Neutron-scattering Techniques Research Articles

Book on ‘Neutron Application in Materials for Energy’ edited by G. J. Kearley and V. K. Peterson, Springer series on ‘Neutron Scattering Applications and Techniques’

Springer International Publishing, Switzerland (2015).Gordon J. Kearley and Vanessa K. Patterson have edited a remarkable and long due book in the Springer series Neutron Scattering Applications an...

Pore-size dependence and characteristics of water diffusion in slitlike micropores.

The temperature dependence of the dynamics of water inside microporous activated carbon fibers (ACF) is investigated by means of incoherent elastic and quasielastic neutron-scattering techniques. The aim is to evaluate the effect of increasing pore size on the water dynamics in these primarily hydrophobic slit-shaped channels. Using two different micropore sizes (∼12 and 18 Å, denoted, respectively, ACF-10 and ACF-20), a clear suppression of the mobility of the water molecules is observed as the pore gap or temperature decreases. This suppression is accompanied by a systematic dependence of the average translational diffusion coefficient D(r) and relaxation time 〈τ(0)〉 of the restricted water on pore size and temperature. The observed D(r) values are tested against a proposed scaling law, in which the translational diffusion coefficient D(r) of water within a porous matrix was found to depend solely on two single parameters, a temperature-independent translational diffusion coefficient D(c) associated with the water bound to the pore walls and the ratio θ of this strictly confined water to the total water inside the pore, yielding unique characteristic parameters for water transport in these carbon channels across the investigated temperature range.

QENS and NMR Study of Water Dynamics in SBA-15 with a Low Water Content

In this study, motions performed by water molecules adsorbed on the silica surface of SBA-15 material with 6.1% of water content (15% of pore filling) were investigated using NMR and Quasielastic Neutron Scattering (QENS) techniques. The results show no sign of translational diffusion of water, but two types of stochastic localized motions were identified, and both described using a model of proton jumps between two sites. For both motions, the characteristic jump distances and correlation times, as well as activation energies, have been extracted and found to differ significantly. On this basis, the faster motion was ascribed to jumps of water molecules between neighboring positions (d = 2.5 A, τ = 4 ps at 300 K, and Ea = 5.2 ± 0.2 kJ/mol from NMR data, and 5.6 ± 1.1 kJ/mol from QENS), while the slower one exhibits a temperature dependent jump distance and was ascribed to jumps of water molecules between more spatially separated positions (d = 2.9–4.3 A, τ = 25 ps at 300 K, and Ea = 16.1 ± 0.3 kJ/mol fro...

Temperature evolution of superparamagnetic clusters in single-crystalLa0.85Sr0.15CoO3characterized by nonlinear magnetic ac response and neutron depolarization

The representative measurements of the second harmonic in ac magnetization complemented by neutron depolarization have been performed for single-crystal ${\mathrm{La}}_{0.85}{\mathrm{Sr}}_{0.15}{\mathrm{CoO}}_{3}$ in the temperature range $97\phantom{\rule{4.pt}{0ex}}\text{K}<T<230\phantom{\rule{4.pt}{0ex}}\text{K}$, where occurrence of a small fraction $(\ensuremath{\lesssim}{10}^{\ensuremath{-}3})$ of nanoscale ferromagnetic clusters (FMC) has been found. Magnetic, geometrical, and dynamical parameters of the FMC system have been evaluated in the temperature range $T<140$ K, where superparamagnetic regime installs, by means of the formalism involving the Fokker-Planck equation. With lowering the temperature, the amount of clusters fraction, the cluster size, and magnetic moment along with its diffusion relaxation time strongly increase, each in its own temperature interval. Below 130 K, FMC contribute essentially to the total linear magnetic susceptibility. The damping factor of the order ${10}^{\ensuremath{-}1}$ proves the importance of precession in thermal relaxation of the cluster magnetic moment. The FMC are a precursor of long-range ferromagnetic correlations seen below 100 K with neutron-scattering techniques.

Model for neutron total cross-section at low energies for nuclear grade graphite

At subthermal neutron energies, polycrystalline graphite shows a large total cross-section due to small angle scattering processes. In this work, a new methodology to determine pore size distributions through the neutron transmission technique at subthermal energies is proposed and its sensitivity is compared with standard techniques. A simple model based on the form factor for spherical particles, normally used in the Small Angle Neutron Scattering technique, is employed to calculate the contribution of small angle effect to the total scattering cross-section, with the width and center of the radii distributions as free parameters in the model. Small Angle X-ray Scattering experiments were performed to compare results as a means to validate the method. The good agreement reached reveals that the neutron transmission technique is a useful tool to explore small angle scattering effects. This fact can be exploited in situations where large samples must be scanned and it is difficult to investigate them with conventional methods. It also opens the possibility to apply this method in energy-resolved neutron imaging. Also, since subthermal neutron transmission experiments are perfectly feasible in small neutron sources, the present findings open new possibilities to the work done in such kind of facilities.

