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Sample records for al ba cu

  1. Al- and Cu-doped BaSi2 films on Si(111) substrate by molecular beam epitaxy and evaluation of depth profiles of Al and Cu atoms

    NASA Astrophysics Data System (ADS)

    Ajmal Khan, M.; Takeishi, M.; Matsumoto, Y.; Saito, T.; Suemasu, T.

    The main objective of the present work is to evaluate and compare the depth profiles of Al and Cu atoms in in-situ doped BaSi2. Furthermore, it is also desired to investigate and compare the carrier concentration of Al-doped as well as Cu-doped BaSi2 films and qualify as a potential dopant-candidate for more efficient solar cells of BaSi2. During the experiment, reactive deposition epitaxy and molecular beam epitaxy were used to develop the samples. X-ray diffraction (XRD) measurements and secondary ion mass spectroscopy (SIMS), were used to determine the structure, depth profile and composition of the already grown films. The electrical properties were characterized by Hall measurement using the van der Pauw method. In case of Al-doped BaSi2 films, it was not encouraging result due to diffusion and segregation of Al in both the surface and BaSi2/ Si interface regions. On the other hand, those phenomena were not observed for Cu-doped BaS2 films. Heavily Cu-doped BaSi2 showed n+ conductivity, differently from our prediction.

  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. On the quasi-1D magnetic behavior of Ba 2MnCoAl 2F 14, Ba 2MnCuAl 2F 14 and related compounds

    NASA Astrophysics Data System (ADS)

    le Lirzin, A.; Darriet, J.; Georges, R.; Soubeyroux, J. L.

    1992-02-01

    Two new fluorides Ba 2MnCoAl 2F 14 and Ba 2MnCoAl 2F 14, isostructural with the natural compound usovite Ba 2CaMgAl 2F 14, have been synthesized. The nuclear structures of both compounds, refined from neutron diffraction data, give evidence for strongly disordered bimetallic chains MnCu or MnCo along the b-axis: two new theoretical treatments are suggested in order to account for the magnetic behavior of each compound but, due to their intrinsic limitations, they are in fact applied here to solid solutions between the parent compound and BaMnAlF 7, namely Ba 2Mn 1+ yCu 1- yAl2F14 and Ba 2Mn1+ yCo1- yAl 2F 14, leading to a rather good agreement with the measured values of the susceptibilities.

  4. Synthesis of Y1-xAlxBa2Cu3O7-δ via combustion route: Effects of Al2O3 nanoparticles on superconducting properties

    NASA Astrophysics Data System (ADS)

    Mohd Suan, Mohd Shahadan; Johan, Mohd Rafie

    2017-02-01

    Combustion reaction was used to synthesis Al2O3 nanoparticles embedded Y1-xAlxBa2Cu3O7-δ simultaneously. The effects of Al2O3 nanoparticles with nominal molar mass (xmol) of 0.02, 0.04, 0.06, 0.08 and 0.10 towards the critical current density JC of Y1-xAlxBa2Cu3O7-δ were verified by magnetic measurement. Resulted XRD patterns revealed that the calcined samples consist of pure Al2O3 and Y1-xAlxBa2Cu3O7-δ phases which had been confirmed by EDX results. The SEM images showed that Al2O3 nanoparticles ( 10 nm) were distributed in polycrystalline YBa2Cu3O7-δ grains and grain boundaries. The presence of higher concentration of Al2O3 nanoparticles has developed Al3+ rich spots which diffused within the YBa2Cu3O7-δ superconducting matrix to form Y1-xAlxBa2Cu3O7-δ and was confirmed by EDX analysis. The samples were electrically superconducting at temperature above 85 K as measured by using standard four-probe technique. The magnetic field (H) dependent magnetization (M), M-H hysteresis loops measured at 77 K for xmol≤0.06 samples are significantly improved attributed to the increase of trapped fluxes in the samples. Remarkable increase of magnetic JC (H) in Al2O3 nanoparticles added samples compared to the as prepared polycrystalline YBa2Cu3O7-δ sample indicating strong pinning effect. It is suggested that well-distributed Al2O3 nanoparticles in the polycrystalline YBa2Cu3O7-δ matrix achieved via auto-combustion reaction has efficiently pin the magnetic vortex. The magnetic JC was optimized to 6 kAcm-2 in xmol=0.06 sample. On the other hand, insignificant magnetic JC improvement in xmol≥0.08 samples is probably resulted from the agglomerated Al2O3 nanoparticles in Y1-xAlxBa2Cu3O7-δ phase.

  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. Electrical transport and Raman spectral studies of (110)-oriented PrBa2 (Cu0.8M0.2)3O7 (M = Ga, Al, Zn, Ni) thin films

    NASA Astrophysics Data System (ADS)

    Kandel, Hom; Chen, Tar-Pin; Iliev, Milko N.; Bourdo, Shawn; Seo, Hye-Won; Watanabe, Fumiya; Viswanathan, Tito

    2013-04-01

    The electrical transport and Raman spectral studies of (110)-oriented PrBa2 (Cu0.8M0.2)3O7 (M = Ga, Al, Ni, Zn) (PBCMO) thin films have been investigated. The electrical resistivity, ρ(T), of (110)-oriented PrBa2 (Cu0.8Ga0.2)3O7 (PBCGO) and PrBa2 (Cu0.8Al0.2)3O7 (PBCAO) thin films are many orders of magnitude higher than that of the (110)-oriented PrBa2Cu3O7 (PBCO) thin films and follow Mott's 3D variable range hopping law up to room temperature. The electrical resistivity and Raman spectroscopic studies show that Al and Ga ions replace the Cu ions in the Cu-O chains of (110)-oriented PBCO and cause an extensive localization of charge carriers (holes) in the chains site of the PBCO. Our transport studies on YBa2Cu3O7 (YBCO)/PBCGO and YBCO/PBCAO multilayers suggest that PBCAO and PBCGO thin films possess very less or no proximity effects. These results show (110)-oriented PBCGO and PBCAO thin films may serve as very effective insulators in YBCO based superconductor/insulator/superconductor tunneling Josephson junction.

