STRUCTURE OF FAST-ION CONDUCTING CHALCOGENIDE GLASSES - THE AG-AS-SE SYSTEM

The coordination environment of Ag in bulk-quenched Ag4AS37.6Se58.3 an d Ag2As3Se4 glasses is investigated by using the method of isotopic su bstitution in neutron diffraction. It is found that there is little ch ange in the short-range order about Ag between the two compositions: A g is covalently bonded to an average of almost-equal-to 3 Se atoms at a distance of almost-equal-to 2.68 angstrom in both samples. The absen ce of a pronounced change in the structure about the metal atom in the Ag-As-Se system, between glass compositions where the electrical cond uctivity is electronic (4 at.% Ag) and where it is predominantly ionic (22.2 at.% Ag), is by direct contrast with the case observed for glas ses in the Ag-As-S system.