[Show abstract][Hide abstract] ABSTRACT: Lithium-rich anti-perovskites (LiRAPs), with general formula Li3OX (X = Cl, Br), recently reported as superionic conductors with 3-dimensional Li+ migrating channels, are emerging as promising candidates for solid electrolytes in all-solid-state lithium-ion batteries (LIBs). However, great challenges remain in the fabrication of pure LiRAPs due to difficulties such as low yield, impurity phases, thermodynamic instabilities, and moisture-sensitivity. In this work, we thoroughly studied the formation mechanism of Li3OCl and Li3OBr using various solid-state reaction routes. Different experimental strategies were developed to improve the syntheses, namely, for the purposes of phase stability, phase purity, and large-scale production. One feasible method is to use the strong reducing agents Li metal or LiH to eliminate the OH species. The results show that LiH is more effective than Li metal, mainly due to negatively charged H− and reaction uniformity. The other successful method employs a solid diffusion approach using Li2O and LiX as the starting reagents, thereby avoiding OH entirely; ball milling of reagents under Ar atmosphere was utilized to decrease initial grain size and increase the reaction rate. Fourier transform infrared spectroscopy (FTIR), thermal analyses, and first-principles calculations were performed to give indications on the reaction pathway.
Full-text · Article · Jan 2016 · Solid State Ionics
[Show abstract][Hide abstract] ABSTRACT: The study of mineral–water interfaces is of great importance to a variety of applications including oil and gas extraction, gas subsurface storage, environmental contaminant treatment, and nuclear waste repositories. Understanding the fundamentals of that interface is key to the success of those applications. Confinement of water in the interlayer of smectite clay minerals provides a unique environment to examine the interactions among water molecules, interlayer cations, and clay mineral surfaces. Smectite minerals are characterized by a relatively low layer charge that allows the clay to swell with increasing water content. Montmorillonite and beidellite varieties of smectite were investigated to compare the impact of the location of layer charge on the interlayer structure and dynamics. Inelastic neutron scattering of hydrated and dehydrated cation-exchanged smectites was used to probe the dynamics of the interlayer water (200–900 cm–1 spectral region) and identify the shift in the librational edge as a function of the interlayer cation. Molecular dynamics simulations of equivalent phases and power spectra, derived from the resulting molecular trajectories, indicate a general shift in the librational behavior with interlayer cation that is generally consistent with the neutron scattering results for the monolayer hydrates. Both neutron scattering and power spectra exhibit librational structures affected by the location of layer charge and by the charge of the interlayer cation. Divalent cations (Ba2+ and Mg2+) characterized by large hydration enthalpies typically exhibit multiple broad librational peaks compared to monovalent cations (Cs+ and Na+), which have relatively small hydration enthalpies.
No preview · Article · Nov 2015 · The Journal of Physical Chemistry C
[Show abstract][Hide abstract] ABSTRACT: The forms of water and their thermal stability in bedded salt are crucial in determining the material's suitability for heat-generating nuclear waste storage. Here we show first-of-its-kind incoherent inelastic neutron scattering (IINS) results of bedded salts to distinguish three water environments: intergranular water molecules confined to grain boundaries, water trapped as brine in fluid inclusions, and structural water in intracrystalline hydrous minerals. Sixteen spectral lines can be distinguished unambiguously in the 0-1100 cm(-1) multiphonon and librational domain, yielding an unprecedented high resolution for a natural material. The spectral response to temperature illustrates the bimodality of the technique enabling the intergranular water component to be distinguished from that of brine, shedding light on a nearly 30-year-old problem in characterizing different forms of water in rock salt. This pioneering study shows that IINS provides insight into the cause and effect of moisture migration and its coupling to thermomechanical properties in salt formations. Our results are pertinent to subsurface energy exploration and storage, including nuclear waste storage, in salts.
[Show abstract][Hide abstract] ABSTRACT: The atomic structures of calcium silicate hydrate (C–S–H) and calcium (–sodium) aluminosilicate hydrate (C–(N)–A–S–H) gels, and their presence in conventional and blended cement systems, have been the topic of significant debate over recent decades. Previous investigations have revealed that synthetic C–S–H gel is nanocrystalline and due to the chemical similarities between ordinary Portland cement (OPC)-based systems and low-CO2 alkali-activated slags, researchers have inferred that the atomic ordering in alkali-activated slag is the same as in OPC–slag cements. Here, X-ray total scattering is used to determine the local bonding environment and nanostructure of C(–A)–S–H gels present in hydrated tricalcium silicate (C3S), blended C3S–slag and alkali-activated slag, revealing the large intrinsic differences in the extent of nanoscale ordering between C–S–H derived from C3S and alkali-activated slag systems, which may have a significant influence on thermodynamic stability, and material properties at higher length scales, including long term durability of alkali-activated cements.