  7. /Cu-Al System

    NASA Astrophysics Data System (ADS)

    Kish, Orel; Froumin, Natalya; Aizenshtein, Michael; Frage, Nachum

    2014-05-01

    Wettability and interfacial interaction of the Ta2O5/Cu-Al system were studied. Pure Cu does not wet the Ta2O5 substrate, and improved spreading is achieved when relatively a high fraction of the active element (~40 at.% Al) was added. The Al2O3 and AlTaO4 phases were observed at the Ta2O5/Cu-Al interface. A thermodynamic evaluation allowed us to suggest that the lack of wetting bellow 40 at.% Al is due to the presence of a native oxide, which covers the drop. The conditions of the native oxide decomposition and the formation of the volatile Al2O suboxide strongly depend on the vacuum level during sessile drop experiments and the composition of the Cu-Al alloy. In our case, Al contents greater than 40% provides thermodynamic conditions for the formation of Al2O (as a result of Al reaction with Al2O3) and the drop spreading. It was suggested that the final contact angle in the Ta2O5/Cu-Al system (50°) is determined by Ta adsorption on the newly formed alumina interlayer.

  8. Doping of the quadruple perovskites of type Nd 2Ba 2Cu 2Ti 2- xO xO 11,  Mn, Fe, Co, Al and NdBa 3Cu 2Ti 1+ xNb 1- xNb 1- xO 11

    NASA Astrophysics Data System (ADS)

    Rentschler, Thomas

    1997-02-01

    The synthesis of new ceramic materials NdBa 3Cu 2Ti 1+ xNb 1- xO 11 and Nd 2Ba 2Cu 2Ti 2- xM xO 11, M  Mn, Fe, Co, Al with a quadruple perovskite structure was successfully performed. Rietveld refinements verified the oxygen deficient layered a p ∗ a p ∗ 4a p superstructure (space group P4/mmm). Heterovalent doping in these groups of materials was carried out in order to provide a hole carrier concentration in the CuO 2 layers structurally related to the high- Tc superconductors. However, superconductivity was not observed. The formation of oxygen defects is discussed.

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

    DOE PAGES

    Wu, S. F.; Richard, P.; van Roekeghem, A.; ...

    2015-06-08

    In this study, 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 ofmore » 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. In conclusion, our results confirm the prediction that BaCu2As2 is an sp metal with weak electronic correlations.« less

  11. Al-Cu-Zr (050)

    NASA Astrophysics Data System (ADS)

    Carow-Watamura, U.; Louzguine, D. V.; Takeuchi, A.

    This document is part of Part 1 http://dx.doi.org/10.1007/9getType="URL"/> 'Systems from Ag-Al-Ca to Au-Pd-Si' of Subvolume B 'Physical Properties of Ternary Amorphous Alloys' of Volume 37 'Phase Diagrams and Physical Properties of Nonequilibrium Alloys' of Landolt-Börnstein - Group III 'Condensed Matter'. It contains the Chapter 'Al-Cu-Zr (050)' with the content:

  12. 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

  13. 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.

  14. 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%.

  15. 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.

  16. Superconducting EuBa 2Cu 3O 7-δ and YbBa 2Cu 3O 7-δ produced by oxidation of microcrystalline precursor alloys

    NASA Astrophysics Data System (ADS)

    Weiss, F.; Yavari, A. R.; Rouault, A.; Hadar, R.; Senateur, J. P.; Desre, P.

    1988-06-01

    EuBa2Cu3 and YbBa2Cu3 microcrystalltne alloys obtained by rapid solidification have been oxidized completely in flowing oxygen at a temperature higher than 900° C with subsequent slow cooling and have yield the high temperature oxides EuBa2Cu37-δ and YbBa2Cu3O7-δ. The onset of superconductivity occured at 92 K in the case of Eu and at 89 K in the case of Yb. The resistivity in the normal state ( ρ at 100 K) is lower than in sintered powder materials Sue to a better compaction and to a better intergrain coupling.

  17. Interfacial Phenomena in Al/Al, Al/Cu, and Cu/Cu Joints Soldered Using an Al-Zn Alloy with Ag or Cu Additions

    NASA Astrophysics Data System (ADS)

    Pstruś, Janusz; Gancarz, Tomasz

    2014-05-01

    The studies of soldered joints were carried out in systems: Al/solder/Al, Al/solder/Cu, Cu/solder/Cu, where the solder was (Al-Zn)EUT, (Al-Zn)EUT with 0.5, 1.0, and 1.5 at.% of Ag and (Al-Zn)EUT with 0.5, 1.0, and 1.5 at.% of Cu addition. Brazing was performed at 500 °C for 3 min. The EDS analysis indicated that the composition of the layers starting from the Cu pad was CuZn, Cu5Zn8, and CuZn4, respectively. Wetting tests were performed at 500 °C for 3, 8, 15, and 30 min, respectively. Thickness of the layers and their kinetics of growth were measured based on the SEM micrographs. The formation of interlayers was not observed from the side of Al pads. On the contrary, dissolution of the Al substrate and migration of Al-rich particles into the bulk of the solder were observed.

