U. Hoppe et al., The change of the Ge-O coordination number in potassium germanate glasses probed by neutron diffraction with high real-space resolution, J NON-CRYST, 248(1), 1999, pp. 1-10
Neutron diffraction experiments of high real-space resolution are used for
studying the Ge-O coordination numbers and the Ge-O bond lengths in two K2O
-GeO2 glasses (11 and 20 mol% K2O). On the long-distance side of the first-
neighbour Ge-O peak lying at 175 pm, which is likewise found for vitreous G
eO2, appears a clear shoulder. This feature indicates the existence of GeOn
units larger than GeO4 tetrahedra. The shoulder is not resolved as a separ
ate peak which could be attributed to Ge-O bonds of GeO6 octahedra unambigu
ously. Hence, it cannot be differentiated between GeO5 or GeO6 polyhedra be
ing formed in addition to the GeO4 tetrahedra. The increase of the Ge-O coo
rdination number complies with the concept of a lack of non-bridging oxygen
atoms in alkali germanate glasses up to concentrations of about 20 mol% K2
O where the additional oxygen atoms are incorporated in Ge-O-Ge bridges. (C
) 1999 Elsevier Science B.V. All rights reserved.