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Sample records for al ba cu

  1. Cu/Ba/bauxite: an Inexpensive and Efficient Alternative for Pt/Ba/Al2O3 in NOx Removal

    PubMed Central

    Wang, Xiuyun; Chen, Zhilin; Luo, Yongjin; Jiang, Lilong; Wang, Ruihu

    2013-01-01

    Cu/Ba/bauxite possesses superior NOx storage and reduction (NSR) performances, high thermal stability, strong resistance against SO2 poisoning and outstanding regeneration ability in comparison with Pt/Ba/Al2O3. It can serve as a cheap and promising alternative for traditional Pt/Ba/Al2O3 in NOx removal from lean-burn engines. PMID:23536149

  2. Conductor-backed coplanar waveguide resonators of Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O on LaAlO3

    NASA Technical Reports Server (NTRS)

    Miranda, F. A.; Bhasin, K. B.; Stan, M. A.; Kong, K. S.; Itoh, T.

    1992-01-01

    Conductor-backed coplanar waveguide (CBCPW) resonators operating at 10.8 GHz have been fabricated from Tl-Ba-Ca-O (TBCCO) and Y-Ba-Cu-O (YBCO) thin films on LaAlO3. The resonators consist of a coplanar waveguide (CPW) patterned on the superconducting film side of the LaAlO3 substrate with a gold ground plane coated on the opposite side. These resonators were tested in the temperature range from 14 to 106 K. At 77 K, the best of our TBCCO and YBCO resonators have an unloaded quality factor (Qo) 7 and 4 times, respectively, larger than that of a similar all-gold resonator. In this study, the Qo's of the TBCCO resonators were larger than those of their YBCO counterparts throughout the aforementioned temperature range.

  3. Ferroelectric property of (Ba,Bi)(Ti,M)O3 (M; Cu, Mn, Al, Fe, In, Y, Yb) ceramics

    NASA Astrophysics Data System (ADS)

    Shiroki, K.; Kumada, N.; Ogiso, H.; Yonesaki, Y.; Takei, T.; Kinomura, N.; Wada, S.

    2011-10-01

    Two types of solid solutions, (Ba1-2xBi2x)(CuxTi1-x)O3 (x <= 0.04) and (Ba1-xBix)(MxTi1-x)O3 (M; Al, Mn, Fe, In, Y, Yb; x <= 0.03) were prepared by conventional high temperature reaction. For the solid solution of (Ba1-2xBi2x)(CuxTi1-x)O3 single phases with the tetragonal cell was obtained in the region of x <= 0.04 and for the solid solutions of (Ba1-xBix)(MxTi1-x)O3 (M; Al, Mn, Fe, In, Y, Yb) single phases with the tetragonal cell was observed in the region of x <= 0.03 except the sample of M = Al in which a small amount of the second phase was contained. In these solid solutions the Tc increased with the value of x except for M = Al, and was 144.7°C for x = 0.020 of M = Cu, and the highest Tc was observed for x = 0.020 of every M atom and the order of the highest Tc was Cu (144.7°C), Y (141.4°C), Yb (140.8°C), In (138.5°C), Mn (135.5°C) and Fe (131.3°C). The highest apparent piezoelectric constant, (d33 = 258 pm/V) in these solid solutions was observed for x = 0.010 of Al.

  4. Synthesis and properties of superconducting (Hg,Re)-Ba-Ca-Cu-O thick films on polycrystalline LaAlO 3 substrate obtained by screen-printing method

    NASA Astrophysics Data System (ADS)

    Przybylski, K.; Brylewski, T.; Bućko, M.; Prażuch, J.; Morawski, A.; Łada, T.

    2003-05-01

    A superconducting Hg 0.7Re 0.3Ba 2Ca 2Cu 3O 8+ δ thick film on a polycrystalline LaAlO 3 (LAO) substrate was obtained by a two-step method by screen-printing a Re 0.3Ba 2Ca 2Cu 3O x precursor coating on the substrate followed by high-pressure gas firing in Hg vapour. Morphological observations have revealed that the adherent to the ceramic substrate film exhibited highly porous microstructure composed of plate-like crystallites characterized by a superconducting transition temperature of about 110 K. The major phases identified were a high- Tc (Hg,Re)-1223 phase and a low- Tc (Hg,Re)-1212 phase. Non-superconducting secondary impurity phases were also identified. Energy dispersion X-ray spectroscopy analyses at the substrate/film boundary showed a thin continuous layer of BaLa 2O 4 compound, the presence of which confirmed chemical interaction between the LAO substrate and (Hg,Re)-Ba-Ca-Cu-O film.

  5. Characterization of ZrO2 buffer layers for sequentially evaporated Y-Ba-CuO on Si and Al2O3 substrates

    NASA Technical Reports Server (NTRS)

    Valco, George J.; Rohrer, Norman J.; Pouch, John J.; Warner, Joseph D.; Bhasin, Kul B.

    1988-01-01

    Thin film high temperature superconductors have the potential to change the microwave technology for space communications systems. For such applications it is desirable that the films be formed on substrates such as Al2O3 which have good microwave properties. The use of ZrO2 buffer layers between Y-Ba-Cu-O and the substrate has been investigated. These superconducting films have been formed by multilayer sequential electron beam evaporation of Cu, BaF2 and Y with subsequent annealing. The three layer sequence of Y/BaF2/Cu is repeated four times for a total of twelve layers. Such a multilayer film, approximately 1 micron thick, deposited directly on SrTiO3 and annealed at 900 C for 45 min produces a film with a superconducting onset of 93 K and critical temperature of 85 K. Auger electron spectroscopy in conjunction with argon ion sputtering was used to obtain the distribution of each element as a function of depth for an unannealed film, the annealed film on SrTiO3 and annealed films on ZrO2 buffer layers. The individual layers were apparent. After annealing, the bulk of the film on SrTiO3 is observed to be fairly uniform while films on the substrates with buffer layers are less uniform. The Y-Ba-Cu-O/ZrO2 interface is broad with a long Ba tail into the ZrO2, suggesting interaction between the film and the buffer layer. The underlying ZrO2/Si interface is sharper. The detailed Auger results are presented and compared with samples annealed at different temperatures and durations.

  6. Preparation and characterization of Tl sub 2 Ba sub 2 CaCu sub 2 O sub 8 films on (100) LaAlO sub 3

    SciTech Connect

    Holstein, W.L.; Parisi, L.A.; Kountz, D.J.; Wilker, C.; Matthews, A.L. ); Arendt, P.N. ); Taber, R.C. )

    1991-03-01

    A two-step process for the fabrication of 0.12-1.20 {mu}m-thick Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} films on (100) LaAlO{sub 3} has been developed. The process involves the deposition of a BaCaCuO precursor film at low temperature by rf magnetron sputtering, followed by annealing in the presence of Tl{sub 2}O vapor to convert the precursor film into Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8}. Over a distance of 4 cm, film composition was Tl:Ba:Ca:Cu = 2.05 {plus minus} 0.09:2.05 {plus minus} 0.06:1.0 {plus minus} 0.3:1.94 {plus minus} 0.6 and thickness was uniform to within 6%. The films contain only trace quantities of secondary phases and are epitaxially oriented, with the c-axis of Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} perpendicular to the surface and the two a-axes aligned with the pseudo-cubic a-axes of the underlying LaAlO{sub 3} substrate. Films had a T{sub c} for zero dc resistivity of 106.5 {plus minus} 0.5 K,a transport critical current density for continuous current of 2.9 {times} 10{sup 6} A-cm{sup {minus}2} at 77 K, and a sharp ({lt}0.3{degrees} C) ac inductance transition with an onset temperature of 105 {plus minus} 2 K. Surface resistance at 20 GHz less than 2 m{Omega}, about 10X lower than Cu, was routinely achieved for temperatures below 90 K and, for the best films, at temperatures up to 100 K. Surface resistance at about 10 GHz on one film was 0.067 m{Omega} at 4.2 K, 0.36 m{Omega} at 77 K, and 0.74 m{Omega} at 90 K. Films have been reproducibly fabricated on substrates up to 2.54 cm square.

  7. Characteristics of Y-Ba-Cu-O superconductor films on GaAs with an Al sub 2 O sub 3 or AlGaO sub 3 buffer layer

    SciTech Connect

    Shewchun, J.; Chen, Y.; Hoelder, J.S.; Uher, C. )

    1991-06-10

    By depositing a buffer layer of Al{sub 2}O{sub 3} on GaAs, we have been able to laser ablate a superconducting film of Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} overtop. The onset of superconductivity is 92 K and zero resistance is observed at 80 K in a structure with a suitably annealed Al{sub 2}O{sub 3} film which is converted to AlGaO{sub 3}. Both the Al{sub 2}O{sub 3}-GaAs and the Al{sub 2}O{sub 3}-Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} interfaces are remarkably well preserved with virtually no interdiffusion or interaction. The Al{sub 2}O{sub 3} or homolog AlGaO{sub 3} film also prevents decomposition of the GaAs at the deposition temperature of 730 {degree}C.

  8. Performance of two-pole bandpass filters photodefined on double-sided Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O thin films

    NASA Technical Reports Server (NTRS)

    Miranda, F. A.; Toncich, S. S.; Bhasin, K. B.

    1993-01-01

    The performance of 7.3-GHz two-pole bandpass filters (5% bandwidth) fabricated on double-sided Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O thin films deposited on LaAlO3 is discussed. At 77 K, the Tl-Ba-Ca-Cu-O and Y-Ba-Cu-O superconducting filters exhibited minimum passband insertion losses of 0.3 and 1.2 dB, respectively. An insertion loss of 3.4 dB was measured for an all-gold filter at 77 K.

  9. Crystalline orientations of Tl2Ba2Ca2Cu3O(x) grains on MgO, SrTiO3, and LaAlO3 substrates

    NASA Technical Reports Server (NTRS)

    Liou, S. H.; Wu, C. Y.

    1992-01-01

    Crystalline orientations of Tl2Ba2Ca2Cu3O(x) grains in magnetron sputtered films on MgO (001), SrTiO3 (001), and LaAlO3 (001) substrates were investigated by scanning electron microscopy. In contrast to the nearly single crystalline films on the lattice matched substrates SrTiO3 and LaAlO3, films on the MgO (001) substrate, being polycrystalline in nature, exhibit several preferred in-plane grain orientations. These orientations agree well with a simplified theory of near-coincidence site lattices between Tl2Ba2Ca2Cu3O(x) and MgO.

  10. ESR experiments and spectra simulations in YBa2Cu3O7-x, Y2BaCuO5, and BaCuO2+x

    NASA Astrophysics Data System (ADS)

    de Mesquita, R. N.; Castilho, J. H.; Barberis, G. E.; Rettori, C.; Torriani, I.; de Lima, O. F.; Gama, S.; Jardim, R. F.; Terrile, M. C.; Basso, H.; Nascimento, O. R.

    1989-04-01

    Room-temperature X- and Q-band ESR spectra of the high-Tc superconductor YBa2Cu3O7-x and the semiconductors Y2BaCuO5 and BaCuO2+x are studied experimentally and theoretically by measuring, calculating, and fitting the powder spectra corresponding to an anisotropic Zeeman Hamiltonian for Cu2+ in orthorhombic and tetragonal local symmetries. ESR and x-ray studies in their correspoinding oxygen-deficient stoichiometries, obtained by heat treatment under vacuum, were also done. Our results support those of Bowden et al. and Vier et al. in RBa2Cu3O7-x (R=Y, Eu), indicating that the Cu(1) and Cu(2) atoms in the pure YBa2Cu3O7-x phase are not ESR active and the small resonance observed in these compounds comes from other residual phases. The purest YBa2Cu3O7-xsamples that we were able to prepare still have 0.1-0.5 % mass fraction of other residual copper compounds which are responsible for the observed resonance.

  11. Effect of YBa2Cu3O7-δ film thickness on the dielectric properties of Ba0.1Sr0.9TiO3 in Ag /Ba0.1Sr0.9TiO3/YBa2Cu3O7-δ/LaAlO3 multilayer structures

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaohong; Peng, Wei; Li, Jie; Chen, Yingfei; Tian, Haiyan; Xu, Xiaoping; Zheng, Dongning

    2005-01-01

    Ferroelectric and superconductor bilayers of Ba0.1Sr0.9TiO3 (BSTO)/YBa2Cu3O7-δ (YBCO), with different YBCO film thicknesses, have been fabricated in situ by pulsed-laser deposition on 1.2° vicinal LaAlO3 substrates. The dielectric properties of BSTO thin films were measured with a parallel-plate capacitor configuration in the temperature range of 77-300K. We observed a strong dependence of the dielectric properties of BSTO thin films on the thickness of the YBCO layer. As the YBCO-film thickness increases, the temperature of the dielectric permittivity maximum of BSTO thin films shifts to higher values, and the leakage current and dielectric loss increase drastically, while the dielectric constant and dielectric tunability decrease remarkably. The results are explained in terms of the transformation in the growth mode of the YBCO layer from two-dimensional step flow to three-dimensional island that leads to significant deterioration in the dielectric properties of BSTO thin films. We propose that improved dielectric properties could be obtained by reasonably manipulating the growth mode of the YBCO layer in the multilayer structures.

  12. Preparation of BaTiO3/Cu2O and BaTiO3/Cu2O/Au Complexes: Their Photocatalytic and Antipathogenic Effect.

    PubMed

    Cho, Sung-Woo; Nam, Dae-Hyun; Kim, Lee-Han; Jung, Dongwoon

    2016-05-01

    BaTiO3/Cu2O and BaTiO3/Cu2O/Au complexes were prepared from CuCl2, HAuCl4 solution, and BaTiO3 by the solution method. BaTiO3 particles were dispersed in a CuCl2 solution, and the BaTiO3/CuO complex was produced through crystallization of CuO onto the BaTiO3 surface by hydrolysis of CuCl2 in the first stage. After the reaction, CuO was reduced to Cu2O by treatment with glucose, thereby yielding the BaTiO3/Cu2O complex. The BaTiO3/Cu2O/Au complex was prepared by treating the BaTiO3/Cu2O particles with HAuCl4. Under visible light, the obtained BaTiO3/Cu2O0/Au complex showed higher photocatalytic activity than the Degussa P-25sample. In addition, the BaTiO3/Cu2O complex showed excellent antipathogenic effect. PMID:27483887

  13. Processing, electrical and microwave properties of sputtered Tl-Ca-Ba-Cu-O superconducting thin films

    NASA Technical Reports Server (NTRS)

    Subramanyam, G.; Kapoor, V. J.; Chorey, C. M.; Bhasin, K. B.

    1993-01-01

    A reproducible fabrication process has been established for TlCaBaCuO thin films on LaAlO3 substrates by RF magnetron sputtering and post-deposition processing methods. Electrical transport properties of the thin films were measured on patterned four-probe test devices. Microwave properties of the films were obtained from unloaded Q measurements of all-superconducting ring resonators. This paper describes the processing, electrical and microwave properties of Tl2Ca1Ba2Cu2O(x) 2122-plane phase thin films.

  14. Pulsed laser deposition of epitaxial Ba{sub x}Sr{sub 1{minus}x}TiO{sub 3}/YBa{sub 2}Cu{sub 3}O{sub 7} bilayers on LaAlO{sub 3} substrates

    SciTech Connect

    Harkness, S.D.; Yue, C.F.; Borek, M.A.; Singh, R.K.

    1994-09-01

    YBa{sub 2}Cu{sub 3}O{sub 7}/Ba{sub x}Sr{sub 1{minus}x}TiO{sub 8} bilayers were grown epitaxially on LaAlO{sub 3} substrates using the pulsed laser deposition method. A microstructural investigation revealed that all compositions of Ba{sub x}Sr{sub 1{minus}x}TiO{sub 3} investigated from x = 0 to x = 1 showed (001) orientation and epitaxy across the interface as analyzed by Rutherford backscattering spectroscopy channel yields of <8% for BaTiO{sub 8} on YBa{sub 2}Cu{sub 3}O{sub 7} films. Dielectric properties including the dielectric constant, k, and the loss tangent, tan {delta}, were measured as a function of composition, and it was found that the highest k-values (k = 400) existed for the x = 0.72 composition. 9 refs., 4 figs., 2 tabs.

  15. Processing of R-Ba-Cu-O superconductors

    SciTech Connect

    Wu, H.

    1998-02-23

    Precipitation processes were developed to introduce second phases as flux pinning centers in Gd-Ba-Cu-O and Nd-Ba-Cu-O superconductors. In Gd-Ba-Cu-O, precipitation is caused by the decrease of the upper solubility limit of Gd{sub 1+x}Ba{sub 2{minus}x}Cu{sub 3}O{sub 7} solid solution (Gd123ss) in low oxygen partial pressure. Processing of supersaturated Gd{sub 1.2}Ba{sub 1.8}Cu{sub 3}O{sub 7} in low oxygen partial pressure can produce dispersed second phases. Gd211 is formed as a separate phase while extensive Gd124 type stacking fault is formed instead of a separate CuO phase. As a result of the precipitation reaction, the transition temperature and critical current density are increased. In Nd-Ba-Cu-O, precipitation is caused by the decrease of the lower solubility limit of Nd{sub 1+x}Ba{sub 2{minus}x}Cu{sub 3}O{sub 7} solid solution (Nd123ss) in oxygen. DTA results reveal the relative stability of Nd123ss in different oxygen partial pressures. In 1 bar oxygen partial pressure, Nd123ss with x = 0.1 is the most stable phase. In lower oxygen partial pressures, the most stable composition shifts towards the stoichiometric composition. The relative stability changes faster with decreasing oxygen partial pressure. Therefore, processing in oxygen and air tends to produce broad superconducting transitions but sharp transitions can be achieved in 0.01 bar and 0.001 bar oxygen partial pressures. While the lower solubility limits in 0.01 bar and 0.001 bar oxygen partial pressures remain at x = 0.00, the solubility limits in oxygen and air show a narrowing with decreasing temperature. Because of the narrowing of the solubility range in oxygen, oxygen annealing of Nd123 initially processed in low oxygen partial pressures will result in precipitation of second phases. The equilibrium second phase is BaCuO{sub 2} for temperature above 608 C, and at lower temperatures the equilibrium second phases are Ba{sub 2}CuO{sub 3.3} and Ba{sub 2}Cu{sub 3}O{sub 5+y}. However, annealing at

  16. Chemical fabrication of superconducting Y-Ba-Cu oxide films

    NASA Astrophysics Data System (ADS)

    Hussain, A. A.; Sayer, M.

    1992-02-01

    High-Tc superconducting films of Y-Ba-Cu oxide were prepared on 100-plane MgO substrates by a sol-gel method. A procedure is described for preparing a superconducting film using acetate compounds dissolved in salicylic or lactic acids in the presence of ethylene glycol. This solution has superior qualities in terms of homogeneity, viscosity, and stability against atmospheric hydration. The results indicate that the nature of the solvent influences the microstructure and superconducting properties of Y-Ba-Cu-O films. X-ray diffraction analysis reveals that the annealed films are textured and had orthorhombic orientation. A correlation between the crystal structure and the superconducting properties of the Y-Ba-Cu-O films is presented.

  17. Cross sections for the production of residual nuclides by low- and medium-energy protons from the target elements C, N, O, Mg, Al, Si, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Sr, Y, Zr, Nb, Ba and Au

    NASA Astrophysics Data System (ADS)

    Michel, R.; Bodemann, R.; Busemann, H.; Daunke, R.; Gloris, M.; Lange, H.-J.; Klug, B.; Krins, A.; Leya, I.; Lüpke, M.; Neumann, S.; Reinhardt, H.; Schnatz-Büttgen, M.; Herpers, U.; Schiekel, Th.; Sudbrock, F.; Holmqvist, B.; Condé, H.; Malmborg, P.; Suter, M.; Dittrich-Hannen, B.; Kubik, P.-W.; Synal, H.-A.; Filges, D.

    1997-07-01

    Cross sections for residual nuclide production by p-induced reactions were measured from thresholds up to 2.6 GeV using accelerators at CERN/Geneve, IPN/Orsay, KFA/Jülich, LANL/Los Alamos, LNS/Saclay, PSI/Villigen, TSL/Uppsala, LUC/Louvain La Neuve. The target elements C, N, O, Mg, Al, Si, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Sr, Y, Zr, Nb, Ba and Au were investigated. Residual nuclides were measured by X- and γ-spectrometry and by Accelerator Mass Spectrometry (AMS). The measured cross sections were corrected for interfering secondary particles in experiments with primary proton energies above 200 MeV. Our consistent database covers presently ca 550 nuclear reactions and contains nearly 15000 individual cross sections of which about 10000 are reported here for the first time. They provide a basis for model calculations of the production of cosmogenic nuclides in extraterrestrial matter by solar and galactic cosmic ray protons. They are of importance for many other applications in which medium energy nuclear reactions have to be considered ranging from astrophysics over space and environmental sciences to accelerator technology and accelerator-based nuclear waste transmutation and energy amplification. The experimental data are compared with theoretical ones based on calculations using an INC/E model in form of the HETC/KFA2 code and on the hybrid model of preequilibrium reactions in form of the AREL code.>

  18. Electron microscopy of a Gd-Ba-Cu-O superconductor

    NASA Technical Reports Server (NTRS)

    Ramesh, R.; Thomas, G.; Meng, R. L.; Hor, P. H.; Chu, C. W.

    1989-01-01

    An electron microscopy study has been carried out to characterize the microstructure of a sintered Gd-Ba-Cu-O superconductor alloy. The GdBa2Cu3O(7-x) phase in the oxygen annealed sample is orthorhombic, while in the vacuum annealed sample it is tetragonal. It is shown that the details of the fine structure in the 001-line zone axis convergent beam patterns can be used to distinguish between the orthorhombic form and the tetragonal form. In addition to this matrix phase, an amorphous phase is frequently observed at the triple grain junctions. Gd-rich inclusions have been observed inside the matrix phase.

  19. Incorporation of Ba in Al and Fe pollucite

    NASA Astrophysics Data System (ADS)

    Vance, Eric R.; Gregg, Daniel J.; Griffiths, Grant J.; Gaugliardo, Paul R.; Grant, Charmaine

    2016-09-01

    Ba, the transmutation product of radioactive Cs, can be incorporated at levels of up to ∼0.07 formula units in Cs(1-2x)BaxAlSi2O6 aluminium pollucite formed by sol-gel methods and sintering at 1400 °C, with more Ba forming BaAl2Si2O8 phases. The effect of Ba substitution in pollucite-structured CsFeSi2O6 was also studied and no evidence of Ba substitution in the pollucite structure via cation vacancies or Fe2+ formation was obtained. The Ba entered a Fe-silicate glass structure. Charge compensation was also attempted with a Cs+ + Fe3+ ↔ Ba2+ + Ni2+ scheme but again the Ba formed a glass and NiO was evident. PCT leaching data showed CsFeSi2O6 to be very leach resistant.

  20. Crystal structure and superconductivity in (Cu,Hg)Ba2Ca4Cu5Oy

    NASA Astrophysics Data System (ADS)

    Akimoto, J.; Kawaguchi, K.; Sohma, M.; Hayakawa, H.; Gotoh, Y.; Oosawa, Y.; Tokiwa, K.; Iyo, A.; Ihara, H.

    1997-02-01

    A new solid-solution superconductor, (Cu,Hg)Ba2Ca4Cu5Oy with the tetragonal lattice parameters a = 3.849(2) Å and c = 21.496(3) Å, has been synthesized by the high-temperature and high-pressure technique. The structure refinement of the as-prepared (Cu,Hg)-1245 by the single-crystal X-ray diffraction method confirmed the substitutional composition (Cu0.76Hg0.24)Ba2Ca4Cu5O12.45, whose cationic composition was close to that obtained by chemical analysis. The additional Cu atoms at the mercury site construct the chain-like oxygen coordination. The superstructure observed in Cu-1245 disappeared by the partial substitution of mercury for copper in the present (Cu,Hg)-1245. The structure refinement of the as-prepared Hg-1245 revealed the mercury-site deficiency of about 20%.

  1. Growth and transport properties of Y-Ba-Cu-O/Pr-Ba-Cu-O superlattices

    SciTech Connect

    Lowndes, D.H.; Norton, D.P.; Budai, J.D.; Christen, D.K.; Klabunde, C.E.; Warmack, R.J.; Pennycook, S.J.

    1990-01-01

    The pulsed-laser deposition method has been used to fabricate epitaxial, nonsymmetric M(Y) {times} N(Pr) superlattices in which YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) layers either M = 1,2,3,4,8, or 16 c-axis unit cells thick are separated by insulating PrBa{sub 2}Cu{sub 3}O{sub 7-x} (PBCO) layers N unit cells thick (N = 1 to {approximately}32). The zero-resistance superconducting transition temperature, T{sub c0}, initially decreases rapidly with increasing PBCO layer thickness, but then saturates at T{sub c0} {approximately} 19 K, 54 K, 71 K, or 80 K, or structures containing 1-,2-,3-, or 4-cell-thick YBCO layers, respectively. Critical current density measurements carried out on structures with 16- or 32-cell thick YBCO layers show that the magnitude of J{sub c}(H = 0) {approximately} 1-2 MA/cm{sup 2}, as well as the magnetic field dependence and the anisotropy of J{sub c}(H) all are in good agreement with corresponding measurements on thicker, single-layer YBCO films. Thus, there is no evidence of an enhanced J{sub c}(H) due to the multi-layered structure, for the layer thickness investigated to date. The systematic variation of T{sub c0}, as a function of the YBCO and PBCO layer thickness, is discussed in light of other recent experiments and theoretical model calculations. The superlattices' structural and compositional order are characterized using x-ray diffraction, transmission electron microscopy, and scanning tunneling microscopy, and details of the pulsed-laser deposition process are reported. 42 refs., 7 figs.

  2. Epitaxial Ba-Y-Cu-O ceramic superconducting film on perovskite structure substrate

    SciTech Connect

    Chai, B.H.

    1991-07-09

    This patent describes a superconducting structure. It comprises a crystal substrate having a superconducting film epitaxially deposited thereon, wherein the substrate is a crystal selected from the group consisting of LaAlO{sub 3}, LaGaO{sub 3}, PrGaO{sub 3} and NdGaO{sub 3}, and wherein the superconducting film is a Ba- Y- Cu- O superconductor.

  3. Cu/Ba/bauxite: an inexpensive and efficient alternative for Pt/Ba/Al₂O₃ in NOx removal.

    PubMed

    Wang, Xiuyun; Chen, Zhilin; Luo, Yongjin; Jiang, Lilong; Wang, Ruihu

    2013-01-01

    Cu/Ba/bauxite possesses superior NOx storage and reduction (NSR) performances, high thermal stability, strong resistance against SO₂ poisoning and outstanding regeneration ability in comparison with Pt/Ba/Al₂O₃. It can serve as a cheap and promising alternative for traditional Pt/Ba/Al₂O₃ in NOx removal from lean-burn engines.

  4. Electrical-transport properties and microwave device performance of sputtered TlCaBaCuO superconducting thin films

    NASA Technical Reports Server (NTRS)

    Subramanyam, G.; Kapoor, V. J.; Chorey, C. M.; Bhasin, K. B.

    1992-01-01

    The paper describes the processing and electrical transport measurements for achieving reproducible high-Tc and high-Jc sputtered TlCaBaCuO thin films on LaAlO3 substrates, for microelectronic applications. The microwave properties of TlCaBaCuO thin films were investigated by designing, fabricating, and characterizing microstrip ring resonators with a fundamental resonance frequency of 12 GHz on 10-mil-thick LaAlO3 substrates. Typical unloaded quality factors for a ring resonator with a superconducting ground plane of 0.3 micron-thickness and a gold ground plane of 1-micron-thickness were above 1500 at 65 K. Typical values of penetration depth at 0 K in the TlCaBaCuO thin films were between 7000 and 8000 A.

  5. Method of forming superconducting Tl-Ba-Ca-Cu-O films

    DOEpatents

    Wessels, Bruce W.; Marks, Tobin J.; Richeson, Darrin S.; Tonge, Lauren M.; Zhang, Jiming

    1993-01-01

    A method of forming a superconducting Tl-Ba-Ca-Cu-O film is disclosed, which comprises depositing a Ba-Ca-Cu-O film on a substrate by MOCVD, annealing the deposited film and heat-treating the annealed film in a closed circular vessel with TlBa.sub.2 Ca.sub.2 Cu.sub.3 O.sub.x and cooling to form said superconducting film of TlO.sub.m Ba.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+2, wherein m=1,2 and n=1,2,3.

  6. Submillimeter and microwave residual losses in epitaxial films of Y-Ba-Cu-O and Tl-Ca-Ba-Cu-O

    SciTech Connect

    Miller, D.; Richards, P.L. ); Garrison, S.M.; Newman, N. ); Eom, C.B.; Geballe, T.H. . Dept. of Applied Physics); Etemad, S.; Inam, A.; Venkatesan, T. ); Martens, J.S. (Sandia National Labs., Albuquerque, NM (Unite

    1992-03-01

    We have used a novel bolometric technique and a resonant technique to obtain accurate submillimeter and microwave residual loss data for epitaxial thin films of YBa{sub 2}Cu{sub 3}O{sub 7}, Tl{sub 2}Ca{sub 2}Ba{sub 2}Cu{sub 3}O{sub 10} and Tl{sub 2}CaBa{sub 2}Cu{sub 2}O{sub 8}. For all films we obtain good agreement between the submillimeter and microwave data, with the residual losses in both the Y-Ba-Cu-O and Tl-Ca-Ba-Cu-O films scaling approximately as frequency squared below {approximately} 1 THz. We are able to fit the losses in the Y-Ba-Cu-O films to a weakly coupled grain model for the a-b plane conductivity, in good agreement with results from a Kramers-Kronig analysis of the loss data. We observe strong phonon structure in the Tl-Ca-Ba-Cu-O films for frequencies between 2 and 21 THz, and are unable to fit these losses to the simple weakly coupled grain model. This is in strong contrast to the case for other high {Tc} superconductors such as YBa{sub 2}Cu{sub 3}O{sub 7}, where phonon structure observed in ceramic samples is absent in epitaxial oriented films and crystals because of the electronic screening due to the high conductivity of the a-b planes.

  7. Mechanical properties of DyBaCuO superconducting bulks

    NASA Astrophysics Data System (ADS)

    Fujimoto, H.; Shimada, H.; Yoshizawa, S.

    2007-10-01

    Melt-processed REBaCuO (RE: rare earth) superconductors have a high Jc at 77 K and a high magnetic field, which are expected to be used for high field applications such as superconducting permanent magnets with liquid nitrogen refrigeration, flywheels, current leads and so on. Mechanical properties such as flexural strength, fracture toughness and ductility are very crucial as well as the superconducting properties: Tc, Jc, and Hirr for industrial applications of high-Tc oxide superconductors. However, oxide superconductors have the intrinsic brittleness of the perovskite structure, thus, the strength and the fracture toughness of REBaCuO superconductors have been reported to be low and anisotropic. Therefore, we should investigate and improve mechanical properties to achieve structural reliability for applications. Large single domain of melt-processed REBaCuO (Dy-123) superconductors with Dy2BaCuO5 (Dy-211) particles and Ag2O of 10 wt% was fabricated with a seeding and temperature gradient method in air. In this study, we discuss mechanical properties such as the hardness and the surface roughness, and the flexural strength of the RE-123 bulk, measured at RT. The results of Vickers hardness, surface roughness and the flexural strength showed very important information for evaluating characteristics of RE-123 bulks.

  8. On the existence of a homologous series of Ba mCu m+nO y oxides with the cubic structure of the BaCuO 2 oxide

    NASA Astrophysics Data System (ADS)

    Klinkova, L. A.; Nikolaichik, V. I.; Barkovskii, N. V.; Fedotov, V. K.

    2010-12-01

    Phase relations have been studied in the BaO-CuO x system in the range of 42.0-83.0 mol.% CuO at P(O 2) = 21 kPa (air) by visual polythermal analysis (VPA), powder X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TGA), chemical analysis (CA), and electron diffraction (ED) with simultaneous elemental analysis (EA) in a transmission electron microscope (TEM). The existence of discrete crystallization fields of barium-copper oxides of cation compositions Ba 4Cu 5O y, Ba 5Cu 6O y, Ba 7Cu 8O y, Ba 12Cu 13O y, and Ba 24Cu 25O y, which have the cubic structure of the BaCuO 2 oxide, is revealed in the studied region of the system. The oxides may be represented as members of a Ba mCu m+nO y homologous series. The BaCuO 2 oxide does not exist in the subsolidus region and does not have its own crystallization field. The oxygen-deficient oxide BaCuO 1.78 of the cation composition (Ba:Cu) 1:1 with the BaCuO 2 cubic structure is found in melted samples of the 50.0 mol.% CuO composition quenched at 1020-1060 °С.

  9. Microstructures and properties of superconducting Y-ErBaCuO thin films obtained from disordered Y-ErBaF2Cu films

    NASA Technical Reports Server (NTRS)

    Cikmach, P.; Diociaiuti, M.; Fontana, A.; Giovannella, C.; Iannuzzi, M.; Lucchini, C.; Merlo, V.; Messi, R.; Paoluzi, L.; Scopa, L.

    1991-01-01

    The preparation procedure used to obtain superconducting thin films by radio frequency magnetron sputtering of a single mosaic target is described in detail. The single mosaic target is composed of (Y-Er), BaF2, and Cu.

  10. Microstructures and properties of superconducting Y-Er-BaCu-O thin films obtained from disordered Y-Er-BaF2-Cu films

    NASA Technical Reports Server (NTRS)

    Cikmach, P.; Diociaiuti, M.; Fontana, A.; Giovannella, C.; Iannuzzi, M.; Lucchini, C.; Messi, R.; Paoluzi, L.; Scopa, L.; Tripodi, P.

    1990-01-01

    Since the first reports on superconducting thin films obtained by evaporating BaF2, Cu and Y(sup 1), or Yb or Er(sup 2), several others have followed. All these reports describe thin films prepared by means of molecular beam cells or electron guns. Researchers show that films with similar properties can be obtained by radio frequency sputtering of a single mosaic target composed by Y-Er, BaF2 and Cu. Process steps are described.

  11. Resistance to micro-plastic deformation in superconducting Y-Ba-Cu-O

    NASA Astrophysics Data System (ADS)

    Nishi, Yoshitake; Tokunaga, Shigeki; Toyama, Toshinobu

    1988-01-01

    The stress-strain behavior of a Y-Ba-Cu-O superconducting ceramic (Tc above 90 K) is investigated experimentally under conditions of microplastic deformation using X-ray diffraction analysis and Vickers hardness measurements. The resistance of YBa2Cu3O(9-y) specimens to microplastic deformation is estimated at HV 520 at the surface and 300 in the bulk. It is further shown that polishing increases Tc by removing a surface layer of sintered Y-Ba-Cu oxide.

  12. Activity and diffusivity of oxygen in liquid Ag-Yb1Ba2Cu3 and Tl1Ba2Ca2Cu3 alloys

    NASA Astrophysics Data System (ADS)

    Chou, H.; Chen, H. S.; Fang, W. C.; Wu, M. K.

    1992-12-01

    We have measured the activity and diffusivity of oxygen in liquid Ag-Yb1Ba2Cu3 and Tl1Ba2Ca2Cu3 at 930 and 900 °C, respectively, by a modified coulometric titration method on the galvanic cell: O_ in liquid alloys/yttria stabilized zirconia/air, Pt. The standard Gibbs formation energy and the diffusivity of oxygen in liquid Ag-Yb1Ba2Cu3 alloy for 1/2O2(1 atm)→O_(1 at. %) are determined to be ΔG=-247.4 kJ/g atom, and D=1.52×10-4 cm2/s. The oxygen solubility Cs in the Ag-Yb1Ba2Cu3 alloy is 0.0913 at. %, a factor of 5.5 higher than that in Yb1Ba2Cu3 alloy. The addition of Ag does not alter the growth mechanism and the oxygen diffusion controls the film growth. The growth speed is enhanced as a result of the enhanced oxygen solubility. ΔG and the diffusion coefficient of oxygen in the Tl1Ba2Ca2Cu3 liquid alloy are -257 kJ/g atom and 1.2×10-4 cm2/s, respectively. The oxygen solubility of the Tl1Ba2Ca2Cu3 alloy at 900 °C is found to be very high at ˜5.74 at. %. All thermodynamic data for oxygen in the precursor alloys are consistent with each other but there is a deviation of activity coefficient with composition for the different alloys from the theoretical model.

  13. Characterization of LiF/CuO-Codoped BaTiO3 for Embedded Capacitors

    NASA Astrophysics Data System (ADS)

    Lee, Kyoungho

    2015-03-01

    Sintering additives for BaTiO3 were studied in order to facilitate the use of BaTiO3 as a material for embedded decoupling capacitors in high-density multilayered low-temperature cofired ceramic (LTCC) modules for mobile communication systems and three-dimensional (3D) printing modules. Among the studied additives, the CuO/LiF mixture was the most promising sintering additive for cofiring BaTiO3 with a commercial low-permittivity ( ɛ r) LTCC sheet (MLS-22, NEG Co.). The temperature dependence of the dielectric properties of BaTiO3 was successfully controlled by adjusting the CuO/LiF amount and ratio and the sintering temperature. BaTiO3 codoped with 10 wt.% LiF/CuO (1:1 ratio) and sintered at 860°C for 30 min showed 95% sintering density. The room-temperature permittivity ( ɛ r) of LiF/CuO-codoped BaTiO3 was 1620 at 1 MHz, and the temperature coefficient of capacitance satisfied the X5R specification. After cofiring this LiF/CuO-codoped BaTiO3 ceramic with an MLS-22 sheet at 860°C, there was no crack formation at the layer boundary. Also a chemical compatibility test revealed that there were no severe reactions between the LiF/CuO-codoped BaTiO3 and an Ag electrode.

  14. 10 kbar phase equilibria in the Y-Ba-Cu oxide system at 950 C

    SciTech Connect

    Lawanier, J.P.; Meen, J.K.; Elthon, D.

    1996-02-01

    Phase equilibria in the YO{sub 1.5}BaO-CuO system have been determined at 950 C at 10 kbar using a piston-cylinder apparatus. The oxide phases stable under these conditions are Y{sub 2}O{sub 3}, Y{sub 2}Cu{sub 2}O{sub 5}, CuO, Y{sub 2}BaCuO{sub 5}, YBa{sub 2}Cu{sub 3}O{sub 6.5}, BaCuO{sub 2}, Y{sub 2}BaO{sub 4}, Y{sub 2}Ba{sub 3}O{sub 6}, and YBa{sub 4}Cu{sub 2}O{sub 7.5}. The phase stabilities observed at 950 C at 10 kbar are identical to those observed at 950 C in air or oxygen at 1 atm for compositions with < 40% Ba of the cations. In more Ba-rich portions of the phase diagram, carbonates and oxycarbonates are stabilized and a systematic determination of the phase equilibria has not been successful.

  15. Yttrium enrichment and improved magnetic properties in partially melted Y-Ba-Cu-O materials

    NASA Technical Reports Server (NTRS)

    Alterescu, Sidney; Hojaji, Hamid; Barkatt, Aaron; Michael, Karen A.; Hu, Shouxiang

    1990-01-01

    The yttrium-rich compositions in the Y-Ba-Cu-O system were mapped out in a systematic manner to quantify their magnetic properties and to correlate them with the microstructure and phase composition as determined by scanning electron microscopy and X-ray diffraction analysis. It is found that the microstructure of Y-Ba-Cu-O compositions is a sensitive function of both their composition and processing conditions. Measurements of magnetic susceptibility and maximum (low-field) and remanent magnetization for the system Y:Ba:Cu = x:2:3 show highest values for x = 2. The corresponding structures involve numerous small crystals of Y2BaCuO5 (211) embedded in highly ordered assemblages of continous YBa2Cu3O(7-y) (123) layers.

  16. Superconductivity in the Sn-Ba-Sr-Y-Cu-O system

    NASA Technical Reports Server (NTRS)

    Aleksandrov, K. S.; Khrustalev, B. P.; Krivomazov, S. N.; Petrov, M. I.; Vasilyev, A. D.; Zwegintsev, S. A.

    1991-01-01

    After the discovery of high-T(sub c) superconductivity in the La-Ba-Cu-O compound, several families of superconducting oxides were synthesized. Here, researchers report the results of the search for superconductivity in the compounds based on tin which has a lone electron pair like Bi, Tl, and Pb. The following compounds were synthesized: Sn1Ba1Sr1Cu3O(sub x), Sn1Ba1Ca1Cu3O(sub x), Sn1Ba1Mg1Cu3O(sub x), Sn1Sr1Ca1Cu3O(sub x), Sn1Sr1Mg1Cu3O(sub x), and Sn1Ca1Mg1Cu3O(sub x). The initial components were oxides and carbonates of the appropriate elements. A standard firing-grinding procedure was used. Final heating was carried out at 960 C during 12 hours. Then the samples were cooled inside the furnace. All the synthesis cycles were carried out in air atmosphere. Among the synthesized compounds only Sn1Ba1Sr1Cu3O(sub x) showed remarkable conductivity. Other compounds were practically dielectrics. Presence of a possible superconductivity in Sn1Ba1Sr1Cu3O(sub x) was defined by using the Meissner effect. At low temperature a deviation from paramagnetic behavior is observed. The hysteresis loops obtained at lower temperature undoubtly testify to the presence of a superconductive phase in the sample. However, the part of the superconductive phase in the Sn1Ba1Sr1Cu3O(sub x) ceramic turned out to be small, less than 2 percent, which agrees with the estimation from magnetic data. In order to increase the content of the superconductive phase, two-valent cations Ba and Sr were partially substituted by univalent (K) and three-valent ones (Y).

  17. Superconductivity in the Sn-Ba-Sr-Y-Cu-O system

    NASA Technical Reports Server (NTRS)

    Aleksandrov, K. S.; Khrustalev, B. P.; Krivomazov, S. N.; Petrov, M. I.; Vasilyev, A. D.; Zwegintsev, S. A.

    1990-01-01

    Since Bednorz and Muller discovered high-T(sub c) superconductivity in the La-Ba-Cu-O compound, several families of superconducting oxides have been synthesized. Here, researchers report the results of search for superconductivity in the compounds based on tin, which has a lone electron pair like Bi, Tl, Pb. The following compounds were synthesized: Sn1Ba1Sr1Cu3Ox, Sn1Ba1Ca1Cu3Ox, Sn1Ba1Mg1Cu3Ox, Sn1Sr1Ca1Cu3Ox, Sn1Sr1Mg1Cu3Ox, Sn1Ca1Mg1Cu3Ox. The initial components were oxides and carbonates of the appropriate elements. Standard firing-grinding procedure was used. Final heating was carried out at 960 C during 12 hours. Then the samples were cooled inside the furnace. All the synthesis cycles were carried out in air atmosphere. Among the synthesized compounds only Sn1Ba1Sr1Cu3Ox showed remarkable conductivity. Other compounds were practically dielectrics. Presence of a possible superconductivity in Sn1Ba1Sr1Cu3Ox was defined by using the Meissner effect. At low temperature a deviation from paramagnetic behavior is observed. The hysteresis loops obtained at lower temperatures undoubtly testify to the presence of a superconductive phase in the sample. However, the part of the superconductive phase in the Sn1Ba1Sr1Cu3Ox ceramic turned out to be small, less than 2 percent, which agrees with the estimation from magnetic data. In order to increase the content of the superconductive phase two-valent cations Ba, Sr were partially substituted by univalent (K) and three-valent ones (Y).

  18. Superconductivity in the Sn-Ba-Sr-Y-Cu-O system

    NASA Astrophysics Data System (ADS)

    Aleksandrov, K. S.; Khrustalev, B. P.; Krivomazov, S. N.; Petrov, M. I.; Vasilyev, A. D.; Zwegintsev, S. A.

    1990-04-01

    Since Bednorz and Muller discovered high-T(sub c) superconductivity in the La-Ba-Cu-O compound, several families of superconducting oxides have been synthesized. Here, researchers report the results of search for superconductivity in the compounds based on tin, which has a lone electron pair like Bi, Tl, Pb. The following compounds were synthesized: Sn1Ba1Sr1Cu3Ox, Sn1Ba1Ca1Cu3Ox, Sn1Ba1Mg1Cu3Ox, Sn1Sr1Ca1Cu3Ox, Sn1Sr1Mg1Cu3Ox, Sn1Ca1Mg1Cu3Ox. The initial components were oxides and carbonates of the appropriate elements. Standard firing-grinding procedure was used. Final heating was carried out at 960 C during 12 hours. Then the samples were cooled inside the furnace. All the synthesis cycles were carried out in air atmosphere. Among the synthesized compounds only Sn1Ba1Sr1Cu3Ox showed remarkable conductivity. Other compounds were practically dielectrics. Presence of a possible superconductivity in Sn1Ba1Sr1Cu3Ox was defined by using the Meissner effect. At low temperature a deviation from paramagnetic behavior is observed. The hysteresis loops obtained at lower temperatures undoubtly testify to the presence of a superconductive phase in the sample. However, the part of the superconductive phase in the Sn1Ba1Sr1Cu3Ox ceramic turned out to be small, less than 2 percent, which agrees with the estimation from magnetic data. In order to increase the content of the superconductive phase two-valent cations Ba, Sr were partially substituted by univalent (K) and three-valent ones (Y).

  19. Superconducting behaviors in (Y1 - xLax)Ba2Cu3Oy (0 <= x <= 1)

    NASA Astrophysics Data System (ADS)

    Okada, M.; Matsuoka, D.; Zou, H.; Homma, M.

    1988-11-01

    The superconducting behavior of (Y1-xLax)Ba2Cu3Oy compounds for 0≤x≤1 was studied. It was found that Tc decreased with increasing La content. (Y1-xLax)Ba2Cu3Oy for 0≤x≤0.4, fired at 1050 °C in air, shows onset temperatures above 90 K. Annealing (Y1-xLax)Ba2Cu3Oy at 300 °C in O2 enhanced the onset temperature above 70 K for all studied compositions (x=0-1), and altered the crystal structure from tetragonal to orthorhombic.

  20. Room Temperature Radiolytic Synthesized Cu@CuAlO2-Al2O3 Nanoparticles

    PubMed Central

    Abedini, Alam; Saion, Elias; Larki, Farhad; Zakaria, Azmi; Noroozi, Monir; Soltani, Nayereh

    2012-01-01

    Colloidal Cu@CuAlO2-Al2O3 bimetallic nanoparticles were prepared by a gamma irradiation method in an aqueous system in the presence of polyvinyl pyrrolidone (PVP) and isopropanol respectively as a colloidal stabilizer and scavenger of hydrogen and hydroxyl radicals. The gamma irradiation was carried out in a 60Co gamma source chamber with different doses up to 120 kGy. The formation of Cu@CuAlO2-Al2O3 nanoparticles was observed initially by the change in color of the colloidal samples from colorless to brown. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of bonds between polymer chains and the metal surface at all radiation doses. Results of transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD) showed that Cu@CuAlO2-Al2O3 nanoparticles are in a core-shell structure. By controlling the absorbed dose and precursor concentration, nanoclusters with different particle sizes were obtained. The average particle diameter increased with increased precursor concentration and decreased with increased dose. This is due to the competition between nucleation, growth, and aggregation processes in the formation of nanoclusters during irradiation. PMID:23109893

  1. Room temperature radiolytic synthesized Cu@CuAlO(2)-Al(2)O(3) nanoparticles.

    PubMed

    Abedini, Alam; Saion, Elias; Larki, Farhad; Zakaria, Azmi; Noroozi, Monir; Soltani, Nayereh

    2012-01-01

    Colloidal Cu@CuAlO(2)-Al(2)O(3) bimetallic nanoparticles were prepared by a gamma irradiation method in an aqueous system in the presence of polyvinyl pyrrolidone (PVP) and isopropanol respectively as a colloidal stabilizer and scavenger of hydrogen and hydroxyl radicals. The gamma irradiation was carried out in a (60)Co gamma source chamber with different doses up to 120 kGy. The formation of Cu@CuAlO(2)-Al(2)O(3) nanoparticles was observed initially by the change in color of the colloidal samples from colorless to brown. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of bonds between polymer chains and the metal surface at all radiation doses. Results of transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD) showed that Cu@CuAlO(2)-Al(2)O(3) nanoparticles are in a core-shell structure. By controlling the absorbed dose and precursor concentration, nanoclusters with different particle sizes were obtained. The average particle diameter increased with increased precursor concentration and decreased with increased dose. This is due to the competition between nucleation, growth, and aggregation processes in the formation of nanoclusters during irradiation. PMID:23109893

  2. Evidence for superconductivity above 40 K in the La-Ba-Cu-O compound system

    NASA Technical Reports Server (NTRS)

    Chu, C. W.; Hor, P. H.; Meng, R. L.; Gao, L.; Huang, Z. J.

    1987-01-01

    An apparent superconducting transition with an onset temperature above 40 K has been detected under pressure in the La-Ba-Cu-O compound system synthesized directly from a solid-state reaction of La2O3, CuO, and BaCO3 followed by a decomposition of the mixture in a reduced atmosphere. The experiment is described and the results of effects of magnetic field and pressure are discussed.

  3. PrBa{sub 2}Cu{sub 3}O{sub 7}: A new superconductor

    SciTech Connect

    Blackstead, H.A.; Dow, J.D.

    1995-10-01

    PrBa{sub 2}Cu{sub 3}O{sub 7} superconducts, provided Pr is kept off Ba-sites - experimentally confirming the prediction of the oxygen model and indicating that superconductivity originates in the chains, not in the planes.

  4. The Composition and Structure of Y-Ba-Cu-O Superconductors

    NASA Astrophysics Data System (ADS)

    Hua, Z. Y.; Jia, C. L.; Cheng, H. S.; Cai, Y. M.; Jiang, A. R.

    High Tc superconductors of Y-Ba-Cu-O system with (Y+Ba):Cu=1~2 have been investigated. Results show that any sample in this system with a proportion of Y:Cu between 0.6 and 1.2 is oxygen-deficient and will be superconductive after sintering in an oxygen flow. In this system all superconductors with different nominal composition have a superconductive phase of perovskite-1ike YBa2Cu3O7 (Phase A), and the difference of constituents is shown in another phase (Phase B) which acts as a gettering center. When the composition has an excess of Y, there will be a third phase (Phase C) which has been identified as small particles of Y2O3. For an exact nominal proportion of Y:Ba:Cu=1:2:3, single-phase superconductors can be prepared.

  5. Crystal structure of the oxides BaCuGd/sub 2/O/sub 5/ and Ba/sub 2/Cu/sub 3/GdO/sub 7-//sub x/

    SciTech Connect

    Campa, J.A.; de Salazar, J.M.G.; Gutierrez-Puebla, E.; Monge, M.A.; Rasines, I.; Ruiz-Valero, C.

    1988-01-01

    We have grown crystals of BaCuGd/sub 2/O/sub 5/ and Ba/sub 2/Cu/sub 3/GdO/sub 7-//sub x/ and determined their structures by single-crystal x-ray diffraction. Green and black BaCuGd/sub 2/O/sub 5/ are roughly identical. In the refinement of Ba/sub 2/Cu/sub 3/GdO/sub 7-//sub x/ a value of x = 0.5 is obtained. The existence of oxygen vacancies is compatible with an incommensurable system and also with high-order superstructures.

  6. Co2FeAl based magnetic tunnel junctions with BaO and MgO/BaO barriers

    NASA Astrophysics Data System (ADS)

    Rogge, J.; Hetaba, W.; Schmalhorst, J.; Bouchikhaoui, H.; Stender, P.; Baither, D.; Schmitz, G.; Hütten, A.

    2015-07-01

    We succeed to integrate BaO as a tunneling barrier into Co2FeAl based magnetic tunnel junctions (MTJs). By means of Auger electron spectroscopy it could be proven that the applied annealing temperatures during BaO deposition and afterwards do not cause any diffusion of Ba neither into the lower Heusler compound lead nor into the upper Fe counter electrode. Nevertheless, a negative tunnel magnetoresistance (TMR) ratio of -10% is found for Co2FeAl (24 nm) / BaO (5 nm) / Fe (7 nm) MTJs, which can be attributed to the preparation procedure and can be explained by the formation of Co- and Fe-oxides at the interfaces between the Heusler and the crystalline BaO barrier by comparing with theory. Although an amorphous structure of the BaO barrier seems to be confirmed by high-resolution transmission electron microscopy (TEM), it cannot entirely be ruled out that this is an artifact of TEM sample preparation due to the sensitivity of BaO to moisture. By replacing the BaO tunneling barrier with an MgO/BaO double layer barrier, the electric stability could effectively be increased by a factor of five. The resulting TMR effect is found to be about +20% at room temperature, although a fully antiparallel state has not been realized.

  7. ESR, SIMS and TEMF of an Y-Ba-Cu-O superconductor

    NASA Technical Reports Server (NTRS)

    Kirschner, I.; Giber, J.; Halasz, I.

    1995-01-01

    Superconducting transition comes into being between 92 K and 82 K in the samples having a Meissner's state value of 68 vol. percent. The main material content has an orthorhombic unit cell of Y1Ba2Cu408 accompanied by low quantity CuO and a sporadic phase. A proof of anisotropic superconductivity, an unusually high Cu ion concentration and a temperature dependent transition of charge carriers have been observed.

  8. Synthesis of Y1Ba2Cu3O(sub x) superconducting powders by intermediate phase reaction

    NASA Technical Reports Server (NTRS)

    Moore, C.; Fernandez, J. F.; Recio, P.; Duran, P.

    1990-01-01

    One of the more striking problems for the synthesis of the Y1Ba2Cu3Ox compound is the high-temperature decomposition of the BaCO3. This compound is present as raw material or as an intermediate compound in chemical processes such as amorphous citrate, coprecipitation oxalate, sol-gel process, acetate pyrolisis, etc. This fact makes difficult the total formation reaction of the Y1Ba2Cu3Ox phase and leads to the presence of undesirable phases such as the BaCuO2 phase, the 'green phase', Y2BaCuO5 and others. Here, a new procedure to overcome this difficulty is studied. The barium cation is previously combined with yttrium and/or copper to form intermediate compounds which can react between them to give Y1Ba2Cu3Ox. BaY2O4 and BaCu2O3 react according to the equation BaY2O4+3BaCu2O3 yields 2Y1Ba2Cu3Ox. BaY2O4 is a stable compound of the Y2O3-BaO system; BaCu2O3 is an intimate mixture of BaCuO2 and uncombined CuO. The reaction kinetics of these phases have been established between 860 and 920 C. The phase evolution has been determined. The crystal structure of the Y1Ba2Cu3Ox obtained powder was studied. According to the results obtained from the kinetics study the Y1Ba2Cu3Ox the synthesis was performed at temperatures of 910 to 920 C for short treatment times (1 to 2 hours). Pure Y1Ba2Cu3Ox was prepared, which develops orthorombic type I structure despite of the cooling cycle. Superconducting transition took place at 91 K. The sintering behavior and the superconducting properties of sintered samples were studied. Density, microstructure and electrical conductivity were measured. Sintering densities higher than 95 percent D(sub th) were attained at temperatures below 940 C. Relatively fine grained microstructure was observed, and little or no-liquid phase was detected.

  9. Elastocaloric effect in CuAlZn and CuAlMn shape memory alloys under compression.

    PubMed

    Qian, Suxin; Geng, Yunlong; Wang, Yi; Pillsbury, Thomas E; Hada, Yoshiharu; Yamaguchi, Yuki; Fujimoto, Kenjiro; Hwang, Yunho; Radermacher, Reinhard; Cui, Jun; Yuki, Yoji; Toyotake, Koutaro; Takeuchi, Ichiro

    2016-08-13

    This paper reports the elastocaloric effect of two Cu-based shape memory alloys: Cu68Al16Zn16 (CuAlZn) and Cu73Al15Mn12 (CuAlMn), under compression at ambient temperature. The compression tests were conducted at two different rates to approach isothermal and adiabatic conditions. Upon unloading at a strain rate of 0.1 s(-1) (adiabatic condition) from 4% strain, the highest adiabatic temperature changes (ΔTad) of 4.0 K for CuAlZn and 3.9 K for CuAlMn were obtained. The maximum stress and hysteresis at each strain were compared. The stress at the maximum recoverable strain of 4.0% for CuAlMn was 120 MPa, which is 70% smaller than that of CuAlZn. A smaller hysteresis for the CuAlMn alloy was also obtained, about 70% less compared with the CuAlZn alloy. The latent heat, determined by differential scanning calorimetry, was 4.3 J g(-1) for the CuAlZn alloy and 5.0 J g(-1) for the CuAlMn alloy. Potential coefficients of performance (COPmat) for these two alloys were calculated based on their physical properties of measured latent heat and hysteresis, and a COPmat of approximately 13.3 for CuAlMn was obtained.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'. PMID:27402936

  10. Elastocaloric effect in CuAlZn and CuAlMn shape memory alloys under compression.

    PubMed

    Qian, Suxin; Geng, Yunlong; Wang, Yi; Pillsbury, Thomas E; Hada, Yoshiharu; Yamaguchi, Yuki; Fujimoto, Kenjiro; Hwang, Yunho; Radermacher, Reinhard; Cui, Jun; Yuki, Yoji; Toyotake, Koutaro; Takeuchi, Ichiro

    2016-08-13

    This paper reports the elastocaloric effect of two Cu-based shape memory alloys: Cu68Al16Zn16 (CuAlZn) and Cu73Al15Mn12 (CuAlMn), under compression at ambient temperature. The compression tests were conducted at two different rates to approach isothermal and adiabatic conditions. Upon unloading at a strain rate of 0.1 s(-1) (adiabatic condition) from 4% strain, the highest adiabatic temperature changes (ΔTad) of 4.0 K for CuAlZn and 3.9 K for CuAlMn were obtained. The maximum stress and hysteresis at each strain were compared. The stress at the maximum recoverable strain of 4.0% for CuAlMn was 120 MPa, which is 70% smaller than that of CuAlZn. A smaller hysteresis for the CuAlMn alloy was also obtained, about 70% less compared with the CuAlZn alloy. The latent heat, determined by differential scanning calorimetry, was 4.3 J g(-1) for the CuAlZn alloy and 5.0 J g(-1) for the CuAlMn alloy. Potential coefficients of performance (COPmat) for these two alloys were calculated based on their physical properties of measured latent heat and hysteresis, and a COPmat of approximately 13.3 for CuAlMn was obtained.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'.

  11. Magnetic and transport properties of some Ln-Ba-Cu-O (Ln=Yb, Tm, Sm) superconducting oxides

    NASA Astrophysics Data System (ADS)

    Marcus, J.; Escribe-Filippini, C.; Schlenker, C.; Buder, R.; Devenyi, J.; Reydet, P. L.

    1987-07-01

    Powders of Yb-Ba-Cu-O, Tm-Ba-Cu-O and Sm-Ba-Cu-O have been synthetized. Electrical resistivity and magnetic susceptibility measurements show that they are superconducting with onset transition temperatures in the range 91 K - 85 K. The thermopower, in these oxides as well as in Sr xLa 2-xCuO 4-δ and Ba 2YCu 3O 7-δ, is found to be positive between T c and 300 K. Hysteresis of the diamagnetic magnetization is also reported.

  12. Phase correlations in the CuAlSe2-CuAlTe2 system

    NASA Astrophysics Data System (ADS)

    Korzun, B. V.; Fadzeyeva, A. A.; Bente, K.; Schmitz, W.; Kommichau, G.

    2005-07-01

    Alloys in the CuAlSe2-CuAlTe2 system were synthesized in BN-crucibles in silica tubes under vacuum to obtain the corresponding phase equilibria. X-ray powder diffraction and thermal analytic data of the T-x phase diagram revealed a complete solid solutions series in the subsolidus region. Within the CuAlSe2xTe2(1-x) system the refined lattice parameters a and c approximately obey the Vegard rule and also the cell volume and the heat of fusion confirm linear correlations with the composition of the mixed crystals. The anion position parameter calculated after S. C. Abrahams & J. L. Bernstein (uAB) and J. E Jaffe & A. Zunger (uJZ) is greater than 0.25 and reveals a linear dependence on composition. The liquidus part of the CuAlSe2xTe2(1-x) system with x < 0.35 exhibits vertical section behaviour with a ternary peritectic followed up by a ternary monotectic whereas the region with x > 0.35 shows quasibinary equilibria.

  13. Intermetallic Phase Formation in Explosively Welded Al/Cu Bimetals

    NASA Astrophysics Data System (ADS)

    Amani, H.; Soltanieh, M.

    2016-08-01

    Diffusion couples of aluminum and copper were fabricated by explosive welding process. The interface evolution caused by annealing at different temperatures and time durations was investigated by means of optical microscopy, scanning electron microscopy equipped with energy dispersive spectroscopy, and x-ray diffraction. Annealing in the temperature range of 573 K to 773 K (300 °C to 500 °C) up to 408 hours showed that four types of intermetallic layers have been formed at the interface, namely Al2Cu, AlCu, Al3Cu4, and Al4Cu9. Moreover, it was observed that iron trace in aluminum caused the formation of Fe-bearing intermetallics in Al, which is near the interface of the Al-Cu intermetallic layers. Finally, the activation energies for the growth of Al2Cu, AlCu + Al3Cu4, Al4Cu9, and the total intermetallic layer were calculated to be about 83.3, 112.8, 121.6, and 109.4 kJ/mol, respectively. Considering common welding methods ( i.e., explosive welding, cold rolling, and friction welding), although there is a great difference in welding mechanism, it is found that the total activation energy is approximately the same.

  14. The reaction of vapor-deposited Al with Cu oxides

    SciTech Connect

    Taylor, T.N.; Martin, J.A.

    1990-01-01

    Interfaces formed by controlled deposition of Al on Cu oxides at 300K have been characterized using Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS). When Al is deposited onto a thin oxide grown on Cu(110) by atmospheric exposure, it completely scavenges the oxygen from the substrate material, increasing the O(1s) binding energy by 2.0 eV to give the value found for atmospheric oxidation of a thin Al film. Similar oxygen behavior is seen for Al deposition on sputter-deposited CuO with an enriched oxygen surface region, where multilayers of Al erase the shakeup satellites in the Cu(2p) region of the XPS spectrum to give features like those exhibited by Cu{sub 2}O or metallic Cu. Having calibrated the fluence of the Al source with Rutherford backscattering spectrometry, the attenuation of the Cu 2p{sub 1/2} satellite after approximately one monolayer of Al deposition is associated with the removal of oxygen from the top 20 {angstrom} of the CuO. Approximately 7--8 equivalent monolayers of Al are converted to an oxide in the initial rapid reaction process. Further deposition leads to progressive development of the metallic Al signature in both the XPS and AES spectra. These measurements clearly demonstrate the dominant role played by Al, a strong oxide former, when it is placed in intimate contact with the distinctively weaker Cu oxide. 9 refs., 5 figs.

  15. Water-soluble, recombinant CuA-domain of the cytochrome ba3 subunit II from Thermus thermophilus.

    PubMed

    Slutter, C E; Sanders, D; Wittung, P; Malmström, B G; Aasa, R; Richards, J H; Gray, H B; Fee, J A

    1996-03-19

    Recently, the genes of cytochrome ba3 from thermus thermophilus [Keightley, J.A., et al. (1995) J. Biol. Chem. 270, 20345-20358], a homolog of the heme-copper oxidase family, have been cloned. We report here expression of a truncated gene, encoding the copper A (CuA) domain of cytochrome ba3, that is regulated by a T7 RNA polymerase promoter in Escherichia coli. The CuA-containing domain is purified in high yields as a water-soluble, thermostable, purple-colored protein. Copper analysis by chemical assay, mass spectrometry, X-ray fluorescence, and EPR spin quantification show that this protein contains two copper ions bound in a mixed-valence state, indicating that the CuA site in cytochrome ba3, is a binuclear center. The absorption spectrum of the CuA site, free of the heme interference in cytochrome ba3, is similar to the spectra of other soluble fragments from the aa3-type oxidase of Parachccus denitrificans [Lappalainen, P., et al. (1993) J. Biol Chem. 268, 26416-26421] and the caa3-type oxidase of Bacillus subtilis [von Wachenfeldt, C. et al. (1994) FEBS Lett. 340, 109-113]. There are intense bands at 480 nm (3100 M(-1) cm(-1)) and 530 nm (3200 M(-1) cm(-1)), a band in the near -IR centered at 790 nm (1900 M(-1) cn(-1)), and a weaker band at 363 nm (1300M(-1) cm(-1)). The visible CD spectrum shows a positive-going band at 460 nm and a negative-going band at 527 nm, the opposite signs of which may result from the binuclear nature of the site. The secondary structure prediction from the far-UV CD spectrum indicates that this domain is predominantly beta-sheet, in agreement with the recent X-ray structure reported for the complete P. denitrificans cytochrome aa3 molecule [Iwata, S., et al. (1995) Nature 376, 660-669] and the engineered, purple CyoA protein [Wilmanns, M., et al. (1996) Proc. Natl Acad. Sci. U.S.A. 92, 11955-11959]. However, the thermostability of the fragment described here (Tm approximately 80 degrees C) and the stable binding of copper over a

  16. Enhanced dehalogenation of halogenated methanes by bimetallic Cu/Al.

    PubMed

    Lien, Hsing-Lung; Zhang, Weixian

    2002-10-01

    A low-cost and high effective copper/aluminum (Cu/Al) bimetal has been developed for treatments of halogenated methanes, including dichloromethane, in near neutral and high pH aqueous systems. Bimetallic Cu/Al was prepared by a simple two-step synthetic method where Cu was deposited onto the Al surface. The presence of Cu on Al significantly enhanced rates of degradation of halogenated methanes and reduced toxic halogenated intermediates. The stability of Cu/Al was preliminarily studied by a multi-spiking batch experiment where complete degradation of carbon tetrachloride was achieved for seven times although the Cu/Al aging was found. Roles of Cu may involve protecting Al against an undesirable oxidation with water, enhancing reaction rates through the galvanic corrosion, and increasing the selectivity to a benign compound (i.e., methane). Kinetic analyses indicated that the activity of bimetallic Cu/Al was comparable to that of iron-based bimetals (e.g., palladized iron) and zero-valent metals. Bimetallic Cu/Al could be a promising reactive reagent for remediation of halogenated solvents-contaminated groundwater associated with high pH problems.

  17. Pulsed laser deposition of Tl-Ca-Ba-Cu-O films

    NASA Technical Reports Server (NTRS)

    Ianno, N. J.; Liou, S. H.; Woollam, John A.; Thompson, D.; Johs, B.

    1990-01-01

    Pulsed laser deposition is a technique commonly used to deposit high quality thin films of high temperature superconductors. This paper discusses the results obtained when this technique is applied to the deposition of Tl-Ca-Ba-Cu-O thin films using a frequency doubled Nd:YAG laser operating at 532 nm and an excimer laser operating at 248 nm. Films with onset temperatures of 125 K and zero resistance temperatures of 110 K deposited on (100) oriented MgO from a composite Tl2Ca2Ba2Cu3Ox target were obtained at both wavelengths upon appropriate post deposition annealing. Films deposited at 532 nm exhibit a rough surface, while those deposited at 248 nm are smooth and homogeneous. Upon annealing, films deposited at both wavelengths are single phase Tl2Ca2Ba2Cu3Ox.

  18. Transport and structural properties of the Ho1Ba2Cu3O9 - delta superconductor

    NASA Astrophysics Data System (ADS)

    Lee, Sung-Ik; Golben, John P.; Song, Yi; Lee, Sang Young; Noh, Tae W.; Chen, Xiao-dong; Testa, Joe; Gaines, J. R.; Tettenhorst, Rodney T.

    1987-07-01

    The compound Ho1Ba2Cu3O9-δ has been found to be a high Tc superconductor. The onset of the superconducting transition is 88 K with zero resistance achieved at 87 K. The x-ray diffraction spectrum of this material shows it to be a single-phase perovskite similar to the Y1Ba2Cu3O9-δ compound but different from the K2NiF4 perovskite which is believed to be the superconducting phase for the La2(1-x) Ba2xCuO4-δ system. Possible oxygen deficiencies in several of the unit cell planes are discussed. The room-temperature resistance, the superconducting onset temperature, and the emergence of the single phase all depend upon the sample preparation firing conditions.

  19. Superconductivity in the Tl-Ca-Ba-Cu-O System:. Synthesis, Characterization and Mechanism

    NASA Astrophysics Data System (ADS)

    Ganguli, A. K.; Swamy, K. S. Nanjunda; Subbanna, G. N.; Rajumon, M. K.; Sarma, D. D.; Rao, C. N. R.

    Synthesis and characterization of some of the members of the Tl-Ca-Ba-Cu-O system are presented. Tc in both the TlCan-1Ba2CunO2n+3 and Tl2Can-1Ba2CunO2n+4 series increase with the number of Cu-O layers, n; Tc in the latter series with two Tl-O layers are generally higher than in the former with a single Tl-O layer. Tl in the cuprates is in the 3+ state while Cu is in the 1+ and 2+ states, showing the importance of oxygen holes. The concentration of these holes seems to increase with the number of Tl-O layers.

  20. Facile synthesis of dendritic Cu by electroless reaction of Cu-Al alloys in multiphase solution

    NASA Astrophysics Data System (ADS)

    Wang, Ying; Liang, Shuhua; Yang, Qing; Wang, Xianhui

    2016-11-01

    Two-dimensional nano- or micro-scale fractal dendritic coppers (FDCs) were synthesized by electroless immersing of Cu-Al alloys in hydrochloric acid solution containing copper chloride without any assistance of template or surfactant. The FDC size increases with the increase of Al content in Cu-Al alloys immersed in CuCl2 + HCl solution. Compared to Cu40Al60 and Cu45Al55 alloys, the FDC shows hierarchical distribution and homogeneous structures using Cu17Al83 alloy as the starting alloy. The growth direction of the FDC is <110>, and all angles between the trunks and branches are 60°. Nanoscale Cu2O was found at the edge of FDC. Interestingly, nanoporous copper (NPC) can also be obtained through Cu17Al83 alloy. Studies showed that the formation of FDC depended on two key factors: the potential difference between CuAl2 intermetallic and α-Al phase of dual-phase Cu-Al alloys; a replacement reaction that usually occurs in multiphase solution. The electrochemical experiment further proved that the multi-branch dendritic structure is very beneficial to the proton transfer in the process of catalyzing methanol.

  1. EPR study of La 2- xM xCuO 4 (M = Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Khan, Shakeel; Singh, Arti; Singh, R. J.

    1998-06-01

    EPR spectra of deoxygenated La 1.81Sr 0.19CuO 4 and La 1.94Ba 0.06CuO 4 have been investigated. In both of them 4 Cu 2+ ions are found to combine ferromagnetically to give S = 2 spectra. At low {Sr}/{Ba} content the spins probably start getting polarised in the ab plane. Spin-Hamiltonian parameters for all the spectra have been determined. Dependence of Tc on the content of Sr or Ba has been attempted to be explained. It seems that holes which are generated on the substitution of La 3+ by Sr 2+ or Ba 2+ and are current carriers first get uniformly distributed over the LaO plane but on increasing Sr 2+ or Ba 2+ content, they may combine together to form O 22- peroxide ions and become unable to carry current. On further increasing the Sr 2+ or Ba 2+ content, the same process is repeated, until the substance becomes metallic or until further amounts of the substituents can bot be dissolved in the parent compound.

  2. Influence of Cu-site substitution on La2Ca1Ba2Cu5Oz superconducting system

    NASA Astrophysics Data System (ADS)

    Bhalodia, J. A.; Mankadia, S. R.; Dalsaniya, S. M.; Gonal, M. R.

    2012-07-01

    We have prepared a series of La2CaBa2Cu5-xCoxOz; x = 0.0, 0.1, 0.2, 0.5, 1.0, 2.0, 5.0 (La-2125) compounds by the standard solid state reaction method and characterized for their structural, superconducting, magnetic properties and oxygen content through X-ray diffraction, scanning electron microscopy, d. c. resistivity, magnetic susceptibility and iodometric titration respectively. All the compounds crystallize with the tetragonal LaBa2Cu3Oz type structure, space group P4/mmm. Here the effect of higher Co substitution for Cu in the La2CaBa2Cu5-xCoxOz system has been studied. It is observed that only 2 at. % Co substitution for Cu destroys the superconductivity of the sample. For heavily doped samples (with x >= 0.1) are found non-superconducting presumably because of magnetic pair- breaking effect. These samples do not show superconductivity but are of interest for understanding the interplay between superconductivity and magnetism. Possible reasons for destruction of superconductivity are discussed in this communication.

  3. Intermetallic compound formation at Cu-Al wire bond interface

    SciTech Connect

    Bae, In-Tae; Young Jung, Dae; Chen, William T.; Du Yong

    2012-12-15

    Intermetallic compound (IMC) formation and evolution at Cu-Al wire bond interface were studied using focused ion beam /scanning electron microscopy, transmission electron microscopy (TEM)/energy dispersive x-ray spectroscopy (EDS), nano beam electron diffraction (NBED) and structure factor (SF) calculation. It was found that discrete IMC patches were formed at the Cu/Al interface in as-packaged state and they grew toward Al pad after high temperature storage (HTS) environment at 150 Degree-Sign C. TEM/EDS and NBED results combined with SF calculation revealed the evidence of metastable {theta} Prime -CuAl{sub 2} IMC phase (tetragonal, space group: I4m2, a = 0.404 nm, c= 0.580 nm) formed at Cu/Al interfaces in both of the as-packaged and the post-HTS samples. Two feasible mechanisms for the formation of the metastable {theta} Prime -CuAl{sub 2} phase are discussed based on (1) non-equilibrium cooling of wire bond that is attributed to highly short bonding process time and (2) the epitaxial relationships between Cu and {theta} Prime -CuAl{sub 2}, which can minimize lattice mismatch for {theta} Prime -CuAl{sub 2} to grow on Cu.

  4. Stability limits of the perovskite structure in the Y-Ba-Cu-O system

    NASA Astrophysics Data System (ADS)

    Bormann, R.; Nölting, J.

