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

Raman and XANES spectroscopy of permanently densified vitreous silica

“…As the Si-O-Si bond angles are reduced, coulombic SiÁ Á ÁSi repulsive forces increase (as a function of inverse interatomic separation squared), requiring Si-O bond lengths to be increased in order to maintain adequate separation between the two highly charged cations. Evidence for longer Si-O bonds in densified vitreous silica has also been found using electron spin resonance [14], in which, with increasing density of the glass, monitoring the isotropic hyperfine coupling constant enabled the authors to estimate a bond length increase from 1.618 A for the undensified glass to 1.623…”

Nature of polymerization and properties of silicate melts and glasses at high pressure

“…The distortion of network polyhedra associated with Si-O bond length distribution has also been positively correlated with pressure (Devine and Arndt, 1987). The fraction of highly coordinated Si (e.g., 5 or 6 coordinated Si, [5,6] Si) or Al in partially depolymerized melts (e.g., Na 2 Si 4 O 9 and Na 3 AlSi 7 O 17 ) gradually increases with pressure, a phenomenon that has been related to the anomalous transport properties of aluminosilicate melts, wherein the diffusivity first increases, then decreases with increasing pressure (Waff, 1975;Xue et al, 1989;Poe et al, 1997;Diefenbacher et al, 1998;Poe et al, 2001).…”

Structural properties of silicon dioxide thin films densified by medium-energy particles

“…It is mainly associated to the structural "building block" of the network, the Si(O 1/2 ) 4 tetrahedron. Both numerical simulations [13][14][15] and experiment [16][17][18] have shown the SRO correlations in permanently-densified (20%) a-SiO 2 recovered from high pressures (∼ 15-20 GPa) to be essentially the same as in the "normal" material.…”