Sample records for 3sosub 3sub 2peosub

  1. Optical constants of CH3sub>NH3sub>PbBr3sub> perovskite thin films measured by spectroscopic ellipsometry.


    Alias, Mohd Sharizal; Dursun, Ibrahim; Saidaminov, Makhsud I; Diallo, Elhadj Marwane; Mishra, Pawan; Ng, Tien Khee; Bakr, Osman M; Ooi, Boon S


    The lack of optical constants information for hybrid perovskite of CH3sub>NH3sub>PbBr3sub> in thin films form can delay the progress of efficient LED or laser demonstration. Here, we report on the optical constants (complex refractive index and dielectric function) of CH3sub>NH3sub>PbBr3sub> perovskite thin films using spectroscopic ellipsometry. Due to the existence of voids, the refractive index of the thin films is around 8% less than the single crystals counterpart. The energy bandgap is around 2.309 eV as obtained from photoluminescence and spectrophotometry spectra, and calculated from the SE analysis. The precise measurement of optical constants will be useful in designing optical devices using CH3sub>NH3sub>PbBr3sub> thin films. PMID:27464113

  2. Visible blind ultraviolet photodetector based on CH3sub>NH3sub>PbCl3sub> thin film.


    Wang, Wenzhen; Xu, Haitao; Cai, Jiang; Zhu, Jiabin; Ni, Chaowei; Hong, Feng; Fang, Zebo; Xu, Fuzong; Cui, Siwei; Xu, Run; Wang, Linjun; Xu, Fei; Huang, Jian


    We report a prototypical device of CH3sub>NH3sub>PbCl3sub> film ultraviolet photodetectors that were fabricated with a coplanar metal-semiconductor-metal Au interdigital electrode configuration. Pure phase CH3sub>NH3sub>PbCl3sub> films with a good crystallinity were formed by a hybrid sequential deposition process featured with inter-diffusion of PbCl2 and CH3sub>NH3sub>Cl upon annealing. The CH3sub>NH3sub>PbCl3sub> film photodetector exhibits a high responsivity of 7.56 A /W at 360 nm, a ultraviolet/visible rejection ratio (R360 nm/R500 nm) was about two orders of magnitude and fast response speed with a rising time of 170 μs and a decay time of 220 μs. All the above results demonstrate CH3sub>NH3sub>PbCl3sub> film photodetector as a competitive candidate in the application of visible blind UV detectors. PMID:27137279

  3. Thermochemistry of Lewis Adducts of BH3sub> and Nucleophilic Substitution of Triethylamine on NH3sub>BH3sub> in Tetrahydrofuran

    SciTech Connect

    Potter, Robert G.; Camaioni, Donald M.; Vasiliu, Monica; Dixon, David A.


    The thermochemistry of the formation of Lewis base adducts of BH3sub> in tetrahydrofuran (THF) solution and the gas phase and the kinetics of substitution on ammonia borane by triethylamine are reported. The dative bond energy of Lewis adducts were predicted using density functional theory at the B3LYP/DZVP2 and B3LYP/6-311+G** levels and correlated ab initio molecular orbital theories, including MP2, G3(MP2), and G3(MP2)B3LYP, and compared with available experimental data and accurate CCSD(T)/CBS theory results. The analysis showed that the G3 methods using either the MP2 or the B3LYP geometries reproduce the benchmark results usually to within ~1 kcal/mol. Energies calculated at the MP2/aug-cc-pVTZ level for geometries optimized at the B3LYP/DZVP2 or B3LYP/6-311+G** levels give dative bond energies 2-4 kcal/mol larger than benchmark values. The enthalpies for forming adducts in THF were determined by calorimetry and compared with the calculated energies for the gas phase reaction: THFBH3sub> + L → LBH3sub> + THF. The formation of NH3sub>BH3sub> in THF was observed to yield significantly more heat than gas phase dative bond energies predict, consistent with strong solvation of NH3sub>BH3sub>. Substitution of NEt3sub> on NH3sub>BH3sub> is an equilibrium process in THF solution (K ≈ 0.2 at 25 °C). The reaction obeys a reversible bimolecular kinetic rate law with the Arrhenius parameters: log A = 14.7 ± 1.1 and Ea = 28.1 ± 1.5 kcal/mol. Finally, simulation of the mechanism using the SM8 continuum solvation model shows the reaction most likely proceeds primarily by a classical SN2 mechanism.

  4. Upper limit to magnetism in LaAIO3sub>/SrTiO3sub> heterostructures

    SciTech Connect

    Fitzsimmons, Michael R.; Hengartner, N. W.; Singh, S.; Zhernenkov, M.; Bruno, F. Y.; Santamaria, J.; Brinkman, A.; Huijben, M.; Molegraaf, H.; de la Venta, J.; Schuller, Ivan K.


    In 2004 Ohtomo and Hwang reported unusually high conductivity in LaAl03sub> and SrTi03sub> bilayer samples. Since then, metallic conduction, superconductivity, magnetism, and coexistence of superconductivity and ferromagnetism have been attributed to LaAl03sub>/SrTi03sub> interfaces. Very recently, two studies have reported large magnetic moments attributed to interfaces from measurement techniques that are unable to distinguish between interfacial and bulk magnetism. Consequently, it is imperative to perform magnetic measurements that by being intrinsically sensitive to interface magnetism are impervious to experimental artifacts suffered by bulk measurements. Using polarized neutron reflectometry we measured the neutron spin dependent reflectivity from four LaAl03sub>/SrTi03sub> superlattices. Our results indicate the upper limit for the magnetization averaged over the lateral dimensions of the sample induced by an 11 T magnetic field at 1.7 K is less than 2 G. SQUID magnetometry of the neutron superlattice samples sporadically finds an enhanced moment (consistent with past reports), possibly due to experimental artifacts. These observations set important restrictions on theories which imply a strongly enhanced magnetism at the interface between LaAI03sub> and SrTi03sub>.

  5. Magnetic ordering-induced multiferroic behavior in [CH3sub>NH3sub>][Co(HCOO)3sub>] metal-organic framework.

    SciTech Connect

    Gomez-Aguirre, Lilian Claudia; Zapf, Vivien S.; Pato-Doldan, Breogan; Mira, Jorge; Castro-Garcia, Socorro; Senaris-Rodriguez, Maria Antonia; Sanchez-Andujara, Manuel; Singleton, John


    Here, we present the first example of magnetic ordering-induced multiferroic behavior in a metal–organic framework magnet. This compound is [CH3sub>NH3sub>][Co(HCOO)3sub>] with a perovskite-like structure. The A-site [CH3sub>NH3sub>]+ cation strongly distorts the framework, allowing anisotropic magnetic and electric behavior and coupling between them to occur. This material is a spin canted antiferromagnet below 15.9 K with a weak ferromagnetic component attributable to Dzyaloshinskii–Moriya (DM) interactions and experiences a discontinuous hysteretic magnetic-field-induced switching along [010] and a more continuous hysteresis along [101]. Coupling between the magnetic and electric order is resolved when the field is applied along this [101]: a spin rearrangement occurs at a critical magnetic field in the ac plane that induces a change in the electric polarization along [101] and [10-1]. The electric polarization exhibits an unusual memory effect, as it remembers the direction of the previous two magnetic-field pulses applied. The data are consistent with an inverse-DM mechanism for multiferroic behavior.

  6. Low Surface Recombination Velocity in Solution-Grown CH3sub>NH3sub>PbBr3sub> Perovskite Single Crystal

    SciTech Connect

    Yang, Ye; Yan, Yong; Yang, Mengjin; Choi, Sukgeun; Zhu, Kai; Luter, Joseph M.; Beard, Matthew C.


    Organic-inorganic hybrid perovskites are attracting intense research effort due to their impressive performance in solar cells. While the carrier transport parameters such as mobility and bulk carrier lifetime shows sufficient characteristics, the surface recombination, which can have major impact on the solar cell performance, has not been studied. Here we measure surface recombination dynamics in CH3sub>NH3sub>PbBr3sub> perovskite single crystals using broadband transient reflectance spectroscopy. The surface recombination velocity is found to be 3.4±0.1 103 cm s-1, B2–3 orders of magnitude lower than that in many important unpassivated semiconductors employed in solar cells. Our result suggests that the planar grain size for the perovskite thin films should be larger thanB30 mm to avoid the influence of surface recombination on the effective carrier lifetime.

  7. Electronic structure evolution of fullerene on CH3sub>NH3sub>PbI3sub>

    SciTech Connect

    Wang, Chenggong; Wang, Congcong; Liu, Xiaoliang; Kauppi, John; Shao, Yuchuan; Xiao, Zhengguo; Bi, Cheng; Huang, Jinsong; Gao, Yongli


    The thickness dependence of fullerene on CH3sub>NH3sub>PbI3sub> perovskitefilm surface has been investigated by using ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy(XPS), and inverse photoemission spectroscopy (IPES). The lowest unoccupied molecular orbital and highest occupied molecular orbital (HOMO) can be observed directly with IPES and UPS. It is observed that the HOMO level in fullerene shifts to lower binding energy. The XPS results show a strong initial shift of core levels to lower binding energy in the perovskite, which indicates that electrons transfer from the perovskitefilm to fullerene molecules. Further deposition of fullerene forms C60 solid, accompanied by the reduction of the electron transfer. As a result, the strongest electron transfer happened at 1/4 monolayer of fullerene.

  8. Optical characterization of voltage-accelerated degradation in CH3sub>NH3sub>PbI3sub> perovskite solar cells.


    Handa, Taketo; Tex, David M; Shimazaki, Ai; Aharen, Tomoko; Wakamiya, Atsushi; Kanemitsu, Yoshihiko


    We investigate the performance degradation mechanism of CH3sub>NH3sub>PbI3sub> perovskite solar cells under bias voltage in air and nitrogen atmospheres using photoluminescence and electroluminescence techniques. When applying forward bias, the power conversion efficiency of the solar cells decreased significantly in air, but showed no degradation in nitrogen atmosphere. Time-resolved photoluminescence measurements on these devices revealed that the application of forward bias in air accelerates the generation of non-radiative recombination centers in the perovskite layer buried in the device. We found a negative correlation between the electroluminescence intensity and the injected current intensity in air. The irreversible change of the perovskite grain surface in air initiates the degradation of the perovskite solar cells. PMID:27409964

  9. Synthesis, Crystal and Electronic Structures of the Pnictides AE3sub>TrPn3sub> (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

    SciTech Connect

    Stoyko, Stanislav; Voss, Leonard; He, Hua; Bobev, Svilen


    New ternary arsenides AE3sub>TrAs3sub> (AE = Sr, Ba; Tr = Al, Ga) and their phosphide analogs Sr3sub>GaP3sub> and Ba3sub>AlP3sub> have been prepared by reactions of the respective elements at high temperatures. Single-crystal X-ray diffraction studies reveal that Sr3sub>AlAs3sub> and Ba3sub>AlAs3sub> adopt the Ba3sub>AlSb3sub>-type structure (Pearson symbol oC56, space group Cmce, Z = 8). This structure is also realized for Sr3sub>GaP3sub> and Ba3sub>AlP3sub>. Likewise, the compounds Sr3sub>GaAs3sub> and Ba3sub>GaAs3sub> crystallize with the Ba3sub>GaSb3sub>-type structure (Pearson symbol oP56, space group Pnma, Z = 8). Both structures are made up of isolated pairs of edge-shared AlPn4 and GaPn4 tetrahedra (Pn = pnictogen, i.e., P or As), separated by the alkaline-earth Sr2+ and Ba2+ cations. In both cases, there are no homoatomic bonds, hence, regardless of the slightly different atomic arrangements, both structures can be rationalized as valence-precise [AE2+]3sub>[Tr3+][Pn3-]3sub>, or rather [AE2+]6[Tr2Pn6]12-, i.e., as Zintl phases.

  10. Transparent Conducting Properties of SrSnO3sub> and ZnSnO3sub>

    SciTech Connect

    Ong, Khuong P.; Fan, Xiaofeng; Subedi, Alaska; Sullivan, Michael B.; Singh, David J.


    We report optical properties of doped n-type SrSnO3sub> and ZnSnO3sub> in relation to potential application as transparent conductors. We find that the orthorhombic distortion of the perovskite structure in SrSnO3sub> leads to absorption in the visible as the doping level is increased. This arises from interband transitions. We find that strain tuning could modify this absorption, but does not eliminate it. On the other hand, we find that ZnSnO3sub> although also having a non-cubic structure, can retain excellent transparency when doped, making it a good candidate transparent conductor.

  11. Electron attachment to Ni(PF{sub 3}){sub 4} and Pt(PF{sub 3}){sub 4}

    SciTech Connect

    Friedman, Jeffrey F.; Miller, Thomas M.; Friedman-Schaffer, Jessica K.; Rekha, G. K.; Stevens, Amy E.; Viggiano, A. A


    An experimental study has been made of thermal electron attachment to the transition-metal trifluorophosphine complexes Ni(PF{sub 3}){sub 4} and Pt(PF{sub 3}){sub 4} using a flowing-afterglow Langmuir-probe apparatus. Both complexes are efficient at electron attachment, although the rate constants are somewhat less than collisional. The rate constant for electron attachment to Ni(PF{sub 3}){sub 4} is 1.9x10{sup -7} cm{sup 3} s{sup -1} at room temperature, about a factor of 2 less than collisional. The activation energy is 39{+-}5 meV for the attachment reaction. The rate constant for electron attachment to Pt(PF{sub 3}){sub 4} is 5.4x10{sup -8} cm{sup 3} s{sup -1} at room temperature, and the activation energy is 84{+-}8 meV. For both complexes, a PF{sub 3} ligand is lost on electron attachment, and only the M(PF{sub 3}){sub 3}{sup -} ion is observed in the negative-ion mass spectrum. Density functional calculations were carried out on Ni(PF{sub 3}){sub 4} and various fragments in order to describe the thermochemistry of the attachment reaction.

  12. Mechanism of the H+O3sub> reaction

    SciTech Connect

    Chen, Maynard M. L.; Wetmore, Ross W.; Schaefer, III, Henry F.


    The H+O3sub> reaction has played an important role in the evolution of modern chemical kinetics. We investigate certain aspects of the HO3sub> potential energy hypersurface using nonempirical molecular electronic structure theory. For the qualitative purposes of the present study, most wave functions were of the self-consistent-field (SCF) variety, constructed from a double zeta basis set of contracted Gaussian functions. Two low energy pathways were established for the reaction. The first involves a coplanar transition state with a nearly linear H–O–O arrangement. The second possible mechanism allows the hydrogen atom to descend perpendicularly upon the ozone molecule. Finally, the two mechanisms are evaluated in light of the current experimental understanding of the H+O3sub>reaction.

  13. Oxygen octahedral distortions in LaMO3sub>/SrTiO3sub> superlattices

    SciTech Connect

    Sanchez-Santolino, Gabriel; Cabero, Mariona; Varela, Maria; Garcia-Barriocanal, Javier; Leon, Carlos; Pennycook, Stephen J.; Santamaria, Jacobo


    Here we study the interfaces between the Mott insulator LaMnO3sub> (LMO) and the band insulator SrTiO3sub> (STO) in epitaxially grown superlattices with different thickness ratios and different transport and magnetic behaviors. Using atomic resolution electron energy-loss spectrum imaging, we analyze simultaneously the structural and chemical properties of these interfaces. We find changes in the oxygen octahedral tilts within the LaMnO3sub> layers when the thickness ratio between the manganite and the titanate layers is varied. Superlattices with thick LMO and ultrathin STO layers present unexpected octahedral tilts in the STO, along with a small amount of oxygen vacancies. On the other hand, thick STO layers exhibit undistorted octahedra while the LMO layers present reduced O octahedral distortions near the interfaces. In conclusion, these findings will be discussed in view of the transport and magnetic differences found in previous studies.

  14. SU(3){sub c} x SU(3){sub L} x U(1){sub X} models with four families

    SciTech Connect

    Benavides, Richard H.; Ponce, William A.; Giraldo, Yithsbey


    In the context of the local gauge group SU(3){sub c} x SU(3){sub L} x U(1){sub X}, we look for possible four family models, where all the particles carry ordinary electric charges. Thirteen different anomaly-free fermion structures emerge, out of which only two are realistic. For the simplest physical structure, we calculate the charged and neutral weak currents and the tree-level Fermion masses. We also look for new sources of flavor changing neutral currents in the quark sector in connection with the upcoming experimental results at the Large Hadron Collider.

  15. Neutrino masses in supersymmetric SU(3){sub c} x SU(3){sub L} x U(1){sub X} models

    SciTech Connect

    Rodriguez, J-Alexis; Duarte, J.


    The mass spectra and the superpotential of two different supersymetric models based on the gauge symmetry SU(3){sub C} x SU(3){sub L} x U(1){sub X}(331) without any exotic charges assigned to the fermionic spectra are studied. These two models have three families in different representations of the gauge group. In these kind of models, the diagonalization of the neutralino mass matrix allows that three light neutrinos get different mass values. Possible values for the neutrino masses are calculated covering the parameter space of the models. These values have to agree with the available data coming from the neutrino oscillations experiments. Therefore, a reduced space of parameters for the superpotential and the vacuum expectation values allowed in the framework of the 331 supersymetric models can be obtained.

  16. Electron-hole diffusion lengths >175 μm in solution-grown CH3sub>NH3sub>PbI3sub> single crystals

    SciTech Connect

    Dong, Qingfeng; Fang, Yanjun; Shao, Yuchuan; Mulligan, Padhraic; Qiu, Jie; Cao, Lei; Huang, Jinsong


    Long, balanced electron and hole diffusion lengths greater than 100 nanometers in the polycrystalline organolead trihalide compound CH3sub>NH3sub>PbI3sub> are critical for highly efficient perovskite solar cells. We found that the diffusion lengths in CH3sub>NH3sub>PbI3sub> single crystals grown by a solution-growth method can exceed 175 micrometers under 1 sun (100 mW cm–2) illumination and exceed 3 millimeters under weak light for both electrons and holes. The internal quantum efficiencies approach 100% in 3-millimeter-thick single-crystal perovskite solar cells under weak light. These long diffusion lengths result from greater carrier mobility, longer lifetime, and much smaller trap densities in the single crystals than in polycrystalline thin films. As a result, the long carrier diffusion lengths enabled the use of CH3sub>NH3sub>PbI3sub> in radiation sensing and energy harvesting through the gammavoltaic effect, with an efficiency of 3.9% measured with an intense cesium-137 source.

  17. Synthesis and structure of In(IO{sub 3}){sub 3} and vibrational spectroscopy of M(IO{sub 3}){sub 3} (M=Al, Ga, In)

    SciTech Connect

    Ngo, Nhan; Kalachnikova, Katrina; Assefa, Zerihun; Haire, Richard G.; Sykora, Richard E. . E-mail:


    The reaction of Al, Ga, or In metals and H{sub 5}IO{sub 6} in aqueous media at 180{sup o}C leads to the formation of Al(IO{sub 3}){sub 3}, Ga(IO{sub 3}){sub 3,} or In(IO{sub 3}){sub 3}, respectively. Single-crystal X-ray diffraction experiments have shown In(IO{sub 3}){sub 3} contains the Te{sub 4}O{sub 9}-type structure, while both Al(IO{sub 3}){sub 3} and Ga(IO{sub 3}){sub 3} are known to exhibit the polar Fe(IO{sub 3}){sub 3}-type structure. Crystallographic data for In(IO{sub 3}){sub 3}, trigonal, space group R3-bar , a=9.7482(4)A, c=14.1374(6)A, V=1163.45(8) Z=6, R(F)=1.38% for 41 parameters with 644 reflections with I>2{sigma}(I). All three iodate structures contain group 13 metal cations in a distorted octahedral coordination environment. M(IO{sub 3}){sub 3} (M=Al, Ga) contain a three-dimensional network formed by the bridging of Al{sup 3+} or Ga{sup 3+} cations by iodate anions. With In(IO{sub 3}){sub 3}, iodate anions bridge In{sup 3+} cations in two-dimensional layers. Both materials contain distorted octahedral holes in their structures formed by terminal oxygen atoms from the iodate anions. The Raman spectra have been collected for these metal iodates; In(IO{sub 3}){sub 3} was found to display a distinctively different vibrational profile than Al(IO{sub 3}){sub 3} or Ga(IO{sub 3}){sub 3}. Hence, the Raman profile can be used as a rapid diagnostic tool to discern between the different structural motifs.

  18. Growth and characterization of acentric BaHf(BO{sub 3}){sub 2} and BaZr(BO{sub 3}){sub 2}

    SciTech Connect

    Mączka, Mirosław; Szymborska-Małek, Katarzyna; Gągor, Anna; Majchrowski, Andrzej


    Growth, single crystal X-ray diffraction, polarized Raman and infrared (IR) studies of BaHf(BO{sub 3}){sub 2} are presented. Raman and IR spectra of polycrystalline BaZr(BO{sub 3}){sub 2} are also reported to facilitate assignment of modes. BaHf(BO{sub 3}){sub 2} borate crystallizes in trigonal system, space group R3c, with lattice parameters: a=5.1540(4) Å, c=33.901(3) Å. It accommodates dolomite-like structure doubled in the c direction, which is built of alternating layers of HfO{sub 6} octahedra and BaO{sub 6} distorted trigonal prisms that are connected through borate groups. The obtained structural as well as spectroscopic data show that BaHf(BO{sub 3}){sub 2} is isostructural with BaZr(BO{sub 3}){sub 2} and the deviations from centrosymmetry is small. - Graphical abstract: Arrangement of BO{sub 3} groups in BaHf(BO{sub 3}){sub 2} along the c direction in one unit cell. Dark and light blue denote different borate groups. - Highlights: • BaHf(BO{sub 3}){sub 2} single crystals were grown. • X-ray diffraction showed that this borate crystallizes in the acentric R3c structure. • Raman and IR spectra were measured for BaHf(BO{sub 3}){sub 2} and BaZr(BO{sub 3}){sub 2}, respectively. • Assignment of modes is proposed.

  19. Octonary resistance states in La0.7Sr0.3sub>MnO3sub>/BaTiO3sub>/La0.7Sr0.3sub>MnO3sub> multiferroic tunnel junctions

    SciTech Connect

    Yue -Wei Yin; Tao, Jing; Huang, Wei -Chuan; Liu, Yu -Kuai; Yang, Sheng -Wei; Dong, Si -Ning; Zhu, Yi -Mei; Li, Qi; Li, Xiao -Guang


    General drawbacks of current electronic/spintronic devices are high power consumption and low density storage. A multiferroic tunnel junction (MFTJ), employing a ferroelectric barrier layer sandwiched between two ferromagnetic layers, presents four resistance states in a single device and therefore provides an alternative way to achieve high density memories. Here, an MFTJ device with eight nonvolatile resistance states by further integrating the design of noncollinear magnetization alignments between the ferromagnetic layers is demonstrated. Through the angle-resolved tunneling magnetoresistance investigations on La0.7Sr0.3sub>MnO3sub>/BaTiO3sub>/La0.7Sr0.3sub>MnO3sub> junctions, it is found that, besides collinear parallel/antiparallel magnetic configurations, the MFTJ shows at least two other stable noncollinear (45° and 90°) magnetic configurations. As a result, combining the tunneling electroresistance effect caused by the ferroelectricity reversal of the BaTiO3sub> barrier, an octonary memory device is obtained, representing potential applications in high density nonvolatile storage in the future.

  20. Gold-rich R3sub>Au7Sn3sub>: Establishing the interdependence between electronic features and physical properties

    SciTech Connect

    Provino, Alessia; Steinberg, Simon; Smetana, Volodymyr; Kulkarni, Ruta; Dhar, Sudesh K.; Manfrinetti, Pietro; Mudring, Anja -Verena


    Two new polar intermetallic compounds Y3sub>Au7Sn3sub> (I) and Gd3sub>Au7Sn3sub> (II) have been synthesized and their structures have been determined by single crystal X-ray diffraction (P63sub>/m; Z = 2, a = 8.148(1)/8.185(3), and c = 9.394(2)/9.415(3) for I/II, respectively). They can formally be assigned to the Cu10Sn3sub> type and consist of parallel slabs of Sn centered, edge-sharing trigonal Au6 antiprisms connected through R3sub> (R = Y, Gd) triangles. Additional Au atoms reside in the centres of trigonal Au6 prisms forming Au@Au6 clusters with Au–Au distances of 2.906–2.960 Å, while the R–R contacts in the R3sub> groups are considerably larger than the sums of their metallic radii. These exclusive structural arrangements provide alluring systems to study the synergism between strongly correlated systems, particularly, those in the structure of (II), and extensive polar intermetallic contacts, which has been inspected by measurements of the magnetic properties, heat capacities and electrical conductivities of both compounds. Gd3sub>Au7Sn3sub> shows an antiferromagnetic ordering at 13 K, while Y3sub>Au7Sn3sub> is a Pauli paramagnet and a downward curvature in its electrical resistivity at about 1.9 K points to a superconducting transition. DFT-based band structure calculations on R3sub>Au7Sn3sub> (R = Y, Gd) account for the results of the conductivity measurements and different spin ordering models of (II) provide conclusive hints about its magnetic structure. As a result, chemical bonding analyses of both compounds indicate that the vast majority of bonding originates from the heteroatomic Au–Gd and Au–Sn interactions, while homoatomic Au–Au bonding is evident within the Au@Au6 clusters.

  1. Structurally induced magnetization in a La2/3sub>Sr4/3sub>MnO4 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 La2/3sub>Sr4/3sub>MnO4, 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 L2,3sub> 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 La2/3sub>Sr4/3sub>MnO4 supperlattice.

  2. Test results of a Nb3sub>Al/Nb3sub>Sn subscale magnet for accelerator application

    SciTech Connect

    Iio, Masami; Xu, Qingjin; Nakamoto, Tatsushi; Sasaki, Ken -ichi; Ogitsu, Toru; Yamamoto, Akira; Kimura, Nobuhiro; Tsuchiya, Kiyosumi; Sugano, Michinaka; Enomoto, Shun; Higashi, Norio; Terashima, Akio; Tanaka, Kenichi; Okada, Ryutaro; Takahashi, Naoto; Ikemoto, Yukiko; Kikuchi, Akihiro; Takeuchi, Takao; Sabbi, Gianluca; Zlobin, Alexander; Barzi, Emanuela


    The High Energy Accelerator Research Organization (KEK) has been developing a Nb3sub>Al and Nb3sub>Sn subscale magnet to establish the technology for a high-field accelerator magnet. The development goals are a feasibility demonstration for a Nb3sub>Al cable and the technology acquisition of magnet fabrication with Nb3sub>Al superconductors. KEK developed two double-pancake racetrack coils with Rutherford-type cables composed of 28 Nb3sub>Al wires processed by rapid heating, quenching, and transformation in collaboration with the National Institute for Materials Science and the Fermi National Accelerator Laboratory. The magnet was fabricated to efficiently generate a high magnetic field in a minimum-gap common-coil configuration with two Nb3sub>Al coils sandwiched between two Nb3sub>Sn coils produced by the Lawrence Berkeley National Laboratory. A shell-based structure and a “bladder and key” technique have been used for adjusting coil prestress during both the magnet assembly and the cool down. In the first excitation test of the magnet at 4.5 K performed in June 2014, the highest quench current of the Nb3sub>Sn coil, i.e., 9667 A, was reached at 40 A/s corresponding to 9.0 T in the Nb3sub>Sn coil and 8.2 T in the Nb3sub>Al coil. The quench characteristics of the magnet were studied.

  3. Gold-rich R3sub>Au7Sn3sub>: Establishing the interdependence between electronic features and physical properties

    SciTech Connect

    Provino, Alessia; Steinberg, Simon; Smetana, Volodymyr; Kulkarni, Ruta; Dhar, Sudesh K.; Manfrinetti, Pietro; Mudring, Anja -Verena


    Two new polar intermetallic compounds Y3sub>Au7Sn3sub> (I) and Gd3sub>Au7Sn3sub> (II) have been synthesized and their structures have been determined by single crystal X-ray diffraction (P63/m; Z = 2, a = 8.148(1)/8.185(3), and c = 9.394(2)/9.415(3) for I/II, respectively). They can formally be assigned to the Cu10Sn3sub> type and consist of parallel slabs of Sn centered, edge-sharing trigonal Au6 antiprisms connected through R3sub> (R = Y, Gd) triangles. Additional Au atoms reside in the centres of trigonal Au6 prisms forming Au@Au6 clusters with Au–Au distances of 2.906–2.960 Å, while the R–R contacts in the R3sub> groups are considerably larger than the sums of their metallic radii. These exclusive structural arrangements provide alluring systems to study the synergism between strongly correlated systems, particularly, those in the structure of (II), and extensive polar intermetallic contacts, which has been inspected by measurements of the magnetic properties, heat capacities and electrical conductivities of both compounds. Gd3sub>Au7Sn3sub> shows an antiferromagnetic ordering at 13 K, while Y3sub>Au7Sn3sub> is a Pauli paramagnet and a downward curvature in its electrical resistivity at about 1.9 K points to a superconducting transition. DFT-based band structure calculations on R3sub>Au7Sn3sub> (R = Y, Gd) account for the results of the conductivity measurements and different spin ordering models of (II) provide conclusive hints about its magnetic structure. As a result, chemical bonding analyses of both compounds indicate that the vast majority of bonding originates from the heteroatomic Au–Gd and Au–Sn interactions, while homoatomic Au–Au bonding is evident within the Au@Au6 clusters.

  4. Electronic structure, irreversibility line and magnetoresistance of Cu0.3sub>Bi2Se3sub> superconductor

    SciTech Connect

    Hemian, Yi; Gu, Genda; Chen, Chao -Yu; Sun, Xuan; Xie, Zhuo -Jin; Feng, Ya; Liang, Ai -Ji; Peng, Ying -Ying; He, Shao -Long; Zhao, Lin; Liu, Guo -Dong; Dong, Xiao -Li; Zhang, Jun; Chen, Chuang -Tian; Xu, Zu -Yan; Zhou, X. -J.


    CuxBi2Se3sub> is a superconductor that is a potential candidate for topological superconductors. We report our laser-based angle-resolved photoemission measurement on the electronic structure of the CuxBi2Se3sub> superconductor, and a detailed magneto-resistance measurement in both normal and superconducting states. We find that the topological surface state of the pristine Bi2Se3sub> topological insulator remains robust after the Cu-intercalation, while the Dirac cone location moves downward due to electron doping. Detailed measurements on the magnetic field-dependence of the resistance in the superconducting state establishes an irreversibility line and gives a value of the upper critical field at zero temperature of ~4000 Oe for the Cu0.3sub>Bi2Se3sub> superconductor with a middle point Tc of 1.9K. The relation between the upper critical field Hc2 and temperature T is different from the usual scaling relation found in cuprates and in other kinds of superconductors. Small positive magneto-resistance is observed in Cu0.3sub>Bi2Se3sub> superconductors up to room temperature. As a result, these observations provide useful information for further study of this possible candidate for topological superconductors.

  5. Strong M1 components in 3{sub i}{sup -}->3{sub 1}{sup -} transitions in nearly spherical nuclei: Evidence for isovector-octupole excitations

    SciTech Connect

    Scheck, M.; Butler, P. A.; Fransen, C.; Werner, V.; Yates, S. W.


    An evaluation of data obtained in (n,n{sup '}gamma) experiments reveals strong M1 3{sub i}{sup -}->3{sub 1}{sup -} transitions in nuclei near the N=50 ({sup 92}Zr, {sup 94}Mo, and {sup 96}Mo), Z=50 ({sup 112}Cd and {sup 114}Cd), and N=82 ({sup 144}Nd) shell closures. The observed <3{sub 1}{sup -}||M1||3{sub i}{sup -}> matrix elements scale with the <2{sub 1}{sup +}||M1||2{sub ms}{sup +}> matrix elements connecting the mixed-symmetric and symmetric quadrupole excitations. In accordance with a picture of a mixed two-component quantum system, the energy difference between the initial 3{sub i}{sup -} state and the 3{sub 1}{sup -} octupole phonon is proportional to the |<3{sub 1}{sup -}||E3||0{sub gs}{sup +}>| matrix element. The possibility of assigning the 3{sup -} states of interest as octupole isovector states is discussed.

  6. From thermoelectric bulk to nanomaterials: Current progress for Bi 2 Te 3sub> and CoSb 3sub>: From thermoelectric bulk to nanomaterials

    SciTech Connect

    Peranio, N.; Eibl, O.; Bäßler, S.; Nielsch, K.; Klobes, B.; Hermann, R. P.; Daniel, M.; Albrecht, M.; Görlitz, H.; Pacheco, V.; Bedoya-Martínez, N.; Hashibon, A.; Elsässer, C.


    We synthesized Bi2Te3sub> and CoSb3sub> based nanomaterials and their thermoelectric, structural, and vibrational properties analyzed to assess and reduce ZT-limiting mechanisms. The same preparation and/or characterization methods were applied in the different materials systems. Single-crystalline, ternary p-type Bi15Sb29Te56, and n-type Bi38Te55Se7 nanowires with power factors comparable to nanostructured bulkmaterialswere prepared by potential-pulsed electrochemical deposition in a nanostructured Al2O3sub> matrix. p-type Sb2Te3sub>, n-type Bi2Te3sub>, and n-type CoSb3sub> thin films were grown at room temperature using molecular beam epitaxy and were subsequently annealed at elevated temperatures. It yielded polycrystalline, single phase thin films with optimized charge carrier densities. In CoSb3sub> thin films the speed of sound could be reduced by filling the cage structure with Yb and alloying with Fe yielded p-type material. Bi2(Te0.91Se0.09)3sub>/SiC and (Bi0.26Sb0.74)2Te3sub>/SiC nanocomposites with low thermal conductivities and ZT values larger than 1 were prepared by spark plasma sintering. Nanostructure, texture, chemical composition, as well as electronic and phononic excitations were investigated by X-ray diffraction, nuclear resonance scattering, inelastic neutron scattering, M ossbauer spectroscopy, and transmission electron microscopy. Furthermore, for Bi2Te3sub> materials, ab-initio calculations together with equilibrium and non-equilibrium molecular dynamics simulations for point defects yielded their formation energies and their effect on lattice thermal conductivity, respectively. Current advances in thermoelectric Bi2Te3sub> and CoSb3sub> based nanomaterials are

  7. Electric-field-induced linear birefringence in TmAl3sub>(BO3sub>)4.


    Pashchenko, M I; Bedarev, V A; Merenkov, D N; Gnatchenko, S L; Bezmaternykh, L N; Sukhachev, A L; Temerov, V L


    The linear birefringence induced by the electric field was first detected in a TmAl3sub>(BO3sub>)4 single crystal. The electric field dependence of the birefringence was investigated. The estimation of the electro-optical coefficient of the material gives ≈1.5×10-10  cm/V for a wavelength 632.8 nm. PMID:27140114

  8. Thermodynamic Properties of α-Fe2O3sub> and Fe3sub>O4 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-Fe2O3sub> (hematite) and Fe3sub>O4 (magnetite) nanoparticles. In addition to 9 nm Fe3sub>O4, three α-e2O3sub>nanoparticles samples of different sizes (11, 14, and 25 nm) and bulk α-e2O3sub> 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-e2O3sub> 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.

  9. Origin and elimination of photocurrent hysteresis by fullerene passivation in CH3sub>NH3sub>PbI3sub> planar heterojunction solar cells

    SciTech Connect

    Shao, Yuchuan; Xiao, Zhengguo; Bi, Cheng; Yuan, Yongbo; Huang, Jinsong


    The large photocurrent hysteresis observed in many organometal trihalide perovskite solar cells has become a major hindrance impairing the ultimate performance and stability of these devices, while its origin was unknown. Here we demonstrate the trap states on the surface and grain boundaries of the perovskite materials to be the origin of photocurrent hysteresis and that the fullerene layers deposited on perovskites can effectively passivate these charge trap states and eliminate the notorious photocurrent hysteresis. Fullerenes deposited on the top of the perovskites reduce the trap density by two orders of magnitude and double the power conversion efficiency of CH3sub>NH3sub>PbI3sub> solar cells. As a result, the elucidation of the origin of photocurrent hysteresis and its elimination by trap passivation in perovskite solar cells provides important directions for future enhancements to device efficiency.

  10. Method of preparing (CH.sub.3).sub.3 SiNSO and byproducts thereof


    Spicer, Leonard D.; Bennett, Dennis W.; Davis, Jon F.


    (CH.sub.3).sub.3 SiNSO is produced by the reaction of ((CH.sub.3).sub.3 Si).sub.2 NH with SO.sub.2. Also produced in the reaction are ((CH.sub.3).sub.3 Si).sub.2 O and a new solid compound [NH.sub.4 ][(CH.sub.3).sub.3 SiOSO.sub.2 ]. Both (CH.sub.3).sub.3 SiNSO and [NH.sub.4 ][(CH.sub.3).sub.3 SiOSO.sub.2 ] have fluorescent properties. The reaction of the subject invention is used in a method of measuring the concentration of SO.sub.2 pollutants in gases. By the method, a sample of gas is bubbled through a solution of ((CH.sub.3).sub.3 Si).sub.2 NH, whereby any SO.sub.2 present in the gas will react to produce the two fluorescent products. The measured fluorescence of these products can then be used to calculate the concentration of SO.sub.2 in the original gas sample. The solid product [NH.sub.4 ][(CH.sub.3).sub.3 SiOSO.sub.2 ] may be used as a standard in solid state NMR spectroscopy.

  11. Synthesis and crystal structures of nitratocobaltates Na{sub 2}[Co(NO{sub 3}){sub 4}], K{sub 2}[Co(NO{sub 3}){sub 4}], and Ag[Co(NO{sub 3}){sub 3}] and potassium nitratonickelate K{sub 2}[Ni(NO{sub 3}){sub 4}

    SciTech Connect

    Morozov, I. V. Fedorova, A. A.; Albov, D. V.; Kuznetsova, N. R.; Romanov, I. A.; Rybakov, V. B.; Troyanov, S. I.


    The cobalt(II) and nickel(II) nitrate complexes with an island structure (Na{sub 2}[Co(NO{sub 3}){sub 4}] (I) and K{sub 2}[Co(NO{sub 3}){sub 4}] (II)] and a chain structure [Ag[Co(NO{sub 3}){sub 3}] (III) and K{sub 2}[Ni(NO{sub 3}){sub 4}] (IV)] are synthesized and investigated using X-ray diffraction. In the anionic complex [Co(NO{sub 3}){sub 4}]{sup 2-} of the crystal structure of compound I, the Co coordination polyhedron is a twisted tetragonal prism formed by the O atoms of four asymmetric bidentate nitrate groups. In the anion [Co(NO{sub 3}){sub 4}]{sup 2-} of the crystal structure of compound II, one of the four NO{sub 3} groups is monodentate and the other NO{sub 3} groups are bidentate (the coordination number of the cobalt atom is equal to seven, and the cobalt coordination polyhedron is a monocapped trigonal prism). The crystal structures of compounds III and IV contain infinite chains of the compositions [Co(NO{sub 3}){sub 2}(NO{sub 3}){sub 2/2}]{sup -} and [Ni(NO{sub 3}){sub 3}(NO{sub 3}){sub 2/2}]{sup 2-}, respectively. In the crystal structure of compound III, seven oxygen atoms of one monodentate and three bidentate nitrate groups form a dodecahedron with an unoccupied vertex of the A type around the Co atom. In the crystal structure of compound IV, the octahedral polyhedron of the Ni atom is formed by five nitrate groups, one of which is terminal bidentate. The data on the structure of Co(II) coordination polyhedra in the known nitratocobaltates are generalized.

  12. Interfacial dislocations in (111) oriented (Ba0.7Sr0.3sub>)TiO3sub> films on SrTiO3sub> single crystal

    SciTech Connect

    Shen, Xuan; Yamada, Tomoaki; Lin, Ruoqian; Kamo, Takafumi; Funakubo, Hiroshi; Wu, Di; Xin, Huolin L.; Su, Dong


    In this study, we have investigated the interfacial structure of epitaxial (Ba,Sr)TiO3sub> films grown on (111)-oriented SrTiO3sub> single-crystal substrates using transmission electron microscopy (TEM) techniques. Compared with the (100) epitaxial perovskite films, we observe dominant dislocation half-loop with Burgers vectors of a<110> comprised of a misfit dislocation along <112>, and threading dislocations along <110> or <100>. The misfit dislocation with Burgers vector of a <110> can dissociate into two ½ a <110> partial dislocations and one stacking fault. We found the dislocation reactions occur not only between misfit dislocations, but also between threading dislocations. Via three-dimensional electron tomography, we retrieved the configurations of the threading dislocation reactions. The reactions between threading dislocations lead to a more efficient strain relaxation than do the misfit dislocations alone in the near-interface region of the (111)-oriented (Ba0.7Sr0.3sub>)TiO3sub> films.

  13. Advanced Nodal P3sub>/SP3sub> Axial Transport Solvers for the MPACT 2D/1D Scheme

    SciTech Connect

    Stimpson, Shane G; Collins, Benjamin S


    As part of its initiative to provide multiphysics simulations of nuclear reactor cores, the Consortium for Advanced Simulation of Light Water Reactors (CASL) is developing the Virtual Environment for Reactor Applications Core Simulator (VERA-CS). The MPACT code, which is the primary neutron transport solver of VERA-CS, employs the two-dimensional/one-dimensional (2D/1D) method to solve 3-dimensional neutron transport problems and provide sub-pin-level resolution of the power distribution. While 2D method of characteristics is used to solve for the transport effects within each plane, 1D-nodal methods are used axially. There have been extensive studies of the 2D/1D method with a variety nodal methods, and the P3sub>/SP3sub> solver has proved to be an effective method of providing higher-fidelity solutions while maintaining a low computational burden.The current implementation in MPACT wraps a one-node nodal expansion method (NEM) kernel for each moment, iterating between them and performing multiple sweeps to resolve flux distributions. However, it has been observed that this approach is more sensitive to convergence problems. This paper documents the theory and application two new nodal P3sub>/SP3sub> approaches to be used within the 2D/1D method in MPACT. These two approaches aim to provide enhanced stability compared with the pre-existing one-node approach. Results from the HY-NEM-SP3sub> solver show that the accuracy is consistent with the one-node formulations and provides improved convergence for some problems; but the solver has issues with cases in thin planes. Although the 2N-SENM-SP3sub> solver is still under development, it is intended to resolve the issues with HY-NEM-SP3sub> but it will incur some additional computational burden by necessitating an additional 1D-CMFD-P3sub> solver to generate the second moment cell-averaged scalar flux.

  14. The distribution alloying elements in alnico 8 and 9 magnets: Site preference of ternary Ti, Fe, Co, and Ni additions in DO3sub> Fe3sub>Al, Co3sub>Al, and Ni3sub>Al based intermetallic phases

    SciTech Connect

    Samolyuk, G. D.; Újfalussy, B.; Stocks, G. M.


    Recently, interest in alnico magnetic alloys has been rekindled due to their potential to substitute for rare-earth based permanent magnets provided modest improvements in their coercivity can be achieved without loss of saturation magnetization. Recent experimental studies have indicated that atomic and magnetic structure of the two phases (one AlNi-based, the other FeCo-based) that comprise these spinodally decomposed alloy is not as simple as previously thought. A key issue that arises is the distribution of Fe, Co and Ti within the AlNi-based matrix phase. In our paper we report the results of first-principles calculations of the site preference of ternary alloying additions in DO3sub> Fe3sub>Al, Co3sub>Al and Ni3sub>Al alloys, as models for the aluminide phase. For compound compositions that are Al rich, which corresponds to experimental situation, Ti and Fe are found to occupy the sites, while Co and Ni prefer the sites of the DO3sub> lattice. Finally, an important finding is that the magnetic moments of transition metals in Fe3sub>Al and Co3sub>Al are ordered ferromagnetically, whereas the Ni3Al were found to be nonmagnetic unless the Fe or Co are added as a ternary element.

  15. Pressure dependence of the monoclinic phase in (1–x)Pb(Mg1/3sub>Nb2/3sub>)O3sub>-xPbTiO₃ solid solutions

    SciTech Connect

    Ahart, Muhtar; Sinogeikin, Stanislav; Shebanova, Olga; Ikuta, Daijo; Ye, Zuo-Guang; Mao, Ho-kwang; Cohen, R. E.; Hemley, Russell J.


    We combine high-pressure x-ray diffraction, high-pressure Raman scattering, and optical microscopy to investigate a series of (1–x)Pb(Mg1/3sub>Nb2/3sub>)O3sub>-xPbTiO₃ (PMN-xPT) solid solutions (x=0.2, 0.3, 0.33, 0.35, 0.37, 0.4) in diamond anvil cells up to 20 GPa at 300 K. The Raman spectra show a peak centered at 380 cm⁻¹ starting above 6 GPa for all samples, in agreement with previous observations. X-ray diffraction measurements are consistent with this spectral change indicating a structural phase transition; we find that the triplet at the pseudocubic (220) Bragg peak merges into a doublet above 6 GPa. Our results indicate that the morphotropic phase boundary region (x=0.33–0.37) with the presence of monoclinic symmetry persists up to 7 GPa. The pressure dependence of ferroelectric domains in PMN-0.32PT single crystals was observed using a polarizing optical microscope. The domain wall density decreases with pressure and the domains disappear at a modest pressure of 3 GPa. We propose a pressure-composition phase diagram for PMN-xPT solid solutions.

  16. Addition of CFCl3sub> to Aromatic Aldehydes via in Situ Grignard Reaction

    SciTech Connect

    Barkakaty, Balaka; Talukdar, Bandana; Lokitz, Bradley


    In the case of synthetic modification of trichlorofluoromethane (CFCl3sub>) to non-volatile and useful fluorinated precursors, we realized that it is a cost-effective and an environmentally benign strategy for the safe consumption/destruction of the ozone depleting potential of the reagent. In our report, we present a novel method for in situ Grignard reaction using magnesium powder and CFCl3sub> for synthesis of dichlorofluoromethyl aromatic alcohols.

  17. Phenomenology of the SU(3){sub c}xSU(3){sub L}xU(1){sub X} model with exotic charged leptons

    SciTech Connect

    Salazar, Juan C.; Ponce, William A.; Gutierrez, Diego A.


    A phenomenological analysis of the three-family model based on the local gauge group SU(3){sub c}xSU(3){sub L}xU(1){sub X} with exotic charged leptons, is carried out. Instead of using the minimal scalar sector able to break the symmetry in a proper way, we introduce an alternative set of four Higgs scalar triplets, which combined with an anomaly-free discrete symmetry, produce quark and charged lepton mass spectrum without hierarchies in the Yukawa coupling constants. We also embed the structure into a simple gauge group and show some conditions to achieve a low energy gauge coupling unification, avoiding possible conflict with proton decay bounds. By using experimental results from the CERN-LEP, SLAC linear collider, and atomic parity violation data, we update constraints on several parameters of the model.

  18. Structure determination and optical properties of CsSm(PO{sub 3}){sub 4}

    SciTech Connect

    Ben Hassen, N.; Ferhi, M. Horchani-Naifer, K.; Férid, M.


    Graphical abstract: Projection of the CsSm(PO{sub 3}){sub 4} structure viewing along the a axis. - Highlights: • Single crystal of a new polyphosphate CsSm(PO{sub 3}){sub 4} has been synthesized. • The obtained compound has been characterized by several techniques. • The crystal structure of CsSm(PO{sub 3}){sub 4} has been resolved. • Spectroscopic properties of Sm{sup 3+} in CsSm(PO{sub 3}){sub 4} have been performed. - Abstract: A new alkali metal-rare earth polyphosphate CsSm(PO{sub 3}){sub 4} has been synthesized by flux method. The obtained compound has been characterized by means of single crystal X-ray diffraction, Fourier transform infrared (FTIR) and Raman scattering spectroscopies. It crystallizes in the monoclinic space group P2{sub 1}/n with the following unit-cell parameters: a = 10.382(2), b = 8.978(6), c = 11.205(4) Å, β = 106.398(3)° and Z = 4. The structure of CsSm(PO{sub 3}){sub 4} is an infinite three-dimensional framework made up of double spiral (PO{sub 3}){sub n} chains linked with neighboring SmO{sub 8} and CsO{sub 11} polyhedra. Spectroscopic properties of Sm{sup 3+} in this new compound including excitation, emission, and kinetic measurement have been performed. The emission spectrum shows four transitions characteristics of Sm{sup 3+} in the orange–red region by excitation wavelength at 400 nm. The decay time curve of {sup 4}G{sub 5/2} → {sup 6}H{sub 7/2} transition has been also registered and fitted to a single exponential function.

  19. Induced Ferromagnetism at BiFeO3sub>/YBa2Cu3sub>O7 Interfaces

    SciTech Connect

    Zhu, Jian-Xin; Wen, Xiao-Dong; Haraldsen, J. T.; He, Mi; Panagopoulos, C.; Chia, Elbert E. M.


    We report that transition metal oxides (TMOs) exhibit many emergent phenomena ranging from high-temperature superconductivity and giant magnetoresistance to magnetism and ferroelectricity. In addition, when TMOs are interfaced with each other, new functionalities can arise, which are absent in individual components. Here, we report results from first-principles calculations on the magnetism at the BiFeO3sub>/YBa2Cu3sub>O7 interfaces. By comparing the total energy for various magnetic spin configurations inside BiFeO3sub>, we are able to show that a metallic ferromagnetism is induced near the interface. We further develop an interface exchange-coupling model and place the extracted exchange coupling interaction strengths, from the first-principles calculations, into a resultant generic phase diagram. Our conclusion of interfacial ferromagnetism is confirmed by the presence of a hysteresis loop in field-dependent magnetization data. Lastly, the emergence of interfacial ferromagnetism should have implications to electronic and transport properties.

  20. Field-dependent magnetization of BiFeO3sub> in ultrathin La0.7Sr0.3sub>MnO3sub>/BiFeO3sub> superlattice

    SciTech Connect

    Fitzsimmons, Michael R.; Jia, Quanxi X.; Singh, Surendra; Chen, A. P.; Xiong, J.


    We report the observation of field-induced magnetization of BiFeO3sub> (BFO) in an ultrathin La0.7Sr0.3sub>MnO3sub> (LSMO)/BFO superlattice using polarized neutron reflectivity (PNR). The depth dependent structure and magnetic characterization of subnano layer thick (thickness ~ 0.7 nm each) LSMO/BFO hetrostructure is carried out using X-ray reflectivity and PNR techniques. Our PNR results indicate parallel alignment of magnetization as well as enhancement in magnetic moment across LSMO/BFO interfaces. The study showed an increase in average magnetization on increasing applied magnetic field at 10K. As a result, we observed a saturation magnetization of 110 ± 15 kA/m (~0.8 μB/Fe) for ultrathin BFO layer (~2 unit cell) sandwiched between ultrathin LSMO layers (~ 2 unit cell).

  1. Electronic and Magnetic Properties of Epitaxial Perovskite SrCrO3sub>(001)

    SciTech Connect

    Zhang, K. H. L.; Du, Y.; Sushko, P. V.; Bowden, M. E.; Shutthanandan, V.; Qiao, L.; Cao, G. X.; Gai, Z.; Sallis, S.; Piper, L. F. J.; Chambers, S. A.


    We investigated the intrinsic properties of SrCrO3sub> epitaxial thin films synthesized by molecular beam epitaxy. We found compelling evidence that SrCrO3sub> is a correlated metal. X-ray photoemission valence band and O K-edge x-ray absorption spectra indicate a strongly hybridized Cr3sub>d–O2p state crossing the Fermi level, leading to metallic behavior. Furthermore, a comparison between valence band spectra near the Fermi level and the densities of states calculated using density functional theory (DFT) suggests the presence of coherent and incoherent states and points to strong electron correlation effects. The magnetic susceptibility can be described by Pauli paramagnetism at temperatures above 100 K, but reveals antiferromagnetic behavior at lower temperatures, possibly resulting from orbital ordering.

  2. Epitaxial growth of high quality WO3sub> thin films

    SciTech Connect

    Leng, X.; Pereiro, J.; Strle, J.; Bollinger, A. T.; Bozovic, I.


    We have grown epitaxial WO3sub> films on various single-crystal substrates using radio-frequency (RF) magnetron sputtering. While pronounced surface roughness is observed in films grown on LaSrAlO4 substrates, films grown on YAlO3sub> substrates show atomically flat surfaces, as demonstrated by atomic force microscopy (AFM) and X-ray diffraction (XRD) measurements. The crystalline structure has been confirmed to be monoclinic by symmetric and skew-symmetric XRD. Furthermore, the dependence of the growth modes and the surface morphology on the lattice mismatch is discussed.

  3. Fragile structural transition in Mo3sub>Sb7

    SciTech Connect

    Yan, Jiaqiang -Q.; McGuire, Michael A; May, Andrew F; Parker, David S.; Mandrus, D. G.; Sales, Brian C.


    Mo3sub>Sb7 single crystals lightly doped with Cr, Ru, or Te are studied in order to explore the interplay between superconductivity, magnetism, and the cubic-tetragonal structural transition. The structural transition at 53 K is extremely sensitive to Ru or Te substitution which introduces additional electrons, but robust against Cr substitution. We observed no sign of a structural transition in superconducting Mo2.91Ru0.09Sb7 and Mo3sub>Sb6.975Te0.025. In contrast, 3 at.% Cr doping only slightly suppresses the structural transition to 48 K while leaving no trace of superconductivity above 1.8 K. Analysis of magnetic properties suggests that the interdimer interaction in Mo3sub>Sb7 is near a critical value and essential for the structural transition. Futhermore, all dopants suppress the superconductivity of Mo3sub>Sb7. The tetragonal structure is not necessary for superconductivity.

  4. Ferromagnetism of Fe3sub>Sn and alloys

    SciTech Connect

    Sales, Brian C.; Saparov, Bayrammurad; McGuire, Michael A.; Singh, David J.; Parker, David S.


    Hexagonal Fe3sub>Sn has many of the desirable properties for a new permanent magnet phase with a Curie temperature of 725 K, a saturation moment of 1.18 MA/m. and anisotropy energy, K1 of 1.8 MJ/m3. However, contrary to earlier experimental reports, we found both experimentally and theoretically that the easy magnetic axis lies in the hexagonal plane, which is undesirable for a permanent magnet material. One possibility for changing the easy axis direction is through alloying. We used first principles calculations to investigate the effect of elemental substitutions. The calculations showed that substitution on the Sn site has the potential to switch the easy axis direction. Transition metal substitutions with Co or Mn do not have this effect. We attempted synthesis of a number of these alloys and found results in accord with the theoretical predictions for those that were formed. However, the alloys that could be readily made all showed an in-plane easy axis. The electronic structure of Fe3sub>Sn is reported, as are some are magnetic and structural properties for the Fe3sub>Sn2, and Fe5Sn3sub> compounds, which could be prepared as mm-sized single crystals.

  5. A Novel Pressure-induced Phase Transition in CaZrO3sub>

    SciTech Connect

    Yang, Xue; Li, Quanjun; Liu, Ran; Liu, Bo; Jiang, Shuqing; Yang, Ke; Liu, Jing; Chen, Zhiqiang; Zou, Bo; Cui, Tian; Liu, Bingbing


    The high pressure synchrotron X-ray diffraction measurements on CaZrO3sub> were carried out in a diamond anvil cell up to 50.1 GPa at room temperature. It was found that the orthorhombic phase can be stable up to 30 GPa. A new pressure-induced phase transition was observed in CaZrO3sub> beyond 30 GPa. The high pressure structure of CaZrO3sub> was determined to be a monoclinic phase which is distinct from the high pressure structures that were previously reported for other perovskite oxides. Upon release of pressure, the high pressure phase transforms into the initial orthorhombic phase. Likewise, a fit of the compression data to the third-order Birch–Murnaghan equation of state yields a bulk modulus K0 of 193(14) GPa. We propose that the unique distorted structure probably plays a crucial role in the high pressure behavior of CaZrO3sub>. Especially, the distinct phase transformation may be related to the rotation or tilting of the ZrO6 octahedra.

  6. Investigation of Bismuth Triiodide (BiI3sub>) for Photovoltaic Applications

    SciTech Connect

    Brandt, Riley E.; Kurchin, Rachel C.; Hoye, Robert L. Z.; Poindexter, Jeremy R.; Wilson, Mark W. B.; Sulekar, Soumitra; Lenahan, Frances; Yen, Patricia; Stevanovic, Vladan; Nino, Juan C.; Bawendi, Moungi G.; Buonassisi, Tonio


    We investigate bismuth triiodide (BiI3sub>) as a candidate thin-film photovoltaic (PV) absorber. BiI3sub> was chosen for its optical properties and the potential for “defect-tolerant” charge transport properties, which we test experimentally by measuring optical absorption and recombination lifetimes. We synthesize phase-pure BiI3sub> thin films by physical vapor transport and solution processing and single-crystals by an electrodynamic gradient vertical Bridgman method. The bandgap of these materials is ~1.8 eV, and they demonstrate room-temperature band-edge photoluminescence. We measure monoexponential recombination lifetimes in the range of 180–240 ps for thin films, and longer, multiexponential dynamics for single crystals, with time constants up to 1.3 to 1.5 ns. We discuss the outstanding challenges to developing BiI3sub> PVs, including mechanical and electrical properties, which can also inform future selection of candidate PV absorbers.

  7. Infrared spectroscopy of Li(NH{sub 3}){sub n} clusters for n=4-7

    SciTech Connect

    Salter, Tom E.; Mikhailov, Victor A.; Evans, Corey J.; Ellis, Andrew M.


    Infrared spectra of Li(NH{sub 3}){sub n} clusters as a function of size are reported for the first time. Spectra have been recorded in the N-H stretching region for n=4{yields}7 using a mass-selective photodissociation technique. For the n=4 cluster, three distinct IR absorption bands are seen over a relatively narrow region, whereas the larger clusters yield additional features at higher frequencies. Ab initio calculations have been carried out in support of these experiments for the specific cases of n=4 and 5 for various isomers of these clusters. The bands observed in the spectrum for Li(NH{sub 3}){sub 4} can all be attributed to N-H stretching vibrations from solvent molecules in the first solvation shell. The appearance of higher frequency N-H stretching bands for n{>=}5 is assigned to the presence of ammonia molecules located in a second solvent shell. These data provide strong support for previous suggestions, based on gas phase photoionization measurements, that the first solvation shell for Li(NH{sub 3}){sub n} is complete at n=4. They are also consistent with neutron diffraction studies of concentrated lithium/liquid ammonia solutions, where Li(NH{sub 3}){sub 4} is found to be the basic structural motif.

  8. Search for compounds of the NaBaR(BO{sub 3}){sub 2} family (R = La, Nd, Gd, and Yb) and the new NaBaYb(BO{sub 3}){sub 2} orthoborate

    SciTech Connect

    Svetlyakova, T. N. Kokh, A. E.; Kononova, N. G.; Fedorov, P. P.; Rashchenko, S. V.; Maillard, A.


    A search for compounds of the NaBaR(BO{sub 3}){sub 2} composition (where R = La{sup 3+}, Nd{sup 3+}, Gd{sup 3+}, or Yb{sup 3+}) is performed by solid state synthesis and spontaneous crystallization. A new compound, NaBaYb(BO{sub 3}){sub 2}, is found in this series. It crystallizes in space group R3{sup -} and belongs to the family of sublayer complex orthoborates with isolated BO{sub 3} groups NaBaR(BO{sub 3}){sub 2} (R = Y, Sc, and Yb). Theoretical X-ray powder diffraction patterns of NaBaY(BO{sub 3}){sub 2}, NaBaSc(BO{sub 3}){sub 2}, and NaBaYb(BO{sub 3}){sub 2} are calculated based on single-crystal data.

  9. SU(3){sub C}xSU(3){sub L}xU(1){sub X} model with two Higgs triplets

    SciTech Connect

    Dong, P.V.; Long, H.N.; Nhung, D.T.; Soa, D.V.


    The SU(3){sub C}xSU(3){sub L}xU(1){sub X} gauge model with the minimal scalar sector (two Higgs triplets) is studied in detail. One of the vacuum expectation values u is a source of lepton-number violations and a reason for the mixing among the charged gauge bosons--the standard model W and the bilepton (with L=2) gauge bosons as well as among neutral non-Hermitian X{sup 0} and neutral gauge bosons: the photon, the Z, and the new Z{sup '}. Because of these mixings, the lepton-number violating interactions exist in both charged and neutral gauge boson sectors. An exact diagonalization of the neutral gauge boson sector is derived and bilepton mass splitting is also given. The lepton-number violation happens only in the neutrino but not in the charged lepton sector. In this model, lepton-number changing ({delta}L={+-}2) processes exist but only in the neutrino sector. Constraints on vacuum expectation values of the model are estimated and u{approx_equal}O(1) GeV, v{approx_equal}v{sub weak}=246 GeV, and {omega}{approx_equal}O(1) TeV.

  10. Structural and spectroscopic properties of pure and doped LiCe(PO{sub 3}){sub 4}

    SciTech Connect

    Abdelhedi, M.; Horchani-Naifer, K.; Dammak, M.; Ferid, M.


    Graphical abstract: Emission and excitation and spectra of Eu{sup 3+} doped LiCe(PO{sub 3}){sub 4} host lattice with 1, 2, 3 and 4 mol%. - Highlights: • Europium–doped LiCe(PO{sub 3}){sub 4} were prepared by flux method. • It was analyzed by infrared and Raman spectroscopy, and luminescence spectroscopy. • LiCe(PO{sub 3}){sub 4} doped with Eu{sup 3+} ions as luminophore host materials to produce an intense red. - Abstract: Single crystals of LiCe(PO{sub 3}){sub 4} polyphosphate have been synthesized by the flux method and its structural and luminescence properties have been investigated. This compound crystallizes in the space group C2/c with unit cell dimensions a = 16.52(7) Å, b = 7.09(4) Å, c = 9.83 (4)Å, β = 126.29(4)°, Z = 8 and V = 927.84(3) Å{sup 3}. The obtained polytetraphosphate exhibits very small crystals and the dopant Eu{sup 3+} ions were successfully incorporated into the sites of Ce{sup 3+} ions of the host lattice. The spectroscopy properties confirm the potentiality of present LiCe(PO{sub 3}){sub 4} doped with Eu{sup 3+} ions as luminophore host materials to produce an intense red luminescence at 628 nm corresponding to {sup 5}D{sub 0} → {sup 7}F{sub 2} emission level and have significant importance in the development of emission optical systems.

  11. Crystal structure and optical study of praseodymium polyphosphate Pr(PO{sub 3}){sub 3}

    SciTech Connect

    Jouini, Anis; Ferid, Mokhtar; Gacon, Jean-Claude; Grosvalet, Laurent; Thozet, Alain; Trabelsi-Ayadi, Malika


    Single crystals of praseodymium polyphosphate Pr(PO{sub 3}){sub 3} were grown for the first time using a flux method and characterized by single-crystal X-ray diffraction. Pr(PO{sub 3}){sub 3} is isostructural with Nd(PO{sub 3}){sub 3} and La(PO{sub 3}){sub 3}. It crystallizes in the orthorhombic system with space group C222{sub 1} (D{sub 2}{sup 5}), with lattice parameters: a=11.234(1) A, b=8.5289(8) A, c=7.3199(8) A. The crystal structure was resolved with final R(F{sup 2})=0.0359 and R{sub w}(F{sup 2})=0.0924 for 402 independent reflections (F{sub 0}{sup 2}{>=}2{sigma}(F{sub 0}{sup 2})). In the Pr(PO{sub 3}){sub 3} structure, oxygen atoms form a PO{sub 4} tetrahedron around each P atom and a PrO{sub 8} polyhedron around each Pr atom. The PO{sub 4} tetrahedra share corners to produce helical chains and the PrO{sub 8} polyhedra share edges to form zigzag chains. The shortest Pr-Pr distance is 4.253 A. The energies of the vibrational modes of the crystal are obtained from the infrared and Raman spectra. Measurements of emission spectra under pulsed laser excitation in the Pr{sup 3+} (4f{sup 2}) {sup 3}P{sub J} (J=0, 1, 2) levels and decay times of the observed emissions are reported both at room and liquid-helium temperatures. X-ray excitation leads to intense ultraviolet 4f{sup 1}5d{sup 1}{yields}4f{sup 2} band emissions in the 200-300 nm spectral range with decay times in the order of 6 ns both at room and low temperatures.

  12. Synthesis of superconducting Nb3sub>Sn coatings on Nb substrates

    SciTech Connect

    Barzi, E.; Franz, S.; Reginato, F.; Turrioni, D.; Bestetti, M.


    In the present work the electrochemical and thermal syntheses of superconductive Nb3sub>Sn films are investigated. The Nb3sub>Sn phase is obtained by electrodeposition of Sn layers and Cu intermediate layers onto Nb substrates followed by high temperature diffusion in inert atmosphere. Electrodeposition was performed from aqueous solutions at current densities in the 20 to 50 mA/cm2 range and at temperatures between 40 and 50°C. Subsequent thermal treatments were realized to obtain the Nb3sub>Sn superconductive phase. Glow discharge optical emission spectrometry (GDOES) demonstrated that after thermal treatment interdiffusion of Nb and Sn occurred across a thickness of about 13 μm. Scanning Electron Microscopy (SEM) allowed accurately measuring the thickness of the Nb3sub>Sn phase, whose average for the various types of film samples was between 5.7 and 8.0 μm. X-ray diffraction (XRD) patterns confirmed the presence of a cubic Nb3sub>Sn phase (A15 structure) having (210) preferred orientation. The maximum obtained Tc was 17.68 K and the Bc20 ranged between 22.5 T and 23.8 T. With the procedure described in the present paper, coating complex shapes cost-effectively becomes possible, which is typical of electrochemical techniques. Furthermore, this approach can be implemented in classical wire processes such as "Jelly Roll" or "Rod in Tube", or directly used for producing superconducting surfaces. In conclusion, the potential of this method for Superconducting Radiofrequency (SRF) structures is also outlined.

  13. New isoformula iodates In(IO{sub 3}){sub 3} and Sm(IO{sub 3}){sub 3} with different crystal structures: Specific structural features of I{sup 5+} compounds

    SciTech Connect

    Gurbanova, O. A. Ivanova, A. G.; Belokoneva, E. L.; Dimitrova, O. V.; Mochenova, N. N.


    New iodates, namely, In(IO{sub 3}){sub 3} (space group R3-bar) and Sm(IO{sub 3}){sub 3} (space group P2{sub 1}/a), are synthesized under hydrothermal conditions. The original crystal structure of the In(IO{sub 3}){sub 3} compound is determined without prior knowledge of the chemical formula. The Sm(IO{sub 3}){sub 3} compound is isostructural to the Gd(IO{sub 3}){sub 3} compound. The [IO{sub 4}]{sup 3-} tetrahedra with three short I-O bonds have an umbrella coordination, which is characteristic of pentavalent iodine, and form anionic radicals, such as a ring radical in the In(IO{sub 3}){sub 3} iodate, a triple helix in the isoformula compound Fe(IO{sub 3}){sub 3}, a complex chain in the Sm(IO{sub 3}){sub 3} iodate, and a linear triortho group in the Sm(IO{sub 3}){sub 3}.H{sub 2}O compound. All radicals contain triortho groups. The structural differences are determined by different ionic radii and shapes of the coordination polyhedra of the cations (indium and iron octahedra and an eight-vertex samarium polyhedron)

  14. Electronic and magnetic properties of epitaxial perovskite SrCrO3sub>(001)

    SciTech Connect

    Zhang, K. H. L.; Du, Y.; Sushko, P. V.; Bowden, M. E.; Shutthanandan, V.; Cao, Guixin; Gai, Zheng; Sallis, S.; Piper, L. F. J.; Chambers, S. A.; Qiao, L.


    We have investigated the intrinsic properties of SrCrO3sub> epitaxial thin films synthesized by molecular beam epitaxy. We find compelling evidence that SrCrO3sub> is a correlated metal. X-ray photoemission valence band and O K-edge x-ray absorption spectra indicate a strongly hybridized Cr3d-O2p state crossing the Fermi level, leading to metallic behavior. Comparison between valence band spectra near the Fermi level and the densities of states calculated using density functional theory (DFT) suggests the presence of coherent and incoherent states and points to strong electron correlation effects. Here, the magnetic susceptibility can be described by Pauli paramagnetism at temperatures above 100 K, but reveals antiferromagnetic behavior at lower temperatures, possibly resulting from orbital ordering.

  15. Growth of (Er,Yb):YAl{sub 3}(BO{sub 3}){sub 4} laser crystals

    SciTech Connect

    Pilipenko, O. V. Mal'tsev, V. V.; Koporulina, E. V.; Leonyuk, N. I.; Tolstik, N. A.; Kuleshov, N. V.


    (Er,Yb):YAl{sub 3}(BO{sub 3}){sub 4} single crystals of optical quality, up to 15 x 10 x 10 mm{sup 3} in size, have been grown from a (Er{sub 0.023}Yb{sub 0.116}Y{sub 0.862})Al{sub 3}(BO{sub 3}){sub 4} solution in a Y{sub 2}O{sub 3}-B{sub 2}O{sub 3}-K{sub 2}Mo{sub 3}O{sub 10} melt. The initial borate concentration was 17 wt %, and the flux cooling rate increased from 0.08 to 0.12 deg. C/h in the range 1060-1000 deg. C. The physical properties of the single crystals grown are good enough that they can be used as laser elements in systems with diode pumping and radiation near 1.5 {mu}m.

  16. On the magnetic order of Gd5Ge3sub>

    SciTech Connect

    Cadogan, J M; Ryan, D H; Mudryk, Ya.; Pecharsky, V K; Gschneidner, K A


    We have investigated the magnetic structure of Gd5Ge3sub> by neutron powder diffraction down to 3.6 K. This compound presents three events in the heat capacity which we show are related to fundamental changes in the magnetic order. The primary antiferromagnetic ordering occurs at 82(2) K and produces a magnetic cell that is tripled with respect to the underlying orthorhombic crystal cell. The propagation vector is k1=[00⅓] . At 74(2) K, the magnetic order becomes “anti-C” with a propagation vector k2 = [1 0 0]. A third change in the magnetic order occurs at 40(2) K, and the new magnetic structure is essentially the “anti-C” structure but with the addition of a tripled magnetic component corresponding to a propagation vector k3sub> = [⅓ 0 0] .

  17. Electronic and magnetic properties of Si substituted Fe3sub>Ge

    SciTech Connect

    Shanavas, Kavungal Veedu; McGuire, Michael A.; Parker, David S.


    Using first principles calculations we studied the effect of Si substitution in the hexagonal Fe3sub>Ge. We find the low temperature magnetic anisotropy in this system to be planar and originating mostly from the spin-orbit coupling in Fe-d states. Reduction of the unitcell volume reduces the in-plane magnetic anisotropy, eventually turning it positive which reorients the magnetic moments to the axial direction. We find that substituting Ge with the smaller Si ions also reduces the anisotropy, potentially enhancing the region of stability of the axial magnetization, which is beneficial for magnetic applications. Thus our experimental measurements on samples of Fe3sub>Ge1–xSix confirm these predictions and show that substitution of about 6% of the Ge with Si increases by approximately 35 K the temperature range over which anisotropy is uniaxial.

  18. Integrated Data Collection Analysis (IDCA) Program - NaClO3sub>/Icing Sugar

    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 NaClO3sub> and icing sugar—NaClO3sub>/icing sugar mixture. The mixture was found to: be more sensitive than RDX but less sensitive than PETN in impact testing (180-grit sandpaper); be more sensitive than RDX and about the same sensitivity as PETN in BAM fiction testing; be less sensitive than RDX and PETN except for one participant found the mixture more sensitive than PETN in ABL ESD testing; and to have one to three exothermic features with the lowest temperature event occurring at ~ 160°C always observed in thermal testing. Variations in testing parameters also affected the sensitivity.

  19. The unusual magnetism of nanoparticle LaCoO3sub>

    SciTech Connect

    Durand, A. M.; Belanger, D. P.; Hamil, T. J.; Ye, F.; Chi, S.; Fernandez-Baca, J. A.; Booth, C. H.; Abdollahian, Y.; Bhat, M.


    Bulk and nanoparticle powders of LaCoO3sub> (LCO) were synthesized and their magnetic and structural properties were studied using SQUID magnetometry and neutron diffraction. The bulk and large nanoparticles exhibit weak ferromagnetism (FM) below T≈85K and a crossover from strong to weak antiferromagnetic (AFM) correlations near a transition expressed in the lattice parameters, To ≈ 40 K. This crossover does not occur in the smallest nanoparticles; instead, the magnetic behavior is predominantly ferromagnetic. The amount of FM in the nanoparticles depends on the amount of Co3sub>O4 impurity phase, which induces tensile strain on the LCO lattice. A core-interface model is introduced, with the core region exhibiting the AFM crossover and with FM in the interface region near surfaces and impurity phases.

  20. Integrated Data Collection Analysis (IDCA) Program - KClO3sub>/Dodecane Mixture

    SciTech Connect

    Sandstrom, Mary M.; Brown, Geoffrey W.; Preston, Daniel N.; Pollard, Colin J.; Warner, Kirstin F.; Sorenson, Daniel N.; Remmers, Daniel L.; Shelley, Timothy J.; Whinnery, LeRoy L.; 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 KClO3sub> and dodecane—KClO3sub>/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 more sensitive to impact than RDX, and PETN, 2) less sensitive to friction than PETN, and 3) less sensitive to spark than RDX. The thermal analysis showed little or no exothermic features suggesting that the dodecane volatilized at low temperatures. A prominent endothermic feature was observed assigned to melting of KClO3sub>. 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 KClO3sub>/dodecane mixture are Lawrence Livermore National Laboratory (LLNL), Los Alamos National Laboratory (LANL), and Indian Head Division, Naval Surface Warfare Center, (NSWC IHD). These tests are conducted as a proficiency study in order to establish some consistency in test protocols, procedures, and experiments and to understand

  1. Plentiful magnetic moments in oxygen deficient SrTiO3sub>.

    SciTech Connect

    Lopez Bezanilla, Alejandro; Ganesh, P.; Littlewood, Peter B.


    Correlated band theory is employed to investigate the magnetic and electronic properties of different arrangements of oxygen di- and tri-vacancy clusters in SrTiO3sub>. Hole and electron doping of oxygen deficient SrTiO3sub> yields various degrees of magnetization as a result of the interaction between localized magnetic moments at the defected sites. Different kinds of Ti atomic orbital hybridization are described as a function of the doping level and defect geometry. We find that magnetism in SrTiO3sub>-d is sensitive to the arrangement of neighbouring vacancy sites, charge carrier density, and vacancy-vacancy interaction. Permanent magnetic moments in the absence of vacancy doping electrons are observed. Our description of the charged clusters of oxygen vacancies widens the previous descriptions of mono and multi-vacancies and points out the importance of the controlled formation at the atomic level of defects for the realization of transition metal oxide based devices with a desirable magnetic performance.

  2. Superconductivity in strong spin orbital coupling compound Sb2Se3sub>

    SciTech Connect

    Kong, P. P.; Sun, F.; Xing, L. Y.; Zhu, J.; Zhang, S. J.; Li, W. M.; Liu, Q. Q.; Wang, X. C.; Feng, S. M.; Yu, X. H.; Zhu, J. L.; Yu, R. C.; Yang, W. G.; Shen, G. Y.; Zhao, Y. S.; Ahuja, R.; Mao, H. K.; Jin, C. Q.


    Recently, A2B3sub> type strong spin orbital coupling compounds such as Bi2Te3sub>, Bi2Se3sub> and Sb2Te3sub> were theoretically predicated to be topological insulators and demonstrated through experimental efforts. The counterpart compound Sb2Se3sub> on the other hand was found to be topological trivial, but theoretical studies indicated that the pressure might induce Sb2Se3sub> into a topological nontrivial state. We report on the discovery of superconductivity in Sb2Se3sub> single crystal induced via pressure. Our experiments indicated that Sb2Se3sub> became superconductive at high pressures above 10 GPa proceeded by a pressure induced insulator to metal like transition at ~3 GPa which should be related to the topological quantum transition. The superconducting transition temperature (TC) increased to around 8.0 K with pressure up to 40 GPa while it keeps ambient structure. As a result, high pressure Raman revealed that new modes appeared around 10 GPa and 20 GPa, respectively, which correspond to occurrence of superconductivity and to the change of TC slop as the function of high pressure in conjunction with the evolutions of structural parameters at high pressures.

  3. Magnetism and Raman spectroscopy of the dimeric lanthanide iodates Ln(IO{sub 3}){sub 3} (Ln=Gd, Er) and magnetism of Yb(IO{sub 3}){sub 3}

    SciTech Connect

    Sykora, Richard E. Khalifah, Peter; Assefa, Zerihun; Albrecht-Schmitt, Thomas E.; Haire, Richard G.


    Colorless single crystals of Gd(IO{sub 3}){sub 3} or pale pink single crystals of Er(IO{sub 3}){sub 3} have been formed from the reaction of Gd metal with H{sub 5}IO{sub 6} or Er metal with H{sub 5}IO{sub 6} under hydrothermal reaction conditions at 180 deg. C. The structures of both materials adopt the Bi(IO{sub 3}){sub 3} structure type. Crystallographic data are (MoK{alpha}, {lambda}=0.71073 A): Gd(IO{sub 3}){sub 3}, monoclinic, space group P2{sub 1}/n, a=8.7615(3) A, b=5.9081(2) A, c=15.1232(6) A, {beta}=96.980(1){sup o}, V=777.03(5) Z=4, R(F)=1.68% for 119 parameters with 1930 reflections with I>2{sigma}(I); Er(IO{sub 3}){sub 3}, monoclinic, space group P2{sub 1}/n, a=8.6885(7) A, b=5.9538(5) A, c=14.9664(12) A, {beta}=97.054(1){sup o}, V=768.4(1) Z=4, R(F)=2.26% for 119 parameters with 1894 reflections with I>2{sigma}(I). In addition to structural studies, Gd(IO{sub 3}){sub 3}, Er(IO{sub 3}){sub 3}, and the isostructural Yb(IO{sub 3}){sub 3} were also characterized by Raman spectroscopy and magnetic property measurements. The results of the Raman studies indicated that the vibrational profiles are adequately sensitive to distinguish between the structures of the iodates reported here and other lanthanide iodate systems. The magnetic measurements indicate that only in Gd(IO{sub 3}){sub 3} did the 3+ lanthanide ion exhibit its full 7.9 {mu}{sub B} Hund's rule moment; Er{sup 3+} and Yb{sup 3+} exhibited ground state moments and gap energy scales of 8.3 {mu}{sub B}/70 K and 3.8 {mu}{sub B}/160 K, respectively. Er(IO{sub 3}){sub 3} exhibited extremely weak ferromagnetic correlations (+0.4 K), while the magnetic ions in Gd(IO{sub 3}){sub 3} and Yb(IO{sub 3}){sub 3} were fully non-interacting within the resolution of our measurements ({approx}0.2 K). - Graphical abstract: Three f-element iodates Ln(IO{sub 3}){sub 3} (Ln=Gd, Er, Yb), all containing the Bi(IO{sub 3}){sub 3} structure type, were characterized by Raman spectroscopy and magnetic property measurements

  4. Visible Light Assisted Photocatalytic Hydrogen Generation by Ta2O5/Bi2O3sub>, TaON/Bi2O3sub>, and Ta3sub>N5/Bi2O3sub> Composites

    SciTech Connect

    Adhikari, Shiba; Hood, Zachary D.; More, Karren Leslie; Ivanov, Ilia N.; Zhang, Lifeng; Gross, Michael; Lachgar, Abdou


    Composites comprised of two semiconducting materials with suitable band gaps and band positions have been reported to be effective at enhancing photocatalytic activity in the visible light region of the electromagnetic spectrum. Here, we report the synthesis, complete structural and physical characterizations, and photocatalytic performance of a series of semiconducting oxide composites. UV light active tantalum oxide (Ta2O5) and visible light active tantalum oxynitride (TaON) and tantalum nitride (Ta3sub>N5) were synthesized, and their composites with Bi2O3sub> were prepared in situ using benzyl alcohol as solvent. The composite prepared using equimolar amounts of Bi2O3sub> and Ta2O5 leads to the formation of the ternary oxide, bismuth tantalate (BiTaO4) upon calcination at 1000 °C. The composites and single phase bismuth tantalate formed were characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) surface area measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–Vis diffuse reflectance spectroscopy, and photoluminescence. The photocatalytic activities of the catalysts were evaluated for generation of hydrogen using aqueous methanol solution under visible light irradiation (λ ≥ 420 nm). The results show that as-prepared composite photocatalysts extend the light absorption range and restrict photogenerated charge-carrier recombination, resulting in enhanced photocatalytic activity compared to individual phases. The mechanism for the enhanced photocatalytic activity for the heterostructured composites is elucidated based on observed activity, band positions calculations, and photoluminescence data.

  5. Ultrafast Magnetization Dynamics of SrRuO3 sub>Thin Films

    SciTech Connect

    Langner, Matthew C.


    Itinerant ferromagnet SrRuO3sub> has drawn interest from physicists due to its unusual transport and magnetic properties as well as from engineers due to its low resistivity and good lattice-matching to other oxide materials. The exact electronic structure remains a mystery, as well as details of the interactions between magnetic and electron transport properties. This thesis describes the use of time-resolved magneto-optical Kerr spectroscopy to study the ferromagnetic resonance of SrRuO3sub> thin films, where the ferromagnetic resonance is initiated by a sudden change in the easy axis direction in response to a pump pulse. The rotation of the easy axis is induced by laser heating, taking advantage of a temperature-dependent easy axis direction in SrRuO3sub> thin films. By measuring the change in temperature of the magnetic system in response to the laser pulse, we find that the specific heat is dominated by magnons up to unusually high temperature, ~100 K, and thermal diffusion is limited by a boundary resistance between the film and the substrate that is not consistent with standard phonon reflection and scattering models. We observe a high FMR frequency, 250 GHz, and large Gilbert damping parameter, α ≈1, consistent with strong spin-orbit coupling. We observe a time-dependent change in the easy axis direction on a ps time-scale, and we find that parameters associated with the change in easy axis, as well as the damping parameter, have a non-monotonic temperature dependence similar to that observed in anomalous Hall measurements.

