The structure of Ge20Sb10S70, Ge23Sb12S65 and Ge26Sb13S61 glasses was investigated by neutron diffraction (ND), X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) measurements ...at the Ge and Sb K-edges as well as Raman scattering. For each composition, large scale structural models were obtained by fitting simultaneously diffraction and EXAFS data sets in the framework of the reverse Monte Carlo (RMC) simulation technique. Ge and S atoms have 4 and 2 nearest neighbors, respectively. The structure of these glasses can be described by the chemically ordered network model: Ge-S and Sb-S bonds are always preferred. These two bond types adequately describe the structure of the stoichiometric glass while S-S bonds can also be found in the S-rich composition. Raman scattering data show the presence of Ge-Ge, Ge-Sb and Sb-Sb bonds in the S-deficient glass but only Ge-Sb bonds are needed to fit diffraction and EXAFS datasets. A significant part of the Sb-S pairs has 0.3–0.4 Å longer bond distance than the usually accepted covalent bond length (∼2.45 Å). From this observation it was inferred that a part of Sb atoms have more than 3 S neighbors.
•Structural models of GeSbS glasses consistent with multiple datasets are constructed.•Structure of these glasses can be described by the chemically ordered network model.•Ge and S atoms obey the Mott-rule and have 4 and 2 nearest neighbors, respectively.•Long Sb-S bonds were observed, suggesting that SbS5 units may exist in this system.
We report an investigation of the structure and vibrational modes of Ge–In–S–AgI bulk glasses using X-ray diffraction, EXAFS spectroscopy, Reverse Monte-Carlo (RMC) modelling, Raman spectroscopy, and ...density functional theoretical (DFT) calculations. The combination of these techniques made it possible to elucidate the short- and medium-range structural order of these glasses. Data interpretation revealed that the AgI-free glass structure is composed of a network where GeS4/2 tetrahedra are linked with trigonal InS3/2 units; S3/2Ge–GeS3/2 ethane-like species linked with InS4/2− tetrahedra form sub-structures which are dispersed in the network structure. The addition of AgI into the Ge–In–S glassy matrix causes appreciable structural changes, enriching the Indium species with Iodine terminal atoms. The existence of trigonal species InS2/2I and tetrahedral units InS3/2I− and InS2/2I2− is compatible with the EXAFS and RMC analysis. Their vibrational properties (harmonic frequencies and Raman activities) calculated by DFT are in very good agreement with the experimental values determined by Raman spectroscopy.
Experiment (XRD, EXAFS, RMC, Raman scattering) and density functional calculations are employed to study the structure of AgI-doped Ge–In–S glasses. The role of mixed structural units as illustrated in the figure is elucidated Display omitted .
► Doping Ge–In–S glasses with AgI causes significant changes in glass structure. ► Experiment and DFT are combined to elucidate short- and medium-range structural order. ► Indium atoms form both (InS4/2)− tetrahedra and InS3/2 planar triangles. ► (InS4/2)− tetrahedra bond to (S3/2Ge–GeS3/2)2+ ethane-like units forming neutral sub-structures. ► Mixed chalcohalide species (InS3/2I)− offer vulnerable sites for the uptake of Ag+.
The local atomic structure of the glassy Al(92)U(8) alloy was modelled by the reverse Monte Carlo (RMC) method, fitting x-ray diffraction (XRD) and extended x-ray absorption fine structure (EXAFS) ...signals. The final structural model was analysed by means of partial pair correlation functions, coordination number distributions and Voronoi tessellation. In our study we found that the most probable atomic separations between Al-Al and U-Al pairs in the glassy Al(92)U(8) alloy are 2.7 Å and 3.1 Å with coordination numbers 11.7 and 17.1, respectively. The Voronoi analysis did not support evidence of the existence of well-defined building blocks directly embedded in the amorphous matrix. The dense-random-packing model seems to be adequate for describing the connection between solvent and solute atoms.
