Open AccessBond angle distribution in amorphous germania and silica
Author(s) -
Neuefeind Jörg,
Liss K.D.
Publication year - 1996
Publication title -
berichte der bunsengesellschaft für physikalische chemie
Language(s) - English
Resource type - Journals
ISSN - 0005-9021
DOI - 10.1002/bbpc.19961000812
Subject(s) - amorphous solid , molecular geometry , diffraction , bond length , neutron diffraction , materials science , crystallography , distribution (mathematics) , structure factor , momentum transfer , molecular physics , chemistry , optics , physics , scattering , crystal structure , molecule , mathematics , organic chemistry , mathematical analysis
The distribution of Ge‐O‐Ge and Si‐O‐Si bond angles α in amorphous germania and silica is re‐determined on the basis of diffraction experiments. The bond angle α 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 Å −1 . In photon diffraction experiments on GeO 2 the contribution of the OO pairs is very small. To obtain a similar information for amorphous SiO 2 , high energy photon diffraction experiments [1] have been combined with neutron diffraction data [2, 3] on amorphous silica in order to eliminate the OO‐partial structure factor. With this technique it is shown that the Si‐O‐Si angle distribution is fairly narrow (σ = 7.5°) and in fact comparable in width to the Ge‐O‐Ge angle distribution (σ = 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 29 Si‐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 bond angle distribution can be excluded within the reached real space resolution of 0.09 Å.