Development of SuperHRPD, a TOF neutron powder diffractomter at J-PARC

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.

A method to obtain all geometric ambiguities in powder indexing

It is known that different unit cells can have the same computed lines in some cases (Figure). The phenomenon was first called geometrical ambiguity and studied in [1]. In all the high-symmetric cases provided in [1], such unit cells correspond to derivative lattices of each other. Although this is not true in general for 3-dimensional lattices, this has been assumed in methods to search for geometrical ambiguities (e.g., [2]). Thus, a method to obtain all the geometrical ambiguities in very short time for a given unit cell parameters is provided. Because such a method has not been used for powder indexing, it will have impact in the following sense: firstly, it is useful for checking powder indexing solutions promptly. Some powder auto-indexing methods cannot obtain all the geometrical ambiguities. Even for the software including Conograph which can gain all the ambiguities, it is not straightforward to search for them from many indexing solutions using the figures of merit which are sometimes not reliable [3]. Secondly, the new method indicates that powder indexing has only finitely many solutions at least if peak search succeeds in obtaining all (but a few) diffraction peaks with q-values smaller than some calculated value. (Note that infinitely many solutions may exist for lattices of dimension more than 4.) The result seems to provide a foundation of automatic powder crystal structure analysis, because it is possible to obtain all the ambiguities by computation. The introduced method was implemented in the newest version of Conograph, which will be distributed on the web (http://research.kek.jp/people/rtomi/ConographGUI/web_page.html) by IUCr2014. ACKNOWLEDGEMENT: this research was partly supported by a JSPS KAKENHI grant (No.22740077) and by Ibaraki Prefecture (J-PARC-23D06).

In operando and wide-d neutron diffraction measurements at J-PARC

Since the operation start for J-PARC/MLF at 2008, neutron diffraction experiment using high intensity pulse neutron beam became possible. For example, if there are 1g typical oxide samples, it is possible to get one diffraction pattern in about ten minutes for `Rietveld-analysis-quality' at iMATERIA. Four neutron powder diffractometer, iMATERIA (IBARAKI Materials Design Diffractometer[1]), SPICA (special environment powder diffractometer dedicated for battery study), SuperHRPD (Super high resolution powder diffractometer, d/d = 0.03 %) and NOVA (high intensity total scattering diffractometer) are operating at J-PARC/MLF. In our previous neutron facility, the neutron intensity is not so strong to carry out routinely in operando neutron diffraction experiments. In J-PARC, however, it became possible to measure quickly changing neutron diffraction patterns in operando condition. iMATERIA is a versatile neutron diffractometer funded by Ibaraki prefecture for industrial application. In iMATERIA, Some user group was trying to in-situ measurements for battery. SPICA is optimized for an in operando neutron diffraction study to clarify the structural changes of battery materials at the atomic level. It has already typical results of time resolved measurements for a commercialized Li-ion battery. The structural changes of the material, which is dependent on the lithium content, were clearly observed. We will report the status of J-PARC/MLF diffractometers and recent result of in operando experiments.

Development of a new special environment powder neutron diffractomter, SPICA

SPICA, a new special environment powder neutron diffractometer was built at BL09 in the Material and Life science Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). This is the first instrument dedicated solely to the study of next-generation batteries in J-PARC and is optimized for in situ measurements to clarify the structural changes of battery materials at the atomic level. Our approach with this diffractometer is to reveal the reactions in batteries and to determine factors of safety and degradation over long periods in practical battery systems. To make in situ measurements of real batteries more fruitful, we need high Δd/d resolution with wider d ranges to detect many phases during chemical reaction, high neutron intensity to know the specific reaction process in high speed charge/discharge, low background and large sample area to install big sample environment and a dedicated chemistry area to carry out long-term scheduled experiments with many sets of on-beam measurements and off-beam charge-discharge measurements. The in situ measurements can be performed in realistic environment with external variables such as temperature, electric field (current density, pulsed current, and etc.), and high pressure in time-resolved conditions by the 2 m sample space. The reliability of the diffraction data has achieved a sufficiently high level for the structural analysis of materials using the Rietveld method. In the beginning stage of the commissioning, the structural changes of the materials, which are dependent on the lithium content in a commercialized Li-ion battery, were clearly observed. The lattice parameters for the anode and cathode materials as a function of the lithium content were extracted from the diffraction patterns. The current status of SPICA will be reported. ACKNOWLEDGEMENT: This work was predominantly supported by the RISING project of NEDO.