Biopolymer deuteration for neutron scattering and other isotope-sensitive techniques.

The use of microbial biosynthesis to produced deuterated recombinant proteins is a well-established practice in investigations of the relationship between molecular structure and function using neutron scattering and nuclear magnetic resonance spectroscopy. However, there have been few reports of using microbial synthetic capacity to produce labeled native biopolymers. Here, we describe methods for the production of deuterated polyhydroxyalkanoate biopolyesters in bacteria, the polysaccharide chitosan in the yeast Pichia pastoris, and cellulose in the bacterium Gluconacetobacter xylinus. The resulting molecules offer not only multiple options in creating structural contrast in polymer blends and composites in structural studies but also insight into the biosynthetic pathways themselves.

Characterization of Dipeptide-based Sorbent Materials using Combined Thermodynamic and Inelastic Neutron Scattering Techniques

ABSTRACTUsing a combination of x-ray diffraction, volumetric adsorption and inelastic neutron scattering (INS) the adsorption properties of methane within the channels of L-Isoleucyl-L-Valine (IV) and L-Valyl-L-Alanine (VA) dipeptides have been investigated. These biomaterials have quasi one-dimensional channels of tunable diameters in the range of 3-6 Å and offer possibilities for selective adsorption, as well as, water and gas transport properties. High-resolution volumetric methane adsorption measurements performed near 100K for IV find that this biomaterial exhibits an adsorption capacity of ∼100 m2/g. High-resolution Inelastic Neutron Scattering (INS) measurements were performed at the Spallation Neutron Source using the BASIS spectrometer with ∼ 3.5 μeV resolution. The data clearly indicate that at least two spectral features at energy transfers near 100 and 200 μeV are present, which suggests a lowering of the hindering potential for methane reorientation primarily about the three-fold axis within the IV channels. Such features play a key role in understanding details concerning the potential energy surface. These thermodynamic and INS studies suggest that the flexibility and dynamical motion within the dipeptide channels may play a significant role in the adsorption properties.

Small Angle Neutron Scattering Study of Ferritic ODS Alloys

Small Angle Neutron Scattering (SANS) technique allows characterizing the nanomicrostructure of the ferritic Oxide Dispersion Strengthened (ODS) steels which are candidates for the structure material of fusion reactor and fast reactor. A SANS study of domestic ferritic ODS alloys are presented. The main objective is to study the evolution of the oxide dispersion nanoparticle during the different stages of the fabrication and different content.

Dynamics of water in prussian blue analogues: Neutron scattering study

Dynamics of crystal water in Prussian blue (PB), Fe(III)4[Fe(II)(CN)6]3.14H2O and its analogue Prussian green (PG), ferriferricynaide, Fe(III)4[Fe(III)(CN)6]4.16H2O have been investigated using Quasielastic Neutron Scattering (QENS) technique. PB and its analogue compounds are important materials for their various interesting multifunctional properties. It is known that crystal water plays a crucial role towards the multifunctional properties of Prussian blue analogue compounds. Three structurally distinguishable water molecules: (i) coordinated water molecules at empty nitrogen sites, (ii) non-coordinated water molecules in the spherical cavities, and (iii) at interstitial sites exist in PB. Here spherical cavities are created due to the vacant sites of Fe(CN)6 units. However, PG does not have any such vacant N or Fe(CN)6 units, and only one kind of water molecules, exists only at interstitial sites. QENS experiments have been carried out on both the compounds in the temperature range of 260–360 K to elucidate the dynamical behavior of different kinds of water molecules. Dynamics is found to be much more pronounced in case of PB, compared to PG. A detailed data analysis showed that localized translational diffusion model could describe the observed data for both PB and PG systems. The average diffusion coefficient is found to be much larger in the PB than PG. The obtained domain of dynamics is found to be consistent with the geometry of the structure of the two systems. Combining the data of the two systems, a quantitative estimate of the dynamics, corresponding to the water molecules at different locations is made.

Water management in proton exchange membrane fuel cell at sub-zero temperatures: An in operando SANS-EIS coupled study

The water management in a proton exchange membrane fuel cell (PEMFC) was studied in operando at sub-zero temperatures combining Small-Angle Neutron Scattering (SANS) and Electrochemical Impedance Spectroscopy (EIS) techniques. The two main processes which control the water repartition within the fuel cell, namely the electro-osmosis and the back-diffusion of water in the membrane can be separated by the decrease of the operating temperature along with the use of a thick membrane compared to state-of-the-art material. It is shown that an increase of the current load at sub-zero temperature induces reversible membrane dehydration despite a higher production of water. This effect is revealed by the very good correlation between the increase of the membrane resistance measured by EIS and the decrease of water content in the membrane quantified from the SANS spectra. The predominance of the electro-osmosis on the back-diffusion, in addition to water accumulation, most probably in supercooled state, in the channel and in the gas diffusion layer, especially at the cathode side, could explain the difficulty to operate a fuel cell at sub-zero temperature.

