Sample records for 3sub 2ruchsub 2chsub

  1. 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.

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

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    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.

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

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    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.

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

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    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.

  5. 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.

  6. Transparent Conducting Properties of SrSnO3sub> and ZnSnO3sub>

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    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.

  7. 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.

  8. 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.

  9. Orbital configuration in CaTiO3sub> films on NdGaO3sub>

    SciTech Connect

    Cao, Yanwei; Park, Se Young; Liu, Xiaoran; Choudhury, D.; Middey, S.; Meyers, D.; Kareev, M.; Shafer, P.; Arenholz, E.; Chakhalian, J.


    Despite its use as a constituent layer for realization of a polar metal and interfacial conductivity, the microscopic study of electronic structure of CaTiO3sub> is still very limited. Here, we epitaxially stabilized CaTiO3sub> films on NdGaO3sub> (110) substrates in a layer-by-layer way by pulsed laser deposition. The structural and electronic properties of the films were characterized by reflection-high-energy-electron-diffraction, X-ray diffraction, and element-specific resonant X-ray absorption spectroscopy. To reveal the orbital polarization and the crystal field splitting of the titanium 3d state, X-ray linear dichroism was carried out on CaTiO3sub> films, demonstrating the orbital configuration of dxz/dyz < dxy < d3z2-r2 < dx2-y2. To further explore the origin of this configuration, we performed the first-principles density function theory calculations, which linked the orbital occupation to the on-site energy of Ti 3d orbitals. Finally, these findings can be important for understanding and designing exotic quantum states in heterostructures based on CaTiO3sub>.

  10. 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.

  11. 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.

  12. Multiferroic properties of the PbTiO3sub>/La2/3sub>Sr1/3sub>MnO3sub> interface studied from first principles.


    Borisov, Vladislav; Ostanin, Sergey; Mertig, Ingrid


    Magnetoelectric coupling and spin polarization at the multiferroic PbTiO3sub>/La2/3sub>Sr1/3sub>MnO3sub> (PTO/LSMO) interface is studied from first principles in view of the recent experimental observation of the tunneling magnetoresistance sign inversion in Co/PZT/LSMO tunnel junctions (D. Pantel et al., Nat. Mater. 11, 289 (2012)). Our results confirm the stabilization of the locally antiferromagnetic order in the manganite when the PTO polarization points away from the LSMO side, which changes the interface magnetization by 6.3-6.9 μB per surface unit cell in agreement with previous studies. We contribute by analyzing the charge transfer from the half-metallic LSMO side which induces metallicity and local magnetic moments in the interface PTO layers. This results in either p- or n-doped conductive behavior, depending on the polarization direction. Electronic correlations were determined to qualitatively change the picture for certain configurations, as far as the magnetic phase transition in the manganite and the spin character of the interface states are concerned. Most importantly, depending on the interface termination, the spin polarization of the PTO/LSMO interface is positive for one polarization state of PTO and acquires a "spin-valve" character upon the ferroelectric switching.

  13. 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.

  14. Monitoring a Silent Phase Transition in CH3sub>NH3sub>PbI3sub> Solar Cells via Operando X-ray Diffraction

    SciTech Connect

    Schelhas, Laura T.; Christians, Jeffrey A.; Berry, Joseph J.; Toney, Michael F.; Tassone, Christopher J.; Luther, Joseph M.; Stone, Kevin H.


    The relatively modest temperature of the tetragonal-to-cubic phase transition in CH3sub>NH3sub>PbI3sub> perovskite is likely to occur during real world operation of CH3sub>NH3sub>PbI3sub> solar cells. In this work, we simultaneously monitor the structural phase transition of the active layer along with solar cell performance as a function of the device operating temperature. The tetragonal to cubic phase transition is observed in the working device to occur reversibly at temperatures between 60.5 and 65.4 degrees C. In these operando measurements, no discontinuity in the device performance is observed, indicating electronic behavior that is insensitive to the structural phase transition. Here, this decoupling of device performance from the change in long-range order across the phase transition suggests that the optoelectronic properties are primarily determined by the local structure in CH3sub>NH3sub>PbI3sub>. That is, while the average crystal structure as probed by X-ray diffraction shows a transition from tetragonal to cubic, the local structure generally remains well characterized by uncorrelated, dynamic octahedral rotations that order at elevated temperatures but are unchanged locally.

  15. Hydroxyacetone production from C3sub> Criegee intermediates

    SciTech Connect

    Taatjes, Craig A.; Liu, Fang; Rotavera, Brandon; Kumar, Manoj; Caravan, Rebecca; Osborn, David L.; Thompson, Ward H.; Lester, Marsha I.


    Hydroxyacetone (CH3sub>C(O)CH2OH) is observed as a stable end product from reactions of the (CH3sub>)2COO Criegee intermediate, acetone oxide, in a flow tube coupled with multiplexed photoionization mass spectrometer detection. In the experiment, the isomers at m/z = 74 are distinguished by their different photoionization spectra and reaction times. Hydroxyacetone is observed as a persistent signal at longer reaction times at a higher photoionization threshold of ca. 9.7 eV than Criegee intermediate and definitively identified by comparison with the known photoionization spectrum. Complementary electronic structure calculations reveal multiple possible reaction pathways for hydroxyacetone formation, including unimolecular isomerization via hydrogen atom transfer and –OH group migration as well as self-reaction of Criegee intermediates. Varying the concentration of Criegee intermediates suggests contributions from both unimolecular and self-reaction pathways to hydroxyacetone. As a result, the hydroxyacetone end product can provide an effective, stable marker for the production of transient Criegee intermediates in future studies of alkene ozonolysis.

  16. 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.

  17. High ferroelectric polarization in c-oriented BaTiO3sub> epitaxial thin films on SrTiO3sub>/Si(001)

    SciTech Connect

    Scigaj, M.; Chao, C. H.; Gázquez, J.; Fina, I.; Moalla, R.; Saint-Girons, G.; Chisholm, M. F.; Herranz, G.; Fontcuberta, J.; Bachelet, R.; Sánchez, F.


    The integration of epitaxial BaTiO3sub> films on silicon, combining c-orientation, surface flatness, and high ferroelectric polarization is of main interest towards its use in memory devices. This combination of properties has been only achieved so far by using yttria-stabilized zirconia buffer layers. Here, the all-perovskite BaTiO3sub>/LaNiO3sub>/SrTiO3sub> heterostructure is grown monolithically on Si(001). The BaTiO3sub> films are epitaxial and c-oriented and present low surface roughness and high remnant ferroelectric polarization around 6 μC/cm2. Lastly, this result paves the way towards the fabrication of lead-free BaTiO3sub> ferroelectric memories on silicon platforms.

  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. Influence of hydration water on CH3sub>NH3sub>PbI3sub> perovskite films prepared through one-step procedure.


    Wang, Ziyi; Yuan, Sijian; Li, Dahai; Jin, Feng; Zhang, Rongjun; Zhan, Yiqiang; Lu, Ming; Wang, Songyou; Zheng, Yuxiang; Guo, Junpeng; Fan, Zhiyong; Chen, Liangyao


    Organic-inorganic perovskites were fabricated through a one-step procedure with different levels of hydration water in precursor solutions. The optical properties of CH3sub>NH3sub>PbI3sub> films were investigated through spectroscopic ellipsometry and photoluminescence measurements. With the measured optical constants, the efficiency limit of perovskite solar cells is predicted with a detailed balance model. By comparing the optical measurement to that of planar heterojunction solar cells, we conclude that the radiative efficiency and porosity of the perovskite film significantly influence the performance of perovskite solar cells. An optimized hydration-water concentration is obtained for the 3CH3sub>NH3sub>I:1PbAc2•xH2O precursor solution. The results can provide guidance for further optimization of the device performance of perovskite solar cells by utilizing hydration water.

  20. 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.

  1. 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.

  2. Enhanced structural stability and photo responsiveness of CH3sub>NH3sub>SnI3sub> perovskite via pressure-induced amorphization and recrystallization

    SciTech Connect

    Lu, Xujie; Wang, Yonggang; Stoumpos, Constantinos C.; Hu, Qingyang; Guo, Xiaofeng; Chen, Haijie; Yang, Liuxiang; Smith, Jesse S.; Yang, Wenge; Zhao, Yusheng; Xu, Hongwu; Kanatzidis, Mercouri G.; Jia, Quanxi


    An organic–inorganic halide CH3sub>NH3sub>SnI3sub> perovskite with significantly improved structural stability is obtained via pressure-induced amorphization and recrystallization. In situ high-pressure resistance measurements reveal an increased electrical conductivity by 300% in the pressure-treated perovskite. Photocurrent measurements also reveal a substantial enhancement in visible-light responsiveness. In conclusion, the mechanism underlying the enhanced properties is shown to be associated with the pressure-induced structural modification.

  3. 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.

  4. 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.

  5. High-pressure compressibility and vibrational properties of (Ca,Mn)CO 3sub>

    SciTech Connect

    Liu, Jin; Caracas, Razvan; Fan, Dawei; Bobocioiu, Ema; Zhang, Dongzhou; Mao, Wendy L.


    Knowledge of potential carbon carriers such as carbonates is critical for our understanding of the deep-carbon cycle and related geological processes within the planet. Here we investigated the high-pressure behavior of (Ca,Mn)CO3sub> up to 75 GPa by synchrotron single-crystal X-ray diffraction, laser Raman spectroscopy, and theoretical calculations. MnCO3sub>-rich carbonate underwent a structural phase transition from the CaCO3sub>-I structure into the CaCO3sub>-VI structure at 45–48 GPa, while CaCO3sub>-rich carbonate transformed into CaCO3sub>-III and CaCO3sub>-VI at approximately 2 and 15 GPa, respectively. The equation of state and vibrational properties of MnCO3sub>-rich and CaCO3sub>-rich carbonates changed dramatically across the phase transition. The CaCO3sub>-VI-structured CaCO3sub>-rich and MnCO3sub>-rich carbonates were stable at room temperature up to at least 53 and 75 GPa, respectively. The addition of smaller cations (e.g., Mn2+, Mg2+, and Fe2+) can enlarge the stability field of the CaCO3sub>-I phase as well as increase the pressure of the structural transition into the CaCO3sub>-VI phase.

  6. 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.

  7. 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.

  8. 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

  9. Highly Unsaturated Platinum and Palladium Carbenes PtC3sub> and PdC3sub> Isolated and Characterized in the Gas Phase

    SciTech Connect

    Bittner, Dror M.; Zaleski, Daniel P.; Tew, David P.; Walker, Nicholas R.; Legon, Anthony C.


    Carbenes of platinum and palladium, PtC3sub> and PdC3sub> , were generated in the gas phase through laser vaporization of a metal target in the presence of a low concentration of a hydrocarbon precursor undergoing supersonic expansion. Rotational spectroscopy and abinitio calculations confirm that both molecules are linear. The geometry of PtC3sub> was accurately determined by fitting to the experimental moments of inertia of twenty-six isotopologues. In conclusion, the results are consistent with the proposal of an autogenic isolobal relationship between O, Au+ , and Ptatoms.

  10. Enhancing Electron Mobility at the LaAlO 3sub> /SrTiO 3sub> Interface by Surface Control

    SciTech Connect

    Xie, Yanwu; Bell, Christopher; Hikita, Yasuyuki; Harashima, Satoshi; Hwang, Harold Y.


    Mobility of electrons confined at the LaAlO3sub>/SrTiO3sub> interface is significantly enhanced by surface control using surface charges and adsorbates, reaching a low temperature value more than 20 000 cm2 V-1s-1. A uniform trend that mobility increases with decreasing sheet carrier density is observed.

  11. Reversal of the Upper Critical Field Anisotropy and Spin-Locked Superconductivity in K2Cr3sub>As3sub>

    SciTech Connect

    Balakirev, Fedor Fedorovich; Kong, T.; Jaime, Marcelo; McDonald, Ross David; Mielke, Charles H.; Gurevich, A.; Canfield, P. C.; Bud'ko, S. L.


    Recently, superconductivity in K2Cr3sub>As3sub> (Tc =6.1 K) was discovered. The crystalline lattice contains an array of weakly coupled, double well [(Cr3sub>As3sub>)2-] linkages stretched along the c axis, suggesting the possibility of quasi-one-dimensional superconductivity. Moderately anisotropic upper critical field was revealed in single crystals, with very large initial slopes, dHc2 /dT=12 T/K along the Cr chains and dHperpendicularc2 /dT =7 T/K perpendicular to the chains. Given the ambiguity of conclusions based on the extrapolations of Hc2(T) measured near Tc to low temperatures, we performed high-field measurements of Hc2(T) on K2Cr3sub>As3 sub>single crystals in pulsed magnetic fields which enabled us to reveal the full anisotropic Hc2(T) curves from Tc down to 600 mK.

  12. Non-linear conduction due to depinning of charge order domains in Fe3sub>O2BO3sub>.


    Carvalho Dos Santos, Éverton; da Silva, Everlin; Fernandes, João; Ghivelder, Luis; Freitas, Daniele; Continentino, Mucio A; Walmsley, Lygia


    The oxyborate Fe3sub>O2BO3sub> presents a charge density wave (CDW) transition close to room tem- perature. As we show here, this is associated with a well defined anomaly in the specific heat. Below this transition, when applying in a single crystal of Fe3sub>O2BO3sub> a DC voltage above a temperature dependent threshold, a high current is liberated in this material. We study the conduction in single crystals of Fe3sub>O2BO3sub> with voltage applied parallel and perpendicular to the crystallographic c-axis direction. The observed currents are attributed to the depinning of charge ordered domains above a threshold voltage VT2 that gives rise to a collective conduction due to coherent domains. Compliance limited DC data shows that above a lower threshold voltage depinning is smooth and follows a power law scaling. Similar depinning with power law scaling is also revealed in the AC conductivity.

  13. 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.

  14. Anti-site mixing and magnetic properties of Fe3sub>Co3sub>Nb2 studied via neutron powder diffraction

    SciTech Connect

    Xu, Xiaoshan; Zhang, Xiaozhe; Yin, Yuewei; Balasubramanian, Balamurugan; Das, Bhaskar; Liu, Yaohua; Huq, Ashfia; Sellmyer, David


    We studied the crystal structure and magnetic properties of the rare-earth-free intermetallic compound Fe3sub>Co3sub>Nb2, which has recently been demonstrated to have potentially high magnetic anisotropy, using temperature-dependent neutron powder diffraction. The temperature dependence of the diffraction spectra reveals a magnetic transition between 300 and 400 K, in agreement with the magnetometry measurements. According to the structural refinement of the paramagnetic state and the substantial magnetic contribution to the diffuse scattering in the ferromagnetic state, the Fe/Co anti-site mixing is so strong that the site occupation for Fe and Co is almost random. The projection of the magnetic moments turned out to be non-zero along the c axis and in the a–b plane of Fe3sub>Co3sub>Nb2, most likely because of the exchange interactions between the randomly orientated nanograins in the samples. As a result, these findings suggest that future studies on the magnetism of Fe3sub>Co3sub>Nb2 need to take the Fe/Co anti-site mixing into account, and the exchange interactions need to be suppressed to obtain large remanence and coercivity.

  15. Visible-light-driven Bi 2 O 3sub> /WO 3sub> composites with enhanced photocatalytic activity

    SciTech Connect

    Adhikari, Shiba P.; Dean, Hunter; Hood, Zachary D.; Peng, Rui; More, Karren L.; Ivanov, Ilia; Wu, Zili; Lachgar, Abdou


    Semiconductor heterojunctions (composites) have been shown to be effective photocatalytic materials to overcome the drawbacks of low photocatalytic efficiency that results from electron–hole recombination and narrow photo-response range. We prepared a novel visible-light-driven Bi2O3sub>/WO3sub> composite photocatalyst by hydrothermal synthesis. The composite was characterized by scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area, Raman spectroscopy, photoluminescence spectroscopy (PL) and electrochemical impedance spectroscopy (EIS) to better understand the structures, compositions, morphologies and optical properties. Bi2O3sub>/WO3sub> heterojunction was found to exhibit significantly higher photocatalytic activity towards the decomposition of Rhodamine B (RhB) and 4-nitroaniline (4-NA) under visible light irradiation compared to that of Bi2O3sub> and WO3sub>. A tentative mechanism for the enhanced photocatalytic activity of the heterostructured composite is discussed based on observed activity, band position calculations, photoluminescence, and electrochemical impedance data. Our study provides a new strategy for the design of composite materials with enhanced visible light photocatalytic performance.

  16. Induced Ti magnetization at La0.7Sr0.3sub>MnO3sub> and BaTiO3sub> interfaces

    SciTech Connect

    Liu, Yaohua; Tornos, J.; te Velthuis, S. G. E.; Freeland, J. W.; Zhou, H.; Steadman, P.; Bencok, P.; Leon, C.; Santamaria, J.


    In artificial multiferroics hybrids consisting of ferromagnetic La0.7Sr0.3sub>MnO3sub> (LSMO) and ferroelectric BaTiO3sub> epitaxial layers, net Ti moments are found from polarized resonant soft x-ray reflectivity and absorption. Moreover, the Ti dichroic reflectivity follows the Mn signal during the magnetization reversal, indicating exchange coupling between the Ti and Mn ions. But, the Ti dichroic reflectivity shows stronger temperature dependence than the Mn dichroic signal. Besides a reduced ferromagnetic exchange coupling in the interfacial LSMO layer, this may also be attributed to a weak Ti-Mn exchange coupling that is insufficient to overcome the thermal energy at elevated temperatures.

  17. Material properties of perovskites in the quasi-ternary system LaFeO3sub>–LaCoO3sub>–LaNiO3sub>

    SciTech Connect

    Tietz, F.; Arul Raj, I.; Ma, Q.; Baumann, S.; Mahmoud, A.; Hermann, R. P.


    We present an overview on the variation of electrical conductivity, oxygen permeation, oxygen surface exchange and thermal expansion coefficient as a function of the composition of perovskites in the quasi-ternary system LaFeO3sub>–LaCoO3sub>–LaNiO3sub>. Powders of thirteen nominal perovskite compositions were synthesized under identical conditions by the Pechini method. The powder X-ray diffraction data of two series, namely La(Ni0.5Fe0.5)1-xCoxO3sub> and LaNi0.5- xFexCo0.5O3sub>, are presented after the powders had been sintered at 1100 C for 6 h in air. The measurements revealed a rhombohedral structure for all compositions except LaNi0.5Fe0.5O3sub> for which 60% rhombohedral and 40% orthorhombic phase was found. Moreover, the maximum DC electrical conductivity value of the perovskites at 800 C was 1229 S cm-1 for the composition LaCoO3sub> and the minimum was 91 S cm-1 for the composition LaCo0.5Fe0.5O3sub>. The oxygen permeation of samples with promising conductivities at 800 C was one order of magnitude lower than that of La0.6Sr0.4Co0.8Fe0.2O3sub> (LSCF). The highest value of 0.017 ml cm-2 min-1 at 950 C was obtained with LaNi0.5Co0.5O3sub>. The coefficients of thermal expansion varied in the range of 13.2 x 10-6 K-1 and 21.9 x 10-6 K-1 for LaNi0.5Fe0.5O3sub> and LaCoO3sub>, respectively. 57Fe M ssbauer spectroscopy was used as probe for the oxidation states, local environment and magnetic properties of iron ions as a function of chemical composition. Ultimately, the substitution had a great influence on the chemical properties of the materials.

  18. Direct observation of electronic-liquid-crystal phase transitions and their microscopic origin in La1/3sub>Ca2/3sub>MnO3sub>

    SciTech Connect

    Tao, J.; Sun, K.; Yin, W. -G.; Wu, L.; Xin, H.; Wen, J. G.; Luo, W.; Pennycook, S. J.; Tranquada, J. M.; Zhu, Y.


    The ground-state electronic order in doped manganites is frequently associated with a lattice modulation, contributing to their many interesting properties. However, measuring the thermal evolution of the lattice superstructure with reciprocal-space probes alone can lead to ambiguous results with competing interpretations. Here, we provide direct observations of the evolution of the superstructure in La1/3sub>Ca2/3sub>MnO3sub> in real space, as well as reciprocal space, using transmission electron microscopic (TEM) techniques. We show that the transitions are the consequence of a proliferation of dislocations plus electronic phase separation. The resulting states are well described by the symmetries associated with electronic-liquid-crystal (ELC) phases. Furthermore, our results resolve the long-standing controversy over the origin of the incommensurate superstructure and suggest a new structural model that is consistent with recent theoretical calculations.

  19. 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.

  20. Simplification of femtosecond transient absorption microscopy data from CH3sub>NH3sub>PbI3sub> perovskite thin films into decay associated amplitude maps

    SciTech Connect

    Doughty, Benjamin; Simpson, Mary Jane; Yang, Bin; Xiao, Kai; Ma, Ying -Zhong


    Our work aims to simplify multi-dimensional femtosecond transient absorption microscopy (TAM) data into decay associated amplitude maps that describe the spatial distributions of dynamical processes occurring on various characteristic timescales. Application of this method to TAM data obtained from a model methyl-ammonium lead iodide (CH3sub>NH3sub>PbI3sub>) perovskite thin film allows us to simplify the dataset consisting of a 68 time-resolved images into 4 decay associated amplitude maps. Furthermore, these maps provide a simple means to visualize the complex electronic excited-state dynamics in this system by separating distinct dynamical processes evolving on characteristic timescales into individual spatial images. This approach provides new insight into subtle aspects of ultrafast relaxation dynamics associated with excitons and charge carriers in the perovskite thin film, which have recently been found to coexist at spatially distinct locations.

  1. 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.

  2. Gold in the layered structures of R3sub>Au7Sn3sub>: From relativity to versatility

    SciTech Connect

    Provino, Alessia; Steinberg, Simon Alexander; Smetana, Volodymyr; Paramanik, Uday; Manfrinetti, Pietro; Dhar, Sudesh Kumar; Mudring, Anja -Verena


    A new isotypic series of ternary rare earth element-gold-tetrel intermetallic compounds has been synthesized and their structures and properties have been characterized. R3sub>Au7Sn3sub> (R = Y, La-Nd, Sm, Gd-Tm, Lu) crystallize with the hexagonal Gd3sub>Au7Sn3sub> prototype (Pearson symbol hP26; P63/m, a = 8.110-8.372 Å, c = 9.351-9.609 Å, Vcell = 532.7-583.3 Å3, Z = 2), an ordered variant of the Cu10Sn3sub>-type. Their structure is built up by GdPt2Sn-type layers, which feature edge-sharing Sn@Au6 trigonal antiprisms connected by trigonal R3 groups. Additional insertion of gold atoms leads to the formation of new homoatomic Au clusters, Au@Au6; alternatively, the structure can be considered as a superstructural polyhedral packing of the ZrBeSi-type. The magnetization, heat ca-pacity and electrical resistivity have been measured for R3sub>Au7Sn3sub> (R = Ce, Pr, Nd and Tb). All four compounds order antiferromagnetically with the highest TN of 13 K for Tb3sub>Au7Sn3sub>. In Ce3sub>Au7Sn3sub>, which has a TN of 2.9 K, the heat capacity and electrical resistivity data in zero and applied fields indicate the presence of Kondo interactions. The coefficient of the linear term in the electronic heat capacity, γ, derived from the heat capacity data below 0.5 K is 211 mJ/Ce mol K2 suggesting strong electronic correlations due to the Kondo interaction. The electronic structure calculations based on the projector augmented wave method for particular representatives of the series suggest different tendencies of the localized R-4f AOs to hybridize with the valence states. LMTO-based bonding analysis on the non-magnetic La3sub>Au7Sn3sub> indicates that the integrated crystal orbital Hamilton popu-lations (COHPs) are

  3. Mechanical properties of non-centrosymmetric CePt3sub>Si and CePt3sub>B.


    Rogl, Gerda; Legut, Dominik; Sykora, Rudolf; Müller, Peter; Müller, Herbert; Bauer, Ernst; Puchegger, Stephan; Zehetbauer, M; Rogl, Peter


    Elastic moduli, hardness (both at room temperature) and thermal expansion (4.2 to 670 K) have been experimentally determined for polycrystalline CePt3sub>Si and its prototype compound CePt3sub>B as well as for single-crystalline CePt3sub>Si. Resonant ultrasound spectroscopy was used to determine elastic properties (Young's modulus E and Poissons ratio ν) via the eigenfrequencies of the sample and the knowledge of sample mass and dimensions. Bulk and shear moduli were calculated from E and ν, and the respective Debye temperatures were derived. In addition, ab-initio DFT calculations were carried out for both compounds. A comparison of parameters evaluated from DFT with those of experiments revealed, in general, satisfactory agreement. Positive and negative thermal expansion values obtained from CePt3sub>Si single crystal data are fairly well explained in terms of the crystalline electric field model, using CEF parameters derived recently from inelastic neutron scattering. DFT calculations, in addition, demonstrate that the atomic vibrations keep almost unaffected by the antisymmetric spin-orbit coupling present in systems with crystal structures having no inversion symmetry. This is opposite to electronic properties, where the antisymmetric spin-orbit interaction has shown to distinctly influence features like the superconducting condensate of CePt3sub>Si.

  4. Current understanding of structure-processing-property relationships in BaTiO3sub>-Bi(M)O3sub> dielectrics

    SciTech Connect

    Beuerlein, Michaela A.; Kumar, Nitish; Usher, Tedi -Marie; Brown-Shaklee, Harlan James; Raengthon, Natthaphon; Reaney, Ian M.; Cann, David P.; Jones, Jacob L.; Brennecka, Geoff L.


    Here, as part of a continued push for high permittivity dielectrics suitable for use at elevated operating temperatures and/or large electric fields, modifications of BaTiO3sub> with Bi(M)O3sub>, where M represents a net-trivalent B-site occupied by one or more species, have received a great deal of recent attention. Materials in this composition family exhibit weakly coupled relaxor behavior that is not only remarkably stable at high temperatures and under large electric fields, but is also quite similar across various identities of M. Moderate levels of Bi content (as much as 50 mol%) appear to be crucial to the stability of the dielectric response. In addition, the presence of significant Bi reduces the processing temperatures required for densification and increases the required oxygen content in processing atmospheres relative to traditional X7R-type BaTiO3sub>-based dielectrics. Although detailed understanding of the structure–processing–property relationships in this class of materials is still in its infancy, this article reviews the current state of understanding of the mechanisms underlying the high and stable values of both relative permittivity and resistivity that are characteristic of BaTiO3sub>-Bi(M)O3sub> dielectrics as well as the processing challenges and opportunities associated with these materials.

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

    SciTech Connect

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


    : Lithiated graphitic carbon n.itride (C3sub>N4 ) was fabricated by electrochemical and solid-state reactions. The addition of Li to C3sub>N4 results in a reaction between the Li and the graphite-like C3sub>N species in C3sub>N4. This irreversible reaction leads to the formation of Li-CH=NR and Li-N=CR2 species, which are detrimental to anode properties. Suitable nitrogen-doped carbon structures for anode applications are predicted to need high concentrations of pyridinic C-N-C terminal bonds and low concentrations of w quaternary C3sub>N species to boost electronic conductivity and reversibly cycle Li ions.

  6. 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.

  7. 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.

  8. Ultrafast relaxation dynamics in BiFeO3sub>/YBa2Cu3sub>O7 bilayers

    SciTech Connect

    Springer, D.; Nair, Saritha K.; He, Mi; Lu, C. L.; Cheong, S. A.; Wu, T.; Panagopoulos, C.; Chia, Elbert E. M.; Zhu, Jianxin


    The temperature dependence of the relaxation dynamics in the bilayer thin film heterostructure composed of multiferroic BiFeO3sub> (BFO) and superconducting YBa2Cu3sub>O7 (YBCO) grown on (001) SrTiO3sub> substrate is studied by time-resolved pump-probe technique, and compared with that of pure YBCO thin film grown under the same growth conditions. The superconductivity of YBCO is found to be retained in the heterostructure. We observe a speeding up of the YBCO recombination dynamics in the superconducting state of the heterostructure, and attribute it to the presence of weak ferromagnetism at the BFO/YBCOinterface as observed inmagnetization data. An extension of the Rothwarf-Taylor model is used to fit the ultrafast dynamics of BFO/YBCO, that models an increased quasiparticle occupation of the ferromagnetic interfacial layer in the superconducting state of YBCO.

  9. 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.

  10. 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.

  11. Pressure-induced ferroelectric to paraelectric transition in LiTaO3sub> and (Li,Mg)TaO3sub>

    SciTech Connect

    Yamanaka, Takamitsu; Nakamoto, Yuki; Takei, Fumihiko; Ahart, Muhtar; Mao, Ho-kwang; Hemley, Russell J.


    X-ray powder diffraction and Raman scattering of LiTaO3sub> (LT) and (Li,Mg)TaO3sub> (LMT) have been measured under pressure up to 46 GPa. Above 30 GPa, the ferroelectric rhombohedral phase (R3c, Z – 6) of LiTaO3sub> transforms to a paraelectric orthorhombic phase (Pnma with Z – 4) with a large hysteresis. Rietveld profile fitting analysis shows that the Li-O bond is compressed and approaches that of Ta-O with pressure. The cation distribution analysis of the orthorhombic perovskite structure shows that Li and Ta are located in the octahedral 8-fold coordination sites. Difference Fourier |Fobs(hkl)| - |Fcal(hkl)| maps of LiTaO3sub> and (Li,Mg)TaO3sub> indicate polarization in the c axis direction and a more distinct electron density distribution around the Ta position for (Li,Mg)TaO3sub> compared to LiTaO3sub>. The observed effective charges indicate that for (Li,Mg)TaO3sub> without vacancies Ta5+ becomes less ionized as a function of Mg substitution. Considering both site occupancy and effective charge analysis, Ta5+ is reduced to Ta4.13+. Mg2+ and O2- change to Mg1.643+ and O1.732 -, respectively. The space- and time-averaged structures of the dynamical vibration of atoms can be elucidated from the electron density analysis by difference Fourier and temperature factors T(hkl) in the structure refinement. The refinement of the temperature factor is consistent with the cation distribution assuming full stoichiometry. The residual electron density induced from the excess electron in (Li,Mg)TaO3sub> indicates more electrons around the Ta site, as confirmed by the effective charge analysis. Raman spectra of LiTaO3sub> and (Li,Mg)TaO3sub> show notable changes over the measured pressure range. Raman peaks centered at 250 cm–1 and 350 cm–1 at ambient pressure merge

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Conducting interfaces between amorphous layers and SrTiO3sub>(110) and SrTiO3sub>(111)

    SciTech Connect

    Varela, Maria; Scigaj, Mateusz; Gazquez, Jaume; Fontcuberta, Josep; Herranz, Gervasi; Sanchez, Florencio


    Interfaces between (110) and (111)SrTiO3sub> (STO) single crystalline substrates and amorphous oxide layers, LaAlO3sub> (a-LAO), Y:ZrO2 (a-YSZ), and SrTiO3sub> (a-STO) become conducting above a critical thickness tc. Here we show that tc for a-LAO does not depend on the substrate orientation, i.e. tc (a-LAO/(110)STO) ≈ tc(a-LAO/(111)STO) interfaces, whereas it strongly depends on the composition of the amorphous oxide: tc(a-LAO/(110)STO) < tc(a-YSZ/(110)STO) < tc(a-STO/(110)STO). It is concluded that the formation of oxygen vacancies in amorphous-type interfaces is mainly determined by the oxygen affinity of the deposited metal ions, rather than orientation-dependent enthalpy vacancy formation and diffusion. Furthermore, scanning transmission microscopy characterization of amorphous and crystalline LAO/STO(110) interfaces shows much higher amount of oxygen vacancies in the former, providing experimental evidence of the distinct mechanism of conduction in these interfaces.

  18. Chemical instability leads to unusual chemical-potential-independent defect formation and diffusion in perovskite solar cell material CH 3sub> NH 3sub> PbI 3sub>

    SciTech Connect

    Ming, Wenmei; Chen, Shiyou; Du, Mao-Hua


    Methylammonium (MA) lead triiodide (MAPbI3sub>) has recently emerged as a promising solar cell material. But, MAPbI3 is known to have chemical instability, i.e., MAPbI3 is prone to decomposition into MAI and PbI2 even at moderate temperatures (e.g. 330 K). Here, we show that the chemical instability, as reflected by the calculated negligible enthalpy of formation of MAPbI3sub> (with respect to MAI and PbI2), has an unusual and important consequence for defect properties, i.e., defect formation energies in low-carrier-density MAPbI3sub> are nearly independent of the chemical potentials of constituent elements and thus can be uniquely determined. This allows straightforward calculations of defect concentrations and the activation energy of ionic conductivity (the sum of the formation energy and the diffusion barrier of the charged mobile defect) in MAPbI3sub>. Furthermore, the calculated activation energy for ionic conductivity due to V$+\\atop{1}$ diffusion is in excellent agreement with the experimental values, which demonstrates unambiguously that V$+\\atop{1}$ is the dominant diffusing defect and is responsible for the observed ion migration and device polarization in MAPbI3 solar cells. The calculated low formation energy of a Frenkel pair (V$+\\atop{1}$ -I$-\\atop{i}$ and low diffusion barriers of V$+\\atop{1}$ and Image I$-\\atop{i}$ suggest that the iodine ion migration and the resulting device polarization may occur even in single-crystal devices and grain-boundary-passivated polycrystalline thin film devices (which were previously suggested to be free from ion-migration-induced device polarization), leading to device degradation. Moreover, the device polarization due to the Frenkel pair (which has a relatively low concentration) may take a long time to develop and thus may avoid the appearance of the current–voltage hysteresis at typical scan rates.

  19. 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.

  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. Thermo-magnetic instabilities in Nb3sub>Sn superconducting accelerator magnets

    SciTech Connect

    Bordini, Bernardo


    The advance of High Energy Physics research using circulating accelerators strongly depends on increasing the magnetic bending field which accelerator magnets provide. To achieve high fields, the most powerful present-day accelerator magnets employ NbTi superconducting technology; however, with the start up of Large Hadron Collider (LHC) in 2007, NbTi magnets will have reached the maximum field allowed by the intrinsic properties of this superconductor. A further increase of the field strength necessarily requires a change in superconductor material; the best candidate is Nb3sub>Sn. Several laboratories in the US and Europe are currently working on developing Nb3sub>Sn accelerator magnets, and although these magnets have great potential, it is suspected that their performance may be fundamentally limited by conductor thermo-magnetic instabilities: an idea first proposed by the Fermilab High Field Magnet group early in 2003. This thesis presents a study of thermo-magnetic instability in high field Nb3sub>Sn accelerator magnets. In this chapter the following topics are described: the role of superconducting magnets in High Energy Physics; the main characteristics of superconductors for accelerator magnets; typical measurements of current capability in superconducting strands; the properties of Nb3sub>Sn; a description of the manufacturing process of Nb3sub>Sn strands; superconducting cables; a typical layout of superconducting accelerator magnets; the current state of the art of Nb3sub>Sn accelerator magnets; the High Field Magnet program at Fermilab; and the scope of the thesis.

  2. Composition dependence of spin transition in (Mg,Fe)SiO3sub> bridgmanite

    SciTech Connect

    Dorfman, Susannah M.; Badro, James; Rueff, Jean -Pascal; Chow, Paul; Xiao, Yuming; Gillet, Philippe


    Spin transitions in (Mg,Fe)SiO3sub> bridgmanite have important implications for the chemistry and dynamics of Earth’s lower mantle, but have been complex to characterize in experiments. We examine the spin state of Fe in highly Fe-enriched bridgmanite synthesized from enstatites with measured compositions (Mg0.61Fe0.38Ca0.01)SiO3sub> and (Mg0.25Fe0.74Ca0.01)SiO3sub>. Bridgmanite was synthesized at 78-88 GPa and 1800-2400 K and X-ray emission spectra were measured on decompression to 1 bar (both compositions) and compression to 126 GPa ((Mg0.61Fe0.38Ca0.01)SiO3sub> only) without additional laser heating. Observed spectra confirm that Fe in these bridgmanites is dominantly high spin in the lower mantle. However, the total spin moment begins to decrease at ~50 GPa in the 74% FeSiO3sub> composition. Lastly, these results support density functional theory predictions of a lower spin transition pressure in highly Fe-enriched bridgmanite and potentially explain the high solubility of FeSiO3sub> in bridgmanite at pressures corresponding to Earth’s deep lower mantle.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Non-stoichiometry in U3sub>Si2

    SciTech Connect

    Middleburgh, Simon C.; Grimes, Robin W.; Lahoda, Ed J.; Stanek, Christopher Richard; Andersson, David A.


    Uranium silicides, in particular U3sub>Si2, are being explored as an advanced nuclear fuel with increased accident tolerance as well as competitive economics compared to the baseline UO2 fuel. Here we use density functional theory calculations and thermochemical analysis to assess the stability of U3sub>Si2 with respect to non-stoichiometry reactions in both the hypo- and hyper-stoichiometric regimes. We find that the degree of non-stoichiometry in U3sub>Si2 is much smaller than in UO2 and at most reaches a few percent at high temperature. Non-stoichiometry impacts fuel performance by determining whether the loss of uranium due to fission leads to a non-stoichiometric U3sub>Si2±x phase or precipitation of a second U-Si phase. Lastly, we also investigate the U5Si4 phase as a candidate for the equilibrium phase diagram.

  8. Single-domain multiferroic BiFeO3sub> films

    SciTech Connect

    Kuo, Chang -Yang; Hu, Z.; Yang, J. C.; Liao, S. -C.; Huang, Y. L.; Vasudevan, R. K.; Okatan, M. B.; Jesse, Stephen; Kalinin, Sergei V.; Li, L.; Liu, H. J.; Lai, C. -H.; Pi, T. W.; Agrestini, S.; Chen, K.; Ohresser, P.; Tanaka, A.; Tjeng, L. H.; Chu, Ying -Hao


    The strong coupling between antiferromagnetism and ferroelectricity at room temperature found in BiFeO3sub> generates high expectations for the design and development of technological devices with novel functionalities. However, the multi-domain nature of the material tends to nullify the properties of interest and complicates the thorough understanding of the mechanisms that are responsible for those properties. Here we report the realization of a BiFeO3sub> material in thin film form with single-domain behaviour in both its magnetism and ferroelectricity: the entire film shows its antiferromagnetic axis aligned along the crystallographic b axis and its ferroelectric polarization along the c axis. With this we are able to reveal that the canted ferromagnetic moment due to the Dzyaloshinskii–Moriya interaction is parallel to the a axis. Moreover, by fabricating a Co/BiFeO3sub> heterostructure, we demonstrate that the ferromagnetic moment of the Co film does couple directly to the canted moment of BiFeO3sub>.

  9. 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.

  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. 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.

  12. 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)

  13. Pressure dependence of carbonate exchange with [NpO2(CO3sub>)3sub>]4– in aqueous solutions

    SciTech Connect

    Pilgrim, Corey D.; Zavarin, Mavrik; Casey, William H.


    Here, the rates of ligand exchange into the geochemically important [NpO2(CO3sub>)3sub>]4– aqueous complex are measured as a function of pressure in order to complement existing data on the isostructural [UO2(CO3sub>)3sub>]4– complex. Experiments are conducted at pH conditions where the rate of exchange is independent of the proton concentration. Unexpectedly, the experiments show a distinct difference in the pressure dependencies of rates of exchange for the uranyl and neptunyl complexes.

  14. CO Oxidation and Subsequent CO2 Chemisorption on Alkaline Zirconates: Li2 ZrO3sub> and Na2 ZrO3sub>

    SciTech Connect

    Alcántar-Vázquez, Brenda; Duan, Yuhua; Pfeiffer, Heriberto


    Here, two different alkaline zirconates (Li2ZrO3sub> and Na2ZrO3sub>) were studied as possible bifunctional catalytic-captor materials for CO oxidation and the subsequent CO2 chemisorption process. Initially, CO oxidation reactions were analyzed in a catalytic reactor coupled to a gas chromatograph, using Li2ZrO3sub> and Na2ZrO3sub>, under different O2 partial flows. We found results clearly showed that Na2ZrO3sub> possesses much better catalytic properties than Li2ZrO3sub>. After the CO-O2 oxidation catalytic analysis, CO2 chemisorption process was analyzed by thermogravimetric analysis, only for the Na2ZrO3sub> ceramic. The results confirmed that Na2ZrO3sub> is able to work as a bifunctional material (CO oxidation and subsequent CO2 chemisorption), although the kinetic CO2 capture process was not the best one under the physicochemical condition used in this case. For Na2ZrO3sub>, the best CO conversions were found between 445 and 580 °C (100%), while Li2ZrO3sub> only showed a 35% of efficiency between 460 and 503 °C. However, in the Na2ZrO3sub> case, at temperatures higher than 580 °C its catalytic activity gradually decreases as a result of CO2 capture process. Finally, all these experiments were compared and supported with theoretical thermodynamic data.

  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. 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.

  17. 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] .

  18. 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.

  19. 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.

  20. 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.

  1. High pressure transport and structural studies on Nb3sub>Ga superconductor

    SciTech Connect

    Mkrtcheyan, Vahe; Kumar, Ravhi; Baker, Jason; Connolly, Anthony; Antonio, Daniel; Cornelius, Andrew; Zhao, Yusheng


    We investigated the crystal structure of A-15 superconductor Nb3sub>Ga with a critical temperature Tc = 16.5 K by high pressure x-ray diffraction (HPXRD) using synchrotron x-rays and a diamond anvil cell under Ne pressure medium. Furthermore, the high pressure structural results indicate that Nb3sub>Ga is stable up to 41 GPa. The P-V plot shows an anomaly around 15 GPa even though there are no pressure induced structural transitions are observed. High pressure resistance measurements were performed up to 0.5 GPa to understand the variation of Tc under pressure. Finally, our results show a positive pressure effect on Tc.

