Sample records for 3sub 2ruchsub 2chsub

  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.