Large in-plane deformation of RuO₆ octahedron and ferromagnetism of bulk SrRuO₃

Glazer tilting system with tilting and rotation of oxygen octahedron, can describe ABO3 perovskite structure effectively. In highest symmetry, Pm-3m(No. 221) crystal structure is a0a0a0 without tilting and rotation. If temperature is lower, the different atomic radius of A and B causes tilting and rotation of BO6 octahedron. Glazer tiling notation of Pbnm(No. 62, cab lattice) orthorhombic structure is a-a-c+ with antiphase tilting along [110]cubic and in-phase rotation along [001]cubic for neighboring octahedron. SrRuO3 is rare example of itinerant ferromagnetic among 4d oxides. It shows zero thermal expansion, so called Invar effect below ferromagnetic transition(Tc=165 K). Otherwise, paramagnetic CaRuO3 has same Pbnm crystal structure without magnetic transition. To understand Invar effect and ferromagnetism of SrRuO3, We carried out high resolution Time-of-flight powder neutron diffraction using SuperHRPD beamline in J-PARC, with the best resolution Δd/d=0.03% of backscattering bank. Itinerant ferromagnetic SrRuO3 shows 50 fetometer increase of <Ru-O> mean bond below ferromagnetic transition while paramagnetic CaRuO3 shows decrease of <Ru-O> and follows well by the usual thermal expansion. For SrRuO3, Glazer tilting with deformation of RuO6 octahedron explains Invar effect and why lattice a is larger than lattice b in Pbnm structure. The increased <Ru-O> mean bond is considered as coupled order parameter with ferromagnetic transition. The band width of CaRuO3 is almost constant in the whole temperature range whereas ones of SrRuO3 decrease at low temperature. Then more localized Ru 4d orbitals probably contribute ferromagnetic transition.

Neutron powder diffraction analysis of guanosine dihydrate using MEM

In majority of the crystals of pharmaceutical compounds, hydrogen bonds play a crucial role. Determination of a hydrogen position is highly important, in order to investigate hydrogen bonds especially in the case of hydrates. We have been investigating humidity-induced phase transitions of hydrates systematically [1,2]. Unique characteristics of hydration water molecules have prompted us to explore the phenomena more precisely. Neutron diffraction analysis is a powerful tool to determine hydrogen positions. However, large single crystals are required because of weak neutron diffraction intensities. Under such background, we carried out neutron powder diffraction analysis of guanosine dihydrate using the Maximum Entropy Method (MEM). Neutron powder diffraction data of guanosine dihydrate (C10H13N5O5.2H2O; crystal data: monoclinic, space group P21, a = 17.518, b = 11.278, c = 6.658 Å, β= 98.17⁰, Z = 4) were measured by iMATERIA at MLF in J-PARC (Figure 1(a)). Rietveld analysis was carried out using atomic coordinates of non-hydrogen atoms determined by X-ray analysis and those of hydrogen atoms which were placed on the geometrically calculated positions using the averaged X-H bond lengths determined by neutron analysis referencing the hydrogen positions estimated by X-ray analysis. Using Fo and σ by Rietveld analysis, the nuclear density distribution was calculated by MEM (Figure 1(b)). Nuclear densities of the hydrogen atoms of one water molecule (W1 in Figure 1) were elongated, which is consistent with the results of molecular dynamic simulation [2]. The effective usage of MEM to elucidate hydrogen atom positions from neutron powder diffraction data will be discussed together with that of difference Fourier calculations.