Structural Evolution of SiO2 Glass with Si Coordination Number Greater than 6

Pair distribution function measurement of SiO2 glass up to 120 GPa reveals changes in the first-, second-, and third-neighbor distances associated with an increase in Si coordination number C-Si to >6 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 C-Si = 6 to >6. Structural constraints in terms of ionic radius ratio of Si and O, and ratio of nonbonded radius to bonded Si-O distance support the structural evolution of SiO2 glass with C-Si > 6 at high pressures.