Improving our microscopic understanding of heat transport is central to design energy materials and devices reaching higher efficiencies, in particular for thermoelectric applications. Thus, establishing a complete picture of phonon dispersions and mean-free-paths is crucial, in order to obtain a realistic microscopic characterization of thermal conductivity, against which theories of phonon transport can be tested. Thanks to recent advances in experimental facilities, combined with developments in data modeling, inelastic neutron scattering can now be used to map phonon excitations across the entire volume of the Brillouin zone. Our neutron scattering measurements of phonons in single-crystals directly probe features in phonon dispersions and lifetimes that are associated with a rich variety of scattering mechanisms, including: phonon anharmonicity, electron-phonon coupling, and scattering by point-defects or nanostructures. These different processes may be combined to increase phonon scattering rates, and improve thermoelectric efficiency, for example. Our neutron scattering investigations are also complemented with synchrotron x-ray scattering experiments of the structure and dynamics. In addition, we leverage first-principles simulations of atomic dynamics, including effects of anharmonicity and defects, to extract key scientific insights from large experimental datasets. We present results from several studies of important thermoelectric materials [1,2], illustrating how this integrated approach, combining scattering experiments and computational modeling, was used to obtain a new level of microscopic understanding of thermal conductivity in advanced materials. Our results suggest avenues to improve the performance of thermoelectric materials.
[1] O. Delaire, J. Ma, K. Marty, A. F. May, M. A. McGuire, M.-H. Du, D. J. Singh, A. Podlesnyak, G. Ehlers, M. Lumsden, B. C. Sales, “Giant Anharmonic Phonon Scattering in PbTe”, Nature Materials 10, 614 (2011).
[2] J. Ma*, O. Delaire*, A. F. May, C. E. Carlton, M. A. McGuire, L. H. VanBebber, D. L. Abernathy, G. Ehlers, Tao Hong, A. Huq, Wei Tian, V. M. Keppens, Y. Shao-Horn, and B. C. Sales, “Glass-like phonon scattering from a spontaneous nanostructure in AgSbTe2”, Nature Nanotechnology 8, 445 (2013).
We acknowledge funding from the US Department of Energy, Office of Basic Energy Sciences, Materials Science and Engineering Division, and through the S3TEC Energy Frontier Research Center.

Copper selenide is a mixed ionic-electronic conductor and received attention from the technological and physical points of view in particular due to a high ionic conductivity and highest value of thermoelectric figure of merit among the any bulk materials [1, 2]. The characteristic feature of Cu_2-xSe compounds is the presence of low-energy phonon modes similar to other Cu and Ag fast ionic conductors.
We studied the crystal structure, short-range order and lattice dynamics in Cu_2-xSe compounds using neutron scattering. Strong diffuse scattering found in superionic phase arises from correlated thermal displacements of the ions. Theoretical calculations show that diffuse is related to correlated thermal vibrations, mainly of Se-Cu(8c, 32f) and Cu(8c)-Cu(8c) atoms.
In the measurements of phonon dispersion we found that TA [100], TA [111] and TA1 [110] acoustic branches demonstrate an optic-like behaviour and strong broadening of phonon peaks at wavevectors q>0.5. Experimental results are compared with density functional theoretical calculations showing the presence of unstable soft mode related to ordering of Cu atoms observed in Cu_1.8Se at room temperature followed by α-β phase transition at a lower temperature. Superstructure arising from the ordering causes effects similar to the folding of the Brillouin zone, although phonon intensities at new Brillouin zone centres are weak. The coupling of low-energy phonon modes with displacement of mobile ions explains the strong broadening of acoustic phonons at q>0.5 and optic modes in the energy range 10-15 meV related mostly to Cu vibrations. Observed strong phonon damping may be responsible for the low values of lattice component of thermal conductivity in this material.
[1]. H Liu, et al. Nature Materials, http://dx.doi.org/10.1038/nmat3273
[2]. X. Xing-Xing, et al. Chin. Phys. B Vol. 20, No. 8 (2011) 087201

Thermoelectric materials can convert waste heat into electrical energy, and have attracted much attention in recent years for power generation. IV-VI compounds in rock salt structure include some of the most efficient thermoelectric materials and giant phonon anharmonicity is believed to contribute to the low thermal conductivity. In this work, phonon dispersions and linewidths in single-crystalline SnTe were measured at a series of temperatures using time-of-flight and triple-axis neutron spectrometers to study the temperature dependence of the phonon dynamics and phonon anharmonicity. Phonon calculations and molecular dynamics simulations with first-principles methods were used to identify the anomalies in phonon modes and the results were compared to the measurements. Because the phonons involved have an important contribution to the lattice thermal conductivity in this system, the anharmonic coupling is likely to provide a key insight in understanding the surprisingly low thermal conductivity of the rock salt tellurides in general.

Thermal conductivity plays a vital role in the phonon glass electron crystal (PCEC) approach to the design of high performance thermoelectric materials. It is generally expected that low and glasslike thermal conductivity can be realized in crystalline intercalated framework compounds. A proposal for the low thermal conductivity is a strong exchange of energy between the lattice phonons and the localized vibrations of the intercalated atoms inside the Brillouin zone. Neutron and x-ray inelastic scattering experiments have been performed to characterize this phenomenon. The results, however, are non-conclusive. We have studied this phenomenon using clathrate hydrate as the model and complemented by direct calculation of the thermal conductivity to uncover the mechanism for energy transport in this system. The results reveal a consistent explanation on how resonant scattering of lattice phonons by guest vibrations that helps to lower the lattice thermal conductivity.

Materials that exhibit fast and large reversible shape changes upon application of external magnetic fields are desirable for magnetomechanical/ electromechanical energy transduction, mechatronics and biomedical devices. Recently, ferromagnetic martensitic alloys such as Ni-Mn-Ga have been particularly promising in this regard. However, further advances in materials and devise technologies will require a comprehensive understanding of the interrelations between the local atomic/electronic structures and microscopic twin boundary motion. Results from recent diffraction and inelastic experiments, first principle calculations and phenomenological modeling are presented that provide crucial insights in these areas.
The crystallographic structural details of an off-stoichiometric Ni2Mn1.14Ga0.86 alloy, including the modulations of the atomic site displacements, site occupancies and magnetic moments, are obtained from the refinement of high-resolution single-crystal neutron diffraction data, following a (3+1)-dimensional superspace formalism. In particular, the structure is found to adopt a P2/m(α0γ) superspace group symmetry, a commensurate periodicity of 5M and a modulation wave vector of q=2/5c. The magnetic moments are aligned along the shorter b axis and the overall magnetic moment per formula unit of Ni2Mn1.14Ga0.86 is 2.7 mu;B.
Large magnetic-field-induced strain in ferromagnetic martensites essentially arises from strong magnetic anisotropy, which was obtained from both the experiment and the relativistic electronic structure calculations. The anisotropic classical Heisenberg model Hamiltonian was adopted to describe the magnetic properties of the Ni2Mn1.14Ga0.86. The Heisenberg model exchange interactions were calculated using a linear response approach. The applicability of the obtained Hamiltonian was verified by comparison with experimental spin waves measured by inelastic neutron scattering.
A strong spin-orbital coupling for Ni2Mn1.14Ga0.86 results in a reorientation of the martensitic twins when a magnetic field is applied along the magnetic hard axis. Microscopically, twin reorientation proceeds through the process of nucleation and growth. The temporal evolution of twin reorientation under magnetic fields, as observed by in situ X-ray diffraction, is described as a result of thermally activated sideways creep of twin boundaries over a distribution of energy barriers. The dynamical creep exponent is mu; ~ 0.5. Following scaling laws, it is therefore proposed that twin reorientation creep occurs as a result of competition between the longer range elastic fields of twin boundaries and the short-range elastic fields of twinning disconnections.
Future directions in materials development and characterization techniques for applications under dynamic operating conditions will be discussed.

