SMALL-ANGLE X-RAY-SCATTERING AND THE STRUCTURE OF GE-S AND GES2-AG2S GLASSY SYSTEMS

The homogeneity of binary GeS(X) (1.5 less-than-or-equal-to x less-than-or-equal-to 5) and ternary (1-y) GeS2+yAg2S (0.05 less-than-or-equal-to y less-than-or-equal-to 0.5) glasses has been characterized from SAXS experiments. The scattering intensity of GeSx binary glasses is weak and present a monotonous decay only fitted by using a Debye-Bueche model. These results seem to indicate that GeSx glassy network have only weak fluctuations of electron density, correlated in a few hundred of Angstroms in agreement with a rather continuous glassy network picture, without definite clusters in the structure. On the other hand, the ternary glasses show an important evolution versus composition. For small amount of Ag2S, the glassy network modifier is not well ''dilute'' in the glass former GeS2. This induces the formation of Ag2S clusters which are characterized by a correlation peak and a Porod region. When the Ag2S proportion increases, the ''dilution'' of the glass modifier is improved due to the typical depolymerization of the glass matrix. This lead for Ag2S enriched composition (y>0.3) to a more homogeneous distribution of silver in the glass which is characterized also by a Debye-Bueche model for the scattered intensity.