Wide-angle Neutron Diffraction Research Articles

Hybridization of Wide-Angle X-ray and Neutron Diffraction Techniques in the Crystal Structure Analyses of Synthetic Polymers

The development in the crystal structure analysis of synthetic polymers using the hybridized combination of wide-angle X-ray and neutron diffraction (WAXD and WAND, respectively) techniques has been reviewed with many case studies performed by the authors. At first, the technical development was reviewed, in which the usage of high-energy synchrotron X-ray source was emphasized for increasing the total number of the observable diffraction peaks, and several examples were introduced. Secondly, the usage of the WAND method was introduced, in which the successful extraction of hydrogen atomic positions was described. The third example is to show the importance for the hybrid combination of these two diffraction methods. The quantitative WAXD data analysis gave the crystal structures of at-poly(vinyl alcohol) (at-PVA) and at-PVA-iodine complex. However, the thus-proposed structure models were found not to reproduce the observed WAND data very much. The reason came from the remarkable difference in the atomic scattering powers of the constituting atomic species between WAXD and WAND phenomena. The introduction of statistical disorder solved this serious problem, which reproduced both of the observed WAXD and WAND data consistently. The more systematic combination of WAXD and WAND methods, or the so-called X-N method, was applied also to the quantitative evaluation of the bonded electron density distribution along the skeletal chains, where the results about polydiacetylene single crystals were presented as the first successful study. Finally, the application of WAND technique in the trace of structural changes induced under the application of external stress or temperature was described. The future perspective is described for the development of structural science of synthetic polymers on the basis of the combined WAXD/WAND techniques.

In operando studies of rotating prismatic Li-ion batteries using monochromatic wide-angle neutron diffraction

An experimental method of collecting high-resolution neutron powder diffraction data in a wide angular range on permanently rotating prismatic Li-ion batteries cell, which allows to eliminate a need of complex absorption correction due to highly anisotropic attenuation paths for thermal neutrons in prismatic cells, is proposed. Neutron diffraction data, in quality enabling Rietveld refinement, was collected ex situ at discrete (predefined) cell states-of-charge (SOC = 100% and 0%). Besides this, an in operando neutron powder diffraction study on a permanently rotating prismatic cell is reported, where cell connection to potentiostat was supplied using slip ring electric contact. An excellent agreement between experimental data on prismatic and 18650-type Li-ion cells was noticed. The proposed methodology opens new experimental capabilities for in operando neutron powder diffraction studies on prismatic cells (either commercial or lab based) at different experimental conditions (state-of-charge, charging protocol, current rate, state-of-health, temperature and/or cell chemistry etc).

Structure Analysis and Derivation of Deformed Electron Density Distribution of Polydiacetylene Giant Single Crystal by the Combination of X-ray and Neutron Diffraction Data

The crystal structure of polydiacetylene giant single crystal has been analyzed on the basis of the two different methods of wide-angle neutron diffraction and X-ray diffraction. The X-ray result gives us the total electron density distribution [ρ(x)] of polymer chain. The neutron result tells the positions of atomic nuclei, which can allow us to speculate the electron density distributions [ρ0(x)] around the nonbonded isolated atoms. As a result, the so-called bonded (or deformed) electron density Δρ(x) [≡ ρ(x) – ρ0(x) = ρX(x) – ρN(x)], i.e., the electron density distribution due to the conjugation among the covalently bonded atoms along the polymer chain, can be estimated using the two information obtained by the X-ray and neutron data analyses (the so-called X-ray–neutron subtraction (X–N) method). The present report is the first example of the application of X–N method to the synthetic polymer species. The Δρ(x) derived for polydiacetylene was found similar to that of the low-molecular-weight model co...

Phase transformations in opals under thermal and thermobaric actions

The ultrasmall- and wide-angle neutron diffraction methods are used to study multiscale structures and phase transformations in synthetic opals at different temperatures and pressures (as high as 1500°C and 10 GPa, respectively). Monodisperse colloidal particles of amorphous silica dioxide (a-SiO2) with an average diameter of 150‒1700 nm whose deviation from the mean is less than 5% are synthesized to fabricate the samples. Opal matrices up to 3 cm thick are obtained via the natural sedimentation of a SiO2-globule suspension followed by drying and heat treatment. Neutron-diffraction processes are investigated using a DISK multidetector superposition diffractometer mounted at the IR-8 reactor of the National Research Centre Kurchatov Institute at a neutron wavelength of 1.668 A. Ultrasmall-angle diffraction experiments are performed in the two-crystal mode of a STOIK spectrometer.

