Spallation Neutron Source

Abstract In this paper, we report on a high‐throughput (gram quantities) solvothermal method for the synthesis of copper terephthalate metal–organic frameworks in dmf. While the structure of MOF‐2 and some of the associated polymorphs are well known, we know of no equivalent structural studies for the isostructural copper terephthalate (Cu–tpa). The material we have made crystallizes in the C 2/ m space group. Cu–tpa also exhibits reversible solvent‐exchange properties. These properties make this material useful for potential applications in gas storage and catalysis applications. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

X-ray and neutron diffraction, Raman spectroscopy, complex impedance spectroscopy and electron microscopy were used to characterize the tetragonal <italic>vs.</italic> cubic phase stability in superionic conducting garnet-oxide electrolyte.

Abstract High‐Ni layered oxide cathodes are considered to be one of the most promising cathodes for high‐energy‐density lithium‐ion batteries due to their high capacity and low cost. However, surfice residues, such as NiO‐type rock‐salt phase and Li 2 CO 3 , are often formed at the particle surface due to the high reactivity of Ni 3+ , and inevitably result in an inferior electrochemical performance, hindering the practical application. Herein, unprecedentedly clean surfaces without any surfice residues are obtained in a representative LiNi 0.8 Co 0.2 O 2 cathode by Ti‐gradient doping. High‐resolution transmission electron microscopy (TEM) reveals that the particle surface is composed of a disordered layered phase (≈6 nm in thickness) with the same rhombohedra structure as its interior. The formation of this disordered layered phase at the particle surface is electrochemically favored. It leads to the highest rate capacity ever reported and a superior cycling stability. First‐principles calculations further confirm that the excellent electrochemical performance has roots in the excellent chemical/structural stability of such a disordered layered structure, mainly arising from the improved robustness of the oxygen framework by Ti doping. This strategy of constructing the disordered layered phase at the particle surface could be extended to other high‐Ni layered transition metal oxides, which will contribute to the enhancement of their electrochemical performance.

The high-voltage doped spinel oxides LiMn1.5Ni0.5–xMxO4 (M = Cr, Fe, and Ga; 0 ≤ x ≤ 0.08) synthesized at 900 °C have been investigated systematically before and after postannealing at 700 °C. Neutron diffraction studies reveal that the cation-ordered domain size tends to increase upon annealing at 700 °C. Time-of-flight secondary-ion mass spectroscopy data reveal that the dopant cations M = Cr, Fe, and Ga segregate preferentially to the surface, resulting in a more stable cathode–electrolyte interface and superior cyclability at both room temperature and 55 °C with conventional electrolytes. The doping with Cr and Fe stabilizes the structure with a significant disordering of the cations in the 16d sites even after postannealing at 700 °C, resulting in high rate capability due to low charge-transfer resistance and polarization loss. In contrast, the Ga-doped and undoped LiMn1.5Ni0.5O4 samples experience an increase in cation ordering upon postannealing at 700 °C, resulting in degradation in the rate capability due to an increase in the charge-transfer resistance and polarization loss.

Here we present diffraction data that yield the oxygen-oxygen pair distribution function, g(OO)(r) over the range 254.2-365.9 K. The running O-O coordination number, which represents the integral of the pair distribution function as a function of radial distance, is found to exhibit an isosbestic point at 3.30(5) Å. The probability of finding an oxygen atom surrounding another oxygen at this distance is therefore shown to be independent of temperature and corresponds to an O-O coordination number of 4.3(2). Moreover, the experimental data also show a continuous transition associated with the second peak position in g(OO)(r) concomitant with the compressibility minimum at 319 K.

The defect structure of bulk and nano-indium-tin oxide was investigated by a combination of experimental techniques, including high-resolution synchrotron x-ray diffraction, extended x-ray absorption fine structure, and time-of-flight neutron diffraction on powder specimens. The structural results include atomic positions, cation distributions, and oxygen interstitial populations for oxidized and reduced materials. These structural parameters were correlated with theoretical calculations and in situ electrical conductivity and thermopower measurements as well as existing defect models, with special reference to the model of Frank and Köstlin [G. Frank and H. Köstlin, Appl. Phys. A 27, 197 (1982)].

