A Trial on Detecting Fluctuations in Bulk Metallic Glass Beams by Strain Contrast Variation Method-Use of High Energy Small-Angle Scattering

Heterogeneity in annealed Zr-Cu-Al alloys with high ductility has been examined by high-energy small-angle scattering with strain variation method. Although the statistics is still poor for detailed analysis, it was found that the heterogeneity in the sample showed clear enhancement by applied tensile strain, and the characteristic size of the heterogeneity was of the same order of magnitude as the one observed by high resolution electron microscopy. With surface insensitivity of the present method, anomalous small-angle scattering results at Cu K absorption edge for the same sample was briefly discussed

Temperature-dependent structure of methanol-water mixtures on cooling: X-ray and neutron diffraction and molecular dynamics simulations

Methanol-water liquid mixtures have been investigated by high-energy synchrotron X-ray and neutron diffraction at low temperatures. We are thus able to report the first complete sets of both X-ray and neutron weighted total scattering structure factors over the entire composition range (at 12 different methanol concentrations (xM) from 10 to 100 mol%) and at temperatures from ambient down to the freezing points of the mixtures. The new diffraction data may later be used as reference in future theoretical and simulation studies. The measured data are interpreted by molecular dynamics simulations, in which the all atom OPLS/AA force field model for methanol is combined with both the SPC/E and TIP4P/2005 water potentials. Although the TIP4P/2005 water model was found to be somewhat more successful, both combinations provide at least semi-quantitative agreement with measured diffraction data. From the simulated particle configurations, partial radial distribution functions, as well as various distributions of the number of hydrogen bonds have been determined. As a general trend, the average number of hydrogen bonds increases upon cooling. However, the number of hydrogen bonds between methanol molecules slightly decreases with lowering temperatures in the concentration range between ca. 30 and 60 mol% alcohol content. The same is valid for water-water hydrogen bonds above 70 mol% of methanol content, from room temperature down to 193 K

Hydrogen bonding and percolation in propan-2-ol -- water liquid mixtures: X-ray diffraction experiments and computer simulations

Synchrotron X-ray diffraction measurements have been conducted on aqueous mixtures of propan-2-ol (a.k.a. isopropanol, or 2-propanol), for alcohol contents between 10 and 90 molar %, from room temperature down to 230 K. Molecular dynamics simulations, by using an all-atom parametrization of the propan-2-ol molecule and the well-known TIP4P/2005 water model, were able to provide semi-quantitative descriptions of the measured total structure factors. Various quantities related to hydrogen bonding, like hydrogen bond numbers, size distribution of cyclic entities and cluster size distributions, have been determined from the particle co-ordinates obtained from the simulations. The percolation threshold at room temperature could be estimated to be between isopropanol concentrations of 62 and 74 molar %, whereas at very low temperature, calculations yielded a value above 90 molar %

X-ray and Neutron Study on the Structure of Hydrous SiO2 Glass up to 10 GPa

The structure of hydrous amorphous SiO2 is fundamental in order to investigate the effects of water on the physicochemical properties of oxide glasses and magma. The hydrous SiO2 glass with 13 wt.% D2O was synthesized under high-pressure and high-temperature conditions and its structure was investigated by small angle X-ray scattering, X-ray diffraction, and neutron diffraction experiments at pressures of up to 10 GPa and room temperature. This hydrous glass is separated into two phases: a major phase rich in SiO2 and a minor phase rich in D2O molecules distributed as small domains with dimensions of less than 100 angstrom. Medium-range order of the hydrous glass shrinks compared to the anhydrous SiO2 glass by disruption of SiO4 linkage due to the formation of Si-OD deuterioxyl, while the response of its structure to pressure is almost the same as that of the anhydrous SiO2 glass. Most of D2O molecules are in the small domains and hardly penetrate into the void space in the ring consisting of SiO4 tetrahedra

Structural basis for the fast phase change of Ge2Sb2Te5: Ring statistics analogy between the crystal and amorphous states

The three-dimensional atomic configuration of amorphous Ge2Sb2Te5 and GeTe were derived by reverse Monte Carlo simulation with synchrotron-radiation x-ray diffraction data. The authors found that amorphous Ge2Sb2Te5 can be regarded as "even-numbered ring structure," because the ring statistics is dominated by four- and six-fold rings analogous to the crystal phase. On the other hand, the formation of Ge–Ge homopolar bonds in amorphous GeTe constructs both odd- and even-numbered rings. They believe that the unusual ring statistics of amorphous Ge2Sb2Te5 is the key for the fast crystallization speed of the material