A contribution to the structure of Ge-Se-Ag glasses

Glasses from the Ge-rich region [Ge(0.5-0.33x, Ag0.33xSe0.5] of the Ge-Se-Ag phase diagram are synthesised for x=0.6, 0.7 and 0.8. For comparison a special sample Ge3Se9Ag4 (Ge0.1875Se0.562Ag0.25)from the Se-rich region has also been prepared. For the concentrations studied both the x-ray scattering curves as well as the radial electron distribution functions (RDF) are nearly identical. The analysis of the first maximum of the RDF shows that it is composed mainly from GeSe4 tetrahedra with a bonding distance Ge-Se=2-37 A and from AgS4 tetrahedra with a bonding distance Ag-Se=2.63 A. There is a certain amount of edge-bound tetrahedra as could be shown by the interpretation of the RDF in the region of 3 A. The most important conclusion following from the direct analysis of x-ray scattering, is that the structure of Ge-Se-Ag glasses is predominantly formed by a GeSe2-like network (corner- and edge-bound tetrahedra), which is interpenetrated and disrupted by AgSe4 tetrahedra, which for stoichiometric reasons tend to cluster. This results in corner- and edge-sharing of AgSe4 tetrahedra. These groups form the migration channels for ionic transport (Ag+)