  18. Electronic properties of BaCuChF (Ch=S,Se,Te) surfaces and BaCuSeF/ZnPc interfaces

    NASA Astrophysics Data System (ADS)

    Zakutayev, Andriy; Tate, Janet; Platt, Heather A. S.; Keszler, Douglas A.; Hein, Corinna; Mayer, Thomas; Klein, Andreas; Jaegermann, Wolfram

    2010-05-01

    BaCuChF (Ch=S,Se,Te) surfaces and BaCuSeF interfaces with zinc phthalocyanine (ZnPc) were studied by photoelectron spectroscopy. BaCuChF compounds oxidize when exposed to ambient atmosphere. Se capping layers were studied as a means to produce representative surfaces for photoelectron spectroscopic measurements. Decapped BaCuSeF surfaces remain O-free and C-free when the Se layer is evaporated but they become F-deficient. The resulting surfaces have work functions of 4.85 eV and Fermi levels located 0.25 eV above the valence band maximum. In situ stepwise deposition of ZnPc on a BaCuSeF film surface produced a chemically inert interface with a hole-injection barrier of 0.11 eV.

  19. Fabrication and Characterization of PrBa2[CuxM1-x]3O7 (M=Ga, Al ,x=0.2) Epitaxial Thin Films

    NASA Astrophysics Data System (ADS)

    Kandel, Hom; Chen, Tar-Pin; Seo, Hye-Won; Iliev, Milko; Wadekar, Paritosh; Cui, Jing-Biao; Chen, Quark; Watanabe, Fumiya

    2010-03-01

    We have fabricated epitaxial thin films of highly resistive material PrBa2(Cu1-xMx)3O7 (M=Al, Ga, x = 0.2) by substituting Cu with Ga and Al in PrBa2Cu3O7.The electrical resistivity in these materials are many orders higher than in PrBa2Cu3O7 at 77K, which will provide an effective potential barrier to YBa2Cu3O7 in high Tc S-I-S Josephson junction. X-ray diffraction, atomic force microscopy, Raman and temperature dependent resistivity measurements were performed to characterize the thin films. We will discuss the results of Raman spectroscopy with regard to the site detection of incorporated dopants in PrBa2(Cu1-xMx)3O7 and transport studies with regard to the mechanism of hopping conductivity.

  20. Comparative Study between Similarly Processed YBa2Cu3O7-x Films with Y2BaCuO5 or BaSnO3 Additions (Postprint)

    DTIC Science & Technology

    2009-07-15

    14. ABSTRACT A special YBa2Cu3O7-x ( YBCO ) target with a thin sector of second phase material, in this case either Y2BaCuO5 (Y211) or BaSnO3 (BSO...was used to deposit YBCO films with non-layered nanoparticles on single crystal LaAlO3 and biaxially textured Ni-5 at.% W substrates buffered with...case of YBCO +Y211, and evenly spaced BSO nanocolumns in the case of YBCO +BSO, form in the YBCO films. While YBCO plane buckling was observed at many

  1. 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.

  2. Flux Creep in Sintered Superconducting Y-Ba-Cu-O

    NASA Astrophysics Data System (ADS)

    Matsushita, Teruo; Funaba, Seiji; Nagamatsu, Yoshiyuki; Ni, Baorong; Funaki, Kazuo; Yamafuji, Kaoru

    1989-09-01

    The flux creep rate in sintered superconducting Y-Ba-Cu-O was measured at 77 K and in fields of up to 0.1 T. The pinning potential mainly caused by flux pinning inside grains was 0.25 eV at B{=}50 mT and decreased monotonically with increasing magnetic field. The obtained results can be explained by the theoretical model with observed intragrain current density. This theoretical model suggests that the flux creep at high fields is notable even if a superconducting wire with the critical current density of 2× 1010 A/m2 at B{=}5 T is realized.

  3. Low-Temperature Synthesis, Structure, and Stability of Ba 2+ yCu 3O 6

    NASA Astrophysics Data System (ADS)

    Brosha, Eric L.; Garzon, Fernando H.; Raistrick, Ian D.; Davies, Peter K.

    1996-02-01

    Single-phase powders of Ba2Cu3O6have been prepared at 620°C under 1 atm of oxygen using freeze-dried nitrate precursors. Calcinations utilizing a precursor with a 1:1 Ba:Cu stoichiometry produced a two-phase mixture of BaO2+ Ba2Cu3O6and confirmed the stable, oxidized barium cuprate exists with a metal ion ratio close to 2:3. Diffraction studies suggest that Ba2Cu3O6(Ba0.67CuO2) crystallizes in a structure closely related to the linear chain KCuO2and NaCuO2cuprates. It is proposed that the reduction of copper and accompanying loss of oxygen observed above 620°C are accommodated by an increase in the Ba content of the structure and the formation of Ba2+yCu3O6with 0 ≤y≤ 0.25. Above 710°C, the high-yend member is metastable with respect to BaCuO2, although it decomposes slowly even at elevated temperatures.

  4. 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.

  5. 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.

  6. 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.

  7. Superconductivity in Al-substituted Ba8Si46 clathrates

    NASA Astrophysics Data System (ADS)

    Li, Yang; Garcia, Jose; Chen, Ning; Liu, Lihua; Li, Feng; Wei, Yuping; Bi, Shanli; Cao, Guohui; Feng, Z. S.

