Structural characterization of germanium-arsenic-sulfur chalcogenide glasses and understanding structural relaxation in oxide glasses

The structures of chalcogenide glasses in the GexAsx S100-2x system with 33.3 ≤ 100-2x ≤ 70.0 are investigated using neutron/x-ray diffraction. Ge and As atoms are primarily heteropolar bonded to S atoms in glasses near stoichiometry (x ≤ 18.2). Large scale three-dimensional structural models obtained from reverse Monte Carlo (RMC) simulations are used to investigate the nature of intermediate-range structural order in these ternary glasses. Heteropolar bonded mixed GeS2 and As2S3 network in glasses with compositions near stoichiometry is transformed into a heterogeneous glass with mixed GeS2 network and As-rich clusters with increasing S-deficiency. The latter structure is largely homogenized with further increase in metal content.;Structural mechanisms of densification of a molecular chalcogenide glass of composition Ge2.5As51.25S46.25 are studied in situ in a panoramic cell equipped with Moissanite (SiC) anvils at pressures ranging from 1 atm to 11 GPa at ambient temperature as well as ex situ on a sample quenched from 12 GPa in a multi-anvil cell using high-energy x-ray diffraction.;11B MAS NMR spectroscopy is employed to monitor relaxation kinetics of boron coordination environments in a borosilicate glass in response to temperature jumps. The relaxation timescale of the BO4:BO 3 ratio is found to be closely comparable with those of the bulk properties, namely refractive index, density and viscosity.;The behavior of density and enthalpy fluctuations during glass relaxation is investigated theoretically and experimentally employing the Mauro-Loucks enthalpy landscape model and in situ small angle x-ray scattering, respectively. It is shown that the magnitude of these fluctuations relaxes non-monotonically as glass anneals at constant temperature.;Combined neutron/x-ray diffraction, Ge and As K-edge EXAFS and Raman spectroscopy are employed to study the compositional dependence of the short- and intermediate-range structures of As-rich GexAs yS100-x-y glasses with x:y = 1:17.3. The structures of glasses with compositions near stoichiometry consist mainly of heteropolar-bonded As2S3 network. However, increasing metal content (x+y = 55) results in a novel glass consisting predominantly of As4S 3 molecules with near-zero connectivity and dimensionality. Formation of As-As homopolar bonded structural regions that coexist with As4S 3 molecules is observed with further increase in metal content (60 ≤ x+y ≤ 65).