Silver oxide (Ag2O) with the cuprite structure has anomalous thermal properties, including negative thermal expansion (NTE) at low temperatures. Phonon densities of states were measured by inelastic neutron scattering on Ag2O from 40 to 400 K with the wide angular -range chopper spectrometer, ARCS, at the Spallation Neutron Source at Oak Ridge National Laboratory. Even over this range of low temperatures, the measured phonon densities of states (DOS) showed unusually large anharmonic behavior as phonon energy shifts and phonon lifetime broadenings.
First principles molecular dynamics (MD) calculations were performed at various temperatures. These calculations accurately accounted for the NTE and local dynamics of cuprite Ag2O, such as the contraction of the Ag-Ag shell and the large distortion of the OAg4 tetrahedra. A normal mode analysis identified the rigid unit modes and the bending modes of the OAg4 tetrahedra which play key roles in the NTE.
Using the Fourier-transformed velocity autocorrelation method, a phonon DOS was obtained. The theoretical calculations reproduced the large anharmonic effects of Ag2O, and were in excellent agreement with the neutron scattering data. Strong anharmonic effects were attributed to phonon-phonon interactions, and it was found that the quasiharmonic model could not account for much of the phonon behavior.
Large effects of phonon DOS and phonon kinematics on phonon lifetime of cuprite Ag2O can be understood with anharmonic phonon perturbation theory of the cubic anharmonicity. The phonon interaction channels for three-phonon processes were calculated from the two-phonon DOS, weighted approximately by the phonon coupling strength. The lifetime broadenings of several different phonon modes are explained by anharmonic perturbation theory, which showed rich interactions between the Ag-dominated modes and the O-dominated modes in both up-conversion and down-conversion processes. Although part of the NTE can be understood by quasiharmonic theory, a substantial part of the behavior originates from pure anharmonicity.

The use of magnetoelectrics in novel spintronic memories is currently limited by a poor grasp of magnetoelectric coupling dynamics and the factors that control such coupling. While previous studies of magnetoelectric coupling in La_1-xSr_xMnO₃ (LSMO) - PbZr_xTi_1-xO₃ (PZT) have provided much insight into fundamental mechanisms, direct measurement of piezoelectrically-induced magnetization changes (flexomagnetism) is needed. Here we present a series of magnetization studies utilizing direct in situ electrical biasing and switching of the PZT layer. We show significant changes in bulk saturation magnetization of LSMO that arise from a piezoelectric strain effect. We complement these measurements with novel in situ polarized neutron reflectometry measurements that reveal the spatial extent of induced magnetization. We then correlate these magnetic measurements with local structural and chemical probes. Our results will help designers control magnetoelectric coupling for device applications, while the in situ techniques developed in the course of this work will benefit the broader neutron scattering community.

A great example of constructive synergy in nature is the strongly correlated electron systems. Not only do they open the door for physics to push its boundaries, but they oftentimes exhibit exciting new physical phenomena with associated properties that have viable technological applications. Advancement of this field necessitates a way to probe and tune its various microscopic states to reveal the mechanisms behind the phenomena and based on this understanding, possibly fabricate materials by design in the future. In this talk, the discussion will focus on the contributions of neutron scattering on an important field of experimental condensed matter physics centered on studying correlated electron systems including examples of unconventional superconductors (isoelectronic doping in Fe-based superconductors) and multifunctional systems, such as multiferroic compounds (field effect in Ba2CoGe2O7) as well as the recent work on iridate compounds (Sr2IrO4) exhibiting strong spin-orbit interactions. The use of the premier neutron scattering instruments housed at the Spallation Neutron Source and the High Flux isotope reactor at ORNL
are crucial in advancing the central theme in understanding correlated electron systems, which is to make the correlation between structure, magnetism and physical properties.

It is widely believed that the superconducting mechanism in layered cuprates depends on the presence of antiferromagnetic spin correlations, and inelastic neutron scattering is the technique that has provided much of our knowledge of spin fluctuations in the cuprates. I will discuss what we have learned about the evolution of spin correlations with carrier density, from the antiferromagnetically ordered state of the insulating parent compounds, through the regime of maximum superconducting transition temperature (at "optimal" doping), to the "over-doped" regime where superconductivity and antiferromagnetic spin correlations disappear. The observation (in special cases) of stripe order, in which stripes of doped charge carriers from antiphase domain walls between antiferromagnetic strips, provides a basis for understanding how spin fluctuations with the character of the parent correlated insulator survive in the superconducting phase. Spin fluctuations up to the energy scale of the superconducting pairing gap reflect the stripe correlations, while excitations at higher energies look like those of a short-range commensurate antiferromagnet, until they become highly over-damped above the "pseudogap" energy scale due to interactions with single-electron excitations.
Work at Brookhaven is supported by the Office of Basic Energy Sciences, Materials Sciences and Engineering Division, U.S. Department of Energy, through Contract No. DE-AC02-98CH10886.

Unconventional superconductivity is usually associated with the proximity of the superconducting (SC) state to an antiferromagnetic (AFM) ordered state. In many materials, such as the cuprates, heavy fermions, and now the iron arsenides, SC is often induced by chemical substitution that acts to suppress the AFM order. Thus, the SC state develops in the midst of strong magnetic fluctuations that have been implicated in the formation of electron pairs. In this talk, I will discuss the nature of the magnetic excitations in chemically substituted Ba(Fe1-xMx)2As2 and related compounds. Using inelastic neutron scattering, we find that M = Co substitutions affect primarily the low energy spin fluctuations and the onset of SC is associated with strong Landau damping. This can be compared to the magnetic excitations found for chemical substitutions (such as M = Mn and Cu) that do not lead to a SC state. I will also discuss the fascinating and diverse array of itinerant magnetism that develops in SrCo2As2 and BaMn2As2 compounds that reside in the same family as BaFe2As2.

We report the effect of quasi-hydrostatic and hydrostatic pressure on single crystals of the aliovalent La-doped Ca1-xLaxFe2As2 by measuring transport and neutron scattering properties. In contrast to transition metal-doped 122 Fe-based superconductors where superconductivity and antiferromagnetism coexist, these two phases appear to be mutually exclusive in the rare-earth doped series in a manner similar to the 1111-type Fe-based superconductors, suggesting that this high-Tc phase is intrinsic. The unusual dichotomy between lower-Tc systems that happily coexist with AFM and the tendency for the highest-Tc systems to show phase separation provides an important clue to the pairing mechanism in iron-based superconductors.

Recent neutron scattering investigations at the NCNR of the crystal structures, magnetic structures, and spin dynamics of the iron-based superconductors will be presented [1]. We will very briefly review the (nearly) universal behavior exhibited by the undoped materials, where a tetragonal-to-orthorhombic structural transition occurs between ~140-220 K, at or below which the Fe moments order antiferromagnetically. In between the structural and magnetic transitions nematic behavior is expected, and recent measurements addressing this issue will be presented [2]. Rare earth doping in (Ca-R)Fe2As2 can transform the system from a magnetically ordered orthorhombic material to a `collapsed' non-magnetic tetragonal system, similar to the behavior found under pressure. However, with rare earth doping superconductivity is observed, with transition temperatures up to 47 K [3].. For the spin dynamics in the ‘parent&’ materials, the exchange interactions are strong with spin-wave bandwidths ~200 meV. In the superconducting regime a clear magnetic resonance in the magnetic excitation spectrum that tracks the superconducting order parameter is observed, reminiscent of the cuprate superconductors. However, unlike the cuprates, the iron-based materials are more three dimensional, with the spin waves in the parent systems exhibiting substantial dispersion along the c-axis, and even with some dispersion of the resonance in the superconducting phase. Recent spin dynamics results and their consequences for the pairing symmetry will be discussed [4].
It is a pleasure to acknowledge that various portions of the NCNR work were carried out in collaborations with the following groups: P. Dai (U. Tennessee), N. L. Wang (Beijing), R. J. Cava (Princeton U.), R. J. McQueeney, A. I. Goldman (Ames Lab), W. Bao (Renmin U. China), S. Dhar (TIFR), J. P. Paglione (U. Maryland), R. J. Birgeneau (UC-Berkeley). Please see http://www.ncnr.nist.gov/staff/jeff for a complete list of articles and coauthors.
[1] For a recent neutron review see J. W. Lynn and P. Dai, Physica C 469, 469 (2009).
[2] D. M. Pajerowski, et al. Phys. Rev. B 87, 134507 (2013); K. Kirshenbaum, et al. Phys. Rev. B 86, 060504(R) (2012); Yu Song, et al. Phys. Rev. B 87, 184511 (2013).
[3] S. R. Saha, et al., Phys. Rev. B 85, 024525 (2012); Saha, et al. (preprint).
[4] Meng Wang, et al., Phys. Rev. B 83, 220515(R) (2011); Chenglin Zhang, et al., Scientific Reports 1, 115 (2011); Songxue Chi, et al., Phys. Rev. B 84, 214407 (2011); Huiqian Luo, et al., Phys. Rev. Lett. 108, 247002 (2012).

