Si—O bond-length modification in pressure-densified amorphousSiO2

Abstract

The hyperfine splitting of the oxygen-vacancy center resonance in amorphous ${\mathrm{SiO}}_2$ has been measured as a function of density in samples densified under pressure at high temperature. Densification of ∼24% is found to produce an increase in the isotropic hyperfine coupling constant of 11.5% which is interpreted as resulting from a reduction in the mean O—Si—O tetrahedral bond angle of the three Si—O backbonds from 108.3° to 107.2°. This reduction corresponds to an increase in mean Si—O bond length from 1.618 to 1.623 Å and to a reduction in the mean Si—O—Si bond angle associated with the defect back bonds and adjacent ${\mathrm{SiO}}_4$ tetrahedra of 5.1°. This reduction is in excellent agreement with that estimated from x-ray scattering and nuclear magnetic resonance studies on the densified ${\mathrm{SiO}}_2$ network.