The observation of neutrons turning into antineutrons would constitute a discovery of fundamental importance for particle physics and cosmology. Observing the n–n̄ transition would show that baryon number (B) is violated by two units and that matter containing neutrons is unstable. It would provide a clue to how the matter in our universe might have evolved from the B=0 early universe. If seen at rates observable in foreseeable next-generation experiments, it might well help us understand the observed baryon asymmetry of the universe. A demonstration of the violation of B–L by 2 units would have a profound impact on our understanding of phenomena beyond the Standard Model of particle physics. Slow neutrons have kinetic energies of a few meV. By exploiting new slow neutron sources and optics technology developed for materials research, an optimized search for oscillations using free neutrons from a slow neutron moderator could improve existing limits on the free oscillation probability by at least three orders of magnitude. Such an experiment would deliver a slow neutron beam through a magnetically-shielded vacuum chamber to a thin annihilation target surrounded by a low-background antineutron annihilation detector. Antineutron annihilation in a target downstream of a free neutron beam is such a spectacular experimental signature that an essentially background-free search is possible. An authentic positive signal can be extinguished by a very small change in the ambient magnetic field in such an experiment. It is also possible to improve the sensitivity of neutron oscillation searches in nuclei using large underground detectors built mainly to search for proton decay and detect neutrinos. This paper summarizes the relevant theoretical developments, outlines some ideas to improve experimental searches for free neutron oscillations, and suggests avenues both for theoretical investigation and for future improvement in the experimental sensitivity.

Recent calculations and experimental data suggest that understanding the local ordering behavior of Ni/Mn will be critical to optimize the electrochemical properties of LiNi0.5Mn1.5O4 (LNMO) high voltage spinel. In this study, we systematically controlled the evolution of Ni and Mn ordering in LNMO samples by annealing them at 700 °C in air for different dwelling times, followed by quenching to room temperature. The long- and short-range ordering behavior of Ni and Mn were analyzed by combining neutron powder diffraction, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) data. The results show that the fraction of ordered phase increases rapidly during initial annealing at 700 °C for 6 h, and accompanied by decreasing amounts of secondary phases. Annealing longer than 6 h led to the growth in size of ordered domains (i.e., increased segregation of ordered and disordered domains) along with a slow increase in the fraction of ordered phase. The dependence of open circuit voltages (OCVs) of the LNMO on the degree of ordering agrees well with recent calculations using the density functional theory. The increase in the degree of ordering increases the open circuit voltage (OCV) and the initial capacity but reduces cycle life and rate capability. The LNMO delivered optimal battery performances (capacity, cycle life, and rate capability) after annealing at 700 °C for 2 h. This partially ordered sample showed the respective advantages from both disordered and ordered spinels: better spinel-phase purity (thus, higher initial capacity) from the ordered LNMO and better cycle life and rate capability from the disordered LNMO. © 2014 American Chemical Society.

Despite extensive efforts in experimental and computational studies, the microscopic understanding of dynamics of biological macromolecules remains a great challenge. It is known that hydrated proteins, DNA and RNA, exhibit a so-called "dynamic transition." It appears as a sharp rise of their mean-squared atomic displacements r2 at temperatures above 200-230 K. Even after a long history of studies, this sudden activation of biomolecular dynamics remains a puzzle and many contradicting models have been proposed. By combining neutron and dielectric spectroscopy data, we were able to follow protein dynamics over an extremely broad frequency range. Our results show that there is no sudden change in the dynamics of the protein at temperatures around approximately 200-230 K. The protein's relaxation time exhibits a smooth temperature variation over the temperature range of 180-300 K. Thus the experimentally observed sharp rise in r2 is just a result of the protein's structural relaxation reaching the limit of the experimental frequency window. The microscopic mechanism of the protein's structural relaxation remains unclear.

Abstract The production of pure deuterium and the removal of tritium from nuclear waste are the key challenges in separation of light isotopes. Presently, the technological methods are extremely energy- and cost-intensive. Here we report the capture of heavy hydrogen isotopes from hydrogen gas by selective adsorption at Cu(I) sites in a metal-organic framework. At the strongly binding Cu(I) sites (32 kJ mol −1 ) nuclear quantum effects result in higher adsorption enthalpies of heavier isotopes. The capture mechanism takes place most efficiently at temperatures above 80 K, when an isotope exchange allows the preferential adsorption of heavy isotopologues from the gas phase. Large difference in adsorption enthalpy of 2.5 kJ mol −1 between D 2 and H 2 results in D 2 -over-H 2 selectivity of 11 at 100 K, to the best of our knowledge the largest value known to date. Combination of thermal desorption spectroscopy, Raman measurements, inelastic neutron scattering and first principles calculations for H 2 /D 2 mixtures allows the prediction of selectivities for tritium-containing isotopologues.