  6. Pressure-induced phase transitions in acentric BaHf(BO{sub 3}){sub 2}

    SciTech Connect

    Mączka, Mirosław; Szymborska-Małek, Katarzyna; Sousa Pinheiro, Gardenia de; Cavalcante Freire, Paulo Tarso; Majchrowski, Andrzej


    High-pressure Raman scattering studies revealed that BaHf(BO{sub 3}){sub 2} is more compressible than calcite-type orthoborates and calcite, aragonite or dolomite carbonates. It undergoes a first-order reversible pressure-induced phase transition in the 3.9–4.4 GPa pressure range. Second structural change is observed at 9.2 GPa. The intermediate phase is most likely trigonal. However, Raman results suggest increase in the number of distinct BO{sub 3} groups from two in the ambient pressure phase to at least three in the intermediate phase. This intermediate phase is also strongly compressible and strong pressure dependence of the lattice modes proves that the main changes under pressure occur within the layers built from BaO{sub 6} and HfO{sub 6} octahedra. The second phase transition leads most likely to lowering of the trigonal symmetry, as evidenced by significant increase of the number of observed bands. The pressure coefficients of the Raman bands of the high-pressure phase are relatively small, suggesting more dense arrangement of the metal–oxygen polyhedra and BO{sub 3} groups in this phase. It is worth noting that the high-pressure phase was not reached in the second compression experiment up to 10 GPa. This behavior can be most likely attributed to worse hydrostatic conditions of the first experiment. - Graphical abstract: Raman spectra of BaHf(BO{sub 3}){sub 2} recorded at different pressures during compression showing onset of pressure-induced phase transitions. - Highlights: • High-pressure Raman spectra were measured for BaHf(BO{sub 3}){sub 2.} • BaHf(BO{sub 3}){sub 2} undergoes a reversible first-order phase transition at 3.9–4.4 GPa into a trigonal phase. • The intermediate trigonal phase is strongly compressible second structural transformation is observed at 9.2 GPa under non-perfect hydrostatic conditions.

  7. YCa{sub 4}O(BO{sub 3}){sub 3} (YCOB) high temperature vibration sensor

    SciTech Connect

    Kim, Kyungrim; Huang Wenbin; Jiang Xiaoning; Zhang Shujun; Yu Fapeng


    A shear-mode piezoelectric accelerometer using YCa{sub 4}O(BO{sub 3}){sub 3} (YCOB) single crystal was designed, fabricated and successfully tested for high temperature vibration sensing applications. The prototyped sensor was tested at temperatures ranging from room temperature to 1000 deg. C and at frequencies ranging from 80 Hz to 1 kHz. The sensitivity of the sensor was found to be 5.7 pC/g throughout the tested frequency and temperature range. In addition, YCOB piezoelectric accelerometers remained the same sensitivity at 1000 deg. C for a dwell time of four hours, exhibiting high stability and reliability.

  8. Improved Electrochemical Performance of Carbon-Coated LiFeBO3sub> Nanoparticles for Lithium-Ion Batteries

    SciTech Connect

    Li, Zhaoping; Wang, Yiping; Hu, Querui; Yang, Ying; Wu, Zhuangchun; Ban, Chunmei


    Carbon-coated LiFeBO3 sub>nanoparticles have been successfully prepared by surfactant-assisted ball milling and a size selection process based on centrifugal separation. We observed monodispersed LiFeBO3sub> nanoparticles with dimensions of 10–20 nm by transmission electron microscope. The introduced surfactant acts as the dispersant as well as the carbon source for LiFeBO3sub> nanoparticles. Greatly improved discharge capacities of 190.4 mA h g–1 at 0.1 C and 106.6 mA h g–1 at 1 C rate have been achieved in the LiFeBO3sub> nanoparticles when cycling the cells between 1.0 V and 4.8 V. Meanwhile, the as-prepared micro-size LiFeBO3sub> electrodes show lower discharge capacities of 142 mA h g–1 and 93.3 mA h g–1 at 0.1 C and 1 C rates. Moreover, the post-treated LiFeBO3sub> nanostructure has drastically enhanced the electrochemical performance due to the short diffusion length and ameliorated electrical contract between LiFeBO3sub> nano particles.

  9. Synthesis, characterization and optical properties of NH{sub 4}Dy(PO{sub 3}){sub 4}

    SciTech Connect

    Chemingui, S.; Ferhi, M. Horchani-Naifer, K.; Férid, M.


    Polycrystalline powders of NH{sub 4}Dy(PO{sub 3}){sub 4} polyphosphate have been grown by the flux method. This compound was found to be isotopic with NH{sub 4}Ce(PO{sub 3}){sub 4} and RbHo(PO{sub 3}){sub 4}. It crystallizes in the monoclinic space group P2{sub 1/n} with unit cell parameters a=10.474(6) Å, b=9.011(4) Å, c=10.947(7) Å and β=106.64(3)°. The title compound has been transformed to triphosphate Dy(PO{sub 3}){sub 3} after calcination at 800 °C. Powder X-ray diffraction, infrared and Raman spectroscopies and the differential thermal analysis have been used to identify these materials. The spectroscopic properties have been investigated through absorption, excitation, emission spectra and decay curves of Dy{sup 3+} ion in both compounds at room temperature. The emission spectra show the characteristic emission bands of Dy{sup 3+} in the two compounds, before and after calcination. The integrated emission intensity ratios of the yellow to blue (I{sub Y}/I{sub B}) transitions and the chromaticity properties have been determined from emission spectra. The decay curves are found to be double-exponential. The non-exponential behavior of the decay rates was related to the resonant energy transfer as well as cross-relaxation between the donor and acceptor Dy{sup 3+} ions. The determined properties have been discussed as function of crystal structure of both compounds. They reveal that NH{sub 4}Dy(PO{sub 3}){sub 4} is promising for white light generation but Dy(PO{sub 3}){sub 3} is potential candidates in field emission display (FED) and plasma display panel (PDP) devices. - Graphical abstract: The CIE color coordinate diagrams showing the chromatic coordinates of Dy{sup 3+} luminescence in NH{sub 4}Dy(PO{sub 3}){sub 4} and Dy(PO{sub 3}){sub 3}. - Highlights: • The polycrystalline powders of NH{sub 4}Dy(PO{sub 3}){sub 4} and Dy(PO{sub 3}){sub 3} are synthesized. • The obtained powders are characterized. • The spectroscopic properties of Dy{sup 3+} ion

  10. Results from the first single cell Nb3sub>Sn cavity coatings at JLab

    SciTech Connect

    Eremeev, Grigory


    Nb3sub>Sn is a promising superconducting material for SRF applications and has the potential to exceed the limitations of niobium. We have used the recently commissioned Nb3sub>Sn coating system to investigate Nb3sub>Sn coatings on several single cell cavities by applying the same coating procedure on several different single cells with different history and pre-coating surface preparation. We report on our findings with four 1.5 GHz CEBAF-shape single cell and one 1.3 GHz ILC-shape single cavities that were coated, inspected, and tested.

  11. Coexistence of Weak Ferromagnetism and Polar Lattice Distortion in Epitaxial NiTiO3sub> thin films of the LiNbO3sub>-Type Structure

    SciTech Connect

    Varga, Tamas; Droubay, Timothy C.; Bowden, Mark E.; Colby, Robert J.; Manandhar, Sandeep; Shutthanandan, Vaithiyalingam; Hu, Dehong; Kabius, Bernd C.; Apra, Edoardo; Shelton, William A.; Chambers, Scott A.


    We report the magnetic and structural characteristics of epitaxial NiTiO3sub> films grown by pulsed laser deposition that are isostructural with acentric LiNbO3sub> (space group R3c). Optical second harmonic generation and magnetometry demonstrate lattice polarization at room temperature and weak ferromagnetism below 250 K, respectively. These results appear to be consistent with earlier predictions from first-principles calculations of the coexistence of ferroelectricity and weak ferromagnetism in a series of transition metal titanates crystallizing in the LiNbO3 sub>structure. This acentric form of NiTiO3sub> is believed to be one of the rare examples of ferroelectrics exhibiting weak ferromagnetism generated by a Dzyaloshinskii-Moriya interaction.

  12. Brønsted acid-base reactions with anhydrous sulfamates as a pathway to [SO3sub>N]3--containing compounds: Preparation of Li3sub>SO3sub>N

    SciTech Connect

    Kurzman, Joshua A.; Jouan, Gauthier; Courty, Matthieu; Palacín, M. Rosa; Armand, Michel; Recham, Nadir


    Li3sub>SO3sub>N has been prepared by the mechanochemical reaction between lithium sulfamate (LiSO3sub>NH2) and lithium amide or lithium hydride. This is the first example of an anhydrous compound containing the rare [SO3sub>N]3- polyanion. Li3sub>SO3sub>N adopts the low-temperature Pmn21β structure of isoelectronic Li3sub>PO4. Structural refinement from neutron powder diffraction data supports disordering of nitrogen over two of the three anion sites, although a fully disordered model cannot be conclusively refuted. While the compound is a poor ionic conductor, it is electrochemically stable to at least 5 V vs. Li+/Li0. This simple mechanochemical pathway should be suitable for preparing a host of other alkali-rich nitrogen-containing polyanionic compounds.

  13. Growth of (Er,Yb):YAl{sub 3}(BO{sub 3}){sub 4} laser crystals

    SciTech Connect

    Pilipenko, O. V. Mal'tsev, V. V.; Koporulina, E. V.; Leonyuk, N. I.; Tolstik, N. A.; Kuleshov, N. V.


    (Er,Yb):YAl{sub 3}(BO{sub 3}){sub 4} single crystals of optical quality, up to 15 Multiplication-Sign 10 Multiplication-Sign 10 mm{sup 3} in size, have been grown from a (Er{sub 0.023}Yb{sub 0.116}Y{sub 0.862})Al{sub 3}(BO{sub 3}){sub 4} solution in a Y{sub 2}O{sub 3}-B{sub 2}O{sub 3}-K{sub 2}Mo{sub 3}O{sub 10} melt. The initial borate concentration was 17 wt %, and the flux cooling rate increased from 0.08 to 0.12 Degree-Sign C/h in the range 1060-1000 Degree-Sign C. The physical properties of the single crystals grown are good enough that they can be used as laser elements in systems with diode pumping and radiation near 1.5 {mu}m.

  14. Synthesis and identification of the monocation Tc(CPI) sub 6 sup + in Tc(CNC(CH sub 3 ) sub 2 COOCH sub 3 ) sub 6 Cl and its hydrolysis products. [Tc(CNC(CH sub 3 ) sub 2 COOCH sub 3 ) sub 6 Cl and monocation Tc(CPI) sub 6 sup +

    SciTech Connect

    Kronauge, J.F.; Davison, A.; Roseberry, A.M.; Costello, C.E.; Maleknia, S. ); Jones, A.G. )


    The complex Tc(CNC(CH{sub 3}){sub 2}COOCH{sub 3}){sub 6}Cl (cation designated as Tc(CPI){sub 6}{sup +}) is one of a series of isonitrile-coordinated technetium complexes being investigated as a prototype radiopharmaceutical to evaluate myocardial perfusion. It has been prepared from the pertechnetate ion by aqueous Na{sub 2}S{sub 2}O{sub 4} reduction in the presence of the functionalized isocyanide ligand. The octahedral compound with its relatively reactive ester substituents is stable under aqueous aerobic conditions within the pH range 5-7. At high pH, however, the ester moieties undergo random, base-catalyzed hydrolysis while the six ligands remain coordinated in a fixed geometry to the central metal. The nine predicted carboxylic acid containing species were separated and identified by RP-HPLC, FAB-MS, IR, and {sup 99}Tc NMR methods. Specific k' values obtained from the RP-HPLC of these characterized compounds were used to identify technetium containing metabolites of the radiopharmaceutical. Varying rates of in vitro enzymatic hydrolysis at the terminal ester moieties of the coordinated ligands were shown to occur when this compound was incubated with blood serum from different animal species.

  15. Strong spin-lattice coupling in CrSiTe3sub>

    SciTech Connect

    Casto, L. D.; Clune, A. J.; Yokosuk, M. O.; Musfeldt, J. L.; Williams, T. J.; Zhuang, H. L.; Lin, M. -W.; Xiao, K.; Hennig, R. G.; Sales, B. C.; Yan, J. -Q.; Mandrus, D.


    CrSiTe3sub> has attracted recent interest as a candidate single-layer ferromagnetic semiconductor, but relatively little is known about the bulk properties of this material. Here, we report single-crystal X-ray diffraction, magnetic properties, thermal conductivity, vibrational, and optical spectroscopies and compare our findings with complementary electronic structure and lattice dynamics principles calculations. The high temperature paramagnetic phase is characterized by strong spin-lattice interactions that give rise to glassy behavior, negative thermal expansion, and an optical response that reveals that CrSiTe3sub> is an indirect gap semiconductor with indirect and direct band gaps at 0.4 and 1.2 eV, respectively. Measurements of the phonons across the 33 K ferromagnetic transition provide additional evidence for strong coupling between the magnetic and lattice degrees of freedom. In conclusion, the Si-Te stretching and Te displacement modes are sensitive to the magnetic ordering transition, a finding that we discuss in terms of the superexchange mechanism. Lastly, spin-lattice coupling constants are also extracted.

  16. An in-situ phosphorus source for the synthesis of Cu3sub>P and the subsequent conversion to Cu3sub>PS4 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 (Cu3sub>P) and copper thiophosphate (Cu3sub>PS4). Herein, we report a one-pot, solution-based synthesis of Cu3sub>P 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 Cu3sub>P nanocrystals with a phosphorous-rich surface are synthesized. The subsequent reaction of the Cu3sub>P nanocrystals with decomposing thiourea forms nanoscale Cu3sub>PS4 particles having p-type conductivity and an effective optical band gap of 2.36 eV.

  17. Nuclear and magnetic supercells in the multiferroic candidate: Pb3sub>TeMn3sub>P2O14

    SciTech Connect

    Silverstein, Harlyn J.; Huq, Ashfia; Lee, Minseong; Choi, Eun Sang; Zhou, Haidong; Wiebe, Christopher R.


    Here we report that the dugganites, Te6+-containing members of the langasite series, have attracted recent interest due to their complex low-temperature magnetic unit cells, magnetodielectric, and potentially multiferroic properties. For Pb2+-containing dugganites, a large monoclinic supercell was reported and was found to have a profound effect on the low temperature magnetism and spin excitation spectra. Pb3sub>TeMn3sub>P2O14 is another dugganite previously shown to distort away from the canonical P321 langasite unit cell, although this supercell was never fully solved. We report the full crystal and magnetic structure solution of Pb3sub>TeMn3sub>P2O14 using synchrotron x-ray and neutron diffraction data: a large trigonal supercell is observed in this material, which is believed to be the first supercell of its kind in the langasite family. Here, the magnetic structure, high-magnetic field behavior, and dielectric properties of Pb3sub>TeMn3sub>P2O14 are presented. In addition to showing weak magnetoelectric behavior similar to other langasites, it was found that a phase transition occurs at 3 T near the antiferromagnetic transition temperature.

  18. Crystal and molecular structure of the coordination compounds of Er{sup 3+} with 1-(methoxydiphenylphosphoryl)-2-diphenylphosphorylbenzene [ErL{sub 2}{sup 1}(NO{sub 3}){sub 2}]{sub 2}[Er(NO{sub 3}){sub 2}(H{sub 2}O){sub 5}]{sub 0.333}(NO{sub 3}){sub 2.333} · 2.833H{sub 2}O and its ethyl substituted derivative [ErL{sub 2}{sup 2}(NO{sub 3}){sub 2}][Er(NO{sub 3}){sub 5}]{sub 0.5} · 0.5H{sub 2}O

    SciTech Connect

    Polyakova, I. N.; Baulin, V. E.; Ivanova, I. S.; Pyatova, E. N.; Sergienko, V. S.; Tsivadze, A. Yu.


    The coordination compounds of Er{sup 3+} with 1-(methoxydiphenylphosphoryl)-2-diphenylphosphorylbenzene [ErL{sub 2}{sup 1}(NO{sub 3}){sub 2}]{sub 2}[Er(NO{sub 3}){sub 2}(H{sub 2}O){sub 5}]{sub 0.333}(NO{sub 3}){sub 2.333} · 2.833H{sub 2}O (I) and its ethyl substituted derivative [ErL{sub 2}{sup 2}(NO{sub 3}){sub 2}][Er(NO{sub 3}){sub 5}]{sub 0.5} · 0.5H{sub 2}O (II) are synthesized and their crystal structures are studied. I and II contain [ErL{sub 2}(NO{sub 3}){sub 2}]{sup +} complex cations of identical composition and close structure. The eight-vertex polyhedron of the Er atom in the shape of a distorted octahedron with two split trans vertices is formed by the O atoms of the phosphoryl groups of L ligands and nitrate anions. L ligands close nine-membered metallocycles. The structures contain spacious channels which are populated differently, namely, by disordered [Er(NO{sub 3}){sub 2}(H{sub 2}O){sub 5}]{sup +} complex cations, NO{sub 3}{sup −} anions, and crystallization water molecules in I and disordered [Er(NO{sub 3}){sub 5}]{sup 2−} complex anions and crystallization water molecules in II. The IR spectra of I and II are studied.

  19. Caffeine increases striatal dopamine D2/D3sub> receptor availability in the human brain

    SciTech Connect

    Volkow, N. D.; Wang, G. -J.; Logan, J.; Alexoff, D.; Fowler, J. S.; Thanos, P. K.; Wong, C.; Casado, V.; Ferre, S.; Tomasi, D.


    Caffeine, the most widely consumed psychoactive substance in the world, is used to promote wakefulness and enhance alertness. Like other wake-promoting drugs (stimulants and modafinil), caffeine enhances dopamine (DA) signaling in the brain, which it does predominantly by antagonizing adenosine A2A receptors (A2AR). However, it is unclear if caffeine, at the doses consumed by humans, increases DA release or whether it modulates the functions of postsynaptic DA receptors through its interaction with adenosine receptors, which modulate them. We used positron emission tomography and [11C]raclopride (DA D2/D3sub> receptor radioligand sensitive to endogenous DA) to assess if caffeine increased DA release in striatum in 20 healthy controls. Caffeine (300mg p.o.) significantly increased the availability of D2/D3sub> receptors in putamen and ventral striatum, but not in caudate, when compared with placebo. In addition, caffeine-induced increases in D2/D3sub> receptor availability in the ventral striatum were associated with caffeine-induced increases in alertness. Our findings indicate that in the human brain, caffeine, at doses typically consumed, increases the availability of DA D2/D3sub> receptors, which indicates that caffeine does not increase DA in the striatum for this would have decreased D2/D3sub> receptor availability. Instead, we interpret our findings to reflect an increase in D2/D3sub> receptor levels in striatum with caffeine (or changes in affinity). Furthermore, the association between increases in D2/D3sub> receptor availability in ventral striatum and alertness suggests that caffeine might enhance arousal, in part, by upregulating D2/D3sub> receptors.

  20. Structural phase transitions in Bi2Se3sub> under high pressure

    SciTech Connect

    Yu, Zhenhai; Gu, Genda; Wang, Lin; Hu, Qingyang; Zhao, Jinggeng; Yan, Shuai; Yang, Ke; Sinogeikin, Stanislav; Mao, Ho -kwang


    Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3sub>) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3sub> crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint that the I4/mmm phase Bi2Se3sub> can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3sub> from this work (two independent runs) are still Raman active up to ~35 GPa. Furthermore, it is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3sub> may explain why Bi2Se3sub> shows different structural behavior than isocompounds Bi2Te3sub> and Sb2Te3sub>.

  1. Ultrathin nanosheets of CrSiTe3sub>. A semiconducting two-dimensional ferromagnetic material

    SciTech Connect

    Lin, Ming -Wei; Zhung, Houlong L.; Yan, Jiaqiang; Ward, Thomas Zac; Puretzky, Alexander A.; Rouleau, Christopher M.; Gai, Zheng; Liang, Liangbo; Meunier, Vincent; Ganesh, Panchapakesan; Kent, Paul R. C.; Sumpter, Bobby G.; Mandrus, David G.; Geohegan, David B.; Xiao, Kai


    Finite range ferromagnetism and antiferromagnetism in two-dimensional (2D) systems within an isotropic Heisenberg model at non-zero temperature were originally proposed to be impossible. However, recent theoretical studies using an Ising model have recently shown that 2D magnetic crystals can exhibit magnetism. Experimental verification of existing 2D magnetic crystals in this system has remained elusive. In this work we for the first time exfoliate the CrSiTe3sub>, a bulk ferromagnetic semiconductor, to mono- and few-layer 2D crystals onto a Si/SiO2 substrate. The Raman spectra show the good stability and high quality of the exfoliated flakes, consistent with the computed phonon spectra of 2D CrSiTe3sub>, giving a strong evidence for the existence of 2D CrSiTe3sub> crystals. When the thickness of the CrSiTe3sub> crystals is reduced to few-layers, we observed a clear change in resistivity at 80~120 K, consistent with the theoretical calculations on the Curie temperature (Tc) of ~80 K for the magnetic ordering of 2D CrSiTe3sub> crystals. As a result, the ferromagnetic mono- and few-layer 2D CrSiTe3sub> indicated here should enable numerous applications in nano-spintronics.

  2. The signaling phospholipid PIP3sub> creates a new interaction surface on the nuclear receptor SF-1

    SciTech Connect

    Blind, Raymond D.; Sablin, Elena P.; Kuchenbecker, Kristopher M.; Chiu, Hsiu-Ju; Deacon, Ashley M.; Das, Debanu; Fletterick, Robert J.; Ingraham, Holly A.


    We previously reported that lipids PI(4,5)P2 (PIP2) and PI(3,4,5)P3sub> (PIP3sub>) bind NR5A nuclear receptors to regulate their activity. Here, the crystal structures of PIP2 and PIP3sub> bound to NR5A1 (SF-1) define a new interaction surface that is organized by the solvent-exposed PIPn headgroups. We find that stabilization by the PIP3sub> ligand propagates a signal that increases coactivator recruitment to SF-1, consistent with our earlier work showing that PIP3sub> increases SF-1 activity. This newly created surface harbors a cluster of human mutations that lead to endocrine disorders, thus explaining how these puzzling mutations cripple SF-1 activity. Finally, we propose that this new surface acts as a PIP3sub>-regulated interface between SF-1 and coregulatory proteins, analogous to the function of membrane-bound phosphoinositides.

  3. Syntheses, structures, and vibrational spectroscopy of the two-dimensional iodates Ln(IO{sub 3}){sub 3} and Ln(IO{sub 3}){sub 3}(H{sub 2}O) (Ln =Yb, Lu)

    SciTech Connect

    Assefa, Zerihun . E-mail:; Ling Jie; Haire, Richard G.; Albrecht-Schmitt, Thomas E.; Sykora, Richard E. . E-mail:


    The reaction of Lu{sup 3+} or Yb{sup 3+} and H{sub 5}IO{sub 6} in aqueous media at 180 {sup o}C leads to the formation of Yb(IO{sub 3}){sub 3}(H{sub 2}O) or Lu(IO{sub 3}){sub 3}(H{sub 2}O), respectively, while the reaction of Yb metal with H{sub 5}IO{sub 6} under similar reaction conditions gives rise to the anhydrous iodate, Yb(IO{sub 3}){sub 3}. Under supercritical conditions Lu{sup 3+} reacts with HIO{sub 3} and KIO{sub 4} to yield the isostructural Lu(IO{sub 3}){sub 3}. The structures have been determined by single-crystal X-ray diffraction. Crystallographic data are (MoK{alpha}, {lambda}=0.71073 A): Yb(IO{sub 3}){sub 3}, monoclinic, space group P2{sub 1}/n, a=8.6664(9) A, b=5.9904(6) A, c=14.8826(15) A, {beta}=96.931(2){sup o}, V=766.99(13), Z=4, R(F)=4.23% for 114 parameters with 1880 reflections with I>2{sigma}(I); Lu(IO{sub 3}){sub 3}, monoclinic, space group P2{sub 1}/n, a=8.6410(9), b=5.9961(6), c=14.8782(16) A, {beta}=97.028(2){sup o}, V=765.08(14), Z=4, R(F)=2.65% for 119 parameters with 1756 reflections with I>2{sigma}(I); Yb(IO{sub 3}){sub 3}(H{sub 2}O), monoclinic, space group C2/c, a=27.2476(15), b=5.6296(3), c=12.0157(7) A, {beta}=98.636(1){sup o}, V=1822.2(2), Z=8, R(F)=1.51% for 128 parameters with 2250 reflections with I>2{sigma}(I); Lu(IO{sub 3}){sub 3}(H{sub 2}O), monoclinic, space group C2/c, a=27.258(4), b=5.6251(7), c=12.0006(16) A, {beta}=98.704(2){sup o}, V=1818.8(4), Z=8, R(F)=1.98% for 128 parameters with 2242 reflections with I>2{sigma}(I). The f elements in all of the compounds are found in seven-coordinate environments and bridged with monodentate, bidentate, or tridentate iodate anions. Both Lu(IO{sub 3}){sub 3}(H and Yb(IO{sub 3}){sub 3}(H{sub 2}O) display distinctively different vibrational profiles from their respective anhydrous analogs. Hence, the Raman profile can be used as a complementary diagnostic tool to discern the different structural motifs of the compounds. - Graphical abstract: Four new metal iodates, Yb(IO{sub 3

  4. Synthesis and crystal structure of oxonitrate complexes Cs[VO{sub 2}(NO{sub 3}){sub 2}], Cs[MoO{sub 2}(NO{sub 3}){sub 3}], and MoO{sub 2}(NO{sub 3}){sub 2}

    SciTech Connect

    Morozov, I. V. Palamarchuk, D. M.; Kozlovsky, V. F.; Troyanov, S. I.


    Cs[VO{sub 2}(NO{sub 3}){sub 2}] (I), MoO{sub 2}(NO{sub 3}){sub 2} (II), and Cs[MoO{sub 2}(NO{sub 3}){sub 3}] (III) complexes have been obtained by crystallization from nitric solutions and studied by single-crystal X-ray diffraction. Complexes I and II contain infinite zigzag chains of similar compositions, [VO{sub 2}(NO{sub 3}){sub 2}]{sup -} and [MoO{sub 2}(NO{sub 3}){sub 2}], in which V and Mo atoms form, respectively, trigonal- and pentagonal-bipyramidal polyhedra. Each of these polyhedrons also contains one terminal and two bridge O atoms and two terminal NO{sub 3} groups which are monodentate and bidentate in complexes I and II, respectively. Complex III has an island structure and consists of Cs{sup +} cations and [MoO{sub 2}(NO{sub 3}){sub 3}]{sup -} anions, in which the Mo atom is surrounded by one bidentate NO{sub 3} group and two monodentate NO{sub 3} groups and two terminal O atoms in the cis-positions; oxygen atoms form a polyhedron in the form of distorted octahedron. According to the ab initio calculation of isolated MoO{sub 2}(NO{sub 3}){sub 2} molecules in the gas phase and solution, the coordination environment of the Mo atom, similarly to the Cr(VI) atom in CrO{sub 2}(NO{sub 3}){sub 2}, is formed by two bidentate nitrate groups and two terminal O atoms (polyhedron- twisted trigonal prism).

  5. New thallium iodates-Synthesis, characterization, and calculations of Tl(IO{sub 3}){sub 3} and Tl{sub 4}(IO{sub 3}){sub 6}, [Tl{sup +}{sub 3}Tl{sup 3+}(IO{sub 3}){sub 6}

    SciTech Connect

    Yeon, Jeongho; Kim, Sang-Hwan; Halasyamani, P. Shiv


    Two new thallium iodates have been synthesized, Tl(IO{sub 3}){sub 3} and Tl{sub 4}(IO{sub 3}){sub 6} [Tl{sup +}{sub 3}Tl{sup 3+}(IO{sub 3}){sub 6}], and characterized by single-crystal X-ray diffraction. Both materials were synthesized as phase-pure compounds through hydrothermal techniques using Tl{sub 2}CO{sub 3} and HIO{sub 3} as reagents. The materials crystallize in space groups R-3 (Tl(IO{sub 3}){sub 3}) and P-1 (Tl{sub 4}(IO{sub 3}){sub 6}). Although lone-pairs are observed for both I{sup 5+} and Tl{sup +}, electronic structure calculations indicate the lone-pair on I{sup 5+} is stereo-active, whereas the lone-pair on Tl{sup +} is inert. - Graphical abstract: Visualization of the stereo-active lone-pair (purple) through ELFs for Tl{sub 4}(IO{sub 3}){sub 6}. The spherical nature of the ELFs around the Tl{sup +} cation indicates the lone-pair is inert.

  6. MoO3sub> Films Spin-Coated from Nanoparticle Suspension for Efficient Hole-Injection in Organic Electronics

    SciTech Connect

    Meyer, Jens; Khalandovsky, Rebecca; Görrn, Patrick; Kahn, Antoine


    MoO3sub> films spin-coated from a suspension of nanoparticles, which offers energetic properties nearly identical to those of thermally evaporated MoO3sub> films, are reported. It is demonstrated that our solution-based MoO3sub> acts as a very efficient hole-injection layer for organic devices.

  7. Structure and optical properties of a noncentrosymmetric borate RbSr{sub 4}(BO{sub 3}){sub 3}

    SciTech Connect

    Xia, M.J.; Li, R.K.


    A new noncentrosymmetric borate, RbSr{sub 4}(BO{sub 3}){sub 3} (abbreviated as RSBO), has been grown from Rb{sub 2}O--B{sub 2}O{sub 3}--RbF flux and its crystal structure was determined by single crystal x-ray diffraction. It crystallizes in space group Ama2 with cell parameters of a=11.128(10) A, b=12.155(15) A, c=6.952(7) A, Z=4. The basic structural units are isolated planar BO{sub 3} groups. Second harmonic generation (SHG) test of the title compound by the Kurtz-Perry method shows that RSBO can be phase matchable with an effective SHG coefficient about two-thirds as large as that of KH{sub 2}PO{sub 4} (KDP). Finally, based on the anionic group approximation, the optical properties of the title compound are compared with those of the structure-related apatite-like compounds with the formula 'A{sub 5}(TO{sub n}){sub 3}X'. - Graphical abstract: RbSr{sub 4}(BO{sub 3}){sub 3} and some other borate NLO compounds, namely Ca{sub 5}(BO{sub 3}){sub 3}F RCa{sub 4}(BO{sub 3}){sub 3}O (R=Y or Gd) and Na{sub 3}La{sub 2}(BO{sub 3}){sub 3} can be viewed as the derivatives of apatite. They have similar formula composed of five cations and three anion groups (we call them 5/3 structures). The detailed SHG coefficients and optical properties of the apatite-like NLO crystals were compared and summarized. Highlights: Black-Right-Pointing-Pointer A new noncentrosymmetric borate RbSr{sub 4}(BO{sub 3}){sub 3} was grown from flux. Black-Right-Pointing-Pointer The RbSr{sub 4}(BO{sub 3}){sub 3} can be viewed as a derivative of the apatite-like structure. Black-Right-Pointing-Pointer The structure and its relationship to the optical properties of RbSr{sub 4}(BO{sub 3}){sub 3} are compared with other NLO crystals with apatite-like structures. Black-Right-Pointing-Pointer The basic structural units are the planar BO{sub 3} groups in the structure. Black-Right-Pointing-Pointer Second harmonic generation (SHG) test shows that RbSr{sub 4}(BO{sub 3}){sub 3} can be phase matchable with an

  8. Electrochemical Reduction of CO2 to CH3sub>OH at Copper Oxide Surfaces

    SciTech Connect

    Le, Minh; Ren, Maoming; Zhang, Ziyu; Sprunger, Phillip T.; Kurtz, Richard L.; Flake, John C.


    The direct reduction of CO2 to CH3sub>OH is known to occur at several types of electrocatalysts including oxidized Cu electrodes. In this work, we examine the yield behavior of an electrodeposited cuprous oxide thin film and explore relationships between surface chemistry and reaction behavior relative to air-oxidized and anodized Cu electrodes. CH3sub>OH yields (43 μmol cm-2 h-1) and Faradaic efficiencies (38%) observed at cuprous oxide electrodes were remarkably higher than air-oxidized or anodized Cu electrodes suggesting Cu(I) species may play a critical role in selectivity to CH3sub>OH. Experimental results also show CH3sub>OH yields are dynamic and the copper oxides are reduced to metallic Cu in a simultaneous process. Yield behavior is discussed in comparison with photoelectrochemical and hydrogenation reactions where the improved stability of Cu(I) species may allow continuous CH3sub>OH generation.

  9. Coupling of Crystal Structure and Magnetism in the Layered, Ferromagnetic Insulator CrI 3sub>

    SciTech Connect

    McGuire, Michael A.; Dixit, Hemant; Cooper, Valentino R.; Sales, Brian C.


    Here, we examine the crystallographic and magnetic properties of single crystals of CrI3sub>, an easily cleavable, layered and insulating ferromagnet with a Curie temperature of 61 K. Our X-ray diffraction studies reveal a first-order crystallographic phase transition occurring near 210–220 K upon warming, with significant thermal hysteresis. The low-temperature structure is rhombohedral (R$\\bar{3}$, BiI3sub>-type) and the high-temperature structure is monoclinic (C2/m, AlCl3sub>-type). Evidence for coupling between the crystallographic and magnetic degrees of freedom in CrI3sub> was found; we observed an anomaly in the interlayer spacing at the Curie temperature and an anomaly in the magnetic susceptibility at the structural transition. First-principles calculations reveal the importance of proper treatment of the long-ranged interlayer forces, and van der Waals density functional theory does an excellent job of predicting the crystal structures and their relative stability. Our calculations suggest that the ferromagnetic order found in the bulk material may persist into monolayer form, suggesting that CrI3sub> and other chromium trihalides may be promising materials for spintronic and magnetoelectronic research.

  10. Effects of Mg doping on the remarkably enhanced electrochemical performance of Na3sub>V2(PO4)3sub> cathode materials for sodium ion batteries

    SciTech Connect

    Li, Hui; Yu, Xiqian; Bai, Ying; Wu, Feng; Wu, Chuan; Liu, Liang-Yu; Yang, Xiao-Qing


    Na3sub>V2-xMgx(PO4)3sub>/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 Na3sub>V2-xMgx(PO4)3sub>/C composites exhibit significant improvements on the electrochemistry performances in terms of the rate capability and cycle performance, especially for the Na3sub>V1.95Mg0.05(PO4)3sub>/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.

  11. Controlled Formation of Mixed Nanoscale Domains of High Capacity Fe2O3sub>–FeF3sub> Conversion Compounds by Direct Fluorination

    SciTech Connect

    Zhou, Hui; Ruther, Rose E.; Adcock, Jamie; Zhou, Wu; Dai, Sheng; Nanda, Jagjit


    In this paper, we report a direct fluorination method under fluorine gas atmosphere using a fluidized bed reactor for converting nanophase iron oxide (n-Fe2O3sub>) to an electrochemically stable and higher energy density iron oxyfluoride/fluoride phase. Interestingly, no noticeable bulk iron oxyfluoride phase (FeOF) phase was observed even at fluorination temperature close to 300 °C. Instead, at fluorination temperatures below 250 °C, scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS) and X-ray photoelectron spectroscopy (XPS) analysis showed surface fluorination with nominal composition, Fe2O3-xF2x (x < 1). At fluorination temperatures of 275 °C, STEM-EELS results showed porous interconnected nanodomains of FeF3sub> and Fe2O3sub> coexisting within the same particle, and overall the particles become less dense after fluorination. We performed potentiometric intermittent titration and electrochemical impedance spectroscopy studies to understand the lithium diffusion (or apparent diffusion) in both the oxyfluoride and mixed phase FeF3sub> + Fe2O3sub> composition, and correlate the results to their electrochemical performance. Finally and further, we analyze from a thermodynamical perspective, the observed formation of the majority fluoride phase (77% FeF3sub>) and the absence of the expected oxyfluoride phase based on the relative formation energies of oxide, fluoride, and oxyfluorides.

  12. Scalar-quark systems and chimera hadrons in SU(3){sub c} lattice QCD

    SciTech Connect

    Iida, H.; Takahashi, T. T.; Suganuma, H.


    In terms of mass generation in the strong interaction without chiral symmetry breaking, we perform the first study for light scalar-quarks {phi} (colored scalar particles with 3{sub c} or idealized diquarks) and their color-singlet hadronic states using quenched SU(3){sub c} lattice QCD with {beta}=5.70 (i.e., a{approx_equal}0.18 fm) and lattice size 16{sup 3}x32. We investigate ''scalar-quark mesons'' {phi}{sup {dagger}}{phi} and ''scalar-quark baryons'' {phi}{phi}{phi} as the bound states of scalar-quarks {phi}. We also investigate the color-singlet bound states of scalar-quarks {phi} and quarks {psi}, i.e., {phi}{sup {dagger}}{psi}, {psi}{psi}{phi}, and {phi}{phi}{psi}, which we name ''chimera hadrons.'' All the new-type hadrons including {phi} are found to have a large mass even for zero bare scalar-quark mass m{sub {phi}}=0 at a{sup -1}{approx_equal}1 GeV. We find a ''constituent scalar-quark/quark picture'' for both scalar-quark hadrons and chimera hadrons. Namely, the mass of the new-type hadron composed of m {phi}'s and n {psi}'s, M{sub m{phi}}{sub +n{psi}}, approximately satisfies M{sub m{phi}}{sub +n{psi}}{approx_equal}mM{sub {phi}}+nM{sub {psi}}, where M{sub {phi}} and M{sub {psi}} are the constituent scalar-quark and quark masses, respectively. We estimate the constituent scalar-quark mass M{sub {phi}} for m{sub {phi}}=0 at a{sup -1}{approx_equal}1 GeV as M{sub {phi}}{approx_equal}1.5-1.6 GeV, which is much larger than the constituent quark mass M{sub {psi}}{approx_equal}400 MeV in the chiral limit. Thus, scalar quarks acquire a large mass due to large quantum corrections by gluons in the systems including scalar quarks. Together with other evidences of mass generation of glueballs and charmonia, we conjecture that all colored particles generally acquire a large effective mass due to dressed gluon effects. In addition, the large mass generation of pointlike colored scalar particles indicates that plausible diquarks used in effective hadron models cannot

  13. High-energy passively Q-switched laser operation of Yb:Ca3sub>La2(BO3sub>)4 disordered crystal.


    Wang, Lisha; Han, Wenjuan; Pan, Zhongben; Xu, Honghao; Chen, Xiaowen; Liu, Junhai; Yu, Haohai; Zhang, Huaijin


    Efficient high-energy passively Q-switched laser operation was demonstrated with Yb:Ca3sub>La2(BO3sub>)4 disordered crystal, producing an average output power of 3.0 W at 1018.7 nm, at a pulse repetition frequency of 5.0 kHz; the resulting pulse energy, duration, and peak power were 600 μJ, 5.3 ns, and 113.2 kW, respectively. PMID:27140354

  14. Capturing ultrafast photoinduced local structural distortions of BiFeO3sub>

    SciTech Connect

    Wen, Haidan; Sassi, Michel JPC; Luo, Zhenlin; Adamo, Carolina; Schlom, Darrell; Rosso, Kevin M.; Zhang, Xiaoyi


    The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3sub> film. The out-of-plane elongation of the unit cell is accompanied by the in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This uniaxial elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated nonequilibrium processes in polar materials.

  15. Understanding strain-induced phase transformations in BiFeO3sub> thin films

    SciTech Connect

    Dixit, Hemant; Beekman, Christianne; Schlepütz, Christian M.; Siemons, Wolter; Yang, Yongsoo; Senabulya, Nancy; Clarke, Roy; Chi, Miaofang; Christen, Hans M.; Cooper, Valentino R.


    Experiments demonstrate that under large epitaxial strain a coexisting striped phase emerges in BiFeO₃ thin films, which comprises a tetragonal-like (T´) and an intermediate S´ polymorph. It exhibits a relatively large piezoelectric response when switching between the coexisting phase and a uniform T´ phase. This strain-induced phase transformation is investigated through a synergistic combination of first-principles theory and experiments. The results show that the S´ phase is energetically very close to the T´ phase, but is structurally similar to the bulk rhombohedral (R) phase. By fully characterizing the intermediate S´ polymorph, it is demonstrated that the flat energy landscape resulting in the absence of an energy barrier between the T´ and S´ phases fosters the above-mentioned reversible phase transformation. This ability to readily transform between the S´ and T´ polymorphs, which have very different octahedral rotation patterns and c/a ratios, is crucial to the enhanced piezoelectricity in strained BiFeO3sub> films. Additionally, a blueshift in the band gap when moving from R to S´ to T´ is observed. These results emphasize the importance of strain engineering for tuning electromechanical responses or, creating unique energy harvesting photonic structures, in oxide thin film architectures.

  16. Magnetism and Metal-Insulator Transition in Oxygen Deficient SrTiO3sub>

    SciTech Connect

    Lopez-Bezanilla, Alejandro; Ganesh, Panchapakesan; Littlewood, Peter B.


    First-principles calculations to study the electronic and magnetic properties of bulk, oxygen-deficient SrTiO3sub> (STO) under different doping conditions and densities have been conducted. The appearance of magnetism in oxygen-deficient STO is not determined solely by the presence of a single oxygen vacancy but by the density of free carriers and the relative proximity of the vacant sites. We find that while an isolated vacancy behaves as a nonmagnetic double donor, manipulation of the doping conditions allows the stability of a single-donor state, with emergent local moments coupled ferromagnetically by carriers in the conduction band. Strong local lattice distortions enhance the binding of this state. The energy of the in-gap local moment can be further tuned by orthorhombic strain. Consequently we find that the free-carrier density and strain are fundamental components to obtaining trapped spin-polarized electrons in oxygen-deficient STO, which may have important implications in the design of optical devices.

  17. Electric control of magnetism at the Fe/BaTiO3sub> interface

    SciTech Connect

    Radaelli, G.; Petti, D.; Plekhanov, E.; Fina, I.; Torelli, P.; Salles, B. R.; Cantoni, M.; Rinaldi, C.; Gutiérrez, D.; Panaccione, G.; Varela, M.; Picozzi, S.; Fontcuberta, J.; Bertacco, R.


    Interfacial magnetoelectric coupling (MEC) is a viable path to achieve electrical writing of magnetic information in spintronic devices. For the prototypical Fe/BaTiO3sub> (BTO) system, only tiny changes of the interfacial Fe magnetic moment upon reversal of the BTO dielectric polarization have been predicted so far. Here, by using X-ray magnetic circular dichroism in combination with high resolution electron microscopy and first principles calculations, we report on an undisclosed physical mechanism for interfacial MEC in the Fe/BTO system. At the Fe/BTO interface, an ultrathin FeOx layer exists, whose magnetization can be electrically and reversibly switched on-off at room-temperature by reversing the BTO polarization. The suppression / recovery of interfacial ferromagnetism results from the asymmetric effect that ionic displacements in BTO produces on the exchange coupling constants in the adjacent FeOx layer. The observed giant magnetoelectric response holds potential for optimizing interfacial MEC in view of efficient, low-power spintronic devices.

  18. BF3sub>-promoted electrochemical properties of quinoxaline in propylene carbonate

    SciTech Connect

    Carino, Emily V.; Diesendruck, Charles E.; Moore, Jeffrey S.; Curtiss, Larry A.; Assary, Rajeev S.; Brushett, Fikile R.


    Electrochemical and density functional studies demonstrate that coordination of electrolyte constituents to quinoxalines modulates their electrochemical properties. Quinoxalines are shown to be electrochemically inactive in most electrolytes in propylene carbonate, yet the predicted reduction potential is shown to match computational estimates in acetonitrile. We find that in the presence of LiBF4 and trace water, an adduct is formed between quinoxaline and the Lewis acid BF3, which then displays electrochemical activity at 1–1.5 V higher than prior observations of quinoxaline electrochemistry in non-aqueous media. Direct synthesis and testing of a bis-BF3sub> quinoxaline complex further validates the assignment of the electrochemically active species, presenting up to a ~26-fold improvement in charging capacity, demonstrating the advantages of this adduct over unmodified quinoxaline in LiBF4-based electrolyte. The use of Lewis acids to effectively “turn on” the electrochemical activity of organic molecules may lead to the development of new active material classes for energy storage applications.

  19. Classification of AB O 3sub> perovskite solids: a machine learning study

    SciTech Connect

    Pilania, G.; Balachandran, P. V.; Gubernatis, J. E.; Lookman, T.


    Here we explored the use of machine learning methods for classifying whether a particularABO3sub>chemistry forms a perovskite or non-perovskite structured solid. Starting with three sets of feature pairs (the tolerance and octahedral factors, theAandBionic radii relative to the radius of O, and the bond valence distances between theAandBions from the O atoms), we used machine learning to create a hyper-dimensional partial dependency structure plot using all three feature pairs or any two of them. Doing so increased the accuracy of our predictions by 2–3 percentage points over using any one pair. We also included the Mendeleev numbers of theAandBatoms to this set of feature pairs. Moreover, doing this and using the capabilities of our machine learning algorithm, the gradient tree boosting classifier, enabled us to generate a new type of structure plot that has the simplicity of one based on using just the Mendeleev numbers, but with the added advantages of having a higher accuracy and providing a measure of likelihood of the predicted structure.

  20. Capturing ultrafast photoinduced local structural distortion of BiFeO3sub>

    SciTech Connect

    Wen, Haidan; Sassi, Michel; Luo, Zhenlin; Adamo, Carolina; Schlom, Darrell G.; Rosso, Kevin M.; Zhang, Xiaoyi


    The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3sub> film. The out-of-plane elongation of the unit cell is accompanied by the in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This anisotropic elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated non-equilibrium processes in polar materials.

  1. A SCR Model Calibration Approach with Spatially Resolved Measurements and NH3sub> Storage Distributions

    SciTech Connect

    Song, Xiaobo; Parker, Gordon G.; Johnson, John H.; Naber, Jeffrey D.; Pihl, Josh A.


    The selective catalytic reduction (SCR) is a technology used for reducing NO x emissions in the heavy-duty diesel (HDD) engine exhaust. In this study, the spatially resolved capillary inlet infrared spectroscopy (Spaci-IR) technique was used to study the gas concentration and NH3sub> storage distributions in a SCR catalyst, and to provide data for developing a SCR model to analyze the axial gaseous concentration and axial distributions of NH3sub> storage. A two-site SCR model is described for simulating the reaction mechanisms. The model equations and a calculation method was developed using the Spaci-IR measurements to determine the NH3sub> storage capacity and the relationships between certain kinetic parameters of the model. Moreover, a calibration approach was then applied for tuning the kinetic parameters using the spatial gaseous measurements and calculated NH3 storage as a function of axial position instead of inlet and outlet gaseous concentrations of NO, NO2, and NH3sub>. The equations and the approach for determining the NH3sub> storage capacity of the catalyst and a method of dividing the NH3sub> storage capacity between the two storage sites are presented. It was determined that the kinetic parameters of the adsorption and desorption reactions have to follow certain relationships for the model to simulate the experimental data. Finally, the modeling results served as a basis for developing full model calibrations to SCR lab reactor and engine data and state estimator development as described in the references (Song et al. 2013a, b; Surenahalli et al. 2013).

  2. Engineering two-dimensional superconductivity and Rashba spin–orbit coupling in LaAlO3sub>/SrTiO3sub> quantum wells by selective orbital occupancy

    SciTech Connect

    Herranz, Gervasi; Singh, Gyanendra; Bergeal, Nicolas; Jouan, Alexis; Lesueur, Jérôme; Gázquez, Jaume; Varela, María; Scigaj, Mateusz; Dix, Nico; Sánchez, Florencio; Fontcuberta, Josep


    We find the discovery of two-dimensional electron gases (2DEGs) at oxide interfaces—involving electrons in narrow d-bands—has broken new ground, enabling the access to correlated states that are unreachable in conventional semiconductors based on s- and p- electrons. There is a growing consensus that emerging properties at these novel quantum wells—such as 2D superconductivity and magnetism—are intimately connected to specific orbital symmetries in the 2DEG sub-band structure. Here we show that crystal orientation allows selective orbital occupancy, disclosing unprecedented ways to tailor the 2DEG properties. By carrying out electrostatic gating experiments in ​LaAlO3sub>/​SrTiO3sub> wells of different crystal orientations, we show that the spatial extension and anisotropy of the 2D superconductivity and the Rashba spin–orbit field can be largely modulated by controlling the 2DEG sub-band filling. Such an orientational tuning expands the possibilities for electronic engineering of 2DEGs at ​LaAlO3sub>/​SrTiO3sub> interfaces.

  3. Direct observation of oxygen-vacancy-enhanced polarization in a SrTiO3sub>-buffered ferroelectric BaTiO3sub> film on GaAs

    SciTech Connect

    Qiao, Q.; Zhang, Y.; Contreras-Guerrero, Rocio; Droopad, Ravi; Pantelides, S. T.; Pennycook, Stephen J.; Ogut, Serdar; Klie, Robert F.


    The integration of functional oxide thin-films on compound semiconductors can lead to a class of reconfigurable spin-based optoelectronic devices if defect-free, fully reversible active layers are stabilized. However, previous first-principles calculations predicted that SrTiO3sub> thin filmsgrown on Si exhibit pinned ferroelectric behavior that is not switchable, due to the presence of interfacial vacancies. Meanwhile, piezoresponse force microscopy measurements have demonstrated ferroelectricity in BaTiO3sub> grown on semiconductor substrates. The presence of interfacial oxygen vacancies in such complex-oxide/semiconductor systems remains unexplored, and their effect on ferroelectricity is controversial. We also use a combination of aberration-corrected scanning transmission electron microscopy and first-principles density functional theory modeling to examine the role of interfacial oxygen vacancies on the ferroelectricpolarization of a BaTiO3sub> thin filmgrown on GaAs. Moreover, we demonstrate that interfacial oxygen vacancies enhance the polar discontinuity (and thus the single domain, out-of-plane polarization pinning in BaTiO3sub>), and propose that the presence of surface charge screening allows the formation of switchable domains.

  4. Strain tuning of electronic structure in Bi4Ti3sub>O12-LaCoO3sub> epitaxial thin films

    SciTech Connect

    Choi, Woo Seok; Lee, Ho Nyung


    In this study, we investigated the crystal and electronic structures of ferroelectric Bi4Ti3sub>O12 single-crystalline thin films site-specifically substituted with LaCoO3sub> (LCO). The epitaxial films were grown by pulsed laser epitaxy on NdGaO3sub> and SrTiO3sub> 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.

  5. Technetium incorporation into hematite (α-Fe2O3sub>)

    SciTech Connect

    Skomurski, Frances N; Rosso, Kevin M; Krupka, Kenneth M; McGrail, B Peter


    Quantum-mechanical methods were used to evaluate mechanisms for possible structural incorporation of Tc species into the model iron oxide, hematite (α-Fe2O3sub>). Using periodic supercell models, energies for charge-neutral incorporation of Tc4+ or TcO4- ions were calculated using either a Tc4+/Fe2+ substitution scheme on the metal sublattice, or by insertion of TcO4- as an interstitial species within a hypothetical vacancy cluster. Although pertechnetate incorporation is found to be invariably unfavorable, incorporation of small amounts of Tc4+ (at least 2.6 wt %) is energetically feasible. Energy minimized bond distances around this impurity are provided to aid in future spectroscopic identification of these impurity species. The calculations also show that Fe2+ and Tc4+ prefer to cluster in the hematite lattice, likely due to less net Coulombic repulsion relative to that of Fe3+-Fe3+. These modeling predictions are generally consistent with observed selective association of Tc with iron oxide under reducing conditions, and in residual waste solids from underground storage tanks at the U.S. Department of Energy Hanford Site (Washington, U.S.A.). Here, even though relatively high pH and oxidizing conditions are dominant, Tc incorporation into iron oxides and (oxy)hydroxides is prospectively enabled by prior reduction of TcO4- to Tc4+ due to interaction with radiolytic species.

  6. Structure and luminescence properties of silver-doped NaY(PO{sub 3}){sub 4} crystal

    SciTech Connect

    El Masloumi, M.; Jubera, V.; Pechev, S.; Chaminade, J.P.; Videau, J.J. Mesnaoui, M.; Maazaz, M.; Moine, B.


    Single crystals of NaY(PO{sub 3}){sub 4} and Ag{sub 0.07}Na{sub 0.93}Y(PO{sub 3}){sub 4} have been synthesized by flux method. These new compounds turned out to be isostructural to NaLn(PO{sub 3}){sub 4}, with Ln=La, Nd, Gd and Er [monoclinic, P2{sub 1}/n, a=7.1615(2) A, b=13.0077(1) A, c=9.7032 (3) A, {beta}=90.55 (1){sup o}, V=903.86(14) A{sup 3} and Z=4]. The structure is based upon long polyphosphate chains running along the shortest unit-cell direction and made up of PO{sub 4} tetrahedra sharing two corners, linked to yttrium and sodium polyhedra. Infrared and Raman spectra at room temperature confirms this atomic arrangement. The luminescence of silver ions was reported in metaphosphate of composition Ag{sub 0.07}Na{sub 0.93}Y(PO{sub 3}){sub 4}. One luminescent centre was detected and assigned to single Ag{sup +} ions. - Graphical abstract: The presence of only one Ag{sup +} luminescence centre is the result from the perfect isolation (Ag{sup +}-Ag{sup +}=5.90 A) of each oxygenated silver site (AgO{sub 8} polyhedra) sharing two faces and one corner with three yttrium polyhedra.

  7. Complex doping of group 13 elements In and Ga in caged skutterudite CoSb3sub>

    SciTech Connect

    Xi, Lili; Qiu, Yting; Zheng, Shang; Shi, Xun; Yang, Jiong; Chen, Lidong; Singh, David J.; Yang, Jihui; Zhang, Wenqing


    The complex doping behavior of Ga and In in CoSb3sub> has been investigated using ab initio total-energy calculations and thermodynamics. The formation energies of void filling, Sb substitution and complex dual-site occupancy defects with different charge states, and their dependence on chemical potentials of species, were studied. Results show that Ga predominantly forms dual-site 2GaVF–GaSb defects and substitutes for Sb only at very high Fermi levels or electron concentrations. In, on the other hand, can play multiple roles in skutterudites, including filling in the crystalline voids, substituting for Sb atoms or forming dual-site occupancy, among which the fully charge-compensated dual-site defects (2InVF–InSb and 4InVF–2InSb) are dominant. The equilibrium concentration ratio of impurities at void-filling sites to those at Sb-substitution sites for Ga-doped CoSb3sub> is very close to be 2:1, while this value markedly deviates from 2:1 for In-doped CoSb3sub>. Furthermore, the 2:1 ratio of Ga doping in CoSb3sub> leads to low electron concentration (~2 × 1019 cm–3) and makes the doped system a semiconductor.

  8. A facile solvothermal synthesis of octahedral Fe3sub>O4 nanoparticles

    SciTech Connect

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


    Anisotropic Fe3sub>O4 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.

  9. Atomic Layer Deposition of Fe2O3sub> Using Ferrocene and Ozone

    SciTech Connect

    Martinson, Alex B.F.; DeVries, Michael J.; Libera, J. A.; Christensen, S. T.; Hupp, Joseph T.; Pellin, Michael J.; Elam, Jeffrey W.


    Growing interest in Fe2O3sub> as a light harvesting layer in solar energy conversion devices stems from its unique combination of stability, nontoxicity, and exceptionally low material cost. Unfortunately, the known methods for conformally coating high aspect ratio structures with Fe2O3sub> leave a glaring gap in the technologically relevant temperature range of 170-350 °C. Here, we elucidate a self-limiting atomic layer deposition (ALD) process for the growth of hematite, α-Fe2O3sub>, over a moderate temperature window using ferrocene and ozone. At 200 °C, the self-limiting growth of Fe2O3sub> is observed at rates up to 1.4 Å/cycle. Dense and robust thin films grown on both fused quartz and silicon exhibit the expected optical bandgap (2.1 eV). In situ mass spectrometric analysis reveals the evolution of two distinct cyclic reaction products during the layer-by-layer growth. The readily available and relatively high vapor pressure iron precursor is utilized to uniformly coat a high surface area template with aspect ratio ~150.

  10. Composite WO3sub>/TiO2 nanostructures for high electrochromic activity

    SciTech Connect

    Reyes-Gil, Karla R.; Stephens, Zachary D.; Stavila, Vitalie; Robinson, David B.


    A composite material consisting of TiO2 nanotubes (NT) with WO3sub> electrodeposited on its surface has been fabricated, detached from its Ti substrate, and attached to a fluorine-doped tin oxide (FTO) film on glass for application to electrochromic (EC) reactions. Several adhesion layers were tested, finding that a paste of TiO2 made from commercially available TiO2 nanoparticles creates an interface for the TiO2 NT film to attach to the FTO glass, which is conductive and does not cause solution-phase ions in an electrolyte to bind irreversibly with the material. The effect of NT length and WO3sub> concentration on the EC performance were studied. As a result, the composite WO3sub>/TiO2 nanostructures showed higher ion storage capacity, better stability, enhanced EC contrast, and longer memory time compared with the pure WO3sub> and TiO2 materials

  11. Observation on the Ion Association Equilibria in NaNO3sub> Droplets Using Micro-Raman Spectroscopy

    SciTech Connect

    Yu, Jun-Ying; Zhang, Yun; Tan, See-Hua; Liu, Yong; Zhang, Yun-Hong


    Ion association ratios as a function of concentration were estimated in single NaNO3sub> droplets (5–60 μm) on a polytetrafluoroethylene (PTFE) substrate with molar water-to-solute ratios (WSRs) of 0.8–28 and bulk NaNO3sub> solutions with WSRs of 35–200 by combining micro-Raman spectroscopy and component band analysis. Concentrations of the NaNO3sub> droplets were accurately controlled by adjusting relative humidity (RH) in a sample chamber. As the WSRs decreased from 200 to 0.8, symmetric stretching band (ν1-NO3sub>–) was observed to shift from 1047 to 1058 cm–1 along with a change in full width at half-maximum (fwhm) from ~10 to ~16 cm–1, indicative of formation of ion pairs with different structures. Through the component band analysis of the ν1-NO3sub>– band, five bands centered at 1040.0, 1042.9, 1048.5, 1053.5, and 1057.0 cm–1 were identified and assigned to coupled wagging modes of water molecules hydrated with nitrate ions, free hydrated nitrate anions, solvent-shared ion pairs (SIPs), contact ion pairs (CIPs), and the complex ion aggregates (CIAs), respectively. There were large amounts of SIPs and CIPs in dilute NaNO3sub> solution even at an extremely low concentration (WSR ~ 200), and each accounted for 50% and 20% of total nitrate species, respectively. This finding is in good agreement with earlier reported observations. In the dilute solutions (45 < WSR < 200), there is the same amount of free hydrated ions transformed into SIPs as that of SIPs transformed into CIPs. As a result, the overall amount of SIPs remained unchanged over the concentration range. With a decrease in WSR from 45 to 0.8, the amounts of SIPs and free solvated NO3sub>– ions kept decreasing, whereas the amount of CIPs rose to a maximum at WSR = 7 and then fell with a further decreasing WSR. Formation of CIAs started at WSR ~ 45, and its amount continuously

  12. Selective interlayer ferromagnetic coupling between the Cu spins in YBa2Cu3sub>O7–x grown on top of La0.7Ca0.3sub>MnO3sub>

    SciTech Connect

    Huang, S. W.; Wray, L. Andrew; Jeng, Horng -Tay; Tra, V. T.; Lee, J. M.; Langner, M. C.; Chen, J. M.; Roy, S.; Chu, Y. H.; Schoenlein, R. W.; Chuang, Y. -D.; Lin, J. -Y.


    Studies to date on ferromagnet/d-wave superconductor heterostructures focus mainly on the effects at or near the interfaces while the response of bulk properties to heterostructuring is overlooked. Here we use resonant soft x-ray scattering spectroscopy to reveal a novel c-axis ferromagnetic coupling between the in-plane Cu spins in YBa2Cu3sub>O7–x (YBCO) superconductor when it is grown on top of ferromagnetic La0.7Ca0.3sub>MnO3sub> (LCMO) manganite layer. This coupling, present in both normal and superconducting states of YBCO, is sensitive to the interfacial termination such that it is only observed in bilayers with MnO2 but not with La0.7Ca0.3sub>O interfacial termination. Thus, such contrasting behaviors, we propose, are due to distinct energetic of CuO chain and CuO2 plane at the La0.7Ca0.3sub>O and MnO2 terminated interfaces respectively, therefore influencing the transfer of spin-polarized electrons from manganite to cuprate differently. Our findings suggest that the superconducting/ferromagnetic bilayers with proper interfacial engineering can be good candidates for searching the theorized Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state in cuprates and studying the competing quantum orders in highly correlated electron systems.

  13. Sonochemical synthesis of highly luminescent Ln2O3sub>:Eu3+ (Y, La, Gd) nanocrystals

    SciTech Connect

    Alammar, Tarek; Cybinska, Joanna; Campbell, Paul S.; Mudring, Anja -Verena


    In this study, sonication of Ln(CH3sub>COO)3sub>·H2O, Eu(CH3sub>COO)3sub>·H2O and NaOH dissolved in the ionic liquid-butyl-3-methylimidazolium bis(trifluoromethane)sulfonylamide lead to Ln(OH)3sub>:Eu (Ln: Gd, La, Y) nanoparticles. Subsequent calcination at 800 °C for 3 h allowed to obtain Ln2O3sub>:Eu nanopowders. Gd2O3sub> and Y2O3sub> were obtained in the C-type lanthanide sequioxide structure, whereas La2O3sub> crystallized in the A-type. Structure, morphology, and luminescent properties of the nano-oxides were investigated by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), dispersive X-ray (EDX), and photoluminescence (PL). SEM studies revealed that the synthesized Gd2O3sub>:Eu, La2O3sub>:Eu, and Y2O3sub>:Eu formed nano-spindle, -sheets, and -rods in shape, respectively. The nanoscale materials show very efficient red emission due to the intraconfigurational f–f transitions of Eu3+. The quantum yields for Ln2O3sub>:Eu (5%) were determined to be 4.2% for Ln=Gd, 13.8% for Ln=Y and 5.2% for Ln=La. The asymmetric ratio I02/I01 of Eu3+ varies from 5.3 for Gd2O3sub>, to 5.6 for Y2O3sub> to 6.5 for La2O3sub>, which increased the color chromaticity.

  14. Tomography and High-Resolution Electron Microscopy Study of Surfaces and Porosity in a Plate-Like γ-Al2O3sub>

    SciTech Connect

    Kovarik, Libor; Genc, Arda; Wang, Chong M.; Qiu, Annie; Peden, Charles HF; Szanyi, Janos; Kwak, Ja Hun


    Morphological and surface characteristics of gamma-Al2O3sub> are topics of high relevance in the field of catalysis. Using tomography and high-resolution S/TEM imaging, we have studied the surface characteristics of a model gamma-Al2O3sub> synthesized in the shape of platelets and macroscopically defined by (110)Al2O3sub> and (111)Al2O3sub> surface facets. We show that the dominant (110)Al2O3sub> surface of the synthesized gamma-Al2O3sub> is not atomically flat but undergoes a significant reconstruction, forming nanoscale (111)Al2O3sub> terraces. In addition to high resolution imaging, tomographic analysis was carried out, enabling an examination of the pores/voids, which were found to be mostly enclosed within the bulk and inaccessible to gasses or metals. Tomographic analysis shows that the surfaces of the pores are defined exclusively by (100)Al2O3sub> and (111)Al2O3sub> facets. The importance of these findings is discussed in the context of relative surface energies of low index surfaces and ethanol desorption characteristics.

  15. Analysis of Bonding Patterns in the Valence Isoelectronic series O3sub>, S3sub>, SO2 and OS2 in Terms of Oriented Quasi-Atomic Molecular Orbitals

    SciTech Connect

    Glezakou, Vassiliki Alexandra; Elbert, Stephen T; Xantheas, Sotiris S; Ruedenberg, Klaus


    A novel analysis of the chemical bonding pattern in the valence isoelectronic series of triatomic molecules O3sub>, S3sub>, SO2 and OS2 is reported. The analysis is based on examining the bond order matrix elements between the Oriented Localized Molecular Orbitals (OLMOs) that are localized on the three individual left (L), center (C) and right (R) atoms. The analysis indicates that there is a (L-C) and (C-R) π-bonding interaction and a (L-R) π-antibonding interaction. This finding supports the previously proposed "partial biradical" interpretation of these triatomic systems, which had recently been challenged.

  16. Interesting radiative patterns of neutrino mass in an SU(3){sub C}xSU(3){sub L}xU(1){sub X} model with right-handed neutrinos

    SciTech Connect

    Chang, Darwin; Hoang Ngoc Long


    We investigate a simple model of neutrino mass based on SU(3){sub C}xSU(3){sub L}xU(1){sub X} gauge unification. The Yukawa coupling of the model has automatic lepton-number symmetry which is broken only by the self-couplings of the Higgs boson. At tree level, the neutrino spectrum contains three Dirac fermions, one massless and two degenerate in mass. At the two-loop level, neutrinos obtain Majorana masses and correct the tree-level result which naturally gives rise to an inverted hierarchy mass pattern and interesting mixing which can fit the current data with minor fine-tuning. In another scenario, one can pick the scales such that the loop-induced Majorana mass matrix is bigger than the Dirac one and thus reproduces the usual seesaw mechanism.

  17. Sub-80 femtosecond pulses generation from a diode-pumped mode-locked Nd:Ca3sub>La2(BO3sub>)4 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:Ca3sub>La2(BO3sub>)4 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. PMID:27192242

  18. Eye-safe 1.55  μm passively Q-switched Er,Yb:GdAl3sub>(BO3sub>)4 diode-pumped laser.


    Gorbachenya, K N; Kisel, V E; Yasukevich, A S; Maltsev, V V; Leonyuk, N I; Kuleshov, N V


    We report for the first time, to the best of our knowledge, on a diode-pumped passively Q-switched Er,Yb:GdAl3sub>(BO3sub>)4 laser. By using a Co2+:MgAl2O4 crystal as a saturable absorber, Q-switched laser pulses with a duration of 12 ns and a maximum energy of 18.7 μJ at a repetition rate of 32 kHz corresponding to an average output power of 0.6 W were obtained at 1550 nm under continuous-wave pumping. In the burst mode of operation, Q-switched laser pulses with the highest energy up to 44 μJ were realized with a pulse repetition rate of 6.5 kHz. PMID:26974080

  19. Effect of Particle Size and Operating Conditions on Pt3sub>Co PEMFC Cathode Catalyst Durability

    SciTech Connect

    Gummalla, Mallika; Ball, Sarah; Condit, David; Rasouli, Somaye; Yu, Kang; Ferreira, Paulo; Myers, Deborah; Yang, Zhiwei


    The initial performance and decay trends of polymer electrolyte membrane fuel cells (PEMFC) cathodes with Pt3sub>Co catalysts of three mean particle sizes (4.9 nm, 8.1 nm, and 14.8 nm) with identical Pt loadings are compared. Even though the cathode based on 4.9 nm catalyst exhibited the highest initial electrochemical surface area (ECA) and mass activity, the cathode based on 8.1 nm catalyst showed better initial performance at high currents. Owing to the low mass activity of the large particles, the initial performance of the 14.8 nm Pt3Co-based electrode was the lowest. The performance decay rate of the electrodes with the smallest Pt3sub>Co particle size was the highest and that of the largest Pt3sub>Co particle size was lowest. Interestingly, with increasing number of decay cycles (0.6 to 1.0 V, 50 mV/s), the relative improvement in performance of the cathode based on 8.1 nm Pt3sub>Co over the 4.9 nm Pt3sub>Co increased, owing to better stability of the 8.1 nm catalyst. The electron microprobe analysis (EMPA) of the decayed membrane-electrode assembly (MEA) showed that the amount of Co in the membrane was lower for the larger particles, and the platinum loss into the membrane also decreased with increasing particle size. This suggests that the higher initial performance at high currents with 8.1 nm Pt3sub>Co could be due to lower contamination of the ionomer in the electrode. Furthermore, lower loss of Co from the catalyst with increased particle size could be one of the factors contributing to the stability of ECA and mass activity of electrodes with larger cathode catalyst particles. To delineate the impact of particle size and alloy effects, these results are compared with prior work from our research group on size effects of pure platinum catalysts. The impact of PEMFC operating conditions, including upper potential, relative humidity, and temperature on the alloy catalyst decay trends, along with the EMPA analysis

  20. Line positions and intensities of the phosphine (PH3sub>) Pentad near 4.5μm

    SciTech Connect

    Malathy Devi, V.; Kleiner, Isabelle; Sams, Robert L.; Brown, Linda R.; Benner, D. Chris; Fletcher, Leigh N.


    In order to improve the spectroscopic database for remote sensing of the giant planets, line positions and intensities are determined for the five bands (2ν2, ν2 + ν4, 2ν4, ν1 and ν3sub>) that comprise the Pentad of PH3sub> between 1950 and 2450 cm-1. Knowledge of PH3sub> spectral line parameters in this region is important for the exploration of dynamics and chemistry on Saturn, (using existing Cassini/VIMS observations) and future near-IR data of Jupiter from Juno and ESA’s Jupiter Icy Moons Explorer (JUICE). For this study, spectra of pure PH3sub> from two Fourier transform spectrometers were obtained: (a) five high-resolution (0.00223 cm-1), high signal-to-noise (~1800) spectra recorded at room temperature (298.2 K) with the Bruker IFS 125HR Fourier transform spectrometer (FTS) at the Pacific Northwest National Laboratory (PNNL), Richland, Washington and (b) four high-resolution (at 0.0115 cm-1 resolution), high signal-to-noise (~700) spectra recorded at room temperature in the region 1800–5200 cm-1 using the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory (NSO) on Kitt Peak. Individual line parameters above 2150 cm-1 were retrieved by simultaneous multispectrum fittings of all five Bruker spectra, while retrievals with the four Kitt Peak spectra were done in the 1938–2168 cm-1 range spectrum by spectrum and averaged. In all, positions and intensities were obtained for more than 4400 lines. These included 53 A+A- split pairs of transitions (arising due to vibration–rotation interactions (Coriolis-type interaction) between the ν3sub> and ν1 fundamental bands) for K" = 3, 6, and 9. Over 3400 positions and 1750 intensities of these lines were ultimately identified as relatively unblended and modeled up to J = 14 and K = 12 with rms values of 0


    SciTech Connect

    McCauley, Patrick I.; Mangum, Jeffrey G.; Wootten, Alwyn


    We present Green Bank Telescope observations of the 3{sub 12}-3{sub 13} (29 GHz) and 4{sub 13}-4{sub 14} (48 GHz) transitions of the H{sub 2}CO molecule toward a sample of 23 well-studied star-forming regions. Analysis of the relative intensities of these transitions can be used to reliably measure the densities of molecular cores. Adopting kinetic temperatures from the literature, we have employed a large velocity gradient (LVG) model to derive the average hydrogen number density (n(H{sub 2})) within a 16'' beam toward each source. Densities in the range of 10{sup 5.5}-10{sup 6.5} cm{sup -3} and ortho-formaldehyde column densities per unit line width between 10{sup 13.5} and 10{sup 14.5} cm{sup -2} (km s{sup -1}){sup -1} are found for most objects, in general agreement with existing measurements. A detailed analysis of the advantages and limitations to this densitometry technique is also presented. We find that H{sub 2}CO 3{sub 12}-3{sub 13}/4{sub 13}-4{sub 14} densitometry proves to be best suited to objects with T{sub K} {approx}> 100 K, above which the H{sub 2}CO LVG models become relatively independent of kinetic temperature. This study represents the first detection of these H{sub 2}CO K-doublet transitions in all but one object in our sample. The ease with which these transitions were detected, coupled with their unique sensitivity to spatial density, makes them excellent monitors of density in molecular clouds for future experiments. We also report the detection of the 9{sub 2}-8{sub 1} A {sup -} (29 GHz) transition of CH{sub 3}OH toward six sources.

  2. Simple and low-temperature preparation of Co{sub 3}O{sub 4} sphere-like nanoparticles via solid-state thermolysis of the [Co(NH{sub 3}){sub 6}](NO{sub 3}){sub 3} complex

    SciTech Connect

    Farhadi, Saeid; Pourzare, Kolsoum


    Highlights: ► [Co(NH{sub 3}){sub 6}](NO{sub 3}){sub 3} precursor was used for synthesizing pure Co{sub 3}O{sub 4} nanocrystals. ► Co{sub 3}O{sub 4} nanocrystals were synthesized at low temperature of 200 °C. ► Co{sub 3}O{sub 4} nanocrystals show a weak ferromagnetic behavior at room temperature. ► This simple method is low-cost and suitable for high-scale production of Co{sub 3}O{sub 4}. -- Abstract: In this work, spinel-type Co{sub 3}O{sub 4} spherical nanoparticles were easily prepared via decomposition of the hexamminecobalt(III) nitrate complex, [Co(NH{sub 3}){sub 6}](NO{sub 3}){sub 3}, at low temperature (200 °C). The product was characterized by thermal analysis (TGA/DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, UV–vis spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer–Emmett–Teller (BET) specific surface area measurement and magnetic measurements. The results confirmed that pure single-phase Co{sub 3}O{sub 4} nanoparticles with weak ferromagnetic behavior were obtained by this method. TEM images showed that the Co{sub 3}O{sub 4} nanoparticles are sphere-like with an average diameter size of around 15 nm. The optical spectrum indicated two direct band gaps at 2.15 and 3.56 eV which are blue-shifted relative to reported values for the bulk sample. Using this fast and simple method, Co{sub 3}O{sub 4} nanoparticles can be produced without expensive and toxic solvents or complicated equipment.

  3. Jahn-Teller versus quantum effects in the spin-orbital material LuVO3sub>

    SciTech Connect

    Skoulatos, M.; Toth, S.; Roessli, B.; Enderle, M.; Habicht, K.; Sheptyakov, D.; Cervellino, A.; Freeman, P. G.; Reehuis, M.; Stunault, A.; McIntyre, G. J.; Tung, L. D.; Marjerrison, C.; Pomjakushina, E.; Brown, P. J.; Khomskii, D. I.; Rüegg, Ch.; Kreyssig, A.; Goldman, A. I.; Goff, J. P.


    In this article, we report on combined neutron and resonant x-ray scattering results, identifying the nature of the spin-orbital ground state and magnetic excitations in LuVO3sub> as driven by the orbital parameter. In particular, we distinguish between models based on orbital-Peierls dimerization, taken as a signature of quantum effects in orbitals, and Jahn-Teller distortions, in favor of the latter. In order to solve this long-standing puzzle, polarized neutron beams were employed as a prerequisite in order to solve details of the magnetic structure, which allowed quantitative intensity analysis of extended magnetic-excitation data sets. The results of this detailed study enabled us to draw definite conclusions about the classical versus quantum behavior of orbitals in this system and to discard the previous claims about quantum effects dominating the orbital physics of LuVO3sub> and similar systems.

  4. Size-dependent amorphization of nanoscale Y2O3sub> at high pressure

    SciTech Connect

    Wang, Lin; Yang, Wenge; Ding, Yang; Ren, Yang; Xiao, Siguo; Liu, Bingbing; Sinogeikin, Stanislav V.; Meng, Yue; Gosztola, David J.; Shen, Guoyin; Hemley, Russell J.; Mao, Wendy L.; Mao, Ho-kwang


    Y2 O3sub> with particle sizes ranging from 5 nm to 1 μm were studied at high pressure using x-ray diffraction and Raman spectroscopy techniques. Nanometer-sized Y2 O3sub> particles are shown to be more stable than their bulk counterparts, and a grain size-dependent crystalline-amorphous transition was discovered in these materials. High-energy atomic pair distribution function measurements reveal that the amorphization is associated with the breakdown of the long-rang order of the YO6 octahedra, while the nearest-neighbor edge-shared octahedral linkages are preserved.

  5. Integrated Data Collection Analysis (IDCA) Program — KClO3sub>/Icing Sugar (-100 mesh) Mixture

    SciTech Connect

    Sandstrom, Mary M.; Brown, Geoffrey W.; Preston, Daniel N.; Pollard, Colin J.; Warner, Kirstin F.; Sorenson, Daniel N.; Remmers, Daniel L.; Moran, Jesse S.; Shelley, Timothy J.; Hsu, Peter C.; Whipple, Richard E.; 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 scanning calorimetry analysis of a mixture of KClO3sub> sized through a 100-mesh sieve mixed with icing sugar, also sized through a 100-mesh sieve—KClO3sub>/icing sugar (-100) mixture. This material was selected because of the challenge of performing SSST testing of a mixture of two solid materials. The mixture was found to be: 1) more sensitive to impact than RDX, with sensitivity similar to PETN, 2) the same or more sensitive to friction than PETN, and 3) less sensitive to spark than RDX. The analysis showed that the mixture has thermally stability similar to RDX and is perhaps more energetic upon decomposition but variable results indicate sampling issues.

  6. Amphoteric doping of praseodymium Pr3+ in SrTiO3sub> grain boundaries

    SciTech Connect

    Yang, H.; Lee, H. S.; Kotula, P. G.; Sato, Y.; Ikuhara, Y.; Browning, N. D.


    Charge Compensation in rare-earth Praseodymium (Pr3+) doped SrTiO3sub> plays an important role in determining the overall photoluminescence properties of the system. Here, the Pr3+ doping behavior in SrTiO3sub> grain boundaries (GBs) is analyzed using aberration corrected scanning transmission electron microscopy (STEM). The presence of Pr3+ induces structure variations and changes the statistical prevalence of GB structures. In contrast to the assumption that Pr3+ substitutes for A site as expected in the bulk, Pr3+ is found to substitute both Sr and Ti sites inside GBs with the highest concentration in the Ti sites. As a result, this amphoteric doping behavior in the boundary plane is further confirmed by first principles theoretical calculations.

  7. Commissioning results of Nb3sub>Sn cavity vapor diffusion deposition system at JLab

    SciTech Connect

    Eremeev, Grigory; Clemens, William A.; Macha, Kurt M.; Park, HyeKyoung; Williams, R.


    Nb3sub>Sn as a BCS superconductor with a superconducting critical temperature higher than that of niobium offers potential benefit for SRF cavities via a lower-than-niobium surface resistance at the same temperature and frequency. A Nb3sub>Sn vapor diffusion deposition system designed for coating of 1.5 and 1.3 GHz single-cell cavities was built and commissioned at JLab. As the part of the commissioning, RF performance at 2.0 K of a single-cell 1.5 GHz CEBAF-shaped cavity was measured before and after coating in the system. Before Nb3sub>Sn coating the cavity had a Q0 of about 1010 and was limited by the high field Q-slope at Eacc ≅ 27 MV/m. Coated cavity exhibited the superconducting transition at about 17.9 K. The low-field quality factor was about 5∙109 at 4.3 K and 7∙109 at 2.0 K decreasing with field to about 1∙109 at Eacc ≅ 8 MV/m at both temperatures. The highest field was limited by the available RF power.

  8. On the peculiar properties of triangular-chain EuCr{sub 3}(BO{sub 3}){sub 4} antiferromagnet

    SciTech Connect

    Gondek, Ł.; Szytuła, A.; Przewoźnik, J.; Żukrowski, J.; Prokhorov, A.; Chernush, L.; Zubov, E.; Dyakonov, V.; Tyvanchuk, Yu.


    In this paper we report studies on EuCr{sub 3}(BO{sub 3}){sub 4} compound, that is a member of newly discovered family of huntite-related specimens for non-linear optics. For the first time, the uncommon temperature dependence of the EuCr{sub 3}(BO{sub 3}){sub 4} lattice parameters is reported. Additionally, the magnetism of this compound is extremely interesting. Namely, a possible interplay in between potentially magnetic rare-earth ions and 3d metal stacked within quasi-1D chain that can lead to a great variety of magnetic behaviour. Indeed, in our studies we have found 3D-long range ordering with metamagnetic behaviour, while at higher temperature the magnetic chains become uncoupled. - Graphical abstract: Torsion-like vibrations are the key to understand negative thermal expansion along the a-axis. Display Omitted - Highlights: • EuCr{sub 3}(BO{sub 3}){sub 4} is a peculiar triangular-chain antiferromagnet. • Rare earth sublattice is non-magnetic with Eu{sup 3+} configuration. • Cr{sup 3+} magnetic moments show 1-D behaviour along with spin fluctuations. • Torsion vibrations of Cr triangular tubes lead to anomalous expansion of unit cell.

  9. Integrated Data Collection Analysis (IDCA) Program — KClO3sub> (as received)/Icing Sugar

    SciTech Connect

    Sandstrom, Mary M.; Brown, Geoffrey W.; Preston, Daniel N.; Pollard, Colin J.; Warner, Kirstin F.; Sorenson, Daniel N.; Remmers, Daniel L.; Shelley, Timothy J.; Reyes, Jose A.; Hsu, Peter C.; Whipple, Richard E.; 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 KClO3sub> as received from the manufacturer mixed with icing sugar, sized through a 100-mesh sieve—KClO3sub>/icing sugar (AR) mixture. This material was selected because of the challenge of performing SSST testing of a mixture of two solid materials. The mixture was found to: 1) be more sensitive to impact than RDX, similar to PETN, 2) be the same or less sensitive to friction than PETN, and 3) to be less sensitive to spark than RDX. The thermal analysis showed that the mixture has thermally stability similar to RDX and is perhaps more energetic upon decomposition but variable results indicate sampling issues. Compared to the 100-mesh sieved counter part, the KClO3sub>/icing sugar (-100) mixture, the AR mixture was found to be about the same sensitivity towards impact, friction and ESD.

  10. Correlating Local Structure with Electrochemical Activity in Li2MnO3sub>

    SciTech Connect

    Nanda, Jagjit; Sacci, Robert L.; Veith, Gabriel M.; Dixit, Hemant M.; Cooper, Valentino R.; Pezeshki, Alan M.; Ruther, Rose E.


    Li2MnO3sub> is of interest as one component of the composite lithium-rich oxides, which are under development for high capacity, high voltage cathodes in lithium ion batteries. Despite such practical importance, the mechanism of electrochemical activity in Li2MnO3sub> is contested in the literature, as are the effects of long-term electrochemical cycling. Here, Raman spectroscopy and mapping are used to follow the chemical and structural changes that occur in Li2MnO3sub>. Both conventional slurry electrodes and thin films are studied as a function of the state of charge (voltage) and cycle number. Thin films have similar electrochemical properties as electrodes prepared from slurries, but allow for spectroscopic investigations on uniform samples without carbon additives. Spectral changes correlate well with electrochemical activity and support a mechanism whereby capacity is lost upon extended cycling due to the formation of new manganese oxide phases. Raman mapping of both thin film and slurry electrodes charged to different voltages reveals significant variation in the local structure. Poor conductivity and slow kinetics associated with a two-phase reaction mechanism contribute to the heterogeneity.