Neutron Scattering Techniques and Applications in Structural Biology

Neutron scattering is exquisitely sensitive to the position, concentration, and dynamics of hydrogen atoms in materials and is a powerful tool for the characterization of structure-function and interfacial relationships in biological systems. Modern neutron scattering facilities offer access to a sophisticated, nondestructive suite of instruments for biophysical characterization that provides spatial and dynamic information spanning from Ångstroms to microns and from picoseconds to microseconds, respectively. Applications in structural biology range from the atomic-resolution analysis of individual hydrogen atoms in enzymes through to meso- and macro-scale analysis of complex biological structures, membranes, and assemblies. The large difference in neutron scattering length between hydrogen and deuterium allows contrast variation experiments to be performed and enables H/D isotopic labeling to be used for selective and systematic analysis of the local structure, dynamics, and interactions of multi-component systems. This overview describes the available techniques and summarizes their practical application to the study of biomolecular systems.

Third School on the Applications of Neutron Scattering Techniques in Structural Biology, Oak Ridge, TN

Third School on the Applications of Neutron Scattering Techniques in Structural Biology, Oak Ridge, TN

Quasi-Elastic Neutron Scattering Study of Water Confined in Periodic Mesoporous Organosilicas

Water confined in nanoscale space behaves significantly differently from bulk water. We have applied the Quasi-Elastic Neutron Scattering technique to investigate diffusive properties of water confined in porous silicate coated with hydrophobic organic functional groups, at two different levels of hydration. The measurements were performed over a wide range of temperatures, and although we cannot exclude subdiffusion, the data are more easily understood from a distribution in the diffusive dynamics ranging from static water monolayer at the pore surface to much greater mobility towards the pore centre. There is some evidence for a local diffusive motion with an effective radius of about 3.5 A. The overall diffusion constants are significantly less than bulk water over the same temperature ranges.

中性子小角散乱法とその材料開発へのインパクト

中性子小角散乱法とその材料開発へのインパクト

Spin dynamics of molecular nanomagnets unravelled at atomic scale by four-dimensional inelastic neutron scattering

Molecular nanomagnets are among the first examples of finite-size spin systems and have been test beds for addressing several phenomena in quantum dynamics. In fact, for short-enough timescales the spin wavefunctions evolve coherently according to an appropriate spin Hamiltonian, which can be engineered to meet specific requirements. Unfortunately, so far it has been impossible to determine these spin dynamics directly. Here we show that recently developed instrumentation yields the four-dimensional inelastic-neutron scattering function in vast portions of reciprocal space and enables the spin dynamics to be determined directly. We use the Cr8 antiferromagnetic ring as a benchmark to demonstrate the potential of this approach which allows us, for example, to examine how quantum fluctuations propagate along the ring or to test the degree of validity of the Néel-vector-tunnelling framework. Understanding the spin dynamics in magnetic nanostructures is important for spintronics, but so far it has been impossible to probe the spin dynamics directly. A neutron-scattering technique providing direct information about dynamical two-spin correlations in a molecular nanomagnet has now been demonstrated.

Investigating the Defect Structures in Transparent Conducting Oxides Using X-ray and Neutron Scattering Techniques

Transparent conducting oxide (TCO) materials are implemented into a wide variety of commercial devices because they possess a unique combination of high optical transparency and high electrical conductivity. Created during the processing of the TCOs, defects within the atomic-scale structure are responsible for their desirable optical and electrical properties. Therefore, studying the defect structure is essential to a better understanding of the behavior of transparent conductors. X-ray and neutron scattering techniques are powerful tools to investigate the atomic lattice structural defects in these materials. This review paper presents some of the current developments in the study of structural defects in n-type TCOs using x-ray diffraction (XRD), neutron diffraction, extended x-ray absorption fine structure (EXAFS), pair distribution functions (PDFs), and x-ray fluorescence (XRF).