    2013-05-01

    There is a great deal of interest vested in the superconductivity of Si clathrate compounds with sp3 network, in which the structure is dominated by strong covalent bonds among silicon atoms, rather than the metallic bonding that is more typical of traditional superconductors. A joint experimental and theoretical investigation of superconductivity in Al-substituted type-I silicon clathrates is reported. Samples of the general formula Ba8Si46-xAlx, with different values of x were prepared. With an increase in the Al composition, the superconducting transition temperature TC was observed to decrease systematically. The resistivity measurement revealed that Ba8Si42Al4 is superconductive with transition temperature at TC = 5.5 K. The magnetic measurements showed that the bulk superconducting Ba8Si42Al4 is a type II superconductor. For x = 6 sample Ba8Si40Al6, the superconducting transition was observed down to TC = 4.7 K which pointed to a strong suppression of superconductivity with increasing Al content as compared with TC = 8 K for Ba8Si46. Suppression of superconductivity can be attributed primarily to a decrease in the density of states at the Fermi level, caused by reduced integrity of the sp3 hybridized networks as well as the lowering of carrier concentration. These results corroborated by first-principles calculations showed that Al substitution results in a large decrease of the electronic density of states at the Fermi level, which also explains the decreased superconducting critical temperature within the BCS framework. The work provided a comprehensive understanding of the doping effect on superconductivity of clathrates.

  8. Crystal structure and physical properties of the new chalcogenides Ba3Cu(17-x)(S,Te)11 and Ba3Cu(17-x)(S,Te)11.5 with two different Cu clusters.

    PubMed

    Kuropatwa, Bryan A; Assoud, Abdeljalil; Kleinke, Holger

    2011-08-15

    The sulfide-tellurides Ba(3)Cu(17-x)(S,Te)(11) and Ba(3)Cu(17-x)(S,Te)(11.5) were synthesized from the elements in stoichiometric ratios heated to 1073 K, followed by slow cooling to 873 K over 100 h. Ba(3)Cu(17-x)(S,Te)(11) is isostructural to Ba(3)Cu(17-x)(Se,Te)(11) when [S] > [Te], space group R ̅3m, with lattice dimensions of a = 12.009(1) Å, c = 27.764(2) Å, V = 3467.6(5) Å(3), for Ba(3)Cu(15.7(4))S(7.051(5))Te(3.949) (Z = 6). The structure is composed of Cu atoms forming paired hexagonal antiprisms, capped on the two outer hexagonal faces, where each Cu atom is tetrahedrally coordinated by four Q (= S, Te) atoms. The new variant is formed when [Te] > [S]; then Ba(3)Cu(17-x)(S,Te)(11.5) adopts space group Fm3̅m with a = 17.2095(8) Å, V = 5096.9(4) Å(3), for Ba(3)Cu(15.6(2))S(5.33(4))Te(6.17) (Z = 8). This structure consists of eight Te-centered Cu(16) icosioctahedra per cell interconnected by cubic Cu(8) units centered by Q atoms. Electronic structure calculations and property measurements illustrate that these compounds behave as extrinsic p-type semiconductors-toward metallic behavior for the latter compound. With standard oxidation states Ba(2+), Cu(+), and Q(2-), the electron precise formulas are Ba(3)Cu(16)Q(11) and Ba(3)Cu(17)Q(11.5).

  9. Bulk superconductivity in Tl 2Ba 2CaCu 2O 8 and TlBa 2Ca 2Cu 3O 9 phases

    NASA Astrophysics Data System (ADS)

    Sulpice, A.; Giordanengo, B.; Tournier, R.; Hervieu, M.; Maignan, A.; Martin, C.; Michel, C.; Provost, J.

    1988-09-01

    Well-crystallized Tl 2Ba 2CaCu 2O 8 phases have been observed superconducting or normal below 108 K depending on their stoichiometry. This observation is an evidence that a (Cu IL&.zbnd;O -) mixed valence induced by vacancies or substitution on different sites gives rise to superconductivity in this phase. The new phase TlBa 2Ca 2CuO 9 which intrinsically contains a mixed valence has been observed as having a sharp transition to bulk superconductivity in the Meissner effect at a critical temperature of 120 K. This temperature is much higher than the recently observed one.

  10. Critical currents and pinning forces in a-axis oriented EuBa2Cu3O7/PrBa2Cu3O7 superlattices

    NASA Astrophysics Data System (ADS)

    Vélez, M.; Martín, J. I.; Vicent, J. L.

    1995-11-01

    a-axis oriented EuBa2Cu3O7/PrBa2Cu3O7 (EBCO/PBCO) superlattices have been grown by dc sputtering. The critical current (JC) behavior is modified by the pinning force arising from the insulating PrBa2Cu3O7 layers, which in a-axis oriented superlattices are perpendicular to the Cu-O planes. Depending on the EBCO and PBCO layer thicknesses the pinning forces deviate from the usual scaling laws as a function of temperature observed in single films. When B is perpendicular to the sample, an exponential dependence of JC(B) appears as the PBCO thickness is increased (coupling is reduced), and also as the thickness of the EBCO layer is reduced.

  11. Study of Dissolution Process of Solid Cu in Liquid Al

    NASA Astrophysics Data System (ADS)

    Chen, Shuying; Wu, Yang; Chang, Guowei; Zhu, Changxu; Li, Qingchun

    2016-09-01

    The dissolution process of solid Cu in liquid Al influences the compound quality directly when fabricating the copper cladding aluminum (CCA) composite castings utilizing the casting aluminum method. Dissolution rate of solid Cu is investigated utilizing the method of quenching rapidly. Effects of liquid Al temperature and the contact time between solid Cu and liquid Al on the dissolution rate of Cu are investigated; meanwhile, the dissolution mechanism of Cu is explored. Subsequently, the influences of processing parameters on the dissolution thickness of Cu are examined. The results indicate that chemical compounds, such as AlCu2, Cu5Al, CuAl2 and Cu2Al3, may form on the contact surface between solid Cu and liquid Al. These chemical compounds are contributed to decompose the solid Cu, Cu5Al exerts the greatest effect. The dissolution of Cu is affected by the contact time between solid Cu and liquid Al, temperature and cooling method of Cu plate. The dissolution of Cu cannot terminate immediately even though the Cu plate is cooled by the spray. The experimental results will provide a reference for controlling the composite layer thickness.

