Structural Evolution of SiO 2 Glass with Si Coordination Number Greater than 6

Pair distribution function measurement of ${\mathrm{SiO}}_{2}$ glass up to 120 GPa reveals changes in the first-, second-, and third-neighbor distances associated with an increase in Si coordination number ${\text{C}}_{\text{Si}}$ to $g6$ above 95 GPa. Packing fractions of Si and O determined from the first- and second-neighbor distances show marked changes accompanied with the structural evolution from ${\text{C}}_{\text{Si}}=6$ to $g6$. Structural constraints in terms of ionic radius ratio of Si and O, and ratio of nonbonded radius to bonded $\mathrm{Si}─\mathrm{O}$ distance support the structural evolution of ${\mathrm{SiO}}_{2}$ glass with ${\text{C}}_{\text{Si}}g6$ at high pressures.