Sample records for 2sesub 4sub 4sesub

  1. Thermodynamic Model for the Solubility of Ba(SeO4sub>, SO4sub>) Precipitates

    SciTech Connect

    Rai, D.; Felmy, Andrew R.; Moore, Dean A.; Kitamura, Akira; Yoshikawa, Hideki; Doi, Reisuke; Yoshida, Yasushi


    The solubility of Ba(SeO4sub>, SO4sub>) precipitates was determined as a function of the BaSeO4sub> mole fractions, ranging from 0.0015 to 0.3830, and time with an equilibration period extending to as long as 302 days. Equilibrium/steady state conditions in this system are reached in ≤ 65 days. Pitzer’s ion interaction model was used to calculate solid and aqueous phase activity coefficients. Thermodynamic analyses showed that the data do not satisfy Gibbs-Duhem equation, thereby demonstrating that a single-solid solution phase does not control both the selenate and sulfate concentrations. Our extensive data with log 10 [Ba] ranging from -3.6 to -5.9 mol kg-1, log 10 [SeO4sub>] rangingfrom-3.6 to -5.2 mol kg-1, and log 10 [SO4sub>] ranging from-4.0 to -5.3 mol kg-1 can be explained with the formation of an ideal BaSeO4sub> solid solution phase that controls the selenium concentrations and a slightly disordered/less-crystalline BaSO4sub>(s) (log 10Κ°sp = -9.5 instead of -10.05 for barite) that controls the sulfate concentrations. In these experiments the BaSO4sub> component of the solid solution phase never reaches thermodynamic equilibrium with the aqueous phase. Thermodynamic interpretations of the data show that both the ideal BaSeO4sub> solid solution phase and less-crystalline BaSO4sub> (s) phase are in equilibrium with each other in the entire range of BaSeO4sub> mole fractions investigated in this study.

  2. Solvate Structures and Computational/Spectroscopic Characterization of LiBF4sub> Electrolytes

    SciTech Connect

    Seo, D. M.; Boyle, Paul D.; Allen, Joshua L.; Han, Sang D.; Jonsson, Erlendur; Johansson, Patrik; Henderson, Wesley A.


    Crystal structures have been determined for both LiBF4sub> and HBF4sub> solvates—(acetonitrile)2:LiBF4sub>, (ethylene glycol diethyl ether)1:LiBF4sub>, (diethylene glycol diethyl ether)1:LiBF4sub>, (tetrahydrofuran)1:LiBF4, (methyl methoxyacetate)1:LiBF4sub>, (suc-cinonitrile)1:LiBF4sub>, (N,N,N',N",N"-pentamethyldiethylenetriamine)1:HBF4sub>, (N,N,N',N'-tetramethylethylenediamine)3/2:HBF4sub> and (phenanthroline)2:HBF4sub>. These, as well as other known LiBF4sub> solvate structures, have been characterized by Raman vibrational spectroscopy to unambiguously assign the anion Raman band positions to specific forms of BF4sub>-...Li+ cation coordination. In addition, complementary DFT calculations of BF4sub>-...Li+ cation complexes have provided additional insight into the challenges associated with accurately interpreting the anion interactions from experimental Raman spectra. This information provides a crucial tool for the characterization of the ionic association interactions within electrolytes.

  3. Structural study of the ammonium octafluoroneptunate, [NH4sub>]4sub>NpF8

    SciTech Connect

    Poineau, Frederic; Silva, Chinthaka M.; Yeamans, Charles B.; Cerefice, Gary S.; Sattelberger, Alfred P.; Czerwinski, Kenneth R.


    The [NH4sub>]4sub>NpF8 salt was prepared from the solid-state reaction of NpO2 with NH4sub>HF2 and characterized by powder X-ray diffraction and X-ray absorption fine structure spectroscopy. The diffraction results confirm the compound to be isostructural to [NH4sub>]4sub>UF8 with the following lattice parameter (a = 13.054(4) Å, b = 6.681(2) Å, c = 13.676(5) Å, ß = 121.14 Å). For the first time, a Neptunium fluoride complex has been characterized by XAFS spectroscopy. The energy position of the white line and inflection of the XANES spectra of [NH4sub>]4sub>NpF8 are consistent with the presence of Np(IV). Adjustment of the EXAFS spectra indicates that the coordination number (7.4±1.5) and the average Np-F distance (2.26(1) Å) are consistent with the presence of the NpF8 dodecahedron. The average Np-F distance is ~0.02 Å shorter than the U-F distance in [NH4sub>]4sub>UF8 and is a result of the actinide contraction.

  4. Hybridization gap in the semiconducting compound SrIr4sub>In2Ge4sub>

    SciTech Connect

    Calta, Nicholas P.; Im, Jino; Fang, Lei; Chasapis, Thomas C.; Bugaris, Daniel E.; Chung, Duck Young; Kwok, Wai -Kwong; Kanatzidis, Mercouri G.


    Here, large single crystals of SrIr4sub>In2Ge4sub> were synthesized using the In flux method. This compound is a hybridization gap semiconductor with an experimental optical band gap of Eg = 0.25(3) eV. It crystallizes in the tetragonal EuIr4sub>In2Ge4sub> structure type with space group 1$\\overline{4}$2m and unit cell parameters a = 6.9004(5) Å and c = 8.7120(9) Å. The electronic structure is very similar to both EuIr4sub>In2Ge4sub> and the parent structure Ca3Ir4sub>Ge4sub>, suggesting that these compounds comprise a new family of hybridization gap materials that exhibit indirect gap, semiconducting behavior at a valence electron count of 60 per formula unit, similar to the Heusler alloys.

  5. Dirac node arcs in PtSn4sub>

    SciTech Connect

    Wu, Yun; Wang, Lin -Lin; Mun, Eundeok; Johnson, D. D.; Mou, Daixiang; Huang, Lunan; Lee, Yongbin; Bud’ko, S. L.; Canfield, P. C.; Kaminski, Adam


    In topological quantum materials1,2,3 the conduction and valence bands are connected at points or along lines in the momentum space. A number of studies have demonstrated that several materials are indeed Dirac/Weyl semimetals4,5,6,7,8. However, there is still no experimental confirmation of materials with line nodes, in which the Dirac nodes form closed loops in the momentum space2,3. Here we report the discovery of a novel topological structure—Dirac node arcs—in the ultrahigh magnetoresistive material PtSn4sub> using laser-based angle-resolved photoemission spectroscopy data and density functional theory calculations. Unlike the closed loops of line nodes, the Dirac node arc structure arises owing to the surface states and resembles the Dirac dispersion in graphene that is extended along a short line in the momentum space. Here, we propose that this reported Dirac node arc structure is a novel topological state that provides an exciting platform for studying the exotic properties of Dirac fermions.

  6. Molecular and electronic structure of Re2Br4sub>(PMe3)4sub>

    SciTech Connect

    Johnstone, Erik V.; Poineau, Frederic; Todorova, Tanya K.; Forster, Paul M.; Sorensen, Lasse K.; Fdez. Galvan, Ignacio; Lindh, Roland; Czerwinski, Kenneth R.; Sattelberger, Alfred P.


    The dinuclear rhenium(II) complex Re2Br4sub>(PMe3)4sub> was prepared from the reduction of [Re2Br8]2– with (n-Bu4sub>N)BH4sub> in the presence of PMe3 in propanol. The complex was characterized by single-crystal X-ray diffraction (SCXRD) and UV–visible spectroscopy. It crystallizes in the monoclinic C2/c space group and is isostructural with its molybdenum and technetium analogues. The Re–Re distance (2.2521(3) Å) is slightly longer than the one in Re2Cl4sub>(PMe3)4sub> (2.247(1) Å). The molecular and electronic structure of Re2X4sub>(PMe3)4sub> (X = Cl, Br) were studied by multiconfigurational quantum chemical methods. The computed ground-state geometry is in excellent agreement with the experimental structure determined by SCXRD. The calculated total bond order (2.75) is consistent with the presence of an electron-rich triple bond and is similar to the one found for Re2Cl4sub>(PMe3)4sub>. The electronic absorption spectrum of Re2Br4sub>(PMe3)4sub> was recorded in benzene and shows a series of low-intensity bands in the range 10 000–26 000 cm–1. The absorption bands were assigned based on calculations of the excitation energies with the multireference wave functions followed by second-order perturbation theory using the CASSCF/CASPT2 method. As a result, calculations predict that the lowest energy band corresponds to the δ* → σ* transition, while the next higher energy bands were attributed to the δ* → π*, δ → σ*, and δ → π* transitions.

  7. Solution-processable glass LiI-Li4sub>SnS4sub> superionic conductors for all-solid-state Li-ion batteries

    SciTech Connect

    Kern Ho Park; Oh, Dae Yang; Choi, Young Eun; Nam, Young Jin; Han, Lili; Kim, Ju -Young; Xin, Huolin; Lin, Feng; Oh, Seung M.; Jung, Yoon Seok


    The new, highly conductive (4.1 × 10–4 S cm–1 at 30 °C), highly deformable, and dry-air-stable glass 0.4LiI-0.6Li4sub>SnS4sub> is prepared using a homogeneous methanol solution. Furthermore, the solution process enables the wetting of any exposed surface of the active materials with highly conductive solidified electrolytes (0.4LiI-0.6Li4sub>SnS4sub>), resulting in considerable improvements in electrochemical performances of these electrodes over conventional mixture electrodes.

  8. U(v) in Metal Uranates. A Combined Experimental And Theoretical Study of MgUO4sub>, CrUO4sub> and FeUO4sub>

    SciTech Connect

    Guo, Xiaofeng; Tiferet, Eitan; Qi, Liang; Solomon, J.; Lanzirotti, Anthony; Newville, Mathew; Engelhard, Mark H.; Kukkadapu, Ravi K.; Wu, Di; Ilton, Eugene S.; Asta, Mark D.; Sutton, Steve; Xu, Hongwu; Navrotsky, Alexandra


    Pentavalent uranium can exist in aqueous solution, but its presence in the solid state is uncommon. Metal monouranates, MgUO4sub>, CrUO4sub> and FeUO4sub> were synthesized for detailed structural and energetic investigations. Structural characteristics of these uranates used powder X-ray diffraction, synchrotron X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and 57Fe-Mössbauer spectroscopy. Enthalpies of formation were measured by high temperature oxide melt solution calorimetry. Density functional theory (DFT) calculations provided both structural and energetic information. The measured structural and thermodynamic properties show good consistency with those predicted from DFT. Moreover, the presence of U5+ has been solidly confirmed in CrUO4sub> and FeUO4sub>, which are thermodynamically stable compounds, and the origin and stability of U5+ in the system was elaborated by DFT. The structural and thermodynamic behaviour of U5+ elucidated in this work is relevant to fundamental actinide redox chemistry and to applications in the nuclear industry and radioactive waste disposal.

  9. U(v) in metal uranates: A combined experimental and theoretical study of MgUO4sub>, CrUO4sub>, and FeUO4sub>

    SciTech Connect

    Guo, Xiaofeng; Tiferet, Eitan; Qi, Liang; Solomon, Jonathan M.; Lanzirotti, Antonio; Newville, Matthew; Engelhard, Mark H.; Kukkadapu, Ravi K.; Wu, Di; Ilton, Eugene S.; Asta, Mark; Sutton, Stephen R.; Xu, Hongwu; Navrotsky, Alexandra


    Although pentavalent uranium can exist in aqueous solution, its presence in the solid state is uncommon. Metal monouranates, MgUO4sub>, CrUO4sub> and FeUO4sub> were synthesized for detailed structural and energetic investigations. Structural characteristics of these uranates used powder X-ray diffraction, synchrotron X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and 57Fe-Mossbauer spectroscopy. Enthalpies of formation were measured by high temperature oxide melt solution calorimetry. Density functional theory (DFT) calculations provided both structural and energetic information. The measured structural and thermodynamic properties show good consistency with those predicted from DFT. The presence of U5+ has been solidly confirmed in CrUO4sub> and FeUO4sub>, which are thermodynamically stable compounds, and the origin and stability of U5+ in the system was elaborated by DFT. Lastly, the structural and thermodynamic behaviour of U5+ elucidated in this work is relevant to fundamental actinide redox chemistry and to applications in the nuclear industry and radioactive waste disposal.

  10. Characterization of uranium tetrafluoride (UF4sub>) with Raman spectroscopy

    SciTech Connect

    Villa-Aleman, Eliel; Wellons, Matthew S.


    The Raman spectrum of uranium tetrafluoride (UF4sub>) is unambiguously characterized with multiple Raman excitation laser sources for the first time. Across different laser excitation wavelengths, UF4sub> demonstrates 16 distinct Raman bands within the 50-400 cm-1 region. The observed Raman bands are representative of various F-F vibrational modes. UF4sub> also shows intense fluorescent bands in the 325 – 750 nm spectral region. Comparison of the UF4sub> spectrum with the ZrF4sub> spectrum, its crystalline analog, demonstrates a similar Raman band structure consistent with group theory predictions for expected Raman bands. Additionally, a demonstration of combined scanning electron microscopy (SEM) and in situ Raman spectroscopy microanalytical measurements of UF4 sub>particulates shows that despite the inherent weak intensity of Raman bands, identification and characterization are possible for micron-sized particulates with modern instrumentation. The published well characterized UF4sub> spectrum is extremely relevant to nuclear materials and nuclear safeguard applications.

  11. Revealing the Restructured Surface of Li[Mn2]O4sub>

    SciTech Connect

    Amos, Charles D.; Roldan, Manuel A.; Varela, Maria; Goodenough, John B.; Ferreira, Paulo J.


    The spinel Revealing the Restructured Surface of Li[Mn2]O4sub> is a candidate cathode for a Li-ion battery, but its capacity fades over a charge/discharge cycle of Li1–x[Mn2]O4sub> (0 < x < 1) that is associated with a loss of Mn to the organic-liquid electrolyte. It is known that the disproportionation reaction 2Mn3+ = Mn2+ + Mn4+ occurs at the surface of a Mn spinel, and it is important to understand the atomic structure and composition of the surface of Revealing the Restructured Surface of Li[Mn2]O4sub> in order to understand how Mn loss occurs. We report a study of the surface reconstruction of Revealing the Restructured Surface of Li[Mn2]O4sub> by aberration-corrected scanning transmission electron microscopy. The atomic structure coupled with Mn-valence and the distribution of the atomic ratio of oxygen obtained by electron energy loss spectroscopy reveals a thin, stable surface layer of Mn3O4sub>, a subsurface region of Li1+x[Mn2]O4sub> with retention of bulk Li[Mn2]O4sub>. We conclude that this observation is compatible with the disproportionation reaction coupled with oxygen deficiency and a displacement of surface Li+ from the Mn3O4sub> surface phase. These results provide a critical step toward understanding how Mn is lost from Li[Mn2]O4sub>, once inside a battery.

  12. Synthesis of silicated hydroxyapatite Ca{sub 10}(PO{sub 4}){sub 6-x}(SiO{sub 4}){sub x}(OH){sub 2-x}

    SciTech Connect

    Palard, Mickael; Champion, Eric Foucaud, Sylvie


    The preparation of silicated hydroxyapatite Ca{sub 10}(PO{sub 4}){sub 6-x}(SiO{sub 4}){sub x}(OH){sub 2-x} (SiHA) with 0{<=}x{<=}2 was investigated using a wet precipitation method followed by a heat treatment. X-ray diffraction and Rietveld refinement, Fourier transformed IR (FTIR) spectroscopy, elemental analyses, transmission electron microscopy and thermal analyses were used to characterize the samples. The raw materials were composed of a partially silicated and carbonated apatite and a secondary minor phase containing the excess silicon. Single phase silicated hydroxyapatites, with 0{<=}x{<=}1, could be synthesized after a thermal treatment of the raw powders above 700 deg. C. The presence of carbonate groups in the raw apatite played an important role in the incorporation of silicates during heating. From the different results, the mechanisms of formation of SiHA are discussed. - Graphical abstract: The preparation of pure silicated hydroxyapatite Ca{sub 10}(PO{sub 4}){sub 6-x}(SiO{sub 4}){sub x}(OH){sub 2-x} powders with controlled silicon content was investigated. The synthesis route included a precipitation in aqueous media. It required an additional high temperature solid-state reaction to fully incorporate the silicon into the apatite crystals.

  13. Aqueous Sulfate Separation by Sequestration of [(SO4sub>)2(H2O)4sub>]4sub> Clusters within Highly Insoluble Imine-Linked Bis-Guanidinium Crystals

    SciTech Connect

    Custelcean, Radu; Williams, Neil J.; Seipp, Charles A.; Ivanov, Aleksandr; Bryantsev, Vyacheslav


    Quantitative removal of sulfate from seawater was achieved by selective crystallization of the anion with a bis(guanidinium) ligand self-assembled in situ through imine condensation of simple components. The resulting crystalline salt has an exceptionally low aqueous solubility, on a par with BaSO4sub>. Single-crystal X-ray diffraction analysis revealed pairs of sulfate anions clustered together with four water molecules within the crystals.

  14. Native defects in Tl6SI4sub>: Density functional calculations

    SciTech Connect

    Shi, Hongliang; Du, Mao -Hua


    In this study, Tl6SI4sub> is a promising room-temperature semiconductor radiation detection material. Here, we report density functional calculations of native defects and dielectric properties of Tl6SI4sub>. Formation energies and defect levels of native point defects and defect complexes are calculated. Donor-acceptor defect complexes are shown to be abundant in Tl6SI4sub>. High resistivity can be obtained by Fermi level pinning by native donor and acceptor defects. Deep donors that are detrimental to electron transport are identified and methods to mitigate such problem are discussed. Furthermore, we show that mixed ionic-covalent character of Tl6SI4sub> gives rise to enhanced Born effective charges and large static dielectric constant, which provides effective screening of charged defects and impurities.

  15. Origin of modulated phases and magnetic hysteresis in TmB4sub>

    SciTech Connect

    Wierschem, Keola; Sunku, Sai Swaroop; Kong, Tai; Ito, Toshimitsu; Canfield, Paul C.; Panagopoulos, Christos; Sengupta, Pinaki


    In this study, we investigate the low-temperature magnetic phases in TmB4sub>, a metallic quantum magnet on the geometrically frustrated Shastry-Sutherland lattice, using coordinated experimental and theoretical studies. Our results provide an explanation for the appearance of the intriguing fractional plateau in TmB4sub> and accompanying magnetic hysteresis. Together with observation of the bump in the half plateau, our results support the picture that the magnetization plateau structure in TmB4sub> is strongly influenced by the zero-field modulated phases. We present a phenomenological model to explain the appearance of the modulated phases and a microscopic Hamiltonian that captures the complete magnetic behavior of TmB4sub>.

  16. The hydrogen permeability of Pd4sub>S

    SciTech Connect

    O’Brien, Casey P.; Gellman, Andrew J.; Morreale, Bryan D.; Miller, James B.


    Hydrogen permeates rapidly through pure Pd membranes, but H2S, a common minor component in hydrogencontaining streams, produces a Pd4sub>S film on the Pd surface that severely retards hydrogen permeation. Hydrogen still permeates through the bi-layered Pd4sub>S/Pd structure, indicating that the Pd4sub>S surface is active for H2 dissociation; the low hydrogen permeability of the Pd4sub>S film is responsible for the decreased rate of hydrogen transport. In this work, the hydrogen permeability of Pd4sub>S was determined experimentally in the 623-773 K temperature range. Bi-layered Pd4sub>S/Pd foils were produced by exposing pure Pd foils to H2S. H2 fluxes through the bi-layered Pd4sub>S/Pd foils were measured during exposure to both pure H2 and a 1000 ppm H2S in H2 gas mixture. Our results show that H2S slows hydrogen permeation through Pd mainly by producing a Pd4S film on the Pd surface that is roughly an order-of-magnitude less permeable to hydrogen (kPd4S = 10-7.5 exp(-0.22 eV/kBT)molH2/m/s/Pa-1/2) than pure Pd. The presence of H2S in the gas stream results in greater inhibition of hydrogen transport than can be explained by the very low permeability of Pd4sub>S. H2S may block H2 dissociation sites at the Pd4sub>S surface.

  17. The role of carbonic anhydrase in C4sub> photosynthesis

    SciTech Connect

    Studer, Anthony


    Current pressures on the global food supply have accelerated the urgency for a second green revolution using novel and sustainable approaches to increase crop yield and efficiency. This proposal outlines experiments to address fundamental questions regarding the biology of C4sub> photosynthesis, the method of carbon fixation utilized by the most productive food, feed and bioenergy crops. Carbonic anhydrase (CA) has been implicated in multiple cellular functions including nitrogen metabolism, water use efficiency, and photosynthesis. CA catalyzes the first dedicated step in C4sub> photosynthesis, the hydration of CO2 into bicarbonate, and is potentially rate limiting in C4sub> grasses. Using insertional mutagenesis, we have generated CA mutants in maize, and propose the characterization of these mutants using phenotypic, physiological, and transcriptomic profiling to assay the plant’s response to altered CA activity. In addition, florescent protein tagging experiments will be employed to study the subcellular localization of CA paralogs, providing critical data for modeling carbon fixation in C4sub> plants. Finally, I propose parallel experiments in Setaria viridis to explore its relevance as model C4sub> grass. Using a multifaceted approach, this proposal addresses important questions in basic biology, as well as the need for translation research in response to looming global food challenges.

  18. Electrochemical and Solid-State Lithiation of Graphitic C 3 N 4sub>

    SciTech Connect

    Veith, Gabriel M.; Baggetto, Loïc; Adamczyk, Leslie A.; Guo, Bingkun; Brown, Suree S.; Sun, Xiao-Guang; Albert, Austin A.; Humble, James R.; Barnes, Craig E.; Bojdys, Michael J.; Dai, Sheng; Dudney, Nancy J.


    : Lithiated graphitic carbon n.itride (C3N4sub> ) was fabricated by electrochemical and solid-state reactions. The addition of Li to C3N4sub> results in a reaction between the Li and the graphite-like C3N species in C3N4sub>. This irreversible reaction leads to the formation of Li-CH=NR and Li-N=CR2 species, which are detrimental to anode properties. Suitable nitrogen-doped carbon structures for anode applications are predicted to need high concentrations of pyridinic C-N-C terminal bonds and low concentrations of w quaternary C3N species to boost electronic conductivity and reversibly cycle Li ions.

  19. Integrated Data Collection Analysis (IDCA) Program - KClO4sub>/Aluminum Mixture

    SciTech Connect

    Sandstrom, Mary M.; Brown, Geoffrey W.; Preston, Daniel N.; Pollard, Colin J.; Warner, Kirstin F.; Sorensen, Daniel N.; Remmers, Daniel L.; Whinnery, LeRoy L.; Shelley, Timothy J.; Reyes, Jose A.; Hsu, Peter C.; Reynolds, John G.


    The Integrated Data Collection Analysis (IDCA) program is conducting a Proficiency Test for Small-Scale Safety and Thermal (SSST) testing of homemade explosives (HMEs). Described here are the results for impact, friction, electrostatic discharge, and differential scanning calorimetry analysis of a mixture of KClO4sub> and aluminum—KClO4sub>/Al mixture. This material was selected because of the challenge of performing SSST testing of a mixture of two solids. The mixture was found to be: 1) much less sensitive to impact than RDX, (LLNL being the exception) and PETN, 2) more sensitive to friction than RDX and PETN, and 3) extremely sensitive to spark. The thermal analysis showed little or no exothermic character. One prominent endothermic feature was observed in the temperature range studied and identified as a phase transition of KClO4sub>.

  20. Novel Solution Process for Fabricating Ultra-Thin-Film Absorber Layers in Fe2SiS4sub> and Fe2GeS4sub> Photovoltaics

    SciTech Connect

    Orefuwa, Samuel A.; Lai, Cheng-Yu; Dobson, Kevin D.; Ni, Chaoying; Radu, Daniela R.


    Fe2SiS4sub> and Fe2GeS4sub> crystalline materials posses direct bandgaps of ~1.55 and ~1.4 eV respectively and an absorption coefficient larger than 10^5 cm–1; their theoretical potential as solar photovoltaic absorbers has been demonstrated. However, no solar devices that employ either Fe2SiS4sub> or Fe2GeS4sub> have been reported to date. In the presented work, nanoprecursors to Fe2SiS4sub> and Fe2GeS4sub> have been fabricated and employed to build ultra-thin-film layers via spray coating and rod coating methods. Temperature-dependent X-Ray diffraction analyses of nanoprecursors coatings show an unprecedented low temperature for forming crystalline Fe2SiS4sub> and Fe2GeS4sub>. Fabricating of ultra-thin-film photovoltaic devices utilizing Fe2SiS4sub> and Fe2GeS4sub> as solar absorber material is presented.

  1. Characterization of nanosized Al{sub 2}(WO{sub 4}){sub 3}

    SciTech Connect

    Nihtianova, D.; Velichkova, N.; Nikolova, R.; Koseva, I.; Yordanova, A.; Nikolov, V.


    Graphical abstract: TEM method allows to detect small quantities of impurities not detectable by other methods. In our case impurities of W{sub 5}O{sub 14} are detected in Al{sub 2}(WO{sub 4}){sub 3} nanopowder. Highlights: {yields} Nanosized Al{sub 2}(WO{sub 4}){sub 3} by simple co-precipitation method. {yields} Spherical particles with mean size of 22 nm distributed between 10 and 40 nm at 630 {sup o}C. {yields} XRD, DTA and TEM confirm well defined products with perfect structure. {yields} TEM locality allows detection of impurities not detectable by XRD and DTA. -- Abstract: Nanosized aluminum tungstate Al{sub 2}(WO{sub 4}){sub 3} was prepared by co-precipitation reaction between Na{sub 2}WO{sub 4} and Al(NO{sub 3}){sub 3} aqueous solutions. The powder size and shape, as well as size distribution are estimated after different conditions of powder preparation. The purity of the final product was investigated by XRD and DTA analyses, using the single crystal powder as reference. Between the specimen and the reference no difference was detected. The crystal structure of Al{sub 2}(WO{sub 4}){sub 3} nanosized powder was confirmed by TEM (SAED, HRTEM). In additional, TEM locality allows to detect some W{sub 5}O{sub 14} impurities, which are not visible by conventional X-ray powder diffraction and thermal analyses.

  2. The superionic phase transitions in (NH{sub 4}){sub 3}H(SeO{sub 4}){sub 2} under hydrostatic pressure up to 400 MPa

    SciTech Connect

    Lindner, Ł.; Zdanowska-Frączek, M. Pawłowski, A.; Frączek, Z. J.


    The effect of hydrostatic pressure on proton conductivity of (NH{sub 4}){sub 3}H(SeO{sub 4}){sub 2} superionic crystal was studied in a wide temperature range and different isobaric conditions by means of impedance spectroscopy method. The measurements were performed along the trigonal c axis of the crystal, i.e., along the direction perpendicular to the plane in which, in the superionic phases, a dynamically disordered H-bond network is formed. The obtained pressure-temperature phase diagram is linear with increasing pressure. The triple point, which is the point of coexistence of the three phases: ferroelastic phase IV, ferroelastic phase III, and superionic phase II was found at p = 116.3 MPa and T = 287.3 K. High pressure leads to increase in the temperature range of stability of both superionic phases and to a drastic decrease in the temperature width of the ferroelastic phase III. With increasing pressure, the range of the superionic phase II expands at the expense of the range of the ferroelastic phase III, which is unstable and vanishes at the triple point.

  3. Shape resonances in the photoionization of CF4sub>

    SciTech Connect

    Stephens, J. A.; Dill, Dan; Dehmer, Joseph L.


    Calculations of photoionization cross sections and photoelectron angular distributions have been performed for all occupied orbitals of CF4sub> using the multiple-scattering model. Results are compared with very recent experiments which employ synchrotron radiation to measure these quantities, namely the measurements of Truesdale e t a l. for the carbonK shell, and measurements of Carlson e t a l. and Novak e t a l. for the five outermost valence levels. The calculations predict intense shape resonances below 3 eV in continua of a1 and t2 final state symmetry. Qualitative agreement is attained on comparing much of the theory with experiment, notably the five outer valence levels, which serves to establish a one-electron picture of the photoionization dynamics of CF4sub>.

  4. Sub-nanosecond Yb:KLu(WO4sub>)2 microchip laser.


    Loiko, P; Serres, J M; Mateos, X; Yumashev, K; Yasukevich, A; Petrov, V; Griebner, U; Aguiló, M; Díaz, F


    A diode-pumped Yb:KLu(WO4sub>)2 microchip laser passively Q-switched by a Cr4+:YAG saturable absorber generated a maximum average output power of 590 mW at 1031 nm with a slope efficiency of 55%. The pulse characteristics were 690 ps/47.6 μJ at a pulse repetition frequency of 12.4 kHz. The output beam had an excellent circular profile with M2<1.05. Yb:KLu(WO4sub>)2 is very promising for ultrathin sub-ns microchip lasers.

  5. First-principles calculated decomposition pathways for LiBH4sub> nanoclusters

    SciTech Connect

    Huang, Zhi -Quan; Chen, Wei -Chih; Chuang, Feng -Chuan; Majzoub, Eric H.; Ozolins, Vidvuds


    Here, we analyze thermodynamic stability and decomposition pathways of LiBH4sub> nanoclusters using grand-canonical free-energy minimization based on total energies and vibrational frequencies obtained from density-functional theory (DFT) calculations. We consider (LiBH4sub>)n nanoclusters with n = 2 to 12 as reactants, while the possible products include (Li)n, (B)n, (LiB)n, (LiH)n, and Li2BnHn; off-stoichiometric LinBnHm (m ≤ 4n) clusters were considered for n = 2, 3, and 6. Cluster ground-state configurations have been predicted using prototype electrostatic ground-state (PEGS) and genetic algorithm (GA) based structural optimizations. Free-energy calculations show hydrogen release pathways markedly differ from those in bulk LiBH4sub>. While experiments have found that the bulk material decomposes into LiH and B, with Li2B12H12 as a kinetically inhibited intermediate phase, (LiBH4sub>)n nanoclusters with n ≤ 12 are predicted to decompose into mixed LinBn clusters via a series of intermediate clusters of LinBnHm (m ≤ 4n). The calculated pressure-composition isotherms and temperature-pressure isobars exhibit sloping plateaus due to finite size effects on reaction thermodynamics. Generally, decomposition temperatures of free-standing clusters are found to increase with decreasing cluster size due to thermodynamic destabilization of reaction products.

  6. Topotactic insertion of lithium in the layered structure Li{sub 4}VO(PO{sub 4}){sub 2}: The tunnel structure Li{sub 5}VO(PO{sub 4}){sub 2}

    SciTech Connect

    Satya Kishore, M.; Pralong, V. Caignaert, V.; Malo, S.; Hebert, S.; Varadaraju, U.V.; Raveau, B.


    A new V(III) lithium phosphate Li{sub 5}VO(PO{sub 4}){sub 2} has been synthesized by electrochemical insertion of lithium into Li{sub 4}VO(PO{sub 4}){sub 2}. This phase, which crystallizes in the space group I4/mcm, exhibits a tunnel structure closely related to the layered structure of Li{sub 4}VO(PO{sub 4}){sub 2} and to the tunnel structure of VO(H{sub 2}PO{sub 4}){sub 2}. The topotactic reactions that take place during lithium exchange and intercalation, starting from VO(H{sub 2}PO{sub 4}){sub 2} and going to the final phase Li{sub 5}VO(PO{sub 4}){sub 2} are explained on the basis of the flexible coordinations of V{sup 4+} and V{sup 3+} species. The electrochemical and magnetic properties of this new phase are also presented and explained on the basis of the structure dimensionality. - Graphical abstract: Electrochemical synthesis of a new 3D V(III) lithium phosphate, Li{sub 5}VO(PO{sub 4}){sub 2}. Starting from the 2D Li{sub 4}VO(PO{sub 4}){sub 2}, the topotactic reaction that take place during lithium intercalation is explained on the basis of the flexible coordinations of V{sup 4+} and V{sup 3+} species.

  7. Mild hydrothermal synthesis, crystal structure, thermal behavior, spectroscopic and magnetic properties of the (NH{sub 4})[Fe(AsO{sub 4}){sub 1-x}(PO{sub 4}){sub x}F] (x=0.3, 0.6, 0.8) series. Thermal transformation of (NH{sub 4})[Fe(AsO{sub 4}){sub 0.7}(PO{sub 4}){sub 0.3}F] into the textural porous orthorhombic Fe(AsO{sub 4}){sub 0.7}(PO{sub 4}){sub 0.3}

    SciTech Connect

    Berrocal, Teresa


    The (NH{sub 4})[Fe(AsO{sub 4}){sub 1-x}(PO{sub 4}){sub x}F] (x=0.3, 0.6, 0.8) series of compounds has been synthesized under mild hydrothermal conditions. The compounds crystallize in the orthorhombic Pna2{sub 1} space group, with the unit-cell parameters a=13.1718(1), b=6.5966(6), c=10.797(1) A for x=0.3; a=13.081(1), b=6.5341(6), c=10.713(1) A for x=0.6 and a=13.0329(9), b=6.4994(4), c=10.6702(6) A for x=0.8, with the volumes 938.6(1), 915.7(1) and 903.8(1) A{sup 3}, respectively, with Z=8. Single crystals of (NH{sub 4})[Fe(AsO{sub 4}){sub 0.7}(PO{sub 4}){sub 0.3}F] heated under air atmosphere at 465 deg. C remain as single crystals, changing the composition to Fe(AsO{sub 4}){sub 0.7}(PO{sub 4}){sub 0.3}. This later phase belongs to the orthorhombic Imam space group, with the unit cell parameters a=13.328(2), b=6.5114(5), c=10.703(1) A, V=928.9(2) A{sup 3} and Z=12. The crystal structure of the ammonium phases consists of a KTP three-dimensional framework constructed by chains formed by alternating Fe(2)O{sub 4}F{sub 2} or Fe(1)O{sub 4}F{sub 2} octahedra and As/P(2)O{sub 4} or As/P(1)O{sub 4} tetrahedra, respectively. These octahedra and tetrahedra are linked by a common oxygen vertex. The chains run along the 'a' and 'b' crystallographic axes. The crystal structure of Fe(AsO{sub 4}){sub 0.7}(PO{sub 4}){sub 0.3} is a three-dimensional skeleton derived from that of the precursor, formed from (100) sheets stacked along the [001] direction, and interconnected by chains of alternating Fe(2)O{sub 6} octahedra and As/P(2)O{sub 4} tetrahedra sharing a vertex in the 'a' direction. Transmission electronic microscopy of this compound indicates the existence of unconnected external cavities with a BET surface area of 3.91(3) m{sup 2} g{sup -1}. The diffuse reflectance spectra in the visible region show the forbidden electronic transitions characteristic of the Fe(III) d{sup 5}-high spin cation in slightly distorted octahedral geometry, for all the compounds. The ESR spectra

  8. Crystal Chemistry of Electrochemically and Chemically Lithiated Layered αI-LiVOPO4sub>

    SciTech Connect

    He, Guang; Bridges, Craig A.; Manthiram, Arumugam


    LiVOPO4sub> is an attractive cathode for lithium-ion batteries with a high operating voltage and the potential to achieve the reversible insertion of two lithium ions between VOPO4sub> and Li2VOPO4sub>. Among the three known forms of LiVOPO4sub> (α, β, and αI), the αI-LiVOPO4sub> has a layered structure that could promote better ionic mobility and reversibility than others. However, a comprehensive study of its lithiated product is not available as αI-LiVOPO4sub> is metastable and difficult to prepare by conventional approaches. We present here a facile synthesis of highly crystalline αI-LiVOPO4sub> and αI-LiVOPO4sub>/rGO nanocomposite by a microwave-assisted solvothermal method and its electrochemical/chemical lithiation. The LiVOPO4sub>/rGO cathodes exhibit a high reversible capacity of 225 mAh g–1, indicating the insertion of more than one lithium into VOPO4sub>. Both electrochemical and chemical lithiation imply a solid-solution reaction mechanism on inserting the second lithium into αI-LiVOPO4sub>, but a two-phase reaction feature could also occur under certain conditions such as insufficient time for equilibration of Li+ diffusion in the structure. The fully lithiated new αI-Li2VOPO4sub> phase was characterized by combined Rietveld refinement of neutron diffraction and X-ray diffraction data and by bond-valence sum maps. The results suggest that αI-Li2VOPO4sub> retains the tetragonal P4/nmm symmetry of the parent αI-LiVOPO4sub> structure, where the second lithium ions are located in the lithium layers rather than in the VOPO4sub> layers

  9. C4sub> and CAM Plant Biology Symposium 2013 Website

    SciTech Connect

    Leakey, Andrew D. B.


    This project funded the C4sub> and CAM (crassulacean acid metabolism) Plant Biology 2013 symposium, held at the University of Illinois at Urbana-Champaign, IL, on August 6-9, 2013. The symposium brought together a diverse group of scientists to discuss the evolution, ecology, functional biology, genomics and biotechnological engineering of C4sub> and CAM plants. These two groups of plants possess evolutionary modifications to their photosynthetic machinery that improve their performance in hot and dry conditions. Maize and pineapple are classic examples of C4sub> and CAM plants, respectively. The meeting discussed how lessons learned from these groups of plants can be harnessed to improve crop production of biofuel feedstocks in an era of global climate change. The interdisciplinary nature of the meeting meant that the delegation members typically do not collectively attend any one scientific society meeting. As a result, the symposium was a unique opportunity for knowledge transfer, initiation of new collaborations, and recruitment and exposure of early career scientists.

  10. Quaternary (FeIn{sub 2}S{sub 4}){sub x}(MnIn{sub 2}S{sub 4}){sub 1-x} alloys and photosensitive structures on their basis

    SciTech Connect

    Bodnar, I. V.; Rud, V. Yu.; Rud, Yu. V.; Lozhkin, D. V.


    Using directional crystallization of the melt of the (FeIn{sub 2}S{sub 4}){sub x}(MnIn{sub 2}S{sub 4}){sub 1-x} alloy, homogeneous crystals of a similar atomic composition are grown over the entire range of compositions 1 {>=} x {>=} 0. It is established that the crystals of the continuous series of quaternary alloys in the range x = 0-1 crystallize in the spinel structure and lattice parameter a linearly depends on x. It is established that it is possible to obtain In(Al)/(FeIn{sub 2}S{sub 4}){sub x}(MnIn{sub 2}S{sub 4}){sub 1-x} photosensitive structures. Room-temperature spectra of relative quantum efficiency of photoconversion of the In(Al)/(FeIn{sub 2}S{sub 4}){sub x}(MnIn{sub 2}S{sub 4}){sub 1-x} structures fabricated for the first time are obtained. From the analysis of these spectra, activation energies of direct and indirect band-to-band transitions for the crystals of the (FeIn{sub 2}S{sub 4}){sub x}(MnIn{sub 2}S{sub 4}){sub 1-x} alloys are determined and the dependence of these parameters on the composition of the position-disordered phases of mentioned alloys is discussed. It is concluded that the crystals of the (FeIn{sub 2}S{sub 4}){sub x}(MnIn{sub 2}S{sub 4}){sub 1-x} alloys can be used in broadband photoconverters of optical radiation.

  11. Neutron diffraction studies of the Na-ion battery electrode materials NaCoCr{sub 2}(PO{sub 4}){sub 3}, NaNiCr{sub 2}(PO{sub 4}){sub 3}, and Na{sub 2}Ni{sub 2}Cr(PO{sub 4}){sub 3}

    SciTech Connect

    Yahia, H. Ben; Essehli, R.; Avdeev, M.; Park, J-B.; Sun, Y-K.; Al-Maadeed, M.A.; Belharouak, I.


    The new compounds NaCoCr{sub 2}(PO{sub 4}){sub 3}, NaNiCr{sub 2}(PO{sub 4}){sub 3}, and Na{sub 2}Ni{sub 2}Cr(PO{sub 4}){sub 3} were synthesized by sol-gel method and their crystal structures were determined by using neutron powder diffraction data. These compounds were characterized by galvanometric cycling and cyclic voltammetry. NaCoCr{sub 2}(PO{sub 4}){sub 3}, NaNiCr{sub 2}(PO{sub 4}){sub 3}, and Na{sub 2}Ni{sub 2}Cr(PO{sub 4}){sub 3} crystallize with a stuffed α-CrPO{sub 4}-type structure. The structure consists of a 3D-framework made of octahedra and tetrahedra that are sharing corners and/or edges generating channels along [100] and [010], in which the sodium atoms are located. Of significance, in the structures of NaNiCr{sub 2}(PO{sub 4}){sub 3}, and Na{sub 2}Ni{sub 2}Cr(PO{sub 4}){sub 3} a statistical disorder Ni{sup 2+}/Cr{sup 3+} was observed on both the 8g and 4a atomic positions, whereas in NaCoCr{sub 2}(PO{sub 4}){sub 3} the statistical disorder Co{sup 2+}/Cr{sup 3+} was only observed on the 8g atomic position. When tested as negative electrode materials, NaCoCr{sub 2}(PO{sub 4}){sub 3}, NaNiCr{sub 2}(PO{sub 4}){sub 3}, and Na{sub 2}Ni{sub 2}Cr(PO{sub 4}){sub 3} delivered specific capacities of 352, 385, and 368 mA h g{sup −1}, respectively, which attests to the electrochemical activity of sodium in these compounds. - Highlights: • NaCoCr{sub 2}(PO{sub 4}){sub 3}, NaNiCr{sub 2}(PO{sub 4}){sub 3}, and Na{sub 2}Ni{sub 2}Cr(PO{sub 4}){sub 3} were synthesized by sol-gel method. • The crystal structures were determined by using neutron powder diffraction data. • The three compounds crystallize with a stuffed α-CrPO{sub 4}-type structure. • The three compounds were tested as anodes in sodium-ion batteries. • Relatively high specific capacities were obtained for these compounds.

  12. Integrated Data Collection Analysis (IDCA) Program - KClO4sub>/Carbon Mixture

    SciTech Connect

    Sandstrom, Mary M.; Brown, Geoffrey W.; Preston, Daniel N.; Pollard, Colin J.; Warner, Kirstin F.; Sorensen, Daniel N.; Remmers, Daniel L.; Shelley, Timothy J.; Reyes, Jose A.; Hsu, Peter C.; Reynolds, John G.


    The Integrated Data Collection Analysis (IDCA) program is conducting a proficiency study for Small- Scale Safety and Thermal (SSST) testing of homemade explosives (HMEs). Described here are the results for impact, friction, electrostatic discharge, and differential scanning calorimetry analysis of a mixture of KClO4sub> and activated carbon—KClO4sub>/C mixture. This material was selected because of the challenge of performing SSST testing of a mixture of two solids. The mixture was found to be insensitive to impact, friction, and thermal stimulus, and somewhat sensitive to spark discharge. This effort, funded by the Department of Homeland Security (DHS), ultimately will put the issues of safe handling of these materials in perspective with standard military explosives. The study is adding SSST testing results for a broad suite of different HMEs to the literature. Ultimately the study has the potential to suggest new guidelines and methods and possibly establish the SSST testing accuracies needed to develop safe handling practices for HMEs. Each participating testing laboratory uses identical test materials and preparation methods wherever possible. Note, however, the test procedures differ among the laboratories. The results are compared among the laboratories and then compared to historical data from various sources. The testing performers involved for the KClO4sub>/carbon mixture are Lawrence Livermore National Laboratory (LLNL), Los Alamos National Laboratory (LANL), Indian Head Division, Naval Surface Warfare Center, (NSWC IHD), and Air Force Research Laboratory (AFRL/RXQL). These tests are conducted as a proficiency study in order to establish some consistency in test protocols, procedures, and experiments and to understand how to compare results when these testing variables cannot be made consistent.

  13. Discovery of a metastable Al20Sm4sub> phase

    SciTech Connect

    Ye, Z.; Zhang, F.; Sun, Y.; Mendelev, M. I.; Ott, R. T.; Park, E.; Besser, M. F.; Kramer, M. J.; Ding, Z.; Wang, C. -Z.; Ho, K. -M.


    In this study, we present an efficient genetic algorithm, integrated with experimental diffraction data, to solve a nanoscale metastable Al20Sm4sub> phase that evolves during crystallization of an amorphous magnetron sputtered Al90Sm10 alloy. The excellent match between calculated and experimental X-ray diffraction patterns confirms an accurate description of this metastable phase. Molecular dynamic simulations of crystal growth from the liquid phase predict the formation of disordered defects in the devitrified crystal.

  14. Integrated Data Collection Analysis (IDCA) program--KClO4sub>/Dodecane Mixture

    SciTech Connect

    Sandstrom, Mary M.; Brown, Geoffrey W.; Preston, Daniel N.; Pollard, Colin J.; Warner, Kirstin F.; Sorensen, Daniel N.; Remmers, Daniel L.; Shelley, Timothy J.; Reyes, Jose A.; Hsu, Peter C.; Reynolds, John G.


    The Integrated Data Collection Analysis (IDCA) program is conducting a proficiency study for Small- Scale Safety and Thermal (SSST) testing of homemade explosives (HMEs). Described here are the results for impact, friction, electrostatic discharge, and differential scanning calorimetry analysis of a mixture of KClO4sub> and dodecane—KClO4sub>/dodecane mixture. This material was selected because of the challenge of performing SSST testing of a mixture of solid and liquid materials. The mixture was found to: 1) be less sensitive to impact than RDX, and PETN, 2) less sensitive to friction than RDX and PETN, and 3) less sensitive to spark than RDX and PETN. The thermal analysis showed little or no exothermic features suggesting that the dodecane volatilized at low temperatures. A prominent endothermic feature was observed and assigned to a phase transition of KClO4sub>. This effort, funded by the Department of Homeland Security (DHS), ultimately will put the issues of safe handling of these materials in perspective with standard military explosives. The study is adding SSST testing results for a broad suite of different HMEs to the literature. Ultimately the study has the potential to suggest new guidelines and methods and possibly establish the SSST testing accuracies needed to develop safe handling practices for HMEs. Each participating testing laboratory uses identical test materials and preparation methods wherever possible. Note, however, the test procedures differ among the laboratories. The results are compared among the laboratories and then compared to historical data from various sources. The testing performers involved for the KClO4sub>/dodecane mixture are Lawrence Livermore National Laboratory (LLNL), Los Alamos National Laboratory (LANL), Indian Head Division, Naval Surface Warfare Center, (NSWC IHD), and Air Force Research Laboratory (AFRL/RXQL). These tests are conducted as a proficiency study in order to establish some

  15. Elasticity and magnetocaloric effect in MnFe4sub>Si3

    SciTech Connect

    Herlitschke, Marcus; Klobes, B.; Sergueev, I.; Hering, Paul; Persson, Joerg; Hermann, Raphael P.


    The room temperature magnetocaloric material MnFe4sub>Si3 was investigated with nuclear inelastic scattering (NIS) and resonant ultrasound spectroscopy (RUS) at different temperatures and applied magnetic fields in order to assess the infuence of the magnetic transition and the magnetocaloric effect on the lattice dynamics. The NIS data give access to phonons with energies above 3 meV, whereas RUS probes the elasticity of the material in the MHz frequency range and thus low energy, ~5 neV, phonon modes. A significant infuence of the magnetic transition on the lattice dynamics is observed only in the low energy region. Here, MnFe4sub>Si3 and other compounds in the Mn5-xFexSi3 series were also investigated with vibrating sample magnetometry, resistivity measurements and Moessbauer spectroscopy in order to study the magnetic transitions and to complement the obtained results on the lattice dynamics.

  16. A dispersive treatment of Kl4sub> decays

    SciTech Connect

    Colangelo, Gilberto; Passemar, Emilie; Stoffer, Peter


    Kl4sub> decays offer several reasons of interest: they allow an accurate measurement of ππ-scattering lengths; they provide the best source for the determination of some low-energy constants of xPT; one form factor is directly related to the chiral anomaly, which can be measured here. We present a dispersive treatment of Kl4sub> decays that provides a resummation of ππ- and Kπ-rescattering effects. In addition, the free parameters of the dispersion relation are fitted to the data of the high-statistics experiments E865 and NA48/2. The matching toxPT at NLO and NNLO enables us to determine the LECs Lr1, Lr2 and Lr3. With recently published data from NA48/2, the LEC Lr9 can be determined as well. In contrast to a pure chiral treatment, the dispersion relation describes the observed curvature of one of the form factors, which we understand as a rescattering effect beyond NNLO.

  17. Synthesis, structure, and optical properties of CsU{sub 2}(PO{sub 4}){sub 3}

    SciTech Connect

    Oh, George N.; Ringe, Emilie; Van Duyne, Richard P.; Ibers, James A.


    CsU{sub 2}(PO{sub 4}){sub 3} was synthesized in highest yield by the reaction in a fused-silica tube of U, P, and Se in a CsCl flux at 1273 K. It crystallizes with four formula units in space group P2{sub 1}/n of the monoclinic system in a new structure type. The structure of CsU{sub 2}(PO{sub 4}){sub 3} is composed of U and Cs atoms coordinated by PO{sub 4}{sup 3-} units in distorted octahedral arrangements. Each U atom corner shares with six PO{sub 4}{sup 3-} units. Each Cs atom face shares with one, edge shares with two, and corner shares with three PO{sub 4}{sup 3-} units. The structure shares some features with the sodium zirconium phosphate structure type. X-ray powder diffraction results demonstrate that the present CsU{sub 2}(PO{sub 4}){sub 3} compound crystallizes in a structure different from the previously reported {beta} Prime - and {gamma}-CsU{sub 2}(PO{sub 4}){sub 3} compounds. CsU{sub 2}(PO{sub 4}){sub 3} is highly pleochroic, as demonstrated by single-crystal optical absorption measurements. - Graphical abstract: Stacking of the layers in CsU{sub 2}(PO{sub 4}){sub 3}, viewed along [100]. Highlights: Black-Right-Pointing-Pointer Compound CsU{sub 2}(PO{sub 4}){sub 3} crystallizes in a new structure type. Black-Right-Pointing-Pointer Structure shares some features with the sodium zirconium phosphate structure type. Black-Right-Pointing-Pointer CsU{sub 2}(PO{sub 4}){sub 3} is highly pleochroic, as demonstrated by single-crystal optical absorption measurements.

  18. Theoretical kinetics of O + C2H4sub>

    SciTech Connect

    Li, Xiaohu; Jasper, Ahren W.; Zádor, Judit; Miller, James A.; Klippenstein, Stephen J.


    The reaction of atomic oxygen with ethylene is a fundamental oxidation step in combustion and is prototypical of reactions in which oxygen adds to double bonds. For 3O+C2H4sub> and for this class of reactions generally, decomposition of the initial adduct via spin-allowed reaction channels on the triplet surface competes with intersystem crossing (ISC) and a set of spin-forbidden reaction channels on the ground-state singlet surface. The two surfaces share some bimolecular products but feature different intermediates, pathways, and transition states. In addition, the overall product branching is therefore a sensitive function of the ISC rate. The 3O+C2H4sub> reaction has been extensively studied, but previous experimental work has not provided detailed branching information at elevated temperatures, while previous theoretical studies have employed empirical treatments of ISC. Here we predict the kinetics of 3O+C2H4sub> using an ab initio transition state theory based master equation (AITSTME) approach that includes an a priori description of ISC. Specifically, the ISC rate is calculated using Landau–Zener statistical theory, consideration of the four lowest-energy electronic states, and a direct classical trajectory study of the product branching immediately after ISC. The present theoretical results are largely in good agreement with existing low-temperature experimental kinetics and molecular beam studies. Good agreement is also found with past theoretical work, with the notable exception of the predicted product branching at elevated temperatures. Above ~1000 K, we predict CH2CHO+H and CH2+CH2O as the major products, which differs from the room temperature preference for CH3+HCO (which is assumed to remain at higher temperatures in some models) and from the prediction of a previous detailed master equation study.

  19. Heat capacity and neutron diffraction studies on the frustrated magnetic Co{sub 2}(OH)(PO{sub 4}){sub 1-x}(AsO{sub 4}){sub x} [0{<=}x{<=}1] solid solution

    SciTech Connect

    Pedro, I. de; Rojo, J.M.; Rodriguez Fernandez, J.; Sanchez Marcos, J.; Fernandez-Diaz, M.T.; Rojo, T.


    The Co{sub 2}(OH)(PO{sub 4}){sub 1-x}(AsO{sub 4}){sub x} [0{<=}x{<=}1] solid solution exhibits a complex magnetic behaviour due to the bond-frustration in its magnetic structure. Heat capacity measurements of the (x=0.1-0.5) phases show a three-dimensional magnetic ordering ({lambda} anomaly) that shifts to lower temperatures and becomes broader as the AsO{sub 4}{sup 3-} content increases. For x=0.75, no significant feature was observed whereas for higher arsenate ion content, x=0.9 and 1, a small maximum was detected. The magnetic structures of solid solution are consistent with the existence of predominant antiferromagnetic superexchange interactions through the |OH| and |XO{sub 4}| (X=P and As) groups between the Co{sup +2} ions. The substitution of PO{sub 4}{sup 3-} by AsO{sub 4}{sup 3-} anions by more than 90% substantially modifies the magnetic exchange pathways in the solid solution, leading to an incommensurate antiferromagnetic structure in Co{sub 2}(OH)(PO{sub 4}){sub 1-x}(AsO{sub 4}){sub x} [x=0.9 and 1] phases. - Graphical abstract: Magnetic structures of Co{sub 2}(OH)(PO{sub 4}){sub 1-x}(AsO{sub 4}){sub x} [0{<=}x{<=}1]. The ordering of the magnetic moments of Co{sup 2+} is in c direction for the two crystallographic positions (dimers and chains) in all compounds. The unit cell is surrounded by a red line. Highlights: Black-Right-Pointing-Pointer Synthesis of a new adamite-type compounds, Co{sub 2}(OH)(PO{sub 4}){sub 1-x}(AsO{sub 4}){sub x} (0.1, 0.25, 0.5, 0.75, 0.9) phases. Black-Right-Pointing-Pointer Co{sub 2}(OH)(PO{sub 4}){sub 1-x}(AsO{sub 4}){sub x} (0-1) solid solution; magnetic frustrated system. Black-Right-Pointing-Pointer High resolution neutron powder diffraction to determine the crystal structures. Black-Right-Pointing-Pointer Incommensurate magnetic structures at low temperature. Black-Right-Pointing-Pointer Magnetostructural correlations in cobalt-based Co{sub 2}(OH)XO{sub 4} (X=P and As) insulation compounds.

  20. Pressure-induced phase transitions in multiferroic RbFe(MoO{sub 4}){sub 2}-Raman scattering study

    SciTech Connect

    Maczka, M.; Ptak, M.; Luz-Lima, C.; Freire, P.T.C.; Paraguassu, W.; Guerini, S.; Hanuza, J.


    High pressure Raman scattering experiments were performed on RbFe(MoO{sub 4}){sub 2}. These experiments revealed that two phase transitions take place in RbFe(MoO{sub 4}){sub 2} at very low pressures, i.e. between ambient pressure and 0.2 GPa and between 0.4 and 0.7 GPa. Raman results showed that at the first phase transition the room temperature P3-bar m1 phase transforms into the P3-bar phase, which is also observed at ambient pressure below 190 K. The second pressure-induced phase transition occurs into a low symmetry phase of unknown symmetry. The performed lattice dynamics calculations for the P3-bar m1 phase and ab initio calculation of the structural changes under hydrostatic pressure helped us to get better insights into the mechanism of the observed phase transitions. - Graphical abstract: Raman spectra of RbFe(MoO{sub 4}){sub 2} crystal in the high wavenumber region recorded at different pressures during compression experiment. Highlights: > RbFe(MoO{sub 4}){sub 2} exhibits two pressure-induced phase transitions below 0.7 GPa. > First phase transition is from the P3-bar m1 into P3-bar structure. > Phase transitions in RbFe(MoO{sub 4}){sub 2} are similar as in KFe(MoO{sub 4}){sub 2}. > Transitions' pressures are much lower for the rubidium compound.

  1. A reduced graphene oxide/Co3O4sub> composite for supercapacitor electrode

    SciTech Connect

    Xiang, Chengcheng; Li, Ming; Zhi, Mingjia; Manivannan, Ayyakkannu; Wu, Nianqiang


    20 nm sized Co3O4sub> nanoparticles are in-situ grown on the chemically reduced graphene oxide (rGO) sheets to form a rGO-Co3O4sub> composite during hydrothermal processing. The rGO-Co3O4sub> composite is employed as the pseudocapacitor electrode in the 2 M KOH aqueous electrolyte solution. The rGOCo3O4sub> composite electrode exhibits a specific capacitance of 472 F/g at a scan rate of 2 mV/s in a two-electrode cell. 82.6% of capacitance is retained when the scan rate increases to 100 mV/s. The rGOCo3O4sub> composite electrode shows high rate capability and excellent long-term stability. It also exhibits high energy density at relatively high power density. The energy density reaches 39.0 Wh/kg at a power density of 8.3 kW/kg. The super performance of the composite electrode is attributed to the synergistic effects of small size and good redox activity of the Co3O4sub> particles combined with high electronic conductivity of the rGO sheets.

  2. Second harmonic generation of diamond-blade diced KTiOPO4sub> ridge waveguides.


    Chen, Chen; Rüter, Christian E; Volk, Martin F; Chen, Cheng; Shang, Zhen; Lu, Qingming; Akhmadaliev, Shavkat; Zhou, Shengqiang; Chen, Feng; Kip, Detlef


    We report on the fabrication of ridge waveguides in KTiOPO4sub> nonlinear optical crystals through carbon ion irradiation followed by precise diamond blade dicing. The diced side-walls have low roughness, which allows for low propagation loss of ~1dB/cm in fabricated of ridges. The waveguide property investigation has been performed at 1064 nm as well as 532 nm, showing good guidance at both TE and TM polarizations. Based on type II phase matching configuration, efficient second harmonic generation of green light at room temperature has been realized. High conversion efficiencies of ~1.12%W-1 and ~12.4% have been obtained for frequency doubling under the pump of continuous-wave (CW) and pulsed fundamental waves at 1064 nm, respectively.

  3. Anomalous magnetic structure and spin dynamics in magnetoelectric LiFePO4sub>

    SciTech Connect

    Toft-Petersen, Rasmus; Reehuis, Manfred; Jensen, Thomas B. S.; Andersen, Niels H.; Li, Jiying; Le, Manh Duc; Laver, Mark; Niedermayer, Christof; Klemke, Bastian; Lefmann, Kim; Vaknin, David


    We report significant details of the magnetic structure and spin dynamics of LiFePO4sub> obtained by single-crystal neutron scattering. Our results confirm a previously reported collinear rotation of the spins away from the principal b axis, and they determine that the rotation is toward the a axis. In addition, we find a significant spin-canting component along c. Furthermore, the possible causes of these components are discussed, and their significance for the magnetoelectric effect is analyzed. Inelastic neutron scattering along the three principal directions reveals a highly anisotropic hard plane consistent with earlier susceptibility measurements. While using a spin Hamiltonian, we show that the spin dimensionality is intermediate between XY- and Ising-like, with an easy b axis and a hard c axis. As a result, it is shown that both next-nearest neighbor exchange couplings in the bc plane are in competition with the strongest nearest neighbor coupling.

  4. Two-Dimensional Nb-Based M 4sub> C 3 Solid Solutions (MXenes)

    SciTech Connect

    Yang, Jian; Naguib, Michael; Ghidiu, Michael; Pan, Li-Mei; Gu, Jian; Nanda, Jagjit; Halim, Joseph; Gogotsi, Yury; Barsoum, Michel W.; Zhou, Y.


    Two new two-dimensional Nb4sub>C3-based solid solutions (MXenes), (Nb0.8,Ti0.2)4sub>C3Tx and (Nb0.8,Zr0.2)4sub>C3Tx (where T is a surface termination) were synthesizedas confirmed by X-ray diffractionfrom their corresponding MAX phase precursors (Nb0.8,Ti0.2)4sub>AlC3 and (Nb0.8,Zr0.2)4sub>AlC3. In our report we discuss Zr-containing MXene. We also studied intercalation of Li ions into these two compositions, and Nb4sub>C3Tx in order to determine the potential of those materials for energy storage applications. Lithiation and delithiation peaks at 2.26 and 2.35 V, respectively, appeared in the case of Nb4sub>C3Tx, but were not present in Nb2CTx. After 20 cycles at a rate of C/4, the specific capacities of (Nb0.8,Ti0.2)4sub>C3Txand (Nb0.8,Ti0.2)4sub>C3Tx were 158 and 132 mAh/g, respectively, both slightly lower than the capacity of Nb4sub>C3Tx.

  5. Thermal properties and phase transition in the fluoride, (NH{sub 4}){sub 3}SnF{sub 7}

    SciTech Connect

    Kartashev, A.V.; Gorev, M.V.; Bogdanov, E.V.; Flerov, I.N.; Laptash, N.M.


    Calorimetric, dilatometric and differential thermal analysis studies were performed on (NH{sub 4}){sub 3}SnF{sub 7} for a wide range of temperatures and pressures. Large entropy (δS{sub 0}=22 J/mol K) and elastic deformation (δ(ΔV/V){sub 0}=0.89%) jumps have proven that the Pa-3↔Pm-3m phase transition is a strong first order structural transformation. A total entropy change of ΔS{sub 0}=32.5 J/mol K is characteristic for the order–disorder phase transition, and is equal to the sum of entropy changes in the related material, (NH{sub 4}){sub 3}TiF{sub 7}, undergoing transformation between the two cubic phases through the intermediate phases. Hydrostatic pressure decreases the stability of the high temperature Pm-3m phase in (NH{sub 4}){sub 3}SnF{sub 7}, contrary to (NH{sub 4}){sub 3}TiF{sub 7}, characterised by a negative baric coefficient. The effect of experimental conditions on the chemical stability of (NH{sub 4}){sub 3}SnF{sub 7} was observed. - Graphical abstract: Strong first order structural transformation Pa-3↔Pm-3m in (NH{sub 4}){sub 3}SnF{sub 7} is associated with very large total entropy change of ΔS{sub 0}=32.5 J/mol K characteristic for the ordering processes and equal to the sum of entropy changes in the related (NH{sub 4}){sub 3}TiF{sub 7} undergoing transformation between the same two cubic phases through the intermediate phases. - Highlights: • (NH{sub 4}){sub 3}SnF{sub 7} undergoes strong first order Pa-3↔Pm-3m phase transition. • Anomalous behaviour of ΔC{sub p} and ΔV/V exists far below phase transition temperature. • Structural distortions are accompanied by huge total entropy change ΔS≈Rln50. • High pressure strongly increases the stability of Pa-3 phase in (NH{sub 4}){sub 3}SnF{sub 7}. • Entropy of the Pa-3↔Pm-3m phase transition does not depend on pressure.

  6. Luminescence properties of phosphate phosphor Ba{sub 3}Y(PO{sub 4}){sub 3}:Sm{sup 3+}

    SciTech Connect

    Yang, Fu; Liu, Yufeng; Tian, Xiaodong; Dong, Guoyi; Yu, Quanmao


    A series of reddish orange-emitting phosphate phosphors Ba{sub 3}Y{sub 1−x}(PO{sub 4}){sub 3}:xSm{sup 3+}(0.01≤x≤0.20) were synthesized by solid-state reaction. X-ray diffraction and photoluminescence spectra were utilized to characterize the structure and luminescence properties of as-synthesized phosphors. The optimized phosphors Ba{sub 3}Y{sub 0.95}(PO{sub 4}){sub 3}:0.05Sm{sup 3+} present several excitation bands from 300 to 500 nm, and exhibit intense reddish orange-emitting properties. The energy transfer type between Sm{sup 3+} ions was confirmed as d–d interaction by using Van Uitert model. The chromatic properties of the typical sample Ba{sub 3}Y(PO{sub 4}){sub 3}:0.05Sm{sup 3+} phosphor have been found to have chromaticity coordinates of (0.583, 0.405), which are located in reddish orange region under the excitation of 401 nm. These results indicated that Ba{sub 3}Y(PO{sub 4}){sub 3}:Sm{sup 3+} phosphors have potential applications in the field of lighting and display due to their effective excitation in the near-ultraviolet range. - Graphical abstract: The color coordinates for 5 mol% Sm{sup 3+} doped Ba{sub 3}Y(PO{sub 4}){sub 3} phosphor were calculated to be (0.583, 0.405), which are located in reddish orange region under the excitation of 401 nm. The peaks of Ba{sub 3}Y{sub 0.95}(PO{sub 4}){sub 3}:0.05Sm{sup 3+} phosphor with the highest emission intensity at 600 nm are broader than those of Y{sub 2}O{sub 3}:Eu{sup 3+} and Y{sub 2}O{sub 2}S:Eu{sup 3+} phosphors. All these characteristics suggest that Ba{sub 3}Y(PO{sub 4}){sub 3}:Sm{sup 3+} phosphors are suitable for near-UV (370–410 nm) excitation and can be applicable to near UV-based WLEDs. ▪ - Highlights: • Different concentration Sm{sup 3+}-doped Ba{sub 3}Y(PO{sub 4}){sub 3} phosphors were fabricated by solid state method. • The optimized phosphors present the several excitation bands from 300 to 500 nm. • The Ba{sub 3}Y(PO{sub 4}){sub 3}:Sm{sup 3+} shows bright reddish orange

  7. Insights into the structure of mixed CO2/CH4sub> in gas hydrates

    SciTech Connect

    Everett, S. Michelle; Rawn, Claudia J.; Chakoumakos, Bryan C.; Keffer, David J.; Huq, Ashfia; Phelps, Tommy J.


    The exchange of carbon dioxide for methane in natural gas hydrates is an attractive approach to harvesting CH4sub> for energy production while simultaneously sequestering CO2. In addition to the energy and environmental implications, the solid solution of clathrate hydrate (CH4sub>)1-x(CO2)x·5.75H2O provides a model system to study how the distinct bonding and shapes of CH4sub> and CO2 influence the structure and properties of the compound. In this paper, high-resolution neutron diffraction was used to examine mixed CO2/CH4sub> gas hydrates. CO2-rich hydrates had smaller lattice parameters, which were attributed to the higher affinity of the CO2 molecule interacting with H2O molecules that form the surrounding cages, and resulted in a reduction in the unit-cell volume. Experimental nuclear scattering densities illustrate how the cage occupants and energy landscape change with composition. Finally, these results provide important insights on the impact and mechanisms for the structure of mixed CH4sub>/CO2 gas hydrate.

  8. Magnetic structures of the {alpha}-Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3-} {sub x} (AsO{sub 4}) {sub x} (x=1, 1.5, 2, 3) solid solution

    SciTech Connect

    Goni, Aintzane; Wattiaux, Alain; Olazcuaga, Roger; Isabel Arriortua, Maria . E-mail:


    Moessbauer spectroscopy and neutron diffraction studies have been carried out for the {alpha}-Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3-} {sub x} (AsO{sub 4}) {sub x} (x=1, 1.5, 2, 3) solid solution, potential candidate for the cathode material of the lithium secondary batteries. The crystal and magnetic structures of all these phases are based on the structural and magnetic model corresponding to the {alpha}-Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} phosphate parent, but with some differences promoted by the arsenate substitution. The PO{sub 4} and AsO{sub 4} groups have a random distribution in the structure. In all compounds the coupling of the magnetic moments takes place in the (001) plane, but the value of the angle between the moments and the x direction decreases from 38.3 deg. ({alpha}-Li{sub 3}Fe{sub 2}(AsO{sub 4}){sub 3}) to 4.7{sup o} ({alpha}-Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 2}(AsO{sub 4}){sub 1}). This rotation arises from the change in the tilt angle between the Fe(1)O{sub 6} and Fe(2)O{sub 6} crystallographically and magnetically independent octahedra in the structures, and affects the effectiveness of the magnetic exchange pathways. The ordering temperature T{sub N} decreases with the increase of phosphate amount in the compounds. The existence of a phenomenon of canting and the evolution of the ferrimagnetic behavior in this solid solution is also discussed.

  9. Soft A4sub>→Z3 symmetry breaking and cobimaximal neutrino mixing

    SciTech Connect

    Ma, Ernest


    In this study, I propose a model of radiative charged-lepton and neutrino masses with A4sub> symmetry. The soft breaking of A4sub> to Z3 lepton triality is accomplished by dimension-three terms. The breaking of Z3 by dimension-two terms allows cobimaximal neutrino mixing (θ13 ≠ 0, θ23 = π/4, δcp=π/2) to be realized with only very small finite calculable deviations from the residual Z3 lepton triality. This construction solves a long-standing technical problem inherent in renormalizable A4sub> models since their inception.

  10. Spin Hall magnetoresistance in CoFe2O4sub>/Pt films

    SciTech Connect

    Wu, Hao; Qintong, Zhang; Caihua, Wan; Ali, Syed Shahbaz; Yuan, Zhonghui; You, Lu; Wang, Junling; Choi, Yongseong; Han, Xiufeng


    Pulse laser deposition and magnetron sputtering techniques have been employed to prepare MgO(001)//CoFe2O4sub>/Pt samples. Cross section transmission electron microscope results prove that the CoFe2O4sub> film epitaxially grew along (001) direction. X-ray magnetic circular dichroism results show that magnetic proximity effect in this sample is negligible. Magnetoresistance (MR) properties confirm that spin Hall MR (SMR) dominates in this system. Spin Hall effect-induced anomalous Hall voltage was also observed in this sample. Lastly, these results not only demonstrate the universality of SMR effect but also demonstrate the utility in spintronics of CoFe2O4sub> as a new type of magnetic insulator.

  11. Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of Snl4sub>

    SciTech Connect

    Liu, Hanyu; Tse, John S.; Hu, Michael Y.; Bi, Wenli; Zhao, Jiyong; Alp, E. Ercan; Pasternak, Moshe; Taylor, R. Dean; Lashley, Jason C.


    The pressure-induced amorphization and subsequent recrystallization of SnI4sub> have been investigated using first principles molecular dynamics calculations together with high-pressure 119Sn nuclear resonant inelastic x-ray scattering measurements. Above ~8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ~64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI4sub> under ambient conditions. Although high pressure structures of SnI4sub> were thought to be determined by random packing of equal-sized spheres, we detected electron charge transfer in each phase. As a result, this charge transfer results in a crystal structure packing determined by larger than expected iodine atoms. (C) 2015 AIP Publishing LLC.

  12. Biodiesel production using lipase immobilized on epoxychloropropane-modified Fe3O4 sub-microspheres.


    Zhang, Qian; Zheng, Zhong; Liu, Changxia; Liu, Chunqiao; Tan, Tianwei


    Superparamagnetic Fe3O4 sub-microspheres with diameters of approximately 200 nm were prepared via a solvothermal method, and then modified with epoxychloropropane. Lipase was immobilized on the modified sub-microspheres. The immobilized lipase was used in the production of biodiesel fatty acid methyl esters (FAMEs) from acidified waste cooking oil (AWCO). The effects of the reaction conditions on the biodiesel yield were investigated using a combination of response surface methodology and three-level/three-factor Box-Behnken design (BBD). The optimum synthetic conditions, which were identified using Ridge max analysis, were as follows: immobilized lipase:AWCO mass ratio 0.02:1, fatty acid:methanol molar ratio 1:1.10, hexane:AWCO ratio 1.33:1 (mL/g), and temperature 40 °C. A 97.11% yield was obtained under these conditions. The BBD and experimental data showed that the immobilized lipase could generate biodiesel over a wide temperature range, from 0 to 40 °C. Consistently high FAME yields, in excess of 80%, were obtained when the immobilized lipase was reused in six replicate trials at 10 and 20 °C.

  13. A high performance hybrid battery based on aluminum anode and LiFePO4sub> cathode

    SciTech Connect

    Sun, Xiao-Guang; Bi, Zhonghe; Liu, Hansan; Bridges, Craig A.; Paranthaman, Mariappan Parans; Dai, Sheng; Brown, Gilbert M.


    A unique battery hybrid utilizes an aluminum anode, a LiFePO4sub> cathode and an acidic ionic liquid electrolyte based on 1-ethyl-3-methylimidazolium chloride (EMImCl) and aluminum trichloride (AlCl 3) (EMImCl-AlCl 3, 1-1.1 in molar ratio) with or without LiAlCl4sub> is proposed. This hybrid ion battery delivers an initial high capacity of 160 mAh g-1 at a current rate of C/5. It also shows good rate capability and cycling performance.

  14. Structural and conductivity studies of CsK(SO{sub 4}){sub 0.32}(SeO{sub 4}){sub 0.68}Te(OH){sub 6}

    SciTech Connect

    Djemel, M.; Abdelhedi, M.; Dammak, M.; Kolsi, A.W.


    The compound CsK(SO{sub 4}){sub 0.32}(SeO{sub 4}){sub 0.68}Te(OH){sub 6} crystallizes in the monoclinic P2{sub 1}/n space group. It was analyzed, at room temperature, using X-ray diffractometer data. The main feature of these atomic arrangements is the coexistence of three and different anions (SO{sub 4}{sup 2-}, SeO{sub 4}{sup 2-} and TeO{sub 6}{sup 6-}groups) in the unit cell, connected by hydrogen bonds which make the building of the crystal. The thermal analysis of the title compound shows three distinct endothermal peaks at 435, 460 and 475 K. Complex impedance measurements are performed on this material as a function of both temperature and frequency. The electric conduction has been studied. The temperature dependence on the conductivity indicates that the sample became an ionic conductor at high temperature. - Graphical abstract: Projection of crystal structure CsK(SO{sub 4}){sub 0.32}(SeO{sub 4}){sub 0.68}Te(OH){sub 6} on the ab plane. Highlights: Black-Right-Pointing-Pointer We have studied the results of the crystal structure of the new mixed compound. Black-Right-Pointing-Pointer We have characterized the phase transition observed in DSC curve. Black-Right-Pointing-Pointer The protonic conduction in our material is probably due to a hopping mechanism.

  15. Theoretical Study of the Molecular and Electronic Structures of TiO4sub>H4sub>, Ti2O7H6, and Ti2O6H4sub>

    SciTech Connect

    Tsuchiya, Takashi; Whitten, Jerry L.


    State-of-the-art multistate configuration interaction (CI) calculations were performed for a series of titanium complexes, namely, TiO4sub>H4sub>, Ti2O7H6, and Ti2O6H4sub>, which were chosen to identify features present in titanium oxide nanoclusters and titanium dioxide surfaces. All electrons were included in the calculations, and transformation methods were employed to achieve high accuracy for the excitations of interest. The electronic structures of the ground and excited states are discussed, and excitation energies are reported for different molecular conformations. Of particular interest is the extent of localization of the electron-hole pair formed upon excitation from the oxygen 2p molecular orbitals. Singlet and triplet excited states were resolved, and energies of electronic states are reported as a function of molecular geometry.

  16. Solvothermal indium fluoride chemistry: Syntheses and crystal structures of K{sub 5}In{sub 3}F{sub 14}, beta-(NH{sub 4}){sub 3}InF{sub 6} and [NH{sub 4}]{sub 3}[C{sub 6}H{sub 21}N{sub 4}]{sub 2}[In{sub 4}F{sub 21}

    SciTech Connect

    Jayasundera, Anil C.A.; Goff, Richard J.; Li Yang; Finch, Adrian A.; Lightfoot, Philip


    The solvothermal syntheses and crystal structures of three indium fluorides are presented. K{sub 5}In{sub 3}F{sub 14} (1) and beta-(NH{sub 4}){sub 3}InF{sub 6} (2) are variants on known inorganic structure types chiolite and cryolite, respectively, with the latter exhibiting a complex and apparently novel structural distortion. [NH{sub 4}]{sub 3}[C{sub 6}H{sub 21}N{sub 4}]{sub 2}[In{sub 4}F{sub 21}] (3) represents a new hybrid composition displaying a unique trimeric metal fluoride building unit. - Graphical abstract: Solvothermal synthesis has been used to prepare three indium fluorides, including a novel hybrid material containing a unique [In{sub 3}F{sub 15}] trimer templated by tren.

  17. Mixed-Valent NaCu 4sub> Se 3: A Two-Dimensional Metal

    SciTech Connect

    Sturza, Mihai; Bugaris, Daniel E.; Malliakas, Christos D.; Han, Fei; Chung, Duck Young; Kanatzidis, Mercouri G.


    The new ternary copper selenide NaCu4sub>Se3 crystallizes in the RbCd4sub>As3 structure type with the trigonal space group R3m and lattice constants a = 4.0316(4) angstrom and c = 31.438(8) angstrom. Its structure is built from two-dimensional slabs of 2 [Cu4sub>Se3] separated by Na+ cations. The compound is formally mixed-valent with Se2-/Se- atoms and exhibits metallic properties. It is a hole conductor with an electrical conductivity of similar to 300 S cm-1 at room temperature and a thermopower of similar to 10 mu V K-1. Hall effect measurements indicate holes as the dominant carrier with a concentration of similar to 6.12(1) X 1021 cm-3 at 300 K. Density functional theory electronic structure calculations indicate p -type metallic behavior for the 2 [Cu4sub>Se3] framework, which is in a good agreement with the experimental metallic conductivity and Pauli paramagnetism.

  18. A facile solvothermal synthesis of octahedral Fe3O4sub> nanoparticles

    SciTech Connect

    DuChene, Joseph S.; Qiu, Jingjing; Graham, Jeremy O.; Engelhard, Mark H.; Cao, Guixin; Gai, Zheng; Wei, Wei David; Ooi, Frances


    Anisotropic Fe3O4sub> octahedrons are obtained via a simple solvothermal synthesis with appropriate sizes for various technological applications. Here, a complete suite of materials characterization methods confirms the magnetite phase for these structures, which exhibit substantial saturation magnetization and intriguing morphologies for a wide range of applications.

  19. New mixed-valence chromium structure type: NH{sub 4}Cr(CrO{sub 4}){sub 2}

    SciTech Connect

    Casari, Barbara M. . E-mail:; Wingstrand, Erica; Langer, Vratislav


    Synthesis and crystal structure of a new structure type of mixed Cr(III)/Cr(VI) chromates is reported. NH{sub 4}Cr(CrO{sub 4}){sub 2} was prepared from CrO{sub 3} in the presence of (NH{sub 4}){sub 2}Ce(NO{sub 3}){sub 6}. Since this is the first preparation of mixed valence ternary chromium oxides from aqueous solution, a reaction pathway for this synthesis is suggested. The crystal structure of NH{sub 4}Cr(CrO{sub 4}){sub 2} has been determined from three-dimensional X-ray data collected at low temperature, 173K. The structure belongs to the orthorhombic space group Pnma, with a=14.5206(10), b=5.4826(4), c=8.7041(7)A and Z=4. The title compound consists of corner-sharing chromium(III) octahedra and chromium(VI) tetrahedra forming a three-dimensional network with the composition [Cr(CrO{sub 4}){sub 2}]{sub n}{sup n-}, containing channels in which zigzag rows of ammonium ions balance the net charge.

  20. LiV2O4sub>: A heavy fermion transition metal oxide

    SciTech Connect

    Kondo, Shinichiro


    The format of this dissertation is as follows. In the remainder of Chapter 1, brief introductions and reviews are given to the topics of frustration, heavy fermions and spinels including the precedent work of LiV2O4sub>. In Chapter 2, as a general overview of this work the important publication in Physical Review Letters by the author of this dissertation and collaborators regarding the discovery of the heavy fermion behavior in LiV2O4sub> is introduced [removed for separate processing]. The preparation methods employed by the author for nine LiV2O4sub> and two Li1+xTi2-xO4sub> (x = 0 and 1/3) polycrystalline samples are introduced in Chapter 3. The subsequent structural characterization of the LiV2O4sub> and Li1+xT2-xO4sub> samples was done by the author using thermogravimetric analysis (TGA), x-ray diffraction measurements and their structural refinements by the Rietveld analysis. The results of the characterization are detailed in Chapter 3. In Chapter 4 magnetization measurements carried out by the author are detailed. In Chapter 5, after briefly discussing the resistivity measurement results including the single-crystal work by Rogers et al., for the purpose of clear characterization of LiV2O4sub> it is of great importance to introduce in the following chapters the experiments and subsequent data analyses done by his collaborators. Heat capacity measurements (Chapter 6) were carried out and analyzed by Dr. C.A. Swenson, and modeled theoretically by Dr. D.C. Johnston. In Chapter 7 a thermal expansion study using neutron diffraction by Dr. O. Chmaissem et al. and capacitance dilatometry measurements by Dr. C.A. Swenson are introduced. The data analyses for the thermal expansion study were mainly done by Dr. O. Chmaissem (for neutron diffraction) and Dr. C.A. Swendon (for dilatometry), with assistances by Dr. J

  1. Structural transformations in the Na{sub 4+x}VO(PO{sub 4}){sub 2} vanadylphosphates

    SciTech Connect

    Shpanchenko, Roman V. . E-mail:; Dikarev, Evgeny V.; Mironov, Andrey V.; Mudretsova, Svetlana N.; Antipov, Evgeny V.


    The crystal structures of new sodium vanadylphosphate, Na{sub 4.35}VO(PO{sub 4}){sub 2} (a=15.4450(11)A, b=14.7690(10)A, c=6.9870(5)A, Z=8, S.G. Ibam), and new ({gamma}-) modification of Na{sub 4}VO(PO{sub 4}){sub 2} (a=15.4455(15)A, b=14.8433(10)A, c=7.0081(5)A, Z=8, S.G. Pbc2{sub 1}) have been investigated by X-ray single-crystal diffraction. Both structures contain isolated infinite chains of the corner-sharing VO{sub 6} octahedra. The octahedra within the chains are additionally linked to each other by the tetrahedral PO{sub 4} groups. Sodium atoms are situated in the positions between the chains. Depending on the conditions of synthesis, the number of sodium atoms in the unit cell of the Na{sub 4+x}VO(PO{sub 4}){sub 2} compounds may vary resulting in a change of the oxidation state of vanadium atoms and a change of their coordination environment. In Na{sub 4.35}VO(PO{sub 4}){sub 2} vanadium atoms have almost regular octahedral coordination with six close V-O separations and all chains in the structure are equivalent. The crystal structure of {gamma}-Na{sub 4}VO(PO{sub 4}){sub 2} contains two non-equivalent chain types: the first one is similar to that found in Na{sub 4.35}VO(PO{sub 4}){sub 2} whereas the second one contains VO{sub 6} octahedra with the short vanadyl bonds. The charge re-distribution was supposed in the new {gamma}-modification of Na{sub 4}VO(PO{sub 4}){sub 2} where the V{sup 4+{delta}} and V{sup 4-{delta}} cations orderly occupy octahedral positions in different chains. The origin of this phenomena is discussed.

  2. Magnetic structure of the antiferromagnetic Kondo lattice compounds CeRhAl4sub>Si2 and CeIrAl4sub>Si2

    SciTech Connect

    Ghimire, N. J.; Calder, S.; Janoschek, M.; Bauer, E. D.


    In this article, we have investigated the magnetic ground state of the antiferromagnetic Kondo-lattice compounds CeMAl4sub>Si2(M = Rh, Ir) using neutron powder diffraction. Although both of these compounds show two magnetic transitions TN1 and TN2 in the bulk properties measurements, evidence for magnetic long-range order was only found below the lower transition TN2. Analysis of the diffraction profiles reveals a commensurate antiferromagnetic structure with a propagation vector k = (0, 0, 1/2). The magnetic moment in the ordered state of CeRhAl4sub>Si2 and CeIrAl4sub>Si2 were determined to be 1.14(2) and 1.41(3) μB/Ce, respectively, and are parallel to the crystallographic c-axis in agreement with magnetic susceptibility measurements.

  3. Cr/B4sub>C multilayer mirrors: Study of interfaces and X-ray reflectance

    SciTech Connect

    Burcklen, C.; Soufli, R.; Gullikson, E.; Meltchakov, E.; Dennetiere, D.; Polack, F.; Capitanio, B.; Thomasset, M.; Jerome, A.; de Rossi, S.; Delmotte, F.


    Here, we present an experimental study of the effect of layer interfaces on the x-ray reflectance in Cr/B4sub>C multilayer interference coatings with layer thicknesses ranging from 0.7 nm to 5.4 nm. The multilayers were deposited by magnetron sputtering and by ion beam sputtering. Grazing incidence x-ray reflectometry, soft x-ray reflectometry, and transmission electron microscopy reveal asymmetric multilayer structures with a larger B4sub>C-on-Cr interface, which we modeled with a 1–1.5 nm thick interfacial layer. Reflectance measurements in the vicinity of the Cr L2,3 absorption edge demonstrate fine structure that is not predicted by simulations using the currently tabulated refractive index (optical constants) values for Cr.

  4. Investigation of room temperature ferromagnetic nanoparticles of Gd5Si4sub>

    SciTech Connect

    Hadimani, R. L.; Gupta, S.; Harstad, S. M.; Pecharsky, V. K.; Jiles, D. C.


