L. L. Daemen

Los Alamos National Laboratory, Los Alamos, California, United States

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Publications (163)266.1 Total impact

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    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.
    Chemical communications (Cambridge, England). 08/2014;
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    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.
    Chemistry of Materials. 04/2014; 26(8):2693–2702.
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    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.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 02/2014; 738:1. · 1.14 Impact Factor
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    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.
    Molecular Pharmaceutics 02/2014; · 4.57 Impact Factor
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    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.
    Physics and Chemistry of Minerals 11/2013; · 1.30 Impact Factor
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    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 [1]. 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.
    Neutron News 10/2013; 24(4):24.
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    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 battery applications.
    03/2013;
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    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.
    03/2013;
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    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.
    Chemical Physics 01/2013; · 1.96 Impact Factor
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    ABSTRACT: Prussian Blue Analogs consists of MC6 and AN6 octahedra connected by cyanide ligands (M, A= metals). They typically crystallize in cubic structures. We have studied temperature and field dependence of the magnetization and the susceptibility of 3d-metal Prussian Blue Analogs, namely the hexacyanocobaltates, -ferrates and -chromates. All compounds exhibit modified Curie --Weiss behavior in the paramagnetic region. The observed effective moments of those compounds were compared with the ones of the respective free-ion values. Furthermore, we find evidence that a few of the compounds exhibit a transition to long-range magnetic order at low temperatures.
    10/2012;
  • Yusheng Zhao, Luke L Daemen
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    ABSTRACT: Lithium ion batteries have shown great promise in electrical energy storage with enhanced energy density, power capacity, charge-discharge rates, and cycling lifetimes. However common fluid electrolytes consisting of lithium salts dissolved in solvents are toxic, corrosive, or flammable. Solid electrolytes with superionic conductivity can avoid those shortcomings and work with a metallic lithium anode, thereby allowing much higher energy densities. Here we present a novel class of solid electrolytes with three-dimensional conducting pathways based on lithium-rich anti-perovskites (LiRAP) with ionic conductivity of σ > 10(-3) S/cm at room temperature and activation energy of 0.2-0.3 eV. As temperature approaches the melting point, the ionic conductivity of the anti-perovskites increases to advanced superionic conductivity of σ > 10(-2) S/cm and beyond. The new crystalline materials can be readily manipulated via chemical, electronic, and structural means to boost ionic transport and serve as high-performance solid electrolytes for superionic Li(+) conduction in electrochemistry applications.
    Journal of the American Chemical Society 07/2012; 134(36):15042-7. · 10.68 Impact Factor
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    ABSTRACT: We analyze the interplay between proton transfer in the hydrogen-bond bridge, O···H···O, and lattice dynamics in the model system tetraacetylethane (TAE) (CH(3)CO)(2)CH═CH(COCH(3))(2) using density functional theory. Lattice dynamics calculations and molecular dynamics simulations are validated against neutron scattering data. Hindrance to the cooperative reorientation of neighboring methyl groups at low temperatures gives a preferred O atom for the bridging proton. The amplitude of methyl torsions becomes larger with increasing temperature, so that the free-energy minimum for the proton becomes flat over 0.2 Å. For the isolated molecule, however, we show an almost temperature-independent symmetric double-well potential persists. This difference arises from the much higher barriers to methyl torsion in the crystal that make the region of torsional phase space that is most crucial for symmetrization poorly accessible. Consequently, the proton-transfer potential remains asymmetric though flat at the base, even at room temperature in the solid.