Slow and Very Fast MAS Solid State NMR Study of Biopolymers

SummaryIn the first part of article, the “NMR Crystallography” approach as tool to fine refinement of solid state structure of biopolymers is presented, employing the α polymorph of L‐polylactide (PLLA) as model. Slow Magic Angle Spinning (MAS) technique (with spinning rate of sample in range from 1.2 kHz to 8.0 kHz) was used to assign 13C isotropic chemical shifts and values of 13C δii principal elements of chemical shifts tensors (CST). Theoretical 13C shielding parameters σii were obtained employing GIPAW (Gauge Invariant Projector Augmented Wave) method and compared with experimental 13C δii elements. The computed and experimental 13C CP/MAS spectra for WAND (Wide Angle Neutron Diffraction) geometry of powdered α PLLA were evaluated. It was revealed that the computed model of α PLLA model better fit to experimental NMR spectra.In the second part of article the applications of the new NMR methodology, so called very fast MAS (VF MAS) with sample spinning over 60 kHz are presented. The power of this approach is shown employing the 13C and 15N labeled protein, ubiquitin. We revealed that Cross‐Polarization with Variable Contact (CPVC) time sequence under very‐fast MAS condition performed in two‐dimensional (2D) mode is very efficient method to measure accurately the CH and NH distances, and to analyze the dynamics of proteins with overlapped resonances in aliphatic and aromatic regions.

Modelling borosilicate glasses of nuclear interest with the help of RMC, WAXS, neutron diffraction and 11B NMR

In this study, the structures of four borosilicate glasses of nuclear interest were investigated by performing Reverse Monte Carlo (RMC) simulations with the help of experimental data from Wide Angle X-ray Scattering (WAXS), neutron diffraction and 11B Nuclear Magnetic Resonance (NMR). Three to six oxide glasses based on Si, B, Na, Ca, Al and Zr species were modelled. For each glass, the boron coordination calculated relied on the experimental value, enabling accurate four-fold boron proportions to be obtained. The local environment and medium range order of glasses were inferred from the atomistic configurations, with an emphasis on the six oxide glass. Both proportion variations in structural units centred on silica atoms and atomic triplet average angles XOY (X, Y=Si, B, Al, Zr) and OXO were also quantified. More generally, we showed that EPSR succeeds in modelling local and medium range order of borosilicate glasses, even with complex compositions.

Crystal Structure Analysis of Poly(l-lactic Acid) α Form On the basis of the 2-Dimensional Wide-Angle Synchrotron X-ray and Neutron Diffraction Measurements

The crystal structure of poly(l-lactic acid) (PLLA) α form has been analyzed in detail by utilizing the 2-dimensional wide-angle X-ray (WAXD) and neutron diffraction (WAND) data measured for the ultradrawn sample. The WAXD data were collected using a synchrotron-sourced high-energy X-ray beam of wavelength 0.328 Å at SPring-8, Japan and the WAND data were measured using a neutron beam of wavelength 1.510 Å with a cylindrical imaging-plate camera of BIX-3 system at Japan Atomic Energy Agency. The initial crystal structure model was extracted successfully by a direct method under the assumption of the space group P212121 using about 700 X-ray reflections observed at −150 °C, the number of which was overwhelmingly large compared with the data reported by the previous other researchers and allowed us to perform more precise structural analysis. The crystal structure model obtained by the direct method was refined so that the best agreement between the observed and calculated integrated intensities was obtained or the reliability factor (R) became minimal: R was 18.2% at −150 °C and 23.2% at 25 °C. The thus-obtained chain conformation took the distorted (10/3) helical form with 21 helical symmetry along the chain axis. However, the symmetrically forbidden reflections 003, 007, 009 etc. were detected in a series of the 00L reflections, requiring us to erase the 21 screw symmetry along the molecular chain. By assuming the space group symmetry P1211, the structural refinement was made furthermore and the finally obtained R factor was 19.3% at −150 °C and 19.4% at 25 °C. Although the structural deviation from the 21 screw symmetry was only slightly, this refined model was found to reproduce the observed reflection profiles well for all the layer lines. The thus X-ray-analyzed crystal structure was transferred to the WAND data analysis to determine the hydrogen atomic positions. The R factor was 23.0% for the 92 observed reflections at 25 °C. The agreement between the observed and calculated layer line profiles was good. In this way the crystal structure of PLLA α form has been established on the basis of both the X-ray and neutron diffraction analyses.

