The structure of Ni67Zr33 amorphous alloy was studied in terms of interatomic space. The three-dimensional atomic configuration of this amorphous alloy was analysed by using a method of decomposing ...the whole volume into basic polyhedra with only triangular faces formed by nearest neighbour distances. Various types of polyhedra were identified through the analysis. The tetrahedra account for approximately 60% of the whole volume, and most of them are densely packed but some are loosely packed. The large polyhedra have empty spaces commensurate with their own sizes but they are often deformed and non-spherical in shape. That is, spherical empty spaces are not as large as atomic volumes and there is no space in which any atoms enter. These low density polyhedra are more likely to gather together and they form the loosely packed clusters about the size of several nanometers.
•Most of the tetrahedral holes are densely packed but some of them are loosely packed.•Large polyhedral holes have a certain empty space but there is no space in which any atoms enter.•Low density polyhedral holes form the loosely packed clusters about the size of 2–3 nm.
Pulsed neutron diffraction and synchrotron X-ray diffraction measurements were performed on a melt-quenching Ni67Zr33 amorphous alloy sample. The Ni-Ni, Ni-Zr and Zr-Zr nearest neighbour ...distributions were obtained from differences in the scattering intensities between the two probes in conjunction with the Gaussian fitting. The results demonstrate that the Ni-Zr and Zr-Zr nearest neighbour distributions are respectively represented by single Gaussian peaks but the Ni-Ni one is an asymmetric shape. Three-dimensional structure models were constructed by using reverse Monte Carlo (RMC) modelling method with fitting to the neutron and X-ray diffraction data sets. The Voronoi-Delaunay method was used on the RMC configurations to investigate the local packing properties of each coordination cluster. With reference to the macroscopic packing fraction, inhomogeneous structural feature arising from dense and loose packing domains is observed in the structure of Ni67Zr33 amorphous alloy.
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•Inhomogeneous structural feature arising from dense and loose packing domains is observed.•The average size of dense packing domains is estimated to be 10–20 Å.•The dense packing domains are formed by strong atomic bonds and have thermodynamically stable structure.
High-temperature superconductivity appears as a consequence of doping charge carriers into an undoped parent compound exhibiting antiferromagnetic order; therefore, ground-state properties of the ...parent compound are highly relevant to the superconducting state. On the basis of this logic, spin fluctuations have been considered as the origin of pairing of the superconducting electrons in the cuprates. As possible pairing mechanisms, there is growing interest in unconventional spin fluctuations or advanced orbital fluctuations owing to the characteristic multi-orbital states in iron pnictides. Here, we report the discovery of an antiferromagnetic phase as well as a unique structural transition in electron-overdoped LaFeAsO1-x Hx (x thick ~ 0.5), whereby a second parent phase is uncovered, albeit heavily doped. The unprecedented two-dome superconducting phases observed in this material can be interpreted as a consequence of the carrier doping starting from the original x thick ~ 0 and additional x thick ~ 0.5 parent phases towards the intermediate region. The bipartite parent phases with distinct physical properties in the second magnetic phase provide us with an interesting example to illustrate the intimate interplay between the magnetic interaction, structural change and orbital degree of freedom in iron pnictide superconductors.
PLANET is a time-of-flight (ToF) neutron beamline dedicated to high-pressure and high-temperature experiments. The large six-axis multi-anvil high-pressure press designed for ToF neutron diffraction ...experiments enables routine data collection at high pressures and high temperatures up to 10GPa and 2000K, respectively. To obtain clean data, the beamline is equipped with the incident slits and receiving collimators to eliminate parasitic scattering from the high-pressure cell assembly. The high performance of the diffractometer for the resolution (Δd/d~0.6%) and the accessible d-spacing range (0.2–8.4Å) together with low-parasitic scattering characteristics enables precise structure determination of crystals and liquids under high pressure and temperature conditions.
Using inelastic neutron scattering and molecular dynamics simulations on a model Zr-Cu-Al metallic glass, we show that transverse phonons persist well into the high-frequency regime, and can be ...detected at large momentum transfer. Furthermore, the apparent peak width of the transverse phonons was found to follow the static structure factor. The one-to-one correspondence, which was demonstrated for both Zr-Cu-Al metallic glass and a three-dimensional Lennard-Jones model glass, suggests a universal correlation between the phonon dynamics and the underlying disordered structure. This remarkable correlation, not found for longitudinal phonons, underscores the key role that transverse phonons hold for understanding the structure-dynamics relationship in disordered materials.
The structures of Cu–Zr and Ni–Zr metallic glasses have been studied by neutron diffraction and Reverse Monte Carlo (RMC) modeling. A pre-peak at
Q∼17
nm
−1 was observed in the structure factor,
S(
...Q), of Ni–Zr metallic glasses, and this is associated with the Ni–Ni partial structure factor was well reproduced by the RMC modeling. An analysis of Voronoi polyhedra in the RMC simulations was used to characterise the different atomic configurations around Zr, Ni and Cu atoms. The Zr environments are very similar in the two systems, but there are marked differences between the polyhedra around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by trigonal prismatic-like, Archimedian antiprismatic-like, and similar polyhedra, with smaller total coordination numbers less than 10. In contrast, icosahedron-like polyhedra with total coordination numbers in excess of 11 are preferred for Cu.
Development of a neutron detector with a GEM Ohshita, H.; Uno, S.; Otomo, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2010, Letnik:
623, Številka:
1
Journal Article
Recenzirano
We are developing a neutron beam monitor with a gas electron multiplier (GEM) for the high-intensity total diffractometer at J-PARC. In order to analyze the basic characteristics of the GEM-based ...detector, a neutron irradiation test was carried out at J-PARC. The wavelength-spectrum distribution obtained from the test is consistent with the calculations, and the beam profiles agree with the simple Monte Carlo (MC) simulation. The position resolution of the GEM-based detector is estimated to be approximately 1.2mm. Therefore we found that as a neutron beam monitor, the GEM-based detector has good two-dimensional imaging ability.
Reverse Monte Carlo modeling was carried out for Li7P3S11 metastable crystal and (Li2S)70(P2S5)30 glass based on time-of-flight neutron and synchrotron X-ray diffraction data. Polyhedral analysis of ...three-dimensional structures for Li7P3S11 metastable crystal and (Li2S)70(P2S5)30 glass were gave us not only structural characteristics but also structural origins related to their high ionic conductivity.
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