    1989-05-01

    The equilibrium (molecular) oxygen partial pressure of the Y1Ba2Cu3O7-x phase has been measured by an electrochemical method. The investigations are focused on the low-temperature range between 560 and 750 °C and on oxygen stoichiometries close to the oxygen-poor phase boundary. In particular, the oxygen partial pressure has been determined below which the perovskite structure becomes thermodynamically unstable. This critical value should be considered during the preparation of high Tc Y1Ba2Cu3O7-x superconductors, especially in the case of an in situ preparation of thin films.

  5. Critical currents of aligned grains of Tl-Ba-Ca-Cu-O compounds

    NASA Technical Reports Server (NTRS)

    Fang, M. M.; Finnemore, D. K.; Farrell, D. E.; Bansal, N. R.

    1989-01-01

    A study of irreversibility in the magnetization curves of Tl2Ba2Ca2Cu3O10 and Tl2Ba2Ca1Cu2O8 was undertaken to determine the intragranular critical currents and the effects of flux-creep in grain-aligned samples of these materials. For fields of greater than 0.3 T, and H parallel to c axis, the critical supercurrent falls approximately exponentially with both magnetic field and temperature. Flux-creep is found to be linear in the logarithm of time at low fields over a wide temperature range.

  6. Composition dependence of superconductivity in YBa2(Cu(3-x)Al(x))Oy

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.

    1991-01-01

    Eleven different compositions in the system YBa2(Cu(3-x)Al(x))O(y) (x = 0 to 0.3) have been synthesized and characterized by electrical resistivity measurements, powder x-ray diffraction, and scanning electron microscopy. The superconducting transition temperature T sub c (onset) was almost unaffected by the presence of alumina due to its limited solubility in YBa2Cu3O(7-x). However, T sub c(R = 0) gradually decreased, and the resistive tails became longer with increasing Al2O3 concentration. This was probably due to formation of BaAl2O4 and other impurity phases from chemical decomposition of the superconducting phase by reaction with Al2O3.

  7. Composition dependence of superconductivity in YBa2(Cu(3-x)Al(x))O(y)

    NASA Technical Reports Server (NTRS)

    Bansal, N. P.

    1993-01-01

    Eleven different compositions in the system YBa2(Cu(3-x)Al(x))O(y) (x = 0 to 0.3) have been synthesized and characterized by electrical resistivity measurements, powder X-ray diffraction, and scanning electron microscopy. The superconducting transition temperature T sub c (onset) was almost unaffected by the presence of alumina due to its limited solubility in YBa2Cu3O(7-x). However, T sub c(R = 0) gradually decreased, and the resistive tails became longer with increasing Al2O3 concentration. This was probably due to formation of BaAl2O4 and other impurity phases from chemical decomposition of the superconducting phase by reaction with Al2O3.

  8. Chemical and orbital fluctuations in Ba3CuSb2O9

    NASA Astrophysics Data System (ADS)

    Wakabayashi, Yusuke; Nakajima, Daisuke; Ishiguro, Yuki; Kimura, Kenta; Kimura, Tsuyoshi; Tsutsui, Satoshi; Baron, Alfred Q. R.; Hayashi, Kouichi; Happo, Naohisa; Hosokawa, Shinya; Ohwada, Kenji; Nakatsuji, Satoru

    2016-06-01

    Structural fluctuation in Ba3CuSb2O9 , which is proposed to exhibit a spin-orbital entangled state, has been studied by diffuse x-ray scattering, x-ray fluorescence holography, and inelastic x-ray scattering. Two kinds of spatial fluctuations are observed: temperature-independent and temperature-dependent ones. The former is related to Cu/Sb arrangement. The short-range chemical correlation in Ba3CuSb2O9 is honeycomblike, whereas the correlation length is as short as the diameter of the honeycomb unit. The temperature variation of ferro- and antiferro-orbital correlations is extracted from Huang scattering intensity distributions. Both of these correlations increase with decreasing temperature down to 60 K, which corresponds to the energy of magnetic interaction of Ba3CuSb2O9 . A wide distribution of the characteristic time scale of the orbital motion is proposed from the spatial fluctuation of the ionic arrangement in Ba3CuSb2O9 .

  9. Synthesis of HgBa 2CuO 4+δ under controlled mercury and oxygen pressures

    NASA Astrophysics Data System (ADS)

    Alyoshin, V. A.; Mikhailova, D. A.; Antipov, E. V.

    1996-02-01

    A three-temperature synthesis technique to obtain pure HgBa 2CuO 4+δ under controlled mercury and oxygen partial pressures was developed. Mixtures of Co 3O 4/CoO (or CuO/Cu 2O) oxides and HgBa 2CuO 4+δ/Ba 2CuO 3+ x heated at different temperatures were used to adjust P(O 2) and P(Hg), respectively. At equilibrium conditions for the reaction: HgBa 2CuO 4+ δ ↔ Ba 2CuO 3+ x + Hg(g) + (1 + δ - x)/2 O 2, 0.09 < P(O 2) < 0.62 bar and 1009 < T < 1153 K, the mercury partial pressure was found to vary from 1.7 to 6.5 bar. With these conditions, the lower boundary of HgBa 2CuO 4+δ formation as a function of P(Hg), P(O 2) and T was determined as: log P(Hg) + 6040/ T + 0.266 log P(O 2) > 5.959. It was also found, that slow cooling down to 600°C under fixed oxygen pressure is required to prepare pure HgBa 2CuO 4+δ.

  10. High-precision abundances of Sc, Mn, Cu, and Ba in solar twins. Trends of element ratios with stellar age

    NASA Astrophysics Data System (ADS)

    Nissen, P. E.

    2016-09-01

    Aims: A previous study of correlations between element abundances and ages of solar twin stars in the solar neighborhood is extended to include Sc, Mn, Cu, and Ba to obtain new information on the nucleosynthetic history of these elements. Methods: HARPS spectra with S/N ≳ 600 are used to derive very precise (σ ~ 0.01 dex) differential abundances of Sc, Mn, Cu, and Ba for 21 solar twins and the Sun. The analysis is based on MARCS model atmospheres with parameters determined from the excitation and ionization balance of Fe lines. Stellar ages with internal errors less than 1 Gyr are obtained by interpolation in the log g - Teff diagram between isochrones based on the Aarhus Stellar Evolution Code. Results: For stars younger than 6 Gyr, [Sc/Fe], [Mn/Fe], [Cu/Fe], and [Ba/Fe] are tightly correlated with stellar age, which is also the case for the other elements previously studied; linear relations between [X/Fe] and age have χ^2red ˜ 1, and for most stars the residuals do not depend on elemental condensation temperature. For ages between 6 and 9 Gyr, the [X/Fe] - age correlations break down and the stars split up into two groups having respectively high and low [X/Fe] for the odd-Z elements Na, Al, Sc, and Cu. Conclusions: While stars in the solar neighborhood younger than ~ 6 Gyr were formed from interstellar gas with a smooth chemical evolution, older stars seem to have originated from regions enriched by supernovae with different neutron excesses. Correlations between abundance ratios and stellar age suggest that: (i) Sc is made in Type II supernovae along with the α-capture elements; (ii) the Type II to Ia yield ratio is about the same for Mn and Fe; (iii) Cu is mainly made by the weak s-process in massive stars; (iv) the Ba/Y yield ratio for asymptotic giant branch stars increases with decreasing stellar mass; (v) [Y/Mg] and [Y/Al] can be used as chemical clocks when determining ages of solar metallicity stars. Based on data products from observations made

  11. Percolated Superconductivity and Electron-Electron Exchange Mechanism in Ba-La-Cu-O

    NASA Astrophysics Data System (ADS)

    Tao, Ruibao

    It is found that the oxygen vacancies at the Cu-O basal plane of oxide (La1-xBax)2CuO4-y (Balacuo) will break the bonds of Cu-O-Cu to make the hopping between those coppers disappear so that the electrical conduction in the Cu-O basal plane would become a bond percolation system consisting of an infinite cluster carrying the current with a great number of finite clusters hanging around. It is favorable to create some mechanism of electron-electron exchange so that the transition temperature Tc of superconductivity could be increased significantly. The comparison with Y1Ba2Cu3O9-y is also discussed briefly.

  12. KrF laser-induced ablation and patterning of Y--Ba--Cu--O films

    SciTech Connect

    Heitz, J.; Wang, X.Z.; Schwab, P.; Baeuerle, D. ); Schultz, L. )

    1990-09-01

    The ablation and patterning of Y--Ba--Cu--O films on (100) SrTiO{sub 3} and (100) MgO substrates by KrF excimer-laser light projection was investigated. Three different regimes of laser-material interactions were observed. Transition temperatures and critical current densities in laser-fabricated strip lines were investigated.

  13. Coexistence of metallic and nonmetallic charge transport in PrBa2Cu3O7

    NASA Astrophysics Data System (ADS)

    Lee, Mark; Suzuki, Y.; Geballe, T. H.

    1995-06-01

    Magnetotransport measurements on highly oriented thin films of PrBa2Cu3O7 demonstrate a unique coexistence of nonmetallic hopping conduction with metallic Boltzmann transport. At high temperature (T>10 K) hopping transport dominates, but when the inelastic conduction freezes out at low temperature, metallic behavior can be distinguished. The hopping conduction is assigned to the CuO2 planes, while the Boltzmann transport arises from the CuO chain structure, in agreement with recent electronic-structure calculations.

  14. 120 K superconductor TlBaCaCu/sub 2/O/sub y/

    SciTech Connect

    Zhao, Z.X.; Chen, L.Q.; Mai, Z.H.; Huang, Y.Z.; Xiao, Z.L.; Chu, X.; Zheng, D.N.; Jia, S.L.; Wang, J.H.; Chen, G.H.

    1988-01-01

    The author have prepared 120K superconductor in Tl-Ba-Ca-Cu oxide system. This 120K superconductor has been investigated by x-ray diffraction and EDAX micro-analysis. EDAX analysis shows that the composition of this superconductor is very close to TLBa(Ca/sub 1/-/sub x/Cu/sub x/)CuO/sub y/(chi - 0.3). Most of the x-ray powder diffractions including all the strong ones can be indexed according to a tetragonal structure with /alpha/ = 5.46 A and c = 36.2A which means that the sample is nearly a single phase material.

  15. Electronic properties of Y-Ba-Cu-O superconductors as seen by Cu and O NMR/NQR

    NASA Technical Reports Server (NTRS)

    Brinkmann, D.

    1995-01-01

    Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) allow the investigation of electronic properties at the atomic level. We will report on such studies of typical members of the the Y-Ba-Cu-O family such as YBa2Cu30(6 + x) (1-2-3-(6 + x)), YBa2Cu4O8 (1-2-4) and Y2Ba4Cu7015 (2-4-7) with many examples of recent work performed in our laboratory. In particular, we will deal with Knight shift and relaxation studies of copper and oxygen. We will discuss important issues of current studies such as: (1) Existence of a common electronic spin-susceptibility in the planes (and perhaps in the chains) of 1-2-4; (2) Strong evidence for the existence of a pseudo spin-gap of the antiferromagnetic fluctuations in 1-2-4 and 2-4-7; (3) Evidence for d-wave pairing in 1-2-4; (4) Strong coupling of inequivalent Cu-O planes in 2-4-7 and possible origin for the high Tc value of this compound; and (5) The possibility to describe NMR data in the framework of a charge-excitation picture.

  16. Barium aluminides Ba{sub x}Al{sub 5}(x=3,3.5,4)

    SciTech Connect

    Jehle, Michael; Scherer, Harald; Wendorff, Marco; Roehr, Caroline

    2009-05-15

    Three aluminides of the series Ba{sub x}Al{sub 5}(x=3,3.5,4) were synthesized from stoichiometric ratios of the elements in Ta crucibles. The crystal structure of the new compound Ba{sub 7}Al{sub 10} was determined using single crystal X-ray data (space group R3-barm, a=604.23(9), c=4879.0(12)pm, Z=3, R1=0.0325). The compound exhibits Al Kagome (3.6.3.6.) nets in which half of the triangles form the basis of trigonal bipyramids Al{sub 5}. The apical Al are thus three-bonded assuming a charge of -2 ({sup 27}Al-NMR chemical shift delta=660pm), whereas the Al atoms of the basal triangle (i.e. of the Kagome net) are four-bonded and thus of formal charge -1(delta=490ppm). The total charge of the anion is thus exactly compensated by the Ba cations, i.e. the compound can be interpreted as an electron precise Zintl phase, exhibiting a distinct pseudo-band gap at the Fermi level of the calculated tDOS. According to the total formula, the structure displays a combination the stacking sequences of Ba{sub 3}Al{sub 5} and Ba{sub 4}Al{sub 5}, the structures of which have been redetermined with current methods (both hexagonal with space group P6{sub 3}/mmc; Ba{sub 3}Al{sub 5}: a=606.55(7), c=1461.8(2)pm, Z=2, R1=0.0239; Ba{sub 4}Al{sub 5}: a=609.21(7), c=1775.8(3)pm, Z=2, R1=0.0300). These three compounds with slightly different electron counts but similar polyanions allow to compare the bond lengths, the electronic structures and the overall bonding situation in dependence of positive or negative deviation of the electron count in relation to the novel formally electron precise Zintl compound Ba{sub 7}Al{sub 10}. - Al{sub 5} layers of Kagome nets in the new binary electron precise Zintl compound Ba{sub 3.5}Al{sub 5}, also found in Ba{sub 3}Al{sub 5} and Ba{sub 4}Al{sub 5}.

  17. Multi-seeding melt growth process of bulk Y-Ba-Cu-O superconductors for engineering applications

    NASA Astrophysics Data System (ADS)

    Wongsatanawarid, A.; Seki, H.; Murakami, M.

    2010-06-01

    We have prepared polycrystalline and four-domain Y-Ba-Cu-O superconductors in a molar ratio of Y123: Y211 = 10: 4 with lwt% Ce02 addition by melt-processing in air. Trapped field measurements showed that four sharp peaks were observed in a four-domain bulk sample, showing that four grains were successfully formed without defects by a multi-seeding method. Force measurements showed that a four-domain Y-Ba-Cu-O sample exhibited higher repulsive forces and smaller hysteresis loops than polycrystalline Y-Ba-Cu-O sample during the increasing and decreasing field processes, which implies higher pinning performance of the four-domain sample. With the aim of studying the transferable torque forces, we used a multi-pole magnet circuit with NSNS configuration. We confirmed that with the interaction of the magnet circuit, a four-domain Y-Ba-Cu-O sample showed larger forces than a polycrystalline sample both in the field-cooled and the zero-field-cooled mode. We also measured the torque forces acting between the magnet circuit and bulk Y-Ba-Cu-O samples by twisting the magnet circuit in the levitated state. Again a four-domain Y-Ba-Cu-O sample exhibited much higher torque forces than a polycrystalline sample. These results showed that multi-seeded Y-Ba-Cu-O sample with four-domains can be used for torque transfer apllications.

  18. Nucleation and Growth of Cu-Al Intermetallics in Al-Modified Sn-Cu and Sn-Ag-Cu Lead-Free Solder Alloys

    NASA Astrophysics Data System (ADS)

    Reeve, Kathlene N.; Anderson, Iver E.; Handwerker, Carol A.

    2015-03-01

    Lead-free solder alloys Sn-Cu (SC) and Sn-Ag-Cu (SAC) are widely used by the microelectronics industry, but enhanced control of the microstructure is needed to improve solder performance. For such control, nucleation and stability of Cu-Al intermetallic compound (IMC) solidification catalysts were investigated by variation of the Cu (0.7-3.0 wt.%) and Al (0.0-0.4 wt.%) content of SC + Al and SAC + Al alloys, and of SAC + Al ball-grid array (BGA) solder joints. All of the Al-modified alloys produced Cu-Al IMC particles with different morphologies and phases (occasionally non-equilibrium phases). A trend of increasing Cu-Al IMC volume fraction with increasing Al content was established. Because of solidification of non-equilibrium phases in wire alloy structures, differential scanning calorimetry (DSC) experiments revealed delayed, non-equilibrium melting at high temperatures related to quenched-in Cu-Al phases; a final liquidus of 960-1200°C was recorded. During cooling from 1200°C, the DSC samples had the solidification behavior expected from thermodynamic equilibrium calculations. Solidification of the ternary alloys commenced with formation of ternary β and Cu-Al δ phases at 450-550°C; this was followed by β-Sn, and, finally, Cu6Sn5 and Cu-Al γ1. Because of the presence of the retained, high-temperature phases in the alloys, particle size and volume fraction of the room temperature Cu-Al IMC phases were observed to increase when the alloy casting temperature was reduced from 1200°C to 800°C, even though both temperatures are above the calculated liquidus temperature of the alloys. Preliminary electron backscatter diffraction results seemed to show Sn grain refinement in the SAC + Al BGA alloy.

  19. Synthesis and superconducting properties of Tl-Ba-Ca-Cu-O films

    NASA Technical Reports Server (NTRS)

    Liou, S. H.; Chan, V. K.; Foong, F.; Lee, W. Y.; Gou, Y. S.

    1991-01-01

    Tl-Ba-Ca-Cu-O superconducting films were synthesized by sputtering either from a single target or from two oxide targets in a symmetric configuration. Films with zero resistance Tc of up to 122 K were obtained after various postannealing treatments at 870-950 C under an oxygen atmosphere. The composition of the films is not very homogeneous on the submicrometer scale. The critical current of these films at 77 K is in the 1000 A/sq cm to 10,000 A/sq cm range, which is much smaller than that of films prepared on SrTiO3 and LaAlO3 substrates. The low critical current density in these films is probably due to the granularity in the films. The morphology, structure, and magnetic and superconducting properties of the films were studied. Films prepared by two different sputtering techniques have similar results which depend mostly on the film compositions and their annealing conditions. It is found that the induced magnetic flux in the film decreases rapidly with increasing temperature, indicating weak flux pinning.

  20. High temperature superconductor step-edge Josephson junctions using Ti-Ca-Ba-Cu-O

    DOEpatents

    Ginley, D.S.; Hietala, V.M.; Hohenwarter, G.K.G.; Martens, J.S.; Plut, T.A.; Tigges, C.P.; Vawter, G.A.; Zipperian, T.E.

    1994-10-25

    A process is disclosed for formulating non-hysteretic and hysteretic Josephson junctions using HTS materials which results in junctions having the ability to operate at high temperatures while maintaining high uniformity and quality. The non-hysteretic Josephson junction is formed by step-etching a LaAlO[sub 3] crystal substrate and then depositing a thin film of TlCaBaCuO on the substrate, covering the step, and forming a grain boundary at the step and a subsequent Josephson junction. Once the non-hysteretic junction is formed the next step to form the hysteretic Josephson junction is to add capacitance to the system. In the current embodiment, this is accomplished by adding a thin dielectric layer, LaA1O[sub 3], followed by a cap layer of a normal metal where the cap layer is formed by first depositing a thin layer of titanium (Ti) followed by a layer of gold (Au). The dielectric layer and the normal metal cap are patterned to the desired geometry. 8 figs.

  1. High temperature superconductor step-edge Josephson junctions using Ti-Ca-Ba-Cu-O

    DOEpatents

    Ginley, David S.; Hietala, Vincent M.; Hohenwarter, Gert K. G.; Martens, Jon S.; Plut, Thomas A.; Tigges, Chris P.; Vawter, Gregory A.; Zipperian, Thomas E.

    1994-10-25

    A process for formulating non-hysteretic and hysteretic Josephson junctions using HTS materials which results in junctions having the ability to operate at high temperatures while maintaining high uniformity and quality. The non-hysteretic Josephson junction is formed by step-etching a LaAlO.sub.3 crystal substrate and then depositing a thin film of TlCaBaCuO on the substrate, covering the step, and forming a grain boundary at the step and a subsequent Josephson junction. Once the non-hysteretic junction is formed the next step to form the hysteretic Josephson junction is to add capacitance to the system. In the current embodiment, this is accomplished by adding a thin dielectric layer, LaA1O.sub.3, followed by a cap layer of a normal metal where the cap layer is formed by first depositing a thin layer of titanium (Ti) followed by a layer of gold (Au). The dielectric layer and the normal metal cap are patterned to the desired geometry.

  2. Thermal stability of Al-Cu-Fe icosahedral alloys

    NASA Astrophysics Data System (ADS)

    Bessière, M.; Quivy, A.; Lefebvre, S.; Devaud-Rzepski, J.; Calvayrac, Y.

    1991-12-01

    A stable ideally quasiperiodic phase exists in a small range of concentration, close to the composition Al{62}Cu{25.5}Fe{12.5}. Reducing the iron content, or replacing small amounts of copper by aluminium, lead to icosahedral alloys which exhibit around 650 ^{circ}C structural transformations of unclear nature: in the X-ray powder diffraction pattern, the peak profiles become purely Lorentzian (Al{62.3}Cu{25.3}Fe{12.4}) or diffuse “side-bands” appear in the tails of the Bragg peaks (Al{63}Cu{24.5}Fe{12.5}). In the last case long annealing treatments eventually transform the Bragg peaks into diffuse peaks located at positions clearly off the ideal icosahedral symmetry. Small deviations from this composition range lead to Bragg peaks with shoulders whatever the heat-treatment may be; perfect icosahedral order is never obtained for these compositions (Al{63,25}Cu{24,5}Fe{12,25}, Al{64}Cu{24}Fe{12}, Al{63}Cu{25}Fe{12}). Une phase stable idéalement quasipériodique existe dans un petit domaine de concentration, au voisinage de la composition Al{62}Cu{25,5}Fe{12,5}. La diminution de la teneur en fer, ou le remplacement de faibles quantités de cuivre par de l'aluminium, conduisent à des alliages icosaédriques qui subissent vers 650 ^{circ}C des transformations structurales dont la nature n'est pas clairement identifiée: dans le diagramme de diffraction des rayons X sur poudre, les profils de raies deviennent purement Lorentziens (Al{62,3}Cu{25,3}Fe{12,4}) ou bien des raies diffuses apparaissent dans le pied des pics de Bragg (Al{63}Cu{24,5}Fe{12,5}). Dans ce dernier cas un long traitement de recuit transforme finalement les pics de Bragg en des pics diffus localisés à des positions clairement en dehors de celles correspondant à la symétrie icosaédrique idéale. De faibles écarts à ce domaine de compositions conduisent à des diagrammes de rayons X où les pics de Bragg sont épaulés quel que soit le traitement thermique ; l'ordre icosaédrique parfait n

  3. Sm-Ba-Cu-O bulk superconductors melt-processed in air

    NASA Astrophysics Data System (ADS)

    Fujimoto, Hiroyuki; Cai, Chuanbing; Ohtabara, Emi

    2002-08-01

    Recent development shows that melt-processed YBaCuO (Y123) and light rare-earth (LRE) BaCuO superconductors have a high Jc at 77 K and high magnetic field. Solidification processes for producing RE123 superconductors are effective for obtaining high Jc and are very promising for high field application as a superconducting permanent magnet with the liquid nitrogen refrigeration. LRE BaCuO bulk superconductors melt-processed in a reduced oxygen atmosphere, named oxygen-controlled-melt-growth process, have a high Tc and Jc. However, processing in air is preferable for practical applications. In this study, we discuss Sm123 bulks melt-processed in air, and their characteristic superconducting properties. Isothermal undercooling growth in air with oxygen annealing and Nd123/MgO thin film cold seeding technique were applied in Sm 1.8Ba 2.4Cu 3.4O y/Ag system to seek the high efficiency of process, homogeneity of composition, and feasibility of batch production. Single-domain growth was achieved using this technique. The result implies that melt-processed in air applying isothermal method and thin film seeding in Sm system is fit for producing larger bulks in large scale applications.

  4. Positron lifetime studies of decomposition in 2024 (Al-Cu-Mg) and 7010 (Al-Zn-Cu-Mg) alloys

    SciTech Connect

    Dlubek, G. |; Lademann, P.; Krause, H.; Krause, S.; Unger, R.

    1998-09-04

    In the current paper, the decomposition behavior of the engineering alloys 2024 (Al-Cu-Mg) and 7010 (Al-Zn-Cu-Mg) is studied using positron lifetime measurements. Positrons probe open volume defects such as vacancies and dislocations. However, they may also be used to investigate coherent zones and incoherent precipitates. In order to understand the rather complicated precipitation sequences and the response of positrons to different type of precipitates occurring in 2024 and 7010 alloys, binary and ternary laboratory alloys were also investigated under the same experimental conditions as the engineering alloys. The interpretations of the results are based on experiences of the group from extensive positron studies of laboratory alloys such as Al-Zn, Al-Zn-Mg, Al-Cu, and further Al alloys (see also the review (4)). Their collected results are shown as lifetimes and curve-shape parameters S of the electron-positron momentum distribution curves characteristic for different precipitates in Al alloys.

  5. Delocalization of vortex in SmBa2Cu3O7-δ superconducting films with BaHfO3 nano-rods

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Yuji; Awaji, Satoshi; Watanabe, Kazuo; Miura, Shun; Ichino, Yusuke; Yoshida, Yutaka; Matsumoto, Kaname

    2016-09-01

    Transport measurements revealed flux pinning properties and vortex phases in SmBa2Cu3O7-δ (Sm123) superconducting films with BaHfO3 nano-rods on LaAlO3 substrates. The films have large matching fields BΦ up to 9.9 T, nano-rod diameters of ˜6 nm, and a slight Tc degradation with Tc ˜ 91.8 K by using the low temperature growth technique. According to the transport results, a small critical exponent ˜4 indicates the presence of a Bose-glass phase in the films. Double peaks of the flux pinning force density are unexpectedly observed at high temperatures over 80 K, which is accompanied by steep drops of the crossover magnetic fields between the single vortex pinning and the collective pinning states. The drops are explained by the delocalization of the vortex where the vortex is pinned by many nano-rods in the single vortex pinning state. From the viewpoint of the vortex delocalization, we conclude that BΦ should be less than 11 T for applications at liquid nitrogen temperature.

  6. Secondary-phase orientation probed by EPR:mY2 BaCuO5sin YBa2 Cu3 O7-xs

    NASA Astrophysics Data System (ADS)

    Pellerin, N.; Simon, P.; Odier, P.; Gotor, F. J.; Poirot, N. J.; Vutien, L.; Durand, L.; Monot, I.

    1997-01-01

    Textured YBa2 Cu3 O7-x samples have been studied by electronic paramagnetic resonance.mEPR spectroscopy allows us to analyze the Y2 BaCuO5 second phase present as inclusions in the YBa2 Cu3 O6 textured matrix. All samples were deoxygenated in order to limit the skin effect due to conductivity. This is applied to samples textured according to different techniques. Preferential orientation of these particles according to the 123 matrix can be observed. For instance, if texturing under a magnetic field, the particular Y2 BaCuO5 orientation is observed of the b211 axis (b=7.132 Å) parallel to c123 and to the magnetic field direction. By appropriate calculations from initial spectra, the fraction of preferred orientation of these Y2 BaCuO5 grains can be quantified. This orientation comprises 16+/-2 % of the Y2 BaCuO5 weight for texturing under a magnetic field, presently one of the highest values obtained. It involves the longest size of Y2 BaCuO5 elongated grains lying in YBa2 Cu3 O6 planes, facilitating the texturation process. Texturing on Y2 O3 by the modified melt textured growth method leads to a preferential orientation of Y2 BaCuO5 grains too, but in another direction, i.e., b211 perpendicular to c123 . There is no Y2 BaCuO5 preferential orientation if texturing with a thermal gradient or on a monocrystalline MgO substrate. This type of analysis can be applied easily to other systems (nanocomposites, dispersoids, etc.), providing that the signal of the secondary phase can be clearly separated from the signal of the primary one.

  7. Interfacial Reaction during Friction Stir Welding of Al and Cu

    NASA Astrophysics Data System (ADS)

    Genevois, C.; Girard, M.; Huneau, B.; Sauvage, X.; Racineux, G.

    2011-08-01

    Commercially pure copper was joined to a 1050 aluminum alloy by friction stir welding. A specific configuration where the tool pin was fully located in the aluminum plate was chosen. In such a situation, there is no mechanical mixing between the two materials, but frictional heating gives rise to a significant thermally activated interdiffusion at the copper/aluminum interface. This gives rise to the formation of defect-free joints where the bonding is achieved by a very thin intermetallic layer at the Cu/Al interface. Nanoscaled grains within this bonding layer were characterized using transmission electron microscopy (TEM). Two phases were identified, namely, Al2Cu and Al4Cu9 phases. The nucleation and growth of these two phases are discussed and compared to the standard reactive interdiffusion reactions between Cu and Al.

  8. PrBa{sub 2}Cu{sub 3}O{sub 7{minus}y}: Superconducting or anomalously magnetic?

    SciTech Connect

    Narozhnyi, V.N.; Eckert, D.; Nenkov, K.A.; Fuchs, G.; Mueller, K.H.; Uvarova, T.G.

    1999-12-20

    In PrBa{sub 2}Cu{sub 3}O{sub 7{minus}y} (Pr123) single crystals grown by the flux method the kink in the magnetic susceptibility {chi}{sub ab}(T), connected with antiferromagnetic ordering of Pr, disappears after field cooling (FC) in a field H {parallel} ab-plane whereas the kink in {chi}{sub c}(T) remains unchanged after FC in H {parallel} c-axis. This seems to be connected with the coupling between the Pr and Cu(2) sublattices. The Curie constant C determined from the data reported for superconducting Pr123 crystals grown by the traveling-solvent floating zone (TSFZ) method (Zou et al, Phys. Rev. Lett., 80, 1074 (1998)) is about one half of that for the flux-grown non-superconducting crystals. Thus, they propose that concentration of Pr in TSFZ crystals seems to be about one half of the nominal concentration for Pr123. Therefore, they propose that superconductivity in TSFZ samples is connected most probably with the partial substitution of Pr by nonmagnetic Ba.

  9. Bioaccessibility of Ba, Cu, Pb, and Zn in urban garden and orchard soils.

    PubMed

    Cai, Meifang; McBride, Murray B; Li, Kaiming

    2016-01-01

    Exposure of young children to toxic metals in urban environments is largely due to soil and dust ingestion. Soil particle size distribution and concentrations of toxic metals in different particle sizes are important risk factors in addition to bioaccessibility of these metals in the particles. Analysis of particle size distribution and metals concentrations for 13 soils, 12 sampled from urban gardens and 1 from orchard found that fine particles (<105 μm) comprised from 22 to 66% by weight of the tested soils, with Ba, Cu, Pb and Zn generally at higher concentrations in the finer particles. However, metal bioaccessibility was generally lower in finer particles, a trend most pronounced for Ba and Pb. Gastric was higher than gastrointestinal bioaccessibility for all metals except Cu. The lower bioaccessibility of Pb in urban garden soils compared to orchard soil is attributable to the higher organic matter content of the garden soils. PMID:26477581

  10. Thick film of HgBa 2Ca 2Cu 3O 8+δ via the sol-gel technique

    NASA Astrophysics Data System (ADS)

    Yoo, S. H.; Wong, K. W.; Xin, Y.

    1997-02-01

    We have prepared superconducting HgBa 2Ca 2Cu 3O 8+δ thick films on polycrystalline MgO substrate via the sol-gel technique together with a slow annealing method. A precursor film of Ba 2Ca 2Cu 3O 7 was annealed with a bulk mixture of unreacted HgBa 2Ca 2Cu 3O 8+δ and a precursor, Ba 2Ca 2Cu 3O 7, pellet that was employed to control the HgO vapor pressure. Our films show an onset superconducting transition temperature of 140 K and a zero resistance temperature of 130 K after oxygen annealing. The high Tc thick films are consistently reproducible.

  11. NOx Uptake Mechanism on Pt/BaO/Al2O3 Catalysts

    SciTech Connect

    Kwak, Ja Hun; Kim, Do Heui; Szailer, Tamas; Peden, Charles HF; Szanyi, Janos

    2006-11-01

    The NOx adsorption mechanism on Pt/BaO/Al2O3 catalysts was investigated by performing NOx storage/reduction cycles, NO2 adsorption and NO + O2 adsorption on 2%Pt/(x)BaO/Al2O3 (x = 2, 8 and 20 wt%) catalysts. NOx uptake profiles on 2%Pt/20%BaO/Al2O3 at 523 K show complete uptake behavior for almost 5 min, and then the NOx level starts gradually increasing with time and it reaches 75% of the inlet NOx concentration after 30 min time-on-stream. Although this catalyst shows fairly high NOx conversion at 523 K, only ~ 2.4 wt% out of 20 wt% BaO is converted to Ba(NO3)2. Adsorption studies by using NO2 and NO + O2 suggest two different NOx adsorption mechanisms. The NO2 uptake profile on 2%Pt/20%BaO/Al2O3 shows the absence of a complete NOx uptake period at the beginning of adsorption and the overall NOx uptake is controlled by the gas-solid equilibrium between NO2 and BaO/Ba(NO3)2 phase. When we use NO + O2, complete initial NOx uptake occurs and the time it takes to convert ~ 4 % of BaO to Ba(NO3)2 is independent of the NO concentration. These NOx uptake characteristics suggest that the NO + O2 reaction on the surface of Pt particles produces NO2 that is subsequently transferred to the neighboring BaO phase by spill over. At the beginning of the NOx uptake, this spill-over process is very fast and so it is able to provide complete NOx storage. However, the NOx uptake by this mechanism slows down as BaO in the vicinity of Pt particles are converted to Ba(NO3)2. The formation of Ba(NO3)2 around the Pt particles results in the development of a diffusion barrier for NO2, and increases the probability of NO2 desorption and consequently, the beginning of NOx slip. As NOx uptake by NO2 spill-over mechanism slows down due to the diffusion barrier formation, the rate and extent of NO2 uptake are determined by the diffusion rate of nitrate ions into the BaO bulk, which, in turn, is determined by the gas phase NO2 concentration.

  12. Stability of Tl-Ba-Ca-Cu-O Superconducting Thin Films

    SciTech Connect

    Siegal, M.P.; Overmyer, D.L.; Venturini, E.L.; Padilla, R.R.; Provencio, P.N.

    1999-08-23

    We report the stability of TlBa{sub 2}CaCu{sub 2}O{sub 7} (Tl-1212) and Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} (T1-2212) thin films and by inference, the stability of TlBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub 9} (Tl-1223) and Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} (Tl-2223) thin films, under a variety of conditions. In general, we observe that the stability behavior of the single Tl-O layer materials (Tl-1212 and Tl-1223)are similar and the double Tl-O layer materials (Tl-2212 and Tl-2223) are similar. All films are stable with repeated thermal cycling to cryogenic temperatures. Films are also stable in acetone and methanol. Moisture degrades film quality rapidly, especially in the form of vapor. Tl-1212 is more sensitive to vapor than Tl-2212. These materials are stable to high temperatures in either N{sub 2}, similar to vacuum for the cuprates, and O{sub 2} ambients. While total degradation of properties (superconducting and structural) occur at the same temperatures for all phases, 600 C in N{sub 2} and 700 C in O{sub 2}, the onset of degradation occurs at somewhat lower temperatures for Tl-1212 than for Tl-2212 films. In all cases, sample degradation is associated with Tl depletion from the films.

  13. Enhanced ultrasonic attenuation of Tl-Ca-Ba-Cu-O at the superconducting transition

    NASA Technical Reports Server (NTRS)

    Sun, K. J.; Winfree, W. P.; Xu, M.-F.; Levy, M.; Sarma, Bimal K.

    1990-01-01

    Temperature-dependent ultrasonic attenuation measurements have been performed on polycrystalline samples of Tl-Ca-Ba-Cu-O at various frequencies. An attenuation anomaly was observed close to the superconducting transition temperature T(c) (103 K) whose temperature position was frequency-independent. The attenuation decreased exponentially with temperature in the superconducting state for both transverse and longitudinal waves. It was also found that the temperature-dependent sound velocity showed a slope change around T(c).

  14. Mechanism and kinetics of sintering of nonstoichiometric Y-Ba-Cu-O powders

    SciTech Connect

    Paritskaya, L.N.; Kaganovskii, Yu.S.; Bogdanov, V.V.

    1995-03-01

    Using high-resolution optical and scanning electron microscopy with x-ray microanalysis at temperatures of 880 to 920{degrees}C, we studied the kinetics and mechanism of the formation of intergranular contacts during sintering of powder-substrate models and also studied the mechanism of shrinkage during sintering of Y-Ba-Cu-O compacts with a stoichiometric composition and two nonstoichiometric compositions, YO{sub O.95}Ba{sub 2}CU{sub 3}O{sub Y} and Y{sub 1.05}Ba{sub 2}CU{sub 3}O{sub Y}. The formation and the shrinkage of powders of different compositions were found to be described by equations of different degrees, which points to different diffusion sintering mechanisms. Powders with stoichiometric and hyperstoichiometric compositions are sintered by a volume diffusion mechanism, which is controlled by the slowest ion, Y{sup 3+}. Powders with a substoichiometric composition (Y-0.95) are sintered like a liquid phase, i.e., is controlled by diffusion through liquid or solid layers where new phases with higher diffusion coefficients are formed as a result of segregation effects.

  15. Synthesis of porous Cu from Al-Cu-Co decagonal quasicrystalline alloys

    NASA Astrophysics Data System (ADS)

    Kalai Vani, V.; Kwon, O. J.; Hong, S. M.; Fleury, E.

    2011-07-01

    The formation of a porous Cu structure from cast Al-Cu-Co decagonal quasicrystalline alloys has been studied using a selective corrosion technique. Two alkaline solutions were selected based on the electrochemical properties of the constituent elements. Selective corrosion of Al and Co was achieved by chemical immersion of the cast Al-Cu-Co alloy in both 5 M NaOH and 0.5 M Na2CO3 solutions; values for BET surface-to-weight ratio of up to 30 m2/g could be reached. Microstructural analyses indicated that the architecture of the resulting porous structures was composed of a needle-type phase, remaining from the decagonal phase, in addition to Cu and Cu-Co phases.

  16. Enhancement of critical current density of liquid-infiltration-processed Y-Ba-Cu-O bulk superconductors using milled Y2BaCuO5 powder

    NASA Astrophysics Data System (ADS)

    Mahmood, A.; Chu, Y. S.; Sung, T. H.

    2012-04-01

    The size effects of a precursor Y2BaCuO5 (Y211) powder on the microstructure and critical current density (Jc) of liquid infiltration growth (LIG)-processed YBa2Cu3O7-y (Y123) bulk superconductors were investigated in terms of milling time (t). Y211 powders were attrition-milled for 0-10 h in 2 h increments at a fixed rotation speed of 400 rpm. Y211 pre-forms were made by pelletizing the milled Y211 powders followed by subsequent sintering, after which an LIG process with top seeding was applied to the Y211/Ba3Cu5O8 (Y035) pre-forms. Spherical pores were observed in all LIG-processed Y123 samples and the pore density gradually decreased as t increased from 0 to 8 h. In addition to the reduced pore density, the Y211 particle size in the final Y123 products also decreased with increasing t. As t increased further to 10 h, unexpected Y211 coarsening and large pore evolutions were observed. The magnetic susceptibility-temperature curves showed that the onset superconducting transition temperature (Tc,onset) of all samples was the same (91.5 K), but the transition width became greater as t increased. The Jc of the Y123 bulk superconductors fabricated in this study was observed to correlate well with t of the Y211 precursor powder. The maximum Jc of 1.0 × 105 A cm-2 (at 77 K, 0 T) was achieved at t = 8 h, which is attributed to the reduction in pore density and Y211 particle size. The prolonged milling time of t = 10 h decreased the Jc of the LIG-processed Y123 superconductor owing to the evolution of large pores and exaggerated Y211 growth.

  17. Direct spectroscopic evidence for completely filled Cu 3d shell in BaCu₂As₂ and α – BaCu₂Sb₂

    DOE PAGES

    Wu, S. F.; Richard, P.; van Roekeghem, A.; Nie, S. M.; Miao, H.; Xu, N.; Qian, T.; Saparov, B.; Fang, Z.; Biermann, S.; et al

    2015-06-08

    We use angle-resolved photoemission spectroscopy to extract the band dispersion and the Fermi surface of BaCu₂As₂ and α - BaCu₂Sb₂. While the Cu 3d bands in both materials are located around 3.5 eV below the Fermi level, the low-energy photoemission intensity mainly comes from As 4p states, suggesting a completely filled Cu 3d shell. The splitting of the As 3d core levels and the lack of pronounced three-dimensionality in the measured band structure of BaCu₂As₂ indicate a surface state likely induced by the cleavage of this material in the collapsed tetragonal phase, which is consistent with our observation of amore » Cu⁺¹ oxidation state. However, the observation of Cu states at similar energy in α - BaCu₂Sb₂ without the pnictide-pnictide interlayer bonding characteristic of the collapsed tetragonal phase suggests that the short interlayer distance in BaCu₂As₂ follows from the stability of the Cu⁺¹ rather than the other way around. Our results confirm the prediction that BaCu₂As₂ is an sp metal with weak electronic correlations.« less

  18. Direct spectroscopic evidence for completely filled Cu 3d shell in BaCu₂As₂ and α – BaCu₂Sb₂

    SciTech Connect

    Wu, S. F.; Richard, P.; van Roekeghem, A.; Nie, S. M.; Miao, H.; Xu, N.; Qian, T.; Saparov, B.; Fang, Z.; Biermann, S.; Sefat, Athena S.; Ding, H.

    2015-06-08

    We use angle-resolved photoemission spectroscopy to extract the band dispersion and the Fermi surface of BaCu₂As₂ and α - BaCu₂Sb₂. While the Cu 3d bands in both materials are located around 3.5 eV below the Fermi level, the low-energy photoemission intensity mainly comes from As 4p states, suggesting a completely filled Cu 3d shell. The splitting of the As 3d core levels and the lack of pronounced three-dimensionality in the measured band structure of BaCu₂As₂ indicate a surface state likely induced by the cleavage of this material in the collapsed tetragonal phase, which is consistent with our observation of a Cu⁺¹ oxidation state. However, the observation of Cu states at similar energy in α - BaCu₂Sb₂ without the pnictide-pnictide interlayer bonding characteristic of the collapsed tetragonal phase suggests that the short interlayer distance in BaCu₂As₂ follows from the stability of the Cu⁺¹ rather than the other way around. Our results confirm the prediction that BaCu₂As₂ is an sp metal with weak electronic correlations.

  19. X-ray photoelectron spectroscopy characterization of a nonsuperconducting Y-Ba-Cu-O superconductor-normal-metal-superconductor barrier material

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Hunt, B. D.; Foote, M. C.; Bajuk, L. J.

    1992-01-01

    A film of a novel nonsuperconducting Y-Ba-Cu-O (YBCO) barrier material was grown using conditions similar to those reported by Agostinelli et al. (1991) for forming a cubic semiconducting (c-YBCO) phase, and the material was characterized using X-ray photoelectron spectroscopy (XPS). A comparison of the XPS spectra of this material to those obtained from the orthorhombic and tetragonal phases of YBCO (o-YBCO and t-YBCO, respectively) showed that the barrier material had spectral characteristics different from those of o-YBCO and t-YBCO, particularly in the O 1s region. Features associated with the Cu-O chain and surface-reconstructed Cu-O planes were absent, consistent with expectations for the simple perovskite crystal structure of c-YBCO proposed by Agostinelli et al.

  20. Icosahedral phase stabilities in Al-Cu-Ru alloys

    SciTech Connect

    Shield, J.E.; Hoppe, C.; McCallum, R.W.; Goldman, A.I. ); Kelton, K.F.; Gibbons, P.C. )

    1992-02-01

    By examining a wide region of the Al-Cu-Ru phase diagram, a thorough analysis of the compositional and thermal stability of the icosahedral phase has been completed. The primary solidification product of rapid solidification was a topologically and chemically disordered icosahedral phase with an extensive compositional region. Crystallization through exothermic events of the as-solidified materials produced crystalline phases, without the formation of the face-centered-icosahedral (FCI) phase. However, the FCI phase does form at higher temperatures through an endothermic reaction, indicating that it is a stable phase of the system, but only at elevated temperatures. Of the alloys studied, the FCI phase field was found to encompass Al{sub 65}Cu{sub 23}Ru{sub 12}, Al{sub 65}Cu{sub 20}Ru{sub 15}, Al{sub 70}Cu{sub 20}Ru{sub 10}, and Al{sub 70}Cu{sub 15}Ru{sub 15}. The transformation to the FCI phase involves an intermediate approximant phase that is very similar to the FCI structure. Also, a cubic approximant containing atomic arrangements with local icosahedral symmetry similar to {alpha}-Al Mn Si was determined to exist near the FCI phase field.

  1. Temperature dependence diode parameters studies of Al/CuPc/n-Si/Al structure

    NASA Astrophysics Data System (ADS)

    Kumar, Ratnesh; Kaur, Ramneek; Sharma, Mamta; Kaur, Maninder; Tripathi, S. K.

    2015-08-01

    This paper presents the fabrication of Al/CuPc/n-Si/Al metal-organic-semiconductor diode. The copper phthalocyanine as organic layer is deposited on Si substrate by thermal evaporation technique. The temperature dependent current-voltage measurements are performed on Al/CuPc/n-Si structure. The important diode parameters i.e. the barrier height and ideality factor have been calculated. The temperature dependence of barrier height and ideality factor has been studied.

  2. Formation Mechanism of CuAlO2 Prepared by Rapid Thermal Annealing of Al2O3/Cu2O/Sapphire Sandwich Structure

    NASA Astrophysics Data System (ADS)

    Shih, C. H.; Tseng, B. H.

    Single-phase CuAlO2 films were successfully prepared by thin-film reaction of an Al2O3/Cu2O/sapphire sandwich structure. We found that the processing parameters, such as heating rate, holding temperature and annealing ambient, were all crucial to form CuAlO2 without second phases. Thermal annealing in pure oxygen ambient with a lower temperature ramp rate might result in the formation of CuAl2O4 in addition to CuAlO2, since part of Cu2O was oxidized to form CuO and caused the change in reaction path, i.e. CuO + Al2O3 → CuAl2O4. Typical annealing conditions successful to prepare single-phase CuAlO2 would be to heat the sample with a temperature rampt rate higher than 7.3 °C/sec and hold the temperature at 1100 °C in air ambient. The formation mechanism of CuAlO2 has also been studied by interrupting the reaction after a short period of annealing. TEM observations showed that the top Al2O3 layer with amorphous structure reacted immediately with Cu2O to form CuAlO2 in the early stage and then the remaining Cu2O reacted with the sapphire substrate.

  3. Synthesis and investigation of (Hg 1- xCu x)Ba 2Ca 2Cu 3O 8+ δ

    NASA Astrophysics Data System (ADS)

    Lokshin, K. A.; Pavlov, D. A.; Kovba, M. L.; Putilin, S. N.; Antipov, E. V.; Bryntse, I.

    2002-02-01

    A reproducible synthesis method for superconducting HgBa 2Ca 2Cu 3O 8+ δ (Hg-1223) has been developed, using sealed silica tubes and a CoO/Co 3O 4 mixture as oxygen getter to achieve a controlled partial pressure of oxygen. Samples containing more than 95% of Hg-1223 were prepared with this technique. A significant range of substitution of Cu for Hg was revealed by EDS analysis in samples synthesized at 900°C. After post-anneal in oxygen the lattice parameters were calculated from XRD data and Tc was determined to be 135 K, by susceptibility methods. We suggest that a high synthesis temperature and a low partial pressure of mercury promote substitution in the Hg-1223 phase.

  4. Microstrip resonators using two-sided metalorganic chemical vapor deposited Er-Ba-Cu-O thin films

    SciTech Connect

    Takemoto, J.H.; Jackson, C.M.; Manasevit, H.M.; St. John, D.C.; Burch, J.F.; Daly, K.P.; Simon, R.W. )

    1991-03-11

    We have measured very low microwave losses in microstrip resonators produced in a newly developed process which deposits high-temperature Er-Ba-Cu-O superconducting films by metalorganic chemical vapor deposition on both sides of a LaAlO{sub 3} substrate. These {ital in} {ital situ} films have critical temperatures of 92 K. High {ital T}{sub {ital c}} superconductor (HTS) linear microstrip resonators demonstrated {ital Q}'s of 3500 at 10 GHz and 4.2 K, corresponding to surface resistances less than 330 {mu}{Omega}, which is 45 times better than measured silver resoantors. HTS meanderline resonators with a fundamental frequency of 1.3 GHz have {ital Q}'s of 9600 at 4.2 K. Identical silver meanderline circuits have 300 times more surface resistance than HTS circuits.

  5. Supercoducting property of Zr-Cu-Al-Ni-Nb alloys

    NASA Astrophysics Data System (ADS)

    Okai, D.; Motoyama, G.; Kimura, H.; Inoue, A.

    The superconducting property of Zr55Cu(30-X)Al10Ni5NbX alloys prepared by arc melting and liquid quenching methods was investigated by magnetic susceptibility measurements. The crystalline alloys with X = 0∼25 at.% prepared by arc melting method exhibited superconductivity with maximum Tc,on of 10.1 K. The alloys (X = 10∼23 at.%) with crystalline particles embedded in an amorphous structure, which were fabricated by melt spinning method, showed superconductivity with Tc,on of less than 4.0 K. The superconducting property of the Zr-Cu-Al-Ni-Nb alloys was attributed to superconducting phases of Zr2Cu, Zr2Ni, Zr65Al10Nb25 and Zr-Nb contained in the Zr-Cu-Al-Ni-Nb alloys. The melt-spun Zr55Cu(30-X)Al10Ni5NbX (X = 10∼20 at.%) alloys exhibited glass transition at 718∼743 K and were found to be superconducting metallic glasses.

  6. New insights into the application of the valence rules in Zintl phases-Crystal and electronic structures of Ba7Ga4P9, Ba7Ga4As9, Ba7Al4Sb9, Ba6CaAl4Sb9, and Ba6CaGa4Sb9

    NASA Astrophysics Data System (ADS)

    He, Hua; Stoyko, Stanislav; Bobev, Svilen

    2016-04-01

    Crystals of three new ternary pnictides-Ba7Al4Sb9, Ba7Ga4P9, and Ba7Ga4As9 have been prepared by reactions of the respective elements in molten Al or Pb fluxes. Single-crystal X-ray diffraction studies reveal that the three phases are isotypic, crystallizing in the orthorhombic Ba7Ga4Sb9-type structure (space group Pmmn, Pearson symbol oP40, Z=2), for which only the prototype is known. The structure is based on TrPn4 tetrahedra (Tr=Al, Ga; Pn=P, As, Sb), connected in an intricate scheme into 1D-ribbons. Long interchain Pn-Pn bonds (dP-P>3.0 Å; dAs-As>3.1 Å; dSb-Sb>3.3 Å) account for the realization of 2D-layers, separated by Ba2+ cations. Applying the classic valance rules to rationalize the bonding apparently fails, and Ba7Ga4Sb9 has long been known as a metallic Zintl phase. Earlier theoretical calculations, both empirical and ab-initio, suggest that the possible metallic properties originate from filled anti-bonding Pn-Pn states, and the special roles of the "cations" in this crystal structure. To experimentally probe this hypothesis, we sought to synthesize the ordered quaternary phases Ba6CaTr4Sb9 (Tr=Al, Ga). Single-crystal X-ray diffraction work confirms Ba6.145(3)Ca0.855Al4Sb9 and Ba6.235(3)Ca0.765Ga4Sb9, with Ca atoms preferably substituting Ba on one of the three available sites. The nuances of the five crystal structures are discussed, and the chemical bonding in Ba7Ga4As9 is interrogated by tight-binding linear muffin-tin orbital calculations.

  7. Influence of an electric current on the crystallization of YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} in BaO/CuO/CuO{sub 0.5} flux melts

    SciTech Connect

    Aigner, M.L.; Ritter, F.; Assmus, W.

    1999-11-01

    The influence of an electric current on the ternary BaO/CuO/CuO{sub 0.5} system and the quaternary YO{sub 1.5}/BaO/CuO/CuO{sub 0.5} system has been investigated by modified differential thermal analysis. Increasing the current in the ternary system leads to the crystallization of an additional phase. In the quaternary system they find a splitting of the solidification of the residual melt BaO/CuO/CuO{sub 0.5} indicating the formation of two different eutectics. In both systems, they find a preferential deposition of material at the positive electrode. Crystal growth experiments including electric current show a preferential formation of YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} crystals at the positive electrode.

  8. AC magnetic response of superconducting YBa2Cu3O7/PrBa2Cu3O7 superlattices

    NASA Astrophysics Data System (ADS)

    Miu, L.; Ivan, I.; Ionescu, A. M.; Miu, D.

    2016-06-01

    Vortex activation energy UAC in the critical-state related AC magnetic response of superconductors (appearing in the vicinity of the DC irreversibility line) takes large values, as often reported, which is not yet understood. This behavior is essentially different from that of the vortex-creep activation energy at long relaxation time scales, and may become important for AC applications of superconductors. To elucidate this aspect, we investigated the AC signal of almost decoupled [Y Ba2Cu3O7]n/[PrBa2Cu3O7]4 superlattices (with n = 11 or 4 units cells) in perpendicular DC and AC magnetic fields. In these model samples, the length of the hopping vortex segment is fixed by the thickness of superconducting layers and vortices are disentangled, at least at low DC fields. It is shown that the high UAC values result from the large contribution of the pinning enhanced viscous drag in the conditions of thermally activated, non-diffusive vortex motion at short time scales, where the influence of thermally induced vortex fluctuations on pinning is weak.

  9. Synthesis and characterization of high-Tc superconductors in the Tl-Ca-Ba-Cu-O system

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Farrell, D. E.

    1989-01-01

    Both Tl2Ca2Ba2Cu3O10 and TlCa3BaCu3O8.5 are investigated for superconductivity as a function of the sintering temperature, time, atmosphere, and quench rate in an effort to synthesize the high-Tc superconducting phase in the thallium system. The samples are characterized by electrical resistivity measurements, X-ray diffraction, and scanning electron microscopy. Samples of starting composition Tl2Ca2Ba2Cu3O10 fired in air at 860-900 C and rapidly quenched show a Tc of 96-107 K. In contrast, specimens of starting composition TlCa3BaCu3O8.5 when baked at 900 C and slowly cooled in oxygen superconduct at 116 K and above and consist of Tl2Ca2Ba2Cu3O(10+x) as the dominant phase. The results also show that, in contrast to the case of YBa2Cu3O(7-x), doping with a small concentration of fluorine sharpens the resistive transition and produces a large Tc increase in thallium-based superconductors.

  10. Synthesis and characterization of high-Tc superconductors in the Tl-Ca-Ba-Cu-O system

    NASA Astrophysics Data System (ADS)

    Bansal, Narottam P.; Farrell, D. E.

    1989-05-01

    Both Tl2Ca2Ba2Cu3O10 and TlCa3BaCu3O8.5 are investigated for superconductivity as a function of the sintering temperature, time, atmosphere, and quench rate in an effort to synthesize the high-Tc superconducting phase in the thallium system. The samples are characterized by electrical resistivity measurements, X-ray diffraction, and scanning electron microscopy. Samples of starting composition Tl2Ca2Ba2Cu3O10 fired in air at 860-900 C and rapidly quenched show a Tc of 96-107 K. In contrast, specimens of starting composition TlCa3BaCu3O8.5 when baked at 900 C and slowly cooled in oxygen superconduct at 116 K and above and consist of Tl2Ca2Ba2Cu3O(10+x) as the dominant phase. The results also show that, in contrast to the case of YBa2Cu3O(7-x), doping with a small concentration of fluorine sharpens the resistive transition and produces a large Tc increase in thallium-based superconductors.

  11. Calculation of phase diagrams for the YO/sub 1. 5/-BaO-CuO/sub x/ system

    SciTech Connect

    Lee, B.J.; Lee, D.N.

    1989-02-01

    Thermodynamic data for YO/sub 1.5/-BaO, BaO-CuO/sub x/, and YO/sub 1.5/-CuO/sub x/ binary systems from experimental phase diagram data. The equilibrium liquidus surface and the isothermal sections of the ternary system at 900/sup 0/, 925/sup 0/, 950/sup 0/, 975/sup 0/, and 1000 /sup 0/C were calculated. The isopleths containing YBa/sub 2/Cu/sub 3/O/sub 7-/delta// were also calculated.

  12. Electronic Structure of Tl2Ba2CuO(6+Delta) Epitaxial Films Measured by X-Ray Photoemission

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Ren, Z. F.; Wang, J. H.

    1996-01-01

    The valence electronic structure and core levels of Tl2Ba2CuO(6 + delta) (Tl-2201) epitaxial films have been measured with X-ray photoelectron spectroscopy and are compared to those of Tl2Ba2CaCu2O(8 + delta) (Tl-2212). Changes in the Tl-2201 core-level binding energies with oxygen doping are consistent with a change in the chemical potential. Differences between the Tl-2201 and Tl-2212 measured densities of states are consistent with the calculated Cu 3d and Tl 6s partial densities of states.

  13. Fabrication and chemical composition of RF magnetron sputtered Tl-Ca-Ba-Cu-O high Tc superconducting thin films

    NASA Technical Reports Server (NTRS)

    Subramanyam, G.; Radpour, F.; Kapoor, V. J.; Lemon, G. H.

    1990-01-01

    The preparation of TlCaBaCuO superconducting thin films on (100) SrTiO3 substrates is described, and the results of their characterization are presented. Sintering and annealing the thin films in a Tl-rich ambient yielded superconductivity with a Tc of 107 K. The results of an XPS study support two possible mechanisms for the creation of holes in the TlCaBaCuO compound: (1) partial substitution of Ca(2+) for Tl(3+), resulting in hole creation, and (2) charge transfer from Tl(3+) to the CuO layers, resulting in a Tl valence between +3 and +1.

  14. High critical currents in heavily doped (Gd,Y)Ba2Cu3Ox superconductor tapes

    SciTech Connect

    Selvamanickam, V; Gharahcheshmeh, MH; Xu, A; Galstyan, E; Delgado, L; Cantoni, C

    2015-01-19

    REBa2Cu3Ox ((REBCO), RE = rare earth) 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 50K 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 (J(c)) above 20 MA/cm(2) at 30 K, 3 T in heavily doped (25 mol.% Zr-added) (Gd,Y)Ba2Cu3Ox superconductor tapes, which is more than three times higher than the J(c) typically obtained in moderately doped tapes. Pinning force levels above 1000 GN/m(3) have also been attained at 20 K. A composition map of lift factor in J(c) (ratio of J(c) at 30 K, 3 T to the J(c) 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 BaZrO3 (BZO) nanocolumn defect density of nearly 7 x 10(11) cm(-2) as well as 2-3 nm sized particles rich in Cu and Zr have been found in the high J(c) films. (C) 2015 AIP Publishing LLC.

  15. Sequentially evaporated thin Y-Ba-Cu-O superconductor films: Composition and processing effects

    NASA Technical Reports Server (NTRS)

    Valco, George J.; Rohrer, Norman J.; Warner, Joseph D.; Bhasin, Kul B.

    1988-01-01

    Thin films of YBa2Cu3O(7-beta) have been grown by sequential evaporation of Cu, Y, and BaF2 on SrTiO3 and MgO substrates. The onset temperatures were as high as 93 K while T sub c was 85 K. The Ba/Y ratio was varied from 1.9 to 4.0. The Cu/Y ratio was varied from 2.8 to 3.4. The films were then annealed at various times and temperatures. The times ranged from 15 min to 3 hr, while the annealing temperatures used ranged from 850 C to 900 C. A good correlation was found between transition temperature (T sub c) and the annealing conditions; the films annealed at 900 C on SrTiO3 had the best T sub c's. There was a weaker correlation between composition and T sub c. Barium poor films exhibitied semiconducting normal state resistance behavior while barium rich films were metallic. The films were analyzed by resistance versus temperature measurements and scanning electron microscopy. The analysis of the films and the correlations are reported.

  16. High critical currents in heavily doped (Gd,Y)Ba2Cu3Ox superconductor tapes

    DOE PAGES

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

    2015-01-20

    REBa2Cu3Ox 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)Ba2Cu3Ox superconductor tapes, which is more than three times higher thanmore » 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 BaZrO3 (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.« less

  17. Local Probe Studies of the Quantum Honeycomb Antiferromagnet Ba3CuSb2O9

    NASA Astrophysics Data System (ADS)

    Quilliam, Jeffrey; Bert, Fabrice; Kermarrec, Edwin; Payen, Christophe; Guillot-Deudon, Cathérine; Bonville, Pierre; Mendels, Philippe

    2013-03-01

    The 6H-perovskites, Ba3 M Sb2O9, have generated an enormous amount of interest in the last two years following the possible discovery of quantum spin liquid physics in two such materials. We present local probe studies (muon spin rotation and nuclear magnetic resonance) on the spin-1/2 honeycomb antiferromagnet Ba3CuSb2O9. We show that the system presents no spin freezing down to temperatures as low as 20 mK. NMR measurements show evidence of a spin gap and suggest that the material has a random singlet ground state rather than the alternative spin-orbital liquid state. We acknowledge support from ANR, EC FP6 and NSERC.

  18. Synthesis, rheology and forming of Y-Ba-Cu-O ceramics

    SciTech Connect

    Green, T.M.

    1993-07-01

    A chemical synthesis route is discussed which results in a low- temperature precursor to Y-Ba-Cu-O ceramics; it is based on use of molten Ba(OH){sub 2}{center_dot}8H{sub 2}O flux. Two different chemical systems have been examined; the first one, based on nitrate salts, has been demonstrated to be a viable precursor material for tape casting and extrusion; the second, made from acetate salts, has been used for powder synthesis and extrusion. Rheology of pastes shows that their flow may be fit to either Bingham Plastic or Hershel- Bulkley models. Yield stress is controlled in both pastes by volume fraction solids. Viscosity also follows solids loading in the paste. Shear thinning is controlled by colloidal nature of precursor. The paste has colloidal microstructure. Comparison of concentric cylinder rheometry and piston extrusion rheometry shows order of magnitude differences in yield stress, resulting from the test method and paste dilation.

  19. Preparation of high T(c) Tl-Ba-Ca-Cu-O thin films by pulsed laser evaporation and Tl2O3 vapor processing

    NASA Technical Reports Server (NTRS)

    Johs, B.; Thompson, D.; Ianno, N. J.; Woollam, John A.; Liou, S. H.

    1989-01-01

    Tl-Ba-Ca-Cu-O superconducting thin films with zero-resistance temperatures up to 115 K have been prepared using a Tl2O3 vapor process on Ba-Ca-Cu-O precursor thin films. The Ba-Ca-Cu-O thin films were made by laser deposition on Y-stabilized ZrO2 substrates. This technique minimizes problems caused by the toxicity of Tl2O3, and its subsequent decomposition to the volatile and toxic Tl2O upon heating. Therefore, it may have practical application in the fabrication of high T(c) Tl-Ba-Ca-Cu-O superconducting thin-film devices.

  20. Singlet Ground State of the Quantum Antiferromagnet Ba3CuSb2O9

    NASA Astrophysics Data System (ADS)

    Quilliam, J. A.; Bert, F.; Kermarrec, E.; Payen, C.; Guillot-Deudon, C.; Bonville, P.; Baines, C.; Luetkens, H.; Mendels, P.

    2012-09-01

    We present local probe results on the honeycomb lattice antiferromagnet Ba3CuSb2O9. Muon spin relaxation measurements in a zero field down to 20 mK show unequivocally that there is a total absence of spin freezing in the ground state. Sb NMR measurements allow us to track the intrinsic susceptibility of the lattice, which shows a maximum at around 55 K and drops to zero in the low-temperature limit. The spin-lattice relaxation rate shows two characteristic energy scales, including a field-dependent crossover to exponential low-temperature behavior, implying gapped magnetic excitations.

  1. Superconductivity in 2-2-3 system Y2Ba2Cu2O(8+delta)

    NASA Technical Reports Server (NTRS)

    Joshi, H. H.; Baldha, G. J.; Jotania, R. B.; Joshi, S. M.; Mohan, H.; Pandya, P. B.; Pandya, H. N.; Kulkarni, R. G.

    1991-01-01

    Researchers synthesized a new high T(sub c) 2-2-3 superconductor Y2Ba2Cu3O(8+delta) by a special preparation technique and characterized it by ac-susceptibility measurements. Diamagnetism and Meissner effect sets in at low fields and superconducting transition onsets at 90 K. The systematic investigation of the real and imaginary components of ac-susceptibility as a function of temperature and applied ac magnetic field reveals that the magnetic behavior is that of a granular type superconductor.

  2. Microwave surface resistance of bulk Tl-Ba-Ca-Cu-O superconductors

    SciTech Connect

    Newman, H.S.; Singh, A.K.; Sadananda, K.; Imam, M.A.

    1989-01-23

    The first measurements of the microwave surface resistance at 18 GHz of bulk Tl-Ba-Ca-Cu-O superconductors produced by the hot isostatic pressing (HIP) process are reported. The superconducting samples, prepared by solid-state reaction with subsequent sintering and consolidation to obtain ideal density, were measured by replacing the end wall of a TE/sub 011/ circular mode gold-plated copper cavity with the sample and determining the cavity Q for the temperature range 4--300 K. Results indicated that HIP samples which underwent subsequent annealing exhibit, below the critical temperature, a surface resistance approaching an order of magnitude less than copper.

  3. Imperfections of the crystal structure of Y-Ba-Cu-O superconducting ceramic following shock compression

    NASA Astrophysics Data System (ADS)

    Khudiakov, A. V.; Malovitskii, Iu. N.; Safronov, P. P.; Kotov, E. A.; Abramova, E. B.

    1989-10-01

    Cylindrical (20 mm in diameter, 160 mm long) specimens produced by the shock compression of a superconducting Y-Ba-Cu-O powder were characterized by a variety of methods, including differential thermal analysis, X-ray diffraction analysis, gravimetry, and resistance measurements. The experimentally observed scatter of the critical temperature along the length of the specimens in the range 88-91 K and the broadening of the superconducting transition are attributed to the imperfections in the crystal structure of the specimens resulting from the shock loading.

  4. Fabrication of Y-Ba-Cu-O Superconducting Wire by the Powder-Sol Method

    NASA Astrophysics Data System (ADS)

    Enomoto, Ryo; Tamaki, Masanori; Ohno, Satoshi; Fuwa, Mayumi; Takei, Humihiko

    1989-07-01

    Y-Ba-Cu-O superconducting wires have been prepared by using the powder-sol method. Wires with a typical diameter of 280 μm were made by extruding a suspension of YBCO powder with a mixture of organic metal compounds, followed by sintering at a temperature between 910°C and 940°C in flowing oxygen. The maximum current density of 2020 A/cm2 in liquid nitrogen was obtained on the wires fired at 930°C.

  5. Development of Y-Ba-Cu-O Superconductors for Magnetic Bearings

    NASA Technical Reports Server (NTRS)

    Selvamanickam, V.; Pfaffenbach, K.; Sokolowski, R. S.; Zhang, Y.; Salama, K.

    1996-01-01

    The material requirements, material manufacturing and magnetic properties that are relevant to fabrication of High Temperature Superconductor (HTS) magnetic bearings have been discussed. It is found that the seeded-melt-texturing method can be used to fabricate the single domain material that is required to achieve the best magnetic properties. Trapped-field mapping has been used as a non-destructive tool to determine the single-domain nature of the HTS material and quantity of the HTS disks. Both the trapped field and the levitation force of the Y-Ba-Cu-O disks are found to be strongly sensitive to the oxygen content.

  6. Hyper- and hypobaric processing of Tl-Ba-Ca-Cu-O superconductors

    SciTech Connect

    Goretta, K.C.; Routbort, J.L.; Shi, Donglu; Chen, J.G.; Hash, M.C.

    1989-11-01

    Tl-based superconductors of initial composition Tl:Ca:Ba:Cu equal to 2:2:2:3 and 1:3:1:3 were heated in oxygen at pressures of 10{sup 4} to 6 {times} 10{sup 5} Pa. The 2:2:2:3 composition formed primarily the 2-layer superconductor with zero resistance from 77 to 104 K. The 1:3:1:3 composition formed nearly phase pure 3-layer superconductor with a maximum zero resistance temperature of 120 K. Application of hyperbaric pressure influenced phase purities and transition temperatures slightly; phase purities decreased significantly with application of hypobaric pressures. 10 refs., 1 fig.

  7. Hyper- and hypobaric processing of Tl-Ba-Ca-Cu-O superconductors

    NASA Astrophysics Data System (ADS)

    Goretta, K. C.; Routbort, J. L.; Shi, Donglu; Chen, J. G.; Hash, M. C.

    1989-11-01

    Tl-based superconductors of initial composition Tl:Ca:Ba:Cu equal to 2:2:2:3 and 1:3:1:3 were heated in oxygen at pressures of 10(sup 4) to 6 (times) 10(sup 5) Pa. The 2:2:2:3 composition formed primarily the 2-layer superconductor with zero resistance from 77 to 104 K. The 1:3:1:3 composition formed nearly phase pure 3-layer superconductor with a maximum zero resistance temperature of 120 K. Application of hyperbaric pressure influenced phase purities and transition temperatures slightly; phase purities decreased significantly with application of hypobaric pressures.

  8. Telegraph-like noise in Y-Ba-Cu oxide thin-film dc SQUID's

    SciTech Connect

    Matsuda, M.; Kuriki, S.

    1988-08-15

    We have observed a telegraph-like noise in dc superconducting quantum interference devices (SQUID's) made of low-temperature synthesized superconducting Y-Ba-Cu oxide thin films. The voltage of the SQUID jumps among two to four discrete levels randomly with time, and exhibits a Lorentzian type frequency dependence in the power spectrum. Periodic modulations of the voltage with magnetic flux are observed in a SQUID having narrow bridges of submicrometer width. The flux noise of the SQUID is dominated by the telegraph-like noise at low frequencies.

  9. Characterization of Cu-exchanged SSZ-13: a comparative FTIR, UV-Vis, and EPR study with Cu-ZSM-5 and Cu-β with similar Si/Al and Cu/Al ratios.

    PubMed

    Giordanino, Filippo; Vennestrøm, Peter N R; Lundegaard, Lars F; Stappen, Frederick N; Mossin, Susanne; Beato, Pablo; Bordiga, Silvia; Lamberti, Carlo

    2013-09-21

    Cu-SSZ-13 has been characterized by different spectroscopic techniques and compared with Cu-ZSM-5 and Cu-β with similar Si/Al and Cu/Al ratios and prepared by the same ion exchange procedure. On vacuum activated samples, low temperature FTIR spectroscopy allowed us to appreciate a high concentration of reduced copper centres, i.e. isolated Cu(+) ions located in different environments, able to form Cu(+)(N2), Cu(+)(CO)n (n = 1, 2, 3), and Cu(+)(NO)n (n = 1, 2) upon interaction with N2, CO and NO probe molecules, respectively. Low temperature FTIR, DRUV-Vis and EPR analysis on O2 activated samples revealed the presence of different Cu(2+) species. New data and discussion are devoted to (i) [Cu-OH](+) species likely balanced by one framework Al atom; (ii) mono(μ-oxo)dicopper [Cu2(μ-O)](2+) dimers observed in Cu-ZSM-5 and Cu-β, but not in Cu-SSZ-13. UV-Vis-NIR spectra of O2 activated samples reveal an intense and finely structured d-d quadruplet, unique to Cu-SSZ-13, which is persistent under SCR conditions. This differs from the 22,700 cm(-1) band of the mono(μ-oxo)dicopper species of the O2 activated Cu-ZSM-5, which disappears under SCR conditions. The EPR signal intensity sets Cu-β apart from the others. PMID:23842567

  10. Quantitative X-Ray Phase Analysis and EPR Spectra in the System Y 2BaCuO 5-YBa 2Cu 3O 6+ x

    NASA Astrophysics Data System (ADS)

    Hanic, F.; Plesch, G.; Buchta, Š.; Dobrovodský, J.; Danielik, L.

    1995-04-01

    The quantitative phase analysis in the system Y2BaCuO5(2-1-1)-YBa2Cu3O6+x(1-2-3) was performed by the X-ray powder diffraction (XRPD) method based on the comparison of the integral intensities of the X-ray diffractions of the investigated system with the corresponding intensities of standard mixtures of (2-1-1) and (1-2-3) components of known composition. To avoid the orientation effects of the (1-2-3) components, the selected mixtures were homogenized by the admixture of 50 mass% α-AL2O3. The constituent (2-1-1) showed no preferential orientation, neither in the bulk textured materials prepared by the quench and melt growth technique, nor in the samples ground to powder. The X-ray diffraction results were in accordance with the semiquantitative estimation of the concentration of the paramagnetic (2-1-1) phase obtained from the results of EPR measurements on powdered samples. On the other hand, the intensity of the EPR spectra strongly decreased in bulk materials due to the skin effect. The electric conductivity of (1-2-3) at room temperature causes the microwave fields to penetrate to a depth of approximately 10 μm, which is the only EPR active region.

  11. Thermodynamic stability of radiogenic Ba in CsAlSi2O6 pollucite

    NASA Astrophysics Data System (ADS)

    Jaffe, John; van Ginhoven, Renée; Jiang, Weilin

    2013-03-01

    Pollucite, a zeolite-like nanoporous aluminosilicate structure with nominal composition CsAlSi2O6, has been suggested as a nuclear waste storage form for fission-product radioactive isotopes of cesium, especially 137Cs. One factor affecting the long-term stability of this waste form is the valence change associated with the beta decay that converts Cs into barium. We have used first-principles density functional total energy calculations to evaluate the thermodynamic stability of pollucite with Ba replacing Cs at regular lattice sites with respect to the precipitation of Ba, Cs or their oxides. We included small clusters of substitutional BaCs as well as localized complexes of BaCs with compensating electron donor defects, specifically Cs vacancies and interstitial oxygen. We conclude that Cs-Ba pollucite is thermodynamically stable against precipitation of Cs or its oxide, but that partial precipitation of Ba or BaO may be thermodynamically favored under some conditions. Even this change may be kinetically limited, however. Fuel Cycle Research and Development, U.S. Department of Energy Waste Form Campaign

  12. Computer modeling of Y-Ba-Cu-O thin film deposition and growth

    SciTech Connect

    Burmester, C.; Gronsky, R. ); Wille, L. . Dept. of Physics)

    1991-07-01

    The deposition and growth of epitaxial thin films of YBa{sub 2}Cu{sub 3}O{sub 7} are modeled by means of Monte Carlo simulations of the deposition and diffusion of Y, Ba, and Cu oxide particles. This complements existing experimental characterization techniques to allow the study of kinetic phenomena expected to play a dominant role in the inherently non-equilibrium thin film deposition process. Surface morphologies and defect structures obtained in the simulated films are found to closely resemble those observed experimentally. A systematic study of the effects of deposition rate and substrate temperature during in-situ film fabrication reveals that the kinetics of film growth can readily dominate the structural formation of the thin film. 16 refs., 4 figs.

