journal menu
abstracts
SuperHRPD is one of six time-of-flight neutron powder diffractometers in the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). SuperHRPD is looking at a newly developed high resolution moderator which gives narrow & symmetrical neutron pulse with less tails. With using this moderator and lower repetition rate of 25Hz as well as the flight path shorter than 100 m, a high resolution and wide dynamical range is attainable with limited loss of neutrons. The designed highest resolution of SuperHRPD is as high as Δd/d = 0.035 % in the backward bank. Although unplanned shutdown for two years due to the earthquake and the Hadron radiation accident, SuperHRPD has been upgraded repeatedly by the scattering chamber replacement, the increase of detector solid angle, and the improvement of the detector systems, and improvement of resolution. Sample environments cover 4 K – 1000 K, 10GPa and 14 T with up to d = 40 Å. It is emphasized the magnet was designed to detect tiny structural changes precisely as well as magnetic reflections up to 14 T. After three years of operation, we confirmed higher resolution can reduce systematic errors in structural analyses. The current status of SuperHRPD will be reported.
abstracts
RMn2O5 (R = Y, Bi, rare-earth) is one of the prototypical multiferroic materials that exhibits a rich variety of magnetoelectric effects. Since the successive magnetic and ferroelectric phase transitions simultaneously take place, magnetic order has been thought to be a primary order parameter for the ferroelectricity in this system. We recently have found that in neutron diffraction study of 153EuMn2O5, magnetic phase transition is induced by applying hydrostatic pressure. As temperature decreases upon p = 1.4 GPa, the magnetic propagation wave vector changes from qM = (1/2, 0, 1/3) to (1/2, 0, 1/2), indicating that the period of magnetic unit cell as well as the magnetic structure change at the phase transition. We have also carried out the dielectric and polarization measurements under pressure and established magnetic and dielectric phase diagram as functions of temperature and pressure as shown in the figure. This study has revealed that the ferroelectric (FE1) - ferroelectric (FE2) phase transition concomitantly occurs at the magnetic phase transition, where the electric polarization is enhanced. To clarify the relevance between the ferroelectricity and the magnetic structure, we carried out single crystal magnetic structure analysis of 153EuMn2O5 upon ambient- and high-pressure. In the magnetic phase with qM = (1/2, 0, 1/3), cycloidal magnetic structure of manganese spins propagating along c-axis is realized. On the contrary in the magnetic phase with qM = (1/2, 0, 1/2), the spins arrange almost collinearly along c-axis. The result indicates that the presence of the cycloidal spin structure plays an important role for inducing (or reducing) the electric polarization in this compound. This study was supported by "KAKENHI"-programs of Scientific Research (B) (24340064), Scientific Research (A) (21244051), Challenging Exploratory Research (23654098) and of Scientific Research on Priority Areas "Novel States of Matter Induced by Frustration" (19052001).
abstracts
It might not be well recognized, most reflections are contaminated by multiple diffractions (MD). Therefore high redundancy data could not coincide with high accuracy data when MDs are not avoided. We collected both data set of MD-avoided and no MD-avoided ones and investigated its effectiveness in electron density measurement. For data collection, four-circle diffractometer at KEK-PF BL14A (Tsukuba, Japan) was used. In MD-avoided measurement, each reflection is collected at angle setting of least of MD contamination which calculated by psi-scan simulation software MDC [1]. In no MD-avoided measurement, usual bisect setting were used. In no MD-avoided measurement, intensities of forbidden reflections of YMn2O5 are more than 10 times largely observed than for MD-avoided one, and resulting residual density map is also highly contaminated reflecting the tendency of Fo>>Fc which is typical for reflections of weak intensity. Figure 1 shows this situation. Figure 2 is the deformation density of YTiO3 for MD-avoided data. Where model density of without Ti-3d1 valence electrons is subtracted from experimentally observed electron density. In the figure, quenching of angular momentum of Ti-3d1 electron is clearly observed. Although Rint could not be an ideal indicator of data accuracy since it cannot perceive Fo>>Fc, Rint(F) of MD-avoided measurement for YTiO3 is significantly reduced to ~0.5%. For no MD-avoided one, Rint(F) is ~1.2%. Since accuracy of MD-avoidance technique is confirmed, the next step is to exploit informations of only a few numbers of valence electrons among F(000) electrons. To accomplish this, wave function based refinement such as XAO [2] should be applied and studied.