  2. Enhanced ionic conductivity with Li7O2Br3sub> phase in Li3sub>OBr anti-perovskite solid electrolyte

    SciTech Connect

    Zhu, Jinlong; Li, Shuai; Zhang, Yi; Howard, John W.; Lu, Xujie; Li, Yutao; Wang, Yonggang; Kumar, Ravhi S.; Wang, Liping; Zhao, Yusheng


    Cubic anti-perovskites with general formula Li3sub>OX (X = Cl, Br, I) were recently reported as superionic conductors with the potential for use as solid electrolytes in all-solid-state lithium ion batteries. These electrolytes are nonflammable, low-cost, and suitable for thermoplastic processing. However, the primary obstacle of its practical implementation is the relatively low ionic conductivity at room temperature. In this work, we synthesized a composite material consisting of two anti-perovskite phases, namely, cubic Li3sub>OBr and layered Li7O2Br3sub>, by solid state reaction routes. The results indicate that with the phase fraction of Li7O2Br3sub> increasing to 44 wt. %, the ionic conductivity increased by more than one order of magnitude compared with pure phase Li3sub>OBr. Formation energy calculations revealed the meta-stable nature of Li7O2Br3sub>, which supports the great difficulty in producing phase-pure Li7O2Br3sub> at ambient pressure. Here, methods of obtaining phase-pure Li7O2Br3sub> will continue to be explored, including both high pressure and metathesis techniques.

  3. 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

  4. On information loss in AdS3sub>/CFT2

    SciTech Connect

    Fitzpatrick, A. Liam; Kaplan, Jared; Li, Daliang; Wang, Junpu


    We discuss information loss from black hole physics in AdS3sub>, focusing on two sharp signatures infecting CFT2 correlators at large central charge c: ‘forbidden singularities’ arising from Euclidean-time periodicity due to the effective Hawking temperature, and late-time exponential decay in the Lorentzian region. We study an infinite class of examples where forbidden singularities can be resolved by non-perturbative effects at finite c, and we show that the resolution has certain universal features that also apply in the general case. Analytically continuing to the Lorentzian regime, we find that the non-perturbative effects that resolve forbidden singularities qualitatively change the behavior of correlators at times t ~SBH, the black hole entropy. This may resolve the exponential decay of correlators at late times in black hole backgrounds. By Borel resumming the 1/c expansion of exact examples, we explicitly identify ‘information-restoring’ effects from heavy states that should correspond to classical solutions in AdS3sub>. Lastly, our results suggest a line of inquiry towards a more precise formulation of the gravitational path integral in AdS3sub>.

  5. Elasticity and magnetocaloric effect in MnFe4Si3sub>

    SciTech Connect

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


    The room temperature magnetocaloric material MnFe4Si3sub> was investigated with nuclear inelastic scattering (NIS) and resonant ultrasound spectroscopy (RUS) at different temperatures and applied magnetic fields in order to assess the infuence of the magnetic transition and the magnetocaloric effect on the lattice dynamics. The NIS data give access to phonons with energies above 3 meV, whereas RUS probes the elasticity of the material in the MHz frequency range and thus low energy, ~5 neV, phonon modes. A significant infuence of the magnetic transition on the lattice dynamics is observed only in the low energy region. Here, MnFe4Si3sub> and other compounds in the Mn5-xFexSi3sub> series were also investigated with vibrating sample magnetometry, resistivity measurements and Moessbauer spectroscopy in order to study the magnetic transitions and to complement the obtained results on the lattice dynamics.

  6. Dimensional changes of Nb3sub>Sn Rutherford cables during heat treatment

    SciTech Connect

    Rochepault, E.; Ferracin, P.; Ambrosio, G.; Anerella, M.; Ballarino, A.; Bonasia, A.; Bordini, B.; Cheng, D.; Dietderich, D. R.; Felice, H.; Fajardo, L. Garcia; Ghosh, A.; Holik, E. F.; Bermudez, S. Izquierdo; Perez, J. C.; Pong, I.; Schmalzle, J.; Yu, M.


    In high field magnet applications, Nb3sub>Sn coils undergo a heat treatment step after winding. During this stage, coils radially expand and longitudinally contract due to the Nb3sub>Sn phase change. In order to prevent residual strain from altering superconducting performances, the tooling must provide the adequate space for these dimensional changes. The aim of this paper is to understand the behavior of cable dimensions during heat treatment and to provide estimates of the space to be accommodated in the tooling for coil expansion and contraction. In addition, this paper summarizes measurements of dimensional changes on strands, single Rutherford cables, cable stacks, and coils performed between 2013 and 2015. These samples and coils have been performed within a collaboration between CERN and the U.S. LHC Accelerator Research Program to develop Nb3sub>Sn quadrupole magnets for the HiLumi LHC. The results are also compared with other high field magnet projects.

  7. Electrochemical oxygen reduction catalysed by Ni3sub>(hexaiminotriphenylene)2

    SciTech Connect

    Miner, Elise M.; Fukushima, Tomohiro; Sheberla, Dennis; Sun, Lei; Surendranath, Yogesh; Dinca, Mircea


    Control over the architectural and electronic properties of heterogeneous catalysts poses a major obstacle in the targeted design of active and stable non-platinum group metal electrocatalysts for the oxygen reduction reaction. Here we introduce Ni3sub>(HITP)2 (HITP=2, 3, 6, 7, 10, 11-hexaiminotriphenylene) as an intrinsically conductive metal-organic framework which functions as a well-defined, tunable oxygen reduction electrocatalyst in alkaline solution. Ni3sub>(HITP)2 exhibits oxygen reduction activity competitive with the most active non-platinum group metal electrocatalysts and stability during extended polarization. The square planar Ni-N4 sites are structurally reminiscent of the highly active and widely studied non-platinum group metal electrocatalysts containing M-N4 units. Ni3sub>(HITP)2 and analogues thereof combine the high crystallinity of metal-organic frameworks, the physical durability and electrical conductivity of graphitic materials, and the diverse yet well-controlled synthetic accessibility of molecular species. As a result, such properties may enable the targeted synthesis and systematic optimization of oxygen reduction electrocatalysts as components of fuel cells and electrolysers for renewable energy applications.

  8. Facile fabrication of large-grain CH3sub>NH3sub>PbI3-xBrx films for high-efficiency solar cells via CH3sub>NH3sub>Br-selective Ostwald ripening

    SciTech Connect

    Yang, Mengjin; Zhang, Taiyang; Schulz, Philip; Li, Zhen; Li, Ge; Kim, Dong Hoe; Guo, Nanjie; Berry, Joseph J.; Zhu, Kai; Zhao, Yixin


    Organometallic halide perovskite solar cells (PSCs) have shown great promise as a low-cost, high-efficiency photovoltaic technology. Structural and electro-optical properties of the perovskite absorber layer are most critical to device operation characteristics. Here we present a facile fabrication of high-efficiency PSCs based on compact, large-grain, pinhole-free CH3sub>NH3sub>PbI3-xBrx (MAPbI3-xBrx) thin films with high reproducibility. A simple methylammonium bromide (MABr) treatment via spin-coating with a proper MABr concentration converts MAPbI3sub> thin films with different initial film qualities (for example, grain size and pinholes) to high-quality MAPbI3-xBrx thin films following an Ostwald ripening process, which is strongly affected by MABr concentration and is ineffective when replacing MABr with methylammonium iodide. A higher MABr concentration enhances I-Br anion exchange reaction, yielding poorer device performance. Lastly, this MABr-selective Ostwald ripening process improves cell efficiency but also enhances device stability and thus represents a simple, promising strategy for further improving PSC performance with higher reproducibility and reliability.

  9. 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.

  10. 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.

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

    SciTech Connect

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


    In order to well address the problems of large volume change and dissolution of Fe3sub>O4 nanomaterials during Li+ intercalation/extraction, herein we demonstrate a one-step in situ nanospace-confined pyrolysis strategy for robust yolk–shell nanospindles with very sufficient internal void space (VSIVS) for high-rate and long-term lithium ion batteries (LIBs), in which an Fe3sub>O4@Fe3sub>C core@shell nanoparticle is well confined in the compartment of a hollow carbon nanospindle. This structure can not only introduce VSIVS to accommodate volume change of Fe3sub>O4 but also afford a dual shell of Fe3sub>C and carbon to restrict Fe3sub>O4 dissolution, thus providing dual roles for greatly improving the capacity retention. Consequently, Fe3sub>O4@Fe3sub>C–C yolk–shell nanospindles deliver a high reversible capacity of 1128.3 mAh g–1 at even 500 mA g–1, excellent high rate capacity (604.8 mAh g–1 at 2000 mA g1), and prolonged cycling life (maintaining 1120.2 mAh g–1 at 500 mA g–1 for 100 cycles) for LIBs, which are much better than those of Fe3sub>O4@C core@shell nanospindles and Fe3sub>O4 nanoparticles. The present Fe3sub>O4@Fe3sub>C–C yolk–shell nanospindles are the most efficient Fe3sub>O4-based anode materials ever reported for LIBs.

  12. 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

  13. Strain tuning and strong enhancement of ionic conductivity in SrZrO3sub>-RE2O3sub> (RE = Sm, Eu, Gd, Dy, and Er) nanocomposite films

    SciTech Connect

    Lee, Shinbuhm; Zhang, Wenrui; Khatkhatay, Fauzia; Jia, Quanxi; Wang, Haiyan; MacManus-Driscoll, Judith L.


    Fast ion transport channels at interfaces in thin films have attracted great attention due to a range of potential applications for energy materials and devices, for, solid oxide fuel cells, sensors, and memories. Here, it is shown that in vertical nanocomposite heteroepitaxial films of SrZrO3sub>–RE2O3sub> (RE = Sm, Eu, Gd, Dy, and Er) the ionic conductivity of the composite can be tuned and strongly enhanced using embedded, stiff, and vertical nanopillars of RE2O3sub>. With increasing lattice constant of RE2O3sub> from Er2O3sub> to Sm2O3sub>, it is found that the tensile strain in the SrZrO3sub> increases proportionately, and the ionic conductivity of the composite increases accordingly, by an order of magnitude. Lastly, the results here conclusively show, for the first time, that strain in films can be effectively used to tune the ionic conductivity of the materials.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Solution-processed BiI3sub> thin films for photovoltaic applications: Improved carrier collection via solvent annealing

    SciTech Connect

    Hamdeh, Umar H.; Nelson, Rainie D.; Ryan, Bradley J.; Bhattacharjee, Ujjal; Petrich, Jacob W.; Panthani, Matthew G.


    Here, we report all-inorganic solar cells based on solution-processed BiI3sub>. Two-electron donor solvents such as tetrahydrofuran and dimethylformamide were found to form adducts with BiI3sub>, which make them highly soluble in these solvents. BiI3sub> thin films were deposited by spin-coating. Solvent annealing BiI3sub> thin films at relatively low temperatures (≤100 °C) resulted in increased grain size and crystallographic reorientation of grains within the films. The BiI3 films were stable against oxidation for several months and could withstand several hours of annealing in air at temperatures below 150 °C without degradation. Surface oxidation was found to improve photovoltaic device performance due to the formation of a BiOI layer at the BiI3sub> surface which facilitated hole extraction. Nonoptimized BiI3sub> solar cells achieved the highest power conversion efficiencies of 1.0%, demonstrating the potential of BiI3sub> as a nontoxic, air-stable metal-halide absorber material for photovoltaic applications.

  19. First-principles prediction of a rising star of solar energy material: SrTcO3sub>.


    Chen, Da; Ma, Chun-Lan; Chen, Gao-Yuan; Dai, Cheng-Min; Gu, Ling-Jun; Ge, Li-Juan; Ke, San-Huang; Wu, Rong


    SrTcO3sub> as a new star of solar energy material is investigated in terms of its band gap evolution with biaxial strain from first-principles calculations. Compared to the theoretical equilibrium lattice constant a(b) of bulk SrTcO3sub>, a set of lattice constants with a deviation of -8.75% to +3.35% are considered to include the strain effect. Since the in-plane lattice constant of SrTcO3sub> is larger than that of the commonly used substrate SrTiO3sub>(STO)/La0.3sub>Sr0.7Al0.35Ta0.35O9 (LSAT)/NdGaO3sub>(NGO)/LaAlO3sub>(LAO), we mainly focus on the modulation of compressive strain. It is found that the band gap decreases with increasing compressive/tensile strain. When the compressive strain reaches 8.75%, the band gap drops to zero and an insulator-metal phase transition appears. Particularly, upon a compressive strain of 1.3%/2.2%/2.4%/4.1%, which can be realized by growing SrTcO3sub> on substrate STO/LSAT/NGO/LAO, the band gap becomes 1.56/1.47/1.43/1.12 eV, which falls in the range for efficient solar cell materials. Our work suggests that SrTcO3sub> is a good candidate for a new solar energy material.

  20. 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.

  1. 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

  2. Thermodynamic Studies and Hydride Transfer Reactions from a Rhodium Complex to BX3sub> Compounds

    SciTech Connect

    Mock, Michael T; Potter, Robert G; Camaioni, Donald M; Li, Jun; Dougherty, William G; Kassel, W S; Twamley, Brendan; DuBois, Daniel L


    This study examines the use of transition-metal hydride complexes that can be generated by the heterolytic cleavage of H2 gas to form B–H bonds. Specifically, these studies are focused on providing a reliable and quantitative method for determining when hydride transfer from transition-metal hydrides to three-coordinate BX3sub> compounds will be favorable. This involves both experimental and theoretical determinations of hydride transfer abilities. Thermodynamic hydride donor abilities (ΔG°H-) were determined for HRh(dmpe)2 and HRh(depe)2, where dmpe = 1,2-bis(dimethylphosphinoethane) and depe = 1,2-bis(diethylphosphinoethane), on a previously established scale in acetonitrile. This hydride donor ability was used to determine the hydride donor ability of [HBEt3sub>]⁻ on this scale. Isodesmic reactions between [HBEt3sub>]⁻ and various BX3sub> complexes to form BEt3sub> and [HBX3sub>]⁻ were examined computationally to determine the relative hydride affinities of various BX3sub> compounds. The use of these scales of hydride donor abilities and hydride affinities for transition-metal hydrides and BX3sub> compounds is illustrated with a few selected reactions relevant to the regeneration of ammonia borane. Our findings indicate that it is possible to form B-H bonds from B-X bonds, and the extent to which BX3sub> compounds are reduced by transition-metal hydride complexes forming species containing multiple B-H bonds depends on the heterolytic B-X bond energy. An example is the reduction of B(SPh)3sub> using HRh(dmpe)2 in the presence of triethylamine to form Et3sub>N-BH3sub> in high yields. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  3. 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.

  4. Structure of the Photo-catalytically Active Surface of SrTiO 3sub>

    SciTech Connect

    Plaza, Manuel; Huang, Xin; Ko, J. Y. Peter; Shen, Mei; Simpson, Burton H.; Rodríguez-López, Joaquín; Ritzert, Nicole L.; Letchworth-Weaver, Kendra; Gunceler, Deniz; Schlom, Darrell G.; Arias, Tomás A.; Brock, Joel D.; Abruña, Héctor D.


    A major goal of energy research is to use visible light to cleave water directly, without an applied voltage, into hydrogen and oxygen. Although SrTiO3sub> requires ultraviolet light, after four decades, it is still the "gold standard" for the photo-catalytic splitting of water. It is chemically robust and can carry out both hydrogen and oxygen evolution reactions without an applied bias. While ultrahigh vacuum surface science techniques have provided useful insights, we still know relatively little about the structure of these electrodes in contact with electrolytes under operating conditions. Here, we report the surface structure evolution of a n-SrTiO3sub> electrode during water splitting, before and after "training" with an applied positive bias. Operando high-energy X-ray reflectivity measurements demonstrate that training the electrode irreversibly reorders the surface. Scanning electrochemical microscopy at open circuit correlates this training with a 3-fold increase of the activity toward the photo-induced water splitting. A novel first-principles joint density functional theory simulation, constrained to the X-ray data via a generalized penalty function, identifies an anatase-like structure as the more active, trained surface.

  5. Theoretical study of cubic Rashba effect at SrTiO3sub> (001) surfaces

    SciTech Connect

    Shanavas, Kavungal Veedu


    The origin of Rashba spin splitting in the two-dimensional electron gas at the (001) surface of SrTiO3sub> is studied using first-principles calculations and tight-binding model. Calculations of oxygen vacancies under virtual crystal approximation reveal a two-dimensional electron-gas subband structure similar to polar materials, consistent with observations on SrTiO3sub>. Our studies also confirm that k dependence of the spin splitting is predominantly cubic in the surface Ti–t2g states, even though structural relaxations diminish the effect in dxy bands. A tight-binding model, explicitly including Ti–d and O–p states as well as next-nearest-neighbor interactions, is derived to understand the first-principles results. Effective Rashba Hamiltonians for the surface bands are derived using quasidegenerate perturbation theory and scenarios in which linear k contribution may be suppressed are discussed. Furthermore, the cubic terms in the Hamiltonian are found to be different from the model derived using k ∙ p theory, leading to different pseudospin symmetry in the Brillouin zone.

  6. 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.

  7. Pressure-induced polymerization of P(CN) 3sub>

    SciTech Connect

    Gou, Huiyang; Yonke, Brendan L.; Epshteyn, Albert; Kim, Duck Young; Smith, Jesse S.; Strobel, Timothy A.


    Motivated to explore the formation of novel extended carbon-nitrogen solids via well-defined molecular precursor pathways, we studied the chemical reactivity of highly pure phosphorous tricyanide, P(CN)3sub>, under conditions of high pressure at room temperature. Raman and infrared (IR) spectroscopic measurements reveal a series of phase transformations below 10 GPa, and several low-frequency vibrational modes are reported for the first time. Synchrotron powder Xray diffraction (PXRD) measurements taken during compression show that molecular P(CN)3sub> is highly compressible with a bulk modulus of 10.0±0.3 GPa and polymerizes into an amorphous solid above ~10.0 GPa. Raman and infrared (IR) spectra, together with first-principles molecular-dynamics simulations, show that the amorphization transition is associated with polymerization of the cyanide groups into CN bonds with predominantly sp2 character, similar to known carbon nitrides, resulting in a novel PCN polymeric phase, which is recoverable to ambient pressure.

  8. Coupled domain wall motion, lattice strain and phase transformation in morphotropic phase boundary composition of PbTiO3sub>-BiScO3sub> piezoelectric ceramic

    SciTech Connect

    Khatua, Dipak Kumar; V., Lalitha K.; Fancher, Chris M.; Jones, Jacob L.; Ranjan, Rajeev


    High energy synchrotron X-ray diffraction, in situ with electric field, was carried out on the morphotropic phase boundary composition of the piezoelectric alloy PbTiO3sub>-BiScO3sub>. We demonstrate a strong correlation between ferroelectric-ferroelastic domain reorientation, lattice strain and phase transformation. Lastly, we also show the occurrence of the three phenomena and persistence of their correlation in the weak field regime.

  9. Single-phase tunable white-light-emitting Sr3sub> La(PO4)3sub> : Eu2+, Mn2+ phosphor for white LEDs.


    Wang, Zhijun; Lou, Shuqin; Li, Panlai; Lian, Zhenggang


    A novel, near-ultraviolet-excited white-light-emitting phosphor Sr3sub>La(PO4)3sub>:Eu2+, Mn2+ was synthesized by the solid-state method. Luminescence properties and the energy transfer mechanism were investigated in detail by photoluminescence spectra and decay curves. With the energy transfer between Eu2+ and Mn2+, a cold white light with chromaticity coordinates of (0.2790, 0.2273), correlated color temperature of 6501 K, Ra of 70, and external quantum efficiency of 35.5% was realized by changing the ratios of Eu2+ and Mn2+ in the Sr3sub>La(PO4)3sub>:Eu2+, Mn2+ phosphors. Resonant energy transfer from Eu2+ to Mn2+  ions has been demonstrated to be a dipole-dipole mechanism in Sr3sub>La(PO4)3sub>. The energy transfer efficiency increases with Mn2+ concentration increasing, and reaches a maximum of 55.6%.

  10. pH-regulative synthesis of Na3sub>(VPO4)2F3sub> nanoflowers and their improved Na cycling stability

    SciTech Connect

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


    Na-ion batteries are becoming increasingly attractive as a low cost energy storage device. Sodium vanadium fluorophosphates have been studied extensively recently due to their high storage capacity and high discharge voltage. Shape and size often have a crucial influence over the properties. The controlling synthesis of nanoparticles with special microstructures is significant, which becomes a challenging issue and has drawn considerable attention. In this study, Na3sub>(VPO4)2F3sub> nanoflowers have been synthesized via a pH-regulative low-temperature (120 °C) hydro-thermal route. In particular, it is a green route without any organic compounds involved. The hydro-thermal reaction time for the formation of Na3sub>(VPO4)2F3sub> nanoflowers has also been investigated. A weak acid environment (pH = 2.60) with the possible presence of hydrogen fluoride molecules is necessary for the formation of the desired nanoflower microstructures. Moreover, compared to the nanoparticles obtained by Na2HPO4·12H2O, the as-synthesized Na3sub>(VPO4)2F3sub> nanoflowers showed an excellent Na-storage performance in terms of superior cycle stability, even without any further carbon coating or high-temperature treatment.

  11. 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.

  12. 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.

  13. Enhancement of third-order nonlinear optical susceptibility of Alq3sub> in polar aprotic solvents.


    Derkowska-Zielinska, Beata


    The influence of solvent polarity on nonlinear optical properties of tris-(8-hydroxyquinoline)-aluminum (Alq3sub>) was investigated by the degenerate four-wave mixing method at the 532 nm. It was obtained that the effective values of the third-order nonlinear optical susceptibility (χeff⟨3⟩) and the second-order hyperpolarizability (γeff) of Alq3sub> depend on the solvent polarity. Additionally, it was found that Alq3sub> dissolved in dimethyl sulfoxide has the highest values of χeff⟨3⟩ and γeff. Furthermore, two Stegeman's figures of merit were also calculated. The obtained results suggest that Alq3sub> is also promising material for application in all-optical signal processing devices.

  14. 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.

  15. 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.

  16. 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>.

  17. Multifunctional hybrid Fe2O3sub>-Au nanoparticles for efficient plasmonic heating

    SciTech Connect

    Murph, Simona E. Hunyadi; Larsen, George K.; Lascola, Robert J.


    We describe the synthesis and properties of multifunctional Fe2O3sub>-Au nanoparticles produced by a wet chemical approach and investigate their photothermal properties using laser irradiation. Here, the composite Fe2O3sub>-Au nanoparticles retain the properties of both materials, creating a multifunctional structure with excellent magnetic and plasmonic properties.

  18. Negative ion photoelectron spectroscopy of P 2 N 3sub> - : electron affinity and electronic structures of P 2 N 3sub> ˙

    SciTech Connect

    Hou, Gao-Lei; Chen, Bo; Transue, Wesley J.; Hrovat, David A.; Cummins, Christopher C.; Borden, Weston Thatcher; Wang, Xue-Bin


    The recent successful synthesis of P2N3sub>–, a planar all-inorganic aromatic molecule, represents a breakthrough in inorganic chemistry, because, like its isolobal counterparts C5H5– and cyclo-P5, P2N3sub> has potential to serve as a new ligand for transition metals and a building block in solid-state molecular architectures. In light of its importance, we report here a negative ion photoelectron spectroscopy (NIPES) and ab initio study of P2N3sub>, to investigate the electronic structures of P2N3sub> and its neutral P2N3sub>• radical. The adiabatic detachment energy of P2N3sub> (electron affinity of P2N3sub>•) was determined to be 3.765 ± 0.010 eV, indicating high stability for the P2N3sub> anion. Ab initio electronic structure calculations reveal five low-lying electronic states in the neutral P2N3sub>• radical. Calculation of the Franck-Condon factors (FCFs) for each anion-to-neutral electronic transition and comparison of the resulting simulated NIPE spectrum with the vibrational structure in the observed spectrum allows the first four excited states of P2N3sub>• to be determined to lie 6.2, 6.7, 11.5, and 22.8 kcal/mol above the ground state of the radical, which is found to be a 6π-electron, 2A1, σ state.

  19. 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.

  20. A reduced graphene oxide/Co3sub>O4 composite for supercapacitor electrode

    SciTech Connect

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


    20 nm sized Co3sub>O4 nanoparticles are in-situ grown on the chemically reduced graphene oxide (rGO) sheets to form a rGO-Co3sub>O4 composite during hydrothermal processing. The rGO-Co3sub>O4 composite is employed as the pseudocapacitor electrode in the 2 M KOH aqueous electrolyte solution. The rGOCo3sub>O4 composite electrode exhibits a specific capacitance of 472 F/g at a scan rate of 2 mV/s in a two-electrode cell. 82.6% of capacitance is retained when the scan rate increases to 100 mV/s. The rGOCo3sub>O4 composite electrode shows high rate capability and excellent long-term stability. It also exhibits high energy density at relatively high power density. The energy density reaches 39.0 Wh/kg at a power density of 8.3 kW/kg. The super performance of the composite electrode is attributed to the synergistic effects of small size and good redox activity of the Co3sub>O4 particles combined with high electronic conductivity of the rGO sheets.

  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. 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

  3. Pt3sub>Re alloy nanoparticles as electrocatalysts for the oxygen reduction reaction

    SciTech Connect

    Raciti, David; Kubal, Joseph; Ma, Cheng; Barclay, Michael; Gonzalez, Matthew; Chi, Miaofang; Greeley, Jeffrey; More, Karren L.; Wang, Chao


    Development of renewable energy technologies requires advanced catalysts for efficient electrical-chemical energy conversion reactions. Here in this paper, we report the study of Pt-Re alloy nanoparticles as an electrocatalyst for the oxygen reduction reaction (ORR). An organic solution approach is developed to synthesize monodisperse and homogeneous Pt3sub>Re alloy nanoparticles. Electrochemical studies show that these nanoparticles exhibit an improvement factor of 4 in catalytic activity for the ORR compared to commercial Pt catalysts of similar particle sizes. Fundamental understanding of the structure-property relationship is established by combining material characterization using X-ray spectroscopy and atomically resolved electron microscopy, as well as Density Functional Theory (DFT) calculations. Lastly, our work revealed that an electronic modification of the surface properties of Pt by subsurface Re (ligand effect) accounts for the catalytic enhancement.

  4. Structure and magnetism in LaCoO3sub>

    SciTech Connect

    Belanger, David P.; Keiber, T.; Bridges, Frank; Durand, A. M.; Mehta, A.; Zheng, H.; Mitchell, J. F.; Borzenets, V.


    In this paper, the temperature dependence of the hexagonal lattice parameter c of single crystal LaCoO3sub> (LCO) with H = 0 and 800 Oe, as well as LCO bulk powders with H = 0, was measured using high-resolution x-ray scattering near the transition temperature To ≈ 35 K. The change of c(T ) is well characterized by a power law in T – To for T > To and by a temperature independent constant for T < To when convoluted with a Gaussian function of width 8.5 K. Finally, this behavior is discussed in the context of the unusual magnetic behavior observed in LCO as well as recent generalized gradient approximation calculations.

  5. Field-induced dielectric response saturation in $o$ -TaS3sub>

    SciTech Connect

    Ma, Yongchang; Lu, Cuimin; Wang, Xuewei; Du, Xueli; Li, Lijun; Petrovic, Cedomir


    The temperature and electric field dependent conductivity spectra of o-TaS3sub> sample with 10 μm2 in cross section were measured. Besides the classical electric threshold ET₋Cl, we observed another novel threshold ET₋N at a larger electric field, where an S-shaped I-V relation revealed. The appearance of ET₋N may be due to the establishment of coherence among small charge-density- wave domains. Under a stable field E > ET-N, a sharp dispersion emerged below kHz. At a fixed temperature, the scattering rate of the charged condensate was extremely small and decreased with increasing field. With decreasing temperature, the scattering Fröhlic-mode conductivity would be consistent with the meta-stable state.

  6. Dry (Mg,Fe)SiO3sub> perovskite in the Earth's lower mantle

    SciTech Connect

    Panero, Wendy R.; Pigott, Jeffrey S.; Reaman, Daniel M.; Kabbes, Jason E.; Liu, Zhenxian


    Combined synthesis experiments and first-principles calculations show that MgSiO3sub>-perovskite with minor Al or Fe does not incorporate significant OH under lower mantle conditions. Perovskite, stishovite, and residual melt were synthesized from natural Bamble enstatite samples (Mg/(Fe+Mg) = 0.89 and 0.93; Al2O3sub> < 0.1 wt% with 35 and 2065 ppm wt H2O, respectively) in the laser-heated diamond anvil cell at 1600-2000 K and 25-65 GPa. Combined Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction, and ex-situ transmission electron microscopy (TEM) analysis demonstrates little difference in the resulting perovskite as a function of initial water content. Four distinct OH vibrational stretching bands are evident upon cooling below 100 K (3576, 3378, 3274, and 3078 cm-1), suggesting 4 potential bonding sites for OH in perovskite with a maximum water content of 220 ppm wt H2O, and likely no more than 10 ppm wt H2O. Complementary, Fe-free, first-principles calculations predict multiple potential bonding sites for hydrogen in perovskite, each with significant solution enthalpy (0.2 eV/defect). We calculate that perovskite can dissolve less than 37 ppm wt H2O (400 ppm H/Si) at the top of the lower mantle, decreasing to 31 ppm wt H2O (340 ppm H/Si) at 125 GPa and 3000 K in the absence of a melt or fluid phase. Here, we propose that these results resolve a long-standing debate of the perovskite melting curve and explain the order of magnitude increase in viscosity from upper to lower mantle.

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

    SciTech Connect

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


    Two new two-dimensional Nb4C3sub>-based solid solutions (MXenes), (Nb0.8,Ti0.2)4C3sub>Tx and (Nb0.8,Zr0.2)4C3sub>Tx (where T is a surface termination) were synthesizedas confirmed by X-ray diffractionfrom their corresponding MAX phase precursors (Nb0.8,Ti0.2)4AlC3sub> and (Nb0.8,Zr0.2)4AlC3sub>. In our report we discuss Zr-containing MXene. We also studied intercalation of Li ions into these two compositions, and Nb4C3sub>Tx in order to determine the potential of those materials for energy storage applications. Lithiation and delithiation peaks at 2.26 and 2.35 V, respectively, appeared in the case of Nb4C3sub>Tx, but were not present in Nb2CTx. After 20 cycles at a rate of C/4, the specific capacities of (Nb0.8,Ti0.2)4C3sub>Txand (Nb0.8,Ti0.2)4C3sub>Tx were 158 and 132 mAh/g, respectively, both slightly lower than the capacity of Nb4C3sub>Tx.

  8. Metabolism-Induced CaCO 3sub> Biomineralization During Reactive Transport in a Micromodel: Implications for Porosity Alteration

    SciTech Connect

    Singh, Rajveer; Yoon, Hongkyu; Sanford, Robert A.; Katz, Lynn; Fouke, Bruce W.; Werth, Charles J.


    We investigated the ability of Pseudomonas stutzeri strain DCP-Ps1 to drive CaCO3sub> biomineralization in a microfluidic flowcell (i.e., micromodel) that simulates subsurface porous media. Results indicate that CaCO3sub> precipitation occurs during NO3sub> reduction with a maximum saturation index (SIcalcite) of ~1.56, but not when NO3sub> was removed, inactive biomass remained, and pH and alkalinity were adjusted to SIcalcite ~ 1.56. CaCO3sub> precipitation was promoted by metabolically active cultures of strain DCP-Ps1, which at similar values of SIcalcite, have a more negative surface charge than inactive strain DCP-Ps1. A two-stage NO3sub> reduction (NO3sub> → NO2 → N2) pore-scale reactive transport model was used to evaluate denitrification kinetics, which was observed in the micromodel as upper (NO3sub> reduction) and lower (NO2 reduction) horizontal zones of biomass growth with CaCO3sub> precipitation exclusively in the lower zone. Our model results are consistent with two biomass growth regions and indicate that precipitation occurred in the lower zone because the largest increase in pH and alkalinity is associated with NO2 reduction. CaCO3sub> precipitates typically occupied the entire vertical depth of pores and impacted porosity, permeability, and flow. This study provides a framework for incorporating microbial activity in biogeochemistry models, which often base biomineralization only on SI (caused by biotic or abiotic reactions) and, thereby, underpredict the extent of this complex process. Furthermore, these results have wide-ranging implications for understanding reactive transport in relevance to groundwater remediation, CO2 sequestration, and enhanced oil recovery.

  9. 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.

  10. Exchange-bias effect at La0.75Sr0.25MnO3sub>/LaNiO3sub> interfaces

    SciTech Connect

    Rojas Sánchez, J. C.; Nelson-Cheeseman, B.; Granada, M.; Arenholz, E.; Steren, L. B.


    In this paper, we show that ferromagnetic/paramagnetic La0.75Sr0.25MnO3sub>/LaNiO3sub> multilayers present an unexpected magnetic exchange-bias effect (EBE), observed in field-cooled magnetization loops. The exchange-bias field and the enhancement of the coercivity vanish around 50 K. We demonstrate that the oxidation state of the Ni and Mn cations changes from Mn3+-Ni3+ to Mn4+-Ni2+ in the layers close to the interface probed by x-ray absorption spectroscopy measurements. The variation of the valence states is accompanied by a change in the magnetic behavior of the cations at the La0.75Sr0.25MnO3sub>/LaNiO3sub> interface, possibly giving rise to the formation of magnetic or magnetically frustrated regions that may pin the ferromagnetic a0.75Sr0.25MnO3sub> layers and explain the EBE.

  11. Nucleation of graphene layers on magnetic oxides: Co3sub>O4(111) and Cr2O3sub>(0001) from theory and experiment

    SciTech Connect

    Beatty, John; Cheng, Tao; Cao, Yuan; Driver, M. Sky; Goddard, III, William A.; Kelber, Jeffry A.


    We report directly grown strongly adherent graphene on Co3sub>O4(111) by carbon molecular beam epitaxy (C MBE) at 850 K and density functional theory (DFT) findings that the first graphene layer is reconstructed to fit the Co3sub>O4 surface, while subsequent layers retain normal graphene structure. This adherence to the Co3sub>O4 structure results from partial bonding of half the carbons to top oxygens of the substrate. This structure is validated by X-ray photoelectron spectroscopy and low-energy electron diffraction studies, showing layer-by-layer graphene growth with ~0.08 electrons/carbon atom transferred to the oxide from the first graphene layer, in agreement with DFT. In contrast, for Cr2O3sub> DFT finds no strong bonding to the surface and C MBE on Cr2O3sub>(0001) yields only graphite formation at 700 K, with C desorption above 800 K. As a result, strong graphene-to-oxide charge transfer aids nucleation of graphene on incommensurate oxide substrates and may have implications for spintronics.

  12. 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

  13. 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.

  14. Photochemistry of the α-Al2O3sub>-PETN interface

    SciTech Connect

    Tsyshevsky, Roman V.; Zverev, Anton; Mitrofanov, Anatoly; Rashkeev, Sergey N.; Kuklja, Maija M.


    Optical absorption measurements are combined with electronic structure calculations to explore photochemistry of an α-Al2O3sub>-PETN interface formed by a nitroester (pentaerythritol tetranitrate, PETN, C5H8N4O12) and a wide band gap aluminum oxide (α-Al2O3sub>) substrate. The first principles modeling is used to deconstruct and interpret the α-Al2O3sub>-PETN absorption spectrum that has distinct peaks attributed to surface F0-centers and surfacePETN transitions. We predict the low energy α-Al2O3sub> F0-centerPETN transition, producing the excited triplet state, and α-Al2O3sub> F-0-centerPETN charge transfer, generating the PETN anion radical. This implies that irradiation by commonly used lasers can easily initiate photodecomposition of both excited and charged PETN at the interface. As a result, the feasible mechanism of the photodecomposition is proposed.

  15. Mid-infrared nonlinear absorption in As2S3sub> chalcogenide glass.


    Théberge, Francis; Mathieu, Pierre; Thiré, Nicolas; Daigle, Jean-François; Schmidt, Bruno E; Fortin, Jean; Vallée, Réal; Messaddeq, Younès; Légaré, François


    We report mid-infrared (MIR) nonlinear absorption in As2S3sub> glasses which results from two-photon excitation of valence electron to the Urbach extension followed by strong linear absorption of excited states. The measured MIR nonlinear absorption can be 3 to 4 orders of magnitude stronger than the two-photon absorption in the near-infrared for similar laser intensities and does not result from contaminants, but it is intrinsic to As2S3sub> glasses. As2S3sub> fibers are widely used to generate supercontinuum by pumping them with high peak power laser pulses. For a 100 kilowatt peak power MIR soliton propagating in single mode As2S3sub> fiber, the nonlinear absorption can be of similar magnitude than the fiber background loss. Finally, for laser peak power around 1 MW, the MIR nonlinear absorption can be ~2 orders of magnitude larger than the fiber background loss in single mode As2S3sub> fiber.

  16. Understanding the interactions of CO2 with doped and undoped SrTiO3sub>

    SciTech Connect

    Wu, Qiyuan; Cen, Jiajie; Goodman, Kenneth R.; White, Michael G.; Ramakrishnan, Girish; Orlov, Alexander


    SrTiO3sub> and doped SrTiO3sub> have a wide range of applications in different fields. For example, Rh-doped SrTiO3sub> has been shown to have photocatalytic activity for both hydrogen production and CO2 conversion. In this study, both undoped and Rh-doped SrTiO3sub> were synthesized by hydrothermal and polymerizable complex methods. Different characterizations techniques including X-ray photoelectron spectroscopy (XPS), XRD, Raman, and UV/Vis spectroscopy were utilized to establish correlations between the preparation methods and the electronic/structural properties of Rh-doped SrTiO3sub>. The presence of dopants and oxygen vacancies substantially influenced the CO2 interactions with the surface, as revealed by the in situ infrared spectroscopic study. As a result, the presence of distinctly different adsorption sites was correlated to oxygen vacancies and oxidation states of Ti and Rh.

  17. 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.

  18. Effectiveness of BaTiO3sub> dielectric patches on YBa2Cu3sub>O7 thin films for MEM switches

    SciTech Connect

    Vargas, J.; Hijazi, Y.; Noel, J.; Vlasov, Y.; Larkins, G.


    A micro-electro-mechanical (MEM) switch built on a superconducting microstrip filter will be utilized to investigate BaTiO3sub> dielectric patches for functional switching points of contact. Actuation voltage resulting from the MEM switch provokes static friction between the bridge membrane and BaTiO3sub> insulation layer. Furthermore, the dielectric patch crystal structure and roughness affect the ability of repetitively switching cycles and lifetime. We performed a series of experiments using different deposition methods and RF magnetron sputtering was found to be the best deposition process for the BaTiO3sub> layer. The effect examination of surface morphology will be presented using characterization techniques as x-ray diffraction, SEM and AFM for an optimum switching device. The thin film is made of YBa2Cu3sub>O7 deposited on LaAlO3sub> substrate by pulsed laser deposition. In our work, the dielectric material sputtering pressure is set at 9.5x10-6 Torr. The argon gas is released through a mass-flow controller to purge the system prior to deposition. RF power is 85 W at a distance of 9 cm. The behavior of Au membranes built on ultimate BaTiO3sub> patches will be shown as part of the results. These novel surface patterns will in turn be used in modelling other RF MEM switch devices such as distributed-satellite communication system operating at cryogenic temperatures.

  19. 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.

  20. 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

  1. Dielectric frame, Sellmeier equations, and phase-matching properties of the monoclinic acentric crystal GdCa4O(BO3sub>)3sub>.


    Guo, Feng; Segonds, Patricia; Ménaert, Bertrand; Debray, Jerôme; Aka, Gerard; Loiseau, Pascal; Boulanger, Benoît


    We directly measured the phase-matching properties of the biaxial GdCa4O(BO3sub>)3sub> (GdCOB) crystal using the sphere method. We studied second-harmonic generation and difference frequency generation in two principal planes of the crystal. All these data allowed us to refine the Sellmeier equations of the three principal refractive indices. These equations are valid over the entire transparency range of GdCOB and then could be used to calculate the tuning curves of infrared optical parametric generation.

  2. Novel joining of dissimilar ceramics in the Si3sub>N4-Al2O3sub> system using polytypoid functional gradients

    SciTech Connect

    Lee, Caroline Sunyong


    A unique approach to crack-free joining of heterogeneous ceramics is demonstrated by the use of sialon polytypoids as Functionally Graded Materials (FGM) as defined by the phase diagram in the system, Si3sub>N4-Al2O3sub>. Polytypoids in the Al2O3sub>-Si3sub>N4 system offer a path to compatibility for such heterogeneous ceramics. The first part of the dissertation describes successful hot press sintering of multilayered FGM's with 20 layers of thickness 500 mm each. Transmission Electron Microscopy was used to identify the polytypoids at the interfaces of different areas of the joint. It has been found that the 15R polytypoid was formed in the Al2O3sub>-contained layers and the 12H polytypoid was formed in the Si3sub>N4-contained layers. The second part of the dissertation discusses the mechanical properties of these polytypoidally joined Si3sub>N4-Al2O3sub>. The thermal stresses of this FGM junction were analyzed using a finite element analysis program (FEAP) taking into account both coefficient of thermal expansion (CTE) and modulus variations. From this analysis, the result showed a dramatic decrease in radial, axial and hoop stresses as the FGM changes from three layers to 20 graded layers. Scaling was considered, showing that the graded transition layer should constitute about 75 percent or more of the total sample thickness to reach a minimal residual stress. Oriented Vickers indentation testing was used to qualitatively characterize the strengths of the joint and the various interfaces. The indentation cracks were minimally or not deflected at the sialon layers, implying strong interfaces. Finally, flexural testing was conducted at room temperature and at high temperature. The average strength at room temperature was found to be 581 MPa and the average strength at high temperature (1200 °C) was found to be

  3. Soft A4→Z3sub> symmetry breaking and cobimaximal neutrino mixing

    SciTech Connect

    Ma, Ernest


    In this study, I propose a model of radiative charged-lepton and neutrino masses with A4 symmetry. The soft breaking of A4 to Z3sub> lepton triality is accomplished by dimension-three terms. The breaking of Z3sub> by dimension-two terms allows cobimaximal neutrino mixing (θ13 ≠ 0, θ23 = π/4, δcp=π/2) to be realized with only very small finite calculable deviations from the residual Z3sub> lepton triality. This construction solves a long-standing technical problem inherent in renormalizable A4 models since their inception.