Neutron spin echo (NSE) and small angle neutron scattering (SANS) were used to investigate the correlation between structure and short-time dynamics of lysozyme solutions in the presence of protein clusters as previously reported. It was found that, upon increasing protein concentration, the self-diffusion coefficient at the short time limit becomes much smaller than that of the corresponding hard-sphere and charged colloidal suspensions at the same volume fraction. Contrary to literature conclusions, we find that, at relatively low concentrations, the system consists mostly of monomers or dimers, while, at high concentrations, large dynamic clusters dominate. Our results will benefit the understanding of colloidal systems with both a short-range attraction and an electrostatic repulsion that are ubiquitous in many biologically relevant systems.

Background: The development of cost-competitive biofuels necessitates the realization of advanced biomass pretreatment technologies. Ionic liquids provide a basis for one of the most promising pretreatment technologies and are known to allow effective processing of cellulose and some biomass species. Results & discussion: Here, we demonstrate that the ionic liquid 1-ethyl-3-methyl imidazolium acetate, [C2mim][OAc], induces structural changes at the molecular level in the cell wall of Eucalyptus globulus. Deacetylation of xylan, acetylation of the lignin units, selective removal of guaiacyl units (increasing the syringyl:guaiacyl ratio) and decreased β-ether content were the most prominent changes observed. Scanning electron microscopy images of the plant cell wall sections reveal extensive swelling during [C2mim][OAc] pretreatment. X-ray diffraction measurements indicate a change in cellulose crystal structure from cellulose I to cellulose II after [C2mim][OAc] pretreatment. Enzymatic saccharification of the pretreated material produced increased sugar yields and improved hydrolysis kinetics after [C2mim][OAc] pretreatment. Conclusion: These results provide new insight into the mechanism of ionic liquid pretreatment and reaffirm that this approach may be promising for the production of cellulosic biofuels from woody biomass.

The relaxational dynamics in glass-forming glycerol and glycerol mixed with LiCl is investigated using different neutron scattering techniques. The performed neutron spin echo experiments, which extend up to relatively long relaxation time scales of the order of 10 ns, should allow for the detection of contributions from the so-called excess wing. This phenomenon, whose microscopic origin is controversially discussed, arises in a variety of glass formers and, until now, was almost exclusively investigated by dielectric spectroscopy and light scattering. Here we show that the relaxational process causing the excess wing can also be detected by neutron scattering, which directly couples to density fluctuations.

An amyloid form of the protein α-synuclein is the major component of the intraneuronal inclusions called Lewy bodies, which are the neuropathological hallmark of Parkinson's disease (PD). α-Synuclein is known to associate with anionic lipid membranes, and interactions between aggregating α-synuclein and cellular membranes are thought to be important for PD pathology. We have studied the molecular determinants for adsorption of monomeric α-synuclein to planar model lipid membranes composed of zwitterionic phosphatidylcholine alone or in a mixture with anionic phosphatidylserine (relevant for plasma membranes) or anionic cardiolipin (relevant for mitochondrial membranes). We studied the adsorption of the protein to supported bilayers, the position of the protein within and outside the bilayer, and structural changes in the model membranes using two complementary techniques-quartz crystal microbalance with dissipation monitoring, and neutron reflectometry. We found that the interaction and adsorbed conformation depend on membrane charge, protein charge, and electrostatic screening. The results imply that α-synuclein adsorbs in the headgroup region of anionic lipid bilayers with extensions into the bulk but does not penetrate deeply into or across the hydrophobic acyl chain region. The adsorption to anionic bilayers leads to a small perturbation of the acyl chain packing that is independent of anionic headgroup identity. We also explored the effect of changing the area per headgroup in the lipid bilayer by comparing model systems with different degrees of acyl chain saturation. An increase in area per lipid headgroup leads to an increase in the level of α-synuclein adsorption with a reduced water content in the acyl chain layer. In conclusion, the association of α-synuclein to membranes and its adsorbed conformation are of electrostatic origin, combined with van der Waals interactions, but with a very weak correlation to the molecular structure of the anionic lipid headgroup. The perturbation of the acyl chain packing upon monomeric protein adsorption favors association with unsaturated phospholipids preferentially found in the neuronal membrane.

