Bond angle distribution in amorphous germania and silica

Abstract

The distribution of Ge-0-Ge and Si-0-Si bond angles a in amorphous germania and silica is re-determined on the basis of diffraction experiments. The bond angle a joining adjacent tetrahedra is the central parameter of any continuous random network description (CRN) of these glasses. New high energy photon diffraction experiments on amorphous germania (at photon energies of 97 and 149 keV) are presented, covering the momentum transfer 0.6-33.5 A -'. In photon diffraction experiments on GeO, the contribution of the 00 pairs is very small. To obtain a similar information for amorphous SiO,, high energy photon diffraction experiments [l] have been combined with neutron diffraction data 12, 31 on amorphous silica in order to eliminate the 00-partial structure factor. With this technique it is shown that the Si-0-Si angle distribution is fairly narrow (a = 7.5") and in fact comparable in width to the Ge-0-Ge angle distribution (a = 8.3'), a result which differs from current opinion. The narrower distribution found in this study are in much better agreement to the determinations based on 29Si-MAS-NMR. Among the various models relating the chemical shift to the bond angle, best agreement is found with those models based on the secant model. Sharp components in the bong angle distribution can be excluded within the reached real space resolution of 0.09 A.

Symmetry determined medium range order (MRO) contributions to the first sharp diffraction peak (FSDP) in non‐crystalline oxide and chalcogenide glasses

“…[17], but in agreement a more recent calculation that used a larger range of X-ray energies, and hence k as well [18]. Not including d-state symmetries with Gaussian radial components yield the ionic bonding solution with bond angle of 180…”

“…[20,21]. The staggered configuration in these studies is the geometric arrangement that is required by the symmetry constrains of the O 2pπ-Si 3dπ overlap that provides the charge transfer that stabilizes the Si-O-Si bond angle at a value consistent with the latest X-ray diffraction studies [18].…”

Ab initio calculations for photo‐darkening and photo‐induced structural changes in As 2 S 3 and GeS 2

“…The 9-atom clusters are terminated either by i) Si* pseudo-atoms that preserve Si and O core levels, and dipole moments, or ii) Hatoms with essentially equivalent results. The ab initio calculations give an average Si-O-Si bond angle of 149±1°, and a bond angle distribution of ~19°±2° in good agreement with recently published results [9,10]. This distribution is markedly different from the >30° bond angle spread of Mozzi and Warren [11].…”

The structure of amorphous, crystalline and liquid GeO2

“…A recent neutron and X-ray diffraction investigation [35] has shown that the o using high-energy X-ray diffraction [45]. This bond angle and its distribution are lower than in the case of vitreous silica.…”