  4. Engineered unique elastic modes at a BaTiO3sub>/2x1-Ge(001) interface

    SciTech Connect

    Kumah, D. P.; Dogan, M.; Ngai, J. H.; Qiu, D.; Zhang, Z.; Su, D.; Specht, E. D.; Ismail-Beigi, S.; Ahn, C. H.; Walker, F. J.


    Here, the strong interaction at an interface between a substrate and thin film leads to epitaxy and provides a means of inducing structural changes in the epitaxial film. These induced material phases often exhibit technologically relevant electronic, magnetic, and functional properties. The 2×1 surface of a Ge(001) substrate applies a unique type of epitaxial constraint on thin films of the perovskite oxide BaTiO3sub> where a change in bonding and symmetry at the interface leads to a non-bulk-like crystal structure of the BaTiO3sub>. While the complex crystal structure is predicted using first-principles theory, it is further shown that the details of the structure are a consequence of hidden phases found in the bulk elastic response of the BaTiO3sub> induced by the symmetry of forces exerted by the germanium substrate.

  5. Competing antiferromagnetism in a quasi-2D itinerant ferromagnet: Fe3sub>GeTe2

    SciTech Connect

    Yi, Jieyu; Zhuang, Houlong; Zou, Qiang; Wu, Zhiming; Cao, Guixin; Tang, Siwei; Calder, S. A.; Kent, P. R. C.; Mandrus, David; Gai, Zheng


    Fe3sub>GeTe2 is known as an air-stable layered metal with itinerant ferromagnetism with a transition temperature of about 220 K. From extensive dc and ac magnetic measurements, we have determined that the ferromagnetic layers of Fe3sub>GeTe2 order antiferromagnetically along the c-axis blow 152 K. The antiferromagnetic state was further substantiated by theoretical calculation to be the ground state. A magnetic structure model was proposed to describe the antiferromagnetic ground state as well as competition between antiferromagnetic and ferromagnetic states. Furthermore, Fe3sub>GeTe2 shares many common features with pnictide superconductors and may be a promising system in which to search for unconventional superconductivity.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Dynamic defect correlations dominate activated electronic transport in SrTiO3sub>

    SciTech Connect

    Snijders, Paul C.; Sen, Cengiz; McConnell, Michael P.; Ma, Ying-Zhong; May, Andrew F.; Herklotz, Andreas; Wong, Anthony T.; Ward, Thomas Zac


    Strontium titanate (SrTiO3sub>, STO) is a critically important material for the study of emergent electronic phases in complex oxides, as well as for the development of applications based on their heterostructures. Despite the large body of knowledge on STO, there are still many uncertainties regarding the role of defects in the properties of STO, including their influence on ferroelectricity in bulk STO and ferromagnetism in STO-based heterostructures. In this paper, we present a detailed analysis of the decay of persistent photoconductivity in STO single crystals with defect concentrations that are relatively low but significantly affect their electronic properties. The results show that photo-activated electron transport cannot be described by a superposition of the properties due to independent point defects as current models suggest but is, instead, governed by defect complexes that interact through dynamic correlations. In conclusion, these results emphasize the importance of defect correlations for activated electronic transport properties of semiconducting and insulating perovskite oxides.

  11. Enhanced Bifunctional Oxygen Catalysis in Strained LaNiO3sub> Perovskites

    SciTech Connect

    Petrie, Jonathan R.; Cooper, Valentino R.; Freeland, John W.; Meyer, Tricia L.; Zhang, Zhiyong; Lutterman, Daniel A.; Lee, Ho Nyung


    Strain is known to greatly influence low-temperature oxygen electrocatalysis on noble metal films, leading to significant enhancements in bifunctional activity essential for fuel cells and metal-air batteries. Still, its catalytic impact on transition-metal oxide thin films, such as perovskites, is not widely understood. Here, we epitaxially strain the conducting perovskite LaNiO3sub> to systematically determine its influence on both the oxygen reduction and oxygen evolution reaction. Uniquely, we found that compressive strain could significantly enhance both reactions, yielding a bifunctional catalyst that surpasses the performance of noble metals such as Pt. We attribute the improved bifunctionality to strain-induced splitting of the eg orbitals, which can customize orbital asymmetry at the surface. Lastly, analogous to strain-induced shifts in the d-band center of noble metals relative to the Fermi level, such splitting can dramatically affect catalytic activity in this perovskite and other potentially more active oxides.

  12. 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.

  13. 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.

  14. 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.

  15. Polar-graded multiferroic SrMnO3sub> thin films

    SciTech Connect

    Lupini, Andrew R.; Guzman, Roger; Maurel, Laura; Langenberg, Eric; Algarabel, Pedro A.; Pardo, Jose A.; Magen, Cesar


    Engineering defects and strains in oxides provides a promising route for the quest of thin film materials with coexisting ferroic orders, multiferroics, with efficient magnetoelectric coupling at room temperature. Precise control of the strain gradient would enable custom tailoring of the multiferroic properties but presently remains challenging. Here we explore the existence of a polar-graded state in epitaxially strained antiferromagnetic SrMnO3sub> thin films, whose polar nature was predicted theoretically and recently demonstrated experimentally. By means of aberration-corrected scanning transmission electron microscopy we map the polar rotation of the ferroelectric polarization with atomic resolution, both far from and near the domain walls, and find flexoelectricity resulting from vertical strain gradients. The origin of this particular strain state is a gradual distribution of oxygen vacancies across the film thickness, according to electron energy loss spectroscopy. Furthermore, we present a chemistry-mediated route to induce polar rotations in oxygen-deficient multiferroic films, resulting in flexoelectric polar rotations and with potentially enhanced piezoelectricity.

  16. 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).

  17. Tuning thermoelectricity in a Bi2Se3sub> topological insulator via varied film thickness

    SciTech Connect

    Guo, Minghua; Wang, Zhenyu; Xu, Yong; Huang, Huaqing; Zang, Yunyi; Liu, Chang; Duan, Wenhui; Gan, Zhongxue; Zhang, Shou-Cheng; He, Ke; Ma, Xucun; Xue, Qikun; Wang, Yayu


    We report thermoelectric transport studies on Bi2Se3sub> topological insulator thin films with varied thickness grown by molecular beam epitaxy. We find that the Seebeck coefficient and thermoelectric power factor decrease systematically with the reduction of film thickness. These experimental observations can be explained quantitatively by theoretical calculations based on realistic electronic band structure of the Bi2Se3sub> thin films. Lastly, this work illustrates the crucial role played by the topological surface states on the thermoelectric transport of topological insulators, and sheds new light on further improvement of their thermoelectric performance.

  18. Antiperovskite Li 3sub> OCl superionic conductor films for solid-state Li-ion batteries

    SciTech Connect

    Lü, Xujie; Howard, John W.; Chen, Aiping; Zhu, Jinlong; Li, Shuai; Wu, Gang; Dowden, Paul; Xu, Hongwu; Zhao, Yusheng; Jia, Quanxi


    We prepared antiperovskite Li3sub>OCl superionic conductor films via pulsed laser deposition using a composite target. A significantly enhanced ionic conductivity of 2.0 × 10-4 S cm-1 at room temperature is achieved, and this value is more than two orders of magnitude higher than that of its bulk counterpart. Moreover, the applicability of Li3sub>OCl as a solid electrolyte for Li-ion batteries is demonstrated.

  19. Organic pollutant photodecomposition by Ag/KNbO3sub> nanocomposites: A combined experimental and theoretical study

    SciTech Connect

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


    In this study, Ag nanoparticles supported on well-defined perovskite orthorhombic KNbO3sub> nanowires are synthesized via facile photoreduction and systematically characterized by XRD, Raman, DRUV–vis, XPS, PL, TEM, HRTEM, and HAADF-STEM. The photoreactivity of Ag/KNbO3sub> nanocomposites as a function of Ag contents (0.4–2.8 wt %) is assessed toward aqueous rhodamine B degradation under UV- and visible-light, respectively. It is found that the UV-induced photoreactivity initially increases and then decreases with increasing Ag contents. At an optimal Ag content (ca. 1.7 wt %), the greatest photoreactivity is achieved under UV light, with the photocatalytic reaction rate of 1.7 wt % Ag/KNbO3sub> exceeding that of pristine KNbO3sub> by a factor of ca. 13. In contrast, visible light-induced photoreactivity monotonically increases with increasing Ag contents in the range of 0.4–2.8 wt %. On the basis of the detected active species and intermediate products in the photocatalytic processes, conjugated structure cleavage and N-deethylation are revealed to be the respective predominant pathway under UV and visible-light illumination. To gain an insight into the observed photoreactivity, the electronic properties of Ag/KNbO3sub> have been investigated using spin-polarized DFT calculations. Herein, Ag extended adlayers (1–4 ML) on the slab models of KNbO3sub> (101) are employed to mimic large supported Ag nanoparticles. A Bader analysis of the electron density shows a small net charge transfer (ca. 0.1 e) from KNbO3sub> to Ag. The electron localization function of Ag/KNbO3sub> (101) illustrates that Ag adlayers with thickness larger than 2 ML are essentially metallic, and weak polarization occurs at the interface. In addition, the metallic Ag adlayers generate a continuum of Ag bandgap states, which play a key role in determining different Ag content-dependent behavior between UV and visible-light illumination.

  20. Imaging the surface morphology, chemistry and conductivity of LiNi 1/3sub> Fe 1/3sub> Mn 4/3sub> O 4 crystalline facets using scanning transmission X-ray microscopy

    SciTech Connect

    Zhou, Jigang; Wang, Jian; Cutler, Jeffrey; Hu, Enyuan; Yang, Xiao-Qing


    We have employed scanning transmission X-ray microscopy (STXM) using the X-ray fluorescence mode in order to elucidate the chemical structures at Ni, Fe, Mn and O sites from the (111) and (100) facets of micron-sized LiNi1/3sub>Fe1/3sub>Mn4/3sub>O4 energy material particles. Furthermore, STXM imaging using electron yield mode has mapped out the surface conductivity of the crystalline particles. Our study presents a novel approach that visualizes local element segregation, chemistry and conductivity variation among different crystal facets, which will assist further tailoring of the morphology and surface structure of this high voltage spinel lithium ion battery cathode material.

  1. Characterization of Hierarchical α-MoO3sub> Plates Toward Resistive Heating Synthesis: Electrochemical Activity of α-MoO3sub>/Pt Modified Electrode Toward Methanol Oxidation in Neutral pH.


    Filippo, Emanuela; Baldassarre, Francesca; Tepore, Marco; Guascito, Maria Rachele; Chirizzi, Daniela; Tepore, Antonio


    The growth of MoO3sub> hierarchical plates was obtained by direct resistive heating of molybdenum foil at ambient pressure in absence of any catalysts and templates. Plates synthesized after 60 min resistive heating typically growth in an single-crystalline orthorhombic structure that develop preferentially in [001] direction, as characterized by HRTEM, SAD and Raman-scattering measurements. They are about 100-200nm in thickness and a few tens micrometers in length. As heating time proceeds to 80 min, plates of α-MoO3sub> form a branched structure. A more attentive look shows that a primary plates formed at until 60 min could serve as substrates for the subsequent growth of secondary belts. Moreover, a full electrochemical characterization of α-MoO3sub> plates on platinum electrodes was done by Cyclic Voltammetric experiments, at pH 7 in phosphate buffer, to probe the activity of the proposed composite material as anode to methanol electrooxidation. Reported results indicate that Pt MoO3sub> modified electrodes are appropriate to develop new amperometric non-enzymatic sensor for methanol measurements and as anode in Direct Methanol Fuel Cells (DMFCs) making at neutral pH.

  2. 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.

  3. 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.

  4. 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.

  5. Increased fluorescence intensity in CaTiO3sub>:Pr3+ phosphor due to NH3sub> treatment and Nb Co-doping

    SciTech Connect

    Holliday, K. S.; Kohlgruber, T. A.; Tran, I. C.; Åberg, D.; Seeley, Z. M.; Bagge-Hansen, M.; Srivastava, A. M.; Cherepy, N. J.; Payne, S. A.


    Development of next generation red phosphors for commercial lighting requires understanding of how increased luminescence is achieved by various treatment strategies. In our work, we compare co-doping with Nb to NH3sub> treatment of CaTiO3sub>:Pr phosphors to reveal a general mechanism responsible for the increased luminescence. The phosphors were synthesized using standard solid-state synthesis techniques and the fluorescence was characterized for potential use in fluorescent lighting, with 254 nm excitation. The lifetime of the fluorescence was determined and used to identify a change in a trap state by the co-doping of Nb5+ in the phosphor. Furthermore, the oxidation state of the Pr was probed by NEXAFS and revealed that both Nb5+ co-doping and NH3sub> treatment reduced the number of non-fluorescing Pr4+ centers. We performed calculations in order to determine the energetically favorable defects. Vacuum annealing was also used to further probe the nature of the trap state. It was determined that NH3sub> treatments reduce the number of Pr4+ non-fluorescing centers, while Nb5+ co-doping additionally reduces the number of excess oxygen trap states that quench the fluorescence.

  6. Selective Catalytic Reduction of NO by NH3sub> with WO3sub>-TiO2 Catalysts: Influence of Catalyst Synthesis Method

    SciTech Connect

    He, Yuanyuan; Ford, Michael E.; Zhu, Minghui; Liu, Qingcai; Wu, Zili; Wachs, Israel E.


    A series of supported WO3sub>/TiO2 catalysts was prepared by a new synthesis procedure involving co-precipitation of an aqueous TiO(OH)2 and (NH4)10W12O41*5H2O slurry under controlled pH conditions. The morphological properties, molecular structures, surface acidity and surface chemistry of the supported WO3sub>/TiO2 catalysts were determined with BET, in situ Raman, in situ IR and temperature-programmed surface reaction (TPSR) spectroscopy, respectively. Isotopic 18O-16O exchange demonstrated that tungsten oxide was exclusively present as surface WOx species on the TiO2 support with mono-oxo W=O coordination. In contrast to previous studies employing impregnation synthesis that found only surface one mono-oxo O=WO4 site on TiO2, the co-precipitation procedure resulted in the formation of two distinct surface WOx species: mono-oxo O=WO4 (~1010-1017 cm-1) on low defect density patches of TiO2 and a second mono-oxo O=WO4 (~983-986 cm-1) on high defect density patches of TiO2. The concentration of the second WOx surface species increases as a function of solution pH. Both surface WOx sites, however, exhibited the same NO/NH3sub> SCR reactivity. The co-precipitated WO3sub>-TiO2 catalysts synthesized in alkaline solutions exhibited enhanced performance for the NO/NH3sub> SCR reaction that is ascribed to the greater number of surface defects on the resulting TiO2 support. For the co-precipitated catalyst prepared at pH10, surface NH4+ species on Br nsted acid sites were found to be more reactive than surface NH3sub>* species on Lewis acid sites for SCR of NO with NH3sub>.

  7. Structural properties of Y2O3sub>–Al2O3sub> liquids and glasses: An overview

    SciTech Connect

    Wilding, Martin C.; Wilson, Mark; McMillan, Paul F.; Benmore, Chris J.; Weber, J. K. R.; Deschamps, Thierry; Champagnon, Bernard


    Liquids in the system Y2O3sub>–Al2O3sub> have been the subject of considerable study because of the reported occurrence of a first-order density and entropy-driven liquid-liquid phase transition (LLPT) in the supercooled liquid state. The observations have become controversial because of the presence of crystalline material that can be formed simultaneously and that can mask the nucleation and growth of the lower density liquid. The previous work is summarized here along with arguments for and against the different viewpoints. Also two studies have been undertaken to investigate the LLPT in this refractory system with emphasis on determining the structure of unequivocally amorphous materials. These include the in situ high energy X-ray diffraction (HEXRD) of supercooled Y2O3sub>–Al2O3sub> liquids and the low frequency vibrational dynamics of recovered glasses. Manybody molecular dynamics simulations are also used to interpret the results of both studies. The HEXRD measurements, combined with aerodynamic levitation and rapid data acquisition techniques, show that for the 20 mol% Y2O3sub> (i.e. AlY20) liquid there is a shift in the position of the first peak in the diffraction pattern over a narrow temperature range (2100-1800 K) prior to crystallization. Microbeam Raman spectroscopy measurements made on AlY20 glasses clearly show contrasting spectra in the low frequency part of the spectrum for low(LDA) and high-density (HDA) glassy regions. The molecular dynamics simulations identify contrasting coordination environments around oxygen anions for the high- (HDL) and low-density (LDL) liquids. (C) 2014 Elsevier B.V. All rights reserved.

  8. 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.

  9. Low-temperature crystal and magnetic structure of α – RuCl3sub>

    SciTech Connect

    Cao, Huibo B.; Yan, Jiaqiang; Bridges, Craig A.; Lumsden, Mark D.; Mandrus, D. G.; Chakoumakos, Bryan C.; Nagler, Stephen E.; Banerjee, A.; Tennant, D. A.


    Here, single crystals of the Kitaev spin-liquid candidate α – RuCl3sub> have been studied to determine the low-temperature bulk properties, the structure, and the magnetic ground state. Refinements of x-ray diffraction data show that the low-temperature crystal structure is described by space group C2/m with a nearly perfect honeycomb lattice exhibiting less than 0.2% in-plane distortion. The as-grown single crystals exhibit only one sharp magnetic transition at TN = 7 K. The magnetic order below this temperature exhibits a propagation vector of k=(0,1,1/3), which coincides with a three-layer stacking of the C2/m unit cells. Magnetic transitions at higher temperatures up to 14 K can be introduced by deformations of the crystal that result in regions in the crystal with a two-layer stacking sequence. The best-fit symmetry-allowed magnetic structure of the as-grown crystals shows that the spins lie in the ac plane, with a zigzag configuration in each honeycomb layer. The three-layer repeat out-of-plane structure can be refined as a 120° spiral order or a collinear structure with a spin direction of 35° away from the a axis. The collinear spin configuration yields a slightly better fit and also is physically preferred. The average ordered moment in either structure is less than 0.45(5) μB per Ru3+ ion.

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

    SciTech Connect

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


    The new ternary copper selenide NaCu4Se3sub> crystallizes in the RbCd4As3sub> structure type with the trigonal space group R3m and lattice constants a = 4.0316(4) angstrom and c = 31.438(8) angstrom. Its structure is built from two-dimensional slabs of 2 [Cu4Se3sub>] separated by Na+ cations. The compound is formally mixed-valent with Se2-/Se- atoms and exhibits metallic properties. It is a hole conductor with an electrical conductivity of similar to 300 S cm-1 at room temperature and a thermopower of similar to 10 mu V K-1. Hall effect measurements indicate holes as the dominant carrier with a concentration of similar to 6.12(1) X 1021 cm-3 at 300 K. Density functional theory electronic structure calculations indicate p -type metallic behavior for the 2 [Cu4Se3sub>] framework, which is in a good agreement with the experimental metallic conductivity and Pauli paramagnetism.

  11. 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

  12. Quadruplexes of human telomere dG{sub 3}(TTAG{sub 3}){sub 3} sequences containing guanine abasic sites

    SciTech Connect

    Skolakova, Petra; Bednarova, Klara; Vorlickova, Michaela; Sagi, Janos


    Research highlights: {yields} Loss of a guanine base does not hinder the formation of G-quadruplex of human telomere sequence. {yields} Each depurination strongly destabilizes the quadruplex of dG{sub 3}(TTAG{sub 3}){sub 3} in NaCl and KCl. {yields} Conformational change of the abasic analogs of dG{sub 3}(TTAG{sub 3}){sub 3} is inhibited in KCl. {yields} The effects abasic sites may affect telomere-end structures in vivo. -- Abstract: This study was performed to evaluate how the loss of a guanine base affects the structure and stability of the three-tetrad G-quadruplex of 5'-dG{sub 3}(TTAG{sub 3}){sub 3}, the basic quadruplex-forming unit of the human telomere DNA. None of the 12 possible abasic sites hindered the formation of quadruplexes, but all reduced the thermodynamic stability of the parent quadruplex in both NaCl and KCl. The base loss did not change the Na{sup +}-stabilized intramolecular antiparallel architecture, based on CD spectra, but held up the conformational change induced in dG{sub 3}(TTAG{sub 3}){sub 3} in physiological concentration of KCl. The reduced stability and the inhibited conformational transitions observed here in vitro for the first time may predict that unrepaired abasic sites in G-quadruplexes could lead to changes in the chromosome's terminal protection in vivo.

  13. 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.

  14. 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.

  15. Development of a 15 T Nb3sub>Sn accelerator dipole demonstrator at Fermilab

    SciTech Connect

    Novitski, I.; Andreev, N.; Barzi, E.; Carmichael, J.; Kashikhin, V. V.; Turrioni, D.; Yu, M.; Zlobin, A. V.


    Here, a 100 TeV scale Hadron Collider (HC) with a nominal operation field of at least 15 T is being considered for the post-LHC era, which requires using the Nb3sub>Sn technology. Practical demonstration of this field level in an accelerator-quality magnet and substantial reduction of the magnet costs are the key conditions for realization of such a machine. FNAL has started the development of a 15 T Nb3sub>Sn dipole demonstrator for a 100 TeV scale HC. The magnet design is based on 4-layer shell type coils, graded between the inner and outer layers to maximize the performance and reduce the cost. The experience gained during the Nb3sub>Sn magnet R&D is applied to different aspects of the magnet design. This paper describes the magnetic and structural designs and parameters of the 15 T Nb3sub>Sn dipole and the steps towards the demonstration model fabrication.

  16. 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.

  17. 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.

  18. Ferroelectric Self-Poling, Switching, and Monoclinic Domain Configuration in BiFeO 3sub> Thin Films

    SciTech Connect

    Beekman, C.; Siemons, W.; Chi, M.; Balke, N.; Howe, J. Y.; Ward, T. Z.; Maksymovych, P.; Budai, J. D.; Tischler, J. Z.; Xu, R.; Liu, W.; Christen, H. M.


    Self-poling of ferroelectric films, i.e., a preferred, uniform direction of the ferroelectric polarization in as-grown samples is often observed yet poorly understood despite its importance for device applications. The multiferroic perovskite BiFeO3sub>, which crystallizes in two distinct structural polymorphs depending on applied epitaxial strain, is well known to exhibit self-poling. This study investigates the effect of self-poling on the monoclinic domain configuration and the switching properties of the two polymorphs of BiFeO3sub> (R' and T') in thin films grown on LaAlO3sub> substrates with slightly different La0.3sub>Sr0.7MnO3sub> buffer layers. Our study shows that the polarization state formed during the growth acts as “imprint” on the polarization and that switching the polarization away from this self-poled direction can only be done at the expense of the sample's monoclinic domain configuration. We observed reduction of the monoclinic domain size and found that it was largely reversible; hence, the domain size is restored when the polarization is switched back to its original orientation. This is a direct consequence of the growth taking place in the polar phase (below Tc). Finally, switching the polarization away from the preferred configuration, in which defects and domain patterns synergistically minimize the system's energy, leads to a domain state with smaller (and more highly strained and distorted) monoclinic domains.

  19. Characterization of second-phase plates in a Gd5Ge3sub> intermetallic compound

    SciTech Connect

    Cao, Qing; Chumbley, Leonard S.


    Rare-earth compounds based on the stoichiometry R5(SixGe1-x)4 (R = rare-earth elements) exhibit many unusual features, including possessing R5(SixGe1-x)3sub> thin plates which always precipitate from the matrix despite efforts to suppress their formation. In an effort to better understand the unique relationship between these two intermetallic alloy systems, the bulk microstructure of the compound Gd5Ge3sub> was examined using scanning (SEM) and transmission electron microscopy (TEM) and optical microscopy. Surprisingly, SEM examination revealed a series of thin plates present in the Gd5Ge3sub> matrix similar to what is seen in Gd5Ge4. TEM observation revealed that a role reversal had occurred, with the thin plates possessing the orthorhombic structure and composition of Gd5Ge4. The orientation relationship between Gd5Ge4 thin plates and the Gd5Ge3sub> matrix was determined to be Graphic the same relationship reported for Gd5Ge3sub> plates precipitating from a Gd5Ge4 matrix. However, by exchanging the respective roles of the phases as regards matrix vs. precipitate, the total number of precipitation variants seen can be increased from two to six. The persistence with which these two intermetallic systems co-exist is truly unique. However, understanding exactly the kinetic and thermodynamic conditions that lead to their unique relationship is hampered by the high formation temperatures at which the observed reaction occurs.

  20. 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

  1. 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.

  2. 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.

  3. Large dielectric constant, high acceptor density, and deep electron traps in perovskite solar cell material CsGeI3sub>

    SciTech Connect

    Ming, Wenmei; Shi, Hongliang; Du, Mao-Hua


    Here we report that many metal halides that contain cations with the ns2 electronic configuration have recently been discovered as high-performance optoelectronic materials. In particular, solar cells based on lead halide perovskites have shown great promise as evidenced by the rapid increase of the power conversion efficiency. In this paper, we show density functional theory calculations of electronic structure and dielectric and defect properties of CsGeI3sub> (a lead-free halide perovskite material). The potential of CsGeI3sub> as a solar cell material is assessed based on its intrinsic properties. We find anomalously large Born effective charges and a large static dielectric constant dominated by lattice polarization, which should reduce carrier scattering, trapping, and recombination by screening charged defects and impurities. Defect calculations show that CsGeI3sub> is a p-type semiconductor and its hole density can be modified by varying the chemical potentials of the constituent elements. Despite the reduction of long-range Coulomb attraction by strong screening, the iodine vacancy in CsGeI3 is found to be a deep electron trap due to the short-range potential, i.e., strong Ge–Ge covalent bonding, which should limit electron transport efficiency in p-type CsGeI3sub>. This is in contrast to the shallow iodine vacancies found in several Pb and Sn halide perovskites (e.g., CH3sub>NH3sub>PbI3sub>, CH3sub>NH3sub>SnI3sub>, and CsSnI3sub>). The low-hole-density CsGeI3sub> may be a useful solar absorber material but the presence of the low-energy deep iodine vacancy may significantly reduce the open circuit voltage of the solar cell. Still, on the other hand, CsGeI3sub> may be used as an efficient hole transport material in solar cells due to its small hole effective mass, the absence of low-energy deep hole traps, and the favorable band offset with solar

  4. 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.

  5. Influence of piezoelectric strain on the Raman spectra of BiFeO3sub> films deposited on PMN-PT substrates

    SciTech Connect

    Himcinschi, Cameliu; Guo, Er -Jia; Talkenberger, Andreas; Dorr, Kathrin; Kortus, Jens


    In this study, BiFeO3sub> epitaxial thin films were deposited on piezoelectric 0.72Pb(Mg1/3sub>Nb2/3sub>)O3sub>-0.28PbTiO3sub> (PMN-PT) substrates with a conductive buffer layer (La0.7Sr0.3sub>MnO3sub> or SrRuO3sub>) using pulsed laser deposition. The calibration of the strain values induced by the electric field applied on the piezoelectric PMN-PT substrates was realised using X-Ray diffraction measurements. The method of piezoelectrically induced strain allows to obtain a quantitative correlation between strain and the shift of the Raman-active phonons, ruling out the influence of extrinsic factors, such as growth conditions, crystalline quality of substrates, or film thickness. Using the Poisson number for BiFeO3sub> one can determine the volume change induced by strain, and therefore the Gr neisen parameters for specific phonon modes.

  6. 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

  7. 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

  8. Structure and high-temperature properties of Ti5Si3sub> with interstitial additions

    SciTech Connect

    Williams, Jason


    This study was motivated by the fact that previous research on the structure and properties of Ti5Si3sub> showed unacceptably inconsistent results. The primary reason for these inconsistencies was interstitial contamination of Ti5Si3sub> by carbon, nitrogen and oxygen. Thus, this study measured the effects that these interstitial atoms have on some of the previously reported properties. These properties include crystalline structure, thermal expansion anisotropy, electronic structure and bonding, and high temperature oxidation resistance. In Chapter 2 of this study, the lattice parameters and atomic positions of Ti5Si3sub> as a function of carbon, nitrogen or oxygen content were measured via x-ray and neutron diffraction. Comparing these lattice parameters to those reported in other studies on supposedly pure Ti5Si3sub> confirmed that the majority of the previous studies had samples with a considerable amount of interstitial impurities. In fact, the lattice parameter trends given in Chapter 2 can be used to estimate the types and level of impurities in these studies. Furthermore, Chapter 2 discusses how atomic positions change as interstitial atoms are incorporated into the lattice. These changes in atomic separations suggest that strong bonds form between the interstitial atoms and the surrounding titanium atoms. This is in full agreement with the electronic structure calculations given in Chapter 4. These calculations show that bonding does occur between titanium d-states and interstitial atom p-states at the expense of bonding between some of the titanium and silicon atoms. In addition, carbon seems to be the most strongly bonded interstitial atom. Knowledge of the exact interstitial content and its effect on bonding is important because Chapters 3 and 5 have shown that interstitial atoms have a marked effect on the thermal expansion and oxidation resistance. As discussed in Chapter 3, all

  9. Scintillation properties and electronic structure of the intrinsic and extrinsic mixed elpasolites Cs2 Na RBr3sub>I3sub> (R = La, Y)

    SciTech Connect

    Wei, Hua; Du, Mao -Hua; Stand, Luis; Zhao, Zhao; Zhuravleva, Mariya; Melcher, Charles L.; Shi, Hongliang


    Scintillators attract wide research interest for their distinct applications in radiation detection. Elpasolite halides are among the most promising scintillators due to their high structural symmetry and good scintillation performance. A better understanding of their underlying scintillation mechanism opens up possibilities in scintillator development. In this work, we employ a variety of experimental techniques to study the two mixed-anion elpasolites Cs2NaRBr3sub>I3sub> (R = La, Y). The emission of intrinsic Cs2NaRBr3sub>I3sub> with a light yield ranging from 20 000 to 40 000 ph / MeV is dominant by self-trapped exciton emission. Partial substitution of R with Ce introduces a competing emission, the Ce3+ 5d-to-4f radiative transition. Ab initio calculations are performed to investigate the electronic structures as well as the binding energies of polarons in Cs2NaRBr6. The calculated large self-trapped exciton binding energies are consistent with the observed high light yield due to self-trapped exciton (STE) emission. The unique electronic structure of halide elpasolites as calculated enhances the STE stability and the STE emission. The highly tunable scintillation properties of mixed-anion elpasolites underscore the role of their complex scintillation mechanism. Furthermore, our study provides guidance for the design of elpasolite scintillators with exceptional energy resolution and light yield desirable for applications.

  10. 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.

  11. 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.

  12. Key role of lattice symmetry in the metal-insulator transition of NdNiO3sub> films

    SciTech Connect

    Zhang, Jack Y.; Kim, Honggyu; Mikheev, Evgeny; Hauser, Adam J.; Stemmer, Susanne


    Here, bulk NdNiO3sub> exhibits a metal-to-insulator transition (MIT) as the temperature is lowered that is also seen in tensile strained films. In contrast, films that are under a large compressive strain typically remain metallic at all temperatures. To clarify the microscopic origins of this behavior, we use position averaged convergent beam electron diffraction in scanning transmission electron microscopy to characterize strained NdNiO3sub> films both above and below the MIT temperature. We show that a symmetry lowering structural change takes place in case of the tensile strained film, which undergoes an MIT, but is absent in the compressively strained film. Using space group symmetry arguments, we show that these results support the bond length disproportionation model of the MIT in the rare-earth nickelates. Furthermore, the results provide insights into the non-Fermi liquid phase that is observed in films for which the MIT is absent.

  13. 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.

  14. Quadrupole splittings in the near-infrared spectrum of 14NH3sub>

    SciTech Connect

    Twagirayezu, Sylvestre; Hall, Gregory E.; Sears, Trevor J.


    Sub-Doppler, saturation dip, spectra of lines in the v1 + v3sub>, v1 + 2v4 and v3sub> + 2v4 bands of 14NH3sub> have been measured by frequency comb-referenced diode laser absorption spectroscopy. The observed spectral line widths are dominated by transit time broadening, and show resolved or partially-resolved hyperfine splittings that are primarily determined by the 14N quadrupole coupling. Modeling of the observed line shapes based on the known hyperfine level structure of the ground state of the molecule shows that, in nearly all cases, the excited state level has hyperfine splittings similar to the same rotational level in the ground state. The data provide accurate frequencies for the line positions and easily separate lines overlapped in Doppler-limited spectra. The observed hyperfine splittings can be used to make and confirm rotational assignments and ground state combination differences obtained from the measured frequencies are comparable in accuracy to those obtained from conventional microwave spectroscopy. Furthermore, several of the measured transitions do not show the quadrupole hyperfine splittings expected based on their existing rotational assignments. Either the assignments are incorrect or the upper levels involved are perturbed in a way that affects the nuclear hyperfine structure.

  15. 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.

  16. 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.

  17. Quench protection studies of the 11-T Nb3sub>Sn dipole for the LHC upgrade

    SciTech Connect

    Bermudez, Susana Izquierdo; Auchmann, Bernhard; Bajas, Hugues; Bajko, Marta; Bordini, Bernardo; Bottura, Luca; Chlachidze, Guram; Karppinen, Mikko; Rysti, Juho; Savary, Frederic; Willering, Gerard; Zlobin, Alexander V.


    The planned upgrade of the LHC collimation system foresees additional collimators to be installed in the dispersion suppressor areas. Fermilab and CERN are developing an 11 T Nb3sub>Sn dipole to replace some 8.33 T-15-m-long Nb-Ti LHC main dipoles providing longitudinal space for the collimators. In case of a quench, the large stored energy and the low copper stabilizer fraction make the protection of the 11 T Nb3sub>Sn dipoles challenging. This paper presents the results of quench protection analysis, including quench protection heater design and efficiency, quench propagation and coil heating. The numerical results are compared with the experimental data from the 2-m-long Nb3sub>Sn dipole models. Here, the validated model is used to predict the current decay and hot spot temperature under operating conditions in the LHC and the presently foreseen magnet protection scheme is discussed.

  18. 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.

  19. Magnon spectrum of the helimagnetic insulator Cu2OSeO3sub>

    SciTech Connect

    Portnichenko, P. Y.; Romhányi, J.; Onykiienko, Y. A.; Henschel, A.; Schmidt, M.; Cameron, A. S.; Surmach, M. A.; Lim, J. A.; Park, J. T.; Schneidewind, A.; Abernathy, D. L.; Rosner, H.; van den Brink, Jeroen; Inosov, D. S.


    We report that complex low-temperature-ordered states in chiral magnets are typically governed by a competition between multiple magnetic interactions. The chiral-lattice multiferroic Cu2OSeO3sub> became the first insulating helimagnetic material in which a long-range order of topologically stable spin vortices known as skyrmions was established. Here we employ state-of-the-art inelastic neutron scattering to comprehend the full three-dimensional spin-excitation spectrum of Cu2OSeO3sub> over a broad range of energies. Distinct types of high- and low-energy dispersive magnon modes separated by an extensive energy gap are observed in excellent agreement with the previously suggested microscopic theory based on a model of entangled Cu4 tetrahedra. The comparison of our neutron spectroscopy data with model spin-dynamical calculations based on these theoretical proposals enables an accurate quantitative verification of the fundamental magnetic interactions in Cu2OSeO3sub> that are essential for understanding its abundant low-temperature magnetically ordered phases.

  20. 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>.

  1. Absence of cytotoxicity towards microglia of iron oxide (α-Fe2O3sub>) nanorhombohedra

    SciTech Connect

    Crystal S. Lewis; Wong, Stanislaus S.; Torres, Luisa; Miyauchi, Jeremy T.; Rastegar, Cyrus; Patete, Jonathan M.; Smith, Jacqueline M.; Tsirka, Stella E.


    Understanding the nature of interactions between nanomaterials, such as commercially ubiquitous hematite (α-Fe2O3sub>) nanorhombohedra (N-Rhomb) and biological systems is of critical importance for gaining insight into the practical applicability of nanomaterials. Microglia represent the first line of defense in the central nervous system (CNS) during severe injury or disease such as Parkinson's and Alzheimer's disease as illustrative examples. Hence, to analyze the potential cytotoxic effect of N-Rhomb exposure in the presence of microglia, we have synthesized Rhodamine B (RhB)-labeled α-Fe2O3sub> N-Rhomb, with lengths of 47 ± 10 nm and widths of 35 ± 8 nm. Internalization of RhB-labeled α-Fe2O3sub> N-Rhomb by microglia in the mouse brain was observed, and a dose-dependent increase in the cellular iron content as probed by cellular fluorescence was detected in cultured microglia after nanoparticle exposure. The cells maintained clear functional viability, exhibiting little to no cytotoxic effects after 24 and 48 hours at acceptable, physiological concentrations. Importantly, the nanoparticle exposure did not induce microglial cells to produce either tumor necrosis factor alpha (TNFα) or interleukin 1-beta (IL1β), two pro-inflammatory cytokines, nor did exposure stimulate the production of nitrites and reactive oxygen species (ROS), which are common indicators for the onset of inflammation. Finally, we propose that under the conditions of our experiments, i.e. in the presence of RhB labeled-α-Fe2O3sub> N-Rhomb maintaining concentrations of up to 100 μg mL–1 after 48 hours of incubation, the in vitro and in vivo internalization of RhB-labeled α-Fe2O3sub> N-Rhomb are likely to be clathrin-dependent, which represents a conventional mechanistic uptake route for most cells. Furthermore, given the crucial role that microglia play in many neurological

  2. 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.

  3. Stabilities and defect-mediated lithium-ion conduction in a ground state cubic Li3sub> N structure

    SciTech Connect

    Nguyen, Manh Cuong; Hoang, Khang; Wang, Cai-Zhuang; Ho, Kai-Ming


    A stable ground state structure with cubic symmetry of Li3sub>N (c-Li3sub>N) is found by ab initio initially symmetric random-generated crystal structure search method. Gibbs free energy, calculated within quasi-harmonic approximation, shows that c-Li3sub>N is the ground state structure for a wide range of temperature. The c-Li3sub>N structure has a negative thermal expansion coefficient at temperatures lower than room temperature, due mainly to two transverse acoustic phonon modes. This c-Li3sub>N phase is a semiconductor with an indirect band gap of 1.90 eV within hybrid density functional calculation. We also investigate the migration and energetics of native point defects in c-Li3sub>N, including lithium and nitrogen vacancies, interstitials, and anti-site defects. Lithium interstitials are found to have a very low migration barrier (~0.12 eV) and the lowest formation energy among all possible defects. Thus, the ionic conduction in c-Li3sub>N is expected to occur via an interstitial mechanism, in contrast to that in the well-known α-Li3sub>N phase which occurs via a vacancy mechanism.

  4. 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.

  5. 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.

  6. 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

  7. 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)

  8. Corrigendum to “Thermophysical properties of U3sub>Si2 to 1773 K”

    SciTech Connect

    White, Joshua Taylor; Nelson, Andrew Thomas; Dunwoody, John Tyler; Safarik, Douglas Joseph; McClellan, Kenneth James


    An error was discovered by the authors in the calculation of thermal diffusivity in “Thermophysical properties of U3sub>Si2 to 1773 K”. The error was caused by operator error in entry of parameters used to fit the temperature rise versus time model necessary to calculate the thermal diffusivity. Lastly, this error propagated to the calculation of thermal conductivity, leading to values that were 18%–28% larger along with the corresponding calculated Lorenz values.

  9. 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.

  10. Electroelastic fields in artificially created vortex cores in epitaxial BiFeO3sub> thin films

    SciTech Connect

    Winchester, Ben; Wisinger, Nina Balke; Cheng, X. X.; Morozovska, A. N.; Kalinin, Sergei; Chen, L. Q.


    Here we employ phase-field modeling to explore the elastic properties of artificially created 1-D domain walls in (001)p-oriented BiFeO3sub> thin films, composed of a junction of the four polarization variants, all with the same out-of-plane polarization. It was found that these junctions exhibit peculiarly high electroelastic fields induced by the neighboring ferroelastic/ferroelectric domains. The vortex core exhibits a volume expansion, while the anti-vortex core is more compressive. We also discuss possible ways to control the electroelastic field, such as varying material constant and applying transverse electric field.

  11. Magnetic Ordering in Sr3sub>YCo4O10+x

    SciTech Connect

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


    Transition-metal oxides often exhibit complex magnetic behavior due to the strong interplay between atomic-structure, electronic and magnetic degrees of freedom. Cobaltates, especially, exhibit complex behavior because of cobalt’s ability to adopt various valence and spin state configurations. The case of the oxygen-deficient perovskite Sr3sub>YCo4O10+x (SYCO) has gained considerable attention because of persisting uncertainties about its structure and the origin of the observed room temperature ferromagnetism. Here we report a combined investigation of SYCO using aberration-corrected scanning transmission electron microscopy and density functional theory calculations.

  12. 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.

  13. 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.

  14. Superconductor to Mott insulator transition in YBa2Cu3sub>O7/LaCaMnO3sub> heterostructures

    SciTech Connect

    Gray, B. A.; Middey, S.; Conti, G.; Gray, A. X.; Kuo, C. -T.; Kaiser, A. M.; Ueda, S.; Kobayashi, K.; Meyers, D.; Kareev, M.; Tung, I. C.; Liu, Jian; Fadley, C. S.; Chakhalian, J.; Freeland, J. W.


    The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In this paper, in pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3sub>O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3sub> (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Finally, such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.

  15. Dispersion of nanocrystalline Fe3sub>O4 within composite electrodes: Insights on battery-related electrochemistry

    SciTech Connect

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


    Aggregation of nanosized materials in composite lithium-ion-battery electrodes can be a significant factor influencing electrochemical behavior. In this study, aggregation was controlled in magnetite, Fe3sub>O4, composite electrodes via oleic acid capping and subsequent dispersion in a carbon black matrix. A heat treatment process was effective in the removal of the oleic acid capping agent while preserving a high degree of Fe3sub>O4 dispersion. Electrochemical testing showed that Fe3sub>O4 dispersion is initially beneficial in delivering a higher functional capacity, in agreement with continuum model simulations. However, increased capacity fade upon extended cycling was observed for the dispersed Fe3sub>O4 composites relative to the aggregated Fe3sub>O4 composites. X-ray absorption spectroscopy measurements of electrodes post cycling indicated that the dispersed Fe3sub>O4 electrodes are more oxidized in the discharged state, consistent with reduced reversibility compared with the aggregated sample. Higher charge-transfer resistance for the dispersed sample after cycling suggests increased surface-film formation on the dispersed, high-surface-area nanocrystalline Fe3sub>O4 compared to the aggregated materials. Furthermore, this study provides insight into the specific effects of aggregation on electrochemistry through a multiscale view of mechanisms for magnetite composite electrodes.