    The Journal of Physical Chemistry A 03/2012; 116(9):2283-91. · 2.77 Impact Factor
  • M. Hartl, L. Daemen, Guenter Muhrer
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    ABSTRACT: Over the last three decades water confined in mesoporous silica has been studied extensively. In the vast majority of these studies the water was loaded after the synthesis, which allows the water to be easily released again from the silica at any given time. While this is an advantage for various applications it is a serious disadvantage if considered as a material for neutron moderators. However, if the water is trapped inside the silica during the synthesis this release process is hindered. It is therefore the aim of this paper to investigate water trapped in silica mesospheres during synthesis and to investigate the properties and the structure of the confined water.
    Microporous and Mesoporous Materials 01/2012; 161:7. · 3.37 Impact Factor
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    ABSTRACT: Liquid and solid methane, due to their thermalization qualities, have often been considered as moderator materials. However, practical experience has shown that at sources that are operated at 10s of KW or more the radiation induces a polymerization process, which makes methane rather complicated to operate. Mesitylene has been discussed oven the last 10 years as a possible substitute for methane. While mesitylene has proven to have a much better radiation resistance than methane, it still shows polymerization. It is hypothesized that if mesitylene is confined the polymerization process can be stopped or at least hindered. Therefore, we have investigated mesitylene confined in silica microspheres. We will present inelastic neutron scattering data, small angle neutron scattering data and tramission measurements on mesitylene confined in silica micro-spheres as well as a measured spectrum of a moderator composed of this material. We will discuss the impact of this confinement on the excitation spectrum of the material and on its total cross-section, as well as its potential usefulness as a moderator material.
    ICANS-XX. 01/2012;
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    ABSTRACT: In the search for moderator materials encapsulated materials have been discussed, but very little is known regarding the effect of encapsulation on neutron moderation properties. As a first step toward a better understanding, we present the measured total neutron cross-section of water confined in silica microspheres and compare the measured data to the predicted theoretical cross-section.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2012; 681:91–93. · 1.14 Impact Factor
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    ABSTRACT: In April 2010 the Mark-3 version of the 1L target, which serves the Manual Lujan Jr. Neutron Scattering Center at the Los Alamos National Laboratory, was installed. In June 2010 the Mark-3 target was then put into production mode. Since then operations and the instrument scientists have been working with this new target for almost two full run cycles and had the chance to gain experience with the new target. Based on these experiences we, in cooperation with the instrument scientists, have compiled metrics (wish lists) for Mark-4 for every flight path at the Lujan Center. In this presentation we will discuss these metrics, how we are planning on addressing them and what challenges we are facing.
    ICANS-XX. 01/2012;
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    ABSTRACT: Modeling the pair distribution function (PDF) of molecular compounds is a challenging task because intra‐ and intermolecular interactions lead to very different features in the PDF. This article discusses the different peak shapes in PDFs of molecular compounds in detail. Moreover, the common methods to calculate PDFs from structural models are summarized and evaluated with respect to molecular systems and an approach to calculate PDFs from molecular crystals more accurately is introduced. p‐Terphenyl was chosen as a test compound. It adopts a crystal structure with disordered features and short‐range order. The short‐range order was previously investigated by analyzing single‐crystal diffuse scattering and it was also extracted from experimental PDFs during this study.
    Journal of Applied Crystallography 01/2012; 45(3). · 3.34 Impact Factor
