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

Controlling oxygen coordination and valence of network forming cations

Understanding the structure-property relationship of glass material is still challenging due to a lack of periodicity in disordered materials. Here, we report the properties and atomic structure of vanadium phosphate glasses characterized by reverse Monte Carlo modelling based on neutron/synchrotron X-ray diffraction and EXAFS data, supplemented by Raman and NMR spectroscopy. In vanadium-rich glass, the water durability, thermal stability and hardness improve as the amount of P2O5 increases, and the network former of the glass changes from VOx polyhedra to the interplay between VOx polyhedra and PO4 tetrahedra. We find for the first time that the coordination number of oxygen atoms around a V4+ is four, which is an unusually small coordination number, and plays an important role for water durability, thermal stability and hardness. Furthermore, we show that the similarity between glass and crystal beyond the nearest neighbour distance is important for glass properties. These results demonstrate that controlling the oxygen coordination and valence of the network-forming cation is necessary for designing the properties of glass

Intermediate-range order in lead metasilicate glass

The complementarity of anomalous X-ray scattering (AXS) and neutron diffraction (ND) techniques is used here to investigate the nature and origin of intermediate-range order in lead metasilicate glass. Both X-ray and neutron source factors reveal small peaks at low wave vector which are shown to be associated with intermediate-range order of the Pb-O network. The combination of AXS and ND is shown to be a powerful tool to correlate contributions from the different atom pairs to such a peak. The information thus derived is compared with results from alkali germanate glasses and with structural data on corresponding crystalline compounds

Intermediate- and extended-range order in phosphate glasses

The structure of sodium ultraphosphate glasses, (Na{sub 2}O){sub x}(P{sub 2}O{sub 5}){sub 100-x} (x = 0, 10, 20), and alkali metaphosphate glasses, MePO{sub 3} (Me = Li, Na, K, Rb and Cs) have been studied by neutron diffraction. Structural features in the neutron structure factors S(Q) characteristic of intermediate-range (Q {approx_lt} 3 {angstrom}{sup -1}) order were identified. The feature of intermediate-range order in the pure phosphate glass (v-P{sub 2}O{sub 5}) is accounted for by the P{sub 4}O{sub 10} molecule packing model. The addition of the alkali metal modifier, Na, has drastic affect on the intermediate-range structure due to destruction of the PO{sub 4} network structure. Around x {approximately} 50 a new peak arises at lower Q than the intermediate-range order peak, which is found in the S(Q)`s of all alkali metaphosphate glasses, associated with extended-range order. The length scale of extended-range order increases with Me{sup +} size. These phenomena can be explained by the behavior of oxygen atoms. i.e. PO{sub 4} chain-like units ordering around the Me{sup +}

Structural and Hydrogen Desorption Properties of Aluminum Hydride

The structural and hydrogen/deuterium desorption properties of AlH 3 /AlD 3 were investigated by Raman spectroscopy, high-intensity X-ray/neutron diffraction, and thermogravimetric analysis. The latter revealed that more than 9.6 mass% of hydrogen/18.1 mass% of deuterium desorbs from AlH 3 /AlD 3 , respectively. The presence of -Al 2 O 3 on the surface may prevent the hydrogen/deuterium desorption reaction of AlH 3 /AlD 3 to Al at room temperature

Materials and Life Science Experimental Facility at the Japan Proton Accelerator Research Complex III: Neutron Devices and Computational and Sample Environments

Neutron devices such as neutron detectors, optical devices including supermirror devices and 3He neutron spin filters, and choppers are successfully developed and installed at the Materials Life Science Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC), Tokai, Japan. Four software components of MLF computational environment, instrument control, data acquisition, data analysis, and a database, have been developed and equipped at MLF. MLF also provides a wide variety of sample environment options including high and low temperatures, high magnetic fields, and high pressures. This paper describes the current status of neutron devices, computational and sample environments at MLF

Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex II: Neutron Scattering Instruments

The neutron instruments suite, installed at the spallation neutron source of the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC), is reviewed. MLF has 23 neutron beam ports and 21 instruments are in operation for user programs or are under commissioning. A unique and challenging instrumental suite in MLF has been realized via combination of a high-performance neutron source, optimized for neutron scattering, and unique instruments using cutting-edge technologies. All instruments are/will serve in world-leading investigations in a broad range of fields, from fundamental physics to industrial applications. In this review, overviews, characteristic features, and typical applications of the individual instruments are mentioned