Neutron scattering techniques have been crucial to understanding magnetic structure and dynamics in a broad range of magnetic materials. Recent interest has focussed on new magnetic materials which maintain a complex disordered state to low temperatures due to quantum fluctuations, geometrical frustration, or both. Such materials are well suited to time-of-flight neutron techniques, as much of the relevant momentum and energy response can be simulaneously measured.
We have used these techniques to achieve a detailed and robust understanding of the microscopic spin Hamiltonian in the XY pyrochlore magnets Yb2Ti2O7 and Er2Ti2O7. These materials display net ferromagnetic and antiferromagnetic Curie-Weiss constants, respectively. Both also possess ground state crystal field doublets which are well separated from their corresponding excited states, leading to an effective spin ½ description for the corresponding Yb3+ and Er3+ moments.
Our measurements on Er2Ti2O7, in particular, solve a long-standing problem as to why the particular ground state spin structure of this material is realized through a continuous phase transition. The characteristics of this ground state selection, through the Order-by-Quantum Disorder (ObQD) mechanism will be discussed, along with discussion of the ObQD spin wave gap which is a necessary consequence.

Owing to the staggering demand from our mobile society for portable electronics together with the increased awareness of environmental issues, the Li-ion technology is enjoying a great commercial success. Therefore, this technology falls short in meeting foreseen demands dictated by upcoming EV&’s and grid applications, for costs and sustainability are the overriding factors. Many worldwide groups including ours are searching for new electrode materials capable of meeting such expectations. We found a new class of inorganic compounds based on sulphate polyanions (SO4)2- which, besides being attractive as insertion electrode for Li-ion batteries, present interesting magnetic properties.
Herein we highlight how electrochemically-driven redox reactions, can be useful in tuning the magnetic properties through a careful control of the metal oxidation state. More specifically, a detailed study of new marinite Li2M(SO4)2 phases with M=Fe, Co, Mn will be presented. The structure was solved from combined neutron and synchrotron powder diffraction studies, in order to precisely locate lithium ions. In addition to present an attractive redox potential (3.83V for the Fe2+/Fe3+ couple), they can be regarded as model compounds for super super exchange interactions (i. e. two transition metal atoms linked via a SO4 group). Similarly, the structural/magnetic properties of the electrochemically delithiated LiFe(SO4)2 phase having Fe3+ rather than Fe2+ has been studied as well. All these compounds were found to be antiferromagnetic with TN ranging from 5 to 50 K depending upon the nature of M as well as on the nature of the Fe oxidation state. We discuss these results in the framework of the Goodenough-Kanamori-Anderson rules.

Mn3O4 post-spinel was synthesized at high pressure (=20 GPa) and recovered to ambient conditions. Neutron scattering and heat capacity data reveal a coupled first-order magnetic and structural phase transition of the mixed-valence postspinel compound Mn3O4 at 210 K. Neutron diffraction measurements reveal a magnetic structure in which Mn3+ spins align antiferromagnetically along the edge-sharing a-axis, with a magnetic propagation vector k = [1/2,0,0]. In contrast, the Mn2+ spins, which are geometrically frustrated, do not order until a much lower temperature. Although the Mn2+ spins do not directly participate in the magnetic phase transition at 210 K, structural refinement using neutron diffraction reveal a large atomic shift at this phase transition without any crystal symmetry change. This physical motion scales to 0.3 A°, similar to those values for ferroelectric materials. This “giant” response is due to the coupled effect of built-in strain in the postspinel structure with the orbital realignment of the Mn3+ ion.

Understanding the morphology and composition of phases that exist in the photoactive layer in organic photovoltaics (OPVs) is essential to optimizing conjugated polymer-based solar cells. In this study, the impact of P3HT molecular weight on the morphology and phase composition of poly(3-hexylthiophene) (P3HT): [6,6]-Phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunctions (BHJ) mixture is presented. Careful analysis of small angle neutron scattering data provides a measure of the composition of the miscible amorphous phase of mixed PCBM and P3HT, the average PCBM domain size, and the interfacial area between PCBM and the P3HT-rich phase in P3HT:PCBM systems. The miscibility of PCBM in the amorphous phase of P3HT is found to be dependent on the molecular weight of the P3HT: lower P3HT molecular weight results in a decreased miscibility of PCBM in amorphous P3HT and a decrease in interfacial area between the PCBM phase and the P3HT-rich phase; an increase of PCBM domain size and P3HT crystallinity was also found for the lower P3HT molecular weight studied. Our interpretation of this data is that the incorporation of PCBM into the P3HT amorphous phase is limited for the lower molecular weight P3HT by smaller tie chains between the P3HT crystalline domains.

We discuss the use of diffuse or off-specular neutron reflectometry techniques and methodologies for the study of nanostructured thin organic films, in particular two applications focused on polymer laminates and conjugated organic systems.
Using simple laminate systems composed of nanometre thick polystyrene and poly(methyl methacrylate) multilayers, which form a periodic three-dimensional interfacial structure upon annealing, we show indicative specular reflection and off-specular diffuse scattering data, and propose a simple quantitative model based on the distorted-wave Born approximation and convolution theory. Here the aim is to form an understanding of the general parameter set required to describe a variety of soft-matter interfacial structures (including, for example, both diffuse and laterally patterned interfaces and layers) and suggest a framework for quantitative fitting and simulation of off-specular neutron scattering data.
Secondly, we apply off-specular neutron reflectometry to probe how small, conjugated organic molecules organize and structure at interfaces, with a view towards advancing the understanding and control of molecular packing, orientation and structure formation of organic semiconducting thing layers. Knowledge of the interfacial structure between soft dielectrics and conjugated molecules is paramount for the wide-scale production of efficient organic thin film devices, where one of the crucial aspects governing device functionality and efficiency is the molecular organization at the principle charge transport interfaces. We study a system composed of sub 100 nm thick layers of polyvinylpyrrolidone or poly(methyl methacrylate) covered by a layer of fully deuterated dioctylterthiophene (DOTT) - capable of forming various mesophases - each with differing charge transport properties and molecular ordering. As opposed to a simple ‘hard-wall&’ interaction, the molecular alignment of DOTT at a polymer interface will be influenced by parameters such as a temperature-dependent interfacial width that arises from the interpenetration of DOTT and polymer molecules. Using specular and off-specular neutron reflectometry data we are able to derive quantitative information on the interfacial width and structure, as well as the supramolecular organization of DOTT thin films on or between polymer layers.

