INTERMEDIATE-RANGE ORDER IN PERMANENTLY DENSIFIED VITREOUS SIO2 - A NEUTRON-DIFFRACTION AND MOLECULAR-DYNAMICS STUDY

The structure of pressure-densified vitreous SiO2 has been investigated using neutron-diffraction and molecular-dynamics techniques. After compression to 16 GPa at room temperature, recovered samples have densities 20% higher than normal vitreous SiO2 and show substantial changes in the first sharp diffraction peak (FSDP): an indication of modification in the intermediate-range order. The changes in the FSDP are due to increased frustration caused by the decrease in the Si-O-Si bond angle and a shift in the Si-Si and O-O correlations in the range of 4-8 angstrom toward lower distances.