The nature of intermediate-range order in Ge–As–S glasses: results from reverse MonteCarlo modeling

Abstract

The experimental neutron and x-ray diffraction data for stoichiometric and S-deficientGexAsxS100 − 2x glasseswith x = 18.2, 25.0, and 33.3 at.% have been modeled simultaneously using the reverse Monte Carlo (RMC)technique. Nearest-neighbor coordination environments, as obtained in previous x-rayabsorption spectroscopy and diffraction experiments, have been employed as short-range orderconstraints in these simulations. The large scale three-dimensional structural models thusobtained from RMC simulation are used to investigate the nature and compositional evolutionof intermediate-range structural order in these ternary glasses. The intermediate-rangestructural order is controlled by (1) a corner-shared three-dimensional network ofAsS3 pyramids andGeS4 tetrahedra in thestoichiometric Ge18.2As18.2S63.6 glass, (2) a heterogeneous structure that consists of homopolar bonded As-rich regions coexisting with aGeS2 network in theS-deficient Ge25As25S50 glass, and (3) a homogeneous structure resulting from the disruption of the topological continuity of theGeS2 network and As-rich clusters regions due to the formation of Ge–As bonds in the most S-deficientGe33.3As33.3S33.3 glass. This scenario of the compositional evolution of intermediate-range structural order isconsistent with and provides an atomistic explanation of the corresponding evolution in theposition, width and intensity of the first sharp diffraction peak and the magnitude of smallangle scattering in these glasses.