  11. Hydrogen centers and the conductivity of In2O3sub> single crystals

    SciTech Connect

    Yin, Weikai; Smithe, Kirby; Weiser, Philip; Stavola, Michael; Fowler, W. Beall; Boatner, Lynn A.; Pearton, Stephen J.; Hays, David C.; Koch, Sandro G.


    A series of infrared absorption experiments and complementary theory have been performed in order to determine the properties of OH and OD centers in In2O3sub> single crystals. Annealing In2O3sub> samples in H2 or D2 at temperatures near 450°C produces an n-type layer ≈0.06mm thick with an n-type doping of 1.6×1019 cm-3. The resulting free-carrier absorption is correlated with an OH center with a vibrational frequency of 3306 cm-1 that we associate with interstitial H+. Additional O-H (O-D) vibrational lines are assigned to metastable configurations of the interstitial H+(D+) center and complexes of H (D) with In vacancies. In addition, unlike other oxides studied recently where H trapped at an oxygen vacancy is the dominant shallow donor (ZnO and SnO2, for example), interstitial H+ is found to be the dominant H-related shallow donor in In2O3sub>.

  12. Metastability in the MgAl2O4-Al2O3sub> System

    SciTech Connect

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


    Aluminum oxide must take a spinel form ( γ-Al2O3sub>) at elevated temperatures in order for extensive solid solution to form between MgAl2O4 and α-Al2O3sub>. The solvus line between MgAl2O4 and Al2O3sub> has been defined at 79.6 wt% Al2O3sub> at 1500°C, 83.0 wt% Al2O3sub> at 1600°C, and 86.5 wt% Al2O3sub> 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 Al2O3sub> at elevated temperatures. A minimum in melting at 1975°C and a chemistry of 96 wt% Al2O3sub> rather than a eutectic is present, resulting in no eutectic crystal formation during solidification.

  13. Interfacial charge-mediated non-volatile magnetoelectric coupling in Co0.3sub>Fe0.7/Ba0.6Sr0.4TiO3sub>/Nb:SrTiO3sub> 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 Co0.3sub>Fe0.7/Ba0.6Sr0.4TiO3sub>/Nb:SrTiO3sub> (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.

  14. Enhanced electrocatalytic activity and stability of Pd3sub>V/C nanoparticles with a trace amount of Pt decoration for the oxygen reduction reaction

    SciTech Connect

    Liu, Sufen; Han, Lili; Zhu, Jing; Xiao, Weiping; Wang, Jie; Liu, Hongfang; Xin, Huolin; Wang, Deli


    In this study, carbon supported Pd3sub>V bimetallic alloy nanoparticles (Pd3sub>V/C) have been successfully synthesized via a simple impregnation–reduction method, followed by high temperature treatment under a H2 atmosphere. Electrochemical tests reveal that the half-wave potential of Pd3sub>V/C-500 shifts positively 40 mV compared with Pd/C. However, the catalytic activity of Pd3sub>V/C-500 suffers from serious degradation after 1k cycles. By a spontaneous displacement reaction or co-reduction method, a trace amount of Pt was decorated on the surface or inside of the Pd3sub>V/C nanoparticles. The catalytic activity and stability of the Pd3sub>V@Pt/C and Pt-Pd3sub>V/C catalysts for the oxygen reduction reaction (ORR) are enhanced significantly, and are comparable to commercial Pt/C. In addition, the Pt mass activity of Pd3sub>V@Pt/C and Pt-Pd3sub>V/C improves by factors of 10.9 and 6.5 at 0.80 V relative to Pt/C. Moreover, Pt-decorated Pd3sub>V/C nanoparticles show almost no obvious morphology change after durability tests, because the Pt-rich shell plays an important role in preventing degradation.

  15. Ordered and disordered polymorphs of Na(Ni2/3sub>Sb1/3sub>)O₂: Honeycomb-ordered cathodes for Na-ion batteries

    SciTech Connect

    Ma, Jeffrey; Wu, Lijun; Bo, Shou -Hang; Khalifah, Peter G.; Grey, Clare P.; Zhu, Yimei


    Na-ion batteries are appealing alternatives to Li-ion battery systems for large-scale energy storage applications in which elemental cost and abundance are important. Although it is difficult to find Na-ion batteries which achieve substantial specific capacities at voltages above 3 V (vs Na⁺/Na), the honeycomb-layered compound Na(Ni2/3sub>Sb1/3sub>)O₂ can deliver up to 130 mAh/g of capacity at voltages above 3 V with this capacity concentrated in plateaus at 3.27 and 3.64 V. Comprehensive crystallographic studies have been carried out in order to understand the role of disorder in this system which can be prepared in both “disordered” and “ordered” forms, depending on the synthesis conditions. The average structure of Na(Ni2/3sub>Sb1/3sub>)O₂ is always found to adopt an O3-type stacking sequence, though different structures for the disordered (R3¯m, #166, a = b = 3.06253(3) Å and c = 16.05192(7) Å) and ordered variants (C2/m, #12, a = 5.30458(1) Å, b = 9.18432(1) Å, c = 5.62742(1) Å and β = 108.2797(2)°) are demonstrated through the combined Rietveld refinement of synchrotron X-ray and time-of-flight neutron powder diffraction data. However, pair distribution function studies find that the local structure of disordered Na(Ni2/3sub>Sb1/3sub>)O₂ is more correctly described using the honeycomb-ordered structural model, and solid state NMR studies confirm that the well-developed honeycomb ordering of Ni and Sb cations within the transition metal layers is indistinguishable from that of the ordered phase. The disorder is instead found to mainly occur perpendicular to the honeycomb layers with an observed coherence length of not much more than 1 nm seen in electron diffraction studies. When the Na environment is probed through ²³Na solid state NMR, no evidence is found for prismatic Na environments, and a bulk diffraction analysis finds no evidence

  16. Thermodynamic and activation parameters for dissociation of [CpCr(CO){sub 3}]{sub 2} and [Cp*Cr(CO){sub 3}]{sub 2} into paramagnetic monomers from {sup 1}H NMR shift and line width measurements

    SciTech Connect

    Woska, D.C.; Ni, Y.; Wayland, B.B.


    Substitution of pentamethyl cyclopentadienide (Cp*) for cyclopentadienide (Cp) is commonly used as an approach for increasing ligand steric requirements that can enhance dissociation of M-M bonded complexes. {sup 1}H NMR spectra for solutions prepared by dissolution of [CpCr(CO){sub 3}]{sub 2} and [Cp*Cr(CO){sub 3}]{sub 2} in toluene in the temperature range 190--390 K are interpreted in terms of thermodynamic and kinetic parameters for dissociation of the diamagnetic dimers into the paramagnetic monomers CpCr(CO){sub 3} and Cp*Cr(CO){sub 3}. There is no evidence in this temperature range for thermally populated excited states or non-Curie magnetic behavior of the monomers making a significant contribution to the NMR. An expression for the temperature dependence of the NMR chemical shift at limiting fast interchange of monomer and dimer in terms of the {Delta}H{degree} and {Delta}S{degree} for dimer dissociation is applied in determining the thermodynamic parameters for Cr-Cr bond homolysis of [CpCr(CO){sub 3}]{sub 2} ({Delta}H{sub 1}{degree} = 15.3 {+-} 0.6 kcal mol{sup {minus}1}; {Delta}S{sub 1}{degree} = 39 {+-} 2 cal K{sup {minus}1} mol{sup {minus}1}) and [Cp*Cr(CO){sub 3}]{sub 2} ({Delta}H{sub 2}{degree} = 14.2 {+-} 0.4 kcal mol{sup {minus}1}; {Delta}S{sub 2}{degree} = 47 {+-} 2 cal K{sup {minus}1}mol{sup {minus}1}). Rate constants and activation parameters have been evaluated from {sup 1}H NMR line broadening in the region of slow dimer-monomer interchange for dissociation of [CpCr(CO){sub 3}]{sub 2} ({kappa}{sub 1} (240 K) {approx} 59 s{sup {minus}1}; {Delta}H{sub 1}{double{underscore}dagger} = 17 {+-} 2 kcal mol{sup {minus}1}; {Delta}S{sub 1}{double{underscore}dagger} = 21 {+-} 6 cal K{sup {minus}1} mol{sup {minus}1}) and [Cp*Cr(CO){sub 3}]{sub 2} ({kappa}{sub 2} (240 K) {approx} 1.4 x 10{sup 4} s{sup {minus}1}; {Delta}H{sub 2}{double{underscore}dagger} = 16 {+-} 1 kcal mol{sup {minus}1}; {Delta}S{sub 2}{double{underscore}dagger} = 30 {+-} 6 cal K

  17. Hydrothermal synthesis, structure, Raman spectroscopy, and self-irradiation studies of {sup 248}Cm(IO{sub 3}){sub 3}

    SciTech Connect

    Sykora, Richard E.; Assefa, Zerihun; Haire, Richard G. . E-mail:; Albrecht-Schmitt, Thomas E. . E-mail:


    The study of curium iodate, Cm(IO{sub 3}){sub 3}, was undertaken as part of a systematic investigation of the 4f- and 5f-elements' iodates. The reaction of {sup 248}CmCl{sub 3} with aqueous H{sub 5}IO{sub 6} under mild hydrothermal conditions results in the reduction of IO{sub 6}{sup 5-} to IO{sub 3}{sup -} anions, and the subsequent formation of Cm(IO{sub 3}){sub 3} single crystals. Crystallographic data are: (193K, MoK{alpha}, {lambda}=0.71073A): monoclinic, space group P2{sub 1}/c, a=7.2014(7)A, b=8.5062(9)A, c=13.4622(14)A, {beta}=100.142(2){sup o}, V=811.76(14), Z=4, R(F)=2.11%, Rw(Fo2)=4.43% for 119 parameters with 1917 reflections with I>2{sigma}(I). The structure consists of Cm{sup 3+} cations bound by iodate anions to form [Cm(IO{sub 3}){sub 8}] units, where the local coordination environment around the curium centers can be described as a distorted dodecahedron. There are three crystallographically unique iodate anions within the structure; two iodates bridge between three Cm centers, and one iodate bridges between two Cm centers and has a terminal oxygen atom. The bridging of the curium centers by the iodate anions creates a three-dimensional structure. Three strong Raman bands with comparable intensities were observed at 846, 804, and 760cm{sup -1} and correspond to the I-O symmetric stretching of the three crystallographically distinct iodate ions. The Raman profile suggests a lack of inter-ionic vibrational coupling of the I-O stretching, while intra-ionic coupling provides symmetric and asymmetric components that correspond to each iodate site. Repeated collection of X-ray diffraction data for a crystal of Cm(IO{sub 3}){sub 3} over a period of time revealed a gradual expansion of the unit cell from self-irradiation. After 71 days, the new parameters were: a=7.2132(7)A, b=8.5310(8)A, c=13.505(1)A, {beta}=100.021(2){sup o}, V=818.3(2)

  18. Magnetic properties of the rare-earth ferroborate SmFe{sub 3}(BO{sub 3}){sub 4}

    SciTech Connect

    Demidov, A. A.; Volkov, D. V.; Gudim, I. A.; Eremein, E. V.; Temerov, V. L.


    The magnetic properties of trigonal antiferromagnet SmFe{sub 3}(BO{sub 3}){sub 4} are studied experimentally and theoretically. The measured characteristics are considered in terms of a theoretical approach based on the molecular field approximation and a crystal field model for a rare-earth ion. The temperature dependences of the initial magnetic susceptibility and the field and temperature dependences of magnetization in fields up to 5 T are described, and the anomaly in the magnetization curve for B Up-Tack c near 1 T, which points to a first-order phase transition, is analyzed.

  19. Investigation of SO3sub> absorption line for in situ gas detection inside combustion plants using a 4-μm-band laser source.


    Tokura, A; Tadanaga, O; Nishimiya, T; Muta, K; Kamiyama, N; Yonemura, M; Fujii, S; Tsumura, Y; Abe, M; Takenouchi, H; Kenmotsu, K; Sakai, Y


    We have investigated 4-μm-band SO3sub> absorption lines for in situSO3sub> detection using a mid-infrared laser source based on difference frequency generation in a quasi-phase-matched LiNbO3sub> waveguide. In the wavelength range of 4.09400-4.10600 μm, there were strong SO3sub> absorption lines. The maximum absorption coefficient at a concentration of 170 ppmv was estimated to be about 3.2×10-5  cm-1 at a gas temperature of 190°C. In coexistence with H2O, the reduction of the SO3sub> absorption peak height was observed, which was caused by sulfuric acid formation. We discuss a method of using an SO3sub> equilibrium curve to derive the total SO3sub> molecule concentration. PMID:27607263

  20. Directionally solidified fabrication in planar geometry of Al2O3sub>-Er3sub>Al5O12 eutectic composite for thermophotovoltaic devices.


    Sola, D; Oliete, P B; Peña, J I


    In this work Al2O3sub>-Er3sub>Al5O12 eutectic composite was manufactured in planar geometry departing from eutectic particles both produced by directional solidification using a CO2 laser system at rates of 180 and 720 mm/h. Microstructure and mechanical properties were investigated as a function of the growth rate. Homogeneous and interpenetrated microstructure was found with phase size strongly dependent on the growth rate, decreasing when the processing rate was increased. Thermal emission of eutectic composites was studied in function of thermal excitation by using CO2 laser radiation as a heating source. An intense narrow emission band at 1.55 µm matching with the sensitive region of the InGaAs photoconverter and a low emission band at 1 µm were obtained. Features of thermal emission bands were correlated with collecting angle, microstructure and laser power, and compared to those obtained from departing eutectic particles. PMID:27409955

  1. Anisotropic swelling and microcracking of neutron irradiated Ti3sub>AlC2-Ti5Al2C3sub> materials

    SciTech Connect

    Ang, Caen K.; Silva, Chinthaka M.; Shih, Chunghao Phillip; Koyanagi, Takaaki; Katoh, Yutai; Zinkle, Steven J.


    Mn + 1AXn (MAX) phase materials based on Ti–Al–C have been irradiated at 400 °C (673 K) with fission neutrons to a fluence of 2 × 1025 n/m2 (E > 0.1 MeV), corresponding to ~ 2 displacements per atom (dpa). We report preliminary results of microcracking in the Al-containing MAX phase, which contained the phases Ti3sub>AlC2 and Ti5Al2C3sub>. Equibiaxial ring-on-ring tests of irradiated coupons showed that samples retained 10% of pre-irradiated strength. Volumetric swelling of up to 4% was observed. Phase analysis and microscopy suggest that anisotropic lattice parameter swelling caused microcracking. Lastly, variants of titanium aluminum carbide may be unsuitable materials for irradiation at light water reactor-relevant temperatures.

  2. Structure tracking aided design and synthesis of Li3sub>V2(PO4)3sub> 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 Li3sub>V2(PO4)3sub> (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.

  3. Charge transfer and orbital reconstruction in the (La{sub 2/3}Sr{sub 1/3}MnO{sub 3}){sub m}/(SrRuO{sub 3}){sub n} superlattices

    SciTech Connect

    Lv, Kai; Zhu, H. P.; Zou, W. Q.; Zhang, F. M.; Wu, X. S.


    The structural, electronic, and magnetic properties of (La{sub 2/3}Sr{sub 1/3}MnO{sub 3}){sub m}/(SrRuO{sub 3}){sub n} superlattices have been investigated based on the first principles calculations. An obvious Jahn-Teller distortion, which depends on m, n, appears in MnO{sub 6} octahedron in the superlattices. The stretch along c-axis of MnO{sub 6} octahedron at the interface lifts the Mn e{sub g} orbital degeneracy, with electrons preferring the lower energy 3z{sup 2}−r{sup 2} to the higher energy x{sup 2}−y{sup 2}. Benefitting from the charge transfer at the interface, the still occupied x{sup 2}−y{sup 2} orbital can mediate a robust in-plane double exchange interaction. La{sub 2/3}Sr{sub 1/3}MnO{sub 3} block is ferromagnetic and metallic, even for the superlattice with m = n = 1.

  4. Negative Ion Photoelectron Spectroscopy Confirms the Prediction that D-3h Carbontrioxide (CO3sub>) Has a Singlet Ground State

    SciTech Connect

    Hrovat, David; Hou, Gao-Lei; Chen, Bo; Wang, Xue B.; Borden, Weston


    The CO3sub> radical anion (CO3sub>•–) has been formed by electrospraying carbonate dianion (CO3sub>2–) into the gas phase. The negative ion photoelectron (NIPE) spectrum of CO3sub>•– shows that, unlike trimethylenemethane [C(CH2)3sub>], carbontrioxide (CO3sub>) has a singlet ground state. From the NIPE spectrum, the electron affinity of CO3sub> was determined to be EA = 4.06 ± 0.03 eV, and the singlet-triplet energy difference was found to be ΔEST = - 17.8 ± 0.9 kcal/mol. B3LYP, CCSD(T), and CASPT2 calculations all find that the two lowest triplet states of CO3sub> are very close in energy, a prediction that is confirmed by the relative intensities of the bands in the NIPE spectrum of CO3sub>•–. The 560 cm-1 vibrational progression, seen in the low energy region of the triplet band, enables the identification of the lowest, Jahn-Teller-distorted, triplet state as 3A1, in which both unpaired electrons reside in σ MOs, rather than 3A2, in which one unpaired electron occupies the b2 σ MO, and the other occupies the b1 π MO.

  5. Chemistry, spectroscopy, and isotope-selective infrared photochemistry of volatile uranium compound tailored for 10-. mu. m absorption: U(OCH/sub 3/)/sub 6/

    SciTech Connect

    Cuellar, E.A.; Miller, S.S.; Marks, T.J.; Weitz, E.


    This contribution reports on the chemical, vibrational spectroscopic, and infrared multiphoton photochemical properties of uranium hexamethoxide, U(OCH/sub 3/)/sub 6/, a prototype molecule for laser-induced uranium isotope separation with a carbon dioxide laser. Uranium hexamethoxide can be prepared from UCl/sub 4/ by conversion to Li/sub 2/U(OCH/sub 3/)/sub 6/, followed by oxidation with lead tetraacetate. Vapor pressure studies on U(OCH/sub 3/)/sub 6/ indicate that at 33/sup 0/C, the vapor pressure is 17 mtorr. The vibrational spectra of U(/sup 16/OCH/sub 3/)/sub 6/ and U(/sup 18/OCH/sub 3/)/sub 6/ have been assigned by using infrared and laser Raman data. Under idealized O/sub h/ symmetry, the U(/sup 16/OCH/sub 3/)/sub 6/ U-O stretching fundamentals are assigned at 505.0 (A/sub lg/), 464.8(T/sub 1u/, and 414.0 cm/sup -1/ (E/sub g/). Tentative assignments are also made for several of the overtone and combination transitions evidence for possible lowering of the symmetry is presented. In gas-phase infrared photochemical experiments, the predominant U(OCH/sub 3/)/sub 6/ photoproducts isolated are U(OCH/sub 3/)/sub 5/, methanol, and formaldhyde. These are suggestive of multiphoton U-O bond homolysis to produce uranium pentamethoxide and methoxy radicals. The enrichment of unreacted U(OCH/sub 3/)/sub 6/ in /sup 235/U is maximum at ca 927 cm/sup -1/ (near what may be a U-O stretching overtone transition) and exhibits both a low fluence threshold and diminution at high fluence.

  6. Chemistry, spectroscopy, and isotope-selective infrared photochemistry of a volatile uranium compound tailored for 10-mm absorption: U(OCH/sub 3/)/sub 6/

    SciTech Connect

    Cuellar, E.A.; Miller, S.S.; Marks, T.J.; Weitz, E.


    This contribution reports on the chemical, vibrational spectroscopic, and infrared multiphoton photochemical properties of uranium hexamethoxide, U(OCH/sub 3/)/sub 6/, a prototype molecule for laser-induced uranium isotope separation with a carbon dioxide laser. Uranium hexamethoxide can be prepared from UCl/sub 4/ by conversion to Li/sub 2/U(OCH/sub 3/)/sub 6/, followed by oxidation with lead tetraacetate. Vapor pressure studies on U(OCH/sub 3/)/sub 6/ indicate that sub//sup 0/ = 23 +/- 3 kcal/mol and sub//sup 0/ = 76 +/- 4 eu; at 33/sup 0/C, the vapor pressure is 17 mtorr. The vibrational spectra of U(/sup 16/OCH/sub 3/)/sub 6/ and U(/sup 18/OCH/sub 3/)/sub 6/ have been assigned by using infrared and laser Raman data. Under idealized O/sub h/ symmetry, the U(/sup 16/OCH/sub 3/)/sub 6/U-O stretching fundamentals are assigned at 505.0 (A/sub 1g/), 464.8 (T/sub 1u/), and 414.0 cm/sup -1/ (E/sub g/). Tentative assignments are also made for several of the overtone and combination transitions evidence for possible lowering of the symmetry is presented. In gas-phase infrared photochemical experiments, the predominant U(OCH/sub 3/)/sub 6/ photoproducts isolated are U(OCH/sub 3/)/sub 5/, methanol, and formaldehyde. These are suggestive of multiphoton U-O bond homolysis to produce uranium pentamethoxide and methoxy radicals. The enrichment of unreacted U(OCH/sub 3/)/sub 6/ in /sup 235/U is maximum at ca. 927 cm/sup -1/ (near what may be a U-O stretching overtone transition) and exhibits both a low fluence threshold and dimunution at high fluence.

  7. Giant Magneto-Resistance in Epitaxial (La0.7Sr0.3sub>MnO3sub>)0.5: (ZnO)0.5 Nanocomposites

    SciTech Connect

    Pan, Wei; Jiang, Y. X.; Ihlefeld, Jon; Lu, Ping; Lee, Stephen R.


    A great deal of research has been carried out in oxide material systems. Among them, ZnO and La0.7Sr0.3sub>MnO3sub> (LSMO) are of particular interest due to their superb optical properties and colossal magneto-resistive effect. Here, we report our recent results of magneto-transport studies in self-assembled, epitaxial (ZnO)0.5:(La0.7Sr0.3sub>MnO3sub>)0.5 nanocomposite films.

  8. Synthesis of tris(triphenylsiloxy)yttrium and derivatives: Crystal structure of (Y(OSiPh sub 3 ) sub 3 (THF sub 3 ))ter dot THF

    SciTech Connect

    McGeary, M.J.; Coan, P.S.; Folting, K.; Streib, W.E.; Caoulton, K.G. )


    The synthesis of (Y(OSiPh{sub 3}){sub 3}){sub n} (1) has been accomplished by the reaction of Y(N(SiMe{sub 3}){sub 2}){sub 3} with 3 equivalents of Ph{sub 3}SiOH in toluene. Two monomeric Lewis base adducts were also formed. The product 1 was formed as a colorless, feather-like solid, and {sup 1}H and {sup 13}C NMR spectra gave data consistent with the structure of this compound as an aggregate presumably involving bridging Ph{sub 3}SiO{sup {minus}} ligands. The x-ray structure of the compounds is also reported.

  9. Vibrational spectroscopy of the ammoniated ammonium ions NH sub 4 sup + (NH sub 3 ) sub n (n = 1-10)

    SciTech Connect

    Price, J.M.; Crofton, M.W.; Lee, Y.T. Univ. of California, Berkeley )


    The gas-phase vibration-internal rotation spectra of mass-selected ammoniated ammonium ions, NH{sub 4}{sup +}(NH{sub 3}){sub n} (for n = 1-10), have been observed from 2600 to 4000 cm{sup {minus}1}. The spectra show vibrational features that have been assigned to modes involving both the ion core species, NH{sub 4}{sup +}, and the first shell NH{sub 3} solvent molecules. Nearly free internal rotation of the solvent molecules about their local C{sub 3} axes in the first solvation shell has been observed in the smaller clusters (n = 1-6). For the larger clusters studied (n = 7-10) the spectra converge, with little difference between clusters differing by one solvent molecule. For these clusters, the spectrum in the 3200-3500 cm{sup {minus}1} region is quite similar to that of liquid ammonia, and the entire region of 2600-3500 cm{sup {minus}1} also bears considerable resemblance to the spectra of ammonium salts dissolved in liquid ammonia under some chemical conditions. This indicates the onset of a liquidlike environment for the ion core and first shell solvent molecules in clusters as small as NH{sub 4}{sup +}(NH{sub 3}){sub 8}.

  10. Insights into the structure–photoreactivity relationships in well-defined perovskite ferroelectric KNbO 3sub> nanowires

    SciTech Connect

    Zhang, Tingting; Lei, Wanying; Liu, Ping; Rodriguez, José A.; Yu, Jiaguo; Qi, Yang; Liu, Gang; Liu, Minghua


    Structure–function correlations are a central theme in heterogeneous (photo)catalysis. In this study, the geometric and electronic structure of perovskite ferroelectric KNbO3sub> nanowires with respective orthorhombic and monoclinic polymorphs have been systematically addressed. By virtue of aberration-corrected scanning transmission electron microscopy, we directly visualize surface photocatalytic active sites, measure local atomic displacements at an accuracy of several picometers, and quantify ferroelectric polarization combined with first-principles calculations. The photoreactivity of the as-prepared KNbO3sub> nanowires is assessed toward aqueous rhodamine B degradation under UV light. A synergy between the ferroelectric polarization and electronic structure in photoreactivity enhancement is uncovered, which accounts for the prominent reactivity order: orthorhombic > monoclinic. Additionally, by identifying new photocatalytic products, rhodamine B degradation pathways involving N-deethylation and conjugated structure cleavage are proposed. The findings not only provide new insights into the structure–photoreactivity relationships in perovskite ferroelectric photocatalysts, but also have broad implications in perovskite-based water splitting and photovoltaics, among others.

  11. CaCO3sub> Precipitation, Transport and Sensing in Porous Media with In Situ Generation of Reactants

    SciTech Connect

    George Redden; Don Fox; Chi Zhang; Yoshiko Fujita; Luanjing Guo; Hai Huang


    Ureolytically driven calcite precipitation is a promising approach for inducing subsurface mineral precipitation, but engineered application requires the ability to control and predict precipitate distribution. To study the coupling between reactant transport and precipitate distribution, columns with defined zones of immobilized urease were used to examine the distribution of calcium carbonate precipitation along the flow path, at two different initial flow rates. As expected, with slower flow precipitate was concentrated toward the upstream end of the enzyme zone and with higher flow the solid was more uniformly distributed over the enzyme zone. Under constant hydraulic head conditions the flow rate decreased as precipitates decreased porosity and permeability. The hydrolysis/precipitation zone was expected to become compressed in the upstream direction. However, apparent reductions in the urea hydrolysis rate and changes in the distribution of enzyme activity, possibly due to CaCO3sub>precipitate hindering urea transport to the enzyme, or enzyme mobilization, mitigated reaction zone compression. Co-injected strontium was expected to be sequestered by coprecipitation with CaCO3sub>, but the results suggested that coprecipitation was not an effective sequestration mechanism in this system. In addition, spectral induced polarization (SIP) was used to monitor the spatial and temporal evolution of the reaction zone.

  12. Magnetic Correlations in the Quasi-Two-Dimensional Semiconducting Ferromagnet CrSiTe3sub>

    SciTech Connect

    Williams, Travis J.; Aczel, Adam A.; Lumsden, Mark D.; Nagler, Stephen E.; Stone, Matthew B.; Yan, Jiaqiang -Q.; Mandrus, D.


    Intrinsic, 2D ferromagnetic semiconductors are an important class of materials for overcoming dilute magnetic semiconductors’ limitations for spintronics. CrSiTe3sub> is a particularly interesting material of this class, since it can likely be exfoliated to single layers, for which Tc is predicted to increase dramatically. Establishing the nature of the bulk material’s magnetism is necessary for understanding the thin-film magnetic behavior and the material’s possible applications. In this work, we use elastic and inelastic neutron scattering to measure the magnetic properties of single crystalline CrSiTe3sub>. We find a very small single ion anisotropy that favors magnetic ordering along the c-axis and that the measured spin waves fit well to a model in which the moments are only weakly coupled along that direction. Then, we find that both static and dynamic correlations persist within the ab-plane up to at least 300 K, which is strong evidence of the material's 2D characteristics that are relevant for future studies on thin film and monolayer samples.

  13. Nature of the insulating ground state of the 5d postperovskite CaIrO3sub>

    SciTech Connect

    Kim, Sun -Woo; Liu, Chen; Kim, Hyun -Jung; Lee, Jun -Ho; Yao, Yongxin; Ho, Kai -Ming; Cho, Jun -Hyung


    In this study, the insulating ground state of the 5d transition metal oxide CaIrO3sub> has been classified as a Mott-type insulator. Based on a systematic density functional theory (DFT) study with local, semilocal, and hybrid exchange-correlation functionals, we reveal that the Ir t2g states exhibit large splittings and one-dimensional electronic states along the c axis due to a tetragonal crystal field. Our hybrid DFT calculation adequately describes the antiferromagnetic (AFM) order along the c direction via a superexchange interaction between Ir4+ spins. Furthermore, the spin-orbit coupling (SOC) hybridizes the t2g states to open an insulating gap. These results indicate that CaIrO3sub> can be represented as a spin-orbit Slater insulator, driven by the interplay between a long-range AFM order and the SOC. Such a Slater mechanism for the gap formation is also demonstrated by the DFT + dynamical mean field theory calculation, where the metal-insulator transition and the paramagnetic to AFM phase transition are concomitant with each other.

  14. Direct production of OH radicals upon CH overtone activation of (CH{sub 3}){sub 2}COO Criegee intermediates

    SciTech Connect

    Liu, Fang; Beames, Joseph M.; Lester, Marsha I.


    Ozonolysis of alkenes, a principle non-photolytic source of atmospheric OH radicals, proceeds through unimolecular decay of energized carbonyl oxide intermediates, known as Criegee intermediates. In this work, cold dimethyl-substituted Criegee intermediates are vibrationally activated in the CH stretch overtone region to drive the 1,4 hydrogen transfer reaction that leads to OH radical products. IR excitation of (CH{sub 3}){sub 2}COO reveals the vibrational states with sufficient oscillator strength, coupling to the reaction coordinate, and energy to surmount the effective barrier (≤ 16.0 kcal mol{sup −1}) to reaction. Insight on the dissociation dynamics is gleaned from homogeneous broadening of the spectral features, indicative of rapid intramolecular vibrational energy redistribution and/or reaction, as well as the quantum state distribution of the OH X{sup 2}Π (v = 0) products. The experimental results are compared with complementary electronic structure calculations, which provide the IR absorption spectrum and geometric changes along the intrinsic reaction coordinate. Additional theoretical analysis reveals the vibrational modes and couplings that permit (CH{sub 3}){sub 2}COO to access to the transition state region for reaction. The experimental and theoretical results are compared with an analogous recent study of the IR activation of syn-CH{sub 3}CHOO and its unimolecular decay to OH products [F. Liu, J. M. Beames, A. S. Petit, A. B. McCoy, and M. I. Lester, Science 345, 1596 (2014)].

  15. Giant elastic tunability in strained BiFeO3sub> near an electrically induced phase transition

    SciTech Connect

    Yu, Pu; Vasudevan, Rama K.; Tselev, Alexander; Xue, Fei; Chen, Long -Qing; Maksymovych, Petro; Kalinin, Sergei V.; Balke, Nina; Li, Q.; Cao, Y.; Laanait, N.


    Elastic anomalies are signatures of phase transitions in condensed matters and have traditionally been studied using various techniques spanning from neutron scattering to static mechanical testing. Here, using band-excitation elastic/piezoresponse spectroscopy, we probed sub-MHz elastic dynamics of a tip bias-induced rhombohedral–tetragonal phase transition of strained (001)-BiFeO3sub> (rhombohedral) ferroelectric thin films from ~103 nm3 sample volumes. Near this transition, we observed that the Young's modulus intrinsically softens by over 30% coinciding with 2-3 folds enhancement of local piezoresponse. Coupled with phase-field modeling, we also addressed the influence of polarization switching and mesoscopic structural heterogeneities (e.g., domain walls) on the kinetics of this phase transition, thereby providing fresh insights into the morphotropic phase boundary (MPB) in ferroelectrics. Moreover, the giant electrically tunable elastic stiffness and corresponding electromechanical properties observed here suggest potential applications of BiFeO3sub> in next-generation frequency-agile electroacoustic devices, based on utilization of the soft modes underlying successive ferroelectric phase transitions.

  16. Doping SrTiO3sub> supported FeSe by excess atoms and oxygen vacancies

    SciTech Connect

    Shanavas, Kavungal Veedu; Singh, David J.


    Photoemission studies of FeSe monolayer films on SrTiO3sub> substrate have shown electronic structures that deviate from pristine FeSe, consistent with heavy electron doping. With the help of first-principles calculations we studied the effect of excess Fe and Se atoms on the monolayer and oxygen vacancies in the substrate in order to understand the reported Fermi surface in this system. We find that both excess Fe and Se atoms prefer the same adsorption site above the bottom Se atoms on the monolayer. The adsorbed Fe is strongly magnetic and contributes electrons to the monolayer, while excess Se hybridizes with the monolayer Fe-d states and partially opens a gap just above the Fermi energy. We also find that the two-dimensional electron gas generated by the oxygen vacancies is partly transferred to the monolayer and can potentially suppress the hole pockets around the Γ point. Furthermore, both O vacancies in the SrTiO3sub> substrate and excess Fe over the monolayer can provide high levels of electron doping.

  17. Test of Optimized 120-mm LARP Nb3sub>Sn Quadrupole Coil Using Magnetic Mirror Structure

    SciTech Connect

    Chlachidze, G.


    The U.S. Large Hadron Collider accelerator research program is developing a new generation of large-aperture high-field quadrupoles based on Nb3sub>Sn conductor for the high-luminosity upgrade of the Large Hadron Collider. Tests of the first series of 120-mm-aperture high-gradient quadrupole (HQ) coils revealed the necessity for further optimization of the coil design and fabrication process. Modifications in coil design were gradually implemented in two HQ coils previously tested at Fermi National Accelerator Laboratory using a magnetic mirror structure (HQM01 and HQM02). This paper describes the construction and test of an HQ mirror model with a coil of optimized design and with an interlayer resistive core in the conductor. The cable for this coil was made of a smaller diameter strand, providing more room for coil expansion during reaction. The 0.8-mm strand, used in all previous HQ coils, was replaced with a 0.778-mm Nb3sub>Sn strand of RRP 108/127 subelement design. The coil was instrumented with voltage taps, heaters, and strain gauges to monitor mechanical and thermal properties and quench performance of the coil

  18. Thickness-dependent coherent phonon frequency in ultrathin FeSe/SrTiO3sub> films

    SciTech Connect

    Yang, Shuolong; Sobota, Jonathan A.; Leuenberger, Dominik; Kemper, Alexander F.; Lee, James J.; Schmitt, Felix T.; Li, Wei; Moore, Rob G.; Kirchmann, Patrick S.; Shen, Zhi -Xun


    Ultrathin FeSe films grown on SrTiO3sub> substrates are a recent milestone in atomic material engineering due to their important role in understanding unconventional superconductivity in Fe-based materials. By using femtosecond time- and angle-resolved photoelectron spectroscopy, we study phonon frequencies in ultrathin FeSe/SrTiO3sub> films grown by molecular beam epitaxy. After optical excitation, we observe periodic modulations of the photoelectron spectrum as a function of pump–probe delay for 1-unit-cell, 3-unit-cell, and 60-unit-cell thick FeSe films. The frequencies of the coherent intensity oscillations increase from 5.00 ± 0.02 to 5.25 ± 0.02 THz with increasing film thickness. By comparing with previous works, we attribute this mode to the Se A1g phonon. The dominant mechanism for the phonon softening in 1-unit-cell thick FeSe films is a substrate-induced lattice strain. Results demonstrate an abrupt phonon renormalization due to a lattice mismatch between the ultrathin film and the substrate.

  19. Revisiting the Al/Al2O3sub> Interface: Coherent Interfaces and Misfit Accommodation

    SciTech Connect

    Pilania, Ghanshyam; Thijsse, Barend J.; Hoagland, Richard G.; Lazić, Ivan; Valone, Steven M.; Liu, Xiang-Yang


    We report the coherent and semi-coherent Al/α-Al2O3sub> interfaces using molecular dynamics simulations with a mixed, metallic-ionic atomistic model. For the coherent interfaces, both Al-terminated and O-terminated nonstoichiometric interfaces have been studied and their relative stability has been established. To understand the misfit accommodation at the semi-coherent interface, a 1-dimensional (1D) misfit dislocation model and a 2-dimensional (2D) dislocation network model have been studied. For the latter case, our analysis reveals an interface dislocation structure with a network of three sets of parallel dislocations, each with pure-edge character, giving rise to a pattern of coherent and stacking-fault-like regions at the interface. Structural relaxation at elevated temperatures leads to a further change of the dislocation pattern, which can be understood in terms of a competition between the stacking fault energy and the dislocation interaction energy at the interface. In conclusion, our results are expected to serve as an input for the subsequent dislocation dynamics models to understand and predict the macroscopic mechanical behavior of Al/α-Al2O3sub> composite heterostructures.

  20. Research Update: Magnetic phase diagram of EuTi1-xBxO3sub> (B = Zr, Nb)

    SciTech Connect

    Li, Ling; Zhou, Haidong; Yan, Jiaqiang; Mandrus, David; Keppens, Veerle


    Herein, we report the magnetic phase diagram of EuTi1-xBxO3sub> (B = Zr, Nb), determined from magnetization and heat capacity measurements. Upon Zr-doping, the antiferromagnetic ordering temperature TN of EuTi1-xZrxO3sub> gradually decreases from 5.6 K (x = 0) to 4.1 K (x = 1). Whereas a similar decrease in TN is observed for small amounts of Nb doping (x ≤ 0.05), ferromagnetism is induced in EuTi1-xNbxO3sub> with x > 0.05. Lastly, the ferromagnetic interaction between localized Eu 4f spins mediated by itinerant electrons introduced by Nb doping results in the ferromagnetism in EuTi1-xNbxO3sub>.

  1. Demonstration of High Current Density YBCO Coated Conductors on RE2O3sub>-Buffered Ni Substrates with Two New Alternative Architectures

    SciTech Connect

    Beach, D.B.; Chirayil, T.G.; Christen, D.K.; Cui, X.; Feenstra, R.; Goyal, A.; Kroeger, D.M.; Lee, D.F.; Martin, P.M.; Mathis, J.E.; Morrell, J.S.; Norton, D.P.; Paranthaman, M.; Specht, E.D.; Verebelyi, D.T.


    In continuation of our effort to develop single buffer layer architectures for YBCO (YBa2Cu3sub>O7-g) coated tape conductors, we have studied RE2O3sub> (RE = Y, and rare earths) as candidate materials. Three types of crystal structures including the preferred cubic phase are known for the rare earth oxides. High quality simple cubic RE2O3sub> buffer layers were grown epitaxiahy on {100}<001> textured Ni substrates using both reactive evaporation and sol-gel processing. Detailed X-ray studies have shown that the Y2O3sub>, Eu2O3sub>, Gd2O3sub>, and Yb2O3sub> were grown with a single epitaxial orientation. SEM micrographs indicated that both e-beam and sol-gel grown films were dense, continuous and crack free. High Jc YBCO films were grown on RE2O3sub>-buffered Ni substrates with sputtered cap layers. Two new alternative buffer layer architectures were developed. A high Jc of 1.8 MA/cm2 at 77 K and self-field was obtained on YBCO films with a layer sequence of YBCO (pulsed laser deposition)/Yb2O3sub> (sputtered)/Y2O3sub> (e-beam)/Ni. Also, a high Jc of over 1 MA/cm2 at 77 K and self-field was obtained on YBCO films with a layer sequence of YBCO (ex-situ BaF2 process)/CeO2 (sputtered)YSZ sputtered)/RE2O3sub> (sol-gel or e-beam)Ni. The performance of sol-gel grown buffers approached the quality of e-beam grown buffers.

  2. Constrained Surface Complexation Modeling: Rutile in RbCl, NaCl, and NaCF3sub>SO3sub> Media to 250 °C

    SciTech Connect

    Machesky, Michael L.; Předota, Milan; Ridley, Moira K.; Wesolowski, David J.


    In this paper, a comprehensive set of molecular-level results, primarily from classical molecular dynamics (CMD) simulations, are used to constrain CD-MUSIC surface complexation model (SCM) parameters describing rutile powder titrations conducted in RbCl, NaCl, and NaTr (Tr = triflate, CF3sub>SO3sub>) electrolyte media from 25 to 250 °C. Rb+ primarily occupies the innermost tetradentate binding site on the rutile (110) surface at all temperatures (25, 150, 250 °C) and negative charge conditions (-0.1 and -0.2 C/m2) probed via CMD simulations, reflecting the small hydration energy of this large, monovalent cation. Consequently, variable SCM parameters (Stern-layer capacitance values and intrinsic Rb+ binding constants) were adjusted relatively easily to satisfactorily match the CMD and titration data. The larger hydration energy of Na+ results in a more complex inner-sphere distribution, which shifts from bidentate to tetradentate binding with increasing negative charge and temperature, and this distribution was not matched well for both negative charge conditions, which may reflect limitations in the CMD and/or SCM approaches. Finally, in particular, the CMD axial density profiles for Rb+ and Na+ reveal that peak binding distances shift toward the surface with increasing negative charge, suggesting that the CD-MUSIC framework may be improved by incorporating CD or Stern-layer capacitance values that vary with charge.

  3. Electron-Temperature Dependence of the Recombination of NH4(+)((NH3)(sub n) Ions with Electrons

    NASA Technical Reports Server (NTRS)

    Skrzypkowski, M. P.; Johnson, R.


    The two-body recombination of NH4(+)(NH3)(sub 2,3) cluster-ions with electrons has been studied in an afterglow experiment in which the electron temperature T, was elevated by radio-frequency heating from 300 K up to 900 K. The recombination coefficients for the n = 2 and n = 3 cluster ions were found to be equal, alpha(sub 2, sup(2)) = alpha(sub 3, sup(2)) = (4.8 +/- 0.5) x 10(exp - 6)cu cm/s, and to vary with electron temperature as T(sub c, sup -0.65) rather than to be nearly temperature-independent as had been inferred from measurements in microwave-heated plasmas.

  4. Direct and inverse magnetoelectric effects in HoAl{sub 3}(BO{sub 3}){sub 4} single crystal

    SciTech Connect

    Freydman, A. L.; Balaev, A. D.; Dubrovskiy, A. A.; Eremin, E. V.; Temerov, V. L.; Gudim, I. A.


    The direct (ME{sub H}-) and inverse (ME{sub E}-) magnetoelectric effects in the HoAl{sub 3}(BO{sub 3}){sub 4} single crystal are studied. Temperature and magnetic field dependences of permittivity of the crystal are investigated. A relation between the investigated effects was established. It was found that the magnetoelectric effect can exist in crystals without magnetic order or spontaneous polarization. It was shown that the phenomena investigated are due to magnetostriction or magnetoelastic effect. The thermodynamic potential was considered for describing magnetoelectric effect at low magnetic fields. The results obtained are explained within a proposed qualitative microscopic model, based on interplay of configuration of 4f- electron subshell of the rare-earth element and applied magnetic or electric field.

  5. Characterization of tetragonal phases of SrRuO3sub> under epitaxial strain by density functional theory

    SciTech Connect

    Herklotz, Andreas; Dörr, Kathrin


    Using density functional theory calculations we research the effect of strain on the magnetic and structural properties of tetragonal SrRuO3sub>. All four different oxygen octahedra rotation patterns that are in agreement with tetragonal symmetry are considered and compared with the bulk-like orthorhombic structure. We find that among the tetragonal structures the phase with I4 /mcm symmetry is energetically most favorable. This structure is also lower in energy than the orthorhombic phase for compressive and tensile strain larger than -2.1% and +3.8%, respectively. The stability of the magnetic moment is found to be greatly dependent on the octahedra rotation pattern. Finally, the magnetic moment of the zero or one-tilt systems is quenched under tensile strain, while ferromagnetic order is preserved in the two or three-tilt systems.

  6. Neutron inelastic scattering measurements of low-energy phonons in the multiferroic BiFeO3sub>

    SciTech Connect

    Schneeloch, John A.; Xu, Zhijun; Wen, Jinsheng; Gehring, P. M.; Stock, C.; Matsuda, Masaaki; Winn, Barry L.; Gu, Genda; Shapiro, Stephen M.; Birgeneau, R. J.; Ushiyama, T.; Yanagisawa, Y.; Tomioka, Y.; Ito, T.; Xu, Guangyong


    In this study, we present neutron inelastic scattering measurements of the low-energy phonons in single crystal BiFeO3sub>. The dispersions of the three acoustic phonon modes (LA along [100], TA1 along [010], and TA2 along [110]) and two low-energy optic phonon modes (LO and TO1) have been mapped out between 300 and 700 K. Elastic constants are extracted from the phonon measurements. The energy linewidths of both TA phonons at the zone boundary clearly broaden when the system is warmed toward the magnetic ordering temperature TN=640 K. In conclusion, this suggests that the magnetic order and low-energy lattice dynamics in this multiferroic material are coupled.

  7. Crystal structure and lattice dynamics of Sr{sub 3}Y(BO{sub 3}){sub 3}

    SciTech Connect

    Maczka, M. Waskowska, A.; Majchrowski, A.; Kisielewski, J.; Szyrski, W.; Hanuza, J.


    X-ray, Raman and infrared (IR) studies of the Sr{sub 3}Y(BO{sub 3}){sub 3} (BOYS) single crystal grown by the Czochralski technique are presented. The crystal structure is trigonal, space group R3-bar (no. 148), and comprises six formula units in the unit cell with the hexagonal axes a=12.527(2) and c=9.280(2) A. The assignment of the observed vibrational modes is proposed on the basis of lattice dynamics calculations. The unusual large bandwidth of the internal modes and the enhancement of the principal mean square thermal displacements for BO{sub 3} and Y(1) indicate that some type of disorder is present in the studied crystal. - Graphical abstract: View of the crystal structure of BOYS along the c-axis.

  8. Local structure study of Fe dopants in Ni-deficit Ni3sub>Al alloys

    SciTech Connect

    V. N. Ivanovski; Umicevic, A.; Belosevic-Cavor, J.; Lei, Hechang; Li, Lijun; Cekic, B.; Koteski, V.; Petrovic, C.


    We found that the local electronic and magnetic structure, hyperfine interactions, and phase composition of polycrystalline Ni–deficient Ni 3-x FexAl (x = 0.18 and 0.36) were investigated by means of 57 Fe Mössbauer spectroscopy. The samples were characterized by X–ray diffraction and magnetization measurements. The ab initio calculations performed with the projector augmented wave method and the calculations of the energies of iron point defects were done to elucidate the electronic structure and site preference of Fe doped Ni 3sub> Al. Moreover, the value of calculated electric field gradient tensor Vzz=1.6 1021Vm-2 matches well with the results of Mössbauer spectroscopy and indicates that the Fe atoms occupy Ni sites.

  9. Crystal structure and magnetic properties of Na{sub 2}Ni{sup II}(HPO{sub 3}){sub 2}

    SciTech Connect

    Maalej, Wassim; Vilminot, Serge; Elaoud, Zakaria; Mhiri, Tahar; Kurmoo, Mohamedally


    Na{sub 2}Ni(HPO{sub 3}){sub 2}, obtained as light yellow-green crystals under mild hydrothermal conditions, crystallizes in the orthorhombic Pnma space-group with lattice parameters: a=11.9886(3), b=5.3671(2), c=9.0764(3) A, V=584.01 A{sup 3}, Z=4. The structure consists of zig-zag chains of NiO{sub 6} octahedra bridged by two HPO{sub 3}{sup 2-} and the chains are further connected through HPO{sub 3}{sup 2-} to four nearest chains to form a three dimensional framework, delimiting intersecting tunnels in which the sodium ions are located. The Na cations reside in the irregular Na(1)O{sub 5}, Na-O of 2.276-2.745 A, and Na(2)O{sub 9}, Na-O of 2.342-2.376 A, environments. The presence of the phosphite monoanion has been further confirmed by IR spectroscopy. Due to the 3D framework of Ni connected by O-P-O bridges, the magnetic susceptibility behaves as a paramagnet above 100 K (C=1.49(2) emu K mol{sup -1}, {mu}{sub eff}=3.45 {mu}{sub B}, {Theta}=-39(2) K) and below 6 K, it orders antiferromagnetically as confirmed the sharp drop and the non-Brillouin behavior of the isothermal magnetization at 2 K. - Graphical abstract: The structure of Na{sub 2}Ni(HPO{sub 3}){sub 2} consists of zig-zag chains of NiO{sub 6} octahedra bridged by two HPO{sub 3}{sup 2-} and the chains are further connected through HPO{sub 3}{sup 2-} to four nearest chains to form a three dimensional framework, delimiting intersecting tunnels in which the sodium ions are located. It orders antiferromagnetically at 6 K. Display Omitted

  10. Crystal structures and magnetic properties of lanthanide containing borates LnM(BO{sub 3}){sub 2} (Ln=Y, Ho–Lu; M=Sc, Cr)

    SciTech Connect

    Doi, Yoshihiro Satou, Tatsuya; Hinatsu, Yukio


    The synthesis, crystal structures and magnetic properties of LnM(BO{sub 3}){sub 2} (Ln=Y, Ho–Lu; M=Sc, Cr) were investigated. The LnCr(BO{sub 3}){sub 2} compounds crystallize in the dolomite-type structure with space group R3{sup ¯}, in which the Ln and Cr ions occupy two octahedral sites. From the result of structural analysis, it was found that there is an anti-site disorder between these two sites and its chemical formula is more exactly Ln{sub 1−r}Cr{sub r}[Cr{sub 1−r}Ln{sub r}](BO{sub 3}){sub 2}. On the other hand, the LnSc(BO{sub 3}){sub 2} adopt the calcite-type structure with space group R3{sup ¯}c. The Ln and Sc ions randomly occupy an octahedral site and the chemical formula is represented as (Ln{sub 0.5}Sc{sub 0.5})BO{sub 3}. From the magnetic susceptibility and specific heat measurements, we found that all the LnCr(BO{sub 3}){sub 2} show an antiferromagnetic transition at 6.1–8.1 K. This transition is mainly due to the ordering of Cr{sup 3+} magnetic moments. Among the compounds with magnetic Ln{sup 3+} ions, only YbCr(BO{sub 3}){sub 2} shows an antiferromagnetic ordering of Ln{sup 3+} ion at 2.1 K. - Graphical abstract: The lanthanide containing borates LnM(BO{sub 3}){sub 2} (Ln=Y, Ho–Lu; M=Sc, Cr) have the dolomite-type (Ln=Cr) and calcite-type (Ln=Sc) structures. Both structures are similar to each other except for the difference in the partially or fully disordered arrangements of octahedral sites. At low temperatures, the LnCr(BO{sub 3}){sub 2} compounds show an antiferromagnetic transition due to a long-range ordering of Cr{sup 3+} moments. Among them only YbCr(BO{sub 3}){sub 2} shows an antiferromagnetic ordering of Ln{sup 3+} ion at 2.1 K. Display Omitted - Highlights: • Lanthanide containing borates LnM(BO{sub 3}){sub 2} (Ln=Y, Ho–Lu; M=Sc, Cr) have been synthesized. • LnCr(BO{sub 3}){sub 2} has the dolomite-type structure with an anti-site disorder between Ln and Cr sites. • LnSc(BO{sub 3}){sub 2} has the calcite

  11. Luminescence improvement in Pr{sup 3+} and Gd{sup 3+} activated Sr{sub 2}Mg(BO{sub 3}){sub 2} inorganic phosphor

    SciTech Connect

    Gawande, A.B.; Sonekar, R.P.; Omanwar, S.K.


    Highlights: • Sr{sub 2}Mg(BO{sub 3}){sub 2} doped Gd{sup 3+} and Pr{sup 3+} have been synthesized by solution combustion synthesis technique. • Effect of doping concentration of Gd{sup 3+} and Pr{sup 3+} on the luminescence of synthesized material is discussed. • Effect of charge compensation by Li{sup +}, Na{sup +} and K{sup +} on emission intensity is studied in detail. • Efficient energy transfer from Pr{sup 3+} to Gd{sup 3+} in Sr{sub 2}Mg(BO{sub 3}){sub 2} was observed. • Optimum concentration and critical transfer distance for optimum concentration have been determined. - Abstract: The photoluminescence properties of (Sr{sub 1−x}Pr{sub x}){sub 2}Mg(BO{sub 3}){sub 2}; (Sr{sub 1−2x}Pr{sub x}M{sub x}){sub 2}Mg(BO{sub 3}){sub 2,} (M = Li, Na, K); (Sr{sub 1−x}Gd{sub x}){sub 2}Mg(BO{sub 3}){sub 2}; (Sr{sub 1−2x}Gd{sub x}M{sub x}){sub 2}Mg(BO{sub 3}){sub 2}, (M = Li, Na, K) and (Sr{sub 1−4x}Pr{sub x}Gd{sub x}Na{sub 2x}){sub 2}Mg(BO{sub 3}){sub 2} inorganic phosphors prepared by solution combustion synthesis technique are discussed. The structure of the prepared phosphor characterized using Thermogravimetric–differential thermal analysis, X-ray diffraction and fourier transform-infrared. Scanning electron microscopy images of the prepared materials show irregular grains with agglomerate phenomena. Photoluminescence properties were studied at room temperature. Optimum concentration and critical transfer distance of the synthesized phosphors were determined.

  12. Highly constrained ferroelectric [BaTiO{sub 3}]{sub (1−x)Λ}/[BaZrO{sub 3}]{sub xΛ} superlattices: X-ray diffraction and Raman spectroscopy

    SciTech Connect

    Belhadi, J.; El Marssi, M. Gagou, Y.; El Mendili, Y.; Bouyanfif, H.; Yuzyuk, Yu. I.; Raevski, I. P.; Wolfman, J.


    We report an x-ray diffraction (XRD) and a Raman-scattering investigation of ferroelectric/paraelectric superlattices [BaTiO{sub 3}] {sub (1−x)Λ}/[BaZrO{sub 3}]{sub xΛ} for which the composition varied, 0.15 ≤ x ≤ 0.85, while the superlattice (SL) modulation period Λ was kept constant at about 100 Å. The samples were epitaxially grown by pulsed laser deposition on MgO substrates buffered with La{sub 0.5}Sr{sub 0.5}CoO{sub 3}. Based on the XRD analysis and on polarized Raman spectra, we have showed that the large strain in SLs induced ferroelectricity in BaZrO{sub 3} (BZ) for all SLs, a material that is paraelectric in the bulk form at any temperature and in the single film. The induced polar axis in BZ layers is perpendicular to the plane of substrate while BaTiO{sub 3} (BT) layers exhibit in-plane polar orientation. Raman spectroscopy revealed a lattice ordering in SLs due to the misfit strain generated by the large lattice mismatch between the alternating BZ and BT layers. This strain induced a huge upward frequency of the lowest E(1TO) soft mode from 60 cm{sup −1} in the BT single film to 215 cm{sup −1} in the SL with x = 0.85. These results show that in spite of relatively large periodicity of SLs, they are highly constrained and the variation of BZ ratio allowed modifying strains between layers. The temperature dependence of the Raman spectra for BT{sub 0.3Λ}/BZ{sub 0.7Λ} and BT{sub 0.7Λ}/BZ{sub 0.3Λ} samples revealed giant shift of the ferroelectric phase transition. The phase transition temperature was found to be upshifted by about 300 °C with respect to BT single crystal.

  13. Thermal Reactions of Uranium Metal, UO2, U3sub>O8, UF4, and UO2F2 with NF3sub> to Produce UF6

    SciTech Connect

    McNamara, Bruce K; Scheele, Randall D; Kozelisky, Anne E; Edwards, Matthew K


    The objective of this paper is to demonstrate that NF3sub> fluorinates uranium metal, UO2, UF4, UO3sub>, U3sub>O8, and UO2F2•2H2O to produce the volatile UF6 at temperatures between 100 and 500ºC. Thermogravimetric reaction profiles are described that reflect changes in the uranium oxidation state and discrete chemical speciation. Differences in the onset temperatures for each system indicate that NF3sub>-substrate interactions are important for the temperature at which NF3sub> reacts: U metal > UO3sub> > UO2 > UO2F2 > UF4 and in fact may indicate different fluorination mechanisms for these various substrates. These studies demonstrate that NF3sub> is a potential replacement fluorinating agent in the existing nuclear fuel cycle and in oft-proposed actinide volatility reprocessing.

  14. Interfacial mode coupling as the origin of the enhancement of Tc in FeSe films on SrTiO3sub>

    SciTech Connect

    Lee, J. J.; Schmitt, F. T.; Moore, R. G.; Johnston, S.; Cui, Y. -T.; Li, W.; Yi, M.; Liu, Z. K.; Hashimoto, M.; Zhang, Y.; Lu, D. H.; Devereaux, T. P.; Lee, D. -H.; Shen, Z. -X.; /SIMES, Stanford /SLAC /Stanford U., Geballe Lab.


    Films of iron selenide (FeSe) one unit cell thick grown on strontium titanate (SrTiO3sub> or STO) substrates have recently shown superconducting energy gaps opening at temperatures close to the boiling point of liquid nitrogen (77 K), which is a record for the iron-based superconductors. The gap opening temperature usually sets the superconducting transition temperature Tc, as the gap signals the formation of Cooper pairs, the bound electron states responsible for superconductivity. To understand why Cooper pairs form at such high temperatures, we examine the role of the SrTiO3sub> substrate. Here we report high-resolution angle-resolved photoemission spectroscopy results that reveal an unexpected characteristic of the single-unit-cell FeSe/SrTiO3sub> system: shake-off bands suggesting the presence of bosonic modes, most probably oxygen optical phonons in SrTiO3sub>, which couple to the FeSe electrons with only a small momentum transfer. Such interfacial coupling assists superconductivity in most channels, including those mediated by spin fluctuations. Our calculations suggest that this coupling is responsible for raising the superconducting gap opening temperature in single-unit-cell FeSe/SrTiO3sub>.

  15. Exchange bias effect in Au-Fe3sub>O4 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-Fe3sub>O4 dumbbell nanoparticles in two samples with different sizes of the Au seed nanoparticles (4.1 and 2.7 nm) and same size of Fe3sub>O4 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 Fe3sub>O4 nanoparticles, originating at the interface with the Au nanoparticles. The interface between antiferromagnetic FeO and ferrimagnetic Fe3sub>O4 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 Fe3sub>O4 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.

  16. Study of the solid-liquid equilibria in the LiPO{sub 3}-Y(PO{sub 3}){sub 3} binary system

    SciTech Connect

    Jouini, Anis; Ferid, Mokhtar; Trabelsi-Ayadi, Malika


    The LiPO{sub 3}-Y(PO{sub 3}){sub 3} system has been studied for the first time. Microdifferential thermal analysis ({mu}-DTA), infrared spectroscopy (IR) and X-ray diffraction were used to investigate the liquidus and solidus relations. The only new compound observed within this system is LiY(PO{sub 3}){sub 4}, melting incongruently at 1104 K. An eutectic appears at 4{+-}1 mol% Y(PO{sub 3}){sub 3} at 933 K. LiY(PO{sub 3}){sub 4} crystallizes in the monoclinic system C{sub 2/c} with a unit cell: a=16.201(4) A, b=7.013(2) A, c=9.573(2) A, {beta}=125.589(9) deg. , Z=4 and V=884.5 A{sup 3}, which is isostructural to LiNd(PO{sub 3}){sub 4}. The infrared absorption spectrum indicates that this salt is a chain polyphosphate.

  17. Fe2O3sub>–TiO2 core–shell nanorod arrays for visible light photocatalytic applications

    SciTech Connect

    Yao, Kun; Basnet, Pradip; Sessions, Henry; Larsen, George K.; Murph, Simona E. Hunyadi; Zhao, Yiping


    By using the glancing angle deposition technique and post-deposition annealing, Fe2O3sub>–TiO2 core-shell nanorod arrays with specific crystalline states can be designed and fabricated. The Fe2O3sub>–TiO2 core-shell samples annealed at temperatures greater than 450°C formed α-Fe2O3sub> and anatase TiO2, and showed higher catalytic efficiency for the degradation of methylene blue (MB) under visible light illumination when compared with pure anatase TiO2 or α-Fe2O3sub> nanorod arrays. Solar conversion of carbon dioxide and water vapor in the presence of Fe2O3sub>–TiO2 core-shell nanorod arrays was also investigated. Carbon monoxide, hydrogen, methane, and methanol along with other hydrocarbons were produced after only several hours’ exposure under ambient sunlight. It was determined that the core-shell structure showed greater efficiency for solar CO2 conversion than the pure TiO2 nanorod arrays.

  18. Electrochemical and spectral probes of metal/ligand orbital mixing in Ru(NH sub 3 ) sub 4 (bpy) sup 2+ and Ru(NH sub 3 ) sub 4 (phen) sup 2+

    SciTech Connect

    Mines, G.A.; Roberts, J.A.; Hupp, J.T. )


    An electrochemical variational method has been used to examine experimentally the extent of metal/ligand orbital mixing and electronic coupling in complexes of the type Ru{sup 11}(NH{sub 3}){sub 4}L{sup 2+} (L = 2,2{prime}-bipyridine or 1,10-phenanthroline). From the experiments, strong localization of d{pi} electrons at the ruthenium metal center is indicated. Nevertheless, some mixing of d{pi}(Ru) and {pi}*(bpy; phen) is detected, implying a significant degree of delocalization (ca. 25%). These results differ substantially from those derived from metal-to-ligand charge-transfer (MLCT) oscillator strength measurements. The latter indicate less than 2% delocalization. The difference is particularly surprising in view of the fact that both approaches derive from Mulliken charge-transfer theory and the two are employed at similar (but not identical) levels of approximation. The origin of the discrepancies is unclear, but may be related to the choice of charge-transfer distance which must necessarily be made in the optical analysis. Independent estimates of electronic delocalization, based on partial oxidation-state markers in vibrational Raman spectra, corroborate the electrochemical findings.

  19. Structure and temperature-dependent phase transitions of lead-free Bi1/2Na1/2TiO3sub>-Bi1/2K1/2TiO3sub>-K0.5Na0.5NbO3sub> piezoceramics

    SciTech Connect

    Anton, Eva-Maria; Schmitt, Ljubomira Ana; Hinterstein, Manuel; Trodahl, Joe; Kowalski, Ben; Jo, Wook; Kleebe, Hans-Joachim; Rödel, Jürgen; Jones, Jacob L.


    Structure and phase transitions of (1-y)((1-x)Bi1/2Na1/2TiO3sub>-xBi1/2K1/2TiO3sub>)-yK0.5Na0.5NbO3sub> (x; y) piezoceramics (0.1 ≤ x ≤ 0.4; 0 ≤ y ≤ 0.05) were investigated by transmission electron microscopy, neutron diffraction, temperature-dependent x-ray diffraction, and Raman spectroscopy. The local crystallographic structure at room temperature (RT) does not change by adding K0.5Na0.5NbO3sub> to Bi1/2Na1/2TiO3sub>-xBi1/2K1/2TiO3sub> for x = 0.2 and 0.4. The average crystal structure and microstructure on the other hand develop from mainly long-range polar order with ferroelectric domains to short-range order with polar nanoregions displaying a more pronounced relaxor character. The (0.1; 0) and (0.1; 0.02) compositions exhibit monoclinic Cc space group symmetry, which transform into Cc + P4bm at 185 and 130 °C, respectively. This high temperature phase is stable at RT for the morphotropic phase boundary compositions of (0.1; 0.05) and all compositions with x = 0.2. For the compositions of (0.1; 0) and (0.1; 0.02), local structural changes on heating are evidenced by Raman; for all other compositions, changes in the long-range average crystal structure were observed.

  20. Highly dispersed SiOx/Al2O3sub> catalysts illuminate the reactivity of isolated silanol sites

    SciTech Connect

    Mouat, Aidan R.; George, Cassandra; Kobayashi, Takeshi; Pruski, Marek; van Duyne, Richard P.; Marks, Tobin J.; Stair, Peter C.


    The reaction of γ-alumina with tetraethylorthosilicate (TEOS) vapor at low temperatures selectively yields monomeric SiOx species on the alumina surface. These isolated (-AlO)3sub>Si(OH) sites are characterized by PXRD, XPS, DRIFTS of adsorbed NH3sub>, CO, and pyridine, and 29Si and 27Al DNP-enhanced solid-state NMR spectroscopy. The formation of isolated sites suggests that TEOS reacts preferentially at strong Lewis acid sites on the γ-Al2O3sub> surface, functionalizing the surface with “mild” Brønsted acid sites. As a result, for liquid-phase catalytic cyclohexanol dehydration, these SiOx sites exhibit up to 3.5-fold higher specific activity than the parent alumina with identical selectivity.

  1. Room temperature optical anisotropy of a LaMnO3sub> thin-film induced by ultra-short pulse laser

    SciTech Connect

    Munkhbaatar, Purevdorj; Marton, Zsolt; Tsermaa, Bataarchuluun; Choi, Woo Seok; Seo, Sung Seok A.; Kim, Jin Seung; Nakagawa, Naoyuki; Hwang, H. Y.; Lee, Ho Nyung; Myung-Whun, Kim


    Ultra-short laser pulse induced optical anisotropy of LaMnO3sub> thin films grown on SrTiO3sub> substrates were observed by irradiation with a femto-second laser pulse with the fluence of less than 0.1 mJ/cm2 at room temperature. The transmittance and reflectance showed different intensities for different polarization states of the probe pulse after pump pulse irradiation. The theoretical optical transmittance and re ectance that assumed an orbital ordering of the 3d eg electrons in Mn3+ ions resulted in an anisotropic time dependent changes similar to those obtained from the experimental results, suggesting that the photo-induced optical anisotropy of LaMnO3sub> is a result of photo-induced symmetry breaking of the orbital ordering for an optically excited state.

  2. Observation of a periodic array of flux-closure quadrants in strained ferroelectric PbTiO3sub> films

    SciTech Connect

    Tang, Y. L.; Zhu, Y. L; Ma, Xiuliang; Borisevich, Albina Y; Morozovska, A. N.; Eliseev, Eugene; Wang, W. Y; Wang, Yujia; Xu, Y. B.; Zhang, Z. D.; Pennycook, Stephen J


    Nanoscale ferroelectrics are expected to exhibit various exotic domain configurations, such as the full flux-closure pattern that is well known in ferromagnetic materials. Here we observe not only the atomic morphology of the flux-closure quadrant but also a periodic array of flux closures in ferroelectric PbTiO3sub> films, mediated by tensile strain on a GdScO3sub> substrate. Using aberration-corrected scanning transmission electron microscopy, we directly visualize an alternating array of clockwise and counterclockwise flux closures, whose periodicity depends on the PbTiO3sub> film thickness. In the vicinity of the core, the strain is sufficient to rupture the lattice, with strain gradients up to 109 per meter. We found engineering strain at the nanoscale may facilitate the development of nanoscale ferroelectric devices.

  3. Synergy of elastic and inelastic energy loss on ion track formation in SrTiO3sub>

    SciTech Connect

    Weber, William J.; Zarkadoula, Eva; Pakarinen, Olli H.; Sachan, Ritesh; Chisholm, Matthew F.; Liu, Peng; Xue, Haizhou; Jin, Ke; Zhang, Yanwen


    While the interaction of energetic ions with solids is well known to result in inelastic energy loss to electrons and elastic energy loss to atomic nuclei in the solid, the coupled effects of these energy losses on defect production, nanostructure evolution and phase transformations in ionic and covalently bonded materials are complex and not well understood due to dependencies on electron-electron scattering processes, electron-phonon coupling, localized electronic excitations, diffusivity of charged defects, and solid-state radiolysis. Here we show that a colossal synergy occurs between inelastic energy loss and pre-existing atomic defects created by elastic energy loss in single crystal strontium titanate (SrTiO3sub>), resulting in the formation of nanometer-sized amorphous tracks, but only in the narrow region with pre-existing defects. These defects locally decrease the electronic and atomic thermal conductivities and increase electron-phonon coupling, which locally increase the intensity of the thermal spike for each ion. This work identifies a major gap in understanding on the role of defects in electronic energy dissipation and electron-phonon coupling; it also provides insights for creating novel interfaces and nanostructures to functionalize thin film structures, including tunable electronic, ionic, magnetic and optical properties.

  4. High-performance visible blind ultraviolet photodetector based on KTaO3sub> single crystal.


    Yang, Jing-Ting; Ge, Chen; Jin, Kui-Juan; Lu, Hui-Bin; Yang, Guo-Zhen


    We report a visible-blind ultraviolet photoconductive detector with interdigitated electrodes based on KTaO3sub> (KTO) single crystals. Both the steady spectral responses and the transient photovoltaic measurements clearly exhibit a cutoff wavelength at 344 nm (∼3.6  eV), in accordance with the bandgap of KTO. The KTO photodetectors show a low dark current ∼1.5  pA at 20 V, and a high UV-to-visible rejection ratio with 3 orders of magnitude at room temperature. The quantum efficiency is 37.49% under 20 V bias, and the detectivity D* of 3.85×1012  cm·Hz0.5/W, which is comparable to that of silicon photodetectors in the UV region. The rise time of photoelectric response is ∼260  ps, indicating an ultrafast photoelectric response characteristic. The present work offers appealing prospects for the application of KTO materials in high-performance visible blind ultraviolet photodetectors. PMID:27140560

  5. Thermoelectric properties of the unfilled skutterudite FeSb3sub> from first principles and Seebeck local probes

    SciTech Connect

    Lemal, Sébastien; Nguyen, Ngoc; de Boor, Johannes; Ghosez, Philippe; Varignon, Julien; Klobes, Benedikt; Hermann, Raphaël P.; Verstraete, Matthieu J.


    In this paper, using a combination of first-principles calculations and experimental transport measurements, we study the electronic and magnetic structure of the unfilled skutterudite FeSb3sub>. We employ the hybrid functional approach for exchange correlation. The ground state is determined to be antiferromagnetic with an atomic magnetic moment of 1.6μB/Fe. The Néel temperature TN is estimated at 6 K, in agreement with experiments which found a paramagnetic state down to 10 K. The ground state is semiconducting, with a small electronic gap of 33meV, also consistent with previous experiments on films. Charge carrier concentrations are estimated from Hall resistance measurements. The Seebeck coefficient is measured and mapped using a scanning probe at room temperature that yields an average value of 38.6μVK-1, slightly lower than the theoretical result. Finally, the theoretical conductivity is analyzed as a function of temperature and concentration of charge carriers.

  6. Growth, structural, IR and magnetic studies of a new gadolinium metaphosphate, Gd(PO{sub 3}){sub 3}

    SciTech Connect

    Naili, H. . E-mail:; Ettis, H.; Yahyaoui, S.; Mhiri, T.


    The crystal structure of gadolinium metaphosphate Gd(PO{sub 3}){sub 3} has been established by X-ray diffraction. This compound crystallizes in the orthorhombic system (space group C222{sub 1}, Z=4) with cell parameters: a=8.4530 (3), b=11.0576 (4) and c=7.1952 (2)A. The structure was refined to R{sub 1}=0.0234 and wR{sub 2}=0.0502 using 2180 independent reflections (I>2{sigma}(I)). Phosphorus atoms are in slightly irregular tetrahedral oxygen coordination, gadolinium atoms are in considerably distorted dodecahedral oxygen coordination. Formally, the 3D framework in the structure can be described by the PO{sub 4} tetrahedra sharing corners to form helical chains and the GdO{sub 8} polyhedra sharing edges in a zigzag fashion. The shortest Gd-Gd distance is 4.174 (2)A. The infrared spectrum of the title compound recorded at room temperature in the frequency range of 400-4000cm{sup -1}, confirm the atomic arrangement within the structure. Below T{sub C}=25K, the magnetic susceptibility evolution is characteristic of a ferromagnetic order. In the high-temperature region above 100K, the susceptibility follows a Curie-Weiss law with C=7.91cm{sup 3}Kmol{sup -1} and {theta}=9.96K.

  7. Stabilization of weak ferromagnetism by strong magnetic response to epitaxial strain in multiferroic BiFeO3sub>

    SciTech Connect

    Cooper, Valentino R.; Lee, Jun Hee; Krogel, Jaron T.; Okamoto, Satoshi; Dixit, Hemant M.


    Multiferroic BiFeO3sub> exhibits excellent magnetoelectric coupling critical for magnetic information processing with minimal power consumption. Thus, the degenerate nature of the easy spin axis in the (111) plane presents roadblocks for real world applications. Here, we explore the stabilization and switchability of the weak ferromagnetic moments under applied epitaxial strain using a combination of first-principles calculations and group-theoretic analyses. We demonstrate that the antiferromagnetic moment vector can be stabilized along unique crystallographic directions ([110] and [-110]) under compressive and tensile strains. A direct coupling between the anisotropic antiferrodistortive rotations and Dzyaloshinskii-Moria interactions drives the stabilization of weak ferromagnetism. Furthermore, energetically competing C- and G-type magnetic orderings are observed at high compressive strains, suggesting that it may be possible to switch the weak ferromagnetism on and off under application of strain. These findings emphasize the importance of strain and antiferrodistortive rotations as routes to enhancing induced weak ferromagnetism in multiferroic oxides.

  8. Tuning the metal-insulator crossover and magnetism in SrRuO3sub> by ionic gating

    SciTech Connect

    Yi, Hee Taek; Gao, Bin; Xie, Wei; Cheong, Sang -Wook; Podzorov, Vitaly


    Reversible control of charge transport and magnetic properties without degradation is a key for device applications of transition metal oxides. Chemical doping during the growth of transition metal oxides can result in large changes in physical properties, but in most of the cases irreversibility is an inevitable constraint. We report a reversible control of charge transport, metal-insulator crossover and magnetism in field-effect devices based on ionically gated archetypal oxide system - SrRuO3sub>. In these thin-film devices, the metal-insulator crossover temperature and the onset of magnetoresistance can be continuously and reversibly tuned in the range 90–250 K and 70–100 K, respectively, by application of a small gate voltage. We infer that a reversible diffusion of oxygen ions in the oxide lattice dominates the response of these materials to the gate electric field. These findings provide critical insights into both the understanding of ionically gated oxides and the development of novel applications.

  9. M5Si3sub>(M=Ti, Nb, Mo) Based Transition-Metal Silicides for High Temperature Applications

    SciTech Connect

    Tang, Zhihong


    Transition metal silicides are being considered for future engine turbine components at temperatures up to 1600 C. Although significant improvement in high temperature strength, room temperature fracture toughness has been realized in the past decade, further improvement in oxidation resistance is needed. Oxidation mechanism of Ti5Si3sub>-based alloys was investigated. Oxidation behavior of Ti5Si3sub>-based alloy strongly depends on the atmosphere. Presence of Nitrogen alters the oxidation behavior of Ti5Si3sub> by nucleation and growth of nitride subscale. Ti5Si3.2and Ti5Si3sub>C0.5 alloys exhibited an excellent oxidation resistance in nitrogen bearing atmosphere due to limited dissolution of nitrogen and increased Si/Ti activity ratio. MoSi2 coating developed by pack cementation to protect Mo-based Mo-Si-B composites was found to be effective up to 1500 C. Shifting coating composition to T1+T2+Mo3sub>Si region showed the possibility to extend the coating lifetime above 1500 C by more than ten times via formation of slow growing Mo3sub>Si or T2 interlayer without sacrificing the oxidation resistance of the coating. The phase equilibria in the Nb-rich portion of Nb-B system has been evaluated experimentally using metallographic analysis and differential thermal analyzer (DTA). It was shown that Nbss (solid solution) and NbB are the only two primary phases in the 0-40 at.% B composition range, and the eutectic reaction L {leftrightarrow} NbSS + NbB was determined to occur at 2104 ± 5 C by DTA.

  10. Improved Pharmacological and Structural Properties of HIV Fusion Inhibitor AP3sub> over Enfuvirtide: Highlighting Advantages of Artificial Peptide Strategy

    SciTech Connect

    Zhu, Xiaojie; Zhu, Yun; Ye, Sheng; Wang, Qian; Xu, Wei; Su, Shan; Sun, Zhiwu; Yu, Fei; Liu, Qi; Wang, Chao; Zhang, Tianhong; Zhang, Zhenqing; Zhang, Xiaoyan; Xu, Jianqing; Du, Lanying; Liu, Keliang; Lu, Lu; Zhang, Rongguang; Jiang, Shibo


    Enfuvirtide (T20), is the first HIV fusion inhibitor approved for treatment of HIV/AIDS patients who fail to respond to the current antiretroviral drugs. However, its clinical application is limited because of short half-life, drug resistance and cross-reactivity with the preexisting antibodies in HIV-infected patients. Using an artificial peptide strategy, we designed a peptide with non-native protein sequence, AP3sub>, which exhibited potent antiviral activity against a broad spectrum of HIV-1 strains, including those resistant to T20, and had remarkably longer in vivo half-life than T20. While the preexisting antibodies in HIV-infected patients significantly suppressed T20’s antiviral activity, these antibodies neither recognized AP3sub>, nor attenuated its anti-HIV-1 activity. Structurally different from T20, AP3sub> could fold into single-helix and interact with gp41 NHR. The two residues, Met and Thr, at the N-terminus of AP3sub> form a hook-like structure to stabilize interaction between AP3sub> and NHR helices. Therefore, AP3sub> has potential for further development as a new HIV fusion inhibitor with improved antiviral efficacy, resistance profile and pharmacological properties over enfuvirtide. Meanwhile, this study highlighted the advantages of artificially designed peptides, and confirmed that this strategy could be used in developing artificial peptide-based viral fusion inhibitors against HIV and other enveloped viruses.

  11. Microemulsion-assisted solvothermal synthesis of Nd{sub 2}(CO{sub 3}){sub 3}.8H{sub 2}O microstructures

    SciTech Connect

    Zhu, Wenqing; Ma, Jin; Xing, Xiping; Xu, Lei; Chen, Yashao


    Research highlights: {yields} Pyramid-like and spherical Nd{sub 2}(CO{sub 3}){sub 3}.8H{sub 2}O microstructures were synthesized using a microemulsion-assisted solvothermal method with precise control of the reaction time and reaction temperature. {yields} The obtained products were characterized by X-ray diffraction (XRD), differential scanning calorimetry and thermal gravimetric analysis (DSC-TGA), scanning electron microscope (SEM), transmission electron microscope (TEM) and electron diffraction (ED). {yields} The increase in size of pyramid-like Nd{sub 2}(CO{sub 3}){sub 3}.8H{sub 2}O microstructures with increasing reaction time was attributed to the typical Ostwald ripening process, while the increase in size of spherical Nd{sub 2}(CO{sub 3}){sub 3}.8H{sub 2}O microstructures with increasing reaction temperature was explained by the increasing collision probability of microemulsion droplets. -- Abstract: Microstructures of Nd{sub 2}(CO{sub 3}){sub 3}.8H{sub 2}O with various morphological structures and sizes were successfully synthesized using the microemulsion-assisted solvothermal method. The obtained products were characterized by X-ray diffraction (XRD), differential scanning calorimetry and thermal gravimetric analysis (DSC-TGA), scanning electron microscope (SEM), transmission electron microscope (TEM) and electron diffraction (ED). The results showed that pyramid-like and spherical Nd{sub 2}(CO{sub 3}){sub 3}.8H{sub 2}O microstructures were synthesized depending on the reaction time and reaction temperature. Moreover, the reaction time and temperature also played important roles in controlling the morphologies and sizes of the resulting Nd{sub 2}(CO{sub 3}){sub 3}.8H{sub 2}O microstructures.

  12. Optimized moth-eye anti-reflective structures for As2S3sub> chalcogenide optical fibers.


    Weiblen, R J; Menyuk, C R; Busse, L E; Shaw, L B; Sanghera, J S; Aggarwal, I D


    We computationally investigate moth-eye anti-reflective nanostructures imprinted on the endfaces of As2S3sub> chalcogenide optical fibers. With a goal of maximizing the transmission through the endfaces, we investigate the effect of changing the parameters of the structure, including the height, width, period, shape, and angle-of-incidence. Using these results, we design two different moth-eye structures that can theoretically achieve almost 99.9% average transmisison through an As2S3sub> surface. PMID:27409844

  13. Enhanced electrical transparency by ultra-thin LaAlO3sub> insertion at oxide metal/semiconductor heterointerfaces

    SciTech Connect

    Yajima, Takeaki; Minohara, Makoto; Bell, Christopher; Kumigashira, Hiroshi; Oshima, Masaharu; Hwang, Harold Y.; Hikita, Yasuyuki


    We demonstrate that the electrical conductivity of metal/semiconductor oxide heterojunctions can be increased over 7 orders of magnitude by inserting an ultrathin layer of LaAlO3sub>. This counterintuitive result, that an interfacial barrier can be driven transparent by inserting a wide-gap insulator, arises from the large internal electric field between the two polar LaAlO3sub> surfaces. In conclusion, this field modifies the effective band offset in the device, highlighting the ability to design the electrostatic boundary conditions with atomic precision.

  14. Effect of neutron irradiation on defect evolution in Ti3sub>SiC2 and Ti2AlC

    SciTech Connect

    Tallman, Darin J.; He, Lingfeng; Garcia-Diaz, Brenda L.; Hoffman, Elizabeth N.; Kohse, Gordon; Sindelar, Robert L.; Barsoum, Michel W.


    Here, we report on the characterization of defects formed in polycrystalline Ti3sub>SiC2 and Ti2AlC samples exposed to neutron irradiation – up to 0.1 displacements per atom (dpa) at 350 ± 40 °C or 695 ± 25 °C, and up to 0.4 dpa at 350 ± 40 °C. Black spots are observed in both Ti3sub>SiC2 and Ti2AlC after irradiation to both 0.1 and 0.4 dpa at 350 °C. After irradiation to 0.1 dpa at 695 °C, small basal dislocation loops, with a Burgers vector of b = 1/2 [0001] are observed in both materials. At 9 ± 3 and 10 ± 5 nm, the loop diameters in the Ti3sub>SiC2 and Ti2AlC samples, respectively, were comparable. At 1 × 1023 loops/m3, the dislocation loop density in Ti2AlC was ≈1.5 orders of magnitude greater than in Ti3sub>SiC2, at 3 x 1021 loops/m3. After irradiation at 350 °C, extensive microcracking was observed in Ti2AlC, but not in Ti3sub>SiC2. The room temperature electrical resistivities increased as a function of neutron dose for all samples tested, and appear to saturate in the case of Ti3sub>SiC2. The MAX phases are unequivocally more neutron radiation tolerant than the impurity phases TiC and Al2O3sub>. Based on these results, Ti3sub>SiC2 appears to be a more promising MAX phase candidate for high temperature nuclear applications than Ti2AlC.