  12. 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.

  13. Flux Pinning of Y-Ba-Cu-O Films Doped With BaZrO3 Nanoparticles by Multilayer and Single Target Methods (Postprint)

    DTIC Science & Technology

    2007-06-01

    AFRL-RZ-WP-TP-2012-0130 FLUX PINNING OF Y-Ba-Cu-O FILMS DOPED WITH BaZrO3 NANOPARTICLES BY MULTILAYER AND SINGLE TARGET METHODS (POSTPRINT...To) February 2012 Journal Article Postprint 04 April 2005 – 04 April 2007 4. TITLE AND SUBTITLE FLUX PINNING OF Y-Ba-Cu-O FILMS DOPED WITH BaZrO3...effort was completed in 2007. 14. ABSTRACT The superconducting properties of YBa2Cu3O7-x (YBCO or 123) thin films doped with BaZrO3 (BZO

  14. 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).

  15. 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).

  16. Nonstoichiometry and decomposition of La 1+ zBa 2- zCu 3O y and La 4BaCu 5O 13- w

    NASA Astrophysics Data System (ADS)

    Lindemer, T. B.; Specht, E. D.; MacDougall, C. S.; Taylor, G. M.; Pye, S. L.

    1993-10-01

    The temperature ( T, K) and oxygen pressure ( pO 2, Pa) dependence of oxygen content in La 1+ zBa 2- zCu 3O y (123) and La 4BaCu 5O 13- w (415) were determined over the ranges 10 Pa to 0.1 MPa O 2, 0.0≤ z≤0.7 and 523≤ T≤1223 K. The data for each phase were correlated with chemical thermodynamic representations. For La 1+ zBa 2- zCu 3O y, the T- z- y- pO 2 behavior was modeled as a solution of LaBa 2Cu 3O 7- x and 415. The experimental data demonstrated 7- x values <6 at high temperatures, while they exceed 6.99 only at temperatures approaching ambient at 0.1 MPa O 2. These two characteristics are not known to occur in the lanthanide and Y analogues. The T- z- pO 2 dependence of high-temperature decomposition was determined and, in conjunction with X-ray analysis, permitted construction of the phase diagram lying between LaBa 2Cu 3O 7- x and 415. Effects of residual carbonate content were also determined.

  17. Superconductivity in SrCuO2-BaCuO2 Superlattices: Formation of Artificially Layered Superconducting Materials.

    PubMed

    Norton, D P; Chakoumakos, B C; Budai, J D; Lowndes, D H; Sales, B C; Thompson, J R; Christen, D K

    1994-09-30

    Pulsed-laser deposition was used to synthesize artificially layered high-temperature superconductors. Thin-film compounds were formed when the constraint of epitaxy was used to stabilize SrCuO(2)-BaCuO(2) superlattices in the infinite layer structure. Using this approach, two new structural families, Ba(2)Srn-1,Cun+1 O2n+2+delta and Ba(4)Srn-1 Cun+3O2n+6+delta have been synthesized; these families superconduct at temperatures as high as 70 kelvin.

  18. Multilayer pinning in a-axis-oriented EuBa2Cu3O7/PrBa2Cu3O7 superconducting superlattices

    NASA Astrophysics Data System (ADS)

    Martin, J. I.; Velez, M.; Vicent, J. L.

    1995-08-01

    a-axis EuBa2Cu3O7/PrBa2Cu3O7 superlattices and a-axis films have been grown by dc sputtering to study the interplay between the natural material anisotropy (Cu-O planes) and the artificial layered structure (PrBa2Cu3O7 layers). These a-axis-oriented superlattices are unique because, in comparison with c-axis superlattices, they allow one to separate both effects: in c-axis multilayers Cu-O planes and the artificial layers are parallel whereas in a-axis multilayers the intrinsic and the artificial layers are perpendicular to each other. When B is parallel to the substrate plane, the superlattices show an enhancement of the pinning force in comparison with the behavior of the films that is controlled by the EuBa2Cu3O7 layer thickness. If B is perpendicular to the substrate plane, the flux motion presents a log B dependence of the activation energy up to at least, 40-unit-cell-thick layers.

  19. Dielectric response of Cu/amorphous BaTiO{sub 3}/Cu capacitors

    SciTech Connect

    Gonon, P.; El Kamel, F.

    2007-04-01

    Cu/amorphous BaTiO{sub 3}/Cu capacitors were tested for their dielectric properties in the 0.1 Hz-100 kHz range, from room temperature to 350 degree sign C. The amorphous barium titanate dielectric layer was deposited by rf sputtering on water-cooled copper electrodes. The room-temperature dielectric constant is around 18 and the dissipation factor is 3x10{sup -3} at 100 kHz. When increasing temperature the dielectric response displays an important frequency dispersion with the appearance of a marked loss peak at low frequencies. This dispersion is ascribed to electrode polarization effects, as evidenced by measurements performed on various film thicknesses and by using different electrodes. The electrode polarization phenomenon is discussed using a simple space charge model and is shown to be related to mobile oxygen vacancies.