Static and Dynamic Structure Analyses of Polymer Crystals

Recent development in static and dynamic structure analyses of polymer crystals has been reviewed. Various methods were developed to enhance the reliability of static structure analysis. Usage of synchrotron high-energy X-ray beam allowed us to increase the total number of observed X-ray reflections by one order. Wide-angle neutron diffraction revealed the hydrogen atomic positions accurately, making it possible to evaluate the mechanical property of polymer crystals quantitatively. Time-resolved measurements of wide-angle and small-angle X-ray scatterings as well as infrared and Raman spectra have revealed the structural revolution processes as seen in the studies of isothermal crystallization and mechanical deformation processes.

Structure and texture analysis of PVC foils by neutron diffraction

Crystalline order of molded and then bi-axially stretched foils prepared from atactic PVC resin is investigated by means of wide-angle neutron diffraction (WAND). The observed high-resolution WAND patterns of all samples are dominated by a sharp maximum corresponding to the inter-planar distance 0.52 nm. Two weaker maxima are also resolved at 0.62 and 0.78 nm. Intensities of the peaks vary with deformation ratios of the samples and their diffraction position. Average size of the coherently scattering domains is estimated as approximately 4-8 nm. Based on the experimental data, a novel model of crystalline order of atactic PVC is proposed.

Combinatory usage of X-ray and neutron diffraction techniques for the refined structure analysis of polymer crystals: From hydrogen atoms to bonded electron density distribution

In order to predict the physical property of polymers, we need to know the atomic coordinates including hydrogen atoms as accurately as possible. However, polymer samples give us limited number of broad X-ray reflections in general. In order to improve this problem, we have made many efforts to collect the X-ray diffraction data as accurate as possible. In this paper, we report the structure analysis including the extraction of hydrogen/deuterium atomic positions for the oriented polyoxymethylene by the combination of X-ray diffraction method with neutron diffraction method. In such a cases of polydiacetylene giant single crystal the bonded electron density distribution was evaluated along the skeletal chain by the so-called X-N method based on the wide-angle X-ray diffraction data and the wide-angle neutron diffraction data.

Challenges in Highly-reliable Crystal Structure Analysis of Synthetic Polymers based on the Organized Combination of Wide-Angle X-ray Diffraction and Wide-Angle Neutron Diffraction Methods.

Challenges in Highly-reliable Crystal Structure Analysis of Synthetic Polymers based on the Organized Combination of Wide-Angle X-ray Diffraction and Wide-Angle Neutron Diffraction Methods.

Lamellar Stacking Split by In-Membrane Clustering of Bulky Glycolipids

We developed a simple model to investigate the effect of lipid clustering on the local interlayer distance in a cluster of interacting lamellae. The model, based on nonequilibrium thermodynamics and linear stability theories, explores the early stages of the lamella-lamella phase separation process where the lateral diffusion is much faster than the interlamellar lipid exchange. Results indicate, in the early stages, the presence of locally distorted regions with a higher concentration of one lipid component and an anomalous repeat distance. Experimental cases are presented, consisting of multilamellar-oriented depositions of phospholipids containing minority amounts of ganglioside or sphingomyelin under a low-hydration condition. The minority components are known to form domains within the phospholipid bilayer matrix. The low water content inhibits the lipid exchange among nearby lamellae and strengthens lamella-lamella interaction, allowing for a straightforward comparison with the model. Small-angle and wide-angle neutron diffraction experiments were performed in order to detect interlayer distances and local chain order, respectively. Lamellar stacking splitting has been observed for the ganglioside-containing lamellae, induced by in-phase lipid clustering. In excess water and after long equilibration times, these local structures may further evolve, leading to coexisting lamellar phases with different lipid compositions and interlayer distances.