  16. Structural properties of Sb2S3sub> under pressure: Evidence of an electronic topological transition

    SciTech Connect

    Efthimiopoulos, Ilias; Buchan, Cienna; Wang, Yuejian


    High-pressure Raman spectroscopy and x-ray diffraction of Sb2S3sub> up to 53 GPa reveals two phase transitions at 5 GPa and 15 GPa. The first transition is evidenced by noticeable compressibility changes in distinct Raman-active modes, in the lattice parameter axial ratios, the unit cell volume, as well as in specific interatomic bond lengths and bond angles. By taking into account relevant results from the literature, we assign these effects to a second-order isostructural transition arising from an electronic topological transition in Sb2S3sub> near 5 GPa. Close comparison between Sb2S3sub> and Sb2S3sub> up to 10 GPa reveals a slightly diverse structural behavior for these two compounds after the isostructural transition pressure. This structural diversity appears to account for the different pressure-induced electronic behavior of Sb2S3sub> and Sb2S3sub> up to 10 GPa, i.e. the absence of an insulator-metal transition in Sb2S3sub> up to that pressure. Lastly, the second high-pressure modification appearing above 15 GPa appears to trigger a structural disorder at ~20 GPa; full decompression from 53 GPa leads to the recovery of an amorphous state.

  17. Probing the Electronic and Structural Properties of the Niobium Trimer Cluster and its Mono- and Dioxides. Nb3sub>On- and Nb3sub>On (n=0-2)

    SciTech Connect

    Zhai, Hua Jin; Wang, Bing; Huang, Xin; Wang, Lai S.


    We report a photoelectron spectroscopy and density functional theory (DFT) study on the electronic and structural properties of Nb3sub>-, Nb3sub>O-, Nb3sub>O2-, and the corresponding neutrals. Well-resolved photoelectron spectra are obtained for the anion clusters at different photon energies and are compared with DFT calculations to elucidate their structures and chemical bonding. We find that Nb3sub> - possesses a C2V (3A2) structure, and Nb3sub> is a scalene Cs (2A'') triangle. Both Nb3sub>O- and Nb3sub>O are found to have C2V structures, in which the O atom bridges two Nb atoms in a Nb3sub> triangle. The ground-state of Nb3sub>O2 - is found surprisingly to be a low symmetry C1 (1A) structure, which contains a bridging and a terminal O atom. Molecular orbital analyses are carried out to understand the structures and bonding of the three clusters and provide insights into the sequential oxidation from Nb3sub>- to Nb3sub>O2-. The terminal NbdO unit is common in niobia catalysts, and the Nb3sub>O2- cluster with a NbdO unit may be viewed as a molecular model for the catalytic sites or the initial oxidation of a Nb surface.

  18. 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.

  19. 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.

  20. Wetting of sodium on β''-Al2O3sub>/YSZ composites for low temperature planar sodium-metal halide batteries

    SciTech Connect

    Reed, David; Coffey, Greg; Mast, Eric; Canfield, Nathan; Mansurov, Jirgal; Lu, Xiaochuan; Sprenkle, Vince


    Wetting of Na on B”-Al2O3sub>/YSZ composites was investigated using the sessile drop technique. The effects of moisture and surface preparation were studied at low temperatures. Electrical conductivity of Na/B”-Al2O3sub>-YSZ/Na cells was also investigated at low temperatures and correlated to the wetting behavior. The use of planar B”-Al2O3sub> substrates at low temperature with low cost polymeric seals is realized due to improved wetting at low temperature and conductivity values consistent with the literature.

  1. Yolk–shell Fe2O3sub> ⊙ C composites anchored on MWNTs with enhanced lithium and sodium storage

    SciTech Connect

    Zhao, Yi; Feng, Zhenxing; Xu, Zhichuan J.


    For this research, a unique architecture with yolk–shell Fe2O3sub> ⊙ C composites attached to the surface of MWNTs is designed. Benefiting from the good electrical conductivity of MWNTs and carbon layers, as well as the large void space to accommodate the volume expansion/extraction of Fe2O3sub> during battery cycling, the obtained MWNT@Fe2O3sub> ⊙ C exhibited outstanding lithium and sodium storage performance.

  2. 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.

  3. Exploring Charge Transport in Guest Molecule Infiltrated Cu3sub>(BTC)2 Metal Organic Framework

    SciTech Connect

    Leonard, Francois Leonard; Stavila, Vitalie; Allendorf, Mark D.


    The goal of this Exploratory Express project was to expand the understanding of the physical properties of our recently discovered class of materials consisting of metal-organic frameworks with electroactive ‘guest’ molecules that together form an electrically conducting charge-transfer complex (molecule@MOF). Thin films of Cu3sub>(BTC)2 were grown on fused silica using solution step-by-step growth and were infiltrated with the molecule tetracyanoquinodimethane (TCNQ). The infiltrated MOF films were extensively characterized using optical microscopy, scanning electron microscopy, Raman spectroscopy, electrical conductivity, and thermoelectric properties. Thermopower measurements on TCNQ@Cu3sub>(BTC)2 revealed a positive Seebeck coefficient of ~400 μV/k, indicating that holes are the primary carriers in this material. The high value of the Seebeck coefficient and the expected low thermal conductivity suggest that molecule@MOF materials may be attractive for thermoelectric power conversion applications requiring low cost, solution-processable, and non-toxic active materials.

  4. Analysis of field errors for LARP Nb3sub>Sn HQ03 quadrupole magnet

    SciTech Connect

    Wang, Xiaorong; Ambrosio, Giorgio; Chlachidze, Guram; DiMarco, Joseph; Ghosh, A. K.; Holik, E. F.; Prestemon, S. O.; Sabbi, G. L.; Stoynev, Stoyan


    The U.S. LHC Accelerator Research Program, in close collaboration with CERN, has developed three generations of high-gradient quadrupole (HQ) Nb3sub>Sn model magnets, to support the development of the 150 mm aperture Nb3sub>Sn quadrupole magnets for the High-Luminosity LHC. The latest generation, HQ03, featured coils with better uniformity of coil dimensions and properties than the earlier generations. We tested the HQ03 magnet at FNAL, including the field quality study. The profiles of low-order harmonics along the magnet aperture observed at 15 kA, 1.9 K can be traced back to the assembled coil pack before the magnet assembly. Based on the measured harmonics in the magnet center region, the coil block positioning tolerance was analyzed and compared with earlier HQ01 and HQ02 magnets to correlate with coil and magnet fabrication. Our study the capability of correcting the low-order non-allowed field errors, magnetic shims were installed in HQ03. Furthermore, the expected shim contribution agreed well with the calculation. For the persistent-current effect, the measured a4 can be related to 4% higher in the strand magnetization of one coil with respect to the other three coils. Lastly, we compare the field errors due to the inter-strand coupling currents between HQ03 and HQ02.

  5. 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.

  6. 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.

  7. On the structural origin of the single-ion magnetic anisotropy in LuFeO 3sub>

    SciTech Connect

    Cao, Shi; Zhang, Xiaozhe; Paudel, Tula R.; Sinha, Kishan; Wang, Xiao; Jiang, Xuanyuan; Wang, Wenbin; Brutsche, Stuart; Wang, Jian; Ryan, Philip J.; Kim, Jong-Woo; Cheng, Xuemei; Tsymbal, Evgeny Y.; Dowben, Peter A.; Xu, Xiaoshan


    The electronic structure for the conduction bands of both hexagonal and orthorhombic LuFeO3sub> thin films have been measured using x-ray absorption spectroscopy at oxygen K (O K) edge. Dramatic differences in both the spectral features and the linear dichroism are observed. These differences in the spectra can be explained using the differences in crystal field splitting of the metal (Fe and Lu) electronic states and the differences in O 2p-Fe 3d and O 2p-Lu 5d hybridizations. While the oxidation states have not changed, the spectra are sensitive to the changes in the local environments of the Fe3+ and Lu3+ sites in the hexagonal and orthorhombic structures. Using the crystal-field splitting and the hybridizations that are extracted from the measured electronic structures and the structural distortion information, we derived the occupancies of the spin minority states in Fe3+, which are non-zero and uneven. The single ion anisotropy on Fe3+ sites is found to originate from these uneven occupancies of the spin minority states via spin–orbit coupling in LuFeO3sub>.

  8. Polymerization of Acetonitrile via a Hydrogen Transfer Reaction from CH3sub> to CN under Extreme Conditions

    SciTech Connect

    Zheng, Haiyan; Li, Kuo; Cody, George D.; Tulk, Christopher A.; Dong, Xiao; Gao, Guoying; Molaison, Jamie J.; Liu, Zhenxian; Feygenson, Mikhail; Yang, Wenge; Ivanov, Ilia N.; Basile, Leonardo; Idrobo, Juan-Carlos; Guthrie, Malcolm; Mao, Ho-kwang


    Acetonitrile (CH3sub>CN) is the simplest and one of the most stable nitriles. Reactions usually occur on the C≡N triple bond, while the C-H bond is very inert and can only be activated by a very strong base or a metal catalyst. In this study, it is demonstrated that C-H bonds can be activated by the cyano group under high pressure, but at room temperature. The hydrogen atom transfers from the CH3sub> to CN along the CH···N hydrogen bond, which produces an amino group and initiates polymerization to form a dimer, 1D chain, and 2D nanoribbon with mixed sp2 and sp3 bonded carbon. Lastly, it transforms into a graphitic polymer by eliminating ammonia. This study shows that applying pressure can induce a distinctive reaction which is guided by the structure of the molecular crystal. It highlights the fact that very inert C-H can be activated by high pressure, even at room temperature and without a catalyst.

  9. Fabrication and Analysis of 150-mm-Aperture Nb3sub>Sn MQXF Coils

    SciTech Connect

    Holik, E. F.; Ambrosio, G.; Anerella, M.; Bossert, R.; Cavanna, E.; Cheng, D.; Dietderich, D. R.; Ferracin, P.; Ghosh, A. K.; Bermudez, S. Izquierdo; Krave, S.; Nobrega, A.; Perez, J. C.; Pong, I.; Rochepault, E.; Sabbi, G. L.; Schmalzle, J.; Yu, M.


    The U.S. LHC Accelerator Research Program (LARP) and CERN are combining efforts for the HiLumi-LHC upgrade to design and fabricate 150-mm-aperture, interaction region quadrupoles with a nominal gradient of 130 T/m using Nb3sub>Sn. To successfully produce the necessary long MQXF triplets, the HiLumi-LHC collaboration is systematically reducing risk and design modification by heavily relying upon the experience gained from the successful 120-mm-aperture LARP HQ program. First generation MQXF short (MQXFS) coils were predominately a scaling up of the HQ quadrupole design allowing comparable cable expansion during Nb3sub>Sn formation heat treatment and increased insulation fraction for electrical robustness. A total of 13 first generation MQXFS coils were fabricated between LARP and CERN. Systematic differences in coil size, coil alignment symmetry, and coil length contraction during heat treatment are observed and likely due to slight variances in tooling and insulation/cable systems. Analysis of coil cross sections indicate that field-shaping wedges and adjacent coil turns are systematically displaced from the nominal location and the cable is expanding less than nominally designed. Lastly, a second generation MQXF coil design seeks to correct the expansion and displacement discrepancies by increasing insulation and adding adjustable shims at the coil pole and midplanes to correct allowed magnetic field harmonics.

  10. Magnetic microstructure and magnetic properties of uniaxial itinerant ferromagnet Fe3sub>GeTe2

    SciTech Connect

    León-Brito, Neliza; Bauer, Eric Dietzgen; Ronning, Filip; Thompson, Joe David; Movshovich, Roman


    Here, magnetic force microscopy was used to observe the magnetic microstructure of Fe3sub>GeTe2 at 4 K on the (001) surface. The surface magnetic structure consists of a two-phase domain branching pattern that is characteristic for highly uniaxial magnets in the plane perpendicular to the magnetic easy axis. The average surface magnetic domain width Ds = 1.3 μm determined from this pattern, in combination with intrinsic properties calculated from bulk magnetization data (the saturation magnetization Ms = 376 emu/cm3 and the uniaxial magnetocrystalline anisotropy constant Ku = 1.46 × 107 erg/cm3), was used to determine the following micromagnetic parameters for Fe3sub>GeTe2 from phenomenological models: the domain wall energy γw = 4.7 erg/cm2, the domain wall thickness δw = 2.5 nm, the exchange stiffness constant Aex = 0.95 × 10–7 erg/cm, the exchange length lex = 2.3 nm, and the critical single domain particle diameter dc = 470 nm.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Oxidation and Hydration of U 3sub> O 8 Materials Following Controlled Exposure to Temperature and Humidity

    SciTech Connect

    Tamasi, Alison L.; Boland, Kevin S.; Czerwinski, Kenneth; Ellis, Jason K.; Kozimor, Stosh A.; Martin, Richard L.; Pugmire, Alison L.; Reilly, Dallas; Scott, Brian L.; Sutton, Andrew D.; Wagner, Gregory L.; Walensky, Justin R.; Wilkerson, Marianne P.


    Chemical signatures correlated with uranium oxide processing are of interest to forensic science for inferring sample provenance. Identification of temporal changes in chemical structures of process uranium materials as a function of controlled temperatures and relative humidities may provide additional information regarding sample history. In our study, a high-purity α-U3sub>O8 sample and three other uranium oxide samples synthesized from reaction routes used in nuclear conversion processes were stored under controlled conditions over 2–3.5 years, and powder X-ray diffraction analysis and X-ray absorption spectroscopy were employed to characterize chemical speciation. We measured signatures from the α-U3sub>O8 sample indicated that the material oxidized and hydrated after storage under high humidity conditions over time. Impurities, such as uranyl fluoride or schoepites, were initially detectable in the other uranium oxide samples. After storage under controlled conditions, the analyses of the samples revealed oxidation over time, although the signature of the uranyl fluoride impurity diminished. The presence of schoepite phases in older uranium oxide material is likely indicative of storage under high humidity and should be taken into account for assessing sample history. Finally, the absence of a signature from a chemical impurity, such as uranyl fluoride hydrate, in an older material may not preclude its presence at the initial time of production. LA-UR-15-21495.

  16. Electronic and crystal structure changes induced by in-plane oxygen vacancies in multiferroic YMnO3sub>

    SciTech Connect

    Cheng, Shaobo; Meng, Qingping; Li, Mengli; Duan, Wenhui; Zhao, Y. G.; Sun, X. F.; Zhu, Yimei; Zhu, Jing


    Here, the widely spread oxygen vacancies (VO) in multiferroic materials can strongly affect their physical properties. However, their exact influence has rarely been identified in hexagonal manganites. Here, with the combined use of transmission electron microscopy (TEM) and first-principles calculations, we have systematically studied the electronic and crystal structure modifications induced by VO located at the same Mn atomic plane (in-plane VO). Our TEM experiments reveal that the easily formed in-plane VO not only influence the electronic structure of YMnO3sub> but alter the in-plane Wyckoff positions of Mn ions, which may subsequently affect the intraplane and interplane exchange interaction of Mn ions. The ferroelectricity is also impaired due to the introduction of VO. Further calculations confirm these electronic and structural changes and modifications. Our results indicate that the electronic and crystal structure of YMnO3sub> can be manipulated by the creation of VO.

  17. 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.

  18. 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.

  19. 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

  20. Graphitic C3sub>N4 as a new saturable absorber for the mid-infrared spectral range.


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


    The saturable absorption properties of few-layer graphitic carbon nitride (g-C3sub>N4) nanosheets near 3 μm were investigated. A stable Q-switched Er:Lu2O3sub> laser at 2.84 μm was realized by using a home-made g-C3sub>N4 saturable absorber (SA), generating a pulse duration of 351 ns and an average output power of 1.09 W at a repetition rate of 99 kHz, corresponding to a pulse energy of 11.1 μJ. Our result indicates a great potential of g-C3sub>N4 as a new SA in the 3 μm wavelength range.

  1. A review of molecular beam epitaxy of ferroelectric BaTiO3sub> films on Si, Ge and GaAs substrates and their applications

    SciTech Connect

    Mazet, Lucie; Yang, Sang Mo; Kalinin, Sergei V.; Schamm-Chardon, Sylvie; Dubourdieu, Catherine


    SrTiO3sub> epitaxial growth by molecular beam epitaxy (MBE) on silicon has opened up the route to the monolithic integration of various complex oxides on the complementary metal-oxide-semiconductor silicon platform. Among functional oxides, ferroelectric perovskite oxides offer promising perspectives to improve or add functionalities on-chip. We review the growth by MBE of the ferroelectric compound BaTiO3sub> on silicon (Si), germanium (Ge) and gallium arsenide (GaAs) and we discuss the film properties in terms of crystalline structure, microstructure and ferroelectricity. Lastly, we review the last developments in two areas of interest for the applications of BaTiO3sub> films on silicon, namely integrated photonics, which benefits from the large Pockels effect of BaTiO3sub>, and low power logic devices, which may benefit from the negative capacitance of the ferroelectric.

  2. 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>.

  3. 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.

  4. Synthesis of gadolinium carbonate-conjugated-poly(ethylene)glycol (Gd{sub 2}(CO{sub 3}){sub 3}@PEG) particles via a modified solvothermal method

    SciTech Connect

    Nasution, Erika L. Y.; Ahab, Atika; Nuryadin, Bebeh W.; Haryanto, Freddy; Arif, Idam; Iskandar, Ferry


    PEGylated gadolinium carbonate ((Gd{sub 2}(CO{sub 3}){sub 3})@PEG) powder was successfully synthesized by a modified solvothermal method. The synthesized products were characterized by means of X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS). A systematic change in the chemical surface composition, crystallinity and size properties of the Gd{sub 2}(CO{sub 3}){sub 3}@PEG particles was observed by increasing the reaction time at 5 hours, 7 hours, and 8 hours. The corresponding XRD patterns showed that the Gd{sub 2}(CO{sub 3}){sub 3} particles had hexagonal symmetry (JCPDS No. 37-0559) with a crystallite size of 3.5, 2.9, and 4.6 nm. FTIR spectra showed that the Gd{sub 2}(CO{sub 3}){sub 3})@PEG particles were formed with the PEG as carbonyl and hydroxyl group attached to the surface. SEM analysis showed that the Gd{sub 2}(CO{sub 3}){sub 3})@PEG particles had a flake-like morphology of homogeneous sized particles and agglomerates. EDS analysis confirmed the presence of constituent Gd{sub 2}(CO{sub 3}){sub 3} elements.

  5. Structural and Na-ion conduction characteristics of Na 3sub> PS x Se 4-x

    SciTech Connect

    Bo, Shou-Hang; Wang, Yan; Ceder, Gerbrand


    The recent discovery of the isostructrual cubic Na3sub>PS4 and Na3sub>PSe4 as fast Na-ion conductors provided a general structural framework for the exploration of new sodium superionic conductors. In this work, we systematically investigated the structures and ionic conduction characteristics of a series of compounds with the general chemical formula of Na3sub>PSxSe4-x. Synthesis of Na3sub>PS4 under different conditions (e.g., temperature, reaction vessel, mass of the precursors) reveals the reactivity of the precursors with the reaction tubes, producing different polymorphs. X-ray diffraction studies on the solid solution phases Na3sub>PSxSe4-x identified a tetragonal-to-cubic phase transition with increasing Se concentration. This observation is consistent with the computed stability of the tetragonal and cubic polymorphs, where the energy difference between the two polymorphs becomes very close to zero in Se-rich compositions. Furthermore, ab initio molecular dynamic simulations suggest that the fast Na-ion conduction in Na3sub>PSxSe4-x may not be causally related with the symmetry or the composition of these phases. The formation of defects, instead, enables fast Na-ion conduction in this class of materials.

  6. Imprint control of BaTiO3sub> thin films via chemically induced surface polarization pinning

    SciTech Connect

    Lee, Hyungwoo; Kim, Tae Heon; Patzner, Jacob J.; Lu, Haidong; Lee, Jung -Woo; Zhou, Hua; Chang, Wansoo; Mahanthappa, Mahesh K.; Tsymbal, Evgeny Y.; Gruverman, Alexei; Eom, Chang -Beom


    Surface-adsorbed polar molecules can significantly alter the ferroelectric properties of oxide thin films. Thus, fundamental understanding and controlling the effect of surface adsorbates are crucial for the implementation of ferroelectric thin film devices, such as ferroelectric tunnel junctions. Herein, we report an imprint control of BaTiO3sub> (BTO) thin films by chemically induced surface polarization pinning in the top few atomic layers of the water-exposed BTO films. Our studies based on synchrotron X-ray scattering and coherent Bragg rod analysis demonstrate that the chemically induced surface polarization is not switchable but reduces the polarization imprint and improves the bistability of ferroelectric phase in BTO tunnel junctions. Here, we conclude that the chemical treatment of ferroelectric thin films with polar molecules may serve as a simple yet powerful strategy to enhance functional properties of ferroelectric tunnel junctions for their practical applications.

  7. Fano q-reversal in topological insulator Bi2Se3sub>

    SciTech Connect

    S. V. Dordevic; Petrovic, C.; Foster, G. M.; Wolf, M. S.; Stojilovic, N.; Lei, Hechang; Chen, Z.; Li, Z. Q.; Tung, L. C.


    Here, we studied the magneto-optical response of a canonical topological insulator Bi2Se3sub> with the goal of addressing a controversial issue of electron–phonon coupling. Magnetic-field induced modifications of reflectance are very pronounced in the infrared part of the spectrum, indicating strong electron–phonon coupling. This coupling causes an asymmetric line-shape of the 60 cm–1 phonon mode, and is analyzed within the Fano formalism. The analysis reveals that the Fano asymmetry parameter (q) changes sign when the cyclotron resonance is degenerate with the phonon mode. To the best of our knowledge this is the first example of magnetic field driven q-reversal.

  8. 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.

  9. 42  W femtosecond Yb:Lu2O3sub> regenerative amplifier.


    Caracciolo, E; Pirzio, F; Kemnitzer, M; Gorjan, M; Guandalini, A; Kienle, F; Agnesi, A; Aus Der Au, J


    We report on a femtosecond high-power regenerative amplifier based on Yb:Lu2O3sub>. Exploiting the excellent thermo-mechanical properties of this material, we were able to achieve up to 64.5 W in continuous-wave regime, limited only by the available pump power. In pulsed operation, 42 W of average output power at a repetition rate of 500 kHz with 780 fs long pulses could be demonstrated, resulting in a pulse peak power of ∼100  MW. The spectrum was centered at 1034 nm with an FWHM of 2.4 nm, potentially allowing for even shorter pulses. At the maximum output power the beam was nearly TEM00, with an M2 value of 1.2 in both axes.

  10. 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.

  11. Point-contact Andreev reflection spectroscopy on Bi 2 Se 3sub> single crystals

    SciTech Connect

    Granstrom, C. R.; Fridman, I.; Lei, H. -C.; Petrovic, C.; Wei, J. Y. T.


    In order to study how Andreev reflection (AR) occurs between a superconductor and a three-dimensional topological insulator (TI), we use superconducting Nb tips to perform point-contact AR spectroscopy at 4.2 K on as-grown single crystals of Bi2Se3sub>. Scanning tunneling spectroscopy and scanning tunneling microscopy are also used to characterize the superconducting tip and both the doping level and surface condition of the TI sample. Furthermore, the point-contact measurements show clear spectral signatures of AR, as well as a depression of zero-bias conductance with decreasing junction impedance. The latter observation can be attributed to interfacial Rashba spin-orbit coupling, and the presence of bulk bands at the Fermi level in our samples suggests that bulk states of Bi2Se3 are involved in the observed AR.

  12. Simple production of membrane-based LiNbO3sub> micro-modulators with integrated tapers.


    Courjal, Nadège; Caspar, Alexis; Calero, Venancio; Ulliac, Gwenn; Suarez, Miguel; Guyot, Clément; Bernal, Maria-Pilar


    We report on free-standing electro-optical LiNbO3sub> waveguides with integrated tapers made by optical grade dicing. Membranes with a calibrated thickness are produced simultaneously with tapers acting as spot-size converters. Thereby, thicknesses from 450 to 500 μm can simply be achieved together with integrated tapers guaranteeing low insertion losses. These developments open the way to the low-cost production of compact and low-power-consuming electro-optical components. As an example, a 200 μm-long free-standing electro-optical Fabry-Perot is demonstrated with a figure of merit of only 0.19 V·cm in a 4.5 μm-thick membrane.

  13. 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.

  14. 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.

  15. Trisodium citrate, Na 3sub> (C 6 H 5 O 7 )

    SciTech Connect

    Rammohan, Alagappa; Kaduk, James A.


    The crystal structure of anhydrous trisodium citrate, Na3sub>(C6H5O7), has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional theory (DFT). There are two independent five-coordinate Na+and one six-coordinate Na+cations in the asymmetric unit. The [NaO5] and [NaO6] polyhedra share edges and corners to form a three-dimensional framework. There are channels parallel to theaandbaxes in which the remainder of the citrate anions reside. The only hydrogen bonds are an intramolecular one between the hydroxy group and one of the terminal carboxylate O atoms and an intermolecular one between a methylene group and the hydroxyl O atom.

  16. 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.

  17. Ti 3sub> C 2 T x (MXene)–polyacrylamide nanocomposite films

    SciTech Connect

    Naguib, Michael; Saito, Tomonori; Lai, Sophia; Rager, Matthew S.; Aytug, Tolga; Parans Paranthaman, M.; Zhao, Meng-Qiang; Gogotsi, Yury


    Polymer nanocomposite films are of great interest due to their enhanced properties over base polymers. By incorporating 2D titanium carbide a representative of a new family of 2D materials, MXenes, as nanofillers into a water soluble polyacrylamide (PAM) matrix, the resulting films benefit from the flexibility, robustness, and processability of PAM, as well as the conductivity and mechanical properties of MXene fillers. We report on manufacturing and characterization of MXene-PAM nanocomposite films. Dimethylsulfoxide (DMSO) intercalation in-between the Ti3sub>C2-based MXene layers led to full delamination of the MXene layers and hence a uniform dispersion of hydrophilic MXene nanosheets in aqueous PAM solutions was achieved. Moreover, the polymer composite solutions of up to 75 wt.% MXene loading were sonicated and cast onto large Teflon trays and dried at room temperature to produce shiny black films. The observation of reduced 0002 peaks of Ti3sub>C2Tx phase in X-ray diffraction patterns and TEM images indicate the presence of well dispersed nanoflakes. The as-prepared composite films are flexible and the conductivity was increased significantly to 3 x 10-3 S cm-1 for 6 wt. % MXene-PAM films. With high MXene loading, some non-uniformity between the top and bottom surfaces was observed. This could be due to the segregation of MXene layers in composite films during drying. Finally, the power law dependence of conductivity above the percolation threshold is presented through detailed conductivity measurements.

  18. Etching of UO2 in NF3sub> RF Plasma Glow Discharge

    SciTech Connect

    Veilleux, John M.


    A series of room temperature, low pressure (10.8 to 40 Pa), low power (25 to 210 W) RF plasma glow discharge experiments with UO2 were conducted to demonstrate that plasma treatment is a viable method for decontaminating UO2 from stainless steel substrates. Experiments were conducted using NF3sub> gas to decontaminate depleted uranium dioxide from stainless-steel substrates. Depleted UO2 samples each containing 129.4 Bq were prepared from 100 microliter solutions of uranyl nitrate hexahydrate solution. The amorphous UO2 in the samples had a relatively low density of 4.8 gm/cm3sub>. Counting of the depleted UO2 on the substrate following plasma immersion was performed using liquid scintillation counting with alpha/beta discrimination due to the presence of confounding beta emitting daughter products, 234Th and 234Pa. The alpha emission peak from each sample was integrated using a gaussian and first order polynomial fit to improve quantification. The uncertainties in the experimental measurement of the etched material were estimated at about ± 2%. Results demonstrated that UO2 can be completely removed from stainless-steel substrates after several minutes processing at under 200 W. At 180 W and 32.7 Pa gas pressure, over 99% of all UO2 in the samples was removed in just 17 minutes. The initial etch rate in the experiments ranged from 0.2 to 7.4 μm/min. Etching increased with the plasma absorbed power and feed gas pressure in the range of 10.8 to 40 Pa. A different pressure effect on UO2 etching was also noted below 50 W in which etching increased up to a maximum pressure, ~23 Pa, then decreased with further increases in pressure.

  19. 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

  20. Syntheses, crystal structures and characterizations of BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2}

    SciTech Connect

    Jiang Hailong; Feng Meiling; Mao Jianggao . E-mail:


    Two new barium zinc selenite and tellurite, namely, BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2}, have been synthesized by the solid state reaction. The structure of BaZn(SeO{sub 3}){sub 2} features double chains of [Zn(SeO{sub 3}){sub 2}]{sup 2-} anions composed of four- and eight-member rings which are alternatively along a-axis. The double chains of [Zn{sub 2}(TeO{sub 3}){sub 2}Cl{sub 3}]{sup 3-} anions in BaZn(TeO{sub 3})Cl{sub 2} are formed by Zn{sub 3}Te{sub 3} rings in which each tellurite group connects with three ZnO{sub 3}Cl tetrahedra. BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2} are wide bandgap semiconductors based on optical diffuse reflectance spectrum measurements. -- Graphical abstract: Two new barium zinc selenite and tellurite, namely, BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2}, have been synthesized by solid state reaction. The structure of BaZn(SeO{sub 3}){sub 2} features 1D double chains of [Zn(SeO{sub 3}){sub 2}]{sup 2-} anions composed of four- and eight-member rings which are alternatively along a-axis. The 1D double chains of [Zn{sub 2}(TeO{sub 3}){sub 2}Cl{sub 3}]{sup 3-} anions in BaZn(TeO{sub 3})Cl{sub 2} are formed by Zn{sub 3}Te{sub 3} rings in which each tellurite group connects with one ZnO{sub 3}Cl and two ZnO{sub 2}Cl{sub 2} tetrahedra. BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2} are wide bandgap semiconductors based on optical diffuse reflectance spectrum measurements.

  1. 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

  2. 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.

  3. Passive SCR for lean gasoline NOX control: Engine-based strategies to minimize fuel penalty associated with catalytic NH3sub> generation

    SciTech Connect

    Prikhodko, Vitaly Y.; Parks, James E.; Pihl, Josh A.; Toops, Todd J.


    Lean gasoline engines offer greater fuel economy than common stoichiometric gasoline engines. However, excess oxygen prevents the use of the current three-way catalyst (TWC) to control nitrogen oxide (NOX) emissions in lean exhaust. A passive SCR concept, introduced by General Motors Global R&D, makes use of a TWC that is already onboard to generate NH3sub> under slightly rich conditions, which is stored on the downstream SCR. The stored NH3sub> is then used to reduce NOX emissions when the engine switches to lean operation. In this work, the effect of engine parameters, such as air-fuel equivalence ratio and spark timing, on NH3sub> generation over a commercial Pd-only TWC with no dedicated oxygen storage component was evaluated on a 2.0-liter BMW lean burn gasoline direct injection engine. NOX reduction, NH3sub> formation, and reductant utilization processes were evaluated, and fuel efficiency was assessed and compared to the stoichiometric engine operation case. We found air-fuel equivalence ratio to be one of the most important parameters in controlling the NH3sub> production; however, the rich operation necessary for NH3sub> production results in a fuel consumption penalty. The fuel penalty can be minimized by adjusting spark timing to increase rich-phase engine out NOX emissions and, thereby, NH3sub> levels. Additionally, higher engine out NOX during engine load increase to simulate acceleration resulted in additional fuel savings. Ultimately, a 10% fuel consumption benefit was achieved with the passive SCR approach by optimizing rich air-fuel equivalence ratio and spark timing while also utilizing acceleration load conditions.

  4. Structure and thermodynamic stability of UTa 3sub> O 10 , a U( v )-bearing compound

    SciTech Connect

    Guo, Xiaofeng; Lipp, Christian; Tiferet, Eitan; Lanzirotti, Antonio; Newville, Matthew; Engelhard, Mark H.; Wu, Di; Ilton, Eugene S.; Sutton, Stephen R.; Xu, Hongwu; Burns, Peter C.; Navrotsky, Alexandra


    Heating a mixture of uranyl(VI) nitrate and tantalum(V) oxide in the molar ratio of 2 : 3 to 1400 °C resulted in the formation of a new compound, UTa3sub>O10. The honey colored to yellow brown crystals of UTa3sub>O10 crystallize in an orthorhombic structure with the space group Fddd (no. 70), lattice parameters a = 7.3947(1), b = 12.7599(2), c = 15.8156(2) Å, and Z = 8. Vertex sharing [TaO6]7- octahedra of two crystallographically distinct Ta cations form a three dimensional tantalate framework. Within this framework, six membered rings of [TaO6]7- octahedra are formed within the (001) plane. The center of these rings is occupied by the uranyl cations [UO2]+, with an oxidation state of +5 for uranium. The pentavalence of U and Ta was confirmed by X-ray photoelectron spectroscopy and X-ray adsorption spectroscopy. The enthalpy of formation of UTa3sub>O10 from Ta2O5, β-U3sub>O7, and U3sub>O8 has been determined to be 13.1 ± 18.1 kJ mol-1 using high temperature oxide melt solution calorimetry with sodium molybdate as the solvent at 700 °C. The close to zero enthalpy of formation of UTa3sub>O10 can be explained by closely balanced structural stabilizing and destabilizing factors, which may also apply to other UM3sub>O10 compounds.

  5. 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.

  6. Nanocrystalline SiC and Ti3sub>SiC2 Alloys for Reactor Materials: Diffusion of Fission Product Surrogates

    SciTech Connect

    Henager, Charles H.; Jiang, Weilin


    MAX phases, such as titanium silicon carbide (Ti3sub>SiC2), have a unique combination of both metallic and ceramic properties, which make them attractive for potential nuclear applications. Ti3sub>SiC2 has been suggested in the literature as a possible fuel cladding material. Prior to the application, it is necessary to investigate diffusivities of fission products in the ternary compound at elevated temperatures. This study attempts to obtain relevant data and make an initial assessment for Ti3sub>SiC2. Ion implantation was used to introduce fission product surrogates (Ag and Cs) and a noble metal (Au) in Ti3sub>SiC2, SiC, and a dual-phase nanocomposite of Ti3sub>SiC2/SiC synthesized at PNNL. Thermal annealing and in-situ Rutherford backscattering spectrometry (RBS) were employed to study the diffusivity of the various implanted species in the materials. In-situ RBS study of Ti3sub>SiC2 implanted with Au ions at various temperatures was also performed. The experimental results indicate that the implanted Ag in SiC is immobile up to the highest temperature (1273 K) applied in this study; in contrast, significant out-diffusion of both Ag and Au in MAX phase Ti3sub>SiC2 occurs during ion implantation at 873 K. Cs in Ti3sub>SiC2 is found to diffuse during post-irradiation annealing at 973 K, and noticeable Cs release from the sample is observed. This study may suggest caution in using Ti3sub>SiC2 as a fuel cladding material for advanced nuclear reactors operating at very high temperatures. Further studies of the related materials are recommended.

  7. 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>.

  8. 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.

  9. 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.

  10. Pressure evolution of electrical transport in the 3D topological insulator (Bi,Sb) 2 (Se,Te) 3sub>

    SciTech Connect

    Jeffries, J. R.; Butch, N. P.; Vohra, Y. K.; Weir, S. T.


    The group V-VI compounds|like Bi2Se3sub>, Sb2Te3sub>, or Bi2Te3sub>|have been widely studied in recent years for their bulk topological properties. The high-Z members of this series form with the same crystal structure, and are therefore amenable to isostructural substitution studies. It is possible to tune the Bi-Sb and Te-Se ratios such that the material exhibits insulating behavior, thus providing an excellent platform for understanding how a topological insulator evolves with applied pressure. We report our observations of the pressure-dependent electrical transport and crystal structure of a pseudobinary (Bi,Sb)2(Te,Se)3sub> compound. Similar to some of its sister compounds, the (Bi,Sb)2(Te,Se)3sub> pseudobinary compound undergoes multiple, pressure-induced phase transformations that result in metallization, the onset of a close-packed crystal structure, and the development of distinct superconducting phases.

  11. Non-congruence of high-temperature mechanical and structural behaviors of LaCoO3sub> based perovskites

    SciTech Connect

    Aman, Amjad; Jordan, Ryan; Chen, Yan; Stadelmann, Richard; Lugovy, Mykola; Orlovskaya, Nina; Payzant, E. Andrew; dela Cruz, Clarina; Reece, Michael J.; Graule, Thomas; Kuebler, Jakob


    Our paper presents the mechanical behavior of LaCoO3sub> and La0.8Ca0.2CoO3 ceramics under four-point bending in which the two cobaltites are subjected to a low stress of ~8 MPa at temperatures ranging from room temperature to 1000 °C. Unexpected stiffening is observed in pure LaCoO3sub> in the 700–900 °C temperature range, leading to a significant increase in the measured Young’s modulus, whereas La0.8Ca0.2CoO3sub> exhibits softening from 100 °C to 1000 °C, as expected for most materials upon heating. we use neutron diffraction, X-ray diffraction and micro-Raman spectroscopy to study the crystal structure of the two materials in the RT–1000 °C temperature range. Despite a detailed study, there is no conclusive evidence to explain the stiffening behavior observed in pure LaCoO3sub> as opposed to the softening behavior in La0.8Ca0.2CoO3sub> at high temperatures (above 500 °C).

  12. Kinetic and mechanistic study of bimetallic Pt-Pd/Al2O3sub> catalysts for CO and C3sub>H6 oxidation

    SciTech Connect

    Hazlett, Melanie J.; Moses-Debusk, Melanie; Parks, III, James E.; Allard, Jr., Lawrence Frederick; Epling, William S.


    Low temperature combustion (LTC) diesel engines are being developed to meet increased fuel economy demands. However, some LTC engines emit higher levels of CO and hydrocarbons and therefore diesel oxidation catalyst (DOC) efficiency will be critical. Here, CO and propylene oxidation were studied, as representative LTC exhaust components, over model bimetallic Pt-Pd/γ-Al2O3sub> catalysts. During CO oxidation tests, monometallic Pt suffered the most extensive inhibition which was correlated to a greater extent of dicarbonyl species formation. Pd and Pd-rich bimetallics were inhibited by carbonate formation at higher temperatures. The 1:1 and 3:1 Pt:Pd bimetallic catalysts did not form the dicarbonyl species to the same extent as the monometallic Pt sample, and therefore did not suffer from the same level of inhibition. Similarly they also did not form carbonates to as large an extent as the Pd-rich samples and were therefore not as inhibited from this intermediate surface species at higher temperature. The Pd-rich samples were relatively poor propylene oxidation catalysts; and partial oxidation product accumulation deactivated these catalysts. Byproducts observed include acetone, ethylene, acetaldehyde, acetic acid, formaldehyde and CO. For CO and propylene co-oxidation, the onset of propylene oxidation was not observed until complete CO oxidation was achieved, and the bimetallics showed higher activity. In conclusion, this was again related to less extensive poisoning, less dicarbonyl species formation and less overall partial oxidation product accumulation.

  13. Quench performance and field quality of FNAL twin-aperture 11 T Nb3sub>Sn dipole model for LHC upgrades

    SciTech Connect

    Stoynev, Stoyan; Andreev, Nikolai; Apollinari, Giorgio; Auchmann, Bernhard; Barzi, Emanuela; Bermudez, Susana Izquierdo; Bossert, Rodger; Chlachidze, Guram; DiMarco, Joseph; Karppinen, Mikko; Nobrega, Alfred; Novitski, Igor; Rossi, Lucio; Savary, Frederic; Smekens, David; Strauss, Thomas; Turrioni, Daniele; Velev, Gueorgui V.; Zlobin, Alexander V.


    A 2 m long single-aperture dipole demonstrator and two 1 m long single-aperture models based on Nb3sub>Sn superconductor have been built and tested at FNAL. The two 1 m long collared coils were then assembled in a twin-aperture Nb3sub>Sn dipole demonstrator compatible with the LHC main dipole and tested in two thermal cycles. This paper summarizes the quench performance of the FNAL twin-aperture Nb3sub>Sn 11 T dipole in the temperature range of 1.9-4.5 K. The results of magnetic measurements for one of the two apertures are also presented. Test results are compared to the performance of coils in a single-aperture configuration. Lastly, a summary of quench propagation studies in both apertures is given.

  14. Symmetry and diffusivity of the interstitial hydrogen shallow-donor center in In2O3sub>

    SciTech Connect

    Weiser, Philip; Qin, Ying; Yin, Weikai; Stavola, Michael; Fowler, W. Beall; Boatner, Lynn A.


    Uniaxial stress experiments performed for the 3306 cm-1 vibrational line assigned to the interstitial-hydrogen, shallow-donor center in In2O3sub> reveal its symmetry and transition- moment direction. The defect alignment that can be produced by a [001] stress applied at 165 K is due to a process that is also a hydrogen- diffusion jump, providing a microscopic determination of the diffusion constant for H in In2O3sub> and its mechanism. Lastly, our experimental results strongly complement theoretical predictions for the structure and diffusion of the interstitial hydrogen donor center in In2O3sub>.

  15. Anchorage of γ-Al2O3sub> nanoparticles on nitrogen-doped multiwalled carbon nanotubes

    SciTech Connect

    Rodríguez-Pulido, A.; Martínez-Gutiérrez, H.; Calderon-Polania, G. A.; Lozano, M. A. Gonzalez; Cullen, D. A.; Terrones, H.; Smith, D. J.; Terrones, M.