  13. TlCaBaCuO high Tc superconducting microstrip ring resonators designed for 12 GHz

    NASA Technical Reports Server (NTRS)

    Subramanyam, G.; Kapoor, V. J.; Chorey, C. M.; Bhasin, K. B.

    1993-01-01

    Microwave properties of sputtered Tl-Ca-Ba-Cu-O thin films were investigated by designing, fabricating, and testing microstrip ring resonators. Ring resonators designed for 12 GHz fundamental resonance frequency, were fabricated and tested. From the unloaded Q values for the resonators, the surface resistance was calculated by separating the conductor losses from the total losses. The penetration depth was obtained from the temperature dependence of resonance frequency, assuming that the shift in resonance frequency is mainly due to the temperature dependence of penetration depth. The effective surface resistance at 12 GHz and 77 K was determined to be between 1.5 and 2.75 mOmega, almost an order lower than Cu at the same temperature and frequency. The effective penetration depth at 0 K is approximately 7000 A.

  14. Single crystal growth and characterization of the large-unit-cell compound Cu13Ba

    SciTech Connect

    Jesche, Anton; Budko, Serguei L.; Canfield, Paul C.

    2013-10-31

    Single crystals of Cu13Ba were successfully grown out of Ba–Cu self flux. Temperature dependent magnetization, M (T ), electrical resistivity, ρ(T)ρ(T), and specific heat, Cp(T)Cp(T), data are reported. Isothermal magnetization measurements, M(H)M(H), show clear de Haas-van Alphen oscillations at T = 2 K for applied fields as low as View the MathML sourceμ0H=1T. An anomalous behavior of the magnetic susceptibility is observed up to T ≈ 50 K reflecting the effect of de Haas-van Alphen oscillations at fairly high temperatures. The field- and temperature-dependencies of the magnetization indicate the presence of diluted magnetic impurities with a concentration of the order of 0.01 at.%. Accordingly, the minimum and lower temperature rise observed in the electrical resistivity at and below T = 15 K is attributed to the Kondo-impurity effect.

  15. Partial reduction of re-oxidation processing of Y-Ba-Cu-O sputtered thin films

    SciTech Connect

    Garzon, F.H.; Beery, J.G.; Wilde, D.K.; Raistrick, I.D.

    1989-01-01

    Thin films of Y--Ba--Cu--O were produced by rf sputtering of YBa{sub 2}Cu{sub 3}O{sub 7-x} ceramic targets, using a variety of plasma compositions, rf power levels, and substrate temperatures. Post annealing of these films in oxygen produced superconducting films with T{sub c} values between 40--60 K, broad transition widths and semiconductor-like electrical behavior above T{sub c}. Subsequent annealing at 850{degree}C in an inert gas with a residual oxygen partial pressure of {le}10 ppM followed by an oxygen anneal produced high quality thin films: T{sub c} > 85 K with narrow transition widths. The structure and morphology of these films during reduction-oxidation processing were monitored using x-ray diffraction and electron microscopy. 8 refs., 4 figs.

  16. Reduced Cu concentration in CuAl-LPE-grown thin Si layers

    SciTech Connect

    Wang, T.H.; Ciszek, T.F.; Asher, S.; Reedy, R.

    1995-08-01

    Cu-Al has been found to be a good solvent system to grow macroscopically smooth Si layers with thicknesses in tens of microns on cast MG-Si substrates by liquid phase epitaxy (LPE) at temperatures near 900{degrees}C. This solvent system utilizes Al to ensure good wetting between the solution and substrate by removing silicon native oxides, and employs Cu to control Al doping into the layers. Isotropic growth is achieved because of a high concentration of solute silicon in the solution and the resulting microscopically rough interface. The incorporation of Cu in the Si layers, however, was a concern since Cu is a major solution component and is generally regarded as a bad impurity for silicon devices due to its fast diffusivity and deep energy levels in the band gap. A study by Davis shows that Cu will nonetheless not degrade solar cell performance until above a level of 10{sup 17} cm{sup -3}. This threshold is expected to be even higher for thin layer silicon solar cells owing to the less stringent requirement on minority carrier diffusion length. But to ensure long term stability of solar cells, lower Cu concentrations in the thin layers are still preferred.

  17. Transport and Cu NMR studies of charge and spin dynamics in PrBa{sub 2}Cu{sub 4}O{sub 8}

    SciTech Connect

    Kikuchi, Jun; Terasaki, Ichiro; Machi, Takato; Seiji, Nobuaki

    1996-11-01

    The charge and spin dynamics in PrBa{sub 2}Cu{sub 4}O{sub 8} are investigated by means of transport and Cu NMR measurements. The magnetoresistance was found to be very small at high temperatures and increase rapidly with decreasing temperature below {approximately}100 K, which may be ascribed to the dimensional crossover from one to two dimensions in the charge transport in the CuO double chains. While the NMR signal from the chain Cu sites persists down to 4.2 K without any appreciable line broadening, the signal from the planar Cu sites disappears below {approximately}250 K indicating the long-range antiferromagnetic order of plane Cu moments. This is consistent with the view of metallic conduction along the quasi one-dimensional CuO chains.

  18. Ab initio molecular dynamics simulations of short-range order in Zr50Cu45Al5 and Cu50Zr45Al5 metallic glasses

    DOE PAGES

    Huang, Yuxiang; Huang, Li; Wang, C. Z.; Kramer, M. J.; Ho, K. M.

    2016-02-01

    Comparative analysis between Zr-rich Zr50Cu45Al5 and Cu-rich Cu50Zr45Al5 metallic glasses (MGs) is extensively performed to locate the key structural motifs accounting for their difference of glass forming ability. Here we adopt ab initio molecular dynamics simulations to investigate the local atomic structures of Zr50Cu45Al5 and Cu50Zr45Al5 MGs. A high content of icosahedral-related (full and distorted) orders was found in both samples, while in the Zr-rich MG full icosahedrons < 0,0,12,0 > is dominant, and in the Cu-rich one the distorted icosahedral orders, especially < 0,2,8,2 > and < 0,2,8,1 >, are prominent. And the < 0,2,8,2 > polyhedra in Cu50Zr45Al5more » MG mainly originate from Al-centered clusters, while the < 0,0,12,0 > in Zr50Cu45Al5 derives from both Cu-centered clusters and Al-centered clusters. These difference may be ascribed to the atomic size difference and chemical property between Cu and Zr atoms. Lastly, the relatively large size of Zr and large negative heat of mixing between Zr and Al atoms, enhancing the packing density and stability of metallic glass system, may be responsible for the higher glass forming ability of Zr50Cu45Al5.« less

  19. Comparative study of flux pinning, creep and critical currents between YBaCuO crystals with and without Y2BaCuO5 inclusions

    NASA Technical Reports Server (NTRS)

    Murakami, Masato; Gotoh, Satoshi; Fujimoto, Hiroyuki; Koshizuka, Naoki; Tanaka, Shoji

    1991-01-01

    In the Y-Ba-Cu-O system, YBa2Cu3O(x) phase is produced by the following peritectic reaction: Y2BaCuO5 + liquid yields 2YBa2Cu3O(x). Through the control of processing conditions and starting compositions, it becomes possible to fabricate large crystals containing fine Y2BaCuO5(211) inclusions. Such crystals exhibit Jc values exceeding 10000 A/sq cm at 77 K and 1T. Recently, researchers developed a novel process which can control the volume fraction of 211 inclusions. Elimination of 211 inclusions is also possible. In this study, researchers prepared YBaCuO crystals with and without 211 inclusions using the novel process, and compared flux pinning, flux creep and critical currents. Magnetic field dependence of Jc for YBaCuO crystals with and with 211 inclusions is shown. It is clear that fine 211 inclusions can contribute to flux pinning. It was also found that flux creep rate could be reduced by increasing flux pinning force. Critical current density estimates based on the conventional flux pinning theory were in good agreement with experimental results.

  20. Comparative study of flux pinning flux creep and critical currents between YBaCuO crystals with and without Y2BaCuO5 inclusions

    NASA Technical Reports Server (NTRS)

    Murakami, Masato; Gotoh, Satoshi; Fujimoto, Hiroyuki; Koshizuka, Naoki; Tanaka, Shoji

    1990-01-01

    In the Y-Ba-Cu-O system YBa2Cu3Ox phase is produced by the following peritectic reaction: Y2BaCuO5 + liquid yields 2YBa2Cu3Ox. Through the control of processing conditions and starting compositions it becomes possible to fabricate large crystals containing fine Y2BaCuO5(211) inclusions. Such crystals exhibit Jc values exceeding 10000 A/sq cm at 77 K and 1T. Recently, researchers developed a novel process which can control the volume fraction of 211 inclusions. Elimination of 211 inclusions is also possible. In this study, researchers prepared YBaCuO crystals with and without 211 inclusions using the novel process and compared flux pinning, flux creep and critical currents. Magnetic field dependence of Jc for YBaCuO crystals with and without 211 inclusions is shown. It is clear that fine 211 inclusions can contribute to flux pinning. It was also found that flux creep rate could be reduced by increasing flux pinning force. Critical current density estimates based on the conventional flux pinning theory were in good agreement with experimental results.

  1. Single crystals of the 96 K superconductor (Hg,Cu)Ba2CuO4+δ: Growth, structure and magnetism

    NASA Astrophysics Data System (ADS)

    Pelloquin, D.; Hardy, V.; Maignan, A.; Raveau, B.

    1997-02-01

    Single crystals of the 1201 (n = 1) (Hg,Cu)Ba2CuO4+δ mercury based cuprate have been grown by using a simple process without dry box. The as-synthesized crystals exhibit constant Tc(onset) of 96 K with sharp superconducting transitions. The electron microscopy coupled with EDX analyses evidence a ``1201''-type structure while a mercury deficiency is observed balanced by an excess of copper. The structural refinements based on single-crystal X-ray diffraction data confirm the electron deficiency on the Hg site (0,0,0) and show a splitting of the latter along the c axis correlated to the partial substitution of Cu for Hg. This structural study leads to the following formula Hg0.84Cu0.16Ba2CuO4.19. The magnetic study of a large crystal (1.1 × 0.38 × 0.065 mm3) shows that the (Hg,Cu)-1201 crystals exhibit an irreversibility line higher than that of the 1201 Hg0.8Bi0.2Ba2CuO4+δ crystal (Tc = 75 K). From the reversible magnetization, a λab(0) = 2470 Å value can be extrapolated. Using a 3D-2D decoupling formula, we obtain γ = 29 for the electronic anisotropy of this phase.

  2. Co{sub 2}FeAl based magnetic tunnel junctions with BaO and MgO/BaO barriers

    SciTech Connect

    Rogge, J.; Schmalhorst, J.; Hütten, A.; Hetaba, W.

    2015-07-15

    We succeed to integrate BaO as a tunneling barrier into Co{sub 2}FeAl based magnetic tunnel junctions (MTJs). By means of Auger electron spectroscopy it could be proven that the applied annealing temperatures during BaO deposition and afterwards do not cause any diffusion of Ba neither into the lower Heusler compound lead nor into the upper Fe counter electrode. Nevertheless, a negative tunnel magnetoresistance (TMR) ratio of -10% is found for Co{sub 2}FeAl (24 nm) / BaO (5 nm) / Fe (7 nm) MTJs, which can be attributed to the preparation procedure and can be explained by the formation of Co- and Fe-oxides at the interfaces between the Heusler and the crystalline BaO barrier by comparing with theory. Although an amorphous structure of the BaO barrier seems to be confirmed by high-resolution transmission electron microscopy (TEM), it cannot entirely be ruled out that this is an artifact of TEM sample preparation due to the sensitivity of BaO to moisture. By replacing the BaO tunneling barrier with an MgO/BaO double layer barrier, the electric stability could effectively be increased by a factor of five. The resulting TMR effect is found to be about +20% at room temperature, although a fully antiparallel state has not been realized.

  3. Resin-impregnated bulk RE-Ba-Cu-O current leads for the superconducting magnet on maglev train

    NASA Astrophysics Data System (ADS)

    Tomita, M.; Nagashima, K.; Herai, T.; Murakami, M.

    2002-08-01

    Bulk RE-Ba-Cu-O (RE: rare earth elements) superconductors exhibit high critical current density ( Jc) and low thermal conductivity, that are the characteristics desired for the current lead applications. In this study, we studied whether the resin-impregnated Y-Ba-Cu-O rods can be used as the current lead for the superconducting magnet on a magnetically levitated train. The fatigue test showed that the mechanical properties of resin-impregnated Y-Ba-Cu-O rods are sufficiently good for maglev applications. We could also pass the electric currents of 500 A without heat generation. This was further confirmed by field distribution measurements, which showed that the superconducting state of the current lead was well maintained when the currents of 500 A were passed.

  4. High-temperature superconductivity in Y-Ba-Cu-O: identification of a copper-rich superconducting phase

    SciTech Connect

    Stacy, A.M.; Badding, J.V.; Geselbracht, M.J.; Ham, W.K.; Holland, G.F.; Hoskins, R.L.; Keller, S.W.; Millikan, C.F.; zur Loye, H.C.

    1987-01-01

    For the past 15 years, advances in superconductivity have come about only slowly and even a 0.5 K increase in transition temperature was noteworthy. Until April 1986, the highest transition temperatures were near 23 K. At that time, Bednorz and Mueller reported superconductivity in La-Ba-Cu-O compounds above 30 K. The authors report here the composition and properties of a superconducting phase containing Y, Ba, Cu, and O which is copper-rich compared with Y/sub 1.2/Ba/sub 0.8/CuO/sub 4/. This phase show 10-20% Meissner effect, with T/sub 0/ = 90 K. Further the most exciting aspect of this phase is that it is near a low melting (below 1200 /sup 0/C) eutectic; if the phase metals congruently it will be possible to fashion wires.

  5. Effects of the Formation of Al x Cu y Gradient Interfaces on Mechanical Property of Steel/Al Laminated Sheets by Introducing Cu Binding-Sheets

    NASA Astrophysics Data System (ADS)

    Wei, Aili; Liu, Xinghai; Shi, Quanxin; Liang, Wei

    2015-07-01

    Steel/Cu/Al laminated sheets were fabricated by two-pass hot rolling to improve the mechanical properties of steel/Al sheets. The bonding properties and deformability of the steel/Cu/Al sheets were studied. Steel/Al and steel/Cu/Al samples were rolled at 350°C for 15 min with the first-pass reduction of 40%, and then heated at 600°C for 5 min with different reductions. It was found that the steel/Cu/Al samples rolled by the second-pass reduction of 85% could endure the maximum 90° bend cycle times of 45, exhibiting excellent fatigue resistance as well as deformability. The steel/Al samples could only reach the maximum 90° bend cycle times of 20. Furthermore, the scanning electron microscope, energy-dispersive spectrometer, and electron backscattered diffraction results showed that the preferred growth orientations of Cu, Al4Cu9, and Al2Cu on the steel/Cu/Al laminated sheets are {-1, 1, 2} <1, -1, 1>, {1, 0, 0} <0, 1, 0> and {-1, 1, 2} <1, -1, 1> {1, 1, 0} <0, 0, 1>. The orientation relationships between Cu and Al2Cu are {1, 1, 0}(fcc)//{1, 1, 0}(bct) and {1, 1, 1}(fcc)//{1, 1, 1}(bct). The improved bonding property and excellent fatigue resistance as well as deformability were mainly ascribed to the tight combination and consistent deformability across steel, Al, and the transition layers (Cu, Al4Cu9, and Al2Cu).

  6. The Occurrence of Superconductivity in the TlBa2CuO5-δ-Type (1021) System

    NASA Astrophysics Data System (ADS)

    Ku, H. C.; Tai, M. F.; Shi, J. B.; Shieh, M. J.; Hsu, S. W.; Hwang, G. H.; Ling, D. C.; Watson-Yang, T. J.; Lin, T. Y.

    1989-06-01

    Stable and reproducible superconductivity in the Tl(Ba2-xLax)CuO5-δ (0.0≤x≤0.6) system with the tetragonal TlBa2CuO5-δ-type (1021) structure was reported. A Prototype compound TlBa2CuO5-δ had shown a metastable superconducting onset around 25 K, with zero resistivity at 10 K. With partial substitution of La for Ba ions, Tc (50% resistivity drop) increases to 45 K, Tc0 (zero resistivity) to 42 K and onset around 50 K. A diamagnetic signal was observed with onset as high as 57 K. Tetragonal lattice parameters decrease with the increasing La concentration due to the partial replacement of larger Ba2+ ions by smaller La3+ ions. The Pairing field energy of 170 K and electron-elementary excitation coupling constant λ of 0.76 were derived from the BCS-like Tc formula through comparison with other single Tl-O layer systems TlCan-1Ba2CunO2n+3-δ.

  7. Intermetallic Formation at Interface of Al/Cu Clad Fabricated by Hydrostatic Extrusion and Its Properties.

    PubMed

    Lee, Jongbeom; Jeong, Haguk

    2015-11-01

    Al/Cu clad composed of Al core and Cu sheath has been produced by hydrostatic extrusion at 523 K, at an extrusion rate of 27. The prepared specimen was post-annealed at temperatures of 673 K and 773 K for various time durations, and the effect of annealing conditions have been analyzed. The hardness at the interface between Al and Cu matrix of the Al/Cu bimetal clad increases because of annealing. Results indicate that the hardness is more sensitive to annealing temperature than the annealing time. Three kinds of intermetallic compounds (IMC), namely, CuAl, Cu3Al2, and CuAl2, are formed at the Al-Cu interface, upon annealing at 673 K. On the other hand, four kinds of IMCs, namely, Cu4Al3, CuAl, Cu3Al2, CuAl2, are formed at the annealing temperature of 773 K. The growth of each IMC follows the parabolic law as a function of annealing times at certain annealing temperature. The growth rate of each IMC is limited to its interdiffusion rate constant. The IMC Cu4Al3 appears upon annealing at 773 K, and not during annealing at 673 K, because of the higher value of activation energy associated with its formation, when compared to other IMCs. PMID:26726557

  8. Frustration of Negative Capacitance in Al2O3/BaTiO3 Bilayer Structure

    PubMed Central

    Kim, Yu Jin; Park, Min Hyuk; Lee, Young Hwan; Kim, Han Joon; Jeon, Woojin; Moon, Taehwan; Do Kim, Keum; Jeong, Doo Seok; Yamada, Hiroyuki; Hwang, Cheol Seong

    2016-01-01

    Enhancement of capacitance by negative capacitance (NC) effect in a dielectric/ferroelectric (DE/FE) stacked film is gaining a greater interest. While the previous theory on NC effect was based on the Landau-Ginzburg-Devonshire theory, this work adopted a modified formalism to incorporate the depolarization effect to describe the energy of the general DE/FE system. The model predicted that the SrTiO3/BaTiO3 system will show a capacitance boost effect. It was also predicted that the 5 nm-thick Al2O3/150 nm-thick BaTiO3 system shows the capacitance boost effect with no FE-like hysteresis behavior, which was inconsistent with the experimental results; the amorphous-Al2O3/epitaxial-BaTiO3 system showed a typical FE-like hysteresis loop in the polarization – voltage test. This was due to the involvement of the trapped charges at the DE/FE interface, originating from the very high field across the thin Al2O3 layer when the BaTiO3 layer played a role as the NC layer. Therefore, the NC effect in the Al2O3/BaTiO3 system was frustrated by the involvement of reversible interface charge; the highly stored charge by the NC effect of the BaTiO3 during the charging period could not be retrieved during the discharging process because integral part of the polarization charge was retained within the system as a remanent polarization. PMID:26742878

  9. Fishtail magnetization in single crystal Tl{sub 2}Ba{sub 2}CuO{sub 6}

    SciTech Connect

    Zuo, F.

    1995-12-01

    We report magnetization measurements on single crystals of Tl{sub 2}Ba{sub 2}CuO{sub 6} superconductors. The fishtail magnetization is found to disappear above a characteristic temperature ({approximately}60 K), which corresponds to a crossover temperature in the temperature dependence of the irreversibility line. Since the low temperature irreversibility field can be modeled by a Josephson coupled layered system, we propose that the fishtail magnetization in the Tl{sub 2}Ba{sub 2}CuO{sub 6} system is due to dimensional crossover.

  10. Effect of silver addition on mechanical properties of melt-processed Sm-Ba-Cu-O bulk superconductor

    SciTech Connect

    Sakai, Naomichi; Miyamoto, Takeshi; Seo, Seokjong; Nariki, Shinya; Murakami, Masato

    1999-11-01

    The authors have studied mechanical properties of melt-processed single-grain Sm-Ba-Cu-O (Sm123+Sm211) bulks with and without silver doping. Tensile stress is induced by thermal stress during heat treatment, and also induced by applying magnetic fields. It is found that the silver addition was effective in decreasing the thermal stress and increasing the tensile strength of the Sm-Ba-Cu-O bulk. The tensile strength of the silver doped sample was 37.4MPa, which is about one and half times larger than that of the undoped sample.

  11. Giant thermal vibrations in the framework compounds Ba1 -xSrxAl2O4

    NASA Astrophysics Data System (ADS)

    Kawaguchi, S.; Ishii, Y.; Tanaka, E.; Tsukasaki, H.; Kubota, Y.; Mori, S.

    2016-08-01

    Synchrotron x-ray diffraction experiments were performed on the network compounds Ba1 -xSrxAl2O4 at temperatures between 15 and 800 K. The ferroelectric phase of the parent BaAl2O4 is largely suppressed by substituting a small amount of Sr for Ba and disappears for x ≥0.1 . Structural refinements reveal that the isotropic atomic displacement parameter Biso in the bridging oxygen atom is largely independent of temperature and retains an anomalously large value in the adjacent paraelectric phase even at the lowest temperature. The Biso systematically increases as x increases, exhibiting an especially large value for x =0.5 . According to previous electron diffraction experiments for Ba1 -xSrxAl2O4 with x ≥0.1 , strong thermal diffuse scattering occurs at two reciprocal points relating to two distinct soft modes at the M and K points over a wide range of temperatures below 800 K [Y. Ishii et al., Sci. Rep. 6, 19154 (2016), 10.1038/srep19154]. Although the latter mode disappears at approximately 200 K, the former does not condense, at least down to 100 K. The anomalously large Biso observed in this study is ascribed to these soft modes existing in a wide temperature range.

  12. Synthesis of Al2O3 nanoparticles highly distributed in YBa2Cu3O7 superconductor by citrate-nitrate auto-combustion reaction

    NASA Astrophysics Data System (ADS)

    Suan, Mohd Shahadan Mohd; Johan, Mohd Rafie

    2013-09-01

    The effects of Al2O3 nanoparticles on the structure and superconducting properties of YBa2Cu3O7-δ matrix prepared by auto-combustion reaction were investigated. The auto-combustion reaction has successfully transformed the Al nitrate added YBCO precursor gels to very fine ashes which yielded to Al2O3 and YBCO phases after the calcination process at 900 °C. The resultant reactions produced nanocrystalline YBa2Cu3O7-δ powders having well distributed Al2O3 nanoparticles (∼10 nm). The TG/DTA analysis reveals that the Al nitrate added precursor gels decomposed by two-steps reaction at temperature of 180 and 220 °C due to the decomposition of Al nitrate followed by Y, Ba and Cu nitrates. The XRD pattern showed the orthorhombic structure of Al2O3 added YBa2Cu3O7-δ powders having the particle size ranged in between 20 and 25 nm. SEM analysis showed that Al2O3 nanoparticles were distributed along the grain boundaries of YBa2Cu3O7-δ matrix for the higher mol of Al nitrate. The higher concentration of Al2O3 reacts with the YBa2Cu3O7 matrix to form Al3+ rich spots and diffuse within the YBa2Cu3O7-δ superconducting matrix which was confirmed by EDX analysis. The samples produced in this work were electrically superconducting at temperature above 85 K as measured by using standard four-probe technique. Formation of alumina precipitates and incorporation of Al3+ into YBa2Cu3O7-δ structure was found to significantly reduce the Tc of pure YBa2Cu3O7-δ.

  13. Flux Pinning by Cr Nanoparticles in Cu_{0.5}Tl_{0.5}Ba2Ca2Cu3O_{10-δ } Superconductor

    NASA Astrophysics Data System (ADS)

    Waqee-ur-Rehman, M.; Mumtaz, M.; Qasim, Irfan; Nadeem, K.

    2016-09-01

    Increase in flux pinning strength of Cu_{0.5}Tl_{0.5}Ba2Ca2Cu3O_{10-δ }(CuTl-1223) superconductor has been observed after addition of Cr nanoparticles. We have thoroughly investigated the infield response of Cr nanoparticles-added CuTl-1223 superconductor in an external applied magnetic field in the range of 0-7 T. Solid-state reaction technique has been employed to synthesize (Cr)x-CuTl-1223; x = 0-1.00 wt% nanoparticle-superconductor composites. The flux pinning mechanism has been analyzed on the basis of thermally activated flux flow model in the presence of a small current (10 μ A). The increase in activation energy and decrease in transition width of CuTl-1223 superconducting phase show the enhancement in its flux pinning strength upon the addition of Cr nanoparticles.

  14. Hydrogen isotope trapping in Al-Cu binary alloys

    SciTech Connect

    Chao, Paul; Karnesky, Richard A.

    2016-01-01

    In this study, the trapping mechanisms for hydrogen isotopes in Al–X Cu (0.0 at. % < X < 3.5 at. %) alloys were investigated using thermal desorption spectroscopy (TDS), electrical conductivity, and differential scanning calorimetry. Constant heating rate TDS was used to determine microstructural trap energies and occupancies. In addition to the trapping states in pure Al reported in the literature (interstitial lattice sites, dislocations, and vacancies), a trap site due to Al–Cu intermetallic precipitates is observed. The binding energy of this precipitate trap is (18 ± 3) kJ•mol–1 (0.19 ± 0.03 eV). Typical occupancy of this trap is high; for Al–2.6 at. % Cu (a Cu composition comparable to that in AA2219) charged at 200 °C with 130 MPa D2 for 68 days, there is ca. there is 3.15×10–7 mol D bound to the precipitate trap per mol of Al, accounting for a third of the D in the charged sample.

  15. Hydrogen isotope trapping in Al-Cu binary alloys

    DOE PAGES

    Chao, Paul; Karnesky, Richard A.

    2016-01-01

    In this study, the trapping mechanisms for hydrogen isotopes in Al–X Cu (0.0 at. % < X < 3.5 at. %) alloys were investigated using thermal desorption spectroscopy (TDS), electrical conductivity, and differential scanning calorimetry. Constant heating rate TDS was used to determine microstructural trap energies and occupancies. In addition to the trapping states in pure Al reported in the literature (interstitial lattice sites, dislocations, and vacancies), a trap site due to Al–Cu intermetallic precipitates is observed. The binding energy of this precipitate trap is (18 ± 3) kJ•mol–1 (0.19 ± 0.03 eV). Typical occupancy of this trap is high;more » for Al–2.6 at. % Cu (a Cu composition comparable to that in AA2219) charged at 200 °C with 130 MPa D2 for 68 days, there is ca. there is 3.15×10–7 mol D bound to the precipitate trap per mol of Al, accounting for a third of the D in the charged sample.« less

  16. Viscous and acoustic properties of AlCu melts

    NASA Astrophysics Data System (ADS)

    Khusnutdinoff, R. M.; Mokshin, A. V.; Menshikova, S. G.; Beltyukov, A. L.; Ladyanov, V. I.

    2016-05-01

    The atomic dynamics of the binary Al100- x Cu x system is simulated at a temperature T = 973 K, a pressure p = 1.0 bar, and various copper concentrations x. These conditions (temperature, pressure) make it possible to cover the equilibrium liquid Al100- x Cu x phase at copper concentrations 0 ≤ x ≤ 40% and the supercooled melt in the concentration range 40% ≤ x ≤ 100%. The calculated spectral densities of the time correlation functions of the longitudinal {tilde C_L}( k, ω) and transverse {tilde C_T}( k, ω) currents in the Al100- x Cu x melt at a temperature T = 973 K reveal propagating collective excitations of longitudinal and transverse polarizations in a wide wavenumber range. It is shown that the maximum sound velocity in the v L ( x) concentration dependence takes place for the equilibrium melt at an atomic copper concentration x = 10 ± 5%, whereas the supercooled Al100- x Cu x melt saturated with copper atoms ( x ≥ 40%) is characterized by the minimum sound velocity. In the case of the supercooled melt, the concentration dependence of the kinematic viscosity ν( x) is found to be interpolated by a linear dependence, and a deviation from the linear dependence is observed in the case of equilibrium melt at x < 40%. An insignificant shoulder in the ν( x) dependence is observed at low copper concentrations ( x < 20%), and it is supported by the experimental data. This shoulder is caused by the specific features in the concentration dependence of the density ρ( x).

  17. Indium Helps Strengthen Al/Cu/Li Alloy

    NASA Technical Reports Server (NTRS)

    Blackburn, Linda B.; Starke, Edgar A., Jr.

    1992-01-01

    Experiments on Al/Cu/Li alloys focus specifically on strengthening effects of minor additions of In and Cd. Indium-bearing alloy combines low density with ability to achieve high strength through heat treatment alone. Tensile tests on peak-aged specimens indicated that alloy achieved yield strength approximately 15 percent higher than baseline alloy. Alloy highly suitable for processing to produce parts of nearly net shape, with particular applications in aircraft and aerospace vehicles.

  18. Effectiveness of BaTiO3 dielectric patches on YBa2Cu3O7 thin films for MEM switches

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    A micro-electro-mechanical (MEM) switch built on a superconducting microstrip filter will be utilized to investigate BaTiO3 dielectric patches for functional switching points of contact. Actuation voltage resulting from the MEM switch provokes static friction between the bridge membrane and BaTiO3 insulation layer. The dielectric patch crystal structure and roughness affect the ability of repetitively switching cycles and lifetime. A series of experiments have been performed using different deposition methods and RF magnetron sputtering was found to be the best deposition process for the BaTiO3 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 YBa2Cu3O7 deposited on LaAlO3 substrate by pulsed laser deposition. For this work, the dielectric material sputtering pressure is set at 9.5×10-6 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 BaTiO3 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. Ideal structure of icosahedral Al-Cu-Li quasicrystals

    NASA Astrophysics Data System (ADS)

    Yamamoto, Akiji

    1992-03-01

    A structure model for the icosahedral Al-Cu-Li quasicrystal has been derived. This is described in six-dimensional space as a six-dimensional crystal, having four kinds of occupation domains with complicated polyhedral shape. A general structure-factor formula is derived for such polyhedral domains, and a simple description of the structure using the site symmetry is proposed. The model gives R factors of 0.076 and 0.085 for recent x-ray and neutron-single-crystal-diffraction data [Boissieu, Janot, Dubois, Audier, and Dubost, J. Phys. 3, 1 (1991)]. The structure consists of a large number of icosahedral clusters and linking atoms joining them. It leads to an ideal cubic R-Al-Cu-Li structure and a large number of other cubic crystals when appropriate phason strains are taken into account. Two structures, the ideal R-Al-Cu-Li structure and a fictitious structure with a period (1+ √5 )/2 times longer, are shown.

  20. Synthesis, crystal and electronic structures of the new Zintl phases Ba3Al3Pn5 (Pn = P, As) and Ba3Ga3P5.

    PubMed

    He, Hua; Tyson, Chauntae; Saito, Maia; Bobev, Svilen

    2013-01-01

    The new Zintl compounds Ba(3)Al(3)P(5), Ba(3)Al(3)As(5,) and Ba(3)Ga(3)P(5) have been synthesized using molten metal fluxes. They are isoelectronic and isotypic, crystallizing with a novel rhombohedral structure type in the space group R3c with unit cell constants a = 14.5886(9) Å, c = 28.990(3) Å for Ba(3)Al(3)P(5), a = 14.613(3) Å, c = 28.884(8) Å for Ba(3)Ga(3)P(5), and a = 14.9727(13) Å, c = 29.689(4) Å for Ba(3)Al(3)As(5), respectively. The structures are based on TrPn(4) (Tr = Al, Ga; Pn = P, As) tetrahedra that share both edges and corners, leading to intricate arrangements embodied in the [Tr(4)Pn(9)](15-) and [Tr(3)Pn(6)](9-) strands, interconnected by dimeric [Tr(2)Pn(6)](12-) units. The Ba(2+) cations reside within cylindrical channels within the polyanionic framework and provide the valence electrons needed for Tr-Pn covalent bonding. In spite of the large and complex structure, there are no homoatomic Tr-Tr or Pn-Pn interactions, hence, the structures can be readily rationalized in the context of the Zintl-Klemm formalism as follows [Ba(2+)](3)[Tr(3+)](3)[Pn(3-)](5); calculations on their electronic band-structures confirm this reasoning and reveal about 1.4-1.9 eV energy band gaps, that is, semiconducting behavior. Structural parallels with other known Zintl compounds are also presented.

  1. Crystallographic Study of Mixture CeBa1.8Pb0.2Cu3Oy in the Range of 860 deg. C to 940 deg. C

    SciTech Connect

    Stergiou, A.; Yilmaz, S.; Stergiou, C.

    2007-04-23

    A powder mixture with chemical formula CeBa1.8Pb0.2Cu3Oy was prepared. The mixture was heated in free atmosphere, at temperatures 860 deg. C to 940 deg. C, for 24 to 72h. The samples were measured by X-Ray powder diffraction with CuKa radiation. Each sample was characterized with the help of the PDF and refined, using the Rietveld's ''Powder Profile Analysis''. The first sample (860 deg. C) was identified with the phases: Ba2CeBiO6, CuO and BaCuO2, while all the remaining samples (870 deg. C-940 deg. C) with the phases Ba2CePbO6, CuO and CeO2. The phases Ba2CeBiO6 and Ba2CePbO6 are the main phases with analogous chemical types, but different symmetry. The phase CuO is common in all the samples, while from the remaining phases the BaCuO2 appears only in the first sample and the CeO2 in all, except the first one. The quantity 0.2 of Pb is distributed in the Ba positions, substituting a part of these. The percentages of phases are about 82%, 10% and 8% for the first sample and for all the remaining about 85%, 8% and 7%, respectively with above serious.

  2. Improving the superconducting properties of single grain Sm-Ba-Cu-O bulk superconductors fabricated in air by increased control of Sm/Ba substitution effects

    NASA Astrophysics Data System (ADS)

    Shi, Y.; Desmedt, M.; Durrell, J.; Dennis, A. R.; Cardwell, D. A.

    2013-09-01

    The extreme sensitivity of Sm/Ba at high temperature in air becomes an obstacle to the fabrication of SmBCO single grains that exhibit stable and reliable superconducting properties. In this research, the superconducting properties of SmBCO single grains fabricated by top seeded melt growth (TSMG) from different batches of commercial SmBa2Cu3O7-d (Sm-123) precursor powder using different processing atmospheres (air and 0.1% O2 in Ar), different processing methods (isothermal growth and continuous cooling) and different amounts of BaO2 content to suppress Sm/Ba substitution in air have been investigated in an attempt to understand fully the TSMG process for this system. As a result, based on extensive data, a novel and simple, low temperature post-annealing approach is proposed specifically to overcome the sensitivity of Tc to Sm/Ba substitution in order to simplify the fabrication of SmBCO and to increase its reliability with a view to the practical processing of these materials. Initial processing trials have been performed successfully to demonstrate the viability of the novel post-annealing process.

  3. Band structure calculations of CuAlO2, CuGaO2, CuInO2, and CuCrO2 by screened exchange

    NASA Astrophysics Data System (ADS)

    Gillen, Roland; Robertson, John

    2011-07-01

    We report density functional theory band structure calculations on the transparent conducting oxides CuAlO2, CuGaO2, CuInO2, and CuCrO2. The use of the hybrid functional screened-exchange local density approximation (sX-LDA) leads to considerably improved electronic properties compared to standard LDA and generalized gradient approximation (GGA) approaches. We show that the resulting electronic band gaps compare well with experimental values and previous quasiparticle calculations, and show the correct trends with respect to the atomic number of the cation (Al, Ga, In). The resulting energetic depths of Cu d and O p levels and the valence-band widths are considerable improvements compared to LDA and GGA and are in good agreement with available x-ray photoelectron spectroscopy data. Lastly, we show the calculated imaginary part of the dielectric function for all four systems.

  4. Optimization of YbBa2Cu3Oy Thick Film Formation on MgO Substrates

    NASA Astrophysics Data System (ADS)

    Kawata, S.; Muralidhar, M.; Jirsa, M.; Inoue, K.; Murakami, M.

    We optimized the formation process of the YbBa2Cu3Oy superconducting thick film prepared from the mixture of Yb2BaO4, BaCuO2, and CuO. Thick films of this composite were sintered at various temperatures between 800 ̊C and 1025 ̊C and held for 10 minutes in air, then rapidly quenched in liquid nitrogen. The samples were characterized by XRD, SEM, and magnetization measurements. The XRD analysis indicated that the Yb-123 phase started to form above 800 ̊C, with optimum at 825 ̊C. At even higher temperatures (900 ̊C and 975 ̊C) the secondary phase and liquid phase predominantly formed. Based on these results, we fabricated good quality YbBa2Cu3Oy thick films on an MgO substrate utilizing a double step heating process. According to XRD measurements the Yb-123 films were c-axis oriented, with Tc (onset) 87 K, and high critical current density around 24 kA/cm2 at 77 K, H//c-axis. The Yb-123 superconducting thick films on the MgO substrates are considered as the first step to the production of silver sheathed tapes, an advanced analogue to the Bi-2223 system.

  5. Dielectric properties of Gd3Ba2Mn2Cu2O12 manganocuprate

    NASA Astrophysics Data System (ADS)

    Rayaprol, S.; Kaushik, S. D.; Kumar, N.; Gaur, N. K.; Saha, J.; Patnaik, S.

    2011-04-01

    The magnetocapacitance and magnetoresistance of Gd3Ba2Mn2Cu2O12 (Gd-3222) has been measured in the temperature range of 2-300 K. The capacitance increases with increasing temperature from 2-300 K, and exhibits a steplike feature at ˜95 K (for 1 kHz). On increasing the probe frequency this step gets broaden and shifts to higher temperature ˜150 K (for 75 kHz). The observation of frequency dependence in capacitance and dielectric loss (tan δ) exhibits Maxwell-Wagner type relaxor behavior in this compound. Magnetocapacitance was observed on the application of magnetic field. No observable magnetoresistance could be observed in this compound, indicating that the magnetoelectric coupling observed from the dielectric constant measurement with and without magnetic field, is of capacitive origin. The results of magnetocapacitance and magnetoresistance of the Gd-3222 compound are presented in the light of current interest in exploring manganite systems for multiferroic properties.

  6. Behavior of Double Junction SQUID of Y-Ba-Cu-O Bulk Superconductor

    NASA Astrophysics Data System (ADS)

    Kataria, N. D.; Tomar, V. S.; Ojha, V. N.; Kumar, Mukesh; Reddy, G. S. N.; Gupta, A. K.

    A dc SQUID like geometry with a ring and a pair of constrictions is carved out of bulk Y-Ba-Cu-O superconductor. The I—V curves exhibit hysteresis arising due to trapping of the self fields. The V—Φ curves show multiple flux periodicities with unequal amplitudes. There is twenty fold rise in the amplitude of voltage modulation in cooling from 77 to 4.2 K. The complications of presence of series and parallel arrays of granular junctions are attributed respectively to large and small periodicities observed in V—Φ curves. The modulation structure gets more resolved at 4.2 K due to reduction in thermal noise effects.

  7. Exploring the spin-orbital ground state of Ba3CuSb2O9

    NASA Astrophysics Data System (ADS)

    Smerald, Andrew; Mila, Frédéric

    2014-09-01

    Motivated by the absence of both spin freezing and a cooperative Jahn-Teller effect at the lowest measured temperatures, we study the ground state of Ba3CuSb2O9. We solve a general spin-orbital model on both the honeycomb and the decorated honeycomb lattice, revealing rich phase diagrams. The spin-orbital model on the honeycomb lattice contains an SU(4) point, where previous studies have shown the existence of a spin-orbital liquid with algebraically decaying correlations. For realistic parameters on the decorated honeycomb lattice, we find a phase that consists of clusters of nearest-neighbor spin singlets, which can be understood in terms of dimer coverings of an emergent square lattice. While the experimental situation is complicated by structural disorder, we show qualitative agreement between our theory and a range of experiments.

  8. Ablation studies of Y-Ba-Cu-oxide in oxygen using a pulsed CO 2 laser

    NASA Astrophysics Data System (ADS)

    Dyer, P. E.; Key, P. H.; Monk, P.

    1992-01-01

    The depth of ablation of Y-Ba-Cu-oxide pellets as a function of pulsed CO 2 laser fluence has been measured. Up to fluences of ˜ 5 J cm -2 the data can be well fitted to a Beer's law dependence with absorption coefficient ∝ = 10 4 cm -1 and threshold fluence for ablation of 0.85 J cm -2. At higher fluences a self-regulating ablation rate regime, due to plasma formation, is encountered. Particulate deposits from 10.6 μm laser ablation are found to be much greater than with shorter wavelenghts and evidence of large particle formation by accretion of smaller ablation products is observed. The range of the ablation plume in low pressure oxygen has been studied as a function of laser fluence, irradiation spot size and ambient gas pressure and is compared with modelling.

  9. Performance of TlCaBaCuO 30 GHz 64 element antenna array

    NASA Technical Reports Server (NTRS)

    Lewis, L. L.; Koepf, G.; Bhasin, K. B.; Richard, M. A.

    1993-01-01

    A 64-element, 30-GHz microstrip antenna array with corporate feed network was designed and built on a 0.254-mm (10-mil) thick lanthanum aluminate substrate. One antenna pattern was fabricated from gold film, and a second pattern used TlCaBaCuO high-temperature superconductor. Both antennas used gold ground planes deposited on the reverse side of the substrate. Gain and radiation patterns were measured for both antennas at room temperature and at cryogenic temperatures. Observations agree well with simple models for loss and microwave beam width, with a gain on boresight of 20.3 dB and beam width of 15 deg for the superconducting antenna. The antenna loss is only 1.9 dB.

  10. Vortex fluctuation in HgBa 2Ca 3Cu 4O 10+δ

    NASA Astrophysics Data System (ADS)

    Kim, Mun-Seog; Kim, Wan-Seon; Lee, Sung-Ik; Yu, Seong-Cho; Itskevich, E. S.; Kuzemskaya, I.

    1997-08-01

    Reversible magnetization with the external magnetic fields of 1 T ≤ H ≤ 5 T parallel to the c-axis has been measured for the grain aligned HgBa2Ca3Cu4O10+δ. A strong vortex fluctuation effect was clearly observed and the magnetization is well described by the vortex fluctuation model. From this analysis, the penetration depth λab(0) = 1583 Å and the effective interlayer spacing s = 44.6 Å were estimated. However, the value of s is significantly larger than the lattice parameter c = 19 Å, which is different from the prediction of the vortex fluctuation model. From the model on superconducting fluctuations proposed by Koshelev, in which not only the critical fluctuations at the lowest Landau level but also the Gaussian fluctuations at higher Landau levels were considered, the different value of s = 15.4 Å was obtained.

  11. Improvement of persistent magnetic field trapping in bulk Y-Ba-Cu-O superconductors

    NASA Technical Reports Server (NTRS)

    Chen, In-Gann; Weinstein, Roy

    1993-01-01

    For type-II superconductors, magnetic field can be trapped due to persistent internal supercurrent. Quasi-persistent magnetic fields near 2 T at 60 K (and 1.4 T at 77 K) have been measured in minimagnets made of proton-irradiated melt-textured Y-Ba-Cu-O (MT-Y123) samples. Using the trapping effect, high-field permanent magnets with dipole, quadrupole, or more complicated configurations can be made of existing MT-Y123 material, thus bypassing the need for high-temperature superconductor (HTS) wires. A phenomenological current model has been developed to account for the trapped field intensity and profile in HTS samples. This model is also a guide to select directions of materials development to further improve field trapping properties. General properties such as magnetic field intensities, spatial distributions, stabilities, and temperature dependence of trapped field are discussed.

  12. Mixed Cu-simple metal dimers and trimers - CuLi, CuLi2, CuNa, CuK, CuBe, CuBe2, Cu2Be, CuAl, and CuAl2

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Partridge, Harry; Walch, Stephen P.

    1987-01-01

    Theoretical studies of selected diatomic and triatomic molecules containing copper and the simple metals Li, Na, K, Be, and Al are presented, with emphasis on elucidating the nature of the bonding in mixed transition metal-simple metal systems. Large Gaussian basis sets are used in the diatomic calculations, and are used to calibrate the triatomic calculations, in which somewhat smaller Gaussian basis sets are employed. Electron correlation is incorporated using both the single-reference singles plus doubles configuration interaction and coupled pair functional methods. It is found that alkali atoms form very polar sigma bonds with copper, and that the ionicity increases with the inclusion of higher excitations because they improve the electron affinity of copper, which in turn allows a larger negative charge on copper. Aluminum is found to form stronger bonds than beryllium, since it does not have to undergo sp hybridization. Some of the trimers bond by forming three-center three-electron bonds. These multicenter bonds are quite strong even when compared to the two-electron bonds in the dimers or to other bonding mechanisms in the trimers.

  13. Lateral electric-field control of giant magnetoresistance in Co/Cu/Fe/BaTiO{sub 3} multiferroic heterostructure

    SciTech Connect

    Savitha Pillai, S.; Kojima, H.; Itoh, M.; Taniyama, T.

    2015-08-17

    We report lateral electric-field-driven sizable changes in the magnetoresistance of Co/Cu/Fe tri-layered wires on BaTiO{sub 3} single crystal. While the observed change is marginal in the tetragonal phase of BaTiO{sub 3}, it reaches over 40% in the orthorhombic and rhombohedral phases with an electric field of 66 kV/cm. We attribute it to possible electric-field-induced variations of the spin-dependent electronic structures, i.e., spin polarization, of the Fe via interfacial strain transfer from BaTiO{sub 3}. The contrasting results for the different phases of BaTiO{sub 3} are discussed, associated with the distinct aspects of the ferroelectric polarization switching processes in each phase.

  14. The photosensitivity of carbon quantum dots/CuAlO2 films composites

    NASA Astrophysics Data System (ADS)

    Pan, Jiaqi; Sheng, Yingzhuo; Zhang, Jingxiang; Wei, Jumeng; Huang, Peng; Zhang, Xin; Feng, Boxue

    2015-07-01

    Carbon quantum dots/CuAlO2 films were prepared by a simple route through which CuAlO2 films prepared by sol-gel on crystal quartz substrates were composited with carbon quantum dots on their surface. The characterization results indicated that CuAlO2 films were well combined with carbon quantum dots. The photoconductivity of carbon quantum dots/CuAlO2 films was investigated under illumination and darkness switching, and was demonstrated to be significantly enhanced compared with CuAlO2 films. Through analysis, this enhancement of photoconductivity was attributed to the carbon quantum dots with unique up-converted photoluminescence behavior.

  15. The effect of Ti-B on stabilization of Cu-Zn-Al martensite

    SciTech Connect

    Stipcich, M.; Romero, R. |

    1998-10-05

    The application of shape memory effect in devices requires, in many cases, stable and reliable transformation temperatures. However, as a consequence of diffusional processes, in Cu-based shape memory alloys, reverse transformation temperature significantly rises after aging at temperatures above room temperature. This generally unwanted behavior is usually referred to as the stabilization of martensite. Numerous investigations have been carried out on this subject as reviewed by Ahlers and Chandrasekaran et al. Within the Cu-based alloys the Cu-Zn-Al are claimed to be more prone to stabilization than Cu-Al-Ni on aging. It has been proposed that in the Cu-Zn-Al the stabilization is due to the interchange of Cu and Zn atoms assisted by vacancies, changing, consequently, the long range order inherited from the {beta} phase. In the present work, the authors investigate the stabilization behavior of polycrystalline samples of stress induced Cu-Zn-Al and Cu-Zn-Al-B martensite.

  16. Cu-Al spinel oxide as an efficient catalyst for methanol steam reforming.

    PubMed

    Xi, Hongjuan; Hou, Xiaoning; Liu, Yajie; Qing, Shaojun; Gao, Zhixian

    2014-10-27

    Cu-Al spinel oxide, which contains a small portion of the CuO phase, has been successfully used in methanol steam reforming (MSR) without prereduction. The omission of prereduction not only avoids the copper sintering prior to the catalytic reaction, but also slows down the copper-sintering rate in MSR. During this process, the CuO phase can initiate MSR at a lower temperature, and CuAl2O4 releases active copper gradually. The catalyst CA2.5-900, calcined at 900 °C with n(Al)/n(Cu) = 2.5, has a higher CuAl2O4 content, higher BET surface area, and smaller CuAl2O4 crystal size. Its activity first increases and then decreases during MSR. Furthermore, both fresh and regenerated CA2.5-900 showed better catalytic performance than the commercial Cu-Zn-Al catalyst. PMID:25213737

  17. Al-matrix composite materials reinforced by Al-Cu-Fe particles

    NASA Astrophysics Data System (ADS)

    Bonneville, J.; Laplanche, G.; Joulain, A.; Gauthier-Brunet, V.; Dubois, S.

    2010-07-01

    Al-matrix material composites were produced using hot isostatic pressing technique, starting with pure Al and icosahedral (i) Al-Cu-Fe powders. Depending on the processing temperature, the final reinforcement particles are either still of the initial i-phase or transformed into the tetragonal ω-Al00.70Cu0.20Fe0.10 crystalline phase. Compression tests performed in the temperature range 293K - 823K on the two types of composite, i.e. Al/i and Al/ω, indicate that the flow stress of both composites is strongly temperature dependent and exhibit distinct regimes with increasing temperature. Differences exist between the two composites, in particul ar in yield stress values. In the low temperatureregime (T <= 570K), the yield stress of the Al/ω composite is nearly 75% higher than that of the Al/i composite, while for T > 570K both composites exhibit similar yield stress values. The results are interpreted in terms of load transfer contribution between the matrix and the reinforcement particles and elementary dislocation mechanisms in the Al matrix.

  18. Local Jahn-Teller distortions and orbital ordering in Ba3Cu1 +xSb2 -xO9 investigated by neutron scattering

    NASA Astrophysics Data System (ADS)

    Li, Bing; Louca, Despina; Feygenson, Mikhail; Brown, Craig M.; Copley, John R. D.; Iida, Kazuki

    2016-01-01

    A spin-orbital quantum liquid state is theoretically proposed in the honeycomb lattice of Ba3CuSb2O9 , enabled by dynamic short-range correlations between the spin and orbital degrees of freedom. Using neutron diffraction, the local atomic structure of Ba3Cu1 +xSb2 -xO9 at x =0 and 0.1 is obtained via the pair density function analysis. The results indicate that both compositions exhibit local Jahn-Teller (JT) distortions with the elongated CuO3 octahedral configuration. In Ba3Cu1.1Sb1.9O9 , JT ordering of the distorted CuO3 octahedra gives rise to the orthorhombic symmetry with ferro-orbital order. On the other hand, in Ba3CuSb2O9 , even though the CuO3 octahedra are JT distorted, there is no long-range ordering hence the symmetry is hexagonal. Furthermore, the local singlet excitation at 5.8 meV observed in Ba3CuSb2O9 below 50 K is absent in Ba3Cu1.1Sb1.9O9 . Instead, an excitation at 2.5 meV is observed in the latter, which is likely associated with short-range spin order.

  19. Local Jahn-Teller distortions and orbital ordering in Ba3Cu1+xSb2-xO9 investigated by neutron scattering

    DOE PAGES

    Li, Bing; Feygenson, Mikhail; Brown, Craig M.; Copley, John R. D.; Iida, Kazuki

    2016-01-15

    In this study, a spin-orbital quantum liquid state is theoretically proposed in the honeycomb lattice of Ba3CuSb2O9, enabled by dynamic short-range correlations between the spin and orbital degrees of freedom. Using neutron diffraction, the local atomic structure of Ba3Cu1+xSb2-xO9 at x = 0 and 0.1 is obtained via the pair density function analysis. The results indicate that both compositions exhibit local Jahn-Teller (JT) distortions with the elongated CuO3 octahedral configuration. In Ba3Cu1.1Sb1.9O9, JT ordering of the distorted CuO3 octahedra gives rise to the orthorhombic symmetry with ferro-orbital order. On the other hand, in Ba3CuSb2O9, even though the CuO3 octahedra aremore » JT distorted, there is no long-range ordering hence the symmetry is hexagonal. Furthermore, the local singlet excitation at 5.8 meV observed in Ba3CuSb2O9 below 50 K is absent in Ba3Cu1.1Sb1.9O9. Instead, an excitation at 2.5 meV is observed in the latter, which is likely associated with short-range spin order.« less

  20. Perovskite solid solutions in the BaO-CuO-Y 2O 3-Nb 2O 5 system

    NASA Astrophysics Data System (ADS)

    Bremer, M.; Langbein, H.

    1999-07-01

    Freeze dried complex carboxylates are highly reactive precursors for complex perovskite solid solutions in the system BaO-CuO-Y 2O 3-Nb 2O 5 On thermal decomposition of the amorphous precursors the formation of complex crystalline phases begins at 600 °C. In most cases the themodynamically controlled phase composition is reached after a reaction time of two hours at about 900 °C. Beginning from the perovskite compound Ba 2YNbO 6 a partial substitution of Y by Cu or by a combination 2/3 Cu,1/3 Nb leads to extended fields of solid solutions with cubic perovskite structure. Substitution according to Y 0,5xBa 2(Y 1-0,5xCu xNb)O 6+x is limited to x ≤ 0,4. A compound LBa 2Cu 2NbO 8 (x=2), well characterized for L=La, does not exist for L=Y. The composition of solid solutions depends on the preparation conditions. There are some signs for an inhomogeneous distribution of B-cations in the cubic perovskites.

  1. Pb-DOPING Effects in Hg1-xPbxBa2Ca2Cu3O8+δ

    NASA Astrophysics Data System (ADS)

    Xue, Y. Y.; Huang, Z. J.; Qiu, X. D.; Beauvais, L.; Zhang, X. N.; Sun, Y. Y.; Meng, R.; Chu, C. W.

    Samples with a nominal composition of Hg1-xPbxBa2Ca2Cu3O8+δ (x~0.1, 0.2, and 0.3) have been synthesized and characterized. The Pb-doping promotes the formation of the three CuO2-layer compound Hg1-xPbxBa2Ca2Cu3O8+δ, and reduces the release of Hg vapor at the synthesis temperature. The intergrain electric coupling is also significantly enhanced by the doping, resulting in lower normal-state resistivity and higher intergrain critical current density. The carrier concentration of the as-synthesized samples increases with the increase of x, ranging from underdoped (x~0) to overdoped (x≥0.2).

  2. Synthesis, crystal structure and magnetic properties of superconducting single crystals of HgBa2CuO4+δ

    NASA Astrophysics Data System (ADS)

    Bertinotti, A.; Viallet, V.; Colson, D.; Marucco, J.-F.; Hammann, J.; Forget, A.; Le Bras, G.

    1996-02-01

    Single crystals of HgBa2CuO4+δ of submillimetric sizes were grown with the same one step, low pressure, gold amalgamation technique used to obtain single crystals of HgBa2Ca2Cu3O8+δ. Remarkable superconducting properties are displayed by the samples which are optimally doped as grown. The sharpness of the transition profiles of the magnetic susceptibility, its anisotropy dependence and the volume fraction exhibiting the Meissner effect exceed the values obtained with the best crystal samples of Hg-1223. X-rays show that no substitutional defects have been found in the mercury plane, in particular no mixed occupancy of copper at the mercury site. The interstitial oxygen content at (1/2, 1/2, 0) δ = 0.066+/-0.008 is about one third that observed in optimally doped Hg-1223, resulting in an identical doping level per CuO2 plane in both compounds.

  3. Enthalpies of mixing of liquid systems for lead free soldering: Al-Cu-Sn system.

    PubMed

    Flandorfer, Hans; Rechchach, Meryem; Elmahfoudi, A; Bencze, László; Popovič, Arkadij; Ipser, Herbert

    2011-11-01

    The present work refers to high-temperature drop calorimetric measurements on liquid Al-Cu, Al-Sn, and Al-Cu-Sn alloys. The binary systems have been investigated at 973 K, up to 40 at.% Cu in case of Al-Cu, and over the entire concentrational range in case of Al-Sn. Measurements in the ternary Al-Cu-Sn system were performed along the following cross-sections: x(Al)/x(Cu) = 1:1, x(Al)/x(Sn) = 1:1, x(Cu)/x(Sn) = 7:3, x(Cu)/x(Sn) = 1:1, and x(Cu)/x(Sn) = 3:7 at 1273 K. Experimental data were used to find ternary interaction parameters by applying the Redlich-Kister-Muggianu model for substitutional solutions, and a full set of parameters describing the concentration dependence of the enthalpy of mixing was derived. From these, the isoenthalpy curves were constructed for 1273 K. The ternary system shows an exothermic enthalpy minimum of approx. -18,000 J/mol in the Al-Cu binary and a maximum of approx. 4000 J/mol in the Al-Sn binary system. The Al-Cu-Sn system is characterized by considerable repulsive ternary interactions as shown by the positive ternary interaction parameters.

  4. Multi-frequency EPR evidence for a binuclear CuA center in cytochrome c oxidase: studies with a 63Cu- and 65Cu-enriched, soluble domain of the cytochrome ba3 subunit II from Thermus thermophilus.

    PubMed

    Fee, J A; Sanders, D; Slutter, C E; Doan, P E; Aasa, R; Karpefors, M; Vänngård, T

    1995-07-01

    We have recorded multi-frequency EPR spectra of 63Cu- and 65Cu-labeled, water-soluble CuA-protein from the cytochrome ba3 of T. thermophilus. The spectrum taken at the highest frequency (34.03 GHz) shows no hyperfine structure and is nominally axial with apparent gz approximately 2.18 and gxy approximately 2.00. The spectrum taken at the lowest frequency (3.93 GHz) shows a rich hyperfine structure. Analyses of the spectra show that the observed splitting arises from an interaction of the unpaired electron with two Cu nuclei and support the notion that CuA is a mixed-valent [Cu(II)/Cu(I)] complex in which the unpaired electronic spin is distributed evenly over the two Cu ions.

  5. Growth and oxidation of thin film Al{sub 2}Cu

    SciTech Connect

    Son, K.A.; Missert, N.A.; Barbour, J.C.; Hren, J.J.; Copeland, R.G.; Minor, K.G.

    1999-11-09

    Al{sub 2}Cu thin films ({approximately}382 nm) are fabricated by melting and resolidifying Al/Cu bilayers in the presence of a {approximately}3 nm Al{sub 2}O{sub 3} passivating layer. X-ray Photoelectron Spectroscopy (XPS) measures a 1.0 eV shift of the Cu2p{sub 3/2} peak and a 1.6 eV shift of the valence band relative to metallic Cu upon Al{sub 2}Cu formation. Scanning Electron Microscopy (SEM) and Electron Back-Scattered Diffraction (EBSD) show that the Al{sub 2}Cu film is composed of 30--70 {mu}m wide and 10--25 mm long cellular grains with (110) orientation. The atomic composition of the film as estimated by Energy Dispersive Spectroscopy (EDS) is 67{+-}2% Al and 33{+-}2% Cu. XPS scans of Al{sub 2}O{sub 3}/Al{sub 2}Cu taken before and after air exposure indicate that the upper Al{sub 2}Cu layers undergo further oxidation to Al{sub 2}O{sub 3} even in the presence of {approximately}5 nm Al{sub 2}O{sub 3}. The majority of Cu produced from oxidation is believed to migrate below the Al{sub 2}O{sub 3} layers, based upon the lack of evidence for metallic Cu in the XPS scans. In contrast to Al/Cu passivated with Al{sub 2}O{sub 3}, melting/resolidifying the Al/Cu bilayer without Al{sub 2}O{sub 3} results in phase-segregated dendritic film growth.

  6. Tunneling spectroscopy of Tl{sub 2}Ba{sub 2}CuO{sub 6}.

    SciTech Connect

    Ozyuzer, L.; Yusof, Z.; Zasadzinski, J. F.; Li, T.-W.; Hinks, D. G.; Gray, K. E.; Izmir Inst. of Tech.; IIT

    1999-01-01

    New results from tunneling spectroscopies on near optimally doped single crystals of Tl{sub 2}Ba{sub 2}CuO{sub 6} (Tl-2201) junctions are presented. The superconductor-insulator-normal metal (SIN) tunnel junctions are obtained using the point-contact technique with a Au tip. The tunneling conductances reproducibly show a sharp cusp-like subgap, prominent quasiparticle peaks with a consistent asymmetry, and weakly decreasing backgrounds. A rigorous analysis of the SIN tunneling data is performed using two different models for the d{sub x{sup 2}-y{sup 2}} (d-wave) density of states (DOS). Based on these and earlier results, the tunneling DOS of Tl-2201 has exhibited the most reproducible data that are consistent with a d-wave gap symmetry. We show that the dip feature at 2{Delta} that is clearly seen in SIN tunneling data of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} is also present in Tl-2201, but at a weaker level. The gap values for crystals with a bulk T{sub c}=86 K are in the range of 19-25 meV.

  7. Optical, microstructural, vibrational, and theoretical studies of p-type SrCu2O2 and BaCu2O2 transparent conductive oxides

    NASA Astrophysics Data System (ADS)

    Even, J.; Pedesseau, L.; Modreanu, M.; Huyberechts, G.; Servet, B.; Garry, Guy; Chaix-Pluchery, O.; Durand, O.

    2013-03-01

    Transparent conducting metal oxides (TCO) are unusual semiconducting materials displaying transparency to visible light. TCO materials are used for electrostatic shielding, antistatic screens, transparent heating devices, solar cells and even organic light emitting diodes. However, most TCOs are n-type, while p-type TCOs are scarce. SrCu2O2 is a leading candidate as a p-type transparent conductive oxide. In this paper, we report theoretical calculations and experimental studies on the vibrational, optical and microstructural properties of both bulk and thin films of polycrystalline undoped SrCu2O2 obtained by pulsed laser deposition (PLD). Barium doping of the SrCu2O2 by substitution of Sr atoms is also reported. The simulated crystal structures of both SrCu2O2 and BaCu2O2 materials, obtained through a state-of-the-art implementation of the Density functional theory, are compared with experimental X-ray diffraction data of undoped and Ba-doped SrCu2O2 bulk materials. Raman spectra of both SCO and BCO materials are simulated from the derivatives of the dielectric susceptibility and a symmetry analysis of the optical phonon eigenvectors at the Brillouin zone center is proposed. Good agreement with Raman scattering experimental results is demonstrated.

  8. Solidification behavior and structure of Al-Cu alloy welds

    SciTech Connect

    Brooks, J.A.; Li, M.; Yang, N.C.Y.

    1997-09-01

    The microsegregation behavior of electron beam (EB) and gas tungsten arc (GTA) welds of Al-Cu alloys covering a range from 0.19 to 7.74 wt% Cu were characterized for dendrite core concentrations and fraction eutectic solidification. Although a single weld speed of 12.7 mm/sec was used, some differences were observed in the segregation behavior of the two weld types. The microsegregation behavior was also modeled using a finite differences technique considering dendrite tip and eutectic undercooling and solid state diffusion. Fairly good agreement was observed between measured and calculated segregation behavior although differences between the two weld types could not be completely accounted for. The concept of dendrite tip undercooling was used to explain the formation of a single through thickness centerline grain in the higher alloy content GTA welds.

  9. A new series of oxycarbonate superconductors (Cu(0.5)C(0.5))(m)Ba(m+1)Ca(n-1)Cu(n)O2(m+n)+1

    NASA Technical Reports Server (NTRS)

    Takayama-Muromachi, E.; Kawashima, T.; Matsui, Y.

    1995-01-01

    We found a new series of oxycarbonate superconductors in the Ba-CaCu-C-O system under high pressure of 5 GPa. Their ideal formula is (Cu(0.5)C(0.5)(m)Ba(m+1)Ca(n-1)Cu(n)O2)((m+n)+1) ((Cu,C)-m(m+1)(n-1)n). Thus far, n = 3, 4 members of the m = 1 series, (Cu,C)-1223 and (Cu,C)-1234, have been prepared in bulk while n = 4, 5 members, (Cu,C)-2334 and (Cu,C)-2345, have been prepared for the m = 2 series. (Cu,C)-1223 shows superconductivity below 67 K while T(sub c)'s of other compounds are above 110 K. In particular, (Cu,C)-1234 has the highest T(sub c) of 117 K.

  10. Energy transfer between Eu-Mn and photoluminescence properties of Ba0.75Al11O17.25-BaMgAl10O17:Eu2+,Mn2+ solid solution

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Wang, Yuhua; Liu, Bitao; Li, Feng

    2010-08-01

    In order to evaluate the energy transfer between Eu-Mn in Ba0.75Al11O17.25-BaMgAl10O17 solid solution, Ba0.75Al11O17.25-BaMgAl10O17:Eu2+,Mn2+ phosphors were prepared by flux method. The crystal structure and the morphology of the solid solution were demonstrated by x-ray dirrfactometer and scanning electron microscopy. The photoluminescence mechanisms were explained by the energy transfer of Eu2+ to Mn2+ and the Dexter theory. A redshift of green emission peak and a decrease in decay time with the increase in Mn2+ concentration were observed. These phenomena are attributed to the formation of Mn2+ paired centers after analysis by a method of Pade approximations.

  11. CO sub 2 induced inhibition of the localized corrosion of aluminum, Al-0. 5% Cu, and Al-2% Cu in dilute HF solution

    SciTech Connect

    Scully, J.R. . Dept. of Materials Science); Peebles, D.E. )

    1991-01-01

    This study presents work on corrosion of aluminum, Al-.5% Cu, and Al-2% Cu. Electrochemical tests were performed in dilute HF solutions both with and without CO{sub 2} sparging. It is suggested that CO{sub 2} or its reaction products interact with the passive film so that exposure of Cu in the oxide-solution interface is minimized. CO{sub 2} is investigated as a corrosion inhibitor. 4 refs. (JDL)

  12. Electronic Structure of HgBa2CaCu2O(6+delta) Epitaxial films measured by x-ray Photoemission

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Rupp, M.; Gupta, A.; Tsuei, C. C.

    1995-01-01

    The electronic structure and chemical states of HgBa2CaCu20(sub 6 + delta), epitaxial films have been studied with x-ray photelectron spectroscopy. Signals from the superconducting phase dominate all the core-level spectra, and a clear Fermi edge is observed in the valence-band region. The Ba, Ca, Cu, and O core levels are similar to those of Tl2Ba2CaCu208(+)O(sub 6 + delta), but distinct differences are observed in the valence bands which are consistent with differences in the calculated densities of states.

  13. Elemental fractionation and magnetic properties of melt-based Y1Ba2Cu3Oz containing excess Tb or Pt

    NASA Technical Reports Server (NTRS)

    Hojaji, Hamid; Barkatt, Aaron; Hu, Shouxiang; Michael, Karen A.; Thorpe, Arthur N.; Talmy, Inna G.; Haught, Debbie A.; Alterescu, Sidney

    1990-01-01

    Scanning electron microscopy of certain partially melted Y-Ba-Cu-O materials containing minority metal oxide species (Y:Tb:Ba:Cu = 1:0.1:2:3 or Y:Ba:Cu with Pt impurities), accompanied by both EDX and EMP analysis, indicates that the minority species (Tb or Pt) is quantitatively concentrated in a relatively small number of 123-type grains. High magnetic susceptibility and magnetization observed for these materials indicate that such elemental distribution is not detrimental to superconducting behavior.

  14. The anisotropic nature of the superconducting properties of single crystal Y 1Ba 2Cu 3O 7 - x

    NASA Astrophysics Data System (ADS)

    Worthington, T. K.; Gallagher, W. J.; Kaiser, D. L.; Holtzberg, F. H.; Dinger, T. R.

    1988-06-01

    A series of noncontact magnetic measurements on high-quality single crystals of Y 1Ba 2Cu 3O 7 - x have enabled us to demonstrate that the superconducting-state properties of Y 1Ba 2Cu 3O 7 - x are those of a conventional, anisotropic superconductor with the anisotropy being associated with the highly conducting Cu sbnd O sheets in the Y 1Ba 2Cu 3O 7 - x crystal structure. The anisotropy in the superconducting state is reflected most strongly in the critical current anisotropy, which is as large as 20 to 1 at low temperatures and low fields and gets arbitrarily large at higher temperatures and higher fields. The upper critical field H C2 shows an anisotropy that varies from 6:1 to 10:1 in different crystals of high quality. Along the copper-oxygen sheets the upper critical field is enormous, extrapolating to ∼60 Tesla by 77 K and implying a low-temperature Ginzburg-Landau coherence length normal to the layers of 2Å- 4Å. Strong upward curvature is evident in the H C2 data in both orientations of applied field. This curvature can be interpreted in terms of thermodynamic fluctuations, and, if this explanation is correct, the critical region is enormous, extending more than 25 K below T C.

  15. Photocatalytic property and structural stability of CuAl-based layered double hydroxides

    SciTech Connect

    Lv, Ming; Liu, Haiqiang

    2015-07-15

    Three types of CuMAl layered double hydroxides (LDHs, M=Mg, Zn, Ni) were successfully synthesized by coprecipitation. Powder X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometry (ICP-AES) and UV–Vis diffuse reflectance spectrum (UV–vis) were used to confirm the formation of as-synthesized solids with good crystal structure. The photocatalytic activity of those LDH materials for CO{sub 2} reduction under visible light was investigated. The experimental results show that CuNiAl-LDHs with narrowest band gap and largest surface areas behave highest efficiency for methanol generation under visible light compared with CuMgAl-LDHs and CuZnAl-LDHs. The CuNiAL-LDH showed high yield for methanol production i.e. 0.210 mmol/g h, which was high efficient. In addition, the influence of the different M{sup 2+} on the structures and stability of the CuMAl-LDHs was also investigated by analyzing the geometric parameters, electronic arrangement, charge populations, hydrogen-bonding, and binding energies by density functional theory (DFT) analysis. The theoretical calculation results show that the chemical stability of LDH materials followed the order of CuMgAl-LDHs>CuZnAl-LDHs>CuNiAl-LDHs, which is just opposite with the photocatalytic activity and band gaps of three materials. - Graphical abstract: The host–guest calculation models and XRD patterns of CuMAl-LDHs: CuMgAl-LDHs (a), CuZnAl-LDHs (b) and CuNiAl-LDHs (c). - Highlights: • Three types of CuMAl layered double hydroxides (LDHs, M=Mg, Zn, Ni) has been synthesized. • CuMgNi shows narrower band gap and more excellent textural properties than other LDHs. • The band gap: CuMgAl based on result from UV–vis analysis. • CuMgAl shows the highest stability and lowest photocatalytic activity, while CuNiAl just opposite.

  16. Phase compatibilities of YBa2Cu3O(9-delta) type structure in quintenary systems Y-Ba-Cu-O-X (impurity)

    NASA Technical Reports Server (NTRS)

    Karen, P.; Fjellvag, H.; Kjekshus, A.

    1990-01-01

    Electrical transport properties of the oxidic high T(sub c) superconductors are significantly affected by the presence of minor amounts of various elements adventing as impurities, e.g., from the chemical environment during manufacturing. YBa2Cu3O(9-delta) is prone to an extinction of the superconductivity on (partial) substitution of all four elemental components. E.g., Pr (for Y), La (for Ba), Zn (for Cu) or peroxygroup (for O) substituents will alter some of the superconductivity preconditions, like mixed valence state in Cu3O7/O(9-delta) network or structural distortion of the network. Although various pseudoternary chemical equilibrium phase diagrams of the Y(O)-Ba(O)-Cu(O) system now are available, no consensus is generally shown, however, this is partly due to lack of compatible definitions of the equilibrium conditions. Less information is available about the phase compatibilities in the appropriate quaternary phase diagram (including oxygen) and virtually no information exists about any pentenary phase diagrams (including one impurity). Unfortunately, complexity of such systems, stemming both from number of quaternary or pentenary compounds and from visualizing the five-component phase system, limits this presentation to more or less close surroundings of the YBa2Cu3O(9-delta) type phase in appropriate pseudoquaternary or pseudopseudoternary diagrams, involving Y-Ba-Cu and O, O-CO2, alkaline metals, Mg and alkaline earths, and Sc and most of the 3-d and 4-f elements. The systems were investigated by means of x ray diffraction, neutron diffraction and chemical analytical methods on samples prepared by sol-gel technique from citrates. The superconductivity was characterized by measuring the diamagnetic susceptibility by SQUID.