  20. Superconductivity in noncentrosymmetric BaAl4 derived structures

    NASA Astrophysics Data System (ADS)

    Kneidinger, F.; Salamakha, L.; Bauer, E.; Zeiringer, I.; Rogl, P.; Blaas-Schenner, C.; Reith, D.; Podloucky, R.

    2014-07-01

    Ternary intermetallics Ep-T-X, crystallizing in ordered variants of the BaAl4 structure type, have been investigated systematically with respect to their formation and stability. For this, a comprehensive overview of the BaAl4 derivative structure types including group-subgroup relations was established. Special emphasis was laid on compounds where inversion symmetry is missing in the respective crystal structures and where superconductivity is observed at low temperatures. EpTX3 compounds crystallize in the noncentrosymmetric BaNiSn3 structure type (space-group I4mm; a ≈0.4 and c ≈1 nm), an ordered ternary derivative of BaAl4. Superconductivity below 3 K was found for seven members of this series, as evidenced from heat capacity and electrical resistivity measurements. Although the Rashba-like spin-orbit coupling in noncentrosymmetric systems can enable a mixture of spin-singlet and spin-triplet pairs in the superconducting condensate, the experimental data basically indicate a predominant s-wave superconducting state in all of these compounds. For this family of compounds, fully relativistic density functional theory (DFT) calculations of the electronic structure and phonon properties were done. Despite the different size of spin-orbit coupling depending on the actual choice of elements for Ep, T, and X that result in different spin-orbit splittings of the Fermi surfaces, the experimental observation of a prevalent spin-singlet pairing in the superconducting phases of the EpTX3 compounds is supported.

  1. 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.

  2. 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

  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 structure of BaCu 3O 4 particles occurring on thin HoBa 2Cu 3O 7 films prepared by MOCVD

    NASA Astrophysics Data System (ADS)

    Zandbergen, H. W.; Jansen, J.; Svetchnikov, V. L.; Graboy, I. E.; Samoylenkov, S.; Gorbenko, O.; Kaul, A. R.

    1999-12-01

    The structure of BaCu 3O 4 phase occurring as particles on the surface of (001) RBa 2Cu 3O 7 epitaxial films prepared by metalorganic chemical vapor deposition (MOCVD) has been investigated with quantitative electron diffraction and HREM. The orthorhombic unit cell is a=1.097(9) nm, b=0.554(3) nm, c=0.394(2) nm with space group Cmmm, the values being in agreement with X-ray diffraction (XRD) study. The structure consists of alternating Cu 3O 4 and Ba layers along the c-axis. The compound is stabilised due to the formation of low-energy coherent boundaries with RBa 2Cu 3O 7 and/or perovskite substrate.

  5. The relationship of structure to superconductivity in the Pr-Ba-Cu-O system

    SciTech Connect

    Minseo, Park

    1994-05-10

    The relation of structure to lack of superconductivity in Pr-Ba-Cu-O was systematically investigated. First, the phase equilibria of this system was studied to find the processing parameters which maximize the cation-site ordering between Pr and Ba ions. Second, a comparative study between superconducting Nd-Ba-Cu-0 and non- superconducting Pr-Ba-Cu-0 was performed by forming solid-solution Nd- Pr-Ba-Cu-0. The relation between structure and superconductivity in Ndb1-xPrxBa2Cu3O7-δ is investigated. Tc decreases monotonically with increasing x and superconductivity disappears at around x=0.3-0.4. Tc is enhanced by 10K when the sample is processed at an oxygen partial pressure (PO2) of 0.01 atm, followed by oxygenation at 450C. Depression of (Tc) as a function of x and PO 2 is explained in terms of a charge-transfer model. It is suggested that destruction of superconductivity in the RE1-xPrxBa2CU3O7-δ (RE=rare-earth) system can be viewed as disruption of four-fold planar coordinated Cu ions in the chain-site due to permanent occupation of extra Pr ions on Ba sites.

  6. Theoretical investigation of Cu-containing materials with different valence structure types: BaCu2S2, Li2CuSb, and LiCuS

    NASA Astrophysics Data System (ADS)

    Soliman, S.

    2014-08-01

    Optoelectronics research requires cheap materials with a broad spectrum of optical, electronic, and structural properties. The class of Heusler compounds and ternary structures provide many possibilities for finding alternative group IV and III-V semiconductor compounds. This study introduces wider band gap materials for use in solar cells as an alternative to cadmium sulfide buffer layers. The buffer layer is inserted between the absorber layer (p-type) and the transparent window layer (n-type) to enhance the maximum amount of light transmission. Reasonable calculations are reported for the band gaps of copper-containing materials: LiCuS, BaCu2S2, and Li2CuSb. Previous optical analysis measurements of these films determined that the band gaps were 1.8 and 1.9 eV for BaCu2S2 and LiCuS, respectively. In general, semiconductor compounds have been studied theoretically, but there are major differences between the experimental and theoretically calculated band gaps. A suitable calculation method for semiconductor compounds is described in this study. For the first time, calculations based on the Engel and Vosko method are introduced for these semiconductor compounds. This method yields band gaps that are comparable to the experimental values, which facilitate the development of microscopic analyses of these compounds. Direct band gaps of 1.15 and 1.7 eV were obtained for BaCu2S2 and LiCuS, respectively, whereas the indirect band gap was 0.7 eV for Li2CuSb.

  7. Second Phase (BaGeO3, BaSiO3) Nanocolumns in YBa2Cu3O7-x Films

    NASA Astrophysics Data System (ADS)

    Varanasi, C. V.; Reichart, J.; Burke, J.; Wang, H.; Susner, M.; Sumption, M.; Barnes, P. N.