    Nitrogen-doped multiwalled carbon nanotubes (CNx-MWNTs) have been decorated with γ-Al2O3sub> nanoparticles by a novel method. This process involved a wet chemical approach in conjunction with thermal treatment. During the particle anchoring process, individual CNx-MWNT nanotubes agglomerated into bundles, resulting in arrays of aligned CNx-MWNT coated with γ-Al2O3sub>. Extensive characterization of the resulting γ-Al2O3sub>/CNx-MWNT bundles was performed using a range of electron microscopy imaging and microanalytical techniques. In conclusion, a possible mechanism explaining the nanobundle alignment is described, and possible applications of these materials for the fabrication of ceramic composites using CNx-MWNTs are briefly discussed.

  16. 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.

  17. All-fiber passively Q-switched 604  nm praseodymium laser with a Bi2Se3sub> saturable absorber.


    Lin, Hui-Yu; Li, Wen-Song; Lan, Jing-Long; Guan, Xiao-Feng; Xu, Hui-Ying; Cai, Zhi-Ping


    We experimentally demonstrated a simple passively Q-switched praseodymium (Pr3+)-doped all-fiber laser at 604 nm with a Bi2Se3sub> saturable absorber (SA). A Bi2Se3sub>/polyvinyl alcohol composite film is sandwiched between two ferrules to construct a fiber-compatible Q-switcher. Two fiber end facet mirrors build a compact-linear resonator. The repetition rate of the achieved 604 nm Q-switching pulse can be widely tuned from 86.2 to 187.4 kHz, and the pulse duration can be as narrow as 494 ns. To the best of our knowledge, this is the shortest operation wavelength of a Bi2Se3sub>-based pulsed all-fiber laser at 604 nm.

  18. 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.

  19. Energy criterion and dynamical symmetry breaking in a SU(3){sub L} x U(1){sub X} extension of the standard model

    SciTech Connect

    Doff, A.


    The coupling constants g{sub L} and g{sub X} of some versions of the SU(3){sub L} x U(1){sub X} extension of the standard model are related through to relationship g{sub X}{sup 2}/g{sub L}{sup 2}=sin{sup 2}{theta}{sub W}/(1-4sin{sup 2}{theta}{sub W}). This fact suggest that the SU(3){sub L} x U(1){sub X} gauge symmetry in this class of models can be broken dynamically to the standard model at TeV scale without requiring the introduction of fundamental scalars. This possibility was investigated by Das and Jain who considered the only first version of this class of models. In this brief report we discuss an energy criterion to verify the most probable version of the SU(3){sub L} x U(1){sub X} model that is realized in nature.

  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. 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.

  2. Local structural effects in Sr3sub>NiRhO6 across magnetic transitions

    SciTech Connect

    Singh, Navneet; Khalid, S.; Bindu, R.


    Here, we investigate the temperature dependence of the structural parameters of quasi-one-dimensional Sr3sub>NiRhO6 across the region of magnetic phase transitions using Ni K-edge and Sr K-edge x-ray absorption spectroscopy (XAS). The features in the x-ray absorption near-edge region are identified using multiple scattering calculations. The temperature-dependent extended x-ray absorption fine structure (EXAFS) studies show that the setting of the intra-chain super exchange interaction starts at ~200 K, which is well above the first transition temperature (45 K) revealed by magnetic susceptibility studies. The onset of the inter-chain super–super exchange interaction appears to be at ~125 K. Interestingly, the role played by direct exchange interaction between the Ni 3d and Rh 4d states in stabilising the magnetic interaction is less significant. The present results shed light on the generic features exhibited by isostructural compounds and may help in identifying the magnetic exchange pathways useful for understanding the unusual properties exhibited by such compounds.

  3. THz polariton laser using an intracavity Mg:LiNbO3sub> crystal with protective Teflon coating.


    Ortega, Tiago A; Pask, Helen M; Spence, David J; Lee, Andrew J


    An enhancement in the performance of a THz polariton laser based on an intracavity magnesium-doped lithium niobate crystal (Mg:LiNbO3sub>) in surface-emitted (SE) configuration is demonstrated resulting from the deposition of a protective Teflon coating on the total internal reflection surface of the crystal. In this cavity geometry the resonating fields undergo total internal reflection (TIR) inside the lithium niobate, and laser damage to that surface can be a limiting factor in performance. The protective layer prevents laser damage to the crystal surface, enabling higher pump power, yielding higher THz output power and wider frequency tuning range. With the unprotected crystal, narrow-band THz output tunable from 1.50 to 2.81 THz was produced, with maximum average output power of 20.1 µW at 1.76 THz for 4 W diode pump power (limited by laser damage to the crystal). With the Teflon coating, no laser damage to the crystal was observed, and the system produced narrow-band THz output tunable from 1.46 to 3.84 THz, with maximum average output power of 56.8 µW at 1.76 THz for 6.5 W diode pump power. This is the highest average output power and the highest diode-to-terahertz conversion efficiency ever reported for an intracavity terahertz polariton laser.

  4. 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.

  5. Enhanced metallic properties of SrRuO3sub> thin films via kinetically controlled pulsed laser epitaxy

    SciTech Connect

    Thompson, J.; Nichols, John A.; Lee, Shinbuhm; Ryee, S.; Gruenewald, J. H.; Connell, J. G.; Souri, M.; Johnson, J. M.; Hwang, J.; Han, M. J.; Lee, Ho Nyung; Kim, D. -W.; Seo, Sung Seok A.


    Metal electrodes are a universal element of all electronic devices. Conducting SrRuO3sub> (SRO) epitaxial thin films have been extensively used as electrodes in complex-oxide heterostructures due to good lattice mismatches with perovskite substrates. However, when compared to SRO single crystals, SRO thin films have shown reduced conductivity and Curie temperatures (TC), which can lead to higher Joule heating and energy loss in the devices. In this paper, we report that high-quality SRO thin films can be synthesized by controlling the plume dynamics and growth rate of pulsed laser epitaxy (PLE) with real-time optical spectroscopic monitoring. The SRO thin films grown under the kinetically controlled conditions, down to ca. 16 nm in thickness, exhibit both enhanced conductivity and TC as compared to bulk values, due to their improved stoichiometry and a strain-mediated increase of the bandwidth of Ru 4d electrons. Finally, this result provides a direction for enhancing the physical properties of PLE-grown thin films and paves a way to improved device applications.

  6. Relating electronic and geometric structure of atomic layer deposited BaTiO3sub> to its electrical properties

    SciTech Connect

    Torgersen, Jan; Acharya, Shinjita; Dadlani, Anup Lal; Petousis, Ioannis; Kim, Yongmin; Trejo, Orlando; Nordlund, Dennis; Prinz, Fritz B.


    Atomic layer deposition allows the fabrication of BaTiO3sub> (BTO) ultrathin films with tunable dielectric properties, which is a promising material for electronic and optical technology. Industrial applicability necessitates a better understanding of their atomic structure and corresponding properties. Through the use of element-specific X-ray absorption near edge structure (XANES) analysis, O K-edge of BTO as a function of cation composition and underlying substrate (RuO2 and SiO2) is revealed. By employing density functional theory and multiple scattering simulations, we analyze the distortions in BTO’s bonding environment captured by the XANES spectra. The spectral weight shifts to lower energy with increasing Ti content and provides an atomic scale (microscopic) explanation for the increase in leakage current density. Differences in film morphologies in the first few layers near substrate–film interfaces reveal BTO’s homogeneous growth on RuO2 and its distorted growth on SiO2. As a result, this work links structural changes to BTO thin-film properties and provides insight necessary for optimizing future BTO and other ternary metal oxide-based thin-film devices.

  7. 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.

  8. 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.

  9. Single-Crystalline SrRuO3sub> Nanomembranes: A Platform for Flexible Oxide Electronics

    SciTech Connect

    Paskiewicz, Deborah M.; Sichel-Tissot, Rebecca; Karapetrova, Evguenia; Stan, Liliana; Fong, Dillon D.


    The field of oxide electronics has benefited from the wide spectrum of functionalities available to the ABO3sub> perovskites, and researchers are now employing defect engineering in single crystalline heterostructures to tailor properties. However, bulk oxide single crystals are not conducive to many types of applications, particularly those requiring mechanical flexibility. Here, we demonstrate the realization of an all-oxide, single-crystalline nanomembrane heterostructure. With a surface-to-volume ratio of 2 × 107 , the nanomembranes are fully flexible and can be readily transferred to other materials for handling purposes or for new materials integration schemes. Using in situ synchrotron X-ray scattering, we find that the nanomembranes can bond to other host substrates near room temperature and demonstrate coupling between surface reactivity and electromechanical properties in ferroelectric nanomembrane systems. Finally, the synthesis technique described here represents a significant advancement in materials integration and provides a new platform for the development of flexible oxide electronics.

  10. Finite-element analysis of transverse compressive and thermal loads on Nb3sub>Sn wires with voids

    SciTech Connect

    Zhai, Y.; D'Hauthuille, L.; Barth, C.; Senatore, C.


    High-field superconducting magnets play a very important role in many large-scale physics experiments, particularly particle colliders and fusion confinement devices such as Large Hadron Collider (LHC) and International Thermonuclear Experimental Reactor (ITER). The two most common superconductors used in these applications are NbTi and Nb3sub>Sn. Nb3sub>Sn wires are favored because of their significantly higher Jc (critical current density) for higher field applications. The main disadvantage of Nb3sub>Sn is that the superconducting performance of the wire is highly strain sensitive and it is very brittle. This strain sensitivity is strongly influenced by two factors: plasticity and cracked filaments. Cracks are induced by large stress concentrators that can be traced to the presence of voids in the wire. We develop detailed 2-D and 3-D finite-element models containing wire filaments and different possible distributions of voids in a bronze-route Nb3sub>Sn wire. We apply compressive transverse loads for various cases of void distributions to simulate the stress and strain response of a Nb3sub>Sn wire under the Lorentz force. Furthermore, this paper improves our understanding of the effect voids have on the Nb3sub>Sn wire's mechanical properties, and in so, the connection between the distribution of voids and performance degradation such as the correlation between irreversible strain limit and the void-induced local stress concentrations.

  11. Structure and thermodynamic stability of UTa3sub>O10, aU(v)-bearing compound

    SciTech Connect

    Guo, Xiaofeng; Lipp, Christian; Tiferet, Eitan; Lanzirotti, Antonio; Newville, Matthew; Engelhard, Mark H.; Wu, Di; Ilton, Eugene S.; Sutton, Stephen R.; Xu, Hongwu; Burns, Peter C.; Navrotsky, Alexandra


    Heating a mixture of uranyl(VI) nitrate and tantalum(V) oxide in the molar ratio of 2 : 3 to 1400 °C resulted in the formation of a new compound, UTa3sub>O10. The honey colored to yellow brown crystals of UTa3sub>O10 crystallize in an orthorhombic structure with the space group Fddd (no. 70), lattice parameters a = 7.3947(1), b = 12.7599(2), c = 15.8156(2) Å, and Z = 8. Vertex sharing [TaO6]7– octahedra of two crystallographically distinct Ta cations form a three dimensional tantalate framework. Within this framework, six membered rings of [TaO6]7– octahedra are formed within the (001) plane. The center of these rings is occupied by the uranyl cations [UO2]+, with an oxidation state of +5 for uranium. The pentavalence of U and Ta was confirmed by X-ray photoelectron spectroscopy and X-ray adsorption spectroscopy. The enthalpy of formation of UTa3sub>O10 from Ta2O5, β-U3sub>O7, and U3O8 has been determined to be 13.1 ± 18.1 kJ mol–1 using high temperature oxide melt solution calorimetry with sodium molybdate as the solvent at 700 °C. As a result, the close to zero enthalpy of formation of UTa3sub>O10 can be explained by closely balanced structural stabilizing and destabilizing factors, which may also apply to other UM3sub>O10 compounds.

  12. 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.

  13. 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.

  14. 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.

  15. Theory of Hydride-Proton Transfer (HPT) Carbonyl Reduction by [OsIII(tpy)(Cl)(NH=CHCH3sub>)(NSAr)

    SciTech Connect

    Ess, Daniel H.; Schauer, Cynthia; Meyer, Thomas J.


    Quantum mechanical analysis reveals that carbonyl reduction of aldehydes and ketones by the imine-based reductant cis-[OsIII(tpy)(Cl)(NH=CHCH3sub>)(NSAr)] (2), which is accessible by reduction of the analogous nitrile, occurs by hydride-proton transfer (HPT) involving both the imine and sulfilimido ligands. In carbonyl reduction, water or alcohol is necessary to significantly lower the barrier for proton shuttling between ligands. The -N(H)SAr group activates the carbonyl group through hydrogen bonding while the -NC(H)CH3sub> ligand delivers the hydride.

  16. 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.

  17. Influence of Mg2+ on CaCO3sub> precipitation during subsurface reactive transport in a homogeneous silicon-etched pore network

    SciTech Connect

    Boyd, Victoria; Yoon, Hongkyu; Zhang, Changyong; Oostrom, Martinus; Hess, Nancy J.; Fouke, Bruce W.; Valocchi, Albert J.; Werth, Charles J.


    Calcium carbonate (CaCO3sub>) geochemical reactions exert a fundamental control on the evolution of porosity and permeability in shallow-to-deep subsurface siliciclastic and limestone rock reservoirs. As a result, these carbonate water-rock interactions play a critically important role in research on groundwater remediation, geological carbon sequestration, and hydrocarbon exploration. A study was undertaken to determine the effects of Mg2+ concentration on CaCO3sub> crystal morphology, precipitation rate, and porosity occlusion under flow and mixing conditions similar to those in subsurface aquifers.

  18. 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.

  19. Mesoporous xEr2O3sub>·CoTiO3sub> composite oxide catalysts for low temperature dehydrogenation of ethylbenzene to styrene using CO2 as a soft oxidant

    SciTech Connect

    Yue, Yanfeng; Zhang, Li; Chen, Jihua; Hensley, Dale K.; Dai, Sheng; Overbury, Steven H.


    A series of mesoporous xEr2O3sub>·CoTiO3sub> composite oxide catalysts have been prepared using template method and tested as a new type of catalyst for the oxidative dehydrogenation of ethylbenzene to styrene by using CO2 as a soft oxidant. Among the catalysts tested, the 0.25Er2O3sub> CoTiO3sub> sample with a ratio of 1:4:4 content and calcined at 600 oC exhibited the highest ethylbenzene conversion (58%) and remarkable styrene selectivity (95%) at low temperature (450 °C).

  20. Kinetic modeling and transient DRIFTS–MS studies of CO2 methanation over Ru/Al2O3sub> catalysts

    SciTech Connect

    Wang, Xiang; Hong, Yongchun; Shi, Hui; Szanyi, János


    CO2 methanation was investigated on 5% and 0.5% Ru/Al2O3sub> catalysts (Ru dispersions: ~18% and ~40%, respectively) by steady-state kinetic measurements and transient DRIFTS–MS. Methanation rates were higher over 5% Ru/Al2O3sub> than over 0.5% Ru/Al2O3sub>. The measured activation energies, however, were lower on 0.5% Ru/Al2O3sub> than on 5% Ru/Al2O3sub>. Transient DRIFTS–MS results demonstrated that direct CO2 dissociation was negligible over Ru. CO2 has to first react with surface hydroxyls on Al2O3sub> to form bicarbonates, which, in turn, react with adsorbed H on Ru to produce adsorbed formate species. Formates, most likely at the metal/oxide interface, can react rapidly with adsorbed H forming adsorbed CO, only a portion of which is reactive toward adsorbed H, ultimately leading to CH4 formation. The measured kinetics are fully consistent with a Langmuir–Hinshelwood type mechanism in which the H-assisted dissociation of the reactive CO* is the rate-determining step (RDS). The similar empirical rate expressions (rCH4 = kP$0.1\\atop{CO2}$P$0.3-0.5\\atop{H2}$) and DRIFTS–MS results on the two catalysts under both transient and steady-state conditions suggest that the mechanism for CO2 methanation does not change with Ru particle size under the studied experimental conditions. Kinetic modeling results further indicate that the intrinsic activation barrier for the RDS is slightly lower on 0.5% Ru/Al2O3sub> than on 5% Ru/Al2O3sub>. Due to the presence of unreactive adsorbed CO under reaction conditions, the larger fraction of such surface sites that bind CO too strongly on 0.5% Ru/Al2O3sub> than on 5% Ru/Al2O3sub>, as revealed by FTIR measurements, is regarded as the main reason for the lower rates for CO2

  1. 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.

  2. Pressure induced elastic softening in framework aluminosilicate- albite (NaAlSi3sub>O8)

    SciTech Connect

    Mookherjee, Mainak; Mainprice, David; Maheshwari, Ketan; Heinonen, Olle; Patel, Dhenu; Hariharan, Anant


    Albite (NaAlSi3sub>O8) is an aluminosilicate mineral. Its crystal structure consists of 3-D framework of Al and Si tetrahedral units. We have used Density Functional Theory to investigate the high-pressure behavior of the crystal structure and how it affects the elasticity of albite. Our results indicate elastic softening between 6–8 GPa. This is observed in all the individual elastic stiffness components. Our analysis indicates that the softening is due to the response of the three-dimensional tetrahedral framework, in particular by the pressure dependent changes in the tetrahedral tilts. At pressure <6 GPa, the PAW-GGA can be described by a Birch-Murnaghan equation of state with VGGA0 = 687.4Å3, KGGA0 = 51.7 GPa, and GGGA0 = 4.7. The shear modulus and its pressure derivative are K⊕GGA0 = 33.7 GPa, and G⊕GGA0 = 2.9. At 1 bar, the azimuthal compressional and shear wave anisotropy AVGGAP = 42.8%, and AVGGAS = 50.1%. We also investigate the densification of albite to a mixture of jadeite and quartz. The transformation is likely to cause a discontinuity in density, compressional, and shear wave velocity across the crust and mantle. Furthermore, this could partially account for the Mohorovicic discontinuity in thickened continental crustal regions.

  3. Ultrahigh sensitivity of anomalous Hall effect sensor based on Cr-doped Bi2Te3sub> topological insulator thin films

    SciTech Connect

    Ni, Y.; Zhang, Z.; Nlebedim, I. C.; Jiles, D. C.


    Anomalous Hall effect (AHE) was recently discovered in magnetic element-doped topological insulators (TIs), which promises low power consumption and high efficiency spintronics and electronics. This discovery broadens the family of Hall sensors. In this paper, AHE sensors based on Cr-doped Bi2Te3sub> topological insulator thin films are studied with two thicknesses (15 and 65 nm). It is found, in both cases, that ultrahigh Hall sensitivity can be obtained in Cr-doped Bi2Te3sub>. Hall sensitivity reaches 1666 Ω/T in the sensor with the 15 nm TI thin film, which is higher than that of the conventional semiconductor HE sensor. The AHE of 65 nm sensors is even stronger, which causes the sensitivity increasing to 2620 Ω/T. Furthermore, after comparing Cr-doped Bi2Te3sub> with the previously studied Mn-doped Bi2Te3sub> TI Hall sensor, the sensitivity of the present AHE sensor shows about 60 times higher in 65 nm sensors. Furthermore, the implementation of AHE sensors based on a magnetic-doped TI thin film indicates that the TIs are good candidates for ultrasensitive AHE sensors.

  4. Absence of Significant Structural Changes Near the Magnetic Ordering Temperature in Small-ion Rare Earth Perovskite RMnO3sub>

    SciTech Connect

    Yu, T.; Ty, T.; Chen, H.; Abeykoon, A. M. M.; Chen, Y. -S.; Ahn, K. H.


    The detailed structural measurements on multiple length scales were conducted on a new perovskite phase of ScMnO3sub>, and on orthorhombic LuMnO3sub> as a benchmark. Complementary density functional theory (DFT) calculations were carried out, and predict that ScMnO3sub> possesses E-phase magnetic order at low temperature with displacements of the Mn sites (relative to the high temperature state) of ~0.07 Å, compared to ~0.04 Å predicted for LuMnO3sub>. However, detailed local, intermediate and long-range structural measurements by x-ray pair distribution function analysis, single crystal x-ray diffraction and x-ray absorption spectroscopy, find no local or long-range distortions on crossing into the low temperature E-phase of the magnetically ordered state. Our measurements place upper limits on any structural changes to be at most one order of magnitude lower than DFT predictions and suggest that this theoretical approach does not properly account for the spin–lattice coupling in these oxides and may possibly predict the incorrect magnetic order at low temperatures. The results suggest that the electronic contribution to the electrical polarization dominates and should be more accurately treated in theoretical models.

  5. The role of double TiO2 layers at the interface of FeSe/SrTiO3sub> superconductors

    SciTech Connect

    Zou, Ke; Bozovic, Ian; Mandal, Subhasish; Albright, Stephen; Peng, Rui; Kumah, Divine; Simon, Georg; Dagdeviren, Omur; He, Xi; Schwarz, Udo; Altman, Eric; Feng, Donglai; Walker, F. J.; Ismail-Geigi, Sohrab; Ahn, C. H.


    We determine the surface reconstruction of SrTiO3sub> used to achieve superconducting FeSe films in experiments, which is different from the 1×1 TiO2-terminated SrTiO3sub> assumed by most previous theoretical studies. In particular, we identify the existence of a double TiO2 layer at the FeSe/SrTiO3sub> interface that plays two important roles. First, it facilitates the epitaxial growth of FeSe. Second, ab initio calculations reveal a strong tendency for electrons to transfer from an oxygen deficient SrTiO3sub> surface to FeSe when the double TiO2 layer is present. The double layer helps to remove the hole pocket in the FeSe at the Γ point of the Brillouin zone and leads to a band structure characteristic of superconducting samples. The characterization of the interface structure presented here is a key step towards the resolution of many open questions about this superconductor.

  6. 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.

  7. Perovskite nanoparticle-sensitized Ga2O3sub> nanorod arrays for CO detection at high temperature

    SciTech Connect

    Lin, Hui -Jan; Baltrus, John P.; Gao, Haiyong; Ding, Yong; Nam, Chang -Yong; Ohodnicki, Paul; Gao, Pu -Xian


    Here, noble metal nanoparticles are extensively used for sensitizing metal oxide chemical sensors through the catalytic spillover mechanism. However, due to earth-scarcity and high cost of noble metals, finding replacements presents a great economic benefit. Besides, high temperature and harsh environment sensor applications demand material stability under conditions approaching thermal and chemical stability limits of noble metals. In this study, we employed thermally stable perovskite-type La0.8Sr0.2FeO3sub> (LSFO) nanoparticle surface decoration on Ga2O3sub> nanorod array gas sensors and discovered an order of magnitude enhanced sensitivity to carbon monoxide at 500 °C. The LSFO nanoparticle catalysts was of comparable performance to that achieved by Pt nanoparticles, with a much lower weight loading than Pt. Detailed electron microscopy and X-ray photoelectron spectroscopy studies suggested the LSFO nanoparticle sensitization effect is attributed to a spillover-like effect associated with the gas-LSFO-Ga2O3sub> triple-interfaces that spread the negatively charged surface oxygen ions from LSFO nanoparticles surfaces over to β-Ga2O3sub> nanorod surfaces with faster surface CO oxidation reactions.

  8. Synthesis, some properties, and structure of (Ln(NO/sub 3/)/sub 2/(HMPA)/sub 4/)C(CN)/sub 3/

    SciTech Connect

    Skopenko, V.V.; Kapshuk, A.A.


    A number of coordination compounds with the formula (Ln(NO/sub 3/)/sub 2/(HMPA)/sub 4/)C(CN)/sub 3/, where Ln = Ce through Sm, Gd, Yb, and HMPA stands for OP(NMe/sub 2/)/sub 3/, have been isolated from nonaqueous media. The individuality of the complexes obtained has been confirmed by x-ray diffraction analysis. The type of coordination of the ligands has been established, and conclusions regarding the structure of the complexes have been drawn on the basis of IR-spectroscopic data. An x-ray structural investigation (diffractometer, Mo k..cap alpha.. radiation) of the samarium complex (Sm(NO/sub 3/)/sub 2/(HMPA)/sub 4/)C(CN)/sub 3/ has been carried out. The structure has been refined by the least-square method in the isotropic-anisotropic approximation to R = 0.058. The structural elements of (Sm(NO/sub 3/)/sub 2/(HMPA)/sub 4/)C(CN)/sub 3/ are the complex (Sm(NO/sub 3/)/sub 2/(HMPA)/sub 4/)/sup +/ cation and the C(CN)/sub 3//sup -/ anion, which are located on second-order axes. The coordination number of samarium is equal to 8. The coordination polyhedron is a distorted Hoard dodecahedron.

  9. 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.

  10. 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.

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

    SciTech Connect

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


    In two series of magnetite (Fe3sub>O4) composite electrodes, one group with and one group without added carbon, containing varying quantities of polypyrrole (PPy), and a non-conductive polyvinylidene difluoride (PVDF) binder were constructed and then analyzed using electrochemical and spectroscopic techniques. Galvanostatic cycling and alternating current (AC) impedance measurements were used in tandem to measure delivered capacity, capacity retention, and the related impedance at various stages of discharge and charge. Further, the reversibility of Fe3sub>O4 to iron metal (Fe0) conversion observed during discharge was quantitatively assessed ex-situ using X-ray Absorption Spectroscopy (XAS). The Fe3sub>O4 composite containing the largest weight fraction of PPy (20 wt%) with added carbon demonstrated reduced irreversible capacity on initial cycles and improved cycling stability over 50 cycles, attributed to decreased reaction with the electrolyte in the presence of PPy. Our study illustrated the beneficial role of PPy addition to Fe3sub>O4 based electrodes was not strongly related to improved electrical conductivity, but rather to improved ion transport related to the formation of a more favorable surface electrolyte interphase (SEI).

  12. Local and average structures of BaTiO3sub>-Bi(Zn1/2Ti1/2)O3sub>

    SciTech Connect

    Usher, Tedi-Marie; Iamsasri, Thanakorn; Forrester, Jennifer S.; Raengthon, Natthaphon; Triamnak, Narit; Cann, David P.; Jones, Jacob L.


    The complex crystallographic structures of (1-x)BaTiO3-xBi(Zn1/2Ti1/2)O3sub> (BT-xBZT) are examined using high resolution synchrotron X-ray diffraction, neutron diffraction, and neutron pair distribution function (PDF) analyses. The short-range structures are characterized from the PDFs, and a combined analysis of the X-ray and neutron diffraction patterns is used to determine the long-range structures. Our results demonstrate that the structure appears different when averaged over different length scales. In all compositions, the local structures determined from the PDFs show local tetragonal distortions (i.e., c/a > 1). But, a box-car fitting analysis of the PDFs reveals variations at different length scales. For 0.80BT-0.20BZT and 0.90BT-0.10BZT, the tetragonal distortions decrease at longer atom-atom distances (e.g., 30 vs. 5 ). When the longest distances are evaluated (r > 40 ), the lattice parameters approach cubic. Neutron and X-ray diffraction yield further information about the long-range structure. Compositions 0.80BT-0.20BZT and 0.90BT-0.10BZT appear cubic by Bragg diffraction (no peak splitting), consistent with the PDFs at long distances. However, these patterns cannot be adequately fit using a cubic lattice model; modeling their structures with the P4mm space group allows for a better fit to the patterns because the space group allows for c-axis atomic displacements that occur at the local scale. Furthermore, for the compositions 0.92BT-0.08BZT and 0.94BT-0.06BZT, strong tetragonal distortions are observed at the local scale and a less-distorted tetragonal structure is observed at longer length scales. In Rietveld refinements, the latter is modeled using a tetragonal phase. Since the peak overlap in these two-phase compositions limits the ability to model the local-scale structures as tetragonal, it is approximated in the refinements as a cubic phase. These results demonstrate that alloying BT with BZT results

  13. 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; 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

  14. Deuteron irradiation of W and WO3sub> for production of high specific activity 186Re: Challenges associated with thick target preparation

    SciTech Connect

    Balkin, Ethan R.; Gagnon, Katherine; Strong, Kevin T.; Smith, Bennett E.; Dorman, Eric F.; Emery, Robert C.; Pauzauskie, Peter J.; Fassbender, Michael E.; Cutler, Cathy S.; Ketring, Alan R.; Jurisson, Silvia S.; Wilbur, D. Scott


    This investigation evaluated target fabrication and beam parameters for scale-up production of high specific activity 186Re using deuteron irradiation of enriched 186W via the 186W(d,2n)186Re reaction. Thick W and WO3sub> targets were prepared, characterized and evaluated in deuteron irradiations. Full-thickness targets, as determined using SRIM, were prepared by uniaxi-ally pressing powdered natural abundance W and WO3sub>, or 96.86% enriched 186W, into Al target supports. Alternatively, thick targets were prepared by pressing 186W between two layers of graphite powder or by placing pre-sintered (1105°C, 12 hours) natural abundance WO3sub> pellets into an Al target support. Assessments of structural integrity were made on each target pre-pared. Prior to irradiation, material composition analyses were conducted using SEM, XRD, and Raman spectroscopy. With-in a minimum of 24 hours post irradiation, gamma-ray spectroscopy was performed on all targets to assess production yields and radionuclidic byproducts. Problems were encountered with the structural integrity of some pressed W and WO3sub> pellets before and during irradiation, and target material characterization results could be correlated with the structural integrity of the pressed target pellets. Under the conditions studied, the findings suggest that all WO3sub> targets prepared and studied were unacceptable. By contrast, 186W metal was found to be a viable target material for 186Re production. Lastly, thick targets prepared with powdered 186W pressed between layers of graphite provided a particularly robust target configuration.

  15. Capacitance of Ti3sub>C2Tx MXene in Ionic Liquid Electrolyte

    SciTech Connect

    Lin, Zifeng; Barbara, Daffos; Taberna, Pierre-Louis; Van Aken, Katherine; Anasori, Babak; Gogotsi, Yury G.; Simon, Patrice


    Ti3sub>C2Tx MXene, a two-dimensional (2D) early transition metal carbide, has shown an extremely high volumetric capacitance in aqueous electrolytes, but in a narrow voltage window (less than 1.23 V). The utilization of MXene materials in ionic liquid electrolytes with a large voltage window has never been addressed. Here, we report the preparation of the Ti3sub>C2Tx MXene ionogel film by vacuum filtration for use as supercapacitor electrodes operating in 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI) neat ionic liquid electrolyte. Due to the disordered structure of the Ti3sub>C2Tx hydrogel film and a stable spacing after vacuum drying, achieved through ionic liquid electrolyte immersion of the Ti3sub>C2Tx hydrogel film, the Ti3sub>C2Tx surface became accessible to EMI+ and TFSI- ions. A capacitance of 70 F g-1 together with a large voltage window of 3 V was obtained at a scan rate of 20 mV s-1 in neat EMI-TFSI electrolyte. The electrochemical signature indicates a capacitive behavior even at a high scan rate (500 mV s-1) and a high power performance. This work opens up the possibilities of using MXene materials with various ionic liquid electrolytes.

  16. W:Al2O3sub> nanocomposite thin films with tunable optical properties prepared by atomic layer deposition

    SciTech Connect

    Babar, Shaista; Mane, Anil U.; Yanguas-Gil, Angel; Mohimi, Elham; Haasch, Richard T.; Elam, Jeffrey W.


    Here, a systematic alteration in the optical properties of W:Al2O3sub> nanocomposite films is demonstrated by precisely varying the W cycle percentage (W%) from 0 to 100% in Al2O3sub> during atomic layer deposition. The direct and indirect band energies of the nanocomposite materials decrease from 5.2 to 4.2 eV and from 3.3 to 1.8 eV, respectively, by increasing the W% from 10 to 40. X-ray absorption spectroscopy reveals that, for W% < 50, W is present in both metallic and suboxide states, whereas, for W% ≥ 50, only metallic W is seen. This transition from dielectric to metallic character at W% ~ 50 is accompanied by an increase in the electrical and thermal conductivity and the disappearance of a clear band gap in the absorption spectrum. The density of the films increases monotonically from 3.1 g/cm3 for pure Al2O3sub> to 17.1 g/cm3 for pure W, whereas the surface roughness is greatest for the W% = 50 films. The W:Al2O3sub> nanocomposite films are thermally stable and show little change in optical properties upon annealing in air at 500 °C. These W:Al2O3sub> nanocomposite films show promise as selective solar absorption coatings for concentrated solar power applications.

  17. Instability and efficiency of mixed halide perovskites CH3sub>NH3sub>AI3-xClx (A = Pb and Sn): A first-principles, computational study

    SciTech Connect

    He, Yuping; Galli, Giulia


    Here, we carried out calculations based on density functional theory to investigate the electronic, vibrational, and dielectric properties of mixed halide perovskites CH3sub>NH3sub>AI3–xClx with A = Pb and Sn. Computed free energies indicated that Cl mixed systems may be formed only for Cl concentrations not exceeding 1019 cm–3, and phonon calculations showed that the disorder induced in the host lattice by the presence of a smaller halogen is responsible for mechanical instabilities. However, we found that the presence of chloride may be beneficial to the electronic properties of the perovskites. Chloride anions cause the organic cations to be displaced from the center of the cage; such a displacement induces preferential orientations of the cation dipole, which in turn are responsible for notable changes in the dielectric properties of the material and possibly for the formation of local ferroelectric domains. The latter are instrumental in separating electron hole pairs and hence in contributing to long charge-carrier diffusion lengths, in spite of polarons being more likely formed in mixed perovksites than in CH3sub>NH3sub>AI3sub>.

  18. Molecular and electronic structure of Re2Br4(PMe3sub>)4

    SciTech Connect

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


    The dinuclear rhenium(II) complex Re2Br4(PMe3sub>)4 was prepared from the reduction of [Re2Br8]2– with (n-Bu4N)BH4 in the presence of PMe3sub> in propanol. The complex was characterized by single-crystal X-ray diffraction (SCXRD) and UV–visible spectroscopy. It crystallizes in the monoclinic C2/c space group and is isostructural with its molybdenum and technetium analogues. The Re–Re distance (2.2521(3) Å) is slightly longer than the one in Re2Cl4(PMe3sub>)4 (2.247(1) Å). The molecular and electronic structure of Re2X4(PMe3sub>)4 (X = Cl, Br) were studied by multiconfigurational quantum chemical methods. The computed ground-state geometry is in excellent agreement with the experimental structure determined by SCXRD. The calculated total bond order (2.75) is consistent with the presence of an electron-rich triple bond and is similar to the one found for Re2Cl4(PMe3sub>)4. The electronic absorption spectrum of Re2Br4(PMe3sub>)4 was recorded in benzene and shows a series of low-intensity bands in the range 10 000–26 000 cm–1. The absorption bands were assigned based on calculations of the excitation energies with the multireference wave functions followed by second-order perturbation theory using the CASSCF/CASPT2 method. As a result, calculations predict that the lowest energy band corresponds to the δ* → σ* transition, while the next higher energy bands were attributed to the δ* → π*, δ → σ*, and δ → π* transitions.

  19. Cs{sub 7}Sm{sub 11}[TeO{sub 3}]{sub 12}Cl{sub 16} and Rb{sub 7}Nd{sub 11}[TeO{sub 3}]{sub 12}Br{sub 16}, the new tellurite halides of the tetragonal Rb{sub 6}LiNd{sub 11}[SeO{sub 3}]{sub 12}Cl{sub 16} structure type

    SciTech Connect

    Charkin, Dmitri O.; Black, Cameron; Downie, Lewis J.; Sklovsky, Dmitry E.; Berdonosov, Peter S.; Olenev, Andrei V.; Zhou, Wuzong; Lightfoot, Philip; Dolgikh, Valery A.


    Two new rare-earth – alkali – tellurium oxide halides were synthesized by a salt flux technique and characterized by single-crystal X-ray diffraction. The structures of the new compounds Cs{sub 7}Sm{sub 11}[TeO{sub 3}]{sub 12}Cl{sub 16} (I) and Rb{sub 7}Nd{sub 11}[TeO{sub 3}]{sub 12}Br{sub 16} (II) (both tetragonal, space group I4/mcm) correspond to the sequence of [MLn{sub 11}(TeO{sub 3}){sub 12}] and [M{sub 6}X{sub 16}] layers and bear very strong similarities to those of known selenite analogs. We discuss the trends in similarities and differences in compositions and structural details between the Se and Te compounds; more members of the family are predicted. - Graphical abstract: Two new rare-earth – alkali – tellurium oxide halides were predicted and synthesized. - Highlights: • Two new rare-earth – alkali – tellurium oxide halides were synthesized. • They adopt slab structure of rare earth-tellurium-oxygen and CsCl-like slabs. • The Br-based CsCl-like slabs have been observed first in this layered family.

  20. 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.

  1. 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.

  2. 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.

  3. Saturable absorption in one-dimensional Sb2Se3sub> nanowires in the visible to near-infrared region.


    Yadav, Rajesh Kumar; Sharma, Rituraj; Aneesh, J; Abhiramnath, P; Adarsh, K V


    One-dimensional (1D) free-standing nanowires are particularly important for carrier confinement in two dimensions, which provides a platform to explore the nonlinear optical phenomena at the nanoscale. In this Letter, we demonstrate saturable absorption in the resonant and above-bandgap excitations of both ns and fs pulses in 1D crystalline Sb2Se3sub> nanowires prepared by the facile hydrothermal method. Impressively, the average length of the nanowires extends to a few micrometers with a high aspect ratio of 300. The excited-state to ground-state absorption cross-section ratio in Sb2Se3sub> nanowires is ≈0.23, which suggests that they can be utilized as passive mode lockers.

  4. 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.

  5. 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.

  6. Near-ultraviolet lateral photovoltaic effect in Fe3sub>O4/3C-SiC Schottky junctions.


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


    In this paper, we report a sensitive lateral photovoltaic effect (LPE) in Fe3sub>O4/3C-SiC Schottky junctions with a fast relaxation time at near-ultraviolet wavelengths. The rectifying behavior suggests that the large build-in electric field was formed in the Schottky junctions. This device has excellent position sensitivity as high as 67.8 mV mm-1 illuminated by a 405 nm laser. The optical relaxation time of the LPE is about 30 μs. The fast relaxation and high positional sensitivity of the LPE make the Fe3sub>O4/3C-SiC junction a promising candidate for a wide range of ultraviolet/near-ultraviolet optoelectronic applications.

  7. Investigation of SiO2-Al2O3sub> nanolaminates for protection of silver reflectors.


    Schwinde, S; Schürmann, M; Kaiser, N; Tünnermann, A


    H2S and particles from the atmosphere can damage silver reflectors. These defects lead to scattering and a reduction of reflectivity. With regard to these risks, the suitability of sputtered SiO2, Al2O3sub>, and SiO2-Al2O3sub> nanolaminates for the protection of Ag was analyzed. The optical properties, protection properties against H2S, solubility, film stress, and protection properties against particle-induced defect formation have been investigated. Especially in the case of particle-induced defects on protected Ag, differences between the protective coatings are considerable, and the nanolaminate layers have advantageous properties.

  8. Broadband sum-frequency generation using d33 in periodically poled LiNbO3sub> thin film in the telecommunications band.


    Li, Guangzhen; Chen, Yuping; Jiang, Haowei; Chen, Xianfeng


    We demonstrate the first, to the best of our knowledge, type-0 broadband sum-frequency generation (SFG) based on single-crystal periodically poled LiNbO3sub> (PPLN) thin film. The broad bandwidth property was largely tuned from mid-infrared region to the telecommunications band by engineering the thickness of PPLN from bulk crystal to nanoscale. It provides SFG a solution with both broadband and high efficiency by using the highest nonlinear coefficient d33 instead of d31 in type-I broadband SFG or second-harmonic generation. The measured 3 dB upconversion bandwidth is about 15.5 nm for a 4 cm long single crystal at 1530 nm wavelength. It can find applications in chip-scale spectroscopy, quantum information processing, LiNbO3sub>-thin-film-based microresonator and optical nonreciprocity devices, etc.

  9. Electronic structure of the chiral helimagnet and 3d-intercalated transition metal dichalcogenide Cr1/3sub>NbS2

    SciTech Connect

    Sirca, N.; Mo, S. -K.; Bondino, F.; Pis, I.; Nappini, S.; Vilmercati, P.; Yi, Jieyu; Gai, Zheng; Snijders, Paul C.; Das, P. K.; Vobornik, I.; Ghimire, N. J.; Koehler, Michael R.; Sopkota, D.; Parker, David S.; Mandrus, D. G.; Mannella, Norman


    The electronic structure of the chiral helimagnet Cr1/3sub>NbS2 has been studied with core level and angle-resolved photoemission spectroscopy (ARPES). Intercalated Cr atoms are found to be effective in donating electrons to the NbS2 layers but also cause significant modifications of the electronic structure of the host NbS2 material. Specifically, the data provide evidence that a description of the electronic structure of Cr1/3sub>NbS2 on the basis of a simple rigid band picture is untenable. The data also reveal substantial inconsistencies with the predictions of standard density functional theory. In conclusion, the relevance of these results to the attainment of a correct description of the electronic structure of chiral helimagnets, magnetic thin films/multilayers, and transition metal dichalcogenides intercalated with 3d magnetic elements is discussed.

  10. Enhanced superconductivity due to forward scattering in FeSe thin films on SrTiO3sub> substrates

    SciTech Connect

    Rademaker, Louk; Wang, Yan; Berlijn, Tom; Johnston, Steve


    In this paper, we study the consequences of an electron–phonon (e–ph) interaction that is strongly peaked in the forward scattering (${\\bf{q}}=0$) direction in a two-dimensional superconductor using Migdal–Eliashberg theory. We find that strong forward scattering results in an enhanced T c that is linearly proportional to the strength of the dimensionless e–ph coupling constant ${\\lambda }_{m}$ in the weak coupling limit. This interaction also produces distinct replica bands in the single-particle spectral function, similar to those observed in recent angle-resolved photoemission experiments on FeSe monolayers on SrTiO3sub> and BaTiO3sub> substrates. Finally, by comparing our model to photoemission experiments, we infer an e–ph coupling strength that can provide a significant portion of the observed high T c in these systems.

  11. 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.