The relatively new neutron scattering technique of SERGIS has proved powerful in probing periodic grating samples and there is now some level of maturity in modelling this data. So that it is now possible to extract meaningful lengthscale and periodicities from these real space neutron measurements. We have looked at the SERGIS signal from an organic photovoltaic blend and measured the size of PC60BM crystallites after crystallization. Recent experiments have helped assess to what extent the SERGIS signal from a buried periodic structure could be measured. We used glassy thin film deuterated PMMA polymer samples floated onto a grating structure to make a buried periodic structure. We will present SERGIS data for two thicknesses of buried gratings as well as a dPMMA film that has been heated above Tg and so conformed to the buried grating structure and so gave an added periodicity to the SERGIS signal.

Conjugated polymers and carbon nanoparticle nanocomposites are important energy harvesting materials. For instance, the most promising organic photovoltaics consist of mixtures of conjugated polymers and modified fullerenes, particularly [6,6]-phenyl C61-butyric acid methyl ester (PCBM). Similarly, recent work has demonstrated that mixtures of conjugated polymers with carbon nanotubes are promising organic thermoelectric materials. In this talk, we will report our recent progress in using neutron scattering and reflectivity to determine the miscibility, interfacial structure, and morphological characteristics of conjugated polymer-carbon nanoparticle nanocomposites. Because of the inherent contrast between hydrogenated polymers and carbon nanoparticles, careful data analysis provides interfacial surface area, average domain size, and importantly, phase composition. We will also discuss how the determination of these crucial morphological characteristics enables the correlation of the performance of the nanocomposite to specific controllable structural properties of the resultant nanocomposite, and provides important fundamental information that can be used to rationally design and optimize these polymer nanocomposites for energy harvesting.

We report small angle neutron scattering (SANS) study of undeuterated and deuterated poly(N-isopropylacrylamide) (PNIPAM). Linear polymer chains of PNIPAM undergo Lower critical saturation temperature (LCST) near 32C. To study the conformation change of linear polymer PNIPAM, we prepared two linear polymer samples with undeuterated and deuterated PNIPAM with 60 monomers long chains. We probed both the samples at different temperatures namely below, at, and above LCST using Neutron source of Oakridge National Laboratory. Deuterated PNIPAM polymer sample was synthesized by using deuterated hydrogen on the methyl groups of each monomer. Both the samples were identical in chemical structure and similar in molecular weight. The contrast variation was applied to SANS is presented. The numerical approaches to analyze the data are discussed. Applications of SANS together with contrast variation to model the conformational changes of the systems are presented.

The mechanical, optical and barrier properties of semicrystalline polymers are optimized by tuning their crystalline and amorphous fractions. The structure of interlamellar amorphous material—including tie chains as well as the rigid amorphous fraction and other interphases—significantly impacts these properties but remains difficult to characterize directly. Using deuterated organic solvent vapor selectively absorbed by the amorphous phase, SANS patterns including the long-period peak reveal structural information specific to interlamellar amorphous material. Measuring the peak intensity and other derived parameters as a function of relative vapor pressure allows a detailed study of swelling and the interlamellar amorphous density profile. Here we present data from linear high-density polyethylene as well as a series of ethylene-co-octene polymers with varied crystallinity and crystal layer thickness. Future applications of this technique may include oriented films and fibers, membranes, and interfaces in polymer composites.

Thin films of organic semiconductors have been shown to be effective sensors for the detection of explosive vapors via photoluminescence (PL) quenching. High detection sensitivities have been achieved but selectivity continues to remain a challenge. Understanding how analyte vapors interact and penetrate within an organic thin film is critical for the development of the technology. Similarly, understanding how the change in PL signal relates to the concentration and distribution of explosive analyte within the film is also important. However, determining the concentration of explosive analyte within an organic thin film and correlating that with the PL quenching is difficult because the analyte is typically a vapor and only small quantities will be adsorbed or absorbed by the film.
We present a study on three generations of a family of fluorescent carbazole-based dendrimers that exhibit strong binding with nitroaromatic compounds accompanied by PL quenching, making them attractive sensing materials for the detection of explosives such as 2,4,6-trinitrotoluene (TNT). The absorption and release of the (deuterated) TNT analogue, 4-nitrotoluene (pNT), from thin films of the dendrimers were studied with a combination of time-correlated neutron reflectometry and PL spectroscopy.[1] When saturated with pNT the PL of the films was quenched with the films swelling to accommodate the absorbed analyte. Attempts to restore the PL at ambient conditions proved ineffective and it was only when the films were heated to 40-80 °C under a flow of nitrogen that the PL signal was recovered. Neutron reflectometry performed in situ on the films during this recovery process showed that although the majority of the absorbed pNT was released the films of all three dendrimers still contained similar residual quantities of pNT. However, the proportion of the PL recovered increased strongly with generation with the third generation dendrimer film exhibiting full recovery despite the residual pNT. We attributed this behavior to a combination of two effects. First, the dendrimer films present a range of binding sites for nitroaromatic molecules with the stronger binding sites surviving the thermal recovery process. Second, there is a large decrease of the exciton diffusion coefficient with dendrimer generation, inhibiting migration of the exciton to the remaining bound pNT.
These results illustrate the subtleties involved in performing and interpreting the results from film PL quenching measurements alone and highlight the need to combine fluorescence quenching measurements with a physical method of determining the concentration and distribution of quenchers in the film.
References
[1] P. E. Shaw et al., Phys. Chem. Chem. Phys. 2013, 15, 9845.

The attraction of making solar cells from organic polymers is their ease of manufacture and (potential) low cost compared to other technologies. However, their manufacture has suffered from one inherent flaw - the ultimate morphology is kinetically trapped and not at thermodynamic equilibrium. This makes the processing uniquely important in development of a good device and the processing - structure- properties (p-s-p) triangle is critical. Unfortunately, the very property that makes them attractive, they are made from all carbon - based materials, creates a challenge to their characterization. Small angle neutron scattering is uniquely suited to characterizing these devices and allows a p-s-p triangle to be developed. We have began this effort and a co-continuous network of the electron donor (polymer) and acceptor (a C60 fullerene derivative) is formed. This morphology will be related to the properties in the oral presentation.

Advanced materials characterization, such as in-situ measurements under various external conditions, has been made mundane by the advent of powerful synchrotron and neutron sources worldwide; but at the same time, the availability of many advanced characterization techniques also creates complications: how to choose the right technique(s) given the materials and technical questions to answer. This is especially important for industrial applications for which the ultimate goal of characterization is problem-solving. Being able to identify the most appropriate techniques, considering both time and cost effectiveness, is of great importance for materials and product development. It is still a challenge facing researchers today at both national facilities and industrial labs to take full advantages of synchrotron and neutron sources for solving critical industrial problems. This talk is intended to demonstrate, from the point of view of an industrial researcher, complementary uses of neutron and synchrotron techniques for characterization of several material systems that GE is interested in, including Ni-base superalloys, FeCo magnetic alloys, thermal barrier coatings, and NaMX batteries.

Porous asphalt concrete is a road material used in the surface layers and consists of a bituminous binder and aggregates. Due to the higher proportion of coarse aggregates and lower sand content compared to dense asphalt, interconnected voids are formed resulting in a porosity of about 20 %.
Used as a surface course in pavement systems, porous asphalt is exposed to mechanical (traffic) and environmental loads, both playing a significant role in its durability. It is subjected environmentally to a wide pallet of moisture phenomena, such as (1) rain water impinging its surface, (2) water seepage and drainage in the PA by gravity in the coarse pore system, (3) capillary uptake and redistribution in the fine pore system, (4) film and corner flow on the rough surfaces, (5) drying by diffusion, (6) moisture sorption in the binder, (7) air flow above and through the surface layer of PA, resulting in convective air flow. Drying of porous asphalt is therefore believed to undergo a much more complex process than the two phase drying behavior known for porous materials like rocks and several construction materials. The interactions between the environment and porous asphalt are yet to be fully understood and captured.
Neutron radiography (NR) has demonstrated great potential for the study of porous materials. In this talk results of experimental studies using neutron radiography of the forced convective drying of wet porous asphalt samples placed in a mini-wind tunnel, thus exposed to a controlled shear air flow as well as drying of wet asphalt samples due to gravity [Poulikakos et al. Radiation and Isotopes, 77 (2013) 5-13] are presented. The main aim of this work is to evaluate the performance of neutron radiography for: (1) providing quantitative data of the water content and water loss during drying and drainage; (2) evaluating the water distribution inside the porous asphalt in real-time at a high spatial and temporal resolution and (3) providing detailed experimental data which can be used for validation of numerical models for drying, by using a well-controlled test setup and well-defined boundary conditions. To this end, the water loss and water distribution in the samples are evaluated as a function of time.
The experiments have shown that the drying of PA samples can be visualized and quantified clearly. Behavioral distinctions regarding spatial and temporal patterns of water content and drying between the tested samples representing different materials from the road could be established. NR provided a means to obtain more detailed information on the process of drying, consisted of first a more rapid moisture loss as long as the fluid was connected followed by a slower moisture loss in the presence of disconnected fluid pockets. Water exposure can weaken asphalt concrete and result in inferior mechanical performance. The samples investigated indicate that the material with better in situ performance also had the ability to dry faster.