No preview · Article · Jan 2015 · Cement and Concrete Research
[Show abstract][Hide abstract] ABSTRACT: In this work, we investigated the systems of (Li, Ca)-O-(Cl, Br) under high pressure and temperature for the synthesis of lithium-rich anti-perovskite (LiRAP) halides. We successfully synthesized Li3-xCax/2OCl anti-perovsldte with x = 0.0, 0.1, 02 near 0.5 GPa and temperatures of 400-425 K and Li3OBr anti-perovskite at 3.0 GPa and 450 K. Different from the synthetic route previously reported at ambient pressure, LiA + 2LiOH --> Li(3)OA + H2O, the LiRAP halides under high P-T conditions are formed by dehydration of end-member and Ca-doped halide hydrates with a general formula of Li(2x + 1)A(OH)(2y), where A can be Cl or Br and x must be equal to y. This proposed formula predicts several new halide hydrates including Li3Cl(OH)(2), Li5Cl(OH)(4), Li3Br(OH)(2), and Li5Br(OH)(4), indicating that halide hydrates are structurally flexible to accommodate a range of lithium and hydroxide occupancies in the puckered layers of [Li2x + (1)(OH)(2y)(+)].
Full-text · Article · Oct 2014 · Inorganic Chemistry Communications
[Show abstract][Hide abstract] ABSTRACT: Anti-perovskite solid electrolyte films were prepared by pulsed laser deposition, and their room-temperature ionic conductivity can be improved by more than an order of magnitude in comparison with its bulk counterpart. The cyclability of Li3OCl films in contact with lithium was evaluated using a Li/Li3OCl/Li symmetric cell, showing self-stabilization during cycling test.
Full-text · Article · Aug 2014 · Chemical Communications
[Show abstract][Hide abstract] ABSTRACT: Amorphous calcium/magnesium carbonates are of significant interest in the technology sector for a range of processes, including carbon storage and biomineralization. Here, the atomic structure of one hydrated amorphous magnesium carbonate (hydrated AMC, MgCO3·3D2O) is investigated using an iterative methodology, where quantum chemistry and experimental total scattering data are combined in an interactive iterative manner to produce an experimentally valid structural representation that is thermodynamically stable. The atomic structure of this hydrated AMC consists of a distribution of Mg2+ coordination states, predominately V- and VI-fold, and is heterogeneous due to the presence of Mg2+/CO32--rich regions interspersed with small ‘pores’ of water molecules. This heterogeneity at the atomic length scale is likely to contribute to the dehydration of hydrated AMC by providing a route for water molecules to be removed. We show that this iterative methodology enables wide sampling of the potential energy landscape, which is important for elucidating the true atomic structure of highly disordered metastable materials.
No preview · Article · Apr 2014 · Chemistry of Materials
[Show abstract][Hide abstract] ABSTRACT: A combination of solid state NMR, neutron vibrational spectroscopy, and volumetric adsorption isotherms have been employed to characterize graphene, hydroxylated graphene, and lithium incorporated graphene and the interaction of molecular hydrogen with them. Recent synthetic activities have produced materials with unique properties and when coupled with our ssNMR measurements the results shed some new light on the surface chemical composition of these materials and the role they play in the hydrogen storage capacity. Graphene is found to have significantly higher hydrogen uptake than graphite and randomly oxidized graphite sheets (graphite oxide). Inelastic neutron scattering (INS) provides direct information concerning hydrogen dynamics. We have used INS to examine how the interaction of hydrogen changes when the graphene surface chemistry changes or when lithium is incorporated at the interface.
[Show abstract][Hide abstract] ABSTRACT: New challenges in neutron scattering result in an increased demand in novel moderator concepts. The most direct way to address the problem would be to change the moderator material itself. However the range of available neutron moderator materials is small. In this paper, we discuss triphenylmethane, a possible moderator material especially promising for cold neutron moderator applications. Our investigations include a parallel experimental and theoretical approach ranging from cross-section measurements and inelastic neutron spectroscopy to molecular modeling.
Full-text · Article · Feb 2014 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
[Show abstract][Hide abstract] ABSTRACT: This study focuses on the interplay of molecular flexibility and hydrogen bonding manifested in the monoclinic (form I) and orthorhombic (form II) polymorphs of paracetamol. By means of incoherent inelastic neutron scattering and density functional theory calculations, the relaxation processes related to the methyl side group reorientation were analysed in detail. Our computational study demonstrates the importance of considering quantum effects to explain how methyl reorientations and subtle conformational changes of the molecule are intertwined. Indeed, by analysing the QENS of the neutron data, we were able to show a unique and complex motional flexibility in form II, reflected by a coupling between the methyl and the phenyl reorientation. This is associated with a higher energy barrier of the methyl rotation and a lower Gibbs free energy, when compared to form I. In conclusion, we put forward the idea that correlating solubility and molecular flexibility, through the relation between pKa and methyl rotation activation energy, might bring new insights to understanding and predicting drug bioavailability.
