Abstract
The crystal structure analyses of stishovite were carried out by X-rays using a single crystal under pressure up to 6.09 GPa. The linear compressibilities βa = 1.22×10−3 and βc = 0.64×10−3 GPa−1 and the isothermal bulk modulus of KT = 313 GPa were obtained from the lattice parameters. A shared-edge is the shortest of three kinds of oxygen edges in SiO6 octahedron and is of highest compressibility, resulting in an enhancement of distortion of the octahedron with increasing pressure. The bulk modulus of SiO6 octahedron is evaluated to be 250 GPa which is smaller than that of the tetragonal unit cell. Shortening of the shared-edge of SiO6 octahedron with pressure can be explained by shielding effect for increasing cation-cation interaction along the c-axis and may suggest an increasing tendency of covalent character of stishovite with pressure.