  17. Nuclear Quadrupole Resonance Study of the High-T c Related Cu Oxide La4BaCu5O13+δ

    NASA Astrophysics Data System (ADS)

    Ohno, Takashi; Yasuoka, Hiroshi; Ueda, Yutaka

    1994-10-01

    63Cu and 65Cu NQR line shapes, spin-spin and spin-lattice relaxation rates in a high-T c related Cu oxide, La4BaCu5O13+δ, have been measured to clarify the difference between superconducting and non-superconducting Cu oxides from a microscopic view point. Although there are two crystallographically inequivalent Cu sites, only one pair of 63Cu and 65Cu NQR frequency spectra was observed. From the detailed study of the Fourier transformed spin-echo signal and that of the envelope decay, we attribute the above fact to an accidental coincidence of the NQR frequencies for these two sites. It is shown that the spin-lattice relaxation is manifested by the magnetic interactions in the measured temperature range of 1.4 K 420 K. The relaxation rate, 1/63T1, increases monotonically with increasing temperature, obeying 1/63T1=aT+bT3 above about 80 K, but shows a small swelling at low temperatures, suggesting a magnetic instability.

  18. Critical current density in Ag/YBa2Cu3Ox and PrBa2Cu3Oy/YBa2Cu3Ox multilayers

    NASA Astrophysics Data System (ADS)

    Dang, V. S.; Mikheenko, P.; Sarkar, A.; Abell, J. S.; Crisan, A.

    2010-06-01

    One of successful methods of introducing artificial pinning centres in superconducting films is by alternating layers of superconducting material and incomplete layers (planar distributions of nanodots) of other materials (quasi-superlattice or quasi-multilayer approach). Most of the work on artificial pinning centres has been done on thin YBa2Cu3Ox (YBCO) films and a large variety of quasi-multilayer materials have been explored. It is still difficult to justify the choice of a quasi-multilayer material for particular superconducting applications. One of the properties to be taken into account is compatibility of the crystal lattice of YBCO and the quasi-superlattice material. Here we compare the superconducting behaviour of two very different quasi-multilayers: one with very similar crystal lattices of nanodots and YBCO: PrBa2Cu3Oy (PBCO)/YBCO, and another one with very different, Ag/YBCO. We found that the difference between crystal lattices strongly affects superconducting properties of quasi-multilayers and leads to different types of pinning in the films.

  19. Corrosion behavior of Cu and the Cu-Zn-Al shape memory alloy in simulated uterine fluid.

    PubMed

    Chen, Bangyi; Liang, Chenghao; Fu, Daojun; Ren, Deming

    2005-09-01

    Chemical immersion tests, electrochemical methods and atomic absorption spectrometry were employed to investigate the corrosion behavior of Cu and the Cu-Zn-Al shape memory alloy (SMA) in simulated uterine fluid. The effect of pH on corrosion rate and corrosion potential was also investigated. The results indicated that in the static state in simulated uterine fluid, dealuminumification of the Cu-Zn-Al alloy occurred with Cl- combining with aluminum ions to form hydroxyl aluminum chloride. The hydroxyl aluminum chloride hydrolyzed readily and facilitated further dealuminumification corrosion. The corrosion process of Cu and Cu-Zn-Al SMA in simulated uterine fluid was controlled by cathodic reduction of oxygen. Because the tendency for surface ionization is greater for aluminum than for zinc, a compact protective aluminum layer was formed, which inhibited the cathodic reduction of oxygen. Hence, the corrosion rate of Cu-Zn-Al SMA was smaller than that of Cu in simulated uterine fluid. With increasing pH, the corrosion rate of Cu and Cu-Zn-Al SMA in simulated uterine fluid decreased and the open-circuit potential moved in a positive direction. PMID:16102560

  20. Low-temperature sintering of M-type barium ferrite with BaCu(B 2O 5) additive

    NASA Astrophysics Data System (ADS)

    Chen, Daming; Liu, Yingli; Li, Yuanxun; Zhong, Wenguo; Zhang, Huaiwu

    2012-02-01

    The aim of this work is to lower the sintered temperature of M-type barium ferrite (BaM) by BaCu(B2O5) (BCB) additives. The effects of BCB additives on the sintering behavior, structure and magnetic properties of BaM were also discussed. It was found that the sintered density, saturation magnetization and initial permeability of BaM are modified obviously as small amount of BCB (1-4 wt%) is added. Especially, when BaM with 3 wt% BCB was sintered at 900 °C, the single-phase BaM was obtained and showed excellent properties with sintered density of 4.88 g/cm3, saturation magnetization of 61.4 emu/g and initial permeability of 3.15. In addition, the SEM result revealed that the sample can be co-fired well with the Ag electrode at 900 °C. The reason for this was attributed to be the formation of the BCB liquid phase. It suggests that this M-type barium ferrite can be used as LTCC substrate for millimeter wave circulator, filter and other magnetic microwave devices.

  1. Viscosities of aluminum-rich Al-Cu liquid alloys

    NASA Astrophysics Data System (ADS)

    Ganesan, S.; Speiser, R.; Poirier, D. R.

    1987-06-01

    Viscosity data for Al-Cu liquid alloys in the ranges of 0≤ C L≤33.1 wt pct Cu and 1173≤ T ≤973 K are reviewed. It was found that Andrade's equation can be used to represent the variation of viscosity with temperature for a given composition, but that each of the two parameters in Andrade's equation shows no systematic variation with composition of the liquid-alloys. Consequently, arithmetic averages of the parameters were used and assumed to apply to all compositions in the range 0≤ C L ≤33.1 wt pct Cu. Such a procedure implies that the viscosity happens to vary with composition solely because the specific volume varies with composition. In order to establish the predictability of extrapolating such simple behavior, a more complex model was considered. The latter model was recently presented by Kucharski and relates viscosity to the structure and thermodynamics of liquid alloys. Viscosities obtained by interpolating Andrade's equation and Kucharski's model compare closely; furthermore, values obtained by extrapolations to lower temperatures also compare favorably. Finally the simpler model was used to calculate the viscosity of the interdendritic liquid during solidification.

  2. Enhanced 77 K vortex-pinning in Y Ba2Cu3O7-x films with Ba2Y TaO6 and mixed Ba2Y TaO6 + Ba2Y NbO6 nano-columnar inclusions with irreversibility field to 11 T

    NASA Astrophysics Data System (ADS)

    Rizzo, F.; Augieri, A.; Angrisani Armenio, A.; Galluzzi, V.; Mancini, A.; Pinto, V.; Rufoloni, A.; Vannozzi, A.; Bianchetti, M.; Kursumovic, A.; MacManus-Driscoll, J. L.; Meledin, A.; Van Tendeloo, G.; Celentano, G.

    2016-06-01

    Pulsed laser deposited thin Y Ba2Cu3O7-x (YBCO) films with pinning additions of 5 at. % Ba2Y TaO6 (BYTO) were compared to films with 2.5 at. % Ba2Y TaO6 + 2.5 at. % Ba2Y NbO6 (BYNTO) additions. Excellent magnetic flux-pinning at 77 K was obtained with remarkably high irreversibility fields greater than 10 T (YBCO-BYTO) and 11 T (YBCO-BYNTO), representing the highest ever achieved values in YBCO films.

  3. Clarification and mitigation of marked J c decrease at low magnetic fields of BaHfO3-doped SmBaCuO3 thin films deposited on seed layer

    NASA Astrophysics Data System (ADS)

    Watanabe, Yutaro; Ichino, Yusuke; Yoshida, Yutaka; Ichinose, Ataru

    2016-07-01

    In accordance with the results of our previous research, a low-temperature growth (LTG) technique is effective for expanding the lower growth temperature region of c-axis-orientated SmBa2Cu3O y (SmBCO) thin films. However, BaHfO3 (BHO)-doped LTG films show a marked decrease in J c at low magnetic fields compared with conventional PLD films. In this study, we aimed to clarify the mechanism of J c decrease and investigated the thickness dependence of the seed layer on the (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) (100) single crystal. The obtained results indicate that J c decreased at low magnetic fields as the thickness of the seed layer increased. It is suggested that flux line kinks produced by flux motion in the seed layer would lead to the depinning of flux lines from BHO nanorods in the upper layer. Thus, we added Y2O3 into the seed layer to trap flux lines in the seed layer. Consequently, we improved J c in the low magnetic field region even in the films prepared by using the LTG technique.

  4. Compatibilities of YBa2Cu3O(9-delta) type phase in quintenary systems Y-Ba-Cu-O-X (impurity)

    NASA Technical Reports Server (NTRS)

    Karen, P.; Braaten, O.; Fjellvag, H.; Kjekshus, A.

    1991-01-01

    Isothermal phase diagrams at various oxygen pressures were studied by powder diffraction and chemical analytical methods. The components, Y, Ba, Cu, and O (specifically O2, O2-, and O2 sup 2-) are treated, together with C (specifically CO2 and CO2 sup 2-), alkaline metals, Mg, alkaline earths, Sc, 3-d and 4-f elements. Effects of the substitutions at the structural sites of YBa2Cu3O(9-delta) on T sub c are discussed with respect to changes in crystallochemical characteristics of the substituted phase and to the nature of the substituents.

  5. Thermal, solution and reductive decomposition of Cu-Al layered double hydroxides into oxide products

    SciTech Connect

    Britto, Sylvia; Vishnu Kamath, P.

    2009-05-15

    Cu-Al layered double hydroxides (LDHs) with [Cu]/[Al] ratio 2 adopt a structure with monoclinic symmetry while that with the ratio 0.25 adopt a structure with orthorhombic symmetry. The poor thermodynamic stability of the Cu-Al LDHs is due in part to the low enthalpies of formation of Cu(OH){sub 2} and CuCO{sub 3} and in part to the higher solubility of the LDH. Consequently, the Cu-Al LDH can be decomposed thermally (150 deg. C), hydrothermally (150 deg. C) and reductively (ascorbic acid, ambient temperature) to yield a variety of oxide products. Thermal decomposition at low (400 deg. C) temperature yields an X-ray amorphous residue, which reconstructs back to the LDH on soaking in water or standing in the ambient. Solution decomposition under hydrothermal conditions yields tenorite at 150 deg. C itself. Reductive decomposition yields a composite of Cu{sub 2}O and Al(OH){sub 3}, which on alkali-leaching of the latter, leads to the formation of fine particles of Cu{sub 2}O (<1 {mu}m). - Graphical abstract: SEM image of (a) the Cu{sub 2}O-Al(OH){sub 3} composite obtained on reductive decomposition of CuAl{sub 4}-LDH and (b) Cu{sub 2}O obtained on leaching of Al(OH){sub 3} from (a).

  6. Cu-Al-Ni-SMA-Based High-Damping Composites

    NASA Astrophysics Data System (ADS)

    López, Gabriel A.; Barrado, Mariano; San Juan, Jose; Nó, María Luisa

    2009-08-01

    Recently, absorption of vibration energy by mechanical damping has attracted much attention in several fields such as vibration reduction in aircraft and automotive industries, nanoscale vibration isolations in high-precision electronics, building protection in civil engineering, etc. Typically, the most used high-damping materials are based on polymers due to their viscoelastic behavior. However, polymeric materials usually show a low elastic modulus and are not stable at relatively low temperatures (≈323 K). Therefore, alternative materials for damping applications are needed. In particular, shape memory alloys (SMAs), which intrinsically present high-damping capacity thanks to the dissipative hysteretic movement of interfaces under external stresses, are very good candidates for high-damping applications. A completely new approach was applied to produce high-damping composites with relatively high stiffness. Cu-Al-Ni shape memory alloy powders were embedded with metallic matrices of pure In, a In-10wt.%Sn alloy and In-Sn eutectic alloy. The production methodology is described. The composite microstructures and damping properties were characterized. A good particle distribution of the Cu-Al-Ni particles in the matrices was observed. The composites exhibit very high damping capacities in relatively wide temperature ranges. The methodology introduced provides versatility to control the temperature of maximum damping by adjusting the shape memory alloy composition.

  7. High- J c GdBa 2Cu 3O 7-δ films fabricated by the metal-organic deposition process

    NASA Astrophysics Data System (ADS)

    Lee, J. W.; Shin, G. M.; Moon, S. H.; Yoo, S. I.

    2010-11-01

    We report a successful fabrication of high- J c GdBa 2Cu 3O 7-δ (GdBCO) films by the metal-organic deposition process on the LaAlO 3 (LAO) (0 0 1) substrates. The coating solution was prepared by mixing Gd, Cu fluorine-free sources with Ba trifluoroacetate. Samples were dip-coated, pyrolized within 3 h at the temperature up to 400 °C in a humid oxygen atmosphere, and finally fired at various high temperatures in 100 ppm Ar/O 2 atmosphere. The GdBCO films fired at 775 and 800 °C exhibited J c values of ∼2.1 MA/cm 2 at 77 K in a self-field, which are attributable to both high T c,zero values of ∼89 K and high in-plane textures of 1.3-1.4°. Above 800 °C, however, the superconducting properties of GdBCO films are degraded due to the thermal decomposition of GdBCO film in 100 ppm Ar/O 2 atmosphere.

  8. Study of the Electrodynamic Response of SmBa2Cu3O7-δ Thin Films in the Microwave Region

    NASA Astrophysics Data System (ADS)

    Lamura, G.; di Gennaro, E.; Andreone, A.; Boffa, M.; Cucolo, A. M.

    We present some experimental results on the temperature dependence of the surface resistance Rs and magnetic penetration depth λ of thin films of SmBa2Cu3O7-δ. The samples, 0.25 μm thick, were grown by a dc sputtering technique on (100) K LaAlO3 single crystal substrates, with critical temperatures ranging between 87 and 88 K Accurate measurements af the surface impedance Zs were performed down to 4 K by means of a dielectrically loaded cavity operating in the microwave region (20 GHz). Both λ and Rs show a monotonic temperature behavior, with no evidence of low temperature up-turn characteristic of other rare earth based cuprates like GdBa2Cu3O7-δ. At low temperatures, we observed am almost linear behavior of λ with a slope of ~ 0.3 nm/K up to 25 K, as expected in a d-wave pairing scenario. The real part of complex conductivity σ1, shows a bump at around 40 K, in agreement with previous reports.

  9. Preparation of Ba0.09Sr0.91TiO3/YBa2Cu3O7-x bilayers and investigation of their dielectric properties

    NASA Astrophysics Data System (ADS)

    Jia, Jiqiang; Zhao, Gaoyang; Shi, Xiaoxue; Lei, Li

    2016-08-01

    YBa2Cu3O7-x (YBCO) films of 110 nm thickness were prepared on LaAlO3 (LAO) substrates via the sol-gel method. Subsequently, about 400 nm thick Ba0.09Sr0.91TiO3 (BST) films were epitaxially grown on the YBCO and LNO films surface; the BST films exhibited a strong c-axis orientation. The dielectric adjustability and relative dielectric constant was investigated in the range of 300-83 K. Results indicate that the tunability of the Ba0.09Sr0.91TiO3/YBa2Cu3O7-x (BST/YBCO) displayed an increase relative to c-axis-oriented BST on LaNiO3 (LNO). The tunability was further enhanced as the operating temperature decreased, yet the loss tangent (tanδ) decreased. The tunability and the tanδ at 100 kHz and 83 K were 58% and 0.029, respectively.

  10. Neutron diffraction study of the magnetic ordering of the Cu sup ++ spins in Nd sub 1. 5 Ba sub 1. 5 Cu sub 3 O sub 6+x

    SciTech Connect

    Moudden, A.H.; Hennion, B. - Centre d'Etudes Nucleaires de Saclay, 91 - Gif-sur-Yvette ); Schweiss, P. - Centre d'Etudes Nucleaires de Saclay, 91 - Gif-sur-Yvette Kernforschungszentrum Karlsruhe GmbH . Inst. fuer Nukleare Festkoerperphysik); Gehring, P.M.; Shirane, G. (Brookhaven National Lab., Upton, NY (

    1991-01-01

    Elastic neutron scattering experiments performed on single crystals of Nd{sub 1.5}Ba{sub 1.5}Cu{sub 3}O{sub 6+y} reveal successive antiferromagnetic (AF) ordering of the Cu{sup ++} spins. The as grown single crystals show an AF structure characterized by a Neel temperature T{sub N1} {approximately} 390K and a magnetic wave vector (1/2 1/2 0) referring to the tetragonal structure of NdBa{sub 2}Cu{sub 3}O{sub 6}. As the temperature is lowered below T{sub N2} {approximately} 150K, a spin reorientation develops and a second AF ordering with (1/2 1/2 1/2) wave vector is stabilized. When the samples are oxygenated the tetragonal symmetry and the Neel temperature T{sub N1} remain unchanged, whereas the spin reorientation at T{sub N2} is suppressed. The results indicate that the Nd/Ba substitution increases the stability of the tetragonal structure upon the oxygen content. This may induce new possibilities of local oxygen ordering that favour the presence of holes in the deficient layer.

  11. Cu substitution effects on the local magnetic properties of Ba(Fe(1-x)Cu(x))(2)As(2): a site-selective (75)As and (63)Cu NMR study.

    PubMed

    Takeda, Hikaru; Imai, Takashi; Tachibana, Makoto; Gaudet, Jonathan; Gaulin, Bruce D; Saparov, Bayrammurad I; Sefat, Athena S

    2014-09-12

    We take advantage of the site-selective nature of the ^{75}As and ^{63}Cu NMR techniques to probe the Cu substitution effects on the local magnetic properties of the FeAs planes in Ba(Fe_{1-x}Cu_{x})_{2}As_{2}. We show that the suppression of antiferromagnetic Fe spin fluctuations induced by Cu substitution is weaker than a naive expectation based on a simple rigid band picture, in which each Cu atom would donate three electrons to the FeAs planes. Comparison between ^{63}Cu and ^{75}As NMR data indicates that spin fluctuations are suppressed at the Cu and their neighboring Fe sites in the tetragonal phase, suggesting the strongly local nature of the Cu substitution effects. We attribute the absence of a large superconducting dome in the phase diagram of Ba(Fe_{1-x}Cu_{x})_{2}As_{2} to the emergence of a nearly magnetically ordered FeAs plane under the presence of orthorhombic distortion.

  12. Al-Cu-Li and Al-Mg-Li alloys: Phase composition, texture, and anisotropy of mechanical properties (Review)

    NASA Astrophysics Data System (ADS)

    Betsofen, S. Ya.; Antipov, V. V.; Knyazev, M. I.

    2016-04-01

    The results of studying the phase transformations, the texture formation, and the anisotropy of the mechanical properties in Al-Cu-Li and Al-Mg-Li alloys are generalized. A technique and equations are developed to calculate the amounts of the S1 (Al2MgLi), T1 (Al2CuLi), and δ' (Al3Li) phases. The fraction of the δ' phase in Al-Cu-Li alloys is shown to be significantly higher than in Al-Mg-Li alloys. Therefore, the role of the T1 phase in the hardening of Al-Cu-Li alloys is thought to be overestimated, especially in alloys with more than 1.5% Li. A new model is proposed to describe the hardening of Al-Cu-Li alloys upon aging, and the results obtained with this model agree well with the experimental data. A texture, which is analogous to that in aluminum alloys, is shown to form in sheets semiproducts made of Al-Cu-Li and Al-Mg-Li alloys. The more pronounced anisotropy of the properties of lithium-containing aluminum alloys is caused by a significant fraction of the ordered coherent δ' phase, the deformation mechanism in which differs radically from that in the solid solution.

  13. All a-axis oriented YBa2Cu3O(7-y) - PrBa2Cu3O(7-z) - YBa2Cu3O(7-y) Josephson devices operating at 80 K

    NASA Technical Reports Server (NTRS)

    Barner, J. B.; Rogers, C. T.; Inam, A.; Ramesh, R.; Bersey, S.

    1991-01-01

    The controllable, reproducible fabrication of nonhysteretic Josephson devices with excess-current weak-link characteristics at temperatures up to 80 K have been demonstrated. The devices are patterned from in situ deposited a-axis oriented YBa2Cu3O(7-y) - PrBa2Cu3O(7-y) - YBa2Cu3O(7-y) trilayers grown on SrTiO3(001) substrates. Control of the critical current density and resistance is achieved by varying the thickness of the PrBa2Cu3O(7-z) barrier layer. Critical current densities in excess of 10,000 A/sq cm have been reproducibly measured; good uniformity across the wafer is obtained with device parameters scaling with device area. Strong constant-voltage current steps are observed under 11.2 GHz microwave radiation at temperatures up to and above 80 K.

  14. Structure and superconductivity in Cr-substituted HgBa{sub 2}CuO{sub 4+8}.

    SciTech Connect

    Chmaissem, O.; Jorgensen, J. D.; Hinks, D. G.; Storey, B. G.; Dabrowski, B.; Zhang, H.; Marks, L. D.; Materials Science Divsion - Science Technology Center for Superconductivity; Northwestern Univ.; Northern Illinois Univ.

    1997-05-15

    Chromium-substituted Hg{sub 1-x}Ba{sub 2}CuO{sub 4+{delta}} compounds have been synthesized. Cr can be incorporated into the structure with a solubility limit around x {approx} 0.27. Cr substitutes at the Hg site and is tetrahedrally coordinated to four oxygen atoms. Two of these are apical oxygen atoms that have moved to new positions (O2') and two are in the Hg/Cr plane (O3) at a (x x 0) site. Additional oxygen atoms (O4) in the Hg/Cr plane at (1/2 1/2 0) affect the carrier concentration, as for HgBa{sub 2}CuO{sub 4+{delta}}. In the as-synthesized samples, {Tc} decreases with increasing Cr content. Attempts to adjust the carrier concentration by post annealing in oxygen at low temperature destroy superconductivity because the samples are metastable under ambient conditions.

  15. Magnetic dependent proximity effects of superconductivity and ferromagnetism in Y BaCuO/LaCaMnO bilayers

    NASA Astrophysics Data System (ADS)

    Peng, Lin; Cai, Chuanbing; Chen, Changzhao; Gao, Bo; Ying, Liliang; Liu, Zhiyong

    2008-12-01

    The Y BaCuO/ La 0.88Ca 0.12MnO 3 (YBCO/LCMOi) and Y BaCuO/ La 0.33Ca 0.67MnO 3 (YBCO/LCMOj) bilayers are fabricated with the method of pulsed laser deposition, and the magnetic dependent proximity effects are investigated. The magnetic fields were applied parallel (in-plane) and perpendicular (out-of-plane) to the film plane. Magnetic properties curves in different temperature range and magnetic field along two crystal orientation show a complex behavior due to the interplay between Meissner currents in YBCO layer and the magnetic fields present in LCMOi (or LCMOj) layer. Ac susceptibility measurements show that the suppression of superconductivity in LCMOi and LCMOj bilayers. The obtained results are discussed in terms of the effect of hole charge transfer from YBCO to LCMOi (or LCMOj) on the proximity between superconductivity and ferromagnetism.

  16. The bulk modulus and young's modulus of the superconductor Ba sub 2 Cu sub 3 YO sub 7

    SciTech Connect

    Block, S.; Piermarini, G.J.; Munro, R.G.; Wong-Ng, W. )

    1987-07-01

    The isothermal equation of state of the high temperature superconducting ceramic material Ba{sub 2}Cu{sub 3}YO{sub 7} has been determined by measurements in a diamond anvil pressure cell using an energy dispersive x-ray diffraction method. The orthorhombic unit cell lattice parameters (a = 3.8856 {angstrom}, b = 11.6804 {angstrom}, c = 3.8185 {angstrom}) were found to have compressions of (2.0%, 2.3%, 1.1%) respectively over the pressure range from one atmosphere to 10.6 GPa at room temperature. Subsequent equation of state analysis of the approximately linear compression of the volume determined that the isothermal bulk modulus was 196 {plus minus} 17 GPa. Young's modulus was estimated to be 235 {plus minus} 20 GPa assuming that the Poisson's ratio for Ba{sub 2}Cu{sub 3}YO{sub 7} was 0.3 which is typical of many ceramics.

  17. Highly oriented Tl2Ba2Ca2Cu3O10 thin films by pulsed laser evaporation

    NASA Technical Reports Server (NTRS)

    Liou, S. H.; Aylesworth, K. D.; Ianno, N. J.; Johs, B.; Thompson, D.

    1989-01-01

    Superconducting thin films on MgO (100) substrates with nearly pure Tl2Ba2Ca2Cu3O10 (2:2:2:3) phase using pulsed laser evaporation and postannealing have been fabricated. The films had c axes perpendicular to the substrates. Superconducting films with onset temperatures of 125 K and zero resistance at 110 K were obtained. X-ray microprobe fluorescence measurements indicate that a typical composition of films is Tl(0.66)Ba(1.77)Ca(1.46)Cu3O(x) which is low in Tl compared to that expected for the 2:2:2:3 phase. A typical grain size is greater than 10 microns revealed by scanning electron microscopy.

  18. Upper critical field of high temperature Y(1.2)Ba(0.8)CuO(4-delta) superconductor

    NASA Technical Reports Server (NTRS)

    Hor, P. H.; Meng, R. L.; Huang, J. Z.; Chu, C. W.; Huang, C. Y.

    1987-01-01

    A 20-T high-field magnet is used to measure electrical resistance as a function of temperature in the Y(1.2)Ba(0.8)CuO(4-delta) superconductor. The temperature dependence of the critical field, Hc2(T), is obtained from the superconduction transition. A Hc2(O) value of 166T is determined which is the highest critical field yet reported. Results show Y(1.2)Ba(0.8)CuO(4-delta) to be a 90K Type-II superconductor, with a lower critical field Hc1(O) of about 0.2T and a penetration depth of about 290 A.

  19. Discovery of New Al-Cu-Fe Minerals in the Khatyrka CV3 Meteorite

    NASA Astrophysics Data System (ADS)

    Ma, C.; Lin, C.; Bindi, L.; Steinhardt, P. J.

    2016-08-01

    Our nanomineralogy investigation of Khatyrka has revealed two new alloy minerals (AlCu with a Pm-3m CsCl structure and Al3Fe with a C2/m structure) and associated icosahedrite (quasicrystal Al63Cu26Fe11 with a five-fold symmetry) in section 126A of USNM 7908.

  20. Fabrication and electrical properties of p-CuAlO2/(n-, p-)Si heterojunctions

    NASA Astrophysics Data System (ADS)

    Suzhen, Wu; Zanhong, Deng; Weiwei, Dong; Jingzhen, Shao; Xiaodong, Fang

    2014-04-01

    CuAlO2 thin films have been prepared by the chemical solution deposition method on both n-Si and p-Si substrates. X-ray diffraction analysis indicates that the obtained CuAlO2 films have a single delafossite structure. The current transport properties of the resultant p-CuAlO2/n-Si and p-CuAlO2/p-Si heterojunctions are investigated by current-voltage measurements. The p-CuAlO2/n-Si has a rectifying ratio of ~35 within the applied voltages of -3.0 to +3.0 V, while the p-CuAlO2/p-Si shows Schottky diode-like characteristics, dominated in forward bias by the flow of space-charge-limited current.

  1. Characterization of Al/CuO nanoenergetic multilayer films integrated with semiconductor bridge for initiator applications

    NASA Astrophysics Data System (ADS)

    Zhu, Peng; Shen, Ruiqi; Ye, Yinghua; Fu, Shuai; Li, Dongle

    2013-05-01

    This paper describes the ignition characteristics of Al/CuO nanoenergetic multilayer films (nEMFs) integrated with semiconductor bridge (SCB). The as-deposited Al/CuO nEMFs were identified with SEM and differential scanning calorimetry. Results show that distinct Al/CuO nEMFs are sputter deposited in a layered geometry, and the Al/CuO nEMFs gives a reaction heat equal to 2181 J/g. The firing experiments show that Al/CuO nEMFs have no influence on the electrical properties of SCB. Furthermore, the rapid combustion of Al/CuO nEMFs is able to assist SCB generating high-temperature plasma and products, such that enhance the ignition reliability.

  2. Electronic Structure and Characteristics of Chemical Bonds in CuInSe2, CuGaSe2, and CuAlSe2

    NASA Astrophysics Data System (ADS)

    Maeda, Tsuyoshi; Wada, Takahiro

    2010-04-01

    Electronic structural calculations of chalcopyrite-type CuInSe2 and its related compounds, CuGaSe2 and CuAlSe2, were performed by a recently proposed screened-exchange local density approximation (sX-LDA) method. The theoretical band gaps of CuInSe2, CuGaSe2, and CuAlSe2, obtained by the conventional calculation method using a generalized gradient approximation (GGA) functional, were 0.04, 0.14, and 1.11 eV, respectively. These values were considerably underestimated in comparison with their experimental values of 1.04, 1.68, and 2.67 eV because the exchange-correlation energy was not precisely calculated. Therefore, electronic structural calculations of chalcopyrite-type CuInSe2 and related compounds were performed with an sX-LDA functional to obtain accurate electronic structure. The present sX-LDA calculation successfully reproduced the band gaps of CuInSe2 (0.96 eV), CuGaSe2 (1.36 eV), and CuAlSe2 (2.22 eV). The obtained electronic structures and band gap energies of CuInSe2, CuGaSe2, and CuAlSe2 are discussed on the basis of schematic molecular orbital diagrams of tetrahedral CuSe47-, InSe45-, GaSe45-, and AlSe45- clusters.

  3. Y1Ba2Cu3O(6+delta) growth on thin Y-enhanced SiO2 buffer layers on silicon

    NASA Technical Reports Server (NTRS)

    Robin, T.; Mesarwi, A.; Wu, N. J.; Fan, W. C.; Espoir, L.; Ignatiev, A.; Sega, R.

    1991-01-01

    SiO2 buffer layers as thin as 2 nm have been developed for use in the growth of Y1Ba2Cu3O(6+delta) thin films on silicon substrates. The SiO2 layers are formed through Y enhancement of silicon oxidation, and are highly stoichiometric. Y1Ba2Cu3O(6+delta) film growth on silicon with thin buffer layers has shown c orientation and Tc0 = 78 K.

  4. First principles study of CuAlO2 doping with S

    NASA Astrophysics Data System (ADS)

    Gao, Haigen; Zhou, Jian; Lu, Minghui

    2010-07-01

    We study the electronic properties of CuAlO2 doped with S by the first principles calculations and find that the band gap of CuAlO2 is reduced after the doping. At the same time, the effective masses are also reduced and the density of states could cross the Fermi level. These results show that the conductivity of CuAlO2 could be enhanced by doping the impurities of S, which needs to be further studied.

  5. Ion beam modification of Tl-Ba-Ca-Cu-O type high temperature superconductors during irradiation

    SciTech Connect

    Newcomer, P.P.; Morosin, B.; Wang, L.M.

    1994-12-31

    Microstructural modification of high temperature superconductor (HTS) single-crystal plates of Tl-1212 and Tl-2212 (numbers designate the Tl/Ba/Ca/Cu cation ratio) was studied during 1.5 MeV Kr{sup +} and Xe{sup +} ion irradiation with in-situ electron diffraction and after ion irradiation with high resolution TEM (HRTEM). Similar in-situ temperature dependence effects are seen for both phases. During irradiations from 22K to 673K, an amorphous halo develops after very low ion dose or fluence (1.7 {times} 10{sup 12} ions/cm{sup 2}). During irradiation at 100 and 300K, complete amorphization is obtained, while at 22 and {ge}533K, the halo fades slightly and a polycrystalline ring pattern develops, indicating ion irradiation induced crystallization occurred. After a low ion dose (8.5 {times} 10{sup 12} ions/cm{sup 2}) at 100 and 300K, HRTEM reveals amorphous regions 5-20 nm in size which are not columnar and do not all penetrate the entire sample thickness. At 22 and {ge}533K, Moire fringes and misoriented crystallites of cascade size are observed. The 4-6nm crystallites are thallium-rich.

  6. Low temperature synthesis of Y-Ba-Cu oxide films and preparation of DC-SQUIDS

    SciTech Connect

    Matsuda, M.; Matachi, A.; Kuriki, S.

    1989-03-01

    The authors have synthesized superconducting Y-Ba-Cu oxide thin films by rf sputtering at a relatively low substrate temperature. The films of 300-700 nm thickness have Tc of 60-72K without post-annealing after the deposition. A preferential orientation with a c-axis perpendicular to the film surface was observed. DC-SQUIDs having two parallel microbridges with constriction of submicrometer to 40..mu..m width were fabricated from the oxide films by chemical etching. The microbridges having more than 2..mu..m width did not operate as Josephson devices. The characteristics of these SQUIDs suggested vortex-flow. Periodic modulation of the voltage with magnetic flux was observed in a SQUID having submicrometer microbridges. Telegraph-like noise of the voltage which exhibits switching between two or more discrete levels was observed in all of the SQUIDs irrespective of the width of the microbridges. This telegraph-like noise was also observed in a single microbridge, and its effective switching-rate increased exponentially with the increase of temperature above 15K. A bump structure of Lorentzian due to the telegraph-like noise was dominant in the power spectral density of the flux noise of the SQUID.

  7. Calcium-substituted Y-Ba-Cu-O superconductors with enhanced Tc synthesized at elevated oxygen pressures

    NASA Astrophysics Data System (ADS)

    Morris, D. E.; Narwankar, P.; Sinha, A. P. B.; Takano, K.; Fayn, B.; Shum, V. T.

    1990-03-01

    Calcium substitution in the Y-Ba-Cu-O system at elevated P(O2) results in superconducting compounds with novel and enhanced properties: tetragonal CaxY(1-x)Ba2Cu3Oy with Tc=86 K for x=0.2 prepared at P(O2)=16 bars, and CaxY(1-x)Ba2Cu4Oy (1:2:4) with Tc=89 K for x=0.1 prepared at 50-200 bars. Calcium substitution shifts the phase-stability boundary between 1:2:3, 2:4:7, and 1:2:4 phases to higher P(O2), and stabilizes a tetragonal 1:2:3 structure at moderately elevated P(O2) without substantial decrease in Tc. The Tc of 1:2:4 increases with Ca substitution up to x=0.1, and then decreases gradually for larger x, possibly because of excessive hole concentration.

  8. Spectroscopic studies and antibacterial activities of pure and various levels of Cu-doped BaSO₄ nanoparticles.

    PubMed

    Sivakumar, S; Soundhirarajan, P; Venkatesan, A; Khatiwada, Chandra Prasad

    2015-12-01

    The present study was made to design the pure and various levels of Cu doped (0.025 M, 0.05 M and 0.075 M) BaSO4 NPs synthesized by chemical precipitation method. The synthesized products have been characterised by X-ray Diffractometer (XRD), Fourier transform infrared (FT-IR) spectrometer, thermogravimetric and differential thermal analysis (TG-DTA), UV-Vis-diffused reflectance spectroscopy (UV-Vis-DRS), field emission-scanning electron microscopy with energy dispersive spectroscopy (FE-SEM with EDS), transmission electron microscopy (TEM) and application oriented study like antibacterial activity also reported. The result determined from XRD was affirmed by the results obtained from electron microscopic measurements. XRD study revealed that the synthesized products were composed of orthorhombic structure and highly crystalline in nature. Furthermore, flaky like morphology of pure and Cu-BaSO4 nanoparticles have been observed from the images obtained from these studies. The existence of Cu(2+) was confirmed by EDS analysis. The functional groups of the synthesized samples were analysed by FT-IR study. The band gap energies of pure and doped samples were accomplished using UV-Vis-DRS analysis. Also, the kinetic parameters were evaluated and reported from the thermal stability of nanoparticles. Eventually, gram-negative bacteria shows the less antibacterial activities compared to gram-positive bacteria due to adsorption of BaSO4 nanoparticles on the surface of the used bacteria.

  9. Current dependent angular magnetoresistance in strongly Pr-doped Y Ba2Cu3O7-δ single crystal

    NASA Astrophysics Data System (ADS)

    Sandu, V.; Gyawali, P.; Katuwal, T.; Almasan, C. C.; Taylor, B. J.; Maple, M. B.

    2009-03-01

    We report a strong dependence of the angular magnetoresistance (AMR) on the current density in Y Ba2Cu3O7-δ single crystal above the critical temperature Tc = 13 K for any applied field up to 14 T. We estimated the current dependence from the angular dependence of the top resistance Rtop, as measured on the face where the current is applied, and the bottom resistance Rbot as measured on the opposite face. At any temperature, both below and above Tc, Rtop decreases as the field becomes parallel to the current and ab-plane with an angle dependence that suggests an important contribution arising from the vortex flow. Rbot evolves from a monotonic to nonmonotonic angle dependence with three minima and two maxima in the angle range 0 — 180° as the temperature increases. For less Pr-doped samples, Y0.58Pr0.42Ba2Cu3O7-δ (Tc = 39 K) and Y0.68rP0.32Ba2Cu3O7-δ (Tc = 55 K), where the interplane resistivity is much lower, both Rtop and Rbot follow the same monotonic angle dependence in all temperature and field range.

  10. Enhanced critical currents in (Gd,Y)Ba2Cu3Ox superconducting tapes with high levels of Zr addition

    SciTech Connect

    Selvamanickam, V; Chen, Y; Shi, T; Liu, Y; Khatri, ND; Liu, J; Yao, Y; Xiong, X; Lei, C; Soloveichik, S; Galstyan, E; Majkic, G

    2013-01-21

    The critical current and structural properties of (Gd,Y)BaCuO tapes made by metal organic chemical vapor deposition (MOCVD) with Zr addition levels up to 30 at.% have been investigated. The reduction in critical current beyond the previously optimized Zr addition level of 7.5 at.% was found to be due to structural deterioration of the (Gd,Y)Ba2Cu3Ox film. By a modified MOCVD process,enhanced critical current densities have been achieved with high levels of Zr addition,including 3.83 MA cm(-2) in 15 at.% Zr- added 1.1 mu m thick film at 77 K in zero magnetic field. Critical currents as high as 1072 A/ 12 mm have been reached in (Gd,Y) BaCuO tapes with 15 at.% Zr addition at 30 K in a field of 3 T applied perpendicular to the tape,corresponding to a pinning force value of 268 GN m(-3). The enhanced critical currents achievable with a high density of nanoscale defects by employing high levels of second- phase additions enable the performance targets needed for the use of HTS tapes in coil applications involving high magnetic fields at temperatures below 50 K to be met.

  11. Enhanced critical currents in (Gd,Y)Ba2Cu3Ox superconducting tapes with high levels of Zr addition

    NASA Astrophysics Data System (ADS)

    Selvamanickam, V.; Chen, Y.; Shi, T.; Liu, Y.; Khatri, N. D.; Liu, J.; Yao, Y.; Xiong, X.; Lei, C.; Soloveichik, S.; Galstyan, E.; Majkic, G.

    2013-03-01

    The critical current and structural properties of (Gd,Y)BaCuO tapes made by metal organic chemical vapor deposition (MOCVD) with Zr addition levels up to 30 at.% have been investigated. The reduction in critical current beyond the previously optimized Zr addition level of 7.5 at.% was found to be due to structural deterioration of the (Gd,Y)Ba2Cu3Ox film. By a modified MOCVD process, enhanced critical current densities have been achieved with high levels of Zr addition, including 3.83 MA cm-2 in 15 at.% Zr-added 1.1 μm thick film at 77 K in zero magnetic field. Critical currents as high as 1072 A/12 mm have been reached in (Gd,Y)BaCuO tapes with 15 at.% Zr addition at 30 K in a field of 3 T applied perpendicular to the tape, corresponding to a pinning force value of 268 GN m-3. The enhanced critical currents achievable with a high density of nanoscale defects by employing high levels of second-phase additions enable the performance targets needed for the use of HTS tapes in coil applications involving high magnetic fields at temperatures below 50 K to be met.

  12. Synthesis, structure and superconducting properties of metastable Y(Ba/2-x/Y/x/)Cu3O(7+delta)

    NASA Astrophysics Data System (ADS)

    Iqbal, Z.; Reidinger, F.; Bose, A.; Cipollini, N.; Taylor, T. J.

    1988-01-01

    The synthesis and characterization of a majority (90-95 percent) phase Y1.5Ba1.5Cu3O(7+delta), referred to for historical reasons as Y 3-3-6, prepared by firing an atomically mixed citrate precursor between 810 and 825 C for 2 hrs, are reported. X-ray and powder diffraction data indicate that the Y 3-3-6 is isostructural with its La analog La1.5Ba1.5Cu3O(7+delta). Electron microprobe and thermogravimetry data yield a unit-cell composition Y(Ba/2-x/Y/x/)Cu3O(7+delta), with x = 0.50 and delta = 0.10-0.15 for the parent compound. Specimens of Y 3-3-6 with x = 0.50 and 0.375, which were annealed in O2 at 1 atm and at above 3 atm, displayed semiconducting behavior. Filamentary superconductivity, detected electrically and magnetically, with transition onsets at 80 and 60 K respectively, is observed in specimens annealed in 3 atm O2 at 520 C.

  13. Characteristics of Cu stabilized Nb3Al strands with low Cu ratio

    SciTech Connect

    Kikuchi, A.; Yamada, R.; Barzi, E.; Kobayashi, M.; Lamm, M.; Nakagawa, K.; Sasaki, K.; Takeuchi, T.; Turrioni, D.; Zlobin, A.V.; /NIMC, Tsukuba /Fermilab /Hitachi, Tsuchiura Works /KEK, Tsukuba

    2008-12-01

    Characteristics of recently developed F4-Nb{sub 3}Al strand with low Cu ratio are described. The overall J{sub c} of the Nb{sub 3}Al strand could be easily increased by decreasing of the Cu ratio. Although the quench of a pulse-like voltage generation is usually observed in superconducting unstable conductor, the F4 strand with a low Cu ratio of 0.61 exhibited an ordinary critical transition of gradual voltage generation. The F4 strand does not have magnetic instabilities at 4.2 K because of the tantalum interfilament matrix. The overall J{sub c} of the F4 strand achieved was 80-85% of the RRP strand. In the large mechanical stress above 100 MPa, the overall J{sub c} of the F4 strand might be comparable to that of high J{sub c} RRP-Nb{sub 3}Sn strands. The Rutherford cable with a high packing factor of 86.5% has been fabricated using F4 strands. The small racetrack magnet, SR07, was also fabricated by a 14 m F4 cable. The quench current, I{sub q}, of SR07 were obtained 22.4 kA at 4.5 K and 25.2 kA at 2.2 K. The tantalum matrix Nb{sub 3}Al strands are promising for the application of super-cooled high-field magnets as well as 4.2 K operation magnets.

  14. Electrical conductivity studies on CuBr containing Al2O3 particles

    NASA Technical Reports Server (NTRS)

    Dubec, P. M.; Wagner, J. B., Jr.

    1984-01-01

    The conductivity of CuBr was studied and the role of a second phase, Al2O3, dispersed in CuBr was tested. CuBr melts at 493 C and exhibits three phases in the solid state. CuBr is a good ionic conductor with a transport number for copper ions of virtually unity with weighed proportions of the appropriate chemicals used. The CuBr materials were heated above melting point of CuBr, and the samples were sandwiched between copper electrodes. The ac conductivity, was determined at 1 kHz between 25 and 440 C depending on the sample. It was shown that at low temperatures, the conductivity for CuBr (Al2O3) increased by as much as 100, whereas in the beta phase the conductivity of CuBr containing Al2O3 decreased. The electrical conductivity studies are in agreement with earlier data.

  15. Strengthening mechanism of super-hard nanoscale Cu/Al multilayers with negative enthalpy of mixing

    NASA Astrophysics Data System (ADS)

    Zhou, Q.; Li, S.; Huang, P.; Xu, K. W.; Wang, F.; Lu, T. J.

    2016-09-01

    We present unusual high hardness (up to 7.7 GPa) achieved in Cu/Al multilayers relative to monolithic Cu and Al films (˜2 GPa and ˜1 GPa, respectively). Nanotwins and stacking faults (SFs) were proposed to be the main contributors of hardness enhancement, especially when h < 5 nm. Using molecular dynamics simulations of deposition, we demonstrated that intermixing near Cu/Al interface was paramount in stabilizing the SFs in both Cu and Al layers. Our experimental results indicated that the high strength caused by layer intermixing was in sharp contrast to the general belief that only sharp interface structures could strengthen the multilayers.

  16. A simple method for the normal pressure synthesis of Cu 1- xTl xBa 2Ca 3Cu 4O 12- δ superconductor

    NASA Astrophysics Data System (ADS)

    Khan, Nawazish A.; Khurram, A. A.; Javed, Asim

    2005-05-01

    A very simple method for the direct synthesis of Cu 1- xTl xBa 2Ca 3Cu 4O 12- δ (Cu 1- xTl x-1234) superconductor is reported. A predominant single phase Cu 1- xTl x-1234 is achieved by the solid state reaction of Ba(NO 3) 2, CaCO 3 and Cu(CN) at first stage and with appropriate amount of Tl 2O 3 at the second stage. These materials were fired twice for 24 h at 880 °C followed by intermediate grinding. Thoroughly ground and fired material was mixed with Tl 2O 3 in appropriate amount and pellets were made by applying a pressure of 5 tons. Pellets were wrapped in an aluminum foil and sintered at 880 °C for 3-30 min. A predominantly single phase of Cu 1- xTl xBa 2Ca 3Cu 4O 12- δ was achieved with an inclusion of unknown impurity. The resistivity measurements established the onset temperature of superconductivity [ Tc (onset)] at 120 K and zero resistivity critical temperature [ Tc( R = 0)] at 106 K. Bulk superconductivity was also confirmed by ac-magnetic susceptibility measurements. The surface of the samples was analyzed by electron microscopy and their composition by energy dispersive X-ray spectroscopy (EDX) measurements. For optimizing the carriers in the final compound, post-annealing experiments were carried out in the flowing nitrogen atmosphere. For the study of the doping mechanisms, in the post-annealed samples, the phonon modes of Cu 1- xTl x-1234 were investigated by infrared absorption measurements. The absorption mode of O δ [O3] atoms decreased in intensity after the post-annealing and the apical oxygen modes were softened to lower wave numbers. The softening of these phonon modes suggested the reduction of thallium from Tl 3+ to Tl 1+; which resulted in an increase of [ Tc( R = 0)] of the material.

  17. Photoelectric phenomena in the Cu (Al, In)/p-CuIn{sub 3}Se{sub 5} Schottky barriers

    SciTech Connect

    Bodnar', I. V. Rud, V. Yu. Rud', Yu. V.

    2007-01-15

    Structures are formed on the p-CuIn{sub 3}Se{sub 5} crystals and photoelectric phenomena in the Cu/p-CuIn{sub 3}Se{sub 5}, Al/p-CuIn{sub 3}Se{sub 5}, and In/p-CuIn{sub 3}Se{sub 5} Schottky barriers are studied. The spectra of quantum efficiency for photoconversion in new structures were obtained for the first time. The characteristics of the interband transitions are discussed, and the CuIn{sub 3}Se{sub 5} band gap is determined. It is concluded that CuIn{sub 3}Se{sub 5} crystals can be used in the fabrication of high-efficiency broadband photoconverters of optical radiation.

  18. Influence of Al/CuO reactive multilayer films additives on exploding foil initiator

    SciTech Connect

    Zhou Xiang; Shen Ruiqi; Ye Yinghua; Zhu Peng; Hu Yan; Wu Lizhi

    2011-11-01

    An investigation on the influence of Al/CuO reactive multilayer films (RMFs) additives on exploding foil initiator was performed in this paper. Cu film and Cu/Al/CuO RMFs were produced by using standard microsystem technology and RF magnetron sputtering technology, respectively. Scanning electron microscopy characterization revealed the distinct layer structure of the as-deposited Al/CuO RMFs. Differential scanning calorimetry was employed to ascertain the amount of heat released in the thermite reaction between Al films and CuO films, which was found to be 2024 J/g. Electrical explosion tests showed that 600 V was the most matching voltage for our set of apparatus. The explosion process of two types of films was observed by high speed camera and revealed that compared with Cu film, an extra distinct combustion phenomenon was detected with large numbers of product particles fiercely ejected to a distance of about six millimeters for Cu/Al/CuO RMFs. By using the atomic emission spectroscopy double line technique, the reaction temperature was determined to be about 6000-7000 K and 8000-9000 K for Cu film and Cu/Al/CuO RMFs, respectively. The piezoelectricity of polyvinylidene fluoride film was employed to measure the average velocity of the slapper accelerated by the explosion of the films. The average velocities of the slappers were calculated to be 381 m/s and 326 m/s for Cu film and Cu/Al/CuO RMFs, respectively, and some probable reasons were discussed with a few suggestions put forward for further work.

  19. Crystal growth of YBa2Cu3O(7-x) and reaction of gold crucible with Ba-Cu-rich flux

    NASA Technical Reports Server (NTRS)

    Tao, Y. K.; Chen, H. C.; Martini, L.; Bechtold, J.; Huang, Z. J.; Hor, P. H.

    1991-01-01

    YBa2Cu3O(7-x) crystals are grown in a gold crucible by a self-flux method. The flux moves along the gold surface due to surface wetting and leaves Y123 crystals behind. The obtained crystals are clean and have a size up to two millimeters and a Tc is greater than 90 K. In an effort to recycle the used crucibles, it is found that the used gold is contaminated by copper. A CuO thin film is easily formed on the surface of the crucible that is made of the used gold. This film provides good surface wetting and a buffer layer, which reduces the reaction between gold and the Y-Ba-Cu-oxide melt.

  20. Anomalous shifts of oxygen-mode frequencies in La sub 2 minus x Sr sub x CuO sub 4 , YBa sub 2 Cu sub 3 O sub 7 minus. delta. and Tl sub 2 Ba sub 2 Ca sub 1 minus x Gd sub x Cu sub 2 O sub 8

    SciTech Connect

    Mihailovic, D. J. Stefan Institute, Jamova 39, Ljubljana, ); Foster, C.M.; Voss, K.F. ); Mertelj, T.; Poberaj, I. ); Herron, N. )

    1991-07-01

    Comparison of photoinduced local modes (PILM's) of insulating YBa{sub 2}Cu{sub 3}O{sub 6.3} and Tl{sub 2}Ba{sub 2}Ca{sub 1{minus}{ital x}}Gd{sub {ital x}}Cu{sub 2}O{sub 8} with Raman spectra of their metallic counterparts suggests that carrier injection anomalously increases the frequencies of phonons involving {ital z}-axis apex-oxygen motion in both the dilute (insulator) and concentrated (metallic) limit. In La{sub 2}CuO{sub 4}, we observe PILM's whose frequencies suggest a correspondence with the ghost modes'' observed in neutron scattering (Rietschel {ital et} {ital al}., Physica C 162--164, 1705 (1989)). These data, together with Raman data on apex-oxygen anharmonicity, enable us to discuss the vibronic mode couplings involved in polaron formation in the three materials.

  1. Concentric nano rings observed on Al-Cu-Fe microspheres

    NASA Astrophysics Data System (ADS)

    Li, Chunfei; Wang, Limin; Hampikian, Helen; Bair, Matthew; Baker, Andrew; Hua, Mingjian; Wang, Qiongshu; Li, Dingqiang

    2016-05-01

    It is well known that when particle size is reduced, surface effect becomes important. As a result, micro/nanoparticles tend to have well defined geometric shapes to reduce total surface energy, as opposed to the irregular shapes observed in most bulk materials. The surface of such micro/nanostructures are smooth. Any deviation from a smooth surface implies an increased surface energy which is not energetically favorable. Here, we report an observation of spherical particles in an alloy of Al65Cu20Fe15 nominal composition prepared by arc melting. Such spherical particles stand out from those reported so far due to the decoration of concentric nanorings on the surface. Three models for the formation of these concentric ring patterns are suggested. The most prominent ones assume that the rings are frozen features of liquid motion which could open the door to investigate the kinetics of liquid motion on the micro/nanometer scale.

  2. Microstructure Evolution in Al-Cu-Fe Quasicrystalline Thin Films

    NASA Astrophysics Data System (ADS)

    Widjaja, Edy; Marks, Laurence

    2003-03-01

    Transmission Electron Microscopy (TEM) was performed to study the microstructure evolution in Al-Cu-Fe quasicrystalline thin films. Thin films were grown by magnetron sputtering on sodium chloride crystals which were subsequently dissolved in water to acquire free-standing films. Nanocrystalline films were found in the as-deposited sample. When annealed at 400oC the films changed to metastable crystalline phases that transformed into icosahedral phases upon further annealing at 500oC. TEM imaging combined with electron diffraction revealed various features associated with the phase evolution in the crystalline-quasicrystalline phase transformation. Some grains in the film functioned as sacrificial grains allowing others to grow into icosahedral phases. Elements near the boundary of the sacrificial grains diffused to form the icosahedral phases, resulting in fragments in the center of the grain. The oxide layer of the film was amorphous aluminum oxide that exhibited poor adhesion to the quasicrystalline films.

  3. Refractive index of the CuAlO2 delafossite

    NASA Astrophysics Data System (ADS)

    Pellicer-Porres, J.; Segura, A.; Kim, D.

    2009-01-01

    The refractive index of the CuAlO2 delafossite has been determined from interference measurements in single crystals performed in the visible, near and mid infrared regions of the spectrum. The analysis of the refractive index dispersion corresponding to light polarization perpendicular to the c-axis (P ⊥ c) yields a static dielectric constant of epsilon0 = 7.7 ± 0.8 and a low frequency electronic constant epsilon∞ = 5.1 ± 0.1. The relevant infrared active E^{\\uparrow}_u(\\rm TO) mode is found to be at 550 ± 25 cm-1. The electronic contribution can be well described by a Penn gap at 39 000 ± 1000 cm-1. Both the refractive index and its dispersion are found to be smaller for P||c than for P ⊥ c.

  4. Temperature effect on ideal shear strength of Al and Cu

    NASA Astrophysics Data System (ADS)

    Iskandarov, Albert M.; Dmitriev, Sergey V.; Umeno, Yoshitaka

    2011-12-01

    According to Frenkel’s estimation, at critical shear stress τc=G/2π, where G is the shear modulus, plastic deformation or fracture is initiated even in defect-free materials. In the past few decades it was realized that, if material strength is probed at the nanometer scale, it can be close to the theoretical limit, τc. The weakening effect of the free surface and other factors has been discussed in the literature, but the effect of temperature on the ideal strength of metals has not been addressed thus far. In the present study, we perform molecular dynamics simulations to estimate the temperature effect on the ideal shear strength of two fcc metals, Al and Cu. Shear parallel to the close-packed (111) plane along the [112¯] direction is studied at temperatures up to 800 K using embedded atom method potentials. At room temperature, the ideal shear strength of Al (Cu) is reduced by 25% (22%) compared to its value at 0 K. For both metals, the shear modulus, G, and the critical shear stress at which the stacking fault is formed, τc, decrease almost linearly with increasing temperature. The ratio G/τc linearly increases with increasing temperature, meaning that τc decreases with temperature faster than G. Critical shear strain, γc, also decreases with temperature, but in a nonlinear fashion. The combination of parameters, Gγc/τc, introduced by Ogata as a generalization of Frenkel’s formula, was found to be almost independent of temperature. We also discuss the simulation cell size effect and compare our results with the results of abinitio calculations and experimental data.

  5. Theoretical and experimental studies on wide-band-gap p-type conductive BaCuSeF and related compounds

    NASA Astrophysics Data System (ADS)

    Sakakima, Hiroshi; Nishitani, Mikihiko; Yamamoto, Koichi; Wada, Takahiro

    2015-08-01

    BaCuSeF and related compounds, MCuQF (M = Ba, Sr; Q = Se, S), are known to show p-type conduction. The formation energies of the Cu vacancy ΔH[VCu] in a MCuQF system were computed by first-principles calculation with a generalized gradient approximation (GGA) of the Perdew-Burke-Ernzerhof (PBE) functional as an electron exchange and correlation functional. The density of states (DOS) of BaCuSeF was calculated with the hybrid functional of Heyd-Scuseria-Ernzerhof (HSE) 06. ΔH[VCu] was found to be very small under both the Cu- and Q-rich conditions, which probably contributes to p-type conduction. The electronic structure of BaCuSeF was studied by X-ray photoelectron spectroscopy (XPS) with UV photoelectron yield spectroscopy (UVPYS) and photoemission yield spectroscopy (PYS). The determined depth of the top of the valence band relative to the vacuum level was about 4.9 eV. This value is desirable for applications in compound semiconductor thin-film tandem solar cells since the absorbers of polycrystalline thin-film solar cells, such as CdTe and Cu(In,Ga)Se2, are p-type semiconductors. The DOS of BaCuSeF calculated with the HSE06 functional was almost consistent with the XPS spectrum.

  6. LPE growth of AlN from Cu-Al-Ti solution under nitrogen atmosphere

    NASA Astrophysics Data System (ADS)

    Kamei, K.; Inoue, S.; Shirai, Y.; Tanaka, T.; Okada, N.; Yauchi, A.

    2006-05-01

    Synthesis of single crystalline AlN has long been the subjects of intensive studies since it has exceptional properties suitable for the substrate materials for optoelectronic and electronic devices. The solution growth technique has some advantages over the sublimation growth technique. Its growth temperature is generally much lower than that of the sublimation growth. The obtained crystal is believed to show superior crystallinity since it is grown under nearly equilibrium condition. In the present study we have developed a new solution growth technique using Cu and Ti as solvents under atmospheric pressure of nitrogen. By using this solution, we have grown AlN single crystalline layer on 6H-SiC substrate at relatively low growth temperatures such as 1600-1800 °C. The thickness of the grown layer was larger than 30 μm. TEM observation revealed the fairly low dislocation density such as 105/cm2 in the obtained AlN layers.

  7. Band structure, Fermi surface, elastic, thermodynamic, and optical properties of AlZr 3 , AlCu 3 , and AlCu 2 Zr: First-principles study

    NASA Astrophysics Data System (ADS)

    Parvin, R.; Parvin, F.; Ali, M. S.; Islam, A. K. M. A.

    2016-08-01

    The electronic properties (Fermi surface, band structure, and density of states (DOS)) of Al-based alloys AlM 3 (M = Zr and Cu) and AlCu2Zr are investigated using the first-principles pseudopotential plane wave method within the generalized gradient approximation (GGA). The structural parameters and elastic constants are evaluated and compared with other available data. Also, the pressure dependences of mechanical properties of the compounds are studied. The temperature dependence of adiabatic bulk modulus, Debye temperature, specific heat, thermal expansion coefficient, entropy, and internal energy are all obtained for the first time through quasi-harmonic Debye model with phononic effects for T = 0 K-100 K. The parameters of optical properties (dielectric functions, refractive index, extinction coefficient, absorption spectrum, conductivity, energy-loss spectrum, and reflectivity) of the compounds are calculated and discussed for the first time. The reflectivities of the materials are quite high in the IR-visible-UV region up to ˜ 15 eV, showing that they promise to be good coating materials to avoid solar heating. Some of the properties are also compared with those of the Al-based Ni3Al compound.

  8. Band structure, Fermi surface, elastic, thermodynamic, and optical properties of AlZr 3 , AlCu 3 , and AlCu 2 Zr: First-principles study

    NASA Astrophysics Data System (ADS)

    Parvin, R.; Parvin, F.; Ali, M. S.; Islam, A. K. M. A.

    2016-08-01

    The electronic properties (Fermi surface, band structure, and density of states (DOS)) of Al-based alloys AlM 3 (M = Zr and Cu) and AlCu2Zr are investigated using the first-principles pseudopotential plane wave method within the generalized gradient approximation (GGA). The structural parameters and elastic constants are evaluated and compared with other available data. Also, the pressure dependences of mechanical properties of the compounds are studied. The temperature dependence of adiabatic bulk modulus, Debye temperature, specific heat, thermal expansion coefficient, entropy, and internal energy are all obtained for the first time through quasi-harmonic Debye model with phononic effects for T = 0 K–100 K. The parameters of optical properties (dielectric functions, refractive index, extinction coefficient, absorption spectrum, conductivity, energy-loss spectrum, and reflectivity) of the compounds are calculated and discussed for the first time. The reflectivities of the materials are quite high in the IR–visible–UV region up to ∼ 15 eV, showing that they promise to be good coating materials to avoid solar heating. Some of the properties are also compared with those of the Al-based Ni3Al compound.

  9. Effect of Alternative Insulation Materials on Quench Propagation in ReBa2Cu3O7-delta Coils

    NASA Astrophysics Data System (ADS)

    Phillips, Makita R.

    ReBa2Cu3Odelta-7 (REBCO) coils have the potential to impact a variety of magnet applications but due to slow normal zone propagation velocity (NZPV), quench detection and protection remain difficult. It is therefore important to understand how quench behavior is affected by various aspects of coil design, geometric considerations and material properties. Although past studies have explored the effects of varying the conductor properties, it is important to investigate the influence of insulation as well. In this study, the effect of insulation properties on three-dimensional (3D) quench propagation in REBCO-based coils is investigated. At present, superconducting magnets primarily use insulators that are electrically and thermally insulating; typically Kapton. Here the impact of electrically insulating, thermally conducting insulators on quench behavior was studied. In particular, the behavior of a Kapton insulated coil was compared to doped-TiO2 and ideal Al2O3 insulated coils. A non-insulated coil was also evaluated. Using a mixed-dimensional model the effect of various insulation materials on multiple quench parameters in REBCO coated conductor coils was studied. The comparison of the usage alternative insulation was conducted for a 20 mum and 100 mum case using three models: Concept Model 1, 2 and 3. Concept model 1 studied the effects on 3D propagation behavior, including the 3D current sharing volume (CSV) and key quench parameters, including minimum quench energy, hotspot temperature and NZPV. Concept model 2 (CM 2) cooled a room temperature coil configuration from room temperature to 50 K for a 15 min duration. The radial and hoop stresses were observed at the cleavage edge, middle height and along the conductor width in the central conductor. Concept model 3 (CM 3) determined the thermal stresses based upon the thermal development of CM 1 during a quench. Concept model 1 found that ideal Al2O3 insulation resulted in the highest MQE, lowest peak temperature

  10. Mechanical properties of Al-Cu alloy-SiC composites

    SciTech Connect

    Anggara, B. S.; Handoko, E.; Soegijono, B.

    2014-09-25

    The synthesis of aluminum (Al) alloys, Al-Cu, from mixture 96.2 % Al and 3.8 % Cu has been prepared by melting process at a temperature of 1200°C. The adding 12.5 wt% up to 20 wt% of SiC on Al-Cu alloys samples has been investigated. The structure analyses were examined by X-Ray Diffractometer (XRD) and scanning electron microscope (SEM). Moreover, the morphology of Al-Cu alloys has been seen as structure in micrometer range. The hardness was measured by hardness Vickers method. According to the results, it can be assumed that the 15 wt% of SiC content is prefer content to get better quality of back to back hardness Vickers of Al-Cu alloys.

  11. Optoelectronic properties of novel amorphous CuAlO2/ZnO NWs based heterojunction

    NASA Astrophysics Data System (ADS)

    Bu, Ian Y. Y.

    2013-08-01

    Amorphous p-type CuAlO2 thin films were grown onto n-type crystalline ZnO NWs forming a heterojunction through the combination of sol-gel process and hydrothermal growth method. The effects of temperature on structure and optoelectronic properties of CuAlO2 thin films were investigated through various measurement techniques. It was found that the derived CuAlO2 is Al-rich with thin film. UV-Vis measurements showed that the deposited CuAlO2 films are semi-transparent with maximum transmittance ∼82% at 500 nm. Electrical characterization and integration into pn junction confirms that the amorphous CuAlO2 is p-type and exhibited photovoltaic behavior.

  12. Improvement of critical current density in thallium-based (Tl,Bi)Sr(1.6)Ba(0.4)Ca2Cu3O(x) superconductors

    NASA Technical Reports Server (NTRS)

    Ren, Z. F.; Wang, C. A.; Wang, J. H.; Miller, D. J.; Goretta, K. C.

    1995-01-01

    Epitaxial (Tl,Bi)Sr(1.6)Ba(0.4)Ca2Cu3O(x) ((Tl,Bi)-1223) thin films on (100) single crystal LaAlO3 substrates were synthesized by a two-step procedure. Phase development, microstructure, and relationships between film and substrate were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Resistance versus temperature, zero-field-cooled and field cooled magnetization, and transport critical current density (J(sub c)) were measured. The zero-resistance temperature was 105-111 K. J(sub c) at 77 K and zero field was greater than 2 x 10(exp 6) A/sq cm. The films exhibited good flux pinning properties.

  13. μSR study of charge neutrally doped RE1-2xCaxPrxBa2Cu3O7-δ (RE=Y,Nd)

    NASA Astrophysics Data System (ADS)

    Lundqvist, P.; Hartmann, O.; Karlsson, E.; Wäppling, R.; Hegedüs, Z.; Rapp, Ö.

    1996-02-01

    Pr substitution in the 123 superconductors lowers the critical temperature, Tc, drastically. Equal amounts of Ca and Pr were doped into the RE1-2xCaxPrxBa2Cu3O7-δ superconductors (RE=Y, x≤0.2 and Nd, x≤0.1) to isolate the linear term in this depression, often assigned to magnetic pair breaking. Uemura et al found a universal linear relation between Tc and the muon spin relaxation rate δ in high Tc cuprate superconductors with a saturation close to the maximum Tc. Our results indicate a faster decrease of Tc with decreasing δ in the saturaton regime than for Pr doping only and this rate is in turn faster than in oxygen doped 123, indicating multiple effects in the depression of Tc with Pr doping only.

  14. Optimization of the deposition conditions and structural characterization of Y1Ba2Cu3O(7-x) thin superconducting films

    NASA Technical Reports Server (NTRS)

    Chrzanowski, J.; Meng-Burany, S.; Xing, W. B.; Curzon, A. E.; Heinrich, B.; Irwin, J. C.; Cragg, R. A.; Zhou, H.; Habib, F.; Angus, V.

    1995-01-01

    Two series of Y1Ba2Cu3O(z) thin films deposited on (001) LaAl03 single crystals by excimer laser ablation under two different protocols have been investigated. The research has yielded well defined deposition conditions in terms of oxygen partial pressure p(O2) and substrate temperature of the deposition process Th, for the growth of high quality epitaxial films of YBCO. The films grown under conditions close to optimal for both j(sub c) and T(sub c) exhibited T(sub c) greater than or equal to 91 K and j(sub c) greater than or equal to 4 x 106 A/sq cm, at 77 K. Close correlations between the structural quality of the film, the growth parameters (p(O2), T(sub h)) and j(sub c) and T(sub c) have been found.

  15. Optimization of the deposition conditions and structural characterization of Y1Ba2Cu3O(7-x) thin superconducting films

    SciTech Connect

    Chrzanowski, J.; Meng-Burany, S.; Xing, W.B.; Curzon, A.E.; Heinrich, B.; Irwin, J.C.; Cragg, R.A.; Zhou, H.; Habib, F.; Angus, V.

    1995-04-01

    Two series of Y1Ba2Cu3O(z) thin films deposited on (001) LaAl03 single crystals by excimer laser ablation under two different protocols have been investigated. The research has yielded well defined deposition conditions in terms of oxygen partial pressure p(O2) and substrate temperature of the deposition process Th, for the growth of high quality epitaxial films of YBCO. The films grown under conditions close to optimal for both J{sub c} and T{sub c} exhibited T{sub c} greater than or equal to 91 K and J{sub c} greater than or equal to 4 x 10{sup 6} A/sq cm, at 77 K. Close correlations between the structural quality of the film, the growth parameters (p(O2), T{sub h}) and J{sub c} and T{sub c} have been found.

  16. Crystallization behavior and properties of BaO-Al2O3-2SiO2 glass matrices

    NASA Technical Reports Server (NTRS)

    Drummond, Charles H., III; Bansal, Narottam P.

    1990-01-01

    Glass of stoichiometric celsian composition, BaO-Al2O3-2SiO2, is a potential glass-ceramic matrix for high-temperature composites. The glass has a density of 3.39 g/cu cm, thermal expansion coefficient of 6.6 x 10(exp -6)/deg C glass transition temperature of 910 C, and dilatometric softening point of 925 C. On heat treatment, only hexacelsian crystallized out on the surface, but both celsian and hexacelsian were present in the bulk. Effects of cold isostatic pressing (CIP), sintering, and hot pressing, in the presence and absence of an additive, on the formation of the celsian phase in the glass were studied. CIP'ed samples, after appropriate heat treatments, always crystallized out as celsian whereas the presence of 5 to 10 weight percent of an additive was necessary for formation of celsian in sintered as well as hot pressed specimens. Green density increased with CIP'ing pressure but had no effect on sintered density. Hot pressing resulted in fully dense samples.

  17. Chemical trend of superconducting transition temperature in hole-doped delafossite of CuAlO2, AgAlO2 and AuAlO2

    NASA Astrophysics Data System (ADS)

    Nakanishi, Akitaka; Katayama-Yoshida, Hiroshi

    2012-12-01

    We have performed the first-principles calculations about the superconducting transition temperature Tc of hole-doped delafossite CuAlO2, AgAlO2 and AuAlO2. Calculated Tc are about 50 K (CuAlO2), 40 K (AgAlO2) and 3 K(AuAlO2) at maximum in the optimum hole-doping concentration. The low Tc of AuAlO2 is attributed to the weak electron-phonon interaction caused by the low covalency and heavy atomic mass.

  18. Characterization of the insulator barrier and the superconducting transition temperature in GdBa{sub 2}Cu{sub 3}O{sub 7−δ}/BaTiO{sub 3} bilayers for application in tunnel junctions

    SciTech Connect

    Navarro, H. Sirena, M.; Haberkorn, N.; Yang, Ilkyu; Kim, Jeehoon

    2015-07-28

    The optimization of the superconducting properties in a bottom electrode and the quality of an insulator barrier are the first steps in the development of superconductor/insulator/superconductor tunnel junctions. Here, we study the quality of a BaTiO{sub 3} tunnel barrier deposited on a 16 nm thick GdBa{sub 2}Cu{sub 3}O{sub 7−δ} thin film by using conductive atomic force microscopy. We find that the tunnel current is systematically reduced (for equal applied voltage) by increasing the BaTiO{sub 3} barrier thickness between 1.6 and 4 nm. The BaTiO{sub 3} layers present an energy barrier of ≈1.2 eV and an attenuation length of 0.35–0.5 nm (depending on the applied voltage). The GdBa{sub 2}Cu{sub 3}O{sub 7−δ} electrode is totally covered by a BaTiO{sub 3} thickness above 3 nm. The presence of ferroelectricity was verified by piezoresponse force microscopy for a 4 nm thick BaTiO{sub 3} top layer. The superconducting transition temperature of the bilayers is systematically suppressed by increasing the BaTiO{sub 3} thickness. This fact can be associated with stress at the interface and a reduction of the orthorhombicity of the GdBa{sub 2}Cu{sub 3}O{sub 7−δ}. The reduction in the orthorhombicity is expected by considering the interface mismatch and it can also be affected by reduced oxygen stoichiometry (poor oxygen diffusion across the BaTiO{sub 3} barrier)

  19. Preparation, photoluminescent properties and luminescent dynamics of BaAlF{sub 5}:Eu{sup 2+} nanophosphors

    SciTech Connect

    Zhang, Wei; Hua, Ruinian; Liu, Tianqing; Zhao, Jun; Na, Liyan; Chen, Baojiu

    2014-12-15

    Graphical abstract: Rice-shaped BaAlF{sub 5}:Eu{sup 2+} nanophosphors were synthesized via one-pot hydrothermal process. The as-prepared BaAlF{sub 5}:Eu{sup 2+} are composed of many particles with an average diameter of 40 nm. When excited at 260 nm, the sharp line emission located at 361 nm of Eu{sup 2+} was observed. The optimum doping concentration of Eu{sup 2+} was confirmed to be 5 mol%. The strong ultraviolet emission of Eu{sup 2+} ions in BaAlF{sub 5}:Eu{sup 2+} nanoparticles suggests that these nanoparticles may have potential applications for sensing, solid-state lasers and spectrometer calibration. - Highlights: • BaAlF{sub 5}:Eu{sup 2+} nanophosphors were synthesized via a mild hydrothermal process. • The Van and Huang models were used to research the mechanism of concentration quenching. • The optimum doping concentration of Eu2+ was confirmed to be 5 mol%. - Abstract: Eu{sup 2+}-doped BaAlF{sub 5} nanophosphors were synthesized via a facile one-pot hydrothermal method. The final products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. XRD results showed that the prepared samples are single-phase. The FE-SEM and TEM images indicated that the prepared BaAlF{sub 5}:Eu{sup 2+} nanophosphors are composed of many rice-shaped particles with an average diameter of 40 nm. When excited at 260 nm, BaAlF{sub 5}:Eu{sup 2+} nanophosphors exhibit the sharp line emissions of Eu{sup 2+} at room temperature. The optimum doping concentration of Eu{sup 2+} was confirmed to be 5 mol%. The Van and Huang models were used to study the mechanism of concentration quenching and the electric dipole–dipole interaction between Eu{sup 2+} can be deduced to be a dominant for quenching fluorescence in BaAlF{sub 5}:Eu{sup 2+} nanophosphors. The strong ultraviolet emission of Eu{sup 2+} in BaAlF{sub 5}:Eu{sup 2+} nanophosphors suggests that

  20. The clathrate Ba{sub 8}Cu{sub x}Ge{sub 46-x-y}square{sub y}: Phase equilibria and crystal structure

    SciTech Connect

    Melnychenko-Koblyuk, Nataliya; Grytsiv, Andriy; Rogl, Peter; Schmid, Harald; Giester, Gerald

    2009-07-15

    Phase relations at 700 deg. C, 800 deg. C and solidus temperatures have been derived for the clathrate system Ba{sub 8}Cu{sub x}Ge{sub 46-x-y}square{sub y} via X-ray single crystal and powder diffractometry combined with electron probe micro analysis and differential thermal analysis. The ternary clathrate phase derives from binary Ba{sub 8}Ge{sub 43}square{sub 3} and extends up to x=6. Structure investigations define cubic primitive symmetry with the space group type Pm3-barn consistent with a clathrate type I structure throughout the entire homogeneity region 0Ba{sub 8}Cu{sub x}Ge{sub 46-x} exists for x>=5.5. - Graphical Abstract: Cages and atom thermal displacement parameters in clathrate Ba{sub 8}Cu{sub x}Ge{sub 46-x-y}square{sub y} for Ba{sub 8}Cu{sub 2}Ge{sub 42}square{sub 2} and Ba{sub 8}Cu{sub 6}Ge{sub 40}.

