Neutron diffraction studies of Ag2S–As2S3 glasses in the percolation and modifier-controlled domains

High-resolution neutron diffraction experiments at scattering vectors up to 40 Å−1 have been carried out for the Ag2S–As2S3 glassy system in order to find differences in the network structural organisation within the percolation and modifier-controlled domains. No significant changes in the short- and intermediate-range order are found in the critical percolation region (x≤1.2 at.% Ag): the intensity and position of the first sharp diffraction peak (FSDP) exhibit relatively small changes as a function of the silver content, and the trigonal arsenic local coordination and two-fold coordinated sulphur species remain essentially intact. These observations agree very well with a model of host network-dependent percolative ion transport. In the modifier-controlled domain (x>10–15 at.% Ag), one observes nearly complete disappearance of the FSDP at 1.25–1.35 Å−1 and remarkable changes in the short-range order, in particular, characteristic Ag–Ag correlations at ≈3 Å, indicating a predominant role of Ag-containing structural units in the modified network organisation. These structural units and their interconnections seem to be similar for many silver-rich chalcogenide glasses, in which the Ag+ ion transport depends on the Ag content but not on the host matrix.