    2010-04-01

    YBa2Cu3O7-x (YBCO) films with BaGeO3 (BGeO), BaSiO3 (BSiO) second phase additions were processed by pulsed laser deposition. Sectored targets with BGO or BSiO wedges as well as pre-mixed targets of YBCO, BGeO or BSiO with appropriate compositions were used to deposit YBCO+BGeO and YBCO+BSiO films on (100) single crystal LaAlO3 substrates. The cross-sectional transmission electron micrographs showed the presence of 20 nm diameter nanocolumns in the YBCO films of both the compositions. However, the critical transition temperature (Tc) of the films was found to significantly decrease. As a result, the critical current density (Jc) in applied magnetic fields was suppressed. The YBCO+BGeO and YBCO+BSiO films made with lower concentrations of additions showed slight improvement in Tc indicating that the substitution of Ge and Si in the lattice is possibly responsible for the Tc depression. This study shows that in addition to the ability to form nanocolumns, the chemical compatibility of BaSnO3 (BSO) and BaZrO3 (BZO) as observed in YBCO+BSO and YBCO+BZO is critical to process high Jc YBCO films.

  8. 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.

  9. The Copper Valence State and the Structure of Li, Ce, Eu, V-Doped Y-Ba-Cu-O System

    NASA Astrophysics Data System (ADS)

    Zhang, J. B.; Qu, L. F.; Hou, K. Y.; Yang, D. L.; Chen, D. J.; Li, X. D.; Zhu, D. B.

    High-Tc superconductors with nominal composition of YBa2Cu3Oy and Y1-xLxBa2Cu3Oy (L=Li, Ce, Eu, V) were synthesis by the solid state reaction of appropriate amount of Y2O3, BaO or BaCO3, Cu2O, CuO, and LOx. The Cu3+/Cu2+ ratio was determined by Iodometric titration and oxygen content in the oxides calculated from the ratio. The crystal structure was determined by electron and powder X-ray diffraction analysis. It shows that that ratio of Cu3+/Cu2+ and the crystal structure could be changed as dopping appropriate amount of metal in the Y-Ba-Cu-O system.

  10. 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, Bayrammurad I.; Fang, Z.; Biermann, S.; Sefat, Athena Safa; Ding, H.

    2015-06-08

    In this study, 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. In conclusion, our results confirm the prediction that BaCu2As2 is an sp metal with weak electronic correlations.

  11. 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.

  12. Growth and Oxidation of Thin Film Al(2)Cu

    SciTech Connect

    SON,KYUNG-AH; MISSERT,NANCY A.; BARBOUR,J. CHARLES; HREN,J.J.; COPELAND,ROBERT GUILD; MINOR,KENNETH G.

    2000-01-18

    Al{sub 2}Cu thin films ({approx} 382 nm) are fabricated by melting and resolidifying Al/Cu bilayers in the presence of a {micro} 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 {micro}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 {approx} 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.

  13. Pressure dependence of the Cu magnetic order in R Ba sub 2 Cu sub 3 O sub 6+ x

    SciTech Connect

    Lynn, J.W.; Li, W. National Institute of Standards and Technology, Gaithersburg, Maryland 20899); Trevino, S.F.; Fisk, Z.

    1989-09-01

    Neutron-diffraction measurements have been carried out as a function of hydrostatic pressure to study the magnetic order of the Cu spins in NdBa{sub 2}Cu{sub 3}O{sub 6.35} and NdBa{sub 2}Cu{sub 3}O{sub 6.1}. In the high-temperature phase, where the Cu planes order antiferromagnetically, we find that the Neel temperature {ital T}{sub {ital N}1} is {ital very} {ital strongly} dependent on pressure, increasing at the rate of {similar to}23 K/kbar. We attribute this phenomenal sensitivity to the two-dimensional-like behavior of this magnetic system. In the low-temperature phase, which is associated with magnetic ordering of the chains, only a small change in the ordering temperature {ital T}{sub {ital N}2} is observed.

  14. Band-offsets at BaTiO3/Cu2O heterojunction and enhanced photoelectrochemical response: theory and experiment(Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Sharma, Dipika; Satsangi, Vibha R.; Dass Kaura, Sahab; Shrivastav, Rohit; Waghmare, Umesh V.

    2016-10-01

    -principles calculations compare well, thus suggesting that such calculations have the potential to be used in screening various metal oxide heterojunction before performing the experiments thereby saving precious chemicals, time and energy. Keywords: Photoelectrochemical, Water splitting, heterojunction, Cu2O, BaTiO3 References: [1] Surbhi Choudhary, et al. Nanostructured bilayered thin films in photoelectrochemical water splitting - A review: International Journal of Hydrogen Energy, (2012). [2] Dipika Sharma, Anuradha Verma, V.R. Satsangi, Rohit shrivastav, Sahab Dass Nanostructured SrTiO3 thin films sensitized by Cu2O for Photoelectrochemical Hydrogen Generation. International journal of Hydrogen Energy;42:,4230-4241, 2014.

  15. 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'.

  16. Synthesis, crystal and electronic structures, and physical properties of caged ternary Cu-rich antimonide: BaCu(7.31(3))Sb5.