  1. Sulfation and Desulfation Behavior of Pt-BaO/MgO-Al2O3 NOx Storage Reduction Catalyst.

    PubMed

    Jeong, Soyeon; Kim, Do Heui

    2016-05-01

    The comparative study between Pt-BaO/Al2O3 and Pt-BaO/MgO-Al2O3 gives the information about the effect of MgO addition to Al2O3 support on the sulfation and desulfation behavior of Pt-BaO/MgO-Al2O3 NOx storage reduction catalyst. The sulfated two samples were analyzed by using element analysis (EA), X-ray diffraction (XRD), H2 temperature programmed reaction (H2 TPRX) and NOx uptake measurement. The amount of sulfur uptake on 2 wt% Pt-20 wt% BaO/Al2O3 and 2 wt% Pt-20 wt% BaO/MgO-Al2O3 are almost identical as 0.45 and 0.40 of S/Ba, respectively, which yields the drastic decrease in NOx uptake for both sulfated samples. However, after desulfa- tion with H2 at 600 degrees C, the residual sulfur amount on MgO-Al2O3 supported catalyst is three times larger than that on Al2O3 supported one, indicating that sulfur species formed on the former are more stable than those on the latter. It is also well corresponding to the H2 TPRX results where the main H2S peak from MgO-Al2O3 supported sample is observed at higher temperature than Al2O3 supported one, resulting in the lower NOx uptake activity of former sample than the latter one. Meanwhile, after desulfation of MgO-Al2O3 supported sample at 700 degrees C and 800 degrees C, the activity is recovered more significantly due to the removal of the large amount of sulfur while Al2O3 supported one decreases monotonically due to the sintering of Pt crystallite and the formation of BaAl2O4 phase. It is summarized that MgO-Al2O3 supported catalyst enhances the thermal stability of the catalyst, however, forms the stable sulfate species, which needs to be improved to develop the more sulfur resistant NSR catalyst system. PMID:27483765

  2. Sulfation and Desulfation Behavior of Pt-BaO/MgO-Al2O3 NOx Storage Reduction Catalyst.

    PubMed

    Jeong, Soyeon; Kim, Do Heui

    2016-05-01

    The comparative study between Pt-BaO/Al2O3 and Pt-BaO/MgO-Al2O3 gives the information about the effect of MgO addition to Al2O3 support on the sulfation and desulfation behavior of Pt-BaO/MgO-Al2O3 NOx storage reduction catalyst. The sulfated two samples were analyzed by using element analysis (EA), X-ray diffraction (XRD), H2 temperature programmed reaction (H2 TPRX) and NOx uptake measurement. The amount of sulfur uptake on 2 wt% Pt-20 wt% BaO/Al2O3 and 2 wt% Pt-20 wt% BaO/MgO-Al2O3 are almost identical as 0.45 and 0.40 of S/Ba, respectively, which yields the drastic decrease in NOx uptake for both sulfated samples. However, after desulfa- tion with H2 at 600 degrees C, the residual sulfur amount on MgO-Al2O3 supported catalyst is three times larger than that on Al2O3 supported one, indicating that sulfur species formed on the former are more stable than those on the latter. It is also well corresponding to the H2 TPRX results where the main H2S peak from MgO-Al2O3 supported sample is observed at higher temperature than Al2O3 supported one, resulting in the lower NOx uptake activity of former sample than the latter one. Meanwhile, after desulfation of MgO-Al2O3 supported sample at 700 degrees C and 800 degrees C, the activity is recovered more significantly due to the removal of the large amount of sulfur while Al2O3 supported one decreases monotonically due to the sintering of Pt crystallite and the formation of BaAl2O4 phase. It is summarized that MgO-Al2O3 supported catalyst enhances the thermal stability of the catalyst, however, forms the stable sulfate species, which needs to be improved to develop the more sulfur resistant NSR catalyst system.

  3. Refinement and growth enhancement of Al2Cu phase during magnetic field assisting directional solidification of hypereutectic Al-Cu alloy

    NASA Astrophysics Data System (ADS)

    Wang, Jiang; Yue, Sheng; Fautrelle, Yves; Lee, Peter D.; Li, Xi; Zhong, Yunbo; Ren, Zhongming

    2016-04-01

    Understanding how the magnetic fields affect the formation of reinforced phase during solidification is crucial to tailor the structure and therefor the performance of metal matrix in situ composites. In this study, a hypereutectic Al-40 wt.%Cu alloy has been directionally solidified under various axial magnetic fields and the morphology of Al2Cu phase was quantified in 3D by means of high resolution synchrotron X-ray tomography. With rising magnetic fields, both increase of Al2Cu phase’s total volume and decrease of each column’s transverse section area were found. These results respectively indicate the growth enhancement and refinement of the primary Al2Cu phase in the magnetic field assisting directional solidification. The thermoelectric magnetic forces (TEMF) causing torque and dislocation multiplication in the faceted primary phases were thought dedicate to respectively the refinement and growth enhancement. To verify this, a real structure based 3D simulation of TEMF in Al2Cu column was carried out, and the dislocations in the Al2Cu phase obtained without and with a 10T high magnetic field were analysed by the transmission electron microscope.

  4. Refinement and growth enhancement of Al2Cu phase during magnetic field assisting directional solidification of hypereutectic Al-Cu alloy.

    PubMed

    Wang, Jiang; Yue, Sheng; Fautrelle, Yves; Lee, Peter D; Li, Xi; Zhong, Yunbo; Ren, Zhongming

    2016-04-19

    Understanding how the magnetic fields affect the formation of reinforced phase during solidification is crucial to tailor the structure and therefor the performance of metal matrix in situ composites. In this study, a hypereutectic Al-40 wt.%Cu alloy has been directionally solidified under various axial magnetic fields and the morphology of Al2Cu phase was quantified in 3D by means of high resolution synchrotron X-ray tomography. With rising magnetic fields, both increase of Al2Cu phase's total volume and decrease of each column's transverse section area were found. These results respectively indicate the growth enhancement and refinement of the primary Al2Cu phase in the magnetic field assisting directional solidification. The thermoelectric magnetic forces (TEMF) causing torque and dislocation multiplication in the faceted primary phases were thought dedicate to respectively the refinement and growth enhancement. To verify this, a real structure based 3D simulation of TEMF in Al2Cu column was carried out, and the dislocations in the Al2Cu phase obtained without and with a 10T high magnetic field were analysed by the transmission electron microscope.

  5. Refinement and growth enhancement of Al2Cu phase during magnetic field assisting directional solidification of hypereutectic Al-Cu alloy.

    PubMed

    Wang, Jiang; Yue, Sheng; Fautrelle, Yves; Lee, Peter D; Li, Xi; Zhong, Yunbo; Ren, Zhongming

    2016-01-01

    Understanding how the magnetic fields affect the formation of reinforced phase during solidification is crucial to tailor the structure and therefor the performance of metal matrix in situ composites. In this study, a hypereutectic Al-40 wt.%Cu alloy has been directionally solidified under various axial magnetic fields and the morphology of Al2Cu phase was quantified in 3D by means of high resolution synchrotron X-ray tomography. With rising magnetic fields, both increase of Al2Cu phase's total volume and decrease of each column's transverse section area were found. These results respectively indicate the growth enhancement and refinement of the primary Al2Cu phase in the magnetic field assisting directional solidification. The thermoelectric magnetic forces (TEMF) causing torque and dislocation multiplication in the faceted primary phases were thought dedicate to respectively the refinement and growth enhancement. To verify this, a real structure based 3D simulation of TEMF in Al2Cu column was carried out, and the dislocations in the Al2Cu phase obtained without and with a 10T high magnetic field were analysed by the transmission electron microscope. PMID:27091383

  6. Refinement and growth enhancement of Al2Cu phase during magnetic field assisting directional solidification of hypereutectic Al-Cu alloy

    PubMed Central

    Wang, Jiang; Yue, Sheng; Fautrelle, Yves; Lee, Peter D.; Li, Xi; Zhong, Yunbo; Ren, Zhongming

    2016-01-01

    Understanding how the magnetic fields affect the formation of reinforced phase during solidification is crucial to tailor the structure and therefor the performance of metal matrix in situ composites. In this study, a hypereutectic Al-40 wt.%Cu alloy has been directionally solidified under various axial magnetic fields and the morphology of Al2Cu phase was quantified in 3D by means of high resolution synchrotron X-ray tomography. With rising magnetic fields, both increase of Al2Cu phase’s total volume and decrease of each column’s transverse section area were found. These results respectively indicate the growth enhancement and refinement of the primary Al2Cu phase in the magnetic field assisting directional solidification. The thermoelectric magnetic forces (TEMF) causing torque and dislocation multiplication in the faceted primary phases were thought dedicate to respectively the refinement and growth enhancement. To verify this, a real structure based 3D simulation of TEMF in Al2Cu column was carried out, and the dislocations in the Al2Cu phase obtained without and with a 10T high magnetic field were analysed by the transmission electron microscope. PMID:27091383

  7. Interconnection between microstructure and microhardness of directionally solidified binary Al-6wt.%Cu and multicomponent Al-6wt.%Cu-8wt.%Si alloys.

    PubMed

    Vasconcelos, Angela J; Kikuchi, Rafael H; Barros, André S; Costa, Thiago A; Dias, Marcelino; Moreira, Antonio L; Silva, Adrina P; Rocha, Otávio L

    2016-05-31

    An experimental study has been carried out to evaluate the microstructural and microhardness evolution on the directionally solidified binary Al-Cu and multicomponent Al-Cu-Si alloys and the influence of Si alloying. For this purpose specimens of Al-6wt.%Cu and Al-6wt.%Cu-8wt.%Si alloys were prepared and directionally solidified under transient conditions of heat extraction. A water-cooled horizontal directional solidification device was applied. A comprehensive characterization is performed including experimental dendrite tip growth rates (VL) and cooling rates (TR) by measuring Vickers microhardness (HV), optical microscopy and scanning electron microscopy with microanalysis performed by energy dispersive spectrometry (SEM-EDS). The results show, for both studied alloys, the increasing of TR and VL reduced the primary dendrite arm spacing (l1) increasing the microhardness. Furthermore, the incorporation of Si in Al-6wt.%Cu alloy to form the Al-6wt.%Cu-8wt.%Si alloy influenced significantly the microstructure and consequently the microhardness but did not affect the primary dendritic growth law. An analysis on the formation of the columnar to equiaxed transition (CET) is also performed and the results show that the occurrence of CET is not sharp, i.e., the CET in both cases occurs in a zone rather than in a parallel plane to the chill wall, where both columnar and equiaxed grains are be able to exist.

  8. Interconnection between microstructure and microhardness of directionally solidified binary Al-6wt.%Cu and multicomponent Al-6wt.%Cu-8wt.%Si alloys.

    PubMed

    Vasconcelos, Angela J; Kikuchi, Rafael H; Barros, André S; Costa, Thiago A; Dias, Marcelino; Moreira, Antonio L; Silva, Adrina P; Rocha, Otávio L

    2016-05-31

    An experimental study has been carried out to evaluate the microstructural and microhardness evolution on the directionally solidified binary Al-Cu and multicomponent Al-Cu-Si alloys and the influence of Si alloying. For this purpose specimens of Al-6wt.%Cu and Al-6wt.%Cu-8wt.%Si alloys were prepared and directionally solidified under transient conditions of heat extraction. A water-cooled horizontal directional solidification device was applied. A comprehensive characterization is performed including experimental dendrite tip growth rates (VL) and cooling rates (TR) by measuring Vickers microhardness (HV), optical microscopy and scanning electron microscopy with microanalysis performed by energy dispersive spectrometry (SEM-EDS). The results show, for both studied alloys, the increasing of TR and VL reduced the primary dendrite arm spacing (l1) increasing the microhardness. Furthermore, the incorporation of Si in Al-6wt.%Cu alloy to form the Al-6wt.%Cu-8wt.%Si alloy influenced significantly the microstructure and consequently the microhardness but did not affect the primary dendritic growth law. An analysis on the formation of the columnar to equiaxed transition (CET) is also performed and the results show that the occurrence of CET is not sharp, i.e., the CET in both cases occurs in a zone rather than in a parallel plane to the chill wall, where both columnar and equiaxed grains are be able to exist. PMID:27254454

  9. High-pressure synthesis, crystal structure and magnetic properties of double perovskite oxide Ba{sub 2}CuOsO{sub 6}

    SciTech Connect

    Feng, Hai L.; Arai, Masao; Matsushita, Yoshitaka; Tsujimoto, Yoshihiro; Yuan, Yahua; Sathish, Clastin I.; He, Jianfeng; Tanaka, Masahiko; Yamaura, Kazunari

    2014-09-15

    A new compositional double perovskite oxide Ba{sub 2}CuOsO{sub 6} was synthesized under high-pressure (6 GPa) and high-temperature (1500 °C) conditions. The polycrystalline Ba{sub 2}CuOsO{sub 6} was characterized by synchrotron X-ray diffraction, thermogravimetric analysis, and magnetic susceptibility, isothermal magnetization, and specific heat measurements. The oxide crystallizes in a double-perovskite structure with an I4/m space group, in which Os(VI) and Cu(II) are ordered in the perovskite B-site. Ba{sub 2}CuOsO{sub 6} is electrically insulating with an activation energy of 0.813(2) eV and shows antiferromagnetic-like characteristics at temperatures of ∼55 K and ∼70 K. The results of the first-principle calculation suggested that the spin–orbit interaction of Os(VI) plays a substantial role in the insulating state. The Jahn–Teller distortion of CuO{sub 6} octahedra influences the magnetic characteristics with regard to possible two-dimensional magnetic correlations. - Graphical abstract: A new compositional double perovskite oxide Ba{sub 2}CuOsO{sub 6} synthesized by a high-pressure (6 GPa) and high-temperature (1500 °C) method. - Highlights: • A new compositional double perovskite oxide Ba{sub 2}CuOsO{sub 6} was synthesized. • Ba{sub 2}CuOsO{sub 6} is electrically insulating and antiferromagnetic below ∼70 K. • The Jahn–Teller distortion of CuO{sub 6} has relevance to possible magnetic anisotropy.

  10. Luminescent Characteristics of Ba(1--x)Al2Si2O8:xTb3+ Green Phosphors.

    PubMed

    Hakeem, D A; Kim, Y; Park, K

    2016-02-01

    Ba(1--x)Al2Si2O8:xTb3+ (0.03 < or = x < or = 0.12) green phosphors are prepared by solution combustion method. The photoluminescence properties of the Ba(1--x)Al2Si2O8:xTb3+ phosphors are studied as a function of Tb3+ concentration. The Ba(1--x)Al2Si2O8:xTb3+ phosphors crystallize in a hexagonal crystal structure. The excitation spectra consist of two broad bands with maxima at 238 nm and 265 nm and several weak peaks in the range of 310-500 nm. Strong emission peaks are observed at 484, 540, 589, and 612 nm due to the (5)D4 --> (7)F6, (5)D4 --> (7)F5, (5)D4 --> (7)F4, and (5)D4 --> (7)F3 tran- sitions of the Tb3+, respectively. The emission peak (540 nm) from the (5)D4 --> (7)F3 transition is dominant, indicating green light emission. Ba(1--x)Al2Si2O8:xTb3+ phosphor shows the strongest green emission intensity. The Ba(1--x)Al2Si2O8:xTb3+ can be considered a promising green phosphor for white LEDs applications. PMID:27433666

  11. Suppression of structural phase transition by Sr substitution in the improper ferroelectric BaAl2O4

    NASA Astrophysics Data System (ADS)

    Mori, Shigeo; Ishii, Yui; Tanaka, Eri; Tsukasaki, Hirofumi; Kawaguchi, Shogo

    2015-10-01

    To clarify lattice fluctuations and precursor phenomena accompanied by structural phase transition in stuffed tridymite compounds, changes in diffuse scattering as a function of temperature in Ba0.6Sr0.4Al2O4 have been carefully investigated by powder X-ray diffraction using synchrotron radiation, electron diffraction and transmission electron microscopy (TEM) experiments. In situ electron diffraction experiments revealed that Ba0.6Sr0.4Al2O4 exhibits lattice fluctuation manifested as a unique honeycomb-shaped diffuse scattering in the wide temperature range between 298 and 100 K. Unlike in the case of BaAl2O4, Ba0.6Sr0.4Al2O4 shows no structural phase transition to the ferroelectric structure with the hexagonal P63 space group in the temperature range. In contrast, it is revealed that the electron beam irradiation to the Ba0.6Sr0.4Al2O4 sample inside the transmission electron microscope induced structural change from the hexagonal P6322 structure to the modulated structure with double periodicity in the three equivalent <110> directions in the low-temperature region. This implies that the total energy difference between these two structures is small. The hexagonal P6322 structure transforms into the modulated one with short correlation length owing to some small external perturbations.

  12. Pressure-Induced Structural Transition and Enhancement of Energy Gap of CuAlO2

    NASA Astrophysics Data System (ADS)

    Nakanishi, Akitaka

    2011-02-01

    By using first-principles calculations, we studied the stable crystal structures and energy gaps of CuAlO2 under high pressure. Our simulation shows that CuAlO2 transforms from a delafossite structure to a leaning delafossite structure. The critical pressure of the transition was determined to be 60 GPa. The energy gap of CuAlO2 increases through the structural transition due to the enhanced covalency of Cu 3d and O 2p states. We found that a chalcopyrite structure does not appear as a stable structure under high pressure.

  13. Infiltration of Saffil alumina fiber with AlCu and AlSi alloys

    SciTech Connect

    Garbellini, O.; Morando, C.; Biloni, H.; Palacio, H. . Inst. de Fisica de Materiales)

    1999-06-18

    Currently there is a considerable scientific and technological interest in the composite materials, which a strong ceramic reinforcement is incorporated into a metal matrix (MMC) to tailor its properties for specific applications. Among the various techniques for fabricating MMC, the liquid metal infiltration process by means of a pressurized gas is an attractive fabrication route for near net shaped metal matrix composite and has been successfully used to fabricate Al, Mg and more recently, Ni and Ni aluminide matrix composites, which can be reinforced by SiC or Al[sub 2]O[sub 3] particles, whiskers, or short fibers. This paper describes the experimental technique used and presents an experimental investigation of the effects of the process parameters employed, such as the preform and melt temperatures, the volume fraction of fibers in the preform and the applied pressure upon the infiltration length of a chopped preform during a unidirectional infiltration aided by gas pressure casting. The experiments of the present work were conducted to provide kinetic data with a view to optimizing the selection of the process initial conditions for infiltration which have an effect on the infiltration length of the molten matrix alloy into a preform and it is a first step in investigating the correlation between the infiltration length (fluidity) of AlCuSi matrix alloys and the microstructure of the composites fabricated by pressure casting. For this purpose, this paper focuses on AlCu and AlSi matrix alloys reinforced by short-fibers [delta]-alumina SAFFIL. The experiments reported here were performed with the fibers initially at a temperature significantly below the metal melting point. This is the case of practical interest for the fabrication of many fiber-reinforced metal components.

  14. Orientation of embedded Y2BaCuO5 particles within the YBa2Cu3Ox matrix in melt-textured YBCO superconductors

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.; Babu, N. Hari; Cardwell, D. A.; Mücklich, F.; Murakami, M.

    2005-03-01

    Automated electron backscatter diffraction (EBSD) was employed to study the local orientations of embedded Y2BaCuO5 (Y-211) particles within the YBa2Cu3Ox (Y-123) superconducting matrix of large grain, melt-textured Y-Ba-Cu-O (YBCO) samples. High-quality Kikuchi patterns were obtained, enabling automated mapping of the individual crystal orientations and a two-phase analysis of the samples. Investigations were performed on a variety of melt-textured YBCO samples, including samples with different element additions. We observe from the maps that the embedded Y-211 particles do not have any preferred orientation in melt-textured YBCO with (001) orientation, and that the YBCO growth is not altered for certain orientations of the Y-211 particles. In samples with (100) orientation, on the other hand, we observe only a small misorientation within the YBCO matrix, and the embedded Y-211 particles do not exhibit any texture. We can conclude from the EBSD maps obtained that the formation of small Y-211 particles does not disturb the Y-123 matrix growth, whereas the presence of large Y-211 particles leads, significantly, to the formation of subgrains.

  15. Effect of oxygen content variation on flux pinning in Nd-Ba-Cu-O top-seeded melt grown superconductor

    NASA Astrophysics Data System (ADS)

    Babu, N. Hari; Kambara, M.; Cardwell, D. A.; Campbell, A. M.

    2002-05-01

    The magnetization of top-seeded melt grown NdBa2Cu3O7-δ (Nd123) containing 15 mol% Nd4Ba2Cu2O10 (Nd422) processed in both air and under 1% O2 in N2 has been investigated over a wide range of temperatures and fields. The sample processed in air exhibits a peak in the Jc(H) data in the temperature range 40-70 K, which is similar to that observed in a sample processed under reduced oxygen partial pressure at nearly the same reduced temperature (T/Tc) range. The appearance and position of the peak in the Jc(H) data are governed strongly by the oxygen content. Magnetization as a function of temperature measured under zero field and field-cooled conditions exhibit similar magnetic transition behaviour, despite the large difference in the Nd/Ba substitution level within these samples. Significantly, the basic features of the magnetization curves remain virtually the same when the oxygen content in the sample is varied. Comparison between NdBCO and YBCO superconductors indicates clearly that the defects associated with oxygen vacancies and/or disorder play an important role in flux pinning in both types of melt grown material. The pinning centres in NdBCO observed in this study are similar to those observed in YBCO.

  16. Fabrication and Evaluation of Mn-Substituted Ba(Cu1/3Nb2/3)O3 Ceramics

    NASA Astrophysics Data System (ADS)

    Kamimura, Y.; Lee, B.-Y.; Yazawa, K.; Funakubo, H.; Iijima, T.; Uchida, H.

    2011-10-01

    Perovskite oxides with higher phase transition temperature receive much attention as promising candidates which possess excellent and stable dielectric properties over wide temperature range. In the present research, dense ceramics of Ba-based perovskite oxides of Ba(Cu1/3Nb2/3)O3 (BCN) were fabricated by powder sintering. Mn-substituted BCN (Mn-BCN) ceramics were also fabricated for improving the insulating property of the BCN ceramics. Mn-BCN ceramics were fabricated by powder sintering using fine precursor powders derived from sol-gel solutions. The chemical composition of the precursors were Ba[(Cu1/3Nb2/3)1-yMny]O3 with Mn content of y = 0-0.05. The cylindrical compacts of the powders were heat-treated at 1200-1350°C for 1-6 h for sintering. All of Mn-BCN ceramics consisted of perovskite-type crystal structure in tetragonal system at room temperature. The relative density of the pure and Mn-BCN ceramics sintered at 1300°C for 1 h were higher than 90%. The densities were degraded by firing at higher temperature and/or for longer time, owing to the thermal decomposition of the BCN crystalline phase. The Mn-substitution for BCN ceramics resulted in disappearing the dielectric relaxation and suppressing the leakage current conduction.

  17. [CuO-Ru/Al2O3 catalytic ozonation of acetophenone in water].

    PubMed

    Zhang, Hua; Shi, Rui; Zang, Xing-jie; Tong, Shao-ping; Ma, Chun-an

    2010-03-01

    Two-component CuO-Ru based on active Al2O3 (CuO-Ru/Al2O3) catalyst was prepared by incipient wetness impregnation and used to catalytic ozonation of acetophenone (AP). The results showed that doping Ru could significantly improve the catalytic activity of CuO/Al2O3. For example, the COD removal rates of AP solution after 30 min by ozonation alone, CuO/Al2O3/O3, and CuO-Ru/Al2O3/O3 were 6.3%, 20.0% and 54.0%, respectively. The change of pH almost had no affect on degradation efficiency of AP. However, a comparison of COD removal between ozonation alone and catalytic ozonation indicated that CuO-Ru/Al2O3 catalyst was more suitable for application in neutral or acidic condition. CuO-Ru/Al2O3 catalyst could accelerate decomposition rate of ozone in water, and its decomposition rate constant reached 2.58 x 10(-3) s(-1) while that of ozone alone in double-water was 1.19 x 10(-3) s(-1). The experimental result of t-butanol indicated that CuO-Ru/Al2O3 catalytic ozonation of AP followed a radical-type mechanism. PMID:20358832

  18. Mechanism of particle growth of a BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphor by firing with AlF{sub 3}

    SciTech Connect

    Oshio, Shozo; Matsuoka, Tomizo; Tanaka, Shosaku; Kobayashi, Hiroshi

    1998-11-01

    The mechanism of particle growth of the blue emitting BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphor by firing with AlF{sub 3} has been clarified. It was found that the reaction between BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} and AlF{sub 3} during firing, on the basis of the following chemical equation, results in recreation of BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} with particle growth BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} + (4/3)AlF{sub 3} {l_reversible} BaMgF{sub 4}:Eu{sup 2+} + (17/3)Al{sub 2}O{sub 3}, the firing of Ba/MgAl{sub 10}O{sub 17}:Eu{sup 2+} with AlF{sub 3} first converts the phosphor into a mixture of the two compounds, BaMgF{sub 4}:Eu{sup 2+} and Al{sub 2}O{sub 3}, at around 1200 C. The BaMgF{sub 4}:Eu{sup 2+} melts at temperatures over 1000 C, then reacts with Al{sub 2}O{sub 3}, and participates in the recreation of both BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} and AlF{sub 3} through a chemical reaction between the two compounds at 1200 C in BaMgF{sub 4}:Eu{sup 2+} solutions. Recreated AlF{sub 3} appears to sublime immediately because it is a material which sublimates with heating. This paper proposes a mechanism for the growth of particle of recreated BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} by the melting of BaMgF{sub 4}:Eu{sup 2+}.

  19. Optical behavior and structural property of CuAlS₂ and AgAlS₂ wide-bandgap chalcopyrites.

    PubMed

    Ho, Ching-Hwa; Pan, Chia-Chi

    2014-08-01

    Single crystals of CuAlS₂ and AgAlS₂ were grown by chemical vapor transport method using ICl₃ as the transport. The as-grown CuAlS₂ crystals reveal transparent and light-green color. Most of them possess a well-defined (112) surface. The AgAlS₂ crystals essentially show transparent and white color in vacuum. As the AgAlS₂ was put into the atmosphere, the crystal surface gradually darkened and became brownish because of the surface reaction with humidity or hydrogen gas. After a long-term chemical reaction process, the AgAlS₂ will transform into a AgAlO₂ oxide with yellow color. From x-ray diffraction measurements, both CuAlS₂ and AgAlS₂ as-grown crystals show single-phase and isostructural to a chalcopyrite structure. The (112) face is more preferable for the formation of the chalcopyrite crystals. The energies of interband transitions of the CuAlS₂ and AgAlS₂ were determined accurately by thermoreflectance measurements in a wide energy range of 2-6 eV. The valence-band electronic structures of CuAlS₂ and AgAlS₂ have been detailed and characterized using polarized-thermoreflectance measurements in the temperature range between 30 and 300 K. The band-edge transitions belonging to the E(∥) and E(⊥) polarizations have been, respectively, identified. The band edge of AgAlS₂ is near 3.2 eV while that of AgAlS₂ is about 3.5 eV. On the basis of the experimental analyses, optical and sensing behaviors of the chalcopyrite crystals have been realized.

  20. Ba3Pt4Al4-Structure, Properties, and Theoretical and NMR Spectroscopic Investigations of a Complex Platinide Featuring Heterocubane [Pt4Al4] Units.

    PubMed

    Stegemann, Frank; Benndorf, Christopher; Bartsch, Timo; Touzani, Rachid St; Bartsch, Manfred; Zacharias, Helmut; Fokwa, Boniface P T; Eckert, Hellmut; Janka, Oliver

    2015-11-16

    Ba3Pt4Al4 was prepared from the elements in niobium ampules and crystallizes in an orthorhombic structure, space group Cmcm (oP44, a = 1073.07(3), b = 812.30(3), c = 1182.69(3) pm) isopointal to the Zintl phase A2Zn5As4 (A = K, Rb). The structure features strands of distorted [Pt4Al4] heterocubane-like units connected by condensation over Pt/Al edges. These are arranged in a hexagonal rod packing by further condensation over Pt and Al atoms with the barium atoms located inside cavities of the [Pt4Al4](δ-) framework. Structural relaxation confirmed the electronic stability of the new phase, while band structure calculations indicate metallic behavior. Crystal orbital Hamilton bonding analysis coupled with Bader effective charge analysis suggest a polar intermetallic phase in which strong Al-Pt covalent bonds are present, while a significant electron transfer from Ba to the [Pt4Al4](δ-) network is found. By X-ray photoelectron spectroscopy measurements the Pt 4f5/2 and 4f7/2 energies for Ba3Pt4Al4 were found in the range of those of elemental Pt due to the electron transfer of Ba, while PtAl and PtAl2 show a pronounced shift toward a more cationic platinum state. (27)Al magic-angle spinning NMR investigations verified the two independent crystallographic Al sites with differently distorted tetrahedrally coordinated [AlPt4] units. Peak assignments could be made based on both geometrical considerations and in relation to electric field gradient calculations. PMID:26536164

  1. Energy band engineering and controlled p-type conductivity of CuAlO2 thin films by nonisovalent Cu-O alloying

    NASA Astrophysics Data System (ADS)

    Yao, Z. Q.; He, B.; Zhang, L.; Zhuang, C. Q.; Ng, T. W.; Liu, S. L.; Vogel, M.; Kumar, A.; Zhang, W. J.; Lee, C. S.; Lee, S. T.; Jiang, X.

    2012-02-01

    The electronic band structure and p-type conductivity of CuAlO2 films were modified via synergistic effects of energy band offset and partial substitution of less-dispersive Cu+ 3d10 with Cu2+ 3d9 orbitals in the valence band maximum by alloying nonisovalent Cu-O with CuAlO2 host. The Cu-O/CuAlO2 alloying films show excellent electronic properties with tunable wide direct bandgaps (˜3.46-3.87 eV); Hall measurements verify the highest hole mobilities (˜11.3-39.5 cm2/Vs) achieved thus far for CuAlO2 thin films and crystals. Top-gate thin film transistors constructed on p-CuAlO2 films were presented, and the devices showed pronounced performance with Ion/Ioff of ˜8.0 × 102 and field effect mobility of 0.97 cm2/Vs.

  2. Macroscopic magnetic properties in TlBa{sub 2}Ca{sub 3}Cu{sub 4}O{sub 11-{delta}} single crystals

    SciTech Connect

    Zhang, Lu; Collins, C.; Liu, J.Z.; Shelton, R.N.

    1996-11-01

    The four-CuO{sub 2}-layer TlBa{sub 2}Ca{sub 3}Cu{sub 4}O{sub 11{minus}{delta}} compound has a high superconducting transition temperature of 128 K and strong interlayer coupling. The authors have performed magnetic experiments on single crystals of TlBa{sub 2}Ca{sub 3}Cu{sub 4}O{sub 11{minus}{delta}}, which include hysteresis loop, irreversibility line and time relaxation measurements. From these measurements, the authors observed the large critical current density, high irreversibility line and strongly temperature dependent flux creep rate in the TlBa{sub 2}Ca{sub 3}Cu{sub 4}O{sub 11{minus}{delta}} single crystals.

  3. The photosensitivity of carbon quantum dots/CuAlO2 films composites.

    PubMed

    Pan, Jiaqi; Sheng, Yingzhuo; Zhang, Jingxiang; Wei, Jumeng; Huang, Peng; Zhang, Xin; Feng, Boxue

    2015-07-31

    Carbon quantum dots/CuAlO2 films were prepared by a simple route through which CuAlO2 films prepared by sol-gel on crystal quartz substrates were composited with carbon quantum dots on their surface. The characterization results indicated that CuAlO2 films were well combined with carbon quantum dots. The photoconductivity of carbon quantum dots/CuAlO2 films was investigated under illumination and darkness switching, and was demonstrated to be significantly enhanced compared with CuAlO2 films. Through analysis, this enhancement of photoconductivity was attributed to the carbon quantum dots with unique up-converted photoluminescence behavior. PMID:26150398

  4. Radial macrosegregation and dendrite clustering in directionally solidified Al-7Si and Al-19Cu alloys

    NASA Astrophysics Data System (ADS)

    Ghods, M.; Johnson, L.; Lauer, M.; Grugel, R. N.; Tewari, S. N.; Poirier, D. R.

    2016-05-01

    Hypoeutectic Al-7 wt% Si and Al-19 wt% Cu alloys were directionally solidified upward in a Bridgman furnace through a range of constant growth speeds and thermal gradients. Though processing is thermo-solutally stable, flow initiated by gravity-independent advection at, slightly leading, central dendrites moves rejected solute out ahead and across the advancing interface. Here any lagging dendrites are further suppressed which promotes a curved solid-liquid interface and the eventual dendrite "clustering" seen in transverse sections (dendrite "steepling" in longitudinal orientations) as well as extensive radial macrosegregation. Both aluminum alloys showed considerable macrosegregation at the low growth speeds (10 and 30 μm s-1) but not at higher speed (72 μm s-1). Distribution of the fraction eutectic-constituent on transverse sections was determined in order to quantitatively describe radial macrosegregation. The convective mechanisms leading to dendrite-steepling were elucidated with numerical simulations, and their results compared with the experimental observations.

  5. Collective versus local Jahn-Teller distortion in Ba3CuSb2O9 : Raman scattering study

    NASA Astrophysics Data System (ADS)

    Drichko, Natalia; Broholm, Collin; Kimura, K.; Ishii, R.; Nakasutji, Satoru

    2016-05-01

    We present temperature dependent Raman spectra of single crystals of two different samples of the spin-orbital liquid candidate Ba3CuSb2O9 . The "hexagonal" sample is known to show no magnetic order down to low temperatures, while the "orthorhombic" sample undergoes a crossover into an orthorhombic crystal structure below TJT of approximately 200 K and shows spin freezing at 110 μ K . Our Raman scattering results demonstrate a strong influence of disorder in both samples. The frequencies of stretching vibrations of oxygens associated with CuSbO9 octahedra indicate a difference in the crystal structure between the hexagonal and orthorhombic samples even at room temperature. On cooling below TJT we observe new bands in the spectra of the orthorhombic sample due to a lowering of symmetry of the unit cell and a collective Jahn-Teller distortion. The spectra of the hexagonal sample show that average hexagonal symmetry is maintained at least down to 20 K. An analysis of the band shape of stretching oxygen vibrations suggests a weak disordered local Jahn-Teller distortion in the hexagonal sample of Ba3CuSb2O9 which increases slightly on cooling. This Jahn-Teller distortion is either static or dynamic with a frequency below 1.5 THz.

  6. Critical currents, magnetic relaxation, and pinning in NdBa2Cu3O7-delta films with BaZrO3-generated columnar defects

    SciTech Connect

    Ijaduola, Anota O; Wee, Sung Hun; Goyal, Amit; Martin, Patrick M; Li, Jing; Thompson, J. R.; Christen, David K

    2012-01-01

    The critical current density Jc and the magnetic relaxation ( creep ) properties have been studied for a set of NdBa2Cu3O7- (NdBCO) films doped with BaZrO3 (BZO) nanoparticles to form columnar defects. The dependence of Jc on the magnitude and orientation of the applied magnetic field Happ (0 6.5 T); and temperature T (5 K Tc) was investigated. The normalized flux-creep rate S = d ln(J ) / d ln(t) was determined as a function of T. The current dependence of the effective activation energy Ueff(J) was derived using the formalism developed by Maley. The results are well described by an inverse power-law type barrier of the form 0 0 ( ) ~ ( / ) eff U J U J J with fitted values for the pinning energy scale U0 and the glassy exponent . When comparing values for these parameters in the BZO-doped samples with those for their undoped control counterparts, the most striking difference is the larger scale of current density J0 in the doped samples (a factor of 2.4 higher), while the other pinning parameters do not differ strongly. In the BZO-doped materials, the pinning energy scale U0 increases with vortex density and J0 decreases, with both following simple power law dependencies on field.

  7. Structural changes and microstructures in stuffed tridymite-type compounds Ba1-xSrxAl2O4

    NASA Astrophysics Data System (ADS)

    Tanaka, Eri; Ishii, Yui; Tsukasaki, Hirofumi; Taniguchi, Hiroki; Mori, Shigeo

    2014-09-01

    Crystal structures and microstructures in Ba1-xSrxAl2O4 solid solutions between the end members of BaAl2O4 and SrAl2O4 have been carefully investigated by powder X-ray diffraction, electron diffraction and transmission electron microscopy (TEM) imaging experiments. With the help of fast Fourier transform (FFT) calculation, high-resolution TEM images suggested that diffuse streaks along three equivalent <110> directions in the (001) plane, which appear in the P63 structure of Ba1-xSrxAl2O4 for x = 0.4, originate from the large structural fluctuation of the AlO4 tetrahedral network. On the other hand, the monoclinic P21 structure in Ba1-xSrxAl2O4 with x = 0.7 was found to consist of a modulated structure with \\boldsymbol{{q}} = 0,1/2,0. The present experimental results reveal that a structural phase boundary exists at approximately x = 0.6 between the P63 structure with a large structural fluctuation and a monoclinic P21 phase with the single-q modulated structure.

  8. Electron paramagnetic resonance studies of the soluble CuA protein from the cytochrome ba3 of Thermus thermophilus.

    PubMed Central

    Karpefors, M; Slutter, C E; Fee, J A; Aasa, R; Källebring, B; Larsson, S; Vänngård, T

    1996-01-01

    The electron paramagnetic resonance (EPR) spectrum of the binuclear CuA center in the water-soluble subunit II fragment from cytochrome ba3 of Thermus thermophilus was recorded at 3.93, 9.45, and 34.03 GHz, and the EPR parameters were determined by computer simulations. The frequency and M1 dependence of the linewidth was discussed in terms of g strain superimposed on a correlation between the A and g values. The g values were found to be gx = 1.996, gy = 2.011, gz = 2.187, and the two Cu ions contribute nearly equally to the hyperfine structure, with magnitude of Ax magnitude of approximately 15 G, magnitude of Ay magnitude = 29 G, and magnitude of Az magnitude of = 28.5 G (65Cu). Theoretical CNDO/S calculations, based on the x-ray structure of the Paracoccus denitrificans enzyme, yield a singly occupied antibonding orbital in which each Cu is pi*-bonded to one S and sigma*-bonded to the other. In contrast to the equal spin distribution suggested by the EPR simulations, the calculated contributions from the Cu ions differ by a factor of 2. However, only small changes in the ligand geometry are needed to reproduce the experimental results. PMID:8913619

  9. Electron paramagnetic resonance studies of the soluble CuA protein from the cytochrome ba3 of Thermus thermophilus.

    PubMed

    Karpefors, M; Slutter, C E; Fee, J A; Aasa, R; Källebring, B; Larsson, S; Vänngård, T

    1996-11-01

    The electron paramagnetic resonance (EPR) spectrum of the binuclear CuA center in the water-soluble subunit II fragment from cytochrome ba3 of Thermus thermophilus was recorded at 3.93, 9.45, and 34.03 GHz, and the EPR parameters were determined by computer simulations. The frequency and M1 dependence of the linewidth was discussed in terms of g strain superimposed on a correlation between the A and g values. The g values were found to be gx = 1.996, gy = 2.011, gz = 2.187, and the two Cu ions contribute nearly equally to the hyperfine structure, with magnitude of Ax magnitude of approximately 15 G, magnitude of Ay magnitude = 29 G, and magnitude of Az magnitude of = 28.5 G (65Cu). Theoretical CNDO/S calculations, based on the x-ray structure of the Paracoccus denitrificans enzyme, yield a singly occupied antibonding orbital in which each Cu is pi*-bonded to one S and sigma*-bonded to the other. In contrast to the equal spin distribution suggested by the EPR simulations, the calculated contributions from the Cu ions differ by a factor of 2. However, only small changes in the ligand geometry are needed to reproduce the experimental results.

  10. Terahertz superconducting hot electron bolometers: technological issues and predicted mixer performance for Y-Ba-Cu-O devices

    NASA Astrophysics Data System (ADS)

    Ladret, Romain G.; Kreisler, Alain J.; Dégardin, Annick F.

    2014-10-01

    High-TC superconducting (HTS) hot electron bolometers (HEB) are promising THz mixers due to their large expected bandwidth and low local oscillator (LO) power requirements at 60-80 K operating temperature. To obtain HEB efficient mixing, it is mandatory to grow very thin high quality HTS films leading to good micro or nano-bolometer superconducting properties. The challenge for Y-Ba-Cu-O resides, however, in the chemical reactivity of the material and the related aging effects. Early HEB models described the device in terms of thermal reservoirs only, namely the electrons and the phonons of the superconductor. The electron-phonon interaction time, which drives the HEB mixer ultimate response, is 1-2 ps for Y-Ba-Cu-O, with an expected bandwidth close to 100 GHz. Recently, we introduced the hot spot model for Y-Ba-Cu-O HEBs, taking - more realistically - the spatial dependence of the electron temperature along the nano-bolometer (or constriction) length into account. From DC analysis, the I-V characteristics could be deduced. In this paper, we further consider a full description of the constriction impedance at THz frequencies, which allows to work out the mixer performance in terms of double sideband noise temperature TDSB and conversion gain G. For a constriction of technologically achievable dimensions, i.e., 400 nm long x 400 nm wide x 35 nm thick, minimum TDSB = 1900 K at 9 μW LO power, with G = -9.5 dB, is obtained at 400 GHz, assuming impedance matching with a selfcomplementary planar antenna.

  11. Multiple diffraction in an icosahedral Al-Cu-Fe quasicrystal

    NASA Astrophysics Data System (ADS)

    Fan, C. Z.; Weber, Th.; Deloudi, S.; Steurer, W.

    2011-07-01

    In order to reveal its influence on quasicrystal structure analysis, multiple diffraction (MD) effects in an icosahedral Al-Cu-Fe quasicrystal have been investigated in-house on an Oxford Diffraction four-circle diffractometer equipped with an Onyx™ CCD area detector and MoKα radiation. For that purpose, an automated approach for Renninger scans (ψ-scans) has been developed. Two weak reflections were chosen as the main reflections (called P) in the present measurements. As is well known for periodic crystals, it is also observed for this quasicrystal that the intensity of the main reflection may significantly increase if the simultaneous (H) and the coupling (P-H) reflections are both strong, while there is no obvious MD effect if one of them is weak. The occurrence of MD events during ψ-scans has been studied based on an ideal structure model and the kinematical MD theory. The reliability of the approach is revealed by the good agreement between simulation and experiment. It shows that the multiple diffraction effect is quite significant.

  12. SDAS, Si and Cu Content, and the Size of Intermetallics in Al-Si-Cu-Mg-Fe Alloys

    NASA Astrophysics Data System (ADS)

    Sivarupan, Tharmalingam; Taylor, John Andrew; Cáceres, Carlos Horacio

    2015-05-01

    Plates of Al-(a)Si-(b)Cu-Mg-(c)Fe alloys with varying content of (mass pct) Si ( a = 3, 4.5, 7.5, 9, 10, or 11), Cu ( b = 0, 1, or 4), and Fe ( c = 0.2, 0.5 or 0.8) were cast in sand molds with a heavy chill at one end to ensure quasi-directional solidification over a wide range of Secondary Dendrite Arm Spacing (SDAS). Statistical analysis on the size of the β-Al5FeSi, α-Al8Fe2Si, or Al2Cu intermetallics on Backscattered Electron images showed that a high Si content reduced the size of the β platelets in alloys with up to 0.5 Fe content regardless of the SDAS, whereas at small SDAS the refining effect extended up to 0.8 Fe, and involved α-phase intermetallics which replaced the beta platelets at those concentrations. At low Si contents, a high Cu level appeared to have similar refining effects as increased Si, through the formation of α-phase particles in the post-eutectic stage which agglomerated with the Al2Cu intermetallics. A high content of Si appears to make the overall refining process less critical in terms of SDAS/cooling rate.

  13. Images of interlayer Josephson vortices in T1{sub 2}Ba{sub 2}CuO{sub 6+delta}.

    SciTech Connect

    Moler, K. A.; Kirtley, J. R.; Hinks, D. G.; Li, T. W.; Xu, M.; Materials Science Division; Princeton Univ.; IBM T. J. Watson Research Center; Univ. of Chicago

    1998-02-20

    The strength of the interlayer Josephson tunneling in layered superconductors is an essential test of the interlayer tunneling model as a mechanism for superconductivity, as well as a useful phenomenological parameter. A scanning superconducting quantum interference device (SQUID) microscope was used to image interlayer Josephson vortices in Tl{sub 2}Ba{sub 2}CuO{sub 6+{delta}} and to obtain a direct measure of the interlayer tunneling in a high-transition temperature superconductor with a single copper oxide plane per unit cell. The measured interlayer penetration depth, {lambda}{sub c}, is {approx}20 micrometers, about 20 times the penetration depth required by the interlayer tunneling model.

  14. Superconductivity at 93 K in a new mixed-phase Y-Ba-Cu-O compound system at ambient pressure

    NASA Technical Reports Server (NTRS)

    Wu, M. K.; Ashburn, J. R.; Torng, C. J.; Hor, P. H.; Meng, R. L.

    1987-01-01

    A stable and reproducible superconductivity transition between 80 and 93 K has been achieved and maintained in a Y-Ba-Cu-O compound system at ambient pressure in a simple liquid-nitrogen Dewar. An upper critical field Hc2(0) estimate of between 80 and 180 T is obtained, and the paramagnetic limiting field at 0 K for a sample with a T(c) of about 90 K is 165 T. It is suggested that the lattice parameters, the valence ratio, and the sample treatments all play a role in achieving superconductivity above 77 K.

  15. Superconductivity in 2-2-3 Y2Ba2Cu3O(sub 8+ delta)

    NASA Technical Reports Server (NTRS)

    Joshi, H. H.; Baldha, G. J.; Jotania, R. B.; Joshi, S. M.; Mohan, H.; Pandya, P. B.; Pandya, H. N.; Kulkarni, R. G.

    1990-01-01

    Researchers synthesized a new high T(sub c) 2-2-3 superconductor (Y2Ba2Cu3O8+delta) by a special preparation technique and characterized it by ac-susceptibility measurements. Diamagnetism and Meissner effect sets in at low fields and superconducting transition onsets at 90 K. The systematic investigation of the real and imaginary components of ac-susceptibility as a function of temperature and applied ac magnetic field reveals that the magnetic behavior is that of a granular type superconductor.

  16. Properties of large area ErBa2Cu3O(7-x) thin films deposited by ionized cluster beams

    NASA Technical Reports Server (NTRS)

    Levenson, L. L.; Stan, M.; Bhasin, K. B.

    1991-01-01

    Ionized cluster beam (ICB) deposition is employed to produce ErBa2Cu3O(7-x) films on different substrates without post-annealing. Films with diameters of up to 70 mm are grown on SrTiO3 100 plane and exhibit Tc values of 84-87 K, Jc of about 10 exp 6 A/sq m at 77 K. These films are epitaxial with the c-axis perpendicular to the plane of the substrate surface, and they can be routinely produced by ICB with good Jc and Tc.

  17. Grain size dependence of microwave absorption in Y 1Ba 2Cu 3O 7 powders near T c

    NASA Astrophysics Data System (ADS)

    Gould, A.; Jackson, E. M.; Renouard, K.; Crittenden, R.; Bhagat, S. M.; Spencer, N. D.; Dolhert, L. E.; Wormsbecher, R. F.

    1988-11-01

    A systematic study of the relationship between particle dimensions and microwave absorption in micron size powders of superconducting Y 1Ba 2Cu 3O 7 reveals that small particles have negligible absorption at T<0.8 Tc, and that the transition gets sharper as the grains get bigger. However, when the particles get so large as to incorporate multiple grains, the transition broadens and there is significant absorption down to 0.7 Tc. The temperature dependence in the small (≤10 μm) powders is satisfactorily described by a simple extension of London's theory.

  18. Effects of irradiation - fast neutrons and implantation on sintered Y sbnd Ba sbnd Cu sbnd O superconductors

    NASA Astrophysics Data System (ADS)

    Rao, K. V.; PuŹniak, R.; Chen, D.-X.; Karpe, N.; Baran, M.; Wiśniewski, A.; Pytel, K.; Szymczak, H.; Dyrbye, K.; Bøttiger, J.

    1988-06-01

    Effects of irradiation damage by fast neutrons, and nitrogen implantation on magnetic and electrical properties of Y sbnd Ba sbnd Cu sbnd O materials have been studied. The samples were subjected to a fluence of 2 × 10 17 and 1 × 10 17 neutrons / cm 2. In the implantation studies dosages of 10 15 and 10 16ions/ cm 2 of N + were used. Here we will report on the detailed changes in the magnetic hysteresis loop due to irradiation. It is found that the transport inter-grain critical current decreases with irradiation, while the critical current inside the grains is enhanced.

  19. Magnetic properties of superconducting GdBa2Cu3O(6 + delta) at low temperature and high field

    NASA Technical Reports Server (NTRS)

    Huang, C. Y.; Shapira, Y.; Hor, P. H.; Meng, R. L.; Chu, C. W.

    1988-01-01

    The magnetization of antiferromagnetic superconducting GdBa2Cu3O(6 + delta) has been measured for T in the range of 1.5 - 4.2 K for magnetic fields up to about 20 T. It is found that all Gd(3+) spins are nearly parallel at very high fields, and that this saturated spin subsystem coexists with superconductivity. Below the Neel temperature, 2.22 K, the transition from the 'canted' phase to the paramagnetic phase is observed by the application of a high magnetic field. The temperature dependence of this phase transition is also reported.

  20. Mechanism of X-ray excited optical luminescence (XEOL) in europium doped BaAl2O4 phosphor.

    PubMed

    Rezende, Marcos V Dos S; Montes, Paulo J R; Andrade, Adriano B; Macedo, Zelia S; Valerio, Mário E G

    2016-06-29

    This paper reports a luminescence mechanism in Eu-doped BaAl2O4 excited with monochromatic X-rays (also known as X-ray excited optical luminescence - XEOL) from synchrotron radiation. The material was prepared via a proteic sol-gel methodology. The X-ray absorption near edge structures (XANES) at the Ba LIII- and Eu LIII-edges exhibit typical absorption spectra. XEOL spectra recorded in energy ranges, either around the Ba LIII- or Eu LIII-edges, showed important differences concerning the intensity of the Eu(2+) or Eu(3+) emission bands. Nevertheless, the total area under the XEOL spectra increases as the energy of the X-ray photons increases in both ranges (Ba LIII- and Eu LIII-edges). PMID:27306425

  1. Electronic structure and properties of isoelectronically substituted compounds Y{sub 1}Ba{sub 2-m}M{sub m}Cu{sub 3}O{sub 7} and Y{sub 1}Ba{sub 2-m}M{sub m}Cu{sub 4}O{sub 8} (M = Be, Mg, Ca, Sr, Ba, Ra)

    SciTech Connect

    Ermakov, A.I.; Zharikova, E.A.; Markushin, N.A.

    1994-09-01

    According to cluster calculations, the electronic structures of compounds based on Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} and Y{sub 1}Ba{sub 2}Cu{sub 4}O{sub 8} with isoelectronically substituted barium have some qualitative distinctions. These compounds behave differently upon barium substitution by other elements due to differences in the character of their highest occupied and lowest unoccupied molecular orbitals. Substitution of barium by radium is expected to lead to an increase in oxygen stability without a significant decrease in the critical temperature of superconduction transition T{sub s}. In order to raise T{sub s}, it is of interest to study the systems YBa{sub 2-m}(Be or Mg){sub m}Cu{sub 3}O{sub x} and YBa{sub 2-m}(Ca, Sr){sub m}Cu{sub 3}O{sub x}. On partial substitution of barium by calcium in YBa{sub 2}Cu{sub 4}O{sub 8}, the mechanism of T{sub s} elevation may involve contraction of the forbidden band due to oxygen sublattice distortions in the vicinity of Ba centers.

  2. Theoretical investigation of superconductivity in Ba(AlSn) under pressure

    NASA Astrophysics Data System (ADS)

    Parlak, Cihan

    2016-10-01

    The compound of Ba(AlSn) from ternary superconductors exhibits the superconductivity behaviour below the temperature 2.9 K. We report the results of an ab initio study based on electronic, and detailed lattice dynamical properties as a function of pressure of superconducting material. The phonon dispersion curves along the high-symmetry directions and phonon frequencies parameters at the Brillouin zone center are computed by using density functional perturbation theory while the elastic constants are calculated in metric-tensor formulation. The Vickers hardness belonging to the compound is also evaluated clearly. The band structure, partial densities of states and Fermi surface topology are also discussed in detail. At the same time we describe the relationship between the properties determined and superconducting characteristic.

  3. Remarkable Stability of Charge Density Wave Order in La1.875 Ba0.125 CuO4

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    The occurrence of charge-density-wave (CDW) order in underdoped cuprates is now well established, although the precise nature of the CDW and its relationship with superconductivity is not. Theoretical proposals include contrasting ideas such as that pairing may be driven by CDW fluctuations or that static CDWs may intertwine with a spatially modulated superconducting wave function. We test the dynamics of CDW order in La1.825 Ba0.125 CuO4 by using x-ray photon correlation spectroscopy at the CDW wave vector, detected resonantly at the Cu L3 edge. We find that the CDW domains are strikingly static, with no evidence of significant fluctuations up to 2 ¾ h . We discuss the implications of these results for some of the competing theories.

  4. Magnetic vortex lattice in HgBa2CuO4+δ observed by small-angle neutron scattering

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Egetenmeyer, N.; Gavilano, J. L.; Barišić, N.; Greven, M.

    2011-02-01

    We report the direct observation of the magnetic vortex lattice in the model high-temperature superconductor HgBa2CuO4+δ. Using small-angle neutron scattering on high-quality crystals, we observe two equal domains of undistorted triangular vortex lattices well aligned with the tetragonal crystallographic axes. The signal decreases rapidly with increasing magnetic field and vanishes above 0.4 T, which we attribute to a crossover from a three-dimensional to a two-dimensional vortex system, similar to previous results for the more anisotropic compound Bi2.15Sr1.95CaCu2O8+δ. Our result indicates that a triangular vortex lattice (with or without distortion) at low magnetic fields is a generic property of cuprates with critical temperatures above 80 K.

  5. Mechanical properties of pure Ni and Ni-alloy substrate materials for Y Ba Cu O coated superconductors

    NASA Astrophysics Data System (ADS)

    Clickner, C. C.; Ekin, J. W.; Cheggour, N.; Thieme, C. L. H.; Qiao, Y.; Xie, Y.-Y.; Goyal, A.

    2006-06-01

    Mechanical properties of rolling-assisted, biaxially-textured substrates (RABiTS) and substrates for ion-beam assisted deposition (IBAD) coated superconductors are measured at room temperature, 76, and 4 K. Yield strength, Young's modulus, and the proportional limit of elasticity are determined, tabulated and compared. Results obtained are intended to serve as a database of mechanical properties of substrates having the same anneal state and texture as those incorporated in the general class of RE-Ba-Cu-O coated conductor composites (RE = rare earth). The RABiTS materials measured are pure Ni, Ni-13at.%Cr, Ni-3at.%W-2at.%Fe, Ni-10at.%Cr-2at.%W, and Ni-5at.%W. The IBAD substrate materials included Inconel 625 and Hastelloy C-276. The Ni alloys are substantially stronger and show higher strains at the proportional limit than those of pure Ni. Substrates fully coated with buffer layers, ≈1 μm of Y-Ba-Cu-O, and 3-5 μm of Ag have similar mechanical properties (at 76 K) as the substrate alone. Somewhat surprisingly, plating an additional 30-40 μm of Cu stabilizer onto high-yield-strength (690 MPa) Hastelloy coated conductors ˜100 μm thick, reduces the overall yield strength of the composite structure by only about 10-12% at 76 K and 12-14% at room temperature; this indicates that the Cu layer, despite its relatively soft nature, contributes significantly to the overall strength of even high-strength coated conductors.

  6. Surface structures of Al-Pd-Mn and Al-Cu-Fe icosahedral quasicrystals

    SciTech Connect

    Shen, Z.

    1999-02-12

    In this dissertation, the author reports on the surface structure of i-Al-Pd-Mn twofold, threefold, fivefold and i-Al-Cu-Fe fivefold surfaces. The LEED studies indicate the existence of two distinct stages in the regrowth of all four surfaces after Ar{sup +} sputtering. In the first stage, upon annealing at relatively low temperature: 500K--800K (depending on different surfaces), a cubic phase appears. The cubic LEED patterns transform irreversibly to unreconstructed quasicrystalline patterns upon annealing to higher temperatures, indicating that the cubic overlayers are metastable. Based upon the data for three chemically-identical, but symmetrically-inequivalent surfaces, a model is developed for the relation between the cubic overlayers and the quasicrystalline substrate. The model is based upon the related symmetries of cubic close-packed and icosahedral-packed materials. These results may be general among Al-rich, icosahedral materials. STM study of Al-Pd-Mn fivefold surface shows that terrace-step-kink structures start to form on the surface after annealing above 700K. Large, atomic ally-flat terraces were formed after annealing at 900K. Fine structures with fivefold icosahedral symmetry were found on those terraces. Data analysis and comparison of the STM images and structure model of icosahedral Al-Pd-Mn suggest that the fine structures in the STM images may be the pseudo Mackay (PMI) clusters which are the structure units of the structure model. Based upon his results, he can conclude that quasicrystalline structures are the stable structures of quasicrystal surfaces. In other words, quasicrystalline structures extend from the bulk to the surface. As a result of the effort reported in this dissertation, he believes that he has increased his understanding of the surface structure of icosahedral quasicrystals to a new level.

  7. The unusual chemical bonding and thermoelectric properties of a new type Zintl phase compounds Ba3Al2As4

    NASA Astrophysics Data System (ADS)

    Yang, Gui; Zhang, Guangbiao; Wang, Chao; Wang, Yuanxu

    2016-07-01

    Ba3Al2As4 exhibits an unusual anisotropic electrical conductivity, that is, the electrical conductivity along the chain is smaller than those along other two directions. The results is conflict with previous conclusion for Ca5M2Pn6. Earlier studies on Ca5M2Pn6 showed that a higher electrical conductivity could be obtained along the chain. The band decomposed charge density is used to explain such unusual behavior. Our calculations indicate the existence of a conductive pathway near the Fermi level is responsible for the electrons transport. Further, the Ba-As bonding of Ba3Al2As4 has some degree covalency which is novel for the Zintl compounds.

  8. Evaluation of the microstructure of Al-Cu-Li-Ag-Mg Weldalite (tm) alloys, part 4

    NASA Technical Reports Server (NTRS)

    Pickens, Joseph R.; Kumar, K. S.; Brown, S. A.; Gayle, Frank W.

    1991-01-01

    Weldalite (trademark) 049 is an Al-Cu-Li-Ag-Mg alloy designed to have ultrahigh strength and to serve in aerospace applications. The alloy displays significantly higher strength than competitive alloys in both naturally aged and artificially aged tempers. The strengthening phases in such tempers have been identified to, in part, explain the mechanical properties attained. In general, the alloy is strengthened by delta prime Al3Li and Guinier-Preston (GP) zones in the naturally aged tempers. In artificially aged tempers in slightly underaged conditions, strengthening is provided by several phases including GP zones, theta prime Al2Cu, S prime Al2CuMg, T(sub 1) Al2CuLi, and possibly a new phase. In the peak strength artificially aged tempers, T(sub 1) is the predominant strengthening phase.

  9. Research and analysis on the thin films sputtered by the Ba-Al-S:Eu target fabricated by powder sintering

    NASA Astrophysics Data System (ADS)

    Zhang, Dongpu; Xu, Fang; Yu, Zhinong; Xue, Wei

    2014-11-01

    Europium-doped barium thioaluminate (BaAl2S4:Eu) is currently the most efficient blue phosphor for inorganic thin film electroluminescent (iEL) device. To produce the full-color EL device, several kinds of blue-emitting layer were attempted and tested. As a key point of blue-emitting layer fabrication, single target sputtering deposition is an effective method. In this work, new structural target is introduced and the fabricated process is expatiated. The PL spectra of as fabricated targets show that both of two, 3mol% and 5mol% europium-doped, have blue emitting property. According to the PL spectra excited by 290nm, 300nm and 320nm ultraviolet, emission peaks located in the region near 470nm. So the as-fabricated targets can be used in single target sputtering deposition on thin film of BaAl2S4:Eu. XRD pattern indicates that there are 4 different phases, barium tetraaluminum sulfide (BaAl4S7), barium sulfide (BaS), europium sulfide (EuS) and barium aluminum oxide (BaAl2O4), in target 1. Besides these four compounds, other two phases, aluminum sulfide (Al2S3) and barium thioaluminate (BaAl2S4), are detected in target 2. Considering the analysis results, especially the hydrolyzation of Al2S3, target 1 is more suitable for sputtering deposition of BaAl2S4:Eu thin film. XPS and X-ray Fluorescence patterns describe the precise molar ratio of each element. In target 1 the relative atom concentration of barium, aluminum, sulfur and oxygen can be calculated from the pattern and molar ratio is about 9:33:41:17. Molar ratio of barium and europium is about 1:0.03. In short, the barium thioaluminate doped by europium sputtering target 1 is better to be applied in the fabrication of blue-emitting layer in inorganic electro-luminescent devices.

  10. Effect of the composition of Al-Li alloys on the quantitative relation between the δ'(Al3Li), S1(Al2MgLi), and T1(Al2CuLi) phases

    NASA Astrophysics Data System (ADS)

    Betsofen, S. Ya.; Antipov, V. V.; Grushin, I. A.; Knyazev, M. I.; Khokhlatova, L. B.; Alekseev, A. A.

    2015-01-01

    Al-Li alloys are considered. A quantitative approach to the determination of the ratio of the fractions of the binary and ternary intermetallic phases in Al-Mg(Cu)-Li alloys is developed on the basis of chemical and phase composition balance equations and the experimentally measured lattice parameter of the α solid solution. The ratio of the fractions of the δ'(Al3Li) and S1(T1) phases in Al-Mg(Cu)-Li alloys is shown to be determined by the ratio of the mole fractions of Li and Mg(Cu). Equations are proposed for calculating the weight fractions of the S1(Al2MgLi), T1(Al2CuLi) and δ'(Al3Li) phases in domestic and foreign Al-Mg-Li alloys 1420, 1424, 5090 and Al-Cu-Li alloys 1440, 1460, 1461, 1441, 1469, 2090, 2095, 8090, and Weldalite 049.

  11. Microstructural variations in Cu/Nb and Al/Nb nanometallic multilayers

    SciTech Connect

    Polyakov, M. N.; Hodge, A. M.; Courtois-Manara, E.; Wang, D.; Kuebel, C.; Chakravadhanula, K.

    2013-06-17

    Miscible (Al/Nb) and immiscible (Cu/Nb) nanometallic multilayer systems were characterized by means of transmission electron microscopy techniques, primarily by automated crystallographic orientation mapping, which allows for the resolution of crystal structures and orientations at the nanoscale. By using this technique, distinctive Nb orientations in relation to the crystallographic state of the Al and Cu layer structures can be observed. Specifically, the Al and Cu layers were found to consist of amorphous, semi-amorphous, and crystalline regions, which affect the overall multilayer microstructure.

  12. [Catalytic degradation of naphthalene by CuO (-CeO2)/Al2O3].

    PubMed

    Zha, Jian; Zhou, Hong-Cang; He, Du-Liang; Shan, Long; Zhang, Lu; Xie, Jie

    2014-10-01

    Three catalysts CuO/Al2O3, CeO2/Al2O3 and CuO-CeO2/Al2O3 were prepared by the impregnation method. The textural and structural properties of the synthesized catalysts were characterized by N2 adsorption/desorption, SEM and XRD, and the effect of active ingredients, flow rate and reaction temperature on catalytic degradation of naphthalene (NaP) were investigated in fixed-bed reactor. The experimental results show that the prepared 18% CeO2/Al2O3 has a low catalytic activity of NaP. Nevertheless, both 18% CuO/Al2O3 and 9% CuO-9% CeO2/Al2O3 exhibit high catalytic activity whose removal efficiencies at 300°C can reach 91% and 89%, respectively. Besides, compared with CuO/Al2O3, CuO-CeO2/Al2O3 possesses a higher low-temperature activity. Furthermore, the variation of flow rates has little effect on the performance of two catalysts.

  13. [Catalytic degradation of naphthalene by CuO (-CeO2)/Al2O3].

    PubMed

    Zha, Jian; Zhou, Hong-Cang; He, Du-Liang; Shan, Long; Zhang, Lu; Xie, Jie

    2014-10-01

    Three catalysts CuO/Al2O3, CeO2/Al2O3 and CuO-CeO2/Al2O3 were prepared by the impregnation method. The textural and structural properties of the synthesized catalysts were characterized by N2 adsorption/desorption, SEM and XRD, and the effect of active ingredients, flow rate and reaction temperature on catalytic degradation of naphthalene (NaP) were investigated in fixed-bed reactor. The experimental results show that the prepared 18% CeO2/Al2O3 has a low catalytic activity of NaP. Nevertheless, both 18% CuO/Al2O3 and 9% CuO-9% CeO2/Al2O3 exhibit high catalytic activity whose removal efficiencies at 300°C can reach 91% and 89%, respectively. Besides, compared with CuO/Al2O3, CuO-CeO2/Al2O3 possesses a higher low-temperature activity. Furthermore, the variation of flow rates has little effect on the performance of two catalysts. PMID:25693411

  14. Influence of CuO addition to BaSm{sub 2}Ti{sub 4}O{sub 12} microwave ceramics on sintering behavior and dielectric properties

    SciTech Connect

    Zuo Mingwen; Li Wei . E-mail: liwei@mail.sic.ac.cn; Shi Jianlin; Zeng Qun

    2006-06-15

    Microwave dielectric ceramics of tungsten-bronze-type BaSm{sub 2}Ti{sub 4}O{sub 12} were prepared by doping CuO (up to 2 wt.%) as the liquid-phase sintering aid. The effects of CuO additive on the densification, micro structure and dielectric properties were investigated. Due to the liquid-phase effect, the sintering temperature of BaSm{sub 2}Ti{sub 4}O{sub 12} ceramics with 1 wt.% CuO addition can be effectively reduced to 1160 deg. C, about 200 deg. C lower than that of pure BaSm{sub 2}Ti{sub 4}O{sub 12} ceramics, while good microwave dielectric properties of {epsilon} {sub r} = 75.8, Q*f = 4914.6 GHz and {tau} {sub f} = -7.65 ppm/deg. C were still achieved.

  15. Studies of iron impurities in YxPr1-xBa2Cu3O7-delta

    NASA Technical Reports Server (NTRS)

    Swartzendruber, L. J.; Bennett, L. H.; Ritter, J.; Rubinstein, M.; Harford, M. Z.

    1990-01-01

    Pr is the only rare earth which, when substituted for Y in YBa2Cu3O7, significantly alters the superconducting transition temperature T(sub c) without changing the crystal structure. For YxPr1-xBa2Cu3O7-delta with delta approx. equal to 0, T(sub c) is reduced rapidly as x is increased, reaching zero for x about 0.5. For x above 0.5 the compound is antiferromagnetic with a Neel temperature that increases with increasing x, rising to above room temperature for x near 1. A similar behavior is observed when the oxygen deficit delta is increased from zero to 1 with x=0. For the case of Pr substitution, the drop in T(sub c) is believed due to magnetic interactions. For the case of varying delta with x=0, the drop can be attributed to a combination of magnetic interactions, band filling, and changes in crystal structure. To study these effects, the Mossbauer effect of 57 Fe atoms substituted for the Cu atoms has been observed as a function of delta, x, and temperature. The observed spectra are all well described by a two quadrupole-split pairs, a central singlet, and a six-line magnetic hyperfine field pattern. For several Pr compositions both delta and temperature were varied, and the results support the hypothesis that a magnetic interaction exists between the Fe in the Cu lattice and the substitutional Pr atoms.

  16. Pseudo Spin-Gap Spectrum in the Monolayer HgBa 2CuO 4+δ

    NASA Astrophysics Data System (ADS)

    Itoh, Yutaka; Machi, Takato; Adachi, Seiji; Fukuoka, Atsushi; Tanabe, Keiichi; Yasuoka, Hiroshi

    1998-01-01

    We report the doping dependence of the planar 63Cu Knight shift (63K), the nuclear spin-lattice relaxation rate 63(1/T1T) and the Gaussian spin-echo decay rate 63(1/T G) for the high-T c monolayer HgBa2CuO4+δ over a wide doping range [T c=50, 72, 82 K (underdoping), 96 K (optimal doping) and 30 K (overdoping)], measured by the Cu NMR spin-echo technique. We found the following new facts; (1) both the static and the dynamical spin susceptibilities exhibit the pseudo spin-gap behavior over a wide q region around the staggered mode Q, (2) the dynamical pseudo spin-gap in 1/T1T can mainly be ascribed to the static one in 1/T G, and (3) a spin fluctuation amplitude probed by the empirical ratio T1T/(T G)2 is a monotonic decreasing function of the doping level but not proportional to T c. From comparison with La2-xSrxCuO4, we discussed the role of the pseudo spin-gap in the high-T c superconductivity.

  17. Laser soldering of sapphire substrates using a BaTiAl6O12 thin-film glass sealant

    NASA Astrophysics Data System (ADS)

    de Pablos-Martin, A.; Tismer, S.; Benndorf, G.; Mittag, M.; Lorenz, M.; Grundmann, M.; Höche, Th.

    2016-07-01

    Two sapphire substrates are tightly bonded through a BaTiAl6O12-glass thin film, by irradiation with a nanosecond laser. After the laser process, the composition of the glass sealant changes, due to incorporation of Al2O3 from the upper substrate. After annealing of the bonded samples (950 °C for 30 minutes) crystalline structures are observed by TEM which are attributed to crystalline BaTiAl6O12. These crystals together with Al2O3:Ti centers are the responsible of the observed strong blue luminescence of the laser irradiated region upon UV excitation. The structural and optical characterizations of the bonded samples clarify the laser soldering procedure as well as the origin of the luminescence. Bond quality and bond strength were evaluated by scanning acoustic microscopy (SAM) and tensile tests, which results in a tensile stress of nearly 13 MPa, which is an acceptable value for glass sealants.

  18. Properties of large area ErBa2Cu3O(7-x) thin films deposited by ionized cluster beams

    NASA Technical Reports Server (NTRS)

    Levenson, L. L.; Stan, Mark A.; Bhasin, Kul B.

    1991-01-01

    ErBa2Cu3O(7-x) films have been produced by simultaneous deposition of Er, Ba, and Cu from three ionized cluster beam (ICB) sources at acceleration voltages of 0.3 to 0.5 kV. Combining ozone oxidation with ICB deposition at 650 C eliminated any need of post annealing processing. The substrates were rotated at 10 rotations per minute during the deposition which took place at a rate of about 3 to 4 nm. Films with areas up to 70 mm in diameter have been made by ICB deposition. These films, 100 nm thick, were deposited on SrTiO3 (100) substrates at 650 C in a mixture of six percent O3 in O2 at a total pressure of 4 x 10(exp -4) Torr. They had T(sub c) ranging from 84.3 K to 86.8 K over a 70 mm diameter and J(sub c) above 10(exp 6) A/sq cm at 77 K. X ray diffraction measurements of the three samples showed preferential c-axis orientation normal to the substrate surface. Scanning electron micrographs (SEM) of the three samples also show some texture dependence on sample position. For the three samples, there is a correlation between SEM texture, full width at half-maximum of rocking curves and J(sub c) versus temperature curves.

  19. Magnetic properties of Y 1- xGd xBa 2Cu 3O 7- δ polycrystals

    NASA Astrophysics Data System (ADS)

    Theuss, H.; Kronmüller, H.

    1995-02-01

    Y1-xGdxBa2Cu3O7-δ polycrystals are investigated with the purpose to obtain information about the influence of the paramagnetic Gd moments on the superconducting properties. Gd substitution does not affect the superconducting properties seriously but the paramagnetic Gd moments are just superposed to the superconducting diamagnetic moment without significant interaction. Magnetically the substituted Gd atoms behave, as if they were free Gd3+ ions. Relaxation experiments yield activation energies for thermally activated flux motion which are independent of the Gd content x but the critical current density, jc, decreases with increasing Gd content. Therefore the conclusion is drawn, that the pinning potential gets broader under the influence of Gd substitution but the barrier height remains constant. The maximum in the jc(H) curve which has become well known as the “fishtail-effect” is shifted to lower fields as the Gd content is increased. At temperatures below ≈ 10 K antiferromagnetic ordering of the Gd moments is observed, mainly for the fully substituted sample, GdBa2Cu3O7-δ.

  20. The use of buffer pellets to pseudo hot seed (RE)-Ba-Cu-O-(Ag) single grain bulk superconductors

    NASA Astrophysics Data System (ADS)

    Shi, Yunhua; Namburi, Devendra Kumar; Zhao, Wen; Durrell, John H.; Dennis, Anthony R.; Cardwell, David A.

    2016-01-01

    Reliable seeding of the superconducting (RE)Ba2Cu3O7-δ (RE-123) phase is a critical step in the melt growth of large, single grain, (RE)BaCuO ((RE)BCO) bulk superconductors. Recent improvements to the top seeded melt growth (TSMG) processing technique, which is an established method of fabricating bulk (RE)BCO superconductors, based on the use of a buffer layer between the seed and green body preform, has significantly improved the reliability of the single grain growth process. This technique has been used successfully for the primary TSMG and infiltration melt growth of all compositions within the ((RE)BCO-Ag) family of materials (where RE = Sm, Gd and Y), and in recycling processes. However, the mechanism behind the improved reliability of the melt process is not understood fully and its effect on the superconducting properties of the fully processed single grains is not clear. In this paper, we investigate the effect of the use of a buffer pellet between the seed and green body on the microstructure, critical current, critical temperature and trapped field of the bulk superconductor. We conclude that the introduction of the buffer pellet evolves the melt growth process towards that observed in the technologically challenging hot seeding technique, but has the potential to yield high quality single grain samples but by a commercially viable melt process.

