GLASS-FORMATION AND SHORT-RANGE ORDER IN CHALCOGENIDE MATERIALS - THE (AG2S)X(AS2S3)1-X (0 LESS-THAN-OR-EQUAL-TO X LESS-THAN-OR-EQUAL-TO 1) 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. © 1990 The American Physical Society.