    Gd5(SixGe1-x)4sub> compounds undergo first-order phase transitions close to room temperature when x ~ = 0.5, which are accompanied by extreme changes of properties. We report the fabrication of the nanoparticles of one of the parent compounds-Gd5Si4sub>-using high-energy ball milling. Crystal structure, microstructure, and magnetic properties have been investigated. Particles agglomerate at long milling times, and the particles that are milled >20 min lose crystallinity and no longer undergo magnetic phase transition close to 340 K, which is present in a bulk material. The samples milled for >20 min exhibit a slightly increased coercivity. As a result, magnetization at a high temperature of 275K decreases with the increase in the milling time.

  5. Active pulse shaping for end-pumped Nd:YVO4sub> amplifier with high gain.


    Nie, Mingming; Liu, Qiang; Ji, Encai; Cao, Xuezhe; Fu, Xing; Gong, Mali


    We demonstrated the active shaping for a solid-state Nd:YVO4sub> amplifier with a high average gain of 39.2 dB. The average output power was 8.3 W with respect to the input power of 1 mW. A range of common and useful pulse shapes was generated at the final output. In addition, a very flat square pulse was produced with a root-mean-square less than 3% in amplitude. A numerical method was proposed to realize active shaping without an experimental test for the Nd:YVO4sub> amplifier, showing great potential for the design of lasers with both high peak power (>100  kW) and a desired pulse shape.

  6. Stress Induced Charge-Ordering Process in LiMn2O4sub>

    SciTech Connect

    Chen, Yan; Yu, Dunji; An, Ke


    In this letter we report the stress-induced Mn charge-ordering process in the LiMn2O4sub> spinel, evidenced by the lattice strain evolutions due to the Jahn–Teller effects. In situ neutron diffraction reveals the initial stage of this process at low stress, indicating the eg electron localization at the preferential Mn sites during the early phase transition as an underlying charge-ordering mechanism in the charge-frustrated LiMn2O4sub>. The initial stage of this transition exhibits as a progressive lattice and charge evolution, without showing a first-order behavior.

  7. Effects of Nickel Doping on the Multiferroic and Magnetic Phases of MnWO 4sub>

    SciTech Connect

    Poudel, N.; Lorenz, B.; Lv, B.; Wang, Y. Q.; Ye, F.; Wang, Jinchen; Fernandez-baca, J. A.; Chu, C. W.


    There are various orders in multiferroic materials with a frustrated spiral spin modulation inducing a ferroelectric state are extremely sensitive to small perturbations such as magnetic and electric fields, external pressure, or chemical substitutions. A classical multiferroic, the mineral Hubnerite with chemical formula MnWO4sub>, shows three different magnetic phases at low temperature. The intermediate phase between 7.5K < T < 12.7K is multiferroic and ferroelectricity is induced by an inversion symmetry breaking spiral Mn-spin order and strong spin-lattice interactions. Furthermore, the substitution of Ni2+ (spin 1) for Mn2+ (spin 5/2) in MnWO4sub> and its effects on the magnetic and multiferroic phases are studied. The ferroelectric phase is stabilized for low Ni content (up to 10%). Upon further Ni doping, the polarization in the ferroelectric phase is quickly suppressed while a collinear and commensurate magnetic phase, characteristic of the magnetic structure in NiWO4sub>, appears first at higher temperature, gradually extends to lower temperature, and becomes the ground state above 30% doping. Between 10% and 30%, the multiferroic phase coexists with the collinear commensurate phase. In this concentration region, the spin spiral plane is close to the a-b plane which explains the drop of the ferroelectric polarization. Finally, the phase diagram of Mn1-xNixWO4sub> is derived by a combination of magnetic susceptibility, specific heat, electric polarization, and neutron scattering measurements.

  8. Crystal chemistry of M{sup II}M′{sup IV}(PO{sub 4}){sub 2} double monophosphates

    SciTech Connect

    Bregiroux, Damien; Popa, Karin; Wallez, Gilles


    M{sup II}M′{sup IV}(PO{sub 4}){sub 2} compounds have been extensively studied for several decades for their potential applications in the field of several domains such as matrices for actinides conditioning, phosphors etc. In this paper, the relationships between composition and crystal structure of these compounds are established. A review of the various processes used for the synthesis of these compounds is also proposed, as well as their most reported properties. M{sup II}M′{sup IV}(PO{sub 4}){sub 2} structures stem from two different archetypes: the cheralite and the yavapaiite structures, with some exceptions that are also described in this article. The ratio of the cations radii appears to be the most relevant parameter. The high ratio between the ionic radii of the divalent and tetravalent cations in yavapaiite derivates results in the ordering of these cations into well-differentiated polyhedra whereas cheralite is the only non-ordered structure encountered for M{sup II}M′{sup IV}(PO{sub 4}){sub 2} compounds. - Graphical abstract: In this paper, the relationships between composition and crystal structure of M{sup II}M′{sup IV}(PO{sub 4}){sub 2} compounds are established. A review of the various processes used for the synthesis of these compounds is also proposed, as well as their most reported properties. - Highlights: • Crystal structure–composition relationships of MIIM′IV(PO4)2 compounds. • Review of the various processes used for the synthesis of these compounds. • Their most reported properties are described and discussed.

  9. Mode-selective chemistry on metal surfaces: The dissociative chemisorption of CH4sub> on Pt(111)

    SciTech Connect

    Guo, Han; Jackson, Bret


    A quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore CH4sub> dissociation on Pt(111). Computed sticking probabilities for molecules in the ground, 1v3 and 2v3, states are in very good agreement with the available experimental data, reproducing the variation in reactivity with collision energy and vibrational state. As was found in similar studies on Ni(100) and Ni(111), exciting the 1v1 symmetric stretch of CH4sub> is more effective at promoting the dissociative chemisorption of CH4sub> than exciting the 1v3 antisymmetric stretch. This behavior is explained in terms of symmetry, mode-softening, and nonadiabatic transitions between vibrationally adiabatic states. We find that the efficacies of the bending modes for promoting reaction are reasonably large, and similar to the 1v3 state. The vibrational efficacies for promoting reaction on Ni(111) are larger than for reaction on Pt(111), due to the larger nonadiabatic couplings. As a result, our computed sticking probabilities are in good agreement with results from recent ab initio molecular dynamics and reactive force field studies.

  10. Structural behavior of ZnCr2S4sub> spinel under pressure

    SciTech Connect

    Efthimiopoulos, I.; Lochbiler, T.; Tsurkan, V.; Loidl, A.; Felea, V.; Wang, Y.


    Here, the series of Cr-chalcogenide spinels ACr2X4sub> (A = Zn, Cd, Hg; X = S, Se) exhibits a rich phase diagram upon compression, as revealed by our recent investigations. There exist, however, some open questions regarding the role of cations in the observed structural transitions. In order to address these queries, we have performed X-ray diffraction and Raman spectroscopic studies on the ZnCr2S4sub> spinel up to 42 GPa, chosen mainly due to the similarity of the Zn2+ and Cr3+ cationic radii. Two reversible structural transitions were identified at 22 and 33 GPa, into a I4<sub>1/amd and an orthorhombic phase, respectively. Close comparison with the behavior of relevant Cr-spinels revealed that the structural transitions are mainly governed by the competition of the magnetic exchange interactions present in these systems, and not by steric effects. In addition, careful inspection of the starting Fd$\\bar{3}$m phase revealed a previously unnoticed isostructural transition. The latter is intimately related to changes in the electronic properties of these systems, as evidenced by our Raman studies. Our results provide insights for tuning the physical and chemical properties of these materials, even under moderate compression, as well as promoting the understanding of similar pressure-induced effects in relevant systems.

  11. Hydrothermal synthesis and luminescent properties of NaLa(MoO{sub 4}){sub 2}:Dy{sup 3+} phosphor

    SciTech Connect

    Li Linlin; Zi Wenwen; Li Guanghuan; Lan Shi; Ji Guijuan; Gan Shucai; Zou Haifeng; Xu Xuechun


    Pompon-like NaLa(MoO{sub 4}){sub 2}:Dy{sup 3+} phosphors have been successfully prepared via a hydrothermal method using ammonia as pH value regulator. The hydrothermal process was carried out under aqueous condition without the use of any organic solvent, surfactant, and catalyst. The experimental results demonstrate that the obtained NaLa(MoO{sub 4}){sub 2}:Dy{sup 3+} phosphor powders are single-phase scheelite structure with tetragonal symmetry. Moreover, the phosphor under the excitation of 390 and 456 nm exhibited blue emission (486 nm) and yellow emission (574 nm), corresponding to the {sup 4}F{sub 9/2}{yields}{sup 6}H{sub 15/2} transition and {sup 4}F{sub 9/2}{yields}{sup 6}H{sub 13/2} transition of Dy{sup 3+} ions, respectively. In addition, the yellow-to-blue emission intensity ratio (Y/B) can be changed with the doped concentration of Dy{sup 3+} ions. All chromaticity coordinates of the obtained NaLa(MoO{sub 4}){sub 2}:Dy{sup 3+} phosphors are located in the white-light region. The results indicate that this kind of phosphor may has potential applications in the fields of near UV-excited and blue-excited white LEDs. - Graphical abstract: It can be seen from the SEM images that a pompon-like shape was obtained with an average diameter of about 1 {mu}m, and it is composed of many nanoflakes. Highlights: Black-Right-Pointing-Pointer Pompon-like NaLa(MoO{sub 4}){sub 2}:Dy{sup 3+} phosphors have been successfully prepared via a hydrothermal method. Black-Right-Pointing-Pointer Blue emission at 486 nm and yellow emission at 574 nm were obtained from the samples. Black-Right-Pointing-Pointer The yellow-to-blue emission intensity ratio (Y/B) can be changed with the doped concentration of Dy{sup 3+} ions. Black-Right-Pointing-Pointer NaLa(MoO{sub 4}){sub 2}:Dy{sup 3+} can be efficiently excited by the blue light and the near ultraviolet light.

  12. β-NaVOPO4sub> obtained by a low-temperature synthesis process: A new 3.3 V cathode for sodium-ion batteries

    SciTech Connect

    He, Guang; Huq, Ashfia; Manthiram, Arumugam; Kan, Wang Hay


    Vanadyl phosphates (VOPO4sub>) represent a class of attractive cathodes in lithium-ion batteries. However, the exploration of this type of materials in sodium-ion batteries is rare. Here, we report for the first time the synthesis of orthorhombic β-NaVOPO4sub> by first chemically extracting lithium from beta-LiVOPO4sub> and then inserting sodium into the obtained β-VOPO4sub> by a microwave-assisted solvothermal process with NaI, which serves both as a reducing agent and sodium source. Intermediate NaxVOPO4sub> compositions with x = 0.3, 0.5, and 0.8 have also been obtained by controlling the amount of NaI in the reaction mixture. Joint Rietveld refinement of synchrotron X-ray diffraction (XRD) and neutron diffraction confirms that the fully sodiated β-NaVOPO4sub> is isostructural with the lithium counterpart β-LiVOPO4sub>. Bond valence sum maps suggest that sodium ions possibly diffuse along the [010] direction in the lattice, similar to the ionic conduction pathway in β-LiVOPO4sub>. Although the initial discharge capacity is low due to the protons in the structure, it steadily increases with cycling with a long plateau at 3.3 V. As a result, ex situ XRD data of cycled β-VOPO4sub> and β-NaVOPO4sub> electrodes confirm the reversible reaction in sodium cells involving the V4+/V5+ redox couple.

  13. Field Evaluation of Transgenic Switchgrass Plants Overexpressing PvMYB4sub> for Reduced Biomass Recalcitrance

    SciTech Connect

    Baxter, Holly L.; Poovaiah, Charleson R.; Yee, Kelsey L.; Mazarei, Mitra; Rodriguez, Miguel; Thompson, Olivia A.; Shen, Hui; Turner, Geoffrey B.; Decker, Stephen R.; Sykes, Robert W.; Chen, Fang; Davis, Mark F.; Mielenz, Jonathan R.; Davison, Brian H.; Dixon, Richard A.; Stewart, C. Neal


    High biomass yields and minimal agronomic input requirements have made switchgrass, Panicum virgatum L., a leading candidate lignocellulosic bioenergy crop. Large-scale lignocellulosic biofuel production from such crops is limited by the difficulty to deconstruct cell walls into fermentable sugars: the recalcitrance problem. In this study, we assessed the field performance of switchgrass plants overexpressing the switchgrass MYB4sub> (PvMYB4sub>) transcription factor gene. PvMYB4sub> transgenic switchgrass can have great lignin reduction, which commensurately increases sugar release and biofuel production. Our results over two growing seasons showed that one transgenic event (out of eight) had important gains in both biofuel (32% more) and biomass (63% more) at the end of the second growing season relative to non-transgenic controls. These gains represent a doubling of biofuel production per hectare, which is the highest gain reported from any field-grown modified feedstock. In contrast to this transgenic event, which had relatively low ectopic overexpression of the transgene, five of the eight transgenic events planted did not survive the first field winter. The dead plants were all high-overexpressing events that performed well in the earlier greenhouse studies. Disease susceptibility was not compromised in any transgenic events over the field experiments. These results demonstrate the power of modifying the expression of an endogenous transcription factor to improve biofuel and biomass simultaneously, and also highlight the importance of field studies for "sorting" transgenic events. In conclusion, further research is needed to develop strategies for fine-tuning temporal-spatial transgene expression in feedstocks to optimize desired phenotypes.

  14. trans-K3[TcO2(CN)4sub>

    SciTech Connect

    Chatterjee, Sayandev; Del Negro, Andrew S; Edwards, Matthew K; Twamley, Brendan; Krause, Jeanette A; Bryan, Samuel A


    The dioxotetracyanotechnetate anion, [TcO2(CN)4sub>]3-, of the title complex has octahedral symmetry. The technetium is located on a center of inversion and is bound by two oxygen atoms and four cyano ligands. The Tc=O bond distance of 1.7721 (12) Å is consistent with double bond character. The potassium cations [located on special (1/2,0,1) and general positions] reside in octahedral or tetrahedral environments; interionic K···O and K···N interactions occur in the 2.7877 (19)-2.8598 (15) Å range.

  15. Femtosecond pulse generation with an a-cut Nd:CaYAlO4sub> disordered crystal.


    Liu, Shan-De; Dong, Lu-Lu; Xu, Yan; Zhang, Xiao; Ren, Ting-Qi; Xu, Xiao-Dong; Peng, Yan-Dong; Zhang, Yu-Ping; Zhang, Hui-Yun; Li, De-Hua; Zhang, Bai-Tao; He, Jing-Liang


    We experimentally demonstrated a diode-pumped 587 fs ultrafast laser by using an a-cut Nd:CaYAlO4sub> crystal. Pumped by an 808 nm fiber-coupled laser diode, a stable continuous-wave mode-locked ultrafast laser was achieved with a semiconductor saturable absorber. The ultrafast pulses had a repetition rate of 75 MHz at the center wavelength of 1080.8 nm. A maximum average output power of the mode-locked laser reached 375 mW delivering a slope efficiency of 9%.

  16. Hysteretic magnetoresistance and unconventional anomalous Hall effect in the frustrated magnet TmB4sub>

    SciTech Connect

    Sunku, Sai Swaroop; Kong, Tai; Ito, Toshimitsu; Canfield, Paul C.; Shastry, B. Sriram; Sengupta, Pinaki; Panagopoulos, Christos


    We study TmB4sub>, a frustrated magnet on the Archimedean Shastry-Sutherland lattice, through magnetization and transport experiments. The lack of anisotropy in resistivity shows that TmB4 is an electronically three-dimensional system. The magnetoresistance (MR) is hysteretic at low temperature even though a corresponding hysteresis in magnetization is absent. The Hall resistivity shows unconventional anomalous Hall effect (AHE) and is linear above saturation despite a large MR. In conclusion, we propose that complex structures at magnetic domain walls may be responsible for the hysteretic MR and may also lead to the AHE.

  17. Magnetic Ordering in Sr3YCo4sub>O10+x

    SciTech Connect

    Kishida, Takayoshi; Kapetanakis, Myron D.; Yan, Jiaqiang; Sales, Brian C.; Pantelides, Sokrates T.; Pennycook, Stephen J.; Chisholm, Matthew F.


    Transition-metal oxides often exhibit complex magnetic behavior due to the strong interplay between atomic-structure, electronic and magnetic degrees of freedom. Cobaltates, especially, exhibit complex behavior because of cobalt’s ability to adopt various valence and spin state configurations. The case of the oxygen-deficient perovskite Sr3YCo4sub>O10+x (SYCO) has gained considerable attention because of persisting uncertainties about its structure and the origin of the observed room temperature ferromagnetism. Here we report a combined investigation of SYCO using aberration-corrected scanning transmission electron microscopy and density functional theory calculations.

  18. Heterogeneous Nature of Relaxation Dynamics of Room-Temperature Ionic Liquids (EMIm)2[Co(NCS)4sub>] and (BMIm)2[Co(NCS)4sub>

    SciTech Connect

    Hensel-Bielowka, Stella; Wojnarowska, Zaneta; Dzida, Marzena; Zorębski, Edward; Zorębski, Michał; Geppert-Rybczyńska, Monika; Peppel, Tim; Grzybowska, Katarzyna; Wang, Yangyang; Sokolov, Alexei P.; Paluch, Marian


    Dynamic crossover above Tg has been recognized as a characteristic feature of molecular dynamics of liquids approaching glass transition. Experimentally, it is manifested as a change in Vogel–Fulcher–Tammann dependence or a breakdown of the Stokes–Einstein and related relations. In this study, we report the exception from this rather general pattern of behavior. By means of dielectric, ultrasonic, rheological, and calorimetric methods, dynamics of two good ionic conductors (BMIm)2[Co(NCS)4sub>] and (EMIm)2[Co(NCS)4sub>] of less common stoichiometry (2:1) was studied in a very broad temperature range. However, none of the mentioned dynamic changes was observed in the entire studied temperature range. On the contrary, the single VFT and the same fractional Walden coefficient were found for conductivity and viscosity changes over 12 decades. Finally and moreover, ultrasonic studies revealed that the data at temperatures which cover the normal liquid region cannot be fitted by a single exponential decay, and the Cole–Cole function should be used instead.

  19. Morphology control of open-framework zinc phosphate Zn{sub 4}(H{sub 3}O)(NH{sub 4}){sub 3}(PO{sub 4}){sub 4} via microwave-assisted technique

    SciTech Connect

    Ding, Ling; Song, Yu; Yang, Wei; Xue, Run-Miao; Zhai, Shang-Ru; An, Qing-Da


    Open-framework zinc phosphates were synthesized by microwave-assisted technique, and it was shown that the morphology of as-prepared materials could be easily tailored by changing synthesis temperature, reaction time and pH value. During the synthesis, when the reaction temperature increases from 130 °C to 220 °C, the products transformed from hexagonal prisms to polyhedron along with the disappearance of the hexagonal prisms vertical plane. Simultaneously, both the reaction time and pH value could promote the nucleation and growth of crystal particles. More interestingly, the target products with different morphologies could be obtained by varying the usage of NaOH or NH{sub 3}·H{sub 2}O at 130 °C during the microwave synthesis process. - Graphical abstract: Zinc phosphates with variable morphologies can be obtained by simply tuning the microwave-heating temperatures. Display Omitted - Highlights: • Synthesis of open-framework Zn{sub 4} (H{sub 3}O) (NH{sub 4}){sub 3}(PO{sub 4}){sub 4} compounds employing microwave technique. • Dependence of morphology on the reaction conditions. • Morphology transformation from hexagonal prisms to polyhedron was observed.

  20. Tailoring the surface properties of LiNi0.4sub>Mn0.4sub>Co0.2O₂ by titanium substitution for improved high voltage cycling performance

    SciTech Connect

    Wolff-Goodrich, Silas; Xin, Huolin L.; Lin, Feng; Markus, Isaac M.; Nordlund, Dennis; Asta, Mark; Doeff, Marca M.


    The present research aims to provide insights into the behavior of LiNi0.4Mn0.4Co0.2O2 (NMC442) and LiNi0.4sub>Mn0.4sub>Co0.2O₂ (NMC442-Ti02) cathode materials under galvanostatic cycling to high potentials, in the context of previous work which predicted that Ti-substituted variants should deliver higher capacities and exhibit better cycling stability than the unsubstituted compounds. It is found that NMC cathodes containing Ti show equivalent capacity fading but greater specific capacity than those without Ti in the same potential range. When repeatedly charged to the same degree of delithiation, NMC cathodes containing Ti showed better capacity retention. Soft x-ray absorption spectroscopy (XAS) spectra for Mn and Co indicated increased reduction in these elements for NMC cathodes without Ti, indicating that the substitution of Ti for Co acts to suppress the formation of a high impedance rock salt phase at the surface of NMC cathode particles. The results of this study validate the adoption of a facile change to existing NMC chemistries to improve cathode capacity retention under high voltage cycling conditions.

  1. M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba): Crystal structure, phase transitions and thermal expansion

    SciTech Connect

    Popa, Karin; Wallez, Gilles; Bregiroux, Damien; Loiseau, Pascal


    Three earth alkali-germanium monophosphates M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba) were prepared by solid state reaction and their structures, previously unknown, studied by Rietveld analysis. BaGe(PO{sub 4}){sub 2} and high-temperature {beta}-SrGe(PO{sub 4}){sub 2} (space group C2/m, Z=2) are fully isotypic with yavapaiite, whereas CaGe(PO{sub 4}){sub 2} and low-temperature {alpha}-SrGe(PO{sub 4}){sub 2} (C2/c, Z=4) are distorted derivatives. The phase transition between the two forms is observed for the first time. The thermal expansion, resulting from several structural mechanisms, is very anisotropic. - Graphical abstract: The superstructure of SrGe(PO{sub 4}){sub 2} at room temperature ({alpha}) results from the off-centering of cation Sr{sup II}. Highlights: > Crystal structures of yavapaiite-type M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba) have been solved. > Distortion and superstructure result from Ca and Sr off-centering. > A global scheme for the polymorphism of yavapaiites is proposed.

  2. Dispersion of nanocrystalline Fe3O4sub> within composite electrodes: Insights on battery-related electrochemistry

    SciTech Connect

    David C. Bock; Takeuchi, Kenneth J.; Pelliccione, Christopher J.; Zhang, Wei; Wang, Jiajun; Knehr, K. W.; Wang, Jun; Wang, Feng; West, Alan C.; Marschilok, Amy C.; Takeuchi, Esther S.


    Aggregation of nanosized materials in composite lithium-ion-battery electrodes can be a significant factor influencing electrochemical behavior. In this study, aggregation was controlled in magnetite, Fe3O4sub>, composite electrodes via oleic acid capping and subsequent dispersion in a carbon black matrix. A heat treatment process was effective in the removal of the oleic acid capping agent while preserving a high degree of Fe3O4sub> dispersion. Electrochemical testing showed that Fe3O4sub> dispersion is initially beneficial in delivering a higher functional capacity, in agreement with continuum model simulations. However, increased capacity fade upon extended cycling was observed for the dispersed Fe3O4sub> composites relative to the aggregated Fe3O4sub> composites. X-ray absorption spectroscopy measurements of electrodes post cycling indicated that the dispersed Fe3O4sub> electrodes are more oxidized in the discharged state, consistent with reduced reversibility compared with the aggregated sample. Higher charge-transfer resistance for the dispersed sample after cycling suggests increased surface-film formation on the dispersed, high-surface-area nanocrystalline Fe3O4sub> compared to the aggregated materials. Furthermore, this study provides insight into the specific effects of aggregation on electrochemistry through a multiscale view of mechanisms for magnetite composite electrodes.

  3. First-principles predicted low-energy structures of NaSc(BH{sub 4}){sub 4}

    SciTech Connect

    Tran, Huan Doan Amsler, Maximilian; Goedecker, Stefan; Botti, Silvana; Marques, Miguel A. L.


    According to previous interpretations of experimental data, sodium-scandium double-cation borohydride NaSc(BH{sub 4}){sub 4} crystallizes in the crystallographic space group Cmcm where each sodium (scandium) atom is surrounded by six scandium (sodium) atoms. A careful investigation of this phase based on ab initio calculations indicates that the structure is dynamically unstable and gives rise to an energetically and dynamically more favorable phase with C222{sub 1} symmetry and nearly identical x-ray diffraction pattern. By additionally performing extensive structural searches with the minima-hopping method we discover a class of new low-energy structures exhibiting a novel structural motif in which each sodium (scandium) atom is surrounded by four scandium (sodium) atoms arranged at the corners of either a rectangle with nearly equal sides or a tetrahedron. These new phases are all predicted to be insulators with band gaps of 7.9–8.2 eV. Finally, we estimate the influence of these structures on the hydrogen-storage performance of NaSc(BH{sub 4}){sub 4}.

  4. X-Ray Powder Diffraction Study of Synthetic Palmierite, K{sub 2}Pb(SO{sub 4}){sub 2}

    SciTech Connect



    Palmierite (K{sub 2}Pb(SO{sub 4}){sub 2}) has been prepared via a chemical synthesis method. Intensity differences were observed when X-ray powder data from the newly synthesized compound were compared to the published powder diffraction card (PDF) 29-1015 for Palmierite. Investigation of these differences indicated the possibility of preferred orientation and/or chemical inhomogeneity affecting intensities, particularly those of the basal (00{ell}) reflections. Annealing of the Palmierite was found to reduce the effects of preferred orientation. Electron microprobe analysis confirmed K:Pb:S as 2:1:2 for the annealed Palmierite powder. Subsequent least-squares refinement and Rietveld analysis of the annealed powder showed peak intensities very close to that of a calculated Palmierite pattern (based on single crystal data), yet substantially higher than many of the PDF 29-1015 published intensities. Further investigation of peak intensity variation via calculated patterns suggested that the intensity discrepancies between the annealed sample and those found in PDF 29-1015 were potentially due to chemical variation in the K{sub 2}Pb(SO{sub 4}){sub 2} composition. X-ray powder diffraction and crystal data for Palmierite are reported for the annealed sample. Palmierite is Trigonal/Hexagonal with unit cell parameters a = 5.497(1){angstrom}, c = 20.864(2) {angstrom}, space group R-3m (166), and Z = 3.

  5. Electrode Reaction Mechanism of Ag2VO2PO4sub> Cathode

    SciTech Connect

    Zhang, Ruibo; Abtew, Tesfaye A.; Quackenbush, Nicholas F.; Wangoh, Linda W.; Huie, Matthew; Brady, Alexander B.; Bock, David; Efstathiadis, Harry; Whittingham, M. Stanley; Marschilok, Amy C.; Takeuchi, Kenneth J.; Takeuchi, Esther S.; Zhang, Peihong; Piper, Louis F. J.


    In this study, the high capacity of primary lithium-ion cathode Ag2VO2PO4sub> is facilitated by both displacement and insertion reaction mechanisms. Whether the Ag extrusion (specifically, Ag reduction with Ag metal displaced from the host crystal) and V reduction are sequential or concurrent remains unclear. A microscopic description of the reaction mechanism is required for developing design rules for new multimechanism cathodes, combining both displacement and insertion reactions. However, the amorphization of Ag2VO2PO4sub> during lithiation makes the investigation of the electrode reaction mechanism difficult with conventional characterization tools. For addressing this issue, a combination of local probes of pair-distribution function and X-ray spectroscopy were used to obtain a description of the discharge reaction. We determine that the initial reaction is dominated by silver extrusion with vanadium playing a supporting role. In addition, once sufficient Ag has been displaced, the residual Ag+ in the host can no longer stabilize the host structure and V–O environment (i.e., onset of amorphization). After amorphization, silver extrusion continues but the vanadium reduction dominates the reaction. As a result, the crossover from primarily silver reduction displacement to vanadium reduction is facilitated by the amorphization that makes vanadium reduction increasingly more favorable.

  6. Nanocrystalline K{sub 2}Ca{sub 2}(SO{sub 4}){sub 3}: Eu for proton beam dosimetry

    SciTech Connect

    Bahl, Shaila; Lochab, S. P.; Pandey, A.; Aleynikov, V. E.; Molokanov, A.; Kumar, Pratik


    This paper investigates the Thermoluminescent response of nanocrystalline K{sub 2}Ca{sub 2}(SO{sub 4}){sub 3}: Eu, prepared by Co-precipitation technique to 150 MeV proton beam. The particle size was calculated to be 45 nm by the broadening of the XRD peaks using Scherrer's formula. Samples in the form of pellets were irradiated by 150 MeV proton beam with dose range of 0.1 Gy to 325 Gy. Thermoluminescence (TL) glow curves of the irradiated samples were recorded and studied. It has been found that the phosphor shows a characteristic single peak at around 420 K. The TL response is linear in the range upto 200 Gy and then saturates for higher doses. The wider linear TL response of nanocrystalline K{sub 2}Ca{sub 2}(SO{sub 4}){sub 3}: Eu and low fading makes it a superior candidate as a dosimeter to be used for detecting the doses of protons beams for its various applications in the field of space, therapy and research.

  7. Crystal structure, thermally stability and photoluminescence properties of novel Sr{sub 10}(PO{sub 4}){sub 6}O:Eu{sup 2+} phosphors

    SciTech Connect

    Guo, Qingfeng; Liao, Libing Mei, Lefu; Liu, Haikun


    A series of novel luminescent phosphors Sr{sub 10}(PO{sub 4}){sub 6}O:Eu{sup 2+} with apatite structure were synthesized via a high temperature solid-state reaction. The phase structure, photoluminescence (PL) properties, the PL thermal stability, as well as the fluorescence decay curves of the samples were investigated to characterize the resulting samples, and the selected Sr{sub 9.97}(PO{sub 4}){sub 6}O:0.03Eu{sup 2+} phosphor exhibits strong thermal quenching resistance, retaining the luminance of 88.73% at 150 °C. The quenching concentration of Eu{sup 2+} in Sr{sub 10}(PO{sub 4}){sub 6}O was about 0.03 attributing to the dipole–quadrupole interaction. The Sr{sub 10}(PO{sub 4}){sub 6}O:Eu{sup 2+} phosphor exhibited a broad-band blue emission at 439 nm upon excitation at 346 nm. The results indicate that Sr{sub 10}(PO{sub 4}){sub 6}O:Eu{sup 2+} phosphors have potential applications as near UV-convertible phosphors for white-light UV LEDs. - Graphical abstract: Sr{sub 10}(PO{sub 4}){sub 6}O:Eu{sup 2+} phosphors have potential applications as near UV-convertible phosphors for white-light UV LEDs. - Highlights: • Sr{sub 9.97}(PO{sub 4}){sub 6}O:0.03Eu{sup 2+} phosphor exhibits strong thermal quenching resistance. • Two different Eu{sup 2+} emission centers exists in Sr{sub 10}(PO{sub 4}){sub 6}O. • The activation energy was also estimated for the Eu{sup 2+} luminescence center.

  8. Photoluminescence performance of thulium doped Li{sub 4}SrCa(SiO{sub 4}){sub 2} under irradiation of ultraviolet and vacuum ultraviolet lights

    SciTech Connect

    Wang, Zhaofeng; Li, Yezhou; Liu, Xiong; Wei, Xingmin; Chen, Yueling; Zhou, Fei; Wang, Yuhua


    Highlights: • A novel blue-emitting phosphor Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} was reported. • Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} exhibited excellent thermal and irradiation stability. • Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} was found to possess high color purity. - Abstract: In this work, we synthesized Tm{sup 3+} doped Li{sub 4}SrCa(SiO{sub 4}){sub 2} phosphors and investigated their photoluminescence properties under the excitation of ultraviolet and vacuum ultraviolet lights. The crystal structure analysis and variation of cell parameters confirm that Tm{sup 3+} ions have been successfully doped in the structure of Li{sub 4}SrCa(SiO{sub 4}){sub 2} host by occupying the sites of Ca{sup 2+} with the coordination number of 6. The luminescence results suggest that Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} is a good blue-emitting phosphor when excited by ultraviolet and vacuum ultraviolet irradiations. In addition, it is observed that there is nearly no degradation for Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} after undergoing thermal and irradiation treatments. Possible mechanisms for the luminescence processes are proposed on the basis of the discussion of excitation and emission spectra. In particular, the emission color of Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} by excitation of 147 and 172 nm irradiations is very close to the standard blue color, suggesting that it could be potentially applied in plasma display panels and mercury-free fluorescence lamps.

  9. Investigation of the physical properties of the tetragonal CeMAl4sub>Si2 (M = Rh, Ir, Pt) compounds

    SciTech Connect

    Ghimire, N. J.; Ronning, F.; Williams, D. J.; Scott, B. L.; Luo, Yongkang; Thompson, J. D.; Bauer, E. D.


    The synthesis, crystal structure and physical properties studied by means of x-ray diffraction, magnetic, thermal and transport measurements of CeMAl4sub>Si2 (M = Rh, Ir, Pt) are reported, along with the electronic structure calculations for LaMAl4sub>Si2 (M = Rh, Ir, Pt). These materials adopt a tetragonal crystal structure (space group P4/mmm) comprised of BaAl4sub> blocks, separated by MAl2 units, stacked along the c-axis. Both CeRhAl4sub>Si2 and CeIrAl4sub>Si2 order antiferromagnetically below TN1 = 14 and 16 K, respectively, and undergo a second antiferromagnetic transitition at lower temperature (TN2 = 9 and 14 K, respectively). CePtAl4sub>Si2 orders ferromagnetically below TC = 3 K with an ordered moment of μsat = 0.8 μB for a magnetic field applied perpendicular to the c-axis. Electronic structure calculations reveal quasi-2D character of the Fermi surface.

  10. Controlled synthesis, characterization and photoluminescence property of olive-like tetragonal α-Nd{sub 2}(MoO{sub 4}){sub 3}

    SciTech Connect

    Zhang, Youjin; Zheng, Ao; Yang, Xiaozhi; He, Hongmei; Fan, Yun


    Highlights: ► The olive-like tetragonal α-Nd{sub 2}(MoO{sub 4}){sub 3} was gained with EDTA assisted hydrothermal method. ► The product was characterized by XRD, XPS, FTIR, FESEM, and PL. ► The possible formation mechanism for olive-like α-Nd{sub 2}(MoO{sub 4}){sub 3} was proposed. ► The PL in visible region of the olive-like α-Nd{sub 2}(MoO{sub 4}){sub 3} was studied. -- Abstract: The olive-like tetragonal α-Nd{sub 2}(MoO{sub 4}){sub 3} was obtained by a convenient and facile complex agent assisted hydrothermal method. The product was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, field-emission scanning electron microscopy (FESEM) and photoluminescence (PL). The possible formation mechanism of the olive-like α-Nd{sub 2}(MoO{sub 4}){sub 3} was proposed. The photoluminescence property in visible region of the olive-like tetragonal α-Nd{sub 2}(MoO{sub 4}){sub 3} was studied.

  11. New measurement of the {sup 68}Zn(4{sub 1}{sup +}) g factor combined with a reanalysis of previous data

    SciTech Connect

    Moschner, K.; Bernards, C.; Bettermann, L.; Speidel, K.-H.; Leske, J.; Bauer, C.; Moeller, T.; Honma, M.; Maier-Komor, P.; Muecher, D.


    We have remeasured and have redetermined the g factor for the 4{sub 1}{sup +} state in {sup 68}Zn following inconsistencies between earlier measurements and a recent result. We have reanalyzed several former measurements by applying an alternative analysis procedure, which allows for determining the precession effect separately for each gamma detector implying less uncertainties in the background subtraction for the relevant spectra. In addition, all measured g-factor and B(E2) data for the first 2{sup +} and 4{sup +} states in all stable even-A Zn isotopes and the radioactive {sup 62}Zn, are compared with new large-scale shell model calculations based on the most advanced effective interaction in the fpg-shell model space.

  12. Characterization of LiMn2O4sub> cathodes by electrochemical strain microscopy

    SciTech Connect

    Alikin, D. O.; Ievlev, A. V.; Luchkin, S. Yu.; Turygin, A. P.; Shur, V. Ya.; Kalinin, S. V.; Kholkin, A. L.


    Electrochemical strain microscopy (ESM) is a scanning probe microscopy(SPM) method in which the local electrodiffusion is probed via application of AC voltage to the SPM tip and registration of resulting electrochemical strain. In this study, we implemented ESM to measure local strain in bulk LiMn2O4sub> cathodes of a commercial Li-battery in different states of charge to investigate distribution of Li-ion mobility and concentration. Ramped AC ESM imaging and voltage spectroscopy were used to find the most reliable regime of measurements allowing separating and diminishing different contributions to ESM. This is not a trivial task due to complex geometry of the sample and various obstacles resulting in less predictable contributions of different origins into ESM response: electrostatic tip–surface interactions, charge injection, electrostriction, and flexoelectricity. Finally, understanding and control of these contributions is an important step towards quantitative interpretation of ESM data.

  13. Enhanced Thermoelectric Properties of Cu2ZnSnSe4sub> with Ga-doping

    SciTech Connect

    Wei, Kaya; Beauchemin, Laura; Wang, Hsin; Porter, Wallace D.; Martin, Joshua; Nolas, George S.


    Gallium doped Cu2ZnSnSe4sub> quaternary chalcogenides with and without excess Cu were synthesized by elemental reaction and densified using hot pressing in order to investigate their high temperature thermoelectric properties. The resistivity, , and Seebeck coefficient, S, for these materials decrease with increased Ga-doping while both mobility and effective mass increase with Ga doping. The power factor (S2/ρ) therefore increases with Ga-doping. The highest thermoelectric figure of merit (ZT = 0.39 at 700 K) was obtained for the composition that had the lowest thermal conductivity. Our results suggest an approach to achieving optimized thermoelectric properties and are part of the continuing effort to explore different quaternary chalcogenide compositions and structure types, as this class of materials continues to be of interest for thermoelectrics applications.

  14. The role of Sb in solar cell material Cu 2 ZnSnS 4sub>

    SciTech Connect

    Zhang, Xiaoli; Han, Miaomiao; Zeng, Zhi; Duan, Yuhua


    In this study, based on first-principles calculations we report a possible mechanism of the efficiency improvement of the Sb-doped Cu2ZnSnS4sub> (CZTS) solar cells from the Sb-related defect point of view. Different from Sb in CuInSe2 which substituted the Cu atomic site and acted as group-13 elements on the Cu-poor growth condition, we find out that Sb prefers to substitute Sn atomic site and acts as group-14 elements on the Cu-poor growth condition in CZTS. At low Sb concentration, SbSn produces a deep defect level which is detrimental for the solar cell application. At high Sb concentration, Sb 5s states form an isolated half-filled intermediate band at 0.5 eV above the valence band maximum which will increase the photocurrent as well as the solar cell efficiency.

  15. Ionic liquid assisted microwave synthesis route towards color-tunable luminescence of lanthanide- doped BiPO4sub>

    SciTech Connect

    Cybinska, Joanna; Lorbeer, Chantal; Mudring, Anja -Verena


    Ln3+-doped (Ln=Sm, Eu, Tb, Dy) nanoparticles of BiPO4sub> with a particle size below 10 nm were synthesized in a straightforward manner from the appropriate mixture of the respective metal acetates and the task-specific ionic liquids choline or butylammonium dihydrogen-phosphate by conversion in a laboratory microwave (120 °C, 10 min). The ionic liquid acts not only as a solvent and microwave susceptor, but also as the reaction partner and nanoparticle stabilizer. The materials were thoroughly characterized not only with respect to their optical properties but also by PXRD, FT-IR, TEM techniques. Furthermore, depending on the lanthanide, the nanomaterial shows intense luminescence of different colors such as: orange (Sm3+), red (Eu3+), green (Tb3+) or even white (Dy3+).

  16. Beam test evaluation of electromagnetic calorimeter modules made from proton-damaged PbWO4sub> crystals

    SciTech Connect

    Adams, T.; Adzic, P.; Ahuja, S.; Anderson, D.; Andrews, M. B.; Antropov, I.; Antunovic, Z.; Arcidiacono, R.; Arenton, M. W.; Argirò, S.; Askew, A.; Attikis, A.; Auffray, E.; Baccaro, S.; Baffioni, S.; Bailleux, D.; Baillon, P.; Barney, D.; Barone, L.; Bartoloni, A.; Bartosik, N.; Becheva, E.; Bein, S.; Beirāo Da Cruz E Silva, C.; Bell, K. W.; Benaglia, A.; Bendavid, J.; Berry, D.; Besancon, M.; Betev, B.; Bialas, W.; Bianchini, L.; Biino, C.; Bitioukov, S.; Bornheim, A.; Brianza, L.; Brinkerhoff, A.; Brown, R. M.; Brummitt, A.; Busson, P.; Candelise, V.; Montoya, C. A. Carrillo; Cartiglia, N.; Cavallari, F.; Chang, Y. W.; Chen, K. F.; Chevenier, G.; Chipaux, R.; Clement, E.; Cockerill, D. J. A.; Corpe, L.; Couderc, F.; Courbon, B.; Cox, B.; Cucciati, G.; Cussans, D.; D'imperio, G.; Calafiori, D. R. Da Silva Di; Dafinei, I.; Daguin, J.; Daskalakis, G.; Mendes, A. D. Tinoco; Guio, F. De; Degano, A.; Dejardin, M.; Re, D. Del; Ricca, G. Della; Denegri, D.; Depasse, P.; Dev, N.; Deyrail, D.; Marco, E. Di; Diamond, B.; Diemoz, M.; Dissertori, G.; Dittmar, M.; Djambazov, L.; Doan, T. H.; Dobrzynski, L.; Dolgopolov, A.; Donegà, M.; Dordevic, M.; Dröge, M.; Durkin, T.; Dutta, D.; Mamouni, H. El; Elliott-Peisert, A.; Elmalis, E.; Fabbro, B.; Fasanella, G.; Faure, J.; Fay, J.; Fedorov, A.; Ferri, F.; Francis, B.; Frank, N.; Franzoni, G.; Funk, W.; Ganjour, S.; Gascon, S.; Gastal, M.; Geerebaert, Y.; Gelli, S.; Gerosa, R.; Ghezzi, A.; Giakoumopoulou, V. A.; Givernaud, A.; Gninenko, S.; Godinovic, N.; Goeckner-Wald, N.; Golubev, N.; Govoni, P.; Gras, P.; Guilloux, F.; Haller, C.; de Monchenault, G. Hamel; Hansen, M.; Hansen, P.; Hardenbrook, J.; Heath, H. F.; Hill, J.; Hirosky, R.; Hobson, P. R.; Holme, O.; Honma, A.; Hou, W. -S.; Hsiung, Y.; Iiyama, Y.; Ille, B.; Ingram, Q.; Jain, S.; Jarry, P.; Jessop, C.; Jovanovic, D.; Kachanov, V.; Kalafut, S.; Kao, K. Y.; Kellams, N.; Kesisoglou, S.; Khatiwada, A.; Konoplyannikov, A.; Konstantinov, D.; Korzhik, M.; Kovac, M.; Kubota, Y.; Kucher, I.; Kumar, A.; Kumar, A.; Kuo, C.; Kyberd, P.; Kyriakis, A.; Latyshev, G.; Lecoq, P.; Ledovskoy, A.; Lei, Y. J.; Lelas, D.; Lethuillier, M.; Li, H.; Lin, W.; Liu, Y. F.; Locci, E.; Longo, E.; Loukas, D.; Lu, R. -S.; Lucchini, M. T.; Lustermann, W.; Mackay, C. K.; Magniette, F.; Malcles, J.; Malhotra, S.; Mandjavidze, I.; Maravin, Y.; Margaroli, F.; Marinelli, N.; Marini, A. C.; Martelli, A.; Marzocchi, B.; Massironi, A.; Matveev, V.; Mechinsky, V.; Meng, F.; Meridiani, P.; Micheli, F.; Milosevic, J.; Mousa, J.; Musella, P.; Nessi-Tedaldi, F.; Neu, C.; Newman, H.; Nicolaou, C.; Nourbakhsh, S.; Obertino, M. M.; Organtini, G.; Orimoto, T.; Paganini, P.; Paganis, E.; Paganoni, M.; Pandolfi, F.; Panov, V.; Paramatti, R.; Parracho, P.; Pastrone, N.; Paulini, M.; Pauss, F.; Pauwels, K.; Pellegrino, F.; Pena, C.; Perniè, L.; Peruzzi, M.; Petrakou, E.; Petyt, D.; Pigazzini, S.; Piroué, P.; Planer, M.; Plestina, R.; Polic, D.; Prosper, H.; Ptochos, F.; Puljak, I.; Quittnat, M.; Ragazzi, S.; Rahatlou, S.; Rander, J.; Ranjan, K.; Silva, J. Rasteiro Da; Razis, P. A.; Romanteau, T.; Rosowsky, A.; Rovelli, C.; Rusack, R.; Salerno, R.; Santanastasio, F.; Santra, A.; Schönenberger, M.; Seez, C.; Sharma, V.; Shepherd-Themistocleous, C.; Shiu, J. G.; Shivpuri, R. K.; Singovsky, A.; Sinthuprasith, T.; Sirois, Y.; Smiljkovic, N.; Soffi, L.; Sun, M.; Symonds, P.; de Fatis, T. Tabarelli; Tambe, N.; Tarasov, I.; Taroni, S.; Lima, R. Teixeira De; Thea, A.; Theofilatos, K.; Thiant, F.; Titov, M.; Torbet, M.; Trapani, P. P.; Tropea, P.; Tsai, J. f.; Tsirou, A.; Turkewitz, J.; Tyurin, N.; Tzeng, Y. M.; Uzunian, A.; Valls, N.; Varela, J.; Veeraraghavan, V.; Verdini, P. G.; Vichoudis, P.; Vlassov, E.; Wang, J.; Wang, T.; Weinberg, M.; Wolfe, E.; Wood, J.; Zabi, A.; Zahid, S.; Zelepoukine, S.; Zghiche, A.; Zhang, L.; Zhu, K.; Zhu, R.; Zuyeuski, R.


    The performance of electromagnetic calorimeter modules made of proton-irradiated PbWO4sub> crystals has been studied in beam tests. The modules, similar to those used in the Endcaps of the CMS electromagnetic calorimeter (ECAL), were formed from 5×5 matrices of PbWO4sub> crystals, which had previously been exposed to 24 GeV protons up to integrated fluences between 2.1 × 1013 and 1.3 × 1014 cm–2. These correspond to the predicted charged-hadron fluences in the ECAL Endcaps at pseudorapidity η = 2.6 after about 500 fb–1 and 3000 fb–1 respectively, corresponding to the end of the LHC and High Luminosity LHC operation periods. The irradiated crystals have a lower light transmission for wavelengths corresponding to the scintillation light, and a correspondingly reduced light output. A comparison with four crystals irradiated in situ in CMS showed no significant rate dependence of hadron-induced damage. A degradation of the energy resolution and a non-linear response to electron showers are observed in damaged crystals. Direct measurements of the light output from the crystals show the amplitude decreasing and pulse becoming faster as the fluence increases. The latter is interpreted, through comparison with simulation, as a side-effect of the degradation in light transmission. In conclusion, the experimental results obtained can be used to estimate the long term performance of the CMS ECAL.

  17. Syntheses, crystal structures and vibrational spectra of KLn(SO{sub 4}){sub 2}.H{sub 2}O (Ln=La, Nd, Sm, Eu, Gd, Dy)

    SciTech Connect

    Kazmierczak, Karolina; Hoeppe, Henning A.


    The potassium lanthanide double sulphates KLn(SO{sub 4}){sub 2}.H{sub 2}O (Ln=La, Nd, Sm, Eu, Gd, Dy) were obtained by evaporation of aqueous reaction mixtures of rare earth (III) sulphates and potassium thiocyanate at 298 K. X-ray single-crystal investigations show that KLn(SO{sub 4}){sub 2}.H{sub 2}O (Ln=Nd, Sm, Eu, Gd, Dy) crystallise monoclinically (Ln=Sm: P2{sub 1}/c, Z=4, a=10.047(1), b=8.4555(1), c=10.349(1) A, wR2=0.060, R1=0.024, 945 reflections, 125 parameters) while KLa(SO{sub 4}){sub 2}.H{sub 2}O adopts space group P3{sub 2}21 (Z=3, a=7.1490(5), c=13.2439(12) A, wR2=0.038, R1=0.017, 695 reflections, 65 parameters). The coordination environment of the lanthanide ions in KLn(SO{sub 4}){sub 2}.H{sub 2}O is different in the case of the Nd/Sm/Gd and the Eu/Dy compounds, respectively. In the first case the Ln atoms are nine-fold coordinated in contrast to the latter where the Ln ions are eight-fold coordinated by oxygen atoms. The vibrational spectra of KLn(SO{sub 4}){sub 2}.H{sub 2}O and the UV-vis reflection spectra of KEu(SO{sub 4}){sub 2}.H{sub 2}O and KNd(SO{sub 4}){sub 2}.H{sub 2}O are also reported. - Graphical abstract: The lanthanide potassium double sulphates exhibit an unexpected change in the coordination mode by a simple rotation of sulphate tetrahedron 2.

  18. Synthesis, structural and spectroscopic properties of acentric triple molybdate Cs{sub 2}NaBi(MoO{sub 4}){sub 3}

    SciTech Connect

    Savina, A.A.; Atuchin, V.V.; Solodovnikov, S.F.; Solodovnikova, Z.A.; Krylov, A.S.; Maximovskiy, E.A.; Molokeev, M.S.; Oreshonkov, A.S; Pugachev, A.M.; and others


    New ternary molybdate Cs{sub 2}NaBi(MoO{sub 4}){sub 3} is synthesized in the system Na{sub 2}MoO{sub 4}–Cs{sub 2}MoO{sub 4}–Bi{sub 2}(MoO{sub 4}){sub 3}. The structure of Cs{sub 2}NaBi(MoO{sub 4}){sub 3} of a new type is determined in noncentrosymmetric space group R3c, a=10.6435(2), c=40.9524(7) Å, V=4017.71(13) Å{sup 3}, Z=12 in anisotropic approximation for all atoms taking into account racemic twinning. The structure is completely ordered, Mo atoms are tetrahedrally coordinated, Bi(1) and Bi(2) atoms are in octahedra, and Na(1) and Na(2) atoms have a distorted trigonal prismatic coordination. The Cs(1) and Cs(2) atoms are in the framework cavities with coordination numbers 12 and 10, respectively. No phase transitions were found in Cs{sub 2}NaBi(MoO{sub 4}){sub 3} up to the melting point at 826 K. The compound shows an SHG signal, I{sub 2w}/I{sub 2w}(SiO{sub 2})=5 estimated by the powder method. The vibrational properties are evaluated by Raman spectroscopy, and 26 narrow lines are measured. - Graphical abstract: - Highlights: • The crystal structure of Cs{sub 2}NaBi(MoO{sub 4}){sub 3} is defined. • The molybdate Cs{sub 2}NaBi(MoO{sub 4}){sub 3} is stable up to melting point at 826 K. • Vibrational properties of Cs{sub 2}NaBi(MoO{sub 4}){sub 3} are evaluated by Raman spectroscopy.

  19. Synthesis, structures and properties of the new lithium cobalt(II) phosphate Li{sub 4}Co(PO{sub 4}){sub 2}

    SciTech Connect

    Glaum, R.; Gerber, K.; Schulz-Dobrick, M.


    {alpha}-Li{sub 4}Co(PO{sub 4}){sub 2} has been synthesized and crystallized by solid-state reactions. The new phosphate crystallizes in the monoclinic system (P2{sub 1}/a, Z=4, a=8.117(3) Angstrom-Sign , b=10.303(8) Angstrom-Sign , c=8.118(8) Angstrom-Sign , {beta}=104.36(8) Angstrom-Sign ) and is isotypic to {alpha}-Li{sub 4}Zn(PO{sub 4}){sub 2}. The structure of {alpha}-Li{sub 4}Co(PO{sub 4}){sub 2} has been determined from single-crystal X-ray diffraction data {l_brace}R{sub 1}=0.040, wR{sub 2}=0.135, 2278 unique reflections with F{sub o}>4{sigma}(F{sub o}){r_brace}. The crystal structure, which might be regarded as a superstructure of the wurtzite structure type, is build of layers of regular CoO{sub 4}, PO{sub 4} and Li1O{sub 4} tetrahedra. Lithium atoms Li2, Li3 and Li4 are located between these layers. Thermal investigations by in-situ XRPD, DTA/TG and quenching experiments suggest decomposition followed by formation and phase transformation of Li{sub 4}Co(PO{sub 4}){sub 2}: {alpha}-Li{sub 4}Co(PO{sub 4}){sub 2} Long-Rightwards-Double-Arrow {sup 442 Degree-Sign C}{beta}-Li{sub 3}PO{sub 4}+LiCoPO{sub 4} Rightwards-Harpoon-Over-Leftwards-Harpoon {sup 773 Degree-Sign C}{beta}-Li{sub 4}Co(PO{sub 4}){sub 2} Long-Rightwards-Double-Arrow {sup quenchingto25 Degree-Sign C}{alpha}-Li{sub 4} Co(PO{sub 4}){sub 2} According to HT-XRPD at {theta}=850 Degree-Sign C{beta}-Li{sub 4}Co(PO{sub 4}){sub 2} (Pnma, Z=2, 10.3341(8) A, b=6.5829(5) A, c=5.0428(3) Angstrom-Sign ) is isostructural to {gamma}-Li{sub 3}PO{sub 4}. The powder reflectance spectrum of {alpha}-Li{sub 4}Co(PO{sub 4}){sub 2} shows the typical absorption bands for the tetrahedral chromophore [Co{sup II}O{sub 4}]. - Graphical abstract: The complex formation and decomposition behavior of Li{sub 4}Co(PO{sub 4}){sub 2} with temperature has been elucidated. The crystal structure of its {alpha}-phase was determined from single crystal data, HT-XRPD allowed derivation of a structure model for the {beta}-phase. Both

  20. Exchange bias effect in Au-Fe3O4sub> dumbbell nanoparticles induced by the charge transfer from gold

    SciTech Connect

    Feygenson, Mikhail; Bauer, John C; Gai, Zheng; Marques, Carlos; Aronson, Meigan C.; Teng, Xiaowei; Su, Dong; Stanic, Vesna; Urban, Volker S; Kevin, Beyer; Dai, Sheng


    We have studied the origin of the exchange bias effect in the Au-Fe3O4sub> dumbbell nanoparticles in two samples with different sizes of the Au seed nanoparticles (4.1 and 2.7 nm) and same size of Fe3O4sub> nanoparticles (9.8 nm). The magnetization, small-angle neutron scattering, synchrotron x-ray diffraction and scanning transmission electron microscope measurements determined the antiferromagnetic FeO wüstite phase within Fe3O4sub> nanoparticles, originating at the interface with the Au nanoparticles. The interface between antiferromagnetic FeO and ferrimagnetic Fe3O4sub> is giving rise to the exchange bias effect. The strength of the exchange bias fields depends on the interfacial area and lattice mismatch between both phases. We propose that the charge transfer from the Au nanoparticles is responsible for a partial reduction of the Fe3O4sub> into FeO phase at the interface with Au nanoparticles. The Au-O bonds are formed across the interface to accommodate an excess of oxygen released during the reduction of magnetite.

  1. The effect of Mo doping on the charge separation dynamics and photocurrent performance of BiVO 4sub> photoanodes

    SciTech Connect

    Pattengale, Brian; Huang, Jier


    Doping with electron-rich elements in BiVO4sub> photoanodes has been demonstrated as a desirable approach for improving their carrier mobility and charge separation efficiency. However, the effect of doping and dopant concentration on the carrier dynamics and photoelectrochemical performance remains unclear. In this work, we examined the effects of Mo doping on the charge separation dynamics and photocurrent performance in BiVO4sub> photoanodes. We show that the photocurrent of BiVO4sub> photoanodes increases with increasing concentration of the Mo dopant, which can be attributed to both the improved carrier mobility resulting from increased electron density and charge separation efficiency due to the diminishing of trap states upon Mo doping. The effect of doping on the electronic structure, carrier dynamics and photocurrent performance of BiVO4sub> photoanodes resulting from W and Mo dopants was also compared and discussed in this study. The knowledge gained from this work will provide important insights into the optimization of the carrier mobility and charge separation efficiency of BiVO4sub> photoanodes by controlling the dopants and their concentrations.

  2. Discovery of Fe–Ce Oxide/BiVO 4sub> Photoanodes through Combinatorial Exploration of Ni–Fe–Co–Ce Oxide Coatings

    SciTech Connect

    Shinde, Aniketa; Guevarra, Dan; Liu, Guiji; Sharp, Ian D.; Toma, Francesca M.; Gregoire, John M.; Haber, Joel A.


    An efficient photoanode is a prerequisite for a viable solar fuels technology. The challenges to realizing an efficient photoanode include the integration of a semiconductor light absorber and a metal oxide electrocatalyst to optimize corrosion protection, light trapping, hole transport, and photocarrier recombination sites. In order to efficiently explore metal oxide coatings, we employ a high throughput methodology wherein a uniform BiVO4sub> film is coated with 858 unique metal oxide coatings covering a range of metal oxide loadings and the full (Ni-Fe-Co-Ce)Ox pseudo-quaternary composition space. Photoelectrochemical characterization of the photoanodes reveals that specific combinations of metal oxide composition and loading provide up to a 13-fold increase in the maximum photoelectrochemical power generation for oxygen evolution in pH 13 electrolyte. Through mining of the high throughput data we identify composition regions that form improved interfaces with BiVO4sub>. Of particular note, integrated photoanodes with catalyst compositions in the range Fe(0.4-0.6)Ce(0.6-0.4)sub>Ox exhibit high interface quality and excellent photoelectrochemical power conversion. Furthermore, for scaled-up inkjet-printed electrodes and photoanodic electrodeposition of this composition on BiVO4sub> we can confirm the discovery and the synthesis-independent interface improvement of (Fe-Ce)Ox coatings on BiVO4sub>.

  3. CuCo2O4sub> ORR/OER Bi-functional catalyst: Influence of synthetic approach on performance

    SciTech Connect

    Serov, Alexey; Andersen, Nalin I.; Roy, Aaron J.; Matanovic, Ivana; Artyushkova, Kateryna; Atanassov, Plamen


    A series of CuCo2O4sub> catalysts were synthesized by pore forming, sol-gel, spray pyrolysis and sacrificial support methods. Catalysts were characterized by XRD, SEM, XPS and BET techniques. The electrochemical activity for the oxygen reduction and oxygen evolution reactions (ORR and OER) was evaluated in alkaline media by RRDE. Density Functional Theory was used to identify two different types of active sites responsible for ORR/OER activity of CuCo2O4sub> and it was found that CuCo2O4 sub>can activate the O-O bond by binding molecular oxygen in bridging positions between Co or Co and Cu atoms. It was found that the sacrificial support method (SSM) catalyst has the highest performance in both ORR and OER and has the highest content of phase-pure CuCo2O4sub>. It was shown that the presence of CuO significantly decreases the activity in oxygen reduction and oxygen evolution reactions. As a result, the half-wave potential (E1/2) of CuCo2O4sub>-SSM was found as 0.8 V, making this material a state-of-the-art, unsupported oxide catalyst.

  4. Accuracy in the isotope dilution mass spectrometry of uranium in rubidium uranium sulphate Rb[sub 2]U(SO[sub 4])[sub 3

    SciTech Connect

    Ramakumar, K.L.; Jeyakumar, S.; Raman, V.A.; Gnanayyan, L.; Rao, R.; Saxena, M.K.; Kavimandan, V.D.; Jain, H.C. )


    Problems encountered in the determination of uranium in rubidium uranium sulphate (Rb[sub 2]U(SO[sub 4])[sub 3]) employing isotope dilution thermal ionization mass spectrometry (ID-TIMS) are discussed. The positive bias of 0.2 to 0.3% in the determination of uranium in Rb[sub 2]U(SO[sub 4])[sub 3] by ID-TIMS with respect to the stoichiometric composition has been resolved by modifying the chemical exchange procedures. The concentration of uranium in Rb[sub 2]U(SO[sub 4])[sub 3] could be determined with an accuracy better than 0.1% employing the HClO[sub 4] treatment for proper isotopic exchange between the spike and sample isotopes. 12 refs., 1 fig., 5 tabs.

  5. Graphitic C3N4sub> as a new saturable absorber for the mid-infrared spectral range.


    Fan, Mingqi; Li, Tao; Li, Guiqiu; Ma, Houyi; Zhao, Shengzhi; Yang, Kejian; Kränkel, Christian


    The saturable absorption properties of few-layer graphitic carbon nitride (g-C3N4sub>) nanosheets near 3 μm were investigated. A stable Q-switched Er:Lu2O3 laser at 2.84 μm was realized by using a home-made g-C3N4sub> saturable absorber (SA), generating a pulse duration of 351 ns and an average output power of 1.09 W at a repetition rate of 99 kHz, corresponding to a pulse energy of 11.1 μJ. Our result indicates a great potential of g-C3N4sub> as a new SA in the 3 μm wavelength range.

  6. Femtosecond-laser-written Tm:KLu(WO4sub>)2 waveguide lasers.


    Kifle, Esrom; Mateos, Xavier; de Aldana, Javier Rodríguez Vázquez; Ródenas, Airan; Loiko, Pavel; Choi, Sun Yung; Rotermund, Fabian; Griebner, Uwe; Petrov, Valentin; Aguiló, Magdalena; Díaz, Francesc


    Depressed-index channel waveguides with a circular and photonic crystal cladding structures are prepared in a bulk monoclinic Tm:KLu(WO4sub>)2 crystal by 3D direct femtosecond laser writing. The channel waveguide structures are characterized and laser operation is achieved using external mirrors. In the continuous-wave mode, the maximum output power of 46 mW is achieved at 1912 nm corresponding to a slope efficiency of 15.2% and a laser threshold of only 21 mW. Passive Q-switching of a waveguide with a circular cladding is realized using single-walled carbon nanotubes. Stable 7 nJ/50 ns pulses are achieved at a repetition rate of 1.48 MHz. This first demonstration of ∼2  μm fs-laser-written waveguide lasers based on monoclinic double tungstates is promising for further lasers of this type doped with Tm3+ and Ho3+  ions.

  7. The structure of (CENP-A-H4)<sub>2 reveals physical features that mark centromeres

    SciTech Connect

    Sekulic, Nikolina; Bassett, Emily A; Rogers, Danielle J; Black, Ben E


    Centromeres are specified epigenetically, and the histone H3 variant CENP-A is assembled into the chromatin of all active centromeres. Divergence from H3 raises the possibility that CENP-A generates unique chromatin features to mark physically centromere location. Here we report the crystal structure of a subnucleosomal heterotetramer, human (CENP-A-H4)<sub>2, that reveals three distinguishing properties encoded by the residues that comprise the CENP-A targeting domain (CATD; ref. 2): (1) a CENP-A-CENP-A interface that is substantially rotated relative to the H3-H3 interface; (2) a protruding loop L1 of the opposite charge as that on H3; and (3) strong hydrophobic contacts that rigidify the CENP-A-H4 interface. Residues involved in the CENP-A-CENP-A rotation are required for efficient incorporation into centromeric chromatin, indicating specificity for an unconventional nucleosome shape. DNA topological analysis indicates that CENP-A-containing nucleosomes are octameric with conventional left-handed DNA wrapping, in contrast to other recent proposals. Our results indicate that CENP-A marks centromere location by restructuring the nucleosome from within its folded histone core.

  8. Compact KGd(WO4sub>)2 picosecond pulse-train synchronously pumped broadband Raman laser.


    Gao, Xiao Qiang; Long, Ming Liang; Meng, Chen


    We demonstrate an efficient approach to realizing an extra-cavity, synchronously pumped, stimulated Raman cascaded process under low repetition frequency (1 kHz) pump conditions. We also construct a compact KGd(WO4sub>)2 (KGW) crystal picosecond Raman laser that has been configured as the developed method. A pulse-train green laser pumped the corresponding 70 mm long KGW crystal Raman cavity. The pulse train contains six pulses, about 800 ps separated, for every millisecond; thus, it can realize synchronous pumping between pump pulse and the pumped Raman cavity. The investigated system produced a collinear Raman laser output that includes six laser lines covering the 532 to 800 nm spectra. This is the first report on an all-solid-state, high-average-power picosecond collinear multi-wavelength (more than three laser components) laser to our knowledge. This method has never been reported on before in the synchronously pumped stimulated Raman scattering (SRS) realm.

  9. Nonperturbative tests for asymptotic freedom in the PT-symmetric (-{phi}{sup 4}){sub 3+1} theory

    SciTech Connect

    Shalaby, Abouzeid; Al-Thoyaib, Suleiman S.


    In the literature, the asymptotic freedom property of the (-{phi}{sup 4}) theory is always concluded from real-line calculations while the theory is known to be a non-real-line one. In this article, we test the existence of the asymptotic freedom in the (-{phi}{sup 4}){sub 3+1} theory using the mean field approach. In this approach and contrary to the original Hamiltonian, the obtained effective Hamiltonian is rather a real-line one. Accordingly, this work resembles the first reasonable analysis for the existence of the asymptotic freedom property in the PT-symmetric (-{phi}{sup 4}) theory. In this respect, we calculated three different amplitudes of different positive dimensions (in mass units) and find that all of them go to very small values at high energy scales (small coupling) in agreement with the spirit of the asymptotic freedom property of the theory. To test the validity of our calculations, we obtained the asymptotic behavior of the vacuum condensate in terms of the coupling, analytically, and found that the controlling factor {Lambda} has the value ((4{pi}){sup 2}/6)=26.319 compared to the result {Lambda}=26.3209 from the literature, which was obtained via numerical predictions. We assert that the nonblowup of the massive quantities at high energy scales predicted in this work strongly suggests the possibility of the solution of the famous hierarchy puzzle in a standard model with the PT-symmetric Higgs mechanism.

  10. Magnetic susceptibility, specific heat and magnetic structure of CuNi{sub 2}(PO{sub 4}){sub 2}

    SciTech Connect

    Escobal, Jaione; Pizarro, Jose L.; Mesa, Jose L. . E-mail:; Larranaga, Aitor; Fernandez, Jesus Rodriguez; Arriortua, Maria I.; Rojo, Teofilo


    CuNi{sub 2}(PO{sub 4}){sub 2} phosphate has been synthesized by the ceramic method at 800 deg. C in air. The crystal structure consists of a three-dimensional skeleton constructed from MO{sub 4} (M{sup II} =Cu and Ni) planar squares and M{sub 2}O{sub 8} dimers with square pyramidal geometry, which are interconnected by (PO{sub 4}){sup 3-} oxoanions with tetrahedral geometry. The magnetic behavior has been studied on powdered sample by using susceptibility, specific heat and neutron diffraction data. The bimetallic copper(II)-nickel(II) orthophosphate exhibits a three-dimensional magnetic ordering at, approximately, 29.8 K. However, its complex crystal structure hampers any parametrization of the J-exchange parameter. The specific heat measurements exhibit a three-dimensional magnetic ordering ({lambda}-type) peak at 29.5 K. The magnetic structure of this phosphate shows ferromagnetic interactions inside the Ni{sub 2}O{sub 8} dimers, whereas the sublattice of Cu(II) ions presents antiferromagnetic couplings along the y-axis. The change of the sign in the magnetic unit-cell, due to the [1/2, 0, 1/2] propagation vector determines a purely antiferromagnetic structure. - Graphical abstract: Magnetic structure of CuNi2(PO4)2.

  11. SU(4){sub L} x U(1){sub X} three-family model for the electroweak interaction

    SciTech Connect

    Sanchez, Luis A.; Wills-Toro, Luis A.; Zuluaga, Jorge I.


    An extension of the gauge group SU(2){sub L} x U(1){sub Y} of the standard model to the symmetry group SU(4){sub L} x U(1){sub X} (3-4-1 for short) is presented. The model does not contain exotic electric charges and anomaly cancellation is achieved with a family of quarks transforming differently from the other two, thus leading to FCNC. By introducing a discrete Z{sub 2} symmetry we obtain a consistent fermion mass spectrum, and avoid unitarity violation of the Cabibbo-Kobayashi-Maskawa mixing matrix arising from the mixing of ordinary and exotic quarks. The neutral currents coupled to all neutral vector bosons are studied, and by using CERN LEP and SLAC Linear Collider data at Z-pole and atomic parity violation data, we bound parameters of the model related to tree-level Z-Z{sup '} mixing. These parameters are further constrained by using experimental input from neutral meson mixing in the analysis of sources of FCNC present in the model. Constraints coming from the contribution of exotic particles to the one-loop oblique electroweak parameters S, T and U are also briefly discussed. Finally, a comparison is done of the predictions of different classes of 3-4-1 models without exotic electric charges.

  12. Oxygen trapped by rare earth tetrahedral clusters in Nd4sub>FeOS6: Crystal structure, electronic structure, and magnetic properties

    SciTech Connect

    Lin, Qisheng; Taufour, Valentin; Zhang, Yuemei; Wood, Max; Drtina, Thomas; Bud’ko, Sergey L.; Canfield, Paul C.; Miller, Gordon J.


    Single crystals of Nd4sub>FeOS6 were grown from an Fe-S eutectic solution. Single crystal X-ray diffraction analysis revealed a Nd4sub>MnOSe6-type structure (P63mc, a = 9.2693(1) Å, c = 6.6650(1) Å, V = 495.94(1) Å3, Z = 2), featuring parallel chains of face-sharing [FeS6x1/2]4- trigonal antiprisms and interlinked [Nd4sub>OS3]4+ cubane-like clusters. Oxygen atoms were found to be trapped by Nd4 clusters in the [Nd4OS3]4+ chains. Structural differences among Nd4sub>MnOSe6-type Nd4sub>FeOS6 and the related La3CuSiS7- and Pr8CoGa3-type structures have been described. Magnetic susceptibility measurements on Nd4sub>FeOS6 suggested the dominance of antiferromagnetic interactions at low temperature, but no magnetic ordering down to 2 K was observed. Spin-polarized electronic structure calculations revealed magnetic frustration with dominant antiferromagnetic interactions.

  13. New structure of high-pressure body-centered orthorhombic Fe2SiO4sub>

    SciTech Connect

    Yamanaka, Takamitsu; Kyono, Atsushi; Nakamoto, Yuki; Kharlamova, Svetlana; Struzhkin, Viktor V.; Gramsch, Stephen A.; Mao, Ho-kwang; Hemley, Russell J.


    Here, a structural change in Fe2SiO4sub> spinel and the structure of a new high pressure phase are determined by Rietveld 26 profile fitting of x-ray diffraction data up to 64 GPa at ambient temperature. The compression curve of the spinel is discontinuous at approximately 20 GPa. Fe Kβ x-ray emission measurements at high pressure show that the transition from a high spin (HS) to an intermediate spin (IS) state begins at 17 GPa in the spinel phase. The IS electronic state is gradually enhanced with pressure, which results in an isostructural phase transition. A transition from the cubic spinel structure to a body centered orthorhombic phase (I-Fe2SiO4sub>) with space group Imma and Z=4 was observed at approximately 34 GPa. The structure of I-Fe2SiO4sub> has two crystallographically distinct FeO6 octahedra, which are arranged in layers parallel to (101) and (011) and are very similar to the layers of FeO6 octahedra that constitute the spinel structure. Silicon also exists in six-fold coordination in I-Fe2SiO4sub>. The transformation to the new high-pressure phase is reversible under decompression at ambient temperature. A Martensitic transformation of each slab of the spinel structure with translation vector [$\\vec{1/8}$ $\\vec{1/8}$ $\\vec{1/8}$] generates the I-Fe2SiO4sub> structure. Laser heating of I-Fe2SiO4sub> at 1500 K results in a decomposition of the material to rhombohedral FeO and SiO2 stishovite.

  14. Photoluminescence and thermoluminescence properties of Tb{sup 3+} doped K{sub 3}Gd(PO{sub 4}){sub 2} nanophosphor

    SciTech Connect

    Gupta, Palvi; Bedyal, A.K.; Kumar, Vinay; Khajuria, Y.; Lochab, S.P.; Pitale, S.S.; Ntwaeaborwa, O.M.; Swart, H.C.


    Energy level diagram of Tb{sup 3+} ion in the K{sub 3}Gd(PO{sub 4}){sub 2} host lattice. - Highlights: • First time, a detailed TL and PL study on undoped and Tb{sup 3+} doped K{sub 3}Gd(PO{sub 4}){sub 2} nanophosphor. • Combustion method was employed to synthesize the Tb{sup 3+} doped K{sub 3}Gd(PO{sub 4}){sub 2} nanophosphor. • Mechanism of excitation and emission in undoped and Tb{sup 3+} doped K{sub 3}Gd(PO{sub 4}){sub 2} nanophosphor was given. - Abstract: Tb{sup 3+} doped nanoparticulate K{sub 3}Gd(PO{sub 4}){sub 2} phosphor was prepared by combustion method using urea as a fuel. The structure, optical and luminescent properties of the phosphor were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), and thermoluminescence (TL) spectroscopy. In undoped K{sub 3}Gd(PO{sub 4}){sub 2}, the excitation and emission peaks at 273 nm and 323 nm belongs to the {sup 8}S{sub 7/2} → {sup 6}I{sub J(J=7/2)} and {sup 6}P{sub J(J=7/2)} → {sup 8} S{sub 7/2} transitions of Gd{sup 3+} while green emission was observed in the Tb{sup 3+} doped K{sub 3}Gd(PO{sub 4}){sub 2}. TL study was carried out after exposing the samples to γ-radiations (0.1–5 kGy) in the K{sub 3}Gd(PO{sub 4}){sub 2}:Tb{sup 3+} (1.5 mol%). The calculated kinetic parameters were compared with different methods. The band gap of the phosphor was estimated as 5.80 eV. The green shade of the Tb{sup 3+} ion with the CIE coordinates (x, y) as (0.29, 0.54) was in good agreement with the well known green phosphors.

  15. Magnetic, Caloric and Crystallographic Properties of Dy5(SixGe1-x)4sub> Alloys

    SciTech Connect

    Ivchenko, Vitaliy Vladislavovich


    A study of a series of Dy5(SixGe1-x)4sub> alloys using dc and ac magnetic susceptibility, magnetization, heat capacity, and x-ray powder diffraction techniques revealed that the variation of the magnetic properties and crystal structures with composition is similar to that observed in the Gd5(SixGe1-x)4sub> system, except that the magnetic ordering temperatures are lower. The magnetic phase transition temperatures vary from ~ 46K (Dy5Ge4sub>) to ~ 137K (Dy5Si4sub>). The intermediate ternary phase Dy5Si3Ge undergoes a first order magnetic phase transition at ~ 65K. The value of magnetic entropy change for this composition is quite large (-34J/kgK for magnetic field change from 0 to 50kOe), compared to the values for the two end members (-7 J/kgK for Dy5Ge4sub> and -12.5J/kgK for Dy5Si4sub>). The magnetization and ac susceptibility measurements showed that alloys with monoclinic crystal structure have a non-collinear ordering of the magnetic moments at low temperatures. The alloy Dy5Si3Ge appears to exhibit a FM phase transition below the Curie temperature at 65K. Also a series of critical fields are observed at low temperature during magnetization vs magnetic field measurements in all of the Dy5(SixGe1-x)4sub> alloys regardless type of crystal structure. The Dy5(SixGe1-x)4sub> alloys, where 0.67≤x≤1, may be useful magnetic refrigerant materials in the ~50 to ~160K temperature range.

  16. Magnetic structures of R5Ni2In4sub> and R11Ni4sub>In9 ( R = Tb and Ho): Strong hierarchy in the temperature dependence of the magnetic ordering in the multiple rare-earth sublattices

    SciTech Connect

    Ritter, C.; Provino, A.; Manfrinetti, P.; Pecharsky, V. K.; Gschneidner, Jr., K. A.; Dhar, S. K.


    In this study, the magnetic properties and magnetic structures of the R5Ni2In4sub> and the microfibrous R 11Ni4sub>In9 compounds with R = Tb and Ho have been examined using magnetization, heat capacity, and neutron diffraction data. Rare earth atoms occupy three and five symmetrically inequivalent rare earth sites in R5Ni2In4sub> and R 11Ni4sub>In9 compounds, respectively. As a result of the intra- and inter-magnetic sublattice interactions, the magnetic exchange interactions are different for various rare earth sites; this leads to a cascade of magnetic transitions with a strong hierarchy in the temperature dependence of the magnetic orderings.

  17. Synthesis, crystal structure and spectroscopy properties of Na{sub 3} AZr(PO{sub 4}){sub 3} (A=Mg, Ni) and Li{sub 2.6}Na{sub 0.4}NiZr(PO{sub 4}){sub 3} phosphates

    SciTech Connect

    Chakir, M. . E-mail:; El Jazouli, A.; Waal, D. de


    Na{sub 3} AZr(PO{sub 4}){sub 3} (A=Mg, Ni) phosphates were prepared at 750 deg. C by coprecipitation route. Their crystal structures have been refined at room temperature from X-ray powder diffraction data using Rietveld method. Li{sub 2.6}Na{sub 0.4}NiZr(PO{sub 4}){sub 3} was synthesized through ion exchange from the sodium analog. These materials belong to the Nasicon-type structure. Raman spectra of Na{sub 3} AZr(PO{sub 4}){sub 3} (A=Mg, Ni) phosphates present broad peaks in favor of the statistical distribution in the sites around PO{sub 4} tetrahedra. Diffuse reflectance spectra indicate the presence of octahedrally coordinated Ni{sup 2+} ions. - Graphical abstract: Structure of Na{sub 3} AZr(PO{sub 4}){sub 3} (A=Mg, Ni) phosphates. Display Omitted.

  18. Phase transition and multicolor luminescence of Eu{sup 2+}/Mn{sup 2+}-activated Ca{sub 3}(PO{sub 4}){sub 2} phosphors

    SciTech Connect

    Li, Kai; Chen, Daqin; Xu, Ju; Zhang, Rui; Yu, Yunlong; Wang, Yuansheng


    Graphical abstract: We have synthesized Eu{sup 2+} doped and Eu{sup 2+}/Mn{sup 2+} co-doped Ca{sub 3}(PO{sub 4}){sub 2} phosphors. The emitting color varies from blue to green with increasing of Eu{sup 2+} content for the Eu{sup 2+}-doped phosphor, and the quantum yield of the 0.05Eu{sup 2+}: Ca{sub 2.95}(PO{sub 4}){sub 2} sample reaches 56.7%. Interestingly, Mn{sup 2+} co-doping into Eu{sup 2+}: Ca{sub 3}(PO{sub 4}){sub 2} leads to its phase transition from orthorhombic to rhombohedral, and subsequently generates tunable multi-color luminescence from green to red via Eu{sup 2+} → Mn{sup 2+} energy transfer. - Highlights: • A series of novel Eu{sup 2+}: Ca{sub 3}(PO{sub 4}){sub 2} phosphors were successfully synthesized. • Phase transition of Ca{sub 3}(PO{sub 4}){sub 2} from orthorhombic to rhombohedral occurred when Mn{sup 2+} ions were doped. • The phosphors exhibited tunable multi-color luminescence. • The quantum yield of 0.05Eu{sup 2+}: Ca{sub 2.95}(PO{sub 4}){sub 2} phosphor can reach 56.7%. • The analyses of phosphors were carried out by many measurements. - Abstract: Intense blue-green-emitting Eu{sup 2+}: Ca{sub 3}(PO{sub 4}){sub 2} and tunable multicolor-emitting Eu{sup 2+}/Mn{sup 2+}: Ca{sub 3}(PO{sub 4}){sub 2} phosphors are prepared via a solid-state reaction route. Eu{sup 2+}-doped orthorhombic Ca{sub 3}(PO{sub 4}){sub 2} phosphor exhibits a broad emission band in the wavelength range of 400–700 nm with a maximum quantum yield of 56.7%, and the emission peak red-shifts gradually from 479 to 520 nm with increase of Eu{sup 2+} doping content. Broad excitation spectrum (250–420 nm) of Eu{sup 2+}: Ca{sub 3}(PO{sub 4}){sub 2} matches well with the near-ultraviolet LED chip, indicating its potential applications as tri-color phosphors in white LEDs. Interestingly, Mn{sup 2+} co-doping into Eu{sup 2+}: Ca{sub 3}(PO{sub 4}){sub 2} leads to its phase transition from orthorhombic to rhombohedral, and subsequently generates tunable multi

  19. Stabilization of MgAl2O4sub> spinel surfaces via doping

    SciTech Connect

    Hasan, Md. M.; Dholabhai, Pratik P.; Castro, Ricardo H. R.; Uberuaga, Blas P.


    Here, the surface structure of complex oxides plays a vital role in processes such as sintering, thin film growth, and catalysis, as well as being a critical factor determining the stability of nanoparticles. We report atomistic calculations of the low-index stoichiometric magnesium aluminate spinel (MgAl2O4sub>) surfaces, each with two different chemical terminations. High temperature annealing was used to explore the potential energy landscape and provide more stable surface structures. We find that the lowest energy surface is {100} while the highest energy surface is {111}. The surfaces were subsequently doped with three trivalent dopants (Y3+, Gd3+, La3+) and one tetravalent dopant (Zr4+) and both the surface segregation energies of the dopants and surface energies of the doped surface were determined. All of the dopants reduce the surface energy of spinel, though this reduction in energy depends on both the size and valence of the dopant. Dopants with larger ionic radius tend to segregate to the surface more strongly and reduce the surface energy to a greater extent. Furthermore, the ionic valence of the dopants seems to have a stronger influence on the segregation than does ionic size. For both undoped and doped spinel, the predicted crystal shape is dominated by {100} surfaces, but the relative fraction of the various surfaces changes with doping due to the unequal changes in energy, which has implications on equilibrium nanoparticle shapes and therefore on applications sensitive to surface properties.

  20. Single crystal synthesis and magnetism of the BaLn2O4sub> family (Ln = lanthanide)

    SciTech Connect

    Besara, Tiglet; Lundberg, Matthew S.; Sun, Jifeng; Ramirez, Daniel; Dong, Lianyang; Whalen, Jeffrey B.; Vasquez, Rafael; Herrera, Felix; Allen, John R.; Davidson, Michael W.; Siegrist, Theo


    The series of compounds in the BaLn2O4sub> family (Ln = La–Lu, Y) has been synthesized for the first time in single crystalline form, using a molten metal flux. The series crystallizes in the CaV2O4sub> structure type with primitive orthorhombic symmetry (space group Pnma, #62), and a complete structural study of atomic positions, bonds, angles, and distortions across the lanthanide series is presented. With the exception of the Y, La, Eu, and Lu members, magnetic susceptibility measurements were performed between 2 K and 300 K. BaCe2O4sub> and BaYb2O4sub> display large crystal fields effects and suppression of magnetic ordering. As a result, all compounds show signs of magnetic frustration due to the trigonal arrangements of the trivalent lanthanide cations in the structure.

  1. Kondo lattice and antiferromagnetic behavior in quaternary CeTAl4sub>Si2 (T = Rh, Ir) single crystals

    SciTech Connect

    Maurya, Arvind; Kulkarni, Ruta; Thamizhavel, Arumugam; Paudyal, Durga; Dhar, Sudesh Kumar


    Here, we have explored in detail the anisotropic magnetic properties of CeRhAl4sub>Si2 and CeIrAl4sub>Si2, which undergo two antiferromagnetic transitions, at TN1 = 12.6 and 15.5 K, followed by a second transition at TN2 = 9.4 and 13.8 K, respectively, with the [001]-axis as the relatively easy axis of magnetization. The electrical resistivity at ambient and applied pressure provides evidence of Kondo interaction in both compounds, further supported by a reduced value of the entropy associated with the magnetic ordering. The Sommerfeld coefficient γ is inferred to be 195.6 and 49.4 mJ/(mol K2) for CeRhAl4sub>Si2 and CeIrAl4sub>Si2, respectively, classifying these materials as moderate heavy-fermion compounds. The crystal electric field energy levels are derived from the peak seen in the Schottky heat capacity. Furthermore, we have also performed electronic structure calculations by using the local spin density approximation + U [LSDA+U] approach, which provide physical insights on the observed magnetic behavior of these two compounds.

  2. Low Temperature Propane Oxidation over Co3O4sub> based Nano-array Catalysts. Ni Dopant Effect, Reaction Mechanism and Structural Stability

    SciTech Connect

    Ren, Zheng; Wu, Zili; Gao, Puxian; Song, Wenqiao; Xiao, Wen; Guo, Yanbing; Ding, Jun; Suib, Steven L.; Gao, Pu-Xian


    Low temperature propane oxidation has been achieved by Co3O4sub>-based nano-array catalysts featuring low catalytic materials loading. The Ni doping into the Co3O4sub> lattice has led to enhanced reaction kinetics at low temperature by promoting the surface lattice oxygen activity. In situ DRIFTS investigation in tandem with isotopic oxygen exchange reveals that the propane oxidation proceeds via Mars-van Krevelen mechanism where surface lattice oxygen acts as the active site whereas O2 in the reaction feed does not directly participate in CO2 formation. The Ni doping promotes the formation of less stable carbonates on the surface to facilitate the CO2 desorption. The thermal stability of Ni doped Co3O4sub> decreases with increased Ni concentration while catalytic activity increases. A balance between enhanced activity and compromised thermal stability shall be considered in the Ni doped Co3O4sub> nano-array catalysts for low temperature hydrocarbon oxidation. This study provides useful and timely guidance for rational catalyst design toward low temperature catalytic oxidation.