  15. X-ray Microdiffraction from α-Ti0.04Fe1.96O3sub> (0001) Epitaxial Film Grown Over α-Cr2O3sub> Buffer Layer Boundary

    SciTech Connect

    Kim, Chang-Yong


    Ti-doped hematite (α-Ti0.04Fe1.96O3sub>) film grown over patterned α-Cr2O3sub> buffer layer on α-Al2O3sub>(0001) substrate was characterized with synchrotron X-ray microdiffraction. The film was grown by oxygen plasma assisted molecular beam epitaxy method. The film growth mode was correlated to buffer layer boundary and Ti concentration variation. Epitaxial α-Ti0.04Fe1.96O3sub> film was formed on bare substrate adjacent to the buffer layer. The epitaxial film was connected laterally to a strain-relaxed epitaxial α-Ti0.04Fe1.96O3sub> film grown on the buffer layer. On bare α-Al2O3 substrate with diminished Ti concentration only a small portion of α-TixFe1-xO3sub> film was epitaxial either as coherent to the substrate or strain-relaxed form.

  16. Synthesis of the Stereoisomeric Clusters 1,2-Os3sub>(CO)10(trans-dpmn) and 1,2-Os3sub>(CO)10(cis-dpmn) [where dpmn = 2,3-bis(diphenylphosphinomethyl)-5-norbornene]: DFT Evaluation of the Isomeric Clusters 1,2-Os3sub>(CO)10(dpmn) and Isomer-Dependent Diphosphine Ligand Activation

    SciTech Connect

    Yang, Li; Nesterov, Vladimir N.; Wang, Xiaoping; Richmond, Michael G.


    The bicyclic diphosphines trans- and cis-2,3-bis(diphenylphosphinomethyl)-5-norbornene (dpmn) react with 1,2-Os3sub>(CO)10(MeCN)2 (1) to furnish the corresponding ligand-bridged clusters Os3sub>(CO)10(trans-dpmn) (2) and Os3sub>(CO)10(cis-dpmn) (3). Both new products have been isolated and the molecular structures established by X-ray diffraction analyses. The dihydroxyl-bridged cluster 1,2-Os3sub>(CO)8(μ-OH)2(cis-dpmn) (4), which accompanied the formation of 3 in one reaction, has been isolated and characterized by mass spectrometry and X-ray crystallography. Whereas cluster 2 is stable in toluene at 373 K, 3 is thermally sensitive under identical conditions and undergoes loss of CO (2 equiv), coupled with the activation of three norbornene C-H bonds and one P-C(phenyl) bond, to furnish the dihydride cluster H2Os3sub>(CO)83sub>-2-PhPC-3sub>-endo-Ph2PCH2(C7H7)] (5). The solid-state structure of 5 confirms the multiple activation of the cis-dpmn ligand and accompanying formation of the face-capping 2-PhPC-3-endo-Ph2PCH2(C7H7) moiety in the product. DFT calculations on 2 and 3 indicate that the former cluster is the thermodynamically more stable isomer, and the conversion of 3→ 5 + 2CO + benzene is computed to be exergonic by 12.7 kcal/mol and is entropically favored due to the release of the CO and benzene by-products.

  17. Large-scale synthesis of ultralong Sb{sub 2}S{sub 3} sub-microwires via a hydrothermal process

    SciTech Connect

    Zhu, G.Q. Liu, P.; Miao, H.Y.; Zhu, J.P.; Bian, X.B.; Liu, Y.; Chen, B.; Wang, X.B.


    This paper describes an ethylene glycol (EG)-assisted approach to the large-scale ultralong Sb{sub 2}S{sub 3} sub-microwires, formed by a simple hydrothermal reaction between SbCl{sub 3} and Na{sub 2}S in the presence of distilled water. Transmission electron microscopy and scanning electron microscopy studies indicate that these Sb{sub 2}S{sub 3} sub-microwires possess a diameter around 200 nm and length up to 100 {mu}m. High-resolution transmission electron microscopy and selected area electron diffraction studies reveal that each Sb{sub 2}S{sub 3} sub-microwire is a single-crystal along the [0 0 1] direction. The possible formation mechanism of the sub-microwires was discussed. The effects of volume ratio of EG/water, reaction temperature and the concentration of CO(NH{sub 2}){sub 2} on the morphology of Sb{sub 2}S{sub 3} sub-microwires were also investigated.

  18. Synthesis of phase-pure U2N3sub> microspheres and its decomposition into UN

    SciTech Connect

    Silva, Chinthaka M.; Hunt, Rodney Dale; Snead, Lance Lewis; Terrani, Kurt A.


    Uranium mononitride (UN) is important as a nuclear fuel. Fabrication of UN in its microspherical form also has its own merits since the advent of the concept of accident-tolerant fuel, where UN is being considered as a potential fuel in the form of TRISO particles. But, not many processes have been well established to synthesize kernels of UN. Therefore, a process for synthesis of microspherical UN with a minimum amount of carbon is discussed herein. First, a series of single-phased microspheres of uranium sesquinitride (U2N3sub>) were synthesized by nitridation of UO2+C microspheres at a few different temperatures. Resulting microspheres were of low-density U2N3sub> and decomposed into low-density UN. The variation of density of the synthesized sesquinitrides as a function of its chemical composition indicated the presence of extra (interstitial) nitrogen atoms corresponding to its hyperstoichiometry, which is normally indicated as α-U2N3sub>. Average grain sizes of both U2N3sub> and UN varied in a range of 1–2.5 μm. In addition, these had a considerably large amount of pore spacing, indicating the potential sinterability of UN toward its use as a nuclear fuel.

  19. Low Temperature Propane Oxidation over Co3sub>O4 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 Co3sub>O4-based nano-array catalysts featuring low catalytic materials loading. The Ni doping into the Co3sub>O4 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 Co3sub>O4 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 Co3sub>O4 nano-array catalysts for low temperature hydrocarbon oxidation. This study provides useful and timely guidance for rational catalyst design toward low temperature catalytic oxidation.

  20. Damped spin waves in the intermediate ordered phases in Ni3sub>V2O8

    SciTech Connect

    Ehlers, Georg; Podlesnyak, Andrey A.; Frontzek, Matthias D.; Pushkarev, A. V.; Shiryaev, Sergie V.; Barilo, Sergie


    Here, spin dynamics in the intermediate ordered phases (between 4 and 9 K) in Ni3sub>V2O8 have been studied with inelastic neutron scattering. It is found that the spin waves are very diffuse, indicative of short lived correlations and the coexistence of paramagnetic moments with the long-range ordered state.

  1. Improved synthesis and characterization of the copper Lyonsite-type compound Cu4-xMo3sub>O12

    SciTech Connect

    Raw, Adam D.; Ibers, James A.; Poeppelmeier, Kenneth R.


    A novel method involving a molten Ga flux for the synthesis of diffraction quality crystals of the compound Cu3.82(1)Mo3sub>O12, a copper molybdate in the Lyonsite (α-Cu3sub>Fe4(VO4)6) family, has been developed. Single-crystal X-ray diffraction data have been collected. Cu3.82(1)Mo3sub>O12 crystallizes in the space group P212121 with cell dimensions of a=4.9972(1) Å, b=11.0259(3) Å, and c=17.4912(5) Å. Refinement of the resulting structure has enabled modeling of disorder in the channels of the structure and has indicated the localization of copper vacancies to these channel positions. Thermopower measurements indicate that Cu3.82(1)Mo3sub>O12 is a rare and interesting example of a cation-deficient n-type material.

  2. Fabrication of flower-like Ni{sub 3}(NO{sub 3}){sub 2}(OH){sub 4} and their electrochemical properties evaluation

    SciTech Connect

    Kong, Ling-Bin; School of Materials Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 ; Deng, Li; Li, Xiao-Ming; Liu, Mao-Cheng; Luo, Yong-Chun; Kang, Long


    Graphical abstract: Ni{sub 3}(NO{sub 3}){sub 2}(OH){sub 4} nano-flakes materials, which have a flower-like structure, were successfully synthesized by a facile solvothermal method without adding any surfactant. The as-prepared Ni{sub 3}(NO{sub 3}){sub 2}(OH){sub 4} possesses a maximum specific capacitance of 2212.5 F g{sup −1} at the current density of 5 mA, suggesting its potential application in electrode material for secondary batteries and electrochemical capacitors. Highlights: ► Flower-like Ni{sub 3}(NO{sub 3}){sub 2}(OH){sub 4} materials were fabricated in a simple method. ► High specific capacitance of 2212.5 F g{sup −1} has been achieved. ► For the first time the effects of concentration and temperature on its specific capacitance has been studied. -- Abstract: Flower-like Ni{sub 3}(NO{sub 3}){sub 2}(OH){sub 4} was successfully synthesized by a facile solvothermal method. The microstructure and surface morphology of prepared Ni{sub 3}(NO{sub 3}){sub 2}(OH){sub 4} were physically characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and transmission electron microscope (TEM). The electrochemical properties studies were carried out using cyclic voltammetry (CV), chronopotentiometry technology and AC impedance spectroscopy, respectively. The results indicate that the flower-like structure has a profound impact on electrode performance at high discharge capacitance. A maximum specific capacitance of 2212.5 F g{sup −1} at the current density of 5 mA could be achieved, suggesting its potential application in electrode material for secondary batteries and electrochemical capacitors. Furthermore, the effects of Ni(NO{sub 3}){sub 2}·6H{sub 2}O concentration and temperature on the microstructure and specific capacitance of prepared Ni{sub 3}(NO{sub 3}){sub 2}(OH){sub 4} have also been systematically studied. The results show that flower-like structure can be formed when the concentration is appropriate, while the

  3. Deposition of (WO{sub 3}){sub 3} nanoclusters on the MgO(001) surface: A possible way to identify the charge states of the defect centers

    SciTech Connect

    Zhu Jia; Lin Shujuan; Wen Xingwei; Fang Zhenxing; Ding Kaining; Chen Wenkai; Li Yi; Zhang Yongfan; Huang Xin; Ning Lixin


    Periodic density functional theory calculations have been performed to study the most stable structure of the (WO{sub 3}){sub 3} nanocluster deposited on the MgO(001) surface with three kinds of F{sub S} centers (F{sub S}{sup 0}, F{sub S}{sup +}, and F{sub S}{sup 2+}). Our results indicate that the configuration of (WO{sub 3}){sub 3} cluster, including the cyclic conformation and the heights of three W atoms, and the oxidation states are sensitive to the charge state of the F{sub S} center. It is interesting that the electron-riched F{sub S}{sup 0} vacancy on the MgO(001) surface can act as a promoting site to enhance the W-W interaction and the W{sub 3}O{sub 3} cyclic conformation is maintained, while the skeleton of cluster becomes flexible when (WO{sub 3}){sub 3} is adsorbed on the electron-deficient vacancy (F{sub S}{sup +} and F{sub S}{sup 2+}). Accordingly, three F{sub S}-centers exhibit different arrangements of X-ray photoelectron spectra, the scanning tunneling microscopy images, and the vibrational spectra after depositing (WO{sub 3}){sub 3} cluster. Present results reveal that the (WO{sub 3}){sub 3} cluster may be used as a probe to identify the different F{sub S} centers on the MgO(001) surface.

  4. The crystal structure, thermal behaviour and ionic conductivity of a novel lithium gadolinium polyphosphate LiGd(PO{sub 3}){sub 4}

    SciTech Connect

    Ettis, Hasna; Naili, Houcine . E-mail:; Mhiri, Tahar


    Crystal structure and ionic conductivity of lithium gadolinium polyphosphate, LiGd(PO{sub 3}){sub 4}, were investigated. Single crystals of the title compound have been grown by a flux technique. The structure of this novel phosphate was determined by single crystal X-ray diffraction techniques. LiGd(PO{sub 3}){sub 4} is isotypic with LiNd(PO{sub 3}){sub 4}. It crystallizes in the monoclinic space group C2/c with the unit cell parameters a=16.386(2), b=7.059(3), c=9.677(2) A, {beta}=126.12(1){sup o}, V=904.2(4) A{sup 3} and Z=4. The structure refined from 967 independent reflections leads to R {sub 1}=0.0167 and wR {sub 2}=0.0458. The lattice of LiGd(PO{sub 3}){sub 4} is built of twisted zig-zag chains running along with the b direction and make up of PO{sub 4} tetrahedra sharing two corners, connected to the GdO{sub 8} and LiO{sub 4} polyhedra by common oxygen atoms to form a three-dimensional framework. Differential and thermogravimetric thermal analysis are given. The thermal curve of this compound was recorded and interpreted in agreement with impedance measurements. The ionic conductivity has been measured on pellet of the polycrystalline powder and evaluated as a function of temperature. This phase showed the conductivity of 2x10{sup -6} and 2x10{sup -4} {omega}{sup -1} cm{sup -1} at 682 and 951 K, respectively. - Graphical abstract: The structural arrangement of LiGd(PO{sub 3}){sub 4} viewed in the (0 1 0) plane.

  5. Structure of complexes of nitrilo tris methylene phosphonic acid with copper, [CuN(CH{sub 2}PO{sub 3}){sub 3}(H{sub 2}O){sub 3}] and Na{sub 4}[CuN(CH{sub 2}PO{sub 3}){sub 3}]{sub 2} · 19H{sub 2}O, as bactericides and inhibitors of scaling and corrosion

    SciTech Connect

    Somov, N. V.; Chausov, F. F.


    Nitrilotris methylene phosphonate triaqua copper and octasodium bis(nitrilotris methylene phosphonate cuprate(II)) nonadecahydrate have been synthesized and investigated. [CuN(CH{sub 2}PO{sub 3}){sub 3}(H{sub 2}O){sub 3}] is crystallized in the sp. gr. P2{sub 1}/c, Z = 4, a = 9.2506(2) Å, b = 15.9815(2) Å, c = 9.5474(2) Å, β = 113.697(2)°. The copper atom is coordinated by oxygen atoms in the configuration of elongated octahedron; the ligand (of bridge type) links neighboring copper atoms. Na{sub 8}[CuN(CH{sub 2}PO{sub 3}){sub 3}]{sub 2} · 19H{sub 2}O is crystallized in the sp. gr. P2{sub 1}/c, Z = 2, a = 11.24550(10) Å, b = 17.38980(10) Å, c = 13.5852(2) Å, β = 127.8120(10)°. This complex is chelating; the copper atom closes three five-membered N-C-P-O-Cu cycles with a shared Cu-N bond. Copper is coordinated in a distorted trigonal-bipyramidal configuration.

  6. Domain wall motion and electromechanical strain in lead-free piezoelectrics: Insight from the model system (1 - x)Ba(Zr0.2Ti0.8)O3sub>-x(Ba0.7Ca0.3sub>)TiO3sub> using in situ high-energy X-ray diffraction during application of electric fields

    SciTech Connect

    Tutuncu, Goknur; Li, Binzhi; Bowman, Keith; Jones, Jacob L.


    The piezoelectric compositions (1 - x)Ba(Zr0.2Ti0.8)O3sub>–x(Ba0.7Ca0.3sub>)TiO3sub> (BZT-xBCT) span a model lead-free morphotropic phase boundary (MPB) between room temperature rhombohedral and tetragonal phases at approximately x = 0.5. In the present work, in situ X-ray diffraction measurements during electric field application are used to elucidate the origin of electromechanical strain in several compositions spanning the tetragonal compositional range 0.6 ≤ x ≤ 0.9. As BCT concentration decreases towards the MPB, the tetragonal distortion (given by c/a-1) decreases concomitantly with an increase in 90° domain wall motion. The increase in observed macroscopic strain is predominantly attributed to the increased contribution from 90° domain wall motion. The results demonstrate that domain wall motion is a significant factor in achieving high strain and piezoelectric coefficients in lead-free polycrystalline piezoelectrics.

  7. Phase diagrams of the systems Mn(VO{sub 3}){sub 2}-M(VO{sub 3}){sub 2} and Mn{sub 2}V{sub 2}O{sub 7}-M{sub 2}V{sub 2}O{sub 7} (M = Sr, Ba)

    SciTech Connect

    Zhuravlev, V.D.; Surat, L.L.; Velikodnyi, Yu.A.


    In this paper, the authors report results on the phase relations in meta- and pyrovanadate binary systems containing manganese, strontium, or barium and their phase diagrams. Using powder X-ray diffraction and differential thermal analysis, we studied the phase diagrams of the systems Mn(VO{sub 3}){sub 2}-M(VO){sub 3}{sub 2} and Mn{sub 2}V{sub 2}-O{sub 7}-M{sub 2}V{sub 2}O{sub 7} (M=Sr,Ba) in air. Mn{sub 1-x}Sr{sub x}(VO{sub 3}){sub 2}solid solutions and three new compounds, BaMnV{sub 2}O{sub 7}, SrMnV{sub 2}O{sub 7}, and Sr{sub 3}Mn(V{sub 2}O{sub 7}){sub 2}, were found, and their thermal behavior was studied.

  8. High Electrical Conductivity in Ni3sub>(2,3,6,7,10,11-hexaiminotriphenylene)2, a Semiconducting Metal-Organic Graphene Analogue

    SciTech Connect

    Sheberla, Dennis; Sun, Lei; Blood-Forsythe, Martin A.; Er, Süleyman; Wade, Casey R.; Brozek, Carl K.; Aspuru-Guzik, Alán; Dinc,; #259; Mircea,


    Reaction of 2,3,6,7,10,11-hexaaminotriphenylene with Ni2+ in aqueous NH3sub> solution under aerobic conditions produces Ni3sub>(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene), a new two-dimensional metal–organic framework (MOF). The new material can be isolated as a highly conductive black powder or dark blue-violet films. Two-probe and van der Pauw electrical measurements reveal bulk (pellet) and surface (film) conductivity values of 2 and 40 S·cm–1, respectively, both records for MOFs and among the best for any coordination polymer.

  9. Mixed-metal chloro sulfido cluster complex of molybdenum and platinum, (Mo sub 3 Pt sub 2 S sub 4 Cl sub 4 (PEt sub 3 ) sub 6 )

    SciTech Connect

    Saito, Taro; Tsuboi, Toshio; Kajitani, Yoshimichi; Yamagata, Tsuneaki; Imoto, Hideo )


    In the authors recent publication, syntheses of mixed-metal chloro sulfido and chloro selenido complexes of molybdenum and nickel were reported. They were prepared by the reaction of (Mo{sub 3}X{sub 4}Cl{sub 4}(PEt{sub 3}){sub 3}(MeOH){sub 2}) (X = S, Se){sup 2} with Ni(cod){sub 2} (cod = 1,5-cyclooctadiene). In the present study, another excellent building block compound, Pt(cot){sub 2}, was reacted with the same trinuclear molybdenum complex, and the mixed-metal cluster complex (Mo{sub 3}Pt{sub 2}S{sub 4}Cl{sub 4}(PEt{sub 3}){sub 6}) (1) with an unexpected structure was obtained.

  10. Intrinsic quantum anomalous Hall effect in the kagome lattice Cs2LiMn3sub>F12

    SciTech Connect

    Xu, Gang; Lian, Biao; Zhang, Shou -Cheng


    In a kagome lattice, the time reversal symmetry can be broken by a staggered magnetic flux emerging from ferromagnetic ordering and intrinsic spin-orbit coupling, leading to several well-separated nontrivial Chern bands and intrinsic quantum anomalous Hall effect. Based on this idea and ab initio calculations, we propose the realization of the intrinsic quantum anomalous Hall effect in the single layer Cs2Mn3sub>F12 kagome lattice and on the (001) surface of a Cs2LiMn3sub>F12 single crystal by modifying the carrier coverage on it, where the band gap is around 20 meV. Furthermore, a simplified tight binding model based on the in-plane ddσ antibonding states is constructed to understand the topological band structures of the system.

  11. Equations of state and stability of MgSiO3sub> perovskite and post-perovskite phases from quantum Monte Carlo simulations

    SciTech Connect

    Lin, Yangzheng; Cohen, Ronald E.; Stackhouse, Stephen; Driver, Kevin P.; Militzer, Burkhard; Shulenburger, Luke; Kim, Jeongnim


    In this study, we have performed quantum Monte Carlo (QMC) simulations and density functional theory calculations to study the equations of state of MgSiO3sub> perovskite (Pv, bridgmanite) and post-perovskite (PPv) up to the pressure and temperature conditions of the base of Earth's lower mantle. The ground-state energies were derived using QMC simulations and the temperature-dependent Helmholtz free energies were calculated within the quasiharmonic approximation and density functional perturbation theory. The equations of state for both phases of MgSiO3sub> agree well with experiments, and better than those from generalized gradient approximation calculations. The Pv-PPv phase boundary calculated from our QMC equations of state is also consistent with experiments, and better than previous local density approximation calculations. Lastly, we discuss the implications for double crossing of the Pv-PPv boundary in the Earth.

  12. Peculiarities in the magnetic, magnetoelectric, and magnetoelastic properties of SmFe{sub 3}(BO{sub 3}){sub 4} multiferroic

    SciTech Connect

    Popov, Yu. F.; Pyatakov, A. P. Kadomtseva, A. M.; Vorob'ev, G. P.; Zvezdin, A. K.; Mukhin, A. A.; Ivanov, V. Yu.; Gudim, I. A.


    Results of a complex investigation of the magnetic, magnetoelectric, and magnetoelastic properties of a SmFe{sub 3}(BO{sub 3}){sub 4} single crystal are presented. Samarium iron borate is similar to another easy-plane iron borate, NdFe{sub 3}(BO{sub 3}){sub 4}, in that it possesses a large value of the magnetic-field-induced polarization (about 500 {mu}C/m{sup 2}), the sign of which changes when the field direction is changed between axes a and b of the crystal. However, the temperature dependence of the magnetic susceptibility and the field dependence of polarization and magnetostriction of the two compounds are significantly different, which is explained by the weak effect of external magnetic field on the ground-state multiplet of samarium ion, which is characterized by an extremely small value of its g-factor.

  13. Stabilization of heterogeneous silicon lasers using Pound-Drever-Hall locking to Si3sub>N4 ring resonators.


    Spencer, Daryl T; Davenport, Michael L; Komljenovic, Tin; Srinivasan, Sudharsanan; Bowers, John E


    Recent results on heterogeneous Si/III-V lasers and ultra-high Q Si3sub>N4 resonators are implemented in a Pound-Drever-Hall frequency stabilization system to yield narrow linewidth characteristics for a stable on-chip laser reference. The high frequency filtering is performed with Si resonant mirrors in the laser cavity. To suppress close in noise and frequency walk off, the laser is locked to an ultra-high Q Si3sub>N4 resonator with a 30 million quality factor. The laser shows high frequency noise levels of 60 × 103 Hz2/Hz corresponding to 160 kHz linewidth, and the low frequency noise is suppressed 33 dB to 103 Hz2/Hz with the PDH system. PMID:27410367

  14. Highly pure green light emission of perovskite CsPbBr3sub> quantum dots and their application for green light-emitting diodes.


    Li, Cunlong; Zang, Zhigang; Chen, Weiwei; Hu, Zhiping; Tang, Xiaosheng; Hu, Wei; Sun, Kuan; Liu, Xianming; Chen, Weimin


    All-inorganic perovskite CsPbBr3sub> quantum dots (QDs) with an emission peak of around 520 nm were synthesized by a hot-injection method, and were systematically studied as green phosphor for light-emitting diodes (LEDs). Highly pure green light with an emission peak of 534 nm and a full-width at half-maximum (FWHM) about 20 nm was achieved using CsPbBr3sub> QDs and GaN LEDs. Commission Internationale Ed I'Eclairage coordinate of the fabricated green LEDs was (0.203, 0.757). Compared to GaN LEDs, the current-voltage characteristic of the green LED did not show any degradation. Moreover, the green LEDs displayed a luminous efficiency of 31.92 lm/W under an injection current of 10 mA. PMID:27410658

  15. Phase-matched frequency conversion below 150 nm in KBe2BO3sub>F2.


    Nakazato, Tomoharu; Ito, Isao; Kobayashi, Yohei; Wang, Xiaoyang; Chen, Chuangtian; Watanabe, Shuntaro


    Sum frequency mixing has been demonstrated below 150 nm in KBeBO3sub>F2 by using the fundamental with its fourth harmonic of a 6 kHz Ti: sapphire laser system. The wavelength of 149.8 nm is the shortest ever obtained to our knowledge by phase matching in nonlinear crystals. The output powers were 3.6 μW at 149.8 nm and 110 μW at 154.0 nm, respectively. The phase matching angles measured from 149.8 to 158.1 nm are larger by 3-4 degrees than those expected from the existing Sellmeier equation. The measured transmission spectra of KBeBO3sub>F2 crystals support the generation of coherent radiation below 150 nm. PMID:27464165

  16. 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.

  17. Semidirect product gauge group [SU(3){sub c}xSU(2){sub L}]xU(1){sub Y} and quantization of hypercharge

    SciTech Connect

    Hattori, Chuichiro; Matsunaga, Mamoru; Matsuoka, Takeo


    In the standard model the hypercharges of quarks and leptons are not determined by the gauge group SU(3){sub c}xSU(2){sub L}xU(1){sub Y} alone. We show that, if we choose the semidirect product group [SU(3){sub c}xSU(2){sub L}]xU(1){sub Y} as its gauge group, the hyperchages are settled to be n/6 mod Z(n=0,1,3,4). In addition, the conditions for gauge-anomaly cancellation give strong constraints. As a result, the ratios of the hypercharges are uniquely determined and the gravitational anomaly is automatically canceled. The standard charge assignment to quarks and leptons can be properly reproduced. For exotic matter fields their hypercharges are also discussed.

  18. Nitrosyl complexes of rhenium. 2. Neutral and cationic monohydride complexes of rhenium(I) resulting from the reaction of ReH/sub 2/(NO)(PPh/sub 3/)/sub 3/ with perchloric acid

    SciTech Connect

    Grundy, K.R.; Robertson, K.N.


    The rhenium dihydride complex ReH/sub 2/(NO)(PPh/sub 3/)/sub 3/ reacts with HClO/sub 4/ in the presence of CO with the cleavage of only one hydride ligand. Control of the degree of acidity and the solvent system leads to isolation of compounds such as ReH(OR)(CO)(NO)(PPh/sub 3/)/sub 2/ (R = Me, Et) and (ReH(CO)(NO)(PPh/sub 3/)/sub 3/)ClO/sub 4/. The alkoxide complexes are protonated by HClO/sub 4/ to yield alcohol complexes ReH(ROH.OClO/sub 3/)(CO)(NO)(PPh/sub 3/)/sub 2/. Heating ReH(MeOH.OClO/sub 3/)(CO)(NO)(PPh/sub 3/)/sub 2/ in methanol results in the formal 1,2-elimination of dihydrogen with formation of Re(OMe)(OClO/sub 3/)(CO)(NO)(PPh/sub 3/)/sub 2/. A similar elimination reaction occurs when the alcohol complexes are reacted with halide ions to give ReX(OR)(CO)(NO(PPh/sub 3/)/sub 2/ (X = Cl, Br, I). Reacting the alcohol complexes with base or NaBH/sub 4/ however, regenerates ReH(OR)(CO)(NO)(PPh/sub 3/)/sub 2/. The perchlorate complex, Re(OMe)(OClO/sub 3/)(CO)(NO)(PPh/sub 3/)/sub 2/ reacts with NaBH/sub 4/ to give ReH/sub 2/(CO)(NO)(PPh/sub 3/)/sub 2/ via a borohydride complex. The chloro-alkoxy complexes ReCl(OR)(CO)(NO)(PPh/sub 3/)/sub 2/ also react with HClO/sub 4/ to give alcohol complexes. All structural assignments have been made on the basis of elemental analysis, infrared spectroscopy, /sup 1/H NMR spectroscopy, and deuteration studies. 14 references, 2 figures, 2 tables.

  19. Ultrafast terahertz gating of the polarization and giant nonlinear optical response in BiFeO3sub> thin films

    SciTech Connect

    Chen, Frank; Goodfellow, John; Liu, Shi; Grinberg, Ilya; Hoffman, Matthias; Damodaran, Anoop R.; Zhu, Yi; Zhang, Xiaohang; Takeuchi, Ichiro; Rappe, Andrew; Martin, Lane W.; Wen, Haidan; Lindenberg, Aaron M.


    In this article, terahertz pulses are applied as an all-optical bias to ferroelectric thin-film BiFeO3sub> while monitoring the time-dependent ferroelectric polarization through its nonlinear optical response. Modulations in the intensity of the second harmonic light generated by the film correspond to on–off ratios of 220 × gateable on femtosecond timescales. Polarization modulations comparable to the built-in static polarization are observed.

  20. Adventures on the C3sub>H5O potential energy surface: OH+propyne, OH+allene and related reactions

    SciTech Connect

    Zádor, Judit; Miller, James A.


    We mapped out the stationary points and the corresponding conformational space on the C3sub>H5O potential energy surface relevant for the OH + allene and OH + propyne reactions systematically and automatically using the KinBot software at the UCCSD(T)-F12b/cc-pVQZ-F12//M06-2X/6-311++G(d,p) level of theory. We used RRKM-based 1-D master equations to calculate pressure- and temperature-dependent, channel-specific phenomenological rate coefficients for the bimolecular reactions propyne + OH and allene + OH, and for the unimolecular decomposition of the CH3sub>CCHOH, CH3sub>C(OH)CH, CH2CCH2OH, CH2C(OH)CH2 primary adducts, and also for the related acetonyl, propionyl, 2-methylvinoxy, and 3-oxo-1-propyl radicals. The major channel of the bimolecular reactions at high temperatures is the formation propargyl + H2O, which makes the title reactions important players in soot formation at high temperatures. However, below ~1000 K the chemistry is more complex, involving the competition of stabilization, isomerization and dissociation processes. We found that the OH addition to the central carbon of allene has a particularly interesting and complex pressure dependence, caused by the low-lying exit channel to form ketene + CH3sub> bimolecular products. In this study, we compared our results to a wide range of experimental data and assessed possible uncertainties arising from certain aspects of the theoretical framework.

  1. Synthesis and structure of R{sub 2}[UO{sub 2}(NO{sub 3}){sub 2}(NCS){sub 2}] (R = Rb or Cs)

    SciTech Connect

    Serezhkin, V. N.; Peresypkina, E. V.; Grigor’eva, V. A.; Virovets, A. V.; Serezhkina, L. B.


    Crystals Rb{sub 2}[UO{sub 2}(NO{sub 3}){sub 2}(NCS){sub 2}] (I) and Cs{sub 2}[UO{sub 2}(NO{sub 3}){sub 2}(NCS){sub 2}] (II) have been synthesized and studied by IR spectroscopy and X-ray diffraction. Crystals I are monoclinic, with the following parameters: a = 12.2118(5) Å, b = 10.2545(3) Å, c = 11.8754(4) Å, β = 110.287(1)°, sp. gr. C2/c, Z = 4, and R = 0.0523. Crystals II are orthorhombic, with a = 13.7309(3) Å, b = 10.5749(2) Å, c = 10.1891(2) Å, sp. gr. Pnma, Z = 4, and R = 0.0411. The basic structural units of crystals I and II are one-core complexes [UO{sub 2}(NO{sub 3}){sub 2}(NCS){sub 2}]{sup 2−}, which belong to the crystallochemical group cis-AB{sub 2}{sup 01}M{sub 2}{sup 1} (A = UO{sub 2}{sup 2+}, B{sup 01} = NO{sub 3}{sup −}, M{sup 1} = NCS{sup −}), which are combined into a framework via electrostatic interactions with ions of alkaline metals R (R = Rb or Cs). The structural features of crystals I and II, which condition the formation of [UO{sub 2}(NO{sub 3}){sub 2}(NCS){sub 2}]{sup 2−} complexes with a cis rather than a trans position of isothiocyanate ions in the coordination sphere of uranyl ions, are discussed.

  2. Anionic ordering and thermal properties of FeF3sub>·3H2O

    SciTech Connect

    Burbano, Mario; Duttine, Mathieu; Borkiewicz, Olaf; Wattiaux, Alain; Demourgues, Alain; Salanne, Mathieu; Groult, Henri; Dambournet, Damien


    In this study, iron fluoride tri-hydrate can be used to prepare iron hydroxyfluoride with the Hexagonal-Tungsten-Bronze (HTB) type structure, a potential cathode material for batteries. To understand this phase transformation, a structural description of β-FeF3sub>·3H2O is first performed by means of DFT calculations and Mössbauer spectroscopy. The structure of this compound consists of infinite chains of [FeF6]n and [FeF2(H2O)4]n. The decomposition of FeF3sub>·3H2O induces a collapse and condensation of these chains, which lead to the stabilization, under specific conditions, of a hydroxyfluoride network FeF3-x(OH)x with the HTB structure. The release of H2O and HF was monitored by thermal analysis and physical characterizations during the decomposition of FeF3sub>·3H2O. An average distribution of FeF4(OH)2 distorted octahedra in HTB-FeF3-x(OH)x was obtained subsequent to the thermal hydrolysis/olation of equatorial anionic positions involving F- and H2O. This study provides a clear understanding of the structure and thermal properties of FeF3sub>·3H2O, a material that can potentially bridge the recycling of pickling sludge from the steel industry by preparing battery electrodes.

  3. SU(3){sub {ital L}}{circle_times} U(1){sub {ital N}} model for right-handed neutrino neutral currents

    SciTech Connect

    Long, H.N.


    A model based on the SU(3){sub {ital L}}{circle_times}U(1){sub {ital N}} gauge group in which neutrinos have right-handed neutral currents is considered. We argue that in order to have a result consistent with the low-energy one, the right-handed neutrino component must be treated as a correction instead of an equivalent spin state. {copyright} {ital 1996 The American Physical Society.}

  4. Effects of core type, placement, and width on the estimated interstrand coupling properties of QXF-type Nb3sub>Sn Rutherford cables

    SciTech Connect

    Collings, E. W.; Sumption, M. D.; Majoros, M.; Wang, X.; Dietderich, D. R.


    The coupling magnetization of a Rutherford cable is inversely proportional to an effective interstrand contact resistance Reff , a function of the crossing-strand resistance Rc, and the adjacent strand resistance Ra. In cored cables, Reff continuously varies with W, the core width expressed as percent interstrand cover. For a series of un-heat-treated stabrite-coated NbTi LHC-inner cables with stainless-steel (SS, insulating) cores, Reff (W) decreased smoothly as W decreased from 100%, whereas for a set of research-wound SS-cored Nb3sub>Sn cables, Reff plummeted abruptly and remained low over most of the range. The difference is due to the controlling influence of Rc - 2.5 μΩ for the stabrite/NbTi and 0.26 μΩ for Nb3sub>Sn. The experimental behavior was replicated in the Reff (W)’s calculated by the program CUDI, which (using the basic parameters of the QXF cable) went on to show in terms of decreasing W that: 1) in QXF-type Nb3sub>Sn cables (Rc = 0.26 μΩ), Reff dropped even more suddenly when the SS core, instead of being centered, was offset to one edge of the cable; 2) Reff decreased more gradually in cables with higher Rc’s; and 3) a suitable Reff for a Nb3sub>Sn cable can be achieved by inserting a suitably resistive core rather than an insulating (SS) one.

  5. Ultrafast terahertz gating of the polarization and giant nonlinear optical response in BiFeO3sub> thin films

    SciTech Connect

    Chen, Frank; Goodfellow, John; Liu, Shi; Grinberg, Ilya; Hoffmann, Matthias; Damodaran, Anoop R.; Zhu, Yi; Zalden, Peter; Zhang, Xiaohang; Takeuchi, Ichiro; Rappe, Andrew M.; Martin, Lane W.; Wen, Haidan; Lindenberg, Aaron M.


    Terahertz pulses are applied as an all-optical bias to ferroelectric thin-film BiFeO3sub> while monitoring the time-dependent ferroelectric polarization through its nonlinear optical response. Modulations in the intensity of the second harmonic light generated by the film correspond to on–off ratios of 220× gateable on femtosecond timescales. Lastly, polarization modulations comparable to the built-in static polarization are observed.

  6. Superconductivity in the presence of disorder in skutterudite-related La3sub>Co4Sn13 and La3sub>Ru4Sn13 compounds: Electrical transport and magnetic studies

    SciTech Connect

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


    La3sub>Co4Sn13 and La3sub>Ru4Sn13 were categorized as BCS superconductors. In a plot of the critical field Hc2 vs T, La3sub>Ru4Sn13 displays a second superconducting phase at the higher critical temperature Tc*, characteristic of inhomogeneous superconductors, while La3sub>Co4Sn13 shows bulk superconductivity below Tc. We observe a decrease in critical temperatures with external pressure and magnetic field for both compounds. Additionally, for La3sub>Ru4Sn13 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 La3sub>CoxRu4–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.

  7. Solid-state graphene formation via a nickel carbide intermediate phase [Nickel carbide (Ni3sub>C) as an intermediate phase for graphene formation

    SciTech Connect

    Xiong, W; Zhou, Yunshen; Hou, Wenjia; Guillemet, Thomas; Silvain, Jean-François; Lahaye, Michel; Lebraud, Eric; Xu, Shen; Wang, Xinwei; Cullen, David A; More, Karren Leslie; Lu, Yong Feng


    Direct formation of graphene with controlled number of graphitic layers on dielectric surfaces is highly desired for practical applications. Despite significant progress achieved in understanding the formation of graphene on metallic surfaces through chemical vapor deposition (CVD) of hydrocarbons, very limited research is available elucidating the graphene formation process via rapid thermal processing (RTP) of solid-state amorphous carbon, through which graphene is formed directly on dielectric surfaces accompanied by autonomous nickel evaporation. It is suggested that a metastable hexagonal nickel carbide (Ni3sub>C) intermediate phase plays a critical role in transforming amorphous carbon to 2D crystalline graphene and contributing to the autonomous Ni evaporation. Temperature resolved carbon and nickel evolution in the RTP process is investigated using Auger electron spectroscopic (AES) depth profiling and glancing-angle X-ray diffraction (GAXRD). Formation, migration and decomposition of the hexagonal Ni3sub>C are confirmed to be responsible for the formation of graphene and the evaporation of Ni at 1100 °C. The Ni3sub>C-assisted graphene formation mechanism expands the understanding of Ni-catalyzed graphene formation, and provides insightful guidance for controlled growth of graphene through the solid-state transformation process.

  8. Crystal chemistry and ion-exchange properties of the layered uranyl iodate K[UO{sub 2}(IO{sub 3}){sub 3}

    SciTech Connect

    Shvareva, Tatiana Y.; Almond, Philip M.; Albrecht-Schmitt, Thomas E. . E-mail:


    Single crystals of the potassium uranyl iodate, K[UO{sub 2}(IO{sub 3}){sub 3}] (1), have been grown under mild hydrothermal conditions. The structure of 1 contains two-dimensional {sub {infinity}}{sup 2}[UO{sub 2}(IO{sub 3}){sub 3}]{sup 1-} sheets extending in the [ab] plane that consist of approximately linear UO{sub 2}{sup 2+} cations bound by iodate anions to yield UO{sub 7} pentagonal bipyramids. There are three crystallographically unique iodate anions, two of which bridge between uranyl cations to create sheets, and one that is monodentate and protrudes in between the layers in cavities. K{sup +} cations form long ionic contacts with oxygen atoms from the layers forming an eight-coordinate distorted dodecahedral geometry. These cations join the {sub {infinity}}{sup 2}[UO{sub 2}(IO{sub 3}){sub 3}]{sup 1-} sheets together. Ion-exchange reactions have been carried out that indicate the selective uptake of Cs{sup +} over Na{sup +} or K{sup +} by 1. Crystallographic data (193K, MoK{alpha}, {lambda}=0.71073A): 1, orthorhombic, Pbca, a=11.495(1)A, b=7.2293(7)A, c=25.394(2)A, Z=8, R(F)=1.95% for 146 parameters with 2619 reflections with I>2{sigma}(I)

  9. Spin-Induced Polarizations and Nonreciprocal Directional Dichroism of the Room-Temperature Multiferroic BiFeO3sub>

    SciTech Connect

    Fishman, Randy Scott; Lee, Jun Hee; Bordacs, Sandor; Kezsmarki, Istvan; Nagel, Urmas; Room, Toomas


    A microscopic model for the room-temperature multiferroic BiFeO3sub> that includes two Dzyaloshinskii-Moriya interactions and single-ion anisotropy along the ferroelectric polarization predicts both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. Due to simultaneously broken time-reversal and spatial-inversion symmetries, the absorption of light changes as the magnetic field or the direction of light propagation is reversed. We discuss three physical mechanisms that may contribute to this absorption asymmetry known as directional dichroism: the spin current, magnetostriction, and single-ion anisotropy. We conclude that the directional dichroism in BiFeO3sub> is dominated by the spin-current polarization and is insensitive to the magnetostriction and easy-axis anisotropy. With three independent spin-current parameters, our model accurately describes the directional dichroism observed for magnetic field along [1, -1, 0]. Since some modes are almost transparent to light traveling in one direction but opaque for light traveling in the opposite direction, BiFeO3sub> can be used as a room-temperature optical diode at certain frequencies in the GHz to THz range. This work demonstrates that an analysis of the directional dichroism spectra based on an effective spin model supplemented by first-principles calculations can produce a quantitative microscopic theory of the magnetoelectric couplings in multiferroic materials.

  10. Thermodynamic approach to the stability of multi-phase systems. Application to the Y2O3sub>–Fe system

    SciTech Connect

    Samolyuk, German D.; Osetskiy, Yury N.


    Oxide-metal systems (OMSs) are important in many practical applications, and therefore, are under extensive studies using a wide range of techniques. The most accurate theoretical approaches are based on density functional theory (DFT), which are limited to ~102 atoms. Multi-scale approaches, e.g., DFT+Monte Carlo, are often used to model OMSs at the atomic level. These approaches can describe qualitatively the kinetics of some processes but not the overall stability of OMSs. In this paper, we propose a thermodynamic approach to study equilibrium in multiphase systems, which can be sequentially enhanced by considering different defects and microstructures. We estimate the thermodynamic equilibrium by minimization the free energy of the whole multiphase system using a limited set of defects and microstructural objects for which the properties are calculated by DFT. As an example, we consider Y2O3sub>+bcc Fe with vacancies in both the Y2O3sub> and bcc Fe phases, Y substitutions and O interstitials in Fe, Fe impurities and antisite defects in Y2O3sub>. The output of these calculations is the thermal equilibrium concentration of all the defects for a particular temperature and composition. The results obtained confirmed the high temperature stability of yttria in iron. As a result, model development towards more accurate calculations is discussed.

  11. Alternative current conduction mechanisms of organic-inorganic compound [N(CH{sub 3}){sub 3}H]{sub 2}CuCl{sub 4}

    SciTech Connect

    Ben Bechir, M. Karoui, K.; Guidara, K.; Ben Rhaiem, A.; Tabellout, M.


    The [N(CH{sub 3}){sub 3}H]{sub 2}CuCl{sub 4} single crystal has been analyzed by X-ray powder diffraction patterns, differential scanning calorimetry (DSC), and electrical impedance spectroscopy. [N(CH{sub 3}){sub 3}H]{sub 2}CuCl{sub 4} crystallizes at room temperature in the monoclinic system with P2{sub 1}/{sub C} space group. Three phase transitions at T{sub 1} = 226 K, T{sub 2} = 264 K, and T{sub 3} = 297 K have been evidenced by DSC measurements. The electrical technique was measured in the 10{sup −1}–10{sup 7} Hz frequency range and 203–313 K temperature intervals. The frequency dependence of alternative current (AC) conductivity is interpreted in terms of Jonscher's law (developed). The AC electrical conduction in [N(CH{sub 3}){sub 3}H]{sub 2}CuCl{sub 4} compound is studied by two processes which can be attributed to a hopping transport mechanism: the correlated barrier hopping model in phases I, II, and III, the non-overlapping small polaron tunneling model in phase IV. The conduction mechanism is interpreted with the help of Elliot's theory, and the Elliot's parameters are found.

  12. Efficient laser operation based on transparent Nd:Lu2O3sub> ceramic fabricated by Spark Plasma Sintering.


    Xu, Changwen; Yang, Chengdong; Zhang, Han; Duan, Yanmin; Zhu, Haiyong; Tang, Dingyuan; Huang, Huihui; Zhang, Jian


    Efficient laser operation of Nd:Lu2O3sub> ceramic fabricated by Spark Plasma Sintering (SPS) was demonstrated. Transparent Nd:Lu2O3sub> ceramic was successfully fabricated by Spark Plasma Sintering and its laser experiment was done. On the 4F3/2 to 4I11/2 transition, the obtained maximum output is 1.25W at the absorbed pump power of 4.15W with a slope efficiency of 38% and two spectral lines at 1076.7nm and 1080.8nm oscillated simultaneously. The slope efficiency of 38% is near two times higher than the previously demonstrated SPSed Nd:Lu2O3sub> ceramic lasers. On the 4F3/2 to 4I13/2 transition, the laser operated at the wavelength of 1359.7nm and the maximum output of 200mW was obtained at the absorbed pump power of 2.7W. PMID:27607660

  13. Melting of Pb Charge Glass and Simultaneous Pb-Cr Charge Transfer in PbCrO3sub> as the Origin of Volume Collapse

    SciTech Connect

    Yu, Runze; Hojo, Hajime; Watanuki, Tetsu; Mizumaki, Masaichiro; Mizokawa, Takashi; Okada, Kengo; Kim, Hyunjeong; Machida, Akihiko; Sakaki, Kouji; Nakamura, Yumiko; Agui, Akane; Mori, Daisuke; Inaguma, Yoshiyuki; Schlipf, Martin; Rushchanskii, Konstantin; Lezaic, Marjana; Matsuda, Masaaki; Ma, Jie; Calder, Stuart A.; Isobe, Masahiko; Ikuhara, Yuichi; Azuma, Masaki


    A metal to insulator transition in integer or half integer charge systems can be regarded as crystallization of charges. The insulating state tends to have a glassy nature when randomness or geometrical frustration exists. In this paper, we report that the charge glass state is realized in a perovskite compound PbCrO3sub>, which has been known for almost 50 years, without any obvious inhomogeneity or triangular arrangement in the charge system. PbCrO3sub> has a valence state of Pb2+0.5Pb4+0.5Cr3+O3sub> with Pb2+–Pb4+ correlation length of three lattice-spacings at ambient condition. A pressure induced melting of charge glass and simultaneous Pb–Cr charge transfer causes an insulator to metal transition and ~10% volume collapse.

  14. New coordination features; A bridging pyridine and the forced shortest non-covalent distance between two CO3sub>2- species

    SciTech Connect

    Velasco, V.; Aguilà, D.; Barrios, L. A.; Borilovic, I.; Roubeau, O.; Ribas-Ariño, J.; Fumanal, M.; Teat, S. J.; Aromí, G.


    The aerobic reaction of the multidentate ligand 2,6-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-pyridine, H4L, with Co(II) salts in strong basic conditions produces the clusters [Co4(L)2(OH)(py)7]NO3sub> (1) and [Co8Na4(L)4(OH)2(CO3sub>)2(py)10](BF4)2 (2). Analysis of their structure unveils unusual coordination features including a very rare bridging pyridine ligand or two trapped carbonate anions within one coordination cage, forced to stay at an extremely close distance (dO···O = 1.946 Å). This unprecedented non-bonding proximity represents a meeting point between long covalent interactions and “intermolecular” contacts. These original motifs have been analysed here through DFT calculations, which have yielded interaction energies and the reduced repulsion energy experimented by both CO3sub>2- anions when located in close proximity inside the coordination cage.

  15. Impact of the various spin- and orbital-ordering processes on the multiferroic properties of orthovanadate DyVO3sub>

    SciTech Connect

    Zhang, Q; Singh, K; Simon, C; Tung, L D; Balakrishnan, G; Hardy, V


    The orthovanadate DyVO3sub> crystal, known to exhibit multiple structural, spin-, and orbital-ordering transitions, is presently investigated on the basis of magnetization, heat capacity, resistivity, dielectric, and polarization measurements. Our main result is experimental evidence for the existence of multiferroicity below a high TC of 108 K over a wide temperature range including different spin-orbital-ordered states. The onset of ferroelectricity is found to coincide with the antiferromagnetic C-type spin-ordering transition taking place at 108 K, which indicates that DyVO3sub> belongs to type-II multiferroics exhibiting a coupling between magnetism and ferroelectricity. Some anomalies detected on the temperature dependence of electric polarization are discussed with respect to the nature of the spin-orbital-ordered states of the V sublattice and the degree of spin alignment in the Dy sublattice. The orthovanadates RVO3sub> (R= rare earth or Y) form an important new category for searching for high-TC multiferroics.

  16. Blending Cr2O3sub> into a NiO-Ni electrocatalyst for sustained water splitting

    SciTech Connect

    Gong, Ming; Zhou, Wu; Kenney, Michael James; Kapusta, Rich; Cowley, Sam; Wu, Yingpeng; Lu, Bingan; Lin, Meng -Chang; Wang, Di -Yan; Yang, Jiang; Hwang, Bing -Joe; Dai, Hongjie


    The rising H2 economy demands active and durable electrocatalysts based on low-cost, earth-abundant materials for water electrolysis/photolysis. Here we report nanoscale Ni metal cores over-coated by a Cr2O3sub>-blended NiO layer synthesized on metallic foam substrates. The Ni@NiO/Cr2O3sub> triphase material exhibits superior activity and stability similar to Pt for the hydrogen-evolution reaction in basic solutions. The chemically stable Cr2O3sub> is crucial for preventing oxidation of the Ni core, maintaining abundant NiO/Ni interfaces as catalytically active sites in the heterostructure and thus imparting high stability to the hydrogen-evolution catalyst. The highly active and stable electrocatalyst enables an alkaline electrolyzer operating at 20 mA cm–2 at a voltage lower than 1.5 V, lasting longer than 3 weeks without decay. Thus, the non-precious metal catalysts afford a high efficiency of about 15 % for light-driven water splitting using GaAs solar cells.

  17. Pressure-induced isostructural phase transition of a metal-organic framework Co2(4,4'-bpy)3sub>(NO3sub>)4·xH2O

    SciTech Connect

    Zhou, Mi; Wang, Kai; Men, Zhiwei; Sun, Chenglin; Li, Zhanlong; Liu, Bingbing; Zou, Guangtian; Zou, Bo


    Based on the 4,4'-bipyridine organic linker, metal–organic frameworks of Co2(4,4'-bpy)3sub>(NO3sub>)4·xH2O (CB-MOF) have been prepared. The pressure-dependent structure evolution of CB-MOF has been investigated up to 11 GPa. An isostructural phase transition was observed at about 6 GPa followed by negative compressibility along the b axis.

  18. Synthesis and nonlinear optical properties of BaTi(BO{sub 3}){sub 2} and Ba{sub 3}Ti{sub 3}O{sub 6}(BO{sub 3}){sub 2} crystals in glasses with high TiO{sub 2} contents

    SciTech Connect

    Kosaka, Shinji; Benino, Yasuhiko; Fujiwara, Takumi; Dimitrov, Vesselin; Komatsu, Takayuki . E-mail:


    The ternary BaO-TiO{sub 2}-B{sub 2}O{sub 3} glasses containing a large amount of TiO{sub 2} (20-40mol%) are prepared, and their optical basicities ({lambda}), the formation, structural features and second-order optical nonlinearities of BaTi(BO{sub 3}){sub 2} and Ba{sub 3}Ti{sub 3}O{sub 6}(BO{sub 3}){sub 2} crystals are examined to develop new nonlinear optical materials. It is found that the glasses with high TiO{sub 2} contents of 30-40mol% show large optical basicities of {lambda}=0.81-0.87, suggesting the high polarizabity of TiO{sub n} polyhedra (n=4-6) in the glasses. BaTi(BO{sub 3}){sub 2} and Ba{sub 3}Ti{sub 3}O{sub 6}(BO{sub 3}){sub 2} crystals are found to be formed as main crystalline phases in the glasses. It is found that BaTi(BO{sub 3}){sub 2} crystals tend to orient at the surface of crystallized glasses. The new XRD pattern for the Ba{sub 3}Ti{sub 3}O{sub 6}(BO{sub 3}){sub 2} phase is proposed through Rietvelt analysis. The second harmonic intensities of crystallized glasses were found to be 0.8 times as large as {alpha}-quartz powders, i.e., I{sup 2{omega}}(sample)/I{sup 2{omega}}({alpha}-quartz)=0.8, for the sample with BaTi(BO{sub 3}){sub 2} crystals and to be I{sup 2{omega}}(sample)/I{sup 2{omega}}({alpha}-quartz)=68 for the sample with Ba{sub 3}Ti{sub 3}O{sub 6}(BO{sub 3}){sub 2} crystals. The Raman scattering spectra for these two crystalline phases are measured for the first time and their structural features are discussed.

  19. Electronic structure and optical properties of the nonlinear optical crystal Pb{sub 4}O(BO{sub 3}){sub 2} by first-principles calculations

    SciTech Connect

    Yang, Zhihua; Pan, Shilie; Yu, Hongwei; Lee, Ming-Hsien


    Pb{sub 4}O(BO{sub 3}){sub 2} has a layered-type arrangement with optimally aligned BO{sub 3} triangles. The optical band gap is 3.317 eV obtained via the extrapolation method from the UV-vis-IR optical diffuse reflectance spectrum, consequently the absorption edge is about 374 nm. Density functional calculations using a generalized gradient approximation were utilized to investigate the electronic structures and optical properties of Pb{sub 4}O(BO{sub 3}){sub 2}. The calculated band structures show a direct gap of 2.608 eV, which is in agreement with the experimental optical band gap. A delocalized {pi} bonding of BO{sub 3} triangles and the stereo-effect of the lone pair 6s{sup 2} of lead cations are studied in electron densities. The birefringence is about 0.039-0.061 with the wavelength larger than about 375 nm. The calculated second-order susceptibility d{sub 24}=3.5 d{sub 36} (KDP) which is well consistent with the powder SHG intensity. - Graphical abstract: The density of state (DOS) show that the bottom of the valence bands is mainly derived from of the lone pair 6s{sup 2} of Pb{sup 2+}, and the top of the valence band is attributed to the hybridization orbitals from B-O groups. Calculated electronic structures indicate that the BO{sub 3} group with typical delocalization {pi} orbitals and strongly distorted lead oxygen polyhedra with highly asymmetric lobes on lead cations make a large SHG effect in Pb{sub 4}O(BO{sub 3}){sub 2}. Highlights: Black-Right-Pointing-Pointer Lone pair effect on Pb{sup 2+} and delocalization {pi} orbital in BO{sub 3} group is studied. Black-Right-Pointing-Pointer The combination of PbO{sub n} (n=3,4,5) and BO{sub 3} group makes Pb{sub 4}O(BO{sub 3}){sub 2} a large SHG effect. Black-Right-Pointing-Pointer Pb{sub 4}O(BO{sub 3}){sub 2} is a direct gap material with the gap 2.608 eV by the ab initio method. Black-Right-Pointing-Pointer The calculated birefringence is about 0.039-0.061 with the wavelength of about 375 nm. Black

  20. Structures and Energetics of (MgCO3sub> )n Clusters ( n ≤ 16)

    SciTech Connect

    Chen, Mingyang; Jackson, Virgil E.; Felmy, Andrew R.; Dixon, David A.


    There is significant interest in the role of carbonate minerals for the storage of CO2 and the role of prenucleation dusters in their formation. Global minima for (MgCO3sub>)n (n ≤ 16) structures were optimized using a tree growth-hybrid genetic algorithm in conjunction with MNDO/MNDO/d semiempirical molecular orbital calculations followed by density functional theory geometry optimizations with the B3LYP functional. The most stable isomers for (MgCO3sub>)n (n < 5) are approximately 2-dimensional. Mg can be bonded to one or two 0 atoms of a CO3sub>2-, and the 1-O bonding scheme is more favored as the cluster becomes larger. The average C-Mg coordination number increases as the cluster size increases, and at n = 16, the average C-Mg coordination number was calculated to be 5.2. The normalized dissociation energy to form monomers increases as n increases. At n = 16, the normalized dissociation energy is calculated to be 116.2 kcal/mol, as compared to the bulk value of 153.9 kcal/mol. The adiabatic reaction energies for the recombination reactions of (MgO)nclusters and CO2 to form (MgCO3sub>)n were calculated. The exothermicity of the normalized recombination energy < RE >(CO2) decreases as n increases and converged to the experimental bulk limit rapidly. The normalized recombination energy < RE >(CO2) was calculated to be -52.2 kcal/mol for the monomer and -30.7 kcal/mol for n = 16, as compared to the experimental value of -27.9 kcal/mol for the solid phase reaction. Infrared spectra for the lowest energy isomers were calculated, and absorption bands in the previous experimental infrared studies were assigned with our density functional theory predictions. The 13C, 17O, and 25Mg NMR chemical shifts for the clusters were predicted. We found that the results provide insights into the structural and energetic

  1. Mechanism of CO 2 Hydrogenation on Pd/Al 2 O 3sub> Catalysts: Kinetics and Transient DRIFTS-MS Studies

    SciTech Connect

    Wang, Xiang; Shi, Hui; Kwak, Ja Hun; Szanyi, János


    The hydrogenation of CO2 was investigated over a wide range of reaction conditions, using two Pd/γ-Al2O3sub> catalysts with different Pd loadings (5% and 0.5%) and dispersions (~11% and ~100%, respectively). Turnover rates for CO and CH4 formation were both higher over 5% Pd/Al2O3sub> with a larger average Pd particle size than those over 0.5% Pd/Al2O3sub> with a smaller average particle size. The selectivity to methane (22-40%) on 5% Pd/Al2O3sub> was higher by a factor of 2-3 than that on 0.5% Pd/Al2O3sub>. The drastically different rate expressions and apparent energies of activation for CO and CH4 formation lead us to conclude that reverse water gas shift and CO2 methanation do not share the same rate-limiting step on Pd, and that the two pathways are probably catalyzed at different surface sites. Measured reaction orders in CO2 and H2 pressures were similar over the two catalysts, suggesting that the reaction mechanism for each pathway does not change with particle size. In accordance, the DRIFTS results reveal that the prevalent surface species and their evolution patterns are comparable on the two catalysts during transient and steady-state experiments, switching feed gases among CO2, H2 and CO2+H2. The DRIFTS and MS results also demonstrate that no direct dissociation of CO2 takes place over the two catalysts, and that CO2 has to first react with surface hydroxyls on the oxide support. The thus-formed bicarbonates react with dissociatively adsorbed hydrogen on Pd particles to produce adsorbed formate species (bifunctional catalyst: CO2 activation on the oxide support, and H2 dissociation on the metal particles). Formates near the Pd particles (most likely at the metal/oxide interface) can react rapidly with adsorbed H

  2. Influence of holmium impurities on photoelectric properties of As{sub 2}Se{sub 3} and (As{sub 2}S{sub 3}){sub 0.3}(As{sub 2}Se{sub 3}){sub 0.7}

    SciTech Connect

    Burdiyan, I. I.; Senokosov, E. A.; Kosyuk, V. V. Pynzar', R. A.


    The influence of a holmium impurity on the photoelectric properties of bulk and film As{sub 2}Se{sub 3} and (As{sub 2}S{sub 3}){sub 0.3}(As{sub 2}Se{sub 3}){sub 0.7} samples is studied. Measurements of the relative photoconductivity of bulk samples and the spectral distribution of the persistent photoconductivity in film samples showed an increase in the photoconductivity of materials doped with holmium to concentrations equivalent to 0.010-0.015 at %. The spectral distribution of the persistent photoconductivity and optical absorption showed that the band gap monotonically decreases from 1.88 to 1.85 eV for As{sub 2}Se{sub 3} and from 2.05 to 2.00 eV for (As{sub 2}S{sub 3}){sub 0.3}(As{sub 2}Se{sub 3}){sub 0.7} as Ho concentration increases to 0.015 at %, and then weakly increases to the values in initial pure materials.

  3. Centrosymmetric [N(CH{sub 3}){sub 4}]{sub 2}TiF{sub 6} vs. noncentrosymmetric polar [C(NH{sub 2}){sub 3}]{sub 2}TiF{sub 6}: A hydrogen-bonding effect on the out-of-center distortion of TiF{sub 6} octahedra

    SciTech Connect

    Kim, Eun-ah; Lee, Dong Woo; Ok, Kang Min


    The syntheses, structures, and characterization of organically templated zero-dimensional titanium fluoride materials, A{sub 2}TiF{sub 6} (A=[N(CH{sub 3}){sub 4}] or [C(NH{sub 2}){sub 3}]), are reported. Phase pure samples of A{sub 2}TiF{sub 6} were synthesized by either solvothermal reaction method or a simple mixing method. While [N(CH{sub 3}){sub 4}]{sub 2}TiF{sub 6} crystallizes in a centrosymmetric space group, R-3, [C(NH{sub 2}){sub 3}]{sub 2}TiF{sub 6} crystallizes in a noncentrosymmetric polar space group, Cm. The asymmetric out-of-center distortion of TiF{sub 6} octahedra in polar [C(NH{sub 2}){sub 3}]{sub 2}TiF{sub 6} are attributable to the hydrogen-bonding interactions between the fluorine atoms in TiF{sub 6} octahedra and the nitrogen atoms in the [C(NH{sub 2}){sub 3}]{sup +} cation. Powder second-harmonic generation (SHG) measurements on the [C(NH{sub 2}){sub 3}]{sub 2}TiF{sub 6}, using 1064 nm radiation, indicate the material has SHG efficiency of 25 Multiplication-Sign that of {alpha}-SiO{sub 2}, which indicates an average nonlinear optical susceptibility, Left-Pointing-Angle-Bracket d{sub eff} Right-Pointing-Angle-Bracket {sub exp} of 2.8 pm/V. Additional SHG measurements reveal that the material is not phase-matchable (Type 1). The magnitudes of out-of-center distortions and dipole moment calculations for TiF{sub 6} octahedra will be also reported. - Graphical abstract: The out-of-center distortion of TiF{sub 6} octahedron in the polar noncentrosymmetric [C(NH{sub 2}){sub 3}]{sub 2}TiF{sub 6} is attributable to the hydrogen-bonding interactions between the F in TiF{sub 6} octahedron and the H-N in the [C(NH{sub 2}){sub 3}]{sup +}. Highlights: Black-Right-Pointing-Pointer Two titanium fluorides materials have been synthesized in high yields. Black-Right-Pointing-Pointer Hydrogen-bonds are crucial for the out-of-center distortion of TiF{sub 6} octahedra. Black-Right-Pointing-Pointer [C(NH{sub 2}){sub 3}]{sub 2}TiF{sub 6} has a SHG efficiency of 25

  4. High critical currents in heavily doped (Gd,Y)Ba2Cu3sub>Ox superconductor tapes

    SciTech Connect

    Selvamanickam, V.; Gharahcheshmeh, M. Heydari; Xu, A.; Galstyan, E.; Delgado, L.; Cantoni, C.


    REBa2Cu3sub>Ox superconductor tapes with moderate levels of dopants have been optimized for high critical current density in low magnetic fields at 77 K, but they do not exhibit exemplary performance in conditions of interest for practical applications, i.e., temperatures less than 50 K and fields of 2–30 T. Heavy doping of REBCO tapes has been avoided by researchers thus far due to deterioration in properties. Here, we report achievement of critical current densities (Jc) above 20 MA/cm2 at 30 K, 3 T in heavily doped (25 mol. % Zr-added) (Gd,Y)Ba2Cu3sub>Ox superconductor tapes, which is more than three times higher than the Jc typically obtained in moderately doped tapes. Pinning force levels above 1000 GN/m3 have also been attained at 20 K. A composition map of lift factor in Jc (ratio of Jc at 30 K, 3 T to the Jc at 77 K, 0 T) has been developed which reveals the optimum film composition to obtain lift factors above six, which is thrice the typical value. A highly c-axis aligned BaZrO3sub> (BZO) nanocolumn defect density of nearly 7 × 1011 cm–2 as well as 2–3nm sized particles rich in Cu and Zr have been found in the high Jc films.

  5. Twin symmetry texture of energetically condensed niobium thin films on sapphire substrate (a-plane Al2O3sub>)

    SciTech Connect

    Zhao, X.; Phillips, L.; Reece, C. E.; Seo, Kang; Krishnan, M.; Valderrama, E.


    An energetic condensation technique, cathodic arc discharge deposition, is used to growepitaxialNiobium(Nb)thin films on a-plane sapphire (hexagonal-closed-packed Al2O3sub>) at moderate substrate heating temperature (<400 °C). The epitaxial Nb(110)/Al2O3sub>(1,1,-2,0) thin films reached a maximum residual resistance ratio (RRR) value 214, despite using a reactor-grade Nbcathode source whose RRR was only 30. The measurements suggest that the film’s density of impurities and structural defects are lower when compared to Nb films produced by other techniques, such as magnetron sputtering, e-beam evaporation or molecular-beam-epitaxy. At lower substrate temperature, textured polycrystalline Nbthin films were created, and the films might have twin symmetry grains with {110} orientations in-plane. The texture was revealed by x-ray diffraction pole figures. The twin symmetry might be caused by a combination effect of the Nb/Al2O3sub> three-dimensional epitaxial relationship (“3D-Registry” Claassen’s nomenclature) and the “Volmer-Weber” (Island) growth model. However, pole figures obtained by electron backscattering diffraction (EBSD) found no twin symmetry on the thin films’ topmost surface (~50 nm in depth). The EBSD pole figures showed only one Nb{110} crystal plane orientation. Finally, a possible mechanism is suggested to explain the differences between the bulk (XRD) and surface (EBSD) pole figures.

  6. Alternative current conduction mechanisms of organic-inorganic compound [N(CH{sub 3}){sub 3}H]{sub 2}ZnCl{sub 4}

    SciTech Connect

    Ben Bechir, M. Karoui, K.; Guidara, K.; Ben Rhaiem, A.; Tabellout, M.


    [N(CH{sub 3}){sub 3}H]{sub 2}ZnCl{sub 4} has been studied by X-ray powder diffraction patterns, differential scanning calorimetry (DSC), and impedance spectroscopy. The [N(CH{sub 3}){sub 3}H]{sub 2}ZnCl{sub 4} hybrid compound is crystallized at room temperature (T ≈ 300 K) in the orthorhombic system with Pnma space group. Five phase transitions (T{sub 1} = 255 K, T{sub 2} = 282 K, T{sub 3} = 302 K, T{sub 4} = 320 K, and T{sub 5} = 346 K) have been proved by DSC measurements. The electrical technique was measured in the 10{sup −1}-10{sup 7} Hz frequency range and 233–363 K temperature interval. The frequency dependence of alternative current (AC) conductivity is interpreted in terms of Jonscher's law. The AC electrical conduction in [N(CH{sub 3}){sub 3}H]{sub 2}ZnCl{sub 4} is analyzed by different processes, which can be attributed to several models: the correlated barrier hopping model in phase I, the overlapping large polaron tunneling model in phase II, the quantum mechanical tunneling model in phase IV, and the non-overlapping small polaron tunneling model in phases III, V, and VI. The conduction mechanism is studied with the help of Elliot's theory, and the Elliot's parameters are determined.

  7. 266  nm ultraviolet light generation in Ga-doped BaAlBO3sub>F2 crystals.


    Yang, Lei; Yue, Yinchao; Yang, Feng; Hu, Zhanggui; Xu, Zuyan


    BaAlBO3sub>F2 (BABF) crystals are a recently developed and promising nonlinear optical material, notably for the third harmonic generation of ultraviolet (UV) light at 355 nm. However, the fourth harmonic generation of UV light at 266 nm has never been obtained by using a BABF crystal due to its relatively small birefringence. We demonstrate that the birefringence of BABF can be effectively increased by doping it with Ga3+. The fourth harmonic generation of UV light at 266 nm was achieved for the first time in a Ga-doped BABF crystal. PMID:27192296

  8. Optical properties of trigonal single crystals (Yb,Tm)Al{sub 3}(BO{sub 3}){sub 4} grown from fluxes based on the bismuth and lithium molybdates

    SciTech Connect

    Temerov, V. L. Sokolov, A. E.; Sukhachev, A. L.; Bovina, A. F.; Edel'man, I. S.; Malakhovskii, A. V.


    The conditions for synthesis of Yb{sub x}Tm{sub 1-x}Al{sub 3}(BO{sub 3}){sub 4} (x = 0, 0.1, 0.2, 1.0) single crystals from fluxes based on bismuth trimolybdate Bi{sub 2}Mo{sub 3}O{sub 12} and lithium molybdate Li{sub 2}MoO{sub 4} are investigated. It is proposed to grow them by the group method on seeds. The polarized optical absorption spectra are measured for two mutually orthogonal linear polarizations at temperatures of 100 and 300 K.

  9. Integrated chip-scale Si3sub>N4 wavemeter with narrow free spectral range and high stability.


    Xiang, Chao; Tran, Minh A; Komljenovic, Tin; Hulme, Jared; Davenport, Michael; Baney, Doug; Szafraniec, Bogdan; Bowers, John E


    We designed, fabricated, and characterized an integrated chip-scale wavemeter based on an unbalanced Mach-Zehnder interferometer with 300 MHz free spectral range. The wavemeter is realized in the Si3sub>N4 platform, allowing for low loss with ∼62  cm of on-chip delay. We also integrated an optical hybrid to provide phase information. The main benefit of a fully integrated wavemeter, beside its small dimensions, is increased robustness to vibrations and temperature variations and much improved stability over fiber-based solutions. PMID:27420522

  10. Crystal symmetry and high-magnetic-field specific heat of SrCu{sub 2}(BO{sub 3}){sub 2}

    SciTech Connect

    Jorge, G.A.; Jaime, M.; Harrison, N.; Stern, R.; Bonca, J.; El Shawish, S.; Batista, C.D.; Dabkowska, H.A.; Gaulin, B.D.


    We report measurements of the specific heat of the quantum spin liquid system SrCu{sub 2}(BO{sub 3}){sub 2} in continuous magnetic fields H of up to 33 T. The specific heat data, when combined with a finite temperature Lanczos diagonalization of the Shastry-Sutherland Hamiltonian, indicate the presence of a nearest neighbor Dzyaloshinsky-Moriya (DM) interaction that violates the crystal symmetry. Moreover, the same DM interaction is required to explain the observed electron spin resonance lines for H parallel c.

  11. Synthesis and crystal structure of two new cerium rhodium oxides: Ce{sub 2/3-x}Rh{sup 3+}{sub 2}O{sub 4} (x{approx}0.12) with Ce mixed valency and Ce{sup 4+}Rh{sup 3+}{sub 2}O{sub 5}

    SciTech Connect

    Mizoguchi, Hiroshi; Zakharov, L.N.; Bhuvanesh, N.S.P.; Sleight, A.W.; Subramanian, M.A.


    The new compounds Ce{sub 2/3-x}Rh{sub 2}O{sub 4} (x{approx}0.11-0.14) and CeRh{sub 2}O{sub 5} have been prepared. Their structures were determined from single crystal X-ray diffraction data. Electrical and magnetic properties were also evaluated. Based on the structural analysis and physical properties, oxidation states for CeRh{sub 2}O{sub 5} can be assigned as Ce{sup 4+}Rh{sup 3+}{sub 2}O{sub 5}. A small variation in x was detected for Ce{sub 2/3-x}Rh{sub 2}O{sub 4} indicating a formula ranging from Ce{sup 3.64+}{sub 0.55}Rh{sup 3+}{sub 2}O{sub 4} to Ce{sup 3.81+}{sub 0.525}Rh{sup 3+}{sub 2}O{sub 4}. - Graphical abstract: The new compounds Ce{sub 2/3-x}Rh{sub 2}O{sub 4} (x{approx}0.11-0.14) and CeRh{sub 2}O{sub 5} have been prepared and their structures were determined from single crystal X-ray diffraction data. Electrical and magnetic properties were also evaluated. Highlights: > The new compounds CeRh{sub 2}O{sub 5} and Ce{sub 2/3-x}Rh{sub 2}O{sub 4} (x{approx}0.11-0.14) have been prepared. > Their structures were determined from single crystal X-ray diffraction data. > Valence picture is Ce{sup 4+}Rh{sup 3+}{sub 2}O{sub 5} and Ce{sup 3.64+}{sub 0.55}Rh{sup 3+}{sub 2}O{sub 4} to Ce{sup 3.81+}{sub 0.525}Rh{sup 3+}{sub 2}O{sub 4}.

  12. Rapid microwave-assisted sol-gel preparation of Pd-substituted LnFeO3sub> (Ln = Y, La): phase formation and catalytic activity

    SciTech Connect

    Misch, Lauren M.; Birkel, Alexander; Figg, C. Adrian; Fors, Brett P.; Hawker, Craig J.; Stucky, Galen D.; Seshadri, Ram


    We present a rapid microwave-assisted sol–gel approach to Pd-substituted LnFeO3sub> (Ln = Y, La) for applications in C–C coupling reactions. These materials could be prepared in household microwave ovens in less than 15 minutes of reaction time with the final materials displaying well-defined structure and morphology. Phase evolution was studied using time-dependent microwave heatings and then compared with the results obtained from thermogravimetric analyses. Materials were confirmed to be phase pure by laboratory and synchrotron X-ray diffraction. Substituted Pd is ionic as shown by the binding energy shift from X-ray photoelectron spectroscopy. The short heating periods required for phase purity allow these materials less time for sintering as compared to conventional solid state preparation methods, making relatively high surface areas achievable. These materials have been successfully used as catalyst precursor materials for C–C coupling reactions in which the active species is Pd0. Pd-substituted LnFeO3sub> (Ln = Y, La) provides Pd0 in solution which can be complexed by the ligand SPhos, allowing for aryl chloride coupling.

  13. Potential surface of rotation-translation coupled systems: Me(NH{sub 3}){sub 6}(PF{sub 6}){sub 2}, Me=Ni,Co

    SciTech Connect

    Schiebel, P.; Prandl, W.; Buettner, H. G.; Kearley, G. J.; Prager, M.


    One of the most recent developments in the field of rotational dynamics is the discovery of rotation-translation-coupling (RTC) for molecules in an environment of incompatible symmetry. The combination of incompatible molecular and environmental symmetry usually leads to almost free rotation. Ni-and Co-hexamminehexafluorophosphate thus show large ground state tunnel splittings (0.540 meV (Ni) and 0.542 meV (Co)), as observed by inelastic neutron scattering (INS). The tunnelling spectrum of Ni(NH{sub 3}){sub 6}(PF{sub 6}){sub 2} is split into three peaks. Under pressure their relative intensities change, but there is almost no shift of the peak positions. In contrast, the tunnelling spectra of Co(NH{sub 3}){sub 6}(PF{sub 6}){sub 2} shows only one peak, which does not change under pressure. The hexafluorophosphate compounds are unique among the hexammines, because they do not undergo a phase transition on cooling. From a crystallographic view, both compounds are isostructural (Fm3m). Nevertheless, the proton density distributions, observed by neutron diffraction, although almost circular, show an interesting difference, namely their maxima are rotated by 45: in the cobalt compound they are on the axes, whereas in the nickel compound they are on the diagonale at room temperature and on the axes at 5K. This is related with a phase shift between the two terms characterizing the potential surface. Obviously, the potential is very sensitive to weak changes of the environment.

  14. Temperature-dependent adsorption of surfactant molecules and associated crystallization kinetics of noncentrosymmetric Fe(IO{sub 3}){sub 3} nanorods in microemulsions

    SciTech Connect

    El-Kass, Moustafa; Ladj, Rachid; Mugnier, Yannick; Le Dantec, Ronan; Hadji, Rachid; Marty, Jean-Christophe; Rouxel, Didier; Durand, Christiane; Fontvieille, Dominique; Rogalska, Ewa; and others


    Graphical abstract: - Highlights: • Crystallization of Fe(IO{sub 3}){sub 3} in microemulsions probed by hyper-Rayleigh scattering. • A faster growth and a better shape control of nanorods are obtained at 80 °C. • Different persistent cell deformations are related to the crystallization kinetics. • A temperature-dependent adsorption of surfactants on nanorods is suggested. - Abstract: Aggregation-induced crystallization of iron iodate nanorods within organic–inorganic aggregates of primary amorphous precursors is probed by time-dependent hyper-Rayleigh scattering measurements in Triton X-100 based-microemulsions. In the context of a growing interest of noncentrosymmetric oxide nanomaterials in multi-photon bioimaging, we demonstrate by a combination of X-ray diffraction and electron microscopy that an increase in the synthesis of temperature results in faster crystallization kinetics and in a better shape-control of the final Fe(IO{sub 3}){sub 3} nanorods. For initial microemulsions of fixed composition, room-temperature synthesis leads to bundles of 1–3 μm long nanorods, whereas shorter individual nanorods are obtained when the temperature is increased. Results are interpreted in terms of kinetically unfavorable mesoscale transformations due to the strong binding interactions with Triton molecules. The interplay between the nanorod crystallization kinetics and their corresponding unit cell deformation, evidenced by lattice parameter refinements, is attributed to a temperature-dependent adsorption of surfactants molecules at the organic–inorganic interface.

  15. Segregation and trapping of oxygen vacancies near the SrTiO3sub>Σ3 (112) [110] tilt grain boundary

    SciTech Connect

    Liu, Bin; Cooper, Valentino R.; Zhang, Yanwen; Weber, William J.


    In nanocrystalline materials, structural discontinuities at grain boundaries (GBs) and the segregation of point defects to these GBs play a key role in defining the structural stability of a material, as well as its macroscopic electrical/mechanical properties. In this study, the segregation of oxygen vacancies near the Σ3 (1 1 2) [¯110] tilt GB in SrTiO3sub> is explored using density functional theory. We find that oxygen vacancies segregate toward the GB, preferring to reside within the next nearest-neighbor layer. This oxygen vacancy segregation is found to be crucial for stabilizing this tilt GB. Furthermore, we find that the migration barriers of oxygen vacancies diffusing toward the first nearest-neighbor layer of the GB are low, while those away from this layer are very high. Furthermore, the segregation and trapping of the oxygen vacancies in the first nearest-neighbor layer of GBs are attributed to the large local distortions, which can now accommodate the preferred sixfold coordination of Ti. These results suggest that the electronic, transport, and capacitive properties of SrTiO3sub> can be engineered through the control of GB structure and grain size or layer thickness.

  16. Synthesis of hierarchical Ni{sub 11}(HPO{sub 3}){sub 8}(OH){sub 6} superstructures based on nanorods through a soft hydrothermal route

    SciTech Connect

    Liao, Kaiming; Ni, Yonghong


    In this paper, we reported the successful synthesis of hierarchical Ni{sub 11}(HPO{sub 3}){sub 8}(OH){sub 6} superstructures based on nanorods via a facile hydrothermal route, employing NiCl{sub 2}.6H{sub 2}O and NaH{sub 2}PO{sub 2}.H{sub 2}O as the reactants in the presences of polyvinylpyrrolidone (PVP) and CH{sub 3}COONa.3H{sub 2}O. The reaction was carried out at 170 {sup o}C for 10 h. HPO{sub 3}{sup 2-} ions were provided via the dismutation reaction of H{sub 2}PO{sub 2}{sup -} ions in a weak basic solution. The as-obtained products were characterized by X-ray powder diffraction (XRD), energy dispersive spectrometry (EDS), field emission scanning electron microscopy (SEM), selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM). Some factors influencing the morphology of the hierarchical Ni{sub 11}(HPO{sub 3}){sub 8}(OH){sub 6} nanorods, such as the reaction temperature, time, the amounts of PVP and CH{sub 3}COONa, and the initial concentration of Ni{sup 2+} ions, were systematically investigated. A possible growth mechanism was proposed based on experimental results.

  17. K 3sub> Fe(CN) 6 under External Pressure: Dimerization of CN Coupled with Electron Transfer to Fe(III)

    SciTech Connect

    Li, Kuo; Zheng, Haiyan; Wang, Lijuan; Tulk, Christopher A.; Molaison, Jamie J.; Feygenson, Mikhail; Yang, Wenge; Guthrie, Malcolm; Mao, Hokwang


    The addition polymerization of charged monomers like C≡C2– and C≡N– is scarcely seen at ambient conditions but can progress under external pressure with their conductivity significantly enhanced, which expands the research field of polymer science to inorganic salts. Moreover, the reaction pressures of transition metal cyanides like Prussian blue and K3sub>Fe(CN)6 are much lower than that of alkali cyanides. To figure out the effect of the transition metal on the reaction, the crystal structure and electronic structure of K3sub>Fe(CN)6 under external pressure are investigated by in situ neutron diffraction, in situ X-ray absorption fine structure (XAFS), and neutron pair distribution functions (PDF) up to ~15 GPa. The cyanide anions react following a sequence of approaching–bonding–stabilizing. The Fe(III) brings the cyanides closer which makes the bonding progress at a low pressure (2–4 GPa). At ~8 GPa, an electron transfers from the CN to Fe(III), reduces the charge density on cyanide ions, and stabilizes the reaction product of cyanide. Finally, from this study we can conclude that bringing the monomers closer and reducing their charge density are two effective routes to decrease the reaction pressure, which is important for designing novel pressure induced conductor and excellent electrode materials.

  18. Quantifying stoichiometry-induced variations in structure and energy of a SrTiO3sub> symmetric Σ13 {510}/<100> grain boundary

    SciTech Connect

    Yang, Hao; Lee, H. S.; Sarahan, M. C.; Sato, Yoichi; Chi, Miaofang; Moeck, Peter; Ikuhara, Yuichi; Browning, Nigel D.