The elastic strains induced in the constituent wires of parallel wire strands under tensile loading were measured using neutron diffraction. The elastic strains carried by the individual wires depended very strongly on the boundary conditions at the grips and on radial clamping forces. We will discuss the partitioning of applied tensile load between the constituent wires of a strand for the following cases: 1-all wires are under elastic deformation, 2-where one wire within the bundle is undergoing plastic flow and, 3-when one or more wires fracture under load. The results indicate that mechanical interference and friction mechanisms have similar contributions to the load transferred to fractured wires. Both mechanisms should be included in analytical or numerical formulations of strain partitioning in quasi-parallel wire cables.

Small-angle neutron scattering (SANS) is powerful non-destructive technique for characterizing microstructures of the structural materials. Thanks to the high penetration power for the most of the metals and alloys, sample preparations for SANS are extremely simple, "cutting them into the plate shape". Without thinning or needling process, we still can get the nano-scale information. Furthermore, combining with small-angle X-ray scattering (SAXS) brings us information about chemical composition. Accuracy of composition is independent of the size of heterogeneities.
In spite of those attractive features, the use of SANS and SAXS for steel research is still limited. This is mainly attributed to the limitation of the number of neutron facilities and low transmission rate of X-ray when we use laboratory X-ray source. For overcoming the limitation of SAXS, we have used laboratory X-ray system with Mo-source. Due to the short wave length of Mo-Ka, the covered q-range is relatively high (0.1< q < 7 nm^-1) in our system. Fortunately, the q-range is suited for nano-size heterogeneities with 1~3nm in diameter, which is often difficult to be observed by TEM in steels. In contrast, most of the SANS instruments are designed mainly for the low-q measurements and this sometimes cause the insufficient q maximum for characterizing hetero-structure with a few nanometer. When we focus on those fine structures, relatively large delta theta is acceptable for reasonably high theta resolution, defined as (delta theta)/theta. Because of large acceptance angle for this condition, the compact neutron can give strong signal enough to be analyzed.
In this talk, we show some results of the combined use of SAXS and SANS in the microstructural analysis of steels. Then, we will show our new SANS instrument optimized for small neutron source, i-ANS (intermediate Angle Neutron Scattering). Using the compact neutron source driven by electron linear accelerator (1kW), the measurements time is (only) 6 hours at this moment. It can be shortened down to 1 hour by making new cold neutron source. Through this talk, we want to show the future impact of in-house SANS system to the materials science fields.

Precipitation of implanted helium (He) into bubbles degrades the structural integrity and performance of components used in nuclear reactors. Using neutron reflectometry, we show that He bubbles do not form at fcc-bcc interfaces below a critical He concentration. Our findings are in good agreement with previous experimental as well as modeling results and provide evidence for the presence of stable He platelets at fcc/bcc interfaces prior to bubble formation. The stable storage of He at interfaces may provide the basis to design structural materials for nuclear reactors with increased resistance to He-induced degradation.
This material is based upon work supported as part of the Center for Materials at Irradiation and Mechanical Extremes, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number 2008LANL1026.

For conventional zirconium alloys used as light water reactor (LWR) cladding, normal operation results in the formation of a waterside corrosion layer on the external surface and the introduction of H into the metal. Hydrogen pickup increases with the extent of waterside corrosion, thereby causing cladding ductility and failure energy to decrease. It is important for the nuclear industry to evaluate the H induced embrittlement mechanism in used nuclear fuel cladding. The Oak Ridge National Laboratory (ORNL) has developed a non-destructive neutron scattering and radiography method to precisely measure the uptake of total H and the formation and distribution of hydride precipitates in commercial LWR fuel cladding. Ziraloy-4 cladding used in commercial LWRs was used to produce hydrided specimens in a new hydriding system recently developed at ORNL. The hydriding apparatus consists of a closed stainless steel vessel that contains Zr alloy specimens and H gas. By controlling the initial H gas pressure in the vessel and the temperature profile, target H concentrations from tens of wppm to a few thousands of wppm have been successfully achieved. Following H charging, the H content of the hydrided specimens was measured using the vacuum hot extraction method, by which the samples with desired H concentration were selected for the neutron study. Optical microscopy and SEM show that the hydriding procedure results in uniform distribution of circumferential hydrides across the cladding wall. The hydride density increases as the H concentration in the sample increases. Small angle neutron incoherent scattering (SANIS) and neutron radiography were performed in the High Flux Isotope Reactor at ORNL. Hydrogen has a much larger incoherent scattering cross section compared to other elements in Zr cladding which enables SANIS to nondestructively determine H concentration and distribution in Zr cladding. Our study indicates that a very small amount (~20 wppm) H in commercial Zr cladding can be measured very accurately, with the time required to perform the measurement taking only minutes for a wide range of H concentration. The H content and distribution in a tube sample was obtained by scaling the neutron number with a factor determined by a calibration process using the direct chemical analysis method. This scale factor can be used for future testing of specimens with unknown H concentration, thus providing a nondestructive method for absolute H concentration determination. Neutron imaging and computed tomography for determining the local H distribution in hydrided Zr cladding are under way, and will be reported in the near future.

The temperature dependence of long range atomic diffusion process in the glass-forming liquid metals is, in general, non-Arrhenius. A reason for the non-Arrhenius diffusion process is still not understood even after decades of intense research. Here, we unwind the origin of non-Arrhenius diffusion process by studying Pd-P based metallic glass-forming liquids using quasielastic neutron scattering (QENS) and ab initio molecular dynamic simulation (AMDS). Pd-P based alloys are one of the best metallic glass-forming system and we have studied the atomic diffusion process in Ni80P20, Pd40Ni40P20, Pd40Cu40P20 and Pd43Ni10Cu27P20 alloy liquids over a large temperature range above the melting point. The mean relaxation times obtained from the QENS show large Q dependence and this dependence hold up to a maximum measured Q value in all the alloy liquids. This indicates a cooperative long range atomic diffusion process in all these liquids. Surprisingly, we observed that the temperature dependence of atomic diffusion in the above alloys melts, except Pd40Cu40P20, is non-Arrhenius. The Arrhenius behavior of diffusion process observed in the Pd40Cu40P20 melt cannot be explained by the glass-forming ability (GFA) or fragility of the liquid. The GFA of Pd40Cu40P20 is not as good as Pd40Ni40P20 but much better than Ni80P20. Pd40Ni10Cu27P20 has the highest GFA compared to other alloy liquids. The absolute values of diffusion coefficient and its temperature dependence obtained from the ab initio simulations well agree with QENS results. The liquid structure observed from the simulation shows no medium range ordering in Pd40Cu40P20 melts but Pd40Ni40P20 liquid shows strong icosahedral medium range order and it grew on cooling. The ab initio simulation results clearly indicate that the origin of non-Arrhenius diffusion process is due to the growing icosahedral ordering upon cooling the melts.