abstracts
"SENJU" is a newly built pulsed neutron single crystal diffractometer at J-PARC/MLF for structural research of inorganic and organic materials with relatively small cell sizes under multiple extreme environments, such as low temperature and a high magnetic field. Since the launch of the instrument in 2012, SENJU has been commissioned and now tuned to be capable of crystal and magnetic structure analyses with a sample as tiny as 1mm cube or less. SENJU has the total of 37 two-dimensional scintillation detectors installed. Groups of 3 detectors are accommodated in detector banks and 12 detector banks are placed so as to cylindrically surround the sample chamber (Figure), and additional one detector is settled at the bottom. The instrumental parameters including the positions of the detectors and the neutron flight path length were determined in order to obtain accurate lattice parameters of samples. Since the instrumental parameters correlate with each other, series of different measurements were needed in order to obtain unique values for each parameter. As the first step of the procedure, a powder diffraction pattern of diamond was measured in order to determine the scattering angle of 90 [deg] utilizing the nature that a Bragg reflection vertically lines up at 90 [deg]. Simultaneously, we determined the neutron path length L1 from the neutron source to the sample position. As a next step, a Bragg reflection was repeatedly measured as the sample crystal was rotated with small steps. From this data, the equatorial plane on the detectors and the distance between the sample and the detectors L2 were determined. As a third step, many Bragg reflections from a sample with known lattice constants were measured and from the positions of the reflections the positions of each detector were determined. As a result, the lattice parameters can be obtained with the accuracy of about 0.05 % using the determined instrumental parameters.
abstracts
"A new single crystal neutron diffractometer by using a curved two-dimensional position sensitive detector (C-2DPSD) has been installed at HANARO-ST3 beam port [1]. Compared with a conventional point detector, a two-dimensional detector has huge reciprocal space information in general. It has advantages to detect superlattice peaks and diffuse scattering etc. without any pre-information. In order to obtain significant diffraction intensity in the reciprocal space, it is essential the efficient program for handling the measuring data directly. In these several years, we have developed the methodology and the program package "Reciprocal Analyzer", based on many experiments by the C-2DPSD, which includes peak search [2], UB matrix determination, and quantitative assessment of the accurate integrated intensities [3]. And to visualize reciprocal space from raw pixel data of the C-2DPSD, the ""Reciprocal Viewer"" has been developed also. These software are coded by C/C++ and Python with OpenGL as a cross-platform GUI. Figures show the graphical interface of Recipocal Analyzer and Viewer. Details of the feature about these software will be introduced at the presentation."
abstracts
The materials represented as M3H(XO4)2 (M = alkaline metal, X = S or Se) are known to exhibit high protonic conductivities at moderately high temperature. The high protonic conductivity emerges upon a structural phase transition and hydrogen bonds become directionally disordered. The protonic conduction is presumably realized through the disordered hydrogen bonds, but no experimental evidence has been reported. Meanwhile, although the mechanism of the protonic conduction is considered to be the same among this group of materials, the transition temperature (Tc) varies depending on the elements of M and X. For example, the material with M = Rb and X = Se undergoes the transition at 440 K while with M = K and X = Se the transition occurs at 390 K. Since the chemical characteristics of Rb and K are, as a principal, the same, some structural features may play crucial roles in triggering the phase transition. In order to clarify the mechanism of the proton conduction in the superprotonic phase and the relation between the crystal structure and Tc, structural studies on Rb3H(SeO4)2 at high temperature and solid solutions of Rb3H(SeO4)2 and K3H(SeO4)2 (Rb3-xKxH(SeO4)2, x=0,1,2,3) were conducted by means of single crystal neutron diffraction at FONDER at JRR-3M and SENJU at J-PARC/MLF. The proton density distribution map obtained from the high temperature neutron diffraction experiment clearly demonstrates 2-dimensional continuous spread of the proton distribution, which is considered to be the proton conduction path (figure). The structure analyses of Rb3-xKxH(SeO4)2 revealed that K ions tend to occupy one of two possible sites. As the concentration of K ion increases, the distortion of SeO4 appears to be enhanced. The variation of the distortion is consistent with the variation of the transition temperature, suggesting the close relationship between the distortion and the phase transition temperature.
