STRUCTURAL TRANSFORMATION, INTERMEDIATE-RANGE ORDER, AND DYNAMICAL BEHAVIOR OF SIO2 GLASS AT HIGH-PRESSURES

Pressure-induced structural transformation in SiO2 glass is investigated with molecular dynamics. At high densities, the height of the first sharp diffraction Peak is considerably diminished, its position changes from 1.6 to 2.2 angstrom-1, and a new peak appears at 2.85 angstrom-1. At twice the normal density, the Si-O bond length increases, the Si-O coordination changes from 4 to 6, and the O-Si-O band angle changes from 109-degrees to 90-degrees. This is a tetrahedral to octahedral transformation, which was reported recently by Meade, Hemley, and Mao [Phys. Rev. Lett. 69, 1387 (1992)]. Results for phonon density of states also reveal significant changes at high pressures.