  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. Highly Porous Zirconium Metal–Organic Frameworks with β-UH 3sub> -like Topology Based on Elongated Tetrahedral Linkers

    SciTech Connect

    Zhang, Xin; Zhang, Xu; Johnson, Jacob A.; Chen, Yu-Sheng; Zhang, Jian


    Two non-interpenetrated zirconium metal–organic frameworks (Zr-MOFs), NPF-200 and NPF-201, were synthesized via the assembly of elongated tetrahedral linkers with Zr6 and Zr8 clusters. They represent the first examples of MOFs to have the β-UH3sub>-like, 4,12,12T1 topology. Upon activation, NPF-200 exhibits the largest BET surface area (5463 m2 g–1) and void volume (81.6%) among all MOFs formed from tetrahedral ligands. Composed of negative-charged boron-centered tetrahedral linkers, NPF-201 is an anionic Zr-MOF which selectively uptakes photoactive [Ru(bpy)3sub>]2+ for heterogeneous photo-oxidation of thioanisole.

  14. 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.

  15. 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.

  16. Sagnac interferometer hydrogen sensor based on panda fiber with Pt-loaded WO3sub>/SiO2 coating.


    Xu, Ben; Zhao, C L; Yang, Fan; Gong, Huaping; Wang, D N; Dai, JiXiang; Yang, Minghong


    A highly sensitive optical fiber Sagnac interferometer hydrogen sensor is proposed and demonstrated. The device is fabricated by inserting a segment of panda fiber coated with Pt-loaded WO3sub>/SiO2 into a Sagnac interferometer loop. When Pt/WO3sub> film is exposed to hydrogen, the exothermic reaction raises the temperature of the panda fiber, resulting in the resonant wavelength shift of the interferometer, and the resonant dip obtained has a large extinction ratio of ∼25  dB and a narrow linewidth of 2.5 nm. Such a device responds fast to hydrogen, exhibits a high sensitivity of -7.877  nm/% (vol. %) within the range of 0%-1.0% and is robust, low cost, and easy to fabricate.

  17. 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.

  18. Nonlinear Luminescence Response of CaF2:Eu and YAlO3sub>:Ce to Single-Ion Excitation

    SciTech Connect

    Liu, Peng; Zhang, Yanwen; Xiao, Haiyan Y.; Xiang, Xia; Wang, Xuelin; Weber, William J.


    Understanding scintillation physics and nonproportionality is essential to accelerate materials discovery that has been restricted due to the difficulties inherent to large crystal growth and complex nature of gamma-solid interaction. Taking advantage of less restrictive growth and deposition techniques for smaller crystal sizes or thin films and better fundamental understanding of ion-solid interactions, a unique ion approach is demonstrated to effectively screen candidate scintillators with relatively small size and evaluate their nonlinear scintillation response. Response of CaF2:Eu and YAlO3sub>:Ce scintillators to single ions of Hþ, Heþ, and O3sub>þ are measured by the corresponding pulse height over a continuous energy range using a time-of-flight–scintillator–photoelectric multiplier tube apparatus. Nonlinear response of the scintillators under ionizing ion irradiation is quantitatively evaluated by considering the energy partitioning process. In a differential energy deposition region with negligible displacement damage, the low, medium and high excitation energy deposition density (Dexci) can be produced by energetic Hþ, Heþ and O3sub>þ ions, respectively, and significantly different impacts on the response characteristics of these two benchmark scintillators are observed. For CaF2:Eu, the scintillation efficiency under ion irradiation monotonically decreases with increasing excitation-energy density. In contrast, the response efficiency of YAlO3sub>:Ce scintillation initially increases with excitation-energy density at low excitation-energy densities, goes through a maximum, and then decreases with further increasing excitation-energy density. The fundamental mechanism causing these different response behaviours in the scintillators is based on the competition between the scintillation response and the nonradiative quenching process under different excitation densities, which is also the main

  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. 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.

  1. 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.

  2. 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.

  3. Synthesis of five- and six-coordinate alkylidene complexes of the type Mo(CHR)(NAr)[OCMe(CF[sub 3])[sub 2

    SciTech Connect

    Fox, H.H.; Lee, J.K.; Park, L.Y.; Schrock, R.R. )


    Addition of a slight excess of 4-methoxy-1-hexene to Mo(CHCMe[sub 2]Ph)(NAr)(OR[sub F6])[sub 2] (1a) or Mo(CHCMe[sub 3])(NAr)(OR[sub F6])[sub 2] (1b) in pentane (OR[sub F6] = OCMe(CF[sub 3])[sub 2]) yielded crystalline, red-orange anti-Mo[CHCH[sub 2]CH(OMe)CH[sub 2]CH[sub 3

  4. Oxidative Dehydrogenation of Cyclohexane on Cobalt Oxide (Co3sub>O4) Nanoparticles: The Effect of Particle Size on Activity and Selectivity

    SciTech Connect

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


    The oxidative dehydrogenation of cyclohexane by cobalt oxide nanoparticles was studied via temperature programmed reaction combined with in situ grazing incidence X-ray absorption spectroscopy and grazing incidence small-angle X-ray scattering and theoretical calculations on model Co3sub>O4 substrates. Both 6 and 12 nm Co3sub>O4 nanoparticles were made through a surfactant-free preparation and dispersed on an Al2O3sub> surface formed by atomic layer deposition. Under reaction conditions the nanoparticles retained their oxidation state and did not sinter. They instead underwent an assembly/disassembly process and could reorganize within their assemblies. The selectivity of the catalyst was found to be size- and temperature-dependent, with larger particles preferentially producing cyclohexene at lower temperatures and smaller particles predominantly resulting in benzene at higher temperatures. The mechanistic features thought to control the oxidative dehydrogenation of cyclohexane and other light alkanes on cobalt oxide were established by carrying out density functional theory calculations on the activation of propane, a surrogate model alkane, over model Co3sub>O4 surfaces. The initial activation of the alkane (propane) proceeds via hydrogen abstraction over surface oxygen sites. The subsequent activation of the resulting alkoxide intermediate occurs at a second surface oxygen site to form the alkene (propene) which then desorbs from the surface. Hydroxyl recombination results in the formation of water which desorbs from the surface. Finally, oxygen is necessary to regenerate the surface oxygen sites, catalyze C–H activation steps, and minimize catalyst degradation.

  5. 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.

  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. 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.

  8. First-principles approach to the dynamic magnetoelectric couplings for the non-reciprocal directional dichroism in BiFeO3sub>

    SciTech Connect

    Kezsmarki, I.; Fishman, Randy Scott


    Due to the complicated magnetic and crystallographic structures of BiFeO3sub>, its magnetoelectric (ME) couplings and microscopic model Hamiltonian remain poorly understood. By employing a firstprinciples approach, we uncover all possibleMEcouplings associated with the spin-current (SC) and exchange-striction (ES) polarizations, and construct an appropriate Hamiltonian for the long-range spin-cycloid in BiFeO3sub>. First-principles calculations are used to understand the microscopic origins of theMEcouplings.Wefind that inversion symmetries broken by ferroelectric and antiferroelectric distortions induce the SC and the ES polarizations, which cooperatively produce the dynamicME effects in BiFeO3sub>. A model motivated by first principles reproduces the absorption difference of counter-propagating light beams called non-reciprocal directional dichroism. The current paper focuses on the spin-driven (SD) polarizations produced by a dynamic electric field, i.e. the dynamic MEcouplings. Due to the inertial properties of Fe, the dynamic SD polarizations differ significantly from the static SD polarizations. Our systematic approach can be generally applied to any multiferroic material, laying the foundation for revealing hiddenMEcouplings on the atomic scale and for exploiting opticalMEeffects in the next generation of technological devices such as optical diodes.

  9. 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.

  10. 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.

  11. Structural and magnetic phase transitions in EuTi1-xNbxO3sub>

    SciTech Connect

    Li, Ling; Morris, James R.; Koehler, Michael R.; Dun, Zhiling; Zhou, Haidong; Yan, Jiaqiang; Mandrus, David; Keppens, Veerle


    Here, we investigate the structural and magnetic phase transitions in EuTi1-xNbxO3sub> (0≤x≤0.3) with synchrotron powder x-ray diffraction, resonant ultrasound spectroscopy, and magnetization measurements. Upon Nb doping, the Pm$\\bar{3}$m ↔ I4/mcm structural transition shifts to higher temperatures and the room temperature lattice parameter increases while the magnitude of the octahedral tilting decreases. In addition, Nb substitution for Ti destabilizes the antiferromagnetic ground state of the parent compound and long-range ferromagnetic order is observed in the samples with x≥0.1. Moreover, the structural transition in pure and doped compounds is marked by a dramatic step-like softening of the elastic moduli near TS, which resembles that of SrTiO3sub> and can be adequately modeled using the Landau free energy model employing the same coupling between strain and octahedral tilting order parameter as previously used to model SrTiO3sub>.

  12. High performance of a passively Q-switched mid-infrared laser with Bi2Te3sub>/graphene composite SA.


    You, Zhenyu; Sun, Yijian; Sun, Dunlu; Zhu, Zaojie; Wang, Yan; Li, Jianfu; Tu, Chaoyang; Xu, Jinlong


    We report passively Q-switched ∼2 and ∼3  μm mid-infrared (MIR) solid-state lasers with a self-assembly solvothermal-synthesized Bi2Te3sub>/graphene heterostructure saturable absorber (SA) for the first time. Based on the oxidation resistance and high thermal conductivity of graphene, and large modulation depth of Bi2Te3sub> nanosheets, two high-performance Q-switching lasers were realized. One is a Tm:YAP laser with a maximum average output power of 2.34 W and a pulse width of 238 ns at ∼2  μm. The corresponding maximum pulse peak power was 91 W, which was much improved in comparison with the pure graphene-based Tm laser. The other one is an Er:YSGG laser producing a pulse width of 243 ns, which is the shortest among the 2D SAs-based ∼3  μm solid-state lasers, as far as we know. Our results indicate that such a composite Bi2Te3sub>/graphene material is a promising SA for generating high-performance mid-infrared pulse lasers.

  13. 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.

  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. 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.

  16. Summary of the Persistent Current Effect Measurements in Nb 3sub> Sn and NbTi Accelerator Magnets at Fermilab

    SciTech Connect

    Velev, G. V.; Chlachidze, G.; DiMarco, J.; Stoynev, S. E.


    In the past 10 years, Fermilab has been executing an intensive R&D program on accelerator magnets based on Nb3sub>Sn superconductor technology. This R&D effort includes dipole and quadrupole models for different programs, such as LARP and 11 T dipoles for the LHC high-luminosity upgrade. Before the Nb3sub>Sn R&D program, Fermilab was involved in the production of the low-beta quadrupole magnets for LHC based on the NbTi superconductor. Additionally, during the 2003-2005 campaign to optimize the operation of the Tevatron, a large number of Tevatron magnets were re-measured. As a result of this field analysis, a systematic study of the persistent current decay and snapback effect in these magnets was performed. This paper summarizes the result of this study and presents a comparison between Nb3sub>Sn and NbTi dipoles and quadrupoles.

  17. Reaction mechanism studies towards effective fabrication of lithium-rich anti-perovskites Li3sub>OX (X=Cl, Br)

    SciTech Connect

    Li, Shuai; Zhu, Jinlong; Wang, Yonggang; Howard, John W.; Lü, Xujie; Li, Yutao; Kumar, Ravhi S.; Wang, Liping; Daemen, Luke L.; Zhao, Yusheng


    Lithium-rich Anti-perovskite (LiRAP), with general formula Li3sub>OX (X = Cl, Br, I), and recently reported as superionic conductors with 3-dimensional Li+ migrating channels, is emerging as a promising candidate for solid electrolyte of all-solid-state LIBs. But, it is still difficult to fabricate pure LiRAP due to the difficulty of the phase formation and moisture-sensitive nature of the products. In this work, we thoroughly studied the formation mechanism of Li3sub>OCl and Li3sub>OBr in various solid state reaction routes. We developed different experimental strategies in order to improve the syntheses, in purposes of improved phase stability and large-scale production of LiRAP. One feasible method is to use strongly reductive agents Li metal or LiH to eliminate OH species. The results show that LiH is more effective than Li metal because of negatively charged H- and uniform reaction. The other well-established method is using Li2O and LiX mixture as reagents to preventing OH phase at the beginning, and using protected ball milling to make fine powders and hence active the reaction. Finally, IR spectroscopy, thermal analyses and first-principle calculation were performed to give indications on the reaction pathway.

  18. Metallic behavior in the graphene analogue Ni3sub>(HITP)2 and a strategy to render the material a semiconductor.

    SciTech Connect

    Foster, Michael E.; Sohlberg, Karl; Spataru, Dan Catalin; Allendorf, Mark D.


    The metal organic framework material Ni3sub>(2,3,6,7,10,11 - hexaiminotriphenylene)2, (Ni3sub>(HITP)2) is composed of layers of extended conjugated planes analogous to graphene. We carried out Density functional theory (DFT) calculations to model the electronic structure of bulk and monolayer Ni3sub>(HITP)2. The layered 3D material is metallic, similar to graphene. Our calculations predict that there is appreciable band dispersion not only in-plane, but perpendicular to the stacking planes as well, suggesting that, unlike graphene, the conductivity may be nearly isotropic. In contrast, a 2D monolayer of the material exhibits a band gap, consistent with previously published results. Insight obtained from studies of the evolution of the material from semiconducting to metallic as the material is transitioned from 2D to 3D suggests the possibility of modifying the material to render it semiconducting by changing the metal center and inserting spacer moieties between the layers. Furthermore, the DFT calculations predict that the modified material will be structurally stable and exhibit a band gap.

  19. 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.

  20. 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.

  1. 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)

  2. 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.

  3. Boron Substituted Na 3sub> V 2 (P 1 -x B x O 4 ) 3sub> Cathode Materials with Enhanced Performance for Sodium-Ion Batteries

    SciTech Connect

    Hu, Pu; Wang, Xiaofang; Wang, Tianshi; Chen, Lanli; Ma, Jun; Kong, Qingyu; Shi, Siqi; Cui, Guanglei


    The development of excellent performance of Na-ion batteries remains great challenge owing to the poor stability and sluggish kinetics of cathode materials. Herein, B substituted Na3sub>V2P3–xBxO12 (0 ≤ x ≤ 1) as stable cathode materials for Na-ion battery is presented. A combined experimental and theoretical investigations on Na3sub>V2P3–xBxO12 (0 ≤ x ≤ 1) are undertaken to reveal the evolution of crystal and electronic structures and Na storage properties associated with various concentration of B. X-ray diffraction results indicate that the crystal structure of Na3sub>V2P3–xBxO12 (0 ≤ x ≤ 1/3) consisted of rhombohedral Na3sub>V2(PO4)3sub> with tiny shrinkage of crystal lattice. X-ray absorption spectra and the calculated crystal structures all suggest that the detailed local structural distortion of substituted materials originates from the slight reduction of V–O distances. Na3sub>V2P3-1/6B1/6O12 significantly enhances the structural stability and electrochemical performance, giving remarkable enhanced capacity of 100 and 70 mAh g-1 when the C-rate increases to 5 C and 10 C. Spin-polarized density functional theory (DFT) calculation reveals that, as compared with the pristine Na3sub>V2(PO4)3sub>, the superior electrochemical performance of the substituted materials can be attributed to the emergence of new boundary states near the band gap, lower Na+ diffusion energy barriers, and higher structure stability.

  4. 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

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

    SciTech Connect

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


    The electroactive orthophosphate Na2Co2Fe(PO4)(3)sub> was synthesized using a solid state reaction. Its crystal structure was solved using the combination of powder X-ray-and neutron-diffraction data. This material crystallizes according to the alluaudite structure (S.G. C2/c). The structure consists of edge sharing [MO6] octahedra (M = Fe, Co) resulting in chains parallel to [-101]. These chains are linked together via the [PO4] tetrahedra to form two distinct tunnels in which sodium cations are located. The electrochemical properties of Na2Co2Fe(PO4)(3) were evaluated by galvanostatic charge-discharge cycling. During the first discharge to 0.03 V, Na2Co2Fe(PO4)(3)sub> delivers a specific capacity of 604 mA h g(-1). This capacity is equivalent to the reaction of more than seven sodium ions per formula unit. Hence, this is a strong indication of a conversion-type reaction with the formation of metallic Fe and Co. The subsequent charge and discharge involved the reaction of fewer Na ions as expected for a conversion reaction. When discharged to 0.9 V, the material intercalated only one Na+-ion leading to the formation of a new phase Na3sub>Co2Fe(PO4)(3)sub>. This phase could then be cycled reversibly with an average voltage of 3.6 V vs. Na+/Na and a capacity of 110 mA h g(-1). This result is in good agreement with the theoretical capacity expected from the extraction/insertion of two sodium atoms in Na2Co2Fe(PO4)(3)sub>.

  6. Direct measurements of unimolecular and bimolecular reaction kinetics of the Criegee intermediate (CH3sub>)2COO

    SciTech Connect

    Chhantyal-Pun, Rabi; Welz, Oliver; Savee, John D.; Eskola, Arkke J.; Lee, Edmond P. F.; Blacker, Lucy; Hill, Henry R.; Ashcroft, Matilda; Khan, M. Anwar H.; Lloyd-Jones, Guy C.; Evans, Louise; Rotavera, Brandon; Huang, Haifeng; Osborn, David L.; Mok, Daniel K. W.; Dyke, John M.; Shallcross, Dudley E.; Percival, Carl J.; Orr-Ewing, Andrew J.; Taatjes, Craig A.


    Here, the Criegee intermediate acetone oxide, (CH3sub>)2COO, is formed by laser photolysis of 2,2-diiodopropane in the presence of O2 and characterized by synchrotron photoionization mass spectrometry and by cavity ring-down ultraviolet absorption spectroscopy. The rate coefficient of the reaction of the Criegee intermediate with SO2 was measured using photoionization mass spectrometry and pseudo-first-order methods to be (7.3 ± 0.5) × 10–11 cm3 s–1 at 298 K and 4 Torr and (1.5 ± 0.5) × 10–10 cm3 s–1 at 298 K and 10 Torr (He buffer). These values are similar to directly measured rate coefficients of anti-CH3sub>CHOO with SO2, and in good agreement with recent UV absorption measurements. The measurement of this reaction at 293 K and slightly higher pressures (between 10 and 100 Torr) in N2 from cavity ring-down decay of the ultraviolet absorption of (CH3sub>)2COO yielded even larger rate coefficients, in the range (1.84 ± 0.12) × 10–10 to (2.29 ± 0.08) × 10–10 cm3 s–1. Photoionization mass spectrometry measurements with deuterated acetone oxide at 4 Torr show an inverse deuterium kinetic isotope effect, kH/kD = (0.53 ± 0.06), for reactions with SO2, which may be consistent with recent suggestions that the formation of an association complex affects the rate coefficient. The reaction of (CD3)2COO with NO2 has a rate coefficient at 298 K and 4 Torr of (2.1 ± 0.5) × 10–12 cm3 s–1 (measured with photoionization mass spectrometry), again similar to rate for the reaction of anti-CH3sub>CHOO with NO2. Cavity ring-down measurements of the acetone oxide removal without added reagents display a combination of first- and second-order decay kinetics

  7. 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

  8. Tuning of near-infrared-to-near-infrared luminescence from one-photon to two-photon anti-Stokes shift in Ca3sub>Ga2- xCrxGe3sub>O12 via varying Cr3+ content.


    Lin, Huihong; Yu, Ting; Bai, Gongxun; Zhang, Qinyuan; Hao, Jianhua


    Near-infrared-to-near-infrared (NIR-to-NIR) anti-Stokes luminescence from Cr3+ singly doped Ca3sub>Ga2Ge3sub>O12 (CGGG) occurs under the excitation of an 808 nm diode laser. The anti-Stokes processes vary from one photon to two photon, depending on the Cr3+ content (x) in Ca3sub>Ga2-xCrxGe3sub>O12. The results suggest that phonon-assisted anti-Stokes excitation and cooperative energy transfer are involved in the observed upconversion (UC) processes of CGGG:Cr3+. The relevant Cr3+-doping-concentration-dependent NIR-to-NIR anti-Stokes luminescent mechanism, either one-photon or two-photon UC, is investigated. Such an observation on modulating the UC process via varying the doping concentration is helpful in broadening the understanding of UC phenomena.

  9. 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.

  10. Coexistence of two electronic nano-phases on a CH3sub>NH3sub>PbI3–xClx surface observed in STM measurements

    SciTech Connect

    Yost, Andrew J.; Pimachev, Artem; Ho, Chun -Chih; Darling, Seth B.; Wang, Leeyih; Su, Wei -Fang; Dahnovsky, Yuri; Chien, TeYu


    Scanning tunneling microscopy is utilized to investigate the local density of states of a CH3sub>NH3sub>PbI3-xClx perovskite in cross-sectional geometry. Two electronic phases, 10-20 nm in size, with different electronic properties inside the CH3sub>NH3sub>PbI3-xClx perovskite layer are observed by the dI/ dV mapping and point spectra. A power law dependence of the dI/dV point spectra is revealed. In addition, the distinct electronic phases are found to have preferential orientations close to the normal direction of the film surface. Density functional theory calculations indicate that the observed electronic phases are associated with local deviation of I/Cl ratio, rather than different orientations of the electric dipole moments in the ferroelectric phases. Furthermore, by comparing the calculated results with experimental data we conclude that phase A (lower contrast in dI/dV mapping at -2.0 V bias) contains a lower I/Cl ratio than that in phase B (higher contrast in dI/dV).

  11. 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

  12. 125Te NMR and Seebeck Effect in Bi2Te3sub> Synthesized from Stoichiometric and Te-Rich Melts

    SciTech Connect

    Levin, E. M.; Riedemann, T. M.; Howard, A.; Jo, N. H.; Bud’ko, S. L.; Canfield, P. C.; Lograsso, T. A.


    Bi2Te3sub> is a well-known thermoelectric material and, as a new form of quantum matter, a topological insulator. Variation of local chemical composition in Bi2Te3 results in formation of several types of atomic defects, including Bi and Te vacancies and Bi and Te antisite defects; these defects can strongly affect material functionality via generation of free electrons and/or holes. Nonuniform distribution of atomic defects produces electronic inhomogeneity, which can be detected by 125Te nuclear magnetic resonance (NMR). Here we report on 125Te NMR and Seebeck effect (heat to electrical energy conversion) for two single crystalline samples: (#1) grown from stoichiometric composition by Bridgman technique and (#2) grown out of Te-rich, high temperature flux. The Seebeck coefficients of these samples show p- and n-type conductivity, respectively, arising from different atomic defects. 125Te NMR spectra and spin–lattice relaxation measurements demonstrate that both Bi2Te3sub> samples are electronically inhomogeneous at the atomic scale, which can be attributed to a different Te environment due to spatial variation of the Bi/Te ratio and formation of atomic defects. In conclusion, correlations between 125Te NMR spectra, spin–lattice relaxation times, the Seebeck coefficients, carrier concentrations, and atomic defects are discussed. Our data demonstrate that 125Te NMR is an effective probe to study antisite defects in Bi2Te3sub>.

  13. 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.

  14. Mechanism of photocatalytic reduction of CO2 by Re(bpy)(CO)3sub>Cl from differences in carbon isotope discrimination

    SciTech Connect

    Schneider, Taylor W.; Ertem, Mehmed Z.; Muckerman, James T.; Angeles-Boza, Alfredo M.


    The rhenium complex Re(bpy)(CO)3sub>Cl (1, bpy = 2,2'-bipyridine) catalyzes CO2 reduction to CO in mixtures containing triethanolamine (TEOA) as a sacrificial reductant. The mechanism of this reaction under photocatalytic conditions remains to be fully characterized. Here, we report the competitive carbon kinetic isotope effects (13C KIEs) on photocatalytic CO2 reduction by 1 and analyze the results of experimental measurements by comparing with computed KIEs via density functional theory (DFT) calculations as a means of formulating a chemical mechanism and illustrating the utility of this approach. The 13C KIEs, k(12C)/k(13C), in acetonitrile (ACN) and dimethylformamide (DMF) were determined to be 1.0718 ± 0.0036 and 1.0685 ± 0.0075, respectively. When [Ru(bpy)3sub>]Cl2 is added to the reaction mixture in acetonitrile as a photosensitizer, the reduction of CO2 exhibited a 13C KIE = 1.0703 ± 0.0043. These values are consistent with the calculated isotope effect of CO2 binding to the one-electron reduced [ReI(bpy•)(CO)3sub>] species. The findings reported here provide strong evidence that the reactions in the two different solvents have the same first irreversible step and proceed with similar reactive intermediates upon reduction. Theoretically, we found that the major contribution for the large 13C isotope effects comes from a dominant zero-point energy (ZPE) term. Lastly, these results lay the groundwork for combined experimental and theoretical approaches for analysis of competitive isotope effects toward understanding CO2 reduction catalyzed by other complexes.

  15. 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.

  16. Synthesis, crystal structure and magnetic property of a new nickel selenite chloride: Ni{sub 5}(SeO{sub 3}){sub 4}Cl{sub 2}

    SciTech Connect

    Shen Yueling; Mao Jianggao . E-mail:; Jiang Hailong


    The new nickel selenite chloride, Ni{sub 5}(SeO{sub 3}){sub 4}Cl{sub 2}, was obtained by high-temperature solid state reaction of NiCl{sub 2}, Ni{sub 2}O{sub 3} and SeO{sub 2} in a 1:2:4molar ratio at 700{sup o}C in an evacuated quartz tube. Its structure was established by single-crystal X-ray diffraction. Ni{sub 5}(SeO{sub 3}){sub 4}Cl{sub 2} crystallizes in the triclinic system, space group P-1 (No. 2) with cell parameters of a=8.076(2), b=9.288(2), c=9.376(2)A, {alpha}=101.97(3), {beta}=105.60(3), {gamma}=91.83(3){sup o} and Z=2. All nickel(II) ions in Ni{sub 5}(SeO{sub 3}){sub 4}Cl{sub 2} are octahedrally coordinated by selenite oxygens or/and chloride anions (([Ni(1)O{sub 5}Cl], [Ni(2)O{sub 4}Cl{sub 2}], [Ni(3)O{sub 5}Cl], [Ni(4)O{sub 6}] and [Ni(5)O{sub 4}Cl]). The structure of the title compound features a condensed three-dimensional (3D) network built by Ni(II) ions interconnected by SeO{sub 3}{sup 2-} anions as well as Cl{sup -} anions. Magnetic property measurements show strong antiferromagnetic interaction between nickel(II) ions.

  17. 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.

  18. Titania-silica materials from the molecular precursor Ti[OSi(O{sup t}Bu){sub 3}]{sub 4}: Selective epoxidation catalysts

    SciTech Connect

    Coles, M.P.; Lugmair, C.G.; Terry, K.W.; Tilley, T.D.


    The tris(tert-butoxy)siloxy complex Ti[OSi(O{sup t}Bu){sub 3}]{sub 4} was pyrolytically converted at low temperatures to the theoretical yield of homogeneous TiO{sub 2}{center{underscore}dot}4SiO{sub 2} materials. The complex also serves as a soluble model for isolated, tetrahedral titanium atoms in a silica matrix. The molecular route to homogeneous titania-silica materials described here represents an alternative to the sol-gel method, affording materials with surface areas comparable to those of related aerogels and moderate-to-excellent activities for the epoxidation of cyclohexene.

  19. 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.

  20. The selective catalytic reduction of NOx over Ag/Al2O3sub> with isobutanol as the reductant

    SciTech Connect

    Brookshear, Daniel William; Pihl, Josh A.; Toops, Todd J.; West, Brian H.; Prikhodko, Vitaly Y.


    Here, this study investigates the potential of isobutanol (iBuOH) as a reductant for the selective catalytic reduction (SCR) of NOx over 2 wt% Ag/Al2O3sub> between 150 and 550 °C and gas hourly space velocities (GHSV) between 10,000 and 35,000 h-1. The feed gas consists of 500 ppm NO, 5% H2O, 10% O2, and 375-1500 ppm iBuOH (C1:N ratios of 3-12); additionally, blends of 24 and 48% iBuOH in gasoline are evaluated. Over 90% NOx conversion is achieved between 300 and 400 C using pure iBuOH, including a 40% peak selectivity towards NH3sub> that could be utilized in a dual HC/NH3sub> SCR configuration. The iBuOH/gasoline blends are only able to achieve greater than 90% NOx conversion when operated at a GHSV of 10,000 h-1 and employing a C1:N ratio of 12. Iso-butyraldehyde and NO2 appear to function as intermediates in the iBuOH-SCR mechanism, which mirrors the mechanism observed for EtOH-SCR. In general, the performance of iBuOH in the SCR of NOx over a Ag/Al2O3sub> catalyst is comparable with that of EtOH, although EtOH/gasoline blends display higher NOx reduction than iBuOH/gasoline blends. The key parameter in employing alcohols in SCR appears to be the C-OH:N ratio rather than the C1:N ratio.

  1. Spin orientations of the spin-half Ir4+ ions in Sr3sub>NiIrO6, Sr2IrO4 and Na2IrO3sub>: Density functional, perturbation theory and Madelung potential analyses

    SciTech Connect

    Gordon, Elijah E.; Xiang, Hongjun; Koehler, Jurgen; Whangbo, Myung -Hwan


    The spins of the low-spin Ir4+ (S = 1/2, d5) ions at the octahedral sites of the oxides Sr3sub>NiIrO6, Sr2IrO4 and Na2IrO3sub> exhibit preferred orientations with respect to their IrO6 octahedra. We evaluated the magnetic anisotropies of these S = 1/2 ions on the basis of DFT calculations including spin-orbit coupling (SOC), and probed their origin by performing perturbation theory analyses with SOC as perturbation within the LS coupling scheme. The observed spin orientations of Sr3sub>NiIrO6 and Sr2IrO4 are correctly predicted by DFT calculations, and are accounted for by the perturbation theory analysis. As for the spin orientation of Na2IrO3sub>, both experimental studies and DFT calculations have not been unequivocal. Our analysis reveals that the Ir4+ spin orientation of Na2IrO3sub> should have nonzero components along the c- and a-axes directions. The spin orientations determined by DFT calculations are sensitive to the accuracy of the crystal structures employed, which is explained by perturbation theory analyses when interactions between adjacent Ir4+ ions are taken into consideration. There are indications implying that the 5d electrons of Na2IrO3sub> are less strongly localized compared with those of Sr3sub>NiIrO6 and Sr2IrO4. This implication was confirmed by showing that the Madelung potentials of the Ir4+ ions are less negative in Na2IrO3sub> than in Sr3sub>NiIrO6, Sr2IrO4. Most transition-metal S = 1/2 ions do have magnetic anisotropies because the SOC induces interactions among their crystal-field split d-states, and the associated mixing of the states modifies only the orbital parts of the states. This finding cannot be mimicked by a spin Hamiltonian

  2. Negative ion photoelectron spectra of ISO3sub>, IS2O3sub>, and IS2O4 intermediates formed in interfacial reactions of ozone and iodide/sulfite aqueous microdroplets

    SciTech Connect

    Qin, Zhengbo; Hou, Gao-Lei; Yang, Zheng; Valiev, Marat; Wang, Xue-Bin


    Three short-lived, anionic intermediates, ISO3sub>, IS2O3sub>, and IS2O4, are detected during reactions between ozone and aqueous iodine/sulfur oxides microdroplets. These species may play an important role in ozone-driven inorganic aerosol formation; however their chemical properties remain largely unknown. This is the issue addressed in this work using negative ion photoelectron spectroscopy (NIPES) and ab-initio modeling. The NIPE spectra reveal that all of the three anionic species are characterized by high adiabatic detachment energies (ADEs) - 4.62 ± 0.10, 4.52 ± 0.10, and 4.60 ± 0.10 eV for ISO3sub>, IS2O3sub>, and IS2O4, respectively. Vibrational progressions with frequencies assigned to the S–O symmetric stretching modes are also discernable in the ground state transition features. Density functional theory (DFT) calculations show the presence of several low-lying isomers involving different bonding scenarios. Further analysis based on high level CCSD(T) calculations reveal that the lowest energy structures are characterized by formation of I–S and S–S bonds and can be structurally viewed as SO3 linked with I, IS, and ISO for ISO3sub>, IS2O3sub>, and IS2O4, respectively. The calculated ADEs and vertical detachment energies (VDEs) are in excellent agreement with the experimental results, further supporting the identified minimum energy structures. The obtained intrinsic molecular properties of these anionic intermediates and neutral radicals should be useful to help understand their photochemical reactions in the atmosphere.

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

    SciTech Connect

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


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

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

    SciTech Connect

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


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

  5. Lateral photovoltaic effect observed in doping-modulated GaAs/Al0.3sub>Ga0.7As.


    Liu, Ji Hong; Qiao, Shuang; Liang, BaoLai; Wang, ShuFang; Fu, GuangSheng


    For photovoltaic effect (PE), both barrier height and carrier lifetime are all very important factors. However, how to distinguish their contributions to the PE is very difficult. In this paper, we prepared a series of GaAs/Al0.3sub>Ga0.7As two dimensional electron gas (2DEG) with typical Al0.3sub>Ga0.7As doping concentration of 0.6 × 1018/cm3, 1.2 × 1018/cm3, and 2.5 × 1018/cm3, respectively (sample number: #1, #2, #3), and studied their lateral photovoltaic effects (LPEs). It is found that their position sensitivities all increase with both laser wavelength and laser power. However, the position sensitivity exhibits a non-monotonic behavior with increasing doping concentration, which can be mainly ascribed to the doping concentration-dependent carrier lifetime, especially in the low power regime. With increasing laser power gradually, the position sensitivity difference between sample #1 and sample #2 is still large and increases a little, while the position sensitivity of sample #3 approaches to that of sample #2, suggesting that the doping concentration-dependent barrier height also starts to play an important role in the high power regime. Our results will provide important information for the design and development of novel and multifunctional PE devices.

  6. New insights into the negative thermal expansion: Direct experimental evidence for the “guitar-string” effect in cubic ScF3sub>

    SciTech Connect

    Hu, Lei; Chen, Jun; Sanson, Andrea; Wu, Hui; Rodriguez, Clara Guglieri; Olivi, Luca; Ren, Yang; Fan, Longlong; Deng, Jinxia; Xing, Xianran


    The understanding of the negative thermal expansion (NTE) mechanism remains challenging but critical for the development of NTE materials. This study sheds light on NTE of ScF3sub>, one of the most outstanding materials with NTE. The local dynamics of ScF3sub> has been investigated by a combined analysis of synchrotron-based X-ray total scattering, ex-tended X-ray absorption fine structure and neutron powder diffraction. Very interestingly, we observe that i) the Sc-F nearest-neighbor distance strongly expands with increasing temperature while the Sc-Sc next-nearest-neighbor distance contracts, ii) the thermal ellipsoids of relative vibrations be-tween Sc-F nearest-neighbors are highly elongated in the direction perpendicular to the Sc-F bond, indicating that the Sc-F bond is much softer to bend than to stretch, and iii) there is mainly dynamically transverse motion of fluorine atoms, rather than static shifts. Here, these results are the direct experimental evidence for the NTE mechanism, in which the rigid unit is not necessary for the occurrence of NTE, and the key role is played by the transverse thermal vibrations of fluorine atoms through the “guitar-string” effect.

  7. Synthesis, characterization, and energetics of solid solution along the dolomite-ankerite join, and implications for the stability of ordered CaFe(CO{sub 3}){sub 2}

    SciTech Connect

    Chai, L.; Navrotsky, A.


    Samples along the dolomite-ankerite join were synthesized using a piston-cylinder apparatus and the double-capsule method. Some of the ankerite samples may be disordered. Thermal analysis and X-ray diffraction showed that all samples can be completely decomposed to uniquely defined products under calorimetric conditions (770 {degrees}C, O{sub 2}), and a well-constrained thermodynamic cycle was developed to determine the enthalpy of formation. The energetics of ordered and disordered ankerite solid solutions were estimated using data from calorimetry, lattice-energy calculations, and phase equilibria. The enthalpies of formation of ordered dolomite and disordered end-member ankerite from binary carbonates, determined by calorimetry, are -9.29 {+-} 1.97 and 6.98 {+-} 2.08 kJ/mol, respectively. The enthalpy of formation of ordered ankerite appears to become more endothermic with increasing Fe content, whereas the enthalpy of formation of disordered ankerite becomes more exothermic with increasing Fe content, whereas the enthalpy of formation of disordered ankerite becomes more exothermic with increasing Fe content. The enthalpy of disordering in dolomite (approximately 25 kJ/mol) is much larger than that in pure ankerite, CaFe(CO{sub 3}){sub 2} (approximately 10 kJ/mol), which may explain the nonexistence of ordered CaFe(CO{sub 3}){sub 2}. 24 refs., 3 figs., 3 tabs.

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

    SciTech Connect

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


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

  9. Atomic defects in monolayer titanium carbide (Ti3sub>C2Tx) MXene

    SciTech Connect

    Sang, Xiahan; Xie, Yu; Lin, Ming -Wei; Alhabeb, Mohamed; Van Aken, Katherine L.; Gogotsi, Yury G.; Kent, Paul R. C.; Xiao, Kai; Unocic, Raymond R.


    Here, the 2D transition metal carbides or nitrides, or MXenes, are emerging as a group of materials showing great promise in lithium ion batteries and supercapacitors. Until now, characterization and properties of single-layer MXenes have been scarcely reported. Here, using scanning transmission electron microscopy, we determined the atomic structure of freestanding monolayer Ti3sub>C2Tx flakes prepared via the minimally intensive layer delamination method and characterized different point defects that are prevalent in the monolayer flakes. We determine that the Ti vacancy concentration can be controlled by the etchant concentration during preparation. Density function theory-based calculations confirm the defect structures and predict that the defects can influence the surface morphology and termination groups, but do not strongly influence the metallic conductivity. Using devices fabricated from single- and few-layer Ti3sub>C2Tx MXene flakes, the effect of the number of layers in the flake on conductivity has been demonstrated.

  10. Heterogeneous WSx/WO3sub> thorn-bush nanofiber electrodes for sodium-ion batteries

    SciTech Connect

    Ryu, Won -Hee; Wilson, Hope; Sohn, Sungwoo; Li, Jinyang; Tong, Xiao; Shaulsky, Evyatar; Schroers, Jan; Elimelech, Menachem; Taylor, Andre D.


    Heterogeneous electrode materials with hierarchical architectures promise to enable considerable improvement in future energy storage devices. In this study, we report on a tailored synthetic strategy used to create heterogeneous tungsten sulfide/oxide core–shell nanofiber materials with vertically and randomly aligned thorn-bush features, and we evaluate them as potential anode materials for high-performance Na-ion batteries. The WSx (2 ≤ x ≤ 3, amorphous WS3sub> and crystalline WS2) nanofiber is successfully prepared by electrospinning and subsequent calcination in a reducing atmosphere. To prevent capacity degradation of the WSx anodes originating from sulfur dissolution, a facile post-thermal treatment in air is applied to form an oxide passivation surface. Interestingly, WO3sub> thorn bundles are randomly grown on the nanofiber stem, resulting from the surface conversion. We elucidate the evolving morphological and structural features of the nanofibers during post-thermal treatment. The heterogeneous thorn-bush nanofiber electrodes deliver a high second discharge capacity of 791 mAh g–1 and improved cycle performance for 100 cycles compared to the pristine WSx nanofiber. Lastly, we show that this hierarchical design is effective in reducing sulfur dissolution, as shown by cycling analysis with counter Na electrodes.

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

    SciTech Connect

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


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

  12. Phase stability, swelling, microstructure and strength of Ti3sub>SiC2-TiC ceramics after low dose neutron irradiation

    SciTech Connect

    Ang, Caen; Zinkle, Steven; Shih, Chunghao; Silva, Chinthaka; Cetiner, Nesrin; Katoh, Yutai


    In this study, Mn+1AXn (MAX) phase Ti3sub>SiC2 materials were neutron irradiated at ~400, ~630, and 700 °C to a fluence of ~2 × 1025 n/m2 (E > 0.1 MeV). After irradiation at ~400 °C, anisotropic c-axis dilation of ~1.5% was observed. Room temperature strength was reduced from 445 ± 29 MPa to 315 ± 33 MPa and the fracture surfaces showed flat facets and transgranular cracks instead of typical kink-band deformation and bridging ligaments. XRD phase analysis indicated an increase of 10–15 wt% TiC. After irradiation at ~700 °C there were no lattice parameter changes, ~5 wt% decomposition to TiC occurred, and strength was 391 ± 71 MPa and 378 ± 31 MPa. The fracture surfaces indicated kink-band based deformation but with lesser extent of delamination than as-received samples. Finally, Ti3sub>SiC2 appears to be radiation tolerant at ~400 °C, and increasingly radiation resistant at ~630–700 °C, but a higher temperature may be necessary for full recovery.

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

    SciTech Connect

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


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

  14. Engineered Mott ground state in a LaTiO3+δ/LaNiO3sub> heterostructure

    SciTech Connect

    Cao, Yanwei; Liu, Xiaoran; Kareev, M.; Choudhury, D.; Middey, S.; Meyers, D.; Kim, J. -W.; Ryan, P. J.; Freeland, J. W.; Chakhalian, J.


    In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO3sub> have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging from interfacial charge transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of a correlated metal LaNiO3sub> and a doped Mott insulator LaTiO3+δ, and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations. The heterostructure exhibits interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and eg orbital band splitting. Here, our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states.

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

    SciTech Connect

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


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

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

    SciTech Connect

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


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

  17. A model for the compositions of non-stoichiometric intermediate phases formed by diffusion reactions, and its application to Nb3sub>Sn superconductors

    SciTech Connect

    Xu, X.; Sumption, M. D.


    In this work we explore the compositions of non-stoichiometric intermediate phases formed by diffusion reactions: a mathematical framework is developed and tested against the specific case of Nb3sub>Sn superconductors. In the first part, the governing equations for the bulk diffusion and interphase interface reactions during the growth of a compound are derived, numerical solutions to which give both the composition profile and growth rate of the compound layer. The analytic solutions are obtained with certain approximations made. In the second part, we explain an effect that the composition characteristics of compounds can be quite different depending on whether it is the bulk diffusion or grain boundary diffusion that dominates in the compounds, and that “frozen” bulk diffusion leads to unique composition characteristics that the bulk composition of a compound layer remains unchanged after its initial formation instead of varying with the diffusion reaction system; here the model is modified for the case of grain boundary diffusion. Lastly, we apply this model to the Nb3sub>Sn superconductors and propose approaches to control their compositions.