Investigation of metal-matrix composite containing liquid-phase dispersion

Al-Pb binary system is a suitable model system for testing liquid phase dispersion strengthening in bulk materials for structural applications. Liquid Pb islands can be finely dispersed in still solid Al matrix due to the substantial difference of melting points. The Al-Pb system prepared by means of Equal Channel Angular Pressing (ECAP) process was investigated by Small-Angle Neutron Scattering technique (SANS) which enables in-situ measurement of size and morphology parameters of Pb inclusions at elevated temperatures. It was observed that the lead particles were elongated roughly in the direction of ECAP. During the subsequent in-situ thermal cycle RT-400°C-RT, the elongated Pb particles transformed to nearly spherical shape. The change of scattering contrast during melting of Pb mapped the transform of the confined lead particles to the liquid phase. The center of the transition region is around 342°C (615K) for both the as-cast and the ECAP deformed samples, which is a significant shift with respect to the free Pb melting point 327°C (600K). For the ECAP sample, the transition is not sharp, indicating a broad size distribution of lead particles.

Quasi-elastic neutron scattering studies of the slow dynamics of supercooled and glassyaspirin

Aspirin, also known as acetylsalicylic acid (ASA), is not only a wonderful drug, but also agood glass former. Therefore, it serves as an important molecular system to study thenear-arrest and arrested phenomena. In this paper, a high-resolution quasi-elastic neutronscattering (QENS) technique is used to investigate the slow dynamics of supercooled liquidand glassy aspirin from 410 down to 350 K. The measured QENS spectra can beanalyzed with a stretched exponential model. We find that (i) the stretched exponentβ(Q) is independent of thewavevector transfer Q in the measured Q range and (ii) the structural relaxation timeτ(Q) follows a power-lawdependence on Q.Consequently, the Q-independent structural relaxation timeτ0 can beextracted for each temperature to characterize the slow dynamics of aspirin. The temperature dependenceof τ0 can be fitted with the mode-coupling power law, the Vogel–Fulcher–Tammann equationand a universal equation for fragile glass forming liquids recently proposed by Tokuyamain the measured temperature range. The calculated dynamic response functionχT(Q, t) using the experimentally determined self-intermediate scattering function of the hydrogenatoms of aspirin shows direct evidence of the enhanced dynamic fluctuations as the aspirinis increasingly supercooled, in agreement with the fixed-time mean squared displacement⟨x2⟩ and the non-Gaussianparameter α2 extracted from the elastic scattering.

Zn-induced spin dynamics in overdoped La2−xSrxCu1−yZnyO4

Spin fluctuations and the local spin susceptibility in isovalently Zn-substituted La${}_{2\ensuremath{-}x}$Sr${}_{x}$Cu${}_{1\ensuremath{-}y}$Zn${}_{y}$O${}_{4}$ ($x=0.25$, $y\ensuremath{\approx}0.01$) are measured via inelastic neutron-scattering techniques. As Zn${}^{2+}$ is substituted onto the Cu${}^{2+}$-sites, an anomalous enhancement of the local spin susceptibility ${\ensuremath{\chi}}^{\ensuremath{'}\ensuremath{'}}(\ensuremath{\omega})$ appears due to the emergence of a commensurate antiferromagnetic excitation centered at wave vector Q $=(\ensuremath{\pi},\ensuremath{\pi},0)$ that coexists with the known incommensurate spin-density wave excitations at Q${}_{HK}=(\ensuremath{\pi}\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta},\ensuremath{\pi}),(\ensuremath{\pi},\ensuremath{\pi}\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta})$. Our results support a picture of Zn-induced antiferromagnetic (AF) fluctuations appearing through a local staggered polarization of Cu${}^{2+}$ spins, and the simultaneous suppression of T${}_{c}$ as AF fluctuations are slowed in proximity to Zn impurities suggests the continued importance of high-energy AF fluctuations at the far overdoped edge of superconductivity in the cuprates.

Monitoring phase behavior of hydrogen confined in carbon nanopores byin-situSmall Angle Neutron Scattering technique

ABSTRACTWe report on the use ofin-situsmall angle neutron scattering (SANS) technique to study the phase behavior of hydrogen confined in narrow pores of ultramicroporous carbon (UMC) with a very large surface area (2630 m2/g) and pore volume (1.3 cm3/g). The effect of pore size and pressure on hydrogen adsorbed on UMC at room temperature and pressures up to ∼200 bar were investigated. In a previous experiment, we have measured the density of adsorbed H2gas in the nanopores and mesopores of polyfurfuryl alcohol-derived activated carbon (PFAC) by SANS technique. Here, a comparative SANS study between the UMC and PFAC was conducted in order to further investigate the densification of H2as a function of pore size and pressure. Initial results suggest that the density of confined H2in both UMC and PFAC is considerably higher than that of the bulk hydrogen gas. The density is systematically higher in the narrow pores and decreases with increasing pore size. These results clearly demonstrate the advantage of adsorptive storage over compressed gas storage and emphasize the greater efficiency of micropores over mesopores in the adsorption process, which can be used to guide the development of new carbon adsorbents tailored for maximum H2storage capacities at near-ambient temperatures.