  3. Solvothermal synthesis of monodispersed CoZr{sub 4}(PO{sub 4}){sub 6} microspheres and their application as microwave absorber

    SciTech Connect

    Chen, Tingting; Sun, Genban; Ma, Shulan; Yang, Xiaojing; Hu, Changwen


    Graphical abstract: Monodispersed CoZr{sub 4}(PO{sub 4}){sub 6} porous microspheres with shell structure were synthesized via a combined solvothermal method and calcination route. The radar-wave absorbability of the purple sample calcined at 900 Degree-Sign C was strongest at the frequency of about 8.5 GHz. Highlights: Black-Right-Pointing-Pointer In this study we synthesized monodispersed CoZr{sub 4}(PO{sub 4}){sub 6} porous microspheres as microwave absorber. Black-Right-Pointing-Pointer The relationship between microstructures and the electromagnetic properties was indicated. Black-Right-Pointing-Pointer The radar-wave absorbability of the sample was included. -- Abstract: Monodispersed CoZr{sub 4}(PO{sub 4}){sub 6} microspheres with a diameter of 40 {mu}m were achieved via a combining solvothermal and calcination route. The crystallinity of the calcined microspheres with shell structure was improved, while the monodisperse property and morphologies remained. The possible formation mechanism of the porous CoZr{sub 4}(PO{sub 4}){sub 6} microspheres with nanoshell was proposed. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectra (FT-IR) technologies, thermal analysis (TG and DSC), nitrogen adsorption-desorption isotherms and network analyzer. The sample calcined at 900 Degree-Sign C shows a strongest absorbability in the radar-wave absorbability test.

  4. Highly Selective Colorimetric and Luminescence Response of a Square-Planar Platinum(II) Terpyridyl Complex to Aqueous TcO4sub>-

    SciTech Connect

    Chatterjee, Sayandev; Norton, Amie E.; Edwards, Matthew K.; Peterson, James M.; Taylor, Stephen D.; Bryan, Samuel A.; Andersen, Amity; Govind, Niranjan; Albrecht-Schmitt, Thomas E.; Connick, William; Levitskaia, Tatiana G.


    In an effort to address the need for a rapid, selective and economical detection technique for aqueous pertechnetate (TcO4sub>-) anion based on recognition at the molecular level, simple salts of transition metal complexes that undergo a distinct spectroscopic change upon exposure to aqueous anions were explored. The Pt(II) complex [Pt(tpy)Br]SbF6 (tpy=2,2';6',2"-terpyridine) undergoes a dramatic color change and intense luminescence response upon TcO4sub>- uptake due to concomitant enhancement of Pt•••Pt interactions. The spectroscopic response was highly selective and quantitative for aqueous TcO4sub>- among other competing anions. Complimentary Raman spectroscopy and microscopy techniques, structural determination and theoretical methods were employed to achieve molecular-level understanding of the mechanism of the response to aqueous TcO4sub>-.

  5. Li/Ag2VO2PO4sub> batteries: the roles of composite electrode constituents on electrochemistry

    SciTech Connect

    Bock, David C.; Bruck, Andrea M.; Pelliccione, Christopher J.; Zhang, Yiman; Takeuchi, Kenneth J.; Marschilok, Amy C.; Takeuchi, Esther S.


    Silver vanadium phosphorous oxide, Ag2V2OPO4sub>, was used as a model system to systematically study the impact on the constituents of a composite electrode, including polymeric and conductive additives, on electrochemistry. Three different electrode compositions were investigated.

  6. Structure-dependent vibrational dynamics of Mg(BH 4sub> ) 2 polymorphs probed with neutron vibrational spectroscopy and first-principles calculations

    SciTech Connect

    Dimitrievska, Mirjana; White, James L.; Zhou, Wei; Stavila, Vitalie; Klebanoff, Leonard E.; Udovic, Terrence J.


    We investigated the structure-dependent vibrational properties of different Mg(BH4sub>)2 polymorphs (α, β, γ, and δ phases) with a combination of neutron vibrational spectroscopy (NVS) measurements and density functional theory (DFT) calculations, with emphasis placed on the effects of the local structure and orientation of the BH4sub>- anions. DFT simulations closely match the neutron vibrational spectra. The main bands in the low-energy region (20–80 meV) are associated with the BH4- librational modes. The features in the intermediate energy region (80–120 meV) are attributed to overtones and combination bands arising from the lower-energy modes. The features in the high-energy region (120–200 meV) correspond to the BH4sub>- symmetric and asymmetric bending vibrations, of which four peaks located at 140, 142, 160, and 172 meV are especially intense. There are noticeable intensity distribution variations in the vibrational bands for different polymorphs. We can explain these differences using the spatial distribution of BH4sub>- anions within various structures. An example of the possible identification of products after the hydrogenation of MgB2, using NVS measurements, is presented. Our results provide fundamental insights of benefit to researchers currently studying these promising hydrogen-storage materials.

  7. A new structure type of phosphate: Crystal structure of Na{sub 2}Zn{sub 5}(PO{sub 4}){sub 4}

    SciTech Connect

    Ji, L.N.; Ma, H.W. Li, J.B.; Liang, J.K.; Sun, B.J.; Liu, Y.H.; Zhang, J.Y.; Rao, G.H.


    A new compound, Na{sub 2}Zn{sub 5}(PO{sub 4}){sub 4}, was identified in the system ZnO-Na{sub 2}O-P{sub 2}O{sub 5} and high-quality crystal was obtained by the melt method. The crystal structure of this compound was solved by direct method from single crystal X-ray diffraction data. The structure was then refined anisotropically using a full-matrix least square refinement on F{sup 2} and the refinement converged to R{sub 1}=0.0233 and wR{sub 2}=0.0544. This compound crystallizes in the orthorhombic system with space group Pbcn, lattice parameters a=10.381(2) A, b=8.507(1) A, c=16.568(3) A and Z=4. The structure is made up of 3D [Zn{sub 5}P{sub 4}O{sub 16}]{sub n}{sup 2n-} covalent framework consisting of [Zn{sub 4}P{sub 4}O{sub 16}]{sub n}{sup 4n-} layers. The powder diffraction pattern of Na{sub 9}Zn{sub 21}(PO{sub 4}){sub 17} is explained by simulating a theoretical pattern with NaZnPO{sub 4} and Na{sub 2}Zn{sub 5}(PO{sub 4}){sub 4} in the molar ratio of 1:4 and then by Rietveld refinement of experimental pattern. Na{sub 2}Zn{sub 5}(PO{sub 4}){sub 4} melts congruently at 855 deg. C and its conductivity is 5.63x10{sup -9} S/cm. - Graphical abstract: Crystal structure and the relevant properties of Na{sub 2}Zn{sub 5}(PO{sub 4}){sub 4}, the first zincophosphate which having 3D [Zn{sub 5}P{sub 4}O{sub 16}]{sub n}{sup 2n-} covalent framework and the lowest P/Zn atomic ratio, were reported. The powder diffraction pattern of Na{sub 9}Zn{sub 21}(PO{sub 4}){sub 17} was proved to be a mixture of Na{sub 2}Zn{sub 5}(PO{sub 4}){sub 4} and NaZnPO{sub 4} in the molar ratio of 4:1 by Rietveld refinement.

  8. Pressure induced phase transformations in NaZr{sub 2}(PO{sub 4}){sub 3} studied by X-ray diffraction and Raman spectroscopy

    SciTech Connect

    Kamali, K.; Ravindran, T.R.; Chandra Shekar, N.V.; Pandey, K.K.; Sharma, S.M.


    Raman spectroscopic and x-ray diffraction measurements on NaZr{sub 2}(PO{sub 4}){sub 3} were carried out up to 30 GPa at close intervals of pressure, revealing two structural phase transformations around 5 and 6.6 GPa. The second phase at 5.4 GPa is indexed to R3 space group similar to that of RbTi{sub 2}(PO{sub 4}){sub 3}. Bulk modulus decreases abruptly from 53 GPa (B′=4) to 36 GPa (B′=4) in the second phase above 5 GPa. The structure of the phase III at 8.2 GPa is indexed as orthorhombic similar to the case of high temperature phase of monoclinic LiZr{sub 2}(PO{sub 4}){sub 3}. Bulk modulus of this phase III is found to be 65 GPa (B′=4), which is higher than that of the ambient phase. In high pressure Raman studies, modes corresponding to 72 and 112 cm{sup −1} soften in the ambient phase whereas around 5 GPa, the ones at 60, 105, 125 and 190 cm{sup −1} soften with pressure contributing negatively to overall thermal expansion. - Graphical abstract: High pressure study of NaZr{sub 2}(PO{sub 4}){sub 3} shows a reversible phase transition from R-3c to R3 structure at 5 GPa accompanied by an increase in compressibility signaling a polyhedral tilt transition. - Highlights: • NaZr{sub 2}(PO{sub 4}){sub 3} undergoes two reversible phase transitions at 5 and 6.7 GPa. • The transition at 5 is from rhombohedral R-3c to R3 structure. • Bulk modulus of NaZr{sub 2}(PO{sub 4}){sub 3} is lower than that for the isostructural RbTi{sub 2}(PO{sub 4}){sub 3.} • Compressibility increases with substitution of a smaller cation (Na). • Zr-translational and PO{sub 4} librational modes contribute to phase transition.

  9. Magnetic, Caloric and Crystallographic Properties of Dy5(SixGe1-x)4 sub> Alloys

    SciTech Connect

    Ivchenko, Vitaliy Vladislavovich


    Polycrystals of the intermetallic compound of the Dy5(SixGe1-x)4 sub> system, where x = 0, 0.25, 0.5, 0.625, 0.675, 0.725, 0.75, 0.775, 0.825, 0.875, and 1, have been prepared by electric-arc-melting on water-cooled copper hearth in an argon atmosphere. A study of phase relationships and crystallography in the pseudobinary system Dy5(SixGe1-x)4 sub> using X-ray powder diffraction data and optical metallography was completed. It revealed that silicides in the composition range from 0.825 to 1 crystallize in the Gd5Si4sub>-type crystal structure: germanides in the composition range from 0 to 0.625 crystallize in the Sm5Ge4sub>-type structure, and alloys with intermediate composition range from 0.675 to 0.775 crystallize in the monoclinic Gd5Si2Ge2-type structure. The -ΔSm values were determined from magnetization measurements for 7 alloys. The alloys with a monoclinic crystal structure which belong to an intermediate phase region have large MCE value, which exceeds those observed in the other two phase regions by 300 to 500%. The nature of the observed magnetic and structural transformations in the Dy5(SixGe1-x)4 sub> system seems to be similar with those reported for the Gd5(SixGe1-x)4 sub> system. However, the interval and concentration range of three different phase regions in the Dy5(SixGe1-x)4 sub> system are different from that observed in Gd-based alloys. A non-collinear ordering of magnetic moments at low temperature was observed for the alloys with monoclinic crystal structure. The Dy5Si3Ge alloy exhibited FM phase transition below Curie temperature. A series of magnetic transitions were observed at low temperature in the Dy5(SixGe1-x

  10. A novel red long lasting phosphorescent (LLP) material {beta}-Zn{sub 3}(PO{sub 4}){sub 2}:Mn{sup 2+}, Sm{sup 3+}

    SciTech Connect

    Wang Jing; Su Qiang . E-mail:; Wang Shubin


    A novel red long lasting phosphorescent materials {beta}-Zn{sub 3}(PO{sub 4}){sub 2}:Mn{sup 2+},Sm{sup 3+} is firstly synthesized by high-temperature solid-state reaction. The influence of Sm{sup 3+} ions on luminescence and long lasting phosphorescence properties of Mn{sup 2+} in phosphor {beta}-Zn{sub 3}(PO{sub 4}){sub 2}:Mn{sup 2+},Sm{sup 3+} are systematically investigated. It is found that the red phosphorescence ({lambda} = 616 nm) performance of Mn{sup 2+} ion such as brightness and duration is largely improved when Sm{sup 3+} ion is co-doped into the matrix in which Mn{sup 2+} ion acts as luminescent center and Sm{sup 3+} ion plays an important role of electron trap. Thermoluminescence spectrums show that there exists one peak in {beta}-Zn{sub 3}(PO{sub 4}){sub 2}:Mn{sup 2+},Sm{sup 3+}, the depth of which is 0.33 eV, and that there are three peaks in {beta}-Zn{sub 3}(PO{sub 4}){sub 2}:Mn{sup 2+}, among which the depth of the lowest temperature peak in {beta}-Zn{sub 3}(PO{sub 4}){sub 2}:Mn{sup 2+} is 0.37 eV. Such differences in the trap depth result in the improvement of red long lasting phosphorescence of Mn{sup 2+} in present matrix.

  11. Thermoluminescence and glow curves analysis of γ-exposed Eu{sup 3+} doped K{sub 3}Y(PO{sub 4}){sub 2} nanophosphors

    SciTech Connect

    Gupta, Palvi; Bedyal, A.K.; Kumar, Vinay; Singh, Vivek K.; Khajuria, Y.; Ntwaeaborwa, O.M.; Swart, H.C.


    Highlights: • First time, a detailed comparative study of the glow curves and kinetic parameters was made on K{sub 3}Y(PO{sub 4}){sub 2} nanophosphor. • Combustion method was employed to synthesize the Eu{sup 3+} doped K{sub 3}Y(PO{sub 4}){sub 2} nanophosphor. • The nanophosphor exhibited sublinear response suggesting that it is suitable for TL dosimetry. - Abstract: Eu{sup 3+} doped K{sub 3}Y(PO{sub 4}){sub 2} nanophosphor was synthesized by combustion synthesis using urea as a fuel. The crystal structure and particle morphology of the nanophosphor were investigated by using X-ray diffraction and transmission electron microscopy, respectively. A Thermoluminescence (TL) study was carried out after exposing the samples to gamma radiation. The TL glow curves exhibited a prominent peak at 407 K and a small hump at 478 K. The intensity of the peaks increased with the increase in the dose of the gamma rays (0.01–5 kGy). The K{sub 3}Y(PO{sub 4}){sub 2}: Eu{sup 3+} (2.5 mol%) nanophosphor exhibited sublinear TL response to γ-radiation over a wide range of gamma doses (0.01–5 kGy). The TLanal program was used to analyze the glow curves of the K{sub 3}Y(PO{sub 4}){sub 2} nanophosphor at different doses (0.2–5 kGy) and different heating rates (3–10 K/s). A comparative study was done for kinetic trapping parameters that were determined by the peak shape methods of Chen, Grossweiner and Lushchik. The frequency factors (s) for each glow peak were also calculated. The values of the activation energy (E) obtained by the TLanal program were in good agreement with those obtained by the peak shape methods. The effect of different amount of doses and different heating rates are discussed.

  12. Syntheses, crystal structures and optical spectroscopy of Ln{sub 2}(SO{sub 4}){sub 3}.8H{sub 2}O (Ln=Ho, Tm) and Pr{sub 2}(SO{sub 4}){sub 3}.4H{sub 2}O

    SciTech Connect

    Kazmierczak, Karolina; Hoeppe, Henning A.


    The lanthanide sulphate octahydrates Ln{sub 2}(SO{sub 4}){sub 3}.8H{sub 2}O (Ln=Ho, Tm) and the respective tetrahydrate Pr{sub 2}(SO{sub 4}){sub 3}.4H{sub 2}O were obtained by evaporation of aqueous reaction mixtures of trivalent rare earth oxides and sulphuric acid at 300 K. Ln{sub 2}(SO{sub 4}){sub 3}.8H{sub 2}O (Ln=Ho, Tm) crystallise in space group C2/c (Z=4, a{sub Ho}=13.4421(4) A, b{sub Ho}=6.6745(2) A, c{sub Ho}=18.1642(5) A, {beta}{sub Ho}=102.006(1) A{sup 3} and a{sub Tm}=13.4118(14) A, b{sub Tm}=6.6402(6) A, c{sub Tm}=18.1040(16) A, {beta}{sub Tm}=101.980(8) A{sup 3}), Pr{sub 2}(SO{sub 4}){sub 3}.4H{sub 2}O adopts space group P2{sub 1}/n (a=13.051(3) A, b=7.2047(14) A, c=13.316(3) A, {beta}=92.55(3) A{sup 3}). The vibrational and optical spectra of Ho{sub 2}(SO{sub 4}){sub 3}.8H{sub 2}O and Pr{sub 2}(SO{sub 4}){sub 3}.4H{sub 2}O are also reported. -- Graphical abstract: In the lanthanide sulphate octahydrates the cations form slightly undulated layers. Between the layers are voids in which sulphate tetrahedra and water molecules are located. The holmium compound exhibits an Alexandrite effect. Display Omitted Highlights: {yields} Determination of the optimum conditions for the growth of single-crystals of Ln{sub 2}(SO{sub 4}){sub 3}.8H{sub 2}O (Ln=Ho, Tm) and Pr{sub 2}(SO{sub 4}){sub 3}.4H{sub 2}O. {yields} Single-crystal structure elucidation of Ln{sub 2}(SO{sub 4}){sub 3}.8H{sub 2}O (Ln=Ho, Tm) including hydrogen bonds. {yields} Single-crystal structure determination of Pr{sub 2}(SO{sub 4}){sub 3}.4H{sub 2}O including hydrogen bonds. {yields} UV-vis spectra of Ho{sub 2}(SO{sub 4}){sub 3}.8H{sub 2}O and Pr{sub 2}(SO{sub 4}){sub 3}.4H{sub 2}O recorded and interpreted: Assignation of bands and clarification of the Alexandrite effect of the Ho compound. {yields} IR and Raman spectra of Ln{sub 2}(SO{sub 4}){sub 3}.8H{sub 2}O (Ln=Ho, Tm) and Pr{sub 2}(SO{sub 4}){sub 3}.4H{sub 2}O recorded and interpreted.

  13. Structural study and physical properties of a new phosphate KCuFe(PO{sub 4}){sub 2}

    SciTech Connect

    Badri, Abdessalem; Hidouri, Mourad; Lopez, Maria Luisa; Pico, Carlos; Wattiaux, Alain; Ben Amara, Mongi


    Single crystals of a new phosphate KCuFe(PO{sub 4}){sub 2} have been prepared by the flux method and its structural and physical properties have been investigated. This compound crystallizes in the monoclinic system with the space group P2{sub 1}/n and its parameters are: a=7.958(3) A, b=9.931(2) A, c=9.039(2) A, {beta}=115.59(3){sup o} and Z=4. Its structure consists of FeO{sub 6} octahedra sharing corners with Cu{sub 2}O{sub 8} units of edge-sharing CuO{sub 5} polyhedra to form undulating chains extending infinitely along the b-axis. These chains are connected by the phosphate tetrahedra giving rise to a 3D framework with six-sided tunnels parallel to the [101] direction, where the K{sup +} ions are located. The Moessbauer spectroscopy results confirm the exclusive presence of octahedral Fe{sup 3+} ions. The magnetic measurements show the compound to be antiferromagnetic with C{sub m}=5.71 emu K/mol and {theta}=-156.5 K. The derived experimental effective moment {mu}{sub ex}=6.76{mu}{sub B} is somewhat higher than the theoretical one of {mu}{sub th}=6.16{mu}{sub B}, calculated taking only into account the spin contribution for Fe{sup 3+} and Cu{sup 2+} cations. Electrical measurements allow us to obtain the activation energy (1.22 eV) and the conductivity measurements suggest that the charge carriers through the structure are the potassium cations. -- Graphical abstract: A projection along the [101] direction of the structure showing the six-edged tunnels, occupied by the K{sup +} ions. Display Omitted Highlights: {yields} The reported structure is of a new type. {yields} The structural model is supported by a Moessbauer spectroscopy study. {yields} The magnetic susceptibility results are reported. {yields} The electrical properties are discussed.

  14. Combustion synthesized nanocrystalline Li{sub 3}V{sub 2}(PO{sub 4}){sub 3}/C cathode for lithium-ion batteries

    SciTech Connect

    Nathiya, K.; Bhuvaneswari, D.; Gangulibabu; Kalaiselvi, N.


    Graphical abstract: Nanocrystalline Li{sub 3}V{sub 2}(PO{sub 4}){sub 3}/C compound has been synthesized using a novel corn assisted combustion (CAC) method, wherein the composite prepared at 850 °C is found to exhibit superior physical and electrochemical properties than the one synthesized at 800 °C (Fig. 1). Despite the charge disproportionation of V{sup 4+} and a possible solid solution behavior of Li{sub 3}V{sub 2}(PO{sub 4}){sub 3} cathode upon insertion and de-insertion of Li{sup +} ions, the structural stability of the same is appreciable, even with the extraction of third lithium at 4.6 V (Fig. 2). An appreciable specific capacity of 174 mAh g{sup −1} with an excellent columbic efficiency (99%) and better capacity retention upon high rate applications have been exhibited by Li{sub 3}V{sub 2}(PO{sub 4}){sub 3}/C cathode, thus demonstrating the feasibility of CAC method in preparing the title compound to best suit with the needs of lithium battery applications. Display Omitted Highlights: ► Novel corn assisted combustion method has been used to synthesize Li{sub 3}V{sub 2}(PO{sub 4}){sub 3}/C. ► Corn is a cheap and eco benign combustible fuel to facilitate CAC synthesis. ► Li{sub 3}V{sub 2}(PO{sub 4}){sub 3}/C exhibits an appreciable specific capacity of 174 mAh g{sup −1} (C/10 rate). ► Currently observed columbic efficiency of 99% is better than the reported behavior. ► Suitability of Li{sub 3}V{sub 2}(PO{sub 4}){sub 3}/C cathode up to 10C rate is demonstrated. -- Abstract: Nanocrystalline Li{sub 3}V{sub 2}(PO{sub 4}){sub 3}/C composite synthesized using a novel corn assisted combustion method at 850 °C exhibits superior physical and electrochemical properties than the one synthesized at 800 °C. Despite the charge disproportionation of V{sup 4+} and a possible solid solution behavior of Li{sub 3}V{sub 2}(PO{sub 4}){sub 3} cathode upon insertion and extraction of Li{sup +} ions, the structural stability of the same is appreciable, even with

  15. Alluaudite Na 2 Co 2 Fe(PO 4sub> ) 3 as an electroactive material for sodium ion batteries

    SciTech Connect

    Essehli, R.; Belharouak, I.; Ben Yahia, H.; Maher, K.; Abouimrane, A.; Orayech, B.; Calder, S.; Zhou, X. L.; Zhou, Z.; Sun, Y-K.


    The electroactive orthophosphate Na2Co2Fe(PO4sub>)(3) was synthesized using a solid state reaction. Its crystal structure was solved using the combination of powder X-ray-and neutron-diffraction data. This material crystallizes according to the alluaudite structure (S.G. C2/c). The structure consists of edge sharing [MO6] octahedra (M = Fe, Co) resulting in chains parallel to [-101]. These chains are linked together via the [PO4sub>] tetrahedra to form two distinct tunnels in which sodium cations are located. The electrochemical properties of Na2Co2Fe(PO4sub>)(3) were evaluated by galvanostatic charge-discharge cycling. During the first discharge to 0.03 V, Na2Co2Fe(PO4sub>)(3) delivers a specific capacity of 604 mA h g(-1). This capacity is equivalent to the reaction of more than seven sodium ions per formula unit. Hence, this is a strong indication of a conversion-type reaction with the formation of metallic Fe and Co. The subsequent charge and discharge involved the reaction of fewer Na ions as expected for a conversion reaction. When discharged to 0.9 V, the material intercalated only one Na+-ion leading to the formation of a new phase Na3Co2Fe(PO4sub>)(3). This phase could then be cycled reversibly with an average voltage of 3.6 V vs. Na+/Na and a capacity of 110 mA h g(-1). This result is in good agreement with the theoretical capacity expected from the extraction/insertion of two sodium atoms in Na2Co2Fe(PO4sub>)(3).

  16. A{sub 5}RE{sub 4}X[TO{sub 4}]{sub 4} crystal growth: Fluoride flux synthesis of Na{sub 5}Ln{sub 4}F[GeO{sub 4}]{sub 4} (Ln=Pr, Nd), the first quaternary germanate oxyfluorides

    SciTech Connect

    Latshaw, Allison M.; Wilkins, Branford O.; Morrison, Gregory; Smith, Mark D.; Loye, Hans-Conrad zur


    Crystals of Na{sub 5}Pr{sub 4}F[GeO{sub 4}]{sub 4} and Na{sub 5}Nd{sub 4}F[GeO{sub 4}]{sub 4} were synthesized using a eutectic sodium fluoride, sodium chloride flux. Both compounds crystallize in the tetragonal space group I-4 with lattice parameters of a=12.1173(4) Å and c=5.6795(2) Å (Pr) and of a=12.0642(17) Å and c=5.6674(11) Å (Nd). The structure of the reported compounds is three-dimensional with face and corner sharing lanthanide polyhedra which edge and corner share with isolated germanium tetrahedra. These novel compositions represent the first example of quaternary germanium containing oxyfluorides. - Graphical abstract: Structural image of the first examples of quaternary germanate oxyfluorides. Display Omitted - Highlights: • Molten flux growth of crystals of two lanthanide germanate oxyfluorides. • Expansion of the A{sub 5}RE{sub 4}X[TO{sub 4}]{sub 4} family into germanate oxyfluorides. • Synthesis of Na{sub 5}Nd{sub 4}F[GeO{sub 4}]{sub 4} and Na{sub 5}Pr{sub 4}F[GeO{sub 4}]{sub 4}.

  17. Ultrafast bulk diffusion of AlHx in high-entropy dehydrogenation intermediates of NaAlH4sub> [Highly mobile AlHx species and the dehydogenation kinetics of NaAlH4sub>

    SciTech Connect

    Zhang, Feng; Wood, Brandon C.; Wang, Yan; Wang, Cai -Zhuang; Ho, Kai -Ming; Chou, Mei -Yin


    Using first-principles molecular dynamics (FPMD) and total-energy calculations, we demonstrate low-barrier bulk diffusion of Al-bearing species in γ-NaAlH4sub>, a recently proposed high-entropy polymorph of NaAlH4sub>. For charged AlH4sub>– and neutral AlH3 vacancies, the computed barriers for diffusion are <0.1 eV, and we directly observe the predicted diffusive pathways in FPMD simulations at picosecond time scales. In contrast, such diffusion in the α phase is inaccessible to FPMD, consistent with much higher barriers. The transport behavior of γ-NaAlH4sub>, in addition to key dynamical and structural signatures, is consistent with experimental observations of high-mobility species, strongly supporting the idea that an intermediate transition from the α phase to a high-entropy polymorph facilitates the hydrogen-releasing decomposition of NaAlH4. Lastly, our results provide an answer to longstanding questions regarding the responsible agent for the experimentally observed efficient Al transport during dehydrogenation and suggest that mass transport and phase transformation kinetics are coupled. Implications for understanding the (de)hydrogenation of undoped and catalyzed NaAlH4sub> are discussed.

  18. Near-ultraviolet lateral photovoltaic effect in Fe3O4sub>/3C-SiC Schottky junctions.


    Song, Bingqian; Wang, Xianjie; Li, Bo; Zhang, Lingli; Lv, Zhe; Zhang, Yu; Wang, Yang; Tang, Jinke; Xu, Ping; Li, Bingsheng; Yang, Yanqiang; Sui, Yu; Song, Bo


    In this paper, we report a sensitive lateral photovoltaic effect (LPE) in Fe3O4sub>/3C-SiC Schottky junctions with a fast relaxation time at near-ultraviolet wavelengths. The rectifying behavior suggests that the large build-in electric field was formed in the Schottky junctions. This device has excellent position sensitivity as high as 67.8 mV mm-1 illuminated by a 405 nm laser. The optical relaxation time of the LPE is about 30 μs. The fast relaxation and high positional sensitivity of the LPE make the Fe3O4sub>/3C-SiC junction a promising candidate for a wide range of ultraviolet/near-ultraviolet optoelectronic applications.

  19. Anisotropy of an acousto-optic figure of merit for NaBi(MoO4sub>)2 crystals.


    Mys, Oksana; Krupych, Oleh; Vlokh, Rostyslav


    We develop a technique for analyzing the anisotropy of an acousto-optic figure of merit for crystals belonging to tetragonal symmetry groups 4/m, 4, and 4¯. The technique is based on phenomenological relations that describe anisotropies of the effective elasto-optic coefficients and the acoustic wave velocities. Our approach is verified on the example of NaBi(MoO4sub>)2 crystals for all possible types and geometries of acousto-optic interactions. We list and characterize the acousto-optic interaction geometries at which the maximal acousto-optic figures of merit are reached for both isotropic and anisotropic interaction types. Finally, we show that the acousto-optic efficiency of NaBi(MoO4sub>)2 originates mainly from large elasto-optic coefficients.

  20. Sequential energy transfer up-conversion process in Yb3+/Er3+:SrMoO4sub> crystal.


    Zhuang, Renzhong; Wang, Guofu


    This paper reports the dynamic characteristics of sequential energy transfer up-conversion processes in Yb3+/Er3+:SrMoO4sub> crystal. A general method based on the emission intensity has been developed to calculate the nonradiative decay rate. A new macroscopic theory has been developed to calculate the energy transfer parameters based on the crystal structure. According to both new calculating methods, the spectral parameters of Yb3+/Er3+:SrMoO4sub> crystal were calculated, such as up-conversion luminescent quantum efficiencies and threshold pump powers. Both calculating methods may be applied to calculate the spectral parameters of the laser crystal materials.

  1. Robust diamond-like Fe-Si network in the zero-strain NaxFeSiO4sub> cathode

    SciTech Connect

    Ye, Zhuo; Zhao, Xin; Li, Shouding; Wu, Shunqing; Wu, Ping; Nguyen, Manh Cuong; Guo, Jianghuai; Mi, Jinxiao; Gong, Zhengliang; Zhu, Zi -Zhong; Yang, Yong; Wang, Cai -Zhuang; Ho, Kai -Ming


    Sodium orthosilicates Na2MSiO4sub> (M denotes transition metals) have attracted much attention due to the possibility of exchanging two electrons per formula unit. In this work, we report a group of sodium iron orthosilicates Na2FeSiO4sub>. Their crystal structures are characterized by a diamond-like Fe-Si network. The Fe-Si network is quite robust against the charge/discharge process, which explains the high structural stability observed in experiment. Furthermore, using the density functional theory within the GGA + U framework and X-ray diffraction studies, the crystal structures and structural stabilities during the sodium extraction/re-insertion process are systematically investigated.

  2. Strong lattice correlation of non-equilibrium quasiparticles in a pseudospin-1/2 Mott insulator Sr2IrO4sub>

    SciTech Connect

    Li, Yuelin; Schaller, Richard D.; Zhu, Mengze; Walko, Donald A.; Kim, Jungho; Ke, Xianglin; Miao, Ludi; Mao, Z. Q.


    In correlated oxides the coupling of quasiparticles to other degrees of freedom such as spin and lattice plays critical roles in the emergence of symmetry-breaking quantum ordered states such as high temperature superconductivity. We report a strong lattice coupling of photon-induced quasiparticles in spin-orbital coupling Mott insulator Sr2IrO4sub> probed via optical excitation. Combining time-resolved x-ray diffraction and optical spectroscopy techniques, we reconstruct a spatiotemporal map of the diffusion of these quasiparticles. Lastly, due to the unique electronic configuration of the quasiparticles, the strong lattice correlation is unexpected but extends the similarity between Sr2IrO4sub> and cuprates to a new dimension of electron-phonon coupling which persists under highly non-equilibrium conditions.

  3. Theoretical Assessment on the Phase Transformation Kinetic Pathways of Multi-component Ti Alloys: Application to Ti-6Al-4sub>V

    SciTech Connect

    Ji, Yanzhou; Heo, Tae Wook; Zhang, Fan; Chen, Long-Qing


    Here we present our theoretical assessment of the kinetic pathways during phase transformations of multi-component Ti alloys. Employing the graphical thermodynamic approach and an integrated free energy function based on the realistic thermodynamic database and assuming that a displacive structural transformation occurs much faster than long-range diffusional processes, we analyze the phase stabilities of Ti-6Al-4sub>V (Ti-6wt.%Al-4sub>wt.%V). Our systematic analyses predict a variety of possible kinetic pathways for β to (α + β) transformations leading to different types of microstructures under various heat treatment conditions. In addition, the possibility of unconventional kinetic pathways is discussed. Lastly, we also briefly discuss the application of our approach to general multicomponent/multiphase alloy systems.

  4. Magnetic properties of (FeIn{sub 2}S{sub 4}){sub 1-x}(In{sub 2}S{sub 3}){sub x} alloy single crystals

    SciTech Connect

    Bodnar, I. V. Novikova, M. A.; Trukhanov, S. V.


    (FeIn{sub 2}S{sub 4}){sub 1-x}(In{sub 2}S{sub 3}){sub x} alloy single crystals are grown by oriented crystallization in the entire range of component concentrations. For the single crystals, studies of the magnetic properties are carried out in the temperature range 4-300 K and the magnetic-field range 0-14 T. It is established that almost all of the alloys are paramagnetic materials at temperatures down to the lowest achievable temperatures ({approx}4 K). It is shown that the ground magnetic phase state of the alloys is the spin-glass state with the freezing temperature steadily increasing with increasing Fe{sup 2+} cation content. The most probable causes and mechanism of formation of the magnetic state of the (FeIn{sub 2}S{sub 4}){sub 1-x}(In{sub 2}S{sub 3}){sub x} crystals are discussed.

  5. Structure symmetry determination and magnetic evolution in Sr2Ir1–xRhxO4sub>

    SciTech Connect

    Ye, Feng; Wang, Xiaoping; Hoffmann, Christina; Wang, Jinchen; Chi, Songxue; Matsuda, Masaaki; Chakoumakos, Bryan C.; Fernandez-Baca, Jaime A.; Cao, Gang


    We use single-crystal neutron diffraction to determine the crystal structure symmetry and to study the magnetic evolution in the rhodium doped iridates Sr2Ir1–xRhxO4sub> (0 ≤ x ≤ 0.16). Throughout this doping range, the crystal structure retains a tetragonal symmetry (space group I4<sub>1/a) with two distinct magnetic Ir sites in the unit cell forming staggered IrO6 rotation. Upon Rh doping, the magnetic order is suppressed and the magnetic moment of Ir4+ is reduced from 0.21 μB/Ir for x = 0 to 0.18 μB/Ir for x = 0.12. As a result, the magnetic structure at x = 0.12 is different from that of the parent compound while the moments remain in the basal plane.

  6. Structurally induced magnetization in a La2/3Sr4/3MnO4sub> superlattice

    SciTech Connect

    Shah, Amish B.; Nelson-Cheeseman, Brittany B.; Subramanian, Ganesh; Bhattacharya, Anand; Spence, John C.H.


    A structural transition has been observed in a digital superlattice of La2/3Sr4/3MnO4sub>, which is correlated to a magnetization enhancement upon cooling the sample. The artificial superlattices were grown layer-by-layer using ozone-assisted molecular beam epitaxy (MBE). Electron diffraction experiments show a phase transition below 150K in nanopatches of the superlattice, which coincides with an enhanced magnetization starting below 110K. Furthermore, atomic scale electron energy loss spectroscopy (EELS) shows changes in the Mn L2,3 and O K edges, which are related to valence, strain, and the atomic coordination within nanopatches. Atomic resolution image and EELS showing variations of oxygen and lanthanum signature edges in a La2/3Sr4/3MnO4sub> supperlattice.

  7. Neutron scattering studies of the H2a-H2b and (H3-H4)/sub 2/ histone complexes

    SciTech Connect

    Carlson, R.D.


    Neutron scattering experiments have shown that both the (H3-H4)/sub 2/ and H2a-H2b histone complexes are quite asymmetric in solution. The (H3-H4)/sub 2/ tetramer is an oblate or flattened structure, with a radius of gyration almost as large as that of the core octamer. If the tetramer is primarily globular, it must have an axial ratio of about 1:5. It is more likely, however, that this asymmetry results in part from N-terminal arms that extend outward approximately within the major plane of the particle. If this is the case, less asymmetric models for the globular part of the tetramer, including a dislocated disk, can be made consistent with the scattering data. The H2a-H2b dimer, on the other hand, is an elongated structure. 48 references, 12 figures, 1 table.

  8. Structural phase transition and phonon instability in Cu12Sb4sub>S13

    SciTech Connect

    May, Andrew F.; Delaire, Olivier A.; Niedziela, Jennifer L.; Lara-Curzio, Edgar; Susner, Michael A.; Abernathy, Douglas L.; Kirkham, Melanie J.; McGuire, Michael A.


    In this study, a structural phase transition has been discovered in the synthetic tetrahedrite Cu12Sb4sub>S13 at approximately 88 K. Upon cooling, the material transforms from its known cubic symmetry to a tetragonal unit cell that is characterized by an in-plane ordering that leads to a doubling of the unit cell volume. Specific heat capacity measurements demonstrate a hysteresis of more than two degrees in the associated anomaly. A similar hysteresis was observed in powder x-ray diffraction measurements, which also indicate a coexistence of the two phases, and together these results suggest a first-order transition. This structural transition coincides with a recently-reported metal-insulator transition, and the structural instability is related to the very low thermal conductivity κ in these materials. Inelastic neutron scattering was used to measure the phonon density of states in Cu12Sb4sub>S13 and Cu10Zn2Sb4sub>S13, both of which possess a localized, low-energy phonon mode associated with strongly anharmonic copper displacements that suppress κ. In Cu12Sb4sub>S13, signatures of the phase transition are observed in the temperature dependence of the localized mode, which disappears at the structural transition. In contrast, in the cubic Zn-doped material, the mode is at slightly higher-energy but observable for all temperatures, though it softens upon cooling.

  9. Multi-wavelength Yb:YAG/Nd3+:YVO4sub> continuous-wave microchip Raman laser.


    Wang, Xiao-Lei; Dong, Jun; Wang, Xiao-Jie; Xu, Jie; Ueda, Ken-Ichi; Kaminskii, Alexander A


    Multi-wavelength continuous-wave (CW) Raman lasers in a laser diode pumped Yb:YAG/Nd3+:YVO4sub> microchip Raman laser have been demonstrated for the first time to our best knowledge. The multi-wavelength laser of the first Stokes radiation around 1.08 μm has been achieved with a Raman shift of 261  cm-1 for a-cut Nd:YVO4sub> crystal corresponding to the fundamental wavelength at 1.05 μm. Multi-wavelength laser operation simultaneously around 1.05 and 1.08 μm has been achieved under the incident pump power between 1.5 and 1.7 W. Multi-wavelength Raman laser with frequency separation of 1 THz around 1.08 μm has been obtained when the incident pump power is higher than 1.7 W. The maximum Raman laser output power of 260 mW at 1.08 μm is obtained and the corresponding optical-to-optical conversion efficiency is 4.2%. Elliptically polarized fundamental laser and linearly polarized Raman laser were observed in an Yb:YAG/Nd:YVO4sub> CW microchip Raman laser. The experimental results of linearly polarized, multi-wavelength Yb:YAG/Nd:YVO4sub> CW microchip Raman laser with adjustable frequency separation provide a novel approach for developing potential compact laser sources for Terahertz generation.

  10. Li/Ag2VO2PO4sub> batteries: the roles of composite electrode constituents on electrochemistry

    SciTech Connect

    Bock, David C.; Bruck, Andrea M.; Pelliccione, Christopher J.; Zhang, Yiman; Takeuchi, Kenneth J.; Marschilok, Amy C.; Takeuchi, Esther S.


    In this study, we utilize silver vanadium phosphorous oxide, Ag2VO2PO4sub>, as a model system to systematically study the impact of the constituents of a composite electrode, including polymeric and conductive additives, on electrochemistry. Notably, although highly resistive, this bimetallic cathode can be discharged as a pure electroactive material in the absence of a conductive additive as it generates an in situ conductive matrix via a reduction displacement reaction resulting in the formation of silver metal nanoparticles. Also, three different electrode compositions were investigated: Ag2VO2PO4sub> only, Ag2VO2PO4sub>4 with binder, and Ag2VO2PO4sub> with binder and carbon. Constant current discharge, pulse testing and impedance spectroscopy measurements were used to characterize the electrochemical properties of the electrodes as a function of depth of discharge. In situ EDXRD was used to spatially resolve the discharge progression within the cathode by following the formation of Ag0. Ex situ XRD and EXAFS modeling were used to quantify the amount of Ag0 formed. Results indicate that the metal center reduced (V5+ or Ag+) was highly dependent on composite composition (presence of PTFE, carbon), depth of discharge (Ag0 nanoparticle formation), and spatial location within the cathode. The addition of a binder was found to increase cell polarization, and the percolation network provided by the carbon in the presence of PTFE was further increased with reduction and formation of Ag0. Lastly, this study provides insight into the factors controlling the electrochemistry of resistive active materials in composite electrodes.

  11. Lasing properties of sodium-gadolinium tungstate NaGd(WO{sub 4}){sub 2} crystals doped with Tm{sup 3+} ions

    SciTech Connect

    Zharikov, Evgeny V; Lis, Denis A; Popov, A V; Subbotin, Kirill A; Ushakov, S N; Shestakov, A V; Razdobreev, I M


    Lasing is obtained in Tm{sup 3+}-doped sodium-gadolinium tungstate NaGd(WO{sub 4}){sub 2} crystals longitudinally pumped by pulses from a laser diode bar. The slope lasing efficiency is 16%. Lasing was observed at wavelengths of 1957, 1944, 1936, and 1901 nm for the transmission coefficients of the output mirror T{sub out} = 0.3%, 1.4%, 3.3%, and 8.5%, respectively. (lasers)

  12. Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4sub>

    SciTech Connect

    Zvyagin, S. A.; Ozerov, M.; Kamenskyi, D.; Wosnitza, J.; Krzystek, J.; Yoshizawa, D.; Hagiwara, M.; Hu, Rongwei; Ryu, Hyejin; Petrovic, C.; Zhitomirsky, M. E.


    We present on high- field electron spin resonance (ESR) studies of magnetic excitations in the spin- 1/2 triangular-lattice antiferromagnet Cs2CuBr4sub>. Frequency- field diagrams of ESR excitations are measured for different orientations of magnetic fields up to 25 T. We show that the substantial zero- field energy gap, Δ ≈ 9.5 K, observed in the low-temperature excitation spectrum of Cs2CuBr4sub> [Zvyagin et al:, Phys. Rev. Lett. 112, 077206 (2014)], is present well above TN. Noticeably, the transition into the long-range magnetically ordered phase does not significantly affect the size of the gap, suggesting that even below TN the high-energy spin dynamics in Cs2CuBr4sub> is determined by short-range-order spin correlations. The experimental data are compared with results of model spin-wave-theory calculations for spin-1/2 triangle-lattice antiferromagnet.

  13. Synthesis, crystal growth, structural and magnetic characterization of NH4sub>MCl2(HCOO), M=(Fe, Co, Ni)

    SciTech Connect

    Greenfield, Joshua T.; Ovidiu Garlea, V.; Kamali, Saeed; Chen, Michael; Kovnir, Kirill


    In this paper, an ambient-pressure solution route and an improved solvothermal synthetic method have been developed to produce polycrystalline powders and large single crystals of NH4sub>MCl2(HCOO) (M=Fe, Co, Ni). The magnetic structure of the 1D linear chain compound NH4sub>FeCl2(HCOO) has been determined by low-temperature neutron powder diffraction, revealing ferromagnetic intra-chain interactions and antiferromagnetic inter-chain interactions. Finally, the newly-reported Co and Ni analogs are isostructural with NH4sub>FeCl2(HCOO), but there are significant differences in the magnetic properties of each compound; the Ni analog behaves similarly to the Fe compound but with stronger magnetic coupling, exhibiting antiferromagnetic ordering (TN=8.5 K) and a broad metamagnetic transition between 2 and 5 T, while the Co analog does not order magnetically above 2 K, despite strong antiferromagnetic nearest-neighbor interactions.

  14. Unravelling the low thermal expansion coefficient of cation-substituted YBaCo4sub>O7+δ

    SciTech Connect

    Manthiram, Arumugam; Huq, Ashfia; Kan, Wang Hay; Lai, Ke -Yu


    With an aim to understand the origin of the low thermal expansion coefficients (TECs), cation substituted YBaCo4sub>O7-type oxides have been investigated by in-situ neutron diffraction, bond valence sum (BVS), thermogravimetric analysis, and dilatometry. The compositions YBaCo4sub>O7+δ, Y0.9ln0.1BaCo3ZnO7+δ, and Y0.9ln0.1BaCo3Zn0.6Fe0.4sub>O7+δ) were synthesized by solid-state reaction at 1200 °C. Here, Rietveld refinement of the joint synchrotron X-ray and neutron diffraction data shows that the Zn and Fe dopants have different preferences to substitute the Co ions in the 6c and 2a sites.

  15. New insulating antiferromagnetic quaternary iridates MLa10Ir4sub>O24 (M=Sr, Ba)

    SciTech Connect

    Zhao, Qingbiao; Han, Fei; Stoumpos, Constantinos C.; Han, Tian -Heng; Li, Hao; Mitchell, J. F.


    Recently, oxides of Ir4+ have received renewed attention in the condensed matter physics community, as it has been reported that certain iridates have a strongly spin-orbital coupled (SOC) electronic state, Jeff = ½, that defines the electronic and magnetic properties. The canonical example is the Ruddlesden-Popper compound Sr2IrO4sub>, which has been suggested as a potential route to a new class of high temperature superconductor due to the formal analogy between Jeff = ½ and the S = ½ state of the cuprate superconductors. The quest for other iridium oxides that present tests of the underlying SOC physics is underway. In this spirit, here we report the synthesis and physical properties of two new quaternary tetravalent iridates, MLa10Ir4sub>O24 (M = Sr, Ba). The crystal structure of both compounds features isolated IrO6 octahedra in which the electronic configuration of Ir is d5. As a result, both compounds order antiferromagnetically despite the lack of obvious superexchange pathways, and resistivity measurement shows that SrLa10Ir4sub>O24 is an insulator.

  16. Crystal structure, IR and Mössbauer spectroscopy and magnetic properties of KZnFe(PO{sub 4}){sub 2} related to the zeolite-ABW-like compounds

    SciTech Connect

    Badri, Abdessalem; Hidouri, Mourad; Wattiaux, Alain; López, María Luisa; Veiga, María Luisa; Amara, Mongi Ben


    Highlights: • The reported structure of KZnFe(PO{sub 4}){sub 2} is closely related to the zeolite ABW-type. • The structure is described in detail. • The IR and Mössbauer spectroscopy results are reported. • The magnetic properties are developed. - Abstract: The new iron phosphate KZnFe(PO{sub 4}){sub 2} has been synthesized by flux method and solid state reaction, and characterized by X-ray diffraction, IR, Mössbauer spectroscopy and magnetic susceptibility. This compound crystallizes in the monoclinic space group C2/c with the cell parameters: a = 13.514(4) Å, b = 13.273(6) Å, c = 8.742(3) Å and β = 100.07(2)°. It displays strong similarities with the phosphates KCoAl(PO{sub 4}){sub 2} and NaCoPO{sub 4} and features some analogies with the zeolite-ABW structural type. 3D framework is built up by a corner-sharing between MO{sub 4} (M = 0.5 Zn + 0.5 Fe) and PO{sub 4} tetrahedra. The K{sup +} ions are found within crossing tunnels perpendicular to the (1 0 0), (0 1 0) and (0 0 1) planes, delimited by this framework. A Mössbauer study confirmed the presence of Fe{sup 3+} ions in a tetrahedral environment. Magnetic measurements revealed an antiferromagnetic behavior with T{sub N} = 8.5 K.

  17. Energetics of a uranothorite (Th1–xUxSiO4sub>) solid solution

    SciTech Connect

    Guo, Xiaofeng; Szenknect, Stephanie; Wu, Di; Xu, Hongwu; Dacheux, Nicolas; Navrotsky, Alexandra


    High-temperature oxide melt solution calorimetric measurements were completed to determine the enthalpies of formation of the uranothorite, (USiO4sub>)x–(ThSiO4sub>)1–x, solid solution. Phase-pure samples with x values of 0, 0.11, 0.21, 0.35, 0.71, and 0.84 were prepared, purified, and characterized by powder X-ray diffraction, electron probe microanalysis, thermogravimetric analysis and differential scanning calorimetry coupled with in situ mass spectrometry, and high-temperature oxide melt solution calorimetry. This work confirms the energetic metastability of coffinite, USiO4sub>, and U-rich intermediate silicate phases with respect to a mixture of binary oxides. Furthermore, variations in unit cell parameters and negative excess volumes of mixing, coupled with strongly exothermic enthalpies of mixing in the solid solution, suggest short-range cation ordering that can stabilize intermediate compositions, especially near x = 0.5.

  18. Nanosized pure and Cr doped Al{sub 2−x}Sc{sub x}(WO{sub 4}){sub 3} solid solutions

    SciTech Connect

    Yordanova, A.; Koseva, I.; Velichkova, N.; Kovacheva, D.; Rabadjieva, D.; Nikolov, V.


    Highlights: ► Nanosized pure and Cr-doped Al{sub 2−x}Sc{sub x}(WO{sub 4}){sub 3} obtained for a first time. ► Material for ceramics with different application. ► Co-precipitation method for preparation. ► X-ray, DTA, TEM investigations. ► Co-precipitation method gives 10–70 nm particles. -- Abstract: Nanosized solid solutions of the formula Al{sub 2−x−y}Sc{sub x}Cr{sub y}(WO{sub 4}){sub 3}, where x varies from 0 to 2 and y from 0.02 to 0.1 are synthesized for the first time by the co-precipitation method. X-ray powder diffraction, DTA/TG and TEM analyses demonstrate that the powders are pure solid solution compounds with orthorhombic structure, space group Pnca. Particle sizes between 10 and 70 nm are obtained after thermal treatment of the precipitates at 550 °C for 1 h for all compositions except in the case of Sc{sub 1.9}Cr{sub 0.1}(WO{sub 4}){sub 3}. For the last one mean particle size of 64 nm was obtained after thermal treatment at 500 °C. The influence of the concentrations of Sc and Cr as well as of the temperature and duration of the thermal treatment on the particle size and size distribution are established and discussed.

  19. The role of the CeO 2 /BiVO 4sub> interface in optimized Fe–Ce oxide coatings for solar fuels photoanodes

    SciTech Connect

    Shinde, A.; Li, G.; Zhou, L.; Guevarra, D.; Suram, S. K.; Toma, F. M.; Yan, Q.; Haber, J. A.; Neaton, J. B.; Gregoire, J. M.


    Solar fuel generators entail a high degree of materials integration, and efficient photoelectrocatalysis of the constituent reactions hinges upon the establishment of highly functional interfaces. Our recent application of high throughput experimentation to interface discovery for solar fuels photoanodes has revealed several surprising and promising mixed-metal oxide coatings for BiVO4sub>. Furthermore, when using sputter deposition of composition and thickness gradients on a uniform BiVO4sub> film, we systematically explore photoanodic performance as a function of the composition and loading of Fe–Ce oxide coatings. This combinatorial materials integration study not only enhances the performance of this new class of materials but also identifies CeO2 as a critical ingredient that merits detailed study. A heteroepitaxial CeO2(001)/BiVO4(010) interface is identified in which Bi and V remain fully coordinated to O such that no surface states are formed. Ab initio calculations of the integrated materials and inspection of the electronic structure reveals mechanisms by which CeO2 facilitates charge transport while mitigating deleterious recombination. Our results support the observations that addition of Ce to BiVO4sub> coatings greatly enhances photoelectrocatalytic activity, providing an important strategy for developing a scalable solar fuels technology.

  20. Organogold oligomers: Exploiting iClick and aurophilic cluster formation to prepare solution stable Au4sub> repeating units

    SciTech Connect

    Yang, Xi; Wang, Shanshan; Ghiviriga, Ion; Abboud, Khalil A.; Veige, Adam S.


    A novel synthetic method to create gold based metallo–oligomers/polymers via the combination of inorganic click (iClick) with intermolecular aurophilic interactions is demonstrated. Complexes [PEt3Au]4sub>(μ-N3C2C6H5) (1) and [PPhMe2Au]4sub (μ-N3C2C6H5) (2) and {[PEt3Au]4sub>[(μ-N3C2)2-9,9-dihexyl-9H-fluorene]}n (8) have been synthesized via iClick. The tetranuclear structures of 1 and 2, induced by aurophilic bonding, are confirmed in the solid state through single crystal X-ray diffraction experiments and in solution via variable temperature NMR spectroscopy. The extended 1D structure of 8 is constructed by aurophilic induced self-assembly. 1H DOSY NMR analysis reveals that the aurophilic bonds in 1, 2, and 8 are retained in the solution phase. The degree of polymerization within complex 8 is temperature and concentration dependent, as determined by 1H DOSY NMR. The complex 8 is a rare example of a solution stable higher ordered structure linked by aurophilic interactions.

  1. The Electrochemistry of Fe 3 O 4sub> /Polypyrrole Composite Electrodes in Lithium-Ion Cells: The Role of Polypyrrole in Capacity Retention

    SciTech Connect

    Bruck, Andrea M.; Gannett, Cara N.; Bock, David C.; Smith, Paul F.; Marschilok, Amy C.; Takeuchi, Kenneth J.; Takeuchi, Esther S.


    In two series of magnetite (Fe3O4) composite electrodes, one group with and one group without added carbon, containing varying quantities of polypyrrole (PPy), and a non-conductive polyvinylidene difluoride (PVDF) binder were constructed and then analyzed using electrochemical and spectroscopic techniques. Galvanostatic cycling and alternating current (AC) impedance measurements were used in tandem to measure delivered capacity, capacity retention, and the related impedance at various stages of discharge and charge. Further, the reversibility of Fe3O4sub> to iron metal (Fe0) conversion observed during discharge was quantitatively assessed ex-situ using X-ray Absorption Spectroscopy (XAS). The Fe3O4sub> composite containing the largest weight fraction of PPy (20 wt%) with added carbon demonstrated reduced irreversible capacity on initial cycles and improved cycling stability over 50 cycles, attributed to decreased reaction with the electrolyte in the presence of PPy. Our study illustrated the beneficial role of PPy addition to Fe3O4sub> based electrodes was not strongly related to improved electrical conductivity, but rather to improved ion transport related to the formation of a more favorable surface electrolyte interphase (SEI).

  2. Structural and magnetic characterization of the one-dimensional S = 5/2 antiferromagnetic chain system SrMn(VO4sub>)(OH)

    SciTech Connect

    Sanjeewa, Liurukara D.; Garlea, Vasile O.; McGuire, Michael A.; McMillen, Colin D.; Cao, Huibo; Kolis, Joseph W.


    The descloizite-type compound, SrMn(VO4sub>)(OH), was synthesized as large single crystals (1-2mm) using a high-temperature high-pressure hydrothermal technique. X-ray single crystal structure analysis reveals that the material crystallizes in the acentric orthorhombic space group of P212121 (no. 19), Z = 4. The structure exhibits a one-dimensional feature, with [MnO4sub>] chains propagating along the a-axis which are interconnected by VO4sub> tetrahedra. Raman and infrared spectra were obtained to identify the fundamental vanadate and hydroxide vibrational modes. Magnetization data reveal a broad maximum at approximately 80 K, arising from one-dimensional magnetic correlations with intrachain exchange constant of J/kB = 9.97(3) K between nearest Mn neighbors and a canted antiferromagnetic behavior below TN = 30 K. Single crystal neutron diffraction at 4 K yielded a magnetic structure solution in the lower symmetry of the magnetic space group P21 with two unique chains displaying antiferromagnetically ordered Mn moments oriented nearly perpendicular to the chain axis. Lastly, the presence of the Dzyaloshinskii Moriya antisymmetric exchange interaction leads to a slight canting of the spins and gives rise to a weak ferromagnetic component along the chain direction.

  3. Correlation of anisotropy and directional conduction in β-Li3PS4sub> fast Li+ conductor

    SciTech Connect

    Chen, Yan; Cai, Lu; Liu, Zengcai; dela Cruz, Clarina R.; Liang, Chengdu; An, Ke


    Our letter reports the correlation of anisotropy and directional conduction in the fast Li+ conductor β-Li3PS4sub>, one of the low-symmetry crystalline electrolyte candidates. The material has both high conductivity and good stability that serves well for the large-scale energy storage applications of all-solid-state lithium ion batteries. The anisotropic physical properties, demonstrated here by the thermal expansion coefficients, are crucial for compatibility in the solid-state system and battery performance. Neutron and X-ray powder diffraction measurements were done to determine the crystal structure and thermal stability. Moreover, the crystallographic b-axis was revealed as a fast expansion direction, while negligible thermal expansion was observed along the a-axis around the battery operating temperatures. The anisotropic behavior has its structural origin from the Li+ conduction channels with incomplete Li occupancy and a flexible connection of LiS4sub> and PS4sub> tetrahedra within the framework. This indicates a strong correlation in the direction of the ionic transport in the low-symmetry Li+ conductor.

  4. Structural, electronic and thermodynamic properties of britholites Ca{sub 10−x}La{sub x}(PO{sub 4}){sub 6−x}(SiO{sub 4}){sub x}F{sub 2} (0 ≤ x ≤ 6): Experiment and theory

    SciTech Connect

    Njema, H.; Debbichi, M.; Boughzala, K.; Said, M.; Bouzouita, K.


    Highlights: • The structural and electronic properties of apatites with the general formula Ca{sub 10−x}La{sub x}(PO{sub 4}){sub 6−x}(SiO{sub 4}){sub x}F{sub 2} (0 ≤ x ≤ 6) have been investigated by means of the density functional theory. • The calculated enthalpy of formation of the compounds increased with the substitution degree. • The decrease in stability is probably due to the disorder induced in the Ca/LaO{sub 6}F polyhedron, following the substitution. - Abstract: The apatite-type compounds Ca{sub 10−x}La{sub x}(PO{sub 4}){sub 6−x}(SiO{sub 4}){sub x}F{sub 2} with 0 ≤ x ≤ 6 were prepared using a high temperature solid state reaction and were characterized by X-ray diffraction. The crystal structure, chemical bonding, electronic structure and formation energy of all relaxed structures were analyzed by density functional theory (DFT). The calculated results show that the predicted geometry can well reproduce the structural parameters. The incorporation of La{sup 3+} into the fluorapatite (FA) structure induced especially at the level of the S(2) sites a certain disorder which is responsible for the weakening in the stability with x. Excellent agreement were obtained between the calculated and experimental results. Moreover, the band structure indicates that despite the reduction of the band gap with x content all materials remain insulating.

  5. X-ray spectroscopic characterization of Co(IV) and metal–metal interactions in Co4sub>O4sub>: Electronic structure contributions to the formation of high-valent states relevant to the oxygen evolution reaction

    SciTech Connect

    Hadt, Ryan G.; Hayes, Dugan; Brodsky, Casey N.; Ullman, Andrew M.; Casa, Diego M.; Upton, Mary H.; Nocera, Daniel G.; Chen, Lin X.


    In this paper, the formation of high-valent states is a key factor in making highly active transition metal-based catalysts of the oxygen-evolving reaction (OER). These high oxidation states will be strongly influenced by the local geometric and electronic structures of the metal ion, which is difficult to study due to spectroscopically active and complex backgrounds, short lifetimes, and limited concentrations. Here, we use a wide range of complementary X-ray spectroscopies coupled to DFT calculations to study Co4sub>O4sub> cubanes, which provide insight into the high-valent Co(IV) centers responsible for the activity of molecular and heterogeneous OER catalysts. The combination of X-ray absorption and 1s3p resonant inelastic X-ray scattering (Kβ RIXS) allow Co(IV) to be isolated and studied against a spectroscopically active Co(III) background. Co K- and L-edge X-ray absorption data allow for a detailed characterization of the 3d-manifold of effectively localized Co(IV) centers and provide a direct handle on the ligand field environment and covalency of the t2g-based redox active molecular orbital. Kβ RIXS is also shown to provide a powerful probe of Co(IV), and specific spectral features are sensitive to the degree of oxo-mediated metal-metal coupling across Co4sub>O4sub>. Guided by the data, calculations show electron-hole delocalization can actually oppose Co(IV) formation. Computational extension of Co4sub>O4sub> to CoM3O4sub> structures (M = redox-inactive metal) defines electronic structure contri-butions to Co(IV) formation. Redox activity is shown to be linearly related to covalency, and M(III) oxo inductive effects on Co(IV) oxo bonding can tune the covalency of high-valent sites over a large range and thereby tune E0 over hundreds of mVs.

  6. Infrared and Raman spectra of Na{sub 2}Cu(SO{sub 4}){sub 2}{center_dot}2H{sub 2}O and (CH{sub 3}NH{sub 3}){sub 2}M(II)(SO{sub 4}){sub 2}{center_dot}6H{sub 2}O with M(II) = Cu, Zn, and Ni

    SciTech Connect

    Pillai, V.P.M.; Nayar, V.U.; Jordanovska, V.B.


    FTIR and Raman spectra of Na{sub 2}Cu(SO{sub 4}){sub 2}{center_dot}2H{sub 2}O and (CH{sub 3}NH{sub 3}){sub 2}M(II) (SO{sub 4}){sub 2}{center_dot}6H{sub 2}O with M(II) = Cu, Zn, and Ni are recorded and analyzed. Bands are assigned on the basis of SO{sub 4}{sup 2-}, CH{sub 3}NH{sub 3}{sup +}, and H{sub 2}O vibrations. The lifting of degeneracies of {nu}{sub 2}, {nu}{sub 3} and v{sub 4} modes and the appearance of {nu}{sub 1} and {nu}{sub 2} modes in the IR spectra confirm the lowering of symmetry of the SO{sub 4}{sup 2-} ion from T{sub d} to C{sub 1} in all of the title compounds. Bands obtained indicate that the distoration of the SO{sub 4}{sup 2-} ion in the four crystals are in the order, (CH{sub 3}NH{sub 3})Cu(SO{sub 4}){sub 2}{center_dot}6H{sub 2}O > (CH{sub 3}NH{sub 3}){sub 2}Ni(SO{sub 4}){sub 2}{center_dot}6H{sub 2}O > (CH{sub 3}NH{sub 3}){sub 2}Zn(SO{sub 4}){sub 2}{center_dot}6H{sub 2}O > Na{sub 2}Cu(SO{sub 4}){sub 2}{center_dot} 2H{sub 2}O. The appearance of NH{sub 3} stretching modes at wavenumbers lower than the values obtained for the free ion indicates the presence of hydrogen bonds between NH{sub 3} and SO{sub 4}{sup 2-} groups. The appearance of multiple bands in the blending and rocking mode regions and the broad nature of stretching modes show the existence of at least two symmetrically inequivalent water molecules in Na{sub 2}Cu(SO{sub 4}){sub 2}{center_dot}2H{sub 2}O. The shifting of stretching modes to lower wavenumbers and bending modes to higher wavenumbers of water molecules confirms the existence of strong hydrogen bonds in the crystal which is in agreement with the X-ray data. Bands indicate the presence of strong hydrogen bonds involving water molecules in (CH{sub 3}NH{sub 3}){sub 2}Cu(SO{sub 4}){sub 2}{center_dot}6H{sub 2}O and (CH{sub 3}NH{sub 3}){sub 2} Zn(SO{sub 4}){sub 2}{center_dot}6H{sub 2}O and of lesser strength in (CH{sub 3}NH{sub 3}){sub 2}Ni(SO{sub 4}){sub 2}{center_dot}6H{sub 2}O.

  7. Superconductivity in the presence of disorder in skutterudite-related La3Co4sub>Sn13 and La3Ru4sub>Sn13 compounds: Electrical transport and magnetic studies

    SciTech Connect

    Slebarski, A.; Maska, M. M.; Fijalkowski, M.; McElroy, C. A.; Maple, M. B.


    La3Co4sub>Sn13 and La3Ru4sub>Sn13 were categorized as BCS superconductors. In a plot of the critical field Hc2 vs T, La3Ru4sub>Sn13 displays a second superconducting phase at the higher critical temperature Tc*, characteristic of inhomogeneous superconductors, while La3Co4sub>Sn13 shows bulk superconductivity below Tc. We observe a decrease in critical temperatures with external pressure and magnetic field for both compounds. Additionally, for La3Ru4sub>Sn13 we find that Tc*/dP>dTc/dP. The pressure dependences of Tc are interpreted according to the McMillan theory and understood to be a consequence of lattice stiffening. The investigation of the superconducting state of La3CoxRu4–xSn13 shows a Tc* that is larger then Tc for x < 4. Furthermore, this unique and unexpected observation is discussed as a result of the local disorder and/or the effect of chemical pressure when Ru atoms are partially replaced by smaller Co atoms.

  8. Synthesis and X-ray structural investigation of K{sub 8}[(UO{sub 2}){sub 2}(C{sub 2}O{sub 4}){sub 2}(SeO{sub 4}){sub 4}] . 2H{sub 2}O

    SciTech Connect

    Serezhkina, L. B.; Peresypkina, E. V.; Virovets, A. V.; Verevkin, A. G.; Pushkin, D. V.


    Single crystals of the compound K{sub 8}[(UO{sub 2}){sub 2}(C{sub 2}O{sub 4}){sub 2}(SeO{sub 4})4] . 2H{sub 2}O (I) are synthesized, and their structure is investigated using X-ray diffraction. Compound I crystallizes in the monoclinic system with the unit cell parameters a = 14.9290(4) A, b = 7.2800(2) A, c = 15.3165(4) A, {beta} = 109.188(1){sup o}, V = 1572.17(7) A{sup 3}, space group P2{sub 1}/n, Z = 2, and R = 0.0297. The uranium-containing structural units of crystals I are dimers of the composition [(UO {sub 2}){sub 2}(C{sub 2}O{sub 4}){sub 2}(SeO{sub 4}){sub 4}]{sup 8-}, which belong to the crystal-chemical group AB{sup 01}B{sup 2}M{sup 1} (A = UO{sub 2}{sup 2+}, B{sup 01} = C{sub 2}O{sub 4}{sup 2-}, B{sup 2} = SeO{sub 4}{sup 2-}, M{sup 1} = SeO{sub 4}{sup 2-}) of the uranyl complexes. The [(UO{sub 2}){sub 2}(C{sub 2}O{sub 4}){sub 2}(SeO{sub 4}){sub 4}]{sup 8-} dimers are joined into a three-dimensional framework through electrostatic interactions with the outer-sphere potassium cations.

  9. Study of phase relationships in the Sr{sub 3}(PO{sub 4}){sub 2}–CePO{sub 4} system. Phase diagram and thermal characteristics of phases

    SciTech Connect

    Matraszek, Aleksandra


    A diagram representing phase relationships in the Sr{sub 3}(PO{sub 4}){sub 2}–CePO{sub 4} phosphate system has been developed on the basis of results obtained by thermal analysis (DTA/DSC/TGA) and X-ray diffraction (XRD) methods. One intermediate compound with the formula Sr{sub 3}Ce(PO{sub 4}){sub 3} occurs in the Sr{sub 3}(PO{sub 4}){sub 2}–CePO{sub 4} system at temperatures exceeding 1045 °C. The compound has a eulytite structure with the following structural parameters: a=b=c=10.1655(8) Å, α=β=γ=90.00°, V=1050.46(6) Å{sup 3}. It's melting point exceeds 1950 °C. A limited solid solution exists in the system, which possesses the structure of a low-temperature form of Sr{sub 3}(PO{sub 4}){sub 2}. At 1000 °C the maximal concentration of CePO{sub 4} in the solid solution is below 20 mol%. The solid solution phase field narrows with increased temperature. There is a eutectic point in the (Sr{sub 3}(PO{sub 4}){sub 2}+Sr{sub 3}Ce(PO{sub 4}){sub 3}) phase field at 1765 °C and 15 mol% of CePO{sub 4}. The melting temperature of Sr{sub 3}(PO{sub 4}){sub 2} is 1882±15 °C. - Graphical abstract: The phase diagram of Sr{sub 3}(PO{sub 4}){sub 2}–CePO{sub 4} system showing the stability ranges of limited solid solution and Sr{sub 3}Ce(PO{sub 4}){sub 3} phases. - Highlights: • Sr{sub 3}(PO{sub 4}){sub 2} melts at 1882 °C. • Phase diagram of Sr{sub 3}(PO{sub 4}){sub 2}–CePO{sub 4} system has been proposed. • Limited solid solution of CePO{sub 4} in Sr{sub 3}(PO{sub 4}){sub 2} forms in the system. • The Sr{sub 3}Ce(PO{sub 4}){sub 2} phosphate is stable at temperatures above 1045 °C.

  10. Crystal structures of lazulite-type oxidephosphates Ti{sup III}Ti{sup IV}{sub 3}O{sub 3}(PO{sub 4}){sub 3} and M{sup III}{sub 4}Ti{sup IV}{sub 27}O{sub 24}(PO{sub 4}){sub 24} (M{sup III}=Ti, Cr, Fe)

    SciTech Connect

    Schoeneborn, M.; Glaum, R. Reinauer, F.


    Single crystals of the oxidephosphates Ti{sup III}Ti{sup IV}{sub 3}O{sub 3}(PO{sub 4}){sub 3} (black), Cr{sup III}{sub 4}Ti{sup IV}{sub 27}O{sub 24}(PO{sub 4}){sub 24} (red-brown, transparent), and Fe{sup III}{sub 4}Ti{sup IV}{sub 27}O{sub 24}(PO{sub 4}){sub 24} (brown) with edge-lengths up to 0.3 mm were grown by chemical vapour transport. The crystal structures of these orthorhombic members (space group F2dd ) of the lazulite/lipscombite structure family were refined from single-crystal data [Ti{sup III}Ti{sup IV}{sub 3}O{sub 3}(PO{sub 4}){sub 3}: Z=24, a=7.3261(9) A, b=22.166(5) A, c=39.239(8) A, R{sub 1}=0.029, wR{sub 2}=0.084, 6055 independent reflections, 301 variables; Cr{sup III}{sub 4}Ti{sup IV}{sub 27}O{sub 24}(PO{sub 4}){sub 24}: Z=1, a=7.419(3) A, b=21.640(5) A, c=13.057(4) A, R{sub 1}=0.037, wR{sub 2}=0.097, 1524 independent reflections, 111 variables; Fe{sup III}{sub 4}Ti{sup IV}{sub 27}O{sub 24}(PO{sub 4}){sub 24}: Z=1, a=7.4001(9) A, b=21.7503(2) A, c=12.775(3) A, R{sub 1}=0.049, wR{sub 2}=0.140, 1240 independent reflections, 112 variables). For Ti{sup III}Ti{sup IV}O{sub 3}(PO{sub 4}){sub 3} a well-ordered structure built from dimers [Ti{sup III,IV}{sub 2}O{sub 9}] and [Ti{sup IV,IV}{sub 2}O{sub 9}] and phosphate tetrahedra is found. The metal sites in the crystal structures of Cr{sub 4}Ti{sub 27}O{sub 24}(PO{sub 4}){sub 24} and Fe{sub 4}Ti{sub 27}O{sub 24}(PO{sub 4}){sub 24}, consisting of dimers [M{sup III}Ti{sup IV}O{sub 9}] and [Ti{sup IV,IV}{sub 2}O{sub 9}], monomeric [Ti{sup IV}O{sub 6}] octahedra, and phosphate tetrahedra, are heavily disordered. Site disorder, leading to partial occupancy of all octahedral voids of the parent lipscombite/lazulite structure, as well as splitting of the metal positions is observed. According to Guinier photographs Ti{sup III}{sub 4}Ti{sup IV}{sub 27}O{sub 24}(PO{sub 4}){sub 24} (a=7.418(2) A, b=21.933(6) A, c=12.948(7) A) is isotypic to the oxidephosphates M{sup III}{sub 4}Ti{sup IV}{sub 27}O{sub 24}(PO{sub 4

  11. Mixed tetrahedral anionic framework in the K{sub 3}Ga{sub 2}(PO{sub 4}){sub 3} crystal structure

    SciTech Connect

    Yakubovich, O. V.; Steele, I.; Kireev, V. V.


    The crystal structure of a new synthetic potassium gallophosphate K{sub 3}Ga{sub 2}(PO{sub 4}){sub 3} grown from a solution in the melt of a mixture of GaPO{sub 4} and K{sub 2}MoO{sub 4} is determined using X-ray diffraction (Bruker Smart diffractometer, 2{theta}{sub max}= 56.6{sup o}, R = 0.044 for 2931 reflections, T = 100 K). The main crystal data are as follows: a = 8.661(2) A, b = 17.002(4) A, c = 8.386(2) A, space group Pna2{sub 1}, Z= 4, and {rho}{sub calcd} = 2.91 g/cm{sup 3}. The synthesized crystals represent the third phase in the structure type previously established for the K{sub 3}Al{sub 2}[(As,P)O{sub 4}]{sub 3} compound. It is shown that the structure consists of a three-dimensional anionic microporous tetrahedral framework of the mixed type, which is formed by PO{sub 4} and GaO{sub 4} tetrahedra shared by vertices. Large-sized cations K{sup +} occupy channels of the zeolite-like framework. The crystal chemical features of the formation of structure types of compounds with mixed frameworks described by the general formula A{sub 3}{sup +}M{sub 2}{sup 3+}(TO{sub 4}){sub 3} (where A = K, Rb, (NH{sub 4}), Tl; M = Al, Ga, Fe, Sc, Yb; T = P, As) are analyzed.

  12. Competitive Reduction of Pertechnetate (99TcO4sub>- ) by Dissimilatory Metal Reducing Bacteria and Biogenic Fe(II)

    SciTech Connect

    Plymale, Andrew E.; Fredrickson, James K.; Zachara, John M.; Dohnalkova, Alice C.; Heald, Steve M.; Moore, Dean A.; Kennedy, David W.; Marshall, Matthew J.; Wang, Chongmin; Resch, Charles T.; Nachimuthu, Ponnusamy


    The fate of pertechnetate (99Tc(VII)O4sub>-) during bioreduction was investigated in the presence of 2-line ferrihydrite (Fh) and various dissimilatory metal reducing bacteria (DMRB) (Geobacter, Anaeromyxobacter, Shewanella) in comparison with TcO4sub>- bioreduction in the absence of Fh. In the presence of Fh, Tc was present primarily as a fine-grained Tc(IV)/Fe precipitate that was distinct from the Tc(IV)O2·nH2O solids produced by direct biological Tc(VII) reduction. Aqueous Tc concentrations (<0.2 μm) in the bioreduced Fh suspensions (1.7 to 3.2 × 10-9 mol L-1) were over 1 order of magnitude lower than when TcO4sub>- was biologically reduced in the absence of Fh (4.0 × 10-8 to 1.0 × 10-7 mol L-1). EXAFS analyses of the bioreduced Fh-Tc products were consistent with variable chain length Tc-O octahedra bonded to Fe-O octahedra associated with the surface of the residual or secondary Fe(III) oxide. In contrast, biogenic TcO2·nH2O had significantly more Tc-Tc second neighbors and a distinct long-range order consistent with small particle polymers of TcO2. In Fe-rich subsurface sediments, the reduction of Tc(VII) by Fe(II) may predominate over direct microbial pathways, potentially leading to lower concentrations of aqueous 99Tc(IV).

  13. Crystal structure, vibrational properties and luminescence of NaMg{sub 3}Al(MoO{sub 4}){sub 5} crystal doped with Cr{sup 3+} ions

    SciTech Connect

    Hermanowicz, K.; Maczka, M. . E-mail:; Wolcyrz, M.; Tomaszewski, P.E.; Pasciak, M.; Hanuza, J.


    Crystals of NaMg{sub 3}Al(MoO{sub 4}){sub 5} doped with 0.5% Cr{sup 3+} ions have been synthesized and characterized by a single-crystal X-ray structure analysis and IR, Raman, electron absorption and luminescence spectroscopic studies. It has been shown that NaMg{sub 3}Al(MoO{sub 4}){sub 5} crystallizes in the P1-bar structure, with a=6.8744(8) A, b=6.9342(7) A, c=17.605(2) A, {alpha}=87.788(8){sup o}, {beta}=87.727(9){sup o}, {gamma}=78.501(9){sup o}, Z=2. The characteristic feature of the structure is its enormously large thermal displacement parameter for sodium, even at 105K. The IR and Raman spectra indicate significant interactions between the MoO{sub 4}{sup 2-} ions in the structure. The electron absorption, excitation and luminescence studies have shown that there are at least two different sites of incorporated Cr{sup 3+} ions in the NaMg{sub 3}Al(MoO{sub 4}){sub 5} crystal structure. They differ themselves by strength of crystalline field. One of them is characterized by Cr{sup 3+} in low ligand field and {sup 4}T{sub 2}->{sup 4}A{sub 2} emission whereas the second is characterized by higher strength of the crystal field and dominant {sup 2}E->{sup 4}A{sub 2} emission. Temperature-dependent studies show that the compound does not exhibit any phase transition.0.

  14. Writing of nonlinear optical Sm{sub 2}(MoO{sub 4}){sub 3} crystal lines at the surface of glass by samarium atom heat processing

    SciTech Connect

    Abe, M.; Benino, Y.; Fujiwara, T.; Komatsu, T.; Sato, R.


    Some glasses such as 21.25Sm{sub 2}O{sub 3}.63.75MoO{sub 3}.15B{sub 2}O{sub 3} (mol %) giving the formation of nonlinear optical Sm{sub 2}(MoO{sub 4}){sub 3} crystals through conventional crystallization in an electric furnace and through continuous-wave Nd: yttrium aluminum garnet (YAG) laser (wavelength: 1064 nm) irradiation (samarium atom heat processing) have been developed. It is proposed from x-ray diffraction analyses, micro-Raman-scattering spectra, and second-harmonic generation measurements that the crystal structure of Sm{sub 2}(MoO{sub 4}){sub 3} formed by the crystallization is the {beta}{sup '}-phase structure with an orthorhombic (noncentrosymmetric) symmetry. The lines consisting of nonlinear optical {beta}{sup '}-Sm{sub 2}(MoO{sub 4}){sub 3} crystals are written at the surface of glasses by YAG laser irradiation (laser power: P=0.4 W, laser scanning speed: S=1-10 {mu}m/s), and, in particular, homogeneous crystal lines are formed at the laser scanning speed of 1 {mu}m/s. Refractive index changes (not crystallization) are also induced by YAG laser irradiation of P=0.4 W and a high laser scanning speed of S=25 {mu}m/s. The crystallization mechanism in the laser-irradiated region has been proposed. The present study demonstrates that the samarium atom heat processing is a technique for the writing of rare earth containing optical nonlinear/ferroelectric crystal lines in glass.

  15. Oxidative Dehydrogenation of Cyclohexane on Cobalt Oxide (Co3O4sub>) Nanoparticles: The Effect of Particle Size on Activity and Selectivity

    SciTech Connect

    Tyo, Eric C.; Yin, Chunrong; Di Vece, Marcel; Qian, Qiang; Kwon, Gihan; Lee, Sungsik; Lee, Byeongdu; DeBartolo, Janae E.; Seifert, Sönke; Winans, Randall E.; Si, Rui; Ricks, Brian; Goergen, Simone; Rutter, Matthew; Zugic, Branko; Flytzani-Stephanopoulos, Maria; Wang, Zhi Wei; Palmer, Richard E.; Neurock, Matthew; Vajda, Stefan


    The oxidative dehydrogenation of cyclohexane by cobalt oxide nanoparticles was studied via temperature programmed reaction combined with in situ grazing incidence X-ray absorption spectroscopy and grazing incidence small-angle X-ray scattering and theoretical calculations on model Co3O4sub> substrates. Both 6 and 12 nm Co3O4sub> nanoparticles were made through a surfactant-free preparation and dispersed on an Al2O3 surface formed by atomic layer deposition. Under reaction conditions the nanoparticles retained their oxidation state and did not sinter. They instead underwent an assembly/disassembly process and could reorganize within their assemblies. The selectivity of the catalyst was found to be size- and temperature-dependent, with larger particles preferentially producing cyclohexene at lower temperatures and smaller particles predominantly resulting in benzene at higher temperatures. The mechanistic features thought to control the oxidative dehydrogenation of cyclohexane and other light alkanes on cobalt oxide were established by carrying out density functional theory calculations on the activation of propane, a surrogate model alkane, over model Co3O4sub> surfaces. The initial activation of the alkane (propane) proceeds via hydrogen abstraction over surface oxygen sites. The subsequent activation of the resulting alkoxide intermediate occurs at a second surface oxygen site to form the alkene (propene) which then desorbs from the surface. Hydroxyl recombination results in the formation of water which desorbs from the surface. Finally, oxygen is necessary to regenerate the surface oxygen sites, catalyze C–H activation steps, and minimize catalyst degradation.

  16. Dynamic Oxygen on Surface: Catalytic Intermediate and Coking Barrier in the Modeled CO2 Reforming of CH4sub> on Ni (111)

    SciTech Connect

    Yuan, Kaidi; Zhong, Jian-Qiang; Zhou, Xiong; Xu, Leilei; Bergman, Susanna L.; Wu, Kai; Xu, Guo Qin; Bernasek, Steven L.; Li, He Xing; Chen, Wei


    We identify Ni-O phases as important intermediates in a model dry (CO2) reforming of methane catalyzed by Ni (111), based on results from in operando near ambient X-ray photoelectron spectroscopy (NAP-XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). We find that under a CO2 or CO2-CH4sub> atmosphere, the Ni-O phases exist as p(2×2) structured chemisorbed oxygen (Chem-O), epitaxial NiO (111), or oxygen-rich NixOy (x2O3), depending on the chemical potential. The growth rates of the Ni-O phases have a negative correlation with temperature from 600 K to 900 K, proving that their dynamic concentrations in the reaction are not limited by CO2 activation, but by their thermal stability. Between 300 K and 800 K (1:1 CH4sub> and CO2 mixture), oxidation by CO2is dominant, resulting in a fully Ni-O covered surface. Between 800 K and 900 K, a partially oxidized Ni (111) exists which could greatly facilitate the effective conversion of CH4sub>. As CH4sub> is activation-limited and dissociates mainly on metallic nickel, the released carbon species can quickly react with the adjacent oxygen (Ni-O phases) to form CO. After combining with carbon and releasing CO molecules, the Ni-O phases can be further regenerated through oxidation by CO2. In this way, the Ni-O phases participate in the catalytic process, acting as an intermediate in addition to the previously reported Ni-C phases. We also reveal the carbon phobic property of the Ni-O phases, which links to the intrinsic coking resistance of the catalysts. The low dynamic coverage of surface oxygen at higher temperatures (>900 K) is inferred to be an underlying factor causing carbon aggregation. Therefore solutions based on Ni-O stabilization are proposed in developing coking resisting catalysts.

  17. High power TEM00 picosecond output based on a Nd:GdVO4sub> discrete path Innoslab amplifier.


    Guo, Jie; Lin, Hua; Li, Jinfeng; Gao, Peng; Liang, Xiaoyan


    We propose a technique for eliminating self-lasing and suppressing amplified spontaneous emission in a partially pumped slab amplifier with a discrete path configuration. High gain character and homogeneous gain distribution were well preserved with the proposed scheme. Based on the Nd:GdVO4sub> crystal, a 99 W, 12.4 ps TEM00 laser output was achieved with a 42% extraction efficiency. The diffraction limited beam quality remained undisturbed after amplification with Mx2=1.09 and My2=1.07 in the orthogonal directions.

  18. Global maxima for the acousto-optic effect in SrB4sub>O7 crystals.


    Oleh, Buryy; Nazariy, Andrushchak; Andriy, Ratych; Natalia, Demyanyshyn; Bohdan, Mytsyk; Anatoliy, Andrushchak


    For the first time, the global maxima of the acousto-optic interaction are theoretically determined for biaxial SrB4sub>O7 crystals by the extreme surfaces method. As it is shown, the highest value of the acousto-optic figure-of-merit M2 is equal to 6.3×10-16  s3/kg and achieved in the case of the isotropic diffraction of the electromagnetic wave propagating in the [010] direction on the fast quasi-transversal acoustic wave.

  19. Improved synthesis and crystal structure of the flexible pillared layer porous coordination polymer: Ni(1,2-bis(4-pyridyl)ethylene)[Ni(CN)4sub>

    SciTech Connect

    Wong-Ng, W.; Culp, J. T.; Chen, Y. S.; Zavalij, P.; Espinal, L.; Siderius, D. W.; Allen, A. J.; Scheins, S.; Matranga, C.