    Grain boundaries (GBs) in complex oxides such as perovskites have been shown to readily accommodate nonstoichiometry changing the electrostatic potential at the boundary plane and effectively controlling material properties such as capacitance, magnetoresistance and superconductivity. Understanding and quantifying exactly how variations in atomic scale nonstoichiometry at the boundary plane extend to the practical mesoscale operating length of the system is therefore critical for improving the overall properties. Bicrystals of SrTiO3sub> were fabricated to provide the model GB model structures that are analysed in this paper. We show that statistical analysis of aberration-corrected scanning transmission electron microscope images acquired from a large area of GB is an effective routine to understanding the variation in boundary structure that occurs to accommodate nonstoichiometry. In the case of the SrTiO3sub> 22.6° Σ13 (510)/[100] GB analysed here, the symmetric atomic structures observed from a micron-long GB can be categorized as two different competing structural arrangements, with and without a rigid-body translation along the boundary plane. How this quantified experimental approach can provide direct insights into the GB energetics is further confirmed from the first principles density functional theory, and the effect of nonstoichiometry in determining the GB energies is quantified.

  19. Coherent phonon study of (GeTe){sub l}(Sb{sub 2}Te{sub 3}){sub m} interfacial phase change memory materials

    SciTech Connect

    Makino, Kotaro Saito, Yuta; Fons, Paul; Kolobov, Alexander V.; Nakano, Takashi; Tominaga, Junji; Hase, Muneaki


    The time-resolved reflectivity measurements were carried out on the interfacial phase change memory (iPCM) materials ([(GeTe){sub 2}(Sb{sub 2}Te{sub 3}){sub 4}]{sub 8} and [(GeTe){sub 2}(Sb{sub 2}Te{sub 3}){sub 1}]{sub 20}) as well as conventional Ge{sub 2}Sb{sub 2}Te{sub 5} alloy at room temperature and above the RESET-SET phase transition temperature. In the high-temperature phase, coherent phonons were clearly observed in the iPCM samples while drastic attenuation of coherent phonons was induced in the alloy. This difference strongly suggests the atomic rearrangement during the phase transition in iPCMs is much smaller than that in the alloy. These results are consistent with the unique phase transition model in which a quasi-one-dimensional displacement of Ge atoms occurs for iPCMs and a conventional amorphous-crystalline phase transition takes place for the alloy.

  20. Vapor-liquid equilibrium of the Mg(NO/sub 3/)/sub 2/-HNO/sub 3/-H/sub 2/O system

    SciTech Connect

    Thompson, B.E.; Derby, J.J.; Stalzer, E.H.


    The vapor-liquid equilibrium of the Mg(NO/sub 3/)/sub 2/-HNO/sub 3/-H/sub 2/O system in concentrations of 0 to 70 wt % Mg(NO/sub 3/)/sub 2/ and 0 to 75 wt % HNO/sub 3/ at atmospheric pressure was correlated by two approaches. One was based on a dissociation equilibrium expression in which the activities of the reacting species (HNO/sub 3/, NO/sub 3//sup -/, and H/sup +/) were approximated with mole fractions. The activity coefficients of the undissociated HNO/sub 3/ and H/sub 2/O were correlated as functions of the concentrations of magnesium nitrate and nitric acid by second-order polynomials. The average absolute difference between predicted and experimental values was 8% for the mole fraction of acid in the vapor and 8/sup 0/K for the bubble-point temperature. The second approach was to correlate the mean ionic rational activity coefficient of water with a form of the excess Gibbs energy composed of two terms. One term, a function of the ionic strength, accounts for the coulombic (ionic) interactions; the other term accounts for the non-coulombic (molecular) interactions. The average absolute difference between predicted and experimental values was 9% for the mole fraction of acid in the vapor, and 10/sup 0/K for the bubble-point temperature.

  1. Atomic and electronic structures of single-layer FeSe on SrTiO3sub>(001): The role of oxygen deficiency

    SciTech Connect

    Bang, Junhyeok; Li, Zhi; Sun, Y. Y.; Samanta, Amit; Zhang, Y. Y.; Zhang, Wenhao; Wang, Lili; Chen, X.; Ma, Xucun; Xue, Q.-K.; Zhang, S. B.


    Using first-principles calculation, we propose an interface structure for single triple-layer FeSe on the SrTiO3sub>(001) surface, a high-Tc superconductor found recently. The key component of this structure is the oxygen deficiency on the top layer of the SrTiO3sub> substrate, as a result of Se etching used in preparing the high-Tc samples. The O vacancies strongly bind the FeSe triple layer to the substrate giving rise to a (2×1) reconstruction, as observed by scanning tunneling microscopy. The enhanced binding correlates to the significant increase of Tc observed in experiment. The O vacancies also serve as the source of electron doping, which modifies the Fermi surface of the first FeSe layer by filling the hole pocket near the center of the surface Brillouin zone, as suggested from angle-resolved photoemission spectroscopy measurement.

  2. Carbonylation of hydrocarbons via C-H activation catalyzed by RhCl(CO)(PMe sub 3 ) sub 2 under irradiation

    SciTech Connect

    Sakakura, Toshiyasu; Sodeyama, Touru; Tanaka, Masato ); Sasaki, Koushi; Wada, Keisuke )


    C-H bonds in hydrocarbons are carbonylated into aldehydes by reaction with carbon monoxide in the presence of RhCl(CO)(PR{sub 3}){sub 2} under irradiation. The reaction proceeds at an ambient temperature under an atmospheric pressure of CO. The catalytic activity of RhCl(CO)(PR{sub 3}){sub 2} decreases in the order PMe{sub 3} {approx} 1,3,4-trimethylphospholane {approx} 1,3,4-trimethylphospholene > P(CH{sub 2}O){sub 3}CMe > PEt{sub 3} {approx} PBu{sub 3} > P(i-Pr){sub 3} {approx} P(OMe){sub 3} > dppe. The thiocyanato complex exhibits a similar catalytic activity to the chloro complex. The use of other complexes of Co, Ir, and Ru resulted in much lower catalytic activities. In the carbonylation of benzene, benzophenone and benzyl alcohol are formed as byproducts. The yield of benzaldehyde reached 3.3% on the basis of benzene. Monosubstituted benzenes are converted mainly to meta-substituted benzaldehydes. In the reaction of n-alkanes, a terminal methyl group is selectively carbonylated to give a linear aldehyde.

  3. Lithium ions in the van der Waals gap of Bi2Se3sub> single crystals

    SciTech Connect

    Bludska, J.; Jakubec, I.; Karamazov, S.; Horak, J.; Uher, Ctirad


    Insertion/extraction of lithium ions into/from Bi2Se3sub> crystals was investigated by means of cyclic voltammetry. The process of insertion is reflected in the appearance of two bands on voltammograms at ~1.7 and ~1.5 V, corresponding to the insertion of Li+ ions into octahedral and tetrahedral sites of the van der Waals gap of these layered crystals. The process of extraction of Li+ ions from the gap results in the appearance of four bands on the voltammograms. The bands 1 and 2 at ~2.1 and ~2.3 V correspond to the extraction of a part of Li+ guest ions from the octahedral and tetrahedrals sites and this extraction has a character of a reversible intercalation/deintercalation process. A part of Li+ ions is bound firmly in the crystal due to the formation of negatively charged clusters of the (LiBiSe2.Bi3sub>Se4-) type. A further extraction of Li+ ions from the van der Waals gap is associated with the presence of bands 3 and 4 placed at ~2.5 and ~2.7 V on the voltammograms as their extraction needs higher voltage due to the influence of negative charges localized on these clusters.

  4. Temperature-dependent excitonic photoluminescence excited by two-photon absorption in perovskite CsPbBr3sub> quantum dots.


    Wei, Ke; Xu, Zhongjie; Chen, Runze; Zheng, Xin; Cheng, Xiangai; Jiang, Tian


    Recently, lead halide perovskite quantum dots have been reported with potential for photovoltaic and optoelectronic applications due to their excellent luminescent properties. Herein excitonic photoluminescence (PL) excited by two-photon absorption in perovskite CsPbBr3sub> quantum dots (QDs) has been studied at a broad temperature range, from 80 to 380 K. Two-photon absorption has been investigated and the absorption coefficient is up to 0.085 cm/GW at room temperature. Moreover, the PL spectrum excited by two-photon absorption shows a linear blue-shift (0.32 meV/K) below the temperature of 220 K. However, for higher temperatures, the PL peak approaches a roughly constant value and shows temperature-independent chromaticity up to 380 K. This behavior is distinct from the general red-shift for semiconductors and can be attributed to the result of thermal expansion, electron-phonon interaction and structural phase transition around 360 K. The strong nonlinear absorption and temperature-independent chromaticity of CsPbBr3sub> QDs observed in temperature range from 220 to 380 K will offer new opportunities in nonlinear photonics, light-harvesting, and light-emitting devices. PMID:27519098

  5. Atomic layer epitaxy of Ruddlesden-Popper SrO(SrTiO{sub 3}){sub n} films by means of metalorganic aerosol deposition

    SciTech Connect

    Jungbauer, M.; Hühn, S.; Moshnyaga, V.; Egoavil, R.; Tan, H.; Verbeeck, J.; Van Tendeloo, G.


    We report an atomic layer epitaxial growth of Ruddlesden-Popper (RP) thin films of SrO(SrTiO{sub 3}){sub n} (n = ∞, 2, 3, 4) by means of metalorganic aerosol deposition (MAD). The films are grown on SrTiO{sub 3}(001) substrates by means of a sequential deposition of Sr-O/Ti-O{sub 2} atomic monolayers, monitored in-situ by optical ellipsometry. X-ray diffraction and transmission electron microscopy (TEM) reveal the RP structure with n = 2–4 in accordance with the growth recipe. RP defects, observed by TEM in a good correlation with the in-situ ellipsometry, mainly result from the excess of SrO. Being maximal at the film/substrate interface, the SrO excess rapidly decreases and saturates after 5–6 repetitions of the SrO(SrTiO{sub 3}){sub 4} block at the level of 2.4%. This identifies the SrTiO{sub 3} substrate surface as a source of RP defects under oxidizing conditions within MAD. Advantages and limitations of MAD as a solution-based and vacuum-free chemical deposition route were discussed in comparison with molecular beam epitaxy.

  6. Structural distortions in the spin-gap regime of the quantum antiferromagnet SrCu{sub 2}(BO{sub 3}){sub 2}

    SciTech Connect

    Vecchini, C.; Adamopoulos, O.; Chapon, L.C.; Lappas, A.; Kageyama, H.; Ueda, Y.; Zorko, A.


    We report the first crystallographic study within the low-temperature (<40 K) spin-gap region of the two-dimensional frustrated antiferromagnet SrCu{sub 2}(BO{sub 3}){sub 2}. The crystal system does not deviate from the tetragonal I-42m space group symmetry. However, our high-resolution neutron powder diffraction measurements uncover subtle structural modifications below 34 K, concomitant to the formation of the dimer singlet ground state. Intimate spin-lattice coupling leads to negative thermal expansion of the tetragonal structure, which reflects into particular local lattice adjustments. The extracted structural parameters suggest the reduction of the buckling found in the copper-borate planes and the strengthening of the leading, in-plane intra-dimer superexchange interaction. The observed contraction along the c-axis, associated with the inter-dimer exchange in adjacent layers, indicates the involvement of weaker three-dimensional interactions in the magnetic properties. The rules posed by the crystal symmetry do not preclude Dzyaloshinsky-Moriya interactions, which therefore remain as an important source of spin anisotropy necessary to rationalise the ground state behaviour. - Abstract: We report the first crystallographic study within the low-temperature spin-gap region of the two-dimensional frustrated antiferromagnet SrCu{sub 2}(BO{sub 3}){sub 2}. Subtle spin-lattice coupling was unveiled in the low-temperature region. Display Omitted

  7. Band-Gap Reduction and Dopant Interaction in Epitaxial La,Cr Co-doped SrTiO3sub> Thin Films

    SciTech Connect

    Comes, Ryan B.; Sushko, Petr; Heald, Steve M.; Colby, Robert J.; Bowden, Mark E.; Chambers, Scott A.


    We show that by co-doping SrTiO3sub> (STO) epitaxial thin films with equal amounts of La and Cr it is possible to produce films with an optical band gap ~0.9 eV lower than that of undoped STO. Sr1-xLaxTi1-xCrxO3sub> thin films were deposited by molecular beam epitaxy and characterized using x-ray photoelectron spectroscopy and x-ray absorption near-edge spectroscopy to show that the Cr dopants are almost exclusively in the Cr3+ oxidation state. Extended x-ray absorption fine structure measurements and theoretical modeling suggest that it is thermodynamically preferred for La and Cr dopants to occupy nearest neighbor A- and B-sites in the lattice. Transport measurements show that the material exhibits variable-range hopping conductivity with high resistivity. These results create new opportunities for the use of doped STO films in photovoltaic and photocatalytic applications.

  8. Synthesis and Luminescence Characteristics of Cr3+ doped Y3sub>Al5O12 Phosphors

    SciTech Connect

    Smith, Brenda A.; Dabestani, Reza T.; Lewis, Linda A.; Thompson, Cyril V.; Collins, Case T.; Aytug, Tolga


    Luminescence performance of yttrium aluminum garnet (Y3sub>Al5O12) phosphors as a function of Cr3+ concentration has been investigated via two different wet-chemical synthesis techniques, direct- (DP) and hydrothermal-precipitation (HP). Using either of these methods, the red-emitting phosphor [Y3sub>Al5-xCrxO12 (YAG: Cr3+)] showed similar photoluminescence (PL) intensities once the dopant concentration was optimized. Specifically, the YAG: Cr3+ PL emission intensity reached a maximum at Cr3+ concentrations of x = 0.02 (0.4 at.%) and x = 0.13 (2.6 at.%) for DP and HP processed samples, respectively. The results indicated the strong influence of the processing method on the optimized YAG: Cr3+ performance, where a more effective energy transfer rate between a pair of Cr3+ activators at low concentration levels was observed by using the DP synthesis technique. Development of a highly efficient phosphor, using a facile synthesis approach, could significantly benefit consumer and industrial applications by improving the operational efficiency of a wide range of practical devices.

  9. Bond-bending isomerism of Au2I3sub>-: Competition between covalent bonding and aurophilicity

    SciTech Connect

    Li, Wan -Lu; Liu, Hong -Tao; Jian, Tian; Lopez, Gary V.; Piazza, Zachary A.; Huang, Dao -Ling; Chen, Teng -Teng; Su, Jing; Yang, Ping; Chen, Xin; Wang, Lai -Sheng; Li, Jun


    We report a joint photoelectron spectroscopy and theoretical investigation of the gaseous Au2I3sub> cluster, which is found to exhibit two types of isomers due to competition between Au–I covalent bonding and Au–Au aurophilic interactions. The covalent bonding favors a bent IAuIAuI structure with an obtuse Au–I–Au angle (100.7°), while aurophilic interactions pull the two Au atoms much closer, leading to an acutely bent structure (72.0°) with an Au–Au distance of 3.08 Å. The two isomers are separated by a small barrier and are nearly degenerate with the obtuse isomer being slightly more stable. At low temperature, only the obtuse isomer is observed; distinct experimental evidence is observed for the co-existence of a combination of isomers with both acute and obtuse bending angles at room temperature. As a result, the two bond-bending isomers of Au2I3sub> reveal a unique example of one molecule being able to oscillate between different structures as a result of two competing chemical forces.

  10. Measurements of reactive trace gases and variable O3sub> formation rates in some South Carolina biomass burning plumes

    SciTech Connect

    Akagi, S. K.; Yokelson, R. J.; Burling, I. R.; Meinardi, S.; Simpson, I.; Blake, D. R.; McMeeking, G. R.; Sullivan, A.; Lee, T.; Kreidenweis, S.; Urbanski, S.; Reardon, J.; Griffith, D. W. T.; Johnson, T. J.; Weise, D. R.


    In October-November 2011 we measured the trace gas emission factors from 7 prescribed fires in South Carolina, U.S. using two Fourier transform infrared spectrometer (FTIR) systems and whole air sampling (WAS) into canisters followed by gas-chromatographic analyses. The fires were intended to emulate high-intensity burns as they were lit during the dry season and in most cases represented stands that had not been treated with prescribed burns in 10+ years, if at all. A total of 97 trace gas species are reported here from both airborne and ground-based platforms making this one of the most detailed field studies of fire emissions to date. The measurements included the first data for a suite of monoterpene compounds emitted via distillation of plant tissues during real fires. The known chemistry of the monoterpenes and their measured abundance of ~0.40% of CO (molar basis), ~3.9% of NMOC (molar basis), and ~21% of organic aerosol (mass basis), suggests that they impacted post-emission formation of ozone, aerosol, and small organic trace gases such as methanol and formaldehyde in the sampled plumes. The variability in the terpene emissions in South Carolina (SC) fire plumes was high and, in general, the speciation of the emitted gas-phase non-methane organic compounds was surprisingly different from that observed in a similar study in nominally similar pine forests in North Carolina ~20 months earlier. It is likely that the slightly different ecosystems, time of year and the precursor variability all contributed to the variability in plume chemistry observed in this study and in the literature. The ΔHCN/ΔCO emission ratio, however, is fairly consistent at 0.9 ± 0.06 % for airborne fire measurements in coniferous-dominated ecosystems further confirming the value of HCN as a good biomass burning indicator/tracer. The SC results also support an earlier finding that C3sub>-C4 alkynes may be of use as biomass burning indicators on the time-scale of

  11. Calorimetric, spectroscopic and structural investigations of phase polymorphism in [Ru(NH{sub 3}){sub 6}](BF{sub 4}){sub 3}. Part I

    SciTech Connect

    Dolega, Diana; Mikuli, Edward; Inaba, Akira; Gorska, Natalia; Holderna-Natkaniec, Krystyna; Nitek, Wojciech


    Four crystalline phases of the coordination compound [Ru(NH{sub 3}){sub 6}](BF{sub 4}){sub 3} are identified by adiabatic calorimetry. Three phase transitions, one at T{sub C3}(IV{yields}III)=30.7 K, the second at T{sub C2}(III{yields}II)=91.7 K (both accompanied by comparable entropy changes 3.0 and 3.1 J K{sup -1} mol{sup -1}, respectively) and the third at T{sub C1}(II{yields}I)=241.6 K (accompanied by an entropy change of 8.1 J K{sup -1} mol{sup -1}) were discovered. X-ray single crystal diffraction (at 293 K) demonstrates that phase I is a highly dynamic disordered cubic phase (Fm3{sup Macron }m, No. 225) with two types of BF{sub 4}{sup -} anions differing in a degree of disorder. In phase II (at 170 K) the structure remains cubic (Ia3{sup Macron }, No. 206), with two different types of cations and four different types of anions. Splitting of certain IR bands connected with NH{sub 3} ligands at the observed phase transitions suggests a lowering of the symmetry of the [Ru(NH{sub 3}){sub 6}]{sup 3+} complex cation. Both NH{sub 3} ligands and BF{sub 4}{sup -} anions perform fast reorientations ({tau}{sub R} Almost-Equal-To 10{sup -12} s), which are significantly slowed down below the phase transition at T{sub C3}. {sup 1}H NMR studies led to estimate the values of the activation energy of NH{sub 3} ligands reorientation in the phases II and I as equal to {approx}8 kJ mol{sup -1}. In phase I the whole hexammineruthenium(III) cations reorientation as a tumbling process can be noticed. The activation energy value of this motion is {approx}24 kJ mol{sup -1}. {sup 19}F NMR studies give the values of the activation energy of BF{sub 4}{sup -} anions reorientation as {approx}6 kJ mol{sup -1}. Above the phase transition temperature half of BF{sub 4}{sup -} anions perform a tumbling motion with E{sub a} Almost-Equal-To 8 kJ mol{sup -1}. - Graphical abstract: A series of complementary methods, such as Adiabatic Calorimetry, Differential Scanning Calorimetry, Fourier

  12. Crystal structure of 0.96(Na0.5Bi0.5TiO3sub>)-0.04(BaTiO3sub>) from combined refinement of x-ray and neutron diffraction patterns

    SciTech Connect

    Usher, T -M; Forrester, J S; dela Cruz, C R; Jones, J L


    High-resolution x-ray and neutron diffraction of (0.96)Na0.5Bi0.5TiO3sub>–(0.04)BaTiO3sub> (NBT-4BT) reveal subtle structural distortions that evidence lower symmetry than allowed in the R3c space group. The combined refinement that best models the diffraction patterns is a two phase mixture of a monoclinic Cc phase and a minor fraction of a metrically cubic Pm 3¯ m phase (13 wt. %). The cubic phase is utilized to account for nanometer-scale regions whose local deviations from the long-range symmetry are not observed, such as polar nano-regions or tetragonal platelets. This suggests that the low symmetry found in the NBT-rich phases extends from 0 at. % to at least 4 at. % BT.

  13. Crystal structure of a new basic nitrate of neodymium(III), [Nd{sub 6}O(OH){sub 8}(H{sub 2}O){sub 14}(NO{sub 3}){sub 6}](NO{sub 3}){sub 2} . 2H{sub 2}O

    SciTech Connect

    Charushnikova, I. A. Auwer, C. Den


    A new basic Nd{sup 3+} nitrate, [Nd{sub 6}O(OH){sub 8}(H{sub 2}O){sub 14}(NO{sub 3}){sub 6}](NO{sub 3}){sub 2} . 2H{sub 2}O (I), is isolated in the crystal form and studied. Compound I differs from the basic Ln nitrates containing [Ln{sub 6}O(OH){sub 8}] clusters in that it involves a larger number of water molecules. The incorporation of additional water molecules is accompanied by changes in the coordination environment of one of the three crystallographically independent Nd{sup 3+} cations. Two cations have coordination polyhedra in the form of a monocapped tetragonal antiprism with a coordination number of 9, and the third cation has a polyhedron in the form of a bicapped tetragonal antiprism with a coordination number of 10.

  14. Electrochemically influenced cation inter-diffusion and Co3sub>O4 formation on La0.6Sr0.4CoO3sub> 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 Sm2O3sub>-doped CeO2 (SDC) and La0.6Sr0.4Co0.2Fe0.8O3-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 La0.6Sr0.4CoO3sub> (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 Co3sub>O4 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: Co3sub>O4 forms on LSC arising from local charge balancing between cobalt and oxygen vacancies.

  15. Influence of structural distortions upon photoluminescence properties of Eu{sup 3+} and Tb{sup 3+} activated Na{sub 3}Ln(BO{sub 3}){sub 2} (Ln=Y, Gd) borates

    SciTech Connect

    Asiri Naidu, S.; Boudin, S.; Varadaraju, U.V.; Raveau, B.


    The comparative study of the structure and photoluminescence (PL) properties of the Eu{sup 3+} and Tb{sup 3+} activated Na{sub 3}Ln(BO{sub 3}){sub 2}, with Ln=Y, Gd, showed the important role of the host lattice structure upon PL. Higher emission intensities of Eu{sup 3+} and Tb{sup 3+} are observed for Na{sub 3}Gd(BO{sub 3}){sub 2} than for Na{sub 3}Y(BO{sub 3}){sub 2}, through direct Eu{sup 3+} excitation at 395 nm for Eu{sup 3+} doped borates, and through Gd{sup 3+} excitation around 280 nm for Tb{sup 3+} doped borates. This higher performance for Na{sub 3}Gd(BO{sub 3}){sub 2} is due to the less regular environment of Eu{sup 3+} (Tb{sup 3+}) in the Gd sites than in the Y sites and to energy transfer from Gd{sup 3+} to Eu{sup 3+}(Tb{sup 3+}). The smaller critical concentration in Na{sub 3}Ln{sub 1-x}Tb{sub x}(BO{sub 3}){sub 2} observed for Ln=Gd, x=0.5, compared to x=0.6 for Ln=Y, is explained by shorter Ln-Ln distances (4.11 A for Gd-Gd vs. 4.59 A for Y-Y). Both Na{sub 3}Y{sub 0.4}Tb{sub 0.6}(BO{sub 3}){sub 2} and Na{sub 3}Gd{sub 0.5}Tb{sub 0.5}(BO{sub 3}){sub 2} show intense green emission under UV excitation. - Graphical abstract: The PL properties of Eu{sup 3+} and Tb{sup 3+} are studied in Na{sub 3}Ln(BO{sub 3}){sub 2} (Ln=Y, Gd) borates. Eu{sup 3+} and Tb{sup 3+}exhibits higher emission intensity in Na{sub 3}Gd(BO{sub 3}){sub 2} compared to Na{sub 3}Y(BO{sub 3}){sub 2} due to the less regular environment of the Gd{sup 3+} ion. Energy transfer from Gd{sup 3+} to Tb{sup 3+} is observed. Highlights: Black-Right-Pointing-Pointer Crystal structure of Na{sub 3}Gd(BO{sub 3}){sub 2} by X-ray powder diffraction. Black-Right-Pointing-Pointer Photoluminescence properties of Eu{sup 3+} and Tb{sup 3+} doped Na{sub 3}Ln(BO{sub 3}){sub 2} (Ln=Y, Gd). Black-Right-Pointing-Pointer Higher Eu{sup 3+} and Tb{sup 3+} emission for Na{sub 3}Gd(BO{sub 3}){sub 2} due to an irregular environment of Gd{sup 3+}. Black-Right-Pointing-Pointer Higher Eu{sup 3+} and Tb{sup 3+} emission

  16. Impact of a Mixed Oxide’s Surface Composition and Structure on Its Adsorptive Properties: Case of the (Fe,Cr)3sub>O4(111) Termination of the α-(Fe,Cr)2O3sub>(0001) Surface

    SciTech Connect

    Henderson, Michael A.; Engelhard, Mark H.


    Characterization of an α-(Fe0.75,Cr0.25)2O3sub>(0001) mixed oxide single crystal surface was conducted using x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), low energy electron diffraction (LEED) and temperature programmed desorption (TPD). After sputter/anneal cleaning in ultra-high vacuum (UHV), the mixed oxide surface became terminated with a magnetite-(111) structure based on the presence of (2x2) spots in LEED and Fe2+ in XPS. The composition of the surface was close to that of M3sub>O4 based on XPS, with the metal (M) content of Fe2+/3+ and Cr3+ being close to 1.4:1, despite the fact that the film’s bulk was 3:1 with respect to the metal cations. The enrichment of the surface with Cr was not altered by high temperature oxidation in UHV, but could be returned to that of the bulk film composition by exposure to the ambient. Adsorption of various probe molecules (NO, O2, CO2 and H2O) was used to identify the active cation sites present in the (Fe,Cr)3sub>O4(111) terminated surface. Although XPS and SIMS both indicated that the near-surface region was enriched in Cr3+, no adsorption states typically associated with Cr3+ sites on α-Cr2O3sub> single crystal surfaces were detected. Instead, the TPD behaviors of O2 and CO2 pointed toward the main active sites being Fe2+ and Fe3+, with O2 preferentially adsorbing at the former and CO2 at the latter. NO was observed to bind at both Fe2+ and Fe3+ sites, and H2O TPD looked nearly identical to that for H2O on the Fe3sub>O4(111) surface. Competition for adsorption sites between coadsorbed combinations of CO2, O2, H2O and NO corroborated these

  17. Stripe-like nanoscale structural phase separation in superconducting BaPb1-xBixO3sub>

    SciTech Connect

    Giraldo-Gallo, P.; Zhang, Y.; Parra, C.; Manoharan, H. C.; Beasley, M. R.; Geballe, T. H.; Kramer, M. J.; Fisher, I. R.


    The phase diagram of BaPb1-xBixO3sub> exhibits a superconducting “dome” in the proximity of a charge density wave phase. For the superconducting compositions, the material coexists as two structural polymorphs. Here we show, via high resolution transmission electron microscopy, that the structural dimorphism is accommodated in the form of partially disordered nanoscale stripes. Identification of the morphology of the nanoscale structural phase separation enables determination of the associated length scales, which we compare to the Ginzburg-Landau coherence length. Thus, we find that the maximum Tc occurs when the superconducting coherence length matches the width of the partially disordered stripes, implying a connection between the structural phase separation and the shape of the superconducting dome.

  18. 119Sn-NMR investigations on superconducting Ca3sub>Ir4Sn13: 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 Ca3sub>Ir4Sn13 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.

  19. Multiband Te p Based Superconductivity of Ta4Pd3sub>Te16

    SciTech Connect

    Singh, David J.


    We recently discovered that Ta4Pd3sub>Te16 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.

  20. Bi2Te3sub> based passively Q-switched fiber laser with cylindrical vector beam emission.


    Yan, Ke; Lin, Jian; Zhou, Yong; Gu, Chun; Xu, Lixin; Wang, Anting; Yao, Peijun; Zhan, Qiwen


    We report a passively Q-switched fiber laser with cylindrical vector beam output modes using a few-mode fiber Bragg grating as a polarization-selective output coupler and Bi2Te3sub> as the saturable absorber. Both radially and azimuthally polarized beams can be readily generated, and the output polarization can be switchable by tuning the polarization controllers inside the laser cavity. The repetition rate of the Q-switched laser can be tuned from 31.54 to 49.40 kHz when the pump power increases from 103.5 to 139.5 mW. The fiber laser operates at a single wavelength of 1557.5 nm with a 3 dB linewidth of <0.04  nm. PMID:27139870

  1. Time-resolved terahertz dynamics in thin films of the topological insulator Bi2Se3sub>

    SciTech Connect

    Valdés Aguilar, R.; Qi, J.; Brahlek, M.; Bansal, N.; Azad, A.; Bowlan, J.; Oh, S.; Taylor, A. J.; Prasankumar, R. P.; Yarotski, D. A.


    We use optical pump–THz probe spectroscopy at low temperatures to study the hot carrier response in thin Bi2Se3sub> films of several thicknesses, allowing us to separate the bulk from the surface transient response. We find that for thinner films the photoexcitation changes the transport scattering rate and reduces the THz conductivity, which relaxes within 10 picoseconds (ps). For thicker films, the conductivity increases upon photoexcitation and scales with increasing both the film thickness and the optical fluence, with a decay time of approximately 5 ps as well as a much higher scattering rate. Furthermore, these different dynamics are attributed to the surface and bulk electrons, respectively, and demonstrate that long-lived mobile surface photo-carriers can be accessed independently below certain film thicknesses for possible optoelectronic applications.

  2. Stripe-like nanoscale structural phase separation in superconducting BaPb1-xBixO3sub>

    SciTech Connect

    Giraldo-Gallo, P.; Zhang, Y.; Parra, C.; Manoharan, H. C.; Beasley, M. R.; Geballe, T. H.; Kramer, M. J.; Fisher, I. R.


    The phase diagram of BaPb1-xBixO3sub> exhibits a superconducting dome in the proximity of a charge density wave phase. For the superconducting compositions, the material coexists as two structural polymorphs. Here we show, via high-resolution transmission electron microscopy, that the structural dimorphism is accommodated in the form of partially disordered nanoscale stripes. Identification of the morphology of the nanoscale structural phase separation enables determination of the associated length scales, which we compare with the Ginzburg–Landau coherence length. We find that the maximum Tc occurs when the superconducting coherence length matches the width of the partially disordered stripes, implying a connection between the structural phase separation and the shape of the superconducting dome.

  3. Crystallization and preliminary X-ray diffraction study of phosphopantetheine adenylyltransferase from M. tuberculosis crystallizing in space group P3{sub 2}

    SciTech Connect

    Timofeev, V. I.; Chupova, L. A.; Esipov, R. S.; Kuranova, I. P.


    Crystals of M. tuberculosis phosphopantetheine adenylyltransferase were grown in microgravity by the capillary counter-diffusion method through a gel layer. The X-ray diffraction data set suitable for the determination of the three-dimensional structure at atomic resolution was collected from one crystal at the Spring-8 synchrotron facility to 2.00-Å resolution. The crystals belong to sp. gr. P3{sub 2} and have the following unit-cell parameters: a = b = 106.47 Å, c = 71.32 Å, α = γ = 90°, β = 120°. The structure was solved by the molecular-replacement method. There are six subunits of the enzyme comprising a hexamer per asymmetric unit. The hexamer is a biologically active form of phosphopantetheine adenylyltransferase from M. tuberculosis.

  4. Electronic and thermoelectric analysis of phases in the In2O3sub>(ZnO)k system

    SciTech Connect

    Hopper, E. Mitchell; Zhu, Qimin; Song, Jung-Hwan; Peng, Haowei; Freeman, Arthur J.; Mason, Thomas O.


    The high-temperature electrical conductivity and thermopower of several compounds in the In2O3sub>(ZnO)k system (k = 3, 5, 7, and 9) were measured, and the band structures of the k = 1, 2, and 3 structures were predicted based on first-principles calculations. These phases exhibit highly dispersed conduction bands consistent with transparent conducting oxide behavior. Jonker plots (Seebeck coefficient vs. natural logarithm of conductivity) were used to obtain the product of the density of states and mobility for these phases, which were related to the maximum achievable power factor (thermopower squared times conductivity) for each phase by Ioffe analysis (maximum power factor vs. Jonker plot intercept). With the exception of the k = 9 phase, all other phases were found to have maximum predicted power factors comparable to other thermoelectric oxides if suitably doped.

  5. Crystal structure and electric properties of the organic–inorganic hybrid: [(CH{sub 2}){sub 6}(NH{sub 3}){sub 2}]ZnCl{sub 4}

    SciTech Connect

    Mostafa, M.F. El-khiyami, S.S.


    The new organic-inorganic hybrid [(CH{sub 2}){sub 6}(NH{sub 3}){sub 2}]ZnCl{sub 4}, M{sub r}=325.406 crystallized in a triclinic, P1¯, a=7.2816 (5) Å, b=10.0996 (7) Å, c=10.0972 (7) Å, α=74.368 (4)°, β=88.046 (4)°, γ=85.974 (3)°, V=713.24 (9) Å{sup 3} and Z=2, D{sub x}=1.486 Mg m{sup −3}. Differential thermal scanning and x-ray powder diffraction, permittivity and ac conductivity indicated three phase transitions. Conduction takes place via correlated barrier hopping. - Graphical abstract: Display Omitted.

  6. Giant optical enhancement of strain gradient in ferroelectric BiFeO3sub> thin films and its physical origin

    SciTech Connect

    Li, Yuelin; Adamo, C.; Chen, Pice; Evans, Paul G.; Nakhmanson, Serge M.; Parker, William; Rowland, Clare E.; Schaller, Richard D.; Schlom, Darrell G.; Walko, Donald A.; Wen, Haidan; Zhang, Qingteng


    Through mapping of the spatiotemporal strain profile in ferroelectric BiFeO3sub> epitaxial thin films, we report an optically initiated dynamic enhancement of the strain gradient of 105–106 m-1 that lasts up to a few ns depending on the film thickness. Correlating with transient optical absorption measurements, the enhancement of the strain gradient is attributed to a piezoelectric effect driven by a transient screening field mediated by excitons. In conclusion, these findings not only demonstrate a new possible way of controlling the flexoelectric effect, but also reveal the important role of exciton dynamics in photostriction and photovoltaic effects in ferroelectrics.

  7. Structure and properties of the noncentrosymmetric oxide borate K{sub 2}Ga{sub 2}O(BO{sub 3}){sub 2}

    SciTech Connect

    Smith, R.W.; Dudik, M.J.; Kennard, M.A.


    Crystals of a new, noncentrosymmetric oxide, orthoborate have been grown, and the structure of the material has been determined by X-ray diffraction techniques. The material crystallizes in the space group P321. The structure consists of a continuous, three-dimensional gallium borate framework with channels that run parallel to the [001] direction wherein the potassium atoms are located. The triangular orthoborate groups and the trigonal bases of the gallium-centered tetrahedra form two-dimensional layers through Ga-O-B linkages; these layers are parallel to (001) planes. Ga-O-Ga linkages interconnect adjacent layers to complete the three-dimensional framework. Use as a nonlinear optical material is unlikely because of nonoptimal alignment of the triangular orthoborate groups. In this paper, the authors report the synthesis, thermal properties, and crystal structure of K{sub 2}Ga{sub 2}(BO{sub 3}){sub 2} and describe its potential as a nonlinear optical material.

  8. Interpenetration as a Mechanism for Negative Thermal Expansion in the Metal-Organic Framework Cu3sub>(btb)2 (MOF-14)

    SciTech Connect

    Wu, Yue; Peterson, Vanessa K.; Luks, Emily; Darwish, Tamim A.; Kepert, Cameron J.


    Metal–organic framework materials (MOFs) have recently been shown in some cases to exhibit strong negative thermal expansion (NTE) behavior, while framework interpenetration has been found to reduce NTE in many materials. Using powder and single-crystal diffraction methods we investigate the thermal expansion behavior of interpenetrated Cu3sub>(btb)2 (MOF-14) and find that it exhibits an anomalously large NTE effect. Temperature-dependent structural analysis shows that, contrary to other interpenetrated materials, in MOF-14 the large positive thermal expansion of weak interactions that hold the interpenetrating networks together results in a low-energy contractive distortion of the overall framework structure, demonstrating a new mechanism for NTE.

  9. Generation of 0.19-mJ THz pulses in LiNbO3sub> driven by 800-nm femtosecond laser.


    Zhong, Sen-Cheng; Li, Jun; Zhai, Zhao-Hui; Zhu, Li-Guo; Li, Jiang; Zhou, Ping-Wei; Zhao, Jian-Heng; Li, Ze-Ren


    A cylindrical lens telescope tilted-pulse-front pumping scheme was proposed for high energy terahertz (THz) pulse generation. This scheme allows higher pump energy to be used with lower saturation effects under high pump fluence, and higher THz generation efficiency was achieved within large range of pump energy. The optimum pump pulse duration and crystal cooling temperature for THz generation in LiNbO3sub> (LN) crystal were also researched systematically. Excited by 800-nm laser, up to 0.19 mJ THz pulse energy and 0.27% conversion efficiency was demonstrated under 800-nm 400-fs laser excitation with ~100-mJ pulse energy and 150-K LN cooling temperature. PMID:27410634

  10. Optical diode effect at spin-wave excitations in the room-temperature multiferroic BiFeO3sub>.

    SciTech Connect

    Kezsmarki, I.; Nagel, U.; Bordacs, S.; Fishman, Randy Scott; Lee, Jun Hee; Yi, Hee Taek; Cheong, Sang-Wook; Room, T.


    The ability to read and write a magnetic state current-free by an electric voltage would provide a huge technological advantage. Dynamic or optical ME effects are equally interesting, because they give rise to unidirectional light propagation as recently observed in low-temperature multiferroics. This phenomenon, if realized at room temperature, would allow the development of optical diodes which transmit unpolarized light in one, but not in the opposite, direction. Here, we report strong unidirectional transmission in the room-temperature multiferroic BiFeO3sub> over the gigahertz-terahertz frequency range. The supporting theory attributes the observed unidirectional transmission to the spin-current-driven dynamic ME effect. Our findings are an important step toward the realization of optical diodes, supplemented by the ability to switch the transmission direction with a magnetic or electric field.

  11. Validation of Finite-Element Models of Persistent-Current Effects in Nb3sub>Sn Accelerator Magnets

    SciTech Connect

    Wang, X.; Ambrosio, G.; Chlachidze, G.; Collings, E. W.; Dietderich, D. R.; DiMarco, J.; Felice, H.; Ghosh, A. K.; Godeke, A.; Gourlay, S. A.; Marchevsky, M.; Prestemon, S. O.; Sabbi, G.; Sumption, M. D.; Velev, G. V.; Xu, X.; Zlobin, A. V.


    Persistent magnetization currents are induced in superconducting filaments during the current ramping in magnets. The resulting perturbation to the design magnetic field leads to field quality degradation, in particular at low field where the effect is stronger relative to the main field. The effects observed in NbTi accelerator magnets were reproduced well with the critical-state model. However, this approach becomes less accurate for the calculation of the persistent-current effects observed in Nb3sub>Sn accelerator magnets. Here a finite-element method based on the measured strand magnetization is validated against three state-of-art Nb3Sn accelerator magnets featuring different subelement diameters, critical currents, magnet designs and measurement temperatures. The temperature dependence of the persistent-current effects is reproduced. Based on the validated model, the impact of conductor design on the persistent current effects is discussed. The performance, limitations and possible improvements of the approach are also discussed.

  12. The behavior of thermal conductivity in the chaotic phase of [N(CH{sub 3}){sub 4}]{sub 2}ZnCl{sub 4} crystal

    SciTech Connect

    Sveleba, S. A. Karpa, I. V.; Kunyo, I. M.; Semotyuk, O. V.; Katerynchuk, I. M.; Phitsych, E. I.; Pankivskyi, Yu. I.


    A thermal investigation of the modulated structure dynamics at the transition between metastable states in the incommensurate phase of [N(CH{sub 3}){sub 4}]{sub 2}ZnCl{sub 4} crystal have been performed. It is established that the anomalous behavior of the thermal conductivity in the absence of a defect-density wave is due to the inelastic scattering of thermal phonons from critical phonons of the soft optical branch. In the presence of a defect-density wave, the anomalous increase in thermal conductivity is caused by the existence of a chaotic phase and is related to the contribution that soft optical phonons make to the heat transfer due to the increase in their group velocity.

  13. Crystal structure and properties of [OsO{sub 2}(NH{sub 3}){sub 4}]SO{sub 4} . H{sub 2}O

    SciTech Connect

    Burvikova, J. N. Lin'ko, I. V.; Venskovskiy, N. U.; Rybakov, V. B.


    The structure of a single crystal of tetraammindioxoosmium(VI) sulfate [OsO{sub 2}(NH{sub 3}){sub 4}]SO{sub 4} . H{sub 2}O, which is synthesized by the reaction of K{sub 2}[OsO{sub 2}(OH){sub 4}] with (NH{sub 4}){sub 2}SO{sub 4} in an aqueous solution, is investigated using X-ray diffraction analysis. The compound crystallizes in the monoclinic crystal system, space group P2{sub 1}/c, a = 13.102(2) A, b = 6.158(3) A, c = 11.866(2) A, {beta} = 98.13(2) deg., and Z = 4. The [OsO{sub 2}(NH{sub 3}){sub 4}]SO{sub 4} . H{sub 2}O compound has an island structure. Two crystallographically independent osmium atoms are situated at the centers of symmetry, and their octahedral coordination includes two oxygen atoms and four nitrogen atoms of the ammonia molecules. In both octahedra, the osmyl group is linear. The Os-O distances in the octahedra are identical within the standard deviations [Os(1)-O, 1.762(2) A; Os(2)-O, 1.769(2) A]. The Os-N bond lengths vary from 2.082(3) to 2.101(3) A. The cationic complexes, SO{sub 4} groups, and water molecules are linked via the system of hydrogen bonds. The assignment of the absorption bands in the IR spectrum of the compound synthesized is performed, and its thermal behavior in air is studied.

  14. [N(CH{sub 3}){sub 3}H]{sub 2}ZnCl{sub 4}: Ferroelectric properties and characterization of phase transitions by Raman spectroscopy

    SciTech Connect

    Ben Bechir, M. Karoui, K.; Guidara, K.; Ben Rhaiem, A.; Bulou, A.; Tabellout, M.


    The X-ray powder diffraction pattern shows that at room temperature, [N(CH{sub 3}){sub 3}H]{sub 2}ZnCl{sub 4} is crystallized in the orthorhombic system with Pnma space group. The phase transitions at T{sub 1} = 255 K, T{sub 2} = 282 K, T{sub 3} = 302 K, T{sub 4} = 320 K, and T{sub 5} = 346 K have been confirmed by the differential scanning calorimetry. The electrical technique was measured in the 10{sup −1}–10{sup 7 }Hz frequency range and 233–363 K temperature intervals. The temperature dependence of the dielectric constant at different temperatures proved that this compound is ferroelectric below 282 K. Besides, [N(CH{sub 3}){sub 3 }H]{sub 2}ZnCl{sub 4} shows classical ferroelectric behaviour near curie temperature. In order to characterize the phase transitions, Raman spectra have been recorded in the temperature range of 233–383 K and the frequency range related to the internal and external vibrations of the cations and anions (90–4000 cm{sup −1}). The temperature dependence of the Raman line shifts ν and the half-width Δν detects all phase transitions and confirms their nature, especially at 282 K that corresponds to the ferroelectric-paraelectric phase transition.

  15. Identification of Organic Nitrates in the NO3sub> Radical Initiated Oxidation of α-Pinene by Atmospheric Pressure Chemical Ionization Mass Spectrometry

    SciTech Connect

    Perraud, Veronique M.; Bruns, Emily A.; Ezell, Michael J.; Johnson, Stanley N.; Greaves, John; Finlayson-Pitts, Barbara J.


    The gas-phase reactions of nitrate radicals (NO3sub>) with biogenic organic compounds are a major sink for these organics during night-time. These reactions form secondary organic aerosols, including organic nitrates that can undergo long-range transport, releasing NOx downwind. We report here studies of the reaction of NO3sub> with R-pinene at 1 atm in dry synthetic air(relative humidity ~3%) and at 298K using atmospheric pressure chemical ionization triple quadrupole mass spectrometry (APCI-MS) to identify gaseous and particulate products. The emphasis is on the identification of individual organic nitrates in the particle phase that were obtained by passing the product mixture through a denuder to remove gas-phase reactants and products prior to entering the source region of the mass spectrometer. Filter extracts were also analyzed by GCMS and by APCI time-of-flight mass spectrometry (APCI-ToFMS) with methanol as the proton source. In addition to pinonaldehyde and pinonic acid, five organic nitrates were identified in the particles as well as in the gas phase: 3-oxopinane- 2-nitrate, 2-hydroxypinane-3-nitrate, pinonaldehyde-PAN, norpinonaldehyde-PAN, and (3-acetyl-2,2-dimethyl-3-nitrooxycyclobutyl) acetaldehyde. Furthermore, there was an additional first generation organic nitrate product tentatively identified as a carbonyl hydroxynitrate with a molecular mass of 229. These studies suggest that a variety of organic nitrates would partition between the gas phase and particles in the atmosphere, and serve as a reservoir for NOx.

  16. DNA 3'sub> pp 5' G de-capping activity of aprataxin: effect of cap nucleoside analogs and structural basis for guanosine recognition

    SciTech Connect

    Chauleau, Mathieu; Jacewicz, Agata; Shuman, Stewart


    DNA3'sub> pp 5'G caps synthesized by the 3'-PO4/5'-OH ligase RtcB have a strong impact on enzymatic reactions at DNA 3'-OH ends. Aprataxin, an enzyme that repairs A5'pp5'DNA ends formed during abortive ligation by classic 3'-OH/5'-PO4 ligases, is also a DNA 3' de-capping enzyme, converting DNAppG to DNA3sub>'p and GMP. By taking advantage of RtcB's ability to utilize certain GTP analogs to synthesize DNAppN caps, we show that aprataxin hydrolyzes inosine and 6-O-methylguanosine caps, but is not adept at removing a deoxyguanosine cap. We report a 1.5 Å crystal structure of aprataxin in a complex with GMP, which reveals that: (i) GMP binds at the same position and in the same anti nucleoside conformation as AMP; and (ii) aprataxin makes more extensive nucleobase contacts with guanine than with adenine, via a hydrogen bonding network to the guanine O6, N1, N2 base edge. Alanine mutations of catalytic residues His147 and His149 abolish DNAppG de-capping activity, suggesting that the 3' de-guanylylation and 5' de-adenylylation reactions follow the same pathway of nucleotidyl transfer through a covalent aprataxin-(His147)–NMP intermediate. Alanine mutation of Asp63, which coordinates the guanosine ribose hydroxyls, impairs DNAppG de-capping.

  17. Synthesis of MoS2/g-C3sub>N4 nanocomposites with enhanced visible-light photocatalytic activity for the removal of nitric oxide (NO).


    Wen, M Q; Xiong, T; Zang, Z G; Wei, W; Tang, X S; Dong, F


    Molybdenum disulfide and graphitic carbon nitride (MoS2-g-C3sub>N4) nanocomposites with visible-light induced photocatalytic activity were successfully synthesized by a facile ultrasonic dispersion method. The crystalline structure and morphology of the MoS2-g-C3sub>N4 nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microcopy (TEM), high-resolution TEM (HRTEM) and scanning electron microscopy (SEM). The optical property of the as-prepared nanocomposites was studied by ultraviolet visible diffusion reflection (UV-vis) and photoluminescence(PL) spectrum. It could be observed from the TEM image that the MoS2 nanosheets and g-C3sub>N4 nanoparticles were well combined together. Moreover, the photocatalytic activity of MoS2-g-C3sub>N4 composites was evaluated by the removal of nitric oxide under visible light irradiation (>400nm). The experimental results demonstrated that the nanocomposites with the MoS2 content of 1.5 wt% exhibited optimal photocatalytic activity and the corresponding removal rate of NO achieved 51.67%, higher than that of pure g-C3sub>N4 nanoparticles. A possible photocatalytic mechanism for the MoS2-g-C3sub>N4 nanocomposites with enhanced photocatalytic activity could be ascribed to the hetero-structure of MoS2 and g-C3sub>N4. PMID:27409846

  18. Electrochemical behavior of [(Mn(Bpy))(VO{sub 3}){sub 2}]≈(H{sub 2}O){sub 1.24} and [(Mn(Bpy){sub 0.5})(VO{sub 3}){sub 2}]≈(H{sub 2}O){sub 0.62} inorganic–organic Brannerites in lithium and sodium cells

    SciTech Connect

    Fernández de Luis, Roberto; Rosa Palacín, M.; Karmele Urtiaga, M.


    The performance of MnV{sub 2}O{sub 6} (MnV) and its [(Mn(Bpy))(VO{sub 3}){sub 2}]≈(H{sub 2}O){sub 1.16} (MnBpy) and [(Mn(Bpy){sub 0.5})(VO{sub 3}){sub 2}]≈(H{sub 2}O){sub 0.62}(MnBpy0.5) hybrid derivative compounds was investigated against sodium and lithium counter electrodes. For MnV{sub 2}O{sub 6} stable capacities of 850 mAh/g were achieved in lithium cells, the best value reported so far. The whole capacity is ascribed to a conversion reaction in which the amorphization of the compounds takes place. No significant differences in the capacities for the inorganic compound and the hybrid ones were observed. Interestingly, the potential hysteresis decreases in the hybrid compounds. The difference between Li and Na cell capacity most probably comes from the difference of standard potential of the two redox couples Li{sup +}/Li and Na{sup +}/Na of about ca. 0.3 V leading to an incomplete conversion reaction and thus lowers capacity in the case of Na cells. The Raman and IR ex-situ experiments after cycling indicate that the bipyridine organic ligands are completely decomposed during the electrochemical testing. The IR studies in MnV inorganic and MnBpy and MnBpy0.5 hybrid electrodes after the electrochemical cycling, suggest that the SEI formation and bipyridine degradation give rise to different aliphatic compounds. - Graphical abstract: The electrochemical performance of [(Mn(Bpy))(VO{sub 3}){sub 2}]≈(H{sub 2}O){sub 1.16} and [(Mn(Bpy){sub 0.5})(VO{sub 3}){sub 2}]≈(H{sub 2}O){sub 0.62} against sodium and lithium counter electrodes give rise to the structural collapse of the initial compounds. The IR and Raman studies show that the Bpy organic ligand is completely decomposed during the during the electrochemical testing. However, after the amorphization stable capacities as high as 850 mAh/g for lithium cells were achieved. - Highlights: • We test the lithium and sodium insertion in hybrid brannerites. • Capacities as large as 850 mAh/g were obtained

  19. On the Bonding Nature of Ozone (O3sub>) and Its Sulfur-Substituted Analogues SO2, OS2, and S3sub>: Correlation between Their Biradical Character and Molecular Properties

    SciTech Connect

    Miliordos, Evangelos; Xantheas, Sotiris S.


    We investigate the bonding mechanism in ozone (O3sub>) and its sulfur-substituted analogues, SO2, OS2, and S3sub>. By analyzing their ground-state multireference configuration interaction wave functions, we demonstrate that the bonding in these systems can be represented as a mixture of a closed-shell structure with one and a half bonds between the central and terminal atoms and an open-shell structure with a single bond and two lone electrons on each terminal atom (biradical). The biradical character (β) further emerges as a simple measure of the relative contribution of those two classical Lewis structures emanating from the interpretation of the respective wave functions. Our analysis yields a biradical character of 3.5% for OSO, 4.4% for SSO, 11% for S3sub>, 18% for O3sub>, 26% for SOO, and 35% for SOS. The size/electronegativity of the end atoms relative to the central one is the prevalent factor for determining the magnitude of β: smaller and more electronegative central atoms better accommodate a pair of electrons facilitating the localization of the remaining two lone π-electrons on each of the end atoms, therefore increasing the weight of the second picture in the mixed bonding scenario (larger β). The proposed mixture of these two bonding scenarios allows for the definition of the bond order of the covalent bonds being (3-β)/2, and this accounts for the different O–O, S–S, or S–O bond lengths in the triatomic series. The biradical character was furthermore found to be a useful concept for explaining several structural and energetic trends in the series: larger values of β mark a smaller singlet–triplet splitting, closer bond lengths in the ground 1A' and the first excited 3A' states, and larger bond dissociation and atomization energies in the ground state. Finally, the latter explains the relative energy difference between the OSS/SOS and OOS/OSO isomers due to their

  20. Highly Stable and CO-Tolerant Pt/Ti0.7W0.3sub>O2 Electrocatalyst for Proton-Exchange Membrane Fuel Cells

    SciTech Connect

    Wang, Deli; Subban, Chinmayee V.; Wang, Hongsen; Rus, Eric; DiSalvo, Francis J.; Abruña, Héctor D.


    The current materials used in proton-exchange membrane fuel cells (PEMFCs) are not sufficiently durable for commercial deployment. One of the major challenges lies in the development of an inexpensive, efficient, and CO-tolerant anode catalyst. Here we report the unique CO-tolerant property of Pt nanoparticles supported on Ti0.7W0.3sub>O2. The Ti0.7W0.3sub>O2 nanoparticles (50 nm) were synthesized via a sol-gel process and platinized using an impregnation-reduction technique. Electrochemical studies of Pt/Ti0.7W0.3sub>O2 show unique CO-tolerant electrocatalytic activity for hydrogen oxidation compared to commercial E-TEK PtRu/C catalysts. Differential electrochemical mass spectrometry measurements show the onset potential for CO oxidation on Pt/Ti0.7W0.3sub>O2 to be below 0.1 V (vs RHE). Pt/Ti0.7W0.3sub>O2 is a promising new anode catalyst for PEMFC applications.

  1. Electric-field-induced strain effects on the magnetization of a Pr0.67Sr0.33MnO3sub> film

    SciTech Connect

    Zhang, B.; Sun, C. -J.; Lu, W.; Venkatesan, T.; Han, M. -G.; Zhu, Y.; Chen, J.; Chow, G. M.


    The electric-field control of magnetic properties of Pr0.67Sr0.33MnO3sub> (PSMO) film on piezoelectric Pb(Mg1/3sub>Nb2/3sub>)O3sub>-PbTiO3sub> (PMNT) substrate was investigated. The piezoelectric response of the PMNT substrate to the electric field produced strain that was coupled to the PSMO film. The in-plane compressive (tensile) strain increased (decreased) the magnetization. The change of magnetic moment was associated with the Mn ions. First principle simulations showed that the strain-induced electronic redistribution of the two eg orbitals (3dz2 and 3dx2-y2) of Mn ions was responsible for the change of magnetic moment. This work demonstrates that the magnetoelectric effect in manganite/piezoelectric hetero-structures originates from the change in eg orbital occupancy of Mn ions induced by strain rather than the interfacial effect.

  2. Oxidation of H2S by coadsorbed oxygen on the α-Cr2O3sub>(0001) surface

    SciTech Connect

    Henderson, Michael A; Rosso, Kevin M


    The interactions of H2S and oxygen have been explored on the α-Cr2O3sub>(0001) surface using temperature programmed desorption (TPD), Auger electron spectroscopy (AES) and sticking coefficient measurements. H2S adsorbs with near unity sticking on the clean α-Cr2O3sub>(0001) surface at 125 K up to a coverage of ~1.6 ML (where 1 ML is defined as the surface areal density of Cr3+ sites). Reversible adsorption is evidenced in TPD by three desorption states evolving between 150 and 315 K. Although no S-containing decomposition products were observed in TPD, AES detected S on the surface after TPD indicating that some degree of irreversible decomposition occurred. The level of H2S decomposition on the clean surface was estimated to be between 0.2-0.5 ML using water TPD as an indicator of S site blocking. In contrast, preadsorbed O2 at three temperatures (125, 400 and 800 K) exerted drastic changes on the surface chemistry of H2S seen on the clean surface. At 400 and 800 K, O2 adsorption on clean α-Cr2O3sub>(0001) is dissociative, populating the surface with chromyl groups (Cr=O) in the former case (corresponding to roughly 1 O per Cr3+ surface site) and resulting in a nearly complete O-termination sheet (~3 O per Cr3+) in the latter case. Little or no H2S chemistry is observed on the O-terminated surface based on TPD and AES. However, availability of Cr-coordination sites on the chromyl-terminated surface facilitated H2S adsorption and oxidation during TPD to SO2 (445-470 K) and H2O (320 K). Isotopic-labeling studies suggest that the oxygen atom in the water product originates from dosed oxygen whereas that in the SO2 product comes from the lattice. Similar results were obtained from H2S dosed on the surface pretreated with O2 at 125 K, where O2

  3. Molecular metals based on 1,2,7,8-tetrahydrodicyclopenta[cd:lm]perylene and iodine, (CPP){sub 2}(I{sub 3}){sub 1-{delta}}

    SciTech Connect

    Morgado, J. |; Santos, I.C.; Henriques, R.T.; Almeida, M.; Fourmigue, M.; Matias, P.; Veiros, L.F.; Duarte, M.T.; Alcacer, L.; Calhorda, M.J. |


    The synthesis and characterization of molecular metals derived from 1,2,7,8-tetrahydrodicyclopenta[cd:lm]perylene (CPP) by partial oxidation with iodine and with general formula (CPP){sub 2}(I{sub 3}){sub 1-{delta}}, {delta} = 0-0.13, are reported. Single crystals, obtained either by electrocrystallization or by diffusion-controlled iodine oxidation of CPP, present two types of morphologies, elongated diamond or thinner needle-shaped crystals, both with a monoclinic cell, space group P2{sub 1}/a, a = 4.3757(9), b = 19.3681(11), c = 10.0860(11) {angstrom}, {beta} = 98.050(8){degrees}, V = 846.4(2) {angstrom}{sup 3}, Z = 2. The structure of the diamond-shaped crystal was solved by X-ray diffraction to a final R(F) = 0.096, R{sub w}(F) = 0.069. It consists of regular stacks of CPP molecules along a with a 3.41 {angstrom} spacing and uncorrected one-dimensional chains of I{sub 3}{sup {minus}} located in channels between four CPP stacks corresponding to (CPP){sub 2}(I{sub 3}){sub 0.892}. The thin needle crystals have the same unit cell but an unspecified and slightly different iodine content. Band structure calculations in this structure by the extended Hueckel method indicate a one-dimensional conduction band 0.55 eV wide. These thin needle crystals present, at room temperature, an electrical conductivity along the a axis {alpha}{sub a}(RT) = 200 S/cm and thermopower S{sub a}(RT) = 30 {mu}V/K, while for the diamond-shaped crystals {alpha}{sub a}(RT) = 2 S/cm and S{sub a}(RT) = -8 {mu}V/K. These transport coefficients for both types of crystals indicate a metallic behavior from room temperature down to {approx_equal}63 K, where a metal-to-insular (M-I) transition takes place. EPR studies in single crystals show an almost isotropic line at g = 2.0044 and with a width of {approx_equal}6 G in the range 80-300 K and without significant differences between the two types of crystals. 53 refs., 9 figs., 4 tabs.

  4. A search for temperature induced time-dependent structural transitions in 10mol%Sc2O3sub>–1mol%CeO2–ZrO2 and 8mol%Y2O3sub>–ZrO2 electrolyte ceramics

    SciTech Connect

    Chen, Yan; Orlovskaya, Nina; Payzant, E. Andrew; Graule, Thomas; Kuebler, Jakob


    Both Sc2O3sub>–CeO2-stabilized-ZrO2 (SCSZ) and Y2O3sub>-stabilized-ZrO2 (YSZ) show similar Young's modulus damping at 175–400 °C and 200–400 °C, respectively, by impulse excitation acoustic technique. The phase transition in SCSZ is considered responsible for the damping; however for YSZ, such a phase transition has never been reported. To clarify the relation of damping and structural transition in these two materials, the time-dependent high temperature stabilities are studied by in situ X-ray diffraction, neutron diffraction and Raman scattering during long-term annealing of SCSZ at 350 °C and YSZ at 275 °C. The cubic-to-rhombohedral transition in SCSZ is detected. However, the existence of t' phase in YSZ raw powders is confirmed without significant changes of the cubic structure during isothermal annealing. It is concluded that the phase transition contributes to the Young's modulus damping in SCSZ, while the structural transition is excluded from the reason for damping in YSZ.

  5. Effects of quark family nonuniversality in SU(3){sub c} x SU(4){sub L} x U(1){sub X} models

    SciTech Connect

    Nisperuza, Jorge L.; Sanchez, Luis A.


    Flavor changing neutral currents arise in the SU(3){sub c} x SU(4){sub L} x U(1){sub X} extension of the standard model because anomaly cancellation among the fermion families requires one generation of quarks to transform differently from the other two under the gauge group. In the weak basis the distinction between quark families is meaningless. However, in the mass eigenstates basis, the Cabibbo-Kobayashi-Maskawa mixing matrix motivates us to classify left-handed quarks in families. In this sense there are, in principle, three different assignments of quark weak eigenstates into mass eigenstates. In this work, by using measurements at the Z pole, atomic parity violation data, and experimental input from neutral meson mixing, we examine two different models without exotic electric charges based on the 3-4-1 symmetry, and address the effects of quark family nonuniversality on the bounds on the mixing angle between two of the neutral currents present in the models and on the mass scales M{sub Z{sub 2}} and M{sub Z{sub 3}} of the new neutral gauge bosons predicted by the theory. The heaviest family of quarks must transform differently in order to keep lower bounds on M{sub Z{sub 2}} and M{sub Z{sub 3}} as low as possible without violating experimental constraints.

  6. Magnetic Properties of Sm{sub 0.7}Ho{sub 0.3}Fe{sub 3}(BO{sub 3}){sub 4}

    SciTech Connect

    Demidov, A. A.; Gudim, I. A.; Eremin, E. V.


    The magnetic properties of a ferroborate single crystal of substituted composition Sm{sub 0.7}H{sub 0.3}Fe{sub 3}(BO{sub 3}){sub 4} with competing Sm-Fe and Ho-Fe exchange interactions are studied. The measured properties and effects are interpreted in terms of a general theoretical approach based on the molecular field approximation and calculations using the crystal field model for a rare-earth ion. The experimental temperature dependences of the initial magnetic susceptibility in the temperature range 2-300 K, the anomalies in the magnetization curves for B Double-Vertical-Line c and B Up-Tack c in fields lower than 1.2 T, and the field and temperature dependences of magnetization in fields lower than 9 T are described. The crystal field parameters and the parameters of the R-Fe and Fe-Fe exchange interactions are determined during the interpretation of the experimental data.

  7. Synthesis, Structure, and Pressure-Induced Polymerization of Li 3sub> Fe(CN) 6 Accompanied with Enhanced Conductivity

    SciTech Connect

    Li, Kuo; Zheng, Haiyan; Hattori, Takanori; Sano-Furukawa, Asami; Tulk, Christopher A.; Molaison, Jamie; Feygenson, Mikhail; Ivanov, Ilia N.; Yang, Wenge; Mao, Ho-kwang


    By providing a new route to synthesize inorganic/organic conductors with tunable composition and properties, pressure-induced polymerization of charged triple-bond monomers like acetylide and cyanide could lead to formation of a conductive metal–carbon network composite. The industry application of this promising synthetic method is mainly limited by the reaction pressure needed, which is often too high to be reached for gram amounts of sample. Here we successfully synthesized highly conductive Li3sub>Fe(CN)6 at maximum pressure around 5 GPa and used in situ diagnostic tools to follow the structural and functional transformations of the sample, including in situ X-ray and neutron diffraction and Raman and impedance spectroscopy, along with the neutron pair distribution function measurement on the recovered sample. The cyanide anions start to react around 1 GPa and bond to each other irreversibly at around 5 GPa, which are the lowest reaction pressures in all known metal cyanides and within the technologically achievable pressure range for industrial production. Moreover, the conductivity of the polymer is above 10–3 S·cm–1, which reaches the range of conductive polymers. Our investigation suggests that the pressure-induced polymerization route is practicable for synthesizing some types of functional conductive materials for industrial use, and further research like doping and heating can hence be motivated to synthesize novel materials under lower pressure and with better performances.

  8. Synthesis, crystal structure and vibrational spectra characterization of M{sup I}La(PO{sub 3}){sub 4} (M{sup I}=Na, Ag)

    SciTech Connect

    El Masloumi, Mohamed; Imaz, Inhar . E-mail:; Chaminade, Jean-Pierre; Videau, Jean-Jacques; Couzi, Michel; Mesnaoui, Mohamed; Maazaz, Mohamed


    The single crystals of lanthanum metaphosphate MLa(PO{sub 3}){sub 4} (M=Na, Ag) have been synthesized and studied by a combination of X-ray crystal diffraction and vibrational spectroscopy. The sodium and silver compounds crystallize in the same monoclinic P2{sub 1}/n space group (C{sub 2}{sup 5}h factor group) with the following respective unit cell dimensions: a=7.255(2), b=13.186(3), c=10.076(2)A, {beta}=90.40(2){sup o}, V=963.0(4)A{sup 3}, Z=4 and a=7.300(5), b=13.211(9), c=10.079(7)A, {beta}=90.47(4){sup o}, V=972.09(12)A{sup 3}, Z=4. This three-dimensional framework is built of twisted zig-zag chains running along a direction and made up of PO{sub 4} tetrahedra sharing two corners, connected to the LaO{sub 8} and NaO{sub 7} or AgO{sub 7} polyhedra by common oxygen atoms to the chains. The infrared and Raman vibrational spectra have been investigated. A group factor analysis leads to the determination of internal modes of (PO{sub 3}){sup -} anion in the phosphate chain.

  9. Part 1: Kinetic energy dependencies of selected ion-molecule reactions; Part 2: Photochemistry of (FSO sub 3 ) sub 2 , FSO sub 3 , and FNO

    SciTech Connect

    Burley, J.D.


    In Part 1, guided ion beam mass spectroscopy is used to study the ion-molecule reactions O{sup +}({sup 4}S) + H{sub 2}(D{sub 2}, HD), (O{sup +}{sup 4}S) + N{sub 2}, C{sup +}({sup 2}P) + O{sub 2} and C{sup +}(P) + N{sub 2}. Integral reaction cross sections are measured as a function of kinetic energy in the center-of-mass frame. Reaction mechanisms and dynamics are examined, and the results are compared to the predictions of phase space theory. In some cases, thermochemistry for neutral and ionic species is derived. In Part 2, photoabsorption cross sections are measured for peroxydisulfuryl difluoride, (FSO{sub 3}){sub 2}, and the fluorosulfate radical, FSO{sub 3}. Photoabsorption cross sections of nitrosyl fluoride, FNO, are also measured, and the FNO absorption spectrum is analyzed and assigned. Spectral results for FNO are compared to the predictions and ab initio calculations and to those obtained for the isoelectronic compound HONO. 259 refs., 34 figs., 9 tabs.

  10. Polarization-insensitive, shallow Ti-diffused near-stoichiometric LiTaO3sub> strip waveguide for integrated optics.


    Yang, Xiao-Fei; Zhang, Zi-Bo; Du, Wan-Ying; Zhang, Qun; Wong, Wing-Han; Yu, Dao-Yin; Pun, Edwin Yue-Bun; Zhang, De-Long


    We report on a Ti-diffused near-stoichiometric (NS) LiTaO3sub> strip waveguide fabricated by diffusion of an 8 μm wide, 160 nm thick Ti-strip followed by Li-rich vapor transport equilibration. It is found that the waveguide surface caves in ∼60  nm below the crystal surface. X-ray single-crystal diffraction shows that the indentation is due to Ti-induced lattice contraction. Optical studies show that the waveguide is in an NS composition environment, supports TE and TM single-mode propagation at 1.5 μm wavelength, is polarization insensitive, and has a shallow mode field profile and a loss of 0.2/0.3 dB/cm for the TE/TM mode. Secondary ion mass spectrometry analysis shows that the Ti profile follows a sum of two error functions in the width direction and a Gaussian function in the depth direction of the waveguide. With the optimized fabrication condition, the waveguide is promising for developing an optical-damage-resistant device that requires a shallow mode field profile. PMID:27244402

  11. Annealing influence on the magnetostructural transition in Gd5Si1.3sub>Ge2.7 thin films

    SciTech Connect

    Pires, A. L.; Belo, J. H.; Gomes, I. T.; Hadimani, R. L.; Jiles, D. C.; Fernandes, L.; Tavares, P. B.; Araújo, J. P.; Lopes, A. M. L.; Pereira, A. M.


    Due to the emerging cooling possibilities at the micro and nanoscale, such as the fast heat exchange rate, the effort to synthesize and optimize the magnetocaloric materials at these scales is rapidly growing. Here, we report the effect of different thermal treatments on Gd5Si1.3sub>Ge2.7 thin film in order to evaluate the correlation between the crystal structure, magnetic phase transition and magnetocaloric effect. For annealing temperatures higher than 500ºC, the samples showed a typical paramagnetic behavior. On the other hand, thermal treatments below 500ºC promoted the suppression of the magnetostructural transition at 190 K, while the magnetic transition around 249 K is not affected. This magnetostructural transition extinction was reflected in the magnetocaloric behavior and resulted in a drastic decrease in the entropy change peak value (of about 68%). An increase in TC was reported, proving that at the nanoscale, heat treatments may be a useful tool to optimize the magnetocaloric properties in Gd5(SixGe1-x)4 thin films.

  12. Correlation of anisotropy and directional conduction in β-Li3sub>PS4 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-Li3sub>PS4, 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 LiS4 and PS4 tetrahedra within the framework. This indicates a strong correlation in the direction of the ionic transport in the low-symmetry Li+ conductor.

  13. Free-standing millimetre-long Bi2Te3 sub-micron belts catalyzed by TiO2 nanoparticles.


    Schönherr, Piet; Zhang, Fengyu; Kojda, Danny; Mitdank, Rüdiger; Albrecht, Martin; Fischer, Saskia F; Hesjedal, Thorsten


    Physical vapour deposition (PVD) is used to grow millimetre-long Bi2Te3 sub-micron belts catalysed by TiO2 nanoparticles. The catalytic efficiency of TiO2 nanoparticles for the nanostructure growth is compared with the catalyst-free growth employing scanning electron microscopy. The catalyst-coated and catalyst-free substrates are arranged side-by-side, and overgrown at the same time, to assure identical growth conditions in the PVD furnace. It is found that the catalyst enhances the yield of the belts. Very long belts were achieved with a growth rate of 28 nm/min. A ∼1-mm-long belt with a rectangular cross section was obtained after 8 h of growth. The thickness and width were determined by atomic force microscopy, and their ratio is ∼1:10. The chemical composition was determined to be stoichiometric Bi2Te3 using energy-dispersive X-ray spectroscopy. Temperature-dependent conductivity measurements show a characteristic increase of the conductivity at low temperatures. The room temperature conductivity of 0.20 × 10(5) S m (-1) indicates an excellent sample quality. PMID:27342602

  14. Free-standing millimetre-long Bi2Te3 sub-micron belts catalyzed by TiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Schönherr, Piet; Zhang, Fengyu; Kojda, Danny; Mitdank, Rüdiger; Albrecht, Martin; Fischer, Saskia F.; Hesjedal, Thorsten


    Physical vapour deposition (PVD) is used to grow millimetre-long Bi2Te3 sub-micron belts catalysed by TiO2 nanoparticles. The catalytic efficiency of TiO2 nanoparticles for the nanostructure growth is compared with the catalyst-free growth employing scanning electron microscopy. The catalyst-coated and catalyst-free substrates are arranged side-by-side, and overgrown at the same time, to assure identical growth conditions in the PVD furnace. It is found that the catalyst enhances the yield of the belts. Very long belts were achieved with a growth rate of 28 nm/min. A ˜1-mm-long belt with a rectangular cross section was obtained after 8 h of growth. The thickness and width were determined by atomic force microscopy, and their ratio is ˜1:10. The chemical composition was determined to be stoichiometric Bi2Te3 using energy-dispersive X-ray spectroscopy. Temperature-dependent conductivity measurements show a characteristic increase of the conductivity at low temperatures. The room temperature conductivity of 0.20 × 105 S m -1 indicates an excellent sample quality.

  15. Momentum-space structure of quasielastic spin fluctuations in Ce3sub>Pd20Si6

    SciTech Connect

    Portnichenko, P. Y.; Cameron, A. S.; Surmach, M. A.; Deen, Pascale P.; Paschen, S.; Prokofiev, A.; Mignot, Jean-Michel; Strydom, A. M.; Telling, Mark T. F.; Podlesnyak, Andrey A.; Inosov, D. S.


    Surrounded by heavy-fermion metals, Ce3sub>Pd20Si6 is one of the heaviest-electron systems known to date. Here we used high-resolution neutron spectroscopy to observe low-energy magnetic scattering from a single crystal of this compound in the paramagnetic state. We investigated its temperature dependence and distribution in momentum space, which was not accessible in earlier measurements on polycrystalline samples. At low temperatures, a quasielastic magnetic response with a half-width Γ ≈ 0.1 meV persists with varying intensity all over the Brillouin zone. It forms a broad hump centered at the (111) scattering vector, surrounded by minima of intensity at (002), (220), and equivalent wave vectors. The momentum-space structure distinguishes this signal from a simple crystal-field excitation at 0.31 meV, suggested previously, and rather lets us ascribe it to short-range dynamical correlations between the neighboring Ce ions, mediated by the itinerant heavy f electrons via the Ruderman-Kittel-Kasuya-Yosida mechanism. With increasing temperature, the energy width of the signal follows the conventional T1/2 law, Γ(T)=Γ0+A√T. Lastly, the momentum-space symmetry of the quasielastic response suggests that it stems from the simple-cubic Ce sublattice occupying the 8c Wyckoff site, whereas the crystallographically inequivalent 4a site remains magnetically silent in this material.

  16. Electron-phonon coupling and thermal transport in the thermoelectric compound Mo3sub>Sb7–xTex

    SciTech Connect

    Bansal, Dipanshu; Li, Chen W.; Said, Ayman H.; Abernathy, Douglas L.; Yan, Jiaqiang; Delaire, Olivier A.


    Phonon properties of Mo3sub>Sb7–xTex (x = 0, 1.5, 1.7), a potential high-temperature thermoelectric material, have been studied with inelastic neutron and x-ray scattering, and with first-principles simulations. The substitution of Te for Sb leads to pronounced changes in the electronic struc- ture, local bonding, phonon density of states (DOS), dispersions, and phonon lifetimes. Alloying with tellurium shifts the Fermi level upward, near the top of the valence band, resulting in a strong suppression of electron-phonon screening, and a large overall stiffening of interatomic force- constants. The suppression in electron-phonon coupling concomitantly increases group velocities and suppresses phonon scattering rates, surpassing the effects of alloy-disorder scattering, and re- sulting in a surprising increased lattice thermal conductivity in the alloy. We also identify that the local bonding environment changes non-uniformly around different atoms, leading to variable perturbation strengths for different optical phonon branches. The respective roles of changes in phonon group velocities and phonon lifetimes on the lattice thermal conductivity are quantified. Lastly, our results highlight the importance of the electron-phonon coupling on phonon mean-free-paths in this compound, and also estimates the contributions from boundary scattering, umklapp scattering, and point-defect scattering.

  17. Structural transitions in Pb(In1/2Nb1/2)O 3sub> under pressure

    SciTech Connect

    Ahart, Muhtar; Somayazulu, Maddury; Kojima, Seiji; Yasuda, Naohiko; Prosandeev, Sergey; Hemley, Russell J.


    Room-temperature Raman scattering and x-ray diffraction measurements together with first-principles calculations were employed to investigate the behavior of disordered Pb(In1/2Nb1/2)O3sub> (PIN) under pressure up to 50GPa. Raman spectra show broad bands but a peak near the 380cm-1 increases its intensity with pressure. The linewidth of the band at 550cm-1 also increases with pressure, while two of the Raman peaks merge above 6GPa. Above 16GPa, we observe additional splitting of the band at 50cm-1. The pressure evolution of the diffraction patterns for PIN shows obvious Bragg peaks splitting above 16GPa; consistent with a symmetry lowering transition. The transition at 0.5GPa is identified as a pseudo-cubic to orthorhombic (Pbam) structural change whereas the transition at 16GPa is isostructure and associated with changes in linear compressibility and octahedral titling, and the transition at 30GPa is associated to an orthorhombic to monoclinic change. First-principles calculations indicate that the Pbam structure is ground state with antiferrodisdortion consistent with experiment.


    SciTech Connect

    Favre, C.; Wootten, H. A.; Remijan, A. J.; Brouillet, N.; Despois, D.; Baudry, A.; Wilson, T. L. E-mail: E-mail: E-mail:


    We report the first subarcsecond (0.''65 x 0.''51) image of the dimethyl ether molecule, (CH{sub 3}){sub 2}O, toward the Orion Kleinmann-Low nebula. The observations were carried at 43.4 GHz with the Expanded Very Large Array (EVLA). The distribution of the lower energy transition 6{sub 1,5}-6{sub 0,6}, EE (E {sub u} = 21 K) mapped in this study is in excellent agreement with the published dimethyl ether emission maps imaged with a lower resolution. The main emission peaks are observed toward the Compact Ridge and Hot Core southwest components, at the northern parts of the Compact Ridge and in an intermediate position between the Compact Ridge and the Hot Core. A notable result is that the distribution of dimethyl ether is very similar to that of another important larger O-bearing species, the methyl formate (HCOOCH{sub 3}), imaged at a lower resolution. Our study shows that higher spectral resolution (WIDAR correlator) and increased spectral coverage provided by the EVLA offer new possibilities for imaging complex molecular species. The sensitivity improvement and the other EVLA improvements make this instrument well suited for high sensitivity, high angular resolution, and molecular line imaging.

  19. Enhanced Near-Infrared Upconversion Emission of Yb3+-Tm3+ Co-doped Gd2O3 Sub-microrods

    NASA Astrophysics Data System (ADS)

    Xu, D. K.; Liu, C. F.; Yan, J. W.; Ouyang, H. Q.; Yang, S. H.; Zhang, Y. L.

    Lanthanide-doped rare-earth oxides have aroused great interest in display and bio-probe technology due to their excellent luminescent and magnetic performance. In this paper, Gd2O3 sub-microrods (SMRs) with cubic structure are obtained via heat-treatment from gadolinium hydroxides precursor. Upconversion (UC) spectra show intense near-infrared (NIR) emission which is assigned to 3H4 → 3H6 transition of Tm3+. From the double logarithmic plot of emission intensity versus pump powers, it was seen that typical two photons were involved in the NIR UC process. Moreover, a series of Gd2O3:18%Yb3+,x%Tm3+ (x = 0.1, 0.5, 1, 2, 5) and Gd2O3:y%Yb3+,0.5%Tm3+ (y = 1, 5, 10, 40, 80) SMRs were prepared and characterized to explore their NIR emission properties. Finally, the enhanced NIR emission property was found in Gd2O3:Yb3+,Tm3+ SMRs from the reduced NaOH concentration and the reduced calcinations temperatures.

  20. Three-Dimensionally Mesostructured Fe2O3sub> Electrodes with Good Rate Performance and Reduced Voltage Hysteresi

    SciTech Connect

    Wang, Junjie; Braun, Paul V.; Zhou, Hui; Nanda, Jagjit


    Ni scaffolded mesostructured 3D Fe2O3sub> electrodes were fabricated by colloidal templating and pulsed elec-trodeposition. The scaffold provided short pathways for both lithium ions and electrons in the active phase, enabling fast kinetics and thus a high power density. The scaffold also resulted in a reduced voltage hysteresis. The electrode showed a reversible capacity of ~1000 mA h g-1 at 0.2 A g-1 (~0.2 C) for about 20 cycles, and at a current density of 20 A g-1 (~20 C) the deliverable capacity was about 450 mA h g-1. The room temperature voltage hysteresis at 0.1 A g-1 (~0.1 C) was 0.62 V, which is significantly smaller than that normally reported in the literature. And it could be further reduced to 0.42 V when cycling at 45 ºC. Potentiostatic electrochemical impedance spectroscopy (PEIS) studies indicated the small voltage hysteresis may be due to a reduction in the Li2O/Fe interfacial area in the electrode during cycling relative to convention-al conversion systems.

  1. Microdomain Formation, Oxidation, and Cation Ordering in LaCa2Fe3sub>O8+y

    SciTech Connect

    Price, Patrick M.; Browning, Nigel D.; Butt, Darryl P.


    The compound LaCa2Fe3sub>O8+y, also known as the Grenier phase, is known to undergo an order-disorder transformation (ODT) at high temperatures. Oxidation has been observed when the compound is cooled in air after the ODT. In this study, we have synthesized the Grenier compound in air using traditional solid state reactions and investigated the structure and composition before and after the ODT. Thermal analysis showed that the material undergoes an order-disorder transformation in both oxygen and argon atmospheres with dynamic, temperature dependent, oxidation upon cooling. Results from scanning transmission electron microscopy (STEM) suggest that the Grenier phase has preferential segregation of Ca and La on the two crystallographic A-sites before the ODT, but a random distribution above the ODT temperature. Furthermore, STEM images suggest the possibility that oxygen excess may exist in La-rich regions within microdomains rather than at microdomain boundaries.

  2. Magnetic phase transitions in Nd{sub 1-x}Dy{sub x}Fe{sub 3}(BO{sub 3}){sub 4} ferroborates

    SciTech Connect

    Demidov, A. A.; Gudim, I. A.; Eremin, E. V.


    The magnetic properties of ferroborate single crystals with substituted compositions Nd{sub 1-x}Dy{sub x}Fe{sub 3}(BO{sub 3}){sub 4} (x = 0.15, 0.25) with competing exchange Nd-Fe and Dy-Fe interactions are investigated. For each composition, we observed a spontaneous spin-reorientation transition from the easy-axis to the easy-plane state and step anomalies on the magnetization curves for the spin-flop transition induced by a magnetic field B vertical bar c. The measured parameters and effects are interpreted using a unified theoretical approach based on the molecular field approximation and on calculations performed in the crystal-field model for the rare-earth ion. The experimental temperature dependences of the initial magnetic susceptibility from T = 2 K to T = 300 K, anomalies on the magnetization curves for B vertical bar c in fields up to 1.8 T, and their evolution with temperature, as well as temperature and field dependences of magnetization in fields up to 9 T are described. In the interpretation of experimental data, the crystal-field parameters in trigonal symmetry for the rare-earth subsystem are determined, as well as the parameters of Nd-Fe and Dy-Fe exchange interactions.

