Glass formation and short-range order in chalcogenide materials: The (${\mathrm{Ag}}_2$S${)}_{\mathit{x}}$(${\mathrm{As}}_2$${\mathrm{S}}_3$${)}_{1\mathrm{-}\mathit{x}}$ (0≤x≤1) pseudobinary tie line

The isotopic substitution method in neutron diffraction is applied to two chalcogenide glasses on the (${\mathrm{Ag}}_2$S${)}_{\mathit{x}}$(${\mathrm{As}}_2$ ${\mathrm{S}}_3$ ${)}_{1\mathrm{-}\mathit{x}}$ (0≤x≤1) 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.