    This paper reports our synthesis of flexible coordination polymer, Ni(L)[Ni(CN)4sub>], (L = 1,2-bis(4-pyridyl)ethylene (nicknamed bpene)), and its structural characterization using synchrotron single crystal X-ray diffraction. The structure of the purplish crystals has been determined to be monoclinic, space group P21/m, a = 13.5941(12) Å, b = 14.3621(12) Å, c = 14.2561(12) Å, β = 96.141(2)°, V = 2767.4(4) Å3, Z = 4, Dc = 1.46 g cm-1. Ni(bpene)[Ni(CN)4sub>] assumes a pillared layer structure with layers defined by Ni[Ni(CN)4sub>]n nets and bpene ligands acting as pillars. With the present crystallization technique which involves the use of concentrated ammonium hydroxide solution and dimethyl sulfoxide (DMSO), disordered free bpene ligands and solvents of crystallization (DMSO and water molecules) occupy the pores, resulting in a formula of Ni(bpene)[Ni(CN)4sub>](1/2)bpene∙DMSO2H2O, or Ni2N7C24H25SO3. Without the inclusion of free bpene ligands and solvent molecules, the free volume is approximately 61% of the total volume; this free volume fraction is reduced to 50% with the free ligands present. Pores without the free ligands were found to have a local diameter of 5.7 Å and a main aperture of 3.5 Å. Based on the successful crystal synthesis, we also devised a new bulk synthetic technique which yielded a polycrystalline material with a significantly improved CO2 uptake as compared to the originally reported powder material. The improved synthetic technique yielded a polycrystalline material with 40% higher CO2 uptake compared to the previously reported powder material. An estimated 14.4 molecules of CO2 per unit cell was obtained.

  20. New phases in the system LiMnVO{sub 4}-Mn{sub 3}(VO{sub 4}){sub 2}

    SciTech Connect

    Clemens, Oliver; Haberkorn, Robert; Beck, Horst Philipp


    The synthesis of orthorhombic Mn{sub 3}(VO{sub 4}){sub 2} via a simple solid state route as well as the description of a new tetragonal high temperature phase are reported in this paper. Additionally, the system LiMnVO{sub 4}-Mn{sub 3}(VO{sub 4}){sub 2} (=Mn{sub 1.5}VO{sub 4}), described by the formula Li{sub x}Mn{sub 1.5-x/2}VO{sub 4}, is investigated in detail, showing that substitution of one Mn{sup 2+} in Mn{sub 1.5}VO{sub 4} by two Li{sup +} ions favors the formation of the tetragonal high temperature phase for x{<=}0.22. This substitution is facilitated by the statistical half occupancy of the 4b site by Mn{sup 2+} in tetragonal Mn{sub 1.5}VO{sub 4}, whereas additional crystallographic sites would have to be occupied in the orthorhombic phase. The inverse substitution of Li by Mn in orthorhombic LiMnVO{sub 4} is also shown to be possible in the range 0.72{<=}x{<=}1. For 0.22{<=}x{<=}0.72, there is a large miscibility gap with a two phase mixture of the tetragonal Mn{sub 1.5}VO{sub 4} type and orthorhombic LiMnVO{sub 4} type phases. - Graphical Abstract: The unusual coordination of Mn in the form of a stella quadrangula with the surrounding vanadate groups. Highlights: > First synthesis of orthorhombic Mn{sub 3}(VO{sub 4}){sub 2} via a simple solid state route. > The crystal chemistry of the phases involved is rather complicated and it depends on the amount of Li that is incorporated. > System LiMnVO{sub 4}-Mn{sub 3}(VO{sub 4}){sub 2} (=Mn{sub 1.5}VO{sub 4}), described by the formula Li{sub x}Mn{sub 1.5-x/2}VO{sub 4}, is investigated in detail.

  1. Widely tunable in the mid-IR BaGa4sub>Se7 optical parametric oscillator pumped at 1064  nm.


    Kostyukova, Nadezhda Y; Boyko, Andrey A; Badikov, Valeriy; Badikov, Dmitrii; Shevyrdyaeva, Galina; Panyutin, Vladimir; Marchev, Georgi M; Kolker, Dmitry B; Petrov, Valentin


    A BaGa4sub>Se7 nanosecond optical parametric oscillator (OPO) shows extremely wide idler tunability in the mid-IR (2.7-17 μm) under 1.064 μm pumping. The ∼10  ns pulses at ∼7.2  μm have an energy of 3.7 mJ at 10 Hz. The pump-to-idler conversion efficiency for this wavelength reaches 5.9% with a slope of 6.5% corresponding to a quantum conversion efficiency or pump depletion of 40%.

  2. Unique edge-sharing sulfate-transition metal coordination in Na{sub 2}M(SO{sub 4}){sub 2} (M=Ni and Co)

    SciTech Connect

    Fry, Allyson M.; Sweeney, Owen T.; Adam Phelan, W.; Drichko, Natalia; Siegler, Maxime A.; McQueen, Tyrel M.


    Two compounds, Na{sub 2}Ni(SO{sub 4}){sub 2} and Na{sub 2}Co(SO{sub 4}){sub 2}, were synthesized and their structure and properties were characterized. They adopt a structure that contains a bidentate coordination of sulfate to the transition metal center, which was determined via single crystal X-ray diffraction combined with model refinements to both laboratory X-ray and time-of-flight neutron powder diffraction data. The compounds were both found to crystallize in the C2/c space group with Z=24 and a unit cell of a=23.3461(3) Å, b=10.3004(1) Å, c=17.4115(2) Å, β=98.8659(9)°, and V=4136.99(8) Å{sup 3} for the cobalt analog and a=23.2253(1) Å, b=10.26155(6) Å, c=17.3353(1) Å, β=99.0376(5)°, and V=4080.20(5) Å{sup 3} for the nickel analog. Magnetization measurements show that the transition metal centers have negligible interactions with neighboring sites. Infrared and Raman spectroscopies were used to further probe the unique sulfate-transition metal coordination, and confirm the bidentate binding motif. The resulting pseudo-trigonal bipyramidal coordination produces vivid violet, Na{sub 2}Co(SO{sub 4}){sub 2}, and yellow, Na{sub 2}Ni(SO{sub 4}){sub 2}, colors that were probed by diffuse reflectance. - Graphical abstract: Two blue distorted transition metal octahedra (oxygen in red) bridged by two sulfate tetrahedra are shown here. Each bridging sulfate tetrahedra shares an edge with one octahedron and a corner with the other. All of the remaining corners of the octahedra are corner sharing with four tetrahedra forming a polyhedral network. - Highlights: • Structure of Na2Ni(SO4)2 and Na2Co(SO4)2 is determined. • Unique sulfate-transition metal binding observed in the new structure. • Combined diffraction and spectroscopic techniques were used. • Magnetization measurements show negligible interactions between sites.

  3. Ultrafast dynamics of localized magnetic moments in the unconventional Mott insulator Sr2IrO4sub>

    SciTech Connect

    Krupin, O.; Dakovski, G. L.; Kim, B. J.; Kim, J. W.; Kim, Jungho; Mishra, S.; Chuang, Yi -De; Serrao, C. R.; Lee, W. -S.; Schlotter, W. F.; Minitti, M. P.; Zhu, D.; Fritz, D.; Chollet, M.; Ramesh, R.; Molodtsov, S. L.; Turner, J. J.


    Here, we report a time-resolved study of the ultrafast dynamics of the magnetic moments formed by the ${{J}_{\\text{eff}}}=1/2$ states in Sr2IrO4sub> by directly probing the localized iridium 5d magnetic state through resonant x-ray diffraction. Using optical pump–hard x-ray probe measurements, two relaxation time scales were determined: a fast fluence-independent relaxation is found to take place on a time scale of 1.5 ps, followed by a slower relaxation on a time scale of 500 ps–1.5 ns.

  4. Structure of Cs{sub 4}(HSO{sub 4}){sub 3}(H{sub 2}PO{sub 4}) single crystals

    SciTech Connect

    Makarova, I. P. Grebenev, V. V.; Vasil’ev, I. I.; Dmitricheva, E. V.; Komornikov, V. A.; Dolbinina, V. V.; Mikheikin, A. S.


    Single crystals of Cs{sub 4}(HSO{sub 4}){sub 3}(H{sub 2}PO{sub 4}) are synthesized and studied for the first time. The new compound is found in the course of studies of the phase diagram of the CsHSO{sub 4}–CsH{sub 2}PO{sub 4}–H{sub 2}O triple system. Data on the atomic crystal structure of single-crystalline and powder specimens, as well as on structural phase transitions, are obtained.

  5. Investigation of the structure of Cs{sub 3}(HSO{sub 4}){sub 2}(H{sub 2}PO{sub 4}) single crystals

    SciTech Connect

    Makarova, I. P. Grebenev, V. V.; Vasiliev, I. I.; Dmitricheva, E. V.; Komornikov, V. A.; Dolbinina, V. V.


    Cs{sub 3}(HSO{sub 4}){sub 2}(H{sub 2}PO{sub 4}) single crystals, obtained for the first time based on a systematic study of the phase diagram of the CsH{sub 2}PO{sub 4}–CsHSO{sub 4}–H{sub 2}O ternary system, have been studied by X-ray diffraction. The atomic structure of the crystals at room temperature is determined, and their structural features are analyzed.

  6. Injectable Silica–Permanganate Gel as a Slow-Release MnO4sub>- Source for Groundwater Remediation. Rheological Properties and Release Dynamics

    SciTech Connect

    Yang, Shuo; Oostrom, Martinus; Truex, Michael J.; Li, G.; Zhong, Lirong


    Injectable slow-release permanganate gel (ISRPG), formed by mixing KMnO4sub> solution with fumed silica powder, may have a potential application in remediating chlorinated solvent plumes in groundwater. A series of batch, column, and flow cell experiments has been completed to test the gel behavior under a variety of conditions. The experiments have provided information on ISRPG rheology, permanganate (MnO4sub>- ) release dynamics and distribution, and trichloroethene (TCE) degradation by ISRPG-released oxidant. The gel possesses remarkable shear thinning characteristics, resulting in a relative low viscosity during mixing, and facilitating its subsurface injection and distribution. Batch tests revealed that MnO4sub>- was diffused out from ISRPG into water while the gel did not dissolve or disperse into water but maintained its initial shape. Column experiments showed that MnO4sub>- release from ISRPG lasted considerably longer than the release from aqueous solution. TCE degradation by ISRPG-released MnO4sub>- was much more effective than that when MnO4sub>- was delivered using aqueous solution injection. In two-dimensional flow cell experiments, it was demonstrated that ISRPG slowly released a long-lasting low concentration MnO4sub>- plume sufficient for remediation and sustainable in an aquifer for a long period of time.

  7. Investigations of the R5(SixGe1-x)4sub> Intermetallic Compounds by X-Ray Resonant Magnetic Scattering

    SciTech Connect

    Tan, Lizhi


    The XRMS experiment on the Gd5Ge4sub> system has shown that, below the Neel temperature, TN = 127 K, the magnetic unit cells is the same as the chemical unit cell. From azimuth scans and the Q dependence of the magnetic scattering, all three Gd sites in the structure were determined to be in the same magnetic space group Pnma. The magnetic moments are aligned along the c-axis and the c-components of the magnetic moments at the three different sites are equal. The ferromagnetic slabs are stacked antiferromagnetically along the b-direction. They found an unusual order parameter curve in Gd5Ge4sub>. A spin-reorientation transition is a possibility in Gd5Ge4sub>, which is similar to the Tb5Ge4sub> case. Tb5Ge4sub> possesses the same Sm5Ge4sub>-type crystallographic structure and the same magnetic space group as Gd5Ge4sub> does. The difference in magnetic structure is that Tb5Ge4sub> has a canted one but Gd5Ge4sub> has nearly a collinear one in the low temperature antiferromagnetic phase. The competition between the magneto-crystalline anisotropy and the nearest-neighbor magnetic exchange interactions may allow a 3-dimensional canted antiferromagnetic structure in Tb5Ge4sub>. The spin-reorientation transition in both Gd5Ge4sub> and Tb5Ge4sub> may arise from the competition between the magnetic anisotropy from the spin-orbit coupling of the conduction electrons and the dipolar interactions anisotropy.

  8. Luminescent properties of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} and its luminescence improvement by incorporating A{sup +} (A=Li, Na, and K)

    SciTech Connect

    Li, Panlai Wang, Zhijun Yang, Zhiping; Guo, Qinglin


    A novel green phosphor SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} is synthesized by a high temperature solid-state method, and its luminescent property is investigated. X-ray diffraction patterns of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} indicate a similarity crystalline phase to SrZn{sub 2}(PO{sub 4}){sub 2}. SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} shows green emission under 369 nm excitation, and the prominent luminescence in green (544 nm) due to {sup 5}D{sub 4}–{sup 7}F{sub 5} transition of Tb{sup 3+}. For the 544 nm emission, excitation spectrum has several excitation band from 200 nm to 400 nm. Emission intensity of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} is influenced by Tb{sup 3+} concentration, and concentration quenching effect of Tb{sup 3+} in SrZn{sub 2}(PO{sub 4}){sub 2} is also observed. With incorporating A{sup +} (A=Li, Na, and K) as compensator charge, the emission intensity of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} can be obviously enhanced. CIE color coordinates of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} locate in the green region. The results indicate this phosphor may be a potential application in white LEDs. - Graphical abstract: SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} can produce green emission under near-UV excitation, and its luminescent properties can be improved by incorporating A{sup +} (A=Li, Na, and K). - Highlights: • SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} can produce green emission under near-UV excitation. • Concentration quenching effect of Tb{sup 3+} in SrZn{sub 2}(PO{sub 4}){sub 2} is observed. • Emission intensities of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} are enhanced by codoped A{sup +} (A=Li, Na, K)

  9. Metastability in the MgAl2O4sub>-Al2O3 System

    SciTech Connect

    Wilkerson, Kelley R.; Smith, Jeffrey D.; Hemrick, James G.


    Aluminum oxide must take a spinel form ( γ-Al2O3) at elevated temperatures in order for extensive solid solution to form between MgAl2O4sub> and α-Al2O3. The solvus line between MgAl2O4sub> and Al2O3 has been defined at 79.6 wt% Al2O3 at 1500°C, 83.0 wt% Al2O3 at 1600°C, and 86.5 wt% Al2O3 at 1700°C. A metastable region has been defined at temperatures up to 1700°C which could have significant implications for material processing and properties. Additionally, initial processing could have major implications on final chemistry. The spinel solid solution region has been extended to form an infinite solid solution with Al2O3 at elevated temperatures. A minimum in melting at 1975°C and a chemistry of 96 wt% Al2O3 rather than a eutectic is present, resulting in no eutectic crystal formation during solidification.

  10. Thermodynamic Properties of α-Fe2O3 and Fe3O4sub> Nanoparticles

    SciTech Connect

    Spencer, Elinor C.; Ross, Nancy L.; Olsen, Rebecca E.; Huang, Baiyu; Kolesnikov, Alexander I.; Woodfield, Brian F.


    Here we comprehansively assessed the thermodynamic properties of hydrated α-Fe2O3 (hematite) and Fe3O4sub> (magnetite) nanoparticles. In addition to 9 nm Fe3O4sub>, three α-e2O3nanoparticles samples of different sizes (11, 14, and 25 nm) and bulk α-e2O3 have been evaluated by inelastic neutron scattering methods. The contribution of the two-level magnetic spin flip transition to the heat capacity of the α-e2O3 particles has been determined. The isochoric heat capacity of the water confined on the surface of these two types of iron oxide particles have been calculated from their INS spectra, and is affected by the chemical composition of the underlying particle. Furthermore, the heat capacity and dynamics of the particle hydration layers appear to be influenced by a complex array of factors including particle size, water coverage, and possibly the magnetic state of the particle itself.

  11. Structural instability of the CoO4sub> tetrahedral chain in SrCoO3-δ thin films

    SciTech Connect

    Glamazda, A.; Choi, Kwang-yong; Lemmens, P.; Choi, Woo Seok; Jeen, Hyoungjeen; Meyer, Tricia L.; Lee, Ho Nyung


    Raman scattering experiments together with detailed lattice dynamic calculations are performed to elucidate crystallographic and electronic peculiarities of SrCoO3-δ films. We observe that the 85 cm-1 phonon mode involving the rotation of a CoO4sub> tetrahedron undergoes a hardening by 21 cm-1 when the temperature is decreased. In addition, new phonon modes appear at 651.5 and 697.6 cm-1 . The latter modes are attributed to the Jahn-Teller activated modes. Upon cooling from room temperature, all phonons exhibit an exponential-like increase of intensity with a characteristic energy of about 103–107 K. We attribute this phenomenon to an instability of the CoO4sub> tetrahedral chain structure, which constitutes a key ingredient to understand the electronic and structural properties of the brownmillerite SrCoO2.5.

  12. Monodispersed Li4sub>Ti5O12 with Controlled Morphology as High Power Lithium Ion Battery Anodes

    SciTech Connect

    Li, Yunchao; Fu, Guoyi; Watson, Mark; Harrison, Stephen; Paranthaman, M. Parans


    Monodispersed Li4sub>Ti5O12 (LTO) nanoparticles with controlled microstructure were successfully synthesized by a combination of hydrolysis and hydrothermal method followed by a post-annealing process. The scanning electron microscopy images showed that particles with a size of 30-40 nm were precisely controlled throughout the synthesis process. The electrochemical tests of the as-prepared LTO electrodes in a half-cell proved its high rate performance and outstanding cyclability which benefits from the preserved well-controlled nanoparticle size and morphology. LTO electrodes were also tested in a full cell configuration in pairing with LiFePO4sub> cathodes, which demonstrated a capacity of 147.3 mAh g-1. In addition, we have also demonstrated that LTO materials prepared using lithium salts separated from geothermal brine solutions had good cyclability. These demonstrations provide a promising way for making low-cost, large-scale LTO electrode materials for energy storage applications.

  13. Effect of Yb doping on the refractive index and thermo-optic coefficient of YVO4sub> single crystals.


    Soharab, M; Bhaumik, Indranil; Bhatt, R; Saxena, A; Karnal, A K; Gupta, P K


    Single crystals of YVO4sub> with different doping concentrations of Yb (1.5, 3.0, 8.0, and 15.0 at. %) and with good crystalline quality (FWHM ∼43-55 arc sec of rocking curve) were grown by the optical floating zone technique. Refractive index measurements were carried out at four wavelengths as a function of temperature. The measurements show that as the doping concentration of Yb is increased, the refractive index varies marginally for ne whereas there is a significant change in the value of no. The thermo-optic coefficient (dn/dT) was found to be positive with a value ∼10-5/°C, which is 1 order higher than that for the undoped YVO4sub> crystal. The thermo-optic coefficient is higher for ne compared to that of no. Also, a set of relations describing the wavelength dependence of the thermo-optic coefficient were established that are useful for calculating the thermo-optic coefficient at any temperature in the range 30°C-150°C and at any wavelength in the range 532-1551 nm.

  14. Local Structural Investigations, Defect Formation, and Ionic Conductivity of the Lithium Ionic Conductor Li 4sub> P 2 S 6

    SciTech Connect

    Dietrich, Christian; Sadowski, Marcel; Sicolo, Sabrina; Weber, Dominik A.; Sedlmaier, Stefan J.; Weldert, Kai S.; Indris, Sylvio; Albe, Karsten; Janek, Jürgen; Zeier, Wolfgang G.


    Glassy, glass–ceramic, and crystalline lithium thiophosphates have attracted interest in their use as solid electrolytes in all-solid-state batteries. Despite similar structural motifs, including PS4sub>3–, P2S64–, and P2S74– polyhedra, these materials exhibit a wide range of possible compositions, crystal structures, and ionic conductivities. Here, we present a combined approach of Bragg diffraction, pair distribution function analysis, Raman spectroscopy, and 31P magic angle spinning nuclear magnetic resonance spectroscopy to study the underlying crystal structure of Li4sub>P2S6. In this work, we show that the material crystallizes in a planar structural arrangement as a glass ceramic composite, explaining the observed relatively low ionic conductivity, depending on the fraction of glass content. Calculations based on density functional theory provide an understanding of occurring diffusion pathways and ionic conductivity of this Li+ ionic conductor.

  15. Disorder from order among anisotropic next-nearest-neighbor Ising spin chains in SrHo2O4sub>

    SciTech Connect

    Wen, J. -J.; Tian, W.; Garlea, V. O.; Koohpayeh, S. M.; McQueen, T. M.; Li, H. -F.; Yan, J. -Q.; Rodriguez-Rivera, J. A.; Vaknin, D.; Broholm, C. L.


    In this study, we describe why Ising spin chains with competing interactions in SrHo2O4sub> segregate into ordered and disordered ensembles at low temperatures (T). Using elastic neutron scattering, magnetization, and specific heat measurements, the two distinct spin chains are inferred to have Néel (↑↓↑↓) and double-Néel (↑↑↓↓) ground states, respectively. Below TN = 0.68(2)K, the Néel chains develop three-dimensional long range order (LRO), which arrests further thermal equilibration of the double-Néel chains so they remain in a disordered incommensurate state for T below TS = 0.52(2)K. SrHo2O4sub> distills an important feature of incommensurate low dimensional magnetism: kinetically trapped topological defects in a quasi–d–dimensional spin system can preclude order in d + 1 dimensions.

  16. Magnetic excitations from an S=1/2 diamond-shaped tetramer compound Cu2PO4sub>OH

    SciTech Connect

    Matsuda, Masaaki; Dissanayake, Sachith E.; Abernathy, Douglas L.; Totsuka, K.; Belik, A. A.


    Inelastic neutron scattering experiments have been carried out on a powder sample of Cu2PO4sub>OH, which consists of diamond-shaped tetramer spin units with S=1/2. We have observed two nearly dispersionless magnetic excitations at E1 ~2 and E2 ~0 meV, whose energy width are broader than the instrumental resolution. The simplest square tetramer model with one dominant interaction, which predicts two sharp excitation peaks at E1 and E2(=2E1), does not explain the experimental result. We found that two diagonal intratetramer interactions compete with the main interaction and weak intertetramer interactions connect the tetramers. The main intratetramer interaction is found to split into two inequivalent ones due to a structural distortion below 160 K. Cu2PO4sub>OH is considered to be a good material to study the S=1/2 Heisenberg tetramer system.

  17. In situ studies of surface of NiFe2O4sub> catalyst during complete oxidation of methane

    SciTech Connect

    Zhang, Shiran; Shan, Junjun; Nie, Longhui; Nguyen, Luan; Wu, Zili; Tao, Franklin


    Here, NiFe2O4sub> with an inverse spinel structure exhibits high activity for a complete oxidation of methane at 400 °C–425 °C and a higher temperature. The surface of the catalyst and its adsorbates were well characterized with ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and in situ infrared spectroscopy (IR). In situ studies of the surface of NiFe2O4sub> using AP-XPS suggest the formation of methoxy-like and formate-like intermediates at a temperature lower than 200 °C, supported by the observed vibrational signatures in in situ IR studies. Evolutions of C1s photoemission features and the nominal atomic ratios of C/(Ni + Fe) of the catalyst surface suggest that the formate-like intermediate is transformed to product molecules CO2 and H2O in the temperature range of 250–300 °C. In situ studies suggest the formation of a spectator, – Olattice – CH2 – Olattice –. It strongly bonds to surface through C–O bonds and cannot be activated even at 400 °C.

  18. The effects of cation–anion clustering on defect migration in MgAl2O4sub>

    SciTech Connect

    Zamora, Richard J.; Voter, Arthur F.; Perez, Danny; Perriot, Romain; Uberuaga, Blas P.


    Magnesium aluminate spinel (MgAl2O4sub>), like many other ceramic materials, offers a range of technological applications, from nuclear reactor materials to military body armor. For many of these applications, it is critical to understand both the formation and evolution of lattice defects throughout the lifetime of the material. We use the Speculatively Parallel Temperature Accelerated Dynamics (SpecTAD) method to investigate the effects of di-vacancy and di-interstitial formation on the mobility of the component defects. From long-time trajectories of the state-to-state dynamics, we characterize the migration pathways of defect clusters, and calculate their self-diffusion constants across a range of temperatures. We find that the clustering of Al and O vacancies drastically reduces the mobility of both defects, while the clustering of Mg and O vacancies completely immobilizes them. For interstitials, we find that the clustering of Mg and O defects greatly reduces O interstitial mobility, but has only a weak effect on Mg. Lastly, these findings illuminate important new details regarding defect kinetics relevant to the application of MgAl2O4sub> in extreme environments.

  19. Conduction below 100 °C in nominal Li6ZnNb4sub>O14

    SciTech Connect

    Li, Yunchao; Paranthaman, Mariappan Parans; Gill, Lance W.; Edward W. Hagaman; Wang, Yangyang; Sokolov, Alexei P.; Dai, Sheng; Ma, Cheng; Chi, Miaofang; Veith, Gabriel M.; Manthiram, Arumugam; Goodenough, John B.


    The increasing demand for a safe rechargeable battery with a high energy density per cell is driving a search for a novel solid electrolyte with a high Li+ or Na+ conductivity that is chemically stable in a working Li-ion or Na-ion battery. Li6ZnNb4sub>O14 has been reported to exhibit a σ Li > 10-2 S cm-1 at 250 °C, but to disproportionate into multiple phases on cooling from 850 °C to room temperature. An investigation of the room-temperature Li-ion conductivity in a porous pellet of a multiphase product of a nominal Li6ZnNb4sub>O14 composition is shown to have bulk σ Li 3.3 x 10-5 S cm-1 at room temperature that increases to 1.4 x 10-4 S cm-1 by 50 °C. 7Li MAS NMR spectra were fitted to two Lorentzian lines, one of which showed a dramatic increase with increasing temperature. As a result, a test for water stability indicates that Li+ may move to the particle and grain surfaces to react with adsorbed water as occurs in the garnet Li+ conductors.

  20. NMR Studies of the Vanadium Spin Dynamics and Spin Structure in LiV2O4sub>, CaV2O4sub>, and (LixV1-x)3BO5 (x ≈ 0.33, 0.40)

    SciTech Connect

    Zong, Xiaopeng


    Strong electron correlation is believed to be an essential and unifying factor in diverse properties of condensed matter systems. Ground states that can arise due to electron correlation effects include Mott insulators, heavy fermion, ferromagnetism and antiferromagnetism, spin glasses, and high-temperature superconductivity. The electronic systems in transition metal oxide compounds are often highly correlated. In this thesis, the author presents experimental studies on three strongly correlated vanadium oxide compounds: LiV2O4sub>, (LixV1-x)3BO5, and CaV2O4sub>, which have completely different ground states.

  1. Electron scattering, charge order, and pseudogap physics in La1.6–xNd0.4sub>SrxCuO4sub>: An angle-resolved photoemission spectroscopy study

    SciTech Connect

    Matt, C. E.; Fatuzzo, C. G.; Sassa, Y.; Mansson, M.; Fatale, S.; Bitetta, V.; Shi, X.; Pailhes, S.; Berntsen, M. H.; Kurosawa, T.; Oda, M.; Momono, N.; Lipscombe, O. J.; Hayden, S. M.; Yan, J. -Q.; Zhou, J. -S.; Goodenough, J. B.; Pyon, S.; Takayama, T.; Takagi, H.; Patthey, L.; Bendounan, A.; Razzoli, E.; Shi, M.; Plumb, N. C.; Radovic, M.; Grioni, M.; Mesot, J.; Tjernberg, O.; Chang, J.


    We report an angle-resolved photoemission study of the charge stripe ordered La1.6–xNd0.4sub>SrxCuO4sub> (Nd-LSCO) system. A comparative and quantitative line-shape analysis is presented as the system evolves from the overdoped regime into the charge ordered phase. On the overdoped side (x = 0.20), a normal-state antinodal spectral gap opens upon cooling below 80 K. In this process, spectral weight is preserved but redistributed to larger energies. A correlation between this spectral gap and electron scattering is found. A different line shape is observed in the antinodal region of charge ordered Nd-LSCO x = 1/8. Significant low-energy spectral weight appears to be lost. As a result, these observations are discussed in terms of spectral-weight redistribution and gapping originating from charge stripe ordering.

  2. Rietveld refinement, electronic structure and ionic conductivity of Sr{sub 4}La{sub 6}(SiO{sub 4}){sub 6}F{sub 2} and Sr{sub 4}La{sub 6}(SiO{sub 4}){sub 6}O ceramics

    SciTech Connect

    Boughzala, Khaled; Debbichi, Mourad; Njema, Hela; Bouzouita, Khaled


    In this paper, we report the effect of the tunnel anions on the ionic conductivity of Strontium-Lanthanum silicate apatites. The Sr{sub 4}La{sub 6}(SiO{sub 4}){sub 6}F{sub 2} and Sr{sub 4}La{sub 6}(SiO{sub 4}){sub 6}O ceramics were prepared by the solid state reaction method. X-ray diffraction, NMR spectroscopy and Raman measurements were performed to investigate the crystal structure and vibrational active modes. Moreover, the electronic structures of the crystals were evaluated by the first-principles quantum mechanical calculation based on the density functional theory. Finally, the ionic conductivity was studied according to the complex impedance method. - Graphical abstract: The relaxed primitive unit cell for Sr{sub 4}La{sub 6}Fap. Display Omitted.

  3. Electrochemically influenced cation inter-diffusion and Co3O4sub> formation on La0.6Sr0.4sub>CoO3 infiltrated into SOFC cathodes

    SciTech Connect

    Song, Xueyan; Lee, Shiwoo; Chen, Yun; Gerdes, Kirk


    Nanosized LSC electrocatalyst was infiltrated into a porous scaffold cathode composed of Sm2O3-doped CeO2 (SDC) and La0.6Sr0.4sub>Co0.2Fe0.8O3-δ (LSCF) in a commercial button solid oxide fuel cell (SOFC). To understand the stability of cathodes infiltrated with LSC, the infiltrated composite cells were subjected to both electrochemical operating and thermal aging states at 750 °C for 1500 h. Nanostructure and local chemistry evolution of La0.6Sr0.4sub>CoO3 (LSC) infiltrated cathodes upon operation and aging were investigated by transmission electron microscopy. After operation, the LSC remained a cubic perovskite, and the crystal grains exhibit comparable size to as-infiltrated LSC grains. Inter-diffusion of Fe from the LSCF to a Fe-incorporated LSC layer developed on the LSCF backbone. However, only sharp interfaces were observed between LSC and SDC backbone in the as-infiltrated cathode and such interfaces remain after operation. The infiltrated LSC on the SDC backbone also retains granular particle morphology. Furthermore, newly grown Co3O4sub> nanocrystals were found in the operated cathode. After thermal aging, on the other hand, cation inter-diffusion across the interfaces of the infiltrate particles and the cathode backbones is less than that from the operated cells. Lastly, the following hypothesis is proposed: Co3O4sub> forms on LSC arising from local charge balancing between cobalt and oxygen vacancies.

  4. Full-dimensional quantum calculations of vibrational levels of NH4sub>+ and isotopomers on an accurate ab initio potential energy surface

    SciTech Connect

    Hua -Gen Yu; Han, Huixian; Guo, Hua


    Vibrational energy levels of the ammonium cation (NH4sub>+) and its deuterated isotopomers are calculated using a numerically exact kinetic energy operator on a recently developed nine-dimensional permutation invariant semiglobal potential energy surface fitted to a large number of high-level ab initio points. Like CH4, the vibrational levels of NH4sub>+ and ND4sub>+ exhibit a polyad structure, characterized by a collective quantum number P = 2(v1 + v3) + v2 + v4sub>. As a result, the low-lying vibrational levels of all isotopomers are assigned and the agreement with available experimental data is better than 1 cm–1.

  5. Redox chemistry of a binary transition metal oxide (AB 2 O 4sub> ): a study of the Cu 2+ /Cu 0 and Fe 3+ /Fe 0 interconversions observed upon lithiation in a CuFe 2 O 4sub> battery using X-ray absorption spectroscopy

    SciTech Connect

    Cama, Christina A.; Pelliccione, Christopher J.; Brady, Alexander B.; Li, Jing; Stach, Eric A.; Wang, Jiajun; Wang, Jun; Takeuchi, Esther S.; Takeuchi, Kenneth J.; Marschilok, Amy C.


    Copper ferrite, CuFe2 O 4sub>, is a promising candidate for application as a high energy electrode material in lithium based batteries. Mechanistic insight on the electrochemical reduction and oxidation processes was gained through the first X-ray absorption spectroscopic study of lithiation and delithiation of CuFe2 O 4sub>. A phase pure tetragonal CuFe2 O 4sub> material was prepared and characterized using laboratory and synchrotron X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. We used ex situ X-ray absorption spectroscopy (XAS) measurements to study the battery redox processes at the Fe and Cu K-edges, using X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and transmission X-ray microscopy (TXM) spectroscopies. EXAFS analysis showed upon discharge, an initial conversion of 50% of the copper(II) to copper metal positioned outside of the spinel structure, followed by a migration of tetrahedral iron(III) cations to octahedral positions previously occupied by copper(II). Then, upon charging to 3.5 V, the copper metal remained in the metallic state, while iron metal oxidation to iron(III) was achieved. Our results provide new mechanistic insight regarding the evolution of the local coordination environments at the iron and copper centers upon discharging and charging.

  6. Crystal structure and magnetic properties of NaCu{sup II}[(Cu{sup II}{sub 3}O)(PO{sub 4}){sub 2}Cl

    SciTech Connect

    Jin Tengteng; Liu Wei; Chen Shuang; Prots, Yurii; Schnelle, Walter; Zhao Jingtai; Kniep, Ruediger; Hoffmann, Stefan


    A new copper(II) oxide phosphate chloride, NaCu{sup II}[(Cu{sup II}{sub 3}O)(PO{sub 4}){sub 2}Cl], has been synthesized by flux synthesis. Single-crystal X-ray diffraction data show that the title compound crystallizes in the monoclinic system, space group P2{sub 1}/c (No. 14), with lattice parameters a=8.392(2) A, b=6.3960(10) A, c=16.670(2) A, {beta}=109.470(10) Degree-Sign , V=843.6(3) A{sup 3}, Z=4. The crystal structure is characterized by a complex chain of copper-centered polyhedra running along [0 1 0] which are connected by phosphate tetrahedra. The resulting three-dimensional polyhedra framework exhibits channels filled by additional copper and sodium atoms. Field and temperature dependent measurements of the specific heat and the magnetic susceptibility reveal low-dimensional magnetic behavior. The compound starts to decompose at 700 K under release of oxygen and evaporation of Cu{sup I}Cl as shown by simultaneous thermogravimetry and mass spectrometry. - Graphical abstract: The crystal structure of the new copper(II) phosphate chloride, NaCu{sup II}[(Cu{sup II}{sub 3}O)(PO{sub 4}){sub 2}Cl], exhibits linear chains of copper tetrahedra which show low-dimensional magnetic behavior proven by specific heat and magnetic susceptibility measurements. Highlights: Black-Right-Pointing-Pointer A new copper(II) oxide phosphate chloride, NaCu{sup II}[(Cu{sup II}{sub 3}O)(PO{sub 4}){sub 2}Cl], has been synthesized by flux synthesis. Black-Right-Pointing-Pointer The crystal structure comprises chains of Cu{sub 4}O tetrahedra. Black-Right-Pointing-Pointer Low-dimensional behavior has been proven by magnetic and specific heat measurements. Black-Right-Pointing-Pointer On heating, Cu{sup I}Cl and oxygen are released shown by simultaneous thermogravimetry and mass spectrometry.

  7. Beam quality management by periodic reproduction of wavefront aberrations in end-pumped Nd:YVO4sub> laser amplifiers.


    Liu, Bin; Liu, Chong; Shen, Lifeng; Wang, Chunhua; Ye, Zhibin; Liu, Dong; Xiang, Zhen


    A method for beam quality management is presented in a master oscillator power amplifier (MOPA) using Nd:YVO4sub> as the gain medium by extra-cavity periodic reproduction of wavefront aberrations. The wavefront aberration evolution of the intra-cavity beams is investigated for both symmetrical and asymmetrical resonators. The wavefront aberration reproduction process is successfully realized outside the cavity in four-stage amplifiers. In the MOPA with a symmetrical oscillator, the laser power increases linearly and the beam quality hardly changes. In the MOPA with an asymmetrical oscillator, the beam quality is deteriorated after the odd-stage amplifier and is improved after the even-stage amplifier. The wavefront aberration reproduction during the extra-cavity beam propagation in the amplifiers is equivalent to that during the intra-cavity propagation. This solution helps to achieve the effective beam quality management in laser amplifier chains.

  8. Temperature, Oxygen, and Soot-Volume-Fraction Measurements in a Turbulent C2H4sub>-Fueled Jet Flame

    SciTech Connect

    Kearney, Sean P.; Guildenbecher, Daniel Robert; Winters, Caroline; Farias, Paul Abraham; Grasser, Thomas W.; Hewson, John C.


    We present a detailed set of measurements from a piloted, sooting, turbulent C 2 H 4 sub>- fueled diffusion flame. Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (CARS) is used to monitor temperature and oxygen, while laser-induced incandescence (LII) is applied for imaging of the soot volume fraction in the challenging jet-flame environment at Reynolds number, Re = 20,000. Single-laser shot results are used to map the mean and rms statistics, as well as probability densities. LII data from the soot-growth region of the flame are used to benchmark the soot source term for one-dimensional turbulence (ODT) modeling of this turbulent flame. The ODT code is then used to predict temperature and oxygen fluctuations higher in the soot oxidation region higher in the flame.

  9. New insights into the thermodynamic behavior of 2LiBH4sub>-MgH2 composite for hydrogen storage

    SciTech Connect

    Cova, Federico; Ronnebro, Ewa; Choi, Yong-Joon; Gennari, Fabiana; Larochette, Pierre


    The composite 2LiBH4sub>:MgH2 has been studied as a possible hydrogen storage material due to its high storage capacity. The present work is directed towards the clarification of the thermodynamic behavior of the system, especially in the temperature region above 400°C. We reveal different reaction paths during hydrogen absorption and desorption at various temperatures which has important implication for applications. At temperatures higher than 413°C, the observation of two different absorption pressure plateaus indicates that two different reactions occur, however, below this temperature there is only one plateau present in the system. During desorption, the double plateau can be observed at temperatures as low as 375°C.

  10. The migration mechanism of transition metal ions in LiNi 0.5 Mn 1.5O4sub>

    SciTech Connect

    Xu, Gui-Liang; Qin, Yan; Ren, Yang; Cai, Lu; An, Ke; Amine, Khalil; Chen, Zonghai


    The migration of transition metal ions in the oxygen framework was recently proposed to be responsible for the continuous loss of average working potential of high energy density layered–layered composite cathodes for lithium-ion batteries. The potential migration pathway in a model material, LiNi 0.5 Mn 1.5O4sub> spinel, was investigated using in situ high-energy X-ray diffraction and in situ neutron diffraction during the solid state synthesis process. It was found that the migration of transition metal ions among octahedral sites is possible by using tetrahedral vacancies as intermediate sites. It was also suggested that the number of electrons in 3d orbitals has a significant impact on their mobility in the hosting oxygen framework.

  11. Cw and Q-switched Nd:NaLa(MoO{sub 4}){sub 2} laser noncritical to the temperature drift of the diode pump laser wavelength

    SciTech Connect

    Ushakov, S N; Lis, Denis A; Subbotin, Kirill A; Romanyuk, V A; Shestakov, A V; Ryabochkina, P A; Shestakova, I A; Zharikov, Evgeny V


    Lasing in Nd:NaLa(MoO{sub 4}){sub 2} crystals is obtained without stabilisation of the diode pump wavelength. A dependence of the cw laser power (at a wavelength of 1059 nm) on the pump diode temperature is found within a range of 10-458C. It is shown that the variations in the diode temperature within this region change the lasing efficiency no more than by 30%. In the passive Q-switching regime, the experiments were performed under both pulsed and cw pumping. Upon pulsed pumping, the laser energy was 16 {mu}J at the output pulse duration of 11 ns. The laser wavelength was 1059 nm, as well as in the case of cw operation. Upon cw pumping with a power of 1.5 W, laser pulses were obtained with an energy of 15 {mu}J. (lasers)

  12. Efficient self-stimulated Raman scattering with simultaneously self-mode-locking in a diode-pumped Nd:GdVO4sub> laser.


    Li, Zuohan; Peng, Jiying; Yao, Jianquan; Han, Ming; Jiang, Linghong


    We demonstrated an efficient diode-pumped picosecond self-Raman Nd:GdVO4sub> laser with the simultaneous processes of stimulated Raman scattering and self-mode-locking in the same crystal. The design of self-mode-locked was theoretically analyzed, and a compact and feasible dual-concave cavity was adopted. The maximum output power of the first-Stokes Raman laser was 736 mW with the repetition rate of 1.51 GHz. In addition, the second-harmonic generation of a yellow laser at 586.5 nm is accomplished with an external LiB3O5 crystal.

  13. Diode-end-pumped Ho, Pr:LiLuF4sub> bulk laser at 2.95  μm.


    Nie, Hongkun; Zhang, Peixiong; Zhang, Baitao; Yang, Kejian; Zhang, Lianhan; Li, Tao; Zhang, Shuaiyi; Xu, Jianqiu; Hang, Yin; He, Jingliang


    A diode-end-pumped continuous-wave (CW) and passively Q-switched Ho, Pr:LiLuF4sub> (Ho, Pr:LLF) laser operation at 2.95 μm was demonstrated for the first time, to the best of our knowledge. The maximum CW output power was 172 mW. By using a monolayer graphene as the saturable absorber, the passively Q-switched operation was realized, in which regimes with the highest output power, the shortest pulse duration, and the maximum repetition rate were determined to be 88 mW, 937.5 ns, and 55.7 kHz, respectively. The laser beam quality factor M2 at the maximum CW output power were measured to be Mx2=1.48 and My2=1.47.

  14. 119Sn-NMR investigations on superconducting Ca3Ir4sub>Sn13: Evidence for multigap superconductivity

    SciTech Connect

    Sarkar, R.; Petrovic, C.; Bruckner, F.; Gunther, M.; Wang, Kefeng; Biswas, P. K.; Luetkens, H.; Morenzoni, E.; Amato, A.; Klauss, H. -H.


    In this study, we report bulk superconductivity (SC) in Ca3Ir4sub>Sn13 by means of 119Sn nuclear magnetic resonance (NMR) experiments. Two classical signatures of BCS superconductivity in spin-lattice relaxation rate (1/T1), namely the Hebel–Slichter coherence peak just below the Tc, and the exponential decay in the superconducting phase, are evident. The noticeable decrease of 119Sn Knight shift below Tc indicates spin-singlet superconductivity. The temperature dependence of the spin-lattice relaxation rate 119(1/T1) is convincingly described by the multigap isotropic superconducting gap. NMR experiments do not witness any sign of enhanced spin fluctuations.

  15. Multiband Te p Based Superconductivity of Ta4sub>Pd3Te16

    SciTech Connect

    Singh, David J.


    We recently discovered that Ta4sub>Pd3Te16 is a superconductor that has been suggested to be an unconventional superconductor near magnetism. Here, we report electronic structure calculations showing that despite the layered crystal structure the material is an anisotropic three-dimensional (3D) metal. The Fermi surface contains prominent one-dimensional (1D) and two-dimensional (2D) features, including nested 1D sheets, a 2D cylindrical section, and a 3D sheet. Moreover, the electronic states that make up the Fermi surface are mostly derived from Te p states with small Ta d and Pd d contributions. This places the compound far from magnetic instabilities. The results are discussed in terms of multiband superconductivity.

  16. Nanoparticles of K{sub 2}Ca{sub 2}(SO{sub 4}){sub 3}:Eu as effective detectors for swift heavy ions

    SciTech Connect

    Salah, Numan; Lochab, S. P.; Kanjilal, D.; Ranjan, Ranju; Habib, Sami S.; Rupasov, A. A.; Aleynikov, V. E.


    The modification of thermoluminescence (TL) and photoluminescence (PL) properties of K{sub 2}Ca{sub 2}(SO{sub 4}){sub 3}:Eu nanoparticles by swift heavy ions (SHI), irradiation is studied. Pellets form of the nanomaterials were irradiated by 48 MeV Li{sup 3+}, 75 MeV C{sup 6+}, and 90 MeV O{sup 7+} ion beams. The fluence range is 1x10{sup 9}-1x10{sup 13} ions/cm{sup 2}. The modification in TL glow curves of the nanomaterials irradiated by Li{sup 3+}, C{sup 6+}, and O{sup 7+} ion beams are essentially similar to those induced by {gamma}-ray irradiation. These glow curves have single peaks at around 427 K with a small variation in their positions by around {+-}3 K. The TL intensity of the ion beams irradiated nanomaterials is found to decease, while going from low to high atomic number (Z) ions (i.e., Li{sup 3+}{yields}O{sup 7+}). The TL response curve of the pellets irradiated by Li{sup 3+} ions is linear in the whole range of studied fluences. The curves for C{sup 6+} and O{sup 7+} irradiated samples are linear at lower fluences (1x10{sup 9}-1x10{sup 12} ion/cm{sup 2}) and then saturate at higher fluence. These results for the nanomaterials are much better than that of the corresponding microcrystalline samples irradiated with a Li{sup 3+} ion. The curves were linear up to the fluence 1x10{sup 11} ion/cm{sup 2} and then become sublinear at higher fluences. The TL efficiency values of K{sub 2}Ca{sub 2}(SO{sub 4}){sub 3}:Eu nanoparticles irradiated by 48 MeV Li{sup 3+}, 75 MeV C{sup 6+}, and 90 MeV O{sup 7+} ion beams have been measured relative to {gamma} rays of {sup 60}Co and are found to be 0.515, 0.069, and 0.019, respectively. This value for the Li{sup 3+} ion (0.515) is much higher than that of the corresponding microcrystalline material (0.0014). These superiorities for the nanomaterials make K{sub 2}Ca{sub 2}(SO{sub 4}){sub 3}:Eu nanophosphor a suitable candidate for detecting the doses of swift heavy ions. PL studies on the ion beams irradiated and

  17. One Dimensional(1D)-to-2D Crossover of Spin Correlations in the 3D Magnet ZnMn2O4sub>

    SciTech Connect

    Disseler, S. M.; Chen, Y.; Yeo, S.; Gasparovic, G.; Piccoli, P. M. B.; Schultz, A. J.; Qiu, Y.; Huang, Q.; Cheong, S. -W.; Ratcliff, W.


    In this paper we report on the intriguing evolution of the dynamical spin correlations of the frustrated spinel ZnMn2O4sub>. Inelastic neutron scattering and magnetization studies reveal that the dynamical correlations at high temperatures are 1D. At lower temperature, these dynamical correlations become 2D. Surprisingly, the dynamical correlations condense into a quasi 2D Ising-like ordered state, making this a rare observation of two dimensional order on the spinel lattice. Remarkably, 3D ordering is not observed down to temperatures as low as 300 mK. This unprecedented dimensional crossover stems from frustrated exchange couplings due to the huge Jahn-Teller distortions around Mn3+ ions on the spinel lattice.

  18. Calcium hydroxyapatite, Ca{sub 10}(PO{sub 4}){sub 6}(OH){sub 2} ceramics prepared by aqueous sol-gel processing

    SciTech Connect

    Bogdanoviciene, Irma; Beganskiene, Aldona; Tonsuaadu, Kaia; Glaser, Jochen; Meyer, H.-Juergen . E-mail:; Kareiva, Aivaras . E-mail:


    Aqueous sol-gel chemistry routes based on ammonium-hydrogen phosphate as the phosphorus precursor and calcium acetate monohydrate as source of calcium ions have been developed to prepare calcium hydroxyapatite samples with different morphological properties. In the sol-gel processes, an aqueous solutions of ethylene diamine tetra-acetic acid (EDTA) or tartaric acid (TA) as complexing agents were added to the reaction mixture. The monophasic Ca{sub 10}(PO{sub 4}){sub 6}(OH){sub 2} samples were obtained by calcination of precursor gels for 5 h at 1000 deg. C. The phase transformations, composition and micro-structural features in the polycrystalline samples were studied by thermoanalytical methods (TGA/DTA), infrared spectroscopy (IR), X-ray powder diffraction analysis (XRD) and scanning electron microscopy (SEM). It was shown that adjusting the nature of complexing agent in the aqueous sol-gel processing can be used to control the morphology of the ceramic samples.

  19. Remarkable Stability of Charge Density Wave Order in La1.875Ba0.125CuO4sub>

    SciTech Connect

    Chen, X. M.; Thampy, V.; Mazzoli, C.; Barbour, A. M.; Miao, H.; Gu, G. D.; Cao, Y.; Tranquada, J. M.; Dean, M. P. M.; Wilkins, S. B.


    The occurrence of charge-density-wave (CDW) order in underdoped cuprates is now well established, although the precise nature of the CDW and its relationship with superconductivity is not. Theoretical proposals include contrasting ideas such as that pairing may be driven by CDW uctuations or that static CDWs may intertwine with a spatially-modulated superconducting wave function. We test the dynamics of CDW order in La1.875Ba0.125CuO4sub> by using x-ray photon correlation spectroscopy (XPCS) at the CDW wave vector, detected resonantly at the Cu L3-edge. We nd that the CDW domains are strikingly static, with no evidence of signi cant uctuations up to 2 3/4 hours. We discuss the implications of these results for some of the competing theories.

  20. Negative to positive magnetoresistance and magnetocaloric effect in Pr0.6Er0.4sub>Al2

    SciTech Connect

    Pathak, Arjun K.; Gschneidner, Jr., K. A.; Pecharsky, V. K.


    We report on the magnetic, magnetocaloric and magnetotransport properties of Pr0.6Er0.4sub>Al2. The title compound exhibits a large positive magnetoresistance (MR) for H ≥ 40 kOe and a small but non negligible negative MR for H ≤ 30 kOe. The maximum positive MR reaches 13% at H = 80 kOe. The magnetic entropy and adiabatic temperature changes as functions of temperature each show two anomalies: a broad dome-like maximum below 20 K and a relatively sharp peak at higher temperature. As a result, observed behaviors are unique among other binary and mixed lanthanide compounds.

  1. Enhanced thermoelectric performance driven by high-temperature phase transition in the phase change material Ge4sub>SbTe5

    SciTech Connect

    Williams, Jared B.; Lara-Curzio, Edgar; Cakmak, Ercan; Watkins, Thomas R.; Morelli, Donald T.


    Phase change materials are identified for their ability to rapidly alternate between amorphous and crystalline phases and have large contrast in the optical/electrical properties of the respective phases. The materials are primarily used in memory storage applications, but recently they have also been identified as potential thermoelectric materials. Many of the phase change materials researched today can be found on the pseudo-binary (GeTe)1-x(Sb2Te3)x tie-line. While many compounds on this tie-line have been recognized as thermoelectric materials, here we focus on Ge4sub>SbTe5, a single phase compound just off of the (GeTe)1-x(Sb2Te3)x tie-line, that forms in a stable rocksalt crystal structure at room temperature. We find that stoichiometric and undoped Ge4sub>SbTe5 exhibits a thermal conductivity of ~1.2 W/m-K at high temperature and a large Seebeck coefficient of ~250 μV/K. The resistivity decreases dramatically at 623 K due to a structural phase transition which lends to a large enhancement in both thermoelectric power factor and thermoelectric figure of merit at 823 K. In a more general sense the research presents evidence that phase change materials can potentially provide a new route to highly efficient thermoelectric materials for power generation at high temperature.

  2. Self-powdering and nonlinear optical domain structures in ferroelastic beta'-Gd{sub 2}(MoO{sub 4}){sub 3} crystals formed in glass

    SciTech Connect

    Tsukada, Y.; Honma, T.; Komatsu, T.


    Ferroelastic beta'-Gd{sub 2}(MoO{sub 4}){sub 3}, (GMO), crystals are formed through the crystallization of 21.25Gd{sub 2}O{sub 3}-63.75MoO{sub 3}-15B{sub 2}O{sub 3} glass (mol%), and two scientific curious phenomena are observed. (1) GMO crystals formed in the crystallization break into small pieces with a triangular prism or pyramid shape having a length of 50-500 {mu}m spontaneously during the crystallizations in the inside of an electric furnace, not during the cooling in air after the crystallization. This phenomenon is called 'self-powdering phenomenon during crystallization' in this paper. (2) Each self-powdered GMO crystal grain shows a periodic domain structure with different refractive indices, and a spatially periodic second harmonic generation (SHG) depending on the domain structure is observed. It is proposed from polarized micro-Raman scattering spectra and the azimuthal dependence of second harmonic intensities that GMO crystals are oriented in each crystal grain and the orientation of (MoO{sub 4}){sup 2-} tetrahedra in GMO crystals changes periodically due to spontaneous strains in ferroelastic GMO crystals. - Graphical abstract: This figure shows the polarized optical photograph at room temperature for a particle (piece) obtained by a heat treatment of the glass at 590 deg. C for 2 h in an electric furnace in air. This particle was obtained through the self-powdering behavior in the crystallization of glass. The periodic domain structure is observed. Ferroelastic beta'-Gd{sub 2}(MoO{sub 4}){sub 3} crystals are formed in the particle, and second harmonic generations are detected, depending on the domain structure.

  3. Undoped and Ni-doped CoOx surface modification of porous BiVO4sub> photoelectrodes for water oxidation

    SciTech Connect

    Liu, Ya; Guo, Youhong; Schelhas, Laura T.; Li, Mingtao; Ager, Joel W.


    Surface modification of photoanodes with oxygen evolution reaction (OER) catalysts is an effective approach to enhance water oxidation kinetics, to reduce external bias, and to improve the energy harvesting efficiency of photoelectrochemical (PEC) water oxidation. Here, the surface of porous BiVO4sub> photoanodes was modified by the deposition of undoped and Ni-doped CoOx via nitrogen flow assisted electrostatic spray pyrolysis. This newly developed atmospheric pressure deposition technique allows for surface coverage throughout the porous structure with thickness and composition control. PEC testing of modified BiVO4sub> photoanodes shows that after deposition of an undoped CoOx surface layer, the onset potential shifts negatively by ca. 420 mV and the photocurrent density reaches 2.01 mA cm–2 at 1.23 vs VRHE under AM 1.5G illumination. Modification with Ni-doped CoOx produces even more effective OER catalysis and yields a photocurrent density of 2.62 mA cm–2 at 1.23 VRHE under AM 1.5G illumination. Furthermore, the valence band X-ray photoelectron spectroscopy and synchrotron-based X-ray absorption spectroscopy results show the Ni doping reduces the Fermi level of the CoOx layer; the increased surface band bending produced by this effect is partially responsible for the superior PEC performance.

  4. Complex conductance of ultrathin La2-xSrxCuO4sub> films and heterostructures

    SciTech Connect

    V. A. Gasparov; Bozovic, I.


    We used atomic-layer molecular beam epitaxy to synthesize bilayers of a cuprate metal (La1.55Sr0.45CuO4sub>) and a cuprate insulator (La2CuO4sub>), in which each layer is just one unit cells thick. We have studied the magnetic field and temperature dependence of the complex sheet conductance, σ(ω), of these films. Experiments have been carried out at frequencies between 2 and 50 MHz using the single-spiral coil technique. We found that: (i) the inductive response starts at ΔT = 3 K lower temperatures than Re σ(T), which in turn is characterized by a peak close to the transition, (ii) this shift is almost constant with magnetic field up to 14 mT; (iii) ΔT increases sharply up to 4 K at larger fields and becomes constant up to 8 T; (iv) the vortexdiffusion constant D(T) is not linear with T at low temperatures as in the case of free vortices, but is rather exponential due to pinning of vortex cores, and (v) the dynamic Berezinski–Kosterlitz–Thouless (BKT) transition temperature occurs at the point where Y=(lω/ξ+)2 = 1. As a result, our experimental results can be described well by the extended dynamic theory of the BKT transition and dynamics of bound vortex–antivortex pairs with short separation lengths.

  5. Decoupling of the antiferromagnetic and insulating states in Tb-doped Sr2IrO4sub>

    SciTech Connect

    Wang, J. C.; Aswartham, S.; Ye, Feng; Terzic, J.; Zheng, H.; Haskel, Daniel; Chikara, Shalinee; Choi, Yong; Schlottmann, P.; Custelcean, Radu; Yuan, S. J.; Cao, G.


    Sr2IrO4sub> is a spin-orbit coupled insulator with an antiferromagnetic (AFM) transition at TN = 240 K. We report results of a comprehensive study of single-crystal Sr2Ir1-xTbxO4sub> (0≤x≤0.03). This study found that mere 3% (x=0.03) tetravalent Tb4+(4f7) substituting for Ir4+ (rather than Sr2+) completely suppresses the long-range collinear AFM transition but retains the insulating state, leading to a phase diagram featuring a decoupling of magnetic interactions and charge gap. The insulating state at x = 0.03 is characterized by an unusually large specific heat at low temperatures and an incommensurate magnetic state having magnetic peaks at (0.95, 0, 0) and (0, 0.95, 0) in the neutron diffraction, suggesting a spiral or spin density wave order. It is apparent that Tb doping effectively changes the relative strength of the SOI and the tetragonal CEF and enhances the Hund’s rule coupling that competes with the SOI, and destabilizes the AFM state. However, the disappearance of the AFM accompanies no metallic state chiefly because an energy level mismatch for the Ir and Tb sites weakens charge carrier hopping and renders a persistent insulating state. Furthermore, this work highlights an unconventional correlation between the AFM and insulating states in which the magnetic transition plays no critical role in the formation of the charge gap in the iridate.

  6. Magnetocaloric effect of Gd4sub>(BixSb1-x)3 alloy series

    SciTech Connect

    Niu, Xuejun


    Alloys from the Gd4sub>(BixSb1-x)3 series were prepared by melting a stoichiometric amounts of pure metals in an induction furnace. The crystal structure is of the anti-Th3P4sub> type (space group I$\\bar{4}$3d) for all the compounds tested. The linear increase of the lattice parameters with Bi concentration is attributed to the larger atomic radius of Bi than that of Sb. Magnetic measurements show that the alloys order ferromagnetically from 266K to 330K, with the ordering temperature increasing with decreasing Bi concentration. The alloys are soft ferromagnets below their Curie temperatures, and follow the Curie-Weiss law above their ordering temperatures. The paramagnetic effective magnetic moments are low compared to the theoretical value for a free Gd3+, while the ordered magnetic moments are close to the theoretical value for Gd. The alloys exhibit a moderate magnetocaloric effect (MCE) whose maxima are located between 270K and 338K and have relatively wide peaks. The peak MCE temperature decreases with decreasing Bi concentration while the peak height increases with decreasing Bi concentration. The Curie temperatures determined from inflection points of heat capacity are in good agreement with those obtained from the magnetocaloric effect. The MCE results obtained from the two different methods (magnetization and heat capacity) agree quite well with each other for all of the alloys in the series.

  7. Enhanced ferromagnetic order in Sr{sub 4}Mn{sub 3}O{sub 3}(GeO{sub 4}){sub 3} featuring canted [MnO{sub 4}]{sub ∞} spin chains of mixed-valent Mn(III)/Mn(IV). Aliovalent substitution of the Sr{sub 4−x}Ln{sub x}Mn{sup III}{sub 2+x}Mn{sup IV}{sub 1−x}O{sub 3}(GeO{sub 4}){sub 3} solid-solution

    SciTech Connect

    West, J. Palmer; Sulejmanovic, Dino; Becht, Gregory; He, Jian; Hitchcock, Dale; Yan, Yonggao; Hwu, Shiou-Jyh


    Crystals of Sr{sub 4−x}Ln{sub x}Mn{sub 3}O{sub 3}(GeO{sub 4}){sub 3} (x=0; x∼0.15 for Ln=La, Pr, Nd, Sm. Eu, Gd, Dy; x∼0.3 for Ln=Gd) were isolated upon using high-temperature, solid-state methods in molten-salt media. These compounds are isostructural with the previously reported Na{sub 3}LnMn{sub 3}O{sub 3}(AsO{sub 4}){sub 3} (Ln=La, Sm, Gd) series that contains the same [MnO{sub 4}]{sub ∞} spin chains. The synthesis of the Sr{sub 4}Mn{sub 3}O{sub 3}(GeO{sub 4}){sub 3} (x=0) phase was carried out by a double aliovalent substitution with respect to the Sr{sup 2+} and Ge{sup 4+} ions that replace Na{sup +}/Ln{sup 3+} and As{sup 5+} in Na{sub 3}LnMn{sub 3}O{sub 3}(AsO{sub 4}){sub 3}, respectively. The title series contains mixed-valent Mn(III)/Mn(IV) and shows a limited range of solid solution, both of which were not observed in the previously reported Na{sub 3}LnMn{sub 3}O{sub 3}(AsO{sub 4}){sub 3} series. To form the Sr{sub 4−x}Ln{sub x}Mn{sub 3}O{sub 3}(GeO{sub 4}){sub 3} solid solution, one of the Sr{sup 2+} sites, i.e., the original Ln-site in Na{sub 3}LnMn{sub 3}O{sub 3}(AsO{sub 4}){sub 3}, is partially substituted by Ln{sup 3+} in a statistical disorder of Sr{sub 1−x}/Ln{sub x}. Initial magnetic investigations of selected derivatives reveal higher ferromagnetic ordering temperatures than those reported for the Na{sub 3}LnMn{sub 3}O{sub 3}(AsO{sub 4}){sub 3} series, presumably attributed to a lesser degree of canting as a result of introducing non-Jahn–Teller Mn{sup 4+} ions. Also intriguing is the observation of multiple anomalies at low temperatures which appear to be of electronic origins. - Graphical abstract: Sr{sub 4−x}Ln{sub x}Mn(III){sub 2+x}Mn(IV){sub 1−x}O{sub 3}(GeO{sub 4}){sub 3}. Display Omitted - Highlights: • Double aliovalent substitution: Sr{sub 4}Mn{sub 3}O{sub 3}(GeO{sub 4}){sub 3} with respect to Na{sub 3}LnMn{sub 3}O{sub 3}(AsO{sub 4}){sub 3}. • Solid solution with respect to statistical disorder of Sr{sub 1

  8. Crystal chemistry of anhydrous Li uranyl phosphates and arsenates. II. Tubular fragments and cation-cation interactions in the 3D framework structures of Li{sub 6}[(UO{sub 2}){sub 12}(PO{sub 4}){sub 8}(P{sub 4}O{sub 13})], Li{sub 5}[(UO{sub 2}){sub 13}(AsO{sub 4}){sub 9}(As{sub 2}O{sub 7})], Li[(UO{sub 2}){sub 4}(AsO{sub 4}){sub 3}] and Li{sub 3}[(UO{sub 2}){sub 7}(AsO{sub 4}){sub 5}O

    SciTech Connect

    Alekseev, Evgeny V.; Krivovichev, Sergey V.; Depmeier, Wulf


    Single crystals of the new compounds Li{sub 6}[(UO{sub 2}){sub 12}(PO{sub 4}){sub 8}(P{sub 4}O{sub 13})] (1), Li{sub 5}[(UO{sub 2}){sub 13}(AsO{sub 4}){sub 9}(As{sub 2}O{sub 7})] (2), Li[(UO{sub 2}){sub 4}(AsO{sub 4}){sub 3}] (3) and Li{sub 3}[(UO{sub 2}){sub 7}(AsO{sub 4}){sub 5}O)] (4) have been prepared using high-temperature solid state reactions. The crystal structures have been solved by direct methods: 1-monoclinic, C2/m, a=26.963(3) A, b=7.063(1) A, c=19.639(1) A, beta=126.890(4){sup o}, V=2991.2(6) A{sup 3}, Z=2, R{sub 1}=0.0357 for 3248 unique reflections with |F{sub 0}|>=4sigma{sub F}; 2-triclinic, P1-bar, a=7.1410(8) A, b=13.959(1) A, c=31.925(1) A, alpha=82.850(2){sup o}, beta=88.691(2){sup o}, gamma=79.774(3){sup o}, V=3107.4(4) A{sup 3}, Z=2, R{sub 1}=0.0722 for 9161 unique reflections with |F{sub 0}|>=4sigma{sub F}; 3-tetragonal, I4{sub 1}/amd, a=7.160(3) A, c=33.775(9) A, V=1732(1) A{sup 3}, Z=4, R{sub 1}=0.0356 for 318 unique reflections with |F{sub 0}|>=4sigma{sub F}; 4-tetragonal, P4-bar, a=7.2160(5) A, c=14.6540(7) A, V=763.04(8) A{sup 3}, Z=1, R{sub 1}=0.0423 for 1600 unique reflections with |F{sub 0}|>=4sigma{sub F}. Structures of all the phases under consideration are based on complex 3D frameworks consisting of different types of uranium polyhedra (UO{sub 6} and UO{sub 7}) and different types of tetrahedral TO{sub 4} anions (T=P or As): PO{sub 4} and P{sub 4}O{sub 13} in 1, AsO{sub 4} and As{sub 2}O{sub 7} in 2, and single AsO{sub 4} tetrahedra in 3 and 4. In the structures of 1 and 2, UO{sub 7} pentagonal bipyramids share edges to form (UO{sub 5}){sub i}nfinity chains extended along the b axis in 1 and along the a axis in 2. The chains are linked via single TO{sub 4} tetrahedra into tubular units with external diameters of 11 A in 1 and 11.5 A in 2, and internal diameters of 4.1 A in 1 and 4.5 A in 2. The channels accommodate Li{sup +} cations. The tubular units are linked into 3D frameworks by intertubular complexes. Structures of 3 and 4

  9. Color-tunable photoluminescence and energy transfer properties of single-phase Ba{sub 10}(PO{sub 4}){sub 6}O:Eu{sup 2+}, Mn{sup 2+} phosphors

    SciTech Connect

    Guo, Qingfeng; Liao, Libing Mei, Lefu Liu, Haikun


    Single-phase Ba{sub 10−x−y}(PO{sub 4}){sub 6}O:xEu{sup 2+},yMn{sup 2+} samples with apatite structure have been synthesized via a solid-state reaction method. The phase structure, luminescence properties, lifetime, PL thermal stability, as well as fluorescence decay curves of the samples were investigated. Effective energy transfer occurs from Eu{sup 2+} to Mn{sup 2+} in Ba{sub 10}(PO{sub 4}){sub 6}O and a possible mechanism of the energy-transfer from Eu{sup 2+} to Mn{sup 2+} is proposed. The critical distances R{sub c} was calculated by concentration quenching and turned out to be about 0.817 nm (x{sub c}=0.21). The CIE and thermally stable luminescence behaviors of Ba{sub 9.94}(PO{sub 4}){sub 6}O:0.06Eu{sup 2+} phosphor were also studied in detail. All the results indicate that Ba{sub 10−x−y}(PO{sub 4}){sub 6}O:xEu{sup 2+}, yMn{sup 2+} phosphors have potential applications as near UV-convertible phosphors for white light-emitting diodes. - Graphical abstract: Crystal structure and luminescence property of Ba{sub 10−x−y}(PO{sub 4}){sub 6}O:xEu{sup 2+},yMn{sup 2+} have been discussed. - Highlights: • Ba{sub 10−x−y}(PO{sub 4}){sub 6}O:xEu{sup 2+},yMn{sup 2+} was firstly reported. • Ba{sub 9.94}(PO{sub 4}){sub 6}O:0.06Eu{sup 2+} exhibits high thermal quenching resistance. • The energy transfer between Eu{sup 2+} and Mn{sup 2+} was investigated.

  10. Operando identification of the point of [Mn-2]O-4sub> spinel formation during gamma-MnO2 discharge within batteries

    SciTech Connect

    Gallaway, Joshua W.; Hertzberg, Benjamin J.; Zhong, Zhong; Croft, Mark; Turney, Damon E.; Yadav, Gautam G.; Steingart, Daniel A.; Erdonmez, Can K.; Banerjee, Sanjoy


    The rechargeability of γ-MnO2 cathodes in alkaline batteries is limited by the formation of the [Mn2]O4sub> spinels ZnMn2O4sub> (hetaerolite) and Mn3O4sub> (hausmannite). However, the time and formation mechanisms of these spinels are not well understood. Here we directly observe γ-MnO2 discharge at a range of reaction extents distributed across a thick porous electrode. Coupled with a battery model, this reveals that spinel formation occurs at a precise and predictable point in the reaction, regardless of reaction rate. Observation is accomplished by energy dispersive X-ray diffraction (EDXRD) using photons of high energy and high flux, which penetrate the cell and provide diffraction data as a function of location and time. After insertion of 0.79 protons per γ-MnO2 the α-MnOOH phase forms rapidly. α-MnOOH is the precursor to spinel, which closely follows. ZnMn2O4sub> and Mn3O4sub> form at the same discharge depth, by the same mechanism. The results show the final discharge product, Mn3O4sub> or Mn(OH)2, is not an intrinsic property of γ-MnO2. While several studies have identified Mn(OH)2 as the final γ-MnO2 discharge product, we observe direct conversion to Mn3O4sub> with no Mn(OH)2.

  11. Expanding the Chemistry of Actinide Metallocene Bromides. Synthesis, Properties and Molecular Structures of the Tetravalent and Trivalent Uranium Bromide Complexes: (C5Me4sub>R)2UBr2, (C5Me4sub>R)2U(O-2,6-iPr2C6H3)(Br), and [K(THF)][(C5Me4sub>R)2UBr2] (R = Me, Et)

    SciTech Connect

    Lichtscheidl, Alejandro Gaston; Pagano, Justin K.; Scott, Brian Lindley; Nelson, Andrew Thomas; Kiplinger, Jaqueline Loetsch


    The organometallic uranium species (C5Me4sub>R)2UBr2 (R = Me, Et) were obtained by treating their chloride analogues (C5Me4sub>R)2UCl2 (R = Me, Et) with Me3SiBr. Treatment of (C5Me4sub>R)2UCl2 and (C5Me4sub>R)2UBr2 (R = Me, Et) with K(O-2,6-iPr2C6H3) afforded the halide aryloxide mixed-ligand complexes (C5Me4sub>R)2U(O-2,6-iPr2C6H3)(X) (R = Me, Et; X = Cl, Br). Complexes (C5Me4sub>R)2U(O-2,6-iPr2C6H3)(Br) (R = Me, Et) can also be synthesized by treating (C5Me4sub>R)2U(O-2,6-iPr2C6H3)(Cl) (R = Me, Et) with Me3SiBr, respectively. Reduction of (C5Me4sub>R)2UCl2 and (C5Me4sub>R)2UBr2 (R = Me, Et) with KC8 led to isolation of uranium(III) “ate” species [K(THF)][(C5Me5)2UX2] (X = Cl, Br) and [K(THF)0.5][(C5Me4sub>Et)2UX2] (X = Cl, Br), which can be converted to the neutral complexes (C5Me4sub>R)2U[N(SiMe3)2] (R = Me, Et). Analyses by nuclear magnetic resonance spectroscopy, X-ray crystallography, and elemental analysis are also presented.

  12. Insight into the Atomic Structure of High-Voltage Spinel LiNi0.5Mn1.5O4sub> Cathode Material in the First Cycle

    SciTech Connect

    Huang, Xuejie; Yu, Xiqian; Lin, Mingxiang; Ben, Liubin; Sun, Yang; Wang, Hao; Yang, Zhenzhong; Gu, Lin; Yang, Xiao -Qing; Zhao, Haofei; Yu, Richeng; Armand, Michel


    Application of high-voltage spinel LiNi0.5Mn1.5O4sub> cathode material is the closest and the most realistic approach to meeting the midterm goal of lithium-ion batteries for electric vehicles (EVs) and plug-in hybrid electric vehicles (HEVs). However, this application has been hampered by long-standing issues, such as capacity degradation and poor first-cycle Coulombic efficiency of LiNi0.5Mn1.5O4sub> cathode material. Although it is well-known that the structure of LiNi0.5Mn1.5O4sub> into which Li ions are reversibly intercalated plays a critical role in the above issues, performance degradation related to structural changes, particularly in the first cycle, are not fully understood. Here, we report detailed investigations of local atomic-level and average structure of LiNi0.5Mn1.5O4sub> during first cycle (3.5–4.9 V) at room temperature. We observed two types of local atomic-level migration of transition metals (TM) ions in the cathode of a well-prepared LiNi0.5Mn1.5O4sub>//Li half-cell during first charge via an aberration-corrected scanning transmission electron microscopy (STEM). Surface regions (~2 nm) of the cycled LiNi0.5Mn1.5O4sub> particles show migration of TM ions into tetrahedral Li sites to form a Mn3O4sub>-like structure. However, subsurface regions of the cycled particles exhibit migration of TM ions into empty octahedral sites to form a rocksalt-like structure. The migration of these TM ions are closely related to dissolution of Ni/Mn ions and building-up of charge transfer impedance, which contribute significantly to the capacity degradation and the poor first-cycle Coulombic efficiency of spinel LiNi0.5Mn1.5O4sub> cathode material. Accordingly, we provide suggestions of effective stabilization of LiNi0.5

  13. Beyond Yolk–Shell Nanoparticles: Fe 3 O 4sub> @Fe 3 C Core@Shell Nanoparticles as Yolks and Carbon Nanospindles as Shells for Efficient Lithium Ion Storage

    SciTech Connect

    Zhang, Jianan; Wang, Kaixi; Xu, Qun; Zhou, Yunchun; Cheng, Fangyi; Guo, Shaojun


    In order to well address the problems of large volume change and dissolution of Fe3O4sub> nanomaterials during Li+ intercalation/extraction, herein we demonstrate a one-step in situ nanospace-confined pyrolysis strategy for robust yolk–shell nanospindles with very sufficient internal void space (VSIVS) for high-rate and long-term lithium ion batteries (LIBs), in which an Fe3O4sub>@Fe3C core@shell nanoparticle is well confined in the compartment of a hollow carbon nanospindle. This structure can not only introduce VSIVS to accommodate volume change of Fe3O4sub> but also afford a dual shell of Fe3C and carbon to restrict Fe3O4sub> dissolution, thus providing dual roles for greatly improving the capacity retention. Consequently, Fe3O4sub>@Fe3C–C yolk–shell nanospindles deliver a high reversible capacity of 1128.3 mAh g–1 at even 500 mA g–1, excellent high rate capacity (604.8 mAh g–1 at 2000 mA g1), and prolonged cycling life (maintaining 1120.2 mAh g–1 at 500 mA g–1 for 100 cycles) for LIBs, which are much better than those of Fe3O4sub>@C core@shell nanospindles and Fe3O4sub> nanoparticles. The present Fe3O4sub>@Fe3C–C yolk–shell nanospindles are the most efficient Fe3O4sub>-based anode materials ever reported for LIBs.

  14. High-pressure behavior of cuprospinel CuFe2O4sub>: Influence of the Jahn-Teller effect on the spinel structure

    SciTech Connect

    Kyono, Atsushi; Gramsch, Stephen A.; Nakamoto, Yuki; Sakata, Masafumi; Kato, Masato; Tamura, Tomoya; Yamanaka, Takamitsu


    The Jahn-Teller-effect at Cu2+ in cuprospinel CuFe2O4sub> was investigated using high-pressure, single crystal synchrotron x-ray diffraction (XRD) techniques at beamline BL10A at the Photon Factory, KEK, Japan. Six data sets were collected in the pressure range from ambient to 5.9 GPa at room temperature. Structural refinements based on the data were performed at 0.0, 1.8, 2.7, and 4.6 GPa. The unit cell volume of cuprospinel decreases continuously from 590.8 (6) Å3 to 579.5 (8) Å3 up to 3.8 GPa. Leastsquares fitting to a third-order Birch-Murnaghan equation of state yields zero-pressure volume V0 = 590.7 (1) Å3 and bulk modulus K0 = 188.1 (4.4) GPa with K’ fixed at 4.0. The crystal chemical composition determined by electron-probe analysis and x-ray site-occupancy refinement is represented as [Cu0.526Fe0.474][6][Cu0.074Fe1.926]O4sub>. Most of the Cu2+ are preferentially distributed onto the tetrahedral (T) site of the spinel structure. At 4.6 GPa, a cubic-tetragonal phase transition is indicated by a splitting of the a axis of the cubic structure into a smaller a axis and a longer c axis, with unit cell parameters a = 5.882 (1) Å and c = 8.337 (1) Å. The tetragonal crystal structure with space group I4<sub>1/amd was refined to R1 = 0.0182 and wR2 = 0.0134 using observed 35 x-ray reflections. At the T site, the tetrahedral O-T-O bond angles along the c-axis direction of the unit cell decreases slightly from 109.47 ° to 108.7 (4) °, which generates a stretched tetrahedral geometry along the c-axis. The cubic-totetragonal transition induced by the Jahn-Teller effect at Cu2+ is attributable to the angular distortion at the tetrahedral site. At the octahedral (M) site, on the other hand, the two M-O bonds parallel to the caxis are shortened with respect to the four M-O bonds parallel to

  15. Fabrication and electrical properties of Si-based La{sub 10−x}Bi{sub x}(SiO{sub 4}){sub 6}O{sub 3} apatite ionic conductor

    SciTech Connect

    Kim, Dae-Young; Lee, Sung-Gap


    In this paper we report an investigation about the relationship between Bi content and conductivity for the La{sub 10−x}Bi{sub x}(SiO{sub 4}){sub 6}O{sub 3} (x = 0.5–2) specimens. Increasing Bi content in apatite-type La{sub 10−x}Bi{sub x}(SiO{sub 4}){sub 6}O{sub 3} specimen leads to increasing the average grain size and sinterability because some Bi ion deposited at grain boundaries which promotes grain growth. The relative sintered density of the La{sub 8}Bi{sub 2}(SiO{sub 4}){sub 6}O{sub 3} specimen is 98%. There is a small shift in diffraction angle of XRD peaks, complicated lattice distortion was observed in the X-ray pattern with increasing content of Bi. Electrical conductivity of La{sub 10−x}Bi{sub x}(SiO{sub 4}){sub 6}O{sub 3} specimen increased with increasing Bi contents and the value of the La{sub 8}Bi{sub 2}(SiO{sub 4}){sub 6}O{sub 3} specimen is 2.4 × 10{sup −4} S cm{sup −1} at 700 °C.

  16. Crystal structure and thermal expansion of the low- and high-temperature forms of BaM{sup IV}(PO{sub 4}){sub 2} compounds (M=Ti, Zr, Hf and Sn)

    SciTech Connect

    Bregiroux, D.; Popa, K.; Jardin, R.; Raison, P.E.; Wallez, G.; Quarton, M.; Brunelli, M.; Ferrero, C.; Caciuffo, R.


    The crystal structure of beta-BaZr(PO{sub 4}){sub 2}, archetype of the high-temperature forms of BaM(PO{sub 4}){sub 2} phosphates (with M=Ti, Zr, Hf and Sn), has been solved ab initio by Rietveld analysis from synchrotron X-ray powder diffraction data. The phase transition appears as a topotactic modification of the monoclinic (S.G. C2/m) lamellar alpha-structure into a trigonal one (S.G. P3-barm1) through a simple mechanism involving the unfolding of the [Zr(PO{sub 4}){sub 2}]{sub n}{sup 2-} layers. The thermal expansion is very anisotropic (e.g., -4.14}){sub 2}) and quite different in the two forms, as a consequence of symmetry. It stems from a complex combination of several mechanisms, involving bridging oxygen rocking in M-O-P linkages, and 'bond thermal expansion'. - Graphical abstract: The layered high-temperature form of BaM(PO{sub 4}){sub 2}, only expands along the c-axis.

  17. Temperature-dependent framework–template interaction of |Na{sub 6}(H{sub 2}O){sub 8}|[ZnPO{sub 4}]{sub 6} sodalite

    SciTech Connect

    Robben, Lars Gesing, Thorsten M.


    The partial dehydration followed by the decomposition of sodium-zincophosphate-hydrosodalite caused by the total water loss was examined by temperature-dependent X-ray powder diffraction, Fourier transform infrared (FTIR) and Raman spectroscopy as well as thermogravimetry combined with difference thermoanalysis. The dehydration causing the decomposition of this sodalite could be described in a two step-process. Initially two water molecules per unit-cell were lost, changing the interaction between the zincophosphate framework and the remaining water molecules as well as sodium cations as non-framework constituents. In this stage a 3+3 coordination of water molecules and sodium cations in the sodalite cage is observed. Using the autocorrelation function (AC) for the evaluation of the temperature-dependent FTIR spectra of sodalites is reported here for the first time. Calculating the changes in the AC broadness, structural features could well be analyzed due to its correlation with respective structural parameters. Temperature dependent Raman data was used to give a band assignment of bands at Raman shifts below 300 cm{sup −1}. - Graphical abstract: The thermal decomposition of |Na{sub 6}(H{sub 2}O){sub 8}|[ZnPO{sub 4}]{sub 6} sodalite is a two-step process with an initial loss of two water molecules at 400 K, intermediately stabilizing the highly stressed framework. Further heating leads to a subsequent loss of the remaining six water molecules and a breakup of the sodalite framework. A beryllonite-type NaZnPO{sub 4} is the final product of this process. Display Omitted - Highlights: • The decomposition of |Na{sub 6}(H{sub 2}O){sub 8}|[ZnPO{sub 4}]{sub 6} sodalite is a two-step process. • Initial loss of two water molecule at 400 K stabilizes the sodalite (step 1). • Further heating leads to complete loss of water and structural breakdown. • Autocorrelation of temperature dependent FTIR-spectra gives structural information.

  18. Temperature induced phase transition of CaMn{sub 0.5}Zr{sub 1.5}(PO{sub 4}){sub 3} phosphate

    SciTech Connect

    Orlova, Maria; Perfler, Lukas; Tribus, Martina; Salnikov, Petr; Glorieux, Benoit; Orlova, Albina


    In this work we investigated the structural behaviour of a CaMn{sub 0.5}Zr{sub 1.5}(PO{sub 4}){sub 3}. Due to the presence of divalent Mn{sup 2+} cations this compound can possess interesting luminescence properties. It was recently understood that this phosphate undergoes a temperature induced irreversible phase transition in the range of 800–875 °C. It has also been shown that the 3d–3d luminescence of Mn{sup 2+} increases 10 fold for the high temperature polymorph. To determine the Mn environment structural investigations of both phases have been performed by the X-ray powder diffraction and Raman spectroscopy methods. The low temperature modification adopts the trigonal NZP structure type with a slightly lower symmetry (space group R32, a=8.7850(2) Å, c=22.6496(7) Å, V=1514.8(1) Å{sup 3}). The high temperature form in turn has orthorhombic symmetry (space group Pnma, a=6.2350(3) Å, b=6.6281(3) Å, c=14.4731(6) Å, V=598.13(5) Å{sup 3}). Both structures were solved ab-initio from powder data and structural analysis was performed. In-situ and RT Raman spectra are consistent with the XRD derived structural model. Mn{sup 2+} cations occupy different types of positions in these structures and a change in Mn coordination number (6 for LT phase, 7 for HT phase) results in different Mn–O bond lengths. These differences may explain the change in the optical properties between the polymorphs. - Graphical abstract: The compound CaMn{sub 0.5}Zr{sub 1.5}(PO{sub 4}){sub 3} was synthesized in order to create a material with enhanced luminescent properties. The goal of present studies is to define Mn{sup 2+} environment and its changes due to the structural transformations of the phosphate along phase transition at the T range of 800–875 °C. It was found that LT modification adopts the trigonal NZP structure type, R32, the HT form in turn exhibits orthorhombic symmetry Pnma. Mn2+ cations occupy different types of positions in those structures and a

  19. Ultra-short-period W/B4sub>C multilayers for x-ray optics-microstructure limits on reflectivity

    SciTech Connect

    Walton, Christopher Charles


    Multilayer thin films are used as Bragg reflectors for soft x-rays in the energy range 50eV < E < 1000eV in many x-ray optics applications such as x-ray microscopes and telescopes, reducing optics for extreme ultraviolet (EUV) lithography, and x-ray polarizers and phase retarders. Applications often depend critically on reflectivity, which has not been systematically characterized for multilayer periods below 20Å. For this study, W/B4sub>C multilayers were fabricated by magnetron sputtering on Si(111), with periods from 48Å to as little as 4.7Å. The x-ray reflectivity measured at λ = 1.54Å and at 45° incidence (289 eV < E < 860 eV) was found to decrease sharply for multilayer periods less than 15-20Å. Examination by high-resolution transmission electron microscopy (HRTEM) showed an expansion of the thickness of the W-rich layers of 30-40% from the nominal values, consistent with intermixture of the two materials during sputter growth, and discontinuous W-rich layers for multilayer periods below about 15Å. The experimental data for the specular reflectivity in the hard and soft x-ray regimes and the diffuse scattering fit well to a model of multilayer roughness. The model is expressed as a power-law dependence of roughness on spatial frequency. Analysis of small-angle scattering in transmission from multilayers grown on freestanding Si3N4sub> membranes confirms the onset of discontinuity at periods between 14Å and 22Å. Spectroscopy studies by x-ray absorption (NEXAFS) and electron energy loss (EELS) at the boron K-edge (188eV) are consistent with changes in the average boron bonding environment, as the multilayer period decreases and the W-rich layers are increasingly thin and dispersed. A discrete W-rich phase is present for periods at least as small as 6.3Å.