  1. Magnetic Transport Properties in GdBa2Cu3- x Ru x O7- δ Superconducting Phase

    NASA Astrophysics Data System (ADS)

    Abou-Aly, A. I.; Mahmoud, S. A.; Awad, R.; Ibrahim, I. H.; Barakat, M. Me.

    2012-04-01

    Bulk superconducting samples of type GdBa2Cu3- x Ru x O7- δ phase, Gd-123, with x ranging from 0.0 to 0.15 were prepared by the conventional solid-state reaction technique. X-ray powder diffraction (XRD) and the electrical resistivity measurements were performed in order to investigate the effect of Ru4+ ions substitution on Gd-123 phase. Enhancement of the phase formation and the superconducting transition temperature T c for GdBa2Cu3- x Ru x O7- δ phase up to x=0.05 was observed. The effect of magnetic field up to 4.4 kG on the electrical resistivity behavior of the prepared samples was studied to investigate the flux motion of this phase. The derived flux pinning energy U, based on the thermally activated flux creep TAFC model, decreased with increasing the magnetic field B. The flux pinning energy followed the exponent behavior as U( B)˜ B - β . The superconducting transition width ΔT increased as the magnetic field increased, showing the scaling relation as ΔT˜ B n . Using Ambegaokar and Halperin AH theory, the magnetic field and temperature dependence of U was found to be U( B, T)˜ ΔTB - η , η= β+ n. The critical current density J c (0) enhanced up to x=0.05, beyond which it decreased with further increase in Ru-content.

  2. Preparation and Dielectric Measurements of the Rare Earth Green Phases R2BaCuO(5-x) (R = Y, Sm, Gd, Dy, Ho, Er, Yb)

    NASA Technical Reports Server (NTRS)

    Gonzalez-Titman, Carlos

    1994-01-01

    It has been demonstrated that R2BaCuO(5-x) (R = Y, Sm, Gd, Dy, Ho, Er, Yb) does not undergo significant densification unless the sintering temperatures are near the incongruent melting point or the sintering times are long. Good quality powders of Y2BaCuO(5-x) have been synthesized by using oxide raw materials or precursors such as acetates and nitrates. The acetates- and the nitrates-derived yttrium green phase resulted in finer particle sizes, acceptable dielectric properties and lower melting temperatures than those processed via oxide raw materials. The hot pressing technique has been employed to produce a dense R2BaCuO(5-x) (R=Y,Gd) substrate with satisfactory dielectric properties. Reactivity to reducing conditions, i.e. graphite die, limited the optimization of the properties. A high sensitivity to the annealing atmosphere has been demonstrated in Y2BaCuO,.,,. Oxygen treatment at 950 OC has been shown to improve the dielectric properties while treatment in nitrogen, at the same temperature, degraded desirable properties. A high sensitivity to the annealing atmosphere has been demonstrated in Y2BaCuO(5-x). Oxygen treatment at 950 C has been shown to improve the dielectric properties while treatment in nitrogen, at the same temperature, degraded desirable properties. The dielectric constants of the rare earth green phases R2BaCuO(5-x) were found to be low. Relaxation peaks were detected at low temperatures (T less than 150 K) and at high temperatures (150 less than T greater than 420 K). The dielectric losses and conductivities at 77 K were measured to be in the range of 10(exp -4) and 10(exp -12) (Omega-cm)(exp -1), respectively. Many parameters were found to exhibit dependencies on the rare earth cation sizes.

  3. Epitaxial Growth of YBa2Cu3O7 Films onto LaAlO3 (100) by Using Oxalates

    NASA Astrophysics Data System (ADS)

    Dominguez, A. Bustamante; Felix, L. León; Garcia, J.; Santibañez, J. Flores; Valladares, L. De Los Santos; Gonzalez, J. C.; Anaya, A. Osorio; Pillaca, M.

    Due to the current necessity to obtain epitaxial superconductor films at low cost, we report the growth of YBa2Cu3O7 (Y123) films by chemical deposition. The procedure involved simple steps such as precipitation of stoichiometric amounts of yttrium, barium and copper acetates in oxalic acid (H2C2O4). The precursor solution was dripped onto LaAlO3 (100) substrates with the help of a Fisher pipette. The films were annealed in oxygen atmosphere during 12 h at three different temperatures: 820 °C, 840 °C and 860 °C. After 820 °C and 860 °C annealing, X-ray diffraction (XRD) analysis revealed high intensity of the (00l) reflections denoting that most of the Y123 grains were c-axis oriented. In addition, we also observed a-axis oriented grains ((h00) reflexion), minor randomly oriented grains and other phases (such as Y2BaCuO5 and CuO). In contrast, the sample treated at 840 °C, we noticed c - and a-axis oriented grains, very small amounts of randomly oriented grains without formation of other phases. From the magnetization versus temperature measurements, the critical temperatures were estimated at 70K and 90K for the samples annealed at 820 °C and 860 °C respectively.

  4. Investigations of chemical interaction between Bi-based 2212 and (RE)Ba 2Cu 3O 7 high Tc superconducting materials

    NASA Astrophysics Data System (ADS)

    Cloots, R.; Rulmont, A.; Gillet, F.; Ausloos, M.

    Composite materials have been synthesized by mixing 90% (or 95%) YBa 2Cu 3O 7 and 10% (or 5%) Bi 2Sr 2Ca 1Cu 2O 8 by weight, and firing at 900°C to promote grain growth by inducing a liquid phase (Bi 2Sr 2Ca 1Cu 2O 8) in the system. The influence of the amount of liquid phase on the X-ray diffraction data and electrical properties is reported. Energy dispersive X-ray (EDX) analyses are also reported. The YBiBa 2O 6 phase is formed during the heat treatment and introduces additional chemical heterogeneities at the grain boundaries. A previously reported 2212-related superconducting phase, Bi 2(Sr,Ba) 2(Ca,Y)Cu 2O 8+y, could also be formed during the synthesis process, and its effect on the electrical resistance versus temperature measurements is discussed. Attempts to substitute RE ions (Dy 3+, Er 3+, Ho 3+) for Y 3+ in YBiBa 2O 6 have been successful and are reported in an appendix section. X-ray diffraction data are also reported. EDX analyses have been performed specifically for a typical ErBiBa 2O 6 compound and reveal the presence of a new Er 2Ba 4O 7 phase.

  5. Effect of Pb doping on the structure of HgBa 2CuO 4+δ single crystals

    NASA Astrophysics Data System (ADS)

    Schwer, H.; Kopnin, E.; Molinski, R.; Jun, J.; Meijer, G. I.; Conder, K.; Rossel, C.; Karpinski, J.

    1997-02-01

    X-ray structure analyses were performed with HgBa 2CuO 4+δ and Hg 1- xPb xBa 2CuO 4+δ single crystals. The onset of the superconducting transition of the crystals ranges from 78-92 K. Hg-1201 crystallizes with space group P4/mmm and has lattice pafameters a = 3.8907(2) Å and c = 9.556(1) Å. The structure was refined to R = 0.023 (wR2 = 0.036) in the ideal 1201 type with an excess oxygen content of 6(2)% and an occupancy of 97% at the Hg site. Pb-doping decreases the lattice parameters to a = 3.8836(2) Å and c = 9.553(1) Å, and the refinement converged at R = 0.042 (wR2 = 0.088). Pb atoms are shifted by 0.5 Å to (0.14, 0, 0) and the excess oxygen atom O(3) by 0.45 Å to (0.38, {1}/{2}, 0). It has not a well defined position in the lattice, but is distributed randomly in a ring-like configuration around the ( {1}/{2}, {1}/{2}, 0) site, supporting a Pb clustering model. Rather high anisotropic temperature factors U11 and U22 of Hg and apical O(1) atoms are observed, which are also present in higher members of the Hg(Pb)-12( n - 1) n series. They are discussed in terms of corrugated OHgO bonds. Comparison with other structure refinements of 1201 shows a correlation of the transition temperature with the position of the Ba atom, which seems to be a good indicator for the hole doping evel in 1201.

  6. Critical currents, magnetic relaxation and pinning in NdNdBa2Cu3O7 - δ films with BaZr3 generated columnar defects

    NASA Astrophysics Data System (ADS)

    Ijaduola, A. O.; Wee, S. H.; Goyal, A.; Martin, P. M.; Li, J.; Thompson, J. R.; Christen, D. K.

    2013-03-01

    The critical current density Jc and the magnetic relaxation (creep) properties have been studied for a set of NdBa2 Cu3O7 - δ (NdBCO) films doped with BaZrO3 (BZO) nanoparticles to form columnar defects. The dependence of Jc on the magnitude and orientation of the applied magnetic field Happ (0-6.5 T) and temperature T (5 K-Tc) was investigated. The normalized flux-creep rate S = - dln (J) / dln (t) was determined as a function of T. The current dependence of the effective activation energy Ueff (J) was derived using the formalism developed by Maley. The results are well described by an inverse power law type barrier of the form Ueff (J) ~U0(J0 / J) μ with fitted values for the pinning energy scale U0 and the glassy exponent μ. When comparing values for these parameters in the BZO-doped samples with those for their undoped control counterparts, the most striking difference is the larger scale of current density J0 in the doped samples (a factor of 2.4 higher), while the other pinning parameters do not differ strongly. In the BZO-doped materials, the pinning energy scale U0 increases with vortex density and J0 decreases, with both following simple power law dependences on the field. Support from Department of Energy (Office of Basic Energy Sciences-Materials Sciences and Engineering Division), Oak Ridge Associated Universities and Office of Electricity Delivery and Energy Reliability (Advanced Cables and Conductors).

  7. Tl 2Ba 2- xSr xCuO 6: A system exhibiting a compositionally controlled superconductor-metal transition

    NASA Astrophysics Data System (ADS)

    Ganguli, A. K.; Subramanian, M. A.

    1991-02-01

    Strontium-substituted thallium cuprates of the type Tl 2Ba 2- xSr xCuO 6 have been synthesized for various values of x. Single phases were obtained for x ≤ 1.2. The compounds crystallize in the tetragonal structure with space group {I4}/{mmm} as the parent Tl 2Ba 2CuO 6 oxide. Both a and c lattice parameter decrease with increase in x. Tc decreases gradually from 92 to 77 K ( x = 0.8). Beyond x = 1.0 superconductivity is lost. The x = 1.2 comparison is metallic down to 4.2 K.

  8. Effect of doping on flux pinning of GdBa{sub 2}Cu{sub 3}O{sub 7-y}

    SciTech Connect

    Zhang, L.; Xu, X.B.; Ding, S.Y.; Zheng, M.H.; Xiao, L.; Ren, H.T.; Jiao, Y.L.; Wang, X.L.; Lin, Z.W.; Zhu, J.G.

    2005-05-15

    Cylindrical single grains of GdBa{sub 2}Cu{sub 3}O{sub y} (Gd-123) with a diameter of 25 mm were successfully fabricated by melt-texture growth (MTG) process in air to study the influence of different starting powders on flux pinning. Measurements of the magnetic critical current density (J{sub c}) showed that it was possible to fabricate large Gd-123 single grain with a high J{sub c} at high temperatures and fields by means of properly controlling the starting powders of Gd{sub 2}O{sub 3}, BaCO{sub 3}, and CuO before the MTG process.

  9. COEXISTENCE OF DIFFERENT TYPES OF TRANSVERSE CONDUCTIVITY IN Y1-xPrxBa2Cu3 O7-δ SINGLE CRYSTALS WITH DIFFERENT PRASEODYMIUM CONCENTRATIONS

    NASA Astrophysics Data System (ADS)

    Vovk, R. V.; Vovk, N. R.; Goulatis, I. L.; Chroneos, A.

    2013-10-01

    In this paper, the influence of praseodymium doping on the conductivity across (transverse) the basal plane of high-temperature superconducting Y1-xPrxBa2Cu3O7-δ single crystals is investigated. It is determined that an increase of praseodymium doping leads to increased localization effects and the implementation of a metal-insulator transition Y1-xPrxBa2Cu3O7-δ, which always precedes the superconducting transition. The increase of the praseodymium concentration also leads to a significant displacement of the point of the metal-insulator transition to the low temperature region.

  10. The role of copper species on Cu/γ-Al2O3 catalysts for NH3-SCO reaction

    NASA Astrophysics Data System (ADS)

    Liang, Chunxia; Li, Xinyong; Qu, Zhenping; Tade, Moses; Liu, Shaomin

    2012-02-01

    UV-vis spectra, XRD, H2-TPR, TEM and ESR were used to characterize a series of Cu/γ-Al2O3 catalysts, which were prepared by incipient wetness impregnation using copper nitrate, copper acetate or copper sulfate as precursors, to study the role of Cu species on Cu/γ-Al2O3 catalysts for NH3-SCO reaction. It was found that the mixture of CuO phase and CuAl2O4 phase formed on various Cu/γ-Al2O3 catalysts, and the Cu species and dispersion had significant influence on the Cu/γ-Al2O3 activity. Highly dispersed CuO phase on the support would be related with its high activity for the NH3-SCO reaction.

  11. Nucleation Effects in Thermally Managed Graphite Fiber-Reinforced Al-Cu and Al-Si Composites

    NASA Astrophysics Data System (ADS)

    Seong, H. G.; Lopez, H. F.; Gajdardziska-Josifovska, M.; Rohatgi, P. K.

    2007-11-01

    The influence of heat extraction through fiber reinforcements on the resultant solidification morphologies was investigated in cast Al-Cu and Al-Si alloy composites reinforced with graphite fibers (GRFs). For this purpose, the GRFs were externally cooled by exposing their ends to ambient air during pressure infiltration. It was found that in the Al-Cu system, heat extraction through the fiber ends promoted the development of single α-Al envelopes around the GRFs. In particular, radial growth of the α envelopes occurred with a planar solid/liquid solidification front as a result of heat extraction. Apparently, the high thermal conductivity of GRFs causes significant heat extraction to enable the development of a positive temperature gradient at the GRF/melt interface. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAD) unveiled the occurrence of (002) α-Al//(0002)GR orientation relationship at α-Al/GRF interfaces. Preferential nucleation of primary Si along the graphite surfaces of the GRF-reinforced Al-Si alloy composite was also promoted by external fiber heat extraction. However, in this case, numerous nucleation events along the fiber interfaces were common, as well as nucleation at active substrates within the constrained melt. Finally, differential thermal analysis (DTA) indicated that the onset temperatures for nucleation shift toward higher values (by 7 °C for the Al-Cu composite and 2 °C for the Al-Si composite) when compared with their corresponding matrix alloys.

  12. Catalytic ozonation of petroleum refinery wastewater utilizing Mn-Fe-Cu/Al2O 3 catalyst.

    PubMed

    Chen, Chunmao; Yoza, Brandon A; Wang, Yandan; Wang, Ping; Li, Qing X; Guo, Shaohui; Yan, Guangxu

    2015-04-01

    There is of great interest to develop an economic and high-efficient catalytic ozonation system (COS) for the treatment of biologically refractory wastewaters. Applications of COS require options of commercially feasible catalysts. Experiments in the present study were designed to prepare and investigate a novel manganese-iron-copper oxide-supported alumina-assisted COS (Mn-Fe-Cu/Al2O3-COS) for the pretreatment of petroleum refinery wastewater. The highly dispersed composite metal oxides on the catalyst surface greatly promoted the performance of catalytic ozonation. Hydroxyl radical mediated oxidation is a dominant reaction in Mn-Fe-Cu/Al2O3-COS. Mn-Fe-Cu/Al2O3-COS enhanced COD removal by 32.7% compared with a single ozonation system and by 8-16% compared with Mn-Fe/Al2O3-COS, Mn-Cu/Al2O3-COS, and Fe-Cu/Al2O3-COS. The O/C and H/C ratios of oxygen-containing polar compounds significantly increased after catalytic ozonation, and the biodegradability of petroleum refinery wastewater was significantly improved. This study illustrates potential applications of Mn-Fe-Cu/Al2O3-COS for pretreatment of biologically refractory wastewaters.

  13. Catalytic ozonation of petroleum refinery wastewater utilizing Mn-Fe-Cu/Al2O 3 catalyst.

    PubMed

    Chen, Chunmao; Yoza, Brandon A; Wang, Yandan; Wang, Ping; Li, Qing X; Guo, Shaohui; Yan, Guangxu

    2015-04-01

    There is of great interest to develop an economic and high-efficient catalytic ozonation system (COS) for the treatment of biologically refractory wastewaters. Applications of COS require options of commercially feasible catalysts. Experiments in the present study were designed to prepare and investigate a novel manganese-iron-copper oxide-supported alumina-assisted COS (Mn-Fe-Cu/Al2O3-COS) for the pretreatment of petroleum refinery wastewater. The highly dispersed composite metal oxides on the catalyst surface greatly promoted the performance of catalytic ozonation. Hydroxyl radical mediated oxidation is a dominant reaction in Mn-Fe-Cu/Al2O3-COS. Mn-Fe-Cu/Al2O3-COS enhanced COD removal by 32.7% compared with a single ozonation system and by 8-16% compared with Mn-Fe/Al2O3-COS, Mn-Cu/Al2O3-COS, and Fe-Cu/Al2O3-COS. The O/C and H/C ratios of oxygen-containing polar compounds significantly increased after catalytic ozonation, and the biodegradability of petroleum refinery wastewater was significantly improved. This study illustrates potential applications of Mn-Fe-Cu/Al2O3-COS for pretreatment of biologically refractory wastewaters. PMID:25649390

  14. A Fluctuating State in the Framework Compounds (Ba,Sr)Al2O4

    PubMed Central

    Ishii, Yui; Tsukasaki, Hirofumi; Tanaka, Eri; Mori, Shigeo

    2016-01-01

    The structural fluctuation in hexagonal Ba1−xSrxAl2O4 with a corner-sharing AlO4 tetrahedral network was characterized at various temperatures using transmission electron microscopy experiments. For x ≤ 0.05, soft modes of q ~ (1/2, 1/2, 0) and equivalent wave vectors condense at a transition temperature (TC) and form a superstructure with a cell volume of 2a × 2b × c. However, TC is largely suppressed by Sr-substitution, and disappears for x ≥ 0.1. Furthermore, the q ~ (1/2, 1/2, 0) soft mode deviates from the commensurate value as temperature decreases and survives in nanoscaled regions below ~200 K. These results strongly suggest the presence of a new quantum criticality induced by the soft mode. Two distinct soft modes were observed as honeycomb-type diffuse scatterings in the high-temperature region up to 800 K. This intrinsic structural instability is a unique characteristic of the framework compound and is responsible for this unusually fluctuating state. PMID:26758625

  15. Evidence of electrochemical resistive switching in the hydrated alumina layers of Cu/CuTCNQ/(native AlOx)/Al junctions

    NASA Astrophysics Data System (ADS)

    Knorr, Nikolaus; Bamedi, Ameneh; Karipidou, Zoi; Wirtz, René; Sarpasan, Mustafa; Rosselli, Silvia; Nelles, Gabriele

    2013-09-01

    We have investigated bipolar resistive switching of Cu/CuTCNQ/Al cross-junctions in both vacuum and different gas environments. While the generally observed S-shaped I-V hysteresis was reproduced in ambient air, it was reversibly suppressed in well-degassed samples in vacuum and in dry N2. The OFF-switching currents in ambient air peaked when approximately +2.6 V was applied to the Al electrode at low voltage sweep rates. OFF-switching at constant bias was accelerated in humid and oxygen-rich atmospheres. For unbiased samples stored in air, ON-state (RON) and OFF-state (ROFF) resistances increased with time, and RON surpassed the initial ROFF after approximately one week. Retention times were enhanced for samples stored in vacuum and those with a larger cross-junction area. We suggest that resistive switching occurs in a hydrated native alumina layer at the CuTCNQ/Al interface that grows in thickness during exposure to ambient humidity: ON-switching by electrochemical metallization of free Al and/or Cu ions and OFF-switching by anodic oxidation of the Al electrode and previously grown metal filaments.

  16. Thermoelectric properties of Ni-doped CuAlO 2

    NASA Astrophysics Data System (ADS)

    Wongcharoen, Ngamnit; Gaewdang, Thitinai

    2009-07-01

    The polycrystalline Ni-doped CuAlO2 were obtained by solid state reaction method. The mixture of high purity grade of CuO, Al2O3 and Ni(NO3)2.6H2O powders was ground and then pressed by using uniaxial pressure. The obtained pellet was sintered in air at 1423 K for 24 h. XRD patterns showed the crystal structure of the as-sintered CuAl1-xNixO2 (0≤x≤0.10) belonging to rhombohedral, space group. No evidence of second phase was observed when Ni doping up to x=0.01. At Ni content x≥0.01 CuAl1-xNixO2 solid solution phase along with the CuO and CuAl2O4 phases were observed. From SEM micrographs, the grain size decreased from 6 to 2 μm when the amount of Ni in CuAl1-xNixO2 samples increased. Hall mobility and hole concentration of the as-sintered samples were obtained from Hall effect measurements at room temperature. The activation energy values deduced from the electrical resistivity measurements as a function of temperature were reported. The variation of Seebeck coefficient and power factor as a function of temperature was also investigated. From the experimental results, the substitution of Ni2+ ion in Cu+ site of CuAl1-xNixO2 material may be drawn.

  17. Finite Element Modeling for the Structural Analysis of Al-Cu Laser Beam Welding

    NASA Astrophysics Data System (ADS)

    Hartel, Udo; Ilin, Alexander; Bantel, Christoph; Gibmeier, Jens; Michailov, Vesselin

    Laser beam welding of aluminum and copper (Al-Cu) materials is a cost efficient joining technology to produce e.g. connector elements for battery modules. Distortion low connections can be achieved, which have electrical favorable properties. Numerical simulation of the laser beam welding process of Al-Cu dissimilar materials can provide further insight into principal process mechanisms and mechanical response of the joint parts. In this paper a methodology is introduced to investigate the structural behavior of Al-Cu joints in overlap joint with respect to welding distortions and residual stresses. First the material model of the homogeneous base materials are validated. Next, a generic material model approach is used to simulate the structural behavior of heterogeneous Al-Cu connections.

  18. Synthesis, Crystal and Electronic Structures of the Pnictides AE3TrPn3 (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

    DOE PAGES

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

    2015-09-24

    New ternary arsenides AE3TrAs3 (AE = Sr, Ba; Tr = Al, Ga) and their phosphide analogs Sr3GaP3 and Ba3AlP3 have been prepared by reactions of the respective elements at high temperatures. Single-crystal X-ray diffraction studies reveal that Sr3AlAs3 and Ba3AlAs3 adopt the Ba3AlSb3-type structure (Pearson symbol oC56, space group Cmce, Z = 8). This structure is also realized for Sr3GaP3 and Ba3AlP3. Likewise, the compounds Sr3GaAs3 and Ba3GaAs3 crystallize with the Ba3GaSb3-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.,more » 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+]3[Tr3+][Pn3-]3, or rather [AE2+]6[Tr2Pn6]12-, i.e., as Zintl phases.« less

  19. Fabrication and chemical composition of rf magnetron sputtered Tl-Ca-Ba-Cu-O high T sub c superconducting thin films

    SciTech Connect

    Subramanyam, G.; Radpour, F.; Kapoor, V.J.; Lemon, G.H. )

    1990-08-01

    High-temperature superconducing Tl-Ca-Ba-Cu-O (TlCaBaCuO) thin films were fabricated by rf magnetron sputtering on strontium titanate (SrTiO{sub 3}) substrates. Thin films of 0.5--0.7-{mu}m thickness were deposited by pure argon sputtering from a single composite powder target of Tl{sub 2}Ca{sub 2}Ba{sub 2}Cu{sub 3}O{sub {ital x}} at an rf power of 250 W and a pressure of 5 mTorr. As-deposited thin films were sintered and annealed in a thallium-rich ambient to obtain superconductivity with a zero resistance temperature ({ital T}{sub {ital c}0}) at 107 K. X-ray diffraction results showed highly {ital c}-axis oriented films with Tl{sub 2}Ca{sub 2}Ba{sub 2}Cu{sub 3}O{sub {ital x}} (2223) and Tl{sub 2}Ca{sub 1}Ba{sub 2}Cu{sub 2}O{sub {ital x}} (2122) phases present. Auger electron spectroscopy survey and depth profiles were performed to determine the compositional uniformity and impurity contents of the thin films. X ray photoelectron spectroscopy high-resolution spectra were obtained at the surface, in the bulk, and near the interface with the substrate. Our XPS results support two possible mechanisms for the creation of holes in the TlCaBaCuO compound: (1) partial substitution of Ca{sup 2+} for Tl{sup 3+} and (2) charge transfer from Tl{sup 3+} to the CuO layers resulting in a valence of Tl between +3 and +1 states and the creation of holes in the CuO layers. In addition, a wet chemical etching process was developed for patterning the as-deposited TlCaBaCuO thin films. A 125-{mu}m-wide line was formed using standard photolithography and wet chemical etching which, after heat treatments, showed superconductivity with a {ital T}{sub {ital c}0} of 80 K.

  20. CuO nanoparticles encapsulated inside Al-MCM-41 mesoporous materials via direct synthetic route

    PubMed Central

    Huo, Chengli; Ouyang, Jing; Yang, Huaming

    2014-01-01

    Highly ordered aluminum-containing mesoporous silica (Al-MCM-41) was prepared using attapulgite clay mineral as a Si and Al source. Mesoporous complexes embedded with CuO nanoparticles were subsequently prepared using various copper sources and different copper loadings in a direct synthetic route. The resulting CuO/Al-MCM-41 composite possessed p6mm hexagonally symmetry, well-developed mesoporosity, and relatively high BET surface area. In comparison to pure silica, these mesoporous materials embedded with CuO nanoparticles exhibited smaller pore diameter, thicker pore wall, and enhanced thermal stability. Long-range order in the aforementioned samples was observed for copper weight percentages as high as 30%. Furthermore, a significant blue shift of the absorption edge for the samples was observed when compared with that of bulk CuO. H2-TPR measurements showed that the direct-synthesized CuO/Al-MCM-41 exhibited remarkable redox properties compared to the post-synthesized samples, and most of the CuO nanoparticles were encapsulated within the mesoporous structures. The possible interaction between CuO and Al-MCM-41 was also investigated. PMID:24419589

  1. Step-by-step thermal transformations of a new porous coordination polymer [(H2O)5CuBa(Me2mal)2]n (Me2mal2-=dimethylmalonate): Thermal degradation to barium cuprate

    NASA Astrophysics Data System (ADS)

    Zauzolkova, Natalya; Dobrokhotova, Zhanna; Lermontov, Anatoly; Zorina, Ekaterina; Emelina, Anna; Bukov, Mikhail; Chernyshev, Vladimir; Sidorov, Aleksey; Kiskin, Mikhail; Bogomyakov, Artem; Lytvynenko, Anton; Kolotilov, Sergey; Velikodnyi, Yuriy; Kovba, Maksim; Novotortsev, Vladimir; Eremenko, Igor

    2013-01-01

    The reactions of CuSO4·5H2O, dimethylmalonic acid and Ba(OH)2·H2O (Cu: H2Me2mal: Ba=1: 2: 2) in aqueous and aqueous-ethanol solutions (H2O: EtOH=1: 1) resulted in formation of 3D-porous coordination polymers [(H2O)3(μ-H2O)2CuBa(μ3-Me2mal)(Me2mal)]n (1) and [(μ-H2O)CuBa(μ3-Me2mal)(μ4-Me2mal)]n (2), respectively. It has been shown that compound 2 was an intermediate in the thermal degradation of compound 1. Thorough studies of solid-state thermolysis of 1 and 2 allowed to detect formation of coordination polymer [CuBa(μ4-Me2mal)(μ5-Me2mal)]n (3), structure of which was determined by X-ray powder diffraction. It has been found that the channels in polymer 3 were accessible for guest molecules (MeOH). Theoretical estimation of methanol diffusion barrier was carried out. Complete solid-phase thermolysis of 1 and 2 leads to a mixture of BaCuO2, BaCO3, and CuO. Special conditions for obtaining of a crystalline phase of pure cubic BaCuO2 were determined.

  2. A novel method for the direct synthesis of the Y2Ba4Cu7O15- x superconductor

    NASA Astrophysics Data System (ADS)

    Khan, Nawazish A.; Mazhar, M.; Maqsood, Asghari

    2002-04-01

    We have developed a novel and simple method for the formation of the Y2Ba4Cu7O15-x (Y-247) superconductor at atmospheric oxygen pressure, using cuprous cyanide as the starting copper compound. Cuprous cyanide was found to act as a reaction accelerator and getter of oxygen during the formation of Y-247. Y-247 is prepared by solid-state reaction of Y2O3, BaCO3 and Cu2(CN)2 at the thermal stability temperature of Y-247 (860 °C) for 12 h. However, we found that the formation of the Y-247 phase could be accomplished in just a few minutes due to the high reactivity of cuprous cyanide. We carry out a longer time reaction to reduce the amount of simultaneous growth of a small amount of impurity phases. A predominantly single-phase Y-247 compound (confirmed by x-ray diffraction) with Tc(R = 0) = 93 K and Tc(onset) = 95 K could be achieved very easily by this method. It is worth emphasizing that, even in the quenched Y-247 from 860 °C, Tc(R = 0) = 93 K is confirmed by resistivity and magnetic measurements. The observations have shown that oxygen-deficient YBa2Cu3O6+x blocks in the Y-247 unit cell had enough oxygen required for 95 K superconductivity even at 860 °C. However, the amount of superconductivity was found to increase with post-annealing in an oxygen atmosphere at 350 °C.

  3. Solidification of hypereutectic Al-38 wt pct Cu alloy in microgravity and in unit gravity

    SciTech Connect

    Yu, H.; Tandon, K.N.; Cahoon, J.R.

    1997-05-01

    Solidification in microgravity aboard the space shuttle Endeavour resulted in a dramatic change in the morphology of the primary Al{sub 2}Cu phase compared to ground-based solidification in unit gravity. An Al-38 wt pct Cu ingot directionally solidified at a rate of 0.015 mm/s with a temperature gradient of 1.69 K/mm exhibited large, well-formed dendrites of primary Al{sub 2}Cu phase. Ingots solidified under similar conditions in unit gravity contained primary Al{sub 2}Cu phase with smooth, faceted surfaces. The primary Al{sub 2}Cu phase spacing in the microgravity ingot was much greater than that in the unit gravity ingot, 670 {micro}m compared to 171 {micro}m. It is suggested that thermosolutal mixing in the unit gravity ingot reduces the buildup of an Al-rich layer at the solid/liquid interface, which increases the stability of the interface resulting in smooth, faceted particles of Al{sub 2}Cu phase. It is also suggested that the large difference in primary phase spacings is due mostly to the difference in morphology rather than changes in parameters that might influence dendrite ripening mechanisms. The presence or absence of gravity had no effect on the interlamellar spacing of the inter-Al{sub 2}Cu phase eutectic. The ingot solidified in microgravity exhibited almost no longitudinal macrosegregation, in agreement with the theory of inverse segregation in the absence of thermosolutal convection. The ingot solidified in unit gravity exhibited considerable longitudinal macrosegregation, with the chilled end having about 6 wt pct more Cu than the average composition. It is not clear whether the segregation results from thermosolutal convection during solidification or from sedimentation during melting.

  4. Cu-doped AlN: A possible spinaligner at room-temperature grown by molecular beam epitaxy?

    SciTech Connect

    Ganz, P. R.; Schaadt, D. M.

    2011-12-23

    Cu-doped AlN was prepared by plasma assisted molecular beam epitaxy on C-plane sapphire substrates. The growth conditions were investigated for different Cu to Al flux ratios from 1.0% to 4.0%. The formation of Cu-Al alloys on the surface was observed for all doping level. In contrast to Cu-doped GaN, all samples showed diamagnetic behavior determined by SQUID measurements.

  5. Microstructure and Erosion Resistance Performance of ZrAlN/Cu Coating

    NASA Astrophysics Data System (ADS)

    Du, Jun; Zhu, Xiaoying; Zhang, Ping; Cai, Zhihai

    ZrAlN/Cu coating has been deposited onto Ti-6Al-4 V substrate by reactive magnetron sputtering in order to improve its erosion resistance. The morphology and microstructure were studied combined with Field Emission Scanning Electron Microscrope(FSEM), X-ray Diffraction(XRD), X-ray Photoelectron Spectroscopy(XPS) and Transmission Electron Microscopy(TEM). Coatings hardness and toughness were measured by nano-indentation method and Vicker indentation method respectively. It has been found that Zr0.79Al0.19Cu0.02N coating possess dense columnar structure with 20∼40 nm columnar grains exbibiting (100) preferential orientation. XRD reflection peaks slightly shifts to higher angle, showing some of 19at%Al and 2at%Cu substitutely dissolves into face-centered cubic(FCC) ZrN lattice, XPS proves the existence of AlN and Cu phase in coating. Zr0.79Al0.19Cu0.02N coating demonstrates best erosion resistance at 15°∼90° impingement angle compared with Ti6Al4 V substrate, ZrN and Zr0.80Al0.20N coating, attributing to combination of high hardness(40.7 GPa) and good toughness.

  6. Investigation of thermal, mechanical and magnetic behaviors of the Cu-11%Al alloy with Ag and Mn additions

    SciTech Connect

    Silva, R.A.G.; Paganotti, A.; Gama, S.; Adorno, A.T.; Carvalho, T.M.; Santos, C.M.A.

    2013-01-15

    The investigation of thermal, mechanical and magnetic behaviors of the Cu-11%Al, Cu-11%Al-3%Ag, Cu-11%Al-10%Mn and Cu-11%Al-10%Mn-3%Ag alloys was made using microhardness measurements, differential scanning calorimetry, X-ray diffractometry, scanning electron microscopy, energy dispersion X-ray spectroscopy and magnetic moment change with applied field measurement. The results indicated that the Mn addition changes the phase stability range, the microhardness values and makes undetectable the eutectoid reaction in annealed Cu-11%Al and Cu-11%Al-3%Ag alloys while the presence of Ag does not modify the phase transformation sequence neither microhardness values of the annealed Cu-11%Al and Cu-11%Al-10%Mn alloys, but it increases the magnetic moment of this latter at about 2.7 times and decreases the rates of eutectoid and peritectoid reactions of the former. - Highlights: Black-Right-Pointing-Pointer The microstructure of Cu-Al alloy is modified in the Ag presence. Black-Right-Pointing-Pointer ({alpha} + {gamma}) phase is stabilized down to room temperature when Ag is added to Cu-Al alloy. Black-Right-Pointing-Pointer Ag-rich phase modifies the magnetic characteristics of Cu-Al-Mn alloy.

  7. Studies of Y-Ba-Cu-O single crystals by x-ray absorption spectroscopy

    SciTech Connect

    Krol, A.; Ming, Z.H.; Kao, Y.H.; Nuecker, N.; Roth, G.; Fink, J.; Smith, G.C.; Erband, A.; Mueller-Vogt, G.; Karpinski, J.; Kaldis, E.; Schoenmann, K.

    1992-02-01

    The symmetry and density of unoccupied states of YBa{sub 2}Cu{sub 3}O{sub 7} YBa{sub 2}Cu{sub 4}O{sub 8} have been investigated by orientation dependent x-ray absorption spectroscopy on the O 1s edge using a bulk-sensitive fluorescence-yield-detection method. It has been found that the O 2p holes are distributed equally between the CuO{sub 2} planes and CuO chains and that the partial density of unoccupied O 2p states in the CuO{sub 2} planes are identical in both systems investigated. The upper Hubbard band has been observed in the planes but not in the chains in both systems. 18 refs.

  8. Non-isovalent substitution of Ba 2+ in superconducting YBa 2Cu 3O 7-y

    NASA Astrophysics Data System (ADS)

    Rajarajan, A. K.; Guptasarma, P.; Palkar, V. R.; Ayyub, P.; Multani, M. S.; Gupta, L. C.; Vijayaraghavan, R.

    1988-06-01

    We report the structural, magnetic and superconducting properties of YBa2-xMxCu3O7 (M=La3+ or K+). Single-phase compounds form over a wide range of x in YBa2-xMxCu3O7 and up to x = 0.2 in YBa2-xMxCu3O7. A substituent concentration of 15% triggers an orthorhombic to tetragonal phase15 transition in both systems. In spite of the associated disorder in the Cu(1)-0(1) chains, such a transition does not affect Tc drastically. Tc gets systematically depressed with increasing x. A temperature-dependent paramagnetic response is observed in YBa2-xMxCu3O7 between 90 and 300K.

  9. Photogenerated carriers in La 2CuO 4, YBa 2Cu 3O 7-δ, and Tl 2Ba 2Ca (1-x)Gd xCu 2O 8: Polarizability-induced pairing of polarons

    NASA Astrophysics Data System (ADS)

    Foster, C. M.; Heeger, A. J.; Kim, Y. H.; Stucky, G.; Herron, N.

    1989-12-01

    Photoinduced absorption measurements have been carried out on Tl 2Ba 2Ca (1-x)Gd xCu 2O 8 (x=0.02), YBa 2Cu 3O 7-δ (δ=0.75) and La 2CuO 4. The observation of infrared active vibrational (IRAV) modes and an associated electronic transition with common intensity and temperature dependence indicate the formation of self-localized polarons as photogenerated carriers. The photoinduced electronic transition deep in the infrared implies a major shift of oscillator strength leading to a large local polarizability in the vicinity of the polaron. We suggest that the enhanced local polarizability may provide an important mechanism for pairing.

  10. Formation of CuAlO2 Film by Ultrasonic Spray Pyrolysis

    NASA Astrophysics Data System (ADS)

    Iping, S.; Lockman, Zainovia; Hutagalung, S. D.; Kamsul, A.; Matsuda, Atsunori

    2011-10-01

    Smooth, crack free and homogenous CuAlO2 film was produced by chemical solution deposition process via spray pyrolysis technique on a cleaned Si substrate. The precursor solution used was comprised of a mixture of 45.87 mmol Cu(NO3)2.3H2O and 90 mmol Al(NO3)3.9H2O at ratio of Cu:Al = 1.2:1. The precursor solution was placed in a mist chamber and was atomized by a nebulizer to produce precursor mist. The precursor mist was then carried out by Ar gas and was sprayed onto a heated Si. Two main parameters were studied: the distance between the nozzle of the precursor mist chamber and the Si and the temperature of the Si substrate. It appears that from the XRD data, CuAlO2 can be detected for samples prepared by spraying the precursor mist at temperature of > 550 °C with distance between the nozzle and the substrate of 3cm. Reaction of the Cu and Al ions in the mist near the substrate may have promoted the crystallisation of CuAlO2.

  11. Dissolution of Precipitates During Solution Treatment of Al-Mg-Si-Cu Alloys

    NASA Astrophysics Data System (ADS)

    Zhang, Xukai; Guo, Mingxing; Zhang, Jishan; Zhuang, Linzhong

    2016-02-01

    A model combining classical diffusion-controlled dissolution equation for a single spherical particle and Johnson-Mehl-Avrami-like equation is used to deal with dissolution process for different kinds of precipitations (Si, Mg2Si, Q(Al1.9Mg4.1Si3.3Cu)) in Al-Mg-Si-Cu alloys. The results reveal that the dissolution time of precipitates increases with increasing their sizes and solute concentrations in the alloy matrix; for the same size and concentration, their dissolution times follow Si > Q(Al1.9Mg4.1Si3.3Cu) > Mg2Si. Two precipitates (Mg2Si and Al1.9Mg4.1Si3.3Cu) with a size of about 700 nm were obtained in a cold rolled Al-Mg-Si-Cu-Zn alloy, and the complete dissolution time is about 15 seconds, which is basically the same as the calculated time by the developed model. The theoretical prediction of dissolution time can be greatly used to design solution treatment and thermomechanical processing parameters of Al-Mg-Si-Cu alloys.

  12. Crystallographic Study of Mixtures La1+xBa2-xCu3Oy (x=0,0.2,0.4,0.6) after annealing at 860 deg. C

    SciTech Connect

    Stergiou, A.; Yilmaz, S.; Stergiou, C.

    2007-04-23

    Four powder mixtures with chemical formula La1+xBa2-xCu3Oy was prepared. The mixtures were heated in free atmosphere, at temperature 850 deg. C for 60h and then at 860 deg. C for 40h. XRD measurements were obtained with CuKa radiation. The samples were characterized with the help of the PDF and refined, using the Rietveld's 'Powder Profile Analysis'. Four phases, same for all the samples, were found: (La,Ba)2CuO4, BaCuO2, LaBa2Cu3O7-d, and BaCO3. The percentages of the tour phases are changed, as the x quantity increases, and varied from 38, 25, 18, 19%, for x=0, to 69, 14, 7, 10%, for x=0.6, respectively.

  13. Phase-Transformation-Induced Extra Thermal Expansion Behavior of (SrxBa1-x)TiO3/Cu Composite.

    PubMed

    Sheng, Jie; Wang, Lidong; Li, Shouwei; Yin, Benke; Liu, Xiangli; Fei, Wei-Dong

    2016-01-01

    The properties of metal matrix composites (MMCs) can be optimized effectively through adjusting the type or the volume fraction of reinforcement. Generally, the coefficient of thermal expansion (CTE) of MMCs can be reduced by increasing the volume fraction of the reinforcement with lower CTE than metal matrix. However, it is great challenge to fabricate low CTE MMCs with low reinforcement volume fraction because of the limitation of reinforcement CTEs. SrxBa1-xTiO3 (SBT) powder presents negative thermal expansion behavior during the phase transformation from tetragonal to cubic phase. Here, we demonstrate that the phase transformation of SBT can be utilized to reduce and design the thermal expansion properties of SBT particle-reinforced Cu (SBT/Cu) composite, and ultralow CTE can be obtained in SBT/Cu composite. The X-ray diffraction analysis on heating indicates that the temperature range of phase transformation is extended greatly, therefore, the low CTE can be achieved within wide temperature range. Landau-Devonshire theory study on the phase transformation behaviors of SBT particles in the composite indicates that thermal mismatch stress significantly affects the Curie temperature of SBT particles and the CTE of the composite. The results given in the present study provide a new approach to design the MMCs with low CTE. PMID:27255420

  14. Phase-Transformation-Induced Extra Thermal Expansion Behavior of (SrxBa1-x)TiO3/Cu Composite.

    PubMed

    Sheng, Jie; Wang, Lidong; Li, Shouwei; Yin, Benke; Liu, Xiangli; Fei, Wei-Dong

    2016-01-01

    The properties of metal matrix composites (MMCs) can be optimized effectively through adjusting the type or the volume fraction of reinforcement. Generally, the coefficient of thermal expansion (CTE) of MMCs can be reduced by increasing the volume fraction of the reinforcement with lower CTE than metal matrix. However, it is great challenge to fabricate low CTE MMCs with low reinforcement volume fraction because of the limitation of reinforcement CTEs. SrxBa1-xTiO3 (SBT) powder presents negative thermal expansion behavior during the phase transformation from tetragonal to cubic phase. Here, we demonstrate that the phase transformation of SBT can be utilized to reduce and design the thermal expansion properties of SBT particle-reinforced Cu (SBT/Cu) composite, and ultralow CTE can be obtained in SBT/Cu composite. The X-ray diffraction analysis on heating indicates that the temperature range of phase transformation is extended greatly, therefore, the low CTE can be achieved within wide temperature range. Landau-Devonshire theory study on the phase transformation behaviors of SBT particles in the composite indicates that thermal mismatch stress significantly affects the Curie temperature of SBT particles and the CTE of the composite. The results given in the present study provide a new approach to design the MMCs with low CTE.

  15. Phase-Transformation-Induced Extra Thermal Expansion Behavior of (SrxBa1-x)TiO3/Cu Composite

    NASA Astrophysics Data System (ADS)

    Sheng, Jie; Wang, Lidong; Li, Shouwei; Yin, Benke; Liu, Xiangli; Fei, Wei-Dong

    2016-06-01

    The properties of metal matrix composites (MMCs) can be optimized effectively through adjusting the type or the volume fraction of reinforcement. Generally, the coefficient of thermal expansion (CTE) of MMCs can be reduced by increasing the volume fraction of the reinforcement with lower CTE than metal matrix. However, it is great challenge to fabricate low CTE MMCs with low reinforcement volume fraction because of the limitation of reinforcement CTEs. SrxBa1-xTiO3 (SBT) powder presents negative thermal expansion behavior during the phase transformation from tetragonal to cubic phase. Here, we demonstrate that the phase transformation of SBT can be utilized to reduce and design the thermal expansion properties of SBT particle-reinforced Cu (SBT/Cu) composite, and ultralow CTE can be obtained in SBT/Cu composite. The X-ray diffraction analysis on heating indicates that the temperature range of phase transformation is extended greatly, therefore, the low CTE can be achieved within wide temperature range. Landau-Devonshire theory study on the phase transformation behaviors of SBT particles in the composite indicates that thermal mismatch stress significantly affects the Curie temperature of SBT particles and the CTE of the composite. The results given in the present study provide a new approach to design the MMCs with low CTE.

  16. Investigation on photoluminescence properties and defect chemistry of GdAlO3:Dy3+ Ba2+ phosphors

    NASA Astrophysics Data System (ADS)

    Selvalakshmi, Thangaraj; Sellaiyan, Selvakumar; Uedono, Akira; Semba, Takaaki; Bose, Arumugam Chandra

    2016-08-01

    GdAlO3:Dy3+ Ba2+ phosphors are synthesized by citrate-based sol-gel method. Photoluminescence and positron annihilation studies are used to investigate the emission and defect chemistry of the phosphors respectively. The strong yellow (Dy3+) emission properties of phosphors are discussed for various concentrations of Dy3+ ions. Upon the addition of Ba2+ ion, an enhancement in emission intensity is observed due to the lattice distortions around Dy3+ ion. The positron studies indicate the presence of defects at crystallite boundaries, vacancy clusters and large voids in the materials. The influence of Ba2+ ion on the photoluminescence and lattice distortion around Dy3+ is also explored.

  17. Ba2Cu2Te2P2O13: A new telluro-phosphate with S=1/2 Heisenberg chain

    NASA Astrophysics Data System (ADS)

    Xia, Mingjun; Shen, Shipeng; Lu, Jun; Sun, Young; Li, R. K.

    2015-10-01

    A new telluro-phosphate compound Ba2Cu2Te2P2O13 with S=1/2 Heisenberg chain has been successfully synthesized by solid state reaction and grown by flux method. Single crystal X-ray diffraction reveals that Ba2Cu2Te2P2O13 crystallizes into a monoclinic space group C2/c and cell parameters of a=17.647(3) Å, b=7.255(2) Å, c=9.191(2) Å and β=100.16 (3)°. In the structure of Ba2Cu2Te2P2O13, one dimensional [CuTePO7]3- chains are formed by tetrahedral PO4 and trigonal bi-pyramidal TeO4 joining square planar CuO4 groups. Those [CuTePO7]3- chains are inter-connected by sharing one oxygen atom from the TeO4 group to form two dimensional layers. Magnetic susceptibility and specific heat measurements confirm that the title compound is a model one dimensional Heisenberg antiferromagnetic chain system.

  18. Magnetodielectric detection of magnetic quadrupole order in Ba(TiO)Cu4(PO4)4 with Cu4O12 square cupolas

    NASA Astrophysics Data System (ADS)

    Kimura, K.; Babkevich, P.; Sera, M.; Toyoda, M.; Yamauchi, K.; Tucker, G. S.; Martius, J.; Fennell, T.; Manuel, P.; Khalyavin, D. D.; Johnson, R. D.; Nakano, T.; Nozue, Y.; Rønnow, H. M.; Kimura, T.

    2016-10-01

    In vortex-like spin arrangements, multiple spins can combine into emergent multipole moments. Such multipole moments have broken space-inversion and time-reversal symmetries, and can therefore exhibit linear magnetoelectric (ME) activity. Three types of such multipole moments are known: toroidal; monopole; and quadrupole moments. So far, however, the ME activity of these multipole moments has only been established experimentally for the toroidal moment. Here we propose a magnetic square cupola cluster, in which four corner-sharing square-coordinated metal-ligand fragments form a noncoplanar buckled structure, as a promising structural unit that carries an ME-active multipole moment. We substantiate this idea by observing clear magnetodielectric signals associated with an antiferroic ME-active magnetic quadrupole order in the real material Ba(TiO)Cu4(PO4)4. The present result serves as a useful guide for exploring and designing new ME-active materials based on vortex-like spin arrangements.

  19. Effect of delayed aging on mechanical properties of an Al-Cu-Mg alloy

    SciTech Connect

    Ravindranathan, S.P.; Kashyap, K.T.; Kumar, S.R.; Ramachandra, C.; Chatterji, B.

    2000-02-01

    The effect of delayed aging on mechanical properties is characteristically found in Al-Mg-Si alloys. Delayed aging refers to the time elapsed between solutionizing and artificial aging. Delayed aging leads to inferior properties. This effect was investigated in an Al-Cu-Mg alloy (AU2GN) of nominal composition Al-2Cu-1.5Mg-1Fe-1Ni as a function of delay. This alloy also showed a drop in mechanical properties with delay. The results are explained on the basis of Pashley's kinetic model to qualitatively explain the evolution of a coarse precipitate structure with delay. It is found that all the results of delayed aging in the Al-Cu-Mg alloys are similar to those found in Al-Mg-Si alloys.

  20. Suppression of superconductivity with Pr substitution in Nd 1- xPr xBaCaCu 3O 7 system

    NASA Astrophysics Data System (ADS)

    Awana, V. P. S.; Cardoso, Claudio A.; de Lima, O. F.; Singh, Rajvir; Narlikar, A. V.; Yelon, W. B.; Malik, S. K.

    1999-05-01

    The structural, superconducting and magnetic properties of Nd 1- xPr xBaCaCu 3O 7 system with x=0.0, 0.10, 0.25, 0.35, 0.50, 0.75 and 1.0 have been investigated. X-ray diffraction results reveal that Pr substitutes isostructurally in NdBaCaCu 3O 7 (Nd:1113) superconductor with complete solubility. The superconducting transition temperature ( Tc), measured by ac susceptibility technique, decreases with increasing x. However, suppression of Tc with increasing Pr substitution is less in Nd:1113 superconductor compared to that reported for Nd 1- xPr xBa 2Cu 3O 7 system. Interestingly, in the fully Pr substituted compounds of the above series, i.e., in PrBaCaCu 3O 7 and PrBa 2Cu 3O 7, the Pr moments order antiferromagnetically with TN of 10 and 17 K, respectively. The present results along those reported earlier [V.P.S. Awana, J. Horvat, S.X. Dou, A. Sedky, A.V. Narlikar, J. Magn. Magn. Mater., 182 (1998) L280; V.P.S. Awana, S.X. Dou, S.K. Malik, Rajvir Singh, A.V. Narlikar, D.A. Landinez Tellez, J.M. Ferreira, J. Albino Aguiar, S. Uma, E. Gmelin, W.B. Yelon, J. Magn. Magn. Mater., 187 (1998) 192], clearly suggest that there is a correlation between the Tc suppression due to Pr and the magnetic ordering temperature of the fully substituted Pr moments in these systems. The TN may be taken to be a measure of the strength of hybridization between the Pr-4f electrons with Cu-O conduction band, and hence a lower TN may imply a less deleterious effect on superconductivity.

  1. Suppression of activation energy and superconductivity by the addition of Al{sub 2}O{sub 3} nanoparticles in CuTl-1223 matrix

    SciTech Connect

    Jabbar, Abdul; Qasim, Irfan; Mumtaz, M.; Zubair, M.; Nadeem, K.; Khurram, A. A.

    2014-05-28

    Low anisotropic (Cu{sub 0.5}Tl{sub 0.5})Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10−δ} (CuTl-1223) high T{sub c} superconducting matrix was synthesized by solid-state reaction and Al{sub 2}O{sub 3} nanoparticles were prepared separately by co-precipitation method. Al{sub 2}O{sub 3} nanoparticles were added with different concentrations during the final sintering cycle of CuTl-1223 superconducting matrix to get the required (Al{sub 2}O{sub 3}){sub y}/CuTl-1223, y = 0.0, 0.5, 0.7, 1.0, and 1.5 wt. %, composites. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive X-ray, and dc-resistivity (ρ) measurements. The activation energy and superconductivity were suppressed with increasing concentration of Al{sub 2}O{sub 3} nanoparticles in (CuTl-1223) matrix. The XRD analysis showed that the addition of Al{sub 2}O{sub 3} nanoparticles did not affect the crystal structure of the parent CuTl-1223 superconducting phase. The suppression of activation energy and superconducting properties is most probably due to weak flux pinning in the samples. The possible reason of weak flux pinning is reduction of weak links and enhanced inter-grain coupling due to the presence of Al{sub 2}O{sub 3} nanoparticles at the grain boundaries. The presence of Al{sub 2}O{sub 3} nanoparticles at the grain boundaries possibly reduced the number of flux pinning centers, which were present in the form of weak links in the pure CuTl-1223 superconducting matrix. The increase in the values of inter-grain coupling (α) deduced from the fluctuation induced conductivity analysis with the increased concentration of Al{sub 2}O{sub 3} nanoparticles is a theoretical evidence of improved inter-grain coupling.

  2. Ba(Zn1−2xMnxCux)2As2: A Bulk Form Diluted Ferromagnetic Semiconductor with Mn and Cu Codoping at Zn Sites

    PubMed Central

    Man, Huiyuan; Guo, Shengli; Sui, Yu; Guo, Yang; Chen, Bin; Wang, Hangdong; Ding, Cui; Ning, F.L.

    2015-01-01

    We report the synthesis and characterization of a bulk form diluted magnetic semiconductor Ba(Zn1−2xMnxCux)2As2 with the crystal structure identical to that of “122” family iron based superconductors and the antiferromagnet BaMn2As2. No ferromagnetic order occurs with (Zn, Mn) or (Zn, Cu) substitution in the parent compound BaZn2As2. Only when Zn is substituted by both Mn and Cu simultaneously, can the system undergo a ferromagnetic transition below TC ~ 70 K, followed by a magnetic glassy transition at Tf  ~ 35 K. AC susceptibility measurements for Ba(Zn0.75Mn0.125Cu0.125)2As2 reveal that Tf strongly depends on the applied frequency with and a DC magnetic field dependence of , demonstrating that a spin glass transition takes place at Tf. As large as −53% negative magnetoresistance has been observed in Ba(Zn1−2xMnxCux)2As2, enabling its possible application in memory devices. PMID:26492957

  3. Surface impedance of R 1(Nd xBa 2- x)Cu 3O 7- δ (R=Nd, Y) thin films

    NASA Astrophysics Data System (ADS)

    Salluzzo, M.; Andreone, A.; Cassinese, A.; Di Capua, R.; Di Gennaro, E.; Iavarone, M.; Maglione, M. G.; Vaglio, R.

    2002-08-01

    We have studied the effect of Nd/Ba substitution on the superconducting properties of R 1(Nd xBa 2- x)Cu 3O 7 (R=Nd, Y) thin films by using microwave penetration depth and surface resistance measurements. Data on samples characterised by a Nd-excess of 4-5% have been collected by using a microstrip resonator at frequencies of 1.44 and 9.7 GHz and a symmetric dielectric resonator technique in TE 0 1 1 mode at 19.8 GHz. A quadratic bT2 low temperature dependence of the penetration depth is observed for the Nd-rich samples, with the coefficient b decreasing with the frequency. The data can be reasonably explained in a d-wave framework supposing that Nd at Ba site behaves, both in Nd 1+ x Ba 2- xCu 3O 7 and Y 1(Nd xBa 2- x)Cu 3O 7, as a resonant impurity, as confirmed by scanning tunnelling spectroscopy. The changes of the temperature dependence of the penetration depth with the frequency can be explained with a two fluid approach taking into account the frequency dependence of the complex conductivity.

  4. Ba(Zn(1-2x)MnxCux)2As2: A Bulk Form Diluted Ferromagnetic Semiconductor with Mn and Cu Codoping at Zn Sites.

    PubMed

    Man, Huiyuan; Guo, Shengli; Sui, Yu; Guo, Yang; Chen, Bin; Wang, Hangdong; Ding, Cui; Ning, F L

    2015-10-23

    We report the synthesis and characterization of a bulk form diluted magnetic semiconductor Ba(Zn(1-2x)MnxCux)2As2 (0.025 ≤ x ≤ 0.2) with the crystal structure identical to that of "122" family iron based superconductors and the antiferromagnet BaMn2As2. No ferromagnetic order occurs with (Zn, Mn) or (Zn, Cu) substitution in the parent compound BaZn2As2. Only when Zn is substituted by both Mn and Cu simultaneously, can the system undergo a ferromagnetic transition below TC ~ 70 K, followed by a magnetic glassy transition at Tf  ~ 35 K. AC susceptibility measurements for Ba(Zn0.75Mn0.125Cu0.125)2As2 reveal that Tf strongly depends on the applied frequency with [formula in text] and a DC magnetic field dependence of [formula in text], demonstrating that a spin glass transition takes place at Tf. As large as -53% negative magnetoresistance has been observed in Ba(Zn(1-2x)MnxCux)2As2, enabling its possible application in memory devices.

  5. Ba(Zn1-2xMnxCux)2As2: A Bulk Form Diluted Ferromagnetic Semiconductor with Mn and Cu Codoping at Zn Sites

    NASA Astrophysics Data System (ADS)

    Man, Huiyuan; Guo, Shengli; Sui, Yu; Guo, Yang; Chen, Bin; Wang, Hangdong; Ding, Cui; Ning, F. L.

    2015-10-01

    We report the synthesis and characterization of a bulk form diluted magnetic semiconductor Ba(Zn1-2xMnxCux)2As2 with the crystal structure identical to that of “122” family iron based superconductors and the antiferromagnet BaMn2As2. No ferromagnetic order occurs with (Zn, Mn) or (Zn, Cu) substitution in the parent compound BaZn2As2. Only when Zn is substituted by both Mn and Cu simultaneously, can the system undergo a ferromagnetic transition below TC ~ 70 K, followed by a magnetic glassy transition at Tf  ~ 35 K. AC susceptibility measurements for Ba(Zn0.75Mn0.125Cu0.125)2As2 reveal that Tf strongly depends on the applied frequency with and a DC magnetic field dependence of , demonstrating that a spin glass transition takes place at Tf. As large as -53% negative magnetoresistance has been observed in Ba(Zn1-2xMnxCux)2As2, enabling its possible application in memory devices.

  6. Effect of Sr-substitution on the restitution of superconductivity in Pr-substituted at rare earth and Ba-site in EuBa 2Cu 3O z

    NASA Astrophysics Data System (ADS)

    Thampi, R. S.; Rayaprol, S.; Mavani, Krushna; Kuberkar, D. G.; Gonal, M. R.; Prasad, R.; Kulkarni, R. G.

    2001-06-01

    We report the effect of Sr-substitution in restoring the superconductivity of Pr-doped (Eu 1- xPr x)Ba 2Cu 3O z [A] and Eu(Ba 2- xPr x)Cu 3O z [B] samples. The structural and superconducting properties of these A and B samples have been investigated using X-ray diffraction, a.c. susceptibility, electrical resistivity, d.c. magnetization and iodometric measurements. It is observed that the superconductivity gets suppressed at the rate of 1.6 K per at.% of Pr substitution at Eu-site due to the localization of mobile holes, while the sample with 15% Pr at Ba-site [B(0.3)] becomes non-superconducting mainly due to the hole filling and localization of holes. However, the increasing substitution of Sr at Ba-site in both A(0.4) and B(0.3) samples upto 25% resulted in the restoration of superconductivity (T c∼33 K) due to the delocalization of holes. Interestingly, the increasing substitution of Sr at Eu-site in the non-superconducting B(0.4) sample upto 30%, increases Tc from 0 to 52 K mainly due to the hole doping mechanism which is much faster and larger restoration of superconductivity than the Ba-site doping of Sr in the same sample.

  7. First-principles study of nitrogen-doped CuAlO2

    NASA Astrophysics Data System (ADS)

    Xu, Ying; Ao, Zhi Min; Yuan, Ding Wang

    2012-08-01

    The electronic structure and formation energies of N-doped CuAlO2 are studied using first-principles calculations. It is found that, when a N atom is doped into CuAlO2, the N atom prefers to substitute an O atom rather than to occupy an interstitial site of the Cu layer. The NO acts as a shallow accepter while the Ni acts as a deep accepter. The results of the electronic structure show that the N-doping doesn't alter the band gap of CuAlO2 for the both cases. In the substitutional case, the N impurity states occur at the top of valance band maximum (VBM), which provides holes and increases the p-type conductivity. However, in the interstitial case, the N impurity states occur in the middle of the band gap, which are more localized and this indicates that it is not good for p-type conductivity.

  8. Structural and magnetic characterization of the complete delafossite solid solution (CuAlO₂)₁-x(CuCrO₂)x.

    PubMed

    Barton, Phillip T; Seshadri, Ram; Knöller, Andrea; Rosseinsky, Matthew J

    2012-01-11

    We have prepared the complete delafossite solid solution series between diamagnetic CuAlO(2) and the t(2g)(3)frustrated antiferromagnet CuCrO(2). The evolution with composition x in CuAl(1-x)Cr(x)O(2) of the crystal structure and magnetic properties has been studied and is reported here. The room-temperature unit cell parameters follow the Végard law and increase with x as expected. The μ(eff) is equal to the Cr(3+) spin-only S = 3/2 value throughout the entire solid solution. Θ(CW) is negative, indicating that the dominant interactions are antiferromagnetic, and its magnitude increases with Cr substitution. For dilute Cr compositions, the nearest-neighbor exchange coupling constant J(BB) was estimated by mean-field theory to be 3.0 meV. Despite the sizable Θ(CW), long-range antiferromagnetic order does not develop until x is almost 1, and is preceded by glassy behavior. The data presented here, and those on dilute Al substitution from Okuda et al, suggest that the reduction in magnetic frustration due to the presence of non-magnetic Al does not have as dominant an effect on magnetism as chemical disorder and dilution of the magnetic exchange. For all samples, the 5 K isothermal magnetization does not saturate in fields up to 5 T and minimal hysteresis is observed. The presence of antiferromagnetic interactions is clearly evident in the sub-Brillouin behavior with a reduced magnetization per Cr atom. An inspection of the scaled Curie plot reveals that significant short-range antiferromagnetic interactions occur in CuCrO(2) above its Néel temperature, consistent with its magnetic frustration. Uncompensated short-range behavior is present in the Al-substituted samples and is likely a result of chemical disorder. PMID:22133702

  9. YBa2Cu3O7-δ - ag Sputtered Thin Films on MgO (100) and LaAlO3 (100) Biased and Unbiased Substrates

    NASA Astrophysics Data System (ADS)

    Moshfegh, A. Z.; Akhavan, O.; Salamati, H.; Kameli, P.; Akhavan, M.

    2000-09-01

    In this investigation, we have deposited YBa2Cu3O7-δ - Ag thin films on various biased and unbiased substrates, including MgO (100), LaAlO3 (100) and Si (111), using a single stoichiometric composite target of YBa2Cu3O7-δ with 10 wt.% Ag content, applying DC sputtering technique. The growth parameters are varied as following: sputtering gas pressure PAr = 100 - 300 mtorr, sputtering power P = 30 - 80 W, substrate bias voltage Vb= 0 - 220 V and film thickness t = 500 - 5000 Å. An optimum bias voltage of Vb= - 100 V was obtained under our experimental conditions. The post annealed (930°C for 1 hr in O2 environment) films exhibit superconducting state with Tc (onset) of about 40 K for biased (on - axis), and 86 K for unbiased (off- axis) post annealed (800 ° C, 3 hr) films grown over both MgO(100) and LaAlO3 (100) substrates. According to our SEM analysis, Ag particles are uniformly distributed in the annealed films with average grain size of about 0.3 μm located mostly at the grain boundaries. PIXE compositional analysis of the deposited films indicates deficiency of Cu and Ba for unannealed and Cu rich concentration for the annealed YBCO - Ag films grown over unbiased LaAlO3 (100) substrate.

  10. Micromagnetism of DyBa 2Cu 3O y compounds

    NASA Astrophysics Data System (ADS)

    Bukhanko, F. N.; Doroshenko, N. A.; Kamenev, V. I.

    2002-04-01

    No EPR signal exists in the metallic phase of dysprosium ceramics at 300 K. In the transition to the dielectric phase a resonant microwave absorption appears, consisting of a broad symmetric line and two narrow asymmetric lines. It is supposed that narrow lines correspond to localized exciton-like complexes of the Cu 2+-O - type ( S=1), while the wide line is connected with the ferromagnetic clusters in CuO 2 layers.

  11. Spin dynamics near a putative antiferromagnetic quantum critical point in Cu-substituted BaFe2As2 and its relation to high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Kim, M. G.; Wang, M.; Tucker, G. S.; Valdivia, P. N.; Abernathy, D. L.; Chi, Songxue; Christianson, A. D.; Aczel, A. A.; Hong, T.; Heitmann, T. W.; Ran, S.; Canfield, P. C.; Bourret-Courchesne, E. D.; Kreyssig, A.; Lee, D. H.; Goldman, A. I.; McQueeney, R. J.; Birgeneau, R. J.

    2015-12-01

    We present the results of elastic and inelastic neutron scattering measurements on nonsuperconducting Ba (Fe 0.957Cu 0.043) 2As 2 , a composition close to a quantum critical point between antiferromagnetic (AFM) ordered and paramagnetic phases. By comparing these results with the spin fluctuations in the low-Cu composition as well as the parent compound BaFe2As2 and superconducting Ba (Fe1-xNix) 2As2 compounds, we demonstrate that paramagnon-like spin fluctuations are evident in the antiferromagnetically ordered state of Ba (Fe0.957Cu0.043)2As2 , which is distinct from the AFM-like spin fluctuations in the superconducting compounds. Our observations suggest that Cu substitution decouples the interaction between quasiparticles and the spin fluctuations. We also show that the spin-spin correlation length ξ (T ) increases rapidly as the temperature is lowered and find ω /T scaling behavior, the hallmark of quantum criticality, at an antiferromagnetic quantum critical point.

  12. Quasi-two-dimensional Bose-Einstein condensation of spin triplets in the dimerized quantum magnet Ba2CuSi2O6Cl2

    NASA Astrophysics Data System (ADS)

    Okada, Makiko; Tanaka, Hidekazu; Kurita, Nobuyuki; Johmoto, Kohei; Uekusa, Hidehiro; Miyake, Atsushi; Tokunaga, Masashi; Nishimoto, Satoshi; Nakamura, Masaaki; Jaime, Marcelo; Radtke, Guillaume; Saúl, Andrés

    2016-09-01

    We synthesized single crystals of composition Ba2CuSi2O6Cl2 and investigated their quantum magnetic properties. The crystal structure is closely related to that of the quasi-two-dimensional (2D) dimerized magnet BaCuSi2O6 also known as Han purple. Ba2CuSi2O6Cl2 has a singlet ground state with an excitation gap of Δ /kB=20.8 K. The magnetization curves for two different field directions almost perfectly coincide when normalized by the g factor except for a small jump anomaly for a magnetic field perpendicular to the c axis. The magnetization curve with a nonlinear slope above the critical field is in excellent agreement with exact-diagonalization calculations based on a 2D coupled spin-dimer model. Individual exchange constants are also evaluated using density functional theory (DFT). The DFT results demonstrate a 2D exchange network and weak frustration between interdimer exchange interactions, supported by weak spin-lattice coupling implied from our magnetostriction data. The magnetic-field-induced spin ordering in Ba2CuSi2O6Cl2 is described as the quasi-2D Bose-Einstein condensation of triplets.

  13. High Temperature Superconductivity in Praseodymium Doped (0%, 2%, 4%) in Melt-Textured Y(1-x)Pr(x)Ba2Cu3O(7-delta) Systems

    NASA Technical Reports Server (NTRS)

    James, Claudell

    1995-01-01

    A study of the magnetic and structural properties of the alloy Y(1-x)Pr(x)Ba2Cu3O(7-delta) of 0%, 2%, and 4% doping of praseodymium is presented. The resulting oxides of the alloy series are a high-temperature superconductor Y-Ba-Cu-O, which has an orthorhombic superconducting crystal-lattice. Magnetic relaxation studies have been performed on the Y-Pr-Ba-CuO bulk samples for field orientation parallel to the c-axis, using a vibrating sample magnetometer. Relaxation was measured at several temperatures to obtain the irreversible magnetization curves used for the Bean model. Magnetization current densities were derived from the relaxation data. Field and temperature dependence of the logarithmic flux-creep relaxation was measured in critical state. The data indicates that the effective activation energy U(eff) increases with increasing T between 77 K and 86 K. Also, the data shows that U(eff)(T) and superconducting transition temperature, Tc, decreased as the lattice parameters increased with increasing Pr ion concentration, x, for the corresponding Y(1-x)Pr(x)Ba(x)Cu3O(7-delta) oxides. One contribution to Tc decrease in this sampling is suspected to be due to the larger ionic radius of the Pr(3+) ion. The upper critical field (H(sub c2)) was measured in the presence of magnetic field parallel to the c axis. A linear temperature dependence with H(sub c2) was obtained.

  14. Spin dynamics near a putative antiferromagnetic quantum critical point in Cu-substituted BaFe2As2 and its relation to high-temperature superconductivity

    DOE PAGES

    Kim, M. G.; Wang, M.; Tucker, G. S.; Valdivia, P. N.; Abernathy, D. L.; Chi, Songxue; Christianson, A. D.; Aczel, A. A.; Hong, T.; Heitmann, T. W.; et al

    2015-12-02

    We present the results of elastic and inelastic neutron scattering measurements on nonsuperconducting Ba(Fe0.957Cu0.043)2As2, a composition close to a quantum critical point between antiferromagnetic (AFM) ordered and paramagnetic phases. By comparing these results with the spin fluctuations in the low-Cu composition as well as the parent compound BaFe2As2 and superconducting Ba(Fe1–xNix)2As2 compounds, we demonstrate that paramagnon-like spin fluctuations are evident in the antiferromagnetically ordered state of Ba(Fe0.957Cu0.043)2As2, which is distinct from the AFM-like spin fluctuations in the superconducting compounds. Our observations suggest that Cu substitution decouples the interaction between quasiparticles and the spin fluctuations. In addition, we show that themore » spin-spin correlation length ξ(T) increases rapidly as the temperature is lowered and find ω/T scaling behavior, the hallmark of quantum criticality, at an antiferromagnetic quantum critical point.« less

  15. Bandgap narrowing in the layered oxysulfide semiconductor Ba3Fe2O5Cu2S2: Role of FeO2 layer

    NASA Astrophysics Data System (ADS)

    Han, Zhang; Shifeng, Jin; Liwei, Guo; Shijie, Shen; Zhiping, Lin; Xiaolong, Chen

    2016-02-01

    A new layered Cu-based oxychalcogenide Ba3Fe2O5Cu2S2 has been synthesized and its magnetic and electronic properties were revealed. Ba3Fe2O5Cu2S2 is built up by alternatively stacking [Cu2S2]2- layers and iron perovskite oxide [(FeO2)(BaO)(FeO2)]2- layers along the c axis that are separated by barium ions with Fe3+ fivefold coordinated by a square-pyramidal arrangement of oxygen. From the bond valence arguments, we inferred that in layered CuCh-based (Ch = S, Se, Te) compounds the +3 cation in perovskite oxide sheet prefers a square pyramidal site, while the lower valence cation prefers the square planar sites. The studies on susceptibility, transport, and optical reflectivity indicate that Ba3Fe2O5Cu2S2 is an antiferromagnetic semiconductor with a Néel temperature of 121 K and an optical bandgap of 1.03 eV. The measurement of heat capacity from 10 K to room temperature shows no anomaly at 121 K. The Debye temperature is determined to be 113 K. Theoretical calculations indicate that the conduction band minimum is predominantly contributed by O 2p and 3d states of Fe ions that antiferromagnetically arranged in FeO2 layers. The Fe 3d states are located at lower energy and result in a narrow bandgap in comparison with that of the isostructural Sr3Sc2O5Cu2S2. Project supported by the National Natural Science Foundation of China (Grant Nos. 51472266, 51202286, and 91422303), the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB07020100) and the ICDD.

  16. Electron microscopy of satellite structure and twinning in HoBa 2Cu 3O 7-x

    NASA Astrophysics Data System (ADS)

    Nissen, H.-U.; Kawamata, Y.; Wessicken, R.; Beeli, C.; Hulliger, F.

    1988-06-01

    Two different distributions of satellite reflections in electron diffractograms have been observed in HoBa2Cu3O7-x after intense electron irradiation: diffuse elongated spots from orthorhombic materials, and sharp superlattice spots from material possibly transformed to tetragonal in the electron beam.- Two types of twin texture composed of sets of twin lamellae are observed, each involving four crystal orientations. The first type is assumed to originate in two genetic stages. In the second type, two adjacent crystal orientations occur which differ by about 1° in the more common configuration and by 2° in another configuration. In the junctions of the twin lamellae, the lattice planes are coherently connected and strongly bent.

  17. Images of interlayer Josephson vortices in Tl{sub 2}Ba{sub 2}CuO{sub 6+{gamma}}

    SciTech Connect

    Moler, K.A.; Kirtley, J.R.; Hinks, D.G.

    1998-02-20

    The strength of the interlayer Josephson tunneling in layered superconductors is an essential test of the interlayer tunneling model as a mechanism for superconductivity, as well as a useful phenomenological parameter. A scanning superconducting quantum interface device (SQUID) microscope was used to image interlayer Josephson vortices in Tl{sub 2}Ba{sub 2}CuO{sub 6+{gamma}} and to obtain a direct measure of the interlayer tunneling in a high-transition temperature superconductor with a single copper oxide plane per unit cell. The measured interlayer penetration depth, {lambda}{sub c}, is {approx} 20 micrometers, about 20 times the penetration depth required by the interlayer tunneling model. 26 refs., 3 figs.

  18. A millimeter wave Josephson mixer employing a high-T(c) GdBaCuO point contact

    NASA Technical Reports Server (NTRS)

    Olsson, H. K.; Claeson, T.; Eriksson, S.; Johansson, L.-G.; Mcgrath, W. R.

