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High‐energy X‐ray diffraction was employed to study the structural characteristics of a set of C–S–H samples with 0.6 ≤ C/S ≤ 1.75. It has been observed that Si is tetrahedrally coordinated to O for all samples irrespective of chemical composition and the Ca–O coordination number gradually decreases from ~7 to ~6 with increasing C/S ratio. This suggests that the C–S–H structure evolves from a tobermorite‐like structure into a jennite‐like structure as a function of increasing C/S ratio as the interlayer space decreases from ~1.3 to ~1 nm. Evolution of these short‐ and medium‐range order structural characteristics in the C–S–H system is associated with the alteration of the Ca–O layers and silicate depolymerization with increasing C/S.

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A fundamental understanding of glass relaxation behavior is vital to the glass and polymer science communities. While prior work has focused on relaxation of first-order thermodynamic properties such as enthalpy and density, we present theoretical and experimental results showing that fluctuations in enthalpy and density relax nonmonotonically. These results provide direct evidence for dynamical heterogeneities and their close association with density fluctuations. Our results imply that density fluctuations, and hence light scattering, can be minimized through design of thermal history.

A combination of neutron and x-ray diffraction has been employed to study the compositional dependence of the atomic structures of GexAsxS100−2x glasses with S concentration varying between 33.3 and 70.0 at.%. The nearest-neighbor coordination numbers of Ge and As atoms are always found to be 4 and 3, respectively, irrespective of the glass composition. Ge and As atoms have primarily heteropolar bonding to S atoms in stoichiometric and S-excess glasses with x≤18.2. Low and intermediate levels of deficiency of S (20≤x≤25) are accommodated via the formation of homopolar As–As bonds while Ge atoms remain primarily bonded to four S atoms, resulting in As-rich regions in the glass structure. Ge starts to participate in metal–metal bonding only in the highly S-deficient glasses with 27.5≤x≤33.3. The intermediate-range order and its topological influence on atomic packing in these three compositional regions, in the order of increasing deficiency in S, are controlled by (a) a mixed GeS2 and As2S3 network, (b) the coexistence of a GeS2 network and As clusters, and (c) large Ge–As metal-rich regions. This evolution of the intermediate-range structure with composition is consistent with the corresponding variation of the position, intensity and width of the first sharp diffraction peak in the structure factor.

Combined neutron/X-ray diffraction, Ge and As K-edge extended X-ray absorption fine structure analysis, and Raman spectroscopy are employed to study the compositional dependence of the short-and intermediaterange structures of As-rich Ge x As y S 100-x-y glasses with a constant Ge:As atomic ratio of 1:17.3. The structures of glasses with compositions near stoichiometry (35 e x + y e 43) are dominated by the presence of a predominantly heteropolar-bonded As 2 S 3 network. However, an increasing metal content (x + y ) 55) results in a novel glass consisting predominantly of As 4 S 3 molecules, held together by van der Waals forces. The formation of this "molecular" glass implies an apparently anomalous situation of near-zero connectivity and dimensionality with increasing average coordination number. A further increase in metal content (60 e x + y e 65) results in the formation of As-As homopolar-bonded structural regions that coexist with As 4 S 3 molecules. Such unusual evolution of intermediate-range order is shown to be closely related to the compositional variation of thermophysical properties and density fluctuation in these glasses. IntroductionChalcogenide glasses are of wide-ranging importance in a variety of technological applications in the areas of photonics and telecommunication. 1-6 The unique compositional flexibility of these glasses in the form of continuous alloying enables tuning of optical, electronic, thermomechanical, and other properties via compositional "engineering". The compositiondependent structural characteristics such as formation of homopolar bonds and of molecular and other low-dimensional structural units and violation of chemical order are expected to control a wide range of physical properties relevant to various technological applications of these materials. A number of studies of the short-and intermediate-range atomic structure of simple binary chalcogenide glasses in AsX, PX, and GeX (X ) S, Se) systems have been reported in the literature over the past several decades. 7-19 However, in contrast, structural studies of complex glasses in the ternary and quaternary Ge-As-S/Se/Te systems had been rather limited and had focused mostly on short-range order only. 20-24 This is primarily due to the fact that direct experimental studies of structural characteristics beyond the nearest-neighbor length scale are particularly difficult with spectroscopic techniques alone. A number of previous studies have investigated the compositional evolution of the length scale of intermediate-range order in ternary Ge-As-S glasses along the join GeS 2 -As 2 S 3 in a phenomenological fashion using Raman spectroscopy. [25][26][27] These studies have used the Ioffe-Regel criterion to relate the position of the Boson peak in the Raman spectra to a length scale of intermediate-range order that increased with increasing GeS 2 content and ranged from a few angstrom to 20 Å in GeS 2 -As 2 S 3 glasses. On the other hand, a recent Raman spectroscopic study of ternary (Ge 2 S 3 ) x (As 2 S 3 ) 1-x glasses has...

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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.