  20. Low-temperature synthesis of homogeneous solid solutions of scheelite-structured Ca1-xSrxWO4sub> and Sr1-xBaxWO4sub> nanocrystals

    SciTech Connect

    Culver, Sean P.; Greaney, Matthew J.; Tinoco, Antonio; Brutchey, Richard L.


    Here, a series of compositionally complex scheelite-structured nanocrystals of the formula A1-xA’xWO4sub> (A = Ca, Sr, Ba) have been prepared under benign synthesis conditions using the vapor diffusion sol–gel method. Discrete nanocrystals with sub-20 nm mean diameters were obtained after kinetically controlled hydro- lysis and polycondensation at room temperature, followed by composition-dependent thermal aging at or below 60 °C. Rietveld analysis of X-ray diffraction data and Raman spectroscopy verified the synthesis of continuous and phase-pure nanocrystal solid solutions across the entire composition space for A1-xA’xWO4sub>, where 0 ≤ x ≤ 1. Elemental analysis by X-ray photoelectron and inductively coupled plasma- atomic emission spectroscopies demonstrated excellent agreement between the nominal and experi- mentally determined elemental stoichiometries, while energy dispersive X-ray spectroscopy illustrated good spatial elemental homogeneity within these nanocrystals synthesized under benign conditions.

  1. Multiband electronic transport in α-Yb1₋xSrx AlB4sub> [ x = 0, 0.19(3)] single crystals

    SciTech Connect

    Ryu, Hyejin; Abeykoon, Milinda; Bozin, Emil; Matsumoto, Yosuke; Nakatsuji, S.; Petrovic, C.


    Here we report on the evidence for the multiband electronic transport in α- YbAlB4sub> and α-Yb0.81(2)Sr0.19(3)AlB4sub>. Multiband transport reveals itself below 10 K in both compounds via Hall effect measurements, whereas anisotropic magnetic ground state sets in below 3 K in α-Yb0.81(2)Sr0.19(3)AlB4sub>. Our results show that Sr2+ substitution enhances conductivity, but does not change the quasiparticle mass of bands induced by heavy fermion hybridization.

  2. Spectroscopy and Luminescence Dynamics of Ce 3+ and Sm 3+ in LiYSiO 4sub>

    SciTech Connect

    Shi, Rui; Xu, Jinzhong; Liu, Guokui; Zhang, Xuejie; Zhou, Weihie; Pan, Fengjuan; Huang, Yan; Tao, Ye; Liang, Hongbin


    The lithium yttrium silicate series of LiY1-xLnxSiO4sub> exhibits superb chemical and optical properties, and with Ln = Ce3+, Sm3+, its spectroscopic characteristics and luminescence dynamics are investigated in the present work. Energy transfer and non-radiative relaxation dramatically influence the Ln3+ luminescence spectra and decay dynamics, especially in the Ce3+-Sm3+ co-doped phosphors. It is shown that thermal-quenching of the blue Ce3+ luminescence is primarily due to thermal ionization in the 5d excited states rather than multi-phonon relaxation, whereas cross-relaxation arising from electric dipole-dipole interaction between adjacent Sm3+ ions is the leading mechanism that quenches the red Sm3+ luminescence. In the co-doped systems, Ce3+-Sm3+ energy transfer in competing with the thermal quenching enhance the emission from Sm3+. The combined influences of concentration quenching, thermal ionization, energy transfer including cross-relaxation on the luminescence intensity of single-center and co-doped phosphors are analyzed based on the theories of ion-ion and ion-lattice interactions.

  3. Nitridated Pd/B4sub>C multilayer mirrors for soft X-ray region: internal structure and aging effects.


    Wang, Yiwen; Huang, Qiushi; Yi, Qiang; Kozhevnikov, Igor V; Qi, Runze; Wen, Mingwu; Jonnard, Philippe; Zhang, Jinshuai; Giglia, Angelo; Zhang, Zhong; Wang, Zhanshan


    Reactive sputtering with a mixture of argon and nitrogen (N2 partial pressure of 4%, 8%, and 15%) as the working gas is used to develop the high reflectance Pd/B4sub>C multilayers for soft X-ray region application. Compared to the pure Ar fabricated sample, the interface roughness of the nitridated multilayer is slightly increased while the compressive stress is essentially relaxed from -623 MPa (pure Ar) to -85 MPa (15% N2). A maximum reflectance of 32% is measured at the wavelength of 9.5 nm for the multilayer fabricated with 15% N2. After storing the multilayers in an air environment for 6-17 months, a distinct aging effect is observed on the nitridated samples. The transmission electron microscopy results indicate that a large part of the top layers of the nitridated samples is deteriorated with severe interdiffusion, essential decrease in d-spacing, and compacted multilayer structure. The deterioration is less pronounced for the multilayers fabricated with a higher ratio of N2. Energy dispersive X-ray spectroscopy reveals that the concentration of nitrogen and boron in the degraded area is much reduced compared to the intact layers. A primitive model of upward diffusion of nitrogen and boron is proposed to explain the aging effects of the nitridated structure.

  4. Ultrafast energy- and momentum-resolved dynamics of magnetic correlations in the photo-doped Mott insulator Sr2IrO4sub>

    SciTech Connect

    Dean, M. P. M.; Cao, Y.; Liu, X.; Wall, S.; Zhu, D.; Mankowsky, R.; Thampy, V.; Chen, X. M.; Vale, J. G.; Casa, D.; Kim, Jungho; Said, A. H.; Juhas, P.; Alonso-Mori, R.; Glownia, J. M.; Robert, A.; Robinson, J.; Sikorski, M.; Song, S.; Kozina, M.; Lemke, H.; Patthey, L.; Owada, S.; Katayama, T.; Yabashi, M.; Tanaka, Yoshikazu; Togashi, T.; Liu, J.; Rayan Serrao, C.; Kim, B. J.; Huber, L.; Chang, C. -L.; McMorrow, D. F.; Forst, M.; Hill, J. P.


    Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity1, 2, 3, 4. Recently, photo-excitation has been used to induce similarly exotic states transiently5, 6, 7. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr2IrO4sub>. We find that the non-equilibrium state, 2 ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. In conclusion, the marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.

  5. Stable platinum nanoparticles on specific MgAl2O4sub> spinel facets at high temperatures in oxidizing atmospheres

    SciTech Connect

    Li, Wei-Zhen; Kovarik, Libor; Mei, Donghai; Liu, Jun; Wang, Yong; Peden, Charles H. F.


    The development of thermally stable, nanometer-sized precious metal-based catalysts remains a daunting challenge. Such materials, especially those based on the use of costly platinum metal, are essential and, to date, non-replaceable for a large number of industrially important catalytic processes. Here we report a well-defined cuboctahedral MgAl2O4sub> spinel support material that is capable of stabilizing platinum particles in the range of 1–3 nm on its relatively abundant {111} facets during extremely severe aging at 800 °C in air for 1 week. The aged catalysts retain platinum dispersions of 15.9% with catalytic activities for methanol oxidation being ~80% of that of fresh ones, whereas a conventional Pt/γ-Al2O3 catalyst is severely sintered and nearly inactive. Finally, we reveal the origin of the markedly superior ability of spinel {111} facets, resulting from strong interactions between spinel surface oxygens and epitaxial platinum {111} facets, inspiring the rational design of anti-sintering supported platinum group catalysts.

  6. Passive Q-switching of a Tm,Ho:KLu(WO4sub>)2 microchip laser by a Cr:ZnS saturable absorber.


    Serres, J M; Loiko, P; Mateos, X; Jambunathan, V; Yasukevich, A S; Yumashev, K V; Petrov, V; Griebner, U; Aguiló, M; Díaz, F


    A diode-pumped Tm,Ho:KLu(WO4sub>)2 microchip laser passively Q-switched with a Cr:ZnS saturable absorber generated an average output power of 131 mW at 2063.6 nm with a slope efficiency of 11% and a Q-switching conversion efficiency of 58%. The pulse characteristics were 14  ns/9  μJ at a pulse repetition frequency of 14.5 kHz. With higher modulation depth of the saturable absorber, 9  ns/10.4  μJ/8.2  kHz pulses were generated at 2061.1 nm, corresponding to a record peak power extracted from a passively Q-switched Tm,Ho laser of 1.15 kW. A theoretical model is presented, predicting the pulse energy and duration. The simulations are in good agreement with the experimental results.

  7. Optical gain in capillary light guides filled with NaYF4sub>: Yb3+, Er3+ nanocolloids.


    Patel, Darayas N; Sarkisov, Sergey S; Darwish, Abdalla M; Ballato, John


    A capillary light guide optical amplifier using nanocolloids of Yb3+-Er3+ co-doped NaYF4sub> as a filler was successfully demonstrated. A 7-cm-long and 150-micron-inner-diameter capillary light guide was capable to amplify a pulsed optical signal at 1550 nm with a gain coefficient of 0.15 cm-1 at a pump power of 4 mW (980-nm wavelength). The nanocolloid gain medium was prepared by pulverizing the phosphor powder with a high-speed planetary ball mill. Ball milling of the powder in water produced nanoparticles with a size of approximately 130 nm that after drying were transferred to a liquid with high refractive index (1.551 at 1550 nm) required to maintain light confinement within the fused silica capillary light guide. The results show that RE-doped colloids of nanocrystals can be potentially used as liquid gain media fillers in capillary light guide lasers and amplifiers with high photostability and low toxicity.

  8. Dynamic tensile deformation and damage of B4sub>C-reinforced Al composites: Time-resolved imaging with synchrotron x-rays

    SciTech Connect

    Bie, B. X.; Huang, J. Y.; Su, B.; Lu, L.; Fan, D.; E, J. C.; Sun, T.; Fezzaa, K.; Qi, M. L.; Luo, S. N.


    Dynamic tensile experiments are conducted on 15% and 30% in weight percentage B4sub>C/Al composites with a split Hopkinson tension bar, along with high-speed synchrotron x-ray digital image correlation (XDIC) to map strain fields at μ m and μ s scales. As manifested by bulk-scale stress – strain curves, a higher particle content leads to a higher yield strength but lower ductility. Strain field mapping by XDIC demonstrates that tension deformation and tensile fracture, as opposed to shear and shear failure, dominate deformation and failure of the composites. The fractographs of recovered samples show consistent features. The particle-matrix interfaces are nucleation sites for strain localizations, and their propagation and coalescence are diffused by the Al matrix. The reduced spacing between strain localization sites with increasing particle content, facilitates their coalescence and leads to decreased ductility. Furthermore, designing a particle-reinforced, metallic-matrix composite with balanced strength and ductility should consider optimizing the inter-particle distance as a key par

  9. An air-stable Na3SbS4sub> superionic conductor prepared by a rapid and economic synthetic procedure

    SciTech Connect

    Wang, Hui; Chen, Yan; Hood, Zachary D.; Samuthira Pandian, Amaresh; Keum, Jong Kahk; An, Ke; Sahu, Gayatri; Liang, Chengdu


    All-solid-state sodium batteries, using abundant sodium resources and solid electrolyte, hold much promise for safe, low cost, large-scale energy storage. To realize the practical applications of all solid Na-ion batteries at ambient temperature, the solid electrolytes are required to have high ionic conductivity, chemical stability, and ideally, easy preparation. Ceramic electrolytes show higher ionic conductivity than polymers, but they often require extremely stringent synthesis conditions, either high sintering temperature above 1000 C or long-time, low-energy ball milling. Herein, we report a new synthesis route for Na3SbS4sub>, a novel Na superionic conductor that needs much lower processing temperature below 200 C and easy operation. This new solid electrolyte exhibits a remarkable ionic conductivity of 1.05 mS cm-1 at 25 °C and is chemically stable under ambient atmosphere. In conclusion, this synthesis process provides unique insight into the current state-of-the-art solid electrolyte preparation and opens new possibilities for the design of similar materials.

  10. Pressure effects on magnetic ground states in cobalt doped multiferroic Mn1-xCoxWO4sub>

    SciTech Connect

    Wang, Jinchen; Ye, Feng; Chi, Songxue; Fernandez-Baca, Jaime A.; Cao, Huibo; Tian, Wei; Gooch, Mellisa; Poudel, N.; Wang, Yaqi Q.; Lorenz, Bernd; Chu, C. W.


    Using x-ray and high pressure neutron diffraction, we studied the pressure effect on structural and magnetic properties of multiferroic Mn1-xCoxWO4sub> single crystals (x = 0, 0.05, 0.135 and 0.17), and compared it with the effects of doping. Both Co doping and pressure stretch the Mn-Mn chain along the c direction. At high doping level (x = 0.135 and 0.17), pressure and Co doping drive the system in a very similar way and induce a spin-flop transition for the x = 0.135 compound. In contrast, magnetic ground states at lower doping level (x = 0 and 0.05) are robust against pressure but experience a pronounced change upon Co substitution. As Co introduces both chemical pressure and magnetic anisotropy into the frustrated magnetic system, our results suggest the magnetic anisotropy is the main driving force for the Co induced phase transitions at low doping level, and chemical pressure plays a more significant role at higher Co concentrations.

  11. One-dimensional lone electron pair micelles in the crystal structure of Pb{sub 5}(SiO{sub 4})(VO{sub 4}){sub 2}

    SciTech Connect

    Krivovichev, S.V.; Armbruster, T.; Depmeier, W


    The structure of Pb{sub 5}(SiO{sub 4})(VO{sub 4}){sub 2} (hexagonal, P6{sub 3}/m, a = 9.9865(11), c = 7.3599(12) A, V = 635.67(14) A{sup 3}, Z = 2) has been solved by direct methods and refined to R{sub 1} = 0.051 on the basis of 440 unique observed reflections with vertical bar F{sub o} vertical bar{>=}4{sigma}{sub F}. The compound belongs to the apatite structure type. The Pb coordination polyhedra are distorted due to the presence of stereoactive lone electron pairs {psi}. The structure contains channels running along the c axis and centered at (00z). The channels are most probably occupied by the lone electron pairs of the Pb{sup 2+} cations and thus represent lone electron pair micelles. The existence of such micelles in the structure may well be the reason for the electrogyratory effect and protonic conductivity observed in crystals of the title compound.

  12. X-ray absorption spectroscopy of LiBF 4sub> in propylene carbonate. A model lithium ion battery electrolyte

    SciTech Connect

    Smith, Jacob W.; Lam, Royce K.; Sheardy, Alex T.; Shih, Orion; Rizzuto, Anthony M.; Borodin, Oleg; Harris, Stephen J.; Prendergast, David; Saykally, Richard J.


    Since their introduction into the commercial marketplace in 1991, lithium ion batteries have become increasingly ubiquitous in portable technology. Nevertheless, improvements to existing battery technology are necessary to expand their utility for larger-scale applications, such as electric vehicles. Advances may be realized from improvements to the liquid electrolyte; however, current understanding of the liquid structure and properties remains incomplete. X-ray absorption spectroscopy of solutions of LiBF4sub> in propylene carbonate (PC), interpreted using first-principles electronic structure calculations within the eXcited electron and Core Hole (XCH) approximation, yields new insight into the solvation structure of the Li+ ion in this model electrolyte. By generating linear combinations of the computed spectra of Li+-associating and free PC molecules and comparing to the experimental spectrum, we find a Li+–solvent interaction number of 4.5. This result suggests that computational models of lithium ion battery electrolytes should move beyond tetrahedral coordination structures.

  13. Quantum Monte Carlo analysis of a charge ordered insulating antiferromagnet: the Ti4sub>O7 Magnéli phase

    SciTech Connect

    Benali, Anouar; Shulenburger, Luke; Krogel, Jaron T.; Zhong, Xiaoliang; Kent, Paul R. C.; Heinonen, Olle


    The Magnéli phase Ti4sub>O7 is an important transition metal oxide with a wide range of applications because of its interplay between charge, spin, and lattice degrees of freedom. At low temperatures, it has non-trivial magnetic states very close in energy, driven by electronic exchange and correlation interactions. In this paper, we have examined three low-lying states, one ferromagnetic and two antiferromagnetic, and calculated their energies as well as Ti spin moment distributions using highly accurate quantum Monte Carlo methods. We compare our results to those obtained from density functional theory-based methods that include approximate corrections for exchange and correlation. Our results confirm the nature of the states and their ordering in energy, as compared with density-functional theory methods. However, the energy differences and spin distributions differ. Finally, a detailed analysis suggests that non-local exchange–correlation functionals, in addition to other approximations such as LDA+U to account for correlations, are needed to simultaneously obtain better estimates for spin moments, distributions, energy differences and energy gaps.

  14. Quantum Monte Carlo analysis of a charge ordered insulating antiferromagnet: The Ti4sub>O7 Magneli phase

    SciTech Connect

    Benali, Anouar; Shulenburger, Luke; Krogel, Jaron T.; Zhong, Xiaoling; Kent, Paul R. C.; Heinonen, Olle


    The Magneli phase Ti4sub>O7 is an important transition metal oxide with a wide range of applications because of its interplay between charge, spin, and lattice degrees of freedom. At low temperatures, it has non-trivial magnetic states very close in energy, driven by electronic exchange and correlation interactions. We have examined three low- lying states, one ferromagnetic and two antiferromagnetic, and calculated their energies as well as Ti spin moment distributions using highly accurate Quantum Monte Carlo methods. We compare our results to those obtained from density functional theory- based methods that include approximate corrections for exchange and correlation. Our results confirm the nature of the states and their ordering in energy, as compared with density-functional theory methods. However, the energy differences and spin distributions differ. Here, a detailed analysis suggests that non-local exchange-correlation functionals, in addition to other approximations such as LDA+U to account for correlations, are needed to simultaneously obtain better estimates for spin moments, distributions, energy differences and energy gaps.

  15. Structural transition and orbital glass physics in near-itinerant CoV2O4sub>

    SciTech Connect

    Reig-i-Plessis, D.; Casavant, D.; Garlea, Vasile O.; Aczel, Adam A.; Feygenson, Mikhail; Neuefeind, Joerg C.; Zhou, H. D.; Nagler, Stephen E.; MacDougall, Gregory J.


    In this study, the ferrimagnetic spinel CoV2O4sub> has been a topic of intense recent interest, both as a frustrated insulator with unquenched orbital degeneracy and as a near-itinerant magnet which can be driven metallic with moderate applied pressure. Here, we report on our recent neutron di raction and inelastic scattering measurements on powders with minimal cation site disorder. Our main new result is the identification of a weak (Δa/a ~ 10–4), first order structural phase transition at T* = 90 K, the same temperature where spin canting was seen in recent single crystal measurements. This transition is characterized by a short-range distortion of oxygen octahedral positions, and inelastic data further establish a weak 1.25meV spin gap at low temperature. Together, these findings provide strong support for the local orbital picture and the existence of an orbital glass state at temperatures below T*.

  16. Synthesis of nanostructured LiTi{sub 2}(PO{sub 4}){sub 3} powder by a Pechini-type polymerizable complex method

    SciTech Connect

    Mariappan, C.R.; Galven, C.; Crosnier-Lopez, M.-P.; Le Berre, F.; Bohnke, O. . E-mail:


    The nanostructured NASICON-type LiTi{sub 2}(PO{sub 4}){sub 3} (LTP) material has been synthesized by Pechini-type polymerizable complex method. The use of water-soluble ammonium citratoperoxotitanate (IV) metal complex instead of alkoxides as precursor allows to prepare monophase material. Thermal analyses have been carried out on the powder precursor to check the weight loss and synthesis temperature. X-ray powder diffraction analysis (XRD) has been performed on the LTP powder obtained after heating the powder precursor over a temperature range from 550 to 1050 deg. C for 2 h. By varying the molar ratio of citric acid to metal ion (CA/Ti) and citric acid to ethylene glycol (CA/EG), the grain size of the LTP powder could be modified. The formation of small and well-crystalline grains, in the order of 50-125 nm in size, has been determined from the XRD patterns and confirmed by transmission electron microscopy.

  17. Cation ratio fluctuations in Cu2ZnSnS4sub> at the 20 nm length scale investigated by analytical electron microscopy

    SciTech Connect

    Aguiar, Jeffery A.; Erkan, Mehmet E.; Pruzan, Dennis S.; Nagaoka, Akira; Yoshino, Kenji; Moutinho, Helio; Al-Jassim, Mowafak; Scarpulla, Michael A.


    Kesterite Cu2ZnSn(S,Se)4sub> (CZTSSe) is a sustainable material for thin-film photovoltaics with device efficiencies greater than 12% have been demonstrated. Despite similar crystal structure and polycrystalline film microstructures, there is widespread evidence for larger-amplitude potential and bandgap fluctuations in CZTS than in the analogous Cu(In,Ga)Se2 (CIGSe) chalcopyrite material. This disorder is believed to account for a sizable part of the larger open-circuit voltage (VOC) deficit in CZTS devices, yet the detailed origins and length scales of these fluctuations have not been fully elucidated. Herein, we present a transmission electron microscopy study focusing on composition variation within bulk multicrystals of CZTS grown by the travelling heater method (THM). In these slow-cooled, solution grown crystals we find direct evidence for spatial composition fluctuations of amplitude <1 at.% (~5 x 1020 cm-3) and thus, explainable by point defects. However, rather than being homogeneously-distributed we find a characteristic 20 nm length scale for these fluctuations, which sets a definite length scale for band gap and potential fluctuations. At Σ3 grain boundaries, we find no evidence of composition variation compared to the bulk. The finding highlights such variations reported at grain boundaries in polycrystalline thin-films are direct consequences of processing methods and not intrinsic properties of CZTS itself.

  18. New localized/delocalized emitting state of Eu2+ in orange-emitting hexagonal EuAl2O4sub>

    SciTech Connect

    Liu, Feng; Meltzer, Richard S.; Li, Xufan; Budai, John D.; Chen, Yu -Sheng; Pan, Zhengwei


    Eu2+-activated phosphors are being widely used in illuminations and displays. Some of these phosphors feature an extremely broad and red-shifted Eu2+ emission band; however, convincing explanation of this phenomenon is lacking. Here we report a new localized/delocalized emitting state of Eu2+ ions in a new hexagonal EuAl2O4sub> phosphor whose Eu2+ luminescence exhibits a very large bandwidth and an extremely large Stokes shift. At 77 K, two luminescent sites responsible for 550 nm and 645 nm broadband emissions are recognized, while at room temperature only the 645 nm emission band emits. The 645 nm emission exhibits a typical radiative lifetime of 1.27 μs and an unusually large Stokes shift of 0.92 eV. We identify the 645 nm emission as originating from a new type of emitting state whose composition is predominantly that of localized 4f65d character but which also contains a complementary component with delocalized conduction-band-like character. This investigation gives new insights into a unique type of Eu2+ luminescence in solids whose emission exhibits both a very large bandwidth and an extremely large Stokes shift.

  19. Band alignment of atomic layer deposited (HfZrO{sub 4}){sub 1−x}(SiO{sub 2}){sub x} gate dielectrics on Si (100)

    SciTech Connect

    Heo, Sung; Tahir, Dahlang; Chung, Jae Gwan; Lee, Jae Cheol; Kim, KiHong; Lee, Junho; Lee, Hyung-Ik; Park, Gyeong Su; Oh, Suhk Kun; Kang, Hee Jae; Choi, Pyungho; Choi, Byoung-Deog


    The band alignment of atomic layer deposited (HfZrO{sub 4}){sub 1−x}(SiO{sub 2}){sub x} (x = 0, 0.10, 0.15, and 0.20) gate dielectric thin films grown on Si (100) was obtained by using X-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The band gap, valence band offset, and conduction band offset values for HfZrO{sub 4} silicate increased from 5.4 eV to 5.8 eV, from 2.5 eV to 2.75 eV, and from 1.78 eV to 1.93 eV, respectively, as the mole fraction (x) of SiO{sub 2} increased from 0.1 to 0.2. This increase in the conduction band and valence band offsets, as a function of increasing SiO{sub 2} mole fraction, decreased the gate leakage current density. As a result, HfZrO{sub 4} silicate thin films were found to be better for advanced gate stack applications because they had adequate band gaps to ensure sufficient conduction band offsets and valence band offsets to Si.

  20. Anisotropic lattice thermal expansion of PbFeBO4sub>: A study by X-ray and neutron diffraction, Raman spectroscopy and DFT calculations

    SciTech Connect

    Murshed, M. Mangir; Mendive, Cecilia B.; Curti, Mariano; Nénert, Gwilherm; Kalita, Patricia E.; Lipinska, Kris; Cornelius, Andrew L.; Huq, Ashfia; Gesing, Thorsten M.


    We present the lattice thermal expansion of mullite-type PbFeBO4sub> in this study. The thermal expansion coefficients of the metric parameters were obtained from composite data collected from temperature-dependent neutron and X-ray powder diffraction between 10 K and 700 K. The volume thermal expansion was modeled using extended Grüneisen first-order approximation to the zero-pressure equation of state. The additive frame of the model includes harmonic, quasi-harmonic and intrinsic anharmonic potentials to describe the change of the internal energy as a function of temperature. Moreover, the unit-cell volume at zero-pressure and 0 K was optimized during the DFT simulations. Harmonic frequencies of the optical Raman modes at the Γ-point of the Brillouin zone at 0 K were also calculated by DFT, which help to assign and crosscheck the experimental frequencies. The low-temperature Raman spectra showed significant anomaly in the antiferromagnetic regions, leading to softening or hardening of some phonons. Selected modes were analyzed using a modified Klemens model. The shift of the frequencies and the broadening of the line-widths helped to understand the anharmonic vibrational behaviors of the PbO4, FeO6 and BO3 polyhedra as a function of temperature.

  1. Synthesis and photoluminescence properties of Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} red phosphor for white light emitting diodes

    SciTech Connect

    Zhu, Ge; Ci, Zhipeng; Shi, Yurong; Wang, Yuhua


    Highlights: • A novel red phosphor Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} was synthesized and investigated firstly. • The structure and characteristic luminescence properties are discussed. • The excellent thermal stability was found and investigated. • It has good color saturation, the CIE is close to that of commercial Y{sub 2}O{sub 3}:Eu{sup 3+}. - Abstract: A series of Sm{sup 3+} doped Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14} red phosphors were successfully synthesized. X-ray diffraction analysis indicates that all the samples are single phased. The luminescence property is investigated in detail by measuring their photoluminescence excitation and emission spectra. Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} phosphors show strong absorption in 400–410 nm region, which is suitable for application in LEDs. When excited at 403 nm, Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} phosphor can emit red emission with CIE chromaticity coordinates (0.615, 0.384). The optimal doping concentration of Sm{sup 3+} doped Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14} is measured to be 0.02. The thermal quenching property is also measured and compared with the commercial red phosphor Y{sub 2}O{sub 3}:Eu{sup 3+} (Topstar, TXC-RIA). The results indicate Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} phosphors have potential to serve as a red phosphor for white LEDs.

  2. Scintillation properties of Eu2+-doped KBa2I5 and K2BaI4sub>

    SciTech Connect

    Stand, L.; Zhuravleva, M.; Chakoumakos, Bryan C.; Johnson, J.; Lindsey, Adam; Melcher, Charles L.


    We report two new ternary metal halide scintillators, KBa2I5 and K2BaI4sub>, activated with divalent europium. Single crystal X-ray diffraction measurements confirmed that KBa2I5 has a monoclinic structure (P21/c) and that K2BaI4sub> has a rhombohedral structure (R3c). Differential scanning calorimetry showed singular melting and crystallization points, making these compounds viable candidates for melt growth. We grew 13 mm diameter single crystals of KBa2I5:Eu2+ and K2BaI4sub>:Eu2+ in evacuated quartz ampoules via the vertical Bridgman technique. The optimal Eu2+ concentration was 4% for KBa2I5 and 7% for K2BaI4sub>. The X-ray excited emissions at 444 nm for KBa2I5:Eu 4% and 448 nm for K2BaI4sub>:Eu 7% arise from the 5d-4f radiative transition in Eu2+. KBa2I5:Eu 4% has a light yield of 90,000 photons/MeV, with an energy resolution of 2.4% and K2BaI4sub>:Eu 7% has a light yield of 63,000 ph/MeV, with an energy resolution of 2.9% at 662 keV. Both crystals have an excellent proportional response to a wide range of gamma-ray energies.

  3. Hydrothermal synthesis, structural and physico-chemical characterizations of two Nasicon phosphates: M{sub 0.50}{sup II}Ti{sub 2}(PO{sub 4}){sub 3} (M = Mn, Co)

    SciTech Connect

    Essehli, Rachid; Bali, Brahim El; Benmokhtar, S.; Fejfarova, Karla; Dusek, Michal


    The family of titanium Nasicon-phosphates of generic formula M{sub 0.5}{sup II}Ti{sub 2}(PO{sub 4}){sub 3} has been revisited using hydrothermal techniques. Two phases have been synthesized: Mn{sub 0.5}{sup II}Ti{sub 2}(PO{sub 4}){sub 3} (MnTiP) and Co{sub 0.5}{sup II}Ti{sub 2}(PO{sub 4}){sub 3} (CoTiP). Single crystal diffraction studies show that they exhibit two different structural types. Mn{sub 0.5}{sup II}Ti{sub 2}(PO{sub 4}){sub 3} phosphate crystallizes in the R-3 space group, with the cell parameters a = 8.51300(10) A and c = 21.0083(3) A (V = 1318.52(3) A{sup 3} and Z = 6). The Co{sub 0.5}{sup II}Ti{sub 2}(PO{sub 4}){sub 3} phosphate crystallizes in the R-3c space group, with a = 8.4608(9) A and c = 21.174(2) A (V = 1312.7(2) A{sup 3} and Z = 6). These two compounds are clearly related to the parent Nasicon-type rhombohedral structure, which can be described using [Ti{sub 2}(PO{sub 4}){sub 3}] framework composed of two [TiO{sub 6}] octahedral interlinked via three [PO{sub 4}] tetrahedra. {sup 31}P magic-angle spinning nuclear magnetic resonance (MAS-NMR) data are presented as supporting data. Curie-Weiss-type behavior is observed in the magnetic susceptibility. The phases are also characterized by IR spectroscopy and UV-visible.

  4. Near-infrared quantum-cutting luminescence and energy transfer properties of Ca{sub 3}(PO{sub 4}){sub 2}:Tm{sup 3+},Ce{sup 3+} phosphors

    SciTech Connect

    Dong, S. L.; Lin, H. H. E-mail:; Yu, T.; Zhang, Q. Y. E-mail:


    The phosphors Ca{sub 3}(PO{sub 4}){sub 2}:Tm{sup 3+} by co-doping Ce{sup 3+} have been synthesized by conventional high-temperature solid-state reaction method. Their spectroscopic properties in the UV-VIS-NIR range have been investigated. The first 5d crystal field level location and stokes shift have been determined from the UV excitation and emission spectra of Ca{sub 3}(PO{sub 4}){sub 2}:Ce{sup 3+}. The three-photon NIR quantum-cutting luminescence of Tm{sup 3+} assigned to the electronic transitions of {sup 1}G{sub 4}→{sup 3}H{sub 4}, {sup 3}H{sub 4}→{sup 3}F{sub 4} and {sup 3}F{sub 4}→{sup 3}H{sub 6} is observed, whether in Ca{sub 3}(PO{sub 4}){sub 2}:Tm{sup 3+} or Ca{sub 3}(PO{sub 4}){sub 2}:Tm{sup 3+},Ce{sup 3+}. The energy transfer from Ce{sup 3+} to Tm{sup 3+} takes place with energy-transfer efficiency up to 34.5% for the Ca{sub 3}(PO{sub 4}){sub 2}:Tm{sup 3+},Ce{sup 3+}. A cross relaxation scheme using the 5d states of Ce{sup 3+} and f-f transition of Tm{sup 3+} is proposed. The mechanism is revealed from energy level and decay measurements. The results show that the broadband absorption of Ce{sup 3+} sensitizer not only extends the spectrum conversion in UV region but also greatly enhances the photoluminescence intensities of the three-photon quantum cutting luminescence of Tm{sup 3+} doped Ca{sub 3}(PO{sub 4}){sub 2}.

  5. Growth and structure of K{sub 2}Ni{sub x}Co{sub (1–x)}(SO{sub 4}){sub 2} · 6H{sub 2}O single crystals

    SciTech Connect

    Vasilyeva, N. A. Sorokina, N. I.; Antipin, A. M.; Verin, I. A.; Voloshin, A. E.


    Single crystals of the K{sub 2}Ni{sub x}Co{sub (1–x)}(SO{sub 4}){sub 2} · 6H{sub 2}O composition are grown by spontaneous flux crystallization. More exact chemical formulas of the single crystals are determined based on the diffraction data as K{sub 2}Co(SO{sub 4}){sub 2} · 6H{sub 2}O (I), K{sub 2}(Co{sub 0.657}Ni{sub 0.343})(SO{sub 4}){sub 2} · 6H{sub 2}O (II), K{sub 2}(Co{sub 0.226}Ni{sub 0.774})(SO{sub 4}){sub 2} · 6H{sub 2}O (III), K{sub 2}(Co{sub 0.216}Ni{sub 0.784})(SO{sub 4}){sub 2} · 6H{sub 2}O (IV), and K{sub 2}Ni(SO{sub 4}){sub 2} · 6H{sub 2}O (V). The substitution of nickel atoms for cobalt atoms in structure I results in a shortening of all (Co,Ni)–O interatomic distances. With increasing Ni concentration, the (Co,Ni)–O2 distance shortens to a lesser degree than the (Co,Ni)–O1 and (Co,Ni)–O3 distances and, as a consequence, the distortion of (Co,Ni)O{sub 6} octahedra decreases. NiO{sub 6} polyhedra are less distorted than CoO{sub 6} octahedra. The analysis of difference syntheses of electron density shows that the number of uninterpretable peaks on the maps of mixed crystals II, III, and IV, as well as on the map of K{sub 2}Co(SO{sub 4}){sub 2} · 6H{sub 2}O, is larger with respect to those of structure K{sub 2}Ni(SO{sub 4}){sub 2} · 6H{sub 2}O.

  6. Synthesis and structural study of a new NASICON-type solid solution: Li{sub 1-} {sub x} La {sub x} {sub /3}Zr{sub 2}(PO{sub 4}){sub 3}

    SciTech Connect

    Barre, M.; Crosnier-Lopez, M.P. Le Berre, F.; Suard, E.; Fourquet, J.L.


    A new complete solid solution of NASICON-type compounds between LiZr{sub 2}(PO{sub 4}){sub 3} and La{sub 1/3}Zr{sub 2}(PO{sub 4}){sub 3} was evidenced with the general formula Li{sub 1-} {sub x} La {sub x} {sub /3}Zr{sub 2}(PO{sub 4}){sub 3} (0{<=}x{<=}1). These phases were synthesized by a complex polymerizable method and structurally characterized from Rietveld treatment of their X-ray and neutron powder diffraction data. This solid solution results from the substitution mechanism Li{sup +{yields}}1/3La{sup 3+}+2/3{open_square} leading to an increase of the vacancies number correlated to an increase of the La content. According to this substitution mechanism, the general formula can then be written Li{sub 1-} {sub x} La {sub x} {sub /3}{open_square}{sub 2} {sub x} {sub /3}Zr{sub 2}(PO{sub 4}){sub 3} (0{<=}x{<=}1) in order to underline the correlation between the La content and the vacancies rate. For all the compounds, the structure is clearly related to that of the NASICON family with three crystallographic domains evidenced. For 0{<=}x{<=}0.5, all the members adopt at high temperature the typical NASICON-type structure (s.g. R3-barc), while at lower temperature, their structure distorts to a triclinic form (s.g. C 1-bar), as observed for LiZr{sub 2}(PO{sub 4}){sub 3} prepared above 1100 deg. C. Moreover, in this domain, the reversible transition is clearly soft and the transition temperature strongly depends of the x value. For 0.6{<=}x{<=}0.9, the compounds crystallize in a rhombohedral cell (s.g. R3-bar), while for x=1, the phase La{sub 1/3}Zr{sub 2}(PO{sub 4}){sub 3} is obtained (s.g. P3-bar, Z=6, a=8.7378(2) A, c=23.2156(7) A). This paper is devoted to the structure analysis of the series Li{sub 1-} {sub x} La {sub x} {sub /3}Zr{sub 2}(PO{sub 4}){sub 3} (0{<=}x{<=}1), from X-ray and neutron powder thermo diffraction and transmission electron microscopy (TEM) studies. - Graphical abstract: Schematic drawing of the space group evolution at 800 deg. C in the

  7. Characterization of collision cascade damage in Ca{sub 2}La{sub 8}(SiO{sub 4}){sub 6}O{sub 2} by HRTEM

    SciTech Connect

    Weber, W.J.; Wang, L.M.


    Ca{sub 2}La{sub 8}(SiO{sub 4}){sub 6}O{sub 2} thin crystals become amorphous under ion beam irradiation. The ion dose required for complete amorphization of the thin crystal (critical amorphization dose, D{sub c}) increased with the increasing irradiation temperature and decreased with ion mass at elevated temperatures. Samples irradiated with 1-1.5 MeV Ar{sup +}, Kr{sup +} and Xe{sup +} ions to doses much lower than Dc, in the temperature range from 20 to 498 K were used for a detailed HRTEM study to better understand the amorphization process. The residual collision cascade damage after irradiation appeared as manometer scale amorphous domains. The images of these domains are extremely sensitive to the sample thickness. Small domains of cascade size were only found at the very thin edge of the sample. In thicker regions, amorphous domains appear after higher doses as the result of cascade overlap in projection. At higher temperatures, the observed amorphous domains are smaller indicating thermal recovery at the amorphous/crystalline interface. The amorphous domains are also larger in size after irradiation with ions of higher mass at a fixed ion dose. These results are consistent with the Dc-temperature curves determined by in situ TEM with the HVEM-Tandem Facility at Argonne National Laboratory. The width of the amorphous rim along the edge of the specimen grew with increasing ion dose suggesting that amorphization also proceeds from the sample surface. Images of the collision cascade damage were compared to the cascade sizes calculated with the TRIM code. Some digitally acquired HRTEM images of the cascade damage were processed to reveal more detailed information.

  8. A Raman spectroscopic study of the phase transition of BaZr(PO{sub 4}){sub 2}: Evidence for a trigonal structure of the high-temperature polymorph

    SciTech Connect

    Geisler, Thorsten . E-mail:; Popa, Karin; Konings, Rudy J.M.; Popa, Aurelian F.


    We have studied the structural evolution of monoclinic BaZr(PO{sub 4}){sub 2} during heating up to 835K by Raman spectroscopy. In agreement with previous studies we found a first-order phase transition at about 730K during heating while upon cooling the reverse transition occurs at 705K. However, some disagreement about the crystal structure of the high-temperature polymorph occurs in the literature. While the space group has not yet been determined, the X-ray diffraction pattern of the high-temperature phase has been indexed on either an orthorhombic or a hexagonal unit cell. We found that the number of Raman active internal PO{sub 4} vibrational modes decrease from nine to six during the transition. A group theoretical survey through all orthorhombic, trigonal, and hexagonal factor groups revealed that the observed number of vibrations would only be consistent with the Ba and Zr atoms located at a D{sub 3d}(3-bar m) site, the P and two O atoms at a C{sub 3v}(3m), and six O atoms at a C{sub s}(m) site in the D{sub 3d} factor group. Based on our Raman data, the space group of the high-temperature polymorph is thus either D{sub 3d}{sup 1}(P3-bar 1m), D{sub 3d}{sup 3}(P3-bar m1), or D{sub 3d}{sup 5}(R3-bar m)


    SciTech Connect

    Neufeld, David A.; Wu, Yuanwei; Kraus, Alex; Menten, Karl M.; Tolls, Volker; Melnick, Gary J.; Nagy, Zsofia


    Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared, we have performed mapping observations of the 620.701 GHz 5{sub 32}-4{sub 41} transition of ortho-H{sub 2}O within a {approx}1.'5 Multiplication-Sign 1.'5 region encompassing the Kleinmann-Low nebula in Orion (Orion-KL), and pointed observations of that transition toward the Orion South condensation and the W49N region of high-mass star formation. Using the Effelsberg 100 m radio telescope, we obtained ancillary observations of the 22.23508 GHz 6{sub 16}-5{sub 23} water maser transition; in the case of Orion-KL, the 621 GHz and 22 GHz observations were carried out within 10 days of each other. The 621 GHz water line emission shows clear evidence for strong maser amplification in all three sources, exhibiting narrow ({approx}1 km s{sup -1} FWHM) emission features that are coincident (kinematically and/or spatially) with observed 22 GHz features. Moreover, in the case of W49N-for which observations were available at three epochs spanning a 2 yr period-the spectra exhibited variability. The observed 621 GHz/22 GHz line ratios are consistent with a maser pumping model in which the population inversions arise from the combined effects of collisional excitation and spontaneous radiative decay, and the inferred physical conditions can plausibly arise in gas heated by either dissociative or non-dissociative shocks. The collisional excitation model also predicts that the 22 GHz population inversion will be quenched at higher densities than that of the 621 GHz transition, providing a natural explanation for the observational fact that 22 GHz maser emission appears to be a necessary but insufficient condition for 621 GHz maser emission.

  10. Hydrothermal synthesis, thermal, structural, spectroscopic and magnetic studies of the Mn{sub 5-} {sub x} Co {sub x} (HPO{sub 4}){sub 2}(PO{sub 4}){sub 2}(H{sub 2}O){sub 4} (x=1.25, 2, 2.5 and 3) finite solid solution

    SciTech Connect

    Larrea, Edurne S.


    The Mn{sub 5-} {sub x} Co {sub x} (HPO{sub 4}){sub 2}(PO{sub 4}){sub 2}(H{sub 2}O){sub 4} (x=1.25, 2, 2.5, 3) finite solid solution has been synthesized by mild hydrothermal conditions under autogeneous pressure. The phases crystallize in the C2/c space group with Z=4, belonging to the monoclinic system. The unit-cell parameters obtained from single crystal X-ray diffraction are: a=17.525(1), b=9.0535(6), c=9.4517(7) A, {beta}=96.633(5) {sup o} being R1=0.0436, wR2=0.0454 for Mn75Co25; a=17.444(2), b=9.0093(9), c=9.400(1) A, {beta}=96.76(1) {sup o} being R1=0.0381, wR2=0.0490 for Mn60Co40; a=17.433(2), b=8.9989(9), c=9.405(1) A, {beta}=96.662(9) {sup o} being R1=0.0438, wR2=0.0515 for Mn50Co50 and a=17.4257(9), b=8.9869(5), c=9.3935(5) A, {beta}=96.685(4) {sup o} being R1=0.0296, wR2=0.0460 for Mn40Co60. The structure consists of a three dimensional network formed by octahedral pentameric entities (Mn,Co){sub 5}O{sub 16}(H{sub 2}O){sub 6} sharing vertices with the (PO{sub 4}){sup 3-} and (HPO{sub 4}){sup 2-} tetrahedra. The limit of thermal stability of these compounds is, approximately, 165 deg. C, near to this mean temperature the phases loose their water content in two successive steps. IR spectra show the characteristic bands of the water molecules and the phosphate and hydrogen-phosphate oxoanions. The diffuse reflectance spectra are consistent with the presence of MO{sub 6} octahedra environments in slightly distorted octahedral geometry, except for the M(3)O{sub 6} octahedron which presents a remarkable distortion and so a higher Dq parameter. The mean value for the Dq and B-Racah parameter for the M(1),(2)O{sub 6} octahedra is 685 and 850 cm{sup -1}, respectively. These parameters for the most distorted M(3)O{sub 6} polyhedron are 825 and 880 cm{sup -1}, respectively. The four phases exhibit antiferromagnetic couplings as the major magnetic interactions. However, a small spin canting phenomenon is observed at low temperatures for the two phases with major

  11. Magnetic field, frequency and temperature dependence of complex conductance of ultrathin La1.65Sr0.45CuO4sub>/La2CuO4sub> films and the organic superconductors κ-(BEDT-TTF)2Cu[N(CN)2]Br

    SciTech Connect

    V. A. Gasparov; Bozovic, I.; He, Xi; Dubuis, G.; Pavuna, D.; Kushch, N. D.; Yagubskii, E. B.; Schlueter, J. A.


    In this study, we used atomic-layer molecular beam epitaxy (ALL-MBE) to synthesize bilayer films of a cuprate metal (La1.65Sr0.45CuO4sub>) and a cuprate insulator (La2CuO4sub>), in which interface superconductivity occurs in a layer that is just one-half unit cell thick. We have studied the magnetic field and temperature dependence of the complex sheet conductance, σ(ω), of these films, and compared them to κκ-(BEDT-TTF)2Cu[N(CN)2]Br single crystals. The magnetic field H was applied both parallel and perpendicular to the 2D conducting layers. Experiments have been carried out at frequencies between 23 kHz and 50 MHz using either two-coil mutual inductance technique, or the LC resonators with spiral or rectangular coils. The real and the imaginary parts of the mutual-inductance M(T,ω) between the coil and the sample were measured and converted to complex conductivity. For H perpendicular to the conducting layers, we observed almost identical behavior in both films and κ-Br single crystals: (i) the transition onset in the inductive response, Lk–1(T) occurs at a temperature lower by 2 K than in Re σ(T), (ii) this shift is almost constant with magnetic field up to 8 T; (iii) the vortex diffusion constant D(T) is exponential due to pinning of vortex cores. These results can be described by the extended dynamic theory of the Berezinski–Kosterlitz–Thouless (BKT) transition and dynamics of bound vortex–antivortex pairs with short separation lengths.

  12. Fundamental Understanding of Methane-Carbon Dioxide-Water (CH4sub>-CO2-H2O) Interactions in Shale Nanopores under Reservoir Conditions. Quarterly Report.

    SciTech Connect

    Wang, Yifeng


    This project focuses on the systematic study of CH4sub>-CO2-H2O interactions in shale nanopores under high-pressure and high temperature reservoir conditions. The proposed work will help to develop new stimulation strategies to enable efficient resource recovery from fewer and less environmentally impactful wells.

  13. Ion-redistribution induced efficient upconversion in β-NaYF4sub>:20%Yb3+,2%Er3+ microcrystals with well controlled morphology and size.


    Fan, Shaohua; Wang, Shikai; Yu, Lu; Sun, Hongtao; Gao, Guojun; Hu, Lili


    We develop an efficient green upconversion (UC) β-NaYF4sub>:20%Yb3+,2%Er3+ microcrystal with well controlled morphology and size by hydrothermal method using two different chelating agents of CIT and EDTA-2Na via a simple ion-exchange reaction. Importantly, the UC emission efficiency of newly developed CIT and EDTA-2Na β-NaYF4sub>:20%Yb3+,2%Er3+ microcrystals is almost as strong as that of commercial counterpart by solid-state method. A proof-of-concept β-NaYF4sub>:20%Yb3+,2%Er3+ microcrystal waveguide is demonstrated to extend their applications in modern micro-optoelectronics. The local ion-redistribution process during the ion-exchange reaction, which effectively disperses the locally clustered Yb3+, accounts for the enormously enhanced UC emission in β-NaYF4sub>:20%Yb3+,2%Er3+ microcrystals.

  14. Syntheses and crystal structures of two novel alkaline uranyl chromates A{sub 2}(UO{sub 2})(CrO{sub 4}){sub 2} (A=Rb, Cs) with bidentate coordination mode of uranyl ions by chromate anions

    SciTech Connect

    Siidra, Oleg I.


    Single crystals of Cs{sub 2}(UO{sub 2})(CrO{sub 4}){sub 2} and Rb{sub 2}(UO{sub 2})(CrO{sub 4}){sub 2} were prepared by solid state reactions. The structures are based upon the [(UO{sub 2})(CrO{sub 4}){sub 2}]{sup 2-} chains. Within the chains, UrO{sub 5} pentagonal bipyramids (Ur=uranyl) form Ur{sub 2}O{sub 8} dimers, which are linked via CrO{sub 4} tetrahedra into one-dimensional chains. The CrO{sub 4} tetrahedra coordinate uranyl ions in both mono- and bidentate fashion, which is unusual for uranyl chromates. The bidentate coordination has a strong influence upon geometrical parameters of both U and Cr coordination polyhedra. The conformation of the chains in 1 and 2 is different due to the different size of the Cs{sup +} and Rb{sup +} cations. - Graphical abstract: Uranyl chromate chain with monodentate and bidentate coordination mode of uranyl cations by CrO{sub 4} tetrahedra in Cs{sub 2}(UO{sub 2})(CrO{sub 4}){sub 2}. Highlights: Black-Right-Pointing-Pointer Single crystals of novel uranyl chromates were prepared by solid state reactions. Black-Right-Pointing-Pointer The CrO{sub 4} tetrahedra coordinate uranyl ions in both mono- and bidentate fashion. Black-Right-Pointing-Pointer The bidentate coordination has a strong influence upon geometrical parameters.

  15. Longitudinally diode-pumped 1.06-{mu}m Nd{sup 3+}:NaLa(MoO{sub 4}){sub 2} laser without pump-wavelength stabilisation

    SciTech Connect

    Zharikov, Evgeny V; Lis, Denis A; Subbotin, Kirill A; Ushakov, S N; Onishchenko, A M; Romanyuk, V A; Shestakov, A V


    The spectral and lasing characteristics of a Nd{sup 3+}:NaLa(MoO{sub 4}){sub 2} crystal longitudinally diode-pumped without pump-wavelength stabilisation are studied. A variation in the output power did not exceed 30% when the pump wavelength was changed in the spectral region from 0.794 to 0.811 {mu}m. (lasers)

  16. pH-regulative synthesis of Na3(VPO4sub>)2F3 nanoflowers and their improved Na cycling stability

    SciTech Connect

    Qi, Yuruo; Mu, Linqin; Zhao, Junmei; Hu, Yong -Sheng; Liu, Huizhou; Dai, Sheng


    Na-ion batteries are becoming increasingly attractive as a low cost energy storage device. Sodium vanadium fluorophosphates have been studied extensively recently due to their high storage capacity and high discharge voltage. Shape and size often have a crucial influence over the properties. The controlling synthesis of nanoparticles with special microstructures is significant, which becomes a challenging issue and has drawn considerable attention. In this study, Na3(VPO4sub>)2F3 nanoflowers have been synthesized via a pH-regulative low-temperature (120 °C) hydro-thermal route. In particular, it is a green route without any organic compounds involved. The hydro-thermal reaction time for the formation of Na3(VPO4sub>)2F3 nanoflowers has also been investigated. A weak acid environment (pH = 2.60) with the possible presence of hydrogen fluoride molecules is necessary for the formation of the desired nanoflower microstructures. Moreover, compared to the nanoparticles obtained by Na2HPO4sub>·12H2O, the as-synthesized Na3(VPO4sub>)2F3 nanoflowers showed an excellent Na-storage performance in terms of superior cycle stability, even without any further carbon coating or high-temperature treatment.

  17. In situ determination of the spinel-post-spinel transition in Fe3O4sub> at high pressure and temperature by synchrotron X-ray diffraction

    SciTech Connect

    Schollenbruch, K; Woodland, A B; Frost, D J; Wang, Y; Sanehira, T; Langenhorst, F


    The position of the spinel-post-spinel phase transition in Fe3O4sub> has been determined in pressure-temperature space by in situ measurements using a multi-anvil press combined with white synchrotron radiation. Pressure measurement using the equation of state for MgO permitted pressure changes to be monitored at high temperature. The phase boundary was determined by the first appearance of diffraction peaks of the high-pressure polymorph (h-Fe3O4sub>) during pressure increase and the disappearance of these peaks on pressure decrease along several isotherms. We intersected the phase boundary over the temperature interval of 700-1400 ºC. The boundary is linear and nearly isobaric, with a slightly positive slope. Post-experiment investigation by TEM confirms that the reverse reaction from h-Fe 3O4sub> to magnetite during decompression leads to the formation of microtwins on the (311) plane in the newly formed magnetite. Observations made during the phase transition suggest that the transition has a pseudomartensitic character, explaining in part why magnetite persists at conditions well within the stability field of h-Fe3O4sub>, even at high temperatures. This study emphasizes the utility of studying phase transitions in situ at simultaneously high temperatures and pressures since the reaction kinetics may not be favorable at room temperature.

  18. Origin of Active Oxygen in a Ternary CuOx /Co3O4sub>–CeO 2 Catalyst for CO Oxidation

    SciTech Connect

    Liu, Zhigang; Wu, Zili; Peng, Xihong; Binder, Andrew; Chai, Songhai; Dai, Sheng


    In this paper, we have studied CO oxidation over a ternary CuOx/Co3O4sub>-CeO2 catalyst and employed the techniques of N2 adsorption/desporption, XRD, TPR, TEM, in situ DRIFTS and QMS (Quadrupole mass spectrometer) to explore the origin of active oxygen. DRIFTS-QMS results with labeled 18O2 indicate that the origin of active oxygens in CuOx/Co3O4sub>-CeO2 obeys a model, called as queue mechanism. Namely gas-phase molecular oxygens are dissociated to atomic oxygens and then incorporate in oxygen vacancies located at the interface of Co3O4sub>-CeO2 to form active crystalline oxygens, and these active oxygens diffuse to the CO-Cu+ sites thanks to the oxygen vacancy concentration magnitude and react with the activated CO to form CO2. This process, obeying a queue rule, provides active oxygens to form CO2 from gas-phase O2 via oxygen vacancies and crystalline oxygen at the interface of Co3O4sub>-CeO2.

  19. NaLa(MoO{sub 4}){sub 2}: RE{sup 3+} (RE{sup 3+} = Eu{sup 3+}, Sm{sup 3+}, Er{sup 3+}/Yb{sup 3+}) microspheres: the synthesis and optical properties

    SciTech Connect

    Gao, Zhiyi; Wang, Zhiying; Fu, Linlin; Yang, Xingxing; Fu, Zuoling; Wu, Zhijian; Jeong, Jung Hyun


    The strong green upconversion (UC) emission were observed in various Er{sup 3+}, Yb{sup 3+} co-doped NaLa(MoO{sub 4}){sub 2} samples synthesized via a hydrothermal route. The UC intensity depends on the dopant concentration, and the optimal UC emission was obtained in NaLa(MoO{sub 4}){sub 2}: 0.02Er{sup 3+}/0.10 Yb{sup 3+}. - Highlights: • The NaLa(MoO{sub 4}){sub 2} microspheres doped with Eu{sup 3+}, Sm{sup 3+} and Er{sup 3+}/Yb{sup 3+} were synthesized by a hydrothermal method. • The effects of the EDTA in the initial solution crystal phase and morphology were studied. • The down-conversion luminescence properties of NaLa(MoO{sub 4}){sub 2}: RE{sup 3+} (RE{sup 3+} = Eu{sup 3+}, Sm{sup 3+}) were investigated. • The UC luminescence properties and mechanism of Er{sup 3+}/Yb{sup 3+} co-doped NaLa(MoO{sub 4}){sub 2} was discussed. - Abstract: NaLa(MoO{sub 4}){sub 2}: RE{sup 3+} (RE{sup 3+} = Eu{sup 3+}, Sm{sup 3+}) microspheres have been synthesized at 180 °C via a facile EDTA-mediated hydrothermal route. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), photoluminescence (PL) spectra were employed to characterize the samples. It was found that the amount of EDTA in the initial solution was responsible for crystal phase and shape determination. The effect of Eu{sup 3+} and Sm{sup 3+} doping concentrations on the luminescent intensity was also investigated in details. Furthermore, the up-conversion (UC) emissions have been observed in a series of Er{sup 3+}/Yb{sup 3+} co-doped NaLa(MoO{sub 4}){sub 2} samples. Concentration dependent studies revealed that the optimal composition was realized for a 2% Er{sup 3+} and 10% Yb{sup 3+}-doping concentration.

  20. Ultrasmall, water dispersible, TWEEN80 modified Yb:Er:NaGd(WO4sub>)2 nanoparticles with record upconversion ratiometric thermal sensitivity and their internalization by mesenchymal stem cells.


    Cascales, Concepcion; Paino, Carlos; Bazán, Eulalia; Zaldo, Carlos


    This work presents the synthesis by coprecipitation of diamond shaped Yb:Er:NaGd(WO4sub>)2 crystalline nanoparticles (NPs) with diagonal dimensions in the 5-7 nm × 10-12 nm range which have been modified with TWEEN80 for their dispersion in water, and their interaction with mesenchymal stem cells (MSCs) proposed as cellular NP vehicles. These NPs belong to a large family of tetragonal Yb:Er:NaT(XO4sub>)2 (T=Y, La, Gd, Lu; X= Mo, W) compounds with green (2H11/2+4S3/24I15/2) Er-related upconversion (UC) efficiency comparable to that of Yb:Er:β-NaYF4sub> reference compound, but with a ratiometric thermal sensitivity (S) 2.5-3.5 times larger than that of the fluoride. At the temperature range of interest for biomedical applications (~293-317 K / 20-44 ºC) S= 108-118 × 10-4 K-1 for 20at%Yb:5at%Er:NaGd(WO4sub>)2 NPs, being the largest values so far reported using the 2H11/2/4S3/2 Er intensity ratiometric method. Cultured MSCs, incubated with these water NP emulsions, internalize and accumulate the NPs enclosed in endosomes/lysosomes. Incubations with up to 10 μg of NPs per ml of culture medium maintain cellular metabolism at 72 h. A thermal assisted excitation path is discussed as responsible for the UC behavior of Yb:Er:NaT(XO4sub>)2 compounds.

  1. A study of room-temperature LixMn1.5Ni0.5O4sub> solid solutions

    SciTech Connect

    Saravanan, Kuppan; Jarry, Angelique; Kostecki, Robert; Chen, Guoying


    Understanding the kinetic implication of solid-solution vs. biphasic reaction pathways is critical for the development of advanced intercalation electrode materials. Yet this has been a long-standing challenge in materials science due to the elusive metastable nature of solid solution phases. The present study reports the synthesis, isolation, and characterization of room-temperature LixMn1.5Ni0.5O4sub> solid solutions. In situ XRD studies performed on pristine and chemically-delithiated, micron-sized single crystals reveal the thermal behavior of LixMn1.5Ni0.5O4sub> (0 ≤ x ≤ 1) cathode material consisting of three cubic phases: LiMn1.5Ni0.5O4sub> (Phase I), Li0.5Mn1.5Ni0.5O4sub> (Phase II) and Mn1.5Ni0.5O4sub> (Phase III). A phase diagram capturing the structural changes as functions of both temperature and Li content was established. In conclusion, the work not only demonstrates the possibility of synthesizing alternative electrode materials that are metastable in nature, but also enables in-depth evaluation on the physical, electrochemical and kinetic properties of transient intermediate phases and their role in battery electrode performance.

  2. Micro-Raman and Micro-Infrared Spectroscopic Studies of Pb- and Au-Irradiated ZrSiO4sub>. Optical Properties, Structural Damage and Amorphization

    SciTech Connect

    Zhang, Ming; Boatner, Lynn A.; Salje, Ekhard; Ewing, Rodney C.; Daniel, Philippe; Weber, William J; Zhang, Yanwen; Farnan, Ian E.


    The optical properties of damaged, periodic and aperiodic domains created by Pb+ (280 keV) and Au4+ (10 MeV) implantation of zircon were studied using micro-infrared (IR) and micro-Raman spectroscopy. The Pb+ and Au4+ irradiations caused a dramatic decrease in the IR reflectivity similar to that observed for metamict natural zircon. The irradiation with 10 MeV Au4+ ions (to fluences of 1x1015 Au4+ ions/cm2) also results in the formation of an amorphized phase similar to that observed in metamict zircon. These results show that high-energy, heavy-ion irradiations provide a good simulation of the ballistic effects of the recoil nucleus of an alpha-decay event, and in both cases, the result is the creation of aperiodic domains. Additional IR and Raman features were recorded in samples irradiated with 280 keV Pb+ ions (to fluences of 1x1014 and 1x1015 Pb+ ions/cm2), indicating the formation of an irradiation-induced new phase(s). The frequencies of the features are consistent with lead silicates, ZrO2 and SiO2. The results show that spectral features of the Au4+ and Pb+ irradiated zircon are different from those of quenched ZrSiO4sub> melts, and the finding further confirms that the amorphous state produced by high-energy ion irradiations is structurally different from the glassy state that results from quenching a high temperature melt. In contrast to significant changes in the frequency and width of the Raman v3 band observed in metamict zircon, the Pb+ and Au4+ irradiations do not cause similar variations, indicating that the remaining zircon crystalline domains in irradiated samples have a crystalline structure with fewer defects than those of metamict zircon.

  3. Thermal expansion of phosphates with the NaZr{sub 2}(PO{sub 4}){sub 3} structure containing lanthanides and zirconium: R{sub 0.33}Zr{sub 2}(PO{sub 4}){sub 3} (R = Nd, Eu, Er) and Er{sub 0.33(1–x)} Zr{sub 0.25x}Zr{sub 2}(PO{sub 4}){sup 3}

    SciTech Connect

    Volgutov, V. Yu. Orlova, A. I.


    Phosphates R{sub 0.33}Zr{sub 2}(PO{sub 4}){sub 3} (R = Nd, Eu, or Er) and Er{sub 0.33(1–x)}Zr{sub 0.25}Zr{sub 2}(PO{sub 4}){sub 3} (x = 0, 0.25, 0.5, 0.75, 1.0) of the NaZr{sub 2}(PO{sub 4}){sub 3} family have been synthesized and investigated by high-temperature X-ray diffraction. The crystallochemical approach is used to obtain compounds with expected small and controllable thermal-expansion parameters. Phosphates with close-to-zero thermal-expansion parameters, including those with low thermal-expansion anisotropy, have been obtained: Nd{sub 0.33}Zr{sub 2}(PO{sub 4}){sub 3} with α{sub a} =–2.21 × 10{sup −6} °C{sup −1}, α{sub c} = 0.81 × 10{sup −6} °C{sup −1}, and Δα = 3.02 × 10{sup −6} °C{sup –1} and Er{sub 0.08}Zr{sub 0.19}Zr{sub 2}(PO{sub 4}){sub 3} with α{sub a} =–1.86 × 10{sup −6} °C{sup −1}, α{sub c} = 1.73 × 10{sup −6} °C{sup −1}, and Δα = 3.58 × 10{sup −6} °C{sup −1}.

  4. Dual Phase Li4sub>Ti5O12–TiO2 Nanowire Arrays As Integrated Anodes For High-rate Lithium-ion Batteries

    SciTech Connect

    Liao, Jin; Chabot, Victor; Gu, Meng; Wang, Chong M.; Xiao, Xingcheng; Chen, Zhongwei


    Lithium titanate (Li4sub>Ti5O12) is well known as a zero strain material inherently, which provides excellent long cycle stability as a negative electrode for lithium ion batteries. However, the low specific capacity (175 mA h g-1) limits it to power batteries although the low electrical conductivity is another intrinsic issue need to be solved. In this work, we developed a facile hydrothermal and ion-exchange route to synthesize the self-supported dual-phase Li4sub>Ti5O12–TiO2 nanowire arrays to further improve its capacity as well as rate capability. The ratio of Li4sub>Ti5O12 to TiO2 in the dual phase Li4sub>Ti5O12–TiO2 nanowire is around 2:1. The introduction of TiO2 into Li4sub>Ti5O12 increases the specific capacity. More importantly, by interface design, it creates a dual-phase nanostructure with high grain boundary density that facilitates both electron and Li ion transport. Compared with phase-pure nanowire Li4sub>Ti5O12 and TiO2 nanaowire arrays, the dual-phase nanowire electrode yielded superior rate capability (135.5 at 5 C, 129.4 at 10 C, 120.2 at 20 C and 115.5 mA h g-1 at 30 C). In-situ transmission electron microscope clearly shows the near zero deformation of the dual phase structure, which explains its excellent cycle stability.

  5. Selective Metal Exsolution in BaFe2-yMy(PO4sub>)2 (M = Co2+, Ni2+) Solid Solutions

    SciTech Connect

    Alcover, Ignacio Blazquez; Daviero-Minaud, Sylvie; David, Rénald; Filimonov, Dmitry; Huvé, Marielle; Attfield, J. Paul; Kabbour, Houria; Mentré, Olivier


    The 2D-Ising ferromagnetic phase BaFe2+2(PO4sub>)2 shows exsolution of up to one-third of its iron content (giving BaFe3+1.33(PO4sub>)2) under mild oxidation conditions, leading to nanosized Fe2O3 exsolved clusters. Here we have prepared BaFe2–yMy(PO4sub>)2 (M = Co2+, Ni2+; y = 0, 0.5, 1, 1.5) solid solutions to investigate the feasibility and selectivity of metal exsolution in these mixed metallic systems. For all the compounds, after 600 °C thermal treatment in air, a complete oxidation of Fe2+ to Fe3+ leaves stable M2+ ions, as verified by 57Fe Mössbauer spectroscopy, TGA, TEM, microprobe, and XANES. Furthermore, the size of the nanometric α-Fe2O3clusters coating the main phase strongly depends on the yM metal concentration. For M-rich phases the iron diffusion is hampered so that a significant fraction of superparamagnetic α-Fe2O3 particles (100% for BaFe0.5–xCo1.5(PO4sub>)2) was detected even at 78 K. Although Ni2+and Co2+ ions tend to block Fe diffusion, the crystal structure of BaFe0.67Co1(PO4sub>)2demonstrates a fully ordered rearrangement of Fe3+ and Co2+ ions after Fe exsolution. We found that the magnetic behaviors of the Fe-depleted materials are mostly dominated by antiferromagnetic exchange, while Co2+-rich compounds show metamagnetic transitions reminiscent of the BaCo2(PO4sub>)2 soft helicoidal magnet.

  6. Synthesis and photoluminescence properties of the high-brightness Eu{sup 3+}-doped M{sub 2}Gd{sub 4}(MoO{sub 4}){sub 7} (M=Li, Na) red phosphors

    SciTech Connect

    Zhao Chengchun; Yin Xin; Huang Fuqiang; Hang Yin


    A series of red-emitting phosphors Eu{sup 3+}-doped M{sub 2}Gd{sub 4}(MoO{sub 4}){sub 7} (M=Li, Na) have been successfully synthesized at 850 Degree-Sign C by solid state reaction. The excitation spectra of the two phosphors reveal two strong excitation bands at 396 nm and 466 nm, respectively, which match well with the two popular emissions from near-UV and blue light-emitting diode chips. The intensity of the emission from {sup 5}D{sub 0} to {sup 7}F{sub 2} of M{sub 2}(Gd{sub 1-x}Eu{sub x}){sub 4}(MoO{sub 4}){sub 7} phosphors with the optimal compositions of x=0.85 for Li or x=0.70 for Na is about five times higher than that of Y{sub 2}O{sub 3}:Eu{sup 3+}. The quantum efficiencies of the entitled phosphors excited under 396 nm and 466 nm are also investigated and compared with commercial phosphors Sr{sub 2}Si{sub 5}N{sub 8}:Eu{sup 2+} and Y{sub 3}A{sub 5}O{sub 12}:Ce{sup 3+}. The experimental results indicate that the Eu{sup 3+}-doped M{sub 2}Gd{sub 4}(MoO{sub 4}){sub 7} (M=Li, Na) phosphors are promising red-emitting phosphors pumped by near-UV and blue light. - Graphical Abstract: The intensity of the red emission of M{sub 2}(Gd{sub 1-x}Eu{sub x}){sub 4}(MoO{sub 4}){sub 7} (M=Li, Na) phosphors with the optimal compositions is about five times higher than that of Y{sub 2}O{sub 3}:Eu{sup 3+}. Highlights: Black-Right-Pointing-Pointer Two novel Eu{sup 3+}-doped red phosphors (Na{sub 2}Gd{sub 4}(MoO{sub 4}){sub 2}, Li{sub 2}Gd{sub 4}(MoO{sub 4}){sub 7}) were synthesized. Black-Right-Pointing-Pointer Their emission intensities are about five times higher than that of Y{sub 2}O{sub 3}:Eu{sup 3+}. Black-Right-Pointing-Pointer Their quantum efficiencies are higher than that of commercial red phosphor Sr{sub 2}Si{sub 5}N{sub 8}:Eu{sup 2+}.

  7. Identification of the dominant photochemical pathways and mechanistic insights to the ultrafast ligand exchange of Fe(CO)5 to Fe(CO)4sub>EtOH

    SciTech Connect

    Kunnus, K.; Josefsson, I.; Rajkovic, I.; Schreck, S.; Quevedo, W.; Beye, M.; Weniger, C.; Grübel, S.; Scholz, M.; Nordlund, D.; Zhang, W.; Hartsock, R. W.; Gaffney, K. J.; Schlotter, W. F.; Turner, J. J.; Kennedy, B.; Hennies, F.; de Groot, F. M. F.; Techert, S.; Odelius, M.; Wernet, Ph.; Föhlisch, A.


    We utilized femtosecond time-resolved resonant inelastic X-ray scattering and ab initio theory to study the transient electronic structure and the photoinduced molecular dynamics of a model metal carbonyl photocatalyst Fe(CO)5 in ethanol solution. We propose mechanistic explanation for the parallel ultrafast intra-molecular spin crossover and ligation of the Fe(CO)4sub> which are observed following a charge transfer photoexcitation of Fe(CO)5 as reported in our previous study [Wernet et al., Nature 520, 78 (2015)]. We find that branching of the reaction pathway likely happens in the 1A1 state of Fe(CO)4sub>. A sub-picosecond time constant of the spin crossover from 1B2 to 3B2 is rationalized by the proposed 1B21A13B2 mechanism. Ultrafast ligation of the 1B2 Fe(CO)4sub> state is significantly faster than the spin-forbidden and diffusion limited ligation process occurring from the 3B2 Fe(CO)4sub> ground state that has been observed in the previous studies. We propose that the ultrafast ligation occurs via 1B21A11A' Fe(CO)4sub>EtOH pathway and the time scale of the 1A1 Fe(CO)4sub> state ligation is governed by the solute-solvent collision frequency. In conclusion, our study emphasizes the importance of understanding the interaction of molecular excited states with the surrounding environment to explain the relaxation pathways of photoexcited metal carbonyls in solution.

  8. Design and syntheses of hybrid metal–organic materials based on K{sub 3}[M(C{sub 2}O{sub 4}){sub 3}]·3H{sub 2}O [M(III)=Fe, Al, Cr] metallotectons

    SciTech Connect

    Sun, Yayong; Zong, Yingxia; Ma, Haoran; Zhang, Ao; Liu, Kang; Wang, Debao Wang, Wenqiang; Wang, Lei


    By using K{sub 3}[M(C{sub 2}O{sub 4}){sub 3}]·3H{sub 2}O [M(III)=Fe, Al, Cr] (C{sub 2}O{sub 4}{sup 2−}=oxalate) metallotectons as the starting material, we have synthesized eight novel complexes with formulas [{Fe(C_2O_4)_2(H_2O)_2}{sub 2}]·(H–L{sub 1}){sub 2}·H{sub 2}O 1, [Fe(C{sub 2}O{sub 4})Cl{sub 2}]·(H{sub 2}–L{sub 2}){sub 0.5}·(L{sub 2}){sub 0.5}·H{sub 2}O 2, [{Fe(C_2O_4)_1_._5Cl_2}{sub 2}]·(H–L{sub 3}){sub 4}3, [Fe{sub 2}(C{sub 2}O{sub 4})Cl{sub 8}]·(H{sub 2}–L{sub 4}){sub 2}·2H{sub 2}O 4, K[Al(C{sub 2}O{sub 4}){sub 3}]·(H{sub 2}–L{sub 5})·2H{sub 2}O 5, K[Al(C{sub 2}O{sub 4}){sub 3}]·(H–L{sub 6}){sub 2}·2H{sub 2}O 6, K[Cr(C{sub 2}O{sub 4}){sub 3}]·2H{sub 2}O 7, Na[Fe(C{sub 2}O{sub 4}){sub 3}]·(H–L{sub 6}){sub 2}·2H{sub 2}O 8 (with L{sub 1}=4-dimethylaminopyridine, L{sub 2}=2,3,5,6-tetramethylpyrazine, L{sub 3}=2-aminobenzimidazole, L{sub 4}=1,4-bis-(1H-imidazol-1-yl)benzene, L{sub 5}=1,4-bis((2-methylimidazol-1-yl)methyl)benzene, L{sub 6}=2-methylbenzimidazole). Their structures have been determined by single-crystal X-ray diffraction analyses, elemental analyses, IR spectra and thermogravimetric analyses. Compound 3 is a 2D H-bonded supramolecular architecture. Others are 3D supramolecular structures. Compound 1 shows a [Fe(C{sub 2}O{sub 4}){sub 2}(H{sub 2}O){sub 2}]{sup −} unit and 3D antionic H-bonded framework. Compound 2 features a [Fe(C{sub 2}O{sub 4})Cl{sub 2}]{sup -} anion and 1D iron-oxalate-iron chain. Compound 3 features a [Fe{sub 2}(C{sub 2}O{sub 4}){sub 3}Cl{sub 4}]{sup 4−} unit. Compound 4 features distinct [Fe{sub 2}(C{sub 2}O{sub 4})Cl{sub 8}]{sup 4−} units, which are mutual linked by water molecules to generated a 2D H-bonded network. Compound 5 features infinite ladder-like chains constructed by [Al(C{sub 2}O{sub 4}){sub 3}]{sup 3−} units and K{sup +} cations. The 1D chains are further extended into 3D antionic H-bonded framework through O–H···O H-bonds. Compounds 6–8 show 2D [KAl(C{sub 2}O

  9. X-ray diffraction investigation of Cs/sub 2/UO/sub 2/(SeO/sub 4/)/sub 2//centered dot/2H/sub 2/O

    SciTech Connect

    Serezhkina, L.B.; Tatarinova, E.E.; Serezhkin, V.N.


    The crystallographic characteristics of Cs/sub 2/UO/sub 2/(SeO/sub 4/)/sub 2//centered dot/2H/sub 2/O were established. Assumptions regarding the structure of the compound and its dehydration products are expressed taking into account data from IR spectroscopy and thermography. As a result of additional experiments, we have ascertained that Cs/sub 2/UO/sub 2/(SeO/sub 4/)/sub 2//centered dot/2H/sub 2/O crystals that are suitable for x-ray diffraction study are formed by slow cooling from 330K to 290 K of a saturated aqueous solution containing equimolar amounts of cesium and uranyl selenates.

  10. Neutron-scattering evidence for a periodically modulated superconducting phase in the underdoped cuprate La1.905Ba0.095CuO4sub>

    SciTech Connect

    Xu, Zhijun; Stock, C.; Chi, Songxue; Kolesnikov, A. I.; Xu, Guangyong I.; Gu, Genda; Tranquada, J. M.


    The role of antiferromagnetic spin correlations in high-temperature superconductors remains a matter of debate. We present inelastic neutron-scattering evidence that gapless spin fluctuations coexist with superconductivity in La1.905Ba0.095CuO4sub>. Furthermore, we observe that both the low-energy magnetic spectral weight and the spin incommensurability are enhanced with the onset of superconducting correlations. We propose that the coexistence occurs through intertwining of spatial modulations of the pair wave function and the antiferromagnetic correlations. This proposal is also directly relevant to sufficiently underdoped La2-xSrxCuO4sub> and YBa2Cu3O6+x.

  11. Growth of the (In{sub 2}S{sub 3}){sub x}(FeIn{sub 2}S{sub 4}){sub 1-x} single crystals and properties of photoelectric structures on their basis

    SciTech Connect

    Bodnar, I. V.; Rud, V. Yu.; Rud, Yu. V.; Terukov, E. I.


    Complete mutual solubility in the (In{sub 2}S{sub 3}){sub x}(FeIn{sub 2}S{sub 4}){sub 1-x} system is established. The technology is developed, and single crystals of the continuous series of the (In{sub 2}S{sub 3}){sub x}(FeIn{sub 2}S{sub 4}){sub 1-x} solid solutions are grown for the first time. The linear dependence of the unit cell parameter of single crystals with a cubic spinel lattice on the solid solution composition is found. First, photosensitive Schottky barriers are fabricated, and then, based on studies of their photosensitivity, the character of band-to-band transition is discussed and the values of the band gap depending on the atomic composition are estimated. The possibility of using the obtained solid solutions as broadband photoconverters of optical radiation is revealed.

  12. Strain-relaxation and critical thickness of epitaxial La1.85Sr0.15CuO4sub> films

    SciTech Connect

    Meyer, Tricia L; Jiang, Lu; Park, Sungkyun; Egami, Takeshi; Lee, Ho Nyung


    We report the thickness-dependent strain-relaxation behavior and the associated impacts upon the superconductivity in epitaxial La1.85Sr0.15CuO4sub> films grown on different substrates, which provide a range of strain. We have found that the critical thickness for the onset of superconductivity in La1.85Sr0.15CuO4sub> films is associated with the finite thickness effect and epitaxial strain. In particular, thin films with tensile strain greater than ~0.25% revealed no superconductivity. We attribute this phenomenon to the inherent formation of oxygen vacancies that can be minimized via strain relaxation.

  13. Temperature dependence of the luminescence of calcium-magnesium phosphate Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+}, a blue-emitting material for white light-emitting diodes

    SciTech Connect

    Zhang, Xinmin; Pan, Qi; Kim, Sun Il; Yu, Young Moon; Seo, Hyo Jin


    Graphical abstract: - Highlights: • Emission spectrum at 20 K confirms that Eu{sup 2+} ions occupy three sites. • Decay curves of three types of Eu{sup 2+} reflect the characteristics of energy transfer. • The Eu(I) emission is thermally quenched at 323 K. • Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+} has good thermal stability. • Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+} is a promising phosphor for near UV excited white LEDs. - Abstract: A blue-emitting phosphor Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+} peaking at 450 nm was synthesized by a solid state reaction. The XRD patterns, luminescence properties, decay curves of samples as well as their thermal quenching and comparing the luminescence properties with that of commercial material were investigated. At 20 K, the emission spectrum exhibiting two distinct bands peaking at 437 and 473 nm with a shoulder peak at 510 nm can be attributed to the overlap of Eu(I), Eu(II) and Eu(III) emission bands. At 423 K the PL intensity decreases to 80% of the value at room temperature, and the emission wavelength shifts toward high energy. The derived activation energy indicates that the lowest energy level of the Eu{sup 2+} 4f{sup 6}5d{sup 1} state is well isolated from the host lattice conduction band. The PL spectra and chromaticity coordinates are close to those of BAM. Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+} could be a potential candidate for near-UV excited white LEDs.

  14. Microwave-Assisted Synthesis of Silver Vanadium Phosphorus Oxide, Ag2VO2PO4sub> : Crystallite Size Control and Impact on Electrochemistry

    SciTech Connect

    Huang, Jianping; Marschilok, Amy C.; Takeuchi, Esther S.; Takeuchi, Kenneth J.


    We study silver vanadium phosphorus oxide, Ag2VO2PO4sub>, that is a promising cathode material for Li batteries due in part to its large capacity and high current capability. Herein, a new synthesis of Ag2VO2PO4sub> based on microwave heating is presented, where the reaction time is reduced by approximately 100× relative to other reported methods, and the crystallite size is controlled via synthesis temperature, showing a linear correlation of crystallite size with temperature. Notably, under galvanostatic reduction, the Ag2VO2PO4sub> sample with the smallest crystallite size delivers the highest capacity and shows the highest loaded voltage. Further, pulse discharge tests show a significant resistance decrease during the initial discharge coincident with the formation of Ag metal. Thus, the magnitude of the resistance decrease observed during pulse tests depends on the Ag2VO2PO4sub> crystallite size, with the largest resistance decrease observed for the smallest crystallite size. Additional electrochemical measurements indicate a quasi-reversible redox reaction involving Li+ insertion/deinsertion, with capacity fade due to structural changes associated with the discharge/charge process. In summary, this work demonstrates a faster synthetic approach for bimetallic polyanionic materials which also provides the opportunity for tuning of electrochemical properties through control of material physical properties such as crystallite size.

  15. Structure electronic and ionic conductivity study versus Ca content in Ca{sub 10-x}Sr{sub x}(PO{sub 4}){sub 6}F{sub 2} apatites

    SciTech Connect

    Sghir, B.; Hlil, E.K.; Laghzizil, A.; Boujrhal, F.Z.; Cherkaoui El Moursli, R.; Fruchart, D.


    Substitution effect on the crystallographic structure in Ca{sub 10-x}Sr{sub x}(PO{sub 4}){sub 6}F{sub 2} solid solution are studied by X-ray diffraction patterns and Rietveld refinements. Full potential electronic structure calculations based on LCAO (linear combination atomic orbital) are also performed using the obtained crystallographic parameters. DOS modification and the charge transfer are estimated versus the calcium content. According to the complex impedance method, ionic conductivity changes are explained.

  16. A limited role for carbonic anhydrase in C4sub> photosynthesis as revealed by a ca1ca2 double mutant in maize.

    SciTech Connect

    Studer, Anthony J.; Gandin, Anthony; Kolbe, Allison R.; Wang, Lin; Cousins, Asaph B.; Brutnell, Thomas P.


    Carbonic anhydrase (CA) catalyzes the first biochemical step of the carbon concentrating mechanism of C4sub> plants, and in C4sub> monocots, it has been suggested that CA activity is near limiting for photosynthesis. Here, we test this hypothesis through the characterization of transposon induced mutant alleles of Ca1 and Ca2 in Zea mays. In addition, these two isoforms account for more than 85% of the CA transcript pool. A significant change in isotopic discrimination is observed in mutant plants, which have as little as 3% of wild-type CA activity, but surprisingly, photosynthesis is not reduced under current or elevated pCO2. However, growth and rates of photosynthesis under sub-ambient pCO2 are significantly impaired in the mutants. These findings suggest, that while CA is not limiting for C4sub> photosynthesis in Z. mays at current pCO2, it likely maintains high rates of photosynthesis when CO2 availability is reduced. Current atmospheric CO2 levels now exceed 400 ppm (~40.53 Pa) and contrast the low CO2 partial pressure (pCO2) conditions under which C4sub> plants expanded their range ~10 million years ago when the global atmospheric CO2 was below 300 ppm (~30.40 Pa). Thus, as CO2 levels continue to rise, selective pressures for high levels of CA may be limited to arid climates where stomatal closure reduces CO2 availability to the leaf.

  17. Nonstoichiometry and Transport Properties of Ca3Co4sub>±xO9+δ (x = 0 – 0.4)

    SciTech Connect

    Zhou, Xiao Dong; Pederson, Larry R.; Thomsen, Edwin C.; Nie, Zimin; Coffey, Greg W.


    Nonstoichiometries of Ca3Co4sub>O9+δ and transport properties of Ca3Co4±xO9+δ were investigated. At 1100°C, Ca3Co4sub>O9+δ transformed to CaO and CoO. The reaction products offer a precise baseline for thermogravimetric analysis. At room temperature, δ in Ca3Co4sub>O9+δ is 0.38, which decreases at T ~450°C, indicating the onset point of the formation of oxygen vacancies, and δ is ~0.20 at 900°C. Correspondingly, the average Co valence state is 3.19 at room temperature and 3.10 at 900°C. In contrast to conventional defect chemistry theory in p-type oxide conductors, the formation of oxygen vacancies in Ca3Co4sub>O9+δ has a negligible impact on the carrier density of holes, indicating that oxygen vacancies and the redox couple responsible for hole carriers are in different layers. With control over the ratio of Ca/Co, the phase boundary for the misfit layered structure is between Ca3Co3.95O9+δ and Ca3Co4.05O9+δ. Beyond the phase boundary, the second phase is present, which effectively lowers the electrical conductivity while increasing the Seebeck coefficient.

  18. Structural phase diagram for ultra-thin epitaxial Fe3O4sub> / MgO(0 01) films: thickness and oxygen pressure dependence

    SciTech Connect

    Alraddadi, S.; Hines, W.; Yilmaz, T.; Gu, G. D.; Sinkovic, B.