    1987-01-01

    A Josephson effect heterodyne mixer for the millimeter wave band was investigated employing high-T(c) GdBaCuO point contacts. Mixer performance was in qualitative agreement with theory. A mixing response was observed up to 55 K, the highest operating temperature achieved for such a device to date. The voltage separation of RF-induced steps gave a value of h/2e = 2.08 x 10 to the -15th V s, which is in excellent agreement with the value expected for Cooper pairs. In addition, the temperature dependence of the I(0)R product was found to agree with Bardeen-Cooper-Schrieffer theory in the weak coupling limit.

  19. Synthesis of Y1BaCu3O(x) superconducting powders by intermediate phase reactions

    NASA Technical Reports Server (NTRS)

    Moure, C.; Fernandez, J. F.; Tartaj, J.; Recio, P.; Duran, P.

    1991-01-01

    A procedure for synthesizing Y1Ba2Cu3O(x) by solid state reactions was developed. The method is based on the use of barium compounds, previously synthesized, as intermediate phases for the process. The reaction kinetics of this procedure were established between 860 C and 920 C. The crystal structure and the presence of second phases were studied by means of XRD. The sintering behavior and ceramic parameters were also determined. The orthorhombic type-I structure was obtained on the synthesized bodies after a cooling cycle in an air atmosphere. Superconducting transition took place at 91 K. Sintering densities higher than 95 percent D sub th were attained at temperatures below 940 C.

  20. Neutron scattering study of the antiferromagnetic response of HgBa2CuO4+δ

    NASA Astrophysics Data System (ADS)

    Tang, Yang; Chan, Mun; Dorow, Chelsey; Veit, Mike; Ge, Yang; Greven, Martin; Mangin-Thro, Lucile; Sidis, Yvan; Bourges, Philippe; Zhao, Xudong; Steffens, Paul; Christianson, Andrew; Abernathy, Douglas; Park, Jitae

    Antiferromagnetic correlations have been argued to be the cause of the d-wave superconductivity and of the pseudogap phenomena exhibited by the cuprates. Although neutron scattering experiments of the antiferromagnetic response have been reported for a number of cuprates, results for structurally simple HgBa2CuO4+δ (Hg1201) have begun to emerge only recently. Specifically, we have found for moderately-doped Hg1201 (Tc ~ 71 K, pseudogap temperature T* ~ 305 K) that the two most prominent features of the magnetic spectrum reported for other cuprates are absent: the X-shaped `hourglass' response and the resonance mode in the superconducting state. Instead, the response of Hg1201 is Y-shaped, gapped, and significantly enhanced below T*. Here we will discuss our ongoing efforts to understand the doping dependence of the AF response in Hg1201. Work supported by the DOE Office of Basic Energy Sciences.

  1. Electrical transport in the superconducting and normal states in Y2Ba5Cu7Ox high-temperature superconductor

    NASA Astrophysics Data System (ADS)

    Mazaheri, M.; Jamasb, S.

    2016-05-01

    The resistivity of a recently reported Y2Ba5Cu7Ox (Y257) polycrystalline, high-temperature superconductor has been characterized over temperature in the presence of magnetic field intensities in the 0-15 kOe range. The magnetoresistive behavior of Y257 has been analyzed to determine the functional dependence of the pinning energy, U, associated with the resistive transition. Within the temperature range of 0.60 < T /Tc < 0.95 the Y257 resistivity data are consistent with the thermally activated flux creep model with the pinning energy following the temperature and magnetic field according to (1 - T /Tc) 2H-1. The pinning energy in this temperature range was determined to be in the 0.0125-0.8151 eV range. Furthermore, application of the Mott variable range hopping model to account for the normal-state behavior of resistivity in Y257 is critically assessed.

  2. EBSD characterisation of Y2Ba4CuUOx phase in melttextured YBCO with addition of depleted uranium oxide

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Mücklich, F.; Koblischka, M. R.; Babu, N. Hari; Cardwell, D. A.

    2006-06-01

    Melt-textured YBCO samples processed with added Y2O3 and depleted uranium oxide (DU) contain nano-particles, which have been identified previously as Y2Ba4CuUOx (U-411). This phase has a cubic unit cell, which is clearly distinct from the orthorhombic Y-123 and Y-211 phases within the YBCO system. In samples with a high amount of DU addition (0.8 wt-% DU), U-2411 particles have sizes between 200 nm and several µm, so identification of the Kikuchi patterns of this phase becomes possible. Together with a parallel EDX analysis, the particles embedded in the Y-123 matrix can be identified unambiguously. In this way, a three-phase EBSD scan becomes possible, allowing also the identification of nanometre-sized particles in the sample microstructure.

  3. Microstructure and magnetization of Y-Ba-Cu-O prepared by melt quenching, partial melting and doping

    NASA Technical Reports Server (NTRS)

    Hojaji, Hamid; Hu, Shouxiang; Michael, Karen A.; Barkatt, Aaron; Thorpe, Arthur N.; Alterescu, Sidney

    1991-01-01

    Y-Ba-Cu-O samples prepared by means of a variety of melt-based techniques exhibit high values for their magnetic properties compared with those of samples prepared by solid state sintering. These techniques include single-stage partial melting as well as melt quenching followed by a second heat treatment stage, and they have been applied to the stoichiometric 123 composition as well as to formulations containing excess yttrium or other dopants. The structure of these melt-based samples is highly aligned, and the magnetization readings exhibit large anisotropy. At 77 K and magnetic field intensities of about 2 kOe, diamagnetic susceptibilities as high as -14 x 10(exp -3) emu/g were obtained in the cases of melt-quenched samples and remanent magnetization values as high as 10 emu/g for samples prepared by partial melting.

  4. Ferroelectric properties of (Ba,Sr)TiO3 thin films grown on YBa2Cu3O7 layers

    NASA Astrophysics Data System (ADS)

    Tao, K.; Hao, Z.; Xu, B.; Chen, B.; Miao, J.; Yang, H.; Zhao, B. R.

    2003-09-01

    Ferroelectric and superconductor bilayers of Ba1-xSrxTiO3(BST)/YBa2Cu3 O7 (YBCO) are grown on (001) SrTiO3 substrates by magnetron sputtering and pulsed laser deposition. The BST thin films exhibit typical ferroelectric behavior in their hysteresis loops. Capacitance-voltage curves are measured. From the capacitance, a dielectric constant of 1250 is obtained. The current-voltage curve is fitted to investigate the mechanism of leakage. The Schottky barrier height at the Ag/BST interface is calculated to be 0.521 eV. The trapped level Et in BST is estimated to be 0.335 eV below the conduction-band edge. An energy band diagram of the Ag/BST/YBCO structure is proposed to explain the experimental results.

  5. Properties of grain boundaries in bulk, melt processed Y-Ba-Cu-O fabricated using bridge-shaped seeds

    NASA Astrophysics Data System (ADS)

    Shi, Y.-H.; Durrell, J. H.; Dennis, A. R.; Babu, N. Hari; Mancini, C. E.; Cardwell, D. A.

    2012-04-01

    Single grain RE-Ba-Cu-O ((RE)BCO, where RE is a rare earth element or yttrium) bulk superconducting materials have significant potential for a variety of engineering applications due to their ability to trap high magnetic fields. However, it is well known that the presence of grain boundaries coupled with a high angle of misorientation (typically 5°) significantly reduces the critical current density, Jc, in all forms of high temperature superconducting materials. It is of considerable fundamental and technological interest, therefore, to investigate the grain boundary properties of bulk, film and tape (RE)BCO. We report a successful multi-seeding technique for the fabrication of fully aligned, artificial (0° misalignment) grain boundaries within large grain YBCO bulk superconductors using bridge-shaped seeds. The microstructure and critical current densities of the grain boundaries produced by this technique have been studied in detail.

  6. Time evolution of Meissner effect in EuBa sub 2 Cu sub 3 O sub 7 minus. delta

    SciTech Connect

    Sherbakov, A.S.; Startsev, V.E.; Valivlin, E.G. )

    1990-01-01

    The results of temperature and time (at T = 4.2 K) dependent magnetization (M) measurements on polycrystalline high T{sub c} superconductor EuBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} are reported for different magnetic fields from 2.2 kOe to 35 kOe. The measurements were performed in the field-cooled regime (measuring the Meissner effect). A new phenomenon is found: the magnetization sign inversion from negative to positive during the time at which the external conditions (T,H) remains unchanged. The differential susceptibility in a new mixed state with M {gt} O is diamagnetic. It is shown that origin of this state is not connected with a flux trapping, but rather caused by the unusual nature of the vortex themselves in FC mixed state of high T{sub c} superconductors.

  7. Flux pinning and flux creep in neutron irradiated (Y,Gd)Ba sub 2 Cu sub 3 O sub x

    SciTech Connect

    Willis, J.O. Superconductivity Research Lab., Tokyo ); Sickafus, K.E.; Peterson, D.E. )

    1991-01-01

    Powder samples of Y{sub 0.9}Gd{sub 0.1}Ba{sub 2}Cu{sub 3}O{sub x} were irradiated with mixed spectrum ({approximately}50% E<0.5eV, 50% E>0.5eV) neutrons with most interactions expected to occur at the Gd site. As a function of fluence the samples showed increased ({approximately}X3-X8) magnetically measured critical current densities J{sub c} at low fluences, falling off at the highest values. An analysis of magnetic relaxation data, which allows for a nonlinear pinning potential U vs J relationship, revealed substantial increases in U at constant J, indicating that the irradiation introduced more effective pinning centers than those originally present. 13 refs., 3 figs., 1 tab.

  8. Electrical properties and crystal structures of the homologous series of oxides Nd 2Ba 2Ca mCe nTi 2-δCu 2+δO 11+ m+2 n ( m, n = 0 or 1)

    NASA Astrophysics Data System (ADS)

    Den, T.; Kobayashi, T.; Izumi, F.; Kamiyama, T.; Shimakawa, Y.; Jorgensen, J. D.; Rotella, F. J.; Hitterman, R. L.

    1995-02-01

    Four oxides belonging to the homologous series with the general formula Nd 2Ba 2Ca mCe nTi 2-δCu 2+δO 11+ m+2 n, were prepared for m, n = 0 or 1. Although all of these oxides have two-dimensional CuO 2 planes, they do not show any superconductivity, only a normal paramagnetic behavior. Their crystal structures were analyzed by TOF neutron powder diffraction. Nd 2Ba 2Ti 1.908Cu 2.092O 11 ( m=0, n=0 and δ=0.09) is isomorphous with Gd 2Ba 2Ti 2Cu 2O 11. The structures of the other three oxides can be derived from that of Nd 2Ba 2Ti 1.908Cu 2.092O 11. The structure of Nd 2Ba 2Ti 1.92Cu 2.08O 12 ( m=1, n=0 and δ=0.08) is obtained by the substitution of rock-salt-type (Ca,Nd,Ba)O(Ca,Nd,Ba)O layers for the (Nd,Ba)O layer. The structure of Nd 2Ba 2CeTi 2Cu 2O 13 ( m=0, n=1 and δ=0) is characterized by the insertion of fluorite-type (Nd,Ce)O 2(Nd,Ce) layers in the place of the Nd layer. Nd 2Ba 2CaCeTi 2Cu 2O 14 ( m=1, n=1, and δ=0) results from the alternate substitutions of rock-salt-type and fluorite-type layers for the (Nd,Ba)O and Nd layers, respectively.

  9. Scaling of Dynamic Spin Correlations in BaCu2(Si0.5Ge0.5)2O7

    SciTech Connect

    Zheludev, Andrey I; Masuda, T.; Dhalenne, G.; Revcolevschi, A.; Frost, C.; Perring, T. G.

    2007-01-01

    The magnetic dynamic structure factor of the one-dimensional S=1/2 chain system BaCu{sub 2}(Si{sub 0.5}Ge{sub 0.5}){sub 2}O{sub 7} is studied in a wide range of energy transfers and temperatures. Contrary to previous erroneous reports [T. Masuda et al., Phys. Rev. Lett. 93, 077206 (2004)], the scaling properties observed in the range 0.5-25 meV are found to be fully consistent with expectations for a Luttinger spin liquid. At higher energies, a breakdown of scaling laws is observed and attributed to lattice effects. The results are complementary to those found in literature for other S=1/2 chain compounds, such as KCuF{sub 3} and Cu benzoate.

  10. Processing and microstructural characterization of Al-Cu alloys produced from rapidly solidified powders

    SciTech Connect

    Conlon, K.T.; Maire, E.; Wilkinson, D.S.; Henein, H.

    2000-01-01

    This paper concerns the processing of Al-Cu alloys via a novel powder-metallurgy route. The specific technique used for powder processing involves the rapid solidification of coarse, molten droplets following impulse atomization. This produces a fine, homogeneous, dendritic microstructure within the alloy granules. Following consolidation via hot pressing, the microstructure consists mostly of an Al matrix with fine CuAl{sub 2} particles and partially recrystallized dendrites. Further heat treatment and/or thermomechanical processing completes the spheroidization process in the CuAl{sub 2} phase. Blending powders with different Cu has been used to make materials with a bimodal distribution of the local particle-volume-fraction content. The high temperature (773 K) strength of these materials decreases with increasing CuAl{sub 2} content. This can be explained using a flow model based on superplastic deformation, controlled by diffusion-accommodated sliding at Al grain boundaries. This mechanism may also explain the deformation-enhanced particle coarsening observed during channel-die forging operations.

  11. Multiferroic approach for Cr,Mn,Fe,Co,Ni,Cu substituted BaTiO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Verma, Kuldeep Chand; Kotnala, R. K.

    2016-05-01

    Multiferroic magnetoelectric (ME) at room temperature is significant for new design nano-scale spintronic devices. We have given a comparative study to report multiferroicity in BaTM0.01Ti0.99O3 [TM = Cr,Mn,Fe,Co,Ni,Cu (1 mol% each) substituted BaTiO3 (BTO)] nanoparticles. The TM ions influenced both nano-size and lattice distortion of Ti-O6 octahedra to the BTO. X ray diffraction study indicates that the dopant TM could influence lattice constants, distortion, tetragonal splitting of diffraction peaks (002/200) as well as peak shifting of diffraction angle in the BTO lattice. This can induce lattice strain which responsible to oxygen defects formation to mediate ferromagnetism. Also, the lattice strain effect could responsible to reduce the depolarization field of ferroelectricity and provide piezoelectric and magnetostrictive strains to enhance ME coupling. The size of BTO nanoparticles is varied in 13-51 nm with TM doping. The room temperature magnetic measurement indicates antiferromagnetic exchange interactions in BTO lattice with TM ions. The zero-field cooling and field cooling magnetic measurement at 500 Oe indicates antiferromagnetic to ferromagnetic transition. It also confirms that the substitution of Cr, Fe and Co into BTO could induce strong antiferromagnetic behavior. However, the substitutions of Mn, Ni and Cu have weak antiferromagnetic character. The temperature dependent dielectric measurements indicates polarization enhancement that influenced with both nano-size as well TM ions and exhibits ferroelectric phase transition with relaxor-like characteristics. Dynamic ME coupling is investigated, and the longitudinal ME voltage coefficient, α ME is equivalent to linear ME coupling coefficient, α (={\\varepsilon }{{o}}{\\varepsilon }{{r}}{α }{{ME}}) is also calculated.

  12. Neutron-scattering evidence for a periodically modulated superconducting phase in the underdoped cuprate La1.905Ba0.095CuO4

    DOE PAGES

    Xu, Zhijun; Stock, C.; Chi, Songxue; Kolesnikov, A. I.; Xu, Guangyong I.; Gu, Genda; Tranquada, J. M.

    2014-10-01

    The role of antiferromagnetic spin correlations in high-temperature superconductors remains a matter of debate. We present inelastic neutron-scattering evidence that gapless spin fluctuations coexist with superconductivity in La1.905Ba0.095CuO4. Furthermore, we observe that both the low-energy magnetic spectral weight and the spin incommensurability are enhanced with the onset of superconducting correlations. We propose that the coexistence occurs through intertwining of spatial modulations of the pair wave function and the antiferromagnetic correlations. This proposal is also directly relevant to sufficiently underdoped La2-xSrxCuO4 and YBa2Cu3O6+x.

  13. Microstructural characterization of GdBa2Cu3O7-δ superconductor films with BaHfO3 artificial pinning centers by scanning transmission electron microscopy.

    PubMed

    Yamada, Kazuhiro; Nishiyama, Takeshi; Kaneko, Kenji; Sato, Yukio; Teranishi, Ryo; Kato, Takeharu; Ibi, Akira; Yoshizumi, Masateru; Izumi, Teruo; Shiohara, Yuh

    2014-11-01

    Critical current (IC) of superconductor films under magnetic field is strongly influenced by dispersions and morphologies of artificial pinning centers (APCs) in general [1]. BaHfO3 (BHO) is acknowledged as the best candidates of APCs for REBCO films, which shows utmost thickness dependence and isotropic angular dependence of IC values for REBCO films [2]. Moreover, several researchers have focused on the nanostrains caused by the lattice mismatch at the interface between APCs and REBCO matrix, which are also the source for enhanced vortex pinning of the REBCO films [3]. In this study, we investigated to examine the nanostrain at the interface using spherical aberration (CS) corrected scanning transmission electron microscopy (STEM).BHO introduced GdBa2Cu3O7-δ (GdBCO) film was fabricated by pulsed laser deposition (PLD) method. TEM samples were prepared by focused ion beam (FIB; Quanta 3D 200i, FEI) method followed by Ar ion thinning (NanoMill, Fischione) method. Atomic scale imaging was performed by spherical aberration corrected STEM (JEM-ARM200F, JEOL), then microstructures of BHO/GdBCO interface was then examined by Fourier transformation (FFT).BHO nanorods and nanoparticles were found dispersed in the GdBCO matrix, where {100} and {110} facets were present at BHO/GdBCO interfaces, as shown in Fig. 1. In the case of PLD process, most favorable growth direction of BHO is [001] direction, so that the regular quadrangular prism shaped BHO with {100} facets would be grown along [001] direction of GdBCO matrix [4]. {110} facets of BHO were formed to maintain the minimum surface area at BHO/GdBCO to reduce the interfacial energy.jmicro;63/suppl_1/i27-a/DFU082F1F1DFU082F1Fig. 1.Plan view HAADF-STEM image and FFT image showing facets at BHO/GdBCO interfaces. This work was supported by the Ministry of Economy, Trade and Industry (METI) as "Development of Fundamental Technologies for HTS Coils" and the JSPS KAKENHI (26600046).

  14. Fluctuation induced magneto-conductivity of Y3Ba5Cu8O18±x and YBa2Cu3O7-d

    NASA Astrophysics Data System (ADS)

    Slimani, Y.; Hannachi, E.; Ben Salem, M. K.; Hamrita, A.; Ben Salem, M.; Ben Azzouz, F.

    2015-12-01

    A comparative study of the fluctuation magneto-conductivity in YBa2Cu3O7-d (noted Y-123) and Y3Ba5Cu8O18±x (noted Y-358) polycrystalline samples was carried out. Samples were synthesized in oxygen atmosphere using a standard solid state reaction technique. Phases and microstructure have been systematically investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The magneto-conductivity was measured in a magnetic field ranging from 0 T to 7 T applied perpendicular to the current path direction. The magneto-conductivity data were analyzed in terms of the temperature derivative of the resistivity and the logarithmic temperature derivative of the conductivity χσ = -d(ln Δσ) dT, where Δσ is the fluctuation conductivity. Analyses of the magneto-conductivity data reveal that Y-123 possesses a better quality of intrinsic Josephson junction compared to Y-358 one while in the former one the depression in superconducting temperature is more pronounced. The applied magnetic field narrowed substantially the three dimensions (3D) Gaussian regime and for Y-358 sample this regime is vanished for high magnetic field ( >1 T). Results are discussed in relation with the difference in the structure and microstructure Y-358 and Y-123. The upper critical and the irreversibility magnetic fields were estimated and were found to be higher in the Y-358 sample.

  15. STM study of the atomic structure of the icosahedral Al-Cu-Fe fivefold surface

    NASA Astrophysics Data System (ADS)

    Cai, T.; Fournée, V.; Lograsso, T.; Ross, A.; Thiel, P. A.

    2002-04-01

    We use scanning tunneling microscopy (STM) to investigate the atomic structure of the icosahedral (i-) Al-Cu-Fe fivefold surface in ultra high vacuum (UHV). Studies show that large, atomically flat terraces feature many ten-petal ``flowers'' with internal structure. The observed flower patterns can be associated with features on Al rich dense atomic planes generated from two-dimensional cuts of bulk models based on x-ray and neutron diffraction experiments. The results confirm that the fivefold surface of i-Al-Cu-Fe corresponds to a bulk-terminated plane.

  16. Chemical spray pyrolysis of Tl-Ba-Ca-Cu-O high-T(sub c) superconductors for high-field bitter magnets

    NASA Technical Reports Server (NTRS)

    Derochemont, L. Pierre; Zhang, John G.; Squillante, Michael R.; Hermann, A. M.; Duan, H. M.; Andrews, Robert J.; Kelliher, Warren C.

    1991-01-01

    The deposition of Tl-Ba-Ca-Cu-O thick films by spray pyrolyzing a Ba-Ca-Cu-O precursor film and diffusing thallium into the film to form the superconducting phase is examined. This approach was taken to reduce exposure to thallium and its health and safety hazards. The Tl-Ba-Ca-Cu-O system was selected because it has very attractive features which make it appealing to device and manufacturing engineering. Tl-Ba-Ca-Cu-O will accommodate a number of superconducting phases. This attribute makes it very forgiving to stoichiometric fluctuations in the bulk and film. It has excellent thermal and chemical stability, and appears to be relatively insensitive to chemical impurities. Oxygen is tightly bound into the systems, consequently there is no orthorhombic (conductor) to tetragonal (insulator) transition which would affect a component's lifetime. More significantly, the thallium based superconductors appear to have harder magnetic properties than the other high-Tc oxide ceramics. Estimates using magnetoresistance measurements indicate that at 77 K Tl2Ba2CaCu2O10 will have an upper critical field, H(sub c2) fo 26 Tesla for applied fields parallel to the c-axis and approximately 1000 Tesla for fields oriented in the a-b plane. Results to date have shown that superconducting films can be reproducibly deposited on 100 oriented MgO substrates. One film had a zero resistance temperature of 111.5 K. Furthermore, x ray diffraction analysis of the films showed preferential c-axis orientation parallel to the plane of the substrate. These results have now made it possible to consider the manufacture of a superconducting tape wire which can be configured into a topology useful for high-field magnet designs. The research which leads to the preparation of these films and plans for further development are reviewed.

  17. Tuning the formation of p-type defects by peroxidation of CuAlO{sub 2} films

    SciTech Connect

    Luo, Jie; Lin, Yow-Jon; Yang, Yao-Wei; Hung, Hao-Che; Liu, Chia-Jyi

    2013-07-21

    p-type conduction of CuAlO{sub 2} thin films was realized by the rf sputtering method. Combining with Hall, X-ray photoelectron spectroscopy, energy dispersive spectrometer, and X-ray diffraction results, a direct link between the hole concentration, Cu vacancy (V{sub Cu}), and interstitial oxygen (O{sub i}) was established. It is shown that peroxidation of CuAlO{sub 2} films may lead to the increased formation probability of acceptors (V{sub Cu} and O{sub i}), thus, increasing the hole concentration. The dependence of the V{sub Cu} density on growth conditions was identified for providing a guide to tune the formation of p-type defects in CuAlO{sub 2}. Understanding the defect-related p-type conductivity of CuAlO{sub 2} is essential for designing optoelectronic devices and improving their performance.

  18. Hybridization and spin-orbit coupling effects in the quasi-one-dimensional spin-1/2 magnet Ba3Cu3Sc4O12

    NASA Astrophysics Data System (ADS)

    Badrtdinov, D. I.; Volkova, O. S.; Tsirlin, A. A.; Solovyev, I. V.; Vasiliev, A. N.; Mazurenko, V. V.

    2016-08-01

    We study electronic and magnetic properties of the quasi-one-dimensional spin-1/2 magnet Ba3Cu3Sc4O12 with a distinct orthogonal connectivity of CuO4 plaquettes. An effective low-energy model taking into account spin-orbit coupling was constructed by means of first-principles calculations. On this basis, a complete microscopic magnetic model of Ba3Cu3Sc4O12 , including symmetric and antisymmetric anisotropic exchange interactions, is derived. The anisotropic exchanges are obtained from a distinct first-principles numerical scheme combining, on one hand, the local density approximation taking into account spin-orbit coupling, and, on the other hand, a projection procedure along with the microscopic theory by Moriya [Phys. Rev. 120, 91 (1960), 10.1103/PhysRev.120.91]. The resulting tensors of the symmetric anisotropy favor collinear magnetic order along the structural chains with the leading ferromagnetic coupling J1≃-9.88 meV. The interchain interactions J8≃0.21 and J5≃0.093 meV are antiferromagnetic. Quantum Monte Carlo simulations demonstrate that the proposed model reproduces the experimental Neel temperature, magnetization, and magnetic susceptibility data. The modeling of neutron-diffraction data reveals an important role of the covalent Cu-O bonding in Ba3Cu3Sc4O12 .

  19. Effect of Ag Addition on the Electrochemical Performance of Cu10Al in Artificial Saliva

    PubMed Central

    Salgado-Salgado, R. J.; Sotelo-Mazon, O.; Rodriguez-Diaz, R. A.; Salinas-Solano, G.

    2016-01-01

    In this work we proposed to evaluate the corrosion resistance of four different alloys by electrochemical techniques, a binary alloy Cu10Al, and three ternary alloys Cu10Al-xAg (x = 5, 10, and 15 wt.%) to be used like biomaterials in dental application. Biomaterials proposed were tested in artificial saliva at 37°C for 48 h. In addition, pure metals Cu, Al, Ag, and Ti as reference materials were evaluated. In general the short time tests indicated that the Ag addition increases the corrosion resistance and reduces the extent of localized attack of the binary alloy. Moreover, tests for 48 hours showed that the Ag addition increases the stability of the passive layer, thereby reducing the corrosion rate of the binary alloy. SEM analysis showed that Cu10Al alloy was preferably corroded by grain boundaries, and the Ag addition modified the form of attack of the binary alloy. Cu-rich phases reacted with SCN− anions forming a film of CuSCN, and the Ag-rich phase is prone to react with SCN− anions forming AgSCN. Thus, binary and ternary alloys are susceptible to tarnish in the presence of thiocyanate ions. PMID:27660601

  20. Effect of Ag Addition on the Electrochemical Performance of Cu10Al in Artificial Saliva.

    PubMed

    Salgado-Salgado, R J; Porcayo-Calderon, J; Sotelo-Mazon, O; Rodriguez-Diaz, R A; Salinas-Solano, G; Salinas-Bravo, V M; Martinez-Gomez, L

    2016-01-01

    In this work we proposed to evaluate the corrosion resistance of four different alloys by electrochemical techniques, a binary alloy Cu10Al, and three ternary alloys Cu10Al-xAg (x = 5, 10, and 15 wt.%) to be used like biomaterials in dental application. Biomaterials proposed were tested in artificial saliva at 37°C for 48 h. In addition, pure metals Cu, Al, Ag, and Ti as reference materials were evaluated. In general the short time tests indicated that the Ag addition increases the corrosion resistance and reduces the extent of localized attack of the binary alloy. Moreover, tests for 48 hours showed that the Ag addition increases the stability of the passive layer, thereby reducing the corrosion rate of the binary alloy. SEM analysis showed that Cu10Al alloy was preferably corroded by grain boundaries, and the Ag addition modified the form of attack of the binary alloy. Cu-rich phases reacted with SCN(-) anions forming a film of CuSCN, and the Ag-rich phase is prone to react with SCN(-) anions forming AgSCN. Thus, binary and ternary alloys are susceptible to tarnish in the presence of thiocyanate ions. PMID:27660601

  1. Effect of Ag Addition on the Electrochemical Performance of Cu10Al in Artificial Saliva

    PubMed Central

    Salgado-Salgado, R. J.; Sotelo-Mazon, O.; Rodriguez-Diaz, R. A.; Salinas-Solano, G.

    2016-01-01

    In this work we proposed to evaluate the corrosion resistance of four different alloys by electrochemical techniques, a binary alloy Cu10Al, and three ternary alloys Cu10Al-xAg (x = 5, 10, and 15 wt.%) to be used like biomaterials in dental application. Biomaterials proposed were tested in artificial saliva at 37°C for 48 h. In addition, pure metals Cu, Al, Ag, and Ti as reference materials were evaluated. In general the short time tests indicated that the Ag addition increases the corrosion resistance and reduces the extent of localized attack of the binary alloy. Moreover, tests for 48 hours showed that the Ag addition increases the stability of the passive layer, thereby reducing the corrosion rate of the binary alloy. SEM analysis showed that Cu10Al alloy was preferably corroded by grain boundaries, and the Ag addition modified the form of attack of the binary alloy. Cu-rich phases reacted with SCN− anions forming a film of CuSCN, and the Ag-rich phase is prone to react with SCN− anions forming AgSCN. Thus, binary and ternary alloys are susceptible to tarnish in the presence of thiocyanate ions.

  2. Effect of Ag Addition on the Electrochemical Performance of Cu10Al in Artificial Saliva.

    PubMed

    Salgado-Salgado, R J; Porcayo-Calderon, J; Sotelo-Mazon, O; Rodriguez-Diaz, R A; Salinas-Solano, G; Salinas-Bravo, V M; Martinez-Gomez, L

    2016-01-01

    In this work we proposed to evaluate the corrosion resistance of four different alloys by electrochemical techniques, a binary alloy Cu10Al, and three ternary alloys Cu10Al-xAg (x = 5, 10, and 15 wt.%) to be used like biomaterials in dental application. Biomaterials proposed were tested in artificial saliva at 37°C for 48 h. In addition, pure metals Cu, Al, Ag, and Ti as reference materials were evaluated. In general the short time tests indicated that the Ag addition increases the corrosion resistance and reduces the extent of localized attack of the binary alloy. Moreover, tests for 48 hours showed that the Ag addition increases the stability of the passive layer, thereby reducing the corrosion rate of the binary alloy. SEM analysis showed that Cu10Al alloy was preferably corroded by grain boundaries, and the Ag addition modified the form of attack of the binary alloy. Cu-rich phases reacted with SCN(-) anions forming a film of CuSCN, and the Ag-rich phase is prone to react with SCN(-) anions forming AgSCN. Thus, binary and ternary alloys are susceptible to tarnish in the presence of thiocyanate ions.

  3. Critical current density and irreversibility line of CuBa{sub 2}Ca{sub 3}Cu{sub 4}O{sub y}

    SciTech Connect

    Iyo, A.; Tokumoto, M.; Ihara, H.

    1997-06-01

    The critical current density and irreversibility line of the single-phase polycrystalline sample of CuBa{sub 2}Ca{sub 3}Cu{sub 4}O{sub y} with T{sub c}= 117 K have been estimated from measurements of magnetic hysteresis loops assuming Bean critical state model. Simple power law relations, J{sub c}{proportional_to}H{sup {minus}m}, are observed in the magnetic field dependence of the intragrain J{sub c}. Values of the intragrain J{sub c} in a magnetic field of 1 T are about 10{sup 6} and 10{sup 4} A/cm{sup 2} at temperatures of 5 and 77 K, respectively. An exponential decay of the J{sub c} with increasing temperature, J{sub c}{proportional_to}exp({minus}T/T{sub 0}), is observed below 60 K. The characteristic temperature T{sub 0} of Cu-1234 is T{sub 0}= 16.1 K in a magnetic field of 1.0 T. The dependence of the J{sub c} on temperature is relatively small among the oxide superconductors. Simple power law relations, J{sub c}{proportional_to}(1{minus}T/T{sub c}){sup n}, are found in whole ranges of the temperature and magnetic field. The value of n is 5.24 for a magnetic field of 1.0 T. The irreversibility fields at 70 and 77 K are estimated to be 9.5 and 3.7 T, respectively. The temperature dependence of the H{sub irr} is fitted by H{sub irr}=a(1{minus}T/T{sub c}){sup n} with a=2130 and n=5.91.

  4. Photoluminescence properties of AlN-doped BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphors

    SciTech Connect

    Wang, Yong; Tang, Jianfeng; Ouyang, Xicheng; Liu, Buqiong; Lin, Rong Han

    2013-06-01

    Highlights: ► Ideal hexagonal shape particle size in 5 μm and 2.5–3 μm in thickness are obtained. ► The growth mechanism is studied by a computer simulation. ► The influence of introduced AlN on the sites of Eu{sup 2+} and photoluminescence properties was investigated. - Abstract: The AlN-doped BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphors were synthesized by conventional solid-state reaction. Powder X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectrum (PL) were used for characterization. The growth mechanism was carried out by computer simulation with CASTEP application, and revealed that an ideal hexagonal shape, particle size in 5 μm and 2.5–3 μm in thickness, could be obtained by AlN doping. Additionally, due to the low electronegativity of N{sup 3−}, the AlN-doped sample showed 35% increase in PL intensity and improvement of thermal stability. These fine particle size and better photoluminescence properties are expected to be applicable to industrial production of BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphors.

  5. Adhesion strength and nucleation thermodynamics of four metals (Al, Cu, Ti, Zr) on AlN substrates

    NASA Astrophysics Data System (ADS)

    Tao, Yuan; Ke, Genshui; Xie, Yan; Chen, Yigang; Shi, Siqi; Guo, Haibo

    2015-12-01

    Devices based on AlN generally require adherent and strong interfaces between AlN and other materials, whereas most metals are known to be nonwetting to AlN and form relatively weak interfaces with AlN. In this study, we selected four representative metals (Al, Cu, Ti, and Zr) to study the adhesion strength of the AlN/metal interfaces. Mathematical models were constructed between the adhesion strength and enthalpy of formation of Al-metal solid solutions, the surface energies of the metals, and the lattice mismatch between the metals and AlN, based on thermodynamic parameters calculated using density functional theory. It appears that the adhesion strength is mainly determined by the lattice mismatch, and is in no linear correlation with either the Al-metal solution's formation enthalpies or the metals' surface energies. We also investigated the nucleation thermodynamics of the four metals on AlN substrates. It was found that Ti forms the strongest interface with AlN, and has the largest driving force for nucleation on AlN substrates among the four metals.

  6. Coexisting charge and magnetic orders in the dimer-chain iridate Ba5AlIr2O11

    DOE PAGES

    Terzic, J.; Wang, J. C.; Ye, Feng; Song, W. H.; Yuan, S. J.; Aswartham, S.; DeLong, L. E.; Streltsov, S. V.; Khomskii, Daniel I.; Cao, G.

    2015-06-29

    In this paper, we have synthesized and studied single-crystal Ba5AlIr2O11 that features dimer chains of two inequivalent octahedra occupied by tetravalent Ir4+(5d5) and pentavalent Ir5+(5d4) ions, respectively. Ba5AlIr2O11 is a Mott insulator that undergoes a subtle structural phase transition near TS=210K and a magnetic transition at TM=4.5K; the latter transition is surprisingly resistant to applied magnetic fields μoH≤12T but more sensitive to modest applied pressure (dTM/dp ≈ +0.61K/GPa). All results indicate that the phase transition at TS signals an enhanced charge order that induces electrical dipoles and strong dielectric response near TS. It is clear that the strong covalency andmore » spin-orbit interaction (SOI) suppress double exchange in Ir dimers and stabilize a novel magnetic state that is neither S=3/2 nor J=1/2, but rather lies in an “intermediate” regime between these two states. Finally, the novel behavior of Ba5AlIr2O11 therefore provides unique insights into the physics of SOI along with strong covalency in competition with double-exchange interactions of comparable strength.« less

  7. Assessment of Post-eutectic Reactions in Multicomponent Al-Si Foundry Alloys Containing Cu, Mg, and Fe

    NASA Astrophysics Data System (ADS)

    Javidani, Mousa; Larouche, Daniel; Grant Chen, X.

    2015-07-01

    Post-eutectic reactions occurring in Al-Si hypoeutectic alloys containing different proportions of Cu, Mg, and Fe were thoroughly investigated in the current study. As-cast microstructures were initially studied by optical and electron microscopy to investigate the microconstituents of each alloy. Differential scanning calorimetry (DSC) was then used to examine the phase transformations occurring during the heating and cooling processes. Thermodynamic calculations were carried out to assess the phase formation under equilibrium and in nonequilibrium conditions. The Q-Al5Cu2Mg8Si6 phase was predicted to precipitate from the liquid phase, either at the same temperature or earlier than the θ-Al2Cu phase depending on the Cu content of the alloy. The AlCuFe-intermetallic, which was hardly observed in the as-cast microstructure, significantly increased after the solution heat treatment in the alloys containing high Cu and Fe contents following a solid-state transformation of the β-Al5FeSi phase. After the solution heat treatment, the AlCuFe-intermetallics were mostly identified with the stoichiometry of the Al7Cu2Fe phase. Thermodynamic calculations and microstructure analysis helped in determining the DSC peak corresponding to the melting temperature of the N-Al7Cu2Fe phase. The effect of Cu content on the formation temperature of π-Al8Mg3FeSi6 is also discussed.

  8. Charge-compensation effect of Al on luminescence properties of M2(Si, Al)5N8:Ce3+ (M = Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Kuramoto, Daiki; Horikawa, Takashi; Hanzawa, Hiromasa; Machida, Ken-ichi

    2013-09-01

    The charge-compensated materials, M2AlxSi5-xN8:Ce3+ (M = Ca, Sr, Ba), were synthesized from appropriate mixtures of MSi, MAlSi, (MSiHy, MAlSiHy), Si3N4 and CeF3 by a direct nitriding process in a N2 gas and the luminescence properties were characterized. The resultant phosphors showed green emission suitable for LED illumination by optimizing the mixing ratio of metal elements. These phosphors were effectively excited by violet or blue light (400-430 nm) and the emission bands were observed at various wavelength regions for Ca: 489-528 nm, Sr: 511-520 nm, and Ba: 508-514 nm. Although the emission intensity of Ca2(Si, Al)5N8:Ce3+ was decreased with increasing amount of Al, those of Sr- and Ba-analogues were maximized at x = 0.5 of Al content in M2Si5-xAlxN8:Ce3+.

  9. Doping effect of Cu and Ni impurities on the Fe-based superconductor Ba0.6K0.4Fe2As2

    NASA Astrophysics Data System (ADS)

    Cheng, Peng; Shen, Bing; Han, Fei; Wen, Hai-Hu

    2013-11-01

    Copper and nickel impurities have been doped into the iron pnictide superconductor Ba0.6K0.4Fe2As2. Resistivity measurements reveal that Cu and Ni impurities suppress the superconducting transition temperature Tc with rates of \\Delta T_c/\\text{Cu-}1%= -3.5\\ \\text{K} and \\Delta T_c/\\text{Ni-}1% = -2.9\\ \\text{K} , respectively. The temperature dependence of the Hall coefficient RH of these two series of samples shows that both Cu doping and Ni doping can introduce electrons into Ba0.6K0.4Fe2As2. With more doping, the sign of RH gradually changes from positive to negative, and the changing rate of Cu-doped samples is much faster than that of Ni-doped ones. Combining this with the results of first-principles calculations published previously and the nonmonotonic evolution of the Hall coefficient in the low-temperature region, we argue that when more Cu impurities are introduced into Ba0.6K0.4Fe2As2, the removal of Fermi spectral weight in the hole-like Fermi surfaces is much stronger than that in the electron-like Fermi surfaces, which is equivalent to a significant electron doping effect. DC magnetization and the lattice constants analysis reveal that static magnetic moments and notable lattice compression have formed in Cu-doped samples. It seems that superconductivity can be suppressed by the impurities disregarding whether they are magnetic or nonmagnetic in nature. This gives strong support to a pairing gap with a sign reversal, like S^+/- . However, the relatively slow suppression rates of Tc show the robustness of superconductivity of Ba0.6K0.4Fe2As2 against impurities, implying that multi-pairing channels may exist in the system.

  10. Microstructural changes to AlCu6Ni1 alloy after prolonged annealing at elevated temperature.

    PubMed

    Wierzbińska, M; Sieniawski, J

    2010-03-01

    This work presents results of microstructure examination of AlCu(6)Ni(1) aluminium alloy. The commercial AlCu(4)Ni(2)Mg(2) (M-309) alloy is widely used for elements of aircraft and automotive engines. Modification its chemical composition was aimed at improving the stability of mechanical properties of the alloy subjected to long-term exposure to high temperature. The alloy after standard T6 heat treatment (solution heat treated at 818 K/10 h/water quenched followed by ageing at 498 K/8 h/air cooled) was annealed for 150 h at elevated temperature of 573 K corresponding to the maximum value at which structural elements of jet piston engines made of aluminium alloys operate. It was found that applied heat treatment caused an increasing in the particles of hardening phase (theta'-Al(2)Cu) size. The significant growth of the length of theta'-Al(2)Cu precipitations was observed in particularly. Nevertheless, it did not strongly result in change of its shape - the 'crystallites' and 'rods' were still characteristic of hardening phase morphology. The phenomena of the growth of theta'-Al(2)Cu precipitates caused decreasing the mechanical properties of the alloy, what is the subject of further investigations by the authors.

  11. Electroless Cu Plating on Anodized Al Substrate for High Power LED.

    PubMed

    Rha, Sa-Kyun; Lee, Youn-Seoung

    2015-03-01

    Area-selective copper deposition on screen printed Ag pattern/anodized Al/Al substrate was attempted using a neutral electroless plating processes for printed circuit boards (PCBs), according to a range of variation of pH 6.5-pH 8 at 70 °C. The utilized basic electroless solution consisted of copper(II) sulfate pentahydrate, sodium phosphinate monohydrate, sodium citrate tribasic dihydrate, ammonium chloride, and nickel(II) sulfate hexahydrate. The pH of the copper plating solutions was adjusted from pH 6.5 to pH 8 using NH4OH. Using electroless plating in pH 6.5 and pH 7 baths, surface damage to the anodized Al layer hardly occurred; the structure of the plated Cu-rich films was a typical fcc-Cu, but a small Ni component was co-deposited. In electroless plating at pH 8, the surface of the anodized Al layer was damaged and the Cu film was composed of a lot of Ni and P which were co-deposited with Cu. Finally, in a pH 7 bath, we can make a selectively electroless plated Cu film on a PCB without any lithography and without surface damage to the anodized Al layer. PMID:26413680

  12. Microstructural changes to AlCu6Ni1 alloy after prolonged annealing at elevated temperature.

    PubMed

    Wierzbińska, M; Sieniawski, J

    2010-03-01

    This work presents results of microstructure examination of AlCu(6)Ni(1) aluminium alloy. The commercial AlCu(4)Ni(2)Mg(2) (M-309) alloy is widely used for elements of aircraft and automotive engines. Modification its chemical composition was aimed at improving the stability of mechanical properties of the alloy subjected to long-term exposure to high temperature. The alloy after standard T6 heat treatment (solution heat treated at 818 K/10 h/water quenched followed by ageing at 498 K/8 h/air cooled) was annealed for 150 h at elevated temperature of 573 K corresponding to the maximum value at which structural elements of jet piston engines made of aluminium alloys operate. It was found that applied heat treatment caused an increasing in the particles of hardening phase (theta'-Al(2)Cu) size. The significant growth of the length of theta'-Al(2)Cu precipitations was observed in particularly. Nevertheless, it did not strongly result in change of its shape - the 'crystallites' and 'rods' were still characteristic of hardening phase morphology. The phenomena of the growth of theta'-Al(2)Cu precipitates caused decreasing the mechanical properties of the alloy, what is the subject of further investigations by the authors. PMID:20500428

  13. CuAl{sub 2} revisited: Composition, crystal structure, chemical bonding, compressibility and Raman spectroscopy

    SciTech Connect

    Grin, Yuri . E-mail: grin@cpfs.mpg.de; Wagner, Frank R.; Armbruester, Marc; Kohout, Miroslav; Leithe-Jasper, Andreas; Schwarz, Ulrich; Wedig, Ulrich; Georg von Schnering, Hans

    2006-06-15

    The structure of CuAl{sub 2} is usually described as a framework of base condensed tetragonal antiprisms [CuAl{sub 8/4}]. The appropriate symmetry governed periodic nodal surface (PNS) divides the space of the structure into two labyrinths. All atoms are located in one labyrinth, whereas the second labyrinth seems to be 'empty'. The bonding of the CuAl{sub 2} structure was analyzed by the electron localization function (ELF), crystal orbital Hamiltonian population (COHP) analysis and Raman spectroscopy. From the ELF representation it is seen, that the 'empty' labyrinth is in fact the place of important covalent interactions. ELF, COHP in combination with high-pressure X-ray diffraction and Raman spectroscopy show that the CuAl{sub 2} structure is described best as a network built of interpenetrating graphite-like nets of three-bonded aluminum atoms with the copper atoms inside the tetragonal-antiprismatic cavities. - Graphical abstract: Atomic interactions in the crystal structure of the intermetallic compound CuAl{sub 2}: Three-bonded aluminum atoms form interpenetrating graphite-like nets. The copper atoms are located in the channels of aluminum network by means of three-center bonds. The bonding model is in agreement with the result of polarized Raman spectroscopy and high-pressure X-ray powder diffraction.

  14. Doping dependence of the charge-density-wave order in HgBa2CuO4+δ

    NASA Astrophysics Data System (ADS)

    Yu, Biqiong

    Following the original discovery of short-range charge-density-wave (CDW) order in the orthorhombic double-layer cuprate YBa2Cu3O6+δ (YBCO) below optimal doping, resonant X-ray scattering measurements have revealed that the simple tetragonal single-layer compound HgBa2CuO4+δ (Hg1201; Tc = 71 K) exhibits short-range CDW order as well. Here we report on the doping dependence of the CDW order in Hg1201 and contrast our results with the extensive data available for YBCO. Work done in collaboration with: W. Tabis, G. Yu, M.J. Veit, N. BarisŬić, M.K. Chan, C.J. Dorow, X. Zhao, M. Greven (University of Minnesota); M. Bluschke, E. Weschke (BESSY, Berlin); T. Kolodziej, I. Bialo, A. Kozlowski (AGH, Krakow); M. Hepting, H. Gretarsson, M. Le Tacon, M. Minola, B. Keimer (MPI, Stuttgart); Ronny Sutarto (CLS, Saskatoon); Y. Li (PKU, Beijing); L. Braicovich, G. Dellea, G. Ghiringhelli (CNR-SPIN, Milano); A. Kreyssig, M. Ramazanoglu, A.I. Goldman (Iowa State University and Ames Lab); T. Schmitt (PSI, Switzerland). We acknowledge the support from US Department of Energy, Office of Basic Energy Sciences.

  15. A 10 GHz Y-Ba-Cu-O/GaAs hybrid oscillator proximity coupled to a circular microstrip patch antenna

    NASA Technical Reports Server (NTRS)

    Rohrer, Norman J.; Richard, M. A.; Valco, George J.; Bhasin, Kul B.

    1993-01-01

    A 10 GHz hybrid Y-Ba-Cu-O / GaAs microwave oscillator proximity coupled to a circular microstrip antenna was designed, fabricated and characterized. The oscillator was a reflection mode type using a GaAs MESFET as the active element. The feedline, transmission lines, RF chokes, and bias lines were all fabricated from YBa2Cu3O(7-x) superconducting thin films on a 1 cm x 1 cm lanthanum aluminate substrate. The output feedline of the oscillator was wire bonded to a superconducting feedline on a second 1 cm x 1 cm lanthanum aluminate substrate, which was in turn proximity coupled to a circular microstrip patch antenna. Antenna patterns from this active patch antenna and the performance of the oscillator measured at 77 K are reported. The oscillator had a maximum output power of 11.5 dBm at 77 K, which corresponded to an efficiency of 10 percent. In addition, the efficiency of the microstrip patch antenna together with its high temperature superconducting feedline was measured from 85 K to 30 K and was found to be 71 percent at 77 4 increasing to a maximum of 87.4 percent at 30 K.

  16. Demonstrating the Model Nature of the High-Temperature Superconductor HgBa2CuO4+d

    SciTech Connect

    Barisic, Neven; Li, Yuan; Zhao, Xudong; Cho, Yong-Chan; Chabot-Couture, Guillaume; Yu, Guichuan; Greven, Martin; /SLAC, SSRL /Boskovic Inst., Zagreb /Stanford U., Phys. Dept. /Jilin U. /Stanford U., Appl. Phys. Dept.

    2008-09-30

    The compound HgBa{sub 2}CuO{sub 4+{delta}} (Hg1201) exhibits a simple tetragonal crystal structure and the highest superconducting transition temperature (T{sub c}) among all single Cu-O layer cuprates, with T{sub c} = 97 K (onset) at optimal doping. Due to a lack of sizable single crystals, experimental work on this very attractive system has been significantly limited. Thanks to a recent breakthrough in crystal growth, such crystals have now become available. Here, we demonstrate that it is possible to identify suitable heat treatment conditions to systematically and uniformly tune the hole concentration of Hg1201 crystals over a wide range, from very underdoped (T{sub c} = 47 K, hole concentration p {approx} 0.08) to overdoped (T{sub c} = 64 K, p {approx} 0.22). We then present quantitative magnetic susceptibility and DC charge transport results that reveal the very high-quality nature of the studied crystals. Using XPS on cleaved samples, we furthermore demonstrate that it is possible to obtain large surfaces of good quality. These characterization measurements demonstrate that Hg1201 should be viewed as a model high-temperature superconductor, and they provide the foundation for extensive future experimental work.

  17. [delta] precipitation in an Al-Li-Cu-Mg-Zr alloy

    SciTech Connect

    Prasad, K.S.; Mukhopadhyay, A.K.; Gokhale, A.A.; Banerjee, D. ); Goel, D.B. Univ. of Roorkee . Dept. of Metallurgical Engineering)

    1994-05-15

    AlLi based [delta] phase has an NaTl structure (i.e., a diamond cubic) with a = 0.637nm and is an equilibrium phase in the binary Al-Li system. In heat treated binary Al-Li alloys of appropriate compositions, [delta] phase can format grain boundaries as well as within the grains. In commercially heat treated Al-Li-Cu alloys of 2090 specification, the grain boundary precipitate [delta] of the binary Al-Li system is replaced by a combination of T[sub 2](Al[sub 6]CuLi[sub 3]), R(Al[sub 5]CuLi[sub 3]) and T[sub 1](Al[sub 2]CuLi) phases. In similarly treated Al-Li-Cu-Mg alloys of 8090 specification, the copper rich T[sub 2] phase, present in the form of Al[sub 6]CuLi[sub 3[minus]x]Mg[sub x], is known to be the major coarse g.b. precipitate. The presence of an Al-Li-Cu-Mg based C phase at the grain boundaries of the commercially heat treated 8090 alloys has also been documented. No detailed study has yet been carried out to verify whether the [delta] phase can be present at the grain boundaries of the commercially heat treated 8090 alloys. Given the correlations between the g.b. phase morphology, g.b. phase chemistry, and the stress corrosion cracking resistance of these alloys, it is important that the g.b. precipitates be examined and identified. In this paper results using TEM are presented to show that the [delta] phase can be present in varying amounts at the grain boundaries in an 8090 alloy when heat treated in the temperature range of 170--350 C. An examination is also made of the [delta] precipitation within the grain to establish that the T[sub 2]/[alpha]-Al interface is the dominant nucleation site for the noncoherent [delta] phase.

  18. Two-step reset in the resistance switching of the Al/TiOx/Cu structure.

    PubMed

    Shao, Xing L; Zhao, Jin S; Zhang, Kai L; Chen, Ran; Sun, Kuo; Chen, Chang J; Liu, Kai; Zhou, Li W; Wang, Jian Y; Ma, Chen M; Yoon, Kyung J; Hwang, Cheol S

    2013-11-13

    Two-step reset behaviors in the resistance switching properties of the top Al/TiOx/bottom Cu structure were studied. During the electroforming and set steps, two types of conducting filaments composed of Cu and oxygen vacancies (Cu-CF and V(O)-CF) were simultaneously (or sequentially) formed when Al was negatively biased. In the subsequent reset step with the opposite bias polarity, the Cu-CFs ruptured first at ~0.5 V, and formed an intermediate state. The trap-filled V(O)-CFs were transformed into a trap-empty state, resulting in a high-resistance state at ~1 V. Matrix phase in the electrochemical metallization cell can play an active role in resistance switching. PMID:24099490

  19. High resolution electron microscopy study of a high Cu variant of Weldalite (tm) 049 and a high strength Al-Cu-Ag-Mg-Zr alloy

    NASA Technical Reports Server (NTRS)

    Herring, R. A.; Gayle, Frank W.; Pickens, Joseph R.

    1991-01-01

    Weldalite (trademark) 049 is an Al-Cu-Li-Ag-Mg alloy that is strengthened in artificially aged tempers primarily by very thin plate-like precipitates lying on the set of (111) matrix planes. This precipitate might be expected to be the T(sub 1) phase, Al2CuLi, which has been observed in Al-Cu-Li alloys. However, in several ways this precipitate is similar to the omega phase which also appears as the set of (111) planes plates and is found in Al-Cu-Ag-Mg alloys. The study was undertaken to identify the set of (111) planes precipitate or precipitates in Weldalite (trademark) 049 in the T8 (stretched and artificially aged) temper, and to determine whether T(sub 1), omega, or some other phase is primarily responsible for the high strength (i.e., 700 MPa tensile strength) in this Al-Cu-Li-Ag-Mg alloy.

  20. Influences of film thickness on the structural, electrical and optical properties of CuAlO2 thin films

    NASA Astrophysics Data System (ADS)

    Dong, Guobo; Zhang, Ming; Wang, Mei; Li, Yingzi; Gao, Fangyuan; Yan, Hui; Diao, Xungang

    2014-07-01

    CuAlO2 films with different thickness were prepared by the radio frequency magnetron sputtering technique. The structural, electrical and optical properties of CuAlO2 were studied by X-ray diffraction, atomic force microscope, UV-Vis double-beam spectrophotometer and Hall measurements. The results indicate that the single phase hexagonal CuAlO2 is formed and the average grain size of CuAlO2 films increases with increasing film thickness. The results also exhibit that the lowering of bandgap and the increase of electrical conductivity of CuAlO2 films with the increase of their thickness, which are attributed to the improvement of the grain size and the anisotropic electrical property. According to the electrical and optical properties, the biggest figure of merit is achieved for the CuAlO2 film with the appropriate thickness of 165 nm.

  1. Effect of the Cu and Ni content on the crystallization temperature and crystallization mechanism of La-Al-Cu(Ni) metallic glasses

    NASA Astrophysics Data System (ADS)

    Li, Peiyou

    2016-02-01

    The effect of the Cu and Ni content on the crystallization mechanism and the crystallization temperatures of La-Al-Cu(Ni) metallic glasses (MGs) was studied by differential scanning calorimetry (DSC). The experimental results have shown that the DSC curves obtained for the La-Al-Cu and La-Al-Ni MGs exhibit two and three crystallization temperatures, respectively. The crystallization temperatures of the La-Al-Cu and La-Al-Ni MGs result from the merging and splitting of thermal events related to the corresponding eutectic atomic pairs in the La72Cu28 and La81.6Al18.4 MGs, and La72Ni28 and La81.6Al18.4 MGs, respectively. In addition, Al- and Ni-containing clusters with weak or strong atomic interaction in the Al-Ni atomic pairs strongly affect the crystallization mechanism and thus the crystallization temperature of La-Al-Ni MGs. This study provides a novel understanding of the relation between the crystallization temperature and the underlying crystallization mechanisms in La-Al-Cu(Ni) MGs.

  2. Crystallinity and in-field characterization of high-Tc YBa2Cu408 and Y0.9Ca0.1Ba2Cu4O8 epitaxial films fabricated by low temperature flux method

    NASA Astrophysics Data System (ADS)

    Funaki, S.; Yamada, Y.; Nakayama, F.

    2014-05-01

    REBa2Cu4O8 superconductor has an important advantage that the critical temperature (Tc) is improved by Ca substitution for RE site. We fabricated the YBa2Cu4O8 (Y124) and Y0.9Ca0.1Ba2Cu4O8 (YCa124) films by molten hydroxide method in ambient atmosphere and investigated the crystallinity and in-field characterization. Obtained samples show that the film alignment is biaxial orientation and the grain size is larger than 50 μm, and the irreversibility field of YCa124 film is superior to that of Y124 in all the measured magnetic fields

  3. Chemical Trend of Superconducting Critical Temperatures in Hole-Doped CuBO2, CuAlO2, CuGaO2, and CuInO2

    NASA Astrophysics Data System (ADS)

    Nakanishi, Akitaka; Katayama-Yoshida, Hiroshi; Ishikawa, Takahiro; Shimizu, Katsuya

    2016-09-01

    We calculated the superconducting critical temperature (Tc) for hole-doped CuXO2 (X = B, Al, Ga, and In) compounds using first-principles calculations based on rigid band model. The compounds with X = Al, Ga, and In have delafosite-type structures and take maximum Tc values at 0.2-0.3 with respect to the number of holes (Nh) in the unit-cell: 50 K for CuAlO2, 10 K for CuGaO2, and 1 K for CuInO2. The decrease of Tc for this change in X is involved by covalency reduction and lattice softening associated with the increase of ionic mass and radius. For CuBO2 which is a lighter compound than CuAlO2, the delafosite structure is unstable and a body-centered tetragonal structure emerges as the most stable structure. As the results, the electron-phonon interaction is decreased and Tc is lower by approximately 43 K than that of CuAlO2 at the hole-doping conditions of Nh = 0.2-0.3.

  4. Phase composition and structure of aluminum Al-Cu-Si-Sn-Pb alloys

    NASA Astrophysics Data System (ADS)

    Belov, N. A.; Stolyarova, O. O.; Murav'eva, T. I.; Zagorskii, D. L.

    2016-06-01

    The structure and phase composition of cast and heat treated Al-Cu-Si-Sn-Pb alloys containing 6 wt % Sn, 2 wt % Pb, 0-4 wt % Cu, 0-10 wt % Si have been studied using calculations and experimental methods. Polythermal and isothermal sections are reported, which indicate the existence of two liquid phases. It was found that the low-melting phase is inhomogeneous and consists of individual leadand tin-based particles.

  5. Surface tension of liquid Al-Cu and wetting at the Cu/Sapphire solid-liquid interface

    NASA Astrophysics Data System (ADS)

    Schmitz, J.; Brillo, J.; Egry, I.

    2014-02-01

    For the study of the interaction of a liquid alloy with differently oriented single crystalline sapphire surfaces precise surface tension data of the liquid are fundamental. We measured the surface tension of liquid Al-Cu contactlessly on electromagnetically levitated samples using the oscillating drop technique. Data were obtained for samples covering the entire range of composition and in a broad temperature range. The surface tensions can be described as linear functions of temperature with negative slopes. Moreover, they decrease monotonically with an increase of aluminium concentration. The observed behaviour with respect to both temperature and concentration is in agreement with a thermodynamic model calculation using the regular solution approximation. Surface tensions were used to calculate interfacial energies from the contact angles of liquid Cu droplets, deposited on the C(0001), A(11-20), R(1-102) surfaces of an α-Al2O3 substrate. The contact angles were measured by means of the sessile drop method at 1380 K. In the Cu/α-Al2O3 system, no anisotropy is evident neither for the contact angles nor for the interfacial energies of different surfaces. The work of adhesion of this system is isotropic, too.

  6. First principles study of magnetoelectric coupling in Co2FeAl/BaTiO3 tunnel junctions.

    PubMed

    Yu, Li; Gao, Guoying; Zhu, Lin; Deng, Lei; Yang, Zhizong; Yao, Kailun

    2015-06-14

    Critical thickness for ferroelectricity and the magnetoelectric effect of Co2FeAl/BaTiO3 multiferroic tunnel junctions (MFTJs) are investigated using first-principles calculations. The ferroelectric polarization of the barriers can be maintained upto a critical thickness of 1.7 nm for both the Co2/TiO2 and FeAl/TiO2 interfaces. The magnetoelectric effect is derived from the difference in the magnetic moments on interfacial atoms, which is sensitive to the reversal of electric polarization. The magnetoelectric coupling is found to be dependent on the interfacial electronic hybridizations. Compared with the Co2/TiO2 interface, more net magnetization change is achieved at the FeAl/TiO2 interface. In addition, the in-plane strain effect shows that in-plane compressive strain can lead to the enhancement of ferroelectric polarization stability and intensity of magnetoelectric coupling. These findings suggest that Co2FeAl/BaTiO3 MFTJs could be utilized in the area of electrically controlled magnetism, especially the MFTJ with loaded in-plane compressive strain with the FeAl/TiO2 interface. PMID:25987345

  7. Mössbauer spectroscopy study of Al distribution in BaAl{sub x}Fe{sub 12−x}O{sub 19} thin films

    SciTech Connect

    Przybylski, M. Żukrowski, J.; Harward, I.; Celiński, Z.

    2015-05-07

    Barium hexagonal ferrite (BaM) films grown on Si are a good candidate material for new-generations of on-wafer microwave devices operating at frequencies above 40 GHz. Doping BaM with Al increases the value of anisotropy field even more, and in combination with a large value of remanence, would allow one to create a self-biasing material/structure that would eliminate the need for permanent bias magnets in millimeter wave devices. To examine the occupation of Fe sublattices by Al ions, we carried out Conversion Electron Mössbauer Spectroscopy (CEMS) measurements at room temperature and zero magnetic field (after magnetizing the samples in a strong magnetic field). The spectra can be reasonably fitted with three components (sub-spectra) corresponding to different Fe sublattices. There are significant changes in the spectra with the addition of Al: The magnetic hyperfine field decreases for all three components, and their relative contributions also change remarkably. These observations are in agreement with the fact that the Al substitutes Fe, thus lowering the component contributions and the value of the hyperfine field. In addition, our previous XRD analysis indicates increasing grain misalignment with Al content, further supporting the CEMS data.

  8. Crystal Growth and Photoluminescence Properties of Truncated Cubic BaMgAl10O17:Eu2+ Phosphors for Three-Dimensional Plasma Display Panels.

    PubMed

    Liu, Bitao; Chen, Yuan; Peng, Lingling; Han, Tao; Yu, Hong; Tian, Liangliang; Tu, Mingjing

    2016-04-01

    Monodispersed, truncated cube BaMgAl10O17:Eu2+ phosphors were synthesized by the sol-gel process. Scanning electron microscope (SEM), photoluminescence spectrum, powder X-ray diffraction and decay curves were used to evaluate the truncated cubic BaMgAl10O17:Eu2+ phosphors. The crystal growth process and photoluminescence properties were discussed in detail. The results showed that this truncated cubic morphology can be achieved via a simple sinter process. These truncated cubic BaMgAl10O17:Eu2+ phosphors showed acceptable emission intensity and better thermal properties. This result indicates truncated cubic BaMgAl10O17:Eu2+ phosphors would meet the requirements of plasma display panels (PDPs). PMID:27451727

  9. Field modulated microwave absorption in YBa{sub 2}Cu{sub 3}O{sub 7}/PrBa{sub 2}Cu{sub 3}O{sub 7} multilayers

    SciTech Connect

    Dumas, J.; Thrane, B.P.; Feinberg, D.

    1996-11-01

    The authors describe field modulated microwave absorption measurements on YBa{sub 2}Cu{sub 3}O{sub 7} / PrBa{sub 2}Cu{sub 3}O{sub 7} multilayers with PrBa{sub 2}Cu{sub 3}O{sub 7} thickness in the range 2.5 to 10 nm and with a fixed YBa{sub 2}Cu{sub 3}O{sub 7} thickness of 10 nm. The Fourier spectrum of the reflected microwave power reveals one fundamental frequency which appears at T{sub c} and even harmonics of the modulation field frequency {omega} at lower temperatures. The determination of the irreversibility line near T{sub c} for different values of the PrBa{sub 2}Cu{sub 3}O{sub 7} thickness and inferred from the vanishing of the nonlinear response signal at 2{omega} in the presence of superimposed dc and modulation fields is reported.

  10. Raman scattering measurements of phonon anharmonicity in CuAlO2 thin films

    NASA Astrophysics Data System (ADS)

    Singh, Manoj K.; Dussan, S.; Sharma, Ganpat L.; Katiyar, Ram S.

    2008-12-01

    CuAlO2 thin films were grown on single crystalline sapphire substrates with c-axis orientation by rf sputtering method. The x-ray diffraction data indicate the formation of delafossite structure and tend to be oriented along (001). Temperature dependent Raman spectra of CuAlO2 thin films were measured from 80 to 1273 K, and we observed two optical modes at Eg (˜418 cm-1) and A1g(˜767 cm-1) showing anomalous frequency and linewidth shifts with temperature, which were interpreted as an experimental evidence of combined effect of lattice expansion and anharmonic phonon-phonon interaction in CuAlO2. At high temperature, polaronic state and change in effective mass due to lattice expansion also affect the frequency shift and the linewidth of the observed Raman modes.

  11. Optical and electrical properties of mechanochemically synthesized nanocrystalline delafossite CuAlO2.

    PubMed

    Prakash, T; Prasad, K Padma; Ramasamy, S; Murty, B S

    2008-08-01

    Nanocrystalline p-type semiconductor copper aluminum oxide (CuAlO2) has been synthesized by mechanical alloying using freshly prepared Cu2O and alpha-AlO2O3 nanocrystals in toluene medium. A study on structural property performed with different alloying and post annealing durations, by X-ray diffraction (XRD) reveals the formation of single phase with average crystallite size approximately 45 nm. Optical absorbance onset at 364.5 nm confirms its wide band gap nature (E(g) = 3.4 eV) and the fluorescence emission behaviour (390 nm) confirms its direct band type transition. The activation energy for electrical conduction has been calculated by Arrhenius plots using impedance measurement. Both grain and grain boundary conductivity takes place with almost equal activation energies of approximately 0.45 eV. The paper discusses synthesis, structural, optical and electrical properties of delafossite CuAlO2 in detail. PMID:19049217

  12. Preparation and Electrochemical Characterization of Aluminium Liquid Battery Cells With Two Different Electrolytes (NaCl-BaCl2-AlF3-NaF and LiF-AlF3-BaF2).

    PubMed

    Napast, Viktor; Moškon, Jože; Homšak, Marko; Petek, Aljana; Gaberšček, Miran

    2015-01-01

    The possibility of preparation of operating rechargeable liquid battery cells based on aluminium and its alloys is systematically checked. In all cases we started from aluminium as the negative electrode whereas as the positive electrode three different metals were tested: Pb, Bi and Sn. Two types of electrolytes were selected: Na(3)AlF(6) -AlF(3) - BaCl(2) - NaCl and Li(3)AlF(3) - BaF(2). We show that some of these combinations allowed efficient separation of individual liquid layers. The cells exhibited expected voltages, relatively high current densities and could be charged and discharged several times. The capacities were relatively low (120 mAh in the case of Al-Pb system), mostly due to unoptimised cell construction. Improvements in various directions are possible, especially by hermetically sealing the cells thus preventing salt evaporation. Similarly, solubility of aluminium in alloys can be increased by optimising the composition of positive electrode. PMID:26680707

  13. Preparation and Electrochemical Characterization of Aluminium Liquid Battery Cells With Two Different Electrolytes (NaCl-BaCl2-AlF3-NaF and LiF-AlF3-BaF2).

    PubMed

    Napast, Viktor; Moškon, Jože; Homšak, Marko; Petek, Aljana; Gaberšček, Miran

    2015-01-01

    The possibility of preparation of operating rechargeable liquid battery cells based on aluminium and its alloys is systematically checked. In all cases we started from aluminium as the negative electrode whereas as the positive electrode three different metals were tested: Pb, Bi and Sn. Two types of electrolytes were selected: Na(3)AlF(6) -AlF(3) - BaCl(2) - NaCl and Li(3)AlF(3) - BaF(2). We show that some of these combinations allowed efficient separation of individual liquid layers. The cells exhibited expected voltages, relatively high current densities and could be charged and discharged several times. The capacities were relatively low (120 mAh in the case of Al-Pb system), mostly due to unoptimised cell construction. Improvements in various directions are possible, especially by hermetically sealing the cells thus preventing salt evaporation. Similarly, solubility of aluminium in alloys can be increased by optimising the composition of positive electrode.

  14. Sol-gel production of Cu/Al co-doped zinc oxide: Effect of Al co-doping concentration on its structure and optoelectronic properties

    NASA Astrophysics Data System (ADS)

    Bu, Ian Yi-Yu

    2014-12-01

    Sol-gel deposition of ZnO:Cu:Al thin films were co-doped different Cu:Al ratio. The optoelectronic and structural properties of the resultant film were evaluated using scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy, photoluminescence spectroscopy and UV-VIS spectroscopy. It was found that the Al content leads to narrowing of the band gap and that excessive Al doping concentration greater than 5 at% degrade the film's properties.

  15. Theoretical Study of Electronic Structure and Thermoelectric Properties of Doped CuAlO2

    NASA Astrophysics Data System (ADS)

    Poopanya, P.; Yangthaisong, A.; Rattanapun, C.; Wichainchai, A.

    2011-05-01

    The doping level dependence of thermoelectric properties of delafossite CuAlO2 has been investigated in the constant scattering time ( τ) approximation, starting from the first principles of electronic structure. In particular, the lattice parameters and the energy band structure were calculated using the total energy plane-wave pseudopotential method. It was found that the lattice parameters of CuAlO2 are a = 2.802 Å and c = 16.704 Å, and the internal parameter is u = 0.1097. CuAlO2 has an indirect band gap of 2.17 eV and a direct gap of 3.31 eV. The calculated energy band structures were then used to calculate the electrical transport coefficients of CuAlO2. By considering the effects of doping level and temperature, it was found that the Seebeck coefficient S( T) increases with increasing acceptor doping ( A d) level. The values of S( T) in our experiments correspond to an A d level at 0.262 eV, which is identified as the Fermi level of CuAlO2. Based on our experimental Seebeck coefficient and the electrical conductivity, the constant relaxation time is estimated to be 1 × 10-16 s. The power factor is large for a low A d level and increases with temperature. It is suggested that delafossite CuAlO2 can be considered as a promising thermoelectric oxide material at high doping and high temperature.

  16. Improvement of the shape memory characteristics of a Cu-Zn-Al alloy with manganese and zirconium addition

    SciTech Connect

    Zou, W.H.; Lam, C.W.H.; Chung, C.Y.; Lai, J.K.L.

    1997-04-15

    Cu-based shape memory alloys (SMAs) possess good shape memory effect (SME) and have the advantage of lower price than Ti-Ni SMA. However, there are still some problems which should be solved before they can be used widely. Addition of suitable alloying elements can improve the mechanical properties, stabilization of martensitic transformations and also the SME of Cu-based SMAs significantly. Cu-Zn-Al is an important Cu-based SMA that suffers from the martensite stabilization and intergranular cracking in the processing procedures and service. As a modification of Cu-Zn-Al SMAs, the effects of Mn and Zr addition on the structure and martensite transformation behavior of different heat treated Cu-21Zn-6Al-1Mn-0.5Zr (wt%) SMA have been studied and compared to that of Cu-21Zn-6Al (wt%) SMA in the present paper.

  17. Electronic structure of p-type transparent conducting oxide CuAlO2

    NASA Astrophysics Data System (ADS)

    Mo, Sung-Kwan; Yoon, Joonseok; Liu, Xiaosong; Yang, Wanli; Mun, Bongjin; Ju, Honglyoul

    2014-03-01

    CuAlO2 is a prototypical p-type transparent conducting oxide. Despite its importance for potential applications and number of studies on its band structure and gap characteristics, experimental study on the momentum-resolved electronic structure has been lacking. We present angle-resolved photoemission data on single crystalline CuAlO2 using synchrotron light source to reveal complete band structure. Complemented by the x-ray absorption and emission spectra, we also study band gap characteristics and compare them with theory.

  18. Electron crystallography applied to the structure determination of Nb(Cu,Al,X) Laves phases.

    PubMed

    Gigla, M; Lelatko, J; Krzelowski, M; Morawiec, H

    2006-09-01

    The presence of primary precipitates of the Laves phases considerably improves the mechanical properties and the resistance to thermal degradation of the high-temperature shape memory Cu-Al-Nb alloys. The structure analysis of the Laves phases was carried out on particles contained in the ternary and quaternary alloys as well on synthesized compounds related to the composition of the Nb(Cu,Al,X)(2) phase, where X = Ni, Co, Cr, Ti and Zr. The precise structure determination of the Laves phases was carried out by the electron crystallography method using the CRISP software.

  19. Self-organized homo-epitaxial growth in nonlinear optical BaAlBO3F2 crystal crossing lines patterned by laser in glass

    NASA Astrophysics Data System (ADS)

    Shinozaki, K.; Abe, S.; Honma, T.; Komatsu, T.

    2015-11-01

    Crystallization processing of glasses is important as a novel technique for the development of new optical materials, and laser-induced crystallization provides a new challenge in science and technology of materials. Nonlinear optical BaAlBO3F2 crystal lines with crossing, bending, and spiral shapes were patterned at the surface of 2NiO-49BaF2-24.5Al2O3-24.5B2O3 (mol%) and 2.9NiO-48.5BaF2-24.3Al2O3-24.3B2O3 (mol%) glasses by laser irradiation (Yb:YVO4 laser with a wavelength of 1080 nm) and the orientation state of BaAlBO3F2 crystals was examined from birefringence image observations. The birefringence images indicate that the growth of highly c-axis oriented BaAlBO3F2 crystals follows along the laser scanning direction even if the laser scanning direction changes, and in particular the direction of the c-axis of BaAlBO3F2 crystals changes gradually at the crossing and bending points. The model of "self-organized homo-epitaxial growth" is proposed for the crystal orientation at the crossing and bending points, as a new crystal growth science and engineering beyond the wise providence of nature.

  20. Characterization of Al-Cu-Mg-Ag Alloy RX226-T8 Plate

    NASA Technical Reports Server (NTRS)

    Lach, Cynthia L.; Domack, Marcia S.