Scanning Wide-Angle Neutron Diffraction and Its Application to Local Structures Investigations in Stainless Steel

We applied a spatial scanning measurement technique to neutron diffraction on a powder diffractometer, and performed scanning wide-angle neutron diffraction (SWND) experiments to investigate local structures of materials. The SWND technique has an advantage that one can observe a diffraction pattern over a wide scattering angle range, so that the positional dependence of local crystal structures can be measured for practical durations. Moreover, because neutrons have a larger penetration depth, on the order of a few cm, than X-rays, the SWND technique provides structural information even in internal regions of materials. We succeeded in observing positional dependence of diffraction patterns from small areas (approximately 2 ×5 mm2) of a type-304 stainless steel plate with a dimension of 19.5 ×50 ×4.7 mm3 subjected to a mechanical tensile strain of 90% of the 0.2% offset yield strength. In the SWND experiments, we confirmed that the crystallographic circumstance in the strain-loaded type-304 stainless steel is not homogeneous. For instance, we observed positional deviation in the grain direction of the master-alloy austenite phase, and local distribution of the stress induced martensite phase. The SWND technique is a particularly important probe for estimating the stress-induced phase, because it non-destructively observes even the inside of bulk materials.

Structural Refinement and Extraction of Hydrogen Atomic Positions in Polyoxymethylene Crystal Based on the First Successful Measurements of 2-Dimensional High-Energy Synchrotron X-ray Diffraction and Wide-Angle Neutron Diffraction Patterns of Hydrogenated and Deuterated Species

2-Dimensional X-ray and neutron diffraction patterns have been successfully measured for deuterated and hydrogenated polyoxymethylene (POM) samples obtained by γ-ray induced solid-state polymerization reaction. More than 700 reflections were collected from the X-ray diffraction data at −150 °C by utilizing a high-energy synchrotron X-ray beam at SPring-8, Japan, from which the crystal structure of POM has been refined thoroughly including the extraction of hydrogen atomic positions as clearly seen in the difference Fourier synthesis map. As the first trial the nonuniform (9/5) helical model was analyzed with the reliability factor (R factor) 6.9%. The structural analysis was made also using the X-ray reflections of about 400 observed at room temperature (R 8.8%), and the thermal parameters of constituent atoms were compared between the low and high temperatures to discuss the librational thermal motion of the chains. The 2-dimensional neutron diffraction data, collected for the deuterated and hydrogenated POM samples using an imaging plate system specifically built-up for neutron scattering experiment, have allowed us to pick up the D and H atomic positions clearly in the Fourier synthesis maps. Another possible model, (29/16) helix, which was proposed by several researchers, has been also investigated on the basis of the X-ray diffraction data at −150 °C. The direct method succeeded in extracting this (29/16) model straightforwardly. The R factor was 8.6%, essentially the same as that of (9/5) helical model. This means that the comparison of the diffraction intensity between the data collected from the full-rotation X-ray diffraction pattern and the intensity calculated for both the (9/5) and (29/16) models cannot be used for the unique determination of the superiority of the model, (9/5) or (29/16) helix. However, we have found the existence of 001 and 002 reflections which give the longer repeating period 55.7 A. Besides there observed a series of meridional 00l reflections forbidden for (9/5) helical model. These additional evidences support the nonuniform (29/16) helical model as the most plausible chain conformation of POM crystal.