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

    SciTech Connect

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


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

  19. Thermoelectric properties of Cu-doped n-type (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-x}Cu{sub x}Se{sub 3}){sub 0.1}(x=0-0.2) alloys

    SciTech Connect

    Cui, J.L. Mao, L.D.; Yang, W.; Xu, X.B.; Chen, D.Y.; Xiu, W.J.


    n-Type (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-x}Cu{sub x}Se{sub 3}){sub 0.1} (x=0-0.2) alloys with Cu substitution for Bi were prepared by spark plasma-sintering technique and their structural and thermoelectric properties were evaluated. Rietveld analysis reveals that approximate 9.0% of Bi atomic sites are occupied by Cu atoms and less than 4.0 wt% second phase Cu{sub 2.86}Te{sub 2} precipitated in the Cu-doped parent alloys. Measurements show that an introduction of a small amount of Cu (x{<=}0.1) can reduce the lattice thermal conductivity ({kappa}{sub L}), and improve the electrical conductivity and Seebeck coefficient. An optimal dimensionless figure of merit (ZT) value of 0.98 is obtained for x=0.1 at 417 K, which is obviously higher than those of Cu-free Bi{sub 2}Se{sub 0.3}Te{sub 2.7} (ZT=0.66) and Ag-doped alloys (ZT=0.86) prepared by the same technologies. - Graphical abstract: After Cu-doping with x=0.1, the highest ZT value of 0.98 is obtained at 417 K, which is about 0.32 and 0.12 higher than those of Cu-free Bi{sub 2}Se{sub 0.3}Te{sub 2.7} and the Ag-doped alloys (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-x}Ag{sub x}Se{sub 3}){sub 0.1} (x=0.4), respectively.

  20. Electrochemically influenced cation inter-diffusion and Co3sub>O4 formation on La0.6Sr0.4CoO3sub> infiltrated into SOFC cathodes

    SciTech Connect

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


    Nanosized LSC electrocatalyst was infiltrated into a porous scaffold cathode composed of Sm2O3sub>-doped CeO2 (SDC) and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) in a commercial button solid oxide fuel cell (SOFC). To understand the stability of cathodes infiltrated with LSC, the infiltrated composite cells were subjected to both electrochemical operating and thermal aging states at 750 °C for 1500 h. Nanostructure and local chemistry evolution of La0.6Sr0.4CoO3sub> (LSC) infiltrated cathodes upon operation and aging were investigated by transmission electron microscopy. After operation, the LSC remained a cubic perovskite, and the crystal grains exhibit comparable size to as-infiltrated LSC grains. Inter-diffusion of Fe from the LSCF to a Fe-incorporated LSC layer developed on the LSCF backbone. However, only sharp interfaces were observed between LSC and SDC backbone in the as-infiltrated cathode and such interfaces remain after operation. The infiltrated LSC on the SDC backbone also retains granular particle morphology. Furthermore, newly grown Co3sub>O4 nanocrystals were found in the operated cathode. After thermal aging, on the other hand, cation inter-diffusion across the interfaces of the infiltrate particles and the cathode backbones is less than that from the operated cells. Lastly, the following hypothesis is proposed: Co3sub>O4 forms on LSC arising from local charge balancing between cobalt and oxygen vacancies.

  1. Crystal structure of sodium rare earth oxyborates Na{sub 2}Ln{sub 2}(BO{sub 3}){sub 2}O (Ln = Sm, Eu, and Gd) and optical analysis of Na{sub 2}Gd{sub 2}(BO{sub 3}){sub 2}O:Eu{sup 3+}

    SciTech Connect

    Corbel, G.; Leblanc, M.; Antic-Fidancev, E.; Lemaitre-Blaise, M.


    A new structural family of rare earth oxyborates Na{sub 2}Ln{sub 2}(BO{sub 3}){sub 2}O (Ln = Sm, Eu and Gd) is evidenced. The structure, determined by single crystal X-ray diffraction, is monoclinic, space group P2{sub 1}/c, Z = 4, with a = 10.695(6) {angstrom}, b = 6.320(4) {angstrom}, c = 10.3228(6) {angstrom}, {beta} = 117.80(4){degree}, V = 617.5(9) {angstrom}{sup 3}, R{sub 1} = 0.039, wR{sub 2} = 0.101 for Na{sub 2}Gd{sub 2}(BO{sub 3}){sub 2}O. The three-dimensional network is built up from infinite sheets of LnO{sub 8} polyhedra in the (b,c) plane, which are separated by sodium ions. The luminescence of trivalent europium in polycrystalline Na{sub 2}Gd{sub 2}(BO{sub 3}){sub 2}O:Eu{sup 3+} is analyzed at 77K. The low symmetry of the rare earth sites, deduced from the X-ray diffraction study, is confirmed. The crystal field strength is high for both europium sites.

  2. Probing microstructure and phase evolution of α-MoO3sub> nanobelts for sodium-ion batteries by in situ transmission electron microscopy

    SciTech Connect

    Xia, Weiwei; Xu, Feng; Zhu, Chongyang; Xin, Huolin L.; Xu, Qingyu; Sun, Pingping; Sun, Litao


    The fundamental electrochemical reaction mechanisms and the phase transformation pathways of layer-structured α-MoO3sub> nanobelt during the sodiation/desodiation process to date remain largely unknown. In this study, to observe the real-time sodiation/desodiaton behaviors of α-MoO3sub> during electrochemical cycling, we construct a MoO3sub> anode sodium-ion battery inside a transmission electron microscope (TEM). Utilizing in situ TEM and electron diffraction pattern (EDP) observation, α-MoO3sub> nanobelts are found to undergo a unique multi-step phase transformation. Upon the first sodiation, α-MoO3sub> nanobelts initially form amorphous NaxMoO3 phase and are subsequently sodiated into intermediate phase of crystalline NaMoO2, finally resulting in the crystallized Mo nanograins embedded within the Na2O matrix. During the first desodiation process, Mo nanograins are firstly re-oxidized into intermediate phase NaMoO2 that is further transformed into amorphous Na2MoO3sub>, resulting in an irreversible phase transformation. Upon subsequent sodiation/desodiation cycles, however, a stable and reversible phase transformation between crystalline Mo and amorphous Na2MoO3sub> phases has been revealed. In conclusion, our work provides an in-deepth understanding of the phase transformation pathways of α-MoO3sub> nanobelts upon electrochemical sodiation/desodiation processes, with the hope of assistance in designing sodium-ion batteries with enhanced performance.

  3. Mixed cation FA x PEA 1- x PbI 3sub> with enhanced phase and ambient stability toward high-performance perovskite solar cells

    SciTech Connect

    Li, Nan; Zhu, Zonglong; Chueh, Chu -Chen; Liu, Hongbin; Peng, Bo; Petrone, Alessio; Li, Xiaosong; Wang, Liduo; Jen, Alex K. -Y.


    In this study, different from the commonly explored strategy of incorporating a smaller cation, MA+ and Cs+ into FAPbI3sub> lattice to improve efficiency and stability, it is revealed that the introduction of phenylethylammonium iodide (PEAI) into FAPbI3sub> perovksite to form mixed cation FAxPEA1–xPbI3sub> can effectively enhance both phase and ambient stability of FAPbI3sub> as well as the resulting performance of the derived devices. From our experimental and theoretical calculation results, it is proposed that the larger PEA cation is capable of assembling on both the lattice surface and grain boundaries to form quais-3D perovskite structures. The surrounding of PEA+ ions at the crystal grain boundaries not only can serve as molecular locks to tighten FAPbI3sub> domains but also passivate the surface defects to improve both phase and moisture stablity. Consequently, a high-performance (PCE:17.7%) and ambient stable FAPbI3sub> solar cell could be developed

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

    SciTech Connect

    Wang, X.; Ambrosio, G.; Chlachidze, G.; Collings, E. W.; Dietderich, D. R.; DiMarco, J.; Felice, H.; Ghosh, A. K.; Godeke, A.; Gourlay, S. A.; Marchevsky, M.; Prestemon, S. O.; Sabbi, G.; Sumption, M. D.; Velev, G. V.; Xu, X.; Zlobin, A. V.


    Persistent magnetization currents are induced in superconducting filaments during the current ramping in magnets. The resulting perturbation to the design magnetic field leads to field quality degradation, in particular at low field where the effect is stronger relative to the main field. The effects observed in NbTi accelerator magnets were reproduced well with the critical-state model. However, this approach becomes less accurate for the calculation of the persistent-current effects observed in Nb3sub>Sn accelerator magnets. Here a finite-element method based on the measured strand magnetization is validated against three state-of-art Nb3Sn accelerator magnets featuring different subelement diameters, critical currents, magnet designs and measurement temperatures. The temperature dependence of the persistent-current effects is reproduced. Based on the validated model, the impact of conductor design on the persistent current effects is discussed. The performance, limitations and possible improvements of the approach are also discussed.

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

    SciTech Connect

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


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

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

    SciTech Connect

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


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

  7. Dispersion relations of refractive indices suitable for KBe2BO3sub>F2 crystal deep-ultraviolet applications.


    Li, Rukang; Wang, Lirong; Wang, Xiaoyang; Wang, Guiling; Chen, Chuangtian


    KBe2BO3sub>F2 (KBBF) is the only nonlinear optical crystal available to generate deep-ultraviolet (DUV) laser output by direct harmonic generation. High-precision refractive indices, including in the DUV region, were measured, and starting from a double resonance model of polarizability, new dispersion relations of the refractive indices were deduced from the measured data. The predicted phase matching angles for second-harmonic generation down to 165 nm from the new relations agree well with the previous reported values. Moreover, the new dispersion relations show superior results in an even shorter wavelength range, giving perfectly calculated phase matching angles for fifth-harmonic generation down to as short as 149.8 nm.

  8. Second-generation coil design of the Nb3sub>Sn low-β quadrupole for the high luminosity LHC

    SciTech Connect

    Bermudez, S. Izquierdo; Ambrosio, G.; Ballarino, A.; Cavanna, E.; Bossert, R.; Cheng, D.; Dietderich, D.; Ferracin, P.; Ghosh, A.; Hagen, P.; Holik, E.; Perez, J. C.; Rochepault, E.; Schmalzle, J.; Todesco, E.; Yu, M.


    As part of the Large Hadron Collider Luminosity upgrade (HiLumi-LHC) program, the US LARP collaboration and CERN are working together to design and build a 150 mm aperture Nb3sub>Sn quadrupole for the LHC interaction regions. A first series of 1.5 m long coils were fabricated and assembled in a first short model. A detailed visual inspection of the coils was carried out to investigate cable dimensional changes during heat treatment and the position of the windings in the coil straight section and in the end region. The analyses allow identifying a set of design changes which, combined with a fine tune of the cable geometry and a field quality optimization, were implemented in a new, second-generation, coil design. In this study, we review the main characteristics of the first generation coils, describe the modification in coil lay-out, and discuss their impact on parts design and magnet analysis.

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


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


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

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

    SciTech Connect

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


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

  11. High-power, widely tunable, green-pumped femtosecond BiB3sub>O6 optical parametric oscillator.


    Tian, Wenlong; Wang, Zhaohua; Meng, Xianghao; Zhang, Ninghua; Zhu, Jiangfeng; Wei, Zhiyi


    We report on an efficient high-power, widely tunable femtosecond optical parametric oscillator in BiB3sub>O6, synchronously pumped by a frequency-doubled mode-locked Yb:KGW laser at 515 nm. Using collinear type I (o→e+e) phase matching, a resonant wavelength range of 688-1057 nm at a 151-MHz repetition rate is demonstrated, with a tunable idler range of 1150-1900 nm. The output power at 705 nm is 1.09 W for 3.6 W pump power exceeding 30% conversion efficiency. Near-transform-limited pulses down to 71 fs are achieved by deploying extracavity dispersion compensation in a pair of SF6 prisms.

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

    SciTech Connect

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


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

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

    SciTech Connect

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


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

  14. 119Sn-NMR investigations on superconducting Ca3sub>Ir4Sn13: Evidence for multigap superconductivity

    SciTech Connect

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


    In this study, we report bulk superconductivity (SC) in Ca3sub>Ir4Sn13 by means of 119Sn nuclear magnetic resonance (NMR) experiments. Two classical signatures of BCS superconductivity in spin-lattice relaxation rate (1/T1), namely the Hebel–Slichter coherence peak just below the Tc, and the exponential decay in the superconducting phase, are evident. The noticeable decrease of 119Sn Knight shift below Tc indicates spin-singlet superconductivity. The temperature dependence of the spin-lattice relaxation rate 119(1/T1) is convincingly described by the multigap isotropic superconducting gap. NMR experiments do not witness any sign of enhanced spin fluctuations.

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

    SciTech Connect

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


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

  16. Synthesis of stable spherical platinum diphosphide, PtP{sub 2}/carbon nanocomposite by reacting Pt(PPh{sub 3}){sub 4} at elevated temperature under autogenic pressure

    SciTech Connect

    George, P.P.; Gedanken, A. . E-mail:; Gabashvili, A.


    The synthesis of microsized carbon spheres supporting the semiconductor platinum diphosphide, PtP{sub 2}, was conducted by the thermal decomposition of an organometallic precursor. This novel reaction was carried out using the reaction under autogenic pressure at elevated temperature (RAPET) method by dissociating Pt(PPh{sub 3}){sub 4} at 1000 deg. C. The product was characterized using methods of electron microscopy (scanning electron microscope (SEM), transmission electron microscope (TEM), selected area energy dispersive spectroscopy (SAEDS), elemental analyzer (EA) and energy dispersive X-ray analysis (EDX)) and powder-XRD. Transmission electron microscope images indicate that the particle size of the nanoparticles of PtP{sub 2} coated on the carbon spheres is 50 nm.

  17. Gauge bosons masses in a SU(2){sub TC} x SU(3){sub L} x U(1){sub X} extension of the standard model

    SciTech Connect

    Doff, A.


    In this brief report we explore the full realization of the dynamical symmetry breaking of an 3-3-1 model to U(1){sub em} considering a model based on SU(2){sub TC} x SU(3){sub L} x U(1){sub X}. We compute the mass generated for the charged and neutral gauge bosons of the model that result from the symmetry breaking, and verify the equivalence between a 3-3-1 model with a scalar content formed by the set of the fundamental scalar bosons {chi},{rho} and {eta} with a 3-3-1 model where the dynamical symmetry breaking is implanted by the system formed by the set of composite bosons {Phi}{sub T},{Phi}{sub TC(1)} and {Phi}{sub TC(2)}. In this model the minimal composite scalar content is fixed by the condition of the cancellation of triangular anomaly in the technicolor (TC) sector.

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

    SciTech Connect

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


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

  19. Multiband Te p Based Superconductivity of Ta4Pd3sub>Te16

    SciTech Connect

    Singh, David J.


    We recently discovered that Ta4Pd3sub>Te16 is a superconductor that has been suggested to be an unconventional superconductor near magnetism. Here, we report electronic structure calculations showing that despite the layered crystal structure the material is an anisotropic three-dimensional (3D) metal. The Fermi surface contains prominent one-dimensional (1D) and two-dimensional (2D) features, including nested 1D sheets, a 2D cylindrical section, and a 3D sheet. Moreover, the electronic states that make up the Fermi surface are mostly derived from Te p states with small Ta d and Pd d contributions. This places the compound far from magnetic instabilities. The results are discussed in terms of multiband superconductivity.

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

    SciTech Connect

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


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

  1. Morphology of U3sub>O8 materials following storage under controlled conditions of temperature and relative humidity

    SciTech Connect

    Tamasi, Alison L.; Cash, Leigh J.; Mullen, William Tyler; Pugmire, Alison L.; Ross, Amy R.; Ruggiero, Christy E.; Scott, Brian L.; Wagner, Gregory L.; Walensky, Justin R.; Wilkerson, Marianne P.


    Changes in the visual characteristics of uranium oxide surfaces and morphology following storage under different conditions of temperature and relative humidity may provide insight into the history of an unknown sample. Sub-samples of three α-U3sub>O8 materials—one that was phase-pure and two that were phase-impure—were stored under controlled conditions for two years. We used scanning electron microscopy to image the oxides before and after storage, and a morphology lexicon was used to characterize the images. Finally, temporal changes in morphology were observed in some sub-samples, and changes were greatest following exposure to high relative humidity.

  2. Inductively coupled BCl3sub>/Cl2 /Ar plasma etching of Al-rich AlGaN

    SciTech Connect

    Douglas, Erica A.; Sanchez, Carlos A.; Kaplar, Robert J.; Allerman, Andrew A.; Baca, Albert G.


    Varying atomic ratios in compound semiconductors is well known to have large effects on the etching properties of the material. The use of thin device barrier layers, down to 25 nm, adds to the fabrication complexity by requiring precise control over etch rates and surface morphology. The effects of bias power and gas ratio of BCl3sub> to Cl2 for inductively coupled plasma etching of high Al content AlGaN were contrasted with AlN in this study for etch rate, selectivity, and surface morphology. Etch rates were greatly affected by both bias power and gas chemistry. Here we detail the effects of small variations in Al composition for AlGaN and show substantial changes in etch rate with regards to bias power as compared to AlN.

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

    SciTech Connect

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


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

  4. Crystal structure and properties of [OsO{sub 2}(NH{sub 3}){sub 4}]SO{sub 4} . H{sub 2}O

    SciTech Connect

    Burvikova, J. N. Lin'ko, I. V.; Venskovskiy, N. U.; Rybakov, V. B.


    The structure of a single crystal of tetraammindioxoosmium(VI) sulfate [OsO{sub 2}(NH{sub 3}){sub 4}]SO{sub 4} . H{sub 2}O, which is synthesized by the reaction of K{sub 2}[OsO{sub 2}(OH){sub 4}] with (NH{sub 4}){sub 2}SO{sub 4} in an aqueous solution, is investigated using X-ray diffraction analysis. The compound crystallizes in the monoclinic crystal system, space group P2{sub 1}/c, a = 13.102(2) A, b = 6.158(3) A, c = 11.866(2) A, {beta} = 98.13(2) deg., and Z = 4. The [OsO{sub 2}(NH{sub 3}){sub 4}]SO{sub 4} . H{sub 2}O compound has an island structure. Two crystallographically independent osmium atoms are situated at the centers of symmetry, and their octahedral coordination includes two oxygen atoms and four nitrogen atoms of the ammonia molecules. In both octahedra, the osmyl group is linear. The Os-O distances in the octahedra are identical within the standard deviations [Os(1)-O, 1.762(2) A; Os(2)-O, 1.769(2) A]. The Os-N bond lengths vary from 2.082(3) to 2.101(3) A. The cationic complexes, SO{sub 4} groups, and water molecules are linked via the system of hydrogen bonds. The assignment of the absorption bands in the IR spectrum of the compound synthesized is performed, and its thermal behavior in air is studied.

  5. Characterization of an Fe≡N–NH 2 intermediate relevant to catalytic N2 reduction to NH3sub>

    SciTech Connect

    Anderson, John S.; Cutsail, III, George E.; Rittle, Jonathan; Connor, Bridget A.; Gunderson, William A.; Zhang, Limei; Hoffman, Brian M.; Peters, Jonas C.


    The ability of certain transition metals to mediate the reduction of N2 to NH3sub> has attracted broad interest in the biological and inorganic chemistry communities. Early transition metals such as Mo and W readily bind N2 and mediate its protonation at one or more N atoms to furnish M(NxHy) species that can be characterized and, in turn, extrude NH3sub>. By contrast, the direct protonation of Fe–N2 species to Fe(NxHy) products that can be characterized has been elusive. In this paper, we show that addition of acid at low temperature to [(TPB)Fe(N2)][Na(12-crown-4)] results in a new S = 1/2 Fe species. EPR, ENDOR, Mössbauer, and EXAFS analysis, coupled with a DFT study, unequivocally assign this new species as [(TPB)Fe≡N–NH2]+, a doubly protonated hydrazido(2–) complex featuring an Fe-to-N triple bond. This unstable species offers strong evidence that the first steps in Fe-mediated nitrogen reduction by [(TPB)Fe(N2)][Na(12-crown-4)] can proceed along a distal or “Chatt-type” pathway. Finally, a brief discussion of whether subsequent catalytic steps may involve early or late stage cleavage of the N–N bond, as would be found in limiting distal or alternating mechanisms, respectively, is also provided.

  6. Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H3sub>CC≡C˙) with small alkenes and alkynes

    SciTech Connect

    Kirk, Benjamin B.; Savee, John D.; Trevitt, Adam J.; Osborn, David L.; Wilson, Kevin R.


    The reaction of small hydrocarbon radicals (i.e. ˙CN, ˙C2H) with trace alkenes and alkynes is believed to play an important role in molecular weight growth and ultimately the formation of Titan's characteristic haze. Current photochemical models of Titan's atmosphere largely assume hydrogen atom abstraction or unimolecular hydrogen elimination reactions dominate the mechanism, in contrast to recent experiments that reveal significant alkyl radical loss pathways during reaction of ethynyl radical (˙C2H) with alkenes and alkynes. In this study, the trend is explored for the case of a larger ethynyl radical analogue, the 1-propynyl radical (H3CC≡C˙), a likely product from the high-energy photolysis of propyne in Titan's atmosphere. Using synchrotron vacuum ultraviolet photoionization mass spectrometry, product branching ratios are measured for the reactions of 1-propynyl radical with a suite of small alkenes (ethylene and propene) and alkynes (acetylene and d4-propyne) at 4 Torr and 300 K. Reactions of 1-propynyl radical with acetylene and ethylene form single products, identified as penta-1,3-diyne and pent-1-en-3-yne, respectively. These products form by hydrogen atom loss from the radical-adduct intermediates. The reactions of 1-propynyl radical with d4-propyne and propene form products from both hydrogen atom and methyl loss, (–H = 27%, –CH3sub> = 73%) and (–H = 14%, –CH3sub> = 86%), respectively. Altogether, these results indicate that reactions of ethynyl radical analogues with alkenes and alkynes form significant quantities of products by alkyl loss channels, suggesting that current photochemical models of Titan over predict both hydrogen atom production as well as the efficiency of molecular weight growth in these reactions.

  7. DNA 3'sub> pp 5' G de-capping activity of aprataxin: effect of cap nucleoside analogs and structural basis for guanosine recognition

    SciTech Connect

    Chauleau, Mathieu; Jacewicz, Agata; Shuman, Stewart


    DNA3'sub> pp 5'G caps synthesized by the 3'-PO4/5'-OH ligase RtcB have a strong impact on enzymatic reactions at DNA 3'-OH ends. Aprataxin, an enzyme that repairs A5'pp5'DNA ends formed during abortive ligation by classic 3'-OH/5'-PO4 ligases, is also a DNA 3' de-capping enzyme, converting DNAppG to DNA3sub>'p and GMP. By taking advantage of RtcB's ability to utilize certain GTP analogs to synthesize DNAppN caps, we show that aprataxin hydrolyzes inosine and 6-O-methylguanosine caps, but is not adept at removing a deoxyguanosine cap. We report a 1.5 Å crystal structure of aprataxin in a complex with GMP, which reveals that: (i) GMP binds at the same position and in the same anti nucleoside conformation as AMP; and (ii) aprataxin makes more extensive nucleobase contacts with guanine than with adenine, via a hydrogen bonding network to the guanine O6, N1, N2 base edge. Alanine mutations of catalytic residues His147 and His149 abolish DNAppG de-capping activity, suggesting that the 3' de-guanylylation and 5' de-adenylylation reactions follow the same pathway of nucleotidyl transfer through a covalent aprataxin-(His147)–NMP intermediate. Alanine mutation of Asp63, which coordinates the guanosine ribose hydroxyls, impairs DNAppG de-capping.

  8. Bi{sub 6}(SeO{sub 3}){sub 3}O{sub 5}Br{sub 2}: A new bismuth oxo-selenite bromide

    SciTech Connect

    Berdonosov, Peter S.; Olenev, Andrei V.; Kirsanova, Maria A.; Lebed, Julia B.; Dolgikh, Valery A.


    A new bismuth oxo-selenite bromide Bi{sub 6}(SeO{sub 3}){sub 3}O{sub 5}Br{sub 2} was synthesized and structurally characterized. The crystal structure belongs to the triclinic system (space group P1-bar , Z=2, a=7.1253(7) A, b=10.972(1) A, c=12.117(1) A, {alpha}=67.765(7) Degree-Sign , {beta}=82.188(8) Degree-Sign , {gamma}=78.445(7) Degree-Sign ) and is unrelated to those of other known oxo-selenite halides. It can be considered as an open framework composed of BiO{sub x} or BiO{sub y}Br{sub z} polyhedrons forming channels running along [1 0 0] direction which contain the selenium atoms in pyramidal shape oxygen coordination (SeO{sub 3}E). The spectroscopic properties and thermal stability were studied. The new compound is stable up to 400 Degree-Sign C. - graphical abstract: New bismuth oxo-selenite bromide with new open framework structure. Highlights: Black-Right-Pointing-Pointer New bismuth oxo-selenite bromide was found and structurally characterized. Black-Right-Pointing-Pointer Bi{sub 6}(SeO{sub 3}){sub 3}O{sub 5}Br{sub 2} exhibit a new open framework structure type. Black-Right-Pointing-Pointer BiO{sub x} or BiO{sub y}Br{sub z} polyhedrons form channels in the structure which are decorated by [SeO{sub 3}E] groups.

  9. Magnetocaloric effect of Gd4(BixSb1-x)3sub> alloy series

    SciTech Connect

    Niu, Xuejun


    Alloys from the Gd4(BixSb1-x)3sub> series were prepared by melting a stoichiometric amounts of pure metals in an induction furnace. The crystal structure is of the anti-Th3sub>P4 type (space group I$\\bar{4}$3d) for all the compounds tested. The linear increase of the lattice parameters with Bi concentration is attributed to the larger atomic radius of Bi than that of Sb. Magnetic measurements show that the alloys order ferromagnetically from 266K to 330K, with the ordering temperature increasing with decreasing Bi concentration. The alloys are soft ferromagnets below their Curie temperatures, and follow the Curie-Weiss law above their ordering temperatures. The paramagnetic effective magnetic moments are low compared to the theoretical value for a free Gd3+, while the ordered magnetic moments are close to the theoretical value for Gd. The alloys exhibit a moderate magnetocaloric effect (MCE) whose maxima are located between 270K and 338K and have relatively wide peaks. The peak MCE temperature decreases with decreasing Bi concentration while the peak height increases with decreasing Bi concentration. The Curie temperatures determined from inflection points of heat capacity are in good agreement with those obtained from the magnetocaloric effect. The MCE results obtained from the two different methods (magnetization and heat capacity) agree quite well with each other for all of the alloys in the series.

  10. [N(CH{sub 3}){sub 3}H]{sub 2}ZnCl{sub 4}: Ferroelectric properties and characterization of phase transitions by Raman spectroscopy

    SciTech Connect

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


    The X-ray powder diffraction pattern shows that at room temperature, [N(CH{sub 3}){sub 3}H]{sub 2}ZnCl{sub 4} is crystallized in the orthorhombic system with Pnma space group. The phase transitions at T{sub 1} = 255 K, T{sub 2} = 282 K, T{sub 3} = 302 K, T{sub 4} = 320 K, and T{sub 5} = 346 K have been confirmed by the differential scanning calorimetry. The electrical technique was measured in the 10{sup −1}–10{sup 7 }Hz frequency range and 233–363 K temperature intervals. The temperature dependence of the dielectric constant at different temperatures proved that this compound is ferroelectric below 282 K. Besides, [N(CH{sub 3}){sub 3 }H]{sub 2}ZnCl{sub 4} shows classical ferroelectric behaviour near curie temperature. In order to characterize the phase transitions, Raman spectra have been recorded in the temperature range of 233–383 K and the frequency range related to the internal and external vibrations of the cations and anions (90–4000 cm{sup −1}). The temperature dependence of the Raman line shifts ν and the half-width Δν detects all phase transitions and confirms their nature, especially at 282 K that corresponds to the ferroelectric-paraelectric phase transition.

  11. Spin-phonon coupling and high-pressure phase transitions of RMnO3sub> (R=Ca and Pr): An inelastic neutron scattering and first-principles study

    SciTech Connect

    Mishra, S. K.; Gupta, M. K.; Mittal, R.; Kolesnikov, Alexander I.; Chaplot, S. L.


    Here, we report inelastic neutron scattering measurements over 7–1251 K in CaMnO3sub> covering various phase transitions, and over 6–150 K in PrMnO3sub> covering the magnetic transition. The excitations around 20 meV in CaMnO3sub> and at 17 meV in PrMnO3sub> at low temperatures are found to be associated with magnetic origin. We observe coherent magnetic neutron scattering in localized regions in reciprocal space and show it to arise from long-range correlated magnetic spin-waves below the magnetic transition temperature (TN) and short-range stochastic spin-spin fluctuations above TN. In spite of the similarity of the structure of the two compounds, the neutron inelastic spectrum of PrMnO3sub> exhibits broad features at 150 K unlike well-defined peaks in the spectrum of CaMnO3sub>. This might result from the difference in the nature of interactions in the two compounds (magnetic and Jahn-Teller distortion). Ab initio phonon calculations have been used to interpret the observed phonon spectra. The ab initio calculations at high pressures show that the variations of Mn-O distances are isotropic for CaMnO3sub> and highly anisotropic for PrMnO3sub>. The calculation in PrMnO3sub> shows the suppression of Jahn-Teller distortion and simultaneous insulator-to-metal transition. It appears that this transition may not be associated with the occurrence of the tetragonal phase above 20 GPa as reported in the literature, since the tetragonal phase is found to be dynamically unstable, although it is found to be energetically favored over the orthorhombic phase above 20 GPa. CaMnO3sub> does not show any phase transition up to 60 GPa.

  12. Influence of crustal dust and sea spray supermicron particle concentrations and acidity on inorganic NO3sub> aerosol during the 2013 Southern Oxidant and Aerosol Study

    SciTech Connect

    Allen, H. M.; Draper, D. C.; Ayres, B. R.; Ault, A.; Bondy, A.; Takahama, S.; Modini, R. L.; Baumann, K.; Edgerton, E.; Knote, C.; Laskin, A.; Wang, B.; Fry, J. L.


    Inorganic aerosol composition was measured in the southeastern United States, a region that exhibits high aerosol mass loading during the summer, as part of the 2013 Southern Oxidant and Aerosol Study (SOAS) campaign. Measurements using a Monitor for AeRosols and GAses (MARGA) revealed two periods of high aerosol nitrate (NO3sub>) concentrations during the campaign. These periods of high nitrate were correlated with increased concentrations of supermicron crustal and sea spray aerosol species, particularly Na+ and Ca2+, and with a shift towards aerosol with larger (1 to 2.5 μm) diameters. We suggest this nitrate aerosol forms by multiphase reactions of HNO3sub> and particles, reactions that are facilitated by transport of crustal dust and sea spray aerosol from a source within the United States. The observed high aerosol acidity prevents the formation of NH4NO3sub>, the inorganic nitrogen species often dominant in fine-mode aerosol at higher pH. In addition, calculation of the rate of the heterogeneous uptake of HNO3sub> on mineral aerosol supports the conclusion that aerosol NO3sub> is produced primarily by this process, and is likely limited by the availability of mineral cation-containing aerosol surface area. Modeling of NO3sub> and HNO3sub> by thermodynamic equilibrium models (ISORROPIA II and E-AIM) reveals the importance of including mineral cations in the southeastern United States to accurately balance ion species and predict gas–aerosol phase partitioning.

  13. Nonstoichiometry and Transport Properties of Ca3sub>Co4±xO9+δ (x = 0 – 0.4)

    SciTech Connect

    Zhou, Xiao Dong; Pederson, Larry R.; Thomsen, Edwin C.; Nie, Zimin; Coffey, Greg W.


    Nonstoichiometries of Ca3sub>Co4O9+δ and transport properties of Ca3sub>Co4±xO9+δ were investigated. At 1100°C, Ca3sub>Co4O9+δ transformed to CaO and CoO. The reaction products offer a precise baseline for thermogravimetric analysis. At room temperature, δ in Ca3sub>Co4O9+δ is 0.38, which decreases at T ~450°C, indicating the onset point of the formation of oxygen vacancies, and δ is ~0.20 at 900°C. Correspondingly, the average Co valence state is 3.19 at room temperature and 3.10 at 900°C. In contrast to conventional defect chemistry theory in p-type oxide conductors, the formation of oxygen vacancies in Ca3sub>Co4O9+δ has a negligible impact on the carrier density of holes, indicating that oxygen vacancies and the redox couple responsible for hole carriers are in different layers. With control over the ratio of Ca/Co, the phase boundary for the misfit layered structure is between Ca3sub>Co3.95O9+δ and Ca3sub>Co4.05O9+δ. Beyond the phase boundary, the second phase is present, which effectively lowers the electrical conductivity while increasing the Seebeck coefficient.

  14. Probing charge transfer in a novel class of luminescent perovskite-based heterostructures composed of quantum dots bound to RE-activated CaTiO3sub> phosphors

    SciTech Connect

    Crystal S. Lewis; Wong, Stanislaus S.; Liu, Haiqing; Han, Jinkyu; Wang, Lei; Yue, Shiyu; Brennan, Nicholas A.


    We report on the synthesis and structural characterization of novel semiconducting heterostructures composed of cadmium selenide (CdSe) quantum dots (QDs) attached onto the surfaces of novel high-surface area, porous rare-earth-ion doped alkaline earth titanate micron-scale spherical motifs, i.e. both Eu-doped and Pr-doped CaTiO3sub>, composed of constituent, component nanoparticles. These unique metal oxide perovskite building blocks were created by a multi-pronged synthetic strategy involving molten salt and hydrothermal protocols. Subsequently, optical characterization of these heterostructures indicated a clear behavioral dependence of charge transfer in these systems upon a number of parameters such as the nature of the dopant, the reaction temperature, and particle size. Specifically, 2.7 nm diameter ligand-functionalized CdSe QDs were anchored onto sub-micron sized CaTiO3sub>-based spherical assemblies, prepared by molten salt protocols. We found that both the Pr- and Eu-doped CaTiO3sub> displayed pronounced PL emissions, with maximum intensities observed using optimized lanthanide concentrations of 0.2 mol% and 6 mol%, respectively. Analogous experiments were performed on Eu-doped BaTiO3sub> and SrTiO3sub> motifs, but CaTiO3sub> still performed as the most effective host material amongst the three perovskite systems tested. Furthermore, the ligand-capped CdSe QD-doped CaTiO3sub> heterostructures exhibited effective charge transfer between the two individual constituent nanoscale components, an assertion corroborated by the corresponding quenching of their measured PL signals.

  15. Electrochemical behavior of [(Mn(Bpy))(VO{sub 3}){sub 2}]≈(H{sub 2}O){sub 1.24} and [(Mn(Bpy){sub 0.5})(VO{sub 3}){sub 2}]≈(H{sub 2}O){sub 0.62} inorganic–organic Brannerites in lithium and sodium cells

    SciTech Connect

    Fernández de Luis, Roberto; Rosa Palacín, M.; Karmele Urtiaga, M.


    The performance of MnV{sub 2}O{sub 6} (MnV) and its [(Mn(Bpy))(VO{sub 3}){sub 2}]≈(H{sub 2}O){sub 1.16} (MnBpy) and [(Mn(Bpy){sub 0.5})(VO{sub 3}){sub 2}]≈(H{sub 2}O){sub 0.62}(MnBpy0.5) hybrid derivative compounds was investigated against sodium and lithium counter electrodes. For MnV{sub 2}O{sub 6} stable capacities of 850 mAh/g were achieved in lithium cells, the best value reported so far. The whole capacity is ascribed to a conversion reaction in which the amorphization of the compounds takes place. No significant differences in the capacities for the inorganic compound and the hybrid ones were observed. Interestingly, the potential hysteresis decreases in the hybrid compounds. The difference between Li and Na cell capacity most probably comes from the difference of standard potential of the two redox couples Li{sup +}/Li and Na{sup +}/Na of about ca. 0.3 V leading to an incomplete conversion reaction and thus lowers capacity in the case of Na cells. The Raman and IR ex-situ experiments after cycling indicate that the bipyridine organic ligands are completely decomposed during the electrochemical testing. The IR studies in MnV inorganic and MnBpy and MnBpy0.5 hybrid electrodes after the electrochemical cycling, suggest that the SEI formation and bipyridine degradation give rise to different aliphatic compounds. - Graphical abstract: The electrochemical performance of [(Mn(Bpy))(VO{sub 3}){sub 2}]≈(H{sub 2}O){sub 1.16} and [(Mn(Bpy){sub 0.5})(VO{sub 3}){sub 2}]≈(H{sub 2}O){sub 0.62} against sodium and lithium counter electrodes give rise to the structural collapse of the initial compounds. The IR and Raman studies show that the Bpy organic ligand is completely decomposed during the during the electrochemical testing. However, after the amorphization stable capacities as high as 850 mAh/g for lithium cells were achieved. - Highlights: • We test the lithium and sodium insertion in hybrid brannerites. • Capacities as large as 850 mAh/g were obtained

  16. Electric-field-induced strain effects on the magnetization of a Pr0.67Sr0.33MnO3sub> film

    SciTech Connect

    Zhang, B.; Sun, C. -J.; Lu, W.; Venkatesan, T.; Han, M. -G.; Zhu, Y.; Chen, J.; Chow, G. M.


    The electric-field control of magnetic properties of Pr0.67Sr0.33MnO3sub> (PSMO) film on piezoelectric Pb(Mg1/3sub>Nb2/3sub>)O3sub>-PbTiO3sub> (PMNT) substrate was investigated. The piezoelectric response of the PMNT substrate to the electric field produced strain that was coupled to the PSMO film. The in-plane compressive (tensile) strain increased (decreased) the magnetization. The change of magnetic moment was associated with the Mn ions. First principle simulations showed that the strain-induced electronic redistribution of the two eg orbitals (3dz2 and 3dx2-y2) of Mn ions was responsible for the change of magnetic moment. This work demonstrates that the magnetoelectric effect in manganite/piezoelectric hetero-structures originates from the change in eg orbital occupancy of Mn ions induced by strain rather than the interfacial effect.

  17. Selection of Nuclear Fuel for TREAT: UO2 vs U3sub>O8

    SciTech Connect

    Glazoff, Michael Vasily; Van Rooyen, Isabella Johanna; Coryell, Benjamin David; Parga, Clemente Jose


    The Transient Reactor Test (TREAT) that resides at the Materials and Fuels Complex (MFC) at Idaho National Laboratory (INL), first achieved criticality in 1959, and successfully performed many transient tests on nuclear fuel until 1994 when its operations were suspended. Resumption of operations at TREAT was approved in February 2014 to meet the U.S. Department of Energy (DOE) Office of Nuclear Energy’s objectives in transient testing of nuclear fuels. The National Nuclear Security Administration’s is converting TREAT from its existing highly enriched uranium (HEU) core to a new core containing low enriched uranium (LEU) (i.e., U-235< 20% by weight). The TREAT Conversion project is currently progressing with conceptual design phase activities. Dimensional stability of the fuel element assemblies, predictable fuel can oxidation and sufficient heat conductivity by the fuel blocks are some of the critical performance requirements of the new LEU fuel. Furthermore, to enable the design team to design fuel block and can specifications, it is amongst the objectives to evaluate TREAT LEU fuel and cladding material’s chemical interaction. This information is important to understand the viability of Zr-based alloys and fuel characteristics for the fabrication of the TREAT LEU fuel and cladding. Also, it is very important to make the right decision on what type of nuclear fuel will be used at TREAT. In particular, one has to consider different oxides of uranium, and most importantly, UO2 vs U3sub>O8. In this report, the results are documented pertaining to the choice mentioned above (UO2 vs U3sub>O8). The conclusion in favor of using UO2 was made based on the analysis of historical data, up-to-date literature, and self-consistent calculations of phase equilibria and thermodynamic properties in the U-O and U-O-C systems. The report is organized as follows. First, the criteria that were used to make the

  18. Molecular metals based on 1,2,7,8-tetrahydrodicyclopenta[cd:lm]perylene and iodine, (CPP){sub 2}(I{sub 3}){sub 1-{delta}}

    SciTech Connect

    Morgado, J. |; Santos, I.C.; Henriques, R.T.; Almeida, M.; Fourmigue, M.; Matias, P.; Veiros, L.F.; Duarte, M.T.; Alcacer, L.; Calhorda, M.J. |


    The synthesis and characterization of molecular metals derived from 1,2,7,8-tetrahydrodicyclopenta[cd:lm]perylene (CPP) by partial oxidation with iodine and with general formula (CPP){sub 2}(I{sub 3}){sub 1-{delta}}, {delta} = 0-0.13, are reported. Single crystals, obtained either by electrocrystallization or by diffusion-controlled iodine oxidation of CPP, present two types of morphologies, elongated diamond or thinner needle-shaped crystals, both with a monoclinic cell, space group P2{sub 1}/a, a = 4.3757(9), b = 19.3681(11), c = 10.0860(11) {angstrom}, {beta} = 98.050(8){degrees}, V = 846.4(2) {angstrom}{sup 3}, Z = 2. The structure of the diamond-shaped crystal was solved by X-ray diffraction to a final R(F) = 0.096, R{sub w}(F) = 0.069. It consists of regular stacks of CPP molecules along a with a 3.41 {angstrom} spacing and uncorrected one-dimensional chains of I{sub 3}{sup {minus}} located in channels between four CPP stacks corresponding to (CPP){sub 2}(I{sub 3}){sub 0.892}. The thin needle crystals have the same unit cell but an unspecified and slightly different iodine content. Band structure calculations in this structure by the extended Hueckel method indicate a one-dimensional conduction band 0.55 eV wide. These thin needle crystals present, at room temperature, an electrical conductivity along the a axis {alpha}{sub a}(RT) = 200 S/cm and thermopower S{sub a}(RT) = 30 {mu}V/K, while for the diamond-shaped crystals {alpha}{sub a}(RT) = 2 S/cm and S{sub a}(RT) = -8 {mu}V/K. These transport coefficients for both types of crystals indicate a metallic behavior from room temperature down to {approx_equal}63 K, where a metal-to-insular (M-I) transition takes place. EPR studies in single crystals show an almost isotropic line at g = 2.0044 and with a width of {approx_equal}6 G in the range 80-300 K and without significant differences between the two types of crystals. 53 refs., 9 figs., 4 tabs.