    A systematic investigation of the thickness and oxygen pressure dependence for the structural properties of ultra-thin epitaxial magnetite (Fe3O4sub>) films has been carried out; for such films, the structural properties generally differ from those for the bulk when the thickness ≤10 nm. Iron oxide ultra-thin films with thicknesses varying from 3 nm to 20 nm were grown on MgO (001) substrates using molecular beam epitaxy under different oxygen pressures ranging from 1 × 10-7 torr to 1 × 10-5 torr. The crystallographic and electronic structures of the films were characterized using low energy electron diffraction (LEED) and x-ray photoemission spectroscopy (XPS), respectively. Moreover, the quality of the epitaxial Fe3O4sub> ultra-thin films was judged by magnetic measurements of the Verwey transition, along with complementary XPS spectra. We observed that under the same growth conditions the stoichiometry of ultra-thin films under 10 nm transforms from the Fe3O4sub> phase to the FeO phase. In this work, a phase diagram based on thickness and oxygen pressure has been constructed to explain the structural phase transformation. It was found that high-quality magnetite films with thicknesses ≤20 nm formed within a narrow range of oxygen pressure. An optimal and controlled growth process is a crucial requirement for the accurate study of the magnetic and electronic properties for ultra-thin Fe3O4sub> films. Furthermore, these results are significant because they may indicate a general trend in the growth of other oxide films, which has not been previously observed or considered.

  19. Synthesis, crystal structure and optical investigation of the new phosphates: Na{sub 7}Mg{sub 13}Ln(PO{sub 4}){sub 12} (Ln=La, Eu)

    SciTech Connect

    Jerbi, Hasna; Hidouri, Mourad; Glorieux, Benoit; Darriet, Jacques; Garcia, Alain; Jubera, Veronique; Ben Amara, Mongi


    Two new isostructural rare earth phosphates Na{sub 7}Mg{sub 13}Ln(PO{sub 4}){sub 12} (Ln=La, Eu) have been synthesized and investigated by X-ray diffraction and optical measurements. They crystallize in the orthorhombic system with the Cmc2{sub 1} space group (Z=4). The crystal structure exhibits a new type of framework built up from LnO{sub 8} (Ln=La, Eu), MO{sub 6} (M=0.5Mg+0.5Na) and MgO{sub x} (x=5, 6) polyhedra and PO{sub 4} tetrahedra linked by common corner, edge or face. It can be described in terms of [Mg{sub 4}MP{sub 4}O{sub 22}]{sub {infinity}} layers stacked along the a direction. These layers are interconnected by [Mg{sub 4}LnP{sub 4}O{sub 36}]{sub {infinity}} undulating chains spreading along the b direction. This framework delimits 6 distinct cavities occupied by Na{sup +} cations. The results of the optical study of Na{sub 7}Mg{sub 13}La{sub 1-x}Eu{sub x}(PO{sub 4}){sub 12} (x=0, 0.02, 0.1, 1) reveal the presence of two different Eu{sup 3+} ion environments whereas the X-ray study predicts the existence of only one Eu site. This difference can be explained by the possible presence of the europium element in the sodium sites with small occupancies which cannot be detected by the X-ray structural determination. - Graphical abstract: Emission spectra of Na{sub 7}Mg{sub 13}Eu(PO{sub 4}){sub 12} and Na{sub 7}Mg{sub 13}La{sub 0.9}Eu{sub 0.1}(PO{sub 4}){sub 12} compounds for {lambda}{sub exc}=240, 290 and 393.2 nm.

  20. Synthetic and spectroscopic studies of vanadate glaserites II: Photoluminescence studies of Ln:K{sub 3}Y(VO{sub 4}){sub 2} (Ln=Eu, Er, Sm, Ho, or Tm)

    SciTech Connect

    Kimani, Martin M. McMillen, Colin D. Kolis, Joseph W.


    Glaserite-type potassium yttrium double vanadates (K{sub 3}Y(VO{sub 4}){sub 2}) doped with Eu{sup 3+}, Er{sup 3+}, Sm{sup 3+}, Ho{sup 3+}, or Tm{sup 3+} have been synthesized by solid state reactions at 1000 °C for 48 h and their photoluminescence properties investigated. Efficient energy transfer from the vanadate group to the rare earth ion has been established by photoluminescence investigation. Ultraviolet excitation into the metal to ligand charge transfer band of the vanadate groups results in orange-red, blue and green emissions from Eu{sup 3+} (592 nm), Sm{sup 3+} (602 nm), Tm{sup 3+} (475 nm), Er{sup 3+} (553 nm), and Ho{sup 3+} (541–551 nm) dopant ions. The emission intensities of the lanthanide-doped K{sub 3}Y(VO{sub 4}){sub 2} powders were studied as a function of dopant ion concentrations. Over the concentration ranges studied, no emission quenching was observed for Eu{sup 3+} or Ho{sup 3+} dopants, while Er{sup 3+}, Sm{sup 3+} and Tm{sup 3+} dopants did exhibit such effects for dopant ion concentrations greater than 5%, probably due to cross relaxation processes. - Graphical abstract: Synthesis and photoluminescence in vanadate glaserites. - Highlights: • K{sub 3}Y(VO{sub 4}){sub 2} doped with Eu, Er, Tm, Sm, or Ho were synthesized via solid-state reactions. • Photoluminescence properties are investigated. • The lanthanide doped K{sub 3}Y(VO{sub 4}){sub 2} compounds revealed efficient energy transfer from the vanadate group to the rare earth ions. • The presented compounds are promising materials for light display systems, lasers, and optoelectronic devices.

  1. Consequences of Optimal Bond Valence on Structural Rigidity and Improved Luminescence Properties in SrxBa2-xSiO4sub>:Eu2+ Orthosilicate Phosphors

    SciTech Connect

    Denault, Kristin A.; Brgoch, Jakoah; Gaultois, Michael W.; Mikhailovsky, Alexander; Petry, Ralf; Winkler, Holger; DenBaars, Steven P.; Seshadri, Ram


    The orthosilicate phosphors SrxBa2–xSiO4sub>:Eu2+ have now been known for over four decades and have found extensive recent use in solid-state white lighting. It is well-recognized in the literature and in practice that intermediate compositions in the solid-solutions between the orthosilicates Sr2SiO4sub> and Ba2SiO4sub> yield the best phosphor hosts when the thermal stability of luminescence is considered. We employ a combination of synchrotron X-ray diffraction, total scattering measurements, density functional theory calculations, and low-temperature heat capacity measurements, in conjunction with detailed temperature- and time-resolved studies of luminescence properties to understand the origins of the improved luminescence properties. We observe that in the intermediate compositions, the two cation sites in the crystal structure are optimally bonded as determined from bond valence sum calculations. Optimal bonding results in a more rigid lattice, as established by the intermediate compositions possessing the highest Debye temperature, which are determined experimentally from low-temperature heat capacity measurements. Greater rigidity in turn results in the highest luminescence efficiency for intermediate compositions at elevated temperatures.

  2. Angular Distribution and Recoil Effect for 1 MeV Au+ Ions through a Si3N4sub> Thin Foil

    SciTech Connect

    Jin, Ke; Zhu, Zihua; Manandhar, Sandeep; Liu, Jia; Chen, Chien-Hung; Shutthanandan, V.; Thevuthasan, Suntharampillai; Weber, William J.; Zhang, Yanwen


    The Stopping and Range of Ions in Matter (SRIM) code has been widely used to predict nuclear stopping power and angular distribution of ion-solid collisions. However, experimental validation of the predictions is insufficient for slow heavy ions in nonmetallic compounds. In this work, time-of-flight secondary ion mass spectrometry (ToF-SIMS) is applied to determine the angular distribution of 1 MeV Au ions after penetrating a Si3N4sub> foil with a thickness of ~100 nm. The exiting Au ions are collected by a Si wafer located ~14 mm behind the Si3N4sub> foil, and the resulting 2-dimensional distribution of Au ions on the Si wafer is measured by ToF-SIMS. The SRIM-predicted angular distribution of Au ions through the Si3N4sub> thin foil is compared with the measured results, indicating that SRIM slightly overestimates the nuclear stopping power by up to 10%. In addition, thickness reduction of the suspended Si3N4 foils induced by 1 MeV Au ion irradiation is observed with an average loss rate of ~107 atom/ion.

  3. Synthesis and structural characterization of a flexible metal organic framework {[Ni(dpbz)][Ni(CN4sub>]}n, dpbz = 1,4-bis(4-pyridyl)benzene) with an unusual Ni-N bond

    SciTech Connect

    Wong-Ng, Winnie; Culp, Jeffrey T.; Chen, Yu-S.; Deschamps, Jeffrey R.; Marti, Anna


    The chartreuse monoclinic Ni-dpbz (Ni(L)[Ni(CN)4sub>], (L = 1,4-Bis(4-pyridyl)benzene, or dpbz) crystal assumes a pillared structure with layers defined by 2-D Ni[Ni(CN)4sub>]n nets and dpbz ligands as pillars, linking between coordinated Ni sites. In addition to the hysteretic adsorption/desorption feature of Ni-dpbz, in half of the parallelepiped-shape space enclosed by the pillars and nets, an additional dpbz ligand was found to link between the open ends of two four-fold Ni sites. This arrangement results in an unusual 5-fold pseudo square-pyramid environment for Ni and a significantly long Ni–N distance of 2.369(4) Å. The presence of disordered dimethyl sulfoxide (DMSO) solvent molecules give rise to the formula of Ni(dpbz)[Ni(CN)4sub>]·½dpbz·0.44DMSO. Sorption isotherms showed flexible behavior during the adsorption and desorption of CO2.

  4. Single-phase tunable white-light-emitting Sr3 La(PO4sub>)3 : Eu2+, Mn2+ phosphor for white LEDs.


    Wang, Zhijun; Lou, Shuqin; Li, Panlai; Lian, Zhenggang


    A novel, near-ultraviolet-excited white-light-emitting phosphor Sr3La(PO4sub>)3:Eu2+, Mn2+ was synthesized by the solid-state method. Luminescence properties and the energy transfer mechanism were investigated in detail by photoluminescence spectra and decay curves. With the energy transfer between Eu2+ and Mn2+, a cold white light with chromaticity coordinates of (0.2790, 0.2273), correlated color temperature of 6501 K, Ra of 70, and external quantum efficiency of 35.5% was realized by changing the ratios of Eu2+ and Mn2+ in the Sr3La(PO4sub>)3:Eu2+, Mn2+ phosphors. Resonant energy transfer from Eu2+ to Mn2+  ions has been demonstrated to be a dipole-dipole mechanism in Sr3La(PO4sub>)3. The energy transfer efficiency increases with Mn2+ concentration increasing, and reaches a maximum of 55.6%.

  5. Theoretical analysis of performance enhancement in GeSn/SiGeSn light-emitting diode enabled by Si3N4sub> liner stressor technique.


    Zhang, Qingfang; Liu, Yan; Han, Genquan; Shao, Yao; Gao, Xi; Zhang, Chunfu; Zhang, Jincheng; Hao, Yue


    We comprehensively investigate the energy band diagrams, carrier distribution, spontaneous emission rate rsp, and the internal quantum efficiency ηIQE in the lattice-matched GeSn/SiGeSn double heterostructure light-emitting diode (LED) wrapped in a Si3N4sub> liner stressor. The large tensile strain introduced into the device by the expansion of the Si3N4sub> liner is characterized by numerical simulation. A lower Sn composition required for the indirect to direct bandgap transition and a higher ratio of the electron occupation probability in the Γ conduction valley are achieved in the tensile strained GeSn/SiGeSn LED in comparison with the relaxed device. Analytical calculation shows that the tensile strained LED wrapped in the Si3N4sub> liner stressor exhibits the improved rsp and ηIQE compared to the relaxed device. rsp and ηIQE also can be enhanced by increasing Sn composition, carrier injection density, and n-type doping concentration in the GeSn active layer.

  6. Influence of Ga-concentration on the electrical and magnetic properties of magnetoelectric CoGaxFe2–xO4sub>/BaTiO3 composite

    SciTech Connect

    Ni, Yan; Zhang, Zhen; Nlebedim, Cajetan I.; Jiles, David C.


    Multiferroic materials exhibit magnetoelectric (ME) coupling and promise new device applications including magnetic sensors, generators, and filters. An effective method for developing ME materials with enhanced ME effect is achieved by the coupling through the interfacial strain between piezoelectric and magnetostrictive materials. In this study, the electrical and magnetic properties of Ga doped magnetoelectric CoGaxFe2–xO4sub>/BaTiO3 composite are studied systematically. It is found that Ga doping improves the sensitivity of magnetoelastic response and stabilizes the magnetic phase of the composites. More importantly, Ga doping reduces the electrical conductivity of composite, as well as the dielectric loss. An enhancement of the electrostrain with doping Ga is also observed. Quantitative estimation indicates that magnetoelectric coupling is enhanced for Ga-doped CoGaxFe2–xO4sub>/BaTiO3 composites. As a result, the present work is beneficial to the practical application of composite CoFe2O4sub>/BaTiO3-based multiferroic materials.

  7. Monoclinic Tm3+:MgWO4sub>: a promising crystal for continuous-wave and passively Q-switched lasers at ∼2  μm.


    Loiko, Pavel; Serres, Josep Maria; Mateos, Xavier; Aguiló, Magdalena; Díaz, Francesc; Zhang, Lizhen; Lin, Zhoubin; Lin, Haifeng; Zhang, Ge; Yumashev, Konstantin; Petrov, Valentin; Griebner, Uwe; Wang, Yicheng; Choi, Sun Yung; Rotermund, Fabian; Chen, Weidong


    Monoclinic thulium-doped magnesium monotungstate, Tm3+:MgWO4sub>, is promising for efficient power-scalable continuous-wave (CW) and passively Q-switched lasers at >2  μm. Under diode pumping at 802 nm, a compact CW laser based on Z-cut Tm:MgWO4sub> generated 3.09 W at 2022-2034 nm with a slope efficiency of 50% which represents the highest output power ever achieved with this type of laser host. Stable passive Q-switching of the Tm:MgWO4sub> laser is demonstrated for the first time, to the best of our knowledge, using single-walled carbon nanotubes, graphene, and Cr2+:ZnS saturable absorbers. Using the latter, the best performance is achieved with 16.1 μJ/13.6 ns pulses at 2017.8 nm with a maximum average output power of 0.87 W and a peak power of 1.18 kW.

  8. Engineering of mixed pairing and non-Abelian Majorana states in chiral p-wave superconductor Sr2RuO4sub> and other materials

    SciTech Connect

    Liu, Ying


    This project deals with odd-parity superconductor Sr2RuO4sub> and related material systems, aiming at understanding the unconventional nature of superconductivity in this material. An odd-parity superconductor is expected to feature a novel topological object, the half-flux-quantum vortex that hosts a Majorana anyons. Majorana anyons carry non-Abelian statistics that can be used as the building block for constructing a fault-tolerated topological quantum computer. Half-flux-quantum vortices form in an odd-parity superconductor because of the availability of charge neutral spin supercurrent in addition to the normal supercurrent. Half-height magnetization steps were found in a cantilever magnetometry measurement of doubly connected mesoscopic samples of Sr2RuO4sub> in the presence of an in-plane magnetic field (J. Jang, D. G. Ferguson, V. Vakaryuk, R. Budakian, S. B. Chung, P. M. Goldbart, and Y. Maeno, Science 331, 186 (2011)), which suggests the presence of a half-flux-quantum (Φ0/2 = h/4e) state. Evidence for half flux quantum states, which can be viewed as coreless half vortices, was obtained in mesoscopic samples of Sr2RuO4sub> in the torque magnetomitry measurements. However, the existence of such an important property has not been confirmed by any other independent measurement.

  9. Influence of temperature and frequency on ionic conductivity of Li{sub 3}PO{sub 4}–Pb{sub 3}(PO{sub 4}){sub 2}–BiPO{sub 4} phosphate glasses

    SciTech Connect

    El Moudane, M.; El Maniani, M.; Sabbar, A.; Ghanimi, A.; Tabyaoui, M.; Bellaouchou, A.; Guenbour, A.


    Highlights: • Results of ionic conductivities of Li{sub 3}PO{sub 4}–Pb{sub 3}(PO{sub 4}){sub 2}–BiPO{sub 4} phosphate glasses. • Determination of glass transition temperature using DSC method. • Study of temperature and frequency on ionic conductivity of Li{sub 3}PO{sub 4}–Pb{sub 3}(PO{sub 4}){sub 2}–BiPO{sub 4} phosphate glasses. - Abstract: Lithium–Lead–Bismuth phosphates glasses having, a composition 30Li{sub 3}PO{sub 4}–(70 − x)Pb{sub 3}(PO{sub 4}){sub 2}–xBiPO{sub 4} (45 ≤ x ≤ 60 mol%) were prepared by using the melt quenching method 1000 °C. The thermal stability of theses glasses increases with the substitution of Bi{sub 2}O{sub 3} with PbO. The ionic conductivity of all compositions have been measured over a wide temperature (200–500 °C) and frequency range (1–106 Hz). The ionic conductivity data below and above T{sub g} follows Arrhenius and Vogel–Tamman–Fulcher (VTF) relationship, respectively. The activation energies are estimated and discussed. The dependence in frequency of AC conductivity is found to obey Jonscher’s relation.

  10. Electron-irradiation induced phase transformation in La{sub 1/3}Zr{sub 2}(PO{sub 4}){sub 3}: La{sup 3+} displacement in a preserved NASICON framework

    SciTech Connect

    Crosnier-Lopez, M.P. . E-mail:; Barre, M.; Le Berre, F.; Fourquet, J.L.


    The La{sub 1/3}Zr{sub 2}(PO{sub 4}){sub 3} NASICON-type compound (S.G. P3-bar - neutron and X-ray diffraction experiments) is investigated by transmission electron microscopy (TEM) technique, selected area electron diffraction (SAED) and high-resolution electron microscopy (HREM), in order to study locally the lanthanum distribution. An irreversible structural transformation (P-bar -bar -bar ->P-bar c-bar ->R-bar -bar -bar ) is observed, without modification of the atomic content and cell size, as soon as the phase is illuminated by the electron beam. The progressive disappearance of the spots which do not check the R conditions on the SAED patterns is clearly shown along two zone axis, [001] and [100]. This transformation implies the displacement of the two La{sup 3+} cations in a preserved classical [Zr{sub 2}(PO{sub 4}){sub 3}]{sup -} network. This interesting behavior is in good agreement with the La{sup 3+} ionic conductivity observed in La{sub 1/3}Zr{sub 2}(PO{sub 4}){sub 3} (4.09x10{sup -7}Scm{sup -1} at 700 deg. C). To our knowledge, this is the first time that a complete TEM study is done on a NASICON-type phase.

  11. Temperature-induced changes in the single-crystal structure of K{sub 9}H{sub 7}(SO{sub 4}){sub 8} {center_dot} H{sub 2}O

    SciTech Connect

    Makarova, I. P. Grebenev, V. V.; Chernaya, T. S.; Verin, I. A.; Dolbinina, V. V.; Chernyshov, D. Yu.; Koval'chuk, M. V.


    Interest in superprotonic crystals of M{sub m}H{sub n}(XO{sub 4}){sub (m+n)/2} is associated with the solution to the fundamental problem of modern condensed matter physics: investigations of structural phase transitions and the stabilization of phases with high proton conductivity with the aim of designing new functional materials. The available data suggest that changes in the physical properties in these crystals can occur through different structural mechanisms. To reveal the structural conditionality for anomalies in the physical properties, the crystals of K{sub 9}H{sub 7}(SO{sub 4}){sub 8} {center_dot} H{sub 2}O were studied by X-ray diffraction in the temperature range of 25-463 K, and the crystal structure of the high-temperature phase was determined at 418 K (sp. gr. Pcan). The results of the study indicate that the occurrence of high conductivity in K{sub 9}H{sub 7}(SO{sub 4}){sub 8} {center_dot} H{sub 2}O crystals at high temperatures is associated with the diffusion of water of crystallization, the hydrogen-bond network rearrangement, and the motion of K ions. The hydrogen-bond rearrangement and the hindered back diffusion of water to the crystal stabilize the high-temperature phase and ensure its supercooling to low temperatures.

  12. Investigation of the structure and properties of K{sub 9}H{sub 7}(SO{sub 4}){sub 8} {center_dot} H{sub 2}O single crystals

    SciTech Connect

    Makarova, I. P. Chernaya, T. S.; Grebenev, V. V.; Dolbinina, V. V.; Verin, I. A.; Simonov, A. A.


    The features of the conductivity of K{sub 9}H{sub 7}(SO{sub 4}){sub 8} {center_dot} H{sub 2}O single-crystal samples in the temperature range of superprotonic phase transition have been investigated. The K{sub 9}H{sub 7}(SO{sub 4}){sub 8} {center_dot} H{sub 2}O crystal structure is determined and refined taking into account hydrogen atoms by X-ray diffraction analysis at a temperature of 295 K: monoclinic symmetry, sp. gr. P2{sub 1}/c, Z = 4, a = 7.059(1), b = 19.773(1), c = 23.449(1) Angstrom-Sign , {beta} = 95.33(1) Degree-Sign , R{sub 1}/wR{sub 2} = 2.71/1.71. The structural data obtained suggest that the occurrence of high conductivity in K{sub 9}H{sub 7}(SO{sub 4}){sub 8} {center_dot} H{sub 2}O crystals with an increase in temperature is related to the diffusion of crystallization water and motion of K ions, as well as to the transformation of the system of hydrogen bonds and protonic motion. The stabilization of the high-temperature superprotonic phase and its supercooling to low temperatures are due to the presence of channels for the motion of K ions and slow backward diffusion of water in the crystal.

  13. Nucleation of graphene layers on magnetic oxides: Co3O4sub>(111) and Cr2O3(0001) from theory and experiment

    SciTech Connect

    Beatty, John; Cheng, Tao; Cao, Yuan; Driver, M. Sky; Goddard, III, William A.; Kelber, Jeffry A.


    We report directly grown strongly adherent graphene on Co3O4sub>(111) by carbon molecular beam epitaxy (C MBE) at 850 K and density functional theory (DFT) findings that the first graphene layer is reconstructed to fit the Co3O4sub> surface, while subsequent layers retain normal graphene structure. This adherence to the Co3O4sub> structure results from partial bonding of half the carbons to top oxygens of the substrate. This structure is validated by X-ray photoelectron spectroscopy and low-energy electron diffraction studies, showing layer-by-layer graphene growth with ~0.08 electrons/carbon atom transferred to the oxide from the first graphene layer, in agreement with DFT. In contrast, for Cr2O3 DFT finds no strong bonding to the surface and C MBE on Cr2O3(0001) yields only graphite formation at 700 K, with C desorption above 800 K. As a result, strong graphene-to-oxide charge transfer aids nucleation of graphene on incommensurate oxide substrates and may have implications for spintronics.

  14. Effect of atomic disorder and Ce doping on superconductivity of Ca3Rh4sub>Sn13: Electric transport properties under high pressure

    SciTech Connect

    Ślebarski, A.; Goraus, J.; Maśka, M. M.; Witas, P.; Fijałkowski, M.; Wolowiec, C. T.; Fang, Y.; Maple, M. B.


    Here, we report the observation of a superconducting state below ~8 K coexistent with a spin-glass state caused by atomic disorder in Ce substituted Ca3Rh4sub>Sn13. Measurements of specific heat, resistivity, and magnetism reveal the existence of inhomogeneous superconductivity in samples doped with Ce with superconducting critical temperatures Tc higher than those observed in the parent compound. For Ca3Rh4sub>Sn13, the negative value of the change in resistivity ρ with pressure P, dρ/dP correlates well with the calculated decrease in the density of states (DOS) at the Fermi energy with P. In conclusion, based on band-structure calculations performed under pressure, we demonstrate how the change in DOS would affect Tc of Ca3Rh4sub>Sn13 under negative lattice pressure in samples that are strongly defected by quenching.

  15. Synthesis and X-ray structural investigation of (C{sub 3}N{sub 6}H{sub 7}){sub 4}(CN{sub 3}H{sub 6}){sub 2}[UO{sub 2}(CrO{sub 4}){sub 4}] . 4H{sub 2}O and (H{sub 3}O){sub 6}[UO{sub 2}(CrO{sub 4}){sub 4}

    SciTech Connect

    Serezhkina, L. B.; Peresypkina, E. V.; Virovets, A. V.; Verevkin, A. G.; Pushkin, D. V.


    Single crystals of the compounds (C{sub 3}N{sub 6} H{sub 7}){sub 4}(CN{sub 3}H{sub 6}){sub 2}[UO{sub 2}(CrO{sub 4}){sub 4}] . 4H{sub 2}O (I) and (H{sub 3}O){sub 6}[UO{sub 2}(CrO{sub 4}){sub 4}] (II) are synthesized, and their structures are investigated using X-ray diffraction. Compound I crystallizes in the triclinic system with the unit cell parameters a = 6.3951(8) A, b = 10.8187(16) A, c = 16.9709(18) A, {alpha} = 93.674(4){sup o}, {beta} = 97.127(4){sup o}, {gamma} = 92.020(4){sup o}, space group, P1-barZ = 1, V = 1161.6(3) A{sup 3}, and R = 0.0470. Crystals of compound II belong to the monoclinic system with the unit cell parameters a = 14.3158(4) A, b = 11.7477(3) A, c = 13.1351(4) A, {beta}= 105.836(1){sup o}, space group C2/c, Z = 4, V = 2125.2(1) A{sup 3}, and R = 0.0213. The uranium-containing structural units of crystals I and II are mononuclear anionic complexes of the composition [UO{sub 2}(CrO{sub 4}){sub 4}]{sup 6-} with an island structure, which belong to the crystal-chemical group Am{sub 1}{sup 4} (A = UO{sub 2+}{sup 2}, M{sup 1} = CrO{sub 2-}{sup 4}) of the uranyl complexes. The [UO{sub 2}(CrO{sub 4}){sub 4}]{sup 6-} anionic complexes are joined into a three-dimensional framework through the electrostatic interactions with outer-sphere cations and a system of hydrogen bonds.

  16. Li3Mo4sub>P5O24: A two-electron cathode for lithium-ion batteries with three-dimensional diffusion pathways

    SciTech Connect

    Wen, Bohua; Khalifah, Peter G.; Liu, Jue; Chernova, Natasha A.; Wang, Xiaoya; Janssen, Yuri; Omenya, Fredrick; Whittingham, M. Stanley


    The structure of the novel compound Li3Mo4sub>P5O24 has been solved from single crystal X-ray diffraction data. The Mo cations in Li3Mo4sub>P5O24 are present in four distinct types of MoO6 octahedra, each of which has one open vertex at the corner participating in a Mo=O double bond and whose other five corners are shared with PO4sub> tetrahedra. On the basis of a bond valence sum difference map (BVS-DM) analysis, this framework is predicted to support the facile diffusion of Li+ ions, a hypothesis that is confirmed by electrochemical testing data, which show that Li3Mo4sub>P5O24 can be utilized as a rechargeable battery cathode material. It is found that Li can both be removed from and inserted into Li3Mo4sub>P5O24. The involvement of multiple redox processes occurring at the same Mo site is reflected in electrochemical plateaus around 3.8 V associated with the Mo6+/Mo5+ redox couple and 2.2 V associated with the Mo5+/Mo4+ redox couple. The two-electron redox properties of Mo cations in this structure lead to a theoretical capacity of 198 mAh/g. When cycled between 2.0 and 4.3 V versus Li+/Li, an initial capacity of 113 mAh/g is observed with 80% of this capacity retained over the first 20 cycles. Lastly, this compound therefore represents a rare example of a solid state cathode able to support two-electron redox capacity and provides important general insights about pathways for designing next-generation cathodes with enhanced specific capacities.

  17. Investigation of structural and luminescent properties of Ce{sup 3+}/Mn{sup 2+} ions-doped Ca{sub 5}(PO{sub 4}){sub 3}F

    SciTech Connect

    Zhang, Lei; Fu, Zuoling; Wu, Zhijian; Wang, Yuan; Fu, Xihong; Cui, Tian


    Graphical abstract: The structural and luminescent properties FAP: Ce{sup 3+} and FAP: Ce{sup 3+}, Mn{sup 2+} were investigated in detail by the spectral measurement and theoretical calculation. The emission of Ce{sup 3+} is fitted by two Gaussian functions dashed lines in wavenumber to further confirm the Ce{sup 3+} ion simultaneously occupy the 4f and 6h sites Ca{sub 5}(PO{sub 4})F host. - Highlights: • A simple hydrothermal method has been used to prepare Ca{sub 5}(PO{sub 4}){sub 3}F: Ce{sup 3+}, Mn{sup 2+} powders with structural and luminescent analysis. • The emission of Ce{sup 3+} is fitted by two Gaussian functions to confirm the Ce{sup 3+} ion simultaneously to occupy the 4f and 6h sites in Ca{sub 5}(PO{sub 4}){sub 3}F host. • Due to an efficient energy transfer, the existence of Ce{sup 3+} (sensitizer) can dramatically enhance the green emission of Mn{sup 2+} (activator) in co-doped samples. - Abstract: Ce{sup 3+}/Mn{sup 2+} ions-doped oxyapatite calcium fluorapatite [Ca{sub 5}(PO{sub 4}){sub 3}F, FAP] has been successfully synthesized by a facile one-step hydrothermal method. The luminescent properties of Ce{sup 3+}- and Ce{sup 3+}/Mn{sup 2+}- activated FAP phosphors were investigated using the photoluminescence (PL) and photoluminescence excitation (PLE) spectra. The emission of Ce{sup 3+} was fitted by two Gaussian functions with dashed lines in wavenumber to confirm the Ce{sup 3+} ion simultaneously to occupy the 4f and 6h sites in Ca{sub 5}(PO{sub 4}){sub 3}F host, which was consistent with the calculated results of crystal field based on chemical bond theory. In addition, the existence of Ce{sup 3+} (sensitizer) can dramatically enhance the green emission of Mn{sup 2+} (activator) in Ce{sup 3+}/Mn{sup 2+} ions co-doped samples due to an efficient energy transfer from Ce{sup 3+} to Mn{sup 2+}. All of these results could help us understand the site assignments and optical properties of the rare earth ions doped in hexagonal Ca{sub 5}(PO{sub 4

  18. New alkaline earth-zirconium oxalates M{sub 2}Zr(C{sub 2}O{sub 4}){sub 4}.nH{sub 2}O (M=Ba, Sr, Ca) synthesis, crystal structure and thermal behavior

    SciTech Connect

    Chapelet-Arab, B.; Abraham, F. . E-mail:; Grandjean, S.


    Three new alkaline earth-zirconium oxalates M{sub 2}Zr(C{sub 2}O{sub 4}){sub 4}.nH{sub 2}O have been synthesized by precipitation methods for M=Ba, Sr, Ca. For each compound the crystal structure was determined from single crystals obtained by controlled diffusion of M{sup 2+} and Zr{sup 4+} ions through silica gel containing oxalic acid. Ba{sub 2}Zr(C{sub 2}O{sub 4}){sub 4}.7H{sub 2}O, monoclinic, space group C2/c, a=9.830(2), b=29.019(6), c=9.178(2)A, {beta}=122.248(4){sup o}, V=2214.2(8)A3, Z=4, R=0.0427; Sr{sub 2}Zr(C{sub 2}O{sub 4}){sub 4}.11H{sub 2}O, tetragonal, space group I41/acd, a=16.139(4), c=18.247(6)A, V=4753(2)A3, Z=8, R=0.0403; Ca{sub 2}Zr(C{sub 2}O{sub 4}){sub 4}.5H{sub 2}O, orthorhombic, space group Pna2{sub 1}, a=8.4181(5), b=15.8885(8), c=15.8885(8)A, V=2125(2)A3, Z=4, R=0.0622. The structures of the three compounds consist of chains of edge-shared MO{sub 6}(H{sub 2}O){sub x} (x=2 or 3) polyhedra connected to ZrO{sub 8} polyhedra through oxalate groups. Depending on the arrangement of chains, the ZrO{sub 8} polyhedron geometry (dodecahedron or square antiprism) and the connectivity, two types of three-dimensional frameworks are obtained. For the smallest M{sup 2+} cations (Sr{sup 2+}, Ca{sup 2+}), large tunnels are obtained, running down the c direction of the unit cell, which can accommodate zeolitic water molecules. For the largest Ba{sup 2+} cation, the second framework is formed and is closely related to that of Pb{sub 2}Zr(C{sub 2}O{sub 4}){sub 4}.nH{sub 2}O. The decomposition at 800{sup o}C into strontium carbonate, barium carbonate or calcium oxide and MZrO{sub 3} (M=Sr, Ba, Ca) perovskite is reported from thermal analyses studies and high temperature X-ray powder diffraction.

  19. Ground-based, integrated path differential absorption LIDAR measurement of CO2, CH4sub>, and H2O near 1.6  μm.


    Wagner, Gerd A; Plusquellic, David F


    A ground-based, integrated path, differential absorption light detection and ranging (IPDA LIDAR) system is described and characterized for a series of nighttime studies of CO2, CH4sub>, and H2O. The transmitter is based on an actively stabilized, continuous-wave, single-frequency external-cavity diode laser (ECDL) operating from 1.60 to 1.65 μm. The fixed frequency output of the ECDL is microwave sideband tuned using an electro-optical phase modulator driven by an arbitrary waveform generator and filtered using a confocal cavity to generate a sequence of 123 frequencies separated by 300 MHz. The scan sequence of single sideband frequencies of 600 ns duration covers a 37 GHz region at a spectral scan rate of 10 kHz (100 μs per scan). Simultaneously, an eye-safe backscatter LIDAR system at 1.064 μm is used to monitor the atmospheric boundary layer. IPDA LIDAR measurements of the CO2 and CH4sub> dry air mixing ratios are presented in comparison with those from a commercial cavity ring-down (CRD) instrument. Differences between the IPDA LIDAR and CRD concentrations in several cases appear to be well correlated with the atmospheric aerosol structure from the backscatter LIDAR measurements. IPDA LIDAR dry air mixing ratios of CO2 and CH4sub> are determined with fit uncertainties of 2.8 μmol/mol (ppm) for CO2 and 22 nmol/mol (ppb) for CH4sub> over 30 s measurement periods. For longer averaging times (up to 1200 s), improvements in these detection limits by up to 3-fold are estimated from Allan variance analyses. Two sources of systematic error are identified and methods to remove them are discussed, including speckle interference from wavelength decorrelation and the seed power dependence of amplified spontaneous emission. Accuracies in the dry air retrievals of CO2 and CH4sub> in a 30 s measurement period are estimated at 4 μmol/mol (1% of ambient levels) and 50

  20. Synthesis, crystal structure and properties of alluaudite-like triple molybdate Na{sub 25}Cs{sub 8}Fe{sub 5}(MoO{sub 4}){sub 24}

    SciTech Connect

    Savina, Aleksandra A.; Solodovnikov, Sergey F.; Belov, Dmitry A.; Basovich, Olga M.; Solodovnikova, Zoya A.; Pokholok, Konstantin V.; Stefanovich, Sergey Yu.; Lazoryak, Bogdan I.; Khaikina, Elena G.


    A new triple molybdate Na{sub 25}Cs{sub 8}Fe{sub 5}(MoO{sub 4}){sub 24} was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, Mössbauer and dielectric impedance spectroscopy. Single crystals of Na{sub 25}Cs{sub 8}Fe{sub 5}(MoO{sub 4}){sub 24} were obtained and its structure was solved (the space group P1{sup ¯}, a=12.5814(5), b=13.8989(5), c=28.4386(9) Å, α=90.108(2), β=90.064(2), γ=90.020(2)°, V=4973.0(3) Å{sup 3}, Z=2, R=0.0440). Characteristic features of the structure are polyhedral layers composed of pairs of edge-shared FeO{sub 6} and (Fe, Na)O{sub 6} octahedra, which are connected by bridging MoO{sub 4} tetrahedra. The layers share common vertices with bridging MoO{sub 4} tetrahedra to form an open 3D framework with the cavities occupied by the Cs{sup +} and Na{sup +} cations. The compound undergoes first-order phase transformation at 642 K and above this phase transition, electrical conductivity reaches 10{sup −3}–10{sup −2} S cm{sup −1}. Thus, Na{sub 25}Cs{sub 8}Fe{sub 5}(MoO{sub 4}){sub 24} may be considered as a promising compound for developing new materials with high ionic conductivity. - Graphical abstract: A new triple molybdate Na{sub 25}Cs{sub 8}Fe{sub 5}(MoO{sub 4}){sub 24} was synthesized and structurally characterized, its physicochemical properties were studied. - Highlights: • New compound Na{sub 25}Cs{sub 8}Fe{sub 5}(MoO{sub 4}){sub 24} was synthesized. • Physicochemical properties of the compound were studied. • The first-order phase transformation is observed. • Electrical conductivity above 642 K is (10{sup −2}–10{sup −3}) S cm{sup −1}. • New compound may be considered as promising object with high ionic conductivity.

  1. Microwave sol–gel synthesis and upconversion photoluminescence properties of CaGd{sub 2}(WO{sub 4}){sub 4}:Er{sup 3+}/Yb{sup 3+} phosphors with incommensurately modulated structure

    SciTech Connect

    Lim, Chang Sung; Aleksandrovsky, Aleksandr; Molokeev, Maxim; Oreshonkov, Aleksandr; Atuchin, Victor


    CaGd{sub 2−x}(WO{sub 4}){sub 4}:Er{sup 3+}/Yb{sup 3+} phosphors with the doping concentrations of Er{sup 3+} and Yb{sup 3+} (x=Er{sup 3+}+Yb{sup 3+}, Er{sup 3+}=0.05, 0.1, 0.2 and Yb{sup 3+}=0.2, 0.45) have been successfully synthesized by the microwave sol–gel method. The crystal structure of CaGd{sub 2−x}(WO{sub 4}){sub 4}:Er{sup 3+}/Yb{sup 3+} tungstates have been refined, and upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after the heat-treatment at 900 °C for 16 h, showed a well crystallized morphology. Under the excitation at 980 nm, CaGd{sub 2}(WO{sub 4}){sub 4}:Er{sup 3+}/Yb{sup 3+} particles exhibited a strong 525-nm and a weak 550-nm emission bands in the green region and a very weak 655-nm emission band in the red region. The Raman spectrum of undoped CaGd{sub 2}(WO{sub 4}){sub 4} revealed about 12 narrow lines. The strongest band observed at 903 cm{sup −1} was assigned to the ν{sub 1} symmetric stretching vibration of WO{sub 4} tetrahedrons. The spectra of the samples doped with Er and Yb obtained under the 514.5 nm excitation were dominated by Er{sup 3+} luminescence preventing the recording of these samples Raman spectra. Concentration quenching of the erbium luminescence at {sup 2}H{sub 11/2}→{sup 4}I{sub 15/2} transition is weak in the range of erbium doping level x{sub Er}=0.05–0.2, while, for transition {sup 4}S{sub 3/2}→{sup 4}I{sub 15/2}, the signs of concentration quenching become pronounced at x{sub Er}=0.2. - Graphical abstract: CaGd{sub 2−x}(WO{sub 4}){sub 4}:Er{sup 3+}/Yb{sup 3+} phosphors with the doping concentrations of Er{sup 3+} and Yb{sup 3+} (x=Er{sup 3+}+Yb{sup 3+}, Er{sup 3+}=0.05, 0.1, 0.2 and Yb{sup 3+}=0.2, 0.45) have been successfully synthesized by the microwave sol–gel method and the crystal structure refinement, and upconversion photoluminescence properties have been investigated. - Highlights: • CaGd{sub 2−x}(WO{sub 4}){sub 4}:Er{sup 3+}/Yb

  2. Vacuum ultraviolet and near-infrared excited luminescence properties of Ca{sub 3}(PO{sub 4}){sub 2}:RE{sup 3+}, Na{sup +} (RE=Tb, Yb, Er, Tm, and Ho)

    SciTech Connect

    Zhang Jia; Wang Yuhua; Guo Linna; Zhang Feng; Wen Yan; Liu Bitao; Huang Yan


    Tb{sup 3+}, Yb{sup 3+}, Tm{sup 3+}, Er{sup 3+}, and Ho{sup 3+} doped Ca{sub 3}(PO{sub 4}){sub 2} were synthesized by solid-state reaction, and their luminescence properties were studied by spectra techniques. Tb{sup 3+}-doped samples can exhibit intense green emission under VUV excitation, and the brightness for the optimal Tb{sup 3+} content is comparable with that of the commercial Zn{sub 2}SiO{sub 4}:Mn{sup 2+} green phosphor. Under near-infrared laser excitation, the upconversion luminescence spectra of Yb{sup 3+}, Tm{sup 3+}, Er{sup 3+}, and Ho{sup 3+} doped samples demonstrate that the red, green, and blue tricolored fluorescence could be obtained by codoping Yb{sup 3+}-Ho{sup 3+}, Yb{sup 3+}-Er{sup 3+}, and Yb{sup 3+}-Tm{sup 3+} in Ca{sub 3}(PO{sub 4}){sub 2}, respectively. Good white upconversion emission with CIE chromaticity coordinates (0.358, 0.362) is achieved by quadri-doping Yb{sup 3+}-Tm{sup 3+}-Er{sup 3+}-Ho{sup 3+} in Ca{sub 3}(PO{sub 4}){sub 2}, in which the cross-relaxation process between Er{sup 3+} and Tm{sup 3+}, producing the {sup 1}D{sub 2}-{sup 3}F{sub 4} transition of Tm{sup 3+}, is found. The upconversion mechanisms are elucidated through the laser power dependence of the upconverted emissions and the energy level diagrams. - Graphical abstract: The CPO:0.25Tb{sup 3+}, 0.25Na{sup +} exhibits a comparable brightness to the commercial Zn{sub 2}SiO{sub 4}:Mn{sup 2+} upon 147 nm excitation. Good white light color is achieved in CPO:Yb{sup 3+}-Tm{sup 3+}-Er{sup 3+}-Ho{sup 3+} under 980 nm excitation. Highlights: > Ca{sub 3}(PO{sub 4}){sub 2}:Tb{sup 3+},Na{sup +} exhibits a comparable brightness with commercial Zn{sub 2}SiO{sub 4}:Mn{sup 2+}. > Red, green and blue colors are achieved in Yb{sup 3+}, Ho{sup 3+}, Er{sup 3+}, Tm{sup 3+} doped Ca{sub 3}(PO{sub 4}){sub 2}. > Good white emission is obtained in Yb{sup 3+}-Ho{sup 3+}-Er{sup 3+}-Tm{sup 3+} quadri-doped Ca{sub 3}(PO{sub 4}){sub 2}. > Ca{sub 3}(PO{sub 4}){sub 2}:Tb{sup 3+}, Yb{sup 3+}, Ho

  3. Phase formation in the Li{sub 2}MoO{sub 4}-K{sub 2}MoO{sub 4}-In{sub 2}(MoO{sub 4}){sub 3} system and crystal structures of new compounds K{sub 3}InMo{sub 4}O{sub 15} and LiK{sub 2}In(MoO{sub 4}){sub 3}

    SciTech Connect

    Khal'baeva, Klara M.; Solodovnikov, Sergey F.; Khaikina, Elena G.; Kadyrova, Yuliya M.; Solodovnikova, Zoya A.; Basovich, Olga M.


    XRD study of solid-phase interaction in the Li{sub 2}MoO{sub 4}-K{sub 2}MoO{sub 4}-In{sub 2}(MoO{sub 4}){sub 3} system was performed. The boundary K{sub 2}MoO{sub 4}-In{sub 2}(MoO{sub 4}){sub 3} system is an non-quasibinary join of the K{sub 2}O-In{sub 2}O{sub 3}-MoO{sub 3} system where a new polymolybdate K{sub 3}InMo{sub 4}O{sub 15} isotypic to K{sub 3}FeMo{sub 4}O{sub 15} was found. In the structure (a=33.2905(8), b=5.8610(1), c=15.8967(4) A, {beta}=90.725(1) Degree-Sign , sp. gr. C2/c, Z=8, R(F)=0.0407), InO{sub 6} octahedra, Mo{sub 2}O{sub 7} diortho groups and MoO{sub 4} tetrahedra form infinite ribbons {l_brace}[In(MoO{sub 4}){sub 2}(Mo{sub 2}O{sub 7})]{sup 3-}{r_brace}{sub {infinity}} along the b-axis. Between the chains, 8- to 10-coordinate potassium cations are located. A subsolidus phase diagram of the Li{sub 2}MoO{sub 4}-K{sub 2}MoO{sub 4}-In{sub 2}(MoO{sub 4}){sub 3} system was constructed and a novel triple molybdate LiK{sub 2}In(MoO{sub 4}){sub 3} was revealed. Its crystal structure (a=7.0087(2), b=9.2269(3), c=10.1289(3) A, {beta}=107.401(1) Degree-Sign , sp. gr. P2{sub 1}, Z=2, R(F)=0.0280) contains an open framework of vertex-shared MoO{sub 4} tetrahedra, InO{sub 6} octahedra and LiO{sub 5} tetragonal pyramids with nine- and seven-coordinate potassium ions in the framework channels. - Graphical abstract: Exploring the Li{sub 2}MoO{sub 4}-K{sub 2}MoO{sub 4}-In{sub 2}(MoO{sub 4}){sub 3} system showed its partial non-quasibinarity and revealed new compounds K{sub 3}InMo{sub 4}O{sub 15} (isotypic to K{sub 3}FeMo{sub 4}O{sub 15}) and LiK{sub 2}In(MoO{sub 4}){sub 3} which were structurally studied. An open framework of the latter is formed by vertex-shared MoO{sub 4} tetrahedra, InO{sub 6} octahedra and LiO{sub 5} tetragonal pyramids. Highlights: Black-Right-Pointing-Pointer Subsolidus phase relations in the Li{sub 2}MoO{sub 4}-K{sub 2}MoO{sub 4}-In{sub 2}(MoO{sub 4}){sub 3} system were explored. Black-Right-Pointing-Pointer The K{sub 2}MoO{sub 4}-In

  4. The Nature of the Distinctive Microscopic Features in R5(SixGe1-x)4sub> Magnetic Refrigeration Materials

    SciTech Connect

    Ugurlu, Ozan


    Magnetic refrigeration is a promising technology that offers a potential for high energy efficiency. The giant magnetocaloric effect of the R5(Six, Ge1-x)4sub> alloys (where R=rare-earth and O ≤ x ≤ 1), which was discovered in 1997, make them perfect candidates for magnetic refrigeration applications. In this study the microstructures of Gd5(Six, Ge1-x)4sub> alloys have been characterized using electron microscopy techniques, with the focus being on distinctive linear features first examined in 1999. These linear features have been observed in R5(Six, Ge1-x)4sub> alloys prepared from different rare-earths (Gd, Tb, Dy and Er) with different crystal structures (Gd5Si4sub>-type orthorhombic, monoclinic and Gd5Ge4sub>-type orthorhombic). Systematic scanning electron microscope studies revealed that these linear features are actually thin-plates, which grow along specific directions in the matrix material. The crystal structure of the thin-plates has been determined as hexagonal with lattice parameters a=b=8.53 Å and c=6.40 Å using selected area diffraction (SAD). Energy dispersive spectroscopy analysis, carried out in both scanning and transmission electron microscopes, showed that the features have a composition approximating to R5Six,Ge1-x)3.phase. Orientation relationship between the matrix and the thin-plates has been calculated as [- 1010](1-211)p//[010](10-2)m. The growth direction of the thin plates are calculated as (22 0 19) and (-22 0 19) by applying the Ag approach of Zhang and Purdy to the SAD patterns of this system. High Resolution TEM images of the Gd5Ge4sub> were used to study the crystallographic relationship. A terrace-ledge structure was observed at the interface and a 7° rotation of the reciprocal lattices

  5. Effects of Mg doping on the remarkably enhanced electrochemical performance of Na3V2(PO4sub>)3 cathode materials for sodium ion batteries

    SciTech Connect

    Li, Hui; Yu, Xiqian; Bai, Ying; Wu, Feng; Wu, Chuan; Liu, Liang-Yu; Yang, Xiao-Qing


    Na3V2-xMgx(PO4sub>)3/C composites with different Mg2+ doping contents (x=0, 0.01, 0.03, 0.05, 0.07 and 0.1) were prepared by a facile sol-gel method. The doping effects on the crystal structure were investigated by XRD, XPS and EXAFS. The results show that low dose doping Mg2+ does not alter the structure of the material, and magnesium is successfully substituted for vanadium site. The Mg doped Na3V2-xMgx(PO4sub>)3/C composites exhibit significant improvements on the electrochemistry performances in terms of the rate capability and cycle performance, especially for the Na3V1.95Mg0.05(PO4sub>)3/C. For example, when the current density increased from 1 C to 30 C, the specific capacity only decreased from 112.5 mAh g-1 to 94.2 mAh g-1 showing very good rate capability. Moreover, even cycling at a high rate of 20 C, an excellent capacity retention of 81% is maintained from the initial value of 106.4 mAh g-1 to 86.2 mAh g-1 at the 50th cycle. Enhanced rate capability and cycle performance can be attributed to the optimized particle size, structural stability and enhanced ionic and electronic conductivity induced by Mg doping.

  6. High-temperature X-ray analysis of phase evolution in lithium ion conductor Li{sub 1.5}Al{sub 0.5}Ge{sub 1.5}(PO{sub 4}){sub 3}

    SciTech Connect

    He, Kun Wang, Yanhang; Zu, Chengkui Liu, Yonghua; Zhao, Huifeng; Chen, Jiang; Han, Bin; Ma, Juanrong


    Series of Li{sub 1.5}Al{sub 0.5}Ge{sub 1.5}(PO{sub 4}){sub 3} glass ceramic samples were prepared in this work through the change of heat treatment temperature from 650 to 1050 °C. The structures of glass ceramic samples were characterized by means of high temperature X-ray diffraction and Field Emission Scanning Electron Microscope. And the lithium ionic conductivity was analyzed through AC impedance spectroscopy. Through heat treatment at 850 °C for 4 h for the base glass sample, we obtained a maximum conductivity of 5.8 × 10{sup −4} S/cm at room temperature. - Graphical Abstract: High temperature X-ray diffraction (HT-XRD) and Rietveld refinement of Li{sub 1.5}Al{sub 0.5}Ge{sub 1.5}(PO{sub 4}){sub 3} (LAGP) glass-ceramics were recorded to investigate the phase transformation, cell parameters and the mass fraction of each crystal phase, which occur in the glass to glass-ceramics process during different crystallization temperatures. The relationship between the average grain size and conductivity that originate from and relate to the crystallization temperature was analyzed by SEM micrograph and AC impedance spectroscopy. - Highlights: • Li{sub 1.5}Al{sub 0.5}Ge{sub 1.5}(PO{sub 4}){sub 3} glass-ceramics were prepared from as-prepared glass. • The phases decomposition and mass fraction of each phase were analyzed by HT-XRD. • Conductivity is relate to grain size that influenced by crystallization temperature.

  7. Fluorocarbon assisted atomic layer etching of SiO2 and Si using cyclic Ar/C4sub>F8 and Ar/CHF3 plasma

    SciTech Connect

    Metzler, Dominik; Li, Chen; Engelmann, Sebastian; Bruce, Robert L.; Joseph, Eric A.; Oehrlein, Gottlieb S.


    The need for atomic layer etching (ALE) is steadily increasing as smaller critical dimensions and pitches are required in device patterning. A flux-control based cyclic Ar/C4sub>F8 ALE based on steady-state Ar plasma in conjunction with periodic, precise C4sub>F8 injection and synchronized plasma-based low energy Ar+ ion bombardment has been established for SiO2.1 In this work, the cyclic process is further characterized and extended to ALE of silicon under similar process conditions. The use of CHF3 as a precursor is examined and compared to C4sub>F8. CHF3 is shown to enable selective SiO2/Si etching using a fluorocarbon (FC) film build up. Other critical process parameters investigated are the FC film thickness deposited per cycle, the ion energy, and the etch step length. Etching behavior and mechanisms are studied using in situ real time ellipsometry and X-ray photoelectron spectroscopy. Silicon ALE shows less self-limitation than silicon oxide due to higher physical sputtering rates for the maximum ion energies used in this work, ranged from 20 to 30 eV. The surface chemistry is found to contain fluorinated silicon oxide during the etching of silicon. As a result, plasma parameters during ALE are studied using a Langmuir probe and establish the impact of precursor addition on plasma properties.

  8. Mild hydrothermal synthesis, crystal structure, thermal behaviour, spectroscopic and magnetic properties of (NH{sub 4}){sub 0.80}Li{sub 0.20}[Fe(AsO{sub 4})F

    SciTech Connect

    Berrocal, Teresa


    The (NH{sub 4}){sub 0.80}Li{sub 0.20}[Fe(AsO{sub 4})F] compound has been synthesized under mild hydrothermal conditions. The compound crystallize in the orthorhombic Pna2{sub 1} space group, with cell parameters a=13.352(9), b=6.7049(9), c=10.943(2) A and Z=8. The compound belongs to the KTiO(PO{sub 4}) structure type, with chains alternating FeO{sub 4}F{sub 2} octahedra and AsO{sub 4} tetrahedra, respectively, running along the 'a' and 'b' crystallographic axes. The diffuse reflectance spectrum in the visible region shows the forbidden electronic transitions characteristic of the Fe(III) d{sup 5}-high spin cation in slightly distorted octahedral geometry. The Moessbauer spectrum at room temperature is characteristic of iron (III) cations. The ESR spectra, carried out from room temperature to 200 K, remain isotropic with variation in temperature; the g-value being 1.99(1). Magnetic measurements indicate the predominance of strong antiferromagnetic interactions. - Graphical Abstract: Three-dimensional structure of (NH{sub 4}){sub 0.80}Li{sub 0.20}[Fe(AsO{sub 4})F], a fluoroarsenate containing lithium and ammonium in the structural cavities. Highlights: > (NH{sub 4}){sub 0.80}Li{sub 0.20}[Fe(AsO{sub 4})F] has been synthesized by mild hydrothermal technique. > The compound exhibits a three-dimensional structure. > Moessbauer spectrum indicates the existence of Fe(III) cations. > Visible spectroscopy confirms the hexacoordination of Fe(III). > Magnetic measurements indicate the existence of a global antiferromagnetic ordering.

  9. CW EC-QCL-based sensor for simultaneous detection of H2O, HDO, N2O and CH4sub> using multi-pass absorption spectroscopy

    SciTech Connect

    Yu, Yajun; Sanchez, Nancy P.; Griffin, Robert J.; Tittel, Frank K.


    A sensor system based on a continuous wave, external-cavity quantum-cascade laser (CW EC-QCL) was demonstrated for simultaneous detection of atmospheric H2O, HDO, N2O and CH4sub> using a compact, dense pattern multi-pass gas cell with an effective path-length of 57.6 m. The EC-QCL with a mode-hop-free spectral range of 1225-1285 cm-1 operating at similar to 7.8 mu m was scanned covering four neighboring absorption lines, for H2O at 1281.161 cm-1, HDO at 1281.455 cm-1, N2O at 1281.53 cm-1 and CH4sub> at 1281.61 cm-1. A first-harmonic-normalized wavelength modulation spectroscopy with second-harmonic detection (WMS-2f/1f) strategy was employed for data processing. An Allan-Werle deviation analysis indicated that minimum detection limits of 1.77 ppmv for H2O, 3.92 ppbv for HDO, 1.43 ppbv for N2O, and 2.2 ppbv for CH4sub> were achieved with integration times of 50-s, 50-s, 100-s and 129-s, respectively. In conclusion, experimental measurements of ambient air are also reported.

  10. Thermoluminescence response of K{sub 2}Ca{sub 2}(SO{sub 4}){sub 3} nanophosphor Co-doped with Eu and Ce for gamma ray dosimetry

    SciTech Connect

    Patil, B. J.; Bhadane, Mahesh S.; Dahiwale, S. S.; Bhoraskar, V. N.; Dhole, S. D.; Mandlik, N. T.; Kulkarni, M. S.; Bhatt, B. C.


    K{sub 2}Ca{sub 2}(SO{sub 4}){sub 3} nanophosphors co-doped with Eu and Ce were synthesized by the chemical co-precipitation method. These samples were further annealed at 700 °C structural reformation. The structural and morphological characteristics were studied using XRD and TEM techniques. The particle size calculated from XRD spectra was around 35 nm. The as synthesized sample shows cubic structure annealed at 700 °C. The as synthesized and annealed sample of K{sub 2}Ca{sub 2}(SO{sub 4}){sub 3}: EuCe were irradiated with Co{sup 60} gamma rays for the doses from 2Gy to 1kGy. The TL characteristic sample of co-doped were studied for the dosimetric application by gamma radiation. The TL spectrum of annealed sample has single peaked at 160 °C. The Eu doped sample has a high TL sensitivity than Ce doped sample. But after co-doping with Eu and Ce, TL intensity observed to be decreased. The decrees in TL peak intensity of the phosphor on co-doping of Eu and Ce gives an insight into the emission mechanism of the phosphor which involves energy transfer from Eu to Ce. The TL response of all the samples were found to be linear for the dose from 2 Gy to 1 KGy. Therefore, K{sub 2}Ca{sub 2}(SO{sub 4}){sub 3}: EuCe nanophosphor can be used for the measurement of high dose of gamma radiation.

  11. Dielectric frame, Sellmeier equations, and phase-matching properties of the monoclinic acentric crystal GdCa4sub>O(BO3)3.


    Guo, Feng; Segonds, Patricia; Ménaert, Bertrand; Debray, Jerôme; Aka, Gerard; Loiseau, Pascal; Boulanger, Benoît


    We directly measured the phase-matching properties of the biaxial GdCa4sub>O(BO3)3 (GdCOB) crystal using the sphere method. We studied second-harmonic generation and difference frequency generation in two principal planes of the crystal. All these data allowed us to refine the Sellmeier equations of the three principal refractive indices. These equations are valid over the entire transparency range of GdCOB and then could be used to calculate the tuning curves of infrared optical parametric generation.

  12. Comparative study of SiO2, Si3N4sub> and TiO2 thin films as passivation layers for quantum cascade lasers.


    Ferré, Simon; Peinado, Alba; Garcia-Caurel, Enric; Trinité, Virginie; Carras, Mathieu; Ferreira, Robson


    The aim of this article is to determine the best dielectric between SiO2, Si3N4sub> and TiO2 for quantum cascade laser (QCL) passivation layers depending on the operation wavelength. It relies on both Mueller ellipsometry measurement to accurately determine the optical constants (the refractive index n and the extinction coefficient k) of the three dielectrics, and optical simulations to determine the mode overlap with the dielectric and furthermore the modal losses in the passivation layer. The impact of dielectric thermal conductivities are taken into account and shown to be not critical on the laser performances.

  13. New process of preparation, structure, and physicochemical investigations of the new titanyl phosphate Ti{sub 2}O(H{sub 2}O)(PO{sub 4}){sub 2}

    SciTech Connect

    Benmokhtar, S. El jazouli, A.; Chaminade, J.P.; Gravereau, P.; Menetrier, M.; Bouree, F.


    New titanyl phosphate Ti{sub 2}O(H{sub 2}O)(PO{sub 4}){sub 2} has been prepared and characterized by X-ray and neutron diffraction, nuclear magnetic resonance, infrared and Raman spectroscopies and thermogravimetric analysis. The crystal structure has been solved from neutron powder diffraction data at 300 K by Rietveld method in P2{sub 1} space group. The refinement led to satisfactory profile factors (R{sub p}=2.7%, R{sub wp}=3.2%) and crystal structure model indicators (R{sub B}=5.8%, R{sub F}=3.2%). The cell is monoclinic with a=7.3735 A, b=7.0405 A, c=7.6609 A and {beta}=121.48{sup o}, Z=4. The structure can be described as a three-dimensional framework built up by chains of [TiO{sub 5}(OH{sub 2})] octahedra with alternative short bonds [Ti{sub (1)}-O{sub (12)}; Ti{sub (2)}-O{sub (12)}, 1.88-1.84 A] and long ones [Ti{sub (1)}-O{sub W}; Ti{sub (2)}-O{sub W}, 2.25-2.23 A] along c-axis and connected via [PO{sub 4}] tetrahedra. Oxygen atom denoted O{sub (12)} is only linked to two titanium atoms and Oxygen atom denoted O{sub W} is linked to two titanium atoms and two hydrogen atoms. O{sub (12)} and O{sub W} are not linked to P atoms and justify the titanyl phosphate formulation Ti{sub 2}O(H{sub 2}O)(PO{sub 4}){sub 2}. The infrared and Raman spectra presents peaks due to vibrations of Ti-O, P-O and O-H bonds. The {sup 31}P MAS NMR spectrum reveals two {sup 31}P resonance lines, in agreement with the structure which showed two crystallographic sites for phosphorus. The thermogravimetric analysis show that Ti{sub 2}O(H{sub 2}O)(PO{sub 4}){sub 2} is thermally stable until 400 deg. C. Above this temperature, it losses water and decomposes to Ti{sub 5}O{sub 4}(PO{sub 4}){sub 4} and TiP{sub 2}O{sub 7}. - Graphical abstract: The structure of TiHP can be described as a TiOPO{sub 4} framework constituted by chains of tilted corner-sharing [TiO{sub 6}] octahedra and cross linked by [PO{sub 4}] tetrahedra with empty cavities in the framework.

  14. North American terrestrial CO2 uptake largely offset by CH4sub> and N2O emissions: toward a full accounting of the greenhouse gas budget

    SciTech Connect

    Tian, Hanqin; Chen, Guangsheng; Lu, Chaoqun; Xu, Xiaofeng; Hayes, Daniel J.; Ren, Wei; Pan, Shufen; Huntzinger, Deborah N.; Wofsy, Steven C.


    The terrestrial ecosystems of North America have been identified as a sink of atmospheric CO2 though there is no consensus on the magnitude. However, the emissions of non-CO2 greenhouse gases (CH4sub> and N2O) may offset or even overturn the climate cooling effect induced by the CO2 sink. Using a coupled biogeochemical model, in this study, we have estimated the combined global warming potentials (GWP) of CO2, CH4sub> and N2O fluxes in North American terrestrial ecosystems and quantified the relative contributions of environmental factors to the GWP changes during 1979–2010. The uncertainty range for contemporary global warming potential has been quantified by synthesizing the existing estimates from inventory, forward modeling, and inverse modeling approaches. Our “best estimate” of net GWP for CO2, CH4sub> and N2O fluxes was₋0.50 ± 0.27 Pg CO2 eq/year (1 Pg=1015 g) in North American terrestrial ecosystems during 2001–2010. The emissions of CH4sub> and N2O from terrestrial ecosystems had offset about two thirds (73% ± 14%) of the land CO2 sink in the North American continent, showing large differences across the three countries, with offset ratios of 57% ± 8% in US, 83% ± 17 % in Canada and 329% ± 119 % in Mexico. Climate change and elevated tropospheric ozone concentration have contributed the most to GWP increase, while elevated atmospheric CO2 concentration have contributed the most to GWP reduction. Extreme drought events over certain periods could result in a positive GWP. By integrating the existing estimates, we have found a wide range of uncertainty for the combined GWP. In conclusion, from both climate change science and policy perspectives, it is necessary to integrate ground and satellite observations with models for a more accurate accounting of these three greenhouse gases in

  15. Tunable photoluminescence properties of Ca{sub 8}NaLa(PO{sub 4}){sub 6}F{sub 2}:Eu{sup 2+},Mn{sup 2+} phosphor under UV excitation

    SciTech Connect

    Zhang, Fen; Lan, Tong; Tang, Wanjun


    Highlights: • Ca{sub 8}NaLa(PO{sub 4}){sub 6}F{sub 2}:Eu{sup 2+},Mn{sup 2+} was prepared by a combustion-assisted synthesis method. • The phosphor presents blue and yellow double color emissions. • Efficient energy transfer from Eu{sup 2+} to Mn{sup 2+} in this phosphor is observed obviously. • White emitting was realized in Ca{sub 8}NaGd(PO{sub 4}){sub 6}F{sub 2}:0.10Eu{sup 2+},0.32Mn{sup 2+},0.10B phosphor. - Abstract: A series of Eu{sup 2+} and Mn{sup 2+} coactivated Ca{sub 8}NaLa(PO{sub 4}){sub 6}F{sub 2} (CNLF) phosphors have been synthesized by a combustion-assisted synthesis method. The investigation revealed that Ca{sub 8}NaLa(PO{sub 4}){sub 6}F{sub 2} crystallized in a hexagonal crystal system with the space group P6{sub 3}/m (176). The Eu{sup 2+} activated phosphors can be efficiently excited in the range of 270–400 nm and give intense blue emission peaking at 451 nm. By codoping the Eu{sup 2+} and Mn{sup 2+} ions into the CNLF host and singly varying the doping content of the Mn{sup 2+} ion, tunable colors from blue to white and eventually to yellow are obtained in CNLF:Eu{sup 2+},Mn{sup 2+} phosphors under the irradiation of 330 nm. The energy transfer from Eu{sup 2+} to Mn{sup 2+} in CNLF:Eu{sup 2+},Mn{sup 2+} has been demonstrated to be a resonant type via a dipole–dipole mechanism and the critical distance of energy transfer from Eu{sup 2+} to Mn{sup 2+} was estimated to be about 11.9 Å. The investigation indicates that the obtained samples might have potential application in white LEDs.

  16. Rietveld refinement and ionic conductivity of Ca{sub 8.4}Bi{sub 1.6}(PO{sub 4}){sub 6}O{sub 1.8}

    SciTech Connect

    Tmar Trabelsi, I.; Madani, A.; Mercier, A.M.; Toumi, M.


    The structure of Ca{sub 8.4}Bi{sub 1.6}(PO{sub 4}){sub 6}O{sub 1.8}, isostructural with Fluoroapatite, was determined by X-ray powder diffraction methods. The results of Rietveld refinement revealed that the formula of this compound is [Ca{sub 4}]{sup 4f}[Ca{sub 4.4}Bi{sub 1.6}]{sup 6h}(PO{sub 4}){sub 6}[O{sub 1.8}]{sup 2a}, space group P63/m (a=9.468 (3) A, c=6.957 (3) A). A total substitution of Bi{sup 3+} ions in the (6h) sites was related particularly to the high polarizability of the Bi{sup 3+} ion compared to Ca{sup 2+}. The observed frequencies in the Raman and infrared spectra were explained and discussed on the basis of unit-cell group analyses and in comparison with Fluoroapatite and other oxyapatites. The ionic conductivity over a wide range of temperature was investigated according to the complex impedance method. The highest overall conductivity values were found at {sigma}{sub 700 Degree-Sign C} =5.03 Multiplication-Sign 10{sup -7} S cm{sup -1} and E{sub a}=0.50 eV. - Graphical abstract: The final Rietveld refinement plot of the Ca{sub 8.4}Bi{sub 1.6} (PO{sub 4}){sub 6}O{sub 1.8}. Highlights: Black-Right-Pointing-Pointer The Rietveld refinement revealed that the formula of this compound is Ca{sub 8.4}Bi{sub 1.6}(PO{sub 4}){sub 6}O{sub 1.8}. Black-Right-Pointing-Pointer Vibrational spectroscopy supports the high symmetry P63/m space group for this apatite. Black-Right-Pointing-Pointer This apatite contained channels where oxygen ions were located in 2a sites. Black-Right-Pointing-Pointer The possibility of anionic conduction along these channels was considered.

  17. Solubility of pyromorphite Pb5(PO4sub>)3Cl at 5–65°C and its experimentally determined thermodynamic parameters

    SciTech Connect

    Topolska, Justyna; Manecki, Maciej; Bajda, Tomasz; Borkiewicz, Olaf; Budzewski, Przemysław


    Here, the solubility of synthetic pyromorphite Pb5(PO4sub>)3Cl was determined in a series of dissolution experiments conducted at 5–65 °C and at pH = 2.0. The equilibrium was established within 4 months. The dissolution of pyromorphite was congruent at all the temperatures, and the measured solubility product log Ksp,298 for the dissolution reaction: Pb5(PO4sub>)3Cl ⇌ 5Pb2+ + 3PO4sub>3- + Cl- was determined to be –79.6 ± 0.15. The equilibrium ion activity product of pyromorphite increased with temperature, indicating a positive enthalpy of the dissolution reaction in the temperature range from 5 to 65 °C. The temperature dependence of the log Ksp was nonlinear: log Ksp = A – B/T + D log(T), where A = 478.77 ± 136.62, B = 29,378 ± 6215, and D = –185.81 ± 46.77. This allowed for calculation of ΔG°r = 454.0 ± 1.7 kJ·mol–1, ΔH°r = 101.8 ± 6.0 J·mol–1·K–1, ΔC°p,r = –1545 ± 388.9 J·mol–1·K–1, and ΔS°r = –1181 ± 382 J·mol–1·K–1 of the dissolution reaction. Using these values and the published standard state quantities for constituent ions, the values of ΔG°f = –3764.3 ± 3.5 kJ·mol–1, ΔH°f = –4108.4 ± 7.9 J·mol–1·K–1, S°f = 622 ± 382 J·mol–1·K–1, and C°pf = 402 ± 398 J·mol–1·K–1 were calculated for synthetic pyromorphite Pb5(PO4sub>)3Cl.

  18. Soft chemistry synthesis, structure and electrochemical characterization of iron phosphates Fe(H{sub 2}PO{sub 4}){sub 3} and Fe(PO{sub 3}){sub 3}

    SciTech Connect

    Baies, R.; Pralong, V. . E-mail:; Caignaert, V.; Raveau, B.


    The iron phosphate, Fe(H{sub 2}PO{sub 4}){sub 3}, was synthesized through a precipitation route by means of acidic media. As the compound is highly hygroscopic, the structure was solved ab initio by powder X-ray diffraction under nitrogen flow at room temperature and 200 deg. C. This phase is antiferromagnetic below 30 K. It converts into Fe(PO{sub 3}){sub 3} at 550 deg. C, after dehydration. Electrochemical characterizations, performed on the last compound, show irreversible decomposition into metallic iron.

  19. Novel joining of dissimilar ceramics in the Si3N4sub>-Al2O3 system using polytypoid functional gradients

    SciTech Connect

    Lee, Caroline Sunyong


    A unique approach to crack-free joining of heterogeneous ceramics is demonstrated by the use of sialon polytypoids as Functionally Graded Materials (FGM) as defined by the phase diagram in the system, Si3N4sub>-Al2O3. Polytypoids in the Al2O3-Si3N4sub> system offer a path to compatibility for such heterogeneous ceramics. The first part of the dissertation describes successful hot press sintering of multilayered FGM's with 20 layers of thickness 500 mm each. Transmission Electron Microscopy was used to identify the polytypoids at the interfaces of different areas of the joint. It has been found that the 15R polytypoid was formed in the Al2O3-contained layers and the 12H polytypoid was formed in the Si3N4sub>-contained layers. The second part of the dissertation discusses the mechanical properties of these polytypoidally joined Si3N4sub>-Al2O3. The thermal stresses of this FGM junction were analyzed using a finite element analysis program (FEAP) taking into account both coefficient of thermal expansion (CTE) and modulus variations. From this analysis, the result showed a dramatic decrease in radial, axial and hoop stresses as the FGM changes from three layers to 20 graded layers. Scaling was considered, showing that the graded transition layer should constitute about 75 percent or more of the total sample thickness to reach a minimal residual stress. Oriented Vickers indentation testing was used to qualitatively characterize the strengths of the joint and the various interfaces. The indentation cracks were minimally or not deflected at the sialon layers, implying strong interfaces. Finally, flexural testing was conducted at room temperature and at high temperature. The average strength at room temperature was found to be 581 MPa and the average strength at high temperature (1200 °C) was found to be

  20. Two-micron lasing in NaLa{sub 1/2}Gd{sub 1/2}(WO{sub 4}){sub 2} crystals doped with Tm{sup 3+} ions

    SciTech Connect

    Bolshchikov, F A; Ryabochkina, P A; Zharikov, Evgeny V; Lis, Denis A; Subbotin, Kirill A; Zakharov, N G; Antipov, Oleg L


    Lasing on the {sup 3}F{sub 4{yields}}{sup 3}H{sub 6} transition of Tm{sup 3+} ions in Tm{sup 3+}:NaLa{sub 1/2}Gd{sub 1/2}(WO{sub 4}){sub 2} crystals pumped by a diode laser is obtained for the first time. The {pi}- and {sigma}-polarised laser radiation at wavelengths of 1908 and 1918 nm was generated with a slope efficiency of 28% and 25%, respectively. (lasers)

  1. Copper(II) perrhenate Cu(C{sub 3}H{sub 7}OH){sub 2}(ReO{sub 4}){sub 2}: Synthesis from isopropanol and CuReO{sub 4}, structure and properties

    SciTech Connect

    Mikhailova, D.; Engel, J.M.; Schmidt, M.; Tsirlin, A.A.; Ehrenberg, H.


    The crystal structure of Cu{sup +}Re{sup 7+}O{sub 4} is capable of a quasi-reversible incorporation of C{sub 3}H{sub 7}OH molecules. A room-temperature reaction between CuReO{sub 4} and C{sub 3}H{sub 7}OH under oxidizing conditions leads to the formation of a novel metal-organic hybrid compound Cu{sup 2+}(C{sub 3}H{sub 7}OH){sub 2}(ReO{sub 4}){sub 2}. Upon heating under reducing conditions, this compound transforms back into CuReO{sub 4}, albeit with ReO{sub 2} and metallic Cu as by-products. The crystal structure of Cu(C{sub 3}H{sub 7}OH){sub 2}(ReO{sub 4}){sub 2} solved from single-crystal X-ray diffraction (Pbca, a=10.005(3) Å, b=7.833(2) Å, and c=19.180(5) Å) reveals layers of corner-sharing CuO{sub 6}-octahedra and ReO{sub 4}-tetrahedra, whereas isopropyl groups are attached to both sides of these layers, thus providing additional connections within the layers through hydrogen bonds. Cu(C{sub 3}H{sub 7}OH){sub 2}(ReO{sub 4}){sub 2} is paramagnetic down to 4 K because the spatial arrangement of the Cu{sup 2+} half-filled orbitals prevents magnetic superexchange. The paramagnetic effective moment of 2.0(1) μ{sub B} is slightly above the spin-only value and typical for Cu{sup 2+} ions. - Highlights: • Novel Cu(C{sub 3}H{sub 7}OH){sub 2}(ReO{sub 4}){sub 2} compound has a sequence of inorganic and organic layers. • Hydrogen bonds provide an additional bonding Isopropanol molecules serve as a reducing agent during decomposition. • No direct Cu-O-Re-O-Cu connections via d{sub x2-y2} orbital of Cu{sup 2+} explain paramagnetism. • Hydrogen bonds provide an additional bonding. • Isopropanol molecules serve as a reducing agent during decomposition.

  2. Magnetic and structural transitions in La0.4sub>Na0.6Fe2As2 single crystals

    SciTech Connect

    Yan, Jiaqiang; Nandi, S.; Saparov, Bayrammurad I.; Cermak, P.; Xiao, Y.; Su, Y.; Jin, W. T.; Schneidewind, A.; Bruckel, Th.; McCallum, R. W.; Lograsso, Thomas A.; Sales, B. C.; Mandrus, D. G.


    La0.4sub>Na0.6Fe2As2 single crystals have been grown out of an NaAs flux in an alumina crucible and characterized by measuring magnetic susceptibility, electrical resistivity, specific heat, as well as single-crystal x-ray and neutron diffraction. La0.4sub>Na0.6Fe2As2 single crystals show a structural phase transition from a high-temperature tetragonal phase to a low-temperature orthorhombic phase at Ts=125 K. This structural transition is accompanied by an anomaly in the temperature dependence of electrical resistivity, anisotropic magnetic susceptibility, and specific heat. Concomitant with the structural phase transition, the Fe moments order along the a direction with an ordered moment of 0.7(1) μB at T=5 K. Finally, the low-temperature stripe antiferromagnetic structure is the same as that in other AFe2As2 (A = Ca, Sr, Ba) compounds. La0.5₋xNa0.5+xFe2As2 provides a material platform for the study of iron-based superconductors where the electron-hole asymmetry could be studied by simply varying the La/Na ratio.

  3. Toward understanding the lithiation/delithiation process in Fe0.5TiOPO4sub>/C electrode material for lithium-ion batteries

    SciTech Connect

    Lasri, Karima; Mahmoud, Abdelfattah; Saadoune, Ismael; Sougrati, Moulay Tahar; Stievano, Lorenzo; Lippens, Pierre-Emmanuel; Hermann, Raphaël Pierre; Ehrenberg, Helmut


    We used Fe0.5TiOPO4sub>/C composite as anode material for LIB and exhibits excellent cycling performance when the electrode is cycled in two different voltage ranges [3.0-1.3V] and [3.0- 0.02V] where different insertion mechanisms were involved. Based on in situ X-ray diffraction, in situ XANES spectroscopy results, and various electrochemical analyses at high and low voltage cut-off, we found that Fe0.5TiOPO4sub>/C electrode materials still maintains its structure crystallinity after cycling between [3.0-1.3V] showing formation of new phase at the end of first discharge, with a reversible capacity of 100 mAhg-1 after 50 cycles at C/5 rate. Moreover, at highly lithiated states, [3.0-0.02V] voltage range, a reduction decomposition reaction highlights the Li-insertion/extraction behaviors, and low phase crystallinity is observed during cycling, in addition an excellent rate behavior and a reversible capacity of 250 mAhg- 1 can still be maintained after 50 cycles at high cycling rate 5C.

  4. High-power actively Q-switched single-mode 1342 nm Nd:YVO4sub> ring laser, injection-locked by a cw single-frequency microchip laser.


    Koch, Peter; Bartschke, Juergen; L'huillier, Johannes A


    In this paper we report on the realization of a single-mode Q-switched Nd:YVO4sub> ring laser at 1342 nm. Unidirectional and single-mode operation of the ring laser is achieved by injection-locking with a continuous wave Nd:YVO4sub> microchip laser, emitting a single-frequency power of up to 40 mW. The ring laser provides a single-mode power of 13.9 W at 10 kHz pulse repetition frequency with a pulse duration of 18.2 ns and an excellent beam quality (M2 < 1.05). By frequency doubling of the fundamental 1342 nm laser, a power of 8.7 W at 671 nm with a pulse duration of 14.8 ns and a beam propagation factor of M2 < 1.1 is obtained. The 671 nm radiation features a long-term spectral width of 75 MHz.

  5. Neutron scattering studies of spin-phonon hybridization and superconducting spin gaps in the high temperature superconductor La2-x(Sr;Ba)xCuO4sub>

    SciTech Connect

    Wagman, J. J.; Carlo, Jeremy P.; Gaudet, J.; Van Gastel, G. J.; Abernathy, Douglas L.; Stone, Matthew B.; Granroth, Garrett E.; Kolesnikov, Alexander I.; Savici, Andrei T.; Kim, Young -June; Zhang, H.; Ellis, D.; Zhao, Yang; Clark, L.; Kallin, A. B.; Mazurek, E.; Dabkowska, H. A.; Gaulin, Bruce D.


    We present time-of-flight neutron-scattering measurements on single crystals of La2-xBaxCuO4sub> (LBCO) with 0 ≤ x ≤ 0.095 and La2-xSrxCuO4sub> (LSCO) with x = 0.08 and 0.11. This range of dopings spans much of the phase diagram relevant to high temperature cuprate superconductivity, ranging from insulating, three dimensional commensurate long range antiferromagnetic order for x ≤ 0.02 to two dimensional (2D) incommensurate antiferromagnetism co-existing with superconductivity for x ≥ 0.05. Previous work on lightly doped LBCO with x = 0.035 showed a clear resonant enhancement of the inelastic scattering coincident with the low energy crossings of the highly dispersive spin excitations and quasi-2D optic phonons. The present work extends these measurements across the phase diagram and shows this enhancement to be a common feature to this family of layered quantum magnets. Furthermore we show that the low temperature, low energy magnetic spectral weight is substantially larger for samples with non-superconducting ground states relative to any of the samples with superconducting ground states. Lastly spin gaps, suppression of low energy magnetic spectral weight, are observed in both superconducting LBCO and LSCO samples, consistent with previous observations for superconducting LSCO

  6. The demise of superfluid density in overdoped La2-xSrxCuO4sub> films grown by molecular beam epitaxy

    SciTech Connect

    Bozovic, I.; He, X.; Wu, J.; Bollinger, A. T.


    Here, we synthesize La2–xSrxCuO4sub> thin films using atomic layer-by-layer molecular beam epitaxy (ALL-MBE). The films are high-quality—singe crystal, atomically smooth, and very homogeneous. The critical temperature (Tc) shows a very little (<1 K) variation within a film of 10×10 mm 2 area. The large statistics (over 2000 films) is crucial to discern intrinsic properties. We measured the absolute value of the magnetic penetration depth λ with the accuracy better than 1 % and mapped densely the entire overdoped side of the La2–xSrxCuO4sub> phase diagram. A new scaling law is established accurately for the dependence of Tc on the superfluid density. The scaling we observe is incompatible with the standard Bardeen-Cooper-Schrieffer picture and points to local pairing.

  7. Ahrensite, γ-Fe2SiO4sub>, a new shock-metamorphic mineral from the Tissint meteorite: Implications for the Tissint shock event on Mars

    SciTech Connect

    Ma, Chi; Tschauner, Oliver; Beckett, John R.; Liu, Yang; Rossman, George R.; Sinogeikin, Stanislav V.; Smith, Jesse S.; Taylor, Lawrence A.


    Ahrensite (IMA 2013-028), gamma-Fe2SiO4sub>, is the natural Fe-analog of the silicate-spinel ringwoodite (gamma-Mg2SiO4sub>). It occurs in the Tissint Martian meteorite, where it forms through the transformation of the fayalite-rich rims of olivine megacrysts or Ferich microphenocrysts in contact with shock melt pockets. The typical sequence of phase assemblages traversing across a Tissint melt pocket into olivine is: quenched melt or fayalite-pigeonite intergrowth → bridgmanite + wustite → ahrensite and/or ringwoodite double right arrow highly-deformed olivine + nanocrystalline ringwoodite → deformed olivine. We report the first comprehensive set of crystallographic, spectroscopic, and quantitative chemical analysis of type ahrensite, and show that concentrations of ferric iron and inversion in the type material of this newly approved mineral are negligible. We also report the occurrence of nanocrystalline ringwoodite in strained olivine and establish correlations between grain size and distance from melt pockets. The ahrensite and ringwoodite crystals show no preferred orientation, consistent with random nucleation and incoherent growth within a highly strained matrix of olivine. As a result, grain sizes of ahrensite immediately adjacent to melt pockets are consistent with growth during a shock of moderate duration (1-10 ms).

  8. Evidence for monoclinic distortion in the ground state phase of underdoped La1.95Sr0.05CuO4sub>: A single crystal neutron diffraction study

    SciTech Connect

    Singh, Anar; Schefer, Jurg; Sura, Ravi; Conder, Kazimierz; Sibille, Romain F.; Ceretti, Monica; Frontzek, Matthias; Paulus, Werner


    The existing controversy about the symmetry of the crystal structure of the ground state of the critical doped La1.95Sr0.05CuO4sub> has been resolved by analyzing the single crystal neutron diffraction data collected between 5 and 730 K. We observed small but significant intensities for "forbidden" reflections given by extinction rules of the orthorhombic Bmab space group at low temperatures. A careful investigation of neutron diffraction data reveals that the crystal structure of La1.95Sr0.05CuO4sub> at 5 K is monoclinic with B2/m (2/m 1 1) space group. The monoclinic structure emerges from the orthorhombic structure in a continuous way; however, the structure is stable below similar to 120K which agrees with other observed phenomena. Lastly, our results on symmetry changes are crucial for the interpretation of physical properties also in other high temperature superconductors with similar structures.

  9. Evolution of competing magnetic order in the Jeff=1/2 insulating state of Sr2Ir1-xRuxO4sub>

    SciTech Connect

    Calder, Stuart A.; Kim, Jong-Woo; Cao, Guixin; Cantoni, Claudia; May, Andrew F; Cao, Huibo B.; Aczel, Adam A.; Matsuda, Masaaki; Choi, Yongseong; Haskel, Daniel; Sales, B. C.; Mandrus, David; Lumsden, Mark D.; Christianson, Andrew D.


    We investigate the magnetic properties of the series Sr2Ir1-xRuxO4sub> with neutron, resonant x-ray and magnetization measurements. The results indicate an evolution and coexistence of magnetic structures via a spin flop transition from ab-plane to c-axis collinear order as the 5d Ir4+ ions are replaced with an increasing concentration of 4d Ru4+ ions. The magnetic structures within the ordered regime of the phase diagram (x<0.3) are reported. Despite the changes in magnetic structure no alteration of the Jeff=1/2 ground state is observed. This behavior of Sr2Ir1-xRuxO4sub> is consistent with electronic phase separation and diverges from a standard scenario of hole doping. The role of lattice alterations with doping on the magnetic and insulating behavior is considered. Our results presented here provide insight into the magnetic insulating states in strong spin-orbit coupled materials and the role perturbations play in altering the behavior.