Experimental and theoretical studies show that metallic liquids develop significant short- and medium-range topological order with increased supercooling (i.e. lowering the temperature of the liquid below the equilibrium melting temperature). Icosahedral short-range ordering (ISRO) is typically the dominant type of order that is found in most transition metal liquids and their alloys. This structural ordering can have a significant influence on the crystal nucleation barrier, has been identified to play an important role in the glass transition, and is correlated with chemical ordering. Structural evolution also underlies liquid fragility, which is a dynamical property, typically defined from the shear viscosity. X-ray scattering data obtained at the Advanced Photon Source (APS) and elastic neutron scattering data obtained at the Spallation Neutron Source (SNS) are used to illustrate these points. The data were obtained from liquids processed in a containerless high-vacuum using the technique of electrostatic levitation (ESL). The key features of ESL and how they are integrated into a scattering facility are discussed. The Beamline ESL (BESL) that was designed for use at the APS, and a new facility that is now available at the SNS, the Neutron ESL (NESL), are presented.
Supported by the National Science Foundation (DMR-08-56199, DMR 09-59465 and DMR-12-06707) and NASA (NNX07AK27G & NNX10AU19G).

Bulk metallic glasses (BMGs) are complex structural materials, which have been found in an increasing number of technological applications. To determine the nature of excellent glass-forming ability, it is desirable to investigate crystallization kinetics. Although considerable amount of works have been reported, most of them were carried out on multicomponent alloys with complex chemistry. In order to access the physics of crystallization, it is essential to simplify the chemistry. In this paper we report a time-resolved neutron diffraction study of crystallization kinetics in two ternary alloys, with different glass-forming abilities. The measurements were carried out using NOMAD at the Spallation Neutron Source, Oak Ridge National Laboratory (ORNL). The structural evolution in short- and medium- range order (SRO and MRO) during the amorphous-to-crystalline transformation for these BMGs has been well resolved with a time-resolution of ~ 2 minute. For Zr56Cu36Al8 BMG, the crystallization temperature is ~ 751 K, and total neutron diffraction patterns show highly-ordered crystalline phase after divitrification. For Zr46Cu46Al8 BMG, two crystallization temperatures were identified (~ 776 K and ~ 778 K), much like that in Zr52.5Cu17.9Ni14.6Al10Ti5 BMG (BAM-11), an excellent glass former. The crystalline phase of devitrified Zr46Cu46Al8, with better glass-forming ability, is poorly ordered, also similar to BAM-11. These results suggest that crystallization pathways and the kinetics are very different for alloys with different glass-forming abilities.

Inspired by the ubiquitous existence of ionic interactions in nature such as the sacrificial bonds in bones, we have initiated a new program of reconfigurable materials named “Ionic Molecular Glasses (IMG)”. They are conceived by using small tunable organic polyions linked through electrostatic interactions. By modifying the ionic bonds&’ strength and molecular architecture of the building blocks, we are able to tailor the macroscopic properties of the IMGs such as modulus and malleability. We found an even-odd effect of glass transition temperature while systematically changing the backbone length of the ionic molecules. We performed an elastic and quasi-elastic incoherent neutron scattering experiment and determined the mean squared displacement and the relaxation time of the hydrogen atoms of the backbones and the side chains as a function of temperature. Our result suggests that the glass transition temperature, predominately determined by the molecular backbone motions and modified by the side chain motions, is strongly correlated with the molecular symmetry. The understanding of IMGs will guide the design of novel functional materials with promising properties such as intrinsic self-healing capability.

Polymer networks remain an important part of polymer and material science from both theoretical and experimental points of view. One of the continuing challenges in this field lies in developing a fundamental understanding of how network structure affects the physical and mechanical properties of a given system. For hydrogel systems, the current theory that describes these structure/property relationships is based on the assumption of an ideal network. However, real hydrogel networks contain defects, such as multifunctional junctions, dangling ends, and looping chains. The presence of these defects can result in deviations from the theoretically predicted properties (e.g., modulus, mesh size, degradation rate), and could lead to difficulties when developing hydrogels for specific applications.
The group of Dr. Gregory Tew at UMass Amherst has developed a novel cross-linking technique that utilizes thiol-norbornene chemistry to minimize the formation of network defects in polyethylene glycol (PEG)-based hydrogels. The resulting hydrogels are optically clear and display high toughness and resiliency. In collaboration with the Tew group, we have utilized small-angle neutron scattering (SANS) to investigate the network structure of these systems. Four sets of gels were formed based on four different molecular weights of PEG ranging from 35,000 MW (35K) to 4,000 MW (4K), and varying initial polymer concentrations. The hydrogels were swollen to equilibrium in D2O or deuterated dimethylformamide (d-DMF).
Results from these studies reveal that while the same cross-linking technique was used, the resulting hydrogel network structures are dependent upon the molecular weight of the PEG macromer. Hydrogels formed from high MW PEG have nearly ideal network structures, while those formed from low MW PEG have a unique, two-phase network structure. Results suggested that the two-phase structure occurs due to phase separation of the hydrophobic cross-linker during solvent exchange from d-DMF to D2O. To validate this theory, we performed scattering experiments on hydrogels swollen with d-DMF. As expected, the network structures for the hydrogels of the high MW PEG remain similar, while the low MW PEG hydrogels transition from a two-phase network structure to a more ideal one. However, scattering features at low q indicate that some network defects remain for the low MW PEG hydrogels. This result is further supported by the swelling results for these systems. Further investigations of the mechanical and diffusive properties of these systems are ongoing.

The properties of polymer nanocomposites depend intimately on the nanoparticle dispersion, but, unfortunately, the rational control of nanoparticle dispersion in a polymer matrix is difficult. We have found that soft, organic nanoparticles offer opportunities to enhance dispersion of the nanoparticle in a polymer matrix due to the interpenetration of polymer chains and particles and the reduction in the depletion of entropy in the system. Moreover, soft nanoparticles produced by crosslinking single polymer chains offers an opportunity to carefully tune the structure and softness of nanoparticle. This careful control of nanoparticle structure and dispersion enables the examination of the impact of nanoparticle ‘softness&’ and size on the dynamics of the polymer chain in a polymer matrix.
Thus, soft nanoparticles of polystyrene were synthesized via a nano-emulsion synthesis to form polystyrene chains that are intra-molecularly crosslinked with divinyl benzene. Increasing the crosslink density of the polystyrene nanoparticles alters their shape, size and softness from a soft hairy nanoparticle at 1% crosslink density, to a harder dendritic shape at 11% crosslink density. The impact of the presence of the soft nanoparticles on the diffusion coefficient of polystyrene was determined with neutron reflectivity by monitoring the interdiffusion of deuterated and protonated polystyrene bilayers, with and without the soft nanoparticles dispersed throughout both layers. The molecular weights of the polystyrene layers range from 535 kg/mol, 173 kg/mol and 68 kg/mol in order to study how the ratio of the radius of gyration (R_g) of the polymer chain to that of the nanoparticle influences the dynamics of the polystyrene chain. Initial results indicate that the nanoparticles have the most impact on polymer diffusion when R_g(polymer) > R_g (nanoparticle).

Modern optical instruments for visible and synchrotron light use a variety of focusing devices, such as lenses, Fresnel zone plates and mirrors. These devices help increase the signal rate, resolution, or both. Were such powerful optical tools available for neutron scattering, they might bring significant, even transformative, improvements to rate-limited neutron methods and enable new science. We have recently advanced such a tool: grazing-incidence mirrors based on full figures of revolution, often referred to as Wolter mirrors. Latest demonstrations of imaging and SANS instruments equipped with prototype Wolter mirrors will be presented, along with ray-tracing simulations, which show very good agreement with experiments. Simulations demonstrate that it might be possible to increase the signal rate of existing instruments by a factor of 50 or more, if optimized mirrors are used. Such mirrors can be made of Ni using existing technology. Developments of axisymmetric supermirrors will be reported as well. In contrast to existing toroidal or bent-supermirrors neutron focusing devices, axisymmetric optics offer the possibility of a much greater efficiency, by collecting a relatively large solid angle from a diverging beam. Another important benefit of these mirrors is their ability for high-fidelity achromatic imaging. The combination of the high throughput and high fidelity makes this optics capable of transforming neutron imaging and scattering instruments from pinhole cameras into microscopes in the cold to thermal energy range.