  19. La{sub 4}(Si{sub 5.2}Ge{sub 2.8}O{sub 18})(TeO{sub 3}){sub 4} and La{sub 2}(Si{sub 6}O{sub 13})(TeO{sub 3}){sub 2}: Intergrowth of the lanthanum(III) tellurite layer with the XO{sub 4} (X=Si/Ge) tetrahedral layer

    SciTech Connect

    Kong Fang; Jiang Hailong; Mao Jianggao


    Two novel lanthanum(III) silicate tellurites, namely, La{sub 4}(Si{sub 5.2}Ge{sub 2.8}O{sub 18})(TeO{sub 3}){sub 4} and La{sub 2}(Si{sub 6}O{sub 13})(TeO{sub 3}){sub 2}, have been synthesized by the solid state reactions and their structures determined by single crystal X-ray diffraction. The structure of La{sub 4}(Si{sub 5.2}Ge{sub 2.8}O{sub 18})(TeO{sub 3}){sub 4} features a three-dimensional (3D) network composed of the [(Ge{sub 2.82}Si{sub 5.18})O{sub 18}]{sup 4-} tetrahedral layers and the [La{sub 4}(TeO{sub 3}){sub 4}]{sup 4+} layers that alternate along the b-axis. The germanate-silicate layer consists of corner-sharing XO{sub 4} (X=Si/Ge) tetrahedra, forming four- and six-member rings. The structure of La{sub 2}(Si{sub 6}O{sub 13})(TeO{sub 3}){sub 2} is a 3D network composed of the [Si{sub 6}O{sub 13}]{sup 2-} double layers and the [La{sub 2}(TeO{sub 3}){sub 2}]{sup 2+} layers that alternate along the a-axis. The [Si{sub 6}O{sub 13}]{sup 2-} double layer is built by corner-sharing silicate tetrahedra, forming four-, five- and eight-member rings. The TeO{sub 3}{sup 2-} anions in both compounds are only involved in the coordination with La{sup 3+} ions to form a lanthanum(III) tellurite layer. La{sub 4}(Si{sub 5.2}Ge{sub 2.8}O{sub 18})(TeO{sub 3}){sub 4} is a wide band-gap semiconductor. - Graphical abstract: The first lanthanum(III) silicate/germanate tellurites, namely, La{sub 4}[(Si{sub x}Ge{sub 8-x})O{sub 18}](TeO{sub 3}){sub 4} (x=5.18) and La{sub 2}(Si{sub 6}O{sub 13})(TeO{sub 3}){sub 2}, have been synthesized and structurally determined by single crystal X-ray diffraction. Both compounds feature complicated 3D network structures composed of the silicate/germanate tetrahedral layers alternating with the [LaTeO{sub 3}] layers.

  20. A search for temperature induced time-dependent structural transitions in 10mol%Sc2O3sub>–1mol%CeO2–ZrO2 and 8mol%Y2O3sub>–ZrO2 electrolyte ceramics

    SciTech Connect

    Chen, Yan; Orlovskaya, Nina; Payzant, E. Andrew; Graule, Thomas; Kuebler, Jakob


    Both Sc2O3sub>–CeO2-stabilized-ZrO2 (SCSZ) and Y2O3sub>-stabilized-ZrO2 (YSZ) show similar Young's modulus damping at 175–400 °C and 200–400 °C, respectively, by impulse excitation acoustic technique. The phase transition in SCSZ is considered responsible for the damping; however for YSZ, such a phase transition has never been reported. To clarify the relation of damping and structural transition in these two materials, the time-dependent high temperature stabilities are studied by in situ X-ray diffraction, neutron diffraction and Raman scattering during long-term annealing of SCSZ at 350 °C and YSZ at 275 °C. The cubic-to-rhombohedral transition in SCSZ is detected. However, the existence of t' phase in YSZ raw powders is confirmed without significant changes of the cubic structure during isothermal annealing. It is concluded that the phase transition contributes to the Young's modulus damping in SCSZ, while the structural transition is excluded from the reason for damping in YSZ.

  1. The Dielectric Properties and Phase Transitions of [Pb(Zn{sub 1/3}Nb{sub 2/3})O{sub 3}]{sub 0.905} (PbTiO{sub 3}){sub 0.095}: Influence of Pressure

    SciTech Connect



    Studies of the influences of temperature, hydrostatic pressure, dc biasing field and frequency on the dielectric constant ({epsilon}{prime}) and loss (tan {delta}) of single crystal [pb (Zn{sub 1/3}Nb{sub 2/3})O{sub 3}]{sub 0.905} (PbTiO{sub 3}){sub 0.095}, or PZN-9.5PT for short, have provided a detailed view of the ferroelectric (FE) response and phase transitions of this technologically important material. While at 1 bar, the crystal exhibits on cooling a cubic-to-tetragonal FE transition followed by a second transition to a rhombohedral phase, pressure induces a FE-to-relaxer crossover, the relaxer phase becoming the ground state at pressures {ge}5 kbar. Analogy with earlier results suggests that this crossover is a common feature of compositionally-disordered soft mode ferroelectrics and can be understood in terms of a decrease in the correlation length among polar domains with increasing pressure. Application of a dc biasing electric field at 1 bar strengthens FE correlations, and can at high pressure re-stabilize the FE response. The pressure-temperature-electric field phase diagram was established. In the absence of dc bias the tetragonal phase vanishes at high pressure, the crystal exhibiting classic relaxor behavior. The dynamics of dipolar motion and the strong deviation from Curie-Weiss behavior of the susceptibility in the high temperature cubic phase are discussed.

  2. A new oxytelluride: Perovskite and CsCl intergrowth in Ba3sub>Yb2O5Te

    SciTech Connect

    Whalen, J. B.; Besara, T.; Vasquez, R.; Herrera, F.; Sun, J.; Ramirez, D.; Stillwell, R. L.; Tozer, S. W.; Tokumoto, T. D.; McGill, S. A.; Allen, J.; Davidson, M.; Siegrist, T.


    The new oxytelluride Ba3sub>Yb2O5Te was obtained from an alkaline earth flux. Ba3Yb2O5Te crystallizes in the tetragonal space group P4/mmm (#123), with a=4.3615(3) Å and c=11.7596(11) angstrom, Z=1. The structure combines two distinct building blocks, a Ba2Yb2O5 perovskite-like double layer with square bipyramidal coordination of the ytterbium ions, and a CsCl-type BaTe layer. Short range magnetic order is apparent at below 5 K, with the magnetic behavior above this temperature dominated by crystal field effects. The structure may be considered as an analog to the Ruddlesden-Popper phases, where the NaCl-type layer has been replaced by the CsCl-type layer. Finally, the two-dimensional magnetic behavior is expected based on the highly anisotropic nature of the structure.

  3. Magnetic phase transitions in Nd{sub 1-x}Dy{sub x}Fe{sub 3}(BO{sub 3}){sub 4} ferroborates

    SciTech Connect

    Demidov, A. A.; Gudim, I. A.; Eremin, E. V.


    The magnetic properties of ferroborate single crystals with substituted compositions Nd{sub 1-x}Dy{sub x}Fe{sub 3}(BO{sub 3}){sub 4} (x = 0.15, 0.25) with competing exchange Nd-Fe and Dy-Fe interactions are investigated. For each composition, we observed a spontaneous spin-reorientation transition from the easy-axis to the easy-plane state and step anomalies on the magnetization curves for the spin-flop transition induced by a magnetic field B vertical bar c. The measured parameters and effects are interpreted using a unified theoretical approach based on the molecular field approximation and on calculations performed in the crystal-field model for the rare-earth ion. The experimental temperature dependences of the initial magnetic susceptibility from T = 2 K to T = 300 K, anomalies on the magnetization curves for B vertical bar c in fields up to 1.8 T, and their evolution with temperature, as well as temperature and field dependences of magnetization in fields up to 9 T are described. In the interpretation of experimental data, the crystal-field parameters in trigonal symmetry for the rare-earth subsystem are determined, as well as the parameters of Nd-Fe and Dy-Fe exchange interactions.

  4. Three-Dimensionally Mesostructured Fe2O3sub> Electrodes with Good Rate Performance and Reduced Voltage Hysteresi

    SciTech Connect

    Wang, Junjie; Braun, Paul V.; Zhou, Hui; Nanda, Jagjit


    Ni scaffolded mesostructured 3D Fe2O3sub> electrodes were fabricated by colloidal templating and pulsed elec-trodeposition. The scaffold provided short pathways for both lithium ions and electrons in the active phase, enabling fast kinetics and thus a high power density. The scaffold also resulted in a reduced voltage hysteresis. The electrode showed a reversible capacity of ~1000 mA h g-1 at 0.2 A g-1 (~0.2 C) for about 20 cycles, and at a current density of 20 A g-1 (~20 C) the deliverable capacity was about 450 mA h g-1. The room temperature voltage hysteresis at 0.1 A g-1 (~0.1 C) was 0.62 V, which is significantly smaller than that normally reported in the literature. And it could be further reduced to 0.42 V when cycling at 45 ºC. Potentiostatic electrochemical impedance spectroscopy (PEIS) studies indicated the small voltage hysteresis may be due to a reduction in the Li2O/Fe interfacial area in the electrode during cycling relative to convention-al conversion systems.

  5. Structural transitions in Pb(In1/2Nb1/2)O3sub> under pressure

    SciTech Connect

    Ahart, Muhtar; Somayazulu, Maddury; Kojima, Seiji; Yasuda, Naohiko; Prosandeev, Sergey; Hemley, Russell J.


    Here, Raman scattering, x-ray diffraction, and first-principles calculations were employed to investigate the behavior of disordered Pb(In1/2Nb1/2)O3sub> (PIN) under pressure up to 50 GPa. The experiments were performed at room temperature while ab-initio calculations were carried out at 0 K. Raman spectra for disordered PIN show broad bands but a peak near the 380 cm-1 increases its intensity with pressure. The linewidth of the band at 550 cm-1 also increases with pressure, while two of the Raman peaks merge above 6 GPa. Above 16 GPa, we observe additional splitting of the band at 50 cm-1. The pressure evolution of the diffraction patterns for PIN shows obvious splitting for Bragg peaks above 16 GPa; the results indicate a possible lowering symmetry transition. We identified that the transition at 0.5 GPa is from pseudo-cubic to orthorhombic (Pbam), the transitions at 16 GPa are isostructure transitions due to changes in linear compressibility and octahedral titling, and the transition at 30 GPa is from orthorhombic to monoclinic. First-principles calculations results indicated that ground state is Pbam with antiferrodisdortion consistent with experiment.

  6. Separation of Am-Cm from Al(NO/sub 3/)/sub 3/ waste solutions by in-canyon-tank precipitation as oxalates

    SciTech Connect

    Gray, L.W.; Burney, G.A.; Wilson, T.W.; McKibben, J.M.; Bibler, N.E.; Holtzscheiter, E.W.; Campbell, T.G.


    A process for recovery of Am-Cm residues from high-activity waste concentrates has been developed specifically for application in Savannah River Plant (SRP) canyon tanks. The Am-Cm residues were collected from a campaign to produce plutonium containing high isotopic concentrations of /sup 242/Pu. The separation of Am-Cm from the high-activity waste stream, containing about 2M Al(NO/sub 3/)/sub 3/, is necessary to produce an acceptable feed solution for a later pressurized cation exchange chromatography separation and purification step. The new process includes formic acid denitration, adjustment of contaminating cations by evaporation and water dilution, and oxalate precipitation of the actinides and lanthanides. After washing, the precipitate was dissolved in 8M nitric acid and the oxalate was destroyed by nitric acid oxidation that was catalyzed by manganous ions. This new process generates about one-fourth the waste of the californium solvent extraction process, which it replaced. The new process also produces a cleaner feed solution for the pressurized cation exchange chromatography separation and purification step.

  7. Nanocrystalline SiC and Ti3sub>SiC2 Alloys for Reactor Materials: Thermal and Mechanical Properties

    SciTech Connect

    Henager, Charles H.; Alvine, Kyle J.; Roosendaal, Timothy J.; Shin, Yongsoon; Nguyen, Ba Nghiep; Borlaug, Brennan A.; Jiang, Weilin


    SiC-polymers (pure polycarbosilane and polycarbosilane filled with SiC-particles) are being combined with Si and TiC powders to create a new class of polymer-derived ceramics for consideration as advanced nuclear materials in a variety of applications. Compared to pure SiC these materials have increased fracture toughness with only slightly reduced thermal conductivity. Future work with carbon nanotube (CNT) mats will be introduced with the potential to increase the thermal conductivity and the fracture toughness. At present, this report documents the fabrication of a new class of monolithic polymer derived ceramics, SiC + SiC/Ti3sub>SiC2 dual phase materials. The fracture toughness of the dual phase material was measured to be significantly greater than Hexoloy SiC using indentation fracture toughness testing. However, thermal conductivity of the dual phase material was reduced compared to Hexoloy SiC, but was still appreciable, with conductivities in the range of 40 to 60 W/(m K). This report includes synthesis details, optical and scanning electron microscopy images, compositional data, fracture toughness, and thermal conductivity data.

  8. Annealing influence on the magnetostructural transition in Gd5Si1.3sub>Ge2.7 thin films

    SciTech Connect

    Pires, A. L.; Belo, J. H.; Gomes, I. T.; Hadimani, R. L.; Jiles, D. C.; Fernandes, L.; Tavares, P. B.; Araújo, J. P.; Lopes, A. M. L.; Pereira, A. M.


    Due to the emerging cooling possibilities at the micro and nanoscale, such as the fast heat exchange rate, the effort to synthesize and optimize the magnetocaloric materials at these scales is rapidly growing. Here, we report the effect of different thermal treatments on Gd5Si1.3sub>Ge2.7 thin film in order to evaluate the correlation between the crystal structure, magnetic phase transition and magnetocaloric effect. For annealing temperatures higher than 500ºC, the samples showed a typical paramagnetic behavior. On the other hand, thermal treatments below 500ºC promoted the suppression of the magnetostructural transition at 190 K, while the magnetic transition around 249 K is not affected. This magnetostructural transition extinction was reflected in the magnetocaloric behavior and resulted in a drastic decrease in the entropy change peak value (of about 68%). An increase in TC was reported, proving that at the nanoscale, heat treatments may be a useful tool to optimize the magnetocaloric properties in Gd5(SixGe1-x)4 thin films.

  9. Magnetic anisotropy and magnetoelectric properties of Tb{sub 1-x}Er{sub x}Fe{sub 3}(BO{sub 3}){sub 4} ferroborates

    SciTech Connect

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


    Magnetic and magnetoelectric properties of ferroborate single crystals with complex composition (Tb{sub 1-x}Er{sub x}Fe{sub 3}(BO{sub 3}){sub 4}, x = 0, 0.75) and with competing exchange Tb-Fe and Er-Fe interactions are investigated. Jumps in electric polarization, magnetostriction, and magnetization are observed as a result of spin-flop transitions, as well as a considerable decrease in the critical field upon an increase in the Er concentration, in a field H{sub c} parallel to the c axis. The observed behavior of phase-transition fields is analyzed and explained using a simple model taking into account anisotropy in g factors and exchange splitting of funda-mental doublets of the easy-axis Tb{sup 3+} ion and easy-plane Er{sup 3+} ion. It is established that magnetoelectric and magnetostriction anomalies under spin-flop transitions are mainly controlled by the Tb subsystem. The Tb subsystem makes a nonmonotonic contribution {Delta}P{sub a}(H{sub a}, T) to polarization along the a axis: the value of {Delta}P{sub a} reverses its sign and increases with temperature due to the contribution from the excited states of the Tb{sup 3+} ion.

  10. Structural transitions in Pb(In1/2Nb1/2)O 3sub> under pressure

    SciTech Connect

    Ahart, Muhtar; Somayazulu, Maddury; Kojima, Seiji; Yasuda, Naohiko; Prosandeev, Sergey; Hemley, Russell J.


    Room-temperature Raman scattering and x-ray diffraction measurements together with first-principles calculations were employed to investigate the behavior of disordered Pb(In1/2Nb1/2)O3sub> (PIN) under pressure up to 50GPa. Raman spectra show broad bands but a peak near the 380cm-1 increases its intensity with pressure. The linewidth of the band at 550cm-1 also increases with pressure, while two of the Raman peaks merge above 6GPa. Above 16GPa, we observe additional splitting of the band at 50cm-1. The pressure evolution of the diffraction patterns for PIN shows obvious Bragg peaks splitting above 16GPa; consistent with a symmetry lowering transition. The transition at 0.5GPa is identified as a pseudo-cubic to orthorhombic (Pbam) structural change whereas the transition at 16GPa is isostructure and associated with changes in linear compressibility and octahedral titling, and the transition at 30GPa is associated to an orthorhombic to monoclinic change. First-principles calculations indicate that the Pbam structure is ground state with antiferrodisdortion consistent with experiment.

  11. The C(3P) + NH3sub> reaction in interstellar chemistry. I. Investigation of the product formation channels

    SciTech Connect

    Bourgalais, Jeremy; Capron, Michael; Kailasanathan, Ranjith Kumar Abhinavam; Osborn, David L.; Hickson, Kevin M.; Loison, Jean -Christophe; Wakelam, Valentine; Goulay, Fabien; Picard, Sebastien D. Le


    The product formation channels of ground state carbon atoms, C(3P), reacting with ammonia, NH3, have been investigated using two complementary experiments and electronic structure calculations. Reaction products are detected in a gas flow tube experiment (330 K, 4 Torr) using tunable vacuum-ultraviolet (VUV) photoionization coupled with time of flight mass spectrometry. Temporal profiles of the species formed and photoionization spectra are used to identify primary products of the C + NH3sub> reaction. In addition, H-atom formation is monitored by VUV laser induced fluorescence (LIF) from room temperature to 50 K in a supersonic gas flow generated by the Laval nozzle technique. Electronic structure calculations are performed to derive intermediates, transition states, and complexes formed along the reaction coordinate. The combination of photoionization and LIF experiments supported by theoretical calculations indicate that in the temperature and pressure range investigated, the H + H2CN production channel represents 100% of the product yield for this reaction. As a result, kinetics measurements of the title reaction down to 50 K and the effect of the new rate constants on interstellar nitrogen hydride abundances using a model of dense interstellar clouds are reported in Paper II.

  12. Crystallization of spin superlattices with pressure and field in the layered magnet SrCu2(BO3sub>)2

    SciTech Connect

    Haravifard, S.; Graf, D.; Feiguin, A. E.; Batista, C. D.; Lang, J. C.; Silevitch, D. M.; Srajer, G.; Gaulin, B. D.; Dabkowska, H. A.; Rosenbaum, T. F.


    An exact mapping between quantum spins and boson gases provides fresh approaches to the creation of quantum condensates and crystals. Here we report on magnetization measurements on the dimerized quantum magnet SrCu2(BO3sub>)2 at cryogenic temperatures and through a quantum-phase transition that demonstrate the emergence of fractionally filled bosonic crystals in mesoscopic patterns, specified by a sequence of magnetization plateaus. We apply tens of Teslas of magnetic field to tune the density of bosons and gigapascals of hydrostatic pressure to regulate the underlying interactions. Simulations help parse the balance between energy and geometry in the emergent spin superlattices. In conclusion, the magnetic crystallites are the end result of a progression from a direct product of singlet states in each short dimer at zero field to preferred filling fractions of spin-triplet bosons in each dimer at large magnetic field, enriching the known possibilities for collective states in both quantum spin and atomic systems.

  13. An air-stable Na3sub>SbS4 superionic conductor prepared by a rapid and economic synthetic procedure

    SciTech Connect

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


    All-solid-state sodium batteries, using abundant sodium resources and solid electrolyte, hold much promise for safe, low cost, large-scale energy storage. To realize the practical applications of all solid Na-ion batteries at ambient temperature, the solid electrolytes are required to have high ionic conductivity, chemical stability, and ideally, easy preparation. Ceramic electrolytes show higher ionic conductivity than polymers, but they often require extremely stringent synthesis conditions, either high sintering temperature above 1000 C or long-time, low-energy ball milling. Herein, we report a new synthesis route for Na3sub>SbS4, a novel Na superionic conductor that needs much lower processing temperature below 200 C and easy operation. This new solid electrolyte exhibits a remarkable ionic conductivity of 1.05 mS cm-1 at 25 °C and is chemically stable under ambient atmosphere. In conclusion, this synthesis process provides unique insight into the current state-of-the-art solid electrolyte preparation and opens new possibilities for the design of similar materials.

  14. Synthesis, crystal structure and vibrational spectra characterization of M{sup I}La(PO{sub 3}){sub 4} (M{sup I}=Na, Ag)

    SciTech Connect

    El Masloumi, Mohamed; Imaz, Inhar . E-mail:; Chaminade, Jean-Pierre; Videau, Jean-Jacques; Couzi, Michel; Mesnaoui, Mohamed; Maazaz, Mohamed


    The single crystals of lanthanum metaphosphate MLa(PO{sub 3}){sub 4} (M=Na, Ag) have been synthesized and studied by a combination of X-ray crystal diffraction and vibrational spectroscopy. The sodium and silver compounds crystallize in the same monoclinic P2{sub 1}/n space group (C{sub 2}{sup 5}h factor group) with the following respective unit cell dimensions: a=7.255(2), b=13.186(3), c=10.076(2)A, {beta}=90.40(2){sup o}, V=963.0(4)A{sup 3}, Z=4 and a=7.300(5), b=13.211(9), c=10.079(7)A, {beta}=90.47(4){sup o}, V=972.09(12)A{sup 3}, Z=4. This three-dimensional framework is built of twisted zig-zag chains running along a direction and made up of PO{sub 4} tetrahedra sharing two corners, connected to the LaO{sub 8} and NaO{sub 7} or AgO{sub 7} polyhedra by common oxygen atoms to the chains. The infrared and Raman vibrational spectra have been investigated. A group factor analysis leads to the determination of internal modes of (PO{sub 3}){sup -} anion in the phosphate chain.

  15. 57Fe Mössbauer study of Lu2Fe3sub>Si5 iron silicide superconductor

    SciTech Connect

    Ma, Xiaoming; Ran, Sheng; Pang, Hua; Li, Fashen; Canfield, Paul C.; Bud'ko, Sergey L.


    With the advent of Fe–As based superconductivity it has become important to study how superconductivity manifests itself in details of 57Fe Mössbauer spectroscopy of conventional, Fe-bearing superconductors. The iron-based superconductor Lu2Fe3sub>Si5 has been studied by 57Fe Mössbauer spectroscopy over the temperature range from 4.4 K to room temperature with particular attention to the region close to the superconducting transition temperature (Tc=6.1 K). Consistent with the two crystallographic sites for Fe in this structure, the observed spectra appear to have a pattern consisting of two doublets over the whole temperature range. Furthermore, the value of Debye temperature was estimated from temperature dependence of the isomer shift and the total spectral area and compared with the specific heat capacity data. Neither abnormal behavior of the hyperfine parameters at or near Tc, nor phonon softening were observed.

  16. Raman Study of the Structural Distortion in the Ni1–xCoxTiO3sub> Solid Solution

    SciTech Connect

    Fujioka, Yukari; Frantti, Johannes; Puretzky, Alexander; King, Graham


    In this paper, Raman spectra were collected on Ni1–xCoxTiO3sub> (0 ≤ x ≤ 1) ilmenite samples as a function of the temperature between 4 and 1200 K. An evident symmetry lowering from the prototype R$\\bar{3}$symmetry is observed. The distortion was largest for the x = 0.40 and 0.50 samples and significantly diminished for small and large values of x. The distortion was preserved in the whole temperature range and, except for the x = 0.50 sample, did not show significant changes. Notably, between 25 and 69 K, distortion of the x = 0.40 sample is accompanied by ferromagnetic order. The direct cation–cation and O-mediated indirect interactions are discussed as mechanisms behind the distortion and magnetic order. A reversible order–disorder phase transformation, assigned to occur between the ilmenite and corundum phases, took place at 973 K in the x = 0.50 sample. Completion of the transformation took over 1 h. Finally, the role of the overlap of Co/Ni and Ti 3d orbitals through O octahedral faces for charge transfer is discussed.

  17. Momentum-space structure of quasielastic spin fluctuations in Ce3sub>Pd20Si6

    SciTech Connect

    Portnichenko, P. Y.; Cameron, A. S.; Surmach, M. A.; Deen, Pascale P.; Paschen, S.; Prokofiev, A.; Mignot, Jean-Michel; Strydom, A. M.; Telling, Mark T. F.; Podlesnyak, Andrey A.; Inosov, D. S.


    Surrounded by heavy-fermion metals, Ce3sub>Pd20Si6 is one of the heaviest-electron systems known to date. Here we used high-resolution neutron spectroscopy to observe low-energy magnetic scattering from a single crystal of this compound in the paramagnetic state. We investigated its temperature dependence and distribution in momentum space, which was not accessible in earlier measurements on polycrystalline samples. At low temperatures, a quasielastic magnetic response with a half-width Γ ≈ 0.1 meV persists with varying intensity all over the Brillouin zone. It forms a broad hump centered at the (111) scattering vector, surrounded by minima of intensity at (002), (220), and equivalent wave vectors. The momentum-space structure distinguishes this signal from a simple crystal-field excitation at 0.31 meV, suggested previously, and rather lets us ascribe it to short-range dynamical correlations between the neighboring Ce ions, mediated by the itinerant heavy f electrons via the Ruderman-Kittel-Kasuya-Yosida mechanism. With increasing temperature, the energy width of the signal follows the conventional T1/2 law, Γ(T)=Γ0+A√T. Lastly, the momentum-space symmetry of the quasielastic response suggests that it stems from the simple-cubic Ce sublattice occupying the 8c Wyckoff site, whereas the crystallographically inequivalent 4a site remains magnetically silent in this material.

  18. Spatial potential ripples of azimuthal surface modes in topological insulator Bi2Te3sub> nanowires

    SciTech Connect

    Muñoz Rojo, Miguel; Zhang, Yingjie; Manzano, Cristina V.; Alvaro, Raquel; Gooth, Johannes; Salmeron, Miquel; Martin-Gonzalez, Marisol


    Topological insulators (TI) nanowires (NW) are an emerging class of structures, promising both novel quantum effects and potential applications in low-power electronics, thermoelectrics and spintronics. However, investigating the electronic states of TI NWs is complicated, due to their small lateral size, especially at room temperature. Here, we perform scanning probe based nanoscale imaging to resolve the local surface potential landscapes of Bi2Te3sub> nanowires (NWs) at 300 K. We found equipotential rings around the NWs perimeter that we attribute to azimuthal 1D modes. Along the NW axis, these modes are altered, forming potential ripples in the local density of states, due to intrinsic disturbances. Potential mapping of electrically biased NWs enabled us to accurately determine their conductivity which was found to increase with the decrease of NW diameter, consistent with surface dominated transport. Finally, our results demonstrate that TI NWs can pave the way to both exotic quantum states and novel electronic devices.

  19. Growth control of oxygen stoichiometry in homoepitaxial SrTiO3sub> films by pulsed laser epitaxy in high vacuum

    SciTech Connect

    Lee, Ho Nyung; Ambrose Seo, Sung S.; Choi, Woo Seok; Rouleau, Christopher M.


    In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3sub> (STO) thin films on single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Thus, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but it expands the utility of pulsed laser epitaxy of other materials as well.₃

  20. Nanoscale elastic changes in 2D Ti3sub>C2Tx (MXene) pseudocapacitive electrodes

    SciTech Connect

    Come, Jeremy; Xie, Yu; Naguib, Michael; Jesse, Stephen; Kalinin, Sergei V.; Gogotsi, Yury; Kent, Paul R. C.; Balke, Nina


    Designing sustainable electrodes for next generation energy storage devices relies on the understanding of their fundamental properties at the nanoscale, including the comprehension of ions insertion into the electrode and their interactions with the active material. One consequence of ion storage is the change in the electrode volume resulting in mechanical strain and stress that can strongly affect the cycle life. Therefore, it is important to understand the changes of dimensions and mechanical properties occurring during electrochemical reactions. While the characterization of mechanical properties via macroscopic measurements is well documented, in-situ characterization of their evolution has never been achieved at the nanoscale. Two dimensional (2D) carbides, known as MXenes, are promising materials for supercapacitors and various kinds of batteries, and understating the coupling between their mechanical and electrochemical properties is therefore necessary. Here we report on in-situ imaging, combined with density functional theory of the elastic changes, of a 2D titanium carbide (Ti3sub>C2Tx) electrode in direction normal to the basal plane during cation intercalation. The results show a strong correlation between the Li+ ions content and the elastic modulus, whereas little effects of K+ ions are observed. Moreover, this strategy enables identifying the preferential intercalation pathways within a single particle.

  1. Nonequivalent Yb{sup 3+} centres in Y{sub 1-x}Yb{sub x}Al{sub 3}(BO{sub 3}){sub 4} laser crystals

    SciTech Connect

    Boldyrev, K N; Popova, Marina N; Bezmaternykh, L N; Betinelli, M


    The absorption spectra of nonlinear laser crystals Y{sub 1-x}Yb{sub x}Al{sub 3}(BO{sub 3}){sub 4} grown from bismuth-lithium-molybdate and potassium-molybdate solution-melts are comparatively studied by high-resolution Fourier spectroscopy. The differences observed in the fine structure of the absorption spectra are correlated with the variations in the solution-melt composition and in the concentrations of bismuth and molybdenum impurities in the crystals. It is shown that the concentration of the molybdenum impurity (the main factor hindering lasing in the UV spectral region) in the single crystals grown from the bismuth-lithium-molybdate solutions is more than an order of magnitude smaller than in the crystals grown using the potassium-molybdate solution-melt. The described method can be used for express analysis of the quality of UV laser crystals and for improving the solution-melt technologies of growth of laser crystals and crystals used for generation of the fourth harmonic of Nd:YAG laser radiation. (active media)

  2. Synthesis, Structure, and Pressure-Induced Polymerization of Li 3sub> Fe(CN) 6 Accompanied with Enhanced Conductivity

    SciTech Connect

    Li, Kuo; Zheng, Haiyan; Hattori, Takanori; Sano-Furukawa, Asami; Tulk, Christopher A.; Molaison, Jamie; Feygenson, Mikhail; Ivanov, Ilia N.; Yang, Wenge; Mao, Ho-kwang


    By providing a new route to synthesize inorganic/organic conductors with tunable composition and properties, pressure-induced polymerization of charged triple-bond monomers like acetylide and cyanide could lead to formation of a conductive metal–carbon network composite. The industry application of this promising synthetic method is mainly limited by the reaction pressure needed, which is often too high to be reached for gram amounts of sample. Here we successfully synthesized highly conductive Li3sub>Fe(CN)6 at maximum pressure around 5 GPa and used in situ diagnostic tools to follow the structural and functional transformations of the sample, including in situ X-ray and neutron diffraction and Raman and impedance spectroscopy, along with the neutron pair distribution function measurement on the recovered sample. The cyanide anions start to react around 1 GPa and bond to each other irreversibly at around 5 GPa, which are the lowest reaction pressures in all known metal cyanides and within the technologically achievable pressure range for industrial production. Moreover, the conductivity of the polymer is above 10–3 S·cm–1, which reaches the range of conductive polymers. Our investigation suggests that the pressure-induced polymerization route is practicable for synthesizing some types of functional conductive materials for industrial use, and further research like doping and heating can hence be motivated to synthesize novel materials under lower pressure and with better performances.

  3. Electron-phonon coupling and thermal transport in the thermoelectric compound Mo3sub>Sb7–xTex

    SciTech Connect

    Bansal, Dipanshu; Li, Chen W.; Said, Ayman H.; Abernathy, Douglas L.; Yan, Jiaqiang; Delaire, Olivier A.


    Phonon properties of Mo3sub>Sb7–xTex (x = 0, 1.5, 1.7), a potential high-temperature thermoelectric material, have been studied with inelastic neutron and x-ray scattering, and with first-principles simulations. The substitution of Te for Sb leads to pronounced changes in the electronic struc- ture, local bonding, phonon density of states (DOS), dispersions, and phonon lifetimes. Alloying with tellurium shifts the Fermi level upward, near the top of the valence band, resulting in a strong suppression of electron-phonon screening, and a large overall stiffening of interatomic force- constants. The suppression in electron-phonon coupling concomitantly increases group velocities and suppresses phonon scattering rates, surpassing the effects of alloy-disorder scattering, and re- sulting in a surprising increased lattice thermal conductivity in the alloy. We also identify that the local bonding environment changes non-uniformly around different atoms, leading to variable perturbation strengths for different optical phonon branches. The respective roles of changes in phonon group velocities and phonon lifetimes on the lattice thermal conductivity are quantified. Lastly, our results highlight the importance of the electron-phonon coupling on phonon mean-free-paths in this compound, and also estimates the contributions from boundary scattering, umklapp scattering, and point-defect scattering.

  4. Magnetic Properties of Sm{sub 0.7}Ho{sub 0.3}Fe{sub 3}(BO{sub 3}){sub 4}

    SciTech Connect

    Demidov, A. A.; Gudim, I. A.; Eremin, E. V.


    The magnetic properties of a ferroborate single crystal of substituted composition Sm{sub 0.7}H{sub 0.3}Fe{sub 3}(BO{sub 3}){sub 4} with competing Sm-Fe and Ho-Fe exchange interactions are studied. The measured properties and effects are interpreted in terms of a general theoretical approach based on the molecular field approximation and calculations using the crystal field model for a rare-earth ion. The experimental temperature dependences of the initial magnetic susceptibility in the temperature range 2-300 K, the anomalies in the magnetization curves for B Double-Vertical-Line c and B Up-Tack c in fields lower than 1.2 T, and the field and temperature dependences of magnetization in fields lower than 9 T are described. The crystal field parameters and the parameters of the R-Fe and Fe-Fe exchange interactions are determined during the interpretation of the experimental data.

  5. Mechanical qualification of the support structure for MQXF, the Nb3sub>Sn low-β quadrupole for the high luminosity LHC

    SciTech Connect

    Juchno, M.; Ambrosio, G.; Anerella, M.; Bajas, H.; Bajko, M.; Bourcey, N.; Cheng, D. W.; Felice, H.; Ferracin, P.; Grosclaude, P.; Guinchard, M.; Perez, J. C.; Prin, H.; Schmalzle, J.


    Within the scope of the High Luminosity LHC project, the collaboration between CERN and U.S. LARP is developing new low-β quadrupoles using the Nb3sub>Sn superconducting technology for the upgrade of the LHC interaction regions. The magnet support structure of the first short model was designed and two units were fabricated and tested at CERN and at LBNL. The structure provides the preload to the collars-coils subassembly by an arrangement of outer aluminum shells pre-tensioned with water-pressurized bladders. For the mechanical qualification of the structure and the assembly procedure, superconducting coils were replaced with solid aluminum “dummy coils”, the structure was preloaded at room temperature, and then cooled-down to 77 K. Mechanical behavior of the magnet structure was monitored with the use of strain gauges installed on the aluminum shells, the dummy coils and the axial preload system. As a result, this paper reports on the outcome of the assembly and the cool-down tests with dummy coils, which were performed at CERN and at LBNL, and presents the strain gauge measurements compared to the 3D finite element model predictions.

  6. Part 1: Kinetic energy dependencies of selected ion-molecule reactions; Part 2: Photochemistry of (FSO sub 3 ) sub 2 , FSO sub 3 , and FNO

    SciTech Connect

    Burley, J.D.


    In Part 1, guided ion beam mass spectroscopy is used to study the ion-molecule reactions O{sup +}({sup 4}S) + H{sub 2}(D{sub 2}, HD), (O{sup +}{sup 4}S) + N{sub 2}, C{sup +}({sup 2}P) + O{sub 2} and C{sup +}(P) + N{sub 2}. Integral reaction cross sections are measured as a function of kinetic energy in the center-of-mass frame. Reaction mechanisms and dynamics are examined, and the results are compared to the predictions of phase space theory. In some cases, thermochemistry for neutral and ionic species is derived. In Part 2, photoabsorption cross sections are measured for peroxydisulfuryl difluoride, (FSO{sub 3}){sub 2}, and the fluorosulfate radical, FSO{sub 3}. Photoabsorption cross sections of nitrosyl fluoride, FNO, are also measured, and the FNO absorption spectrum is analyzed and assigned. Spectral results for FNO are compared to the predictions and ab initio calculations and to those obtained for the isoelectronic compound HONO. 259 refs., 34 figs., 9 tabs.

  7. Correlation of anisotropy and directional conduction in β-Li3sub>PS4 fast Li+ conductor

    SciTech Connect

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


    Our letter reports the correlation of anisotropy and directional conduction in the fast Li+ conductor β-Li3sub>PS4, one of the low-symmetry crystalline electrolyte candidates. The material has both high conductivity and good stability that serves well for the large-scale energy storage applications of all-solid-state lithium ion batteries. The anisotropic physical properties, demonstrated here by the thermal expansion coefficients, are crucial for compatibility in the solid-state system and battery performance. Neutron and X-ray powder diffraction measurements were done to determine the crystal structure and thermal stability. Moreover, the crystallographic b-axis was revealed as a fast expansion direction, while negligible thermal expansion was observed along the a-axis around the battery operating temperatures. The anisotropic behavior has its structural origin from the Li+ conduction channels with incomplete Li occupancy and a flexible connection of LiS4 and PS4 tetrahedra within the framework. This indicates a strong correlation in the direction of the ionic transport in the low-symmetry Li+ conductor.

  8. Compositional inhomogeneityand segregation in (K0.5Na0.5)NbO3sub> ceramics

    SciTech Connect

    Chen, Kepi; Tang, Jing; Chen, Yan


    The effects of the calcination temperature of (K0.5Na0.5)NbO3sub> (KNN) powder on the sintering and piezoelectric properties of KNN ceramics have been investigated in this report. KNN powders are synthesized via the solid-state approach. Scanning electron microscopy and X-ray diffraction characterizations indicate that the incomplete reaction at 700 °C and 750 °C calcination results in the compositional inhomogeneity of the K-rich and Na-rich phases while the orthorhombic single phase is obtained after calcination at 900 °C. During the sintering, the presence of the liquid K-rich phase due to the lower melting point has a significant impact on the densification, the abnormal grain growth and the deteriorated piezoelectric properties. From the standpoint of piezoelectric properties, the optimal calcination temperature obtained for KNN ceramics calcined at this temperature is determined to be 800 °C, with piezoelectric constant d33=128.3 pC/N, planar electromechanical coupling coefficient kp=32.2%, mechanical quality factor Qm=88, and dielectric loss tan δ=2.1%.

  9. Gamma and proton irradiation effects and thermal stability of electrical characteristics of metal-oxide-silicon capacitors with atomic layer deposited Al2O3sub> dielectric

    SciTech Connect

    J. M. Rafi; Lynn, D.; Pellegrini, G.; Fadeyev, V.; Galloway, Z.; Sadrozinski, H. F. -W.; Christophersen, M.; Philips, B. F.; Kierstead, J.; Hoeferkamp, M.; Gorelov, I.; Palni, P.; Wang, R.; Seidel, S.


    The radiation hardness and thermal stability of the electrical characteristics of atomic layer deposited Al2O3sub> layers to be used as passivation films for silicon radiation detectors with slim edges are investigated. To directly measure the interface charge and to evaluate its change with the ionizing dose, metal-oxide-silicon (MOS) capacitors implementing differently processed Al2O3sub> layers were fabricated on p-type silicon substrates. Qualitatively similar results are obtained for degradation of capacitance–voltage and current–voltage characteristics under gamma and proton irradiations up to equivalent doses of 30 Mrad and 21.07 Mrad, respectively. While similar negative charge densities are initially extracted for all non-irradiated capacitors, superior radiation hardness is obtained for MOS structures with alumina layers grown with H2O instead of O3sub> as oxidant precursor. Competing effects between radiation-induced positive charge trapping and hydrogen release from the H2O-grown Al2O3sub> layers may explain their higher radiation resistance. Finally, irradiated and non-irradiated MOS capacitors with differently processed Al2O3sub> layers have been subjected to thermal treatments in air at temperatures ranging between 100 °C and 200 °C and the thermal stability of their electrical characteristics has been evaluated. Partial recovery of the gamma-induced degradation has been noticed for O3sub>-grown MOS structures. Lastly, this can be explained by a trapped holes emission process, for which an activation energy of 1.38 ± 0.15 eV has been extracted.

  10. Cooperation between two periplasmic copper chaperones is required for full activity of the cbb3sub>-type cytochrome c oxidase and copper homeostasis in Rhodobacter capsulatus

    SciTech Connect

    Trasnea, Petru -Iulian; Utz, Marcel; Khalfaoui-Hassani, Bahia; Lagies, Simon; Daldal, Fevzi; Koch, Hans -Georg


    Copper (Cu) is an essential micronutrient that functions as a cofactor in several important enzymes, like respiratory heme-copper oxygen reductases. Yet, Cu is also toxic and therefore cells engage a highly coordinated Cu uptake and delivery system to prevent the accumulation of toxic Cu concentrations. In the current work we analyzed Cu delivery to the cbb3sub>-type cytochrome c oxidase (cbb3sub>-Cox) of Rhodobacter capsulatus. We identified the PCuAC-like periplasmic chaperone PccA and analyzed its contribution to cbb3sub>-Cox assembly. Our data demonstrate that PccA is a Cu-binding protein with a preference for Cu(I), which is required for efficient cbb3sub>-Cox assembly, in particular at low Cu concentrations. By using in vivo and in vitro crosslinking we show that PccA forms a complex with the Sco1-homologue SenC. This complex is stabilized in the absence of the cbb3sub>-Cox specific assembly factors CcoGHIS. In cells lacking SenC, the cytoplasmic Cu content is significantly increased, but the simultaneous absence of PccA prevents this Cu accumulation. Lastly, these data demonstrate that the interplay between PccA and SenC is not only required for Cu delivery during cbb3sub>-Cox assembly, but that it also regulates Cu homeostasis in R. capsulatus.