The Ge-O-Ge bond angle distribution in GeO2 glass: a NMR determination

O-17 MAS and static NMR spectra, from amorphous germania and quartz-like GeO2, have been used to estimate the range of O-17 quadrupolar parameters in the glass for different assumed bond angle distributions. The spectra from the quartz-like polymorph of GeO2 were used to provide reference data for oxygen connected to four-fold coordinated germanium. Nuclear quadrupole coupling constants, (C-Q = e(2)qQ/h), asymmetry parameters, (eta), and isotropic chemical shifts, (delta(i)), were obtained from simulations, of glass spectra obtained at different fields, in which a range of quadrupolar parameters were employed, according to various postulated bond angle distributions. Our results show that the Ge-(O) over cap-Ge angle distribution in amorphous germania is consistent with a Gaussian distribution with most probable angle of 130 +/- 1 degrees and sigma close to 4 degrees - smaller than hitherto reported for GeO2. (C) 1999 Elsevier Science B.V. All rights reserved