The demand for engineered nanomaterials in growing research sectors, such as energy and healthcare products require materials with widely disparate physicochemical properties. We developed in situ electrochemical small-angle neutron scattering (eSANS) to measure simultaneously the electrochemical properties and structural properties of solution-dispersed nanomaterials [1]. The oxidation and reduction (redox) properties of nanomaterials are crucial for catalysis, matching semiconductor band gaps for photovoltaics, as well as toxicology, since they may cause oxidative stress by generating reactive-oxygen species. Optical spectroscopy analysis of species undergoing redox reactions quantifies the electron transfer and energetics of the reaction via potential control and are the most common analytical techniques employed for this purpose. However, with conjugation to organic ligands and smaller particle sizes, engineered nanomaterial redox properties characterization would benefit by techniques that provide nm sensitivity to nanoparticle core and ligand structure. By combining the electrochemical signal with SANS, the structure of engineered nanomaterials are followed, simultaneously in one experiment. Specifically, ZnO nanoparticle and poly(ethyleneglycol)-ZnO (PEG-ZnO) covalent complexes were examined as dispersions in pH buffered deuterium oxide solutions under negative electrode potentials. The ZnO and PEG-ZnO disk-shaped nanoparticles, undergo an irreversible phase transformation upon reduction at the electrode. The decrease in average nanoparticle size near a current maximum shows the reduction reaction from ZnO to Zn occurs. This method provides nm scale sensitivity to the nanoparticle shape changes due to an electrochemical reaction that is crucial to understand in energy and other applications. These experiments utilized the EQ-SANS beamline at the Spallation Neutron Source, Oak Ridge National Laboratory that uniquely provides the ability to follow the redox kinetics under quasi-stationary potential step-scans. The methodology, contrast variation, and scattering properties of the micro and nanoporous carbon electrodes will also be described.
[1] V.M. Prabhu and V. Reipa, J. Phys. Chem. Lett. 3, 646 (2012)

Rechargeable lithium ion batteries are widely used in portable electronic devices. There are several advantages to replacing the organic liquid electrolyte with one based on a polymeric material, most notably the ability to use lithium metal as the anode material. Such “solid polymer electrolytes” or SPEs suffer from low conductivity with significant contribution of the anion. In this talk, the latter issue is addressed by considering a single ion conductor, in which the anion is incorporated in the polymer backbone. The single ion conductor contains a PEO spacer, punctuated by an anion-bearing isophalate group. In “traditional” SPEs ion motion is coupled to segmental mobility of the polymer, and a significant fraction of the lithium ions are solvated by the polymer backbone [single ions], with limited pairing and aggregation. The behavior of the single ion conductors is more complex: single ions, ion pairs, and temperature-dependent aggregation are observed. Polymer mobility is influenced by the amounts of single ions and aggregates, both of which form temporary cross links with the polymer chains. The polymer relaxes in two stages: one related to single ions and corresponding to the spacer midpoint, and one related to ionic aggregates. The slow regions are spatially correlated, leading to “dynamic phase separation”. In some cases, ionic aggregation occurs within the slow regions. Manipulating the single ion conductor to create more single ions does not increase ion mobility, in contrast to the expectation that single ions are the main contributors to conductivity. Instead most highly mobile ions hop between pair states, or along the edges of ion clusters. Within string-like aggregates, mechanisms that move charge without similar movement of ion position are observed.

Fuel cells produce a clean and reliable power by directly converting chemical energy stored in the fuel into electricity. Alkaline Anion Exchange Membranes (AAEMs) are an attractive alternative to proton exchange membranes (PEMs) for fuel cell applications since AAEMs enable the use of less expensive non-noble catalysts (e.g. Ni and Ag). However, the current technologies are limited by low hydroxide ion conductivity, chemical/thermal degradation, and poor mechanical stability. One strategy to overcome these challenges is to exploit block copolymer (BCP) electrolytes where one block domain is functionalized to transport ions and the other is designed to provide mechanical strength. Self-assembled BCP structures are a versatile platform for elucidating fundamental structure-property relationships for designing improved AAEMs.
We conduct in-situ small angle neutron scattering (SANS) experiments on novel poly(vinylbenzyltrimethylammonium bromide) -b- (methylbutylene) ([PVBTMA][Br]-b-PMB) membranes to quantify the swelling and water distribution within the ionic domains as a function of hydration. The degree of bromination and molecular mass of the each block were varied to systematically control the ion exchange capacity and the domain width. To enhance neutron scattering length density contrast between the hydrophilic and hydrophobic domains, 100% deuterated water was used; furthermore the ratio between D2O and H2O was varied in an attempt to find a contrast match condition. At the lowest degrees of bromination, a scattering peak corresponding to an ionomer peak, apart from the structural peaks from the lamellar ordering, became evident above 50% of relative humidity while at the highest Br levels, over 80%, this ionomer peak was absent. This is associated with the formation of ionic clusters meaning that at Br levels above 80%, the hydrophilic domains consist of a nearly continuous ionic channel. We fit the SANS scattering data with a scattering length density to quantify the water concentration profile across the BCP domains. These results indicate that at moderate to high levels of relative humidity there is a highly non-uniform distribution of water in the ion conduction domains, reaching a maximum in the center of the domain. This observation is concomitant with an improved ion transport kinetics for the membrane.

For millennia, wood has been used as a structural material because of its availability and exceptional specific strength. Today, forest products, primarily wood and paper, is a major US industry and accounts for about 5% of US manufacturing GDP. However, the US grows far more wood than is harvested. The accumulation of woody biomass in forests fuels forest fires that cost the US government billions of dollars annually. New applications for this woody biomass are being sought, but a hindrance to researchers is the lack of understanding of wood-water relationships. The molecular-level interactions of water in wood are broadly understood in terms of hydrogen bonding between water and hydroxyl groups on wood polymers, but how water is distributed within the microscopic domains inside the cell walls and what controls the moisture content (MC) are not understood. Because of its ability to probe multiple length scales (1-100 nm) and high sensitivity to anisotropy, we selected small angle neutron scattering (SANS) to better understand wood-water relationships. Loblolly pine (Pinus taeda) sections of 0.5 mm thickness and differing orientations were prepared and deuterated by soaking D2O overnight. The deuterated sections were then placed inside a relative humidity chamber incorporated into the beamline. SANS experiments were performed from 0-100% relative humidity. Preliminary analysis shows (1) a difference in semi-crystalline cellulose elementary fibril spacing between different orientations, and (2) elementary fibril spacing increases at higher relative humidity. This study aims to improve our understanding of how moisture-induced swelling occurs in wood, and what controls the amount of moisture that enters the wood cell walls so forest products with improved moisture-related durability can be developed more efficiently.

