Molecular Dynamics Studies of Polymorphism of SiO2 at High Pressures: A Possible New Cubic Polymorph with High Density

Abstract

Considerable attention has been paid in recent years to the possible polymorphs of silica denser than that with the rutile structure (stishovite). First-principles calculations on SiO2 with the fluorite structure have been carried out by Hemley et al. (1985) and Bukowinski and Wolf (1986). Their results indicate that the SiO2-fluorite phase may be at least metastable provided the pressure is extremely high; and below the critical pressure, 160 GPa according to Bukowinski and Wolf (1986), the compound is nonexistent because of lattice dynamical instability. Recently, Jackson and Gordon (1988) carried out an extensive calculation of the stability of various possible polymorphs of SiO2, including those with rutile, α-PbO2, “defect NiAs,” baddeleyite, and fluorite structures. They concluded that the SiO2-fluorite and the SiO2-baddeleyite are less stable than SiO2-rutile even under extremely high-pressure conditions.