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    ABSTRACT: Vibrational spectra of the conjugate acid of Me(2)NCH(2)CH(2)CH(2)CH(2)NMe(2) (N,N,N',N'-tetramethylputrescine) have been examined in the gaseous and crystalline phases using Infrared Multiple Photon Dissociation (IRMPD) spectroscopy, Inelastic Neutron Scattering (INS), and high pressure Raman spectroscopy. A band observed near 530 cm(-1) is assigned to the asymmetric stretch of the bridging proton between the two nitrogens, based on deuterium substitution and pressure dependence. The NN distance measured by X-ray crystallography gives a good match to DFT calculations, and the experimental band position agrees with the value predicted from theory using a 2-dimensional potential energy surface. The reduced dimensionality potential energy surface, which treats the ion as though it possesses a linear NHN geometry, shows low barriers to proton transit from one nitrogen to the other, with zero point levels close to the barrier tops. In contrast, two other related systems containing strong hydrogen bonds do not exhibit the same spectroscopic signature of a low barrier hydrogen bond (LBHB). On the one hand, the IRMPD spectra of the conjugate acid ions of the amino acid N,N,N',N'-tetramethylornithine (in which the two nitrogens have different basicities) show fewer bands and no comparable isotopic shifts in the low frequency domain. On the other hand, the IRMPD spectrum of the shorter homologue Me(2)NCH(2)CH(2)CH(2)NMe(2) (N,N,N',N'-tetramethyl-1,3-propanediamine), for which the NHN bond angle deviates substantially from linearity, displays more than one band in the 1100-1400 cm(-1) domain, which vanish as a consequence of deuteration.
    Physical Chemistry Chemical Physics 12/2011; 13(45):20380-92. · 3.83 Impact Factor
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    ABSTRACT: Prussian Blue Analogs consists of MC6 and AN6 octahedra connected by cyanide ligands (M, A= metals). They typically crystallize in cubic structures. We have studied temperature and field dependence of the magnetization and the susceptibility of selected Prussian Blue Analogs such as hexacyanocobaltates, -ferrates and -chromates. All compounds exhibit modified Curie --Weiss behavior in the paramagnetic region. The observed effective moments of those compounds were compared with the ones of the respective free-ion values. Furthermore, we find evidence that a few of the compounds exhibit a transition to long-range magnetic order at low temperatures.
    10/2011;
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    ABSTRACT: We have investigated the dynamics of the very short hydrogen bond (RO...O = 2.430 Å) of the pyridine N-oxide trichloroacetic acid complex in the solid state by combining vibrational spectroscopy using inelastic neutron scattering with extensive computational studies and analysis of the vibrational spectra. The Density Functional Theory (DFT) computational models used ranged from the isolated gas phase cluster to three approaches with periodic boundary conditions, namely CRYSTAL, CPMD and VASP, all of which, however calculate frequencies in the harmonic approximation. While all but the gas phase calculation yield structural parameters for the hydrogen bond in reasonable agreement with experiment, only the periodic VASP and CPMD approaches resulted in INS spectra (calculated with the program a-climax) that adequately reproduced some of the key features of the experimental spectrum related to the in-plane and out-of-plane bending modes of the H-bond. No clear indication was found either in experiment or computational studies for OH stretching. More sophisticated and time-consuming calculations are therefore indicated to elaborate on the hydrogen bond dynamics including molecular dynamics simulations or the use of quantum dynamics on multidimensional potential energy surfaces.
    Acta Chimica Slovenica 09/2011; 58(3):521-7. · 1.14 Impact Factor

Publication Stats

534 Citations
266.10 Total Impact Points

Institutions

  • 1995–2014
    • Los Alamos National Laboratory
      • • Los Alamos Neutron Science Center
      • • Lujan Neutron Scattering Center
      Los Alamos, California, United States
  • 2012
    • University of Nevada, Las Vegas
      • Department of Physics and Astronomy
      Las Vegas, NV, United States
  • 2010
    • Институт физики высоких энергий
      Protvino, Moskovskaya, Russia
  • 2008–2010
    • CSU Mentor
      • Department of Chemistry and Biochemistry
      Long Beach, California, United States
    • Lawrence Livermore National Laboratory
      Livermore, California, United States
    • University of Rome Tor Vergata
      • Dipartimento di Fisica
      Roma, Latium, Italy
  • 2009
    • Stanford University
      • Department of Geological and Environmental Sciences
      Stanford, CA, United States
  • 2008–2009
    • Arizona State University
      • • Department of Chemistry and Biochemistry
      • • Department of Physics
      Mesa, AZ, United States
  • 2007
    • Los Alamos Medical Center
      Los Alamos, New Mexico, United States
  • 2005
    • University of Chicago
      Chicago, Illinois, United States