Shinya Hashimoto

Study of local atomic order in a ternary Cu0.47Ni0.29Zn0.24 alloy using anomalous scattering of synchrotron radiation

This paper describes the results of the first application of anomalous scattering phenomenon to reveal the local atomic arrangements in multi-component systems. Diffuse scattering from a single crystal of the title alloy has been measured using monochromated synchrotron radiation of the various wavelengths in the close vicinity of the K absorption edges of the constituent elements. From the variation of contrast produced in the total diffuse intensity, partial diffuse intensities corresponding to the three kinds of interatomic correlation have been derived by adopting a least-squares fitting method. It is shown that short-range ordering occurs between Ni and Zn atoms and also between Zn and Cu atoms, while a correlation of the opposite sense exists between Cu and Ni atoms. This type of short-range ordering is consistent with the prediction of ordering energies given by De Rooy et at .

Concept of a new undulator that will suppress the rational harmonics

Abstract A basic consideration has been made of an undulator with magnetic poles quasi-periodically aligned in order not to generate higher harmonics of radiation with integrally factored energies, nE f ( n : integers, E f : the fundamental photon energy), that are harmful in some synchrotron radiation experiments. The new undulator generates harmonics with irrational ratios in energy which are never simultaneously diffracted by a crystal or grating monochromator at the same Bragg angle. A combination of the undulator with a high-resolution crystal monochromator is expected to be very useful on beamlines of high energy radiation in which X-ray mirrors would not be suitable because their critical angle of total reflection would be too small. Realistic arrays of magnetic poles are also discussed.

Multipurpose four‐circle diffractometer with a crystal analyzer for use with synchrotron radiation

This paper describes the performance of a four‐circle diffractometer installed at the Photon Factory for extensive use with synchrotron radiation for various investigations in the field of solid state physics. Its main part is based on a Huber 5020.4 type diffractometer with a crystal analyzer designed for vertical diffraction plane attitude. The diffractometer is mounted on a carriage table, which can precisely adjust the position of the diffractometer with respect to the incident beam monochromatized by successive reflection from a pair of Si(111) crystals. With a perfect crystal used as the analyzer the large size of the ω and 2θ circles enables us to make high resolution (ΔQ/Q∼10−4) measurements of x‐ray scattering intensity distribution from a single crystal. The large space in the center of the diffractometer permits us to put a pressurizing cell or a cryostat on the φ table for scattering measurements at controlled pressures and temperatures. Selected examples of the application are presented.

CONCEPTUAL DESIGN OF QUASIPERIODIC UNDULATOR

A new type of undulator which suppresses the rational harmonics is considered. This undulator consists of quasiperiodic arrays of magnet blocks and generates irrational harmonics which can be eliminated by the conventional crystal monochromators. The radiation power emitted from this undulator and the width of each radiation peak are comparable with that of the conventional periodic undulator of the same periods.

Neutron Diffraction Study on the Short-Range Order in ZrO0.30 Interstitial Solid Solution

Short-range order parameters for oxygen arrangement in a single crystal of ZrO 0.30 quenched from above the order-disorder transition temperature were determined by measurements of elastic neutron diffuse scattering. The preferential configurations of vacancy-oxygen atom pair are found at the first and second neighbors of octahedral interstitial sites in the host hcp metal latitce, whereas the oxygen-oxygen atom pairs occur at the third, fourth and fifth neighbors. These features are similar to those in long-period ordered structures. The first-order atomic displacement parameters for O–Zr pairs indicate that the metal atoms move away from vacancies and no near the oxygen atoms.

