The nearest-neighbor coordination environments of Ge and As atoms in ${\mathrm{Ge}}_x{\mathrm{As}}_y{\mathrm{Se}}_{1-x-y}$ glasses with $x:y=1:2\mathrm{}$ and 1:1 and in ${\mathrm{Ge}}_{0.154}{\mathrm{As}}_{0.308}$ $(\mathrm{S},\mathrm{S}\mathrm{e}{)}_{0.538}$ sulfoselenide glasses with wide-ranging Se contents have been studied with Ge and As K-edge extended x-ray absorption time spectra spectroscopy. The average coordination numbers of Ge and As atoms are found to be 4 and 3, respectively, in all glasses. The compositional makeup of the first coordination shells of Ge and As atoms indicate that chemical order is largely preserved in stoichiometric and Se-excess ${\mathrm{Ge}}_x{\mathrm{As}}_y{\mathrm{Se}}_{1-x-y}$ glasses. On the other hand, chemical order is found to be strongly violated in the case of Se-deficient ${\mathrm{Ge}}_x{\mathrm{As}}_y{\mathrm{Se}}_{1-x-y}$ glasses where the chalcogen deficiency is entirely taken up by the formation of As-As homopolar bonds at low and intermediate levels of Se deficiency. The Ge atoms take part in homopolar bonding only in strongly Se-deficient glasses indicating clustering of As atoms. In the case of sulfoselenide glasses the distribution of S and Se atoms in the first coordination shells of Ge and As atoms is found to be random, signifying a chemically ordered chalcogen “sublattice.” It is shown that the intermediate-range structural and topological aspects of such compositional variation of chemical order may play a central role in controlling properties such as the molar volume of chalcogenide glasses.

• Received 28 May 2002

DOI:https://doi.org/10.1103/PhysRevB.66.134204