The structure of As3Se5Te2 infrared optical glass was investigated by X-ray and neutron diffraction as well as extended X-ray absorption fine structure measurements at the As-, Se- and Te K-edges. ...The five datasets were modelled simultaneously by the reverse Monte Carlo simulation technique. Experimental data could be fitted satisfactorily by allowing As-Se, As-Te and Se-Te bonds only. It was revealed that the affinity of As is much higher to Se than to Te. The nearest As-Se distance is similar to that found in other vitreous As-Se based alloys, while the As-Te bond length is 0.02-0.04 Å shorter in As3Se5Te2 than in binary As-Te glasses.
The short-range atomic order of ternary Fe–Nb–B metallic glasses has been studied by X-ray diffraction, neutron diffraction, X-ray absorption spectroscopy, and reverse Monte-Carlo simulation. The ...similarities and differences in the local structure of the Fe–Nb–B glasses and their crystalline counterparts are revealed. The composition dependences for the Curie temperature of the Fe–Nb–B glasses, which increases by substitution of boron for iron at constant niobium content and decreases by substitution of niobium for iron at constant boron concentration, are discussed in the frame of the coordination-bond model.
The structure of Ge20Sb x Se80–x (x = 5, 15, 20) glasses was investigated by neutron diffraction, X-ray diffraction, and extended X-ray fine structure measurements at the Ge, Sb, and Se K-edges. For ...each composition, large-scale structural models were obtained by fitting simultaneously the experimental data sets in the framework of the reverse Monte Carlo simulation technique. It was found that the structures of these glasses can be described mostly by the chemically ordered network model. Ge–Se and Sb–Se bonds are preferred; Se–Se bonds in the Se-poor composition (x = 20) and M–M (M = Ge, Sb) bonds in strongly Se-rich glass (x = 5) are not needed. The quality of the fits was significantly improved by introducing Ge–Ge bonding in the nearly stoichiometric composition (x = 15), showing a violation of chemical ordering. The structure of Ge20Sb x Se80–x was compared to that of several glasses from the three analogous systems (Ge–As–Se, Ge–As–Te, Ge–Sb–Te), and it was found that chemical short-range order becomes more pronounced upon substituting As with Sb and Se with Te. Ge–As–Se glasses behave as random covalent networks over a very broad composition range. Chemical short-range order and disorder coexist in both Te-rich and Te-poor Ge–As–Te glasses, whereas amorphous Ge14Sb29Te57 and Ge22Sb22Te56 are governed by strict chemical preferences.
Very low density eutectic Ca72Mg28 at.% alloy is a precursor of complex biodegradable alloys with potential use as bioresorbable alloy for orthopaedic applications. The structure of the amorphous ...alloy was investigated by using X-ray, neutron diffraction and reverse Monte Carlo (RMC) modelling. The RMC configuration was decomposed into polyhedral holes whose faces are all triangles consisting of chemical bonds. Free volumes in the respective polyhedral holes were evaluated with reference to the packing efficiency of crystalline CaMg2 HCP phase. The tetrahedral holes, accounting for about 55% of the whole space, are regarded as densely packed units because the average packing efficiency of them is approximately equal to that of the corresponding crystal phase. At the same time, various types of polyhedral holes which have a certain free volume have been observed, and some of them are connected with each other. The densely packed coordination polyhedra consisting only of tetrahedral holes tend to be clustered.
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•Atomic structure of biodegradable Ca72Mg28 at.% glass was fully characterized.•A structural inhomogeneity in free volume distribution was observed.•Densely packed volumes responsible for glass formation were identified.
Partial radial distribution functions for Cu47.5Zr47.5Al5 metallic glass and relevant crystal structures. Display omitted
Cu47.5Zr47.5Al5 metallic glass is studied experimentally by high-energy X-ray ...diffraction, neutron diffraction with isotopic substitution, electron diffraction and X-ray absorption spectroscopy. The atomic structure of the glass is modeled by reverse Monte-Carlo and molecular dynamics simulations. RMC modeling of seven experimental datasets enabled reliable separation of all partial pair distribution functions for Cu47.5Zr47.5Al5 metallic glass. A peculiar structural feature of the ternary alloy is formation of the strong Al–Zr bonds, which are supposed to determine its high viscosity and enhanced bulk glass formation. Analysis of the local atomic order in Cu47.5Zr47.5Al5 glass and Cu10Zr7, CuZr2 and CuZr B2 crystalline structures elucidates their similarities and differences explaining the phase formation sequence by devitrification of the glass.
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