Atomic structure and chemical order in binary Ge-Te and As-Te glasses: A Te K-edge X-ray absorption fine structure spectroscopic study

The nearest-neighbor coordination environments of Te atoms in GexTe100-x glasses with x = 15 and 20 and in AsxTe100-x glasses with 40 <= x <= 65 have been studied with Te K-edge EXAFS spectroscopy. The average coordination number of Te atoms in all glasses is found to be similar to 2.0 and no violation of the 8-N rule is observed. The compositional makeup of the first coordination shell of Te atoms indicates that chemical order is largely preserved in both glass-forming binary systems. Sudden changes in the Te coordination environment and violation of chemical order are observed at the stoichiometric As40Te60 glass implying formation of a constrained network. The compositional dependence of the physical properties in both systems can be correlated to short-range chemical order. (c) 2008 Elsevier B.V. All rights reserved.