No preview · Article · Feb 2014 · Molecular Pharmaceutics
[Show abstract][Hide abstract] ABSTRACT: The aim of this work was to describe the vibrations connected with the short hydrogen bonds of differing geometries in 2,4-dinitrobenzoic acid and in 2,4-dinitrobenzoic acid complexed in two ratios with pyridine. All three compounds contain short hydrogen bonds either between two acid molecules (OH⋯⋯O bond) or between acid and pyridine (NH⋯⋯O bonds) or both. We selectively deuterated the proton of the 2,4-dinitrobenzoic acid molecule involved in the proton transfer to aid in the assignment of the H-bond protonic modes. The compounds have been characterized with single crystal X-ray diffraction, CHN elemental analysis, FT-IR and IINS spectroscopy. We show that our combination of analytical methods with DFT calculations represents a fruitful approach to observe the relationship between the geometries of hydrogen bonds and their dynamics.
No preview · Article · Dec 2013 · Chemical Physics
[Show abstract][Hide abstract] ABSTRACT: To study the structural behavior of brucite at high temperature, we conducted in situ neutron diffraction experiments of a deuterated brucite powder sample, Mg(OD)2, in the temperature range 313–583 K. The sample was stable up to 553 K, above which it started to decompose into periclase (MgO) and D2O vapor. Rietveld analyses of the obtained data were performed using both single-site and three-site split-atom hydrogen models. Our results show that with increasing temperature, unit-cell parameter c increases at a rate ~7.7 times more rapidly than a. This large anisotropy of thermal expansion is primarily due to rapid increase in the interlayer thickness along the c-axis on heating. The amplitudes of thermal vibration for Mg, O, and D increase linearly with increasing temperature; however, the rate of the increase for the lighter D is much larger. In addition, D vibrates anisotropically with a higher magnitude within the (001) plane, as confirmed by our first-principles phonon calculations. On heating, the interatomic distances between a given D and its associated O and D from the adjacent [MgO6] layer increase, whereas the O–D bond length decreases. This behavior suggests weakened D···O and D···D interlayer interactions but strengthened O–D bonding with increasing temperature.
No preview · Article · Nov 2013 · Physics and Chemistry of Minerals
[Show abstract][Hide abstract] ABSTRACT: Historically spallation target physics and source design have been associated with nuclear physics and engineering. This is because the prediction of spallation target systems performance requires the use of complex particle transport codes like MCNPX . However these codes usually make use of very simple models to describe neutron transport within the materials used. Most often the free gas model and ideal polycrystallinity are assumed. While these models work well to predict epithermal neutron transport and thermalization behavior in large volumes, they have limitations when it comes to the transport of thermal or cold neutrons, particularly in smaller volumes. Over the last decade the LANSCE spallation physics team has extended its traditional spallation physics activities and has incorporated chemistry and material science into spallation target and moderator design. We will show in this article how LANSCE has already benefited from this process and what opportunities exist for further exploitation of material science in target and moderator design.
[Show abstract][Hide abstract] ABSTRACT: Neutron vibrational spectroscopy, together with adsorption isotherm
measurements, has been employed to investigate interaction of hydrogen
with graphene, hydroxylated graphene, and lithium incorporated graphene.
The adsorption studies of hydrogen on these materials indicate varying
degrees of hydrogen storage capacity. Graphene is found to have
significantly higher hydrogen uptake than graphite and graphite oxide.
Neutron vibrational spectroscopy provides direct information concerning
hydrogen dynamics including the occurrence of the rotational mode at 119
cm-1; slightly below the free rotor position observed for H2 rotation on
graphite. We have also explored how the interaction of hydrogen changes
when hydroxyl groups are attached onto the graphene surface and when
lithium is incorporated into graphene. The outcome of these studies will
also be discussed.
[Show abstract][Hide abstract] ABSTRACT: We will discuss the structural and electrochemical characterization of
the newly synthesized lithium-rich anti-perovskite, Li3OCl.
The crystal structure of this compound was solved using x-ray
diffraction techniques, and the electronic and ionic conductivities were
measured using electrochemical impedance spectroscopy. This material has
an ionic conductivity ranging approximately from 10-4 S/cm to
10-1 S/cm over the temperature range 25^oC to
270^oC (room temperature to just below the melting point).
The high ionic conductivity of this lithium-rich electrolyte demonstates
strong promise that this material is an ideal candidate for solid state
[Show abstract][Hide abstract] ABSTRACT: Density Functional Theory (DFT) calculations were performed. They were firstly implemented to optimize the structure and refine the stoichiometry of the only ternary compound, CuLi0.08Mg1.92 of the Cu-Li-Mg system. Furthermore using DFT, several possible structures of CuMg2Hx were optimized. Since most of the hydrides are cubic structures or can be considered as distortions of a cubic structure, we have started calculations for CuMg2Hx (x = 4 - 6) with tetragonal and monoclinic structures, similar to those of the hydrides formed by the nearest neighbors of Cu and Mg in the periodic table: NiMg2H4 and CoMg2H5 (e.g. monoclinic C2/c and tetragonal P4/nmm, respectively). It can be concluded that the most stable configuration corresponds to CuMg2H5 with C2/c structure. We have performed several neutron scattering experiments that are in agreement with the first principles calculations.
No preview · Article · Nov 2012 · Materials Science Forum