Lattice Modulation of the e-Phase in a Cu-Sb Alloy

The e-phase in a Cu-Sb binary alloy (19.5 at.% Sb), which is characterized by a two-dimensionally modulated structure, has been investigated by singlecrystal X-ray diffraction at ambient temperature (290 K). The structure analysis was performed based DP63/mmc on a five-dimensional superspace group -p6 ~mm using occupational and displacive modulation waves. The final agreement factors are Ro = 0.086 and R~ = 0.128 for 54 basic reflections and 75 first-order satellites, respectively. Very weak second-order satellites of kl + k2 type are observed using Cu Ka radiation, but the other type of second-order satellites are too weak to detect in the present investigation. The analysis indicates that mixed occupation of Cu and Sb occurs extensively, contrary to the model from a high-resolution electron microscopy study. With regard to the atomic displacements, the transverse component is larger than the longitudinal component, which is in contrast to the Au-Cd alloy. Crystal data of the basic structure: Mr = 74.90, hexagonal, P63/mmc, a = 2.737 (4), c = 4.320 (2) A, V = 28.03 (6) A 3, Z = 2, Dx = 8.88 Mg m-3, A(Mo Ka) = 0.7107 A, /z(Mo Ka) = 39.2 mm-1, F(000)=66.6, two-dimensional wavevectors k~ = 0.430 (1)(bl + b2), k2 = 0.430 (1)(-bl + 2b2).

Development of a nuclear magnetic resonance system for in situ analysis of hydrogen storage materials under high pressures and temperatures

A NMR system for in situ analysis of hydrogen storage materials under high pressure and temperature conditions was developed. The system consists of a gas pressure and flow rate controlling unit, a temperature controller, a high temperature NMR probe tunable for both (1)H and other nuclei, and a sample tube holder. Sample temperature can be controlled up to 623 K by heated N(2) gas flow. Sample tube atmosphere can be substituted by either H(2) or Ar and can be pressurized up to 1 MPa under constant flow rate up to 100 ml/min. During the NMR measurement, the pressure can be adjusted easily by just handle a back pressure valve. On the blank NMR measurement, (1)H background noise was confirmed to be very low. (1)H and (11)B NMR spectrum of LiBH(4) were successfully observed at high temperature for the demonstration of the system. The intensity of the (1)H NMR spectra of H(2) gas was also confirmed to be proportional to the applied pressure.

Microdomain model analysis for the short‐range order diffuse scattering from quenched CuAu and CuPt alloys

High resolution X‐ray diffuse scattering measurements have been carried out with small single crystals by stationary use of the Buerger precession camera. Analysis of the data has been performed on he basis of a microdomain model (Hashimoto, Acta Cryst. A30, 792 (1974). There is a spatial correlation between the microdomains in antiphase relationship in CuAu, but not in CuPt. The average domain shape is found to be nearly spherical with sizes of about 14 A for CuAu and 18 A for CuPt.

X-Ray Diffraction Study of Short-Range Order and Fermi Surface Effects in Cu–Au Alloys

Measurement with improved resolution of X-ray diffuse scattering from short-range ordered Cu–39, 53 and 59 at.%Au alloys has been carried out by photographic method using tiny single crystals. In the pattern taken with both crystal and film kept stationary, diffuse scattering maxima appear as satellite crosses accompanied by streaks at the 110, 210 and other equivalent positions. The separation between the diffuse satellites shows a composition dependence, decreasing with increasing gold content. Fermi-surface-imaging idea suggests that this decrease is attributed to a change in the diameter of the Fermi starface of the alloys. Fourier transformation of the intensities of one of the diffuse maxima gives an interatomic correlation function, which suggests the existence of an antiphase relation between the local L1 0 ordered regions separated by 28 A.

Quasi‐periodic undulator

A basic consideration has been made of a new undulator not to generate the harmonics of radiation which have integrally factored energies and are harmful in some synchrotron radiation experiments. The undulator has magnetic poles quasi‐periodically aligned and generates harmonics with irrational ratios in energy which are not simultaneously diffracted by a crystal monochromator at the same Bragg angle. A combination of the undulator with a high‐resolution crystal monochromator is expected to be very useful on beamlines of high energy radiation for which x‐ray mirrors would not be suitable because their critical angle of total reflection would be too small.