Glass formation and short-range order in chalcogenide materials: The (Ag2S)x(As2S3)1-x (0x1) pseudobinary tie line

The isotopic substitution method in neutron diffraction is applied to two chalcogenide glasses on the (Ag2S)x(As2S3)1-x (0x1) tie line of the Ag-As-S system. It is shown that there is a reduction from 4 to 3 in the average number of S atoms covalently bonded to Ag as x is increased from 0.096 to 0.500, but that As remains threefold coordinated by S. The onset of ionic conductivity as x is increased and the occurrence of two homogeneous glass-forming regions is therefore associated with a change in the coordination environment of the metal atom.