Thermodynamics, Structure, and Dynamics in Room Temperature Ionic Liquids: The Case of 1-Butyl-3-methyl Imidazolium Hexafluorophosphate ([bmim][PF6

A detailed investigation of the phase diagram of 1-butyl-3-methyl imidazolium hexafluorophosphate ([bmim][PF(6)]) is presented on the basis of a wide set of experimental data accessing thermodynamic, structural, and dynamical properties of this important room temperature ionic liquid (RTIL). The combination of quasi adiabatic, continuous calorimetry, wide angle neutron and X-ray diffraction, and quasi elastic neutron scattering allows the exploration of many novel features of this material. Thermodynamic and microscopic structural information is derived on both glassy and crystalline states and compared with results that recently appeared in the literature allowing direct information to be obtained on the existence of two crystalline phases that were not previously characterized and confirming the view that RTILs show a substantial degree of order (even in their amorphous states), which resembles the crystalline order. We highlight a strong connection between structure and dynamics, showing the existence of three temperature ranges in the glassy state across which both the spatial correlation and the dynamics change. The complex crystalline polymorphism in [bmim][PF(6)] also is investigated; we compare our findings with the corresponding findings for similar RTILs. These results provide a strong experimental basis for the exploration of the features of the phase diagram of RTILs and for the further study of longer alkyl chain salts.

Structural investigation of water–acetonitrile mixtures: Small-angle and wide-angle neutron diffraction study compared to molecular dynamics simulation

In present work we report small-angle and wide-angle neutron diffraction study compared to molecular dynamics simulation on water–acetonitrile system. From small-angle scattering measurements resulted that the correlation length, as well as the density and concentration fluctuation have maximum around x an = 0.38; these findings are in agreement with previous results found, namely, that a strong microheterogeneity exists in acetonitrile–water system in the range of x an = 0.2–0.6 acetonitrile mole fraction. The total g( r) functions of mixtures obtained from wide-angle scattering are compared with molecular dynamics simulation results and they show an overall good agreement.

Extraction of Hydrogen-Atom Positions in Polyethylene Crystal Lattice from Wide-Angle Neutron Diffraction Data Collected by a Two-Dimensional Imaging Plate System: Comparison with the X-ray and Electron Diffraction Results

Two-dimensional wide-angle neutron diffraction patterns have been measured successfully for uniaxially oriented fully deuterated and fully hydrogeneous polyethylene samples by using an imaging plate system (BIX-3) installed at the Japan Atomic Energy Research Institute. The detailed data analysis allowed us to extract the positions of hydrogen atoms in the crystal lattice accurately. The results were compared quantitatively with those obtained from the X-ray and electron diffraction experiments as well as the computer simulation result.

Extraction of Hydrogen-Atom Positions of Synthetic Polymers from the2-Dimensional Neutron Diffraction Pattern Taken by an Imaging Plate System

2-Dimensional wide-angle neutron diffraction patterns have been measured successfullyfor the uniaxially-oriented samples of fully-deuterated and fully-hydrogeneouspolyethylene by using BIX-3 imaging plate system installed at the Japan Atomic Energy Research Institute.These data were analyzed in detail and the calculation of Fouriermaps allowed us to extract the positions of hydrogen atoms in the crystal latticeaccurately.The structural parameters obtained after refinement were compared withthose derived from the X-ray and electron diffraction experiments as well as thecomputer simulation result. The accurate determination of hydrogen atomic position byneutron technique makes it possible to perform the exact prediction of physicalproperties of polymer crystals in a quantitative manner.

Interlayer magnetic coupling for Fe/Si multilayers

The antiferromagnetic (AFM) interlayer exchange coupling for sputtered Fe/Si multilayers have been studied by magnetometry, wide-angle neutron diffraction, and spin-polarized neutron reflectometry. Ferromagnetic resonance and Raman scattering measurements have been applied for the characterization of the multilayers. To look for a possible modification of exchange coupling when Si is replaced by Ge, similar Fe/Ge multilayers have been prepared by the same technique. No AFM coupling has been found for Fe/Ge system. Present results differ in part from the literature data and suggest an influence of the sample preparation on the details of its magnetic properties.

Short-period GaMnAs/GaAs superlattices: Optical and magnetic characterization

Superlattices with magnetic layers containing from 8 to 16 GaMnAs monolayers corresponding to the mixed crystal composition between 5 and 6% of Mn and from 4 to 10 GaAs monolayers were grown by the low temperature MBE technique and characterized by Raman scattering. Folded acoustic phonons were observed for all superlattices in the Raman scattering spectra. The interlayer exchange coupling, found previously by the wide-angle neutron diffraction in selected superlattices was investigated by the spin-polarized neutron reflectometry. It was always of ferromagnetic type, no trace of antiferromagnetic coupling was found.