Small angle X-ray scattering and the structure of Ge-S and GeS₂-Ag₂S glassy systems

Abstract
The homogeneity of binary GeS_x (1.5 ≤ x ≤ 5) and ternary (1-y) GeS₂+yAg₂S (0.05 ≤ x ≤ 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-Büeche model. These results seem to indicate that GeS_x 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 ([MATH]) to a more homogeneous distribution of silver in the glass which is characterized also by a Debye-Büeche model for the scattered intensity.