  3. An air-stable Na3sub>SbS4 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 Na3sub>SbS4, 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.

  4. Separation of Am-Cm from Al(NO/sub 3/)/sub 3/ waste solutions by in-canyon-tank precipitation as oxalates

    SciTech Connect

    Gray, L.W.; Burney, G.A.; Wilson, T.W.; McKibben, J.M.; Bibler, N.E.; Holtzscheiter, E.W.; Campbell, T.G.


    A process for recovery of Am-Cm residues from high-activity waste concentrates has been developed specifically for application in Savannah River Plant (SRP) canyon tanks. The Am-Cm residues were collected from a campaign to produce plutonium containing high isotopic concentrations of /sup 242/Pu. The separation of Am-Cm from the high-activity waste stream, containing about 2M Al(NO/sub 3/)/sub 3/, is necessary to produce an acceptable feed solution for a later pressurized cation exchange chromatography separation and purification step. The new process includes formic acid denitration, adjustment of contaminating cations by evaporation and water dilution, and oxalate precipitation of the actinides and lanthanides. After washing, the precipitate was dissolved in 8M nitric acid and the oxalate was destroyed by nitric acid oxidation that was catalyzed by manganous ions. This new process generates about one-fourth the waste of the californium solvent extraction process, which it replaced. The new process also produces a cleaner feed solution for the pressurized cation exchange chromatography separation and purification step.

  5. Magnetic anisotropy and magnetoelectric properties of Tb{sub 1-x}Er{sub x}Fe{sub 3}(BO{sub 3}){sub 4} ferroborates

    SciTech Connect

    Zvezdin, A. K.; Kadomtseva, A. M. Popov, Yu. F.; Vorob'ev, G. P.; Pyatakov, A. P.; Ivanov, V. Yu.; Kuz'menko, A. M.; Mukhin, A. A.; Bezmaternykh, L. N.; Gudim, I. A.


    Magnetic and magnetoelectric properties of ferroborate single crystals with complex composition (Tb{sub 1-x}Er{sub x}Fe{sub 3}(BO{sub 3}){sub 4}, x = 0, 0.75) and with competing exchange Tb-Fe and Er-Fe interactions are investigated. Jumps in electric polarization, magnetostriction, and magnetization are observed as a result of spin-flop transitions, as well as a considerable decrease in the critical field upon an increase in the Er concentration, in a field H{sub c} parallel to the c axis. The observed behavior of phase-transition fields is analyzed and explained using a simple model taking into account anisotropy in g factors and exchange splitting of funda-mental doublets of the easy-axis Tb{sup 3+} ion and easy-plane Er{sup 3+} ion. It is established that magnetoelectric and magnetostriction anomalies under spin-flop transitions are mainly controlled by the Tb subsystem. The Tb subsystem makes a nonmonotonic contribution {Delta}P{sub a}(H{sub a}, T) to polarization along the a axis: the value of {Delta}P{sub a} reverses its sign and increases with temperature due to the contribution from the excited states of the Tb{sup 3+} ion.

  6. 57Fe Mössbauer study of Lu2Fe3sub>Si5 iron silicide superconductor

    SciTech Connect

    Ma, Xiaoming; Ran, Sheng; Pang, Hua; Li, Fashen; Canfield, Paul C.; Bud'ko, Sergey L.


    With the advent of Fe–As based superconductivity it has become important to study how superconductivity manifests itself in details of 57Fe Mössbauer spectroscopy of conventional, Fe-bearing superconductors. The iron-based superconductor Lu2Fe3sub>Si5 has been studied by 57Fe Mössbauer spectroscopy over the temperature range from 4.4 K to room temperature with particular attention to the region close to the superconducting transition temperature (Tc=6.1 K). Consistent with the two crystallographic sites for Fe in this structure, the observed spectra appear to have a pattern consisting of two doublets over the whole temperature range. Furthermore, the value of Debye temperature was estimated from temperature dependence of the isomer shift and the total spectral area and compared with the specific heat capacity data. Neither abnormal behavior of the hyperfine parameters at or near Tc, nor phonon softening were observed.

  7. Gamma and proton irradiation effects and thermal stability of electrical characteristics of metal-oxide-silicon capacitors with atomic layer deposited Al2O3sub> dielectric

    SciTech Connect

    J. M. Rafi; Lynn, D.; Pellegrini, G.; Fadeyev, V.; Galloway, Z.; Sadrozinski, H. F. -W.; Christophersen, M.; Philips, B. F.; Kierstead, J.; Hoeferkamp, M.; Gorelov, I.; Palni, P.; Wang, R.; Seidel, S.


    The radiation hardness and thermal stability of the electrical characteristics of atomic layer deposited Al2O3sub> layers to be used as passivation films for silicon radiation detectors with slim edges are investigated. To directly measure the interface charge and to evaluate its change with the ionizing dose, metal-oxide-silicon (MOS) capacitors implementing differently processed Al2O3sub> layers were fabricated on p-type silicon substrates. Qualitatively similar results are obtained for degradation of capacitance–voltage and current–voltage characteristics under gamma and proton irradiations up to equivalent doses of 30 Mrad and 21.07 Mrad, respectively. While similar negative charge densities are initially extracted for all non-irradiated capacitors, superior radiation hardness is obtained for MOS structures with alumina layers grown with H2O instead of O3sub> as oxidant precursor. Competing effects between radiation-induced positive charge trapping and hydrogen release from the H2O-grown Al2O3sub> layers may explain their higher radiation resistance. Finally, irradiated and non-irradiated MOS capacitors with differently processed Al2O3sub> layers have been subjected to thermal treatments in air at temperatures ranging between 100 °C and 200 °C and the thermal stability of their electrical characteristics has been evaluated. Partial recovery of the gamma-induced degradation has been noticed for O3sub>-grown MOS structures. Lastly, this can be explained by a trapped holes emission process, for which an activation energy of 1.38 ± 0.15 eV has been extracted.

  8. Detection of Amorphous Silica in Air-Oxidized Ti3sub>SiC2 at 500-1000°C by NMR and SIMS

    SciTech Connect

    Pang, Wei Kong; Low, I M; Hanna, J V


    The use of secondary-ion mass spectrometry (SIMS), nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM) to detect the existence of amorphous silica in Ti3sub>SiC2 oxidised at 500-1000 ºC is described. The formation of an amorphous SiO2 layer and its growth in thickness with temperature was monitored using dynamic SIMS. Results of NMR and TEM verify for the first time the direct evidence of amorphous silica formation during the oxidation of Ti3sub>SiC2 at 1000 ºC.

  9. ALD TiO2-Al2O3sub> Stack: An Improved Gate Dielectrics on Ga-polar GaN MOSCAPs

    SciTech Connect

    Wei, Daming; Edgar, James H.; Briggs, Dayrl P.; Srijanto, Bernadeta R.; Retterer, Scott T.; Meyer, III, Harry M.


    This research focuses on the benefits and properties of TiO2-Al2O3sub> nano-stack thin films deposited on Ga2O3sub>/GaN by plasma-assisted atomic layer deposition (PA-ALD) for gate dielectric development. This combination of materials achieved a high dielectric constant, a low leakage current, and a low interface trap density. Correlations were sought between the films’ structure, composition, and electrical properties. The gate dielectrics were approximately 15 nm thick and contained 5.1 nm TiO2, 7.1 nm Al2O3sub> and 2 nm Ga2O3sub> as determined by spectroscopic ellipsometry. The interface carbon concentration, as measured by x-ray photoelectron spectroscopy (XPS) depth profile, was negligible for GaN pretreated by thermal oxidation in O2 for 30 minutes at 850°C. The RMS roughness slightly increased after thermal oxidation and remained the same after ALD of the nano-stack, as determined by atomic force microscopy. The dielectric constant of TiO2-Al2O3sub> on Ga2O3/GaN was increased to 12.5 compared to that of pure Al2O3sub> (8~9) on GaN. In addition, the nano-stack's capacitance-voltage (C-V) hysteresis was small, with a total trap density of 8.74 × 1011 cm-2. The gate leakage current density (J=2.81× 10-8 A/cm2) was low at +1 V gate bias. These results demonstrate the promising potential of plasma ALD deposited TiO2/Al2O3sub> for serving as the gate oxide on Ga2O3sub>/GaN based MOS devices.

  10. Chemistry of the hexaborane(10) analogue (PPh{sub 3}){sub 2}(CO)IrB{sub 5}H{sub 8}: Formation and characterization of the heterobimetallaheptaboranes 1,1,1-(CO){sub 3}-2,2-(CO){sub 2}-2,4-(PPh{sub 3}){sub 2-closo-}-1,2-FeIrB{sub 5}H{sub 4} and 2-(CO)-2,2-(PPh{sub 3}){sub 2}-7-Cl-7-(PMe{sub 2}Ph)-nido-2,7-IrPtB{sub 5}H{sub 7}

    SciTech Connect

    Bould, J.; Rath, N.P.; Fang, H.; Barton, L.


    The chemistry of the hexaborane(10) analogue (PPh{sub 3}){sub 2}(CO)IrB{sub 5}H{sub 8} (4) has been investigated. The two standard reactions in which metal-containing moieties may be incorporated into the B{sub 6}H{sub 10} cage find success when applied to the iridahexaborane (4). The reaction of Fe{sub 2}(CO){sub 9} with (PPh{sub 3}){sub 2}(CO)IrB{sub 5}H{sub 8} in C{sub 6}H{sub 6} solution affords 1,1,1-(CO){sub 3}-2,2-(CO){sub 2}-2,4-(PPh{sub 3}){sub 2-closo}-1,2-FeIrB{sub 5}H{sub 4} (1) in moderate (28.5%) yield. Except for carborane derivatives, 1 is the first pentagonal bipyramidal metallaheptaborane to be structurally characterized. Compound 1 was identified by NMR, IR, and high-resolution mass spectroscopy and by a single-crystal X-ray diffraction study. Treatment of a THF solution of the sodium anion salt of 4, Na[(PPh{sub 3}){sub 2}(CO)IrB{sub 5}H{sub 7}], with [Pt(PMe{sub 2}Ph)Cl{sub 2}]{sub 2} in Ch{sub 2}Cl{sub 2} affords yellow solid 2-(CO)-2,2-(PPh{sub 3}){sub 2}-7-Cl-7-(PM3{sub 2}-Ph)-nido-2,7-IrPtB{sub 5}H{sub 7} (2) in 5% yield. 2 is identified similarily. It exists as a nido seven-vertex cluster formally derived by removal of a vertex of connectivity 5 from a closed triangulated dodecahedral polyhedron. 2 is two skeletal electrons short of the electron count for a classical nido cluster, and it is compared to systems with related structures and also to other systems containing the Pt moiety functioning as a two-orbital two-electon donor.

  11. Structure and Stoichiometry in Supervalent Doped Li7La3sub> Zr2O12

    SciTech Connect

    Mukhopadhyay, Saikat; Thompson, Travis; Sakamoto, Jeff; Huq, Ashfia; Wolfenstine, Jeff; Allen, Jan L.; Bernstein, Noam; Stewart, Derek A.; Johannes, M. D.


    The oxide garnet material Li7La3sub> Zr2O12 shows remarkably high ionic conductivity when doped with supervalent ions that are charge compensated by Li vacancies and is currently one of the best candidates for development of a technologically relevant solid electrolyte. Determination of optimal dopant concentration, however, has remained a persistent problem due to the extreme difficulty of establishing the actual (as compared to nominal) stoichiometry of intentionally doped materials and by the fact that it is still not entirely clear what level of lattice expansion/contraction best promotes. ionic diffusion. By combining careful synthesis, neutron diffraction, high-resolution X-ray diffraction (XRD), Raman measurements, and density functional theory calculations, we show that structure and stoichiometry are intimately related such that the former can in many cases be used as a gauge of the latter. We show that different Li-vacancy creating supervalent ions (Al3+ vs Ta5+) affect the structure very differently, both in terms of the lattice constant, which is easily measurable, and hi terms of the local structure, which can be difficult or impossible to access experimentally but may have important ramifications for conduction. We carefully correlate the lattice constant to dopant type/concentration via Vegard's law and then further correlate these quantities to relevant local structural parameters. In conclusion, our work opens the possibility of developing a codopant scheme that optimizes the Li vacancy concentration and the lattice size simultaneously.

  12. A new promising phosphor, Na{sub 3}La{sub 2}(BO{sub 3}){sub 3}:Ln (Ln=Eu, Tb)

    SciTech Connect

    Li Zhihua; Zeng Jinghui; Zhang Guochun; Li Yadong . E-mail:


    We present an efficient way to search a host for ultraviolet (UV) phosphor from UV nonlinear optical (NLO) materials. With the guidance, Na{sub 3}La{sub 2}(BO{sub 3}){sub 3} (NLBO), as a promising NLO material with a broad transparency range and high damage threshold, was adopted as a host material for the first time. The lanthanide ions (Tb{sup 3+} and Eu{sup 3+})-doped NLBO phosphors have been synthesized by solid-state reaction. Luminescent properties of the Ln-doped (Ln=Tb{sup 3+}, Eu{sup 3+}) sodium lanthanum borate were investigated under UV ray excitation. The emission spectrum was employed to probe the local environments of Eu{sup 3+} ions in NLBO crystal. For red phosphor, NLBO:Eu, the measured dominating emission peak was at 613 nm, which is attributed to {sup 5} D -{sup 7} F {sub 2} transition of Eu{sup 3+}. The luminescence indicates that the local symmetry of Eu{sup 3+} in NLBO crystal lattice has no inversion center. Optimum Eu{sup 3+} concentration of NLBO:Eu{sup 3+} under UV excitation with 395 nm wavelength is about 30 mol%. The green phosphor, NLBO:Tb, showed bright green emission at 543 with 252 nm excited light. The measured concentration quenching curve demonstrated that the maximum concentration of Tb{sup 3+} in NLBO was about 20%. The luminescence mechanism of Ln-doped NLBO (Tb{sup 3+} and Eu{sup 3+}) was analyzed. The relative high quenching concentration was also discussed.

  13. Properties of heteroepitaxial 3C-SiC layer on Si using Si{sub 2}(CH{sub 3}){sub 6} by CVD

    SciTech Connect

    Chen, Y.; Masuda, Y.; Nishio, Y.; Matsumoto, K.; Nishino, S.


    Single crystal cubic silicon carbide (3C-SiC) has been deposited on Si(100) by atmospheric CVD at 1,350 C using Si{sub 2}(CH{sub 3}){sub 6}. The 3C-SiC epilayers were characterized by XRD, Raman scattering and photoluminescence (PL). The 3C-SiC distinct TO near 796 cm{sup {minus}1} and LO near 973 cm{sup {minus}1} were recorded by Raman measurement. The PL spectra of SiC films at 11 K included the nitrogen-bound exciton (N-BE) lines, the defect-related W band near 2.15eV, and 2.13eV peak corresponding to D-A pair recombination as well as the divancy-related D1 peak at 1.97eV. The thickness dependences of Raman and PL measurement were made and it was observed that tensile stress and strain in films decrease with increasing film thickness. Electrical properties of the films were measured by making schottky diodes and using Van der Pauw method. Above 300 K, the electron mobility changed as {micro}{sub H} {approximately} T{sup {minus}1.45 {approximately} {minus}1.56} and the highest mobility was about 400 cm{sup 2} V{sup {minus}1} s{sup {minus}1} at room temperature. In 3C-SiC the scattering processes are affected prominently by acoustic scattering in this temperature range.

  14. Structures and thermoelectric properties of the infinitely adaptive series (Bi{sub 2}){sub m}(Bi{sub 2}Te{sub 3}){sub n}

    SciTech Connect

    Bos, J. W. G.; Cava, R. J.; Zandbergen, H. W.; Lee, M.-H.; Ong, N. P.


    The structures and thermoelectric properties of the (Bi{sub 2}){sub m}(Bi{sub 2}Te{sub 3}){sub n} homologous series, derived from stacking hexagonal Bi{sub 2} and Bi{sub 2}Te{sub 3} blocks, are reported. The end members of this series are metallic Bi and semiconducting Bi{sub 2}Te{sub 3}; nine members of the series have been studied. The structures form an infinitely adaptive series and a unified structural description based on a modulated structure approach is presented. The as-synthesized samples have thermopowers (S) that vary from n type for Bi{sub 2}Te{sub 3} to p type for phases rich in Bi{sub 2} blocks but with some Bi{sub 2}Te{sub 3} blocks present, to n type again for Bi metal. The thermoelectric power factor (S{sup 2}/{rho}) is highest for Bi metal (43 {mu}W/K{sup 2} cm at 130 K), followed by Bi{sub 2}Te{sub 3} (20 {mu}W/K{sup 2} cm at 270 K), while Bi{sub 2}Te (m:n=5:2) and Bi{sub 7}Te{sub 3} (m:n=15:6) have 9 {mu}W/K{sup 2} cm (at 240 K) and 11 {mu}W/K{sup 2} cm (at 270 K), respectively. The results of doping studies with Sb and Se into Bi{sub 2}Te are reported.

  15. Origin of Active Oxygen in a Ternary CuOx /Co3sub>O4–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/Co3sub>O4-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/Co3sub>O4-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 Co3sub>O4-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 Co3sub>O4-CeO2.

  16. Accessing conjugated polymers with precisely controlled heterobisfunctional chain ends via post-polymerization modification of the OTf group and controlled Pd(0)/t-Bu3sub>P-catalyzed Suzuki cross-coupling polymerization

    SciTech Connect

    Hu, Qiao -Sheng; Hong, Kunlun; Zhang, Hong -Hai


    In this study, a general strategy toward the synthesis of well-defined conjugated polymers with controlled heterobisfunctional chain ends via combination of controlled Pd(0)/t-Bu3sub>P Suzuki cross-coupling polymerization with the post-polymerization modification of the triflate (OTf) group was disclosed.

  17. Preparation of silicon nitride-titanium nitride and titanium-titanium nitride composites from (CH{sub 3}){sub 3}SiNHTiCl{sub 3}-coated Si{sub 3}N{sub 4} and Ti particles

    SciTech Connect

    Narula, C.K.; Demczyk, B.G.; Czubarow, P.; Seyferth, D.


    [(Trimethylsilyl)amino]titanium trichloride, (CH{sub 3}){sub 3}-SiNHTiCl{sub 3}, was isolated as a red-orange crystalline solid in 58% Yield from the reaction of TiCl{sub 4} with [(CH{sub 3}){sub 3}Si]{sub 2} NH in 1:1 molar ratio in dichloromethane at {minus}78 C. Pyrolysis of (CH{sub 3}){sub 3}SiNHTiCl{sub 3} at 600 C furnished titanium nitride. This precursor is suitable for the preparation of composites and was employed to prepare Si{sub 3}N{sub 4}-TiN and Ti-TiN powders by adding Si{sub 3}N{sub 4} particles or titanium powders to a solution of (CH{sub 3}){sub 3} SiNHTiCl{sub 3} in dichloromethane, drying and pyrolyzing the resulting solid. This precursor also has been used as a binder to prepare Si{sub 3}N{sub 4}-TiN and Ti-TiN bodies. High-resolution transmission electron microscopic studies of the Si{sub 3}N{sub 4}-TiN composite showed that titanium nitride is concentrated on the surface of the Si{sub 3}N{sub 4} particles.

  18. In situ determination of the spinel-post-spinel transition in Fe3sub>O4 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 Fe3sub>O4 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-Fe3sub>O4) 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 3sub>O4 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-Fe3sub>O4, 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.

  19. Optical Absorption and Spectral Photoconductivity in α-(Fe1-xCrx)2O3sub> Solid-Solution Thin Films

    SciTech Connect

    Chamberlin, Sara E.; Wang, Yong; Lopata, Kenneth A.; Kaspar, Tiffany C.; Cohn, Alicia; Gamelin, Daniel R.; Govind, Niranjan; Sushko, Peter V.; Chambers, Scott A.


    Hematite, α-Fe2O3sub>, is an attractive narrow gap oxide for consideration as an efficient visible light photocatalyst, with significant potential for band gap engineering via doping. We examine optical absorption in α (Fe1-xCrx)2O3sub> epitaxial films and explain the observed excitations, and the nature of the band gap dependence on x, through first principles calculations. The calculated and measured optical band gap becomes smaller than that of the bulk α-Fe2O3sub> and reaches a minimum as the Cr mole fraction increases to 50%. The lowest energy transitions in the mixed-metal alloys involve electron excitation from occupied Cr 3d orbitals to unoccupied Fe 3d orbitals, and they result in a measureable photocurrent. The onset of α-Fe2O3sub> photoconductivity can be reduced by nearly ~0.5 eV through addition of Cr.

  20. Yttria-stabilized zirconia buffered silicon to optimize in-plane electrical conductivity of [Ca{sub 2}CoO{sub 3}]{sub 0.62}[CoO{sub 2}] thin films

    SciTech Connect

    Kraus, T.; Griesser, A.; Klein, O.; Fischer, M.; Schreck, M.; Karl, H.


    The monolithic integration of thermoelectric generators and magnetoresistive functionality on the basis of misfit cobaltate [Ca{sub 2}CoO{sub 3}]{sub 0.62}[CoO{sub 2}] thin films into silicon technology is a prerequisite for their application in miniaturized electric circuits. Here, we report on [Ca{sub 2}CoO{sub 3}]{sub 0.62}[CoO{sub 2}] thin films grown by pulsed laser deposition on (001)-silicon with a thin epitaxial yttria-stabilized zirconia (YSZ) buffer layer. X-ray diffraction and cross-sectional high resolution transmission electron microscopy analysis reveal that high quality c-axis oriented heteroepitaxial [Ca{sub 2}CoO{sub 3}]{sub 0.62}[CoO{sub 2}] films with a 12-fold in-plane rotational symmetry can be grown, which exhibit remarkable lower electrical resistivity compared to those with random in-plane orientation. This result is explained by energetically preferred epitaxial growth directions of the pseudo hexagonal [CoO{sub 2}] sublayer in monoclinic [Ca{sub 2}CoO{sub 3}]{sub 0.62}[CoO{sub 2}] onto the cubic (001)-YSZ surface leading to a highly symmetric in-plane mutual orientation of the charge transporting CoO{sub 2} sublayer domains.

  1. Symmetry of piezoelectric (1–x)Pb(Mg1/3sub>Nb2/3sub>)O₃-xPbTiO₃ (x=0.31) single crystal at different length scales in the morphotropic phase boundary region

    SciTech Connect

    Kim, Kyou-Hyun; Payne, David A.; Zuo, Jian-Min


    We use probes of three different length scales to examine symmetry of (1–x)Pb(Mg1/3sub>Nb2/3sub>)O₃-xPbTiO₃ (PMN-xPT) single crystals in the morphotropic phase boundary (MPB) region at composition x = 0.31 (PMN-31% PT). On the macroscopic scale, x-ray diffraction (XRD) shows a mixture of strong and weak diffraction peaks of different widths. The closest match to XRD peak data is made with monoclinic Pm (MC) symmetry. On the local scale of a few nanometers, convergent beam electron diffraction (CBED) studies, with a 1.6-nm electron probe, reveal no obvious symmetry. These CBED experimental patterns can be approximately matched with simulations based on monoclinic symmetry, which suggests locally distorted monoclinic structure. A monoclinic Cm (MA or MB)-like symmetry could also be obtained from certain regions of the crystal by using a larger electron probe size of several tens of nanometers in diameter. Thus the monoclinic symmetry of single crystal PMN-31%PT is developed only in parts of the crystal by averaging over locally distorted structure on the scale of few tens of nanometers. The macroscopic symmetry observed by XRD is a result of averaging from the local structure in PMN-31%PT single crystal. The lack of local symmetry at a few nanometers scale suggests that the polarization switching results from a change in local displacements, which are not restricted to specific symmetry planes or directions.

  2. Line shape parameters of PH3sub> transitions in the Pentad near 4–5 μm: Self-broadened widths, shifts, line mixing and speed dependence

    SciTech Connect

    Malathy Devi, V.; Benner, D. C.; Kleiner, Isabelle; Sams, Robert L.; Fletcher, Leigh N.


    Accurate knowledge of spectroscopic line parameters of PH3sub> is important for remote sensing of the outer planets, especially Jupiter and Saturn. In a recent study, line positions and intensities for the Pentad bands of PH3sub> have been reported from analysis of high-resolution, high signal-to noise room-temperature spectra recorded with two Fourier transform spectrometers (2014) [1]. The results presented in this study were obtained during the analysis of positions and intensities, but here we focus on the measurements of spectral line shapes (e.g. widths, shifts, line mixing) for the 2ν4, ν2 + ν4, ν1 and ν3sub> bands. A multispectrum nonlinear least squares curve fitting technique employing a non-Voigt line shape to include line mixing and speed dependence of the Lorentz width was employed to fit the spectra simultaneously. The least squares fittings were performed on five room-temperature spectra recorded at various PH3sub> pressures (~2–50 Torr) with the Bruker IFS-125HR Fourier transform spectrometer (FTS) located at the Pacific Northwest National Laboratory (PNNL), in Richland, Washington. Over 840 Lorentz self-broadened half-width coefficients, 620 self-shift coefficients and 185 speed dependence parameters were measured. Line mixing was detected for transitions in the 2ν4, ν1 and ν3sub> bands, and their values were quantified for 10 A+A- pairs of transitions via off-diagonal relaxation matrix element formalism. The dependences of the measured half-width coefficients on the J and K rotational quanta of the transitions are discussed. The self-width coefficients for the ν1 and ν3sub> bands from this study are compared to the self-width coefficients for transitions with the same rotational quanta (J, K) reported for the Dyad (ν2 and ν4) bands. The measurements from present study should be useful for the

  3. Structural phase transition causing anomalous photoluminescence behavior in perovskite (C{sub 6}H{sub 11}NH{sub 3}){sub 2}[PbI{sub 4}

    SciTech Connect

    Yangui, A.; Pillet, S.; Mlayah, A.; Lusson, A.; Bouchez, G.; Boukheddaden, K. E-mail:; Triki, S.; Abid, Y. E-mail:


    Optical and structural properties of the organic-inorganic hybrid perovskite-type (C{sub 6}H{sub 11}NH{sub 3}){sub 2}[PbI{sub 4}] (abbreviated as C{sub 6}PbI{sub 4}) were investigated using optical absorption, photoluminescence (PL), and x-ray diffraction measurements. Room temperature, optical absorption measurements, performed on spin-coated films of C{sub 6}PbI{sub 4}, revealed two absorption bands at 2.44 and 3.21 eV. Upon 325 nm (3.815 eV) laser irradiation, strong green PL emission peaks were observed at 2.41 eV (P1) and 2.24 eV (P2) and assigned to free and localized excitons, respectively. The exciton binding energy was estimated at 356 meV. At low temperature, two additional emission bands were detected at 2.366 eV (P3) and a large band (LB) at 1.97 eV. The former appeared only below 40 K and the latter emerged below 130 K. The thermal dependence of the PL spectra revealed an abnormal behavior accompanied by singularities in the peak positions and intensities at 40 and 130 K. X-ray diffraction studies performed on powder and single crystals as a function of temperature evidenced significant changes of the interlayer spacing at 50 K and ∼138 K. Around 138 K, a commensurate to incommensurate structural phase transition occurred on cooling. It involves a symmetry breaking leading to a distortion of the PbI{sub 6} octahedron. The resulting incommensurate spatial modulation of the Pb–I distances (and Pb–I–Pb angles) causes a spatial modulation of the band gap, which is at the origin of the emergence of the LB below ∼130 K and the anomalous behavior of the position of P1 below 130 K. The change of the interlayer spacing in the 40-50 K range may in turn be related to the significant decrease of the intensity of P2 and the maximum emission of the LB. These results underline the intricate character of the structural and the PL properties of the hybrid perovskites; understanding such properties should benefit to the design of optoelectronic devices with

  4. Metathetical reactions of Re(VII) alkylidene-alkylidyne complexes of the type Re(CR[prime])(CHR[prime])[OCMe(CF[sub 3])[sub 2

    SciTech Connect

    Toreki, R.; Vaughan, G.A.; Schrock, R.R.; Davis, W.M. )


    1-Decene and methyl 9-decenoate react with syn- and anti-Re(C-t-Bu)(CH-t-Bu)(OR[sub F6]) to give syn- and anti-Re(C-t-Bu)[CH(CH[sub 2])[sub 7]Me](OR[sub F6])[sub 2] and syn- and anti-Re(C-t-Bu)[CH(CH[sub 2])[sub 7]CO[sub 2]Me](OR[sub F6])[sub 2], respectively (OR[sub F6] = OCMe(CF[sub 3])[sub 2]). The new alkylidene complexes are unstable in the presence of excess terminal olefin and decompose upon attempted isolation. However, vinylferrocene reacts relatively smoothly and reversibly with syn-Re(C-t-Bu)(CH-t-Bu)(OR[sub F6])[sub 2] in a noncoordinating solvent to yield tert-butylethylene and primarily anti-Re(C-t-Bu)(CHFc)(OR[sub F6])[sub 2] (Fe = ferrocenyl). anti-Re(C-t-Bu)(CHFc)(OR[sub F6])[sub 2]. In the presence of THF or dimethoxyethane, complexes of the type syn- or anti-Re(C-t-Bu)(CHR)(OR[sub F6])S[sub 2] (R = Me, Et, Ph; S = THF or 0.5DME) could be prepared in high yield from Re(C-t-Bu)(CH-t-Bu)(OR[sub F6])[sub 2] and CH[sub 2][double bond]CHR. Heteroatom-substituted (O, S, or N) terminal olefins react more rapidly than ordinary olefins with Re(C-t-Bu)(CH-t-Bu)(OR[sub F6])[sub 2] in the presence of THF to yield complexes of the type syn- or anti-Re(C-t-Bu)(CHX)(OR[sub F6])[sub 2](THF)[sub 2] (X = OR, SR, NR[sub 2], or p-dimethylaminophenyl). 2-Pentene or methyl oleate is metathesized in the presence of Re(C-t-Bu)(CH-t-Bu)(OR[sub F6])[sub 2], and intermediate alkylidene complexes can be observed in each case. Addition of 3-hexene to Re(C-t-Bu)(CH-t-Bu)(OR[sub F6])[sub 2] followed by TMEDA yields Re(C-t-Bu)(CHEt)(OR[sub F6])[sub 2](TMEDA). Internal olefins are metathesized only very slowly by Re(C-t-Bu)(CH-t-Bu)(OR[sub F6])[sub 2] in the presence of several equivalents of THF or DME or especially in neat THF or DME. 58 refs., 4 figs., 4 tabs.

  5. Local structure, pseudosymmetry, and phase transitions in Na1/2Bi1/2TiO3sub>-K1/2Bi1/2TiO3sub> ceramics

    SciTech Connect

    Levin, I; Reaney, I M; Anton, E-M; Jo, Wook; Rödel, J; Pokorny, J; Schmitt, L A; Kleebe, H-J; Hinterstein, M; Jones, J L


    The structural behavior of ceramic solid solutions (1-x)Na1/2Bi1/2TiO3sub>–xK1/2Bi1/2TiO3sub> (NBT-KBT) was studied using high-resolution powder diffraction and transmission electron microscopy. A temperature-independent morphotropic phase boundary (MPB) separating NBT-like pseudorhombohedral (R) and KBT-like pseudotetragonal (T) phases was observed at x ≈ 0.2. For x<0.2, both local and average room-temperature structures are similar to those in NBT. Simultaneous long-range antiphase and short-range in-phase octahedral rotations average, resulting in effective antiphase a-a-c- tilting, which yields monoclinic symmetry when probed by x-ray diffraction (XRD). For these compositions, polar ordering is coupled to antiphase octahedral rotations so that tilting and ferroelectric (FE) domains coincide. Compositions with x>0.2 exhibit a tetragonal-like distortion; however, complex splitting of reflections in XRD patterns suggests that the actual symmetry is lower than tetragonal. For 0.2≤x≤0.5, in-phase octahedral tilting a0b+a0 (or a+b0b0) is present but confined to the nanoscale, while for x>0.5 the structure becomes untilted. In-phase tilting evolves above the ferroelectric transition and occurs around a nonpolar (a or b) axis of the average T structure. The onset of polar order has no significant effect on the coherence length of in-phase tilting, which suggests only weak coupling between the two phenomena. The average symmetry of the T phase is determined by the effective symmetry (Imm2) of assemblages of coherent in-phase tilted nanodomains. Near the MPB, the coexistence of extended R- and T-like regions is observed, but lattice distortions within each phase are small, yielding narrow peaks with a pseudocubic appearance in XRD. The temperature of the FE phase transition exhibits a minimum at the MPB. The

  6. Synthesis,Structure and Electrical Properties of(SnO{sub 2}){sub x}(In{sub 2}O{sub 3}){sub 1-x}(x=0.5-1) Nanocomposites

    SciTech Connect

    Rembeza, S. I.; Voronov, P. E.; Sinelnikov, B. M.; Rembeza, E. S.


    The experimental results of synthesizing thin films (<1 {mu}m thick) of (SnO{sub 2}){sub x}(In{sub 2}O{sub 3}){sub 1-x} (x = 0.5-1 wt) nanocomposites fabricated by high-frequency magnetron sputtering of metal-oxide targets in a controlled Ar + O{sub 2} atmosphere are presented. The films, deposited on hot substrates (400 Degree-Sign C), are studied by the X-ray diffraction analysis, atomic-force microscopy, and optical and electrical methods. The effect of the synthesis conditions and film composition on the size of crystalline grains, band gap, and the concentration and mobility of free charge carriers was determined. It is shown that films of the composition (SnO{sub 2}){sub x}(In{sub 2}O{sub 3}){sub 1-x} with x = 0.9 are the most promising for applications in gas sensorics.

  7. Reactions of methyl groups on a non-reducible metal oxide: The reaction of iodomethane on stoichiometric α-Cr2O3sub>(0001)

    SciTech Connect

    Dong, Yujung; Brooks, John D.; Chen, Tsung-Liang; Mullins, David R.; Cox, David F.


    The reaction of iodomethane on the nearly stoichiometric α-Cr2O3(sub>0001) surface produces gas phase ethylene, methane, and surface iodine adatoms. The reaction is first initiated by the dissociation of iodomethane into surface methyl fragments, -CH3sub>, and iodine adatoms. Methyl fragments bound at surface Cr cation sites undergo a rate-limiting dehydrogenation reaction to methylene, =CH2. The methylene intermediates formed from methyl dehydrogenation can then undergo coupling reactions to produce ethylene via two principle reaction pathways: (1) direct coupling of methylene and (2) methylene insertion into the methyl surface bond to form surface ethyl groups which undergo β-H elimination to produce ethylene. The liberated hydrogen also combines with methyl groups to form methane. Iodine adatoms from the dissociation of iodomethane deactivate the surface by simple site blocking of the surface Cr3+ cations.

  8. Quantum phase transitions and decoupling of magnetic sublattices in the quasi-two-dimensional Ising magnet Co3sub>V2O8 in a transverse magnetic field

    SciTech Connect

    Fritsch, Katharina; Ehlers, G.; Rule, K. C.; Habicht, Klaus; Ramazanoglu, Mehmet K.; Dabkowska, H. A.; Gaulin, Bruce D.


    We study the application of a magnetic field transverse to the easy axis, Ising direction in the quasi-two-dimensional kagome staircase magnet, Co3sub>V2O8, induces three quantum phase transitions at low temperatures, ultimately producing a novel high field polarized state, with two distinct sublattices. New time-of-flight neutron scattering techniques, accompanied by large angular access, high magnetic field infrastructure allow the mapping of a sequence of ferromagnetic and incommensurate phases and their accompanying spin excitations. Also, at least one of the transitions to incommensurate phases at μ0Hc1~6.25 T and μ0Hc2~7 T is discontinuous, while the final quantum critical point at μ0Hc3sub>~13 T is continuous.

  9. 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.

  10. Coherent octave-spanning mid-infrared supercontinuum generated in As2S3sub>-silica double-nanospike waveguide pumped by femtosecond Cr:ZnS laser.


    Xie, Shangran; Tolstik, Nikolai; Travers, John C; Sorokin, Evgeni; Caillaud, Celine; Troles, Johann; Russell, Philip St J; Sorokina, Irina T


    A more than 1.5 octave-spanning mid-infrared supercontinuum (1.2 to 3.6 μm) is generated by pumping a As2S3sub>-silica "double-nanospike" waveguide via a femtosecond Cr:ZnS laser at 2.35 μm. The combination of the optimized group velocity dispersion and extremely high nonlinearity provided by the As2S3sub>-silica hybrid waveguide enables a ~100 pJ level pump pulse energy threshold for octave-spanning spectral broadening at a repetition rate of 90 MHz. Numerical simulations show that the generated supercontinuum is highly coherent over the entire spanning wavelength range. The results are important for realization of a high repetition rate octave-spanning frequency comb in the mid-infrared spectral region. PMID:27410155

  11. Infrared resonance Raman, and excitation profile studies of Os/sub 2/(O/sub 2/CCH/sub 3/)/sub 4/Cl/sub 2/ and Os/sub 2/(O/sub 2/CCD/sub 3/)/sub 4/Cl/sub 2/. The assignment of the osmium-osmium stretching vibration for a complex involving an osmium-osmium multiple bond

    SciTech Connect

    Clark, R.J.H.; Hempleman, A.J.; Tocher, D.A.


    Extensive Raman studies (1525-40 cm/sup /minus/1/) of Os/sub 2/(O/sub 2/CCH/sub 3/)/sub 4/Cl/sub 2/ have led to the identification of the three strong bands, /nu//sub 1/, /nu//sub 2/, and /nu//sub 3/, at 229, 393, and 292 cm/sup /minus/1/ to the key skeletal stretching modes, /nu/(OsOs), /nu/(OsO), and /nu/(OsCl), respectively. Raman spectra of the complex at resonance with the intense electronic band at /lambda//sub max/ = 383 nm lead to the development of a six-membered overtone progression in /nu//sub 1/ as well as combination band progressions in /nu//sub 1/ based upon one quantum of either /nu//sub 2/ or /nu//sub 3/. This indicates that the principal structural change attendant upon excitation to the resonant state is along the OsOs coordinate. Fourier transform infrared spectra (3500-40 cm/sup /minus/1/) have also been obtained. Acetate deuteriation provides conclusive evidence for many of the infrared and Raman band assignments. The study provides the first firm identification of /nu/(OsOs) for a multiply bonded species.

  12. Record figure of merit values of highly stoichiometric Sb2Te3sub> porous bulk synthesized from tailor-made molecular precursors in ionic liquids

    SciTech Connect

    Heimann, Stefan; Schulz, Stephan; Schaumann, Julian; Mudring, Anja; Stötzel, Julia; Maculewicz, Franziska; Schierning, Gabi


    We report on the synthesis of Sb2Te3sub> nanoparticles with record-high figure of merit values of up to 1.5. The central thermoelectric parameters, electrical conductivity, thermal conductivity and Seebeck coefficient, were independently optimized. Critical influence of porosity for the fabrication of highly efficient thermoelectric materials is firstly demonstrated, giving a strong guidance for the optimization of other thermoelectric materials.

  13. Synthesis of rhenium-alkene complexes from the reaction of the heterobimetallic dihydride C sub 5 H sub 5 (CO) sub 2 HRe-PtH(PPh sub 3 ) sub 2 with alkynes

    SciTech Connect

    Casey, C.P.; Rutter, E.W. Jr. )


    Heterobimetallic compounds hold great promise as catalysts since the 2 different metals have the potential of acting cooperatively. The authors report that the new heterobimetallic dihydride C{sub 5}H{sub 5}(CO){sub 2}HRe-PtH(PPh{sub 3}){sub 2} (I){sup 2} acts as a catalyst for ethylene hydrogenation and reacts stoichiometrically with alkynes to produce rhenium-alkene complexes.

  14. Oxidatively induced reductive eliminations. Kinetics and mechanism of the elimination of ethane from the 17-electron cation radical of Cp[sup *]Rh(PPh[sub 3])(CH[sub 3])[sub 2

    SciTech Connect

    Pedersen, A.; Tilset, M. )


    The dimethylrhodium compound Cp[sup *]Rh(PPh[sub 3])(CH[sub 3])[sub 2] (1; Cp[sup *] = [eta][sup 5]-C[sub 5]Me[sub 5]) undergoes an overall 2-electron oxidation at 0.04 V vs the ferrocene/ferrocenium (Fc) couple in 9:1 acetonitrile/dichloromethane, 0.1 M Bu[sub 4]N[sup +]PF[sub 6][sup [minus

  15. A fundamental study on the [(μ-Cl)3sub> Mg2 (THF)6 ]+ dimer electrolytes for rechargeable Mg batteries

    SciTech Connect

    Liu, Tianbiao; Cox, Jonathan T.; Hu, Dehong; Deng, Xuchu; Hu, Jianzhi; Hu, Mary Y.; Xiao, Jie; Shao, Yuyan; Tang, Keqi; Liu, Jun


    We present a fundamental study on [(μ-Cl)3sub> Mg2 (THF)6 ]+ dimer electrolytes using various physical methods including Subambient Pressure Ionization with Nanoelectrospray Mass spectrometry (SPIN-MS), Raman spectroscopy, 25Mg{1H} NMR, 27Al{1H} NMR and electrochemical analysis. For the first time, long time sought THF solvated [MgCl]+ species was experimentally characterized by SPIN mass spectrometry in the solution of the Mgdimer containing electrolyte, confirming the mono-Cl- abstraction reaction between MgCl2 and an Al Lewis acid. Solvated MgCl2 in the electrolyte was confirmed by Raman spectroscopy. The experimental results establish the previously proposed dimerization equilibrium of solvated [MgCl]+ and MgCl2 with [(μ-Cl)3sub>Mg2(THF)6]+. 25Mg{1H} NMR, 27Al{1H} NMR and electrochemical analysis on chloration reaction of [(μ-Cl)3sub>Mg2(THF)6]AlPh3sub>Cl with external Cl- led to further insights on the coordination chemistry of the dimer electrolyte. Finally, a comprehensive mechanism is proposed for the reversible electrochemical Mg deposition and stripping and Mg2+ and Cl- ion transports of the Mg dimer electrolytes in rechargeable Mg batteries.

  16. Synthesis, structure, solid-state thermolysis, and thermodynamic properties of new heterometallic complex Li{sub 2}Co{sub 2}(Piv){sub 6}(NEt{sub 3}){sub 2}

    SciTech Connect

    Dobrohotova, Zn.V.; Sidorov, A.A.; Kiskin, M.A.; Aleksandrov, G.G.; Gavrichev, K.S.; Tyurin, A.V.; Emelina, A.L.; Bykov, M.A.; Bogomyakov, A.S.; Malkerova, I.P.; Alihanian, A.S.; Novotortsev, V.M.; Eremenko, I.L.


    The reaction of lithium pivalate, polymeric cobalt pivalate [Co(Piv){sub 2}]{sub n}, and triethylamine in THF at 60 {sup o}S afforded the new heterometallic antiferromagnetic complex Li{sub 2}Co{sub 2}(Piv){sub 6}(NEt{sub 3}){sub 2} (2). The molecular and crystal structure of complex 2 was established and its magnetic behavior was studied. The vaporization and solid-state thermolysis of 2 were investigated. The thermodynamic characteristics of complex 2 were determined. The results of the present study show that complex 2 can be used as a potential molecular precursor for the synthesis of thin films of lithium cobaltate LiCoO{sub 2}. - Graphical abstract: The solid-state thermolysis, study of the vaporization process, and temperature dependence of S{sub p} for the new heterometallic complex Co{sub 2}Li{sub 2}(Piv){sub 6}(NEt{sub 3}){sub 2} were performed. Decomposition of Co{sub 2}Li{sub 2}(Piv){sub 6}(NEt{sub 3}){sub 2} results in the formation of LiCoO{sub 2}.

  17. The dominant factors affecting the memory characteristics of (Ta{sub 2}O{sub 5}){sub x}(Al{sub 2}O{sub 3}){sub 1−x} high-k charge-trapping devices

    SciTech Connect

    Gong, Changjie; Lan, Xuexin; Yin, Qiaonan; Ou, Xin; Liu, Jinqiu; Sun, Chong; Wang, Laiguo; Lu, Wei; Yin, Jiang Xu, Bo; Xia, Yidong; Liu, Zhiguo; Li, Aidong


    The prototypical charge-trapping memory devices with the structure p-Si/Al{sub 2}O{sub 3}/(Ta{sub 2}O{sub 5}){sub x}(Al{sub 2}O{sub 3}){sub 1−x}/Al{sub 2}O{sub 3}/Pt(x = 0.5, 0.3, and 0.1) were fabricated by using atomic layer deposition and RF magnetron sputtering techniques. A memory window of 7.39 V with a charge storage density of 1.97 × 10{sup 13 }cm{sup −2} at a gate voltage of ±11 V was obtained for the memory device with the composite charge trapping layer (Ta{sub 2}O{sub 5}){sub 0.5}(Al{sub 2}O{sub 3}){sub 0.5}. All memory devices show fast program/erase speed and excellent endurance and retention properties, although some differences in their memory performance exist, which was ascribed to the relative individual band alignments of the composite (Ta{sub 2}O{sub 5}){sub x}(Al{sub 2}O{sub 3}){sub 1−x} with Si.

  18. Synthesis and X-ray diffraction study of [UO{sub 2}(NO{sub 3}){sub 2}(H{sub 2}O){sub 2}] {center_dot} 2C{sub 12}H{sub 18}O

    SciTech Connect

    Serezhkina, L. B.; Vologzhanina, A. V.; Klynin, E. S.; Korlyukov, A. A.; Moiseev, I. K.; Serezhkin, V. N.


    The compound [UO{sub 2}(NO{sub 3}){sub 2}(H{sub 2}O){sub 2}] {center_dot} 2C{sub 12}H{sub 18}O was synthesized and studied by IR spectroscopy and X-ray diffraction. The structure consists of the neutral island groups [UO{sub 2}(NO{sub 3}){sub 2}(H{sub 2}O){sub 2}], which belong to the crystal-chemical group AB{sup 01}{sub 2}M{sup 1}{sub 2} (A = UO{sub 2}{sup 2+}, B{sup 01} = NO{sub 3}{sup -}, M{sup 1} = H{sub 2}O) of uranyl complexes, and 1-adamantyl methyl ketone molecules. The characteristic features of the association of the complexes [UO{sub 2}(NO{sub 3}){sub 2}(H{sub 2}O){sub 2}] and 1-adamantyl methyl ketone molecules in the crystal structure via hydrogen bonds are considered with the use of Voronoi-Dirichlet polyhedra.

  19. Influence of Mn concentration on magnetic topological insulator MnxBi2−xTe3sub> thin-film Hall-effect sensor

    SciTech Connect

    Ni, Y.; Zhang, Z.; Nlebedim, I. C.; Hadimani, R. L.; Jiles, D. C.


    Hall-effect (HE) sensors based on high-quality Mn-doped Bi2Te3sub> topological insulator (TI) thin films have been systematically studied in this paper. Improvement of Hall sensitivity is found after doping the magnetic element Mn into Bi2Te3sub>. The sensors with low Mn concentrations, MnxBi2-xTe3sub>, x = 0.01 and 0.08 show the linear behavior of Hall resistance with sensitivity about 5 Ω/T. And their Hall sensitivity shows weak dependence on temperature. For sensors with high Mn concentration (x = 0.23), the Hall resistance with respect to magnetic field shows a hysteretic behavior. Moreover, its sensitivity shows almost eight times as high as that of the HE sensors with low Mn concentration. The highest sensitivity can reach 43 Ω/T at very low magnetic field. This increase of Hall sensitivity is caused by the occurrence of anomalous HE (AHE) after ferromagnetic phase transition. Our work indicates that the magnetic-element-doped TIs with AHE are good candidates for HE sensors.

  20. Influence of Ga-concentration on the electrical and magnetic properties of magnetoelectric CoGaxFe2–xO4/BaTiO3sub> 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–xO4/BaTiO3sub> 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–xO4/BaTiO3sub> composites. As a result, the present work is beneficial to the practical application of composite CoFe2O4/BaTiO3sub>-based multiferroic materials.

  1. Mid-infrared supercontinuum generation in step-index As2S3sub> fibers pumped by a nanosecond shortwave-infrared supercontinuum pump source.


    Yao, Jinmei; Zhang, Bin; Yin, Ke; Yang, Linyong; Hou, Jing; Lu, Qisheng


    A supercontinuum (SC) source spanning from 2 to 4 μm is demonstrated in As2S3sub>-chalcogenide fibers pumped by a nanosecond supercontinuum pump source in the normal dispersion region. In this experiment, two pieces of 3-m-long step-index As2S3sub> fiber with different core diameters of 7 μm and 9 μm are pumped by a 1.9-2.5 μm nanosecond supercontinuum source. The zero dispersion wavelengths are both beyond 6.6 μm, thus cascaded stimulated Raman scattering is believed to be the dominant mechanism responsible for spectral broadening. With a low peak pump power of ~2.9 kW, both of the output spectra have extended to 4 μm with enhanced power distribution in the MIR region. The maximum output power of the mid-infrared supercontinua is ~140 mW. To the best of our knowledge, it is the first supercontinuum extenting to 4 μm in an As2S3sub> fiber pumped by shortwave-infrared SC pluses in the normal dispersion region. PMID:27410660

  2. Zero Thermal Expansion and Ferromagnetism in Cubic Sc1-xMxF3sub> (M = Ga, Fe) over a Wide Temperature Range

    SciTech Connect

    Hu, Lei; Chen, Jun; Fan, Longlong; Ren, Yang; Rong, Yangchun; Pan, Zhao; Deng, Jinxia; Yu, Ranbo; Xing, Xianran


    The rare physical property of zero thermal expansion (ZTE) is intriguing because neither expansion nor contraction occurs with temperature fluctuations. Most ZTE, however, occurs below room temperature. It is a great challenge to achieve isotropic ZTE at high temperatures. Here we report the unconventional isotropic ZTE in the cubic (Sc1-xMx)F3sub> (M = Ga, Fe) over a wide temperature range (linear coefficient of thermal expansion (CTE), αl = 2.34 × 10-7 K-1, 300-900 K). Such a broad temperature range with a considerably negligible CTE has rarely been documented. The present ZTE property has been designed using the introduction of local distortions in the macroscopic cubic lattice by heterogeneous cation substitution for the Sc site. Even though the macroscopic crystallographic structure of (Sc0.85Ga0.05Fe0.1)F3sub> adheres to the cubic system (Pm3-m) according to the results of Xray diffraction, the local structure exhibits a slight rhombohedral distortion. This is confirmed by pair distribution function analysis of synchrotron radiation Xray total scattering. This local distortion may weaken the contribution from the transverse thermal vibration of fluorine atoms to negative thermal expansion, and thus may presumably be responsible for the ZTE. In addition, the present ZTE compounds of (Sc1-xMx)F3sub> can be functionalized to exhibit high-Tc ferromagnetism and a narrow-gap semiconductor feature. The present study shows the possibility of obtaining ZTE materials with multifunctionality in future work.

  3. Low-Temperature X-ray Diffraction Studies of [(CH{sub 3}){sub 2}NH{sub 2}]{sub 5}Cd{sub 3}Cl{sub 11} Crystals

    SciTech Connect

    Sheleg, A.U.; Zub, E.M.; Yachkovskii, A.Ya.; Kirpichnikova, L.F.


    [(CH{sub 3}){sub 2}NH{sub 2}]{sub 5}Cd{sub 3}Cl{sub 11} crystals are grown by the method of isothermal evaporation from saturated aqueous solutions containing dimethylamine and cadmium chlorides, [(CH{sub 3})2NH{sub 2}]Cl and CdCl{sub 2.5}H{sub 2}O. The crystal grown are studied by the X-ray diffraction method. It is established that the crystals are orthorhombic with the unit-cell parameters at room temperature a = 18.115 {+-} 0.004 A, b = 11.432 {+-} 0.002 A, and c = 15.821 {+-} 0.003 A. The unit-cell parameters a, b, and c of the [(CH{sub 3}){sub 2}NH{sub 2}]{sub 5}Cd{sub 3}Cl{sub 11} crystals are measured as functions of temperature in the temperature range 100-320 K. The data obtained were used to determine the thermal expansion coefficients along the main crystallographic axes. The temperature curves of the unit-cell parameters and thermal expansion coefficients showed pronounced anomalies in the vicinity of the temperatures T{sub 1} = 120, T{sub 2} = 150, and T{sub 3} = 180 K corresponding to the phase transitions in the [(CH{sub 3}){sub 2}NH{sub 2}]{sub 5}Cd{sub 3}Cl{sub 11} crystals. The crystals are also characterized by a pronounced anisotropy of thermal expansion.

  4. Thermodynamic effects of calcium and iron oxides on crystal phase formation in synthetic gasifier slags containing from 0 to 27wt.% V2O3sub>

    SciTech Connect

    Nakano, Jinichiro; Duchesne, Marc; Bennett, James; Kwong, Kyei -Sing; Nakano, Anna; Hughes, Robin


    Thermodynamic phase equilibria in synthetic slags (Al2O3sub>–CaO–FeO–SiO2–V2O3sub>) were investigated with 0–27 wt.% vanadium oxide corresponding to industrial coal–petroleum coke (petcoke) feedstock blends in a simulated gasifier environment. Samples encompassing coal–petcoke mixed slag compositions were equilibrated at 1500 °C in a 64 vol.% CO/36 vol.% CO2 atmosphere (Po2 ≈ 10–8 atm at 1500 °C) for 72 h, followed by rapid water quench, then analyzed by inductively coupled plasma optical emission spectrometry, X-ray diffractometry, and scanning electron microscopy with wavelength dispersive spectroscopy. With increasing CaO content, FeO content, or both; the slag homogeneity region expanded and a composition range exhibiting crystals was reduced. The mullite (Al6Si2O13) crystalline phase was not present in the slags above 9 wt.% FeO while the karelianite (V2O3sub>) crystalline phase was always present in compositions studied if a sufficient amount of vanadium existed in the slag. Furthermore, based on the present experimental equilibrium evaluation, a set of isothermal phase diagrams showing effects of CaO and FeO on thermodynamic phase stabilities in the vanadium-bearing slags is proposed. Some uses of the diagrams for potential industrial practice are discussed.

  5. Spectroscopy and structure of quadruply bonded complexes under extreme pressure (Re sub 2 X sub 8 sup 2 minus , Mo sub 2 Cl sub 4 (PMe sub 3 ) sub 4 )

    SciTech Connect

    Morris, D.E.; Tait, C.D.; Dyer, R.B.; Schoonover, J.R.; Hopkins, M.D.; Sattelberger, A.P.; Woodruff, W.H. Univ. of Pittsburgh, PA )


    Application of pressure (up to 150 kbar, where 1 kbar = 986.9 atm = 0.1 GPa) to solutions of Re{sub 2}X{sub 8}{sup 2{minus}} (X = F, Cl, Br) and Mo{sub 2}Cl{sub 4}(PMe{sub 3}){sub 4} results in smooth, continuous changes in experimental observables related to metal-metal bond length and, for the Re complexes, torsional angle (X-Re-Re-X dihedral angle). Resonance Raman studies show that increasing pressure engenders an increase in the frequency of the metal-metal stretching mode for all of the species studied, and this change is empirically correlated with a decrease in metal-metal bond length. Large red shifts in the energy of the {sup 1}({delta} {yields} {delta}*) transitions with increased pressure for Re{sub 2}Br{sub 8}{sup 2{minus}} and Re{sub 2}Cl{sub 8}{sup 2{minus}}, in contrast to the relative insensitivity of Re{sub 2}F{sub 8}{sup 2{minus}} absorption and Mo{sub 2}Cl{sub 4}(PMe{sub 3}){sub 4} fluorescence transitions, imply a tendency for the former complexes to distort torsionally from an eclipsed configuration toward a staggered configuration due to pressure-induced steric repulsion of the chloride and bromide ligands. Integrated absorption intensities further show that, at higher pressures, even Re{sub 2}F{sub 8}{sup 2{minus}} undergoes some torsional distortion, whereas the steric repulsion of adjacent phosphines located at a 90{degree} dihedral angle on opposite Mo atoms prevents Mo{sub 2}Cl{sub 4}(PMe{sub 3}){sub 4} from distorting along the torsional coordinate. 28 refs., 7 figs., 1 tab.

  6. Mid-infrared supercontinuum generation based on cascaded Raman scattering in a few-mode As2S3sub> fiber pumped by a thulium-doped fiber laser.


    Yao, Jinmei; Zhang, Bin; Yin, Ke; Yang, Linyong; Hou, Jing; Lu, Qisheng


    By pumping a 1.7-m-long As2S3sub> fiber at 2050 nm directly, a fiber-based mid-infrared supercontinuum (SC) source with an output power of 366 mW is demonstrated. This is the first experimental demonstration to obtain such a mid-infrared SC in a piece of chalcogenide fiber pumped at 2 μm directly. The cut-off wavelength of the As2S3sub> fiber is 3.5 μm, indicating that it could support several modes at around 2 μm. It is found that nonlinear spectral broadening mechanisms in the few-mode chalcogenide fiber could be affected through adjusting the butt-coupling position. That is because different positions will excite different modes that correspondingly possess different nonlinearity and dispersion characteristics. When stimulated Raman scattering (SRS) corresponding to the excitation of the fundamental mode becomes dominant in this few-mode fiber, an efficient cascaded SRS-based SC is obtained with five Stokes peaks ranging from 2 μm to 3.4 μm. Results from numerical simulation are in accord with the experimental results, showing that it is feasible to obtain an SRS based mid-infrared SC in a step-index As2S3sub> fiber by using a 2 μm high peak power picosecond laser to pump directly. PMID:27410625

  7. The Effect of Synthetic Method and Annealing Temperature on Metal Site Preference in Al1-xGaxFeO3sub>

    SciTech Connect

    Walker, James D.S.; Grosvenor, Andrew P.


    Magnetoelectric materials couple both magnetic and electronic properties, making them attractive for use in multifunctional devices. The magnetoelectric AFeO3sub> compounds (Pna21; A = Al, Ga) have received attention as the properties of the system depend on composition as well as the synthetic method used. Al1–xGaxFeO3sub> (0 ≤ x ≤ 1) was synthesized by the sol–gel and coprecipitation methods and studied by X-ray absorption near-edge spectroscopy (XANES). Al L2,3⁻, Ga K-, and Fe K-edge XANES spectra were collected to examine how the average metal coordination number (CN) changes with the synthetic method. Al and Fe were found to prefer octahedral sites, while Ga prefers the tetrahedral site. It was found that composition played a larger role in determining site occupancies than synthetic method. Samples made by the sol–gel or ceramic methods (reported previously; Walker, J. D. S.; Grosvenor, A. P. J. Solid State Chem. 2013, 197, 147–153) showed smaller spectral changes than samples made via the coprecipitation method. This is attributed to greater ion mobility in samples synthesized via coprecipitation as the reactants do not have a long-range polymeric or oxide network during synthesis like samples synthesized via the sol–gel or ceramic method. Increasing annealing temperature increases the average coordination number of Al, and to a lesser extent Ga, while the average coordination number of Fe decreases. This study indicates that greater disorder is observed when the Al1–xGaxFeO3sub> compounds have high Al content, and when annealed at higher temperatures.

  8. The first Fe-based Na+-ion cathode with two distinct types of polyanions: Fe3sub>P5SiO19

    SciTech Connect

    Kan, W. H.; Huq, A.; Manthiram, A.


    We report the synthesis, structure, and electrochemistry of the first Na+-ion cathode with two distinct types of polyanions: Fe3sub>P5SiO19. The Fe-based cathode has a reversible capacity of ca. 70 mAh g-1; ca. 1.7 Na+ ions per formula can be inserted/extracted at an average voltage of 2.5 V versus Na+/Na.

  9. Resolving the grain boundary and lattice impedance of hot-pressed Li7La3sub>Zr2O12 garnet electrolytes

    SciTech Connect

    Tenhaeff, Wyatt E.; Wang, Yangyang; Sokolov, Alexei P.; Wolfenstine, Jeff; Sakamoto, Jeffrey; Dudney, Nancy J.; Rangasamy, Ezhiyl


    Here, the cubic-stabilized garnet solid electrolyte with a nominal composition of Li6.28Al0.24La3sub>Zr2O12 is thoroughly characterized by impedance spectroscopy. By varying the frequency of the applied AC signal over 11 orders of magnitude for characterizations from –100 to +60 °C, the relative contributions of grain and grain boundary conduction are unambiguously resolved.

  10. Sr{sub 3}Bi{sub 2}(SeO{sub 3}){sub 6}·H{sub 2}O: A novel anionic layer consisting of second-order Jahn–Teller (SOJT) distortive cations

    SciTech Connect

    Ahn, Hyun Sun; Lee, Eun Pyo; Chang, Hong-Young; Lee, Dong Woo; Ok, Kang Min


    A new layered bismuth selenite hydrate material, Sr{sub 3}Bi{sub 2}(SeO{sub 3}){sub 6}·H{sub 2}O has been synthesized through a hydrothermal reaction using SrCO{sub 3}, Bi{sub 2}O{sub 3}, SeO{sub 2}, and water as reagents. The crystal structure of the reported material has been determined by single crystal X-ray diffraction analysis. The anionic layered framework of Sr{sub 3}Bi{sub 2}(SeO{sub 3}){sub 6}·H{sub 2}O consists of polyhedra of second-order Jahn–Teller (SOJT) distortive cations, Bi{sup 3+} and Se{sup 4+}. Attributable to the variable and asymmetric coordination geometry of the constituent cations, a rich structural chemistry including uni-dimensional bands and linkers is observed in the layer. The material is thermally stable up to about 390 °C and starts decomposing due to the sublimation of SeO{sub 2} above the temperature. The UV–vis diffuse reflectance spectrum suggests a band gap of 3.3 eV. Elemental analysis, infrared spectrum, local dipole moment calculations, and electronic structure calculations are also reported. - Graphical abstract: Ball-and-stick and polyhedral representation of Sr{sub 3}Bi{sub 2}(SeO{sub 3}){sub 6}·H{sub 2}O in the ab-plane. The stereoactive lone pairs are visualized around the Bi{sup 3+} and Se{sup 4+} as lobelike isosurfaces through ELF calculations with η=0.9. - Highlights: • A novel layered bismuth selenite, Sr{sub 3}Bi{sub 2}(SeO{sub 3}){sub 6}·H{sub 2}O has been hydrothermally synthesized. • The layer is only composed of second-order Jahn–Teller distortive cations in asymmetric environments. • The stereoactive lone pairs are visualized as lobelike isosurfaces through ELF calculations.

  11. Circular dichroism of Eu/sup 3 +/ and Nd/sup 3 +/ in a K/sub 3/Nd/sub 2/(NO/sub 3/)/sub 9/ single crystal

    SciTech Connect

    Chatterjee, P.K.; Chowdhury, M.


    The low-resolution circular dichroism in (CD) and absorption spectra of doped Nd/sup 3 +/ crystals primarily with a view to verify the expectations regarding low-resolution lanthanide optical activity is presented. In order to compare the CD of the Nd/sup 3 +/ transition, which are commonly considered as electric-dipole allowed, with that of primarily magnetic-dipole-allowed Eu/sup 3 +/ transitions having an identical environment, we have grown and studied a single crystal of K/sub 3/Nd/sub 2/(NO/sub 3/)/sub 9/ with Eu/sup 3 +/ as dopant.

  12. Connecting thermoelectric performance and topological-insulator behavior: Bi2Te3sub> and Bi2Te2Se from first principles

    SciTech Connect

    Shi, Hongliang; Parker, David S.; Du, Mao-Hua; Singh, David J.


    Thermoelectric performance is of interest for numerous applications such as waste-heat recovery and solid-state energy conversion and will be seen to be closely connected to topological-insulator behavior. In this paper, we here report first-principles transport and defect calculations for Bi2Te2Se in relation to Bi2Te3sub>. The two compounds are found to contain remarkably different electronic structures in spite of being isostructural and isoelectronic. We also discuss these results in terms of the topological-insulator characteristics of these compounds.

  13. Thermal stability and radiation resistance of tin valent states in the structure of the (As{sub 2}Se{sub 3}){sub 1-z}(SnSe){sub z-x}(GeSe){sub x} semiconductor glasses

    SciTech Connect

    Bordovskii, G. A.; Kastro, R. A.; Marchenko, A. V.; Nemov, S. A.; Seregin, P. P.


    The ratio between the content of bivalent and tetravalent tin atoms in the (As{sub 2}Se{sub 3}){sub 1-z}(SnSe){sub z-x}(GeSe){sub x} glasses depends on the rate of quenching of the alloy and on its temperature. Irradiation of these glasses with {gamma}-ray photons brings about a partial oxidation of bivalent tin with formation of amorphous (finely divided) SnO{sub 2} phase blocked by the glass, so that the physicochemical properties of the glasses (density, microhardness, glassformation temperature, and the electrical-conductivity activation energy) are virtually unaffected by irradiation.

  14. Pressure tuning of the charge-density wave in the halogen-bridged transition-metal solid Pt[sub 2]Br[sub 6](NH[sub 3])[sub 4

    SciTech Connect

    Kanner, G.S.; Gammel, J.T.; Love, S.P.; Johnson, S.R.; Scott, B.; Swanson, B.I. )


    We report the pressure dependence up to 95 kbar of Raman-active stretching modes in the quasi-one-dimensional [ital MX] chain solid Pt[sub 2]Br[sub 6](NH[sub 3])[sub 4]. The data indicate that a predicted pressure-induced insulator-to-metal transition does not occur, but are consistent with the solid undergoing either a three-dimensional structural distortion or a transition from a charge-density wave to another broken-symmetry ground state. We show that such a transition can be well modeled within a Peierls-Hubbard Hamiltonian.

  15. Multiple bonds between transition metals and main-group elements. 73. Synthetic routes to rhenium(V) alkyl and rhenium(VII) alkylidyne complexes. X-ray crystal structures of (. eta. sup 5 -C sub 5 Me sub 5 )Re( double bond O)(CH sub 3 )(CH sub 2 C(CH sub 3 ) sub 3 ) and (. eta. sup 5 -C sub 5 Me sub 5 )(Br) sub 3 Re triple bond CC(CH sub 3 ) sub 3

    SciTech Connect

    Herrmann, W.A.; Felixberger, J.K.; Anwander, R.; Herdtweck, E.; Kiprof, P.; Riede, J. )


    Dialkyloxo({eta}{sup 5}pentamethylcyclopentadienyl)rhenium(V) complexes ({eta}{sup 5}-C{sub 5}Me{sub 5})Re({double bond}O)(CH{sub 3})R{prime}(R{prime} = C{sub 2}H{sub 5}, CH{sub 2}Si(CH{sub 3}){sub 3}, CH{sub 2}C(CH{sub 3}){sub 3}), 1c-e, have become accessible through alkylation of ({eta}{sup 5}-C{sub 5}Me{sub 5})Re({double bond}O)(Cl)(CH{sub 3}) (7) with R{prime}MgCl. 1c-e are the first rhenium complexes containing different alkyl ligands. The neopentyl derivative 1e (R{prime} = CH{sub 2}C(CH{sub 3}){sub 3}) crystallizes in the orthorhombic space group Pbca with a = 960.7 (2), b = 2.844.5 (4), c = 1,260.7 (2) pm, and Z = 8. The X-ray crystal structure was refined to R{sub W} = 3.9%. The chiral molecule shows a distorted tetrahedral geometry around the rhenium center. The tribromide 3b has been structurally characterized. Brown crystals of 3b belong to space group P2{sub 1}/c with unit cell dimensions a = 1,311.5 (2), b = 723.0 (1), c = 1,901.6 (2) pm, {beta} = 92.68 (1){degree}, and Z = 4. The structure exhibits a four-legged piano stool geometry with no trans influence of the neopentylidyne ligand to the bromine atom.

  16. New adamantane-like mercury-chalcogen cages. 2. Synthetic and multinuclear ( sup 31 P, sup 77 Se, sup 125 Te, sup 199 Hg) magnetic resonance study of tellurolate-bridged mercury(III) clusters ((. mu. -TeR) sub 6 (HgPR prime sub 3 ) sub 4 ) sup 2+ and ((. mu. -TeR) sub 6 (Hg)(HgPR prime sub 3 ) sub 3 ) sup 2+ and related species with mixed-bridging chalcogenates

    SciTech Connect

    Dean, P.A.W.; Manivannan, V.; Vittal, J.J. )


    The salts (({mu}-TePh){sub 6}(HgPR{prime}{sub 3}){sub 3}(Hg))(ClO{sub 4}){sub 2} (R{prime} = Ph, 4-C{sub 6}H{sub 4}Me, 4-C{sub 6}H{sub 4}Cl) are preparable from Hg(TePh){sub 2}, Mg(PR{prime}{sub 3}){sub 2}(ClO{sub 4}){sub 2}, and PR{prime}P{sub 3} in a 3:1:1 ratio in CH{sub 2}Cl{sub 2} or CHCl{sub 3}. The new cations have been characterized in CH{sub 2}Cl{sub 2} and DMF by multinuclear ({sup 31}P, {sup 125}Te, {sup 199}Hg) magnetic resonance and shown to be of adamantanoid structure with novel tellurolate bridging. These spectra provide clear evidence for preferential formation of one (R{prime} = Ph) or a mixture of both (R{prime} = 4-C{sub 6}H{sub 4}Cl, in DMF solution) of the two C{sub 3} isomers that are possible for adamantane-like ({mu}-TeR){sub 6}M{sub 4} as a result of inversion at the pyramidal Te atoms. Such preferential isomer formation has not been demonstrated previously for any adamantanoid chalcogenate-bridge ({mu}-ER){sub 6}M{sub 4} in solution. Isomer formation at various temperatures is reported. For the cations with R = Ph, the rate of inversion at Te varies with R{prime} in the order alkyl > 4-C{sub 6}H{sub 4}Me > Ph > 4-C{sub 6}H{sub 4}Cl. When R = Ph, R{prime} = 4-C{sub 6}H{sub 4}Me, NMR spectra ({sup 31}P, {sup 77}Se, {sup 125}Te, {sup 199}Hg) of mixtures of ((TeR){sub 6}(HgPR{prime}{sub 3}){sub 4}){sup 2+} and (({mu}-ER){sub 6}(HgPR{prime}{sub 3}){sub 4}){sup 2+} (E = S, Se) provide evidence for the formation of the mixed-chalcogen cores ({mu}-Te){sub 6-m}({mu}-E){sub m}Hg{sub 4}. 35 refs., 8 figs., 3 tabs.

  17. Tetrahedrally coordinated disordered Cu2SnS3sub>-Cu2ZnSnS4-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 Cu2SnS3sub>, Cu2ZnSnS4 (CZTS), and ZnS as (Cu2SnS3sub>)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.

  18. Growth Temperature Dependence of Si Doping Efficiency and Compensating Deep Level Defect Incorporation in Al0.7Ga0.3sub>N

    SciTech Connect

    Armstrong, Andrew; Moseley, Michael William; Allerman, Andrew A.; Crawford, Mary H.; Wierer, Jonathan


    The growth temperature dependence of Si doping efficiency and deep level defect formation was investigated for n-type Al0.7Ga0.3sub>N. It was observed that dopant compensation was greatly reduced with reduced growth temperature. Furthermore, deep level optical spectroscopy and lighted capacitance-voltage were used to understand the role of acceptor-like deep level defects on doping efficiency. Deep level defects were observed at 2.34 eV, 3.56 eV, and 4.74 eV below the conduction band minimum. The latter two deep levels were identified as the major compensators because the reduction in their concentrations at reduced growth temperature correlated closely with the concomitant increase in free electron concentration. Possible mechanisms for the strong growth temperature dependence of deep level formation are considered, which includes thermodynamically driven compensating defect formation that can arise for a semiconductor with very large band gap energy, such as Al0.7Ga0.3sub>N.

  19. Methylene migration and coupling on a non-reducible metal oxide: The reaction of dichloromethane on stoichiometric α-Cr2O3sub>(0001)

    SciTech Connect

    Dong, Yujung; Brooks, John D.; Chen, Tsung-Liang; Mullins, David R.; Cox, David F.


    The reaction of CH2Cl2 over the nearly-stoichiometric α-Cr2O3sub>(0001) surface produces gas phase ethylene, methane and surface chlorine adatoms. The reaction is initiated by the decomposition of CH2Cl2 into surface methylene and chlorine. Photoemission indicates that surface cations are the preferred binding sites for both methylene and chlorine adatoms. Two reaction channels are observed for methylene coupling to ethylene in temperature-programmed desorption (TPD). A desorption-limited, low-temperature route is attributed to two methylenes bound at a single site. The majority of ethylene is produced by a reaction-limited process involving surface migration (diffusion) of methylene as the rate-limiting step. DFT calculations indicate the surface diffusion mechanism is mediated by surface oxygen anions. The source of hydrogen for methane formation is adsorbed background water. Chlorine adatoms produced by the dissociation of CH2Cl2 deactivate the surface by simple site-blocking of surface Cr3+ sites. Finally, a comparison of experiment and theory shows that DFT provides a better description of the surface chemistry of the carbene intermediate than DFT+U using reported parameters for a best representation of the bulk electronic properties of α-Cr2O3sub>.

  20. Evidence and detailed study of a second-order phase transition in the (C{sub 6}H{sub 11}NH{sub 3}){sub 2}[PbI{sub 4}] organic-inorganic hybrid material

    SciTech Connect

    Yangui, A.; Pillet, S.; Garrot, D.; Boukheddaden, K.; Triki, S.; Abid, Y.


    The thermal properties of the organic-inorganic hybrid material (C{sub 6}H{sub 11}NH{sub 3}){sub 2}[PbI{sub 4}] are investigated using diffuse reflectivity, spectroscopic ellipsometry, differential scanning calorimetry, Raman spectroscopy, and X-ray diffraction. The diffuse reflectivity, performed in heating mode, clearly evidences the presence of a singularity at 336 K. This is confirmed by the temperature dependence of the spectroscopic ellipsometry spectra, which points out a second-order phase transition at 336 K with a critical exponent ∼0.5. Differential scanning calorimetry measurements on a polycrystalline powder of (C{sub 6}H{sub 11}NH{sub 3}){sub 2}[PbI{sub 4}] show a reversible phase transition detected at T{sub C} = 336 K without hysteresis. Raman spectroscopy data suggest that this transition arises from a change in the interactions between inorganic sheets (([PbI{sub 4}]{sup 2−}){sub ∞}) and organic protonated molecules ([C{sub 6}H{sub 11}NH{sub 3}]{sup +}). The structural analysis from power X-ray diffraction reveals an incomplete order-disorder transition of the cyclohexylammonium cation, causing a subtle contraction of the inter-plane distance. The transition results from repulsive close contacts between the organic molecules in the interlayer spacing.

  1. Experimental observations of the effects of shear rates and particle concentration on the viscosity of Fe2O3sub>-deionized water nanofluids

    SciTech Connect

    Phuoc, Tran X.; Massoudi, Mehrdad


    We report here some experimental observations on the effects of the shear rates and particle volume fractions on the shear stress and the viscosity of Fe2O3sub>-DW nanofluids with Polyvinylpyrrolidone (PVP) or Poly(ethylene oxide), PEO, as a dispersant. The measurements were performed using a Brookfield DV-II Pro Viscometer with a small sample adapter (SSA18/13RPY). The results reported here clearly demonstrate that these fluids had a yield stress and behaved as shear-thinning non-Newtonian fluids. The yield stress decreased to the Newtonian limit, as the particle volume fraction decreased and still existed even at very low particle volume fractions. It was observed that the prepared Fe2O3sub>-DW-0.2% PVP nanofluids with particle volume fraction Φ less than 0.02 still behaved as a Newtonian fluid. As the volume fraction was increased beyond 0.02, the fluid became non-Newtonian with shear-thinning behavior. Similar results were also observed when DW-0.2% PEO was used. The suspension, however, exhibited its non-Newtonian, shear-thinning behavior at Φ as low as 0.02.

  2. Drift Transport in Al2O3sub>-Sheathed 3-D Transparent Conducting Oxide Photoanodes Observed in Liquid Electrolyte-Based Dye-Sensitized Solar Cells

    SciTech Connect

    Liu, Fa-Qian; Zhu, Kai; Li, Tao; Xu, Tao


    It has long been taken for granted that electron transport in liquid-electrolyte-based dye-sensitized solar cells (DSSCs) undergoes an ambipolar diffusive transport due to the strong coupling between electrons in the photoanode and the nearby mobile cations in liquid electrolyte, which, therefore, screens off any electric field in the photoanodes and consequently eliminates the possibility for drift transport. In this work, we demonstrate the existence of drift transport in liquid electrolyte-based DSSCs using a thin Al2O3sub>-sheathed 3-dimentional (3-D) fluorinated tin oxide (FTO), as photoanodes. The electron diffusion rate in such 3-D TCO based DSSC exhibits a striking enhancement to the value of ~10–2 cm2/s, about 104 times faster than that of the TiO2 nanoparticle-based DSSCs. The electron diffusion coefficient is independent of the photoelectron density, while intensity modulated photocurrent spectroscopy (IMPS) suggests that the time constants of electron transport exhibit a linear dependence on the bias voltage, a strong indication of drift transport behavior in this 3-D FTO hollow nanobeads-based DSSC, despite the use of liquid I/I3sub> electrolyte.

  3. (CN{sub 3}H{sub 6}){sub 2} {center_dot} Zn(HPO{sub 3}){sub 2}: A Three-Dimensional Framework Zincophosphite Containing Polyhedral 12-Rings

    SciTech Connect



    The solution-mediated synthesis and single crystal structure of (CN{sub 3}H{sub 6}){sub 2} {center_dot} Zn(HPO{sub 3}){sub 2} are reported. This phase is built up from a three-dimensional framework of vertex-linked ZnO{sub 4} and HPO{sub 3} building units encapsulating the extra-framework guanidinium cations. The structure is stabilized by template-to-framework hydrogen bonding. The inorganic framework shows a surprising similarity to those of some known zinc phosphates. Crystal data: (CN{sub 3}H{sub 6}){sub 2} {center_dot} Zn(HPO{sub 3}){sub 2}, AI,= 345.50, orthorhombic, space group Fdd2 (No. 43), a = 15.2109 (6) {angstrom}, b = 11.7281 (5) {angstrom}, c = 14.1821 (6) {angstrom}, V = 2530.0 (4){angstrom}{sup 3}, Z = 8, T = 298 (2)K, R(F) = 0.020, wR(F) = 0.025.

  4. The high temperature superconductor YBa2Cu3sub>O7-δ: symmetry of the order parameter, and gradiometers for biomagnetic applications

    SciTech Connect

    Kouznetsov, Konstantin Alexander


    The cuprate YBa2Cu3sub>O7-δ is the material that drives the majority of the technological applications of high transition temperature (Tc) superconductors, particularly in the area of superconducting electronics. Despite the widespread use of high-Tc superconducting materials in a variety of applications, the nature of the superconducting state in these materials remains unknown since their discovery more than a decade ago. Many properties of the high-Tc superconductors are determined by their order parameter, which is a wavefunction describing the superconducting condensate. The symmetry of the order parameter in cuprates has been the subject of intensive investigation, leading to conflicting sets of results. Some experiments supported conventional, s-wave symmetry of the order parameter, while others indicated an unconventional, d-wave symmetry. The first part of this thesis is an experimental study of the symmetry of the order parameter in YBa2Cu3sub>O7-δ. A new class of phase sensitive experiments is described that involve Josephson tunneling along the c-axis of twinned crystals of YBa2Cu3sub>O7-δ. These experiments showed that an s-wave component must reverse sign across the twin boundary, providing direct evidence for a mixed, s+d symmetry of the order parameter in YBa2Cu3sub>O7-δ, and thereby reconciling two conflicting sets of previous findings and establishing the dominant d-wave pairing symmetry. The second part of the thesis focuses on practical applications of YBa2Cu3sub>O7-δ in superconducting electronics. The authors introduce a novel Superconducting Quantum Interference Device (SQUID) gradiometer. The principle of operation of these long baseline high-T{sub c} SQUID gradiometers is based on the inductive coupling of the input coil of a planar flux transformer to the

  5. Local Structure of amorphous (PbO){sub x}[(B{sub 2}O{sub 3}){sub 1-z}(Al{sub 2}O{sub 3}){sub z}]{sub y} (SiO{sub 2}){sub y} Dielectric Materials by Multinuclear Solid State NMR

    SciTech Connect

    Sawvel, A; Chinn, S; Bourcier, W; Maxwell, R


    Structural speciation of glasses in the systems PbO-B{sub 2}O{sub 3}-SiO{sub 2}, PbO-B{sub 2}O{sub 3}-Al{sub 2}O{sub 3}-SiO{sub 2}, and PbO-Al{sub 2}O{sub 3}-SiO{sub 2} were studied using solid-state {sup 29}Si, {sup 27}Al, {sup 11}B, and {sup 207}Pb nuclear magnetic resonance (NMR) and Raman spectroscopy. Application of these methods provided insight into the role of Al{sub 2}O{sub 3} incorporation in the lead-borosilicate glass networks. The general composition range studied was (PbO){sub x} [(B{sub 2}O{sub 3}){sub 1-z} (Al{sub 2}O{sub 3})z]{sub y}(SiO{sub 2}){sub y} where x = 0.35, 0.5, and 0.65, y = (1-x)/2 and z = 0.0, 0.5 and 1.0. Additional insight was obtained via {sup 27}Al 2D-3QMAS experiments. The {sup 207}Pb spin echo mapping spectra showed a transition from ionic (Pb{sup 2+}) to covalently bound lead species with increased PbO contents in the borosilicate glasses. The addition of aluminum to the glass network further enhanced the lead species transition resulting in a higher relative amount of covalent lead bonding in the high PbO content alumino-borosilicate glass. The number of BO{sub 4} units present in the {sup 11}B MAS NMR decreased with increasing PbO contents for both the borosilicate and the alumino-borosilicate glass systems, with the addition of aluminum further promoting the BO{sub 3} species. A deshielding of the {sup 11}B chemical shifts and the {sup 27}Al chemical shifts with increased lead contents (independent of changes in the quadrupolar coupling) was also observed for both glass systems and was attributed to increasingly homogeneous glass structure. The {sup 29}Si spectra of the borosilicate and alumino-borosilicate glasses showed a downfield shift with increased PbO concentrations representing incorporation of Pb into the silicate and aluminosilicate networks. The Raman spectra were characterized by increased intensities of Si-O-Pb peaks and decreased intensities of Q{sup 3} peaks with increased PbO contents and showed no evidence

  6. The synthesis of [Me{sub 4}N]{sub 2}[alpha{sup 2}-B{sub 20}H{sub 16}(NH{sub 3}){sub 2}] and trans-B{sub 20}H{sub 16}(NH{sub 3}){sub 2} from [Me{sub 3}NH][cis-B{sub 20}H{sub 17}NH{sub 3}] and their structural characterization

    SciTech Connect

    Li, F.; Shelly, K.; Knobler, C.B.; Hawthorne, M.F.


