Structure, topology and chemical order in Ge-As-Te glasses: a high-energy x-ray diffraction study.

High-energy x-ray diffraction is employed to study the atomic structure of bulk Ge(x)As(2x)Te(100-3x) glasses with compositions in the range 25 ≤ 3x ≤ 70. The coordination environments of Te atoms suggest significant violation of chemical order in these glasses. Analyses of the nearest-neighbor coordination environments and the parameters for the first sharp diffraction peak indicate that these telluride glasses are structurally and chemically more disordered as compared with their sulfide or selenide analogs. The compositional evolution of the structural parameters is shown to be consistent with the corresponding variation in molar volume and glass transition temperature.

The nature of intermediate-range order in Ge-As-S glasses: results from reverse Monte Carlo modeling.

The experimental neutron and x-ray diffraction data for stoichiometric and S-deficient Ge(x)As(x)S(100-2x) glasses with 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-ray absorption spectroscopy and diffraction experiments, have been employed as short-range order constraints in these simulations. The large scale three-dimensional structural models thus obtained from RMC simulation are used to investigate the nature and compositional evolution of intermediate-range structural order in these ternary glasses. The intermediate-range structural order is controlled by (1) a corner-shared three-dimensional network of AsS(3) pyramids and GeS(4) tetrahedra in the stoichiometric Ge(18.2)As(18.2)S(63.6) glass, (2) a heterogeneous structure that consists of homopolar bonded As-rich regions coexisting with a GeS(2) network in the S-deficient Ge(25)As(25)S(50) glass, and (3) a homogeneous structure resulting from the disruption of the topological continuity of the GeS(2) network and As-rich clusters regions due to the formation of Ge-As bonds in the most S-deficient Ge(33.3)As(33.3)S(33.3) glass. This scenario of the compositional evolution of intermediate-range structural order is consistent with and provides an atomistic explanation of the corresponding evolution in the position, width and intensity of the first sharp diffraction peak and the magnitude of small angle scattering in these glasses.