  10. Influence of electron doping on the ground state of (Sr1-xLax)2IrO4sub>

    SciTech Connect

    Chen, Xiang; Hogan, Tom; Walkup, D.; Zhou, Wenwen; Pokharel, M.; Yao, Mengliang; Tian, Wei; Ward, Thomas Zac; Zhao, Y.; Parshall, Dr. D.; Opeil, C.; Lynn, J. W.; Madhavan, Vidya; Wilson, Stephen


    The evolution of the electronic properties of electron-doped (Sr1-xLax)2IrO4sub> is experimentally explored as the doping limit of La is approached. As electrons are introduced, the electronic ground state transitions from a spin-orbit Mott phase into an electronically phase separated state, where long-range magnetic order vanishes beyond x = 0:02 and charge transport remains percolative up to the limit of La substitution (x =0:06). In particular, the electronic ground state remains inhomogeneous even beyond the collapse of the parent state's long-range antiferromagnetic order, while persistent short-range magnetism survives up to the highest La-substitution levels. Furthermore, as electrons are doped into Sr2IrO4sub>, we observe the appearance of a low temperature magnetic glass-like state intermediate to the complete suppression of antiferromagnetic order. Universalities and di erences in the electron-doped phase diagrams of single layer and bilayer Ruddlesden-Popper strontium iridates are discussed.

  11. Rate theory of solvent exchange and kinetics of Li+ - BF4sub>-/PF6- ion pairs in acetonitrile

    SciTech Connect

    Dang, Liem X.; Chang, Tsun-Mei


    In this paper, we describe our efforts to apply rate theories in studies of solvent exchange around Li+(aq) and the kinetics of ion pairings in lithium-ion batteries (LIB). We report one of the first computer simulations of the exchange dynamics around hydrated Li+ in acetonitrile (ACN), which is common solvent used in LIBs. We also provide details of the ion-pairing kinetics of Li+-[BF4sub>] and Li+-[PF6] in ACN. Using our polarizable force-field models and employing classical rate theories of chemical reactions, we examine the ACN exchange process between the first and second solvation shells around Li+(aq). We calculate exchange rates using transition state theory and weighted them with transmission coefficients determined by the reactive flux and Impey, Madden, and McDonald approaches and Grote-Hynes theory. We found the relaxation times changed from 180 ps to 4600 ps and from 30 ps to 280 ps for Li+-[BF4sub>] and Li+-[PF6] ion pairs, respectively. These results confirm that the solvent response to the kinetics of ion pairing is significant. Our results also show that, in addition to affecting the free energy of solvation into ACN, the anion type also should significantly influence the kinetics of ion pairing. These results will increase our understanding of the thermodynamic and kinetic properties of LIB systems.

  12. Sodium ion transport mechanisms in antiperovskite electrolytes Na3OBr and Na4sub>OI2: An in Situ neutron diffraction study

    SciTech Connect

    Zhu, Jinlong; Wang, Yonggang; Li, Shuai; Howard, John W.; Neuefeind, Jorg; Ren, Yang; Wang, Hui; Liang, Chengdu; Yang, Wenge; Zou, Ruqiang; Jin, Changqing; Zhao, Yusheng


    Na-rich antiperovskites are recently developed solid electrolytes with enhanced sodium ionic conductivity and show promising functionality as a novel solid electrolyte in an all solid-stat battery. In this work, the sodium ionic transport pathways of the parent compound Na3OBr, as well as the modified layered antiperovskite Na4sub>OI2, were studied and compared through temperature dependent neutron diffraction combined with the maximum entropy method. In the cubic Na3OBr antiperovskite, the nuclear density distribution maps at 500 K indicate that sodium ions ho within and among oxygen octahedra, and Br- ions are not involved in the tetragonal Na4sub>OI2 antiperovskite, Na ions, which connect octahedra in the ab plane, have the lowest activation energy barrier. In conclusion, the transport of sodium ions along the c axis is assisted by I- ions.

  13. Spin-lattice coupling mediated multiferroicity in (ND4sub>)2FeCl5 • D2O

    SciTech Connect

    Tian, Wei; Cao, Huibo; Wang, Jincheng; Ye, Feng; Matsuda, Masaaki; Yan, Jiaqiang; Liu, Yaohua; Garlea, Vasile O.; Agrawal, Harish K.; Chakoumakos, Bryan C.; Sales, Brian C.; Fishman, Randy Scott; Fernandez-Baca, Jaime A.


    In this paper, we report a neutron diffraction study of the multiferroic mechanism in (ND4sub>)2FeCl5 • D2O, a molecular compound that exhibits magnetically induced ferroelectricity. This material exhibits two successive magnetic transitions on cooling: a long-range order transition to an incommensurate (IC) collinear sinusoidal spin state at TN = 7.3 K, followed by a second transition to an IC cycloidal spin state at TFE = 6.8 K, the latter of which is accompanied by spontaneous ferroelectric polarization. The cycloid structure is strongly distorted by spin-lattice coupling, as evidenced by the observations of both odd and even higher-order harmonics associated with the cycloid wave vector, and a weak commensurate phase that coexists with the IC phase. The second-order harmonic appears at TFE, thereby providing unambiguous evidence that the onset of the electric polarization is accompanied by a lattice modulation due to spin-lattice interaction. The neutron results, in conjunction with the negative thermal expansion and large magnetostriction observed, indicate that spin-lattice coupling plays a critical role in the ferroelectric mechanism of (ND4sub>)2FeCl5 • D2O.

  14. Magnetic ordering in the frustrated J1 - J2 Ising chain candidate BaNd2O4sub>

    SciTech Connect

    Aczel, Adam A.; Li, Ling; Garlea, Vasile O.; Yan, Jiaqiang; Weickert, Franziska; Jaime, M.; Maiorov, B.; Movshovich, R.; Civale, L.; Keppens, V.; Mandrus, D.


    The AR2O4sub> family (R = rare earth) has recently been attracting interest as a new series of frustrated magnets, with the magnetic R atoms forming zigzag chains running along the c axis. In this paper, we have investigated polycrystalline BaNd2O4sub> with a combination of magnetization, heat-capacity, and neutron powder diffraction measurements. Magnetic Bragg peaks are observed below TN = 1.7 K, and they can be indexed with a propagation vector of k = (0,1/2,1/2). The signal from magnetic diffraction is well described by long-range ordering of only one of the two types of Nd zigzag chains, with collinear up-up-down-down intrachain spin configurations (double Néel state). Furthermore, low-temperature magnetization and heat-capacity measurements reveal two magnetic-field-induced spin transitions at 2.75 and 4 T for T = 0.46 K. The high-field phase is paramagnetic, while the intermediate-field state may arise from a spin transition of the long-range ordered Nd chains. Finally, one possible candidate for the field-induced ordered state corresponds to an up-up-down intrachain spin configuration, as predicted for a classical J1-J2 Ising chain with a double Néel ground state in zero field.

  15. 1.6  MW peak power, 90  ps all-solid-state laser from an aberration self-compensated double-passing end-pumped Nd:YVO4sub> rod amplifier.


    Wang, Chunhua; Liu, Chong; Shen, Lifeng; Zhao, Zhiliang; Liu, Bin; Jiang, Hongbo


    In this paper a delicately designed double-passing end-pumped Nd:YVO4sub> rod amplifier is reported that produces 10.2 W average laser output when seeded by a 6 mW Nd:YVO4sub> microchip laser at a repetition rate of 70 kHz with pulse duration of 90 ps. A pulse peak power of ∼1.6  MW and pulse energy of ∼143  μJ is achieved. The beam quality is well preserved by a double-passing configuration for spherical-aberration compensation. The laser-beam size in the amplifier is optimized to prevent the unwanted damage from the high pulse peak-power density. This study provides a simple and robust picosecond all-solid-state master oscillator power amplifier system with both high peak power and high beam quality, which shows great potential in the micromachining.

  16. An in-situ phosphorus source for the synthesis of Cu3P and the subsequent conversion to Cu3PS4sub> nanoparticle clusters

    SciTech Connect

    Sheets, Erik J.; Stach, Eric A.; Yang, Wei -Chang; Balow, Robert B.; Wang, Yunjie; Walker, Bryce C.; Agrawal, Rakesh


    The search for alternative earth abundant semiconducting nanocrystals for sustainable energy applications has brought forth the need for nanoscale syntheses beyond bulk synthesis routes. Of particular interest are metal phosphides and derivative I-V-VI chalcogenides including copper phosphide (Cu3P) and copper thiophosphate (Cu3PS4sub>). Herein, we report a one-pot, solution-based synthesis of Cu3P nanocrystals utilizing an in-situ phosphorus source: phosphorus pentasulfide (P2S5) in trioctylphosphine (TOP). By injecting this phosphorus source into a copper solution in oleylamine (OLA), uniform and size controlled Cu3P nanocrystals with a phosphorous-rich surface are synthesized. The subsequent reaction of the Cu3P nanocrystals with decomposing thiourea forms nanoscale Cu3PS4sub> particles having p-type conductivity and an effective optical band gap of 2.36 eV.

  17. Fabrication of ultrathin solid electrolyte membranes of β-Li3PS4sub> nanoflakes by evaporation-induced self-assembly for all-solid-state batteries

    SciTech Connect

    Wang, Hui; Hood, Zachary D.; Xia, Younan; Liang, Chengdu


    All-solid-state lithium batteries are attractive candidates for next-generation energy storage devices because of their anticipated high energy density and intrinsic safety. Owing to their excellent ionic conductivity and stability with metallic lithium anodes, nanostructured lithium thiophosphate solid electrolytes such as β-Li3PS4sub> have found use in the fabrication of all-solid lithium batteries for large-scale energy storage systems. However, current methods for preparing air-sensitive solid electrolyte membranes of lithium thiophosphates can only generate thick membranes that compromise the battery's gravimetric/volumetric energy density and thus its rate performance. To overcome this limitation, the solid electrolyte's thickness needs to be effectively decreased to achieve ideal energy density and enhanced rate performance. In this paper, we show that the evaporation-induced self-assembly (EISA) technique produces ultrathin membranes of a lithium thiophosphate solid electrolyte with controllable thicknesses between 8 and 50 μm while maintaining the high ionic conductivity of β-Li3PS4sub> and stability with metallic lithium anodes up to 5 V. Finally, it is clearly demonstrated that this facile EISA approach allows for the preparation of ultrathin lithium thiophosphate solid electrolyte membranes for all-solid-state batteries.

  18. [NH{sub 3}(CH{sub 2}){sub 2}NH{sub 3}][Co(SO{sub 4}){sub 2}(H{sub 2}O){sub 4}]: Chemical preparation, crystal structure, thermal decomposition and magnetic properties

    SciTech Connect

    Rekik, Walid; Naili, Houcine; Mhiri, Tahar; Bataille, Thierry


    Cobalt ethylenediammonium bis(sulfate) tetrahydrate, [NH{sub 3}(CH{sub 2}){sub 2}NH{sub 3}][Co(SO{sub 4}){sub 2}(H{sub 2}O){sub 4}], has been synthesised by slow evaporation at room temperature. It crystallises in the triclinic system, space group P1-bar, with the unit cell parameters: a = 6.8033(2), b 7.0705(2), c = 7.2192(3) A, {alpha} = 74.909(2){sup o}, {beta} = 72.291(2){sup o}, {gamma} = 79.167(2){sup o}, Z = 1 and V = 317.16(2) A{sup 3}. The Co(II) atom is octahedrally coordinated by four water molecules and two sulfate tetrahedra leading to trimeric units [Co(SO{sub 4}){sub 2}(H{sub 2}O){sub 4}]. These units are linked to each other and to the ethylenediammonium cations through OW-H...O and N-H...O hydrogen bonds, respectively. The zero-dimensional structure is described as an alternation between cationic and anionic layers along the crystallographic b-axis. The dehydration of the precursor proceeds through three stages leading to crystalline intermediary hydrate phases and an anhydrous compound. The magnetic measurements show that the title compound is predominantly paramagnetic with weak antiferromagnetic interactions.

  19. Synthesis and X-ray structural investigation of K{sub 2}(H{sub 5}O{sub 2})[UO{sub 2}(C{sub 2}O{sub 4}){sub 2}(HSeO{sub 3})

    SciTech Connect

    Pushkin, D. V.; Peresypkina, E. V.; Serezhkina, L. B.; Marukhnov, A. V.; Virovets, A. V.


    The synthesis and X-ray diffraction analysis of K{sub 2}(H{sub 5}O{sub 2})[UO{sub 2}(C{sub 2}O{sub 4}){sub 2}(HSeO{sub 3})] single crystals have been performed. This compound crystallizes in the triclinic system with the unit-cell parameters a = 6.7665(4) Angstrom-Sign , b = 8.8850(4) Angstrom-Sign , c = 12.3147(7) Angstrom-Sign , {alpha} = 94.73 Degree-Sign , {beta} = 90.16 Degree-Sign , {gamma} = 92.11 Degree-Sign , sp. gr. P1-bar, Z = 2, and R = 0.019. The basic structural units are island [UO{sub 2}(C{sub 2}O{sub 4}){sub 2}(HSeO{sub 3})]{sup 3-} groups, which belong to the AB{sub 2}{sup 01}M{sup 1} crystallochemical group of uranyl complexes (A = UO{sub 2}{sup 2+}, B{sup 01} = C{sub 2}O{sub 4}{sup 2-}, and M{sub 1} = HSeO{sub 3}{sup -}). Uraniumcontaining complexes are linked through K{sup +} and H{sub 5}O{sub 2}{sup +} ions and via a system of hydrogen bonds with the participation of oxonium hydrogen atoms in this structure.

  20. Novel Dy{sup 3+}-doped Ca{sub 2}Gd{sub 8}(SiO{sub 4}){sub 6}O{sub 2} white light phosphors for Hg-free lamps application

    SciTech Connect

    Wang, Yuhua; Wen, Yan; Zhang, Feng


    The luminescent properties of Ca{sub 2}Gd{sub 8(1-x)}(SiO{sub 4}){sub 6}O{sub 2}:xDy{sup 3+} (1% {<=} x {<=} 5%) powder crystals with oxyapatite structure were investigated under vacuum ultraviolet excitation. In the excitation spectrum, the peaks at 166 nm and 191 nm of the vacuum ultraviolet region can be assigned to the O{sup 2-} {yields} Gd{sup 3+}, and O{sup 2-} {yields} Dy{sup 3+} charge transfer band respectively, which is consistent with the theoretical calculated value using J{phi}rgensen's empirical formula. While the peaks at 183 nm and 289 nm are attributed to the f-d spin-allowed transitions and the f-d spin-forbidden transitions of Dy{sup 3+} in the host lattice with Dorenbos's expression. According to the emission spectra, all the samples exhibited excellent white emission under 172 nm excitation and the best calculated chromaticity coordinate was 0.335, 0.338, which indicates that the Ca{sub 2}Gd{sub 8}(SiO{sub 4}){sub 6}O{sub 2}:Dy{sup 3+} phosphor could be considered as a potential candidate for Hg-free lamps application.

  1. Hydrothermal synthesis and crystal structure of a new inorganic/organic hybrid of scandium sulfate: (H{sub 2}en)Sc{sub 2}(SO{sub 4}){sub 4}.(H{sub 2}O){sub 0.72}

    SciTech Connect

    Lu Jianjiang . E-mail:; Schlueter, John A.; Geiser, Urs


    The first organically templated layered structure of scandium sulfate, (H{sub 2}en)Sc{sub 2}(SO{sub 4}){sub 4}.(H{sub 2}O){sub 0.72}, (en=ethylenediamine) was synthesized by a hydrothermal method and characterized by single crystal X-ray diffraction. In the title compound, scandium ions are bridged by sulfate groups with a ratio of 1:2 into a 4{sub 3}{sup 6} layer structure. These layers are parallel packed and separated from each other by ethylenediammonium dications and water molecules. The title compound crystallizes in the monoclinic space group P2/c, with cell parameters a=8.5966(13)A, b=5.1068(8)A, c=18.847(3)A, {beta}=91.210(3){sup o}, V=827.2(2)A{sup 3} and Z=2. Refinement gave R{sub 1}[I>2{sigma}(I)]=0.0354 and wR{sub 2}[I>2{sigma}(I)]=0.0878. Thermogravimetric analysis indicates that this material is thermally stable to above 400 deg. C.

  2. F -state quenching with CH 4sub> for buffer-gas cooled 171 Y b + frequency standard [Methane (CH4) for quenching the F-state in trapped Yb+ ions].

    SciTech Connect

    Jau, Y. -Y.; Hunker, J. D.; Schwindt, P. D. D.


    We report that methane, CH4sub>, can be used as an efficient F-state quenching gas for trapped ytterbium ions. The quenching rate coefficient is measured to be (2.8 ± 0.3) × 106 s-1 Torr-1. For applications that use microwave hyperfine transitions of the ground-state 171Y b ions, the CH4 induced frequency shift coefficient and the decoherence rate coefficient are measured as δν/ν = (-3.6 ± 0.1) × 10-6 Torr-1 and 1/T2 = (1.5 ± 0.2) × 105 s-1 Torr-1. In our buffer-gas cooled 171Y b+ microwave clock system, we find that only ≤10-8 Torr of CH4sub> is required under normal operating conditions to efficiently clear the F-state and maintain ≥85% of trapped ions in the ground state with insignificant pressure shift and collisional decoherence of the clock resonance.

  3. The excited state dynamics of KLa(MoO{sub 4}){sub 2}:Pr{sup 3+}: From a case study to the determination of the energy levels of rare earth impurities relative to the bandgap in oxidising host lattices

    SciTech Connect

    Cavalli, Enrico Boutinaud, Philippe; Bettinelli, Marco; Dorenbos, Pieter


    The luminescence properties of KLa(MoO{sub 4}){sub 2} (KLM) single crystals doped with Pr{sup 3+} have been measured in the 10-600 K temperature range in order to investigate the mechanisms involved in the radiationless processes. At variance with previously studied scheelite-like molybdates activated with Pr{sup 3+}, no effects attributed to the formation of intervalence charge transfer states have been observed. The model proposed in order to account for this behaviour allows the determination of the energy of the Pr{sup 3+} levels relative to the valence and conduction bands of the host. This model has firstly been confirmed for Tb{sup 3+}-doped KLM, for which suitable experimental data are available, and then extended to the other rare earth ions on the basis of the systematic nature of the lanthanide energy levels properties. The obtained conclusions are finally supported in the light of the comparison with some other representative cases. - Graphical abstract: The study of the excited state dynamics of KLa(MoO{sub 4}){sub 2} single crystals doped with Pr{sup 3+} allows to determine the energies of the levels of the active ion relative to the valence and conduction bands of the host. This model has then been extended to the other rare earth ions on the basis of the systematic nature of the lanthanide energy levels properties.

  4. Quadratic general rotary unitized design for doping concentrations and up-conversion luminescence properties of Er{sup 3+}/Yb{sup 3+} co-doped NaLa(MoO{sub 4}){sub 2} phosphors

    SciTech Connect

    Sun, Jiashi Shi, Linlin; Li, Shuwei; Li, Jingjing; Li, Xiangping Zhang, Jinsu; Cheng, Lihong; Chen, Baojiu


    Highlights: • NaLa(MoO4)2: Er3+/Yb3+ phosphor is synthesized by solid state method. • QGRUD is first applied to the codoping concentration option. • Optimized phosphor presents more stable UC emissions than the commercial phosphor. - Abstract: It is still a great challenge that designing proper codoping concentrations of rare earth ions for achieving intensest expected emission from the studied phosphor. In this work, the quadratic general rotary unitized design (QGRUD) was introduced into the codoping concentration option of NaLa(MoO{sub 4}){sub 2}: Er{sup 3+}/Yb{sup 3+} phosphor for upconversion (UC) applications, and the optimum doping concentrations of Er{sup 3+} and Yb{sup 3+} for achieving maximum UC luminescence intensity, which is close to commercial NaYF{sub 4}:Er{sup 3+}/Yb{sup 3+} phosphor, were obtained. The two-photon process was assigned to the green UC emissions in the optimized NaLa(MoO{sub 4}){sub 2}: Er{sup 3+}/Yb{sup 3+} phosphor. It was also demonstrated that the optimized phosphor presented more stable upconversion emissions than the commercial NaYF{sub 4}:Er{sup 3+}/Yb{sup 3+} phosphor.

  5. Origin of periodic domain structure in Er{sup 3+}-doped beta'-(Sm,Gd){sub 2}(MoO{sub 4}){sub 3} crystal lines patterned by laser irradiations in glasses

    SciTech Connect

    Suzuki, Futoshi; Honma, Tsuyoshi; Komatsu, Takayuki


    Er{sup 3+}-doped beta'-(Sm,Gd){sub 2}(MoO{sub 4}){sub 3} crystal lines are patterned on the surface of Er{sub 2}O{sub 3}-Gd{sub 2}O{sub 3}-Sm{sub 2}O{sub 3}-MoO{sub 3}-B{sub 2}O{sub 3} glasses by continuous-wave Yb:YVO{sub 4} laser irradiations (wavelength: 1080 nm, power: 1.3 W, scanning speeds: 5 {mu}m/s), and the origin of the periodicity of self-organized domain structures with high and low refractive index regions in crystal lines is examined from polarized optical microscope (POM) observations, micro-Raman scattering spectrum, and photoluminescence spectrum measurements. It is found that the periodicity of domain structures changes largely depending on Er{sub 2}O{sub 3} content, i.e., the length of high (bright color in POM observations) and low (dark color) refractive index regions increases with increasing Er{sub 2}O{sub 3} content and homogeneous crystal lines with no periodic domain structures are patterned in Er{sub 2}O{sub 3}-Sm{sub 2}O{sub 3}-MoO{sub 3}-B{sub 2}O{sub 3} glass with no Gd{sub 2}O{sub 3}. Considering that the degree of ferroelasticities in beta'-(Sm,Gd){sub 2}(MoO{sub 4}){sub 3} crystals decreases due to the incorporation of Er{sup 3+} ions, it is demonstrated that the origin of periodic domain structures in laser-patterned lines is due to spontaneous strains in ferroelastic beta'-(Sm,Gd){sub 2}(MoO{sub 4}){sub 3} crystals. - Graphical abstract: This figure shows the polarized optical photographs (top view) for the lines patterned by laser irradiations with the power of P=1.3 W and the scanning speed of S=5 {mu}m/s in xEr{sub 2}O{sub 3}-(18.25-x)Gd{sub 2}O{sub 3}-3Sm{sub 2}O{sub 3}-63.75MoO{sub 3}-15B{sub 2}O{sub 3} (mol%) glasses. This figure indicates that the periodicity of domain structures in beta'-(Sm,Gd){sub 2}(MoO{sub 4}){sub 3} crystal lines, i.e., the lengths of bright (high refractive index) and dark (low refractive index) color regions, changes depending on the amount of Er{sub 2}O{sub 3} addition. It is demonstrated that the

  6. Neutron diffraction and thermoelectric properties of indium filled In x Co 4sub> Sb 12 ( x=0.05, 0.2) and indium cerium filled Ce 0.05 In 0.1 Co 4sub> Sb 12 skutterudites: Neutron diffraction and thermoelectric properties of In/Ce skutterudites

    SciTech Connect

    Sesselmann, Andreas; Klobes, Benedikt; Dasgupta, Titas; Gourdon, Olivier; Hermann, Raphael; Mueller, Eckhard


    The thermoelectric properties on polycrystalline single (In) and double filled (Ce, In) skutterudites are characterized between 300 and 700 K. Powder neutron diffraction measurements of the skutterudite compositions InxCo4sub>Sb12 (x= 0.05, 0.2) and Ce0.05In0.1Co4sub>Sb12 as a function of temperature (12- 300 K) were carried out, which gives more insight into the structural data of single and double-filled skutterudites. Our results show that due to the annealing treatment, a Sb deficiency is detectable and thus verifies defects at the Sb lattice site of the skutterudite. Furthermore, we show by electron microprobe analysis that a considerable amount of indium is lost during synthesis and post-processing for the single indium filled samples, but not for the double cerium and indium skutterudite sample. The double-filled skutterudite is superior to the single-filled skutterudite composition due to a higher charge carrier density, a comparable lattice thermal resistivity, and a higher density of states effective mass in our experiment. Finally, we obtained a significantly higher Einstein temperature for the double-filled skutterudite composition in comparison to the single-filled species, which reflects the high sensitivity due to filling of the void lattice position within the skutterudite crystal.

  7. The red-emitting phosphors of Eu{sup 3+}-activated MR{sub 2}(MoO{sub 4}){sub 4} (M = Ba, Sr, Ca; R = La{sup 3+}, Gd{sup 3+}, Y{sup 3+}) for light emitting diodes

    SciTech Connect

    Qin, Lin; Huang, Yanlin; Tsuboi, Taiju; Seo, Hyo Jin


    Graphical abstract: The luminescence quantum efficiencies of Eu{sup 3+}-doped MY{sub 2−x}Eu{sub x}(MoO{sub 4}){sub 4} show the dependence on the Eu{sup 3+} doping (x) for M = Ca (a), Sr (b), Ba (c). Display Omitted Highlights: ► Eu{sup 3+}-activated MY{sub 2}(MoO{sub 4}){sub 4} (M = Ba, Sr, Ca) were firstly prepared. ► Comprehensive investigations of QEs and thermal stabilities of Eu{sup 3+}-activated MR{sub 2}(MoO{sub 4}){sub 4} (M = Ba, Sr, Ca; R = La, Gd). ► BaYEu(MoO{sub 4}){sub 4}, SrY0.6Eu1.4(MoO{sub 4}){sub 4} and CaEu{sub 2}(MoO{sub 4}){sub 4} are the best choice for solid state lighting because of high QEs and thermal stabilities. -- Abstract: A series of red-emitting phosphors of MR{sub 2}(MoO{sub 4}){sub 4}:Eu{sup 3+} (M = Ba, Sr, Ca; R = La{sup 3+}, Gd{sup 3+}, Y{sup 3+}) were prepared by solid-state reaction. The photoluminescence excitation and emission spectra were investigated. The phosphors can be efficiently excited by the near UV light and exhibit a red luminescence corresponding to the electric dipole transition {sup 5}D{sub 0} → {sup 7}F{sub 2} at 615 nm. The optimum doping in MY{sub 2−x}Eu{sub x}(MoO{sub 4}){sub 4} (M = Ba, Sr, Ca) were investigated by the dependence of luminescence quantum efficiency (QE) on the Eu{sup 3+} concentrations. The absolute luminescence quantum efficiencies were measured for all the samples. The luminescence thermal satiability was checked by measuring the temperature-dependent luminescence intensities in temperature region of 10–450 K. The results indicate that the three phosphors of BaYEu(MoO{sub 4}){sub 4}, SrY{sub 0.6}Eu{sub 1.4}(MoO{sub 4}){sub 4} and CaEu{sub 2}(MoO{sub 4}){sub 4} are the best choice for white-LEDs to be used for lighting. This was evaluated in details by taking into account of the properties such as the excitation spectra, the luminescence QEs, the red color coordinates, the luminescence quenching of Eu{sup 3+}-doping concentrations and the thermal stability.

  8. A study of spin canting in Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} with Mössbauer spectroscopy under 5 T

    SciTech Connect

    Kim, Hee Seung; Kim, Chul Sung


    Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} has been actively studied as a Lithium ion battery cathode material for the next-generation energy storage application. Here, we have investigated the changes of magnetic coupling between two different magnetic sub-lattices in Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} with x-ray diffraction (XRD), superconducting quantum interference device (SQUID), and Mössbauer spectroscopy measurements. The experimental XRD pattern was analyzed using Rietveld refinement, confirming single phase. In order to investigate the magnetic property, the SQUID measurement under applied field of 5 T was performed between 4.2 and 295 K. From the temperature-dependent zero-field-cooled and field-cooled magnetization curves, we observed the magnetization decreasing with increasing temperature up to T{sub min} = 13 K, at which the magnetization showed a minimum value. With continuing increase in temperature, the magnetization starts increasing with a maximum value at T{sub max} = 28 K and beyond T{sub max}, the magnetization decreases with the further increase in temperature. Based on the experimentally measured Mössbauer spectra, we identified that the ratios of first and sixth to second and fifth absorption lines were identical around T{sub min}, while with increasing temperature the area of second and fifth absorption line rapidly decreased up to T{sub max}. Our study suggests that the spin canting angle between the applied field and hyperfine field of Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} is constant up to T{sub min}. However, the spin canting angle starts decreasing with increasing temperature, reaching a minimum value at T{sub max}, and beyond T{sub max} it is increasing. We expect that around T{sub max}, the ferrimagnetically coupled spin arrangement is appeared to be collinear along the applied field direction under applied field of 5 T.

  9. Intrinsic Nanostructure in Zr2-xFe4sub>Si16-y(x=0.81, y=6.06)

    SciTech Connect

    Smith, G J; Simonson, J W; Orvis, T; Marques, C; Grose, J E; Kistner-Morris, J J; Wu, L; Cho, Kyuil; Kim, Hyong june; Tanatar, Makariy A; Garlea, V O; Prozorov, Ruslan; Zhu, Y; Aronson, M C


    We present a study of the crystal structure and physical properties of single crystals of a new Fe-based ternary compound, Zr2-xFe4sub>Si16-y(x=0.81,y=6.06). Zr1.19Fe4sub>Si9.94 is a layered compound, where stoichiometric β-FeSi2-derived slabs are separated by Zr-Si planes with substantial numbers of vacancies. High resolution transmission electron microscopy (HRTEM) experiments show that these Zr-Si layers consist of 3.5nm domains where the Zrand Si vacancies are ordered within a supercell sixteen times the volume of the stoichiometric cell. Within these domains, the occupancies of the Zr and Si sites obey symmetry rules that permit only certain compositions, none of which by themselves reproduce the average composition found in x-ray diffraction experiments. Magnetic susceptibility and magnetization measurements reveal a small but appreciable number of magnetic moments that remain freely fluctuating to 1.8K, while neutron diffraction confirms the absence of bulk magnetic order with a moment of 0.2μB or larger down to 1.5K. Electrical resistivity measurements find that Zr1.19Fe4sub>Si9.94 is metallic, and the modest value of the Sommerfeld coefficient of the specific heat γ = C/T suggests that quasi-particle masses are not particularly strongly enhanced. The onset of superconductivity at Tc ≃ 6K results in a partial resistive transition and a small Meissner signal, although a bulk-like transition is found in the specific heat. Sharp peaks in the ac susceptibility signal the interplay of the normal skin depth and the London penetration depth, typical of a system in which nano-sized superconducting grains are separated by a on-superconducting host. Ultra low field differential magnetic susceptibility measurements reveal the presence of a surprisingly large number of trace magnetic and superconducting phases, suggesting that the Zr-Fe-Si ternary system

  10. Synthetic and spectroscopic studies of vanadate glaserites I: Upconversion studies of doubly co-doped (Er, Tm, or Ho):Yb:K{sub 3}Y(VO{sub 4}){sub 2}

    SciTech Connect

    Kimani, Martin M. Chen, Hongyu McMillen, Colin D. Anker, Jeffery N. Kolis, Joseph W.


    The synthesis and upconversion properties of trigonal glaserite-type K{sub 3}Y(VO{sub 4}){sub 2} co-doped with Er{sup 3+}/Yb{sup 3+}, Ho{sup 3+}/Yb{sup 3+}, or Tm{sup 3+}/Yb{sup 3+} were studied. Powder samples were synthesized by solid state reactions at 1000 °C for 48 h, while well-formed hexagonal single crystals of the same were grown hydrothermally using 10 M K{sub 2}CO{sub 3} at 560–650 °C. Infrared-to-visible upconversion by Er{sup 3+}/Yb{sup 3+}, Ho{sup 3+}/Yb{sup 3+}, or Tm{sup 3+}/Yb{sup 3+} codoped-K{sub 3}Y(VO{sub 4}){sub 2} glaserite powder and single crystals was observed, and the upconversion spectral properties were studied as a function of different Er{sup 3+}, Tm{sup 3+}, Ho{sup 3+}, and Yb{sup 3+} ion concentrations. The process is observed under 980 nm laser diode excitation and leads to strong green (552 nm) and red (659 nm) emission for Er{sup 3+}/Yb{sup 3+}, green (549 nm) and red (664 nm) emission for Ho{sup 3+}/Yb{sup 3+}, and blue (475 nm) and red (647 nm) emission for Tm{sup 3+}/Yb{sup 3+}. The main mechanism that allows for up-conversion is attributed the energy transfer among Yb{sup 3+} and the various Er{sup 3+}/Ho{sup 3+}/Tm{sup 3+} ions in excited states. These results illustrate the large potential of co-doped alkali double vanadates for photonic applications involving optoelectronics devices. - Graphical abstract: Synthesis and upconversion in vanadate glaserites. - Highlights: • K{sub 3}Y(VO{sub 4}){sub 2} codoped with Er, Tm, or Ho:Yb were synthesized via solid-state and hydrothermal routes. • Upconversion properties are investigated. • The codoped compounds revealed efficient infrared-to-visible upconversion. • The presented compounds are potential host for solid state lighting.

  11. Preparation and spectroscopic properties of rare-earth (RE) (RE = Sm, Eu, Tb, Dy, Tm)-activated K{sub 2}LnZr(PO{sub 4}){sub 3} (Ln = Y, La, Gd and Lu) phosphate in vacuum ultraviolet region

    SciTech Connect

    Zhang, Zhi-Jun; Lin, Xiao; Zhao, Jing-Tai; Zhang, Guo-Bin


    Graphical abstract: Display Omitted Highlights: ► We report the VUV spectroscopic properties of rare-earth ions in K{sub 2}LnZr(PO{sub 4}){sub 3}. ► The O{sup 2−}-Eu{sup 3+} charge transfer bands at about 220 nm have been observed. ► The 4f–5d spin-allowed and spin-forbidden transitions of Tb{sup 3+} have been observed. ► There is energy transfer between the host and rare-earth activators. -- Abstract: Rare earth (RE = Sm, Eu, Tb, Dy and Tm)-activated K{sub 2}LnZr(PO{sub 4}){sub 3} (Ln = Y, La, Gd and Lu) have been synthesized by solid-state reaction method, and their vacuum ultraviolet (VUV) excitation luminescent characteristics have been investigated. The band in the wavelength range of 130–157 nm and the other one range from 155 to 216 nm with the maximum at about 187 nm in the VUV excitation spectra of these compounds are attributed to the host lattice absorption and O–Zr charge transfer transition, respectively. The charge transfer bands (CTB) of O{sup 2−}-Sm{sup 3+}, O{sup 2−}-Dy{sup 3+} and O{sup 2−}-Tm{sup 3+}, in Sm{sup 3+}, Dy{sup 3+} and Tm{sup 3+}-activated samples, have not been obviously observed probably because the 2p electrons of oxygen are tightly bound to the zirconium ion in the host lattice. For Eu{sup 3+}-activated samples, the relatively weak O{sup 2−}-Eu{sup 3+} CTB at about 220 nm is observed. And for Tb{sup 3+}-activated samples, the bands at 223 and 258 nm are related to the 4f-5d spin-allowed and spin-forbidden transitions of Tb{sup 3+}, respectively. It is observed that there is energy transfer between the host lattice and the luminescent activators (e.g. Eu{sup 3+}, Tb{sup 3+}). From the standpoint of luminescent efficiency, color purity and chemical stability, K{sub 2}GdZr(PO{sub 4}){sub 3}:Sm{sup 3+}, Eu{sup 3+}, Tb{sup 3+} are attractive candidates for novel yellow, red, green-emitting PDP phosphors.

  12. van der Waals forces and confinement in carbon nanopores: Interaction between CH4sub>, COOH, NH3, OH, SH and single-walled carbon nanotubes

    SciTech Connect

    Weck, Philippe F.; Kim, Eunja; Wang, Yifeng


    Interactions between CH4sub>, COOH, NH3, OH, SH and armchair (n,n)(n=4,7,14) and zigzag (n,0)(n=7,12,25) single-walled carbon nanotubes (SWCNTs) have been systematically investigated within the framework of dispersion-corrected density functional theory (DFT-D2). Endohedral and exohedral molecular adsorption on SWCNT walls is energetically unfavorable or weak, despite the use of C6/r6 pairwise London-dispersion corrections. The effects of pore size and chirality on the molecule/SWCNTs interaction were also assessed. Furthermore, chemisorption of COOH, NH3, OH and SH at SWCNT edge sites was examined using a H-capped (7,0) SWCNT fragment and its impact on electrophilic, nucleophilic and radical attacks was predicted by means of Fukui functions.

  13. Sub-80 femtosecond pulses generation from a diode-pumped mode-locked Nd:Ca3La2(BO3)4sub> disordered crystal laser.


    Ma, Jie; Pan, Zhongben; Cai, Huaqiang; Yu, Haohai; Zhang, Huaijin; Shen, Deyuan; Tang, Dingyuan


    We experimentally demonstrated a diode-pumped sub-80 fs Nd:Ca3La2(BO3)4sub> disordered crystal laser. Pumping by an 808 nm fiber coupled laser diode, stable continuous-wave mode-locked pulses as short as 79 fs were achieved with a semiconductor saturable absorber mirror (SESAM). The ultrashort pulses had a repetition rate of ∼98.9  MHz at the central wavelength of about 1068 nm. To the best of our knowledge, this is the first demonstration of sub-100 fs pulses and the shortest mode-locked pulses generated from the Nd3+-doped crystal lasers.

  14. High-Pressure Single-Crystal Neutron Scattering Study of Magnetic and Fe Vacancy Orders in (Tl,Rb)2 Fe4sub> Se5 Superconductor

    SciTech Connect

    Ye, Feng; Bao, Wei; Chi, Song-Xue; Santos, Antonio M. dos; Molaison, Jamie J.; Fang, Ming-Hu; Wang, Hang-Dong; Mao, Qian-Hui; Wang, Jin-Chen; Liu, Juan-Juan; Sheng, Jie-Ming


    We investigate the magnetic and iron vacancy orders in superconducting (Tl,Rb)2Fe4sub>Se5 single-crystals by using a high-pressure neutron diffraction technique. Similar to the temperature effect, the block antiferromagnetic order gradually decreases upon increasing pressure while the Fe vacancy superstructural order remains intact before its precipitous disappearance at the critical pressure Pc = 8.3 GPa. Combined with previously determined Pc for superconductivity, our phase diagram under pressure reveals the concurrence of the block AFM order, the √5 × √5 iron vacancy order and superconductivity for the 245 superconductor. Lastly, a synthesis of current experimental data in a coherent physical picture is attempted.

  15. Synthesis and characterization of Sr{sub (10-x)}Cd{sub x}(PO{sub 4}){sub 6}Y{sub 2} (Y = OH and F): A comparison of apatites containing two divalent cations

    SciTech Connect

    Badraoui, Bechir; Aissa, Abdallah; Bigi, Adriana; Debbabi, Mongi; Gazzano, Massimo


    Cadmium substituted strontium hydroxy- and fluoro-apatites, Sr{sub (10-x)}Cd{sub x}(PO{sub 4}){sub 6}Y{sub 2} (Y = OH and F), have been prepared as single phases in the 0 {<=} x {<=} 4 interval for the former and 0 {<=} x {<=} 6 for the latter compound, respectively. The refinements of the X-ray full powder patterns allowed the structure determination of nine samples, and showed a preference of cadmium atoms for the M(1) site in fluoroapatite samples. IR investigation gave information about the nature of the metal oxygen interactions. The obtained results are used for a comparative discussion about the factors which drive the mutual substitution of Ca, Sr, Cd and Pb in apatites. The important role of electronegativity and polarisability, as well as of ionic radii, is evidenced.

  16. High power, tunable mid-infrared BaGa4sub>Se7 optical parametric oscillator pumped by a 2.1 μm Ho:YAG laser.


    Yuan, Jin-He; Li, Chao; Yao, Bao-Quan; Yao, Ji-Yong; Duan, Xiao-Ming; Li, Ying-Yi; Shen, Ying-Jie; Wu, Yi-Cheng; Cui, Zheng; Dai, Tong-Yu


    We, for the first time, demonstrate a tunable mid-infrared BaGa4sub>Se7-based optical parametric oscillator pumped by a acousto-optical Q-switched Ho:YAG laser at 2090.6 nm. Up to 1.55 W of average power was generated in the 3-5 μm range, corresponding to an optical-to-optical conversion efficiency of 14.4% and a slope efficiency of 19.9%. The mid-IR radiation spectra were also seriously researched at different phase-matched angles. The tunable range was 3.49-4.13 μm for the signal, and 5.19-4.34 μm for the idler.

  17. Wavelength-dependent optical enhancement of superconducting interlayer coupling in La1.885Ba0.115CuO4sub>

    SciTech Connect

    Casandruc, E.; Nicoletti, D.; Rajasekaran, S.; Laplace, Y.; Khanna, V.; Gu, G.; Hill, J. P.; Cavalleri, A.


    We analyze the pump wavelength dependence for the photo-induced enhancement of interlayer coupling in La1.885Ba0.115CuO4sub>, which is promoted by optical melting of the stripe order. In the equilibrium superconducting state (T < TC = 13 K), in which stripes and superconductivity coexist, time-domain THz spectroscopy reveals a photo-induced blue-shift of the Josephson Plasma Resonance after excitation with optical pulses polarized perpendicular to the CuO2 planes. In the striped, non-superconducting state (TC < T < TSO ≃ 40 K) a transient plasma resonance similar to that seen below TC appears from a featureless equilibrium reflectivity. Most strikingly, both these effects become stronger upon tuning of the pump wavelength from the mid-infrared to the visible, underscoring an unconventional competition between stripe order and superconductivity, which occurs on energy scales far above the ordering temperature.

  18. Preservation of fluorescence and Raman gain in the buried channel waveguides in neodymium-doped KGd(WO{sub 4}){sub 2}(Nd:KGW) by femtosecond laser writing

    SciTech Connect

    Liu Xiaoyu; Qu Shiliang; Tan Yang; Chen Feng


    We report on the preservation of fluorescence and Raman gain in low-repetition-rate femtosecond laser written buried channel waveguides in neodymium-doped KGd(WO{sub 4}){sub 2}. The propagation loss index, profile reconstruction, and calculation of the modal intensity distribution by the beam propagation method of the waveguide are presented. Microluminescence spectra of the waveguides show that the fluorescence properties of Nd{sup 3+} ions are not significantly affected by the waveguide formation processing, which indicates a fairly good potential for further laser actions in a compact device. Micro-Raman spectra are also performed to reveal the preservation of the characteristic 768 and 901 cm{sup -1} Raman mode intensities in the guiding regions.

  19. Mechanochemical transformation of mixtures of Ca(OH){sub 2} and (NH{sub 4}){sub 2}HPO{sub 4} or P{sub 2}O{sub 5}

    SciTech Connect

    Gonzalez, G. . E-mail:; Sagarzazu, A.; Villalba, R.


    A detailed comparative study of the mechanochemical transformation of two mixtures: Ca(OH){sub 2}-(NH{sub 4}){sub 2}HPO{sub 4} and Ca(OH){sub 2}-P{sub 2}O{sub 5}, milled in a mortar dry grinder for different periods of time was carried out. The phase transformations obtained at each milling stage were studied by X-ray diffraction, infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry and thermogravimetric analysis. The transformations taking place during the first periods of milling are very different for both mixtures. However, prolonged milling, over nearly the same period, causes amorphization of both mixtures. DSC analysis of the milled powders showed the temperature of crystallization of hydroxyapatite and tricalcium phosphate ({beta}-TCP). Calcinations of all the different milled powders at 800 deg. C for 2 h, results in the formation of hydroxyapatite and {beta}-TCP.

  20. Effect of Spin-Crossover-Induced Pore Contraction on CO2–Host Interactions in the Porous Coordination Polymers [Fe(pyrazine)M(CN)4sub>] (M = Ni, Pt)

    SciTech Connect

    Culp, Jeffrey T; Chen, De-Li; Liu, Jinchen; Chirdon, Danielle; Kauffman, Kristi; Goodman, Angela; Johnson, J Karl


    Variable-temperature in situ ATR-FTIR spectra are presented for the porous spin-crossover compounds [Fe(pyrazine)Ni(CN)4sub>] and [Fe(pyrazine)Pt(CN)4sub>] under CO2 pressures of up to 8 bar. Significant shifts in the ν3 and ν2 IR absorption bands of adsorbed CO2 are observed as the host materials undergo transition between low- and high-spin states. Computational models used to determine the packing arrangement of CO2 within the pore structures show a preferred orientation of one of the adsorbed CO2 molecules with close O=C=O···H contacts with the pyrazine pillar ligands. The interaction is a consequence of the commensurate distance of the inter-pyrazine separations and the length of the CO2 molecule, which allows the adsorbed CO2 to effectively bridge the pyrazine pillars in the structure. The models were used to assign the distinct shifts in the IR absorption bands of the adsorbed CO2 that arise from changes in the O=C=O···H contacts that strengthen and weaken in correlation with changes in the Fe–N bond lengths as the spin state of Fe changes. The results indicate that spin-crossover compounds can function as a unique type of flexible sorbent in which the pore contractions associated with spin transition can affect the strength of CO2–host interactions.

  1. Synthesis, structure and characterisation of Fe{sub 0.50}Ti{sub 2}(PO{sub 4}){sub 3}: A new material with Nasicon-like structure

    SciTech Connect

    Benmokhtar, S. El Jazouli, A.; Aatiq, A.; Chaminade, J.P.; Gravereau, P.; Wattiaux, A.; Fournes, L.; Grenier, J.C.


    A new iron titanyl phosphate Fe{sub 0.50}Ti{sub 2}(PO{sub 4}){sub 3} was synthesized by both solid-state reaction and Cu{sup 2+}-Fe{sup 2+} ion exchange method. The material was then characterized by X-ray diffraction, Mossbauer, magnetic susceptibility measurements and optical absorption. The crystal structure of the compound was refined, using X-ray powder diffraction data, by the Rietveld profile method; it crystallizes in the rhombohedral system, space group R3-bar, with a=8.511(1)A and c=20.985(3)A, V=1316.45(3)A{sup 3} and Z=6. The structure, which is compared to that of Mn{sub 0.50}Ti{sub 2}(PO{sub 4}){sub 3} is built up from [TiO{sub 6}] octahedra and [PO{sub 4}] tetrahedra which are linked by corner sharing along the c-axis. Fe{sup 2+} cations are located in half of the antiprism M{sub I} sites and are orderly distributed with vacancies within the two possible positions of the M{sub I} sites of R3-bar. These results were supported by the Mossbauer studies that showed the presence of one Fe{sup 2+} site in the high spin state (t{sub 2g}{sup 4}e{sub g}{sup 2}). The Curie-Weiss-type behavior is observed in the magnetic susceptibility. Diffuse reflectance spectrum indicates the presence of octahedrally coordinated Fe{sup 2+} ions.

  2. Visible quantum cutting through downconversion in GdPO{sub 4}:Tb{sup 3+} and Sr{sub 3}Gd(PO{sub 4}){sub 3}:Tb{sup 3+}

    SciTech Connect

    Wang Deyin; Kodama, Nobuhiro


    Visible quantum cutting has been observed in GdPO{sub 4}:Tb{sup 3+} upon Tb{sup 3+} 4f{sup 8}-4f{sup 7}5d{sup 1} excitation and host excitation, and in Sr{sub 3}Gd(PO{sub 4}){sub 3}:Tb{sup 3+} upon Tb{sup 3+} 4f{sup 8}-4f{sup 7}5d{sup 1} excitation. In the quantum cutting process, Tb{sup 3+} acts as a quantum cutter, which converts one short wavelength ultraviolet photon or one vacuum ultraviolet photon into more than one visible photon. The quantum cutting involves a cross-relaxation process between two neighboring Tb{sup 3+} and direct energy transfer between Tb{sup 3+} and Tb{sup 3+} or Tb{sup 3+} and Gd{sup 3+}, depending on the excitation wavelength. The quantum efficiency variation of GdPO{sub 4}:xTb{sup 3+} and Sr{sub 3}Gd(PO{sub 4}){sub 3}:xTb{sup 3+} shows a growing trend with increasing of Tb{sup 3+} content from x=1.5% to 13%. - Graphical abstract: The ratio of emission from {sup 5}D{sub 4} level to that attributed to {sup 5}D{sub 3} of Tb{sup 3+} and {sup 6}P{sub J} of Gd{sup 3+} under 210,196 and 157 nm excitations are much stronger than that under 273 nm excitation, indicating visible quantum cutting has occurred in GdPO{sub 4}:Tb{sup 3+} upon Tb{sup 3+} 4f{sup 8}-4f{sup 7}5d{sup 1} excitation and host excitation.

  3. Layered Structures and Disordered Polyanionic Nets in the Cation-Poor Polar Intermetallics CsAu 1.4sub> Ga 2.8 and CsAu 2 Ga 2.6

    SciTech Connect

    Smetana, Volodymyr; Steinberg, Simon; Mudring, Anja-Verena


    Gold intermetallics are known for their unusual structures and bonding patterns. Two new compounds have been discovered in the cation-poor part of the Cs–Au–Ga system. We obtained both compounds directly by heating the elements at elevated temperatures. Structure determinations based on single-crystal X-ray diffraction analyses revealed two structurally and compositionally related formations: CsAu1.4sub>Ga2.8 (I) and CsAu2Ga2.6 (II) crystallize in their own structure types (I: R$\\bar{3}$, a = 11.160(2) Å, c = 21.706(4) Å, Z = 18; II: R$\\bar{3}$, a = 11.106(1) Å, Å, c = 77.243(9) Å, Z = 54) and contain hexagonal cationic layers of cesium. Furthermore, this is a unique structural motif, which has never been observed for the other (lighter) alkali metals in combination with Au and post transition elements. The polyanionic part is characterized in contrast by Au/Ga tetrahedral stars, a structural feature that is characteristic for light alkali metal representatives, and disordered sites with mixed Au/Ga occupancies that occur in both structures with a more significant disorder in the polyanionic component of CsAu2Ga2.6. Examinations of the electronic band structure for a model approximating the composition of CsAu1.4sub>Ga2.8 have been completed using density-functional-theory-based methods and reveal a deep pseudogap at EF. Bonding analysis by evaluating the crystal orbital Hamilton populations show dominant heteroatomic Au–Ga bonds and only a negligible contribution from Cs pairs.

  4. Influence of 6s{sup 2} lone pair electrons of Bi{sup 3+} on its preferential site occupancy in fluorapatite, NaCa{sub 3}Bi(PO{sub 4}){sub 3}F – An insight from Eu{sup 3+} luminescent probe

    SciTech Connect

    Lakshminarasimhan, N. Varadaraju, U.V.


    Graphical abstract: Eu{sup 3+} structural probe – difference in Eu{sup 3+} PL emission in (a) NaCa{sub 3}Bi{sub 0.95}Eu{sub 0.05}(PO{sub 4}){sub 3}F and (b) NaCa{sub 3}La{sub 0.95}Eu{sub 0.05}(PO{sub 4}){sub 3}F suggests Bi{sup 3+} with preferential site occupancy at M(II) site directing Eu{sup 3+} to M(I) site. - Highlights: • Eu{sup 3+} luminescent probe used for establishing the role of 6s{sup 2} lone pair electrons of Bi{sup 3+} in fluorapatite. • Difference in Eu{sup 3+} PL emission spectral features in NaCa{sub 3}Bi{sub 0.95}Eu{sub 0.05}(PO{sub 4}){sub 3}F and NaCa{sub 3}La{sub 0.95}Eu{sub 0.05}(PO{sub 4}){sub 3}F. • Preferential site occupancy of Bi{sup 3+} in M(II) site directs Eu{sup 3+} to M(I) site in NaCa{sub 3}Bi{sub 0.95}Eu{sub 0.05}(PO{sub 4}){sub 3}F. - Abstract: Eu{sup 3+} luminescence was used as a structural probe in understanding the preferential site occupancy of lone pair cation, Bi{sup 3+}, in fluorapatite by comparing the photoluminescence (PL) emission spectral features with that of in analogous La{sup 3+} based fluorapatite. The fluorapatites, NaCa{sub 3}Bi{sub 0.95}Eu{sub 0.05}(PO{sub 4}){sub 3}F and NaCa{sub 3}La{sub 0.95}Eu{sub 0.05}(PO{sub 4}){sub 3}F, were synthesized by conventional high temperature solid state reaction method and characterized by powder X-ray diffraction (XRD) and FT-IR spectroscopy. The Eu{sup 3+} PL results revealed a difference in the emission spectral features in NaCa{sub 3}Bi{sub 0.95}Eu{sub 0.05}(PO{sub 4}){sub 3}F and NaCa{sub 3}La{sub 0.95}Eu{sub 0.05}(PO{sub 4}){sub 3}F. This difference in Eu{sup 3+} PL emission can be attributed to the difference in its site occupancy in the studied fluorapatites.

  5. Steam reforming of fast pyrolysis-derived aqueous phase oxygenates over Co, Ni, and Rh metals supported on MgAl2O4sub>

    SciTech Connect

    Xing, Rong; Dagle, Vanessa Lebarbier; Flake, Matthew; Kovarik, Libor; Albrecht, Karl O.; Deshmane, Chinmay; Dagle, Robert A.


    In this study we examine feasibility for steam reforming the mixed oxygenate aqueous fraction derived from mildly hydrotreated fast pyrolysis bio-oils. Catalysts selective towards hydrogen formation and resistant to carbon formation utilizing feeds with relatively low steam-to-carbon (S/C) ratios are desired. Rh (5 wt%), Pt (5 wt%), Ru (5 wt%), Ir (5 wt%), Ni (15 wt%), and Co (15 wt%) metals supported on MgAl2O4sub> were evaluated for catalytic performance at 500°C and 1 atm using a complex feed mixture comprising of acids, polyols, cycloalkanes, and phenolic compounds. The Rh catalyst was found to be the most active and resistant to carbon formation. The Ni and Co catalysts were found to be more active than the other noble metal catalysts investigated (Pt, Ru, and Ir). However, Ni was found to form significantly more carbon (coke) on the catalyst surface. Furthermore, Co was found to be the most selective towards H2 formation. Evaluating the effect of temperature on stability for the Rh catalyst we found that catalyst stability was best when operated at 500°C as compared to the higher temperatures investigated (700, 800°C). When operating at 700°C significantly more graphitic formation was observed on the spent catalyst surface. Operating at 800°C resulted in reactor plugging as a result of thermal decomposition of the reactants. Thus, a concept analogous to the petroleum industries’ use of a pre-reformer, operated at approximately 500°C for steam reforming of the heavier naphtha components, followed by a high temperature methane reforming operated in the 600-850°C temperature range, could be applied in the case of steam reforming biomass derived oxygenates. Moreover, stability evaluations were performed over the Rh, Ni, and Co catalysts at 500°C and 1 atm, under similar initial conversions, reveal the Co catalyst to be the most stable and selective towards H2 production. Conversion and selectivity to CH4sub

  6. Interrogating the superconductor Ca-10(Pt4sub>As8)(Fe2-xPtxAs2)5 Layer-by-layer

    SciTech Connect

    Kim, Jisun; Zhu, Yimei; Nam, Hyoungdo; Li, Guorong; Karki, A. B.; Wang, Zhen; Shih, Chih-Kang; Zhang, Jiandi; Jin, Rongying; Plummer, E. W.


    Ever since the discovery of high-Tc superconductivity in layered cuprates, the roles that individual layers play have been debated, due to difficulty in layer-by-layer characterization. While there is similar challenge in many Fe-based layered superconductors, the newly-discovered Ca10(Pt4sub>As8)(Fe2As2)5 provides opportunities to explore superconductivity layer by layer, because it contains both superconducting building blocks (Fe2As2 layers) and intermediate Pt4sub>As8 layers. Cleaving a single crystal under ultra-high vacuum results in multiple terminations: an ordered Pt4sub>As8 layer, two reconstructed Ca layers on the top of a Pt4sub>As8 layer, and disordered Ca layer on the top of Fe2As2 layer. The electronic properties of individual layers are studied using scanning tunneling microscopy/spectroscopy (STM/S), which reveals different spectra for each surface. Remarkably superconducting coherence peaks are seen only on the ordered Ca/Pt4sub>As8 layer. Our results indicate that an ordered structure with proper charge balance is required in order to preserve superconductivity.

  7. High-energy magnetic excitations in overdoped La2-xSrxCuO4sub> studied by neutron and resonant inelastic X-ray scattering

    SciTech Connect

    Wakimoto, S.; Ishii, K.; Kimura, H.; Fujita, M.; Dellea, G.; Kummer, K.; Braicovich, L.; Ghiringhelli, G.; Debeer-Schmitt, Lisa M.; Granroth, Garrett E.


    We have performed neutron inelastic scattering and resonant inelastic x-ray scattering (RIXS) at the Cu-L3 edge to study high-energy magnetic excitations at energy transfers of more than 100 meV for overdoped La2₋xSrxCuO4sub> with x=0.25 (Tc=15 K) and x=0.30 (nonsuperconducting) using identical single-crystal samples for the two techniques. From constant-energy slices of neutron-scattering cross sections, we have identified magnetic excitations up to ~250 meV for x=0.25. Although the width in the momentum direction is large, the peak positions along the (π,π) direction agree with the dispersion relation of the spin wave in the nondoped La2CuO4sub> (LCO), which is consistent with the previous RIXS results of cuprate superconductors. Using RIXS at the Cu-L3 edge, we have measured the dispersion relations of the so-called paramagnon mode along both (π,π) and (π,0) directions. Although in both directions the neutron and RIXS data connect with each other and the paramagnon along (π,0) agrees well with the LCO spin-wave dispersion, the paramagnon in the (π,π) direction probed by RIXS appears to be less dispersive and the excitation energy is lower than the spin wave of LCO near (π/2,π/2). Thus, our results indicate consistency between neutron inelastic scattering and RIXS, and elucidate the entire magnetic excitation in the (π,π) direction by the complementary use of two probes. The polarization dependence of the RIXS profiles indicates that appreciable charge excitations exist in the same energy range of magnetic excitations, reflecting the itinerant character of the overdoped sample. Lastly, we find a possible anisotropy in the charge excitation intensity might explain the apparent differences in the paramagnon dispersion in the (π,π) direction as detected by the x-ray scattering.

  8. Evidence of local defects in the oxygen excess apatite La{sub 9.67}(SiO{sub 4}){sub 6}O{sub 2.5} from high resolution neutron powder diffraction

    SciTech Connect

    Guillot, Stephanie; Beaudet-Savignat, Sophie; Lambert, Sebastien; Vannier, Rose-Noelle; Roussel, Pascal; Porcher, Florence


    From neutron diffraction data collected at 3 K on a powder of La{sub 9.67}(SiO{sub 4}){sub 6}O{sub 2.5} composition and a careful examination of the average structure, a model was proposed to explain the oxygen over-stoichiometry in the apatite structure. This model leads to realistic distances to neighbouring atoms. Moreover, it accounts perfectly for the maximum oxygen content observed in these materials. Up to 0.5 oxygen atom located at the vicinity of the 2a site (0, 0, 1/4) would be shifted to a new interstitial position in the channel at (-0.01, 0.04, 0.06), creating a Frenkel defect, with the possibility of a maximum occupancy in this site equal to twice the Frenkel defect numbers. This structural model is in good agreement with the oxygen diffusion pathways recently proposed by Bechade et al. (2009) using computer modeling techniques. It supports preferred oxygen diffusion pathways via interstitial oxygen atoms and vacant sites along [0 0 1], close to the centre of the La(2)-O channels. - Graphical abstract legend: Structural defect position and possible conduction mechanism along the c-axis (representation of two adjacent unit-cells)

  9. Strain tuning of electronic structure in Bi4sub>Ti3O12-LaCoO3 epitaxial thin films

    SciTech Connect

    Choi, Woo Seok; Lee, Ho Nyung


    In this study, we investigated the crystal and electronic structures of ferroelectric Bi4sub>Ti3O12 single-crystalline thin films site-specifically substituted with LaCoO3 (LCO). The epitaxial films were grown by pulsed laser epitaxy on NdGaO3 and SrTiO3 substrates to vary the degree of strain. With increasing the LCO substitution, we observed a systematic increase in the c-axis lattice constant of the Aurivillius phase related with the modification of pseudo-orthorhombic unit cells. These compositional and structural changes resulted in a systematic decrease in the band gap, i.e., the optical transition energy between the oxygen 2p and transition-metal 3d states, based on a spectroscopic ellipsometry study. In particular, the Co 3d state seems to largely overlap with the Ti t2g state, decreasing the band gap. Interestingly, the applied tensile strain facilitates the band-gap narrowing, demonstrating that epitaxial strain is a useful tool to tune the electronic structure of ferroelectric transition-metal oxides.

  10. Bulk modulus of basic sodalite, Na{sub 8}[AlSiO{sub 4}]{sub 6}(OH){sub 2}.2H{sub 2}O, a possible zeolitic precursor in coal-fly-ash-based geopolymers

    SciTech Connect

    Oh, Jae Eun; Moon, Juhyuk; Mancio, Mauricio; Clark, Simon M.; Monteiro, Paulo J.M.


    Synthetic basic sodalite, Na{sub 8}[AlSiO{sub 4}]{sub 6}(OH){sub 2}.2H{sub 2}O, cubic, P43n, (also known as hydroxysodalite hydrate) was prepared by the alkaline activation of amorphous aluminosilicate glass, obtained from the phase separation of Class F fly ash. The sample was subjected to a process similar to geopolymerization, using high concentrations of a NaOH solution at 90 {sup o}C for 24 hours. Basic sodalite was chosen as a representative analogue of the zeolite precursor existing in Na-based Class F fly ash geopolymers. To determine its bulk modulus, high-pressure synchrotron X-ray powder diffraction was applied using a diamond anvil cell (DAC) up to a pressure of 4.5 GPa. A curve-fit with a truncated third-order Birch-Murnaghan equation of state with a fixed K'{sub o} = 4 to pressure-normalized volume data yielded the isothermal bulk modulus, K{sub o} = 43 {+-} 4 GPa, indicating that basic sodalite is more compressible than sodalite, possibly due to a difference in interactions between the framework host and the guest molecules.

  11. Tetrahedrally coordinated disordered Cu2SnS3-Cu2ZnSnS4sub>-ZnS alloys with tunable optical and electronic properties

    SciTech Connect

    Erslev, Peter T.; Young, Matthew R.; Li, Jian V.; Siah, Sin Cheng; Chakraborty, Rupak; Du, Hui; Lad, Robert J.; Buonassisi, Tonio; Teeter, Glenn


    A key requirement for large-scale deployment of photovoltaic technologies is the development of highly functional materials with controllable opto-electronic properties. In this work, we report on the room-temperature synthesis of disordered alloys of the Earth-abundant, tetrahedrally coordinated semiconductors Cu2SnS3, Cu2ZnSnS4sub> (CZTS), and ZnS as (Cu2SnS3)1-x(ZnS)x. The resulting disordered semiconductors are found to have continuously and independently tunable optical and electronic properties. Quasi-isovalent alloying on the cation sublattice allows the optical band gap to be varied continuously from 1.1 eV to 2.8 eV. Aliovalent alloying leads to independent control of carrier concentration over at least three orders of magnitude. A conceptual framework describing these disordered materials is presented, in which the structural disorder, constrained by local tetrahedral coordination of both anions and cations, leads to the observed high degree of tunability of the opto-electronic properties. These materials are not only independently interesting, but the developed framework also applies to the opto-electronic properties of kesterite CZTS materials as well as provides a basis for the development of new semiconductors.

  12. Understanding the Mechanisms Underlying Heterotrophic CO2 and CH4sub> Fluxes in a Peatland with Deep Soil Warming and Atmospheric CO2 Enrichment

    SciTech Connect

    Bridgham, Scott D.; Keller, Jason K.; Zhuang, Qianlai


    This project was funded from June 15, 2012 through June 15, 2015, with a no-cost extension until Sept. 15, 2016. Our project focused on a whole-ecosystem warming and enhanced atmospheric CO2 experiment in the S1 Bog in Marcell Experimental Forest in northern Minnesota, USA called “Spruce and Peatland Responses Under Climatic and Environmental Change” (SPRUCE; Construction of substantial infrastructure required for these treatments was beyond our control and led to a staggered initiation of experimental treatments at this site. Deep peat heating (DPH) was instituted in June 2014, whole-ecosystem warming began in August 2015, and the CO2 enhancement began in June 2016. Prior to the initiation of the experimental treatments, we completed a large amount of research to better understand factors controlling anaerobic carbon (C) cycling, and particularly methane (CH4sub>) dynamics, in northern peatlands in an effort to put the SPRUCE project in a broader context. We additionally focused extensively on the DPH treatment, which provided a unique opportunity to isolate warming effects on the vast reservoir of permanently anaerobic C stored in peatlands below the water table.

  13. O3-type layered transition metal oxide Na(NiCoFeTi)1/4sub>O2 as a high rate and long cycle life cathode material for sodium ion batteries

    SciTech Connect

    Yue, Ji -Li; Yang, Xiao -Qing; Zhou, Yong -Ning; Yu, Xiqian; Bak, Seong -Min; Fu, Zheng -Wen


    High rate capability and long cycle life are challenging goals for the development of room temperature sodium-ion batteries. Here we report a new single phase quaternary O3-type layer-structured transition metal oxide Na(NiCoFeTi)1/4sub>O2 synthesized by a simple solid-state reaction as a new cathode material for sodium-ion batteries. It can deliver a reversible capacity of 90.6 mA h g–1 at a rate as high as 20C. At 5C, 75.0% of the initial specific capacity can be retained after 400 cycles with a capacity-decay rate of 0.07% per cycle, demonstrating a superior long-term cyclability at high current density. X-ray diffraction and absorption characterization revealed reversible phase transformations and electronic structural changes during the Na+ deintercalation/intercalation process. Ni, Co and Fe ions contribute to charge compensation during charge and discharge. Although Ti ions do not contribute to the charge transfer, they play a very important role in stabilizing the structure during charge and discharge by suppressing the Fe migration. Additionally, Ti substitution can also smooth the charge–discharge plateaus effectively, which provides a potential advantage for the commercialization of this material for room temperature sodium-ion batteries.

  14. Phonons of Fe-based superconductor Ca10Pt4sub>As8(Fe1-xPtxAs)10

    SciTech Connect

    Ikeuchi, K.; Kobayashi, Y.; Suzuki, K.; Itoh, M.; Kajimoto, R.; Bourges, P.; Christianson, A. D.; Nakamura, H.; Machida, M.; Sato, M.


    In this paper, we report the results of inelastic neutron scattering measurements on particular phonons of a superconducting (SC) Ca10Pt4sub>As8(Fe1-xPtxAs)10 with the onset transition temperature Tc ~ 33 K to investigate mainly what roles orbital fluctuation plays in Cooper pairing, where we observed a slight softening of the in-plane transverse acoustic mode corresponding to the elastic constant C66. This softening starts at temperature T well above the superconducting Tc, as T decreases. An anomalously strong change of the scattering intensity of in-plane optical modes was observed at the M point of the pseudo tetragonal reciprocal space in the range of 35 < ω < 40 meV with decreasing T from far above Tc. Finally, because this ω region mainly corresponds to the motion of Fe and As atoms in the FeAs planes, the finding presents information on the coupling between the orbital fluctuation of Fe 3d electrons and the lattice system, useful for studying the possible roles of orbital fluctuation in the pairing mechanism and/or the appearance of the so-called nematic phase.

  15. Magnetocaloric effect in gadolinium-oxalate framework Gd{sub 2}(C{sub 2}O{sub 4}){sub 3}(H{sub 2}O){sub 6}⋅(0{sub ⋅}6H{sub 2}O)

    SciTech Connect

    Sibille, Romain Didelot, Emilie; Mazet, Thomas; Malaman, Bernard; François, Michel


    Magnetic refrigerants incorporating Gd{sup 3+} ions and light organic ligands offer a good balance between isolation of the magnetic centers and their density. We synthesized the framework material Gd{sub 2}(C{sub 2}O{sub 4}){sub 3}(H{sub 2}O){sub 6}⋅0.6H{sub 2}O by a hydrothermal route and characterized its structure. The honeycomb lattice of Gd{sup 3+} ions interlinked by oxalate ligands in the (a,c) plane ensures their decoupling in terms of magnetic exchange interactions. This is corroborated by magnetic measurements indicating negligible interactions between the Gd{sup 3+} ions in this material. The magnetocaloric effect was evaluated from isothermal magnetization measurements. The maximum entropy change −ΔS{sub M}{sup max} reaches 75.9 mJ cm{sup −3} K{sup −1} (around 2 K) for a moderate field change (2 T)

  16. A combined experimental and computational study of the mechanism of fructose dehydration to 5-hydroxymethylfurfural in dimethylsulfoxide using Amberlyst 70, PO4sub>3-/niobic acid, or sulfuric acid catalysts

    SciTech Connect

    Zhang, Jing; Das, Anirban; Assary, Rajeev S.; Curtiss, Larry A.; Weitz, Eric


    We report on a combined experimental and theoretical study of the acid catalyzed dehydration of d-fructose in dimethylsulfoxide (DMSO) using; Amberlyst 70, PO4sub>3-/niobic acid, and sulfuric acid as catalysts. The reaction has been studied and intermediates characterized using; 13C, 1H, and 17O NMR, and high resolution electrospray ionization mass spectrometry (HR ESI–MS). High level G4MP2 theory calculations are used to understand the thermodynamic landscape for the reaction mechanism in DMSO. We have experimentally identified two key intermediates in the dehydration of fructose to form HMF that were also identified, using theory, as local minima on the potential surface for reaction. A third intermediate, a species capable of undergoing keto–enol tautomerism, was also experimentally detected. However, it was not possible to experimentally distinguish between the keto and the enol forms. These data with different catalysts are consistent with common intermediates along the reaction pathway from fructose to HMF in DMSO. The role of oxygen in producing acidic species in reactions carried out in DMSO in presence of air is also discussed.

  17. First-Principles Modeling of the Initial Stages of Organic Solvent Decomposition on Li x Mn 2 O 4sub> (100) Surfaces

    SciTech Connect

    Leung, Kevin


    Density functional theory and ab initio molecular dynamics simulations are applied to investigate the migration of Mn(II) ions to above-surface sites on spinel LixMn2O4sub> (100) surfaces, the subsequent Mn dissolution into the organic liquid electrolyte, and the detrimental effects on anode solid electrolyte interphase (SEI) passivating films after Mn(II) ions diffuse through the separator. The dissolution mechanism proves complex; the much-quoted Hunter disproportionation of Mn(III) to form Mn(II) is necessary but far from sufficient. Key steps that facilitate Mn(II) ion migration include concerted liquid/solid-state motions, proton-induced weakening of Mn-O bonds forming mobile OH- surface groups; and chemical reactions of adsorbed decomposed organic fragments. Mn(II) lodged between the inorganic Li2CO3 and organic lithium ethylene dicarbonate (LEDC) anode SEI component facilitates electrochemical reduction and decomposition of LEDC. These findings help inform future design of protective coatings, electrolytes, additives, and interfaces.

  18. In Situ Stress Evolution in Li 1+x Mn 2 O 4sub> Thin Films during Electrochemical Cycling in Li-Ion Cells

    SciTech Connect

    Sheth, Jay; Karan, Naba K.; Abraham, Daniel P.; Nguyen, Cao Cuong; Lucht, Brett L.; Sheldon, Brian W.; Guduru, Pradeep R.


    Real time monitoring of stress evolution in electrodes during electrochemical cycling can help quantify the driving forces that dictate their mechanical degradation. In the present work, in-situ stress evolution in thin films of spinel Li1+x Mn 2 O 4sub> (LMO) was measured by monitoring the change in the elastic substrate curvature during electrochemical cycling in a specially designed beaker cell in the 3.5–4.3 V (vs. Li/Li+) voltage range. The LMO thin films were prepared using a solution deposition technique and their structures and morphologies were characterized by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The stress evolution in the early part of the first delithiation cycle (<4.05 V) was consistent with the XRD data. However, stress evolution during later stages of the first delithiation cycle (>4.05 V) was not consistent with the XRD results, and showed irreversible behavior, suggesting irreversible changes in the electrode. Beyond the first delithiation cycle, the stress evolution was reversible, with a steady buildup of compressive and tensile stress during lithium insertion and extraction, respectively. Measurements on LMO films of varying thicknesses suggest that the first cycle irreversibility in stress response arises primarily from the electrode bulk.

  19. Structural characterization and AC conductivity of bis tetrapropylammonium hexachlorado-dicadmate, [N(C{sub 3}H{sub 7}){sub 4}]{sub 2}Cd{sub 2}Cl{sub 6}

    SciTech Connect

    Hannachi, N.; Guidara, K.; Bulou, A.; Hlel, F.


    Synthesis, crystal structure, vibrational study, {sup 13}C, {sup 111}Cd CP-MAS-NMR analysis and electrical properties of the compound [N(C{sub 3}H{sub 7}){sub 4}]{sub 2}Cd{sub 2}Cl{sub 6}, are reported. The latter crystallizes in the triclinic system (space group P1-bar, Z = 2) with the following unit cell dimensions: a = 9.530(1) A, b = 11.744(1) A, c = 17.433(1) A, {alpha} = 79.31(1){sup o}, {beta} = 84.00(1){sup o} and {gamma} = 80.32(1){sup o}. Besides, its structure was solved using 6445 independent reflections down to R = 0.037. The atomic arrangement can be described by alternating organic and inorganic layers parallel to the (11-bar 0) plan, made up of tetrapropylammonium groups and Cd{sub 2}Cl{sub 6} dimers, respectively. In crystal structure, the inorganic layer, built up by Cd{sub 2}Cl{sub 6} dimers, is connected to the organic ones through van der Waals interaction in order to build cation-anion-cation cohesion. Impedance spectroscopy study, reported in the sample, reveals that the conduction in the material is due to a hopping process. The temperature and frequency dependence of dielectric constants of the single crystal sample has been investigated to determine some related parameters to the dielectric relaxation.

  20. Structure tracking aided design and synthesis of Li3V2(PO4sub>)3 nanocrystals as high-power cathodes for lithium ion batteries

    SciTech Connect

    Wang, Liping; Bai, Jianming; Gao, Peng; Wang, Xiaoya; Looney, J. Patrick; Wang, Feng


    In this study, preparing new electrode materials with synthetic control of phases and electrochemical properties is desirable for battery applications but hardly achievable without knowing how the synthesis reaction proceeds. Herein, we report on structure tracking-aided design and synthesis of single-crystalline Li3V2(PO4sub>)3 (LVP) nanoparticles with extremely high rate capability. A comprehensive investigation was made to the local structural orderings of the involved phases and their evolution toward forming LVP phase using in situ/ex situ synchrotron X-ray and electron-beam diffraction, spectroscopy, and imaging techniques. The results shed light on the thermodynamics and kinetics of synthesis reactions and enabled the design of a cost-efficient synthesis protocol to make nanocrystalline LVP, wherein solvothermal treatment is a crucial step leading to an amorphous intermediate with local structural ordering resembling that of LVP, which, upon calcination at moderate temperatures, rapidly transforms into the desired LVP phase. The obtained LVP particles are about 50 nm, coated with a thin layer of amorphous carbon and featured with excellent cycling stability and rate capability – 95% capacity retention after 200 cycles and 66% theoretical capacity even at a current rate of 10 C. The structure tracking based method we developed in this work offers a new way of designing battery electrodes with synthetic control of material phases and properties.

  1. Magnetic field induced anisotropy of 139La spin-lattice relaxation rates in stripe ordered La1.875Ba0.125CuO4sub>

    SciTech Connect

    S. -H. Baek; Gu, G. D.; Utz, Y.; Hucker, M.; Buchner, B.; Grafe, H. -J.


    We report 139La nuclear magnetic resonance studies performed on a La1.875Ba0.125CuO4sub> single crystal. The data show that the structural phase transitions (high-temperature tetragonal → low-temperature orthorhombic → low-temperature tetragonal phase) are of the displacive type in this material. The 139La spin-lattice relaxation rate T–11 sharply upturns at the charge-ordering temperature TCO = 54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T–11 below the spin-ordering temperature TSO=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state for H ∥ [001], which are completely suppressed for large fields along the CuO2 planes. Lastly, our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.

  2. Persistent luminescence in Ba{sub 5}(PO{sub 4}){sub 3}Cl:Eu{sup 2+},R{sup 3+} (R = Y, La, Ce, Gd, Tb and Lu)

    SciTech Connect

    Ju, Guifang; Hu, Yihua Chen, Li; Wang, Xiaojuan; Mu, Zhongfei


    Graphical abstract: - Highlights: • The persistent luminescence in Ba{sub 5}(PO{sub 4}){sub 3}Cl:Eu{sup 2+},R{sup 3+} was reported. • The influences of auxiliary codopants was discussed. • The concentration quenching of persistent luminescence was discussed. - Abstract: We investigated the persistent luminescence in europium-doped barium chloroapatite upon codoping with auxiliary rare earth ions. Luminescence properties of the phosphors, including photoluminescence, luminescence decay, and thermoluminescence are systematically studied. We formulated a model of persistent luminescence on the basis of the experimental results. In our model, some Eu{sup 2+} ions are oxidized to Eu{sup 3+} under short UV excitation, and the released electrons are trapped at the positive defect. The persistent luminescence arises from the recombination of these trapped electrons with the photo-ionized Eu{sup 3+} ions. The influence of auxiliary codopants was discussed in terms of ionic potential and ionic radius. Eventually, the concentration quenching of persistent luminescence was reported and discussed.

  3. Neutron Diffraction Study of Parasitic Nd-Moment Order in the Checkerboard-Type Phase Nd1.3Sr0.7NiO4sub>

    SciTech Connect

    Kobayashi, Riki; Yoshizawa, Hideki; Matsuda, Masaaki; Kajimoto, Ryoichi; Ishizaka, Kyoko; Tokura, Yoshinori


    In this paper, the Nd-moment order in the layered nickelate Nd2-xSrxNiO4sub> (x = 0.7) has been investigated by performing a neutron diffraction experiment using a single crystal sample. First, the checkerboard (CB)-type charge order was confirmed by observing the temperature dependence of the nuclear superlattice peak at Q=(5,0,0) between 1.9 and 300 K, which indicates that the transition temperature of the CB-type charge order is above 300 K. Magnetic superlattice peaks with the propagation vector k=(1-ε,0,1) appear below 67 K, and the value of ε was determined to be 0.455 in good agreement with previous studies. The intensity of the magnetic superlattice peaks appearing below 67 K shows a sharp increase below ≈20 K. This behavior indicates that the Nd moments freeze under the influence of the Ni ordering. The CB-type antiferromagnetic (AFM) Ni order in the NiO2 layers is stacked antiferromagnetically in the c-axis direction, while the Nd moments in the Nd/SrO2 layers are coupled antiferromagnetically with the Ni moments. Finally, the Nd moments are parallel to the c-axis, while the Ni moments are canted towards the c-axis direction from the basal ab-plane at low temperatures where the Nd moments are well ordered.

  4. Critical Behavior of Thermal Expansion and Magnetostriction in the Vicinity of the First order transition at the Curie Point of Gd5(SixGe1-x)4sub>

    SciTech Connect

    Han, Mangui


    Thermal expansion (TE) and magnetostriction (MS) measurements have been conducted for Gd5(SixGe1-x)4sub> with a series of x values to study its critical behavior in the vicinity of transition temperatures. It was found that the Curie temperature of Gd5(SixGe1-x)4sub> for x 0 ~ 0.5 is dependent on magnetic field, direction of change of temperature (Tc on cooling was lower than Tc on heating), purity of Gd starting material, compositions, material preparation methods, and also can be triggered by the external magnetic field with a different dT/dB rate for different x values. For Gd5(Si1.95Ge2.05), Gd5(Si2Ge2), Gd5(Si2.09Ge1.91), it was also found that the transition is a first order magneto-structural transition, which means the magnetic transition and crystalline structure transition occur simultaneously, and completely reversible. Temperature hysteresis and phase coexistence have been found to confirm that it is a first order transformation. While for Gd5(Si0.15Ge3.85), it is partially reversible at some temperature range between the antiferromagnetic and the ferromagnetic state. For Gd5(Si2.3Ge1.7) and Gd5(Si3Ge1), it was a second order transformation between the paramagnetic and ferromagnetic state, because no ΔT have been found. Giant magnetostriction was only found on Gd5(Si1.95Ge2.05), Gd5(Si2Ge2), Gd5(Si2.09Ge1.91) in their vicinity of first order transformation. MFM images have also been taken on polycrystal sample Gd5(Si2.09Ge1.91) to investigate the transformation process. The results also indicates that the Curie temperature was lower and the thermally

  5. Fluxes of CO2, CH4sub>, CO, BVOCs, NOx, and O3 in an Old Growth Amazonian Forest: Ecosystem Processes, Carbon Cycle, Atmospheric Chemistry, and Feedbacks on Climate

    SciTech Connect

    Wofsy, Steven C.


    A comprehensive, merged data set of trace gases (NO, NO2, CO2, CH4sub> and O3) along with has been tabulated and subjected to meticulous quality assurance and quality control (QA/QC). The merged data set is being submitted to the ARM website dedicated to the Green Ocean Experiment: Analysis using the final data set is in progress to determine the magnitudes of the fluxes for CH4sub>, H2O, CO2, O3, NOx, sensible and latent heat, momentum, and their seasonal variations. Here are summary statements, from the discussion above: Total NO fluxes were calculated following Keller et al., 1986. A vertical gradient is established in the mixing ratio of NO because it is emitted at the soil surface and mixed upward in the atmosphere (see above). Once in the atmosphere, the NO reacts rapidly with O3 to produce NO2 (NO + O3 → NO2 + O2). Therefore, if the vertical profiles of the mixing ratios of NO and O3 are known, the surface flux of NO may be determined. If any other reaction removes NO (e.g., deposition on leaves), FNO should estimate the lower limit to the NO flux from the soil in this forest. Our preliminary results show fluxes of NO averaged 133 x 109 molecules cm-2 s-1, a factor of 4 higher than fluxes previously observed in white sand soils in the Amazon, and a factor of 3 to 14 higher than fluxes observed for yellow clay soils (Bakwin et al., 1990 and references therein). The soil in the km 67 site is predominately oxisol with pockets of sandy ultisols, both having low reduced nutrient contents, mostly due to efficient microorganism decomposition and acid leaching by rain water. Oxisols contain both oxidized and reduced forms of nitrogen, of which concentrations vary independently of leaching (Jordan et al., 1982), with most

  6. Hydrothermal synthesis and the crystal structure of borate cancrinite (Na,Ca){sub 2}[Na{sub 6}(AlSiO{sub 4}){sub 6}](BO{sub 3}) . 2H{sub 2}O

    SciTech Connect

    Shirinova, A. F. Khrustalev, V. N.; Samedov, H. R.; Chiragov, M. I.


    Transparent prismatic single crystals of borate cancrinite (Na,Ca){sub 2}[Na{sub 6}(AlSiO{sub 4}){sub 6}](BO{sub 3}) . 2H{sub 2}O are prepared through hydrothermal crystallization. The parameters of the hexagonal unit cell and intensities of 10806 reflections are measured on an Enraf-Nonius CAD4 automated diffractometer. The compound crystallizes in the hexagonal crystal system with the unit cell parameters a = 12.745(4) A, c = 5.180(2) A, V = 728.6(4) A{sup 3}, and space group P6{sub 3}. The structure is determined by direct methods and refined using the full-matrix least-squares procedure in the anisotropic approximation for the non-hydrogen atoms. The refinement of the structure is performed to the final discrepancy factor R{sub 1} = 0.027 for 2889 unique reflections with I > 2 {sigma} (I). In the structure of the borate cancrinite, the AlO{sub 4} and SiO{sub 4} tetrahedra form a zeolite-like framework in which twelve-membered hexagonal channels are occupied by sodium atoms and BO{sub 3} groups, whereas six-membered channels are filled with sodium and calcium atoms and water molecules. The mean interatomic distances are found to be as follows: (Si-O){sub mean} = 1.614 A and (Al-O){sub mean} = 1.741 A in the AlO{sub 4} and SiO{sub 4} tetrahedra, (Na-O){sub mean} = 2.542 A in the seven-vertex sodium polyhedra, and [(Na,Ca)-O]{sub mean} = 2.589 A in the ditrigonal bipyramids.

  7. Quasi-two-dimensional spin and phonon excitations in La1.965Ba0.035CuO4sub>

    SciTech Connect

    Wagman, J. J.; Parshall, D.; Stone, Matthew B.; Savici, Andrei T.; Zhao, Yang; Dabkowska, H. A.; Gaulin, B. D.