    The chemistry of novel polyhedral borane derivatives has recently attracted new interest because of their potential application in the liposome-mediated boron neutron capture therapy (BNCT) of cancer. The [trans-B{sub 20}H{sub 18}]{sup 2{minus}} polyhedral borane anion has been found to be a versatile source for a variety of these boron-rich derivatives. The synthesis of the stereochemically unprecedented [cis-B{sub 20}H{sub 18}]{sup 2{minus}} and the ammonio-substituted anion [cis-B{sub 20}H{sub 17}NH{sub 3}]{sup {minus}} ([2]{sup {minus}}) has been reported. The two three-center two-electron bonds of [2]{sup {minus}} are electron deficient and susceptible to nucleophilic attack, and the reaction of [2]{sup {minus}} with hydroxide ion produced disubstituted [{alpha}{sup 2}-B{sub 20}H{sub 16}NH{sub 3}(OH)]{sup 3{minus}}. A recent investigation of the reaction of [2]{sup {minus}} with liquid ammonia has led to the discovery of the diammonio-substituted anion, [{alpha}{sup 2}-B{sub 20}H{sub 16}(NH{sub 3}){sub 2}]{sup 2{minus}}. Subsequent aqueous ferric ion oxidation resulted in the neutral derivative, trans-B{sub 20}H{sub 16}(NH{sub 3}){sub 2}. They report here the syntheses and structures of the anion and the neutral compound.

  7. Isolation of an extremely labile dihydrogen complex, Cr(CO){sub 3}(PRr{sup i}{sub 3}){sub 2}(H{sub 2}), containing the shortest ligated H-H bond

    SciTech Connect

    Kubas, G.J.; Nelson, J.E.; Bryan, J.C.


    First-row members of the group 6 series of transition metal dihydrogen complexes Cr(CO){sub 3}(PR{sub 3}){sub 2}({eta}{sup 2}-H{sub 2})(R = Cy, Pr{sup i}) have been synthesized and examined by X-ray crystallography and NMR, infrared, and inelastic neutron scattering spectroscopies. The complexes completely dissociate H{sub 2} in solution to give Cr(CO){sub 3}(PR{sub 3}){sub 2}, which contains an agostic C-H interaction. An X-ray structure of Cr(CO){sub 3}(PPr{sup i}{sub 3}){sub 2}(H{sub 2}) showed a side-bonded dihydrogen ligand with H-H = 0.67(5) {angstrom}, and proton NMR of the HD isotopomer showed a J(HD) value of 35 Hz. Solid-state H NMR spectroscopy of the PCy{sub 3} complex indicated that the H-H separation is 0.85(1) {angstrom}, which is believed to be a more precise and accurate measure of this key parameter. The barrier to rotation of the {eta}{sup 2}-H{sub 2} has been recalculated to be 1.17(10) kcal/mol, as compared with 1.32(10) and 1.9(1) kcal/mol for the Mo and W analogues, based on H-H distances from solid-state NMR. Correlations of properties of the group 6 species indicate that the H{sub 2} {yields} M {sigma}-bonding strength appears to increase as Mo < Cr {approximately} W but that d{pi} {yields} H{sub 2} {sigma}* back-bonding increases down the group. It might be generally concluded that back-bonding is more of a factor than {sigma}-bonding in influencing stability, H-H distance, and possibly overall bond strengths. Crystallographic data: space group P2{sub 1}/c, a = 13.457-(3) {angstrom}, b = 11.493(3) {angstrom}, c = 16.639(4) {angstrom}, {beta} = 102.25(2){sup o}, Z = 4, R = 3.32%.

  8. Local structural distortion and electrical transport properties of Bi(Ni1/2Ti1/2)O3sub> perovskite under high pressure

    SciTech Connect

    Zhu, Jinlong; Yang, Liuxiang; Wang, Hsiu -Wen; Zhang, Jianzhong; Yang, Wenge; Hong, Xinguo; Jin, Changqing; Zhao, Yusheng


    Perovskite-structure materials generally exhibit local structural distortions that are distinct from long-range, average crystal structure. The characterization of such distortion is critical to understanding the structural and physical properties of materials. In this work, we combined Pair Distribution Function (PDF) technique with Raman spectroscopy and electrical resistivity measurement to study Bi(Ni1/2Ti1/2)O3sub> perovskite under high pressure. PDF analysis reveals strong local structural distortion at ambient conditions. As pressure increases, the local structure distortions are substantially suppressed and eventually vanish around 4 GPa, leading to concurrent changes in the electronic band structure and anomalies in the electrical resistivity. We find, consistent with PDF analysis, Raman spectroscopy data suggest that the local structure changes to a higher ordered state at pressures above 4 GPa.

  9. On photo-expansion and microlens formation in (GeS{sub 2}){sub 0.74}(Sb{sub 2}S{sub 3}){sub 0.26} chalcogenide glass

    SciTech Connect

    Knotek, P.; Tichy, L.


    Graphical abstract: Display Omitted Highlights: ► Photo-expansion induced by sub-band-gap photons in GeSbS glass. ► One-step microlens formation. ► The topography of the microlenses detected by AFM and DHM. ► The good mechanical characteristics of the microlenses were obtained. ► Local light-induced overheating of the glass. -- Abstract: Photo-expansion of the bulk of (GeS{sub 2}){sub 0.74}(Sb{sub 2}S{sub 3}){sub 0.26} glass induced by sub-gap photons is studied employing specifically atomic force microscopy (AFM) namely an atomic force acoustic microscopy (AFAM) and a force spectroscopy and digital holographic microscopy. The results are discussed with respect to the possible role of light induced overheating in the process of photo-expansion.

  10. Pressure-induced isomerization of a heterometallic rhodium-gold cluster compound: (Rh sub 2 (. mu. -Cl) sub 2 (CNC sub 8 H sub 9 ) sub 4 (. mu. -AuPPh sub 3 )) sub 2 (PF sub 6 ) sub 2

    SciTech Connect

    Bray, K.L.; Drickamer, H.G.; Shapley, J.R. ); Mingos, D.M.P.; Watson, M.J. )


    Mingos et al. have prepared two isomers of the cluster compound (Rh{sub 2}(mu-Cl{sub 2})(CNC{sub 8}H{sub 9}){sub 4}(mu-AuPPh{sub 3})){sub 2}(PF{sub 6}){sub 2} and have characterized these isomers using single crystal x-ray techniques. The volumes per cluster cation were found to be very similar for both isomers, 1,430 and 1,413 angstroms, and the Rh-Rh bond lengths were found to be 3.262 and 3.008 angstroms for the same isomer. The cluster skeletal geometries were found to differ only at an interior link, and applied pressure appeared to induce a conformational transition around this bond.

  11. Backward optical gain originating from weak localization strengthened three-photon process in Er/Yb co-doped (Pb,La)(Zr,Ti)O3sub> ceramics.


    Xu, Caixia; Zhang, Jingwen; Zou, Yingyin K; Zhao, Hua


    The enhancement of green upconverted emission from the Er3+/Yb3+ co-doped (Pb,La)(Zr,Ti)O3sub> ceramic powder under a pumping light with a wavelength of 1480 nm was observed to be greater than 30 times that from the bulk of the same sample. Weak localization of light supported by the spatial profile of scattered light facilitated the three-photon process contributing to stronger green upconverted emission. Significant backward light amplification was also observed and studied in detail. Additionally, the distribution of the localization zones in the sample was investigated using a probing laser beam with a wavelength of 532 nm. The findings in this work could be used in improving the solar cell efficiency, modulating color, and designing smart devices. PMID:27136772

  12. First laser emission of Yb0.15:(Lu0.5Y0.5)3sub>Al5O12 ceramics.


    Toci, Guido; Pirri, Angela; Li, Jiang; Xie, Tengfei; Pan, Yubai; Babin, Vladimir; Beitlerova, Alena; Nikl, Martin; Vannini, Matteo


    We report the first laser oscillation on Yb0.15:(Lu0.5Y0.5)3sub>Al12 ceramics at room temperature. At 1030 nm we measured a maximum output power of 7.3 W with a corresponding slope efficiency of 55.4% by using an output coupler with a transmission of T = 39.2%. The spectroscopic properties are compared with those of the two parent garnets Yb:YAG and Yb:LuAG. To the best of our knowledge these are the first measurements reported in literature achieved with this new host. PMID:27137574

  13. Low-temperature thermal conductivity of antiferromagnetic S = 1/2 chain material CuCl{sub 2}·2((CH{sub 3}){sub 2}SO)

    SciTech Connect

    Ke, W. P.; Zhang, F. B.; Zhao, Z. Y.; Fan, C.; Sun, X. F.; Shi, J.; Zhao, X.


    We study the heat transport of S = 1/2 chain compound CuCl{sub 2}·2((CH{sub 3}){sub 2}SO) along the b axis (vertical to the chain direction) at very low temperatures. The zero-field thermal conductivity (κ) shows a distinct kink at about 0.9 K, which is related to the long-range antiferromagnetic (AF) transition. With applying magnetic field along the c axis, κ(H) curves also show distinct changes at the phase boundaries between the AF and the high-field disordered states. These results indicate a strong spin-phonon interaction and the magnetic excitations play a role in the b-axis heat transport as phonon scatterers.

  14. Synthesis and crystal structure of bis(3-ammoniumphenyl) sulfone dinitrate [C{sub 12}H{sub 14}N{sub 2}O{sub 2}S](NO{sub 3}){sub 2}

    SciTech Connect

    Mahroug, A.; Belhouchet, M. Mhiri, T.


    A new organic nitrate with the formula [C{sub 12}H{sub 14}N{sub 2}O{sub 2}S](NO{sub 3}){sub 2}, has been prepared and analyzed by X-ray diffraction. This compound crystallizes in the orthorhombic system: a = 16.771 (3), b = 13.884(2), c = 13.884(2) A, V = 3232.7(7)A{sup 3}, Z = 8, space group Pna2{sub 1}. Crystal structure can be described as a succession of organic and inorganic layers parallel to b, c plane. H-bonds between the different species play an important role in the three-dimensional network cohesion.

  15. Second harmonic generation and waveguide properties in perovskite Na0.5Bi0.5TiO3sub> nanowires.


    Zhou, Hong; Wang, Xiaoxia; Zhuang, Xiujuan; Pan, Anlian


    Nanowires with nonlinear optical properties such as second harmonic generation (SHG) are essential elements for an all-optical integrated photonic circuit. However, the existing materials face challenges for applications in a wide wavelength range. To cope with the challenges, ferroelectric nanowires are considered promising candidates, especially for SHG applications. In this Letter, we study SHG and waveguide properties in perovskite Na0.5Bi0.5TiO3sub> (NBT) nanowires. Strong SHG is observed in NBT nanowires illuminated by a 1064 nm laser radiation. For the waveguide studies, these NBT nanowires show a waveguide propagation loss as low as 0.01 dB/μm at 532 nm. This work suggests potential applications in future integrated optics with NBT nanowires. PMID:27519093

  16. Preparations of nano-particles, nano-composites and fibers of ZnO from an amide precursor: Photocatalytic decomposition of (CH{sub 3}){sub 2}S{sub 2} in a continuous flow reactor

    SciTech Connect

    Daniele, Stephane . E-mail:; Ghazzal, Mohamed N.; Hubert-Pfalzgraf, Liliane G.; Duchamp, Christian; Guillard, Chantal; Ledoux, Gilles


    High surface area hexagonal ZnO nano-particles were obtained at room temperature from hydrolysis of the amide derivative Zn[N(SiMe{sub 3}){sub 2}]{sub 2}. The same procedure applied on silica or cellulose substrates led to homogeneous crack-free hybrid materials for which micro- down to nano-meter replication into ZnO cloth was achieved by calcination at 700 deg. C. These materials were characterized by FT-IR, UV-vis, photoluminescence, X-ray diffraction (XRD) and transmission electron microscopy (TEM). They demonstrated enhanced photocatalytic degradation of a tough pollutant such as CH{sub 3}SSCH{sub 3} compared with commercial ZnO powder.

  17. Resolving the structure of Ti3sub>C2Tx MXenes through multilevel structural modeling of the atomic pair distribution function

    SciTech Connect

    Wesolowski, David J.; Wang, Hsiu -Wen; Page, Katharine L.; Naguib, Michael; Gogotsi, Yury


    MXenes are a recently discovered family of two-dimensional (2D) early transition metal carbides and carbonitrides, which have already shown many attractive properties and a great promise in energy storage and many other applications. However, a complex surface chemistry and small coherence length has been an obstacle in some applications of MXenes, also limiting accuracy of predictions of their properties. In this study, we describe and benchmark a novel way of modeling layered materials with real interfaces (diverse surface functional groups and stacking order between the adjacent monolayers) against experimental data. The structures of three kinds of Ti3sub>C2Tx MXenes (T stands for surface terminating species, including O, OH, and F) produced under different synthesis conditions were resolved for the first time using atomic pair distribution function obtained by high-quality neutron total scattering. The true nature of the material can be easily captured with the sensitivity of neutron scattering to the surface species of interest and the detailed third-generation structure model we present. The modeling approach leads to new understanding of MXene structural properties and can replace the currently used idealized models in predictions of a variety of physical, chemical and functional properties of Ti3sub>C2-based MXenes. Furthermore, the developed models can be employed to guide the design of new MXene materials with selected surface termination and controlled contact angle, catalytic, optical, electrochemical and other properties. We suggest that the multi-level structural modeling should form the basis for a generalized methodology on modeling diffraction and pair distribution function data for 2D and layered materials.

  18. Fluorocarbon assisted atomic layer etching of SiO2 and Si using cyclic Ar/C4F8 and Ar/CHF3sub> 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/C4F8 ALE based on steady-state Ar plasma in conjunction with periodic, precise C4F8 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 CHF3sub> as a precursor is examined and compared to C4F8. CHF3sub> 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.

  19. Organometallic complexes of bulky, optically active, C3sub>-symmetric tris(4S-isopropyl-5,5-dimethyl-2-oxazolinyl)phenylborate (ToP*)

    SciTech Connect

    Xu, Songchen; Magoon, Yitzhak; Reinig, Regina R.; Schmidt, Bradley M.; Ellern, Arkady; Sadow, Aaron D.


    A bulky, optically active monoanionic scorpionate ligand, tris(4S-isopropyl-5,5-dimethyl-2-oxazolinyl)phenylborate (ToP*), is synthesized from the naturally occurring amino acid l-valine as its lithium salt, Li[ToP*] (1). That compound is readily converted to the thallium complex Tl[ToP*] (2) and to the acid derivative H[ToP*] (3). Group 7 tricarbonyl complexes ToP*M(CO)3sub> (M = Mn (4), Re (5)) are synthesized by the reaction of MBr(CO)5 and Li[ToP*] and are crystallographically characterized. The νCO bands in their infrared spectra indicate that π back-donation in the rhenium compounds is greater with ToP* than with non-methylated tris(4S-isopropyl-2-oxazolinyl)phenylborate (ToP). The reaction of H[ToP*] and ZnEt2 gives ToP*ZnEt (6), while ToP*ZnCl (7) is synthesized from Li[ToP*] and ZnCl2. The reaction of ToP*ZnCl and KOtBu followed by addition of PhSiH3sub> provides the zinc hydride complex ToP*ZnH (8). In this study, compound 8 is the first example of a crystallographically characterized optically active zinc hydride. We tested its catalytic reactivity in the cross-dehydrocoupling of silanes and alcohols, which provided Si-chiral silanes with moderate enantioselectivity.

  20. Synthesis, structure and electrochemical properties of layered La{sub 2}Li{sub 2x}(CO{sub 3}){sub 1−x}O{sub 2+2x}

    SciTech Connect

    Iqbal, Muhammad; Kobayashi, Genki; Hirayama, Masaaki; Kanno, Ryoji


    An oxide ion conductor, La{sub 2}Li{sub 2x}(CO{sub 3}){sub 1−x}O{sub 2+x} (x=0.15), was synthesized using a solid-state reaction, and its structure was subsequently determined by Rietveld refinement analyses of synchrotron X-ray and high-resolution powder neutron diffraction data. These analyses determined that carbonate groups are situated between (La{sub 2}O{sub 2}{sup 2+}){sub n} layers in an ordered arrangement and that both oxygen vacancies and interstitial oxygen ions exist within the carbonate layers, resulting in a composition of La{sub 2}Li{sub 0.3}(CO{sub 3}){sub 0.85}O{sub 2.3}. This material is structurally stable up to 500 °C and exhibits a conductivity of 5.5×10{sup −5} S cm{sup −1} at 450 °C. Oxide vacancies associated with carbonate anions appear to be responsible for the ionic conduction observed in this material. - Graphical abstract: Thermal ellipsoid projection of the carbonate layer viewed from the c-axis, showing oxygen migration paths: (A, blue line) interstitial hopping and (B, green line) co-operative rotation. Display Omitted - Highlights: • Lithium insertion in the structure causes the structural changes in carbonate layer. • These structural changes create oxygen vacancies within the flexible carbonate layers and introduce interstitial oxygen. • These interstitial oxygen atoms and oxygen vacancies are involved in oxide ion diffusion through the carbonate layer.

  1. Extended networks, porous sheets, and chiral frameworks. Thorium materials containing mixed geometry anions: Structures and properties of Th(SeO{sub 3})(SeO{sub 4}), Th(IO{sub 3}){sub 2}(SeO{sub 4})(H{sub 2}O){sub 3}.H{sub 2}O, and Th(CrO{sub 4})(IO{sub 3}){sub 2}

    SciTech Connect

    Sullens, Tyler A.; Almond, Philip M.; Byrd, Jessica A.; Beitz, James V.; Bray, Travis H.; Albrecht-Schmitt, Thomas E. . E-mail:


    Three novel Th(IV) compounds containing heavy oxoanions, Th(SeO{sub 3})(SeO{sub 4}) (1), Th(IO{sub 3}){sub 2}(SeO{sub 4})(H{sub 2}O){sub 3}.H{sub 2}O (2), and Th(CrO{sub 4})(IO{sub 3}){sub 2} (3), have been synthesized under mild hydrothermal conditions. Each of these three distinct structures contain trigonal pyramidal and tetrahedral oxoanions. Compound 1 adopts a three-dimensional structure formed from ThO{sub 9} tricapped trigonal prisms, trigonal pyramidal selenite, SeO{sub 3}{sup 2-}, anions containing Se(IV), and tetrahedral selenate, SeO{sub 4}{sup 2-}, anions containing Se(VI). The structure of 2 contains two-dimensional porous sheets and occluded water molecules. The Th centers are found as isolated ThO{sub 9} tricapped trigonal prisms and are bound by four trigonal pyramidal iodate anions, two tetrahedral selenate anions, and three coordinating water molecules. In the structure of 3, the Th(IV) cations are found as ThO{sub 9} tricapped trigonal prisms. Each Th center is bound by six IO{sub 3}{sup 1-} anions and three CrO{sub 4}{sup 2-} anions forming a chiral three-dimensional structure. Second-harmonic generation of 532nm light from 1064nm radiation by a polycrystalline sample of 3 was observed. Crystallographic data (193K, MoK{alpha}, {lambda}=0.71073): 1; monoclinic, P2{sub 1}/c; a=7.0351(5)A, b=9.5259(7)A, c=9.0266(7)A, {beta}=103.128(1), Z=4, R(F)=2.47% for 91 parameters with 1462 reflections with I>2{sigma}(I); 2, monoclinic, P2{sub 1}/n, a=7.4889(9)A, b=8.002(1)A, c=20.165(3)A, {beta}=100.142(2), Z=4, R(F)=4.71% for 158 parameters with 2934 reflections with I>2{sigma}(I); 3, orthorhombic, P2{sub 1}2{sub 1}2{sub 1}, a=7.3672(5)A, b=9.3617(6)A, c=11.9201(7)A, Z=4, R(F)=2.04% for 129 parameters with 2035 reflections with I>2{sigma}(I)

  2. Synthesis and characterization of hydrotalcites: [Zn{sub 1{minus}x}Al{sub x}(OH){sub 2}](CO{sub 3}){sub x/2{center_dot}}mH{sub 2}O; x = 0.25--0.66

    SciTech Connect

    Valenzuela, M.A.; Lopez-Salinas, E.; Zapata, B.; Montoya, J.A.


    In this work a series of [Zn{sub 1{minus}x}Al{sub x}(OH){sub 2}](CO{sub 3}){sub x/2{center_dot}}mH{sub 2}O; x = 0.25--0.66 were prepared at constant pH in order to study the effect of the thermal treatment on their crystalline structure. It was found that it is possible to obtain pure Zn-Al hydrotalcite materials within a x = 0.25--0.50 range in comparison with Mg-Al hydrotalcites which yield pure phases in more restricted x ranges (0.25--0.33). All Zn-Al hydrotalcites lost their layered structure at temperatures above 473 K being less stable than their parental Mg-Al hydrotalcite (623 K). Specific surface areas of these materials depended strongly on the Zn/Al ratio and calcination temperature, ranging from 280 to 20 m{sup 2}/g. ZnO and ZnAl{sub 2}O{sub 4} compounds were detected as the calcination products at temperatures higher than 873 K.

  3. Nanoscale Stabilization of New Phases in the PbTe-Sb2Te3sub> System: PbmSb2nTem+3n Nanocrystals

    SciTech Connect

    Soriano, Ronald B; Arachchige, Indika U; Malliakas, Christos D; Wu, Jinsong; Kanatzidis, Mercouri G


    A series of novel rock-salt-type PbmSb2nTem+3n nanocrystals (m = 2, 3, 4, 6, 8, and 10; n = 1 and 2) were successfully prepared using a colloidal synthesis route. These materials are stable only on the nanoscale and have no bulk analogues. Elemental compositions were determined using scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The nanocrystals exhibit well-defined band energies in the mid-IR region that are nearly independent of their atomic compositions. PbmSb2nTem+3n nanocrystals behave as metastable homogeneous solid solutions at room temperature and tend to phase separate into the respective binary PbTe + Sb2Te3sub> at 300 °C. Furthermore, pair distribution function (PDF) analysis suggests that the local structure of these PbmSb2nTem+3n nanocrystals is distorted with respect to the rock-salt structure.

  4. Oxygen atom transfer between rhenium, sulfur, and phosphorus. Characterization and reactivity of Re(O)Cl/sub 3/(Me/sub 2/S)(OPPh/sub 3/) and Re(O)Cl/sub 3/(CNCMe/sub 3/)/sub 2/

    SciTech Connect

    Bryan, J.C.; Stenkamp, R.E.; Tulip, T.H.; Mayer, J.M.


    Re(O)Cl/sub 3/(PPh/sub 3/)/sub 2/ (I) reacts with Me/sub 2/SO to form OPPh/sub 3/ and Re(O)Cl/sub 3/(Me/sub 2/S)(OPPh/sub 3/) (II), not Re(O)Cl/sub 3/(Me/sub 2/SO)(PPh/sub 3/) as had been previously reported. Compounds I and II are catalysts for oxygen atom transfer from Me/sub 2/SO to PPh/sub 3/. The mechanism of these oxygen atom transfer reactions has been studied with oxygen-18 labeling experiments. The rhenium oxo group does not appear to be involved; rather, the rhenium center acts as a Lewis acid activator for a Me/sub 2/SO ligand. The rhenium oxo group does, however, exchange oxygen atoms with Me/sub 2/S/sup 18/O, probably by a similar mechanism. Compound II is an excellent starting material for compounds of the form Re(O)Cl/sub 3/L/sub 2/, with L = isonitriles, phosphines, bipyridine, etc. The compounds Re(O)Cl/sub 3/-(CNR)/sub 2/ (R = CMe/sub 3/ (IV), CHMe/sub 2/, C/sub 6/H/sub 11/) are rare examples of high-valent isonitrile complexes. Data from an X-ray crystal structure of IV are reported. 36 references, 2 figures, 3 tables.

  5. Synthesis and crystal structure of Pb{sub 3}[IO{sub 3}]{sub 2}Cl{sub 4}, a representative of a new iodate-chloride class of compounds

    SciTech Connect

    Belokoneva, E. L. Dimitrova, O. V.


    Compound Pb{sub 3}[IO{sub 3}]{sub 2}Cl{sub 4} (space group C12/c1), representing a new iodate-chloride class of compounds, is synthesized under hydrothermal conditions. Only two minerals, schwartzembergite Pb{sub 3}[IO{sub 3}]Cl{sub 2}O(OH) and seeligerite Pb{sub 3}[IO{sub 3}]Cl{sub 3}O, the structures of which are unknown, are close in composition to this compound. In the iodate-chloride studied, the pentavalent iodine atom has an umbrella-like coordination, which is typical of iodates and consists of three O atoms at short distances and the fourth O atom at a longer distance. [IO{sub 4}]{sup 3-} tetrahedra share edges to form pairs. Lead ions form layers parallel to the ab plane. Along the c axis, these layers alternate with layers of iodate groups. Pb atoms are coordinated by O atoms of iodate groups and Cl atoms. The coordination sphere of the Pb(1) atom contains a free sector which is directed to more distant halogen atoms and possibly accommodates the lone electron pair.

  6. The microscopic structure of charge density waves in underdoped YBa2Cu3sub>O6.54 revealed by x-ray diffraction

    SciTech Connect

    E. M. Forgan; Huecker, M.; Blackburn, E.; Holmes, A. T.; Briffa, A. K. R.; Chang, J.; Bouchenoire, L.; Brown, S. D.; Liang, Ruixing; Bonn, D.; Hardy, W. N.; Christensen, N. B.; von Zimmermann, M.; Hayden, S. M.


    Charge density wave (CDW) order appears throughout the underdoped high-temperature cuprate superconductors, but the underlying symmetry breaking and the origin of the CDW remain unclear. We use X-ray diffraction to determine the microscopic structure of the CDWs in an archetypical cuprate YBa2Cu3sub>O6.54 at its superconducting transition temperature ~60 K. We find that the CDWs in this material break the mirror symmetry of the CuO2 bilayers. The ionic displacements in the CDWs have two components, which are perpendicular and parallel to the CuO2 planes, and are out of phase with each other. The planar oxygen atoms have the largest displacements, perpendicular to the CuO2 planes. Our results allow many electronic properties of the underdoped cuprates to be understood. For example, the CDWs will lead to local variations in the electronic structure, giving an explicit explanation of density-wave states with broken symmetry observed in scanning tunnelling microscopy and soft X-ray measurements.

  7. Phase transitions and thermal-stress-induced structural changes in a ferroelectric Pb (Zr0.80Ti0. 20)O3sub> single crystal

    SciTech Connect

    Frantti, Johannes; Fujioka, Y.; Puretzky, Alexander A.; Xie, Y; Ye, Z. -G.; Parish, Chad M.; Glazer, A. M.


    Zirconium-rich lead-zirconate-titanate (PZT) Pb(Zr0.80Ti0.20)O3sub> single crystal is studied by polarized-Raman scattering experiments as a function of temperature. We show that the crystal possesses complex domain boundaries which show no sign of instability even 200 K above the ferroelectric-to-paraelectric phase transition. The boundary stabilized the domains which had the same orientation after cyclic heating and cooling up to 773 K. The domains transformed normally to the cubic paraelectric phase, but returned to their original state after cooling. Physical mechanism behind the reversible behavior is related to the strain between the boundary region and domain, which forces the domain to grow similarly after each heating and cooling cycle. Electron backscattering diffraction measurements show that macroscopic domains, lengths scale in hundreds of microns, are divided into regions whose Pb-displacements are not correlated. The results are notably interesting for non-volatile memory development as it implies that the original ferroelectric state can be restored after the material has been transformed to a paraelectric phase. Incoherent Pbdisplacements play a role for polarization switching.

  8. Ablation of (GeS{sub 2}){sub 0.3}(Sb{sub 2}S{sub 3}){sub 0.7} glass with an ultra-violet nano-second laser

    SciTech Connect

    Knotek, P.; Navesnik, J.; Cernohorsky, T.; Kincl, M.; Vlcek, M.; Tichy, L.


    Highlights: • The interaction of (GeS{sub 2}){sub 0.3}(Sb{sub 2}S{sub 3}){sub 0.7} bulk glass and film with UV nanosecond laser. • Ablation process, topography of crater and structure of the material were studied. • Ablation threshold fluencies changed with the spot diameter and number of pulses. • The photo-thermal expansion of the material occurred for low laser fluency. • Laser direct writing process applicable for fabrication of passive optical elements. - Abstract: The results of an experimental study of the laser ablation of bulk and thin films of a GeSbS chalcogenide glass using UV nanosecond pulses are reported. The response of the samples to illumination conditions was studied through the use of atomic force spectroscopy, digital holographic microscopy, Raman scattering and scanning electron microscopy. The multi-pulse ablation thresholds were determined for both the bulk and thin film samples for varying number of pulses and illuminated spot diameter. The possible application of direct laser writing into the bulk and thin films of this material is presented.

  9. In-situ luminescence monitoring of ion-induced damage evolution in SiO2 and Al2O3sub>

    SciTech Connect

    Crespillo, Miguel L.; Graham, Joseph T.; Zhang, Yanwen; Weber, William J.


    Real-time, in-situ ionoluminescence measurements provide information of evolution of emission bands with ion fluence, and thereby establish a correlation between point defect kinetics and phase stability. Using fast light ions (2 MeV H and 3.5 He MeV) and medium mass-high energy ions (8 MeV O, E=0.5 MeV/amu), scintillation materials of a-SiO2, crystalline quartz, and Al2O3sub> are comparatively investigated at room temperature with the aim of obtaining a further insight on the structural defects induced by ion irradiation and understand the role of electronic energy loss on the damage processes. For more energetic heavy ions, the electronic energy deposition pattern offers higher rates of excitation deeper into the material and allows to evaluate the competing mechanisms between the radiative and non-radiative de-excitation processes. Irradiations with 8 MeV O ions have been selected corresponding to the electronic stopping regime, where the electronic stopping power is dominant, and above the critical amorphization threshold for quartz. Lastly, the usefulness of IBIL and its specific capabilities as a sensitive tool to investigate the material characterization and evaluation of radiation effects are demonstrated.

  10. Hydrothermal synthesis, crystal structure and spectroscopic and magnetic properties of (C{sub 2}H{sub 10}N{sub 2})[Mn{sub 2.09}Co{sub 0.91}(HPO{sub 3}){sub 4}

    SciTech Connect

    Fernandez-Armas, S.; Mesa, J.L.; Pizarro, J.L.; Pena, A.; Chapman, J.P.; Arriortua, M.I


    (C{sub 2}H{sub 10}N{sub 2})[Mn{sub 2.09}Co{sub 0.91}(HPO{sub 3}){sub 4}] has been synthesized using mild hydrothermal conditions under autogeneous pressure. The compound crystallizes in the triclinic P-1 space group. The unit-cell parameters are a = 5.4061(8), b = 5.4150(7), c = 14.136(2) A, {alpha} = 80.84(1), {beta} = 85.41(1), {gamma} = 60.00(1) and Z = 1. The compound shows a layered structure constructed from M{sub 3}O{sub 12} trimer units linked thorough the (HPO{sub 3}){sup 2-} phosphite oxoanions with the ethylenediammonium cations located between the sheets compensating the anionic charge of the inorganic framework. The IR and Raman spectra confirm the presence of the ethylenediammonium cation and phosphite anion. The diffuse reflectance spectrum is in accordance with the presence of Co(II) and Mn(II) high spin cations in slightly distorted octahedral symmetry. The calculated Dq and Racah parameters for the Co(II) cations are Dq = 710, B = 870 and C = 4100 cm{sup -1}. The magnetic measurements indicate the existence of antiferromagnetic interactions as the major interactions. Hysteresis observed at low temperature indicates a weak ferromagnetic component, due to a non-cancellation of spins, with coercitive field of 900 G and magnetization of 700 emu/mol.

  11. Band alignment of epitaxial SrTiO{sub 3} thin films with (LaAlO{sub 3}){sub 0.3}-(Sr{sub 2}AlTaO{sub 6}){sub 0.7} (001)

    SciTech Connect

    Comes, Ryan B.; Chambers, Scott A.; Xu, Peng; Jalan, Bharat


    SrTiO{sub 3} (STO) epitaxial thin films and heterostructures are of considerable interest due to the wide range of functionalities they exhibit. The alloy perovskite (LaAlO{sub 3}){sub 0.3}-(Sr{sub 2}AlTaO{sub 6}){sub 0.7} (LSAT) is commonly used as a substrate for these material structures due to its structural compatibility with STO and the strain-induced ferroelectric response in STO films grown on LSAT. However, surprisingly little is known about the electronic properties of the STO/LSAT interface despite its potentially important role in affecting the overall electronic structure of system. We examine the band alignment of STO/LSAT heterostructures using x-ray photoelectron spectroscopy for epitaxial STO films deposited using two different molecular beam epitaxy approaches. We find that the valence band offset ranges from +0.2(1) eV to −0.2(1) eV depending on the film surface termination. From these results, we extract a conduction band offset from −2.4(1) eV to −2.8(1) eV, indicating that the conduction band edge is more deeply bound in STO and that LSAT will not act as a sink or trap for electrons in the supported film or multilayer.

  12. Resonant magneto-optic Kerr effect in the magnetic topological insulator Cr:(Sbx,Bi1–x)2Te3sub>

    SciTech Connect

    Patankar, Shreyas; Hinton, J. P.; Griesmar, Joel; Orenstein, J.; Dodge, J. S.; Kou, Xufeng; Pan, Lei; Wang, Kang L.; Bestwick, A. J.; Fox, E. J.; Goldhaber-Gordon, D.; Wang, Jing; Zhang, Shou -Cheng


    Here, we report measurements of the polar Kerr effect, proportional to the out-of-plane component of the magnetization, in thin films of the magnetically doped topological insulator (Cr0.12Bi0.26Sb0.62)2Te3sub>. Measurements of the complex Kerr angle ΘK were performed as a function of photon energy in the range 0.8eV < ℏω < 3.0eV. We observed a peak in the real part of ΘK(ω) and zero crossing in the imaginary part that we attribute to a resonant interaction with a spin-orbit avoided crossing located ≈ 1.6 eV above the Fermi energy. The resonant enhancement allows measurement of the temperature and magnetic field dependence of ΘK in the ultrathin film limit, d ≥ 2 quintuple layers (QL). We find a sharp transition to zero remanent magnetization at 6 K for d < 8 QL, consistent with theories of the dependence of impurity spin interactions on film thickness and their location relative to topological insulator surfaces.

  13. Remarkable charge-trapping efficiency of the memory device with (TiO{sub 2}){sub 0.8}(Al{sub 2}O{sub 3}){sub 0.1} composite charge-storage dielectric

    SciTech Connect

    Jiang, K.; Ou, X.; Cao, Z. Y.; Liu, X. J.; Lu, W.; Xu, B.; Li, A. D.; Xia, Y. D.; Yin, J. Liu, Z. G.; Lan, X. X.; Gong, C. J.


    A memory device p-Si/SiO{sub 2}/(TiO{sub 2}){sub 0.8}(Al{sub 2}O{sub 3}){sub 0.1}(TAO-81)/Al{sub 2}O{sub 3}/Pt was fabricated, in which a composite of two high-k dielectrics with a thickness of 1 nm was employed as the charge-trapping layer to enhance the charge-trapping efficiency of the memory device. At an applied gate voltage of ±9 V, TAO-81 memory device shows a memory window of 8.83 V in its C-V curve. It also shows a fast response to a short voltage pulse of 10{sup −5} s. The charge-trapping capability, the endurance, and retention characteristics of TAO-81 memory device can be improved by introducing double TAO-81 charge-trapping layers intercalated by an Al{sub 2}O{sub 3} layer. The charge-trapping mechanism in the memory device is mainly ascribed to the generation of the electron-occupied defect level in the band gap of Al{sub 2}O{sub 3} induced by the inter-diffusion between TiO{sub 2} and Al{sub 2}O{sub 3}.

  14. Magnetic property, Raman spectroscopy and crystal field analysis of Sm{sub 3+} in Sm(BrO{sub 3}){sub 3}⋅9H{sub 2}O

    SciTech Connect

    Mandal, J.; Chakrabarti, P. K.; Purohit, T.; Chattopadhyay, K. N.; Ghosh, M.


    Single crystals of Sm(BrO{sub 3}){sub 3}⋅9H{sub 2}O (SmBR) were grown and the principal molar susceptibility perpendicular to c-axis (χ{sub ⊥}) was measured from 300 K down to 14 K and χ{sub ‖}, the parallel susceptibility, anisotropy was measured in the temperature range of 300-120 K. A cross-over between χ{sub ‖} and χ{sub ⊥} was observed at ∼ 120 K i.e., below this temperature χ{sub |||}<χ{sub ‖}. Raman spectra of SmBR were recorded in the wave number range of 10-4000 cm{sup −1} and crystal field (CF) Stark energies were extracted from the spectra. A good theoretical simulation of the observed magnetic susceptibilities and observed CF Stark energies of Sm{sup 3+} in SmBR was achieved using the one electron crystal field (CF) interaction with D{sup 3h} site symmetry. The electronic specific heat along with the quadruple splitting and hyperfine heat capacity were calculated by using the results of CF analysis.

  15. Synthesis and characterization of a new monophosphate (5-Cl-2,4-(OCH{sub 3}){sub 2}C{sub 6}H{sub 2}NH{sub 3})H{sub 2}PO{sub 4}

    SciTech Connect

    Kefi, R.; Abid, S.; Nasr, C. Ben . E-mail:; Rzaigui, M.


    Chemical preparation, crystal structure and NMR spectroscopy of a new organic cation 5-chloro(2,4-dimethoxy)anilinium monophosphate H{sub 2}PO{sub 4} are given. This new compound crystallizes in the monoclinic system, with the space group P2{sub 1}/c and the following parameters: a=5.524(2)A, b=9.303(2)A, c=23.388(2)A, {beta}=90.66(4), V=1201.8(2)A{sup 3}, Z=4 and D{sub x}=1.573gcm{sup -3}. Crystal structure has been determined and refined to R=0.031 and R{sub w}=0.080 using 1702 independent reflections. Structure can be described as an infinite (H{sub 2}PO{sub 4}){sub n}{sup n-} corrugated chains in the a-direction. The organic groups (5-Cl-2,4-(OCH{sub 3}){sub 2}C{sub 6}H{sub 2}NH{sub 3}){sup +} are anchored between adjacent polyanions through multiple hydrogen bonds. This compound is also investigated by IR, thermal, and solid-state, {sup 13}C, {sup 31}P MAS NMR spectroscopies.

  16. Magnetic properties of the Nd{sub 0.95}Dy{sub 0.05}Fe{sub 3}(BO{sub 3}){sub 4} ferroborate with small substitution in the rare-earth element subsystem

    SciTech Connect

    Begunov, A. I.; Demidov, A. A.; Gudim, I. A.; Eremin, E. V.


    The magnetic properties of a substituted Nd{sub 0.95}Dy{sub 0.05}Fe{sub 3}(BO{sub 3}){sub 4} ferroborate single crystal with competing Nd-Fe and Dy-Fe exchange interactions are studied experimentally and theoretically. A spontaneous spin-reorientation transition is detected near T = 4.3 K, and anomalies are observed in the low-temperature magnetization curves along trigonal axis c and in basal plane ab. The measured properties and the detected effects are interpreted in terms of a general theoretical approach, which is based on the molecular field approximation and crystal field calculations for a rare-earth ion. The experimental temperature dependences of the initial magnetic susceptibility in the range 2–300 K, the anomalies in the magnetization curves for B ‖ c and B ⊥ c in fields up to 1.5 T, and the field and temperature dependences of magnetization in fields up to 9 T are described. The effect of small substitution in the rare-earth subsystem on the magnetic properties is analyzed. The crystal field parameters and the parameters of the R-Fe and Fe-Fe exchange interactions are determined from the experimental data.

  17. Laser patterning of Y3sub>Al5O12:Ce3+ ceramic phosphor platelets for enhanced forward light extraction and angular color uniformity of white LEDs.


    Wang, Shuai; Li, Yufeng; Feng, Lungang; Zhang, Linzhao; Zhang, Ye; Su, Xilin; Ding, Wen; Yun, Feng


    We present a facile fabrication process to directly fabricate cone-shaped microwells arrays on single crystal Y3sub>Al5O12:Ce3+ (YAG:Ce) ceramic phosphor platelets (CPPs) by short-pulse laser direct patterning. Compared to unpatterned YAG:Ce CPP with smooth surface, the forward-to-total ratio of emission photons of patterned YAG:Ce CPPs was enhanced from 53.2% up to 78.2%, and the total emission within 4-π degree is 6% higher. The fabricated patterns are also beneficial in increasing the color conversion efficiency of YAG:Ce CPPs by 7.6%. The patterned YAG:Ce CPPs display much better correlated color temperature (CCT) uniformity under varied currents. The angular correlated color temperature uniformity (ACU) of patterned YAG:Ce CPPs reaches as high as 0.933 compared to 0.730 of the unpatterned one. These results suggest that laser patterning of YAG:Ce CPP could effectively manipulate its luminance, chromaticity and illumination pattern, which may lead to further technological advancements for diversified applications of film-type CPPs in highly efficient white LEDs. PMID:27464198

  18. 57Fe Mössbauer study of Lu2Fe3sub>Si5 iron silicide superconductor

    SciTech Connect

    Ma, Xiaoming; Ran, Sheng; Pang, Hua; Li, Fashen; Canfield, Paul C.; Bud'ko, Sergey L.


    With the advent of Fe–As based superconductivity it has become important to study how superconductivity manifests itself in details of 57Fe Mössbauer spectroscopy of conventional, Fe-bearing superconductors. The iron-based superconductor Lu2Fe3sub>Si5 has been studied by 57Fe Mössbauer spectroscopy over the temperature range from 4.4 K to room temperature with particular attention to the region close to the superconducting transition temperature (Tc=6.1 K). Furthermore, consistent with the two crystallographic sites for Fe in this structure, the observed spectra appear to have a pattern consisting of two doublets over the whole temperature range. The value of Debye temperature was estimated from temperature dependence of the isomer shift and the total spectral area and compared with the specific heat capacity data. As a result, neither abnormal behavior of the hyperfine parameters at or near Tc, nor phonon softening were observed.

  19. Discovery of the (In{sub 2}S{sub 3}){sub x}(MnIn{sub 2}S{sub 4}){sub 1-x} solid solutions and fabrication of photosensitive structures based on them

    SciTech Connect

    Rud, V. Yu.; Rud, Yu. V.; Osipova, M. A.; Bodnar, I. V.


    A technology of growing single crystals of (In{sub 2}S{sub 3}){sub x}(MnIn{sub 2}S{sub 4}){sub 1-x} solid solutions that provides control over their atomic composition in the entire concentration range 0 {<=} x {<=} 1 is developed. It is shown that, in the range x = 0-1, the single crystals have the cubic spinel structure and the unit cell parameter a follows the linear dependence on x. The exponential character of the temperature dependence of resistivity of solid solutions, on which the first photosensitive Cu/(In{sub 2}S{sub 3})x(MnIn{sub 2}S{sub 4}){sub 1-x} structures are obtained, is revealed. The first photosensitivity spectra of these structures are obtained, and, based on these spectra, dependences of energy of the direct and indirect band-to-band transitions on the composition x are determined. The possibility of applying these structures in broad-band photoconverters of optical radiation is concluded.

  20. Acentric langanite La3sub>Ga5.5Nb0.5O14 crystal: a new nonlinear crystal for the generation of mid-infrared parametric light.


    Lu, Dazhi; Xu, Tianxiang; Yu, Haohai; Fu, Qiang; Zhang, Huaijin; Segonds, Patricia; Boulanger, Benoit; Zhang, Xingyu; Wang, Jiyang


    The mid-infrared spectral range extending from 2 to 6 μm is significant for scientific and technological applications. A promising nonlinear oxide crystal La3sub>Ga5.5Nb0.5O14 (LGN) is proposed and fully characterized for the first time to our knowledge. The transparency range extends between 0.28 and 7.4 μm. The two principal refractive indices were measured and we found that the nonlinear coefficient d11 = 3.0 ± 0.1 pm/V at 0.532 μm. The simultaneous fit of data allowed us to refine the Sellmeier equations of LGN and to calculate the tuning curves for optical parametric generation (OPG) pumped at 1.064 μm. Calculations are consistent with recorded data and also show the generation of a supercontinuum between 1.5 and 3.5 μm when pumped at 0.98 μm by a Ti:Sapphire laser. PMID:27505730

  1. Site-dependent Si KL{sub 23}L{sub 23} resonant Auger electron spectra following inner-shell excitation of Cl{sub 3}SiSi(CH{sub 3}){sub 3}

    SciTech Connect

    Suzuki, Isao H.; Endo, Hikari; Nagai, Kanae; Nagaoka, Shin-ichi; Takahashi, Osamu; Tamenori, Yusuke


    Spectator resonant Auger electron spectra with the Si 1s photoexcitation of Cl{sub 3}SiSi(CH{sub 3}){sub 3} have been measured using an electron spectroscopic technique combined with undulator radiation. The transition with the highest intensity in the total ion yield (TIY) spectrum, coming from excitation of a Si 1s electron on the Cl-side into a vacant valence orbital, generates the resonant Auger decay in which the excited electron remains in this valence orbital. Photoexcitation of 1s electrons into some Rydberg orbitals induces Auger shake-down transitions, because higher-lying Rydberg orbitals in the two Si atoms closely positioned hold spatially overlapping considerably. A broad TIY peak slightly above the 1s ionization thresholds appreciably yields resonant Auger decays in which a slow photoelectron is re-captured into a higher-lying Rydberg orbital. The normal Auger peak shape at this photon energy is distorted due to a post-collision interaction effect. These findings provide a clear understanding on properties of the excited orbitals which are ambiguous in the measurement of the TIY only.

  2. Three-dimensional charge density wave order in YBa2Cu3sub>O6.67 at high magnetic fields

    SciTech Connect

    Gerber, S.; Jang, H.; Nojiri, H.; Matsuzawa, S.; Yasumura, H.; Bonn, D. A.; Liang, R.; Hardy, W. N.; Islam, Z.; Mehta, A.; Song, S.; Sikorski, M.; Stefanescu, D.; Feng, Y.; Kivelson, S. A.; Devereaux, T. P.; Shen, Z. -. X.; Kao, C. -C.; Lee, W. -S.; Zhu, D.; Lee, J. -S.


    In this study, charge density wave (CDW) correlations have recently been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured by x-ray scattering at zero and low fields. Here we combine a pulsed magnet with an x-ray free electron laser to characterize the CDW in YBa2Cu3sub>O6.67 via x-ray scattering in fields up to 28 Tesla. While the zero-field CDW order, which develops below T ~ 150 K, is essentially two-dimensional, at lower temperature and beyond 15 Tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW onsets around the zero-field superconducting transition temperature, yet the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked.

  3. Subsolidus phase equilibria and properties in the system Bi{sub 2}O{sub 3}:Mn{sub 2}O{sub 3+}/-{sub x}:Nb{sub 2}O{sub 5}

    SciTech Connect

    Vanderah, T.A. . E-mail:; Lufaso, M.W.; Adler, A.U.; Levin, I.; Nino, J.C.; Provenzano, V.; Schenck, P.K.


    Subsolidus phase relations have been determined for the Bi-Mn-Nb-O system in air (750-900deg. C). Phases containing Mn{sup 2+}, Mn{sup 3+}, and Mn{sup 4+} were all observed. Ternary compound formation was limited to pyrochlore (A{sub 2}B{sub 2}O{sub 6}O'), which formed a substantial solid solution region at Bi-deficient stoichiometries (relative to Bi{sub 2}(Mn,Nb){sub 2}O{sub 7}) suggesting that {approx}14-30% of the A-sites are occupied by Mn (likely Mn{sup 2+}). X-ray powder diffraction data confirmed that all Bi-Mn-Nb-O pyrochlores form with structural displacements, as found for the analogous pyrochlores with Mn replaced by Zn, Fe, or Co. A structural refinement of the pyrochlore 0.4000:0.3000:0.3000 Bi{sub 2}O{sub 3}:Mn{sub 2}O{sub 3+}/-{sub x}:Nb{sub 2}O{sub 5} using neutron powder diffraction data is reported with the A and O' atoms displaced (0.36 and 0.33A, respectively) from ideal positions to 96g sites, and with Mn{sup 2+} on A-sites and Mn{sup 3+} on B-sites (Bi{sub 1.6}Mn{sup 2+}{sub 0.4}(Mn{sup 3+}{sub 0.8}Nb{sub 1.2})O{sub 7}, Fd3-bar m (-bar 227), a=10.478(1)A); evidence of A or O' vacancies was not found. The displacive disorder is crystallographically analogous to that reported for Bi{sub 1.5}Zn{sub 0.92}Nb{sub 1.5}O{sub 6.92}, which has a similar concentration of small B-type ions on the A-sites. EELS spectra for this pyrochlore were consistent with an Mn oxidation between 2+ and 3+. Bi-Mn-Nb-O pyrochlores exhibited overall paramagnetic behavior with negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. At 300K and 1MHz the relative dielectric permittivity of Bi{sub 1.600}Mn{sub 1.200}Nb{sub 1.200}O{sub 7} was {approx}128 with tan {delta}=0.05; however, at lower frequencies the sample was conductive which is consistent with the presence of mixed-valent Mn. Low-temperature dielectric relaxation such as that observed for Bi{sub 1.5}Zn{sub 0.92}Nb{sub 1

  4. Preparation and photoluminescence properties of RE:Na{sub 3}La{sub 9}O{sub 3}(BO{sub 3}){sub 8} (RE=Er, Yb) crystals

    SciTech Connect

    Liu Zuoliang; Zhang, Guochun; Zhang Jianxiu; Bai Xiaoyan; Fu Peizhen; Wu Yicheng


    Using Na{sub 2}CO{sub 3}-H{sub 3}BO{sub 3}-NaF as fluxes, transparent RE:Na{sub 3}La{sub 9}O{sub 3}(BO{sub 3}){sub 8} (abbr. RE:NLBO, RE=Er, Yb) crystals have been grown by the top seed solution growth (TSSG) method. The X-ray powder diffraction analysis shows that the RE:NLBO crystals have the same structure with NLBO. The element contents were determined by molar to be 0.64% Er{sup 3+} in Er:NLBO, 2.70% Yb{sup 3+} in Yb:NLBO, respectively. The polarized absorption spectra of RE:NLBO have been measured at room temperature and show that both Er:NLBO and Yb:NLBO have a strong absorption bands near 980 nm with wide FWHM (Full Wave at Half Maximum) (21 nm for Er:NLBO and 25 nm for Yb:NLBO). Fluorescence spectra have been recorded. Yb:NLBO has the emission peaks at 985 nm, 1028 nm and 1079 nm and the emission peak of Er:NLBO is at 1536 nm. Spectral parameters have been calculated by the Judd-Ofelt theory for Er:NLBO and the reciprocity method for Yb:NLBO, respectively. The calculated values show that Er:NLBO is a candidate of 1.55 {mu}m laser crystals and Yb:NLBO is a candidate for self-frequency doubling crystal. - Graphical abstract: Fluorescence spectra show the emission peaks at 985, 1028 and 1079 nm of Yb:NLBO and at 1536 nm of Er:NLBO.

  5. Role of ytterbium-erbium co-doped gadolinium molybdate (Gd2(MoO4)3sub>:Yb/Er) nanophosphors in solar cells.


    Jin, Xiao; Li, Haiyang; Li, Dongyu; Zhang, Qin; Li, Feng; Sun, Weifu; Chen, Zihan; Li, Qinghua


    Insufficient harvest of solar light energy is one of the obstacles for current photovoltaic devices to achieve high performance. Especially, conventional organic/inorganic hybrid solar cells (HSCs) based on PTB7 as p-type semiconductor can only utilize 400-800 nm solar spectrum. One effective strategy to overcome this obstacle is the introduction of up-conversion nanophosphors (NPs), in the virtue of utilizing the near infrared region (NIR) of solar radiation. Up-conversion can convert low-energy photons to high-energy ones through multi-photon processes, by which the solar spectrum is tailored to well match the absorptive domain of the absorber. Herein we incorporate erbium-ytterbium co-doped gadolinium molybdate (Gd2(MoO4)3sub>, GMO), denoted as GMO:Yb/Er, into TiO2 acceptor film in HSCs to enhance the light harvest. Here Er3+ acts as activator while Yb-MoO4 2- is the joint sensitizer. Facts proved that the GMO:Yb/Er single crystal NPs are capable of turning NIR photons to visible photons that can be easily captured by PTB7. Studies on time-resolved photoluminescence demonstrate that electron transfer rate at the interface increases sharply from 0.65 to 1.42 × 109 s-1. As a result, the photoelectric conversion efficiency of the GMO:Yb/Er doped TiO2/PTB7 HSCs reach 3.67%, which is increased by around 25% compared to their neat PTB7/TiO2 counterparts (2.94%). This work may open a hopeful way to take the advantage of those conversional rare-earth ion doped oxides that function in tailoring solar light spectrum for optoelectronic applications. PMID:27607730

  6. Fabrication of High Current YBa2Cu3sub>O(sub>7-y) Coated Conductors Using Rolling-Assisted Biaxially Textured Substrates

    SciTech Connect

    Christen, D.K.; Feenstra, R.; Kroeger, D.M.; Lee, D.F.; List, F.A.; Martin, P.M.; Norton, D.P.; Paranthaman, M.; Park, C.; Royal, A.; Specht, E.D.; Verebelyi, D.T.


    High critical current YBa2Cu3sub>O7-y (referred to as YBCO) coated conductors were fabricated with a layer sequence of YBCO/YSZ/CeO2/Ni. The cube (100) texture in the starting Ni substrates was obtained by cold rolling followed by recrystallization. A thin CeO2 (Cerium Oxide) layer with a thickness of 100-200 Å was grown epitaxially on the biaxially textured-Ni substrates using an e-beam evaporation technique. This was followed by the growth of a thick (<= 0.77 µm) YSZ (Yttria Stabilized Zirconia) layer using either e-beam evaporation or rf magnetron sputtering. The e-beam CeO2 film had a dense microstructure. The microstructure of the e-beam YSZ film was porous whereas the sputtered YSZ film was dense. The YBCO films were grown by pulsed laser deposition on both e-beam and sputtered YSZ layers. A transport critical current density of ~ 1 x l06 A/cm2 at 77 K was obtained for ~ 0.8 µm thick YBCO Rims on both YSZ surfaces in zero field. To demonstrate the quality and compatibility of the e-beam CeO2 layers; YBCO films were also grown on CeO2-buffered YSZ (100) single crystal substrates using e-beam co-evaporated Y-BaF2-Cu precursors followed by a post-annealing process. A transport critical current density of over 1 x lO6A/cm2 at 77 K was obtained on a ~ 0.3 µm thick YBCO film in zero field.

  7. Enhanced tunable magnetoresistance properties over a wide temperature range in epitaxial (La{sub 0.7}Sr{sub 0.3}MnO{sub 3}){sub 1−x}:(CeO{sub 2}){sub x} nanocomposites

    SciTech Connect

    Fan, Meng; Khatkhatay, Fauzia; Zhang, Wenrui; Li, Leigang; Wang, Haiyan


    Vertically aligned nanocomposite (VAN) (La{sub 0.7}Sr{sub 0.3}MnO{sub 3}){sub 1−x}:(CeO{sub 2}){sub x} (LSMO:CeO{sub 2}) thin films have been grown on SrTiO{sub 3} (001) substrates by pulsed laser deposition. Tunable magnetoresistance properties as well as microstructures are demonstrated in these VAN films by modulating the film composition (x = 0, 0.3, 0.4, 0.45, 0.5, and 0.55). The sample of x = 0.3 shows a large low-field magnetoresistance (LFMR) in a high temperature range, i.e., over 10% at the range of 280 K to 320 K under 1 T and with a peak value of ∼13.5% at 310 K. In addition, a vast enhancement of LFMR in a low temperature range of 20–150 K with peak of ≈34.3% at 45 K for 1 T could be achieved with x = 0.5. The enhanced LFMR properties can be attributed to both the phase boundary induced spin fluctuation and the magnetic tunneling effect through vertical ferromagnetic/insulator/ferromagnetic structures. The observed enhanced LFMR performance, especially at high temperatures, as well as its simple growth method, offers a great potential for LSMO:CeO{sub 2}nanocomposites to be used in spintronic devices in a large temperature range.

  8. AlF 3sub> Surface-Coated Li[Li 0.2 Ni 0.17 Co 0.07 Mn 0.56 ]O 2 Nanoparticles with Superior Electrochemical Performance for Lithium-Ion Batteries

    SciTech Connect

    Sun, Shuwei; Yin, Yanfeng; Wan, Ning; Wu, Qing; Zhang, Xiaoping; Pan, Du; Bai, Ying; Lu, Xia


    For Li-rich layered cathode materials considerable attention has been paid owing to their high capacity performance for Li-ion batteries (LIBs). In our work, layered Li-rich Li[Li0.2Ni0.17Co0.07Mn0.56]O2 nanoparticles are surface-modified with AlF3sub> through a facile chemical deposition method. The AlF3 sub>surface layers have little impact on the structure of the material and act as buffers to prevent the direct contact of the electrode with the electrolyte; thus, they enhance the electrochemical performance significantly. The 3 wt% AlF3sub>-coated Li-rich electrode exhibits the best cycling capability and has a considerably enhanced capacity retention of 83.1% after 50 cycles. Moreover, the rate performance and thermal stability of the 3 wt% AlF3-coated electrode are also clearly improved. Finally, surface analysis indicates that the AlF3sub> coating layer can largely suppress the undesirable growth of solid electrolyte interphase (SEI) film and, therefore, stabilizes the structure upon cycling.

  9. Hydrothermal synthesis, structure, and magnetic properties of the mixed-valent Np(IV)/Np(V) selenite, Np(NpO{sub 2}){sub 2}(SeO{sub 3}){sub 3}.

    SciTech Connect

    Almond, P. M.; Sykora, R. E.; Skanthakumar, S.; Soderholm, L.; Albrecht-Schmitt, T. E.; Chemistry; Auburn Univ.


    The reaction of NpO{sub 2} with SeO{sub 2} in the presence of CsCl at 180 {sup o}C results in the formation of Np(NpO{sub 2}){sub 2}(SeO{sub 3}){sub 3} (1). The structure of 1 consists of three crystallographically unique Np centers with three different coordination environments in two different oxidation states. Np(1) is found in a neptunyl(V), ONpO{sup +}, unit that is further ligated in the equatorial plane by three chelating SeO{sub 3}{sup 2-} anions to create a hexagonal bipyramidal NpO{sub 8} unit. A second neptunyl(V) cation also occurs for Np(2); it is bound by four bridging selenite anions and by the oxo atom from the Np(1) neptunyl cation to form a pentagonal bipyramidal, NpO{sub 7}, unit. The third neptunium center, Np(3), which contains Np(IV), is found in a distorted NpO{sub 8} dodecahedron. Np(3) is bound by five bridging selenite anions and by three neptunyl units via cation-cation interactions. The NpO{sub 7} pentagonal bipyramids and NpO{sub 8} hexagonal bipyramids share both corners and edges. Both of these polyhedra share corners via cation-cation interactions with the NpO{sub 8} dodecahedra creating a three-dimensional structure with small channels that house the stereochemically active lone pair of electrons on the selenite anions. Magnetic susceptibility data follow Curie-Weiss behavior over the entire temperature range measured (5 {<=} T {<=} 320 K). The effective moment, {mu}{sub eff} = 2.28 {mu}{sub B}, which represents an average over the three crystallographically inequivalent Np atoms, is within the expected range of values. There is no evidence of long-range ordering of the Np moments at temperatures down to 5 K, consistent with the negligible Weiss constant determined from fitting the susceptibility data. Crystallographic data: 1, orthorhombic, space group Pbca, a = 10.6216(5), b = 11.9695(6), and c = 17.8084(8) {angstrom} and Z = 8 (T = 193 K).

  10. Solid-state synthesis, structure and properties of a novel open-framework cadmium selenite bromide: [Cd{sub 10}(SeO{sub 3}){sub 8}Br{sub 4}]·HBr·H{sub 2}O

    SciTech Connect

    Chen, Wen-Tong; Wang, Ming-Sheng; Wang, Guan-E; Chen, Hui-Fen; Guo, Guo-Cong


    A novel open-framework cadmium selenite bromide, [Cd{sub 10}(SeO{sub 3}){sub 8}Br{sub 4}]·HBr·H{sub 2}O (1), has been obtained by a solid-state reaction at 450 °C, and the structure has been determined by single-crystal X-ray diffraction analysis. Compound 1 crystallizes in Pbcm of the orthorhombic system: a=10.882(3), b=16.275(5), c=18.728(6) Å, V=3317(2) Å{sup 3}, R1/wR2=0.0411/0.0659. Compound 1 is characteristic of a novel 3-D open-framework structure, composing {sub ∞}{sup 2}[CdSeO{sub 3}] layers and the pillars of edge-shared CdO{sub 3}Br{sub 2} square pyramids. The lattice water molecules and the HBr molecules locate in the voids of the framework. Optical absorption spectrum of 1 reveals the presence of an optical gap of 1.65 eV. Solid-state photoluminescent study indicates that compound 1 exhibits strong violet emission. TG–DSC measurement shows that compound 1 is thermally stable up to 200 °C. - Graphical abstract: A metal selenite halide has been synthesized and features a 3-D open-framework structure, composing edge-shared CdO{sub 8} decahedra and pillars of edge-sharing pentahedra. UV–vis, TG–DSC and luminescent measurements are also reported. Highlights: • This paper reports a novel cadmium selenite bromide obtained by an intermediate-temperature solid-state reaction. • The title compound is characteristic of a novel 3-D open-framework structure, composing {sub ∞}{sup 2}[CdSeO{sub 3}] layers and the pillars of edge-shared CdO{sub 3}Br{sub 2} square pyramids. • The title compound is thermally stable up to 200 °C. • The title compound has an optical gap of 1.65 eV and exhibits strong violet emission.

  11. Synthesis and crystal structures of the layered uranyl tellurites A{sub 2}[(UO{sub 2}){sub 3}(TeO{sub 3}){sub 2}O{sub 2}] (A=K, Rb, Cs)

    SciTech Connect

    Woodward, Jonathan D.; Almond, Philip M.; Albrecht-Schmitt, Thomas E. . E-mail:


    The reactions of UO{sub 3} and TeO{sub 3} with KCl, RbCl, or CsCl at 800{sup o}C for 5d yield single crystals of A{sub 2}[(UO{sub 2}){sub 3}(TeO{sub 3}){sub 2}O{sub 2}] (A=K (1), Rb (2), and Cs (3)). These compounds are isostructural with one another, and their structures consist of two-dimensional {sub {infinity}}{sup 2}[(UO2)3(TeO3)2O2]2- sheets arranged in a stair-like topology separated by alkali metal cations. These sheets are comprised of zigzagging uranium(VI) oxide chains bridged by corner-sharing trigonal pyramidal TeO{sub 3}{sup 2-} anions. The chains are composed of dimeric, edge-sharing, pentagonal bipyramidal UO{sub 7} moieties joined by edge-sharing tetragonal bipyramidal UO{sub 6} units. The lone-pair of electrons from the TeO{sub 3} groups are oriented in opposite directions with respect to one another on each side of the sheets rendering each individual sheet non-polar. The alkali metal cations form contacts with nearby tellurite oxygen atoms as well as with oxygen atoms from the uranyl moieties. Crystallographic data (193K, MoK{alpha}, {lambda}=0.7107A): 1, triclinic, space group P1-bar , a=6.7985(5)A, b=7.0123(5)A, c=7.8965(6)A, {alpha}=101.852(1){sup o}, {beta}=102.974(1){sup o}, {gamma}=100.081(1){sup o}, V=349.25(4)A3, Z=2, R(F)=2.70% for 98 parameters and 1697 reflections with I>2{sigma}(I); 2, triclinic, space group P1-bar , a=7.0101(6)A, b=7.0742(6)A, c=8.0848(7)A, {alpha}=105.590(2){sup o}, {beta}=101.760(2){sup o}, {gamma}=99.456(2){sup o}, V=367.91(5)A3, Z=2, R(F)=2.36% for 98 parameters and 1817 reflections with I>2{sigma}(I); 3, triclinic, space group P1-bar , a=7.0007(5)A, b=7.5195(6)A, c=8.4327(6)A, {alpha}=109.301(1){sup o}, {beta}=100.573(1){sup o}, {gamma}=99.504(1){sup o}, V=399.49(5)A3, Z=2, R(F)=2.61% for 98 parameters and 1965 reflections with I>2{sigma}(I)

  12. In Situ Observations of Templated Grain Growth in (Na0.5K0.5)0.98Li0.02NbO3sub> Piezoceramics: Texture Development and Template-Matrix Interactions

    SciTech Connect

    Tutuncu, Goknur; Chang, Yunfei; Poterala, Stephen; Messing, Gary L; Jones, Jacob L


    Nucleation, texture development, and phase equilibria were observed during templated grain growth (TGG) of (Na0.5K0.5)0.98Li0.02NbO3sub> (NKLN) via in situ X-ray diffraction (XRD). Initially, NaNbO3sub> templates and NKLN matrix powder exist as distinct phases with unique lattice parameters. Above 850 °C, the templates and matrix begin to react via interdiffusion as characterized by an increase in diffuse scattering between the NaNbO3sub> and NKLN peaks. This process intensifies immediately prior to template growth, leading to merging of diffraction peaks for these two phases. TGG in this system is thus homoepitaxial in nature as it occurs after the NKLN matrix and NaNbO3sub> templates form a solid solution. The degree of alignment in the matrix phase is quantified in situ using the March-Dollase parameters r and f. The degree of orientation of the textured NKLN mirrors the initial alignment of the template particles (r ~ 0.3), while the texture fraction f increases from 0.04 to ~0.67 after 3 h at 1138 °C. This increase in texture fraction follows n = 1/3 power law kinetics consistent with liquid-phase-assisted normal grain growth on plate-like templates. As the observed template-matrix interdiffusion and the onset of texture development proceed extremely rapidly, this work demonstrates the utility of in situ XRD for observing details of TGG that cannot easily be seen via ex situ methods.

  13. Superconductivity versus structural phase transition in the closely related Bi2Rh3.5S2 and Bi2Rh3sub>S2

    SciTech Connect

    Kaluarachchi, Udhara S.; Xie, Weiwei; Lin, Qisheng; Taufour, Valentin; Bud'ko, Sergey L.; Miller, Gordon J.; Canfield, Paul C.


    Single crystals of Bi2Rh3sub>S2 and Bi2Rh3.5S2 were synthesized by solution growth, and the crystal structures and thermodynamic and transport properties of both compounds were studied. In the case of Bi2Rh3sub>S2, a structural first-order transition at around 165 K is identified by single-crystal diffraction experiments, with clear signatures visible in resistivity, magnetization, and specific heat data. No superconducting transition for Bi2Rh3sub>S2 was observed down to 0.5 K. In contrast, no structural phase transition at high temperature was observed for Bi2Rh3.5S2; however, bulk superconductivity with a critical temperature, Tc ≈ 1.7 K, was observed. The Sommerfeld coefficient γ and the Debye temperature (ΘD) were found to be 9.41 mJ mol–1K–2 and 209 K, respectively, for Bi2Rh3sub>S2, and 22 mJ mol–1K–2 and 196 K, respectively, for Bi2Rh3.5S2. As a result, the study of the specific heat in the superconducting state of Bi2Rh3.5S2 suggests that Bi2Rh3.5S2 is a weakly coupled, BCS superconductor.

  14. New polymorphs of Ru{sup III}P{sub 3}O{sub 9}: Cyclo-hexaphosphate Ru{sub 2}P{sub 6}O{sub 18} and metaphosphate Ru(PO{sub 3}){sub 3} with a novel structure

    SciTech Connect

    Fukuoka, Hiroshi; Imoto, Hideo; Saito, Taro


    Two new polymorphs of ruthenium phosphate with RuP{sub 3}O{sub 9} composition were prepared and their crystal structures were determined by single-crystal X-ray diffraction. They are cyclo-hexaphosphate Ru{sub 2}P{sub 6}O{sub 18} and metaphosphate Ru(PO{sub 3}){sub 3}. Ru{sub 2}P{sub 6}O{sub 18} crystallizes in the monoclinic space group P2{sub 1}/c with a = 6.292(2) {angstrom}, b = 15.276(2) {angstrom}, c = 8.365(2) {angstrom}, {beta} = 106.54(2){degrees}, contains cyclo-hexaphosphate rings stacking obliquely along the [100] direction and is isotypic with B-form cyclo-phosphates. Ru(PO{sub 3}){sub 3} has a novel structure and crystallizes in the triclinic space group P1 with a = 6.957(1) {angstrom}, b = 10.324(2) {angstrom},c = 5.030(1) {angstrom}, {alpha} = 92.45(2){degrees}, {beta} = 92.31(2){degrees}, {gamma} = 98.61(1){degrees}, V = 356.5(1) {angstrom}{sup 3}, [PO{sub 3}{sup -}]{sub {infinity}} chains is different from that in the C-form Ru(PO{sub 3}){sub 3}. While the chains in the C-form consisting of PO{sub 3}-O-PO{sub 3} units are condensed in nearly staggered configurations, the units in the new phosphate are eclipsed.

  15. New operation strategy for driving the selectivity of NOx reduction to N2, NH3sub> or N2O during lean/rich cycling of a lean NOx trap catalyst

    SciTech Connect

    Mráček, David; Koci, Petr; Choi, Jae -Soon; Partridge, Jr., William P.


    Periodical regeneration of NOx storage catalyst (also known as lean NOx trap) by short rich pulses of CO, H2 and hydrocarbons is necessary for the reduction of nitrogen oxides adsorbed on the catalyst surface. Ideally, the stored NOx is converted into N2, but N2O and NH3sub> by-products can be formed as well, particularly at low-intermediate temperatures. The N2 and N2O products are formed concurrently in two peaks. The primary peaks appear immediately after the rich-phase inception, and tail off with the breakthrough of the reductant front accompanied by NH3sub> product. In addition, the secondary N2 and N2O peaks then appear at the rich-to-lean transition as a result of reactions between surface-deposited reductants/intermediates (CO, HC, NH3sub>, — NCO) and residual stored NOx under increasingly lean conditions.

  16. Ab initio molecular orbital configuration interaction study of Ni(PH sub 3 ) sub 2 (N sub 2 ). Differences in electron correlation effects between. eta. sup 1 -end-on and. eta. sup 2 -side-on N sub 2 coordination modes

    SciTech Connect

    Sakaki, Shigeyoshi; Ohkubo, Katsutoshi )


    Structure and bonding nature of Ni(PH{sub 3}){sub 2}({eta}{sup 1}-N{sub 2}), Ni(PH{sub 3}){sub 2}({eta}{sup 2}-N{sub 2}) ({eta}{sup 1}-N{sub 2} = {eta}-end-on N{sub 2}, {eta}{sup 2}-N{sub 2} = {eta}{sup 2}-N{sub 2} = {eta}{sup 2}-side-on N{sub 2}), and Ni(PH{sub 3}){sub 2}(C{sub 2}h{sub 4}) are studied with ab initio MO Moeller-Plesset (MP) perturbation and single-double configuration interaction (SD-CI) methods. Introduction of electron correlation effects is indispensable for investigating the relative stability of two coordination modes, {eta}{sup 1}-end-on and {eta}{sup 2}-side-on coordinations, of the N{sub 2} complex. Although the binding energies of both coordination modes are almost the same on the Hartree-Fock level, introducing electron correlation effects with MP2, MP4(DQ), MP4(SDQ), and SD-CI methods yield much larger binding energy of the {eta}{sup 1}-end-on N{sub 2} coordination than that of the {eta}{sup 2}-side-on N{sub 2} coordination. Electron correlation effects on the Ni-N{sub 2} distance are also noticeable; in the {eta}{sup 1}-end-on mode, the Ni-N{sub 2} distance shortens by about 0.1 {angstrom} upon introducing electron correlation effects with MP2, MP4, and SD-CI methods, and the resultant Ni-N{sub 2} distance agrees well with the experimental value. However, introducing electron correlation effects with the SD-CI method only slightly changes the Ni-N{sub 2} distance of Ni(PH{sub 3}){sub 2}({eta}{sup 2}-N{sub 2}) and slightly lengthens the Ni-C distance of Ni(PH{sub 3}){sub 2}(C{sub 2}H{sub 4}), whereas both Ni-N and Ni-C bonds significantly lengthen by about 0.2-0.3 {angstrom} upon MP2 and MP4 calculations. A comparison of the optimized Ni-C distance and the calculated binding energy of the {eta}{sup 1}-end-on N{sub 2} coordination with the experimental values suggests that the SD-CI method is more reliable than the MP method in these complexes.

  17. {alpha}- to {beta}-[C{sub 6}H{sub 4}(NH{sub 3}){sub 2}]{sub 2}Bi{sub 2}I{sub 10} reversible solid-state transition, thermochromic and optical studies in the p-phenylenediamine-based iodobismuthate(III) material

    SciTech Connect

    Hrizi, Chakib; Trigui, Ameni; Abid, Younes; Chniba-Boudjada, Nassira; Bordet, Pierre; Chaabouni, Slaheddine


    {alpha}-[C{sub 6}H{sub 4}(NH{sub 3}){sub 2}]{sub 2}Bi{sub 2}I{sub 10}, which is a new material containing low-dimensional iodobismuthate anions, was synthesized and through its single crystal X-ray diffraction measurements, was proven to crystallize at room temperature in the centrosymmetric space group P2{sub 1}/c. It consists of a p-phenylenediammonium dication and a discrete (0-D) anion built up of edge-sharing bioctahedron. Due to the hydrogen bonds and the interatomic distances (Bi-I, I Midline-Horizontal-Ellipsis I and {pi}-{pi}) changes, {alpha}-phase was transformed into the corresponding centrosymmetric {beta}-phase, {beta}-[C{sub 6}H{sub 4}(NH{sub 3}){sub 2}]{sub 2}Bi{sub 2}I{sub 10}, through a single-crystal to single-crystal transformation occurring upon cooling to -28/-26 Degree-Sign C. Below the transition temperature, {beta}-[C{sub 6}H{sub 4}(NH{sub 3}){sub 2}]{sub 2}Bi{sub 2}I{sub 10} crystallizes in the monoclinic system, centrosymmetric space group P2{sub 1}/n. Besides, the optical transmission measurements on {alpha}-[C{sub 6}H{sub 4}(NH{sub 3}){sub 2}]{sub 2}Bi{sub 2}I{sub 10} thin films have revealed two absorption bands at 2.47 and 3.01 eV. Finally, two room temperature photoluminescence emissions attributed to excitons radiative recombinations confined within the bioctahedra Bi{sub 2}I{sub 10}{sup 4-}, were observed in the red spectral range at 1.9 and 2.05 eV energy. - Graphical abstract: The structure of {alpha}-[C{sub 6}H{sub 4}(NH{sub 3}){sub 2}]{sub 2}Bi{sub 2}I{sub 10} consists of p-phenylenediammonium dications and dimeric decaiododibismuthate tetraanions stacked in a chessboard fashion. The optical properties were investigated by optical absorption and photoluminescence measurements. Highlights: Black-Right-Pointing-Pointer {alpha}-[C{sub 6}H{sub 4}(NH{sub 3}){sub 2}]{sub 2}Bi{sub 2}I{sub 10} is a new material containing low-dimensional iodobismuthate anions. Black-Right-Pointing-Pointer Below -35 Degree-Sign C {alpha}-phase undergoes

  18. 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.

  19. High-pressure high-temperature synthesis and crystal structure of the isotypic rare earth (RE)-thioborate-sulfides RE{sub 9}[BS{sub 3}]{sub 2}[BS{sub 4}]{sub 3}S{sub 3}, (RE=Dy-Lu)

    SciTech Connect

    Borna, Marija; Hunger, Jens; Ormeci, Alim; Zahn, Dirk; Burkhardt, Ulrich; Carrillo-Cabrera, Wilder; Cardoso-Gil, Raul; Kniep, Ruediger


    Application of high-pressure high-temperature conditions (3.5 GPa at 1673 K for 5 h) to mixtures of the elements (RE:B:S=1:3:6) yielded crystalline samples of the isotypic rare earth-thioborate-sulfides RE{sub 9}[BS{sub 3}]{sub 2}[BS{sub 4}]{sub 3}S{sub 3}, (RE=Dy-Lu), which crystallize in space group P6{sub 3} (Z=2/3) and adopt the Ce{sub 6}Al{sub 3.33}S{sub 14} structure type. The crystal structures were refined from X-ray powder diffraction data by applying the Rietveld method. Dy: a=9.4044(2) A, c=5.8855(3) A; Ho: a=9.3703(1) A, c=5.8826(1) A; Er: a=9.3279(12) A, c=5.8793(8) A; Tm: a=9.2869(3) A, c=5.8781(3) A; Yb: a=9.2514(5) A, c=5.8805(6) A; Lu: a=9.2162(3) A, c=5.8911(3) A. The crystal structure is characterized by the presence of two isolated complex ions [BS{sub 3}]{sup 3-} and [BS{sub 4}]{sup 5-} as well as [{open_square}(S{sup 2-}){sub 3}] units. -- Graphical abstract: Isotypic rare earth-thioborate-sulfides RE{sub 9}[BS{sub 3}]{sub 2}[BS{sub 4}]{sub 3}S{sub 3}, (RE=Dy-Lu) were prepared by application of high-pressure high-temperature conditions to mixtures of the elements. Their crystal structures are characterized by presence of the two isolated complex ions [BS{sub 3}]{sup 3-} and [BS{sub 4}]{sup 5-} as well as [{open_square}(S{sup 2-}){sub 3}] units. Quantum mechanical calculations revealed the arrangement of the intrinsic vacancies. Display Omitted Research Highlights: {yields} Application of high-pressure high-temperature conditions to mixtures of the elements yields crystalline samples of the isotypic rare earth-thioborate-sulfides RE{sub 9}[BS{sub 3}]{sub 2}[BS{sub 4}]{sub 3}S{sub 3}, (RE=Dy-Lu). {yields} RE{sub 9}[BS{sub 3}]{sub 2}[BS{sub 4}]{sub 3}S{sub 3}, (RE=Dy-Lu) crystallize in space group P6{sub 3} (Z=2/3) and adopt the Ce{sub 6}Al{sub 3.33}S{sub 14} structure type. {yields} The crystal structure of RE{sub 9}[BS{sub 3}]{sub 2}[BS{sub 4}]{sub 3}S{sub 3}, (RE=Dy-Lu) is characterized by the presence of two isolated complex ions [BS{sub 3

  20. A Straight Forward Route for the Development of Metal-Organic Frameworks Functionalized with Aromatic -OH Groups: Synthesis, Characterization, and Gas (N2, Ar, H2, CO2, CH4, NH3sub>) Sorption Properties

    SciTech Connect

    Spanopoulos, Ioannis; Xydias, Pantelis; Malliakas, Christos D; Trikalitis, Pantelis N


    A facile and general methodology for the development of metal–organic frameworks (MOFs) functionalized with pendant, aromatic hydroxyl (-OH) groups is presented. Extensive gas-sorption studies in representative and important MOFs functionalized with free aromatic -OH groups such as the IRMOF-8 and DUT-6 (or MOF-205), denoted here as 1 and 2, revealed a high CO2/CH4 selectivity for 1 (13.6 at 273 K and 1 bar) and a high NH3sub> uptake of 16.4 mol kg–1 at 298 K and 1 bar for 2.

  1. Highly efficient 2  μm CW and Q-switched Tm3+:Lu2O3sub> ceramics lasers in-band pumped by a Raman-shifted erbium fiber laser at 1670  nm.


    Antipov, Oleg; Novikov, Anton; Larin, Sergey; Obronov, Ivan


    Highly efficient laser oscillations at 2 μm were investigated in Tm:Lu2O3sub> ceramics in-band pumped at 1670 nm by a Raman-shifted erbium fiber laser. Both 23 W CW and 15 W active Q-switched oscillations with 40 ns pulse duration and 15-30 kHz repetition rate were achieved in a high-quality beam. The evolution of two generated waves at 1966 and 2064 nm in dependence on pump power was studied. PMID:27176987

  2. Ferroelectric Nd{sup 3+}:Sr{sub x}Ba{sub 1-x}(NbO{sub 3}){sub 2}-a new nonlinear laser crystal: cw 1-{mu}m stimulated emission ({sup 4}F{sub 3/2}{yields}{sup 4}I{sub 11/2}) and diffuse self-frequency doubling

    SciTech Connect

    Kaminskii, Alexandr A; Garsia, Sole J; Jaque, D; Capmany, J; Bagayev, S N


    Stimulated emission as a result of the inter-Stark transition in the 1-{mu}m {sup 4}F{sub 3/2}{yields}{sup 4}I{sub 11/2} channel of Nd{sup 3+} ions was excited for the first time in an acentric disordered Sr{sub x}Ba{sub 1-x}(NbO{sub 3}){sub 2} (x{approx}0.6) crystal. The low-threshold lasing of this crystal at the 1.0626 {mu}m wavelength was accompanied by diffuse intracavity generation of the second harmonic. (letters to the editor)

  3. A study of suppressed formation of low-conductivity phases in doped Li7La3sub>Zr2O12 garnets by in situ neutron diffraction

    SciTech Connect

    Chen, Yan; Rangasamy, Ezhiylmurugan; dela Cruz, Clarina R.; Liang, Chengdu; An, Ke


    Doped Li7La3sub>Zr2O12 garnets, oxide-based solids with good Li+ conductivity and compatibility, show great potential as leading electrolyte material candidates for all-solid-state lithium ion batteries. Still yet, the conductive bulk usually suffers from the presence of secondary phases and the transition towards a low-conductivity tetragonal phase during synthesis. Dopants are designed to stabilize the high-conductive cubic phase and suppress the formation of the low-conductivity phases. In situ neutron diffraction enables a direct observation of the doping effects by monitoring the phase evolutions during garnet synthesis. It reveals the reaction mechanism involving the temporary presence of intermediate phases. The off-stoichiometry due to the liquid Li2CO3sub> evaporation leads to the residual of the low-conductivity intermediate phase in the as-synthesized bulk. Appropriate doping of an active element may alter the component of the intermediate phases and promote the completion of the reaction. While the dopants aid to stabilize most of the cubic phase, a small amount of tetragonal phase tends to form under a diffusion process. Lastly, the in situ observations provide the guideline of process optimization to suppress the formation of unwanted low-conductivity phases.

