Ge and As x-ray absorption fine structure spectroscopic study of homopolarbonding, chemical order, and topology in Ge-As-S chalcogenide glasses - art. no. 104202

The coordination environments of Ge and As atoms in GexAsyS1-x-y glasses wi th x:y= 1:2, 1:1, and 2.5:1 and with wide-ranging S contents have been stud ied with Ge and As K-edge x-ray absorption fine structure spectroscopy. The coordination numbers of Ge and As atoms are found to be 4 and 3, respectiv ely, in all glasses. The first coordination shells of Ge and As atoms in th e stoichiometric and S-excess glasses consist of S atoms only, implying the preservation of chemical order at least over the length scale, of the firs t coordination shell. As-As homopolar bonds are found to appear at low and intermediate levels of S deficiency, whereas Ge-Ge bonds are formed only in strongly S-deficient glasses indicating clustering of metal atoms and viol ation of chemical order in S-deficient glasses. The composition-dependent v ariation in chemical order in chalcogenide glasses has been hypothesized to result in topological changes in the intermediate-range structural units. The role of such topological transitions in controlling the structure-prope rty relationships in chalcogenide glasses is discussed.