Compositional Variation of Short- and Intermediate-Range Structure and Chemical Order in Ge−As Sulfide Glasses: A Neutron Diffraction Study

Abstract

The structures of chalcogenide glasses in the Ge−As−S system with Ge:As = 1:1 and with S concentration varying between 33.3 and 70.0 atom% have been studied using neutron diffraction. Ge and As atoms are primarily heteropolar bonded to S atoms in stoichiometric and S-excess glasses. Formation of homopolar As−As bonds at low and intermediate levels of S-deficiency results in violation of chemical order and in the formation of As-rich structural moieties. Ge takes part in metal−metal bonding, predominantly via the formation of Ge−As bonds, only in the highly S-deficient glasses once all the As atoms are used up in homopolar bonding. Incorporation of tetrahedrally coordinated Ge into the structure disrupts the topological continuity of the low-dimensional As-rich clusters and the GeS2 network. These intermediate-range order structural orderings are manifested in the compositional dependence of the intensity, position, and width of the first sharp diffraction peak in the structure factor.