  4. ([M(NH{sub 3}){sub 6}][Ag{sub 4}M{sub 4}Sn{sub 3}Se{sub 13}]){sub ∞} (M=Zn, Mn): Three-dimensional chalcogenide frameworks constructed from quaternary metal selenide clusters with two different transition metals

    SciTech Connect

    Xiong, Wei-Wei; Miao, Jianwei; Li, Pei-Zhou; Zhao, Yanli; Liu, Bin; Zhang, Qichun


    Herein we report solvothermal syntheses of two new three-dimensional chalcogenide frameworks ([M(NH{sub 3}){sub 6}][Ag{sub 4}M{sub 4}Sn{sub 3}Se{sub 13}]){sub n} (M=Zn (1), Mn (2)), which consist of quaternary metal selenide clusters with two different transition metals. The compounds represent the first Ag–Zn/Mn–Sn–Se based quaternary anionic frameworks. The optical studies show that the band gaps for 1 and 2 are 2.09 eV and 1.71 eV, respectively. Moreover, the photoelectrochemical study indicates that compound 1 displays n-type semiconducting behaviour and is photoactive under visible light illumination (λ>400 nm). - Graphical abstract: Two 3D framework selenides, [M(NH{sub 3}){sub 6}][Ag{sub 4}M{sub 4}Sn{sub 3}Se{sub 13}] (M=Zn (1), Mn (2)), constructed from quaternary metal selenide clusters, have been solvothermally synthesized and are photoactive under visible light illumination. - Highlights: • Two new three-dimensional selenide frameworks. • Quaternary metal selenide clusters with two different transition metals. • Photoelectrochemical study.

  5. Six novel transition-metal phosphite compounds, with structure related to yavapaiite: Crystal structures and magnetic and thermal properties of A{sup I}[M{sup III}(HPO{sub 3}){sub 2}] (A=K, NH{sub 4}, Rb and M=V, Fe)

    SciTech Connect

    Hamchaoui, Farida; Alonzo, Veronique; Venegas-Yazigi, Diego; Rebbah, Houria; Le Fur, Eric


    Six new transition metal(III) phosphites A{sup I}[V{sup III}(HPO{sub 3}){sub 2}], where A=K (1), NH{sub 4} (2) and Rb (3) and A{sup I}[Fe{sup III}(HPO{sub 3}){sub 2}] where A=K (4), NH{sub 4} (5) and Rb (6) have been synthesized under hydrothermal conditions and the solid-state structures were solved from single-crystal X-ray diffraction data. These compounds crystallize in the hexagonal system, space group P6{sub 3}mc (no. 186), with a=5.3294(2) A and c=12.3130(5) A for 1, a=5.3330(2) A and c=12.8760(4) A for 2, a=5.3459(2) A and c=12.6850(8) A for 3, a=5.3256(1) A and c=12.2362(3) A for 4, a=5.3229(2) A and c=12.8562(4) A for 5, a=5.3393(2) A and c=12.6913(5) A for 6, with Z=2 in the six phases. The crystal structures of these compounds are isotypic and exhibit a layered structure stacked along the c-axis with the A{sup +} cations located in the interlayer space. The [M{sup III}(HPO{sub 3}){sub 2}]{sup -} sheets are formed by MO{sub 6} octahedra interconnected by HPO{sub 3} tetrahedral phosphite oxoanions through sharing vertices. Thermal analysis shows a large range of stability for compounds containing potassium and rubidium cations with decomposition starting around 550 K for stable compounds and above 840 K for the most stable compounds leading in general to pyrophosphate compounds. Triangular nets of metallic centers are observed within the layers in which antiferromagnetic interactions are evidenced by magnetic susceptibility measurements suggesting magnetic frustration. - Graphical abstract: Six new transition metal(III) phosphites A{sup I}[M{sup III}(HPO{sub 3}){sub 2}], where A=K, NH{sub 4}, Rb and M=V, Fe, have been synthesized. The crystal structures of these compounds are isotypic and exhibit a lamellar structure related to Yavapaiite. The M(HPO{sub 3}){sub 2} layers separated by cationic species present the metallic centers in a triangular arrangement. Bulk antiferromagnetic behavior is observed for all the studied compounds. Highlights: Black

  6. Structural, thermal, spectroscopic and magnetic studies of the (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}[Fe {sub x}V{sub 1-x}(HPO{sub 3}){sub 2}] (x = 0.26, 0.52, 0.74) solid solution

    SciTech Connect

    Cisneros, Jose L.; Fernandez-Armas, Sergio; Mesa, Jose L. . E-mail:; Pizarro, Jose L.; Arriortua, Maria I.; Rojo, Teofilo . E-mail:


    The (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}[Fe {sub x}V{sub 1-x}(HPO{sub 3}){sub 2}] (x = 0.26, 0.52 0.74) compounds have been obtained by mild solvothermal conditions in the form of micro-crystalline powder with brown color. The crystal structures were refined by X-ray powder diffraction data using the Rietveld method. The compounds crystallize in the monoclinic system, space group P2/c with the unit-cell parameters, a = 9.262(5) A, b = 8.823(5) A, c = 9.714(6) A, {beta} = 120.84(3){sup o}; a = 9.245(1) A, b = 8.823(1) A, c = 9.698(1)A, {beta} = 120.80(1){sup o} and, a = 9.254(4)A, b = 8.822(4)A, c = 9.702(4)A, {beta} = 120.73(3){sup o} for (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}[Fe{sub 0.26}V{sub 0.74} (HPO{sub 3}){sub 2}] (1) (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}[Fe{sub 0.52}V{sub 0.48}(HPO{sub 3}){sub 2}] (2), and (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}[Fe{sub 0.74}V{sub 0.26}(HPO{sub 3}){sub 2}] (3). The compounds show an open crystalline structure with three-dimensional character, whose formula for the anionic inorganic skeleton is [M(HPO{sub 3}){sub 2}]{sup 2-}. The inorganic framework is formed by [MO{sub 6}] octahedra inter-connected by phosphite groups. The structure of the compounds exhibits channels extended along the [1 0 0] and [0 0 1] directions and the ethylendiammonium cations are located inside these channels, linked through hydrogen bonds and ionic interactions. The infrared spectra show the bands corresponding to the stretching (P-H) vibration of the phosphite group and the band corresponding to the deformation mode of the ethylendiammonium cation, {delta}(NH{sub 3} {sup +}). The thermal and thermodiffractometric behavior show that the compounds are stable up to approximately 300 deg. C, at higher temperatures the decomposition of the crystal structure by calcination of the organic cation starts. The diffuse reflectance spectra show bands of the V{sup 3+} ion (d {sup 2}), and a band of the Fe{sup 3+} ion (d {sup 5}), in a slightly distorted octahedral

  7. Effects of lanthanum dopants on the Curie–Weiss and the local order behaviors for Pb{sub 1−x}La{sub x}(Fe{sub 2/3}W{sub 1/3}){sub 0.7}Ti{sub 0.3}O{sub 3} relaxor ferroelectrics

    SciTech Connect

    Hong, Cheng-Shong; Chu, Sheng-Yuan; Hsu, Chi-Cheng; Su, Hsiu-Hsien


    Graphical abstract: The local order as a function of temperature by using (a) the spin-glass model and (b) the modified-Landau theory for Pb{sub 1−x}La{sub x}(Fe{sub 2/3}W{sub 1/3}){sub 0.7}Ti{sub 0.3}O{sub 3} ceramics with different amounts of lanthanum dopants. Display Omitted Highlights: ► The effects of La are investigated for Pb{sub 1−x}La{sub x}(Fe{sub 2/3}W{sub 1/3}){sub 0.7}Ti{sub 0.3}O{sub 3} ceramics. ► La can change their dielectric properties and ordering state. ► The spin glassy behaviors and the freezing process are also affected by La. ► The response mechanisms of La are proposed for the local polarization behavior. -- Abstract: The effects of lanthanum dopants are investigated on the dielectric responses for Pb{sub 1−x}La{sub x}(Fe{sub 2/3}W{sub 1/3}){sub 0.7}Ti{sub 0.3}O{sub 3} ceramics. According to the experimental data and fitting results, it is concluded that the dielectric characteristics are changed from a long-range-ordered (LRO) ferroelectric state to a short-range-ordered (SRO) relaxor by increasing the amounts of lanthanum dopants. Furthermore, the spin glassy behaviors and the freezing process of local polarizations are not only affected by the ordering degree of B-site cations but also affected by the defect polar pairs. Their response mechanisms are proposed that the growth of the 1:1 ordered domain Pb{sub 1−x}La{sub x}(Fe{sub 1/2}W{sub 1/2})O{sub 3} is impeded since its charge imbalance is enhanced by increasing the amounts of lanthanum dopants, and the defect polar pairs of lead, tungsten and oxygen vacancy are induced by the pyrochlore phase, PbWO{sub 4} or Pb{sub 0.99}La{sub 0.01}WO{sub 4}, when the amount of lanthanum dopants exceed 5 mol.%.

  8. Pressure dependence of the exchange interaction in the dimeric single-molecule magnet [Mn{sub 4}O{sub 3}Cl{sub 4}(O{sub 2}CEt){sub 3}(py){sub 3}]{sub 2} from inelastic neutron scattering

    SciTech Connect

    Sieber, A.; Waldmann, O.; Ochsenbein, S. T.; Carver, G.; Guedel, H. U.; Foguet-Albiol, D.; Christou, G.; Mutka, H.; Fernandez-Alonso, F.; Mezouar, M.; Weber, H. P.


    The low-lying magnetic excitations in the dimers of single-molecule magnets [Mn{sub 4}O{sub 3}Cl{sub 4}(O{sub 2}CEt){sub 3}(py){sub 3}]{sub 2}, or (Mn{sub 4}){sub 2}, are studied by inelastic neutron scattering as a function of hydrostatic pressure. The anisotropy parameters D and B{sub 0}{sup 4}, which describe each Mn{sub 4} subunit, are essentially pressure independent, while the antiferromagnetic exchange coupling J between the two Mn{sub 4} subunits strongly depends on pressure, with an increase of 42% at 17 kbar. Additional pressure-dependent powder x-ray measurements allow a structural interpretation of the findings.

  9. Second order phase transition temperature of single crystals of Gd5Si1.3sub>Ge2.7 and Gd5Si1.4Ge2.6

    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)4 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 Gd5Si1.3sub>Ge2.7 and Gd5Si1.4Ge2.6. 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.

  10. A new organically templated monodimensional mixed valence (Fe{sup II}/Fe{sup III}) phosphite: (C{sub 4}H{sub 12}N{sub 2})[Fe{sup II}Fe{sup III}(HPO{sub 3}){sub 2}F{sub 3}

    SciTech Connect

    Fernandez-Armas, Sergio


    The organically templated (C{sub 4}H{sub 12}N{sub 2})[Fe{sup II}Fe{sup III}(HPO{sub 3}){sub 2}F{sub 3}] compound has been synthesized under mild solvothermal conditions. The crystal structure has been determined from X-ray single-crystal diffraction data. The compound crystallizes in the P2{sub 1}/n monoclinic space group, with the unit-cell parameters a = 12.935(1), b = 6.4476(7), c = 15.693(2) A, {beta} = 105.630(9){sup o} and Z = 4. The crystal structure consists of [Fe{sup II}Fe{sup III}(HPO{sub 3}){sub 2}F{sub 3}]{sup 2-} chains formed by a central chain built of [Fe(2)O{sub 4}F{sub 2}] edge-sharing octahedra, and two side chains formed by alternating [Fe(1)O{sub 3}F{sub 3}] octahedra and [HP(1)O{sub 3}] tetrahedra. The piperazinium cations are placed between the chains linked by ionic and hydrogen interactions. The IR and Raman spectra show the existence of two phosphite crystallographically independent. From the diffuse reflectance spectrum the D {sub q} parameter for the iron(II) cations has been calculated (D {sub q} = 820 cm{sup -1}). The Moessbauer spectrum in the paramagnetic state shows the simultaneous presence of Fe{sup 2+} and Fe{sup 3+}. The magnetic measurements indicate the existence of antiferromagnetic interactions.

  11. Eu3sub>Ir2In15: A mixed-valent and vacancy-filled variant of the Sc5Co4Si10 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, Eu3sub>Ir2In15 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 Eu3sub>Ir2In15 and hypothetical vacancy variant Eu5Ir4In10 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 RE5T4X10 would exist with X as a group 13 elements.

  12. Preparation and characterization of two high oxidation state molybdenum dinitrogen complexes: (MoCp sup * Me sub 3 ) sub 2 (. mu. -N sub 2 ) and (MoCp sup * Me sub 3 )(. mu. -N sub 2 )(WCp prime Me sub 3 )

    SciTech Connect

    Schrock, R.R.; Kolodziej, R.M.; Liu, A.H.; Davis, W.M.; Vale, M. G. )


    (MoCp{sup *}Cl{sub 4}){sub 2} (Cp{sup *} = C{sub 5}Me{sub 5}) is alkylated by MeMgCl in tetrahydrofuran to give red microcrystalline MoCp{sup *}Me{sub 4} in {approximately}70% yield. MoCp{sup *}Me{sub 4} reacts with 1 equiv of HOSO{sub 2}CF{sub 3} in ether to give purple microcrystalline MoCp{sup *}Me{sub 3}(OSO{sub 2}CF{sub 3}) in {approximately}85% yield. Triflate can be displaced readily from MoCp{sup *}Me{sub 3}(OSO{sub 2}Cf{sub 3}) by adding LiOR (OR = pentafluorophenoxide, 2,6-diisopropylphenoxide, 2,6-dimethoxyphenoxide, 2,4,6-trimethoxyphenoxide, 2,6-dimethyl-4-methoxyphenoxide, and catecholate) in ether to yield complexes of the type MoCp{sup *}Me{sub 3}(OR) (MoCp{sup *}Me{sub 2}(cat) in the case of catecholate) in 50-80% yield. The complexes can be oxidized chemically (with the exception of OR = pentafluorophenoxide and catecholate) by (FeCp{sub 2})(PF{sub 6}) in methylene chloride to give complexes of the type (MoCp{sup *}Me{sub 3}(OR))(PF{sub 6}) as orange-brown microcrystalline powders in 80-90% yield. Addition of 3 equiv of hydrazine to (MoCp{sup *}Me{sub 3}(OR))(PF{sub 6}) in ether provides (MoCp{sup *}Me{sub 3}){sub 2}({mu}-N{sub 2}) in low yield after purification by filtration through alumina and recrystallization from ether. (MoCp{sup *}Me{sub 3}){sub 2}({mu}-N{sub 2}) belongs to the space group P2{sub 1}/n.

  13. Solvent-induced and polyether-ligand-induced redox isomerization within an asymmetrically coordinated mixed-valence ion: trans-(py)(NH[sub 3])[sub 4]Ru(4-NCpy)Ru(2,2[prime]-bpy)[sub 2]Cl[sup 4+

    SciTech Connect

    Curtis, J.C.; Massum, M. ); Roberts, J.A.; Blackbourn, R.L.; Dong, Yuhua; Johnson, C.S.; Hupp, J.T. )


    Advantage is taken of oxidation-state-dependent ligand (ammine)/solvent interactions to shift redox potentials and effect redox isomerization in the title complex. In poorly basic solvents, the stable isomeric form is trans-(py)(NH[sub 3])[sub 4]Ru[sup II](NCpy)Ru[sup III](bpy)[sub 2]Cl[sup 4+] (py is pyridine; NCpy is 4-cyanopyridine; bpy is 2,2[prime]-bipyridine). In contrast, in stronger Lewis bases or in a mixture of strong and weak bases (dimethyl sulfoxide + nitromethane), the preferred isomer is trans-(py)(NH[sub 3])[sub 4]Ru[sup III](NCpy)Ru[sup II](bpy)Cl[sup 4+]. Evidence for redox isomerization was obtained, in part, from plots of formal potentials versus solvent Lewis basicity. Confirmatory evidence was obtained from a combination of electrochemical reaction entropy and resonance Raman spectroscopic experiments. UV-vis-near-IR absorption experiments, however, were not found to be useful in demonstrating isomerization. In a released series of experiments, redox isomerization was also demonstrated based on ammine binding by either a low molecular weight poly(ethylene glycol) species or by a macrocyclic ligand, dibenzo-36-crown-12. Much smaller molar amounts of either the polymer (substoichiometric) or crown (approximately stoichiometic) are required, in comparison to basic solvent (several-fold excess), in order to induce isomerization in nitromethane as the initial solvent. The possible general utility of the redox isomerization concept in time-resolved intramolecular charge-transfer studies and in optical studies of competitive hole- and electron hole- and electron-transfer pathways is mentioned.

  14. Synthesis and Structure of In(IO3sub>)3sub> and Vibrational Spectroscopy of M(IO3sub>)3sub> (M = Al, Ga, In)

    SciTech Connect

    Ngo, Nhan; Kalachnikova, Katrina; Assefa, Zerihun; Haire, Richard {Dick} G; Sykora, Richard E.


    The reaction of Al, Ga, or In metals and H5IO6 in aqueous media at 180 C leads to the formation of Al(IO3)3, Ga(IO3)3, or In(IO3)3, respectively. Single-crystal X-ray diffraction experiments have shown In(IO3)3 contains the Te4O9-type structure, while both Al(IO3)3 and Ga(IO3)3 are known to exhibit the polar Fe(IO3)3-type structure. Crystallographic data for In(IO3)3, trigonal, space group View the MathML source, a=9.7482(4) {angstrom}, c=14.1374(6) {angstrom}, V=1163.45(8) Z=6, R(F)=1.38% for 41 parameters with 644 reflections with I>2s(I). All three iodate structures contain group 13 metal cations in a distorted octahedral coordination environment. M(IO3)3 (M=Al, Ga) contain a three-dimensional network formed by the bridging of Al3+ or Ga3+ cations by iodate anions. With In(IO3)3, iodate anions bridge In3+ cations in two-dimensional layers. Both materials contain distorted octahedral holes in their structures formed by terminal oxygen atoms from the iodate anions. The Raman spectra have been collected for these metal iodates; In(IO3)3 was found to display a distinctively different vibrational profile than Al(IO3)3 or Ga(IO3)3. Hence, the Raman profile can be used as a rapid diagnostic tool to discern between the different structural motifs.

  15. High temperature redox reactions with uranium: Synthesis and characterization of Cs(UO{sub 2})Cl(SeO{sub 3}), Rb{sub 2}(UO{sub 2}){sub 3}O{sub 2}(SeO{sub 3}){sub 2}, and RbNa{sub 5}U{sub 2}(SO{sub 4}){sub 7}

    SciTech Connect

    Babo, Jean-Marie; Albrecht-Schmitt, Thomas E.


    Cs(UO{sub 2})Cl(SeO{sub 3}) (1), Rb{sub 2}(UO{sub 2}){sub 3}O{sub 2}(SeO{sub 3}){sub 3} (2), and RbNa{sub 5}U{sub 2}(SO{sub 4}){sub 7} (3) single crystals were synthesized using CsCl, RbCl, and a CuCl/NaCl eutectic mixture as fluxes, respectively. Their lattice parameters and space groups are as follows: P2{sub 1}/n (a=6.548(1) Å, b=11.052(2) Å, c=10.666(2) Å and β=93.897(3)°), P1{sup ¯} (a=7.051(2) Å, b=7.198(2) Å, c=8.314(2) Å, α=107.897(3)°, β=102.687(3)° and γ=100.564(3)°) and C2/c (a=17.862(4) Å, b=6.931(1) Å, c=20.133(4) Å and β=109.737(6)°. The small anionic building units found in these compounds are SeO{sub 3}{sup 2−} and SO{sub 4}{sup 2−} tetrahedra, oxide, and chloride. The crystal structure of the first compound is composed of [(UO{sub 2}){sub 2}Cl{sub 2}(SeO{sub 3}){sub 2}]{sup 2−} chains separated by Cs{sup +} cations. The structure of (2) is constructed from [(UO{sub 2}){sub 3}O{sub 11}]{sup 16−} chains further connected through selenite units into layers stacked perpendicularly to the [0 1 0] direction, with Rb{sup +} cations intercalating between them. The structure of compound (3) is made of uranyl sulfate layers formed by edge and vertex connections between dimeric [U{sub 2}O{sub 16}] and [SO{sub 4}] polyhedra. These layers contain unusual sulfate–metal connectivity as well as large voids. - Graphical abstract: A new family of uranyl selenites and sulfates has been prepared by high-temperature redox reactions. This compounds display new bonding motifs. Display Omitted - Highlights: • Low-dimensional Uranyl Oxoanion compounds. • Conversion of U(IV) to U(VI) at high temperatures. • Dimensional reduction by both halides and stereochemically active lone-pairs.

  16. Plasma-enhanced and thermal atomic layer deposition of Al{sub 2}O{sub 3} using dimethylaluminum isopropoxide, [Al(CH{sub 3}){sub 2}({mu}-O{sup i}Pr)]{sub 2}, as an alternative aluminum precursor

    SciTech Connect

    Potts, Stephen E.; Dingemans, Gijs; Lachaud, Christophe; Kessels, W. M. M.


    The authors have been investigating the use of [Al(CH{sub 3}){sub 2}({mu}-O{sup i}Pr)]{sub 2} (DMAI) as an alternative Al precursor to [Al(CH{sub 3}){sub 3}] (TMA) for remote plasma-enhanced and thermal ALD over wide temperature ranges of 25-400 and 100-400 deg. C, respectively. The growth per cycle (GPC) obtained using in situ spectroscopic ellipsometry for plasma-enhanced ALD was 0.7-0.9 A/cycle, generally lower than the >0.9 A/cycle afforded by TMA. In contrast, the thermal process gave a higher GPC than TMA above 250 deg. C, but below this temperature, the GPC decreased rapidly with decreasing temperature. Quadrupole mass spectrometry data confirmed that both CH{sub 4} and HO{sup i}Pr were formed during the DMAI dose for both the plasma-enhanced and thermal processes. CH{sub 4} and HO{sup i}Pr were also formed during the H{sub 2}O dose but combustion-like products (CO{sub 2} and H{sub 2}O) were observed during the O{sub 2} plasma dose. Rutherford backscattering spectrometry showed that, for temperatures >100 deg. C and >200 deg. C for plasma-enhanced and thermal ALD, respectively, films from DMAI had an O/Al ratio of 1.5-1.6, a H content of {approx}5 at. % and mass densities of 2.7-3.0 g cm{sup -3}. The film compositions afforded from DMAI were comparable to those from TMA at deposition temperatures {>=}150 deg. C At lower temperatures, there were differences in O, H, and C incorporation. 30 nm thick Al{sub 2}O{sub 3} films from the plasma-enhanced ALD of DMAI were found to passivate n- and p-type Si floatzone wafers ({approx}3.5 and {approx}2 {Omega} cm, respectively) with effective carrier lifetimes comparable to those obtained using TMA. Surface recombination velocities of < 3 and < 6 cm s{sup -1} were obtained for the n- and p-type Si, respectively. Using these results, the film properties obtained using DMAI and TMA are compared and the mechanisms for the plasma-enhanced and thermal ALD using DMAI are discussed.

  17. Thermodynamic Model for the Solubility of NdF3sub>(cr) in the Na+-NH4+ – Nd3+–F-–H2O System at 25 °C

    SciTech Connect

    Rai, Dhanpat; Yui, Mikazu; Kitamura, Akira; Yoshikawa, Hideki; Felmy, A. R.


    The objectives of this study were to develop a reliable thermodynamic model for the Nd-F system based on critical review and experimental studies. The SIT model was used to convert concentration constants reported in the literature to constants at zero ionic strengths for cross comparison and selection of reliable values. The critically evaluated thermodynamic constants for the formation of NdF2+ and NdF2+ were then used to interpret the extensive NdF3(cr) solubility data in NaF and NH4F solutions, ranging in concentrations from extremely low values to as high as 1.0, equilibrated for different periods ranging up to as long as 72 days. These efforts have resulted in log βn0 for the reaction [Nd3+ + nF- = NdFn3-n] of (3.81 ± 0.10), (5.89 ± 0.77), and <12.48 for n of 1 through 3, respectively. The log10 Ksp0 for the solubility of NdF3sub>(cr) (NdF3(cr) = Nd3+ + 3F-) was determined to be -(20.49 ± 0.37). Because 1) Nd is an excellent analog for trivalent actinides -- An(III) (e.i., Pu(III), Am(III), and Cm(III)) -- and 2) the available data for the An(III)-F system, especially the solubility products of AnF3sub>(cr), are of extremely poor quality, the critical literature review in combination with the experimental Nd-F system data have been used to assign thermodynamic constants for the An(III)-F reactions until good quality specific data for them becomes available.

  18. Examination of the mechanism for the reversible aging behavior at open circuit when changing the operating temperature of (La0.8Sr0.2)0.95 MnO3sub> electrodes

    SciTech Connect

    Abernathy, Harry; Finklea, Harry O.; Mebane, David S.; Song, Xueyan; Chen, Yun; Gerdes, Kirk


    The aging behavior of symmetrical cells, consisting of either (La0.8Sr0.2)0.95 MnO3sub> (LSM) or La0.6Sr0.4Co0.2Fe0.8O3sub> (LSCF) electrodes screen printed on either 8 mol% yttria-stabilized zirconia (YSZ) or Ce0.8Gd0.2O2 (GDC) electrolyte substrates, is reported as the symmetrical cell is thermally cycled between 700 °C and 800 °C. For LSM, between 700 °C and 850 °C, the polarization resistance exhibits slow increases or decreases with time (on the order of days) after a quick change in temperature. When increasing the temperature, the polarization resistance decreases with time, and when decreasing the temperature, the polarization resistance slowly increases with time. In a previous work, the authors had explained these results with LSM by connecting the testing conditions to literature reports of surface analysis of LSM thin films which demonstrated a change in the amount of surface cation segregation as a function of temperature. In this work, TEM/EDS/XPS analysis of dense LSM pellets thermally cycled under the same conditions as the symmetrical cells does not indicate any significant reversible change in the surface composition of the LSM pellet between 700 °C and 800 °C. An alternative hypothesis is proposed to explain the relationship between polarization resistance and the LSM cation/anion vacancy concentrations controlled by the Schottky reaction. The timescale of aging behavior is related to the time necessary for the cations to move to or from the LSM surface to adjust to the new equilibrium at each temperature. Furthermore, the relevance in understanding the mechanism behind the aging behavior is emphasized with respect to fuel cell sample/stack modeling as well as to proper testing procedures for reaching reliable conclusions when comparing different electrode samples.

  19. Interfacial Electron Transfer Dynamics Following Laser Flash Photolysis of [Ru(bpy)2((4,4'-PO3sub>H2)2bpy)]2+ in TiO2 Nanoparticle Films in Aqueous Environments

    SciTech Connect

    Brennaman, Kyle M.; Patrocinio, Antonio O. T.; Song, Wenjing; Jurss, Jonah W.; Concepcion, Javier J.; Hoertz, Paul G.; Traub, Matthew C.; Murakami Iha, Neyde Y.; Meyer, Thomas J.


    Nanosecond laser flash photolysis has been used to investigate injection and back electron transfer from the complex [(Ru(bpy)2(4,4'-(PO3sub>H2)2bpy)]2+ surface-bound to TiO2 (TiO2-RuII). The measurements were conducted under conditions appropriate for water oxidation catalysis by known single-site water oxidation catalysts. Systematic variations in average lifetimes for back electron transfer, <τbet>, were observed with changes in pH, surface coverage, incident excitation intensity, and applied bias. The results were qualitatively consistent with a model involving rate-limiting thermal activation of injected electrons from trap sites to the conduction band or shallow trap sites followed by site-to-site hopping and interfacial electron transfer, TiO2(e-)-Ru3+{yields}TiO2-Ru2+. The appearance of pH-dependent decreases in the efficiency of formation of TiO2-Ru3+ and in incident-photon-to-current efficiencies with the added reductive scavenger hydroquinone point to pH-dependent back electron transfer processes on both the sub-nanosecond and millisecond–microsecond time scales, which could be significant in limiting long-term storage of multiple redox equivalents.

  20. Effect of metal in M3sub>(btc)2 and M2(dobdc) MOFs for O2/N2 separations: A combined density functional theory and experimental study

    SciTech Connect

    Parkes, Marie V.; Sava Gallis, Dorina F.; Greathouse, Jeffery A.; Nenoff, Tina M.


    Computational screening of metal-organic framework (MOF) materials for selective oxygen adsorption from air could lead to new sorbents for the oxyfuel combustion process feedstock streams. A comprehensive study on the effect of MOF metal chemistry on gas binding energies in two common but structurally disparate metal-organic frameworks has been undertaken. Dispersion-corrected density functional theory methods were used to calculate the oxygen and nitrogen binding energies with each of fourteen metals, respectively, substituted into two MOF series, M2(dobdc) and M3sub>(btc)2. The accuracy of DFT methods was validated by comparing trends in binding energy with experimental gas sorption measurements. A periodic trend in oxygen binding energies was found, with greater oxygen binding energies for early transition-metal-substituted MOFs compared to late transition metal MOFs; this was independent of MOF structural type. The larger binding energies were associated with oxygen binding in a side-on configuration to the metal, with concomitant lengthening of the O-O bond. In contrast, nitrogen binding energies were similar across the transition metal series, regardless of both MOF structural type and metal identity. Altogether, these findings suggest that early transition metal MOFs are best suited to separating oxygen from nitrogen, and that the MOF structural type is less important than the metal identity.

  1. Surface collective modes in the topological insulators Bi2Se3sub> and Bi0.5Sb1.5Te3-xSex

    SciTech Connect

    Kogar, A.; Gu, G.; Vig, S.; Thaler, A.; Wong, M. H.; Xiao, Y.; Reig-i-Plessis, D.; Cho, G. Y.; Valla, T.; Pan, Z.; Schneeloch, J.; Zhong, R.; Hughes, T. L.; MacDougall, G. J.; Chiang, T. -C.; Abbamonte, P.


    In this study, we used low-energy, momentum-resolved inelastic electron scattering to study surface collective modes of the three-dimensional topological insulators Bi2Se3sub> and Bi0.5Sb1.5Te3-xSex. Our goal was to identify the “spin plasmon” predicted by Raghu and co-workers [Phys. Rev. Lett. 104, 116401 (2010)]. Instead, we found that the primary collective mode is a surface plasmon arising from the bulk, free carriers in these materials. This excitation dominates the spectral weight in the bosonic function of the surface χ''(q,ω) at THz energy scales, and is the most likely origin of a quasiparticle dispersion kink observed in previous photoemission experiments. Our study suggests that the spin plasmon may mix with this other surface mode, calling for a more nuanced understanding of optical experiments in which the spin plasmon is reported to play a role.

  2. Mixed uranium chloride fluorides UF{sub 6{minus}n}Cl{sub n} and methoxyuranium fluorides UF{sub 6{minus}n}(OCH{sub 3}){sub n}: A theoretical study of equilibrium geometries, vibrational frequencies, and the role of the f orbitals

    SciTech Connect

    Schreckenbach, G.


    The title compounds, the uranium (VI) fluoride chlorides (UF{sub 6{minus}n}Cl{sub n}, n = 0--6) and methoxyuranium (VI) fluorides [UF{sub 6{minus}n}(OCH{sub 3}){sub n}, n = 0--5], have been studied using relativistic density functional theory. Applying the B3LYP hybrid functional and an effective core potential on uranium, equilibrium, geometries have been calculated for these molecules. In addition, harmonic vibrational frequencies have been computed for the chloride fluorides. Calculated frequencies have been compared to experiment where possible. All experimentally observed bands have been assigned, based on these calculations. The average deviation between theoretical and experimental frequencies is 15.6 cm{sup {minus}1} for 23 experimental modes. Theory always underestimates the experimental frequencies. This can be explained by the calculated bond lengths that are somewhat too long. The electronic structure of the uranium (VI) chloride fluorides has been investigated using scalar relativistic calculations and the PW91 functional. Periodic trends in the role and bonding contribution of the uranium 5f orbitals are discussed.

  3. Syntheses and reactions of polymer-bound molybdenum complexes and hydrogenolyses of an alkynyl cobalt carbonyl cluster. [Co/sub 3/(CO)/sub 9/CCH/sub 2/CCH/sub 2/C(CH/sub 3/)/sub 3/; cyclopentadienyl-(tricarbonyl) hydridomolybdenum

    SciTech Connect

    Frommer, J.E.


    Co/sub 3/(CO)/sub 9/CCH/sub 2/C(CH/sub 3/)/sub 3/ reacted with hydrogen in aromatic solvents to yield 3,3-dimethylbutene, 2,2-dimethylbutane, and 4,4-dimethylpentanal. First order decomposition of starting material and a hydrogen pressure dependence for the rate of appearance of total products were indicated. The hydrogenation was inhibited in the presence of carbon monoxide (CO:H/sub 2/, 3.7:3.7 atm, 60/sup 0/C), but at 85/sup 0/ under the same CO/H/sub 2/ atmosphere, aldehyde production became the predominant reaction pathway at the expense of earlier-formed olefin. Incorporation of independently added olefins in the hydrogenation suggested the intermediacy of olefin aldehyde ad alkane production. A polystyrene-attached n/sup 5/-cyclopentadienyl(tricarbonyl)-hydridomolybdenum complex was prepared and its reactions with several THF-soluble bases were investigated. Enolates of ..beta..-dicarbonyl compounds quantitatively deprotonated this complex, giving polymer-bound salts of the corresponding anion. Little change in pKa in THF was induced by binding the molybdenum hydride to the polymer. Even though the polymer-supported partners rendered the reactions heterogeneous, the systems adhered reasonably well to conventional equilibrium behavior. A polymer-bound carboxylic acid and its conjugate base also displayed essentially conventional equilibrium dynamics.

  4. 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.

  5. Reversible Exsolution of Nanometric Fe2O3 sub> Particles in BaFe2-x(PO4)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(PO4)2 into iron-deficient BaFe2–x(PO4)2 phases and nanometric α-Fe2O3sub> (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+).

  6. Hybrid Inorganic-Organic Materials with an Optoelectronically Active Aromatic Cation: (C7H7)2SnI6 and C7H7PbI3sub>

    SciTech Connect

    Maughan, Annalise E.; Kurzman, Joshua A.; Neilson, James R.


    Inorganic materials with organic constituents—hybrid materials—have shown incredible promise as chemically tunable functional materials with interesting optical and electronic properties. Here, the preparation and structure are reported of two hybrid materials containing the optoelectronically active tropylium ion within tin- and lead-iodide inorganic frameworks with distinct topologies. The crystal structures of tropylium tin iodide, (C7H7)2SnI6, and tropylium lead iodide, C7H7PbI3sub>, were solved using high-resolution synchrotron powder X-ray diffraction informed by X-ray pair distribution function data and high-resolution time-of-flight neutron diffraction. Tropylium tin iodide contains isolated tin(IV)-iodide octahedra and crystallizes as a deep black solid, while tropylium lead iodide presents one-dimensional chains of face-sharing lead(II)-iodide octahedra and crystallizes as a bright red-orange powder. Experimental diffuse reflectance spectra are in good agreement with density functional calculations of the electronic structure. Calculations of the band decomposed charge densities suggest that the deep black color of tropylium tin iodide is attributed to iodide ligand to tin metal charge transfer, while the bright red-orange color of tropylium lead iodide arises from charge transfer between iodine and tropylium states. Understanding the origins of the observed optoelectronic properties of these two compounds, with respect to their distinct topologies and organic–inorganic interactions, provides insight into the design of tropylium-containing compounds for potential optical and electronic applications.

  7. Structural phase transition, narrow band gap, and room-temperature ferromagnetism in [KNbO{sub 3}]{sub 1−x}[BaNi{sub 1/2}Nb{sub 1/2}O{sub 3−δ}]{sub x} ferroelectrics

    SciTech Connect

    Zhou, Wenliang; Yang, Pingxiong Chu, Junhao; Deng, Hongmei


    Structural phase transition, narrow band gap (E{sub g}), and room-temperature ferromagnetism (RTFM) have been observed in the [KNbO{sub 3}]{sub 1−x}[BaNi{sub 1/2}Nb{sub 1/2}O{sub 3−δ}]{sub x} (KBNNO) ceramics. All the samples have single phase perovskite structure, but exhibit a gradual transition behaviour from the orthorhombic to a cubic structure with the increase of x. Raman spectroscopy analysis not only corroborates this doping-induced change in normal structure but also shows the local crystal symmetry for x ≥ 0.1 compositions to deviate from the idealized cubic perovskite structure. A possible mechanism for the observed specific changes in lattice structure is discussed. Moreover, it is noted that KBNNO with compositions x = 0.1–0.3 have quite narrow E{sub g} of below 1.5 eV, much smaller than the 3.2 eV band gap of parent KNbO{sub 3} (KNO), which is due to the increasing Ni 3d electronic states within the gap of KNO. Furthermore, the KBNNO materials present RTFM near a tetragonal to cubic phase boundary. With increasing x from 0 to 0.3, the magnetism of the samples develops from diamagnetism to ferromagnetism and paramagnetism, originating from the ferromagnetic–antiferromagnetic competition. These results are helpful in the deeper understanding of phase transitions, band gap tunability, and magnetism variations in perovskite oxides and show the potential role, such materials can play, in perovskite solar cells and multiferroic applications.

  8. Synthesis, characterization and magnetic property of a new 3D iron phosphite: |C{sub 4}N{sub 3}H{sub 14}|[Fe{sub 3}(HPO{sub 3}){sub 4}F{sub 2}(H{sub 2}O){sub 2}] with intersecting channels

    SciTech Connect

    Qiao Jian; Zhang Lirong; Yu Yang; Li Guanghua; Jiang Tianchan; Huo Qisheng; Liu Yunling


    A new open-framework iron (III) phosphite |C{sub 4}N{sub 3}H{sub 14}|[Fe{sub 3}(HPO{sub 3}){sub 4}F{sub 2}(H{sub 2}O){sub 2}] has been solvothermally synthesized by using diethylenetriamine (DETA) as the structure-directing agent. Single-crystal X-ray diffraction analysis reveals that the compound crystallizes in the monoclinic space group C2/c having unit cell parameters a=12.877(3) A, b=12.170(2) A, c=12.159(2) A, beta=93.99(3){sup o}, V=1900.9(7) A{sup 3}, and Z=4 with R{sub 1}=0.0447, wR{sub 2}=0.0958. The complex structure consists of HPO{sub 3} pseudo-tetrahedra and {l_brace}Fe{sub 3}O{sub 14}F{sub 2}{r_brace} trimer building units. The assembly of these building units generates 3D inorganic framework with intersecting 6-, 8-, and 10-ring channels. The DETA cations are located in the 10-ring channels linked by hydrogen bonds. The Moessbauer spectrum shows that there exhibit two crystallographically independent iron (III) atoms. And the magnetic investigation shows the presence of antiferromagnetic interactions. Further characterization of the title compound was performed using X-ray powder diffraction (XRD), infrared (IR) spectra, thermal gravimetric analyses (TGA), inductively coupled plasma (ICP) and elemental analyses. - Graphical abstract: A new three-dimensional iron phosphite with intersecting 6-, 8-, 10-ring channels has been solvothermally synthesized by using diethylenetriamine (DETA) as the structure-directing agent.

  9. Spectroscopic and laser characterization of Yb0.15:(LuxY1-x)3sub>Al5O12 ceramics with different Lu/Y balance.


    Pirri, Angela; Toci, Guido; Li, Jiang; Xie, Tengfei; Pan, Yubai; Babin, Vladimir; Beitlerova, Alena; Nikl, Martin; Vannini, Matteo


    We report a broad comparative analysis of the spectroscopic and laser properties of solid solution Lutetium-Yttrium Aluminum Garnet (LuYAG, (LuxY1-x)3sub>Al5O12) ceramics doped with Yb. The investigation was mainly aimed to assess the impact of the Lu/Y ratio on the Yb optical and laser properties. Therefore we analyzed a set of samples with different Y/Lu balance, namely 25/75, 50/50 and 75/25, with 15% Yb doping. We found that the Yb absorption and emission spectra changed from YAG to LuAG when gradually increasing in Lu content. Regarding the laser emission, remarkable results were achieved with all samples. Maximum output power was 8.2 W, 7.3 W and 8.7 W for Y/Lu balance 25/75, 50/50 and 75/25 respectively, at 1030 nm; the slope efficiency and the optical-to-optical efficiencies approached or exceeded 60% and 50% respectively. The tuning range was investigated using an intracavity ZnSe prism. The broadest tuning range (998 nm to 1063 nm) was obtained with Y/Lu balance 75/25, whereas the emission of the other two samples extended from 1000 nm to 1058 nm. To the best of our knowledge, this is the first comparative analysis of Yb:LuYAG ceramics or crystals as laser host across such a broad range of Y/Lu ratios. PMID:27505750

  10. [H{sub 3}N(CH{sub 2}){sub 4}NH{sub 3}]{sub 2}[Al{sub 4}(C{sub 2}O{sub 4})(H{sub 2}PO{sub 4}){sub 2}(PO{sub 4}){sub 4}].4[H{sub 2}O]: A new layered aluminum phosphate-oxalate

    SciTech Connect

    Peng Li; Li Jiyang; Yu Jihong . E-mail:; Li Guanghua; Fang Qianrong; Xu Ruren . E-mail:


    A new layered inorganic-organic hybrid aluminum phosphate-oxalate [H{sub 3}N(CH{sub 2}){sub 4}NH{sub 3}]{sub 2}[Al{sub 4}(C{sub 2}O{sub 4})(H{sub 2}PO{sub 4}){sub 2}(PO{sub 4}){sub 4}].4[H{sub 2}O](AlPO-CJ25) has been synthesized hydrothermally, by using 1,4-diaminobutane (DAB) as structure-directing agent. The structure has been solved by single-crystal X-ray diffraction analysis and further characterized by IR, {sup 31}P MAS NMR, TG-DTA as well as compositional analyses. Crystal data: the triclinic space group P-1, a=8.0484(7) A, b=8.8608(8) A, c=13.2224(11) A, {alpha}=80.830(6) deg. , {beta}=74.965(5) deg. , {gamma}=78.782(6) deg. , Z=2, R {sub 1[} {sub I} {sub >2} {sub {sigma}} {sub (} {sub I} {sub )]}=0.0511 and wR {sub 2(alldata)}=0.1423. The alternation of AlO{sub 4} tetrahedra and PO{sub 4} tetrahedra gives rise to the four-membered corner-sharing chains, which are interconnected through AlO{sub 6} octahedra to form the layered structure with 4,6-net sheet. Interestingly, oxalate ions are bis-bidentately bonded by participating in the coordination of AlO{sub 6}, and bridging the adjacent AlO{sub 6} octahedra. The layers are held with each other through strong H-bondings between the terminal oxygens. The organic ammonium cations and water molecules are located in the large cavities between the interlayer regions. -- Graphical abstract: The alternation of AlO{sub 4} tetrahedra and PO{sub 4} tetrahedra gives rise to the four-membered corner-sharing chains, which are interconnected through AlO{sub 6} octahedra to form the layered structure with 4,6-net sheet. Oxalate ions are bis-bidentately boned by participating in the coordination of AlO{sub 6}, and bridging the adjacent AlO{sub 6} octahedra.

  11. Density Functional Calculations of Native Defects in CH 3sub> NH 3sub> PbI 3sub> : Effects of Spin–Orbit Coupling and Self-Interaction Error

    SciTech Connect

    Du, Mao-Hua


    We know that native point defects play an important role in carrier transport properties of CH3NH3PbI3. However, the nature of many important defects remains controversial due partly to the conflicting results reported by recent density functional theory (DFT) calculations. In this Letter, we show that self-interaction error and the neglect of spin–orbit coupling (SOC) in many previous DFT calculations resulted in incorrect positions of valence and conduction band edges, although their difference, which is the band gap, is in good agreement with the experimental value. Moreover, this problem has led to incorrect predictions of defect-level positions. Hybrid density functional calculations, which partially correct the self-interaction error and include the SOC, show that, among native point defects (including vacancies, interstitials, and antisites), only the iodine vacancy and its complexes induce deep electron and hole trapping levels inside of the band gap, acting as nonradiative recombination centers.

  12. Mild hydrothermal synthesis, crystal structure, spectroscopic and magnetic properties of the [M{sub x}{sup II}M{sub 2.5-x}{sup III}(H{sub 2}O){sub 2}(HP{sup III}O{sub 3}){sub y}(P{sup V}O{sub 4}){sub 2-y}F; M=Fe, x=2.08, y=1.58; M=Co, Ni, x=2.5, y=2] compounds

    SciTech Connect

    Orive, Joseba


    The [M{sub x}{sup II}M{sub 2.5-x}{sup III}(H{sub 2}O){sub 2}(HP{sup III}O{sub 3}){sub y}(P{sup V}O{sub 4}){sub 2-y}F; M=Fe (1), x=2.08, y=1.58; M=Co (2), x=2.5, y=2; Ni (3), x=2.5, y=2] compounds have been synthesized using mild hydrothermal conditions at 170 deg. C during five days. Single-crystals of (1) and (2), and polycrystalline sample of (3) were obtained. These isostructural compounds crystallize in the orthorhombic system, space group Aba2, with a=9.9598(2), b=18.8149(4) and c=8.5751(2) A for (1), a=9.9142(7), b=18.570(1) and c=8.4920(5) A for (2) and a=9.8038(2), b=18.2453(2) and c=8.4106(1) A for (3), with Z=8 in the three phases. An X-ray diffraction study reveals that the crystal structure is composed of a three-dimensional skeleton formed by [MO{sub 5}F] and [MO{sub 4}F{sub 2}] (M=Fe, Co and Ni) octahedra and [HPO{sub 3}] tetrahedra, partially substituted by [PO{sub 4}] tetrahedra in phase (1). The IR spectra show the vibrational modes of the water molecules and those of the (HPO{sub 3}){sup 2-} tetrahedral oxoanions. The thermal study indicates that the limit of thermal stability of these phases is 195 deg. C for (1) and 315 deg. C for (2) and (3). The electronic absorption spectroscopy shows the characteristic bands of the Fe(II), Co(II) and Ni(II) high-spin cations in slightly distorted octahedral geometry. Magnetic measurements indicate the existence of global antiferromagnetic interactions between the metallic centers with a ferromagnetic transition in the three compounds at 28, 14 and 21 K for (1), (2) and (3), respectively. Compound (1) exhibits a hysteresis loop with remnant magnetization and coercive field values of 0.72 emu/mol and 880 Oe, respectively. - Abstract: Polyhedral view of the crystal structure of the [M{sub x}{sup II}M{sub 2.5-x}{sup III}(H{sub 2}O){sub 2}(HP{sup III}O{sub 3}){sub y}(P{sup IV}O{sub 4}){sub 2-y}F; M=Fe, x=2.08, y=1.58; M=Co, Ni, x=2.5, y=2] compounds showing the sheets along the [001] direction.

  13. Built-In Potential in Fe 2 O 3sub> -Cr 2 O 3sub> Superlattices for Improved Photoexcited Carrier Separation

    SciTech Connect

    Kaspar, Tiffany C.; Schreiber, Daniel K.; Spurgeon, Steven R.; McBriarty, Martin E.; Carroll, Gerard M.; Gamelin, Daniel R.; Chambers, Scott A.


    We demonstrate that the different surface terminations exhibited by α-Fe2O3 (hematite) and α-Cr2O3 (eskolaite) in superlattices (SL) of these materials, synthesized with exquisite control by molecular beam epitaxy, determine the heterojunction interface structure and result in controllable, non-commutative band offset values. Precise atomic control of the interface structure allowed us to vary the valence band offset from 0.35 eV to 0.79 eV. This controllable band alignment can be harnessed to generate a built-in potential in Fe2O3-Cr2O3 SLs. For instance, in a 2.5-period SL, a built-in potential of 0.8 eV was realized as measured by x-ray photoelectron spectroscopy of Ti dopants as probe species. The high quality of the SL structure was confirmed by atom probe tomography and scanning transmission electron microscopy. Enhanced photocurrents were measured for a thick Fe2O3 epitaxial film capped with an (Fe2O3)3-(Cr2O3)3 SL; this enhancement was attributed to efficient electron-hole separation in the SL as a result of the band alignment. The Fe-O-Cr bonds at the SL interfaces also red-shifted the onset of photoconductivity to ~1.6 eV. Exploiting the band alignment and photoabsorption properties of Fe2O3-Cr2O3 SLs has the potential to increase the efficiency of hematite-based photoelectrochemical water splitting.

  14. Frustration of Tilts and A-Site Driven Ferroelectricity in KNbO3sub>-LiNbO3sub> Alloys

    SciTech Connect

    Bilc, Daniel I; Singh, David J


    Density functional calculations for K0.5Li0.5NbO3 show strong a-site driven ferroelectricity, even though the average tolerance factor is significantly smaller than unity and there is no sterochemically active A-stie ion. This is due to the frustration of tilt instabilities by A-site disorder. There are very large off-centerings of the Li ions, which contribute strongly to the anisotropy between the tetragonal and rhombohedral ferroelectric states, yielding a tetragonal ground state even without strain coupling.

  15. Lattice dynamics in elemental modulated Sb 2 Te 3sub> films: Lattice dynamics in elemental modulated Sb 2 Te 3sub> films

    SciTech Connect

    Bessas, D.; Winkler, M.; Sergueev, I.; König, J. D.; Böttner, H.; Hermann, R. P.


    We investigate the crystallinity and the lattice dynamics in elemental modulated Sbinline imageTeinline image films microscopically using high energy synchrotron radiation diffraction combined with inline imageSb nuclear inelastic scattering. The correlation length is found to be finite but less than 100 . Moreover, the element specific density of phonon states is extracted. A comparison with the element specific density of phonon states in bulk Sbinline imageTeinline image confirms that the main features in the density of phonon states arise from the layered structure. The average speed of sound at inline image inline image, is almost the same compared to bulk Sbinline imageTeinline image at inline image, inline image. Similarly, the change in the acoustic cut-off energy is within the experimental detection limit. Therefore, we suggest that the lattice thermal conductivity in elemental modulated Sbinline imageTeinline image films should not be significantly changed from its bulk value.

  16. Optical Study of the Free Carrier Response of LaTiO3sub>/SrTiO3sub> Superlattices

    SciTech Connect

    Seo, S. S. A.; Choi, W. S.; Lee, Ho Nyung; Yu, L.; Kim, K. W.; Bernhard, C; Noh, Tae Won


    We used infrared spectroscopic ellipsometry to investigate the electronic properties of LaTiO{sub 3}/SrTiO{sub 3} superlattices (SLs). Our results indicated that, independent of the SL periodicity and individual layer thickness, the SLs exhibited a Drude metallic response with sheet carrier density per interface {approx}3x10{sup 14}cm{sup -2}. This is probably due to the leakage of d electrons at interfaces from the Mott insulator LaTiO{sub 3}to the band insulator SrTiO{sub 3}. We observed a carrier relaxation time {approx}35fs and mobility {approx}35cm2V-1s-1 at 10 K, and an unusual temperature dependence of carrier density that was attributed to the dielectric screening of quantum paraelectric SrTiO{sub 3}.

  17. Chemistry of c-trimethylsilyl-substituted main-group heterocarboranes. 6. Lead(II)-inserted. eta. sup 5 -closo-plumbacarboranes and their reactivity toward a bidentate Lewis base: Crystal structures of closo-1-Pb-2-(SiMe sub 3 )-3-(R)-2,3-C sub 2 B sub 4 H sub 4 and 1-Pb(C sub 10 H sub 8 N sub 2 )-2,3-(SiMe sub 3 ) sub 2 -2,3-C sub 2 B sub 4 H sub 4 (R = SiMe sub 3 , Me)

    SciTech Connect

    Hosmane, N.S.; Lu, Kaijuan; Zhu, Hong; Siriwardane, U.; Shet, M.S.; Maguire, J.A. )


    The monosodium salts of the carborane anions (2,3-(SiMe{sub 3}){sub 2}-2,3-C{sub 2}B{sub 4}H{sub 5}){sup {minus}}, (2-(SiMe{sub 3})-3-(Me)-2,3-C{sub 2}B{sub 4}H{sub 5}){sup {minus}}, and (2-(SiMe{sub 3})-2,3-C{sub 2}B{sub 4}H{sub 6}){sup {minus}} react with PbCl{sub 2} to produce the corresponding closo-plumbacarboranes, 1-Pb-2,3-(SiMe{sub 3}){sub 2}-2,3-C{sub 2}B{sub 4}H{sub 4} (I), 1-Pb-2-(SiMe{sub 3})-3-(Me)-2,3-C{sub 2}B{sub 4}H{sub 4} (II), and 1-Pb-2-(SiMe{sub 3})-2,3,-C{sub 2}B{sub 4}H{sub 5} (III) in 25-37% yields. The plumbacarboranes I, II, and III were characterized on the basis of {sup 1}H, {sup 11}B, and {sup 13}C pulse Fourier transform NMR, IR, and mass spectroscopy. The complexes were characterized by {sup 1}H, {sup 11}B, and {sup 13}C NMR, IR, and mass spectroscopy, and IV was also characterized by single-crystal X-ray diffraction.

  18. Model Ziegler-Natta [alpha]-olefin polymerization catalysts derived from [([eta][sup 5]-C[sub 5]Me[sub 4]) SiMe[sub 2] ([eta][sup 1]-NCMe[sub 3])(PMe[sub 3])Sc([mu][sub 2]-H)][sub 2] and [([eta][sup 5]-C[sub 5]Me[sub 4] SiMe[sub 2]([eta][sup 1]-NCMe[sub 3])) Sc([mu][sub 2]CH[sub 2]CH[sub 2]CH[sub 3])][sub 2]. Synthesis, structures, and kinetic and equilibrium investigations of the catalytically active species in solution

    SciTech Connect

    Shapiro, P.J.; Cotter, W.D.; Schaefer, W.P.; Labinger, J.A.; Bercaw, J.E. )


    The scandium hydride complex [(Cp*SiNR)(PMe[sub 3])Sc([mu]-H)][sub 2], (1) ((Cp*SiNR) = (([eta][sup 5]-C[sub 5]Me[sub 4])SiMe[sub 2]([eta][sup 1]-NCMe[sub 3]))) is prepared by hydrogenation of (Cp*SiNR)ScCH(SiMe[sub 3])[sub 2] in the presence of trimethylphosphine. The hydride complex is a catalyst precursor for the polymerization of [alpha]-olefins, yielding atactic products of low molecular weight (M[sub n] = 3000-7000). GC/MS analysis of volatile, oligomeric products revealed that all scandium centers are active during the polymerization. Selectivity for head-to-tail insertion is high (> 99%) and for the tetramer, pentamer, and hexamer formed during propene polymerization, the maximum theoretical numbers of head-to-tail stereoisomers are observed by capillary GC. The stoichiometric reaction between 1 and 2 equiv of ethylene produces the unusual ethylene-bridged dimer [(Cp*SiNR)(PMe[sub 3])Sc][sub 2]([mu], [eta][sup 2]-C[sub 2]H[sub 4]) (2) and an equivalent of ethane, whereas the same reaction with propene affords the phosphine-free, alkyl-bridged scandium dimer [(Cp*SiNR)Sc][sub 2]([mu]-CH[sub 2]CH[sub 2]CH[sub 3])[sub 2] (3). The absence of coordinating phosphine allows the latter complex to function as a more active olefin polymerization catalyst precursor. 1 reacts with styrene to form a unique double-insertion product arising from sequential 1,2- and 2,1-styrene insertion. 41 refs., 13 figs., 9 tabs.

  19. Unusual Mott transition in multiferroic PbCrO 3sub>

    SciTech Connect

    Wang, Shanmin; Zhu, Jinlong; Zhang, Yi; Yu, Xiaohui; Zhang, Jianzhong; Wang, Wendan; Bai, Ligang; Qian, Jiang; Yin, Liang; Sullivan, Neil S.; Jin, Changqing; He, Duanwei; Xu, Jian; Zhao, Yusheng


    The Mott insulator in correlated electron systems arises from classical Coulomb repulsion between carriers to provide a powerful force for electron localization. When turning such an insulator into a metal, the so-called Mott transition, is commonly achieved by "bandwidth" control or "band filling." However, both mechanisms deviate from the original concept of Mott, which attributes such a transition to the screening of Coulomb potential and associated lattice contraction. We report a pressure-induced isostructural Mott transition in cubic perovskite PbCrO3. At the transition pressure of similar to 3 GPa, PbCrO3 exhibits significant collapse in both lattice volume and Coulomb potential. Concurrent with the collapse, it transforms from a hybrid multiferroic insulator to a metal. For the first time to our knowledge, these findings validate the scenario conceived by Mott. Close to the Mott criticality at similar to 300 K, fluctuations of the lattice and charge give rise to elastic anomalies and Laudau critical behaviors resembling the classic liquid-gas transition. Moreover, the anomalously large lattice volume and Coulomb potential in the low-pressure insulating phase are largely associated with the ferroelectric distortion, which is substantially suppressed at high pressures, leading to the first-order phase transition without symmetry breaking.

  20. Magnetron Sputtering of Gold Nanoparticles onto WO3sub> and Activated Carbon

    SciTech Connect

    Veith, Gabriel M; Lupini, Andrew R; Pennycook, Stephen J; Villa, Alberto; Prati, Laura; Dudney, Nancy J


    In this paper we describe the production and investigation of two supported gold catalyst systems prepared by magnetron sputtering: Au on WO3 and Au on activated carbon. The magnetron sputtering technique entails the sputtering of a high purity gold metal target, with an argon plasma, to produce a flux of gold atoms onto a constantly tumbling support material. This technique offers a number of advantages over conventional chemical preparation methods including the flexibility to create gold nanoparticles (diameters < 3 nm) on unusual support materials, such as WO3 and carbon, which are generally not accessible using the ubiquitous deposition-precipitation technique. We present data demonstrating the formation of catalytic gold nanoparticles with average diameters of 1.7 nm (Au/C) and 2.1 nm (Au/WO3) as well as a substantial number of single atom species on the Au/C sample. Prototypical carbon monoxide oxidation (Au/WO3) and glycerol oxidation (Au/C) reactions were performed in order to gauge the activity of these catalysts. The WO3 supported catalyst exhibits substantial catalytic activity from room temperature to 135oC (0.0018 - 0.082 mole CO/mole Au sec) with an apparent transition around 75oC to a more active catalyst. The activity 1 of the Au/C catalysts was compared to a Au/C catalysts prepared from a PVA sol. The smaller catalysts prepared by sputtering are more active than the large gold particles prepared using the PVA sol. However, the larger gold catalyst are substaintially more selective towards the production of intermediate products from the oxidation of glycerol.

  1. Thermoelectric properties of bromine filled CoSb3sub> skutterudite

    SciTech Connect

    Ortiz, Brenden R.; Crawford, Caitlin M.; McKinney, Robert W.; Parilla, Philip A.; Toberer, Eric S.


    Historically, the improved thermoelectric performance of skutterudite compounds has largely been driven by the incorporation of electropositive donors on interstitial sites. These 'rattlers' serve to optimize both electronic and thermal properties by tuning the carrier concentration and scattering phonons. In this work, we show that interstitial bromine can be incorporated into CoSb3 and assess the impact on electronic and thermal transport. In contrast to prior high pressure syntheses with iodine, interstitial bromine incorporation is achieved at ambient pressure. Transport properties are stable up to at least 375 degrees C. Bromine serves as an electronegative acceptor and can induce degenerate (>5 x 1019 cm-3) hole densities. In contrast to other p-type skutterudite compositions, bromine preserves the intrinsically high hole mobility of CoSb3 while significantly reducing the lattice thermal conductivity. The development of a stable p-type dopant for the interstitial filler site enables the development of skutterudites with both donor and acceptor interstitials to maximize phonon scattering while maintaining the high mobility of CoSb3.

  2. Dynamics of Composite Haldane Spin Chains in IPA-CuCl3sub>

    SciTech Connect

    Masuda, Takatsugu; Zheludev, Andrey I; Manaka, H.; Regnault, L.-P.; Chung, J.-H.; Qiu, Y.


    Magnetic excitations in the quasi-one-dimensional antiferromagnet IPA-CuCl{sub 3} are studied by cold neutron inelastic scattering. Strongly dispersive gap excitations are observed. Contrary to previously proposed models, the system is best described as an asymmetric quantum spin ladder. The observed spectrum is interpreted in terms of composite Haldane spin chains. The key difference from actual S = 1 chains is a sharp cutoff of the single-magnon spectrum at a certain critical wave vector.

  3. Nucleation of metastable aragonite CaCO3sub> in seawater

    SciTech Connect

    Sun, Wenhao; Jayaraman, Saivenkataraman; Chen, Wei; Persson, Kristin A.; Ceder, Gerbrand


    Predicting the conditions in which a compound adopts a metastable structure when it crystallizes out of solution is an unsolved and fundamental problem in materials synthesis, and one which, if understood and harnessed, could enable the rational design of synthesis pathways toward or away from metastable structures. Crystallization of metastable phases is particularly accessible via low-temperature solution-based routes, such as chimie douce and hydrothermal synthesis, but although the chemistry of the solution plays a crucial role in governing which polymorph forms, how it does so is poorly understood. Here, we demonstrate an ab initio technique to quantify thermodynamic parameters of surfaces and bulks in equilibrium with an aqueous environment, enabling the calculation of nucleation barriers of competing polymorphs as a function of solution chemistry, thereby predicting the solution conditions governing polymorph selection. We apply this approach to resolve the long-standing “calcite–aragonite problem”––the observation that calcium carbonate precipitates as the metastable aragonite polymorph in marine environments, rather than the stable phase calcite––which is of tremendous relevance to biomineralization, carbon sequestration, paleogeochemistry, and the vulnerability of marine life to ocean acidification. We identify a direct relationship between the calcite surface energy and solution Mg–Ca ion concentrations, showing that the calcite nucleation barrier surpasses that of metastable aragonite in solutions with Mg:Ca ratios consistent with modern seawater, allowing aragonite to dominate the kinetics of nucleation. Our ability to quantify how solution parameters distinguish between polymorphs marks an important step toward the ab initio prediction of materials synthesis pathways in solution.

  4. Intelligent Engine Systems Work Element 1.3: Sub System Health Management

    NASA Technical Reports Server (NTRS)

    Ashby, Malcolm; Simpson, Jeffrey; Singh, Anant; Ferguson, Emily; Frontera, mark


    The objectives of this program were to develop health monitoring systems and physics-based fault detection models for engine sub-systems including the start, lubrication, and fuel. These models will ultimately be used to provide more effective sub-system fault identification and isolation to reduce engine maintenance costs and engine down-time. Additionally, the bearing sub-system health is addressed in this program through identification of sensing requirements, a review of available technologies and a demonstration of a demonstration of a conceptual monitoring system for a differential roller bearing. This report is divided into four sections; one for each of the subtasks. The start system subtask is documented in section 2.0, the oil system is covered in section 3.0, bearing in section 4.0, and the fuel system is presented in section 5.0.

  5. Dense layers of vertically oriented WO 3sub> crystals as anodes for photoelectrochemical water oxidation

    SciTech Connect

    Qin, Dong-Dong; Tao, Chun-Lan; Friesen, Stuart A.; Wang, Tsing-Hai; Varghese, Oomman K.; Bao, Ning-Zhong; Yang, Zheng-Yin; Mallouk, Thomas E.; Grimes, Craig A.


    Films of crystalline WO₃ nanosheets oriented perpendicular to tungsten substrates were grown by a surfactant-free hydrothermal method, followed by sintering. The films exhibit photoelectrochemical oxygen evolution at low overpotential.

  6. Synthesis and oxygen content dependent properties of hexagonal DyMnO{sub 3 + sub delta}.

    SciTech Connect

    Remsen, S.; Dabrowski, B.; Chmaissem, O.; Mais, J.; Szewczyk, A.


    Oxygen deficient polycrystalline samples of hexagonal P6{sub 3}cm (space group No.185) DyMnO{sub 3+{delta}} ({delta} < 0) were synthesized in Ar by intentional decomposition of its perovskite phase obtained in air. The relative stability of these phases is in accord with our previous studies of the temperature and oxygen vacancy dependent tolerance factor. Thermogravimetric measurements have shown that hexagonal samples of DyMnO{sub 3+{delta}} (0 {<=} {delta} {<=} 0.4) exhibit unusually large excess oxygen content, which readily incorporates on heating near 300 C in various partial-pressures of oxygen atmospheres. Neutron and synchrotron diffraction data show the presence of two new structural phases at {delta} {approx} 0.25 (Hex{sub 2}) and {delta} {approx} 0.40 (Hex{sub 3}). Rietveld refinements of the Hex{sub 2} phase strongly suggest it is well modeled by the R3 space group (No.146). These phases were observed to transform back to P6{sub 3}cm above {approx}350 C when material becomes stoichiometric in oxygen content ({delta} = 0). Chemical expansion of the crystal lattice corresponding to these large changes of oxygen was found to be 3.48 x 10{sup -2} mol{sup -1}. Thermal expansion of stoichiometric phases were determined to be 11.6 x 10{sup -6} and 2.1 x 10{sup -6} K{sup -1} for the P6{sub 3}cm and Hex{sub 2} phases, respectively. Our measurements also indicate that the oxygen non-stoichiometry of hexagonal RMnO{sub 3+{delta}} materials may have important influence on their multiferroic properties.

  7. Electron-Impact Dissociation of Ozone Cations O3sub>+

    SciTech Connect

    Deng, Shihu; Vane, C Randy; Bannister, Mark E; FogleJr, Michael R


    Absolute cross sections for electron-impact dissociation of O3+ ions yielding O+ and O2+ fragment ions have been measured using a crossed electron-ion beams method for energies from about 3 eV to 100 eV. While the O2+ channel dominates the dissociation cross section over the measured energy range, a strong enhancement is observed in the O+ channel at low energy.

  8. A novel nanomolecular organic-inorganic hybrid compound: Na{sub 2}[NH(CH{sub 2}CH{sub 2}OH){sub 3}]{sub 4}{l_brace}Mo{sub 36}O{sub 112}(OH{sub 2}){sub 14}[OHCH{sub 2}CH{sub 2}NH(CH{sub 2}CH{sub 2}OH){sub 2}]{sub 2}{r_brace}.nH{sub 2}O (n{approx}72) exhibiting a supramolecular one-dimensional chainlike structure

    SciTech Connect

    Liang Dadong; Liu Shuxia Wang Chunling; Ren Yuanhang


    A novel nanomolecular organic-inorganic hybrid compound, Na{sub 2}[NH(CH{sub 2}CH{sub 2}OH){sub 3}]{sub 4}{l_brace}Mo{sub 36}O{sub 112}(OH{sub 2}){sub 14} [OHCH{sub 2}CH{sub 2}NH(CH{sub 2}CH{sub 2}OH){sub 2}]{sub 2}{r_brace}.nH{sub 2}O (n{approx}72) (1), was synthesized in aqueous acidic medium with a high yield (85%) and characterized by single crystal X-ray crystallography, IR spectroscopy, {sup 1}H NMR, XRD and TG analysis. Compound 1 exhibits a supramolecular one-dimensional chainlike structure which consists of nanosized {l_brace}[Mo{sub 36}O{sub 112}(H{sub 2}O){sub 14}(HOC{sub 2}H{sub 4}){sub 2}NHC{sub 2}H{sub 4}OH]{sub 2}{r_brace}{sup 6-} anions ({l_brace}Mo{sub 36}(TEAH{sup +}){sub 2}{r_brace} for short) and cage-like dimers of TEAH{sup +} cations (TEAH{sup +}=protonated triethanolamine). In the {l_brace}Mo{sub 36}(TEAH{sup +}){sub 2}{r_brace} anion, two TEAH{sup +} cations connect to one ring-like {l_brace}[Mo{sub 36}O{sub 112}(H{sub 2}O){sub 16}]{sup 8-} ({l_brace}Mo{sub 36}{r_brace} for short) anion by covalent bonds via replacing two water ligands by the alkoxy ligands. The {l_brace}Mo{sub 36}(TEAH{sup +}){sub 2}{r_brace} unit could be considered as nanosized chelating ligand with [2N, 4O] donor sets. Crystal Data: triclinic, P-1, a=16.019(9) A, b=17.372(4) A, c=18.287(2) A, {alpha}=101.410(0){sup o}, {beta}=95.904(0){sup o}, {gamma}=116.332(0){sup o}, Z=1. - Graphical abstract: A novel organic-inorganic hybrid material based on macroisopolyanion {l_brace}Mo{sub 36}{r_brace} has been synthesized and characterized by X-ray single-crystal crystallography, XRD, IR spectroscopy, and TG analysis. The material exhibits a supramolecular one-dimensional chainlike structure. The {l_brace}Mo{sub 36}(TEAH{sup +}){sub 2}{r_brace} unit could be considered as nanosized chelating ligand with [2N, 4O] donor sets.

  9. Morphotropic phase boundaries in (BiScO{sub 3}){sub 1-x}(PbTiO{sub 3}){sub x} (0.60

    SciTech Connect

    Chaigneau, J.; Malibert, C.; Bogicevic, C.; Kiat, J. M.


    We have performed a structural study of the morphotropic phase boundary system (1-x)BiScO{sub 3-x}PbTiO{sub 3} in which both A and B sites of the perovskite are randomly occupied. A M{sub A} monoclinic phase coexisting with a tetragonal phase has been evidenced for concentration 0.60

  10. Synthesis of Ternary Nitrides From Intermetallic Precursors: Modes of Nitridation in Model Cr3sub>Pt Alloys to Form Cr3sub>PtN Perovskite and Applications to Other Systems

    SciTech Connect

    Brady, Michael P; Wrobel, Sarah; Lograsso, Tom; Payzant, E Andrew; Hoelzer, David T; Horton Jr, Joe A; Walker, Larry R


    The use of intermetallic alloy precursors is explored as a new means to synthesize complex transition and refractory metal nitrides, carbides, and related phases. The conditions under which model single-phase Cr{sub 3}Pt and two-phase Cr{sub 3}Pt-dispersed Cr alloys form Cr{sub 3}PtN antiperovskite when thermally nitrided were studied. Phenomenological experiments suggest that the key variable to achieving single-phase Cr{sub 3}PtN surface layers is the Cr{sub 3}Pt phase composition. In two-phase {beta}-Cr-Cr{sub 3}Pt alloys, the formation of single-phase Cr{sub 3}PtN at Cr{sub 3}Pt precipitates by in-place internal nitridation was found to be a strong function of the size of the Cr{sub 3}Pt dispersion in the microstructure. Nanoscale Cr{sub 3}Pt dispersions were readily converted to near single-phase Cr{sub 3}PtN, whereas nitridation of coarse Cr{sub 3}Pt particles resulted in a cellular or discontinuous-type reaction to form a lath mixture of Cr{sub 3}PtN and a more Cr-rich Cr{sub 3}Pt or {beta}-Cr. The potential for using such external/internal oxidation phenomena as a synthesis approach to layered or composite surfaces of ternary ceramic phases (nitrides, carbides, borides, etc.) of technological interest such as the Ti{sub 3}AlC{sub 2} phase, bimetallic nitride, and carbide catalysts (Co{sub 3}Mo{sub 3}N and Co{sub 3}Mo{sub 3}C and related phases), and magnetic rare earth nitrides (Fe{sub 17}Sm{sub 2}N{sub x} or Fe{sub 17}Nd{sub 2}N{sub x}) is discussed.

  11. Abnormal crystal growth in CH3sub>NH3sub>PbI3-xClx using a multi-cycle solution coating process

    SciTech Connect

    Dong, Qingfeng; Yuan, Yongbo; Shao, Yuchuan; Fang, Yanjun; Wang, Qi; Huang, Jinsong


    Recently, the efficiency of organolead trihalide perovskite solar cells has improved greatly because of improved material qualities with longer carrier diffusion lengths. Mixing chlorine in the precursor for mixed halide films has been reported to dramatically enhance the diffusion lengths of mixed halide perovskite films, mainly as a result of a much longer carrier recombination lifetime. Here we report that adding Cl containing precursor for mixed halide perovskite formation can induce the abnormal grain growth behavior that yields well-oriented grains accompanied by the appearance of some very large size grains. The abnormal grain growth becomes prominent only after multi-cycle coating of MAI : MACl blend precursor. The large grain size is found mainly to contribute to a longer carrier charge recombination lifetime, and thus increases the device efficiency to 18.9%, but without significantly impacting the carrier transport property. As a result, the strong correlation identified between material process and morphology provides guidelines for future material optimization and device efficiency enhancement.

  12. Uranium extraction selectivities of dibutyl carbitol and tributyl phosphate in the system UO{sub 2}(NO{sub 3}){sub 2}-HNO{sub 3}-H{sub 2}O-Al(NO{sub 3}){sub 3}-solvent

    SciTech Connect

    Birdwell, J.F.


    Historically, both the BUTEX (dibutyl carbitol-based) and PUREX (tributyl phosphate-based) processes have been used for uranium recovery and purification. Currently, BUTEX- and PUREX-type extraction processes are being used in series for recovery of isotopically enriched uranium at the Oak Ridge Y-12 Plant. The use of two solvents is predicated on the differing selectivities of each with regard to the contaminant elements present in the uranium source stream. As part of efforts to streamline plant operations in response to decreasing throughput requirements, the Y-12 Development Division is evaluating options for converting the existing two-solvent operation to a single-solvent process. At the request of the Y-12 Development Division, the Robotics and Process Division at the Oak Ridge National Laboratory has undertaken evaluation of solvents for use in a single-solvent recovery process. Initial efforts have been directed toward development of a single-solvent, dibutyl carbitol- or tributyl phosphate-based process that produces a product with purity equal to or exceeding what is currently obtained in the two-cycle, two-solvent operation. The test effort has involved both laboratory equilibrium determinations and engineering-scale process demonstrations in multistage flowsheets using centrifugal solvent extraction contactors. Excellent uranium recovery results have been obtained from both dibutyl carbitol- and tributyl phosphate-based solvent extraction flowsheets. Contaminant rejection performance by the two solvents is similar for many of the elements considered. Extraction of some contaminant elements by tributyl phosphate is significant enough to conclude that the solvent is not as selective for uranium as is dibutyl carbitol. This determination does not necessarily eliminate tributyl phosphate from consideration for use in a single-solvent process but does indicate a need for effective scrubbing of contaminants from uranium-loaded tributyl phosphate, possibly by partial reflux of the purified, aqueous uranyl nitrate product solution.

  13. Structural and Electronic Properties of Reduced Transition Metal Oxide Clusters, M 3sub> O 8 and M 3sub> O 8 - (M = Cr, W), from Photoelectron Spectroscopy and Quantum Chemical Calculations

    SciTech Connect

    Li, Shenggang; Zhai, Hua-Jin; Wang, Lai-Sheng; Dixon, David A.


    We report a comparative study of reduced transition metal oxide clusters, M₃O₈⁻ (M = Cr, W) anions and their neutrals, via anion photoelectron spectroscopy (PES) and density functional theory (DFT) and molecular orbital theory (CCSD(T)) calculations. Well-resolved PES spectra are obtained for M₃O₈⁻ (M = Cr, W) at 193 and 157 nm photon energies. Different PES spectra are observed for M = Cr versus M = W. ExtensiveDFT and CCSD(T) calculations are performed to locate the ground and low-lying excited states for the neutrals and anions. The ground states of Cr₃O₈ and Cr₃O₈⁻ are predicted to be the ³B₂ and ⁴B₂ states of a C₂v structure, respectively, revealing ferromagnetic spin coupling for Cr 3d electrons. In contrast, the ground states of W₃O₈ and W₃O₈⁻ are predicted to be the ¹A' state (Cs symmetry) and the ²A₁ state (C₂v symmetry), respectively, showing metal-metal d-d bonding in the anion. The current cluster geometries are in qualitative agreement with prior DFT studies at the PBE level for M = Cr and the B3LYP level for M = W. The BP86 and PW91 functionals significantly outperform the B3LYP functional for the Cr species, in terms of relative energies, electron detachment energies, and electronic excitation energies, whereas the B3LYP functional is better for the W species. Accurate heats of formation for the ground states of M₃O₈ are calculated from the clustering energies and the heats of formation of MO₂ and MO₃. The energetics have been used to predict redox reaction thermochemistry.

  14. Thickness-dependent metal-insulator transition in epitaxial SrRuO3sub> ultrathin films

    SciTech Connect

    Shen, Xuan; Qiu, Xiangbiao; Su, Dong; Zhou, Shengqiang; Li, Aidong; Wu, Di


    Transport characteristics of ultrathin SrRuO₃ films, deposited epitaxially on TiO₂-terminated SrTiO₃ (001) single-crystal substrates, were studied as a function of film thickness. Evolution from a metallic to an insulating behavior is observed as the film thickness decreases from 20 to 4 unit cells. In films thicker than 4 unit cells, the transport behavior obeys the Drude low temperature conductivity with quantum corrections, which can be attributed to weak localization. Fitting the data with 2-dimensional localization model indicates that electron-phonon collisions are the main inelastic relaxation mechanism. In the film of 4 unit cells in thickness, the transport behavior follows variable range hopping model, indicating a strongly localized state. As a result, magnetoresistance measurements reveal a likely magnetic anisotropy with the magnetic easy axis along the out-of-plane direction.

  15. Critical Experiments With Aqueous Solutions of {sup 233}UO{sub 2}(NO{sub 3}){sub 2}

    SciTech Connect

    Thomas, J.T.


    This report provides the critical experimenter's interpretations and descriptions of informal critical experiment logbook notes and associated information (e.g., experimental equipment designs/sketches, chemical and isotopic analyses, etc.) for the purpose of formally documenting the results of critical experiments performed in the late 1960s at the Oak Ridge Critical Experiments Facility. The experiments were conducted with aqueous solutions of 97.6 wt % {sup 233}U uranyl nitrate having uranium densities varying between about 346 g U/l and 45 g U/l. Criticality was achieved with single simple units (e.g., cylinders and spheres) and with spaced subcritical simple cylindrical units arranged in unreflected, water-reflected, and polyethylene reflected critical arrays.

  16. Critical Experiments With Aqueous Solutions of {sup 233}UO{sub 2}(NO{sub ;3}){sub 2}

    SciTech Connect

    Thomas, J T


    This report provides the critical experimenter's interpretations and descriptions of informal critical experiment logbook notes and associated information (e.g., experimental equipment designs/sketches, chemical and isotopic analyses, etc.) for the purpose of formally documenting the results of critical experiments performed in the late 1960s at the Oak Ridge Critical Experiments Facility. The experiments were conducted with aqueous solutions of 97.6 wt % {sup 233}U uranyl nitrate having uranium densities varying between about 346 g U/l and 45 g U/l. Criticality was achieved with single simple units (e.g., cylinders and spheres) and with spaced subcritical simple cylindrical units arranged in unreflected, water-reflected, and polyethylene reflected critical arrays.

  17. Quantum oscillations in magnetothermopower measurements of topological insulator Bi2Te3sub>

    SciTech Connect

    Qu, Dong -Xia; Hor, Y. S.; Cava, R. J.


    We report the magnetothermopower measurements of the nonmetallic topological insulator Bi2Te3 in magnetic fields up to 35 T. Quantum oscillations arising from surface states are observed in both thermoelectric and conductivity tensors. The inferred surface thermopower has a peak magnitude ~1 mV/K possibly as a result of surface electron and bulk phonon interaction. At the n = 1 Landau level, we resolve additional quantum oscillations signaling Landau sublevels.

  18. Heuristic modelling of laser written mid-infrared LiNbO3sub> stressed-cladding waveguides.


    Nguyen, Huu-Dat; Ródenas, Airán; Vázquez de Aldana, Javier R; Martínez, Javier; Chen, Feng; Aguiló, Magdalena; Pujol, Maria Cinta; Díaz, Francesc


    Mid-infrared lithium niobate cladding waveguides have great potential in low-loss on-chip non-linear optical instruments such as mid-infrared spectrometers and frequency converters, but their three-dimensional femtosecond-laser fabrication is currently not well understood due to the complex interplay between achievable depressed index values and the stress-optic refractive index changes arising as a function of both laser fabrication parameters, and cladding arrangement. Moreover, both the stress-field anisotropy and the asymmetric shape of low-index tracks yield highly birefringent waveguides not useful for most applications where controlling and manipulating the polarization state of a light beam is crucial. To achieve true high performance devices a fundamental understanding on how these waveguides behave and how they can be ultimately optimized is required. In this work we employ a heuristic modelling approach based on the use of standard optical characterization data along with standard computational numerical methods to obtain a satisfactory approximate solution to the problem of designing realistic laser-written circuit building-blocks, such as straight waveguides, bends and evanescent splitters. We infer basic waveguide design parameters such as the complex index of refraction of laser-written tracks at 3.68 µm mid-infrared wavelengths, as well as the cross-sectional stress-optic index maps, obtaining an overall waveguide simulation that closely matches the measured mid-infrared waveguide properties in terms of anisotropy, mode field distributions and propagation losses. We then explore experimentally feasible waveguide designs in the search of a single-mode low-loss behaviour for both ordinary and extraordinary polarizations. We evaluate the overall losses of s-bend components unveiling the expected radiation bend losses of this type of waveguides, and finally showcase a prototype design of a low-loss evanescent splitter. Developing a realistic waveguide model with which robust waveguide designs can be developed will be key for exploiting the potential of the technology. PMID:27137062