A pressure-induced phase transition from the fcc to a hexagonal close-packed (hcp) structure was found in NiCoCrFe solid solution alloy starting at 13.5 GPa. The phase transition is very sluggish and the transition did not complete at ∼40 GPa. The hcp structure is quenchable to ambient pressure. Only a very small amount (&amp;lt;5%) of hcp phase was found in the isostructural NiCoCr ternary alloy up to the pressure of 45 GPa and no obvious hcp phase was found in NiCoCrFePd system till to 74 GPa. Ab initio Gibbs free energy calculations indicated the energy differences between the fcc and the hcp phases for the three alloys are very small, but they are sensitive to temperature. The critical transition pressure in NiCoCrFe varies from ∼1 GPa at room temperature to ∼6 GPa at 500 K.

A single-axis acoustic levitator was constructed and used to levitate liquid and solid drops of 1-3 mm in diameter at temperatures in the range -40 to +40 degrees C. The levitator comprised (i) two acoustic transducers mounted on a rigid vertical support that was bolted to an optical breadboard, (ii) an acoustic power supply that controlled acoustic intensity, relative phase of the drive to the transducers, and could modulate the acoustic forces at frequencies up to 1 kHz, (iii) a video camera, and (iv) a system for providing a stream of controlled temperature gas flow over the sample. The acoustic transducers were operated at their resonant frequency of approximately 22 kHz and could produce sound pressure levels of up to 160 dB. The force applied by the acoustic field could be modulated to excite oscillations in the sample. Sample temperature was controlled using a modified Cryostream Plus and measured using thermocouples and an infrared thermal imager. The levitator was installed at x-ray beamline 11 ID-C at the Advanced Photon Source and used to investigate the structure of supercooled liquids.

A bimetallic oxide Ni₃(VO₄)₂ has been synthesized to catalyze the hydrogen storage reaction of MgH₂. The formation of the Mg₂Ni alloy and the kinetic modulation of V results in a dehydrogenation temperature of 210 °C. The NiV₂O₄ intermediate active species is also detected.

Hard carbon stands out as an auspicious anode material for commercial sodium-ion batteries, yet the correlation between plateau-potential capacity and its pore architecture remains poorly understood. In this study, we systematically investigated the sodium-ion storage behavior in hard carbons with tailored pore architecture. The plateau-potential capacity of hard carbon is attributed to the filling of sodium clusters within closed nanopores and open nanopores that are impervious to the solvent molecules of the electrolyte. Small-angle X-ray scattering (SAXS) has been shown to be an effective method for estimating the volume of nanopores that can store sodium clusters. A rapid and user-friendly butanol pycnometry technique is designed to assess the volume of nanopores available for sodium-ion storage. This method has established a linear correlation between the nanopore volume detected and the plateau-potential capacity measured experimentally. We identified two scenarios where the plateau-potential capacity deviates from the congruence linear relationship established by SAXS and butanol pycnometry techniques. First, sodium clusters are unable to fill nanopores larger than 4 nm and could only partially fill those larger than 2 nm. Second, the diffusion of Na+ ions is impeded in graphene nanodomains with tight interlayer spacing and extended crystalline planes.

<italic>In situ</italic> neutron diffraction techniques were utilized to provide detailed information about the crystal structure of <italic>n</italic> = 1, <italic>n</italic> = 2, and <italic>n</italic> = 3 Ruddlesden–Popper structures focusing on the oxygen transport pathways created by localization of oxygen vacancies.

This paper describes the ramp up of the beam power for the Spallation Neutron Source by ramping up the pulse length, the repetition rate, and the beam current emerging from the H(-) source. Starting out with low repetition rates (< or = 10 Hz) and short pulse lengths (< or = 0.2 ms), the H(-) source and low-energy beam transport delivered from Lawrence Berkeley National Laboratory exceeded the requirements with almost perfect availability. This paper discusses the modifications that were required to exceed 0.2 ms pulse length and 0.2% duty factor with acceptable availability and performance. Currently, the source is supporting neutron production at 1 MW with 38 mA linac beam current at 60 Hz and 0.9 ms pulse length. The pulse length will be increased to approximately 1.1 ms to meet the requirements for neutron production with a power between 1 and 1.4 MW. A medium-energy beam transport (MEBT) beam current of 46 mA with a 5.4% duty factor has been demonstrated for 32 h. A 56 mA MEBT beam current with a 4.1% duty factor has been demonstrated for 20 min at the conclusion of a 12-day production run. This is close to the 59 mA needed for 3 MW neutron productions. Also notable is the Cs(2)CrO(4) cesium system, which dispenses approximately 10 mg of Cs during the startup of the ion source, sufficient for producing the required 38 mA for 4 weeks without significant degradation.