Structural organization of arsenic selenide liquids: new results from liquid state NMR

Insights into the structure and dynamics of the binary As-Se glass system h ave been obtained from high-temperature Se-77 nuclear magnetic resonance (N MR) studies of molten samples. In materials having As contents < 20 at.%, d ynamic exchange averaging processes are detected and analysed quantitativel y by detailed lineshape simulations. At high-temperatures (1.5 x glass tran sition temperature), only a single averaged Se-77 NMR signal is observed, w hose chemical shift arises from the quantitative distribution of As-Se and Se-Se bonds. A detailed analysis of the compositional dependence reveals a tendency towards chemical ordering, based on the structurally dominant AsSe 3/2 groups. Furthermore, the experimental data serve to differentiate betwe en various intermediate range ordering scenarios and favor a structural des cription in terms of a network in which AsSe3/2 and Se-2/2 groups are rando mly linked. (C) 2001 Elsevier Science B.V. All rights reserved.