Light-harvesting assemblies in nature have many remarkable properties. They utilize subtle structural changes in chromophores and protein assembly templates to guide materials organization into large, mesoscale assemblies that efficiently harvest light, as opposed to uncontrolled aggregates that would suffer from disorder- and defect-induced quenching, much akin to the importance of organization in nanomaterials assembly and function. This work reports on initial steps in producing artificial chromophores on organic scaffolds to develop systems capable of efficient directional energy flow and chemical conversion of light across the optical spectrum. Due to the high affinity of silver cations (Ag+) for DNA bases, following reduction of the Ag+, silver atoms may form short oligonucleotide-encapsulated Ag nanoclusters (<1 nm) without the formation of large particles. Such DNA-templated silver nanoclusters have received significant attention as potential fluorescent labels due to their useful properties, including high molar absorptivities, good quantum yields and photostability, and small size [1-3]. It is thus of great interest to find out the configuration of the Ag nanoclusters which associate with the DNA strands. We have conducted Small Angle Neutron Scattering (SANS) and X-ray Scattering (SAXS) experiments to investigate the formation of the Nanoclusters. By comparing SANS and SAXS data from conjugated samples, pure DNA and DNA/Ag complex, we can characterize the size and position of the Ag clusters along the DNA strand. The time evolution of the DNA/Ag complex can also be studied and can be understood as due to silver oxidation, reduction, or regrouping. We find that the formation and aging of the Ag Nanoclusters are also strongly dependent on the DNA template sequence.
[1] Jaswinder Sharma et al., Nanoscale, 2012, 4, 4107
[2] S.H. Yau et al., Nanoscale, 2012, 4, 4247
[3] M.L. Neidig et al., J. Am. Chem. Soc. 2011, 133, 11837-11839

Solid-state materials with high oxygen ion conductivity at moderate temperatures are of great importance and of much current scientific interest. One of few structures that intercalate oxygen fast belongs to the oxygen deficient Brownmillerite - type. It consists of alternating layers of FeO₄ tetrahedra and FeO₆ octahedra and has 1D ordered vacancy channels in the tetrahedral layers. According to the recent inelastic neutron scattering study the scattering pattern of Brownmillerites polycrystalline sample consists of the acoustic phonons emerging from the Bragg peaks and dominating low-frequency band of optical vibrations merging into acoustic modes [1]. The DFT simulations show that this is a result of large displacements of apical oxygen atoms, which even able to migrate into the vacancy channels of the tetrahedral layer [1]. The oxygen migration in Sr₂Fe₂O₅ is based on structural instabilities and corresponding dynamical fluctuations of oxygen in the tetrahedral chains.
We recently grew the large single crystals of Sr₂Fe₂O₅ and Ca₂Fe₂O₅ by the floating-zone method [2] and perform INS measurements of phonon dispersion curves with triple axis spectrometer TAIPAN at ANSTO [3]. We found that in direction [001] the acoustic transverse mode demonstrates linear behaviour at small phonon wave vectors and flattens up at energy of ~ 6 meV at q > 0.5. The optic mode has unusually low frequency at Brillouin zone centre. At phonon energies below ~ 4 meV the optical mode is overdamped and merges into acoustic intensity. In the overdamped regime phonons are dynamical fluctuations with large amplitude coupled with oxygen migration motions. This gives some indications that that fast oxygen transport kinetics at ambient conditions in Brownmillerite is phonon-assisted.
[1] W. Paulus, et al., J. Am. Chem. Soc., 130 (2008) 16080.
[2] J. Auckett, A. Studer, N. Sharma and C. Ling, Solid State Ionics, 225 (2012) 432.
[3] S. Danilkin and M. Yethiraj, Neutron News, 20 (2009) 37.

Rechargeable batteries such as lithium ion batteries are widely used as power sources for cellular phones, backups and electric vehicles. To improve their performances, it is necessary to elucidate phenomena occurring inside the batteries under operating conditions and to design new batteries based on the analytical results, instead of empirical methods. Batteries are generally sealed and therefore only highly transparent probes can be used to detail the phenomena of the batteries in operation.
Japanese national project for developing innovative batteries, RISING project of NEDO, particularly focuses on neutron- and synchrotron- beam aided in situ analysis and attempts to clarify phenomena inside the batteries.
Neutron diffraction is a powerful tool to analyze battery materials as it can detect both light and heavy elements and has been successful in, for example, site determination of lithium and oxygen in transition metal lithiated compounds. However, the limited time resolution of neutron diffraction has generally been a key issue to apply it to in situ analysis. To clarify the subtle structural changes of battery materials during battery operation, high resolutions of time and d-spacing are both indispensable. For this purpose a new diffractometer called SPICA was installed in J-PARC, Japan. The features and ability of SPICA will be shown together with results obtained by SPICA and synchrotron-beam aided analysis in SPring-8, Japan, to demonstrate the importance of dynamic behavior observation.
Acknowledgment: This work was supported by RISING Project of NEDO.

The increasing demands for alternative energy sources and energy storage systems have created a fast growing global market for rechargeable batteries. Extensive research activities are in progress worldwide aiming to develop reliable, cheap, environmentally benign and high-performance materials for advanced rechargeable batteries. Fundamental materials exploration is critical to achieve the next generation battery technology. Neutrons and X-rays interact with matter in different ways, thus frequently used as complementary tools for studying materials at the electronic, atomic and molecular levels. We have been utilizing neutron and synchrotron x-ray techniques to investigate a large variety of materials for energy applications. In this talk, we will present our recent results on both in-situ and ex-situ studies of battery materials using various neutrons and synchrotron x-ray techniques, including diffraction, imaging and spectroscopy. We will also discuss the challenges in battery materials research, and our future experimental approaches and computational modeling. (Use of the Advanced Photon Source was supported by the U.S. DOE Office of Science under Contract No. DE-AC02-06CH11357.)

The high count rates of modern neutron diffractometers afford the opportunity to collect powder neutron diffraction data at small increments over a wide range of some external variable within a realistic timescale. This allows, for example, the evolution of both nuclear and magnetic structure with temperature to be followed in real time. The value of studies of structure as a function of temperature may be greatly enhanced if relevant bulk properties can be simultaneously investigated, since a more direct correlation of subtle structural changes with physical properties is achieved.
We have sought to couple the collection of powder neutron diffraction patterns as a function of temperature, with the measurement of electrical conduction. Sample cells have been designed and constructed as inserts for standard ISIS furnaces and cryostats. These inserts enable electrical transport properties to be measured over a wide range of temperatures (4.2 le; T/K le; 1000), whilst simultaneously collecting powder diffraction data. The unique properties of the neutron mean that it is thus possible to probe structure, magnetism and transport properties of a material in a single experiment. We have applied the diffraction-resistance technique to a variety of complex metal sulphides, which exhibit discontinuities in the temperature dependence of their electrical conductivity at one or more critical temperatures. The development and construction of these sample cells will be outlined and the new insights diffraction-resistance measurements provide into the structure-property relations of transition-metal sulphides described.

Development of new materials for solid oxide fuel cells (SOFCs) with enhanced electrochemical properties is essential to meet the requirements for low cost, efficient, sustainable energy conversion devices. There has been continuing and growing interest in Ruddlesden-Popper (RP) layered oxides as potential cathodes [1-7], particularly the lanthanide nickelates (LNO, Ln_nNi_n+1O_3n+1), as these materials exhibit fast oxide ion conduction and good electronic conductivity at temperatures of up to 900 °C, and importantly, do not contain Sr, known to deactivate cathode oxygen reduction reactions and increase the area specific resistance of the cell.

Interestingly, the Pr analogue of LNO phases are reported to show better oxide ion conductivity over La based analogues, however questions remain over the stability of the Pr based compounds. This work focuses on variable temperature and atmosphere in situ powder neutron diffraction analysis of the Pr₂NiO_4+d phase in pure and composite material, together with scandia stabilised zirconia (SSZ), allowing determination of phase stability and inter-reactivity.

The neutron data has been corrected for background contributions and fitted by Rietveld refinement, reflecting the expected changes with temperature, but also raising questions about the long term stability of these phases.

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The necessary advancements in solid-state hydrogen storage require an increased knowledge of the both hydrogenation and dehydrogenation mechanisms in canonical systems. This talk will focus on hydrogenation and dehydrogenation studies using in-situ powder diffraction. In these experiments, we have used both synchrotron X-ray and neutron powder diffraction combined with gravimetric to observe, for the first time, the formation and evolution of non-stoichiometric intermediate species in the Li-N-H hydrogen storage system. These observations confirm and expand upon our previously proposed Frenkel defect mechanism for these reactions, showing more complex behaviour than previously expected, and highlight the significant potential of this system.