    2003-01-01

    Aluminum-copper-magnesium-silver (Al-Cu-Mg-Ag) alloys that were developed for thermal stability also offer attractive ambient temperature strength-toughness combinations, and therefore, can be considered for a broad range of airframe structural applications. The current study evaluated Al-Cu-Mg-Ag alloy RX226-T8 in plate gages and compared performance with sheet gage alloys of similar composition. Uniaxial tensile properties, plane strain initiation fracture toughness, and plane stress tearing resistance of RX226-T8 were examined at ambient temperature as a function of orientation and thickness location in the plate. Properties were measured near the surface and at the mid-plane of the plate. Tensile strengths were essentially isotropic, with variations in yield and ultimate tensile strengths of less than 2% as a function of orientation and through-thickness location. However, ductility varied by more than 15% with orientation. Fracture toughness was generally higher at the mid-plane and greater for the L-T orientation, although the differences were small near the surface of the plate. Metallurgical analysis indicated that the microstructure was primarily recrystallized with weak texture and was uniform through the plate with the exception of a fine-grained layer near the surface of the plate. Scanning electron microscope analysis revealed Al-Cu-Mg second phase particles which varied in composition and were primarily located on grain boundaries parallel to the rolling direction. Fractography of toughness specimens for both plate locations and orientations revealed that fracture occurred predominantly by transgranular microvoid coalescence. Introduction High-strength, low-density Al-Cu-Mg-Ag alloys were initially developed to replace conventional 2000 (Al-Cu-Mg) and 7000 (Al-Zn-Cu-Mg) series aluminum alloys for aircraft structural applications [1]. During the High Speed Civil Transport (HSCT) program, improvements in thermal stability were demonstrated for candidate

  1. Effect of thermally stable Cu- and Mg-rich aluminides on the high temperature strength of an AlSi12CuMgNi alloy

    SciTech Connect

    Asghar, Z.

    2014-02-15

    The internal architecture of an AlSi12CuMgNi piston alloy, revealed by synchrotron tomography, consists of three dimensional interconnected hybrid networks of Cu-rich aluminides, Mg-rich aluminides and eutectic/primary Si embedded in an α-Al matrix. The strength at room temperature and at 300°C is studied as a function of solution treatment time at 490°C and compared with results previously reported for an AlSi12Ni alloy. The addition of 1 wt% Cu and 1 wt% Mg to AlSi12CuMgNi increases the room temperature strength by precipitation hardening while the strength at 300°C is similar for both alloys in as-cast condition. The strength of AlSi12CuMgNi decreases with solution treatment time and stabilizes at 4 h solution treatment. The effect of solution treatment time on the strength of the AlSi12CuMgNi alloy is less pronounced than for the AlSi12Ni alloy both at room temperature and at 300°C. - Highlights: • The 3D microstructure of AlSi12CuMgNi is revealed by synchrotron tomography. • An imaging analysis procedure to segment phases with similar contrasts is presented. • 1 wt% Cu and Mg results in the formation of 3D networks of rigid phases. • AlSi12CuMgNi is stronger than AlSi12Ni owing to the stability of the 3D networks.

  2. The determination of interfacial structure and phase transitions in Al/Cu and Al/Ni interfaces by means of surface extended x-ray absorption fine structure

    SciTech Connect

    Barrera, E.V. . Dept. of Mechanical Engineering and Materials Science); Heald, S.M. )

    1991-01-01

    Surface extended x-ray absorption fine structure (SEXAFS) was used to investigate the interfacial conditions of Al/Cu and Al/Ni shallow buried interfaces. Previous studies using glancing angle extended x-ray absorption fine structure, x-ray reflectivity, photoemission, and SEXAFS produced conflicting results as to whether or not the interfaces between Al and Cu and Al and Ni were reacted upon room temperature deposition. In this study polycrystalline bilayers of Al/Cu and Al/Ni and trilayers of Al/Cu/Al and Al/Ni/Al were deposited on tantalum foil at room temperature in ultra high vacuum and analyzed to evaluate the reactivity of these systems on a nanometer scale. It become overwhelming apparent that the interfacial phase reactions were a function of the vacuum conditions. Samples deposited with the optimum vacuum conditions showed reaction products upon deposition at room temperature which were characterized by comparisons to standards and by least squares fitting the be CuAl{sub 2} and NiAl{sub 3} respectively. The results of this study that the reacted zone thicknesses were readily dependent on the deposition parameters. For both Al on Cu and Al on Ni as well as the metal on Al conditions 10{Angstrom} reaction zones were observed. These reaction zones were smaller than that observed for bilayers of Al on Cu (30{Angstrom}) and Al on Ni (60{Angstrom}) where deposition rates were much higher and samples were much thicker. The reaction species are evident by SEXAFS, where the previous photoemission studies only indicated that changes had occurred. Improved vacuum conditions as compared to the earlier experiments is primarily the reason reactions on deposition were seen in this study as compared to the earlier SEXAFS studies.

  3. The determination of interfacial structure and phase transitions in Al/Cu and Al/Ni interfaces by means of surface extended x-ray absorption fine structure

    SciTech Connect

    Barrera, E.V.; Heald, S.M.

    1991-12-31

    Surface extended x-ray absorption fine structure (SEXAFS) was used to investigate the interfacial conditions of Al/Cu and Al/Ni shallow buried interfaces. Previous studies using glancing angle extended x-ray absorption fine structure, x-ray reflectivity, photoemission, and SEXAFS produced conflicting results as to whether or not the interfaces between Al and Cu and Al and Ni were reacted upon room temperature deposition. In this study polycrystalline bilayers of Al/Cu and Al/Ni and trilayers of Al/Cu/Al and Al/Ni/Al were deposited on tantalum foil at room temperature in ultra high vacuum and analyzed to evaluate the reactivity of these systems on a nanometer scale. It become overwhelming apparent that the interfacial phase reactions were a function of the vacuum conditions. Samples deposited with the optimum vacuum conditions showed reaction products upon deposition at room temperature which were characterized by comparisons to standards and by least squares fitting the be CuAl{sub 2} and NiAl{sub 3} respectively. The results of this study that the reacted zone thicknesses were readily dependent on the deposition parameters. For both Al on Cu and Al on Ni as well as the metal on Al conditions 10{Angstrom} reaction zones were observed. These reaction zones were smaller than that observed for bilayers of Al on Cu (30{Angstrom}) and Al on Ni (60{Angstrom}) where deposition rates were much higher and samples were much thicker. The reaction species are evident by SEXAFS, where the previous photoemission studies only indicated that changes had occurred. Improved vacuum conditions as compared to the earlier experiments is primarily the reason reactions on deposition were seen in this study as compared to the earlier SEXAFS studies.

  4. A study of the semiconductor compound СuAlO2 by the method of nuclear quadrupole resonance of Cu

    NASA Astrophysics Data System (ADS)

    Matukhin, V. L.; Khabibulin, I. Kh.; Shul'gin, D. A.; Smidt, S. V.

    2012-07-01

    The method of nuclear quadrupole resonance of Cu (NQR Cu) is used to study the samples of a semiconductor compound CuAlO2. The crystal structure of CuAlO2 belongs to the family of delafossite - the mineral of a basic CuFeO2 structure. Transparent semiconductor oxides, such as CuAlO2, have attracted recent attention as promising thermoelectric materials.

  5. Development of a superconducting joint between a GdBa2Cu3O7-δ-coated conductor and YBa2Cu3O7-δ bulk: towards a superconducting joint between RE (Rare Earth) Ba2Cu3O7-δ-coated conductors

    NASA Astrophysics Data System (ADS)

    Jin, Xinzhe; Yanagisawa, Yoshinori; Maeda, Hideaki; Takano, Yoshiki

    2015-07-01

    We have started to develop a superconducting bridge joint between two GdBa2Cu3O7-δ (Gd123)-coated conductors, where both conductors are placed in an end-to-end arrangement on the surface of a melt-textured YBCO (including Y2BaCuO5 and YBa2Cu3O7-δ) bulk, which acts as a superconducting medium between the coated conductors. As a first step in the development, one half of the bridge joint assembly was modeled and investigated. Experimental results achieved are as follows: (a) the higher-melting-temperature textured Gd123-coated conductor acts as a seed for the melt texture of the YBa2Cu3O7-δ (Y123) bulk, and (b) the superconducting phase continues across the Y123/Gd123 boundary. The critical current of the joint model is 10 A, which is about 10% of the original Gd123-coated conductor, at 77 K in a self-magnetic field. These results are considered to be extensible to the superconducting bridge joint between the Gd123-coated conductors.

  6. Synthesis, Crystal and Electronic Structures of the Pnictides AE3TrPn3 (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

    SciTech Connect

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

    2015-09-24

    New ternary arsenides AE3TrAs3 (AE = Sr, Ba; Tr = Al, Ga) and their phosphide analogs Sr3GaP3 and Ba3AlP3 have been prepared by reactions of the respective elements at high temperatures. Single-crystal X-ray diffraction studies reveal that Sr3AlAs3 and Ba3AlAs3 adopt the Ba3AlSb3-type structure (Pearson symbol oC56, space group Cmce, Z = 8). This structure is also realized for Sr3GaP3 and Ba3AlP3. Likewise, the compounds Sr3GaAs3 and Ba3GaAs3 crystallize with the Ba3GaSb3-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+]3[Tr3+][Pn3-]3, or rather [AE2+]6[Tr2Pn6]12-, i.e., as Zintl phases.

  7. Band alignment at epitaxial BaSnO3/SrTiO3(001) and BaSnO3/LaAlO3(001) heterojunctions

    NASA Astrophysics Data System (ADS)

    Chambers, Scott A.; Kaspar, Tiffany C.; Prakash, Abhinav; Haugstad, Greg; Jalan, Bharat

    2016-04-01

    We have spectroscopically determined the optical bandgaps and band offsets at epitaxial interfaces of BaSnO3 with SrTiO3(001) and LaAlO3(001). 28 u.c. BaSnO3 epitaxial films exhibit direct and indirect bandgaps of 3.56 ± 0.05 eV and 2.93 ± 0.05 eV, respectively. The lack of a significant Burstein-Moss shift corroborates the highly insulating, defect-free nature of the BaSnO3 films. The conduction band minimum is lower in electron energy in 5 u.c. films of BaSnO3 than in SrTiO3 and LaAlO3 by 0.4 ± 0.2 eV and 3.7 ± 0.2 eV, respectively. This result bodes well for the realization of oxide-based, high-mobility, two-dimensional electron systems that can operate at ambient temperature, since electrons generated in the SrTiO3 by modulation doping, or at the BaSnO3/LaAlO3 interface by polarization doping, can be transferred to and at least partially confined in the BaSnO3 film.

  8. Dissolution of Cu/Mg Bearing Intermetallics in Al-Si Foundry Alloys

    NASA Astrophysics Data System (ADS)

    Javidani, Mousa; Larouche, Daniel; Grant Chen, X.

    2016-08-01

    Evolutions of the Cu/Mg bearing intermetallics were thoroughly investigated in four Al-Si hypoeutectic alloys containing various Cu (1 and 1.6 wt pct) and Mg (0.4 and 0.8 wt pct) contents. The area fractions of Cu/Mg bearing phases before and after solution heat treatment (SHT) were quantified to evaluate the solubility/stability of the phases. Two Mg-bearing intermetallics (Q-Al5Cu2Mg8Si6, π-Al8FeMg3Si6) which appear as gray color under optical microscope were discriminated by the developed etchant. Moreover, the concentrations of the elements (Cu, Mg, and Si) in α-Al were analyzed. The results illustrated that in the alloys containing ~0.4 pct Mg, Q-Al5Cu2Mg8Si6 phase was dissolved after 6 hours of SHT at 778 K (505 °C); but containing in the alloys ~0.8 pct Mg, it was insoluble/ partially soluble. Furthermore, after SHT at 778 K (505 °C), Mg2Si was partially substituted by Q-phase. Applying a two-step SHT [6 hours@778 K (505 °C) + 8 hours@798 K (525 °C)] in the alloys containing ~0.4 pct Mg helped to further dissolve the remaining Mg bearing intermetallics and further modified the microstructure, but in the alloys containing ~0.8 pct Mg, it caused partial melting of Q-phase. Thermodynamic calculations were carried out to assess the phase formation in equilibrium and in non-equilibrium conditions. There was an excellent agreement between the experimental results and the predicted results.

  9. Dissolution of Cu/Mg Bearing Intermetallics in Al-Si Foundry Alloys

    NASA Astrophysics Data System (ADS)

    Javidani, Mousa; Larouche, Daniel; Grant Chen, X.

    2016-10-01

    Evolutions of the Cu/Mg bearing intermetallics were thoroughly investigated in four Al-Si hypoeutectic alloys containing various Cu (1 and 1.6 wt pct) and Mg (0.4 and 0.8 wt pct) contents. The area fractions of Cu/Mg bearing phases before and after solution heat treatment (SHT) were quantified to evaluate the solubility/stability of the phases. Two Mg-bearing intermetallics (Q-Al5Cu2Mg8Si6, π-Al8FeMg3Si6) which appear as gray color under optical microscope were discriminated by the developed etchant. Moreover, the concentrations of the elements (Cu, Mg, and Si) in α-Al were analyzed. The results illustrated that in the alloys containing ~0.4 pct Mg, Q-Al5Cu2Mg8Si6 phase was dissolved after 6 hours of SHT at 778 K (505 °C); but containing in the alloys ~0.8 pct Mg, it was insoluble/ partially soluble. Furthermore, after SHT at 778 K (505 °C), Mg2Si was partially substituted by Q-phase. Applying a two-step SHT [6 hours@778 K (505 °C) + 8 hours@798 K (525 °C)] in the alloys containing ~0.4 pct Mg helped to further dissolve the remaining Mg bearing intermetallics and further modified the microstructure, but in the alloys containing ~0.8 pct Mg, it caused partial melting of Q-phase. Thermodynamic calculations were carried out to assess the phase formation in equilibrium and in non-equilibrium conditions. There was an excellent agreement between the experimental results and the predicted results.

  10. Irreversibility in the microwave absorption of ceramic Y-Ba-Cu-O

    SciTech Connect

    Pakulis, E.J.

    1989-05-01

    We find that, for ceramic samples of YBa/sub 2/Cu/sub 3/O/sub x/, the microwave absorption in a dc magnetic field H and at a temperature T is different for field cooling than for zero field cooling, provided T is below a field-dependent irreversibility temperature. Since the microwaves probe only a layer at the surface of the sample, the irreversibility line in H-T space determined in this way is a property of the surface layer with a thickness given by the microwave skin depth. When the applied H is removed, we observe a remanent microwave absorption which decays logarithmically with time.

  11. Temporal stability of Y Ba Cu O nano Josephson junctions from ion irradiation

    SciTech Connect

    Cybart, Shane A.; Roediger, Peter; Chen, Ke; Parker, J. M.; Cho, Ethan Y.; Wong, Travis J.; Dynes, R. C.

    2012-11-29

    We investigate the temporal stability of YBa2Cu3O7 Josephson junctions created by ion irradiation through a nano-scale implant mask fabricated using electron beam lithography and reactive ion etching. A comparison of current-voltage characteristics measured for junctions after fabrication and eight years of storage at room temperature show a slight decrease in critical current and increase in normal state resistance consistent with broadening of the weaklink from diffusion of defects. Shapiro step measurements performed 8 years after fabrication reveal that device uniformity is maintained and is strong evidence that these devices have excellent temporal stability for applications.

  12. Microstructural characterization of Ag-sheathed Tl-Ba-Ca-Cu-O and Bi-Sr-Ca-Cu-O superconducting tapes by analytical electron microscopy

    SciTech Connect

    Hu, J.G.; Miller, D.J.; Goretta, K.C.; Poeppel, R.B.

    1992-09-01

    The microstructures of Tl(1223) and Pb-doped Bi(2223) silver tapes produced by the powder-in-tube (PM) method have been examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). The Tl tapes annealed below the melting point exhibited fine grains and a high density of pores while tapes subjected to partial melting prior to solid state annealing were fully dense with large grains. However, these tapes also showed an increase in the size and density of impurity particles, particularly CaO and a Ba-Cu rich phase. Silver powders added to the precursors tended to promote the growth of Tl(1223) at lower temperatures but also interfered with the development of texture by providing nucleation sites of random orientations. In contrast, the Bi(2223) tape exhibited a high degree of texture and alignment. The incorporation of silver within the superconducting phase was found to be negligible for both the Tl(1223) and Bi(2223) tapes.

  13. Magnetodielectric detection of magnetic quadrupole order in Ba(TiO)Cu4(PO4)4 with Cu4O12 square cupolas

    PubMed Central

    Kimura, K.; Babkevich, P.; Sera, M.; Toyoda, M.; Yamauchi, K.; Tucker, G. S.; Martius, J.; Fennell, T.; Manuel, P.; Khalyavin, D. D.; Johnson, R. D.; Nakano, T.; Nozue, Y.; Rønnow, H. M.; Kimura, T.

    2016-01-01

    In vortex-like spin arrangements, multiple spins can combine into emergent multipole moments. Such multipole moments have broken space-inversion and time-reversal symmetries, and can therefore exhibit linear magnetoelectric (ME) activity. Three types of such multipole moments are known: toroidal; monopole; and quadrupole moments. So far, however, the ME activity of these multipole moments has only been established experimentally for the toroidal moment. Here we propose a magnetic square cupola cluster, in which four corner-sharing square-coordinated metal-ligand fragments form a noncoplanar buckled structure, as a promising structural unit that carries an ME-active multipole moment. We substantiate this idea by observing clear magnetodielectric signals associated with an antiferroic ME-active magnetic quadrupole order in the real material Ba(TiO)Cu4(PO4)4. The present result serves as a useful guide for exploring and designing new ME-active materials based on vortex-like spin arrangements. PMID:27698426

  14. Fabrication and critical current density analysis of YBa2Cu3O7+(BaSnO3)‧/YBa2Cu3O7+(BaSnO3)″ multilayer films

    NASA Astrophysics Data System (ADS)

    Horide, Tomoya; Sakamoto, Nobuhiro; Ichinose, Ataru; Matsumoto, Kaname

    2016-08-01

    Multilayers (MLs) comprising of YBa2Cu3O7(YBCO)+BaSnO3(BSO) layers with different BSO content were fabricated, and their critical current density (J c) was measured to understand influence of ML structure on vortex pinning. Elongated and segmented nanorods were observed in the MLs, and ab-plane aligned nanoparticles appeared depending on BSO content. When BSO formed only elongated and segmented nanorods in MLs, J c exhibited a linear relationship between J c in the single layer films. On the other hand, when MLs contained ab-plane aligned nanoparticles in addition to nanorods, J c decreased with lower-J c-layer fraction more rapidly. These results suggest that J c was degraded due to easy vortex flow along the lower-J c-layers, and that the acceleration of vortex motion depended on the type of lower-J c-layers. Vortex behavior which is not observed in conventional systems such as single layer films and bulk samples is strongly expected in MLs, since fine tuning of pinning center structure is possible.

  15. Microstructural evolution in Al-Zn-Mg-Cu-Sc-Zr alloys during short-time homogenization

    NASA Astrophysics Data System (ADS)

    Liu, Tao; He, Chun-nian; Li, Gen; Meng, Xin; Shi, Chun-sheng; Zhao, Nai-qin

    2015-05-01

    Microstructural evolution in a new kind of aluminum (Al) alloy with the chemical composition of Al-8.82Zn-2.08Mg-0.80Cu-0.31Sc-0.3Zr was investigated. It is found that the secondary phase MgZn2 is completely dissolved into the matrix during a short homogenization treatment (470°C, 1 h), while the primary phase Al3(Sc,Zr) remains stable. This is due to Sc and Zr additions into the Al alloy, high Zn/Mg mass ratio, and low Cu content. The experimental findings fit well with the results calculated by the homogenization diffusion kinetics equation. The alloy shows an excellent mechanical performance after the short homogenization process followed by hot-extrusion and T6 treatment. Consequently, a good combination of low energy consumption and favorable mechanical properties is obtained.

  16. Trigonal Cu2-II-Sn-VI4 (II = Ba, Sr and VI = S, Se) quaternary compounds for earth-abundant photovoltaics.

    PubMed

    Hong, Feng; Lin, Wenjun; Meng, Weiwei; Yan, Yanfa

    2016-02-14

    We propose trigonal Cu2-II-Sn-VI4 (II = Ba, Sr and VI = S, Se) quaternary compounds for earth-abundant solar cell applications. Through density functional theory calculations, we show that these compounds exhibit similar electronic and optical properties to kesterite Cu2ZnSnS4 (CZTS): high optical absorption with band gaps suitable for efficient single-junction solar cell applications. However, the trigonal Cu2-II-Sn-VI4 compounds exhibit defect properties more suitable for photovoltaic applications than those of CZTS. In CZTS, the dominant defects are the deep acceptors, Cu substitutions on Zn sites, which cause non-radiative recombination and limit the open-circuit voltages of CZTS solar cells. On the contrary, the dominant defects in trigonal Cu2-II-Sn-VI4 are the shallow acceptors, Cu vacancies, similar to those in CuInSe2. Our results suggest that the trigonal Cu2-II-Sn-VI4 quaternary compounds could be promising candidates for efficient earth-abundant thin-film solar cell and photoeletrochemical water-splitting applications. PMID:26804024

  17. The Electronic Structure and Formation Energies of Ni-doped CuAlO2 by Density Functional Theory Calculation

    NASA Astrophysics Data System (ADS)

    Xu, Ying; Li, Fei; Sheng, Wei; Nie, Guo-Zheng; Yuan, Ding-Wang

    2014-03-01

    The electronic structure and formation energies of Ni-doped CuAlO2 are calculated by first-principles calculations. Our results show that Ni is good for p-type doping in CuAlO2. When Ni is doped into CuAlO2, it prefers to substitute Al-site. NiAl is a shallow acceptor, while NiCu is a deep acceptor and its formation energy is high. Further electronic structure calculations show that strong hybridization happens between Ni-3d and O-2p states for Ni substituting Al-site, while localized Ni-3d states are found for Ni substituting Cu-site.

  18. A multireference configuration interaction study of CuB and CuAl molecular constants and photoionization spectra.

    PubMed

    Ferrão, Luiz F A; Spada, Rene F K; Roberto-Neto, Orlando; Machado, Francisco B C

    2013-09-28

    Accurate potential energy curves and molecular constants for the low-lying electronic states of CuX(y) (X = B, Al; y = 0, +1) were investigated using the complete active space self-consistent field/multireference configuration interaction (MRCI) methodology with aug-cc-pV5Z basis set. The photoionization spectra of CuX were computed, showing electron detachment in the region of far ultraviolet. The results complement the previous theoretical characterizations and the few experimental studies. A comparative analysis was carried out concerning the different choices of reference configuration state functions in the MRCI calculations with and without the contribution of scalar relativistic effects. The results obtained with a small reference set adequately constructed are competitive to those using a much larger number of configuration state functions, and also the scalar relativistic effects improve significantly the molecular constants in this kind of system containing a 3d metal atom.

  19. Microstructural characteristics and aging response of Zn-containing Al-Mg-Si-Cu alloy

    NASA Astrophysics Data System (ADS)

    Cai, Yuan-hua; Wang, Cong; Zhang, Ji-shan

    2013-07-01

    Al-Mg-Si-Cu alloys with and without Zn addition were fabricated by conventional ingot metallurgy method. The microstructures and properties were investigated using optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), tensile test, hardness test, and electrical conductivity measurement. It is found that the as-cast Al-Mg-Si-Cu-Zn alloy is composed of coarse dendritic grains, long needle-like β/δ-AlFeSi white intermetallics, and Chinese script-like α-AlFeSi compounds. During high temperature homogenization treatment, only harmful needle-like β-AlFeSi phase undergoes fragmentation and spheroidizing at its tips, and the destructive needle-like δ-phase does not show any morphological and size changes. Phase transitions from β-AlFeSi to α-AlFeSi and from δ-AlFeSi to β-AlFeSi are also not found. Zn addition improves the aging hardening response during the former aging stage and postpones the peak-aged hardness to a long aging time. In T4 condition, Zn addition does not obviously increase the yield strength and decrease the elongation, but it markedly improves paint-bake hardening response during paint-bake cycle. The addition of 0.5wt% Zn can lead to an increment of 99 MPa in yield strength compared with the value of 69 MPa for the alloy without Zn after paint-bake cycle.

  20. Demonstration of Y1Ba2Cu3O(7-delta) and complementary metal-oxide-semiconductor device fabrication on the same sapphire substrate

    NASA Technical Reports Server (NTRS)

    Burns, M. J.; De La Houssaye, P. R.; Russell, S. D.; Garcia, G. A.; Clayton, S. R.; Ruby, W. S.; Lee, L. P.

    1993-01-01

    We report the first fabrication of active semiconductor and high-temperature superconducting devices on the same substrate. Test structures of complementary MOS transistors were fabricated on the same sapphire substrate as test structures of Y1Ba2Cu3O(7-delta) flux-flow transistors, and separately, Y1Ba2Cu3O(7-delta) superconducting quantum interference devices utilizing both biepitaxial and step-edge Josephson junctions. Both semiconductor and superconductor devices were operated at 77 K. The cofabrication of devices using these disparate yet complementary electronic technologies on the same substrate opens the door for the fabrication of true semiconductive/superconductive hybrid integrated circuits capable of exploiting the best features of each of these technologies.

  1. Construction and characterization of an inductive superconducting current limiting device based on ceramic Y 1Ba 2Cu 3O 7 - δ O-rings

    NASA Astrophysics Data System (ADS)

    Currás, S. R.; Santos, R.; Domarco, G.; Díaz, A.; Veira, J. A.; Maza, J.; François, M. X.; Vidal, F.

    Experimental results about the response of a small-scale superconducting inductive device as current limiter are reported. The device is based on ring-shaped samples of bulk Y 1Ba 2Cu 3O 7 - δ coupled to a primary coil through a magnetic core. The samples were obtained by pressing into an O-ring shape Y 1Ba 2Cu 3O 7 - δ powders, which reacted following the standard ceramic process. The size of the O-rings was 1 cm internal diameter, 1.6 cm external diameter, and 0.3 cm height. The response of the device was measured at liquid nitrogen temperature as a function of the type of magnetic core, the critical current of each individual superconducting O-ring, the number of O-rings used simultaneously, the frequency of the a.c. current and the number of turns of the primary coil.

  2. Commensurate antiferromagnetic excitations as a signature of the pseudogap in the tetragonal high-Tc cuprate HgBa2CuO4+δ

    PubMed Central

    Chan, M. K.; Dorow, C. J.; Mangin-Thro, L.; Tang, Y.; Ge, Y.; Veit, M. J.; Yu, G.; Zhao, X.; Christianson, A. D.; Park, J. T.; Sidis, Y.; Steffens, P.; Abernathy, D. L.; Bourges, P.; Greven, M.

    2016-01-01

    Antiferromagnetic correlations have been argued to be the cause of the d-wave superconductivity and the pseudogap phenomena exhibited by the cuprates. Although the antiferromagnetic response in the pseudogap state has been reported for a number of compounds, there exists no information for structurally simple HgBa2CuO4+δ. Here we report neutron-scattering results for HgBa2CuO4+δ (superconducting transition temperature Tc≈71 K, pseudogap temperature T*≈305 K) that demonstrate the absence of the two most prominent features of the magnetic excitation spectrum of the cuprates: the X-shaped ‘hourglass' response and the resonance mode in the superconducting state. Instead, the response is Y-shaped, gapped and significantly enhanced below T*, and hence a prominent signature of the pseudogap state. PMID:26940332

  3. Commensurate antiferromagnetic excitations as a signature of the pseudogap in the tetragonal high-Tc cuprate HgBa2CuO4+δ

    DOE PAGES

    Chan, M. K.; Dorow, C. J.; Mangin-Thro, L.; Tang, Y.; Ge, Y.; Veit, M. J.; Yu, G.; Zhao, X.; Christianson, A. D.; Park, J. T.; et al

    2016-03-04

    We report that antiferromagnetic correlations have been argued to be the cause of the d-wave superconductivity and the pseudogap phenomena exhibited by the cuprates. Although the antiferromagnetic response in the pseudogap state has been reported for a number of compounds, there exists no information for structurally simple HgBa2CuO4+δ. We report neutron-scattering results for HgBa2CuO4+δ (superconducting transition temperature Tc≈71 K, pseudogap temperature T*≈305 K) that demonstrate the absence of the two most prominent features of the magnetic excitation spectrum of the cuprates: the X-shaped ‘hourglass’ response and the resonance mode in the superconducting state. Instead, the response is Y-shaped, gapped andmore » significantly enhanced below T*, and hence a prominent signature of the pseudogap state.« less

  4. Commensurate antiferromagnetic excitations as a signature of the pseudogap in the tetragonal high-Tc cuprate HgBa2CuO4+δ

    NASA Astrophysics Data System (ADS)

    Chan, M. K.; Dorow, C. J.; Mangin-Thro, L.; Tang, Y.; Ge, Y.; Veit, M. J.; Yu, G.; Zhao, X.; Christianson, A. D.; Park, J. T.; Sidis, Y.; Steffens, P.; Abernathy, D. L.; Bourges, P.; Greven, M.

    2016-03-01

    Antiferromagnetic correlations have been argued to be the cause of the d-wave superconductivity and the pseudogap phenomena exhibited by the cuprates. Although the antiferromagnetic response in the pseudogap state has been reported for a number of compounds, there exists no information for structurally simple HgBa2CuO4+δ. Here we report neutron-scattering results for HgBa2CuO4+δ (superconducting transition temperature Tc~71 K, pseudogap temperature T*~305 K) that demonstrate the absence of the two most prominent features of the magnetic excitation spectrum of the cuprates: the X-shaped `hourglass' response and the resonance mode in the superconducting state. Instead, the response is Y-shaped, gapped and significantly enhanced below T*, and hence a prominent signature of the pseudogap state.

  5. Electron backscatter diffraction analysis of gold nanoparticles on Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7−δ}

    SciTech Connect

    Bochmann, A.; Teichert, S.; Katzer, C.; Schmidl, F.

    2015-06-07

    It has been shown recently that the incorporation of gold nanoparticles into Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7−δ} enhances the superconducting properties of this material in a significant way. Previous XRD and TEM investigations suggest different crystallographic relations of the gold nanoparticles with respect to the epitaxial Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7−δ}. Here, detailed investigations of the crystal orientations for a large ensemble of gold nanoparticles with electron backscatter diffraction are reported. The average size of the gold nanoparticles is in the range of 60 nm–80 nm. We identified five different types of heteroepitaxial relationships between the gold nanoparticles and the superconductor film, resulting in complex pole figures. The observed different types of crystallographic orientations are discussed based on good lattice matching and the formation of low energy interfaces.

  6. Grain orientations and distribution of Y2Ba4CuUOx phase in melt-textured YBCO with addition of depleted uranium oxide studied by EBSD

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Mücklich, F.; Koblischka, M. R.; Babu, N. Hari; Cardwell, D. A.; Murakami, M.

    2006-07-01

    The local grain orientations and the distribution of Y2Ba4CuUOx (U-2411) phase are measured within melt-textured YBCO samples by means of electron backscatter diffraction (EBSD). In this work, several samples with varying addition (0.1-0.8 wt%) of depleted uranium oxide (DU) were analysed by means of EBSD. The embedded U-2411 particles were found to have sizes around 200 nm, some large particles being present in the samples with a high DU concentration. Combined EBSD and EDX analysis enabled the identification of the Kikuchi patterns of the U-2411 phase, so that a true three-phase EBSD scan (YBCO, Y2BaCuO5 and U-2411) becomes possible.

  7. Commensurate antiferromagnetic excitations as a signature of the pseudogap in the tetragonal high-Tc cuprate HgBa2CuO(4+δ).

    PubMed

    Chan, M K; Dorow, C J; Mangin-Thro, L; Tang, Y; Ge, Y; Veit, M J; Yu, G; Zhao, X; Christianson, A D; Park, J T; Sidis, Y; Steffens, P; Abernathy, D L; Bourges, P; Greven, M

    2016-01-01

    Antiferromagnetic correlations have been argued to be the cause of the d-wave superconductivity and the pseudogap phenomena exhibited by the cuprates. Although the antiferromagnetic response in the pseudogap state has been reported for a number of compounds, there exists no information for structurally simple HgBa2CuO(4+δ). Here we report neutron-scattering results for HgBa2CuO(4+δ) (superconducting transition temperature Tc≈71 K, pseudogap temperature T*≈305 K) that demonstrate the absence of the two most prominent features of the magnetic excitation spectrum of the cuprates: the X-shaped 'hourglass' response and the resonance mode in the superconducting state. Instead, the response is Y-shaped, gapped and significantly enhanced below T*, and hence a prominent signature of the pseudogap state. PMID:26940332

  8. Density and symmetry of unoccupied electronic states of Tl sub 2 Ba sub 2 CaCu sub 2 O sub 8

    SciTech Connect

    Romberg, H.; Nuecker, N.; Alexander, M.; Fink, J. ); Hahn, D.; Zetterer, T.; Otto, H.H.; Renk, K.F. )

    1990-02-01

    The local density and symmetry of unoccupied electronic states at the O and Cu sites in Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} single crystals has been investigated by measuring O 1{ital s} and Cu 2{ital p} absorption edges. High-energy electron-energy-loss spectroscopy in transmission has been used. There are O 2{ital p}{sub {ital x},{ital y}} states at the Fermi level from the CuO{sub 2} planes and O 2{ital p}{sub {ital z}} states from the BaO and TlO layers. The empty Cu 3{ital d} states have predominantly 3{ital d}{sub {ital x}{sup 2}{minus}{ital y}{sup 2}} symmetry. There is an admixture of about 10% probably with 3{ital d}{sub 3{ital z}{sup 2}{minus}{ital r}{sup 2}} character.

  9. Isovalent Ca and Ba substitutions in thermoelectric layer-structured oxyselenide Sr2CoO2Cu2Se2

    NASA Astrophysics Data System (ADS)

    Chou, T. L.; Mustonen, O.; Tripathi, T. S.; Karppinen, M.

    2016-01-01

    Multilayered compounds typically present exotic functionalities, and some of them have been suggested as potential materials for thermoelectric conversion owing to their unique capability to decouple electronic and heat transport. Here we report new [CoO2] and [Cu2Se2] layered A 2CoO2Cu2Se2 compounds in which Sr at the intervening alkaline-earth A site is partially replaced with Ca or Ba. The parent Sr2CoO2Cu2Se2 phase is a direct gap p-type semiconductor, and density functional theory (DFT) calculations indicate its topmost valence band consists of Cu 3d-Se 4p states. Upon the isovalent cation substitution the lattice modification in the ab plane is constrained by the stiff [CoO2] layer such that the lattice shrinkage/expansion mainly happens along the c axis. Substitution of Sr with the heavier and larger Ba significantly enhances the thermopower but more hole states would be required to optimize the thermoelectric performance. Thermal stability is related to the inter-oxide-selenide-layer interaction, and our thermogravimetric measurement data reveal that the A 2CoO2Cu2Se2 materials could operate in the intermediate temperature region.

  10. Plasticity-improved Zr-Cu-Al bulk metallic glass matrix composites containing martensite phase

    NASA Astrophysics Data System (ADS)

    Sun, Y. F.; Wei, B. C.; Wang, Y. R.; Li, W. H.; Cheung, T. L.; Shek, C. H.

    2005-08-01

    Zr48.5Cu46.5Al5 bulk metallic glass matrix composites with diameters of 3 and 4mm were produced through water-cooled copper mold casting. Micrometer-sized bcc based B2 structured CuZr phase containing martensite plate, together with some densely distributed nanocrystalline Zr2Cu and plate-like Cu10Zr7 compound, was found embedded in a glassy matrix. The microstructure formation strongly depends on the composition and cooling rate. Room temperature compression tests reveal significant strain hardening and plastic strains of 7.7% and 6.4% before failure are obtained for the 3-mm- and 4-mm-diam samples, respectively. The formation of the martensite phase is proposed to contribute to the strain hardening and plastic deformation of the materials.

  11. Plasticity-improved Zr-Cu-Al bulk metallic glass matrix composites containing martensite phase

    SciTech Connect

    Sun, Y.F.; Wei, B.C.; Wang, Y.R.; Li, W.H.; Cheung, T.L.; Shek, C.H.

    2005-08-01

    Zr{sub 48.5}Cu{sub 46.5}Al{sub 5} bulk metallic glass matrix composites with diameters of 3 and 4 mm were produced through water-cooled copper mold casting. Micrometer-sized bcc based B2 structured CuZr phase containing martensite plate, together with some densely distributed nanocrystalline Zr{sub 2}Cu and plate-like Cu{sub 10}Zr{sub 7} compound, was found embedded in a glassy matrix. The microstructure formation strongly depends on the composition and cooling rate. Room temperature compression tests reveal significant strain hardening and plastic strains of 7.7% and 6.4% before failure are obtained for the 3-mm- and 4-mm-diam samples, respectively. The formation of the martensite phase is proposed to contribute to the strain hardening and plastic deformation of the materials.

  12. A new series of oxycarbonate superconductors (Cu{sub 0.5}C{sub 0.5}){sub m}Ba{sub m+1}Ca{sub n-1}Cu{sub n}O{sub 2}({sub m+n})+1

    SciTech Connect

    Takayama-Muromachi, E.; Kawashima, T.; Matsui, Y.

    1994-12-31

    We found a new series of oxycarbonate superconductors in the Ba-Ca-Cu-C-O system under high pressure of 5 GPa. Their ideal formula is (Cu{sub 0.5}C{sub 0.5}){sub m}Ba{sub m+1}Ca{sub n-1}Cu{sub n}O{sub 2}({sub m+n})+1 ((Cu,C)-m(m+1)(n-1)n). Thus far, n=3, 4 members of the m=1 series, (Cu,C)-1223 and (Cu,C)-1234, have been prepared in bulk while n=4, 5 members, (Cu,C)-2334 and (Cu,C)-2345, have been prepared for the m=2 series. (Cu,C)-1223 shows superconductivity below 67 K while T{sub c}`s of other compounds are above 110 K. In particular, (Cu,C)=1234 has the highest T{sub c} of 117 K.

  13. New type of Schottky diode-based Cu-Al-Mn-Cr shape memory material films

    NASA Astrophysics Data System (ADS)

    Aksu Canbay, C.; Dere, A.; Mensah-Darkwa, Kwadwo; Al-Ghamdi, Ahmed; Karagoz Genç, Z.; Gupta, R. K.; Yakuphanoglu, F.

    2016-07-01

    Cr-doped CuAlMn shape memory alloys were produced by arc melting method. The effects of Cr content on microstructure and transformation parameters of were investigated. The alloys were characterized by X-ray analysis, optical microscope observations and differential scanning calorimetry measurements. The grain size of the alloys was decreased by the addition of Cr into CuAlMn alloy system. The martensite transformation temperature was shifted both the lower temperature and higher temperature with the addition of chromium. This change was explained on the basis of the change in the thermodynamics such as enthalpy, entropy and activation energy values. The obtained results indicate that the phase transformation temperatures of the CuAlMn alloy system can be controlled by addition of Cr. We fabricated a Schottky barrier diode and observed that ideality factor and barrier height increase with increasing temperature. The diodes exhibited a thermal sensor behavior. This indicates that Schottky diode-based Cu-Al-Mn-Cr shape memory material films can be used as a sensor in high-temperature measurement applications.

  14. Chemical reactions and morphological stability at the Cu/Al2O3 interface.

    PubMed

    Scheu, C; Klein, S; Tomsia, A P; Rühle, M

    2002-10-01

    The microstructures of diffusion-bonded Cu/(0001)Al2O3 bicrystals annealed at 1000 degrees C at oxygen partial pressures of 0.02 or 32 Pa have been studied with various microscopy techniques ranging from optical microscopy to high-resolution transmission electron microscopy. The studies revealed that for both oxygen partial pressures a 20-35 nm thick interfacial CuAlO2 layer formed, which crystallises in the rhombohedral structure. However, the CuAlO2 layer is not continuous, but interrupted by many pores. In the samples annealed in the higher oxygen partial pressure an additional reaction phase with a needle-like structure was observed. The needles are several millimetres long, approximately 10 microm wide and approximately 1 microm thick. They consist of CuAlO2 with alternating rhombohedral and hexagonal structures. Solid-state contact angle measurements were performed to derive values for the work of adhesion. The results show that the adhesion is twice as good for the annealed specimen compared to the as-bonded sample. PMID:12366593

  15. Influence of temperature on AC conductivity of nanocrystalline CuAlO2

    NASA Astrophysics Data System (ADS)

    Prakash, T.

    2012-07-01

    Nanocrystalline CuAlO2 was synthesized by mechanical alloying of Cu2O and α-Al2O3 powders in the molar ratio of 1:1 for 20 h in toluene medium with tungsten carbide balls and vials using planetary ball mill. The ball milling was carried out at 300 rpm with a ball to powder weight ratio of 10:1 and then annealed at 1373 K in a platinum crucible for 20 h to get CuAlO2 phase with average crystallite size 45 nm. Complex impedance spectroscopic measurement in the frequency region 1 Hz to 10 MHz between the temperatures 333 to 473 K was carried out for nanocrystalline CuAlO2 sample. The obtained complex impedance data was analyzed for AC conductivities, DC and AC conductivities correlations and crossover frequencies ( f co ). The BNN (Barton, Nakajima and Namikawa) relation was applied to understand the correlation between DC and AC conductivities. The observed experimental results were discussed in the paper.

  16. Energetic igniters realized by integrating Al/CuO reactive multilayer films with Cr films

    NASA Astrophysics Data System (ADS)

    Zhu, Peng; Shen, Ruiqi; Ye, Yinghua; Zhou, Xiang; Hu, Yan

    2011-10-01

    This paper deals with the energetic igniters realized by integrating Al/CuO reactive multilayer films (RMFs) with Cr Films, which could be used in micro-ignition system. The as-deposited Al/CuO RMFs has been characterized with varied analytical techniques. Results show that distinct Al/CuO RMFs is sputter deposited in a layered geometry, and the Al/CuO RMFs gives a heat of reaction equal to 2760 J/g. The structure of igniter is similar to a capacitor, which may place an electric field across the igniter and allow the instantaneous large-current to drift through the igniter. Firing characteristics of the igniter were accomplished using constant voltage firing set. The experiment shows that the ignition delay time and total released energy of the igniter discharged in 40 V are 0.7 ms and 482.34 mJ, respectively. In addition, the explosion temperature could keep an approximately constant value of 3500 °C for 1.4 ms.

  17. Production of Cu-Al-Ni Shape Memory Alloys by Mechanical Alloy

    SciTech Connect

    Goegebakan, Musa; Soguksu, Ali Kemal; Uzun, Orhan; Dogan, Ali

    2007-04-23

    The mechanical alloying technique has been used to produce shape memory Cu83Al13Ni4 alloy. The structure and thermal properties were examined by using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The morphology of the surface suggests the presence of martensite.

  18. X-ray imaging and controlled solidification of Al-Cu alloys toward microstructures by design

    DOE PAGES

    Clarke, Amy J.; Tourret, Damien; Imhoff, Seth D.; Gibbs, Paul J.; Fezzaa, Kamel; Cooley, Jason C.; Lee, Wah -Keat; Deriy, Alex; Patterson, Brian M.; Papin, Pallas A.; et al

    2015-01-30

    X-ray imaging, which permits the microscopic visualization of metal alloy solidification dynamics, can be coupled with controlled solidification to create microstructures by design. This x-ray image shows a process-derived composite microstructure being made from a eutectic Al-17.1 at.%Cu alloy by successive solidification and remelting steps.

  19. Modification of superconducting and resistive properties of HoBa2Cu3O7-δ single crystals under application-removal of high hydrostatic pressure

    NASA Astrophysics Data System (ADS)

    Vovk, R. V.; Khadzhai, G. Ya.; Dobrovolskiy, O. V.; Kamchatna, S. N.; Chroneos, A.

    2016-06-01

    The influence of a high hydrostatic pressure on the basal-plane electrical resistance along the twin boundaries in underdoped HoBa2Cu3O7-δ single crystals is investigated. An enhancement of the phase segregation caused by the high-pressure-induced redistribution of the labile oxygen has been revealed. The temperature dependences of the electrical resistance above Tc can be approximated well within the framework of the model of s - d electron-phonon scattering.

  20. The preparation of high-J c Gd0.5Y0.5Ba2Cu3O7-δ thin films by the MOCVD process

    NASA Astrophysics Data System (ADS)

    Zhao, R. P.; Zhang, F.; Liu, Q.; Xia, Y. D.; Lu, Y. M.; Cai, C. B.; Tao, B. W.; Li, Y. R.

    2016-06-01

    A home-designed metal organic chemical vapor deposition (MOCVD) system has been employed to prepare high critical current density (J c) Gd0.5Y0.5Ba2Cu3O7-δ (GdYBCO) thin films on LaMnO3/epitaxial MgO/ion beam assisted deposition (IBAD)-MgO/solution deposition planarization (SDP)-Y2O3-buffered Hastelloy tapes; the thin films were directly heated by the Joule effect after applying an heating current (I h ) through the Hastelloy tapes. The effect of the mole ratio of the metal organic sources has been systematically investigated. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses indicated that the GdYBCO films crystallized better and became denser with the increasing of the Cu/Ba ratio from 1.0 to 1.1, yielding a J c at 77 K and 0 T of 200 nm GdYBCO film increasing from 2.5 MA cm-2 to 7 MA cm-2. In addition, SEM and energy dispersive spectrometer (EDS) characterizations revealed that more and more outgrowths appeared and the density of the film was reduced with an increase in the Cu/Ba ratio from 1.1 to 1.2. When the I h was 26.8 A and the mole ratio of Gd(tmhd)3, Y(tmhd)3, Ba(tmhd)2 and Cu(tmhd)2 in the precursor was 0.55:0.55:2:2.2, the critical current (I c) of the deposited 200 nm-thick GdYBCO film reached a 140 A cm-1 width (77 K, 0 T), corresponding to the J c 7 MA cm-2 (77 K, 0 T).

  1. Microstructure and mechanical behavior of spray-deposited Al-Cu-Mg(-Ag-Mn) alloys

    NASA Astrophysics Data System (ADS)

    Del Castillo, L.; Lavernia, E. J.

    2000-09-01

    The effect of alloy composition on the microstructure and mechanical behavior of four spray-deposited Al-Cu-Mg(-Ag-Mn) alloys was investigated. Precipitation kinetics for the alloys was determined using differential scanning calorimetry (DSC) and artificial aging studies coupled with transmission electron microscopy (TEM) analysis. DSC/TEM analysis revealed that the spray-deposited alloys displayed similar precipitation behavior to that found in previously published studies on ingot alloys, with the Ag containing alloys exhibiting the presence of two peaks corresponding to precipitation of both Ω-Al2Cu and θ'-Al2Cu and the Ag-free alloy exhibiting only one peak for precipitation of θ'. The TEM analysis of each of the Ag-containing alloys revealed increasing amounts of Al20Mn3Cu2 with increasing Mn. In the peak and over-aged conditions, Ag-containing alloys revealed the presence of Ω, with some precipitation of θ' for alloys 248 and 251. Tensile tests on each of the alloys in the peak-aged and overaged (1000 hours at 160 °C) conditions were performed at both room and elevated temperatures. These tests revealed that the peak-aged alloys exhibited relatively high stability up to 160 °C, with greater reductions in strength being observed at 200 °C (especially for the high Mn, low Cu/Mg ratio (6.7) alloy 251). The greatest stability of tensile strength following extended exposure at 160 °C was exhibited by the high Cu/Mg ratio (14) alloy 248, which revealed reductions in yield strength of about 2.5 pct, with respect to the peak-aged condition, for the alloys tested at both room temperature and 160 °C.

  2. Influence of temperature on Al/p-CuInAlSe2 thin-film Schottky diodes

    NASA Astrophysics Data System (ADS)

    Parihar, Usha; Ray, Jaymin; Panchal, C. J.; Padha, Naresh

    2016-06-01

    Al/p-CuInAlSe2 Schottky diodes were fabricated using the optimized thin layers of CuInAlSe2 semiconductor. These diodes were used to study their temperature-dependent current-voltage (I-V) and capacitance-voltage (C-V) analysis over a wide range of 233-353 K. Based on these measurements, diode parameters such as ideality factor ( η), barrier height (ϕbo) and series resistance ( R s) were determined from the downward curvature of I-V characteristics using Cheung and Cheung method. The extracted parameters were found to be strongly temperature dependent; ϕbo increases, while η and R s decrease with increasing temperature. This behavior of ϕbo and η with change in temperature has been explained on the basis of barrier inhomogeneities over the MS interface by assuming a Gaussian distribution (GD) of the ϕbo at the interface. GD of barrier height (BH) was confirmed from apparent BH (ϕap) versus q/2 kT plot, and the values of the mean BH and standard deviation (σs) obtained from this plot at zero bias were found to be 1.02 and 0.14 eV, respectively. Also, a modified ln ( {J_{{s}} /T2 } ) - q2 σ_{{s}}2 /2k2 T2 versus q/ kT plot for Al/p-CuInAlSe2 Schottky diodes according to the GD gives ϕbo and Richardson constant ( A ** ) as 1.01 eV and 26 Acm-2 K-2, respectively. The Richardson constant value of 26 Acm-2 K-2 is very close to the theoretical value of 30 Acm-2 K-2. The discrepancy between BHs obtained from I-V and C-V measurements has also been interpreted.

  3. A DFT study on CO oxidation catalyzed by subnanometer AlCu n ( n = 1-3) clusters

    NASA Astrophysics Data System (ADS)

    Dong, Xiaona; Guo, Ling; Wen, Caixia; Ren, Ningning; Niu, Shuangshu

    2014-07-01

    Through the first-principle density-functional theory (DFT) calculations, we have made an exhaustive study of the mechanism of CO oxidation catalyzed by AlCu n ( n = 1-3) clusters on gas phase. It is shown that mixing two different metals (Al and Cu) can have beneficial effects on the catalytic activity than monometallic Cu n + 1 ( n = 1-3) cluster toward the reaction of CO oxidation and the alloyed AlCu3 cluster is proposed as the best effective nanocatalysts.

  4. A basin-hopping Monte Carlo investigation of the structural and energetic properties of 55- and 561-atom bimetallic nanoclusters: the examples of the ZrCu, ZrAl, and CuAl systems

    NASA Astrophysics Data System (ADS)

    De Souza, Douglas G.; Cezar, Henrique M.; Rondina, Gustavo G.; de Oliveira, Marcelo F.; Da Silva, Juarez L. F.

    2016-05-01

    We report a basin-hopping Monte Carlo investigation within the embedded-atom method of the structural and energetic properties of bimetallic ZrCu, ZrAl, and CuAl nanoclusters with 55 and 561 atoms. We found that unary Zr55, Zr561, Cu55, Cu561, Al55, and Al561 systems adopt the well known compact icosahedron (ICO) structure. The excess energy is negative for all systems and compositions, which indicates an energetic preference for the mixing of both chemical species. The ICO structure is preserved if a few atoms of the host system are replaced by different species, however, the composition limit in which the ICO structure is preserved depends on both the host and new chemical species. Using several structural analyses, three classes of structures, namely ideal ICO, nearly ICO, and distorted ICO structures, were identified. As the amounts of both chemical species change towards a more balanced composition, configurations far from the ICO structure arise and the dominant structures are nearly spherical, which indicates a strong minimization of the surface energy by decreasing the number of atoms with lower coordination on the surface. The average bond lengths follow Vegard’s law almost exactly for ZrCu and ZrAl, however, this is not the case for CuAl. Furthermore, the radial distribution allowed us to identify the presence of an onion-like behavior in the surface of the 561-atom CuAl nanocluster with the Al atoms located in the outermost surface shell, which can be explained by the lower surface energies of the Al surfaces compared with the Cu surfaces. In ZrCu and ZrAl the radial distribution indicates a nearly homogeneous distribution for the chemical species, however, with a slightly higher concentration of Al atoms on the ZrAl surface, which can also be explained by the lower surface energy.

  5. A basin-hopping Monte Carlo investigation of the structural and energetic properties of 55- and 561-atom bimetallic nanoclusters: the examples of the ZrCu, ZrAl, and CuAl systems.

    PubMed

    De Souza, Douglas G; Cezar, Henrique M; Rondina, Gustavo G; de Oliveira, Marcelo F; Da Silva, Juarez L F

    2016-05-01

    We report a basin-hopping Monte Carlo investigation within the embedded-atom method of the structural and energetic properties of bimetallic ZrCu, ZrAl, and CuAl nanoclusters with 55 and 561 atoms. We found that unary Zr55, Zr561, Cu55, Cu561, Al55, and Al561 systems adopt the well known compact icosahedron (ICO) structure. The excess energy is negative for all systems and compositions, which indicates an energetic preference for the mixing of both chemical species. The ICO structure is preserved if a few atoms of the host system are replaced by different species, however, the composition limit in which the ICO structure is preserved depends on both the host and new chemical species. Using several structural analyses, three classes of structures, namely ideal ICO, nearly ICO, and distorted ICO structures, were identified. As the amounts of both chemical species change towards a more balanced composition, configurations far from the ICO structure arise and the dominant structures are nearly spherical, which indicates a strong minimization of the surface energy by decreasing the number of atoms with lower coordination on the surface. The average bond lengths follow Vegard's law almost exactly for ZrCu and ZrAl, however, this is not the case for CuAl. Furthermore, the radial distribution allowed us to identify the presence of an onion-like behavior in the surface of the 561-atom CuAl nanocluster with the Al atoms located in the outermost surface shell, which can be explained by the lower surface energies of the Al surfaces compared with the Cu surfaces. In ZrCu and ZrAl the radial distribution indicates a nearly homogeneous distribution for the chemical species, however, with a slightly higher concentration of Al atoms on the ZrAl surface, which can also be explained by the lower surface energy.

  6. Solidification Paths and Phase Components at High Temperatures of High-Zn Al-Zn-Mg-Cu Alloys with Different Mg and Cu Contents

    NASA Astrophysics Data System (ADS)

    Shu, W. X.; Hou, L. G.; Liu, J. C.; Zhang, C.; Zhang, F.; Liu, J. T.; Zhuang, L. Z.; Zhang, J. S.

    2015-11-01

    Studies were carried out systematically on a series of Al-8.5 wt pct Zn- xMg- yCu alloys ( x is about 1.5, 2.0, and 2.5 wt pct, and y is about 1.5, 2.0, 2.5, and 2.9 wt pct). The effects of alloying elements Mg and Cu on the microstructures of as-cast and homogenized alloys were investigated using the computational/experimental approach. It shows that Mg(Zn,Al,Cu)2 ( σ) phase can exist in all the as-cast alloys without any observable Mg32(Al,Zn)49/Al2Mg3Zn3 ( T) or Al2CuMg ( S) phase, whereas Al2Cu ( θ) phase is prone to exist in the alloys with low Mg and high Cu contents. Thermodynamic calculation shows that the real solidification paths of the designed alloys fall in between the Scheil and the equilibrium conditions, and close to the former. After the long-time homogenization [733 K (460 °C)/168 hours] and the two-step homogenization [733 K (460 °C)/24 hours + 748 K (475 °C)/24 hours], the phase components of the designed alloys are generally consistent with the calculated phase diagrams. At 733 K (460 °C), the phase components in the thermodynamic equilibrium state are greatly influenced by Mg content, and the alloys with low Mg content are more likely to be in single-Al phase field even if the alloys contain high Cu content. At 748 K (475 °C), the dissolution of the second phases is more effective, and the phase components in the thermodynamic equilibrium state are dominated primarily by (Mg + Cu) content, except the alloys with (Mg + Cu) ≳ 4.35 wt pct, all designed alloys are in single-Al phase field.

  7. Fabrication of c-axis Oriented Epitaxial EuBa2Cu3O7-δ and EuBa2Cu4O8 Films on SrTiO3 (100) Substrate by Molten Hydroxide Method at 450°C

    NASA Astrophysics Data System (ADS)

    Miyachi, Y.; Funaki, S.; Yamada, Y.

    EuBa2Cu3O7-δ (Eu123) and EuBa2Cu4O8 (Eu124) films oriented in c-axis were deposited on SrTiO3 (100) substrates with eutectic NaOH-KOH flux at 450 °C. Synthesized phase has changed by using various types of barium source materials. Pure Eu124 films showed superconducting transition at ∼70 K, zero-resistance was not observed for Eu123/124 two-phase films. One of the possible reasons of this is Eu/Ba substitution of Eu123 phase. According to Tc of the Eu124, the molten hydroxide method enables to deposit high-quality Eu124 films.

  8. Interfacial chemistry in Al/CuO reactive nanomaterial and its role in exothermic reaction.

    PubMed

    Kwon, Jinhee; Ducéré, Jean Marie; Alphonse, Pierre; Bahrami, Mehdi; Petrantoni, Marine; Veyan, Jean-Francois; Tenailleau, Christophe; Estève, Alain; Rossi, Carole; Chabal, Yves J

    2013-02-01

    Interface layers between reactive and energetic materials in nanolaminates or nanoenergetic materials are believed to play a crucial role in the properties of nanoenergetic systems. Typically, in the case of Metastable Interstitial Composite nanolaminates, the interface layer between the metal and oxide controls the onset reaction temperature, reaction kinetics, and stability at low temperature. So far, the formation of these interfacial layers is not well understood for lack of in situ characterization, leading to a poor control of important properties. We have combined in situ infrared spectroscopy and ex situ X-ray photoelectron spectroscopy, differential scanning calorimetry, and high resolution transmission electron microscopy, in conjunction with first-principles calculations to identify the stable configurations that can occur at the interface and determine the kinetic barriers for their formation. We find that (i) an interface layer formed during physical deposition of aluminum is composed of a mixture of Cu, O, and Al through Al penetration into CuO and constitutes a poor diffusion barrier (i.e., with spurious exothermic reactions at lower temperature), and in contrast, (ii) atomic layer deposition (ALD) of alumina layers using trimethylaluminum (TMA) produces a conformal coating that effectively prevents Al diffusion even for ultrathin layer thicknesses (∼0.5 nm), resulting in better stability at low temperature and reduced reactivity. Importantly, the initial reaction of TMA with CuO leads to the extraction of oxygen from CuO to form an amorphous interfacial layer that is an important component for superior protection properties of the interface and is responsible for the high system stability. Thus, while Al e-beam evaporation and ALD growth of an alumina layer on CuO both lead to CuO reduction, the mechanism for oxygen removal is different, directly affecting the resistance to Al diffusion. This work reveals that it is the nature of the monolayer

  9. Josephson junction and dc SQUID made from superconducting Y-Ba-Cu-O thick film

    SciTech Connect

    Lin, A.Z.; Li, H.Q.; Tang, L.; Liu, F.W.

    1989-03-01

    YBa/sub 2/Cu/sub 3/O/sub 7-x/ thick films were fabricated by the method of screen printing. A zero resistance state was achieved at 90K. The highest critical current density was about 150 A/cm/sup 2/ at 77K. Bridge type Josephson junction and dc SQUID were fabricated from thick films and operated at 77K. The induced steps produced by the ac Josephson effect were observed on the I-V curve when microwave radiation is applied to the junction. The clear periodic patterns of dc SQUID is observable at 77K. Environmental protection and the stability of thick films and devices were discussed.

  10. Superconducting order parameter fluctuations above Tc in polycrystalline Ho 1Ba 2Cu 3O 7-δ compounds

    NASA Astrophysics Data System (ADS)

    Vidal, Félix; Veira, J. A.; Maza, J.; Ponte, J. J.; Amador, J.; Cascales, C.; Casais, M. T.; Rasines, I.

    1988-08-01

    We report measurements of the excess electrical conductivity, Δσ, above Tc in polycrystalline HoBa 2Cu 3O 7-δ single-phase 0 (within 4%) compounds. The relative temperature resolution is of the order of 10 -2 K which, in spite of the broadening of the transition by nonintrinsic effects, should probably make accessible the whole mean-field regime for Δσ and also to penetrate inside the full critical dynamic region. The general behavior of Δσ(ɛ) in these Ho-based samples is very similar to that previously observed in our laboratory for Y-based high-temperature superconductors. In particular, when analyzed in terms of the Aslamazov-Larkin theory and by using some dynamic scaling ideas, the Δσ(ɛ) data are compatible with a superconducting order parameter of two components fluctuating in three dimensions. No influence of the magnetic Ho ions on Δσ is observed in the whole reduced-temperature range studied.

  11. Temperature dependence of the magnetic anisotropy of metallic Y-Ba-Cu-O single crystals in the normal phase

    SciTech Connect

    Miljak, M.; Zlatic, V.; Kos, I.; Aviani, I. ); Hamzic, A. ); Collin, G. )

    1990-12-01

    The magnetic anisotropy measurements of metallic Y-Ba-Cu-O compounds in the normal phase reveal a temperature-dependent diamagnetic component of the susceptibility that increases with decreasing temperature. The temperature variation of the susceptibility anisotropy and its total change do not seem to be much affected by the presence of the superconductivity at some lower temperature and could not be accounted for by superconducting fluctuations. Rather, the data remind one of the behavior of some quasi-two-dimensional metals with anisotropic Fermi surfaces, reflecting the properties of the low-energy excitations in the normal phase. The anisotropy measurements above the bulk superconducting transition temperature {Tc} reveal the nonlinear effects, which are due to the onset of superconductivity in disconnected grains. The existence of a two-step transition, typical for granular superconductors, should be taken into consideration if the normal-phase susceptibility data are compared with the theoretical predictions in the vicinity of {ital T}{sub {ital c}}.

  12. Broad Temperature Pinning Study of 15 mol.% Zr-Added (Gd, Y)-Ba-Cu-O MOCVD Coated Conductors

    SciTech Connect

    Xu, AX; Khatri, N; Liu, YH; Majkic, G; Galstyan, E; Selvamanickam, V; Chen, YM; Lei, CH; Abraimov, D; Hu, XB; Jaroszynski, J; Larbalestier, D

    2015-06-01

    BaZrO3 (BZO) nanocolumns have long been shown to be very effective for raising the pinning force F-p of REBa2Cu3Ox (REBCO, where RE = rare earth) films at high temperatures and recently at low temperatures too. We have successfully incorporated a high density of BZO nanorods into metal organic chemical vapor deposited (MOCVD) REBCO coated conductors via Zr addition. We found that, compared to the 7.5% Zr-added coated conductor, dense BZO nanorod arrays in the 15% Zr-added conductor are effective over the whole temperature range from 77 K down to 4.2 K. We attribute the substantially enhanced J(c) at 30 K to the weak uncorrelated pinning as well as the strong correlated pinning. Meanwhile, by tripling the REBCO layer thickness to similar to 2.8 mu m, the engineering critical current density J(e) at 30 K exceeds J(e) of optimized Nb-Ti wires at 4.2 K.

  13. A comparative study on shock compression of nanocrystalline Al and Cu: Shock profiles and microscopic views of plasticity

    SciTech Connect

    Ma, Wen; Hou, Yong; Zhu, Wenjun

    2013-10-28

    Shock compressions of nanocrystalline (nc) metals Al and Cu with the same grain size and texture are studied by using molecular dynamics simulations. Results have revealed that the shock front of both Al and Cu can be divided into three stages: elastic, grain-boundary-mediated, and dislocation-mediated plastic deformation. The transition planes among these three stages are proven to be non-planar by two-dimensional shock response analysis, including local stress, shear, temperature, and atom configuration. The difference between shocked Al and Cu is that the rise rate of the elastic stage of Cu is slightly higher than that of Al, and that the shock-front width of Al is wider than Cu at the same loading conditions. For the plastic stage, the dislocation density of shocked Al is lower than Cu, and the contribution of grain-boundary-mediated plasticity to shock front and strain for nc Al is more pronounced than for nc Cu. These results are explained through intrinsic material properties and atomistic analysis of the plastic process. In the case of the shocked Al sample, partial dislocations, perfect dislocations, and twins are observed, but few evidence of perfect dislocations and twins are observed in the shocked Cu.

  14. Synthesis and physical properties of (Pr 1-xRE x)Ba 2Cu 4O 8 oxides (RE dbnd Y, Yb, Nd, Gd)

    NASA Astrophysics Data System (ADS)

    Horii, Shigeru; Yamada, Y.; Yamada, N.; Hirabayashi, I.; Mizutani, U.

    1997-08-01

    PrBa 2Cu 4O 8(Pr124) does not exhibit superconductivity, but its resistivity shows a metallic behavior below 180K. This behavior is in a sharp contrast to the semiconducting one of PrBa 2Cu 3O 7-y(Pr123). A substitution of Pr by RE(Rare earth elements) in the Pr123 is known to induce the superconductivity. For example, the critical RE concentration, XTC, corresponding to the onset of superconductivity for RE dbnd Y, Yb, Gd and Nd has been reported to be 0.45, 0.35, 0.5 and 0.65, respectively. In thi study, we could prepare stoichiometric (Pr 1-xRE x)Ba2Cu 4O 8 oxides by using high oxygen pressure technique, and investigated the physical properties. In the case of RE dbnd Y, Yb and Gd, the semiconducting region has disappeared and the superconductivity appeared at x=0.3, 0.25 and 0.4, respectively. This result means that Pr-effect in the 124 system is smaller than that in the 123 system.

  15. Structure and Optical Thermometry Characterization of Er3+/Yb3+ Co-Doped BaGd2CuO5.

    PubMed

    Li, Xiaodong; Song, Yanjie; Yang, Yanmin; Mi, Chao; Liu, Yanzhou; Yu, Fang; Liu, Linlin; Zhang, Jiao; Li, Zhiqiang

    2016-04-01

    Er3+/Yb3+ co-doped BaGd2CuO5 upconversion luminescent materials are obtained by solid phase method. Rietveld refinement on X-ray diffraction data indicates that Er3+/Yb3+ ions are inclined to occupy the Gd(1) site in the structure of BaGd2CuO5 (green phase). Two green emission peaks located at 523 nm and 547 nm have been produced by the excitation of 971 nm LD. The fluorescence intensity ratio (FIR) of the two green emission peaks have been investigated in the temperature range of 290 K-594 K. The maximum sensitivity derived from the FIR technique of the green upconversion emission is approximately 0.0038 K-1, and it has a high transmission power at low excitation density. This result implies that the Er3+/Yb3+ co-doped BaGd2CuO5 phosphors can play an important role in temperature measurements with a better sensitivity. PMID:27451663

  16. Development of Cu alloy anode and separator coated with Al-Ni intermetallic compound

    SciTech Connect

    Toyokura, K.; Hoshino, K.; Yamamoto, M.

    1996-12-31

    Anode made of Cu alloy and separator coated with Al-Ni intermetallic compound have been developed for VCFC. Anode of Ni alloy is usually used. However, the alternative of cost lower than Ni alloy anode should be needed, because Ni is expensive. Cu is attractive as an anode material for VCFC because it is inexpensive and electrochemically noble. However, the creep resistance of Cu is not sufficient, compared with Ni alloy. In this study, strengthening due to oxide-dispersed microstructure has been developed in Cu-Ni-Al alloy with the two-step sintering process. A wet-seal technique has been widely applied for gas-sealing and supporting of electrolyte in MCFC. Since the wet-seal area is exposed to a severe corrosive environment, corrosion resistance of material for wet sealing is related with the cell performance. Al-Ni plating with post-heat treating for stainless steel has been investigated. Stainless steel substrate was plated with Al after being coated with Ni, then heat-treated at 750 {degrees}C for 1 hour in Ar gas atmosphere. Due to the treatment, Al-Ni intermetallic compound ( mainly Al3Ni2 ) layer is formed on stainless steel surface. The long-term immersion test was carried out till 14,500 hours in 62 mol% Li{sub 2}CO{sub 3}-38 mol% K{sub 2}CO{sub 3} at 650 {degrees}C under air-30%CO{sub 2} atmosphere, for the purpose of evaluating the corrosion resistance and thermal stability of Al-Ni intermetallic compound layer in actual generating with VCFC.

  17. Monolithic translucent BaMgAl10O17:Eu2+ phosphors for laser-driven solid state lighting

    NASA Astrophysics Data System (ADS)

    Cozzan, Clayton; Brady, Michael J.; O'Dea, Nicholas; Levin, Emily E.; Nakamura, Shuji; DenBaars, Steven P.; Seshadri, Ram

    2016-10-01

    With high power light emitting diodes and laser diodes being explored for white light generation and visible light communication, thermally robust encapsulation schemes for color-converting inorganic phosphors are essential. In the current work, the canonical blue-emitting phosphor, high purity Eu-doped BaMgAl10O17, has been prepared using microwave-assisted heating (25 min) and densified into translucent ceramic phosphor monoliths using spark plasma sintering (30 min). The resulting translucent ceramic monoliths convert UV laser light to blue light with the same efficiency as the starting powder and provide superior thermal management in comparison with silicone encapsulation.

  18. Co-Dopant Influence on the Persistent Luminescence of BaAl2O4:Eu2+,R3+

    NASA Astrophysics Data System (ADS)

    Rodrigues, Lucas C. V.; Hölsä, Jorma; Carvalho, José M.; Pedroso, Cássio C. S.; Lastusaari, Mika; Felinto, Maria C. F. C.; Watanabe, Shigeo; Brito, Hermi F.

    2014-04-01

    The R3+ (rare earth) co-dopants may have a surprisingly important role in persistent luminescence - enhancement of up to 1-3 orders of magnitude may be obtained in the performance of these phosphor materials - depending strongly on the R3+ ion, of course. In this work, the effects of the R3+ co-dopants in the BaAl2O4:Eu2+,R3+ materials were studied using mainly thermoluminescence (TL) and synchrotron radiation XANES methods. In BaAl2O4, the conventional and persistent luminescence both arise from the 4f7→4f65d1 transition of Eu2+, yielding blue-green emission color. The former, in the presence of humidity, turns to more bluish because of creation of an additional Eu2+ luminescence centre which is not, however, visible in persistent luminescence. The trap structure in the non-co-doped BaAl2O4:Eu2+ is rather complex with 4-5 TL bands above room temperature. With R3+ co-doping, this basic structure is modified though no drastic change can be observed. This underlines the fact that even very small changes in the trap depths can produce significant modifications in the persistent luminescence efficiency. It should be remembered that basically the persistent luminescence performance is controlled by the Boltzmann population law depending exponentially on both the temperature and trap depth. Some mechanisms for persistent luminescence have suggested the presence of either divalent R2+ or tetravalent RIV during the charging of the Eu2+ doped materials. The present XANES measurements on BaAl2O4:Eu2+,R3+ confirmed the presence of only the trivalent form of the R3+ co-dopants excluding both of these pathways. It must thus be concluded, that the energy is stored in intrinsic and extrinsic defects created by the synthesis conditions and charge compensation due to R3+ co-doping. Even though the effect of the R3+ co-dopants was carefully exploited and characterized, the differences in the effect of different R3+ ions with very similar chemical and spectroscopic properties could

  19. Single-component and white light-emitting phosphor BaAl2Si2O8: Dy3+, Eu3+ synthesis, luminescence, energy transfer, and tunable color

    NASA Astrophysics Data System (ADS)

    Ma, Pingchuan; Song, Yanhua; Sheng, Ye; Yuan, Bo; Guan, Hongxia; Xu, Chengyi; Zou, Haifeng

    2016-10-01

    A series of Dy3+ - Eu3+ co-doped BaAl2Si2O8 phosphors were prepared via the conventional solid-state reaction method. Their crystal structure, luminescent characteristic and lifetime were investigated. The optimum doping concentrations of Dy3+and Eu3+ are both 0.05 for Dy3+ or Eu3+ singly doped BaAl2Si2O8. Furthermore, BaAl2Si2O8: 0.05Dy3+ and BaAl2Si2O8: 0.05Eu3+ emits yellow and red light. The emission color of BaAl2Si2O8: Dy3+, Eu3+ could be tuned from yellow to white due to the energy transfer. This energy transfer from Dy3+ to Eu3+ was confirmed and investigated by photoluminescence spectra and the decay time of energy donor Dy3+ ions. With constantly increasing Eu3+ concentration, the energy transfer efficiency from Dy3+ to Eu3+ in BaAl2Si2O8 host increased gradually and reached as high as 81%, the quantum yield was about 47.43%. BaAl2Si2O8: Dy3+, Eu3+ phosphors can be effectively excited by UV (about 348 nm) light and emit visible light from yellow to white by altering the concentration ratio of Dy3+ and Eu3+, indicating that the phosphors have potential applications as a white light-emitting phosphor for display and lighting.

  20. Synthesis, structural characterization and properties of SrAl4-xGex, BaAl4-xGex, and EuAl4-xGex (x≈0.3-0.4)—Rare examples of electron-rich phases with the BaAl4 structure type

    NASA Astrophysics Data System (ADS)

    Zhang, Jiliang; Bobev, Svilen

    2013-09-01

    Three solid solutions with the general formula AEAl4-xGex (AE=Eu, Sr, Ba; 0.32(1)≤x≤0.41(1)) have been synthesized via the aluminum self-flux method, and their crystal structures have been established from powder and single-crystal X-ray diffraction. They are isotypic and crystallize with the well-known BaAl4 structure type, adopted by the three AEAl4 end members. In all structures, Ge substitutes Al only at the 4e Wyckoff site. Results from X-rays photoelectron spectroscopy on EuAl4-xGex and EuAl4 indicate that the interactions between the Eu2+ cations and the polyanionic framework are enhanced in the Ge-doped structure, despite the slightly elevated Fermi level. Magnetic susceptibility measurements confirm the local moment magnetism, expected for the [Xe]4f7 electronic configuration of Eu2+ and suggest strong ferromagnetic interactions at cryogenic temperatures. Resistivity data from single-crystalline samples show differences between the title compounds, implying different bonding characteristics despite the close Debye temperatures. A brief discussion on the observed electron count and homogeneity ranges for AEAl4-xGex (AE=Eu, Sr, Ba) is also presented.