    Here, we present time-of-fight inelastic neutron scattering measurements of La1.965Ba0.035CuO4sub> (LBCO), a lightly doped member of the high temperature superconducting La-based cuprate family. By using time-of-flight neutron instrumentation coupled with single crystal sample rotation we obtain a four-dimensional data set (three Q and one energy) that is both comprehensive and spans a large region of reciprocal space. Our measurements identify rich structure in the energy dependence of the highly dispersive spin excitations, which are centered at equivalent (1/2, 1/2, L) wave-vectors. These structures correlate strongly with several crossings of the spin excitations with the lightly dispersive phonons found in this system. These eects are signicant and account for on the order of 25% of the total inelastic scattering for energies between ≈5 and 40meV at low |Q|. Interestingly, this scattering also presents little or no L-dependence. As the phonons and dispersive spin excitations centred at equivalent (1/2, 1/2, L) wave-vectors are common to all members of La-based 214 copper oxides, we conclude such strong quasi-two dimensional scattering enhancements are likely to occur in all such 214 families of materials, including those concentrations corresponding to superconducting ground states. Such a phenomenon appears to be a fundamental characteristic of these materials and is potentially related to superconducting pairing.

  8. Improved electrochemical performance of spinel LiMn1.5Ni0.5O4sub> through MgF2 nano-coating

    SciTech Connect

    Wu, Qing; Zhang, Xiaoping; Sun, Shuwei; Wan, Ning; Pan, Du; Bai, Ying; Zhu, Huiyuan; Hu, Yong-Sheng; Dai, Sheng


    In this paper, a spinel LiMn1.5Ni0.5O4sub> (LMNO) cathode material synthesized by a sol–gel method is modified by MgF2 nano-coating via a wet coating strategy. The results of X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) showed that the MgF2 nano-coating layers do not physically change the bulk structure of the pristine material. Compared with the pristine compound, the MgF2-coated LMNO electrodes display enhanced cycling stabilities. Particularly, the 5 wt% MgF2-coated LMNO demonstrates the best reversibility, with a capacity retention of 89.9% after 100 cycles, much higher than that of the pristine material, 69.3%. The dQ/dV analysis and apparent Li+ diffusion coefficient calculation prove that the kinetic properties are enhanced after MgF2 surface modification, which partly explains the improved electrochemical performances. Electrochemical impedance spectroscopy (EIS) and Fourier transform infrared spectroscopy (FTIR) data confirm that the MgF2 coating layer helps in suppressing the fast growth of the solid electrolyte interface (SEI) film in repeated cycling, which effectively stabilizes the spinel structure. Finally and additionally, differential scanning calorimetry (DSC) tests show that the MgF2 nano-coating layer also helps in enhancing the thermal stability of the LMNO cathode.

  9. Structural changes correlated with magnetic spin state isomorphism in the S2 state of the Mn4sub>CaO5 cluster in the oxygen-evolving complex of photosystem II

    SciTech Connect

    Chatterjee, Ruchira; Han, Guangye; Kern, Jan; Gul, Sheraz; Fuller, Franklin D.; Garachtchenko, Anna; Young, Iris D.; Weng, Tsu -Chien; Nordlund, Dennis; Alonso-Mori, Roberto; Bergmann, Uwe; Sokaras, Dimosthenis; Hatakeyama, Makoto; Yachandra, Vittal K.; Yano, Junko


    The Mn4sub>CaO5 cluster in photosystem II catalyzes the four-electron redox reaction of water oxidation in natural photosynthesis. This catalytic reaction cycles through four intermediate states (Si, i = 0 to 4), involving changes in the redox state of the four Mn atoms in the cluster. Recent studies suggest the presence and importance of isomorphous structures within the same redox/intermediate S-state. It is highly likely that geometric and electronic structural flexibility play a role in the catalytic mechanism. Among the catalytic intermediates that have been identified experimentally thus far, there is clear evidence of such isomorphism in the S2 state, with a high-spin (5/2) (HS) and a low spin (1/2) (LS) form, identified and characterized by their distinct electron paramagnetic resonance (EPR spectroscopy) signals. We studied these two S2 isomers with Mn extended X-ray absorption fine structure (EXAFS) and absorption and emission spectroscopy (XANES/XES) to characterize the structural and electronic structural properties. The geometric and electronic structure of the HS and LS S2 states are different as determined using Mn EXAFS and XANES/XES, respectively. The Mn K-edge XANES and XES for the HS form are different from the LS and indicate a slightly lower positive charge on the Mn atoms compared to the LS form. Based on the EXAFS results which are clearly different, we propose possible structural differences between the two spin states. As a result, such structural and magnetic redox-isomers if present at room temperature, will likely play a role in the mechanism for water-exchange/oxidation in photosynthesis.

  10. Structural, thermal, magnetic and electrical studies of the iron oxophosphate Rb{sub 7}Fe{sub 7}(PO{sub 4}){sub 8}O{sub 2}.2H{sub 2}O

    SciTech Connect

    Hidouri, Mourad; Lajmi, Besma; Gmati, Nadia; Wattiaux, Alain; Nenert, Gwilherm; Ritter, Clemens; Fournes, Leopold; Darriet, Jacques; Lopez, Maria Luisa; Pico, Carlos; Amara, Mongi B.


    A new iron oxophosphate of composition Rb{sub 7}Fe{sub 7}(PO{sub 4}){sub 8}O{sub 2}.2H{sub 2}O has been synthesized and studied by X-ray diffraction, TG and DTA analysis, magnetic susceptibility, neutron diffraction, Moessbauer spectroscopy and ionic conductivity. This compound crystallizes in the monoclinic system with the P2{sub 1}/c space group and the unit cell parameters a = 8.224(8) A, b = 22.162(6) A, c = 9.962(6) A and {beta} = 109.41(8){sup o}. Its structure is built up from Fe{sub 7}O{sub 32} clusters of edge- and corner-sharing FeO{sub 5} and FeO{sub 6} polyhedra. Neighboring clusters are connected by the phosphate tetrahedra to form a three-dimensional framework. The Rb{sup +} cations and the water molecules are occupying intersecting tunnels parallel to a and c. The presence of water molecules was confirmed by TG and DTA analysis. The magnetic susceptibility measurements have shown the existence of antiferromagnetic ordering below 22 K with a weak ferromagnetic component. Additionally, these measurements show evidence for a strong magnetic frustration characterized by |{theta}/T{sub N}| {approx} 12. Powder neutron diffraction study confirms the presence of a long range antiferromagnetic order coupled to a weak ferromagnetic component along the b-axis. The strongly reduced magnetic moments extracted from the refinement support the existence of a magnetically frustrated ground state. The Moessbauer spectroscopy results confirmed the presence of only Fe{sup 3+} ions in both five and six coordination. The ionic conductivity measurements led to activation energy of 0.81 eV, a value that agrees with the obtained for other rubidium phosphates.

  11. Microstructure study of the rare-earth intermetallic compounds R5(SixGe1-x)4sub> and R5(SixGe1-x)3

    SciTech Connect

    Cao, Qing


    The unique combination of magnetic properties and structural transitions exhibited by many members of the R5(SixGe1-x)4sub> family (R = rare earths, 0 ≤ x ≤ 1) presents numerous opportunities for these materials in advanced energy transformation applications. Past research has proven that the crystal structure and magnetic ordering of the R5(SixGe1-x)4sub> compounds can be altered by temperature, magnetic field, pressure and the Si/Ge ratio. Results of this thesis study on the crystal structure of the Er5Si4sub> compound have for the first time shown that the application of mechanical forces (i.e. shear stress introduced during the mechanical grinding) can also result in a structural transition from Gd5Si4sub>-type orthorhombic to Gd5Si2Ge2-type monoclinic. This structural transition is reversible, moving in the opposite direction when the material is subjected to low-temperature annealing at 500 °C.

  12. Battery Relevant Electrochemistry of Ag7Fe3(P2O7 )4sub> : Contrasting Contributions from the Redox Chemistries of Ag+ and Fe3+

    SciTech Connect

    Zhang, Yiman; Kirshenbaum, Kevin C.; Marschilok, Amy C.; Takeuchi, Esther S.; Takeuchi, Kenneth J.


    Ag7Fe3(P2O7 )4sub> is an example of an electrochemical displacement material which contains two different electrochemically active metal cations, where one cation (Ag+) forms metallic silver nanoparticles external to the crystals of Ag7Fe3(P2O7 )4sub> via an electrochemical reduction displacement reaction, while the other cation (Fe+3) is electrochemically reduced with the retention of iron cations within the anion structural framework concomitant with lithium insertion. These contrasting redox chemistries within one pure cathode material enable high rate capability and reversibility when Ag7Fe3(P2O7 )4sub> is employed as cathode material in a lithium ion battery (LIB). Further, pyrophosphate materials are thermally and electrically stable, desirable attributes for cathode materials in LIBs. In this article, a bimetallic pyrophosphate material Ag7Fe3(P2O7 )4sub> is synthesized and confirmed to be a single phase by Rietveld refinement. Electrochemistry of Ag7Fe3(P2O7 )4sub> is reported for the first time in the context of lithium based batteries using cyclic voltammetry and galvanostatic discharge–charge cycling. The reduction displacement reaction and the lithium (de)insertion processes are investigated using ex situ X-ray absorption spectroscopy and X-ray diffraction of electrochemically reduced and oxidized Ag7Fe3(P2O7 )4sub>. Ag7Fe3(P2O7 )4sub> exhibits good reversibility at the iron centers indicated by ~80% capacity retention over 100 cycles following the initial formation cycle and excellent rate capability exhibited by ~70% capacity retention upon a 4-fold increase in current.

  13. Crystal structures and electronic properties for the over-lithiated and Li–Ag substituted phases of Li{sub 9}V{sub 3}(P{sub 2}O{sub 7}){sub 3}(PO{sub 4}){sub 2} insertion electrode system

    SciTech Connect

    Onoda, Masashige Inagaki, Makoto; Saito, Hiroaki


    For the Li{sub 9}V{sub 3}(P{sub 2}O{sub 7}){sub 3}(PO{sub 4}){sub 2} insertion electrode system with a multiple-electron reaction, the over-lithiated phase Li{sub x}V{sub 3}(P{sub 2}O{sub 7}){sub 3}(PO{sub 4}){sub 2} with 94}){sub 2} with 04}){sub 2} which has (VP2{sub 2}O{sub 7}){sub 3}(P1O{sub 4}){sub 2} layers in the ab-plane built up of VO{sub 6} octahedra sharing corners with P1O{sub 4} tetrahedra and P2{sub 2}O{sub 7} groups. In Li{sub x}V{sub 3}(P{sub 2}O{sub 7}){sub 3}(PO{sub 4}){sub 2}, the over-inserted Li4 ion surrounded by three oxygens in a planar triangular arrangement resides with a significantly large thermal parameter in the tunnels formed by the stacking of the layers and in between the octahedral Li1 sites, leading to a linear chain of Li ions with the distance 3.40 Å parallel to the direction of diffusion pathways. In Li{sub 9−y}Ag{sub y}V{sub 3}(P{sub 2}O{sub 7}){sub 3}(PO{sub 4}){sub 2}, where the Li1 site is substituted by Ag, the reduction of the electron hopping and the electrostatic potential for V ions are revealed in comparison with those of unsubstituted parent, which may account for the increase of mean voltage in the Li ion battery. - Highlights: • Li{sub x}V{sub 3}(P{sub 2}O{sub 7}){sub 3}(PO{sub 4}){sub 2} (x>9) and Li{sub 9−y}Ag{sub y}V{sub 3}(P{sub 2}O{sub 7}){sub 3}(PO{sub 4}){sub 2} (04}){sub 2}, the over-inserted Li4 ion resides in between the Li

  14. Characterizing Fluorocarbon Assisted Atomic Layer Etching of Si Using Cyclic Ar/C4sub>F8 and Ar/CHF3 Plasma

    SciTech Connect

    Metzler, Dominik; Li, Chen; Engelmann, Sebastian; Bruce, Robert L; Joseph, Eric A; Oehrlein, Gottlieb S


    With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching (ALE) processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C4sub>F8 and CHF3), and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J Vac Sci Technol A 32, 020603 (2014), and D. Metzler et al., J Vac Sci Technol A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO2 and Si, but is limited with regard to control over material etching selectivity. Ion energy over the 20 to 30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF3 has a lower FC deposition yield for both SiO2 and Si, and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F8. The thickness of deposited FC layers using CHF3 is found to be greater for Si than for SiO2. X-ray photoelectron spectroscopy was used to study surface chemistry

  15. Second order phase transition temperature of single crystals of Gd5Si1.3Ge2.7 and Gd5Si1.4sub>Ge2.6

    SciTech Connect

    Hadimani, R. L.; Melikhov, Y.; Schlagel, D. L.; Lograsso, T. A.; Dennis, K. W.; McCallum, R. W.; Jiles, D. C.


    Gd5(SixGe1–x)4sub> has mixed phases in the composition range 0.32 < x < 0.41, which have not been widely studied. In this paper, we have synthesized and indexed single crystal samples of Gd5Si1.3Ge2.7 and Gd5Si1.4sub>Ge2.6. In this study, we have investigated the first order and second order phase transition temperatures of these samples using magnetic moment vs. temperature and magnetic moment vs. magnetic field at different temperatures. We have used a modified Arrott plot technique that was developed and reported by us previously to determine the “hidden” second order phase transition temperature of the orthorhombic II phase.

  16. Color-tunable photoluminescence phosphors of Ce{sup 3+} and Tb{sup 3+} co-doped Sr{sub 2}La{sub 8}(SiO{sub 4}){sub 6}O{sub 2} for UV w-LEDs

    SciTech Connect

    Guo, Qingfeng; Liao, Libing Mei, Lefu; Liu, Haikun; Hai, Yun


    A series of new luminescent emission-tunable phosphors Sr{sub 2}La{sub 8}(SiO{sub 4}){sub 6}O{sub 2}:Ce{sup 3+}, Tb{sup 3+} with apatite structure have been synthesized by a high temperature solid-state reaction. The phase structure, photoluminescence emission and excitation spectra, lifetime, as well as the effect of Tb{sup 3+} concentration are investigated to characterize the resulting samples. The critical distance was calculated to be 8.26 Å by using the concentration quenching method. The intense green emission was observed in the Sr{sub 2}La{sub 8}(SiO{sub 4}){sub 6}O{sub 2}:Ce{sup 3+}, Tb{sup 3+} phosphors on the basis of the efficient energy transfer from Ce{sup 3+} to Tb{sup 3+} with an efficiency of 68.55%. And a possible mechanism of the energy-transfer from Ce{sup 3+} to Tb{sup 3+} ion is also proposed. The results indicate that Sr{sub 2}La{sub 8}(SiO{sub 4}){sub 6}O{sub 2}:Ce{sup 3+}, Tb{sup 3+} phosphors have potential applications to be used as near UV-convertible phosphors for white light-emitting diodes because of the broad excitation in the near-ultraviolet range and the efficient green emission light. - Graphical abstract: Crystal structure and luminescence properties of Sr{sub 2}La{sub 8}(SiO{sub 4}){sub 6}O{sub 2}:Ce{sup 3+},Tb{sup 3+} phosphors have been discussed. - Highlights: • Ce{sup 3+} and Tb{sup 3+} ions entered both La sites in SLSO. • The energy transfer efficiency can reach at 68.55%. • The emitting color of SLSO phosphors shifted from the blue to green region.

  17. Phase relations in the system K{sub 2}MoO{sub 4}-KPO{sub 3}-MoO{sub 3}-Bi{sub 2}O{sub 3}: A new phosphate K{sub 3}Bi{sub 5}(PO{sub 4}){sub 6}

    SciTech Connect

    Terebilenko, Kateryna V.; Zatovsky, Igor V. Slobodyanik, Nikolay S.; Domasevitch, Konstantin V.; Pushkin, Denis V.; Baumer, Vyacheslav N.; Sudavtsova, Valentina S.


    Phase equilibrium in the pseudo-quaternary system K{sub 2}O-MoO{sub 3}-P{sub 2}O{sub 5}-Bi{sub 2}O{sub 3} was studied as three-component solvent K{sub 2}MoO{sub 4}-KPO{sub 3}-MoO{sub 3} containing 15 mol% Bi{sub 2}O{sub 3} during slow cooling and spontaneous crystallization. The results of the investigation were shown on a composition diagram, which indicates the crystallization fields of K{sub 2}Bi(PO{sub 4})(MoO{sub 4}), K{sub 5}Bi(MoO{sub 4}){sub 4}, BiPO{sub 4} and K{sub 3}Bi{sub 5}(PO{sub 4}){sub 6}. New phosphate K{sub 3}Bi{sub 5}(PO{sub 4}){sub 6} was characterized by single-crystal X-ray diffraction (space group C2/c, a=17.680(4), b=6.9370(14), c=18.700(4) A, {beta}=113.79(3){sup o}) and FTIR spectroscopy. The possibility of lone electron pair stereoactivity of bismuth was suggested using the calculations of characteristics of the Voronoi-Dirichlet polyhedra for K{sub 3}Bi{sub 5}(PO{sub 4}){sub 6} and K{sub 2}Bi(PO{sub 4})(MoO{sub 4}). - Graphical abstract: Composition diagram of the K{sub 2}MoO{sub 4}-KPO{sub 3}-MoO{sub 3} system containing 15 mol% Bi{sub 2}O{sub 3} with approximate fields of phase formation bismuth phosphates, molybdate and phosphate-molybdate.

  18. Hydrothermal Synthesis and Characterization of Novel Brackebuschite-Type Transition Metal Vanadates: Ba 2 M(VO 4sub> ) 2 (OH), M = V 3+ , Mn 3+ , and Fe 3+ , with Interesting Jahn–Teller and Spin-Liquid Behavior

    SciTech Connect

    Sanjeewa, Liurukara D.; McGuire, Michael A.; Garlea, Vasile O.; Hu, Longyu; Chumanov, George; McMillen, Colin D.; Kolis, Joseph W.


    In a new series of transition metal vanadates, namely, Ba2M(VO4sub>)2(OH) (M = V3+, Mn3+, and Fe3+), was synthesized as large single crystals hydrothermally in 5 M NaOH solution at 580 °C and 1 kbar. This new series of compounds is structurally reminiscent of the brackebuschite mineral type. The structure of Ba2V(VO4sub>)2(OH) is monoclinic in space group P21/m, a = 7.8783(2) Å, b = 6.1369(1) Å, c = 9.1836(2) Å, β = 113.07(3)°, V = 408.51(2) Å3. Moreover, the other structures are similar and consist of one-dimensional trans edge-shared distorted octahedral chains running along the b-axis. The vanadate groups bridge across edges of their tetrahedra. Structural analysis of the Ba2Mn(VO4sub>)2(OH) analogue yielded a new understanding of the Jahn–Teller effect in this structure type. Raman and infrared spectra were investigated to observe the fundamental vanadate and hydroxide vibrational modes. Finally, single-crystal temperature-dependent magnetic studies on Ba2V(VO4sub>)2(OH) reveal a broad feature over a wide temperature range with maximum at ~100 K indicating that an energy gap could exist between the antiferromagnetic singlet ground state and excited triplet states, making it potentially of interest for quantum magnetism studies.

  19. Structural study of (N{sub 2}H{sub 5},H){sub 2.9}U{sub 1.1}Ce{sub 0.9}(C{sub 2}O{sub 4}){sub 5}·10H{sub 2}O from a conventional X-ray diffraction diagram obtained on a powder synthesized by a fast vortex process

    SciTech Connect

    Brackx, E.; Laval, J.P.; Dugne, O.; Feraud, J.P.; Arab-Chapelet, B.


    In the context of research on U/minor actinides for nuclear fuel reprocessing in the transmutation process, developments are first studied with surrogates containing uranium and lanthanides to facilitate testing. The tests consist of precipitating and calcining a hydrazinium uranium/cerium oxalate. The structure of this oxalate had not been previously determined, but was necessary to validate the physicochemical mechanisms involved. The present study, firstly demonstrates the structural similarity of the U/Ce oxalate phase (N{sub 2}H{sub 5},H){sub 2.9}U{sub 1.1}Ce{sub 0.9}(C{sub 2}O{sub 4}){sub 5}·10H{sub 2}O, synthesized using a vortex precipitator for continuous synthesis of actinide oxalates, with previously known oxalates, crystallizing in P6{sub 3}/mmc symmetry, obtained by more classical methods. This fast precipitation process induces massive nucleation of fine powders. Their structural and microstructural determination confirms that the raw and dried phases belong to the same structural family as (NH{sub 4}){sub 2}U{sub 2}(C{sub 2}O{sub 4}){sub 5}·0.7H{sub 2}O whose structure was described by Chapelet-Arab in P6{sub 3}/mmc symmetry, using single crystal data. However, they present an extended disorder inside the tunnels of the structure, even after drying at 100 °C, between water and hydrazinium ions. This disorder is directly related to the fast vortex method. This structure determination can be used as a basis for further semi-quantitative analysis on the U/minor actinides products formed under various experimental conditions. - Highlights: • Uranium cerium oxalate precipitate characterization by X-ray powder diffraction. • Morphology characterization by SEM analysis. • Structure determination by unit cell Rietveld refinement.

  20. Laser power density dependent energy transfer between Tm3+ and Tb3+: tunable upconversion emissions in NaYF4sub>:Tm3+,Tb3+,Yb3+ microcrystals.


    Xue, Xiaojie; Thitsa, Makhin; Cheng, Tonglei; Gao, Weiqing; Deng, Dinghuan; Suzuki, Takenobu; Ohishi, Yasutake


    Energy transfer between Tm3+ and Tb3+ dependent on the power density of pump laser was investigated in NaYF4sub>: Tb3+,Tm3+,Yb3+ microcrystals. Under the excitation of a 976-nm near-infrared laser at various power densities, Tb3+-Tm3+-Yb3+ doped samples exhibited intense visible emissions with tunable color between green and blue. The ratio of blue and green emission were determined by energy transfer between Tm3+ and Tb3+. When the power density of pump laser was low, the energy transfer process from Tm3+ (3F4sub>) to Tb3+ (7F0) occurred efficiently. Upconversion processes in Tm3+ were inhibited, only visible emissions from Tb3+ with green color were observed. When the power density increased, energy transfer from the 3F4sub> (Tm3+) to 7F0 level (Tb3+) was restrained and population on high energy levels of Tm3+ was increased. Contribution of upconversion emissions from Tm3+ gradually became dominant. The emission color was tuned from green to blue with increasing the power density. Energy transfer processes between low-lying levels of activators, such as Tm3+ will greatly reduce the population on certain levels for further high-order upconversion processes. The Tb3+-Tm3+-Yb3+ doped phosphors are promising materials for detecting the condition of power density of the invisible near-infrared laser.

  1. Single-Site Cobalt Catalysts at New Zr 82 -O) 82 -OH) 4sub> Metal-Organic Framework Nodes for Highly Active Hydrogenation of Alkenes, Imines, Carbonyls, and Heterocycles

    SciTech Connect

    Ji, Pengfei; Manna, Kuntal; Lin, Zekai; Urban, Ania; Greene, Francis X.; Lan, Guangxu; Lin, Wenbin


    We report here the synthesis of robust and porous metal–organic frameworks (MOFs), M-MTBC (M = Zr or Hf), constructed from the tetrahedral linker methane-tetrakis(p-biphenylcarboxylate) (MTBC) and two types of secondary building units (SBUs): cubic M82-O)82-OH)4sub> and octahedral M6(μ3-O)4sub>(μ3-OH)4sub>. While the M6-SBU is isostructural with the 12-connected octahedral SBUs of UiO-type MOFs, the M8-SBU is composed of eight MIV ions in a cubic fashion linked by eight μ2-oxo and four μ2-OH groups. The metalation of Zr-MTBC SBUs with CoCl2, followed by treatment with NaBEt3H, afforded highly active and reusable solid Zr-MTBC-CoH catalysts for the hydrogenation of alkenes, imines, carbonyls, and heterocycles. Zr-MTBC-CoH was impressively tolerant of a range of functional groups and displayed high activity in the hydrogenation of tri- and tetra-substituted alkenes with TON > 8000 for the hydrogenation of 2,3-dimethyl-2-butene. Our structural and spectroscopic studies show that site isolation of and open environments around the cobalt-hydride catalytic species at Zr8-SBUs are responsible for high catalytic activity in the hydrogenation of a wide range of challenging substrates. MOFs thus provide a novel platform for discovering and studying new single-site base-metal solid catalysts with enormous potential for sustainable chemical synthesis.

  2. Electronic and Electrochemical Properties of Li 1–x Mn 1.5 Ni 0.5 O 4sub> Spinel Cathodes As a Function of Lithium Content and Cation Ordering

    SciTech Connect

    Moorhead-Rosenberg, Zach; Huq, Ashfia; Goodenough, John B.; Manthiram, Arumugam


    The electronic and electrochemical properties of the high-voltage spinel LiMn1.5Ni0.5O4sub> as a function of cation ordering and lithium content have been investigated. Conductivity and activation energy measurements confirm that charge transfer occurs by small polaron hopping and the charge carrier conduction is easier in the Ni:3d band than in the in Mn:3d band. Seebeck coefficient data reveal that the Ni2+/3+. and Ni3+/4+ redox couples are combined in a single,3d band, and that maximum charge carrier concentration occurs where the average Ni oxidation state is close to 3+, corresponding to x = 0.5 in Li Li1-xMn1.5Ni0.5O4sub>. Furthermore, maximum electronic conductivity is found at x = 0.5, regardless of cation ordering. The thermodynamically stable phases formed during cycling were investigated by recording the X-ray diffraction (XRD) of chemically delithiated powders. The more ordered spinels maintained two separate two-phase regions upon lithium extraction, while the more disordered samples exhibited a solid-solubility region from LiMn1.5Ni0.5O4sub> to Li0.5Mn1.5Ni0.5O4sub>. The conductivity and phase-transformation data of four samples with varying degrees of cation ordering were compared to the electrochemical data collected with lithium cells. Only the most ordered spinel showed inferior rate performance, while the sample annealed for a shorter time performed comparable to the unannealed or disordered samples. Our results challenge the most common beliefs about high-voltage spinel: (i) low Mn3+ content is responsible for poor rate performance and (ii) thermodynamically stable solid-solubility is critical for fast kinetics.

  3. Acoustic emission during the ferroelectric transition Pm3{sup ¯}m to P4mm in BaTiO{sub 3} and the ferroelastic transition R3{sup ¯}m-C2/c in Pb{sub 3}(PO{sub 4}){sub 2}

    SciTech Connect

    Salje, E. K. H.; Dul'kin, E.; Roth, M.


    Acoustic emission (AE) spectroscopy without frequency filtering (∼broadband AE) and moderate time integration is shown to be sensitive enough to allow the investigation of subtle nano-structural changes in ferroelectric BaTiO{sub 3} and ferroelastic Pb{sub 3}(PO{sub 4}){sub 2}. AE signals during weak phase transitions are compatible with avalanche statistics as observed previously in large-strain systems. While the data are too sparse to determine avalanche exponents, they are well suited to determine other thermodynamic parameters such as transition temperatures and critical stresses.

  4. Structural and resonance Raman studies of an oxygen-evolving catalyst. Crystal structure of [(bpy){sub 2}(H{sub 2}O)Ru{sup III}ORu{sup IV}(OH)(bpy){sub 2}](ClO{sub 4}){sub 4}

    SciTech Connect

    Schoonover, J.; Ni, JinFeng; Roecker, L.; White, P.S.; Meyer, T.J. |


    The oxidized form of the blue dimer water oxidation catalyst [(bpy){sub 2}(H{sub 2}O)Ru{sup III}ORu{sup IV}(OH)(bpy){sub 2}](ClO{sub 4}){sub 4} (bpy is 2,2{prime}-bipyridine) has been characterized structurally by X-ray crystallography. Comparisons with [(bpy){sub 2}(H{sub 2}O)Ru{sup III}-ORu{sup III}(OH{sub 2})(bpy){sub 2}](ClO{sub 4}){sub 4}{center_dot}2H{sub 2}O, [(bpy){sub 2}ClRu{sup III}ORu{sup IV}Cl(bpy){sub 2}](ClO{sub 4}){sub 3}{center_dot}H{sub 2}O, and [(tpy)(bpy)Os{sup III}OOs{sup IV}(bpy)-(tpy)]Na(ClO{sub 4}){sub 6}{center_dot}3H{sub 2}O (tpy is 2,2{prime}:6{prime},2{double_prime}-terpyridine) reveal that oxidation of Ru{sup III}-O-Ru{sup III} to Ru{sup III}-O-Ru{sup IV} results in significant structural changes at the {mu}-oxo bridge. There is an increase toward linearity along M-O-M, a decrease in the M-O bond distances at the bridge, and an increase in the H{sub 2}O-Ru-O bridge angle. These changes are discussed in the context of the structural requirements for O...O coupling and O{sub 2} evolution in higher oxidation states. Resonance Raman spectra of these and related complexes reveal that internal ligand vibrations as well as overtone and combination bands of an intense, symmetrical M-O-M stretch at 360-400 cm{sup {minus}1} contribute significantly to the Raman spectra. Additional M-O-M bands are identified near 800 cm{sup {minus}1} and, tentatively, near 130 cm{sup {minus}1}. It is not possible to assign bands to Ru-OH{sub 2} or Ru-OH stretches; bands at low energy appear to originate from modes that are highly mixed.

  5. Phase transitions and unusual behavior of heat capacity in metal organic framework compound Zn{sub 2}(C{sub 8}H{sub 4}O{sub 4}){sub 2}·N{sub 2}(CH{sub 2}){sub 6}

    SciTech Connect

    Paukov, I.E.; Samsonenko, D.G.; Pischur, D.P.; Kozlova, S.G.; Gabuda, S.P.


    Thermodynamic properties of high-porous metal-organic framework (MOF) compound Zn{sub 2}(C{sub 8}H{sub 4}O{sub 4}){sub 2}·N{sub 2}(CH{sub 2}){sub 6} were studied in the temperature range 8.9–300 K using low-temperature adiabatic calorymetry and DSC methods. Phase transitions were observed at ∼15, ∼60, and ∼135 K. It is shown that specific heat of the compound obeys the classical Debye law C{sub p}∼T{sup 3} only below 15 K, whereas above 15 K it is proportional to the first degree of temperature, C{sub p}∼T, to indicate a strong anisotropy of crystal vibrations corresponding to 1D continuum. It is shown that the strong anisotropy can be related to coordination interaction of Zn{sup 2+} and N{sub 2}(CH{sub 2}){sub 6} ligands in the specific structure of compound Zn{sub 2}(C{sub 8}H{sub 4}O{sub 4}){sub 2}·N{sub 2}(CH{sub 2}){sub 6}. - Graphical abstract: Specific heat C{sub p} is proportional to the first degree of temperature showing a strong anisotropy of crystal vibrations corresponding to 1D continuum in Zn{sub 2}(C{sub 8}H{sub 4}O{sub 4}){sub 2}·N{sub 2}(CH{sub 2}){sub 6.} - Highlights: • Specific heat capacity of Zn{sub 2}(C{sub 8}H{sub 4}O{sub 4}){sub 2}·N{sub 2}(CH{sub 2}){sub 6} was first studied at 8.9–300 K. • Phase transitions were observed at ∼15, ∼60, and ∼135 K. • The heat capacity is proportional to the first degree of temperature above 15 K. • The discovered dependency corresponds to a one-dimensional vibration continuum.

  6. Preparation and microwave dielectric properties of Li{sub 3}(Mg{sub 0.92}Zn{sub 0.08}){sub 2}NbO{sub 6}–Ba{sub 3}(VO{sub 4}){sub 2} composite ceramics for LTCC applications

    SciTech Connect

    Zhang, Tianwen; Zuo, Ruzhong Zhang, Chen


    Highlights: • Microwave properties of ϵ{sub r} ∼ 16.3, Q × f ∼ 50,084 GHz and τ{sub f} ∼ 1.5 ppm/°C are achieved. • The τ{sub f} value of the LMZN ceramic can be adjusted to near zero by adding BV. • The LMZN–BV composite ceramic can be well sintered at a relatively low temperature. • The composite ceramic has a good chemical compatibility with Ag electrode. - Abstract: In this work, the (1 − x)Li{sub 3}(Mg{sub 0.92}Zn{sub 0.08}){sub 2}NbO{sub 6}–xBa{sub 3}(VO{sub 4}){sub 2} (x = 0.1–0.35) ceramics were prepared via a conventional solid state reaction route. The phase composition, microstructure and microwave dielectric properties were investigated by an X-ray diffractometer (XRD), a scanning electron microscope and a network analyzer. The XRD results indicated that the Li{sub 3}(Mg{sub 0.92}Zn{sub 0.08}){sub 2}NbO{sub 6} and Ba{sub 3}(VO{sub 4}){sub 2} phases could well coexist without forming any secondary phases. The dielectric constant (ϵ{sub r}) and quality factor (Q × f) values of the Li{sub 3}(Mg{sub 0.92}Zn{sub 0.08}){sub 2}NbO{sub 6} ceramic decreased with the addition of Ba{sub 3}(VO{sub 4}){sub 2} phase, however its temperature coefficient of resonant frequency (τ{sub f}) value was improved significantly. Excellent microwave dielectric properties of ϵ{sub r} ∼ 16.3, Q × f ∼ 50,084 GHz (at 8.64 GHz) and τ{sub f} ∼ 1.5 ppm/°C were achieved for the x = 0.3 sample when sintered at 950 °C for 4 h. The chemical compatibility with Ag electrode indicated that the 0.7Li{sub 3}(Mg{sub 0.92}Zn{sub 0.08}){sub 2}NbO{sub 6}–0.3Ba{sub 3}(VO{sub 4}){sub 2} composite ceramic would be a promising material for the low temperature cofired ceramic applications.

  7. New yellow Ba0.93Eu0.07Al2O4sub> phosphor for warm-white light-emitting diodes through single-emitting-center conversion

    SciTech Connect

    Li, Xufan; Budai, John D.; Liu, Feng; Howe, Jane Y.; Zhang, Jiahua; Wang, Xiao-Jun; Gu, Zhanjun; Sun, Chengjun; Meltzer, Richard S.; Pan, Zhengwei


    Phosphor-converted white light-emitting diodes for indoor illumination need to be warm-white (i.e., correlated color temperature <4000 K) with good color rendition (i.e., color rendering index >80). However, no single-phosphor, single-emitting-center-converted white light-emitting diodes can simultaneously satisfy the color temperature and rendition requirements due to the lack of sufficient red spectral component in the phosphors’ emission spectrum. Here, we report a new yellow Ba0.93Eu0.07Al2O4sub> phosphor that has a new orthorhombic lattice structure and exhibits a broad yellow photoluminescence band with sufficient red spectral component. Warm-white emissions with correlated color temperature <4000 K and color rendering index >80 were readily achieved when combining the Ba0.93Eu0.07Al2O4sub> phosphor with a blue light-emitting diode (440–470 nm). This study demonstrates that warm-white light-emitting diodes with high color rendition (i.e., color rendering index >80) can be achieved based on single-phosphor, single-emitting-center conversion.

  8. Crystal structure of {l_brace}NH{sub 2}C(NHC{sub 6}H{sub 5}){sub 2}{r_brace}{sub 3}[UO{sub 2}(C{sub 2}O{sub 4}){sub 2}(NCS)] . 1.25H{sub 2}O

    SciTech Connect

    Serezhkina, L. B.; Peresypkina, E. V.; Virovets, A. V.; Neklyudova, N. A.; Pushkin, D. V.


    Synthesis and X-ray diffraction study of {l_brace}NH{sub 2}C(NHC{sub 6}H{sub 5}){sub 2}{r_brace}{sub 3}[UO{sub 2}(C{sub 2}O{sub 4}){sub 2}(NCS)] . 1.25H{sub 2}O single crystals have been performed. This compound is crystallized in the orthorhombic system, with the unit-cell parameters a = 45.2646(8) A, b = 57.7359(11) A, c = 7.9244(3) A, sp. gr. Fdd2, Z = 16, V = 20 709.6(10) A{sup 3}, and R = 0.0477. The uranium-containing structural units of the crystals are one-core groups of the [UO{sub 2}(C{sub 2}O{sub 4}){sub 2}(NCS)]{sup 3-} composition, belonging to the crystallochemical group AB{sub 2}{sup 01}M{sup 1} (A = UO{sub 2}{sup +2}, B{sup 01} = C{sub 2}O{sub 4}{sup 2-}, M{sup 1} = NCS{sup -}) of uranyl complexes. The uranium-containing complexes are connected into a three-dimensional framework owing to the electrostatic interactions with the outer-sphere cations and a system of hydrogen bonds.

  9. Performance improvement of Li-rich layer-structured Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 by integration with spinel LiNi 0.5 Mn 1.5 O 4sub>

    SciTech Connect

    Feng, Xin; Yang, Zhenzhong; Tang, Daichun; Kong, Qingyu; Gu, Lin; Wang, Zhaoxiang; Chen, Liquan


    Li-rich layered Li1+xMnyM1-x-yO2 (or denoted xLi2MnO3center dot1-xLiMO2, M = Ni, Co, Mn, etc.) are promising cathode materials for high energy-density Li-ion batteries. However, their commercial applications suffer from problems such as a drop in the capacity and discharge voltage during cycling. In this work, the cycling performance of a layered oxide Li1.2Ni0.13Co0.13Mn0.54O2 is improved by integration with spinel LiNi0.5Mn1.5O4sub> to obtain a layered-spinel composite. Characterization by powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) as well as cyclic voltammetry (CV) indicates that delayed degradation of layered Li2MnO3 and the suppressed growth of LiMn2O4sub>-like spinel are responsible for the performance improvement.

  10. From the ternary Eu(Au/In)2 and EuAu4sub>(Au/In)2 with remarkable Au/In distributions to a new structure type: The gold-rich Eu5Au16(Au/In)6 structure

    SciTech Connect

    Steinberg, Simon; Card, Nathan; Mudring, Anja -Verena


    The ternary Eu(Au/In)2 (EuAu0.46In1.54(2)) (I), EuAu4sub>(Au/In)2 (EuAu4+xIn2–x with x = 0.75(2) (II), 0.93(2), and 1.03(2)), and Eu5Au16(Au/In)6 (Eu5Au17.29In4.71(3)) (III) have been synthesized, and their structures were characterized by single-crystal X-ray diffraction. I and II crystallize with the CeCu2-type (Pearson Symbol oI12; Imma; Z = 4; a = 4.9018(4) Å; b = 7.8237(5) Å; c = 8.4457(5) Å) and the YbAl4sub>Mo2-type (tI14; I4/mmm; Z = 2; a = 7.1612(7) Å; c = 5.5268(7) Å) and exhibit significant Au/In disorder. I is composed of an Au/In-mixed diamond-related host lattice encapsulating Eu atoms, while the structure of II features ribbons of distorted, squared Au8 prisms enclosing Eu, Au, and In atoms. Combination of these structural motifs leads to a new structure type as observed for Eu5Au16(Au/In)6 (Eu5Au17.29In4.71(3)) (oS108; Cmcm; Z = 4; a = 7.2283(4) Å; b = 9.0499(6) Å; c = 34.619(2) Å), which formally represents a one-dimensional intergrowth of the series EuAu2–“EuAu4sub>In2”. The site preferences of the disordered Au/In positions in II were investigated for different hypothetical “EuAu4sub>(Au/In)2” models using the projector-augmented wave method and indicate that these structures attempt to optimize the frequencies of the heteroatomic Au–In contacts. Furthermore, a chemical bonding analysis on two “EuAu5In” and “EuAu4sub>In2” models employed the TB-LMTO-ASA method and reveals that the subtle interplay between the local atomic environments and the bond energies determines the structural and site preferences for these systems.

  11. Negative ion photoelectron spectra of ISO3, IS2O3, and IS2O4sub> intermediates formed in interfacial reactions of ozone and iodide/sulfite aqueous microdroplets

    SciTech Connect

    Qin, Zhengbo; Hou, Gao-Lei; Yang, Zheng; Valiev, Marat; Wang, Xue-Bin


    Three short-lived, anionic intermediates, ISO3, IS2O3, and IS2O4sub>, are detected during reactions between ozone and aqueous iodine/sulfur oxides microdroplets. These species may play an important role in ozone-driven inorganic aerosol formation; however their chemical properties remain largely unknown. This is the issue addressed in this work using negative ion photoelectron spectroscopy (NIPES) and ab-initio modeling. The NIPE spectra reveal that all of the three anionic species are characterized by high adiabatic detachment energies (ADEs) - 4.62 ± 0.10, 4.52 ± 0.10, and 4.60 ± 0.10 eV for ISO3, IS2O3, and IS2O4sub>, respectively. Vibrational progressions with frequencies assigned to the S–O symmetric stretching modes are also discernable in the ground state transition features. Density functional theory (DFT) calculations show the presence of several low-lying isomers involving different bonding scenarios. Further analysis based on high level CCSD(T) calculations reveal that the lowest energy structures are characterized by formation of I–S and S–S bonds and can be structurally viewed as SO3 linked with I, IS, and ISO for ISO3, IS2O3, and IS2O4sub>, respectively. The calculated ADEs and vertical detachment energies (VDEs) are in excellent agreement with the experimental results, further supporting the identified minimum energy structures. The obtained intrinsic molecular properties of these anionic intermediates and neutral radicals should be useful to help understand their photochemical reactions in the atmosphere.

  12. Spin orientations of the spin-half Ir4+ ions in Sr3NiIrO6, Sr2IrO4sub> and Na2IrO3: Density functional, perturbation theory and Madelung potential analyses

    SciTech Connect

    Gordon, Elijah E.; Xiang, Hongjun; Koehler, Jurgen; Whangbo, Myung -Hwan


    The spins of the low-spin Ir4+ (S = 1/2, d5) ions at the octahedral sites of the oxides Sr3NiIrO6, Sr2IrO4sub> and Na2IrO3 exhibit preferred orientations with respect to their IrO6 octahedra. We evaluated the magnetic anisotropies of these S = 1/2 ions on the basis of DFT calculations including spin-orbit coupling (SOC), and probed their origin by performing perturbation theory analyses with SOC as perturbation within the LS coupling scheme. The observed spin orientations of Sr3NiIrO6 and Sr2IrO4sub> are correctly predicted by DFT calculations, and are accounted for by the perturbation theory analysis. As for the spin orientation of Na2IrO3, both experimental studies and DFT calculations have not been unequivocal. Our analysis reveals that the Ir4+ spin orientation of Na2IrO3 should have nonzero components along the c- and a-axes directions. The spin orientations determined by DFT calculations are sensitive to the accuracy of the crystal structures employed, which is explained by perturbation theory analyses when interactions between adjacent Ir4+ ions are taken into consideration. There are indications implying that the 5d electrons of Na2IrO3 are less strongly localized compared with those of Sr3NiIrO6 and Sr2IrO4sub>. This implication was confirmed by showing that the Madelung potentials of the Ir4+ ions are less negative in Na2IrO3 than in Sr3NiIrO6, Sr2IrO4sub>. Most transition-metal S = 1/2 ions do have magnetic anisotropies because the SOC induces interactions among their crystal-field split d-states, and the associated mixing of the states modifies only the orbital parts of the states. This finding cannot be mimicked by a spin Hamiltonian

  13. In Situ Foaming of Porous (La 0.6 Sr 0.4sub> ) 0.98 (Co 0.2 Fe 0.8 ) O 3-δ (LSCF) Cathodes for Solid Oxide Fuel Cell Applications

    SciTech Connect

    Gandavarapu, Sodith; Sabolsky, Edward; Sabolsky, Katarzyna; Gerdes, Kirk


    A binder system containing polyurethane precursors was used to in situ foam (direct foam) a (La{sub 0.6}Sr{sub 0.4}){sub 0.98} (Co{sub 0.2} Fe{sub 0.8}) O{sub 3-{ delta}} (LSCF) composition for solid oxide fuel cell (SOFC) cathode applications. The relation between in situ foaming parameters on the final microstructure and electrochemical properties was characterized by microscopy and electrochemical impedance spectroscopy (EIS), respectively. The optimal porous cathode architecture was formed with a 70 vol% solids loading within a polymer precursor composition with a volume ratio of 8:4:1 (isocyanate: PEG: surfactant) in a terpineol-based ink vehicle. The resultant microstructure displayed a broad pore size distribution with highly elongated pore structure.

  14. Imaging the surface morphology, chemistry and conductivity of LiNi 1/3 Fe 1/3 Mn 4/3 O 4sub> crystalline facets using scanning transmission X-ray microscopy

    SciTech Connect

    Zhou, Jigang; Wang, Jian; Cutler, Jeffrey; Hu, Enyuan; Yang, Xiao-Qing


    We have employed scanning transmission X-ray microscopy (STXM) using the X-ray fluorescence mode in order to elucidate the chemical structures at Ni, Fe, Mn and O sites from the (111) and (100) facets of micron-sized LiNi1/3Fe1/3Mn4/3O4sub> energy material particles. Furthermore, STXM imaging using electron yield mode has mapped out the surface conductivity of the crystalline particles. Our study presents a novel approach that visualizes local element segregation, chemistry and conductivity variation among different crystal facets, which will assist further tailoring of the morphology and surface structure of this high voltage spinel lithium ion battery cathode material.

  15. Reversible Exsolution of Nanometric Fe2O3 Particles in BaFe2-x(PO4sub>)2 (0 ≤ x ≤ 2/3):The Logic of Vacancy Ordering in Novel Metal-Depleted Two-Dimensional Lattices

    SciTech Connect

    Alcover, Ignacio Blazquez; David, Rénald; Daviero-Minaud, Sylvie; Filimonov, Dmitry; Huvé, Marielle; Roussel, Pascal; Kabbour, Houria; Mentré, Olivier


    We show here that the exsolution of Fe2+ ions out of two-dimensional (2D) honeycomb layers of BaFe2(PO4sub>)2 into iron-deficient BaFe2–x(PO4sub>)2 phases and nanometric α-Fe2O3 (typically 50 nm diameter at the grain surface) is efficient and reversible until x = 2/3 in mild oxidizing/reducing conditions. It corresponds to the renewable conversion of 12 wt % of the initial mass into iron oxide. After analyzing single crystal X-ray diffraction data of intermediate members x = 2/7, x = 1/3, x = 1/2 and the ultimate Fe-depleted x = 2/3 term, we then observed a systematic full ordering between Fe ions and vacancies (VFe) that denote unprecedented easy in-plane metal diffusion driven by the Fe2+/Fe3+ redox. Besides the discovery of a diversity of original depleted triangular {Fe2/3+2–xO6} topologies, we propose a unified model correlating the x Fe-removal and the experimental Fe/VFe ordering into periodic one-dimensional motifs paving the layers, gaining insights into predictive crystahemistry of complex low dimensional oxides. When we increased the x values it led to a progressive change of the materials from 2D ferromagnets (Fe2+) to 2D ferrimagnets (Fe2/3+) to antiferromagnets for x = 2/3 (Fe3+).

  16. Defect-Tolerant Diffusion Channels for Mg2+ Ions in Ribbon-Type Borates: Structural Insights into Potential Battery Cathodes MgVBO4sub> and Mgx Fe2–xB2O5

    SciTech Connect

    Bo, Shou-Hang; Grey, Clare P.; Khalifah, Peter G.


    The reversible room temperature intercalation of Mg2+ ions is difficult to achieve, but may offer substantial advantages in the design of next-generation batteries if this electrochemical process can be successfully realized. Two types of quadruple ribbon-type transition metal borates (MgxFe2-xB2O5 and MgVBO4sub>) with high theoretical capacities (186 mAh/g and 360 mAh/g) have been synthesized and structurally characterized through the combined Rietveld refinement of synchrotron and time-of-flight neutron diffraction data. Neither MgVBO4 sub> nor MgxFe2-xB2O5 can be chemically oxidized at room temperature, though Mg can be dynamically removed from the latter phase at elevated temperatures (approximately 200 - 500 °C). Findings show that Mg diffusion in the MgxFe2-xB2O5 structure is more facile for the inner two octahedral sites than for the two outer octahedral sites in the ribbons, a result supported by both the refined site occupancies after Mg removal and by bond valence sum difference map calculations of diffusion paths in the pristine material. Mg diffusion in this pyroborate MgxFe2-xB2O5 framework is also found to be tolerant to the presence of Mg/Fe disorder since Mg ions can diffuse through interstitial channels which bypass Fe-containing sites.

  17. Eu3Ir2In15: A mixed-valent and vacancy-filled variant of the Sc5Co4sub>Si10 structure type with anomalous magnetic properties

    SciTech Connect

    Sarkar, Sumanta; Jana, Rajkumar; Siva, Ramesh; Banerjee, Swastika; Pati, Swapan K.; Balasubramanian, Mahalingam; Peter, Sebastian C.


    Here, a new compound, Eu3Ir2In15 has been synthesized using indium as an active metal flux. The compound crystallizes in tetragonal P4/mbm space group with lattice parameters, a = 14.8580(4) Å, b = 14.8580(4) Å, c = 4.3901(2) Å. It was further characterized by SEM-EDX studies. The temperature dependent magnetic susceptibility suggests that Eu in this compound is exclusively in divalent state. The effective magnetic moment (μeff) of this compound is 7.35 μB/Eu ion with paramagnetic Curie temperature (θp) of -28 K suggesting antiferromagnetic interaction. The mixed valent nature of Eu observed in magnetic measurements was confirmed by XANES measurements. The compound undergoes demagnetization at a low magnetic field (10 Oe), which is quite unusual for Eu based intermetallic compounds. Temperature dependent resistivity studies reveal that the compound is metallic in nature. A comparative study was made between Eu3Ir2In15 and hypothetical vacancy variant Eu5Ir4sub>In10 which also crystallizes in the same crystal structure However our computational studies along with control experiments suggest that the latter is thermodynamically less feasible compared to the former and hence we proposed that it is highly unlikely that a RE5T4sub>X10 would exist with X as a group 13 elements.

  18. Chemical bond parameters and photoluminescence of a natural-white-light Ca{sub 9}La(VO{sub 4}){sub 7}:Tm{sup 3+},Eu{sup 3+} with one O{sup 2−}→V{sup 5+} charge transfer and dual f-f transition emission centers

    SciTech Connect

    Li, Ling; Liu, Xiao Guang; Noh, Hyeon Mi; Jeong, Jung Hyun


    The relationship between the photoluminescence properties and the crystal structure of undoped, Eu{sup 3+} or/ and Tm{sup 3+} singly or codoped Ca{sub 9}La(VO{sub 4}){sub 7} (CLaVO) samples was discussed. Under the excitation of UV light, CLaVO:Tm{sup 3+}, CLaVO, and CLaVO:Eu{sup 3+} exhibit the characteristic emissions of Tm{sup 3+} ({sup 1}G{sub 4}→{sup 3}H{sub 6}, blue), O{sup 2−}→V{sup 5+} charge transfer (CT), and Eu{sup 3+} ({sup 5}D{sub 0}→{sup 7}F{sub 2}, red), respectively. By adjusting the doping concentration of Tm{sup 3+} and Eu{sup 3+} ions in CLaVO, a natural white emission in a single composition with the color temperature at 6181 K was obtained. Based on the dielectric theory of complex crystal, the chemical bond parameters of La-O and V-O bonds were quantitatively calculated. The standard deviation of environmental factor of every bond (EFSD), which can be expressed as σ(h{sub e{sub i}})=√((1/N)∑{sub i=1}{sup N}(h{sub e{sub i}}−μ){sup 2}) (h{sub e{sub i}}=(f{sub c{sub i}}α{sub b{sub i}}){sup 1/2}Q{sub B{sub i}} and μ=(1/N)∑{sub i=1}{sup N}h{sub e{sub i}}), was proposed to quantitatively express the distortion degree of VO{sub 4}{sup 3−} from that of an ideal tetrahedron. The maximum change of EFSD comes from the [VO{sub 4}]{sup −} tetrahedra in CLaVO sample by comparison with that of EFSD of isostructural Ca{sub 9}Gd(VO{sub 4}){sub 7}. This is possible the key reason that the undoped CLaVO sample has self-activated emission while the self-activated emission of its isostructural Ca{sub 9}Gd(VO{sub 4}){sub 7} sample cannot be found. The quantitative calculation also demonstrated that the broad excitation bands at 319 nm in CLaVO:Tm and at 335 nm in CLaVO:Eu were due to the O-V2 and O-V3 (overlap with O-V2) CT, not the CT energy of O{sup 2−}-Eu1{sup 3+} (O{sup 2−}-Tm1{sup 3+}), O{sup 2−}-Eu2{sup 3+} (O{sup 2−}-Tm2{sup 3+}), and O{sup 2−}-Eu3{sup 3+} (O{sup 2−}-Tm3{sup 3+}). The environmental factors surrounding the

  19. Sodium doping effect on physicochemical properties of K{sub 1−x}Na{sub x}CaPb{sub 3}(PO{sub 4}){sub 3} (0 ≤ x ≤ 1) for the determination of mercury(II): Application in seawater samples

    SciTech Connect

    Lahrich, Sara; Manoun, Bouchaib; Mhammedi, Moulay Abderrahim El


    Highlights: • The apatite, K{sub 1−x}Na{sub x}CaPb{sub 3}(PO{sub 4}){sub 3} (0 ≤ x ≤ 1), was synthesized using reaction solid. • The obtained apatite was used to determine mercury in seawater samples from Morocco. • The effect of doping sodium into apatite on physic-chemical parameters was studied. • The influence of the electrochemical variables was investigated to determine mercury. - Abstract: A new chemically modified electrode was synthesized for the determination of mercury(II) using differential pulse anodic stripping voltammetry (DPASV). The electrode was modified by lacunar apatite K{sub 1−x}Na{sub x}CaPb{sub 3}(PO{sub 4}){sub 3} (0 ≤ x ≤ 1) synthesized using solid reaction. These powders were crystallized in the hexagonal system, space group P6{sub 3}/m. The effect of sodium content on structural, thermodynamic and electrochemical properties of prepared apatite has been studied. Therefore, the best results was obtained using NaCaPb{sub 3}(PO{sub 4}){sub 3} (x = 1) as modifier of carbon paste electrode for the electrochemical detection of mercury(II). The later ions were preconcentrated on the surface of the modified electrode and oxidized at 0.06 V vs. Ag/AgCl. The electroanalytical procedure comprises of two steps: the chemical accumulation of the analyte under open-circuit conditions followed by the electrochemical detection of the preconcentrated species using differential pulse voltammetry. The different parameters that govern the two steps were optimized. A linear response was obtained in the concentration range from 1.0 mol L{sup −1} × 10{sup −4} mol L{sup −1} to 2.0 mol L{sup −1} × 10{sup −7} mol L{sup −1} Hg(II) after activation of the electrode surface under the optimized conditions. The standard deviation was evaluated in a high and low concentration of mercury(II). The values ​​obtained for seven consecutive measurements were 1.24% and 5.07% of 1.0 mol L{sup −1} × 10{sup −4} mol L{sup −1} and 5.0 mol

  20. Solvothermal syntheses, crystal structures, and properties of lanthanide(III) thioarsenates [Ln(dien){sub 2}(μ-1κ,2κ{sup 2}-AsS{sub 4})]{sub n} (Ln==Sm, Eu, Gd) and [Ln(dien){sub 2}(1κ{sup 2}-AsS{sub 4})] (Ln==Tb, Dy, Ho)

    SciTech Connect

    Wang, Fang; Tang, Chunying; Chen, Ruihong; Zhang, Yong; Jia, Dingxian


    Solvothermal reactions of Ln{sub 2}O{sub 3}, As and S in diethylenetriamine (dien) at 170 °C for 6 days afforded two structural types of lanthanide thioarsenates with the general formulae [Ln(dien){sub 2}(μ-1κ,2κ{sup 2}-AsS{sub 4})]{sub n} [Ln=Sm(1), Eu(2), Gd(3)] and [Ln(dien){sub 2}(1κ{sup 2}-AsS{sub 4})] [Ln=Tb(4), Dy(5), Ho(6)]. The Ln{sub 2}O{sub 3} oxides were converted to [Ln(dien){sub 2}]{sup 3+} complex units in the solvothermal reactions. The As atom binds four S atoms, forming a tetrahedral AsS{sub 4} unit. In 1−3, the AsS{sub 4} units interconnect the [Ln(dien){sub 2}]{sup 3+} cations via Ln−S bonds as tridentate μ-1κ,2κ{sup 2}-AsS{sub 4} bridging ligands, resulting in the neutral coordination polymers [Ln(dien){sub 2}(μ-1κ,2κ{sup 2}-AsS{sub 4})]{sub n} (Ln1). In 4−6, the AsS{sub 4} units coordinate with the Ln{sup 3+} ion of [Ln(dien){sub 2}]{sup 3+} as 1κ{sup 2}-AsS{sub 4} chelating ligands to form neutral coordination compounds [Ln(dien){sub 2}(1κ{sup 2}-AsS{sub 4})] (Ln2). The Ln{sup 3+} ions are in nine- and eight-coordinated environments in Ln1 and Ln2, respectively. The formation of Ln1 and Ln2 is related with ionic size of the Ln{sup 3+} ions. Optical absorption spectra showed that 1−6 have potential use as semiconductors with the band gaps in the range 2.18−3.21 eV. - Graphical abstract: Two types of Ln-thioarsenates [Ln(dien){sub 2}(μ-1κ,2κ{sup 2}-AsS{sub 4})]{sub n} and [Ln(dien){sub 2}(1κ{sup 2}-AsS{sub 4})] were prepared by solvothermal methods and the soft Lewis basic AsS{sub 4}{sup 3–} ligand to Ln(III) centers with polyamine co-ligand was obtained. Display Omitted - Highlights: • Lanthanide thioarsenates were prepared by solvothermal methods. • The soft Lewis basic AsS{sub 4} ligand coordinate Ln{sup 3+} ions with coexistence polyamine ligands. • Two structural types of Ln-thioarsenates with structural turnover at Tb were obtained along Ln series. • The Ln-thioarsenates are potential semiconductors

  1. Antiferromagnetic Spin Correlations Between Corner-Shared [FeO5]7- and [FeO6]9- Units, in the Novel Iron-Based Compound: BaYFeO4sub>

    SciTech Connect

    Wrobel, Friederike; Kemei, Moureen C; Derakhshan, Shahab


    A novel quaternary compound in the Ba–Y–Fe-O phase diagram was synthesized by solid-state reaction and its crystal structure was characterized using powder X-ray diffraction. The crystal structure of BaYFeO4sub> consists of a unique arrangement of Fe3+ magnetic ions, which is based on alternate corner-shared units of [FeO5]7– square pyramids and [FeO6]9– octahedra. This results in the formation of stairwise channels of FeO polyhedra along the b crystallographic axis. The structure is described in an orthorhombic crystal system in the space group Pnma with lattice parameters a = 13.14455(1) Å, b = 5.694960(5) Å, and c = 10.247630(9) Å. The temperature-dependent magnetic susceptibility data reveal two antiferromagnetic (AFM) transitions at 33 and 48 K. An upturn in the magnetic susceptibility data above these transitions is observed, which does not reach its maximum even at 390 K. The field-dependent magnetization data at both 2 and 300 K show a nearly linear dependence and do not exhibit significant hysteresis. Heat capacity measurements between 2 and 200 K reveal only a broad anomaly without any indication of long-range ordering. The latter data set is not in good agreement with the magnetic susceptibility data, which makes it difficult to exactly determine the magnetic ground state of BaYFeO4sub>. Accordingly, a temperature-dependent neutron diffraction study is in order, which will enable resolving this issue. The theoretical study of the relative strengths of magnetic exchange interactions along various possible pathways, using extended Hückel spin dimer analysis, shows that only interactions between square pyramidal and octahedral centers are significant, and among them, the intrachannel correlations are stronger than interchannel interactions. This is the first physical property study in such a magnetic ion substructure.

  2. Boron Substituted Na 3 V 2 (P 1 -x B x O 4sub> ) 3 Cathode Materials with Enhanced Performance for Sodium-Ion Batteries

    SciTech Connect

    Hu, Pu; Wang, Xiaofang; Wang, Tianshi; Chen, Lanli; Ma, Jun; Kong, Qingyu; Shi, Siqi; Cui, Guanglei


    The development of excellent performance of Na-ion batteries remains great challenge owing to the poor stability and sluggish kinetics of cathode materials. Herein, B substituted Na3V2P3–xBxO12 (0 ≤ x ≤ 1) as stable cathode materials for Na-ion battery is presented. A combined experimental and theoretical investigations on Na3V2P3–xBxO12 (0 ≤ x ≤ 1) are undertaken to reveal the evolution of crystal and electronic structures and Na storage properties associated with various concentration of B. X-ray diffraction results indicate that the crystal structure of Na3V2P3–xBxO12 (0 ≤ x ≤ 1/3) consisted of rhombohedral Na3V2(PO4sub>)3 with tiny shrinkage of crystal lattice. X-ray absorption spectra and the calculated crystal structures all suggest that the detailed local structural distortion of substituted materials originates from the slight reduction of V–O distances. Na3V2P3-1/6B1/6O12 significantly enhances the structural stability and electrochemical performance, giving remarkable enhanced capacity of 100 and 70 mAh g-1 when the C-rate increases to 5 C and 10 C. Spin-polarized density functional theory (DFT) calculation reveals that, as compared with the pristine Na3V2(PO4sub>)3, the superior electrochemical performance of the substituted materials can be attributed to the emergence of new boundary states near the band gap, lower Na+ diffusion energy barriers, and higher structure stability.

  3. X-ray powder diffraction, vibration and thermal studies of [A{sub 0.92}(NH{sub 4}){sub 0.08}]{sub 2}TeCl{sub 4}Br{sub 2} with A = Cs, Rb: Influence of mixed cationic and anionic substitutions

    SciTech Connect

    Aribia, W. Ben; Abdelmouleh, M.; Kabadou, A.; Van Der Lee, A.


    Graphical abstract: The structures of [A{sub 0.92}(NH{sub 4}){sub 0.08}]{sub 2}TeCl{sub 4}Br{sub 2} with A = Cs, Rb belong to the tetragonal {beta}-K{sub 2}SnCl{sub 6} structure type. Highlights: Black-Right-Pointing-Pointer The two new compound crystallises in P4/mnc tetragonal space group. Black-Right-Pointing-Pointer The structure is considered as isolated octahedred TeCl{sub 4}Br{sup 2-}. Black-Right-Pointing-Pointer The octahedra connected by ionic and hydrogen bonding through the Cs/Rb or N atoms. Black-Right-Pointing-Pointer A DTA/TGA experiment reveals one endothermic peak at 780 K for these compounds. Black-Right-Pointing-Pointer One endothermic peak is detected at around 213 K by DSC experiment. -- Abstract: The crystal structures of [A{sub 0.92}(NH{sub 4}){sub 0.08}]{sub 2}TeCl{sub 4}Br{sub 2} with A = Cs, Rb have been determined using X-ray powder diffraction techniques. The two compounds crystallize in the tetragonal space group P4/mnc, with the unit cell parameters: a = 7.452(1) Angstrom-Sign , c = 10.544(3) Angstrom-Sign , Z = 2 and a = 7.315(2) Angstrom-Sign , c = 10.354(4) Angstrom-Sign , Z = 2 in the presence of Cs and Rb, respectively. These two compounds have an antifluorite-type arrangement of NH{sub 4}{sup +}/Rb{sup +}/Cs{sup +} and octahedral TeCl{sub 4}Br{sub 2}{sup 2-} anions. The stability of these structure is by ionic and hydrogen bonding contacts: A Midline-Horizontal-Ellipsis Cl, A Midline-Horizontal-Ellipsis Br and N-H Midline-Horizontal-Ellipsis Cl, N-H Midline-Horizontal-Ellipsis Br. The different vibrational modes of these powders were analysed by FTIR and Raman spectroscopic studies. A DTA/TGA experiment reveals one endothermic peak at 780 K implicating the decomposition of the sample. At low temperature, one endothermic peak in thermal behavior is detected at around 213 K by DSC experiment. This transition was confirmed by dielectric measurements.

  4. Orbital symmetry of charge-density-wave order in La1.875Ba0.125CuO4sub> and YBa2Cu3O6.67

    SciTech Connect

    A. J. Achkar; He, F.; Sutarto, R.; McMahon, C.; Zwiebler, M.; Hucker, M.; Liang, R.; Gu, G.; Bonn, D. A.; Hardy, W. N.; Geck, J.; Hawthorn, D. G.


    Recent theories of charge density wave (CDW) order in high temperature superconductors have predicted a primarily d CDW orbital symmetry. Here, we report on the orbital symmetry of CDW order in the canonical cuprate superconductors La1.875Ba0.125CuO4sub> (LBCO) and YBa2Cu3O6.67 (YBCO), using resonant soft x-ray scattering and a model mapped to the CDW orbital symmetry. From measurements sensitive to the O sublattice, we conclude that LBCO has predominantly s0 CDW orbital symmetry, in contrast to the d orbital symmetry recently reported in other cuprates. Additionally, we show for YBCO that the CDW orbital symmetry differs along the a and b crystal axes and that these both differ from LBCO. This work highlights CDW orbital symmetry as an additional key property that distinguishes the di erent cuprate families.

  5. Enhanced magnetic behavior, exchange bias effect, and dielectric property of BiFeO{sub 3} incorporated in (BiFeO{sub 3}){sub 0.50} (Co{sub 0.4}Zn{sub 0.4}Cu{sub 0.2} Fe{sub 2}O{sub 4}){sub 0.5} nanocomposite

    SciTech Connect

    Mukhopadhyay, K.; Mahapatra, A. S.; Sutradhar, S.; Chakrabarti, P. K.


    Nanoparticles of BiFeO{sub 3} (BFO) are incorporated in the nanocomposite of (BiFeO{sub 3}){sub 0.50} (Co{sub 0.4}Zn{sub 0.4}Cu{sub 0.2} Fe{sub 2}O{sub 4}){sub 0.5}, (BFO-CZCF) and these are prepared by chemical route. The formation of pure crystallographic phase of each component (BFO and CZCF) in the nanocomposite of BFO-CZCF has been confirmed by Rietveld analysis of the X-ray diffractograms using FULLPROF program. Morphology, average particle size and its distribution, crystallographic phase etc. are obtained from the high-resolution transmission electron microscopy of BFO-CZCF. Magnetic measurements of BFO-CZCF have been carried out to explore the modulation of magnetic behavior of BFO in BFO-CZCF. Interestingly, magnetization of BFO-CZCF has been drastically enhanced compared to that of the pristine BFO. An exchange bias effect is also observed in the M vs. H loops of BFO-CZCF recorded in field cooled and zero field cooled conditions, which suggest that nanoparticles of BFO (AFM) are encapsulated by nanoparticles of CZCF (FM) in BFO-CZCF. Thermal variation of dielectric constant of BFO-CZCF is recorded in the range of 300 to 1073 K and a ferroelectric to paraelectric transition is observed at ∼728 K. Enhanced magnetic property of BFO would quite interesting for this important multiferroic.

  6. Itinerant ferromagnetism in the As 4p conduction band of Ba0.6K0.4sub>Mn2As2 identified by x-ray magnetic circular dichroism

    SciTech Connect

    Ueland, B. G.; Pandey, Abhishek; Lee, Y.; Sapkota, A.; Choi, Y.; Haskel, D.; Rosenberg, R. A.; Lang, J. C.; Harmon, B. N.; Johnston, D. C.; Kreyssig, A.; Goldman, A. I.


    In this study, x-ray magnetic circular dichroism (XMCD) measurements on single-crystal and powder samples of Ba0.6K0.4sub>Mn2As2 show that the ferromagnetism below TC ≈ 100 K arises in the As 4p conduction band. No XMCD signal is observed at the Mn x-ray absorption edges. Below TC, however, a clear XMCD signal is found at the As K edge which increases with decreasing temperature. The XMCD signal is absent in data taken with the beam directed parallel to the crystallographic c axis indicating that the orbital magnetic moment lies in the basal plane of the tetragonal lattice. These results show that the previously reported itinerant ferromagnetism is associated with the As 4p conduction band and that distinct local-moment antiferromagnetism and itinerant ferromagnetism with perpendicular easy axes coexist in this compound at low temperature.

  7. Interfacial charge-mediated non-volatile magnetoelectric coupling in Co0.3Fe0.7/Ba0.6Sr0.4sub>TiO3/Nb:SrTiO3 multiferroic heterostructures

    SciTech Connect

    Zhou, Ziyao; Howe, Brandon M.; Liu, Ming; Nan, Tianxiang; Chen, Xing; Mahalingam, Krishnamurthy; Sun, Nian X.; Brown, Gail J.


    The central challenge in realizing non-volatile, E-field manipulation of magnetism lies in finding an energy efficient means to switch between the distinct magnetic states in a stable and reversible manner. In this work, we demonstrate using electrical polarization-induced charge screening to change the ground state of magnetic ordering in order to non-volatilely tune magnetic properties in ultra-thin Co0.3Fe0.7/Ba0.6Sr0.4sub>TiO3/Nb:SrTiO3 (001) multiferroic heterostructures. A robust, voltage-induced, non-volatile manipulation of out-of-plane magnetic anisotropy up to 40 Oe is demonstrated and confirmed by ferromagnetic resonance measurements. This discovery provides a framework for realizing charge-sensitive order parameter tuning in ultra-thin multiferroic heterostructures, demonstrating great potential for delivering compact, lightweight, reconfigurable, and energy-efficient electronic devices.

  8. Low-Temperature Synthesis, Structural Characterization, and Electrochemistry of Ni-Rich Spinel-like LiNi 2–y Mn y O 4sub> (0.4 ≤ y ≤ 1)

    SciTech Connect

    Kan, Wang Hay; Huq, Ashfia; Manthiram, Arumugam


    The thermal conversion of chemically delithiated layered Li0.5Ni1-yMnyO2 (0.2 ≤ y ≤ 0.5) into spinel-like LiNi2-yMnyO4sub> (0.4 ≤ y ≤ 1) has been systematically investigated. The formed spinel-like phases are metastable and cannot be accessed by a conventional high-temperature solid-state method. The layered-to-spinel transformation mechanism has been studied by the Rietveld refinement of in situ neutron diffraction as a function of temperature (25–300 °C). In particular, the ionic diffusion of Li and M ions is quantified at different temperatures. Electrochemistry of the metastable spinel-like phases obtained has been studied in lithium-ion cells. A bond valence sum map has been performed to understand the ionic diffusion of lithium ions in the Ni-rich layered, spinel, and rock-salt structures. The study can aid the understanding of the possible phases that could be formed during the cycling of Ni-rich layered oxide cathodes.

  9. Energetics of phosphate frameworks containing zinc and cobalt: NaZnPO{sub 4}, NaH(ZnPO{sub 4}){sub 2}, NaZnPO{sub 4}.H{sub 2}O, NaZnPO{sub 4}.4/3 H{sub 2}O, and NaCo{sub x}Zn{sub 1-x}PO{sub 4}.4/3 H{sub 2}O

    SciTech Connect

    Le, So-Nhu; Navrotsky, Alexandra


    Differential scanning calorimetry and high temperature oxide melt solution calorimetry were used to study the enthalpy of the {alpha}-{beta} phase transformation of NaZnPO{sub 4} and enthalpies of formation of {alpha}-NaZnPO{sub 4}, NaH(ZnPO{sub 4}){sub 2}, NaZnPO{sub 4}.H{sub 2}O, and NaCo{sub x}Zn{sub 1-x}PO{sub 4}.4/3 H{sub 2}O (x=0, 0.1, 0.2, 0.3). The enthalpies of formation from the oxides of cobalt substituted in NaZnPO{sub 4}.4/3 H{sub 2}O do not depend on cobalt content, confirming similar acid-base interactions for Zn-PO{sub 4} and Co-PO{sub 4}. While water molecules stabilize zinc phosphate frameworks through solvating a cation or forming extra hydrogen bonds, the partial substitution of water for sodium oxide to form NaH(ZnPO{sub 4}){sub 2} represents the formation of an acidic compound with weaker acid-base interactions and less exothermic enthalpy of formation from oxides than Na{sub 2}(ZnPO{sub 4}){sub 2}. - Graphical abstract: Relative stability of NaZnPO{sub 4} dense phases, open frameworks, and hydrated frameworks. Enthalpy of interaction between water and NaZnPO{sub 4} frameworks is presented by reaction: NaZnPO{sub 4} (cr, open framework) + nH{sub 2}O (l) {yields} NaZnPO{sub 4}.nH{sub 2}O (cr, hydrated framework)

  10. Topological analysis of void spaces in tungstate frameworks: Assessing storage properties for the environmentally important guest molecules and ions: CO2, UO2, PuO2, U, Pu, Sr2+, Cs+, CH4sub>, and H2

    SciTech Connect

    Cole, Jacqueline M.; Cramer, Alisha J.; Zeidler, Anita


    The identification of inorganic materials, which are able to encapsulate environmentally important small molecules or ions via host-guest interactions, is crucial for the design and development of next-generation energy sources and for storing environmental waste. Especially sought after are molecular sponges with the ability to incorporate CO2, gas pollutants, or nuclear waste materials such as UO2 and PuO2 oxides or U, Pu, Sr2+ or Cs+ ions. Porous framework structures promise very attractive prospects for applications in environmental technologies, if they are able to incorporate CH4sub> for biogas energy applications, or to store H2, which is important for fuel cells e.g. in the automotive industry. All of these applications should benefit from the host being resistant to extreme conditions such as heat, nuclear radiation, rapid gas expansion, or wear and tear from heavy gas cycling. As inorganic tungstates are well known for their thermal stability, and their rigid open-framework networks, the potential of Na2O-Al2O3-WO3 and Na2O-WO3 phases for such applications was evaluated. To this end, all known experimentally-determined crystal structures with the stoichiometric formula MaM’bWcOd (M = any element) are surveyed together with all corresponding theoretically calculated NaaAlbWcOd and NaxWyOz structures that are statistically likely to form. Network descriptors that categorize these host structures are used to reveal topological patterns in the hosts, including the nature of porous cages which are able to accommodate a certain type of guest; this leads to the classification of preferential structure types for a given environmental storage application. Crystal structures of two new tungstates NaAlW2

  11. Synthesis and characteristics of a novel 3-D organic amine oxalate: (enH{sub 2}){sub 1.5}[Bi{sub 3}(C{sub 2}O{sub 4}){sub 6}(CO{sub 2}CONHCH{sub 2}CH{sub 2}NH{sub 3})].6.5H{sub 2}O

    SciTech Connect

    Yu Xiaohong; Zhang Hanhui . E-mail:; Cao Yanning; Chen Yiping; Wang Zhen


    A novel 3-D compound of (enH{sub 2}){sub 1.5}[Bi{sub 3}(C{sub 2}O{sub 4}){sub 6}(CO{sub 2}CONHCH{sub 2}CH{sub 2}NH{sub 3})].6.5H{sub 2}O has been hydrothermally synthesized and characterized by IR, ultraviolet-visible diffuse reflection integral spectrum (UV-Vis DRIS), fluorescence spectra, TGA and single crystal X-ray diffraction. It crystallizes in the monoclinic system, space group C2/c with a=31.110(8)A, b=11.544(3)A, c=22.583(6)A, {beta}=112.419(3){sup o}, V=7497(3)A{sup 3}, Z=8, R{sub 1}=0.0463 and wR{sub 2}=0.1393 for unique 7686 reflections I>2{sigma}(I). In the title compound, the Bi atoms have eight-fold and nine-fold coordination with respect to the oxygen atoms, with the Bi atoms in distorted dodecahedron and monocapped square antiprism, respectively. The 3-D framework of the title compound contains channels and is composed of linkages between Bi atoms and oxalate units, forming honeycomb-like layers with two kinds of 6+6 membered aperture, and pillared by oxalate ligands and monamide groups. The channels have N-ethylamine oxalate monamide group {sup -}CO{sub 2}CONHCH{sub 2}CH{sub 2}NH{sub 3}{sup +}, which is formed by the in situ reaction of en and oxalate acid. At room temperature, the complex exhibits intense blue luminescence with an emission peak at 445nm.

  12. Influence of Microstructure and Surface Activation of Dual-Phase Membrane Ce 0.8 Gd 0.2 O 2-δ -FeCo 2 O 4sub> on Oxygen Permeation

    SciTech Connect

    Ramasamy, Madhumidha; Baumann, Stefan; Palisaitis, Justinas; Schulze-Küppers, Falk; Balaguer, Maria; Kim, Daejin; Meulenberg, Wilhelm A.; Mayer, Jochim; Bhave, Ramesh; Guillon, Olivier; Bram, Martin; Stevenson, J.


    In dual-phase oxygen transport membranes we noticed that there is fast-growing interest in research for oxyfuel combustion process application. One such potential candidate is CGO-FCO (60wt% Ce0.8Gd0.2O2-δ-40wt% FeCo2O4) identified to provide good oxygen permeation flux with substantial stability in harsh atmosphere. Dense CGO-FCO membranes of 1mm thickness were fabricated by sintering dry pellets pressed from powders synthesized by one-pot method (modified Pechini process) at 1200 degrees C for 10h. Microstructure analysis indicates presence of a third orthorhombic perovskite phase in the sintered composite. We also identified that the spinel phase tends to form an oxygen deficient phase at the grain boundary of spinel and CGO phases. Surface exchange limitation of the membranes was overcome by La0.6Sr0.4sub>Co0.2Fe0.8O3-δ (LSCF) porous layer coating over the composite. Moreover, the oxygen permeation flux of the CGO-FCO screen printed with a porous layer of 10mthick LSCF is 0.11mL/cm2 per minute at 850 degrees C with argon as sweep and air as feed gas at the rates of 50 and 250mL/min.

  13. Performances of YBaCo1.4sub>Cu0.6O5+δ–Ce0.8Sm0.2O1.9 composite cathodes for intermediate-temperature solid oxide fuel cells

    SciTech Connect

    Wang, Lizhong; Peng, Lu; Hu, Michael Z.; Lü, Shiquan; Meng, Xiangwei; Yu, Bo; Wei, Maobin; Fan, Hougang; Yang, Lili


    In this paper, the electrochemical properties of YBaCo1.4sub>Cu0.6O5+δ–xCe0.8Sm0.2O1.9 (YBCC–xSDC, x=20, 30, 40, 50 wt%) have been investigated for the potential application in intermediate-temperature solid oxide fuel cells (IT-SOFCs). No chemical reactions between YBCC cathode and SDC electrolyte, and YBCC and La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) occur. The thermal expansion coefficient (TEC) of YBCC cathode decreases with SDC addition. The TEC of YBCC–30SDC cathode is 13.60×10–6 K-1 from 30 to 850 °C in air and it exhibits the best electrochemical performance among the YBCC–xSDC cathodes. The polarization resistance (Rp) of YBCC–30SDC is 0.027 Ω cm2 at 850 °C, 0.044 Ω cm2 at 800 °C and 0.075 Ω cm2 at 750 °C. The maximum power density value of electrolyte-based cell with YBCC–30SDC cathode is 662, 483 and 319 mW cm-2 at 850, 800 and 750 °C, respectively. Finally, preliminary results indicate that YBCC–30SDC is especially promising as a cathode for IT-SOFCs.

  14. The effect of interstitial carbon on the mechanical properties and dislocation substructure evolution in Fe40.4sub>Ni11.3Mn34.8Al7.5Cr6 high entropy alloys

    SciTech Connect

    Wang, Zhangwei; Baker, Ian; Cai, Zhonghou; Chen, Si; Poplawsky, Jonathan D.; Guo, Wei


    A systematic study of the effects of up to 1.1 at. % carbon on the mechanical properties and evolution of the dislocation substructure in a series of a high entropy alloys (HEA) based on Fe40.4sub>Ni11.3Mn34.8Al7.5Cr6 is presented. Transmission electron microscopy (TEM), synchrotron X-ray diffraction (XRD) and atom probe tomography (APT) were used to show that all the alloys are single-phase f.c.c. random solid solutions. The lattice constant, determined from synchrotron XRD measurements, increases linearly with increasing carbon concentration, which leads to a linear relationship between the yield strength and the carbon concentration. The dislocation substructures, as determined by a TEM, show a transition from wavy slip to planar slip and, at higher strains, and from cell-forming structure (dislocations cells, cell blocks and dense dislocation walls) to non-cell forming structure (Taylor lattice, microbands and domain boundaries) with the addition of carbon, features related to the increase in lattice friction stress. The stacking fault energy (measured via weak-beam imaging of the separation of dislocation partials) decreases with increasing carbon content, which also contributes to the transition from wavy slip to planar slip. The formation of non-cell forming structure induced by carbon leads to a high degree of strain hardening and a substantial increase in the ultimate tensile strength. In conclusion, the consequent postponement of necking due to the high strain hardening, along with the plasticity accommodation arising from the formation of microbands and domain boundaries, result in an increase of ductility due to the carbon addition.

  15. Synthesis, characterization, phase diagrams and superconducting and normal state magnetic properties of La2-xSrxCuO4sub> (0 ≤ x ≤ 0.08) and electrochemically oxidized La2-xSrxCuO4+δ (0 ≤ x ≤ 0.33, 0 ≤ δ ≤ 0.12)

    SciTech Connect

    Chou, Fangcheng


    La2-xSrxCuO4sub> (0 ≤ x ≤ 0.15) can all be intercalated with oxygen by a novel electrochemical oxidation method. Bulk superconductivity is found with an onset Tc~ 40 K for the whole range 0.01 ≤ x ≤ 0.15; for x = 0.25 and 0.33, the electrochemical oxidation did not improve the superconducting properties. The magnetic susceptibility χ(T = 50--320 K) data for La2CuO4.11 and La1.92Sr0.08CuO4.07 are nearly identical with those of conventionally prepared La1.85Sr0.15CuO4sub>, indicating that the hole doping level (p) in the CuO2 planes of the three compounds is nearly the same. Combined thermogravimetric analysis and iodometric titration experiments indicate that part of the intercalated oxygen has a formal valence close to -1. The maximum doped-hole concentration in the CuO2 planes that can be achieved from combined Sr-doping and electrochemical oxygen doping for 0 ≤ x ≤ 0.15 is p ~ 0.16 holes/formula unit. Oxygen can also intercalate into single crystal La2CuO4sub> through a slow electrochemical oxidation process. The required low current and long time for the charging process reflects that the oxygen intercalation for a single crystal is limited by its small specific surface area and long diffusion distance. The anisotropic superconducting, magnetic and transport properties are summarized and compared with those of polycrystalline La2CuO4+δ as well as of YBa2Cu3O7-δ and La2-xSrxCuO4sub> single crystals. The single crystal La2CuO4+δ has a maximum Tc ~ 40 K, which is lower than that (Tc ~ 42--45) of the corresponding polycrystalline samples. The magnetic phase diagram of La2-xSrxCuO4sub> in the antiferromagnetic (AF) regime (0 ≤ x ≤ 0

  16. Local structure of Rb{sub 2}Li{sub 4}(SeO{sub 4}){sub 3}{center_dot}2H{sub 2}O by the modeling of X-ray diffuse scattering - from average-structure to microdomain model

    SciTech Connect

    Komornicka, Dorota; Wolcyrz, Marek; Pietraszko, Adam


    Local structure of dirubidium tetralithium tris(selenate(VI)) dihydrate - Rb{sub 2}Li{sub 4}(SeO{sub 4}){sub 3}{center_dot} 2H{sub 2}O has been determined basing on the modeling of X-ray diffuse scattering. The origin of observed structured diffuse streaks is SeO{sub 4} tetrahedra switching between two alternative positions in two quasi-planar layers existing in each unit cell and formation of domains with specific SeO{sub 4} tetrahedra configuration locally fulfilling condition for C-centering in the 2a Multiplication-Sign 2b Multiplication-Sign c superstructure cell. The local structure solution is characterized by a uniform distribution of rather large domains (ca. thousand of unit cells) in two layers, but also monodomains can be taken into account. Inside a single domain SeO{sub 4} tetrahedra are ordered along ab-diagonal forming two-string ribbons. Inside the ribbons SeO{sub 4} and LiO{sub 4} tetrahedra share the oxygen corners, whereas ribbons are bound to each other by a net of hydrogen bonds and fastened by corner sharing SeO{sub 4} tetrahedra of the neighboring layers. - Graphical abstract: Experimental sections of the reciprocal space showing diffraction effects observed for RLSO. Bragg spots are visible on sections with integer indices (1 kl section - on the left), streaks - on sections with fractional ones (1.5 kl section - on the right). At the center: resulting local structure of the A package modeled as a microdomain: two-string ribbons of ordered oxygen-corners-sharing SeO{sub 4} and LiO{sub 4} terahedra extended along ab-diagonal are seen; ribbons are bound by hydrogen bonds (shown in pink); the multiplied 2a Multiplication-Sign 2b unit cell is shown. Highlights: Black-Right-Pointing-Pointer X-ray diffuse scattering in RLSO was registered and modeled. Black-Right-Pointing-Pointer The origin of diffuse streaks is SeO{sub 4} tetrahedra switching in two structure layers. Black-Right-Pointing-Pointer The local structure is characterized by a uniform

  17. Topological analysis of void space in phosphate frameworks: Assessing storage properties for the environmentally important guest molecules and ions: CO2, H2O, UO2, PuO2, U, Pu, Sr2+, Cs+, CH4sub>, and H2