. The high-pressure phases of MgSiO₃, ilmenite- and perovskite-types, have. SiO₆ octahedra which show a slight expansion in the high-pressure phase. On the other hand, the coordination of Mg-polyhedra change remarkably in high-pressure phase. A linear correlation is observed between phase-transformation pressure and cation polyhedral volume. The Mg_??_Si disorder is not observed in any high-pressure phases of magnesiumsilicates. Effects of Fe²⁺ on the β- and γ-phase structures are also discussed.