    PubMed

    Zheng, Wu-Zui; Wang, Peng; Wu, Li-Ming; Chen, Ling

    2010-08-16

    A new caged Cu-rich antimonide, BaCu(7.31(3))Sb(5), was obtained from a direct combination of the elements in a graphite crucible under a high vacuum by a solid state reaction, and the structure was determined by the single-crystal X-ray diffraction method to be hexagonal P6(3)/mmc (No.194), with a = 7.0154(4) A, c = 12.5423(14) A, V = 534.58(7) A(3), and Z = 2. BaCu(7.31(3))Sb(5) is the first antimonide member of the BaNi(9)P(5)-type barium copper pnictides with a Cu2 site occupancy of 43.7(9)%, and the structure building unit is a 30-vertex Cu(18)Sb(12) cage centered by a Ba atom. The Cu(18)Sb(12) cages form chains along the c axis by sharing the opposite hexagonal (Cu2)(3)(Sb2)(3) faces. Such a cage chain shares (Cu1)(2)(Sb1)(2) rhomboidal faces with six neighboring chains along the [100], [010], and [110] directions to generate a 3D condensed metallic network. The electronic structure calculations by CASTEP indicate the metallic nature, which matches well with the metallic electrical conductivity, small Seebeck coefficient, and Pauli paramagnetism. The calculated formation energies indicate that BaCu(7.5)Sb(5)[triple bond]Ba(2)Cu(15)Sb(10) with the Cu2 site half occupied is the energetically favorable stoichiometry compared with Ba(2)Cu(12)Sb(10) (empty Cu2 site) and Ba(2)Cu(18)Sb(10) (fully occupied Cu2 site).

  17. 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.

  18. Electrical properties of Y-Ba-Na-Cu-O high Tc superconductors thin films

    NASA Astrophysics Data System (ADS)

    Verdyan, A.; Lapsker, I.; Azoulay, J.; Sackler, Raymond; Sackler, Beverly

    1993-04-01

    Y-Ba-Na-Cu-O high Tc superconductors thin films deposited on MgO substrate by resistive evaporation technique were found to have improved electrical properties as compared to pure Y-Ba-Cu-O thin films similarly prepared. A simple conventional inexpensive vacuum system housing a single resistively tungsten heated source was used for the deposition. Pulverized mixture of Y, BaF 2, NaF and Cu in the appropriate atomic proportion was evaporated onto the substrates whose temperature was held constant at 400°C during the evaporation. In situ heat treatment has been carried out at 700°C under oxygen partial pressure of 7 pa. The films thus obtained were found to have the normal superconductors orthorhombic phase at room temperature without any further ex situ heat treatment. The films were characterized and analyzed by x-ray diffraction auger electron spectroscopy and four point dc electrical measurements.

  19. Magnetic levitation and stiffness in melt-textured Y-Ba-Cu-O

    NASA Astrophysics Data System (ADS)

    Hull, J. R.; Mulcahy, T. M.; Salama, K.; Selvamanickam, V.; Weinberger, B. R.; Lynds, L.

    1992-09-01

    Magnetic levitation and stiffness have been measured in several systems composed of a permanent magnet elastically suspended above a stationary melt-textured sample of Y-Ba-Cu-O. The levitation force and vertical stiffness have been calculated on the basis of magnetization measurements of the same system, and the calculated results showed excellent agreement with the experimental measurements. Based on the force and magnetization measurements, it is predicted that the same Y-Ba-Cu-O material configured in a geometry suitable for magnetic bearings could produce a levitation pressure of 100-400 kPa at 20 K.

  20. Magnetic levitation and stiffness in melt-textured Y-Ba-Cu-O

    SciTech Connect

    Hull, J.R.; Mulcahy, T.M. ); Salama, K.; Selvamanickam, V. ); Weinberger, B.R.; Lynds, L. )

    1992-09-01

    Magnetic levitation and stiffness have been measured in several systems composed of a permanent magnet elastically suspended above a stationary melt-textured sample of Y-Ba-Cu-O. The levitation force and vertical stiffness have been calculated on the basis of magnetization measurements of the same system, and the calculated results showed excellent agreement with the experimental measurements. Based on the force and magnetization measurements, it is predicted that the same Y-Ba-Cu-O material configured in a geometry suitable for magnetic bearings could produce a levitation pressure of 100--400 kPa at 20 K.

  1. Metallic properties of Ba{sub 2}Cu{sub 3}P{sub 4} and BaCu{sub 2}Pn{sub 2} (Pn=As, Sb)

    SciTech Connect

    Saparov, Bayrammurad; Sefat, Athena S.

    2012-07-15

    We report the synthesis of ternary barium copper pnictides, Ba{sub 2}Cu{sub 3}P{sub 4} and BaCu{sub 2}Pn{sub 2} (Pn=As, Sb), and their structural, magnetic, and transport properties. They all crystallize in different structures shown by X-ray diffraction, although their structures reveal close relations. The body-centered tetragonal BaCu{sub 2}As{sub 2} adopts ThCr{sub 2}Si{sub 2}-type (I4/mmm) structure, whereas Ba{sub 2}Cu{sub 3}P{sub 4} is a copper-deficient derivative of this phase, crystallizing in the body-centered orthorhombic space group, Ibam. There are two polymorphs of BaCu{sub 2}Sb{sub 2}: {alpha}-BaCu{sub 2}Sb{sub 2} that adopts CaBe{sub 2}Ge{sub 2}-type structure; {beta}-BaCu{sub 2}Sb{sub 2} that is a 2:1 combination of CaBe{sub 2}Ge{sub 2}- and ThCr{sub 2}Si{sub 2}-type structural segments. All phases are metallic and non-magnetic. The room temperature thermal conductivity for polycrystalline BaCu{sub 2}As{sub 2} is Almost-Equal-To 2 W/(m K) and the Seebeck coefficient is Almost-Equal-To 15 {mu}V/K, which result in a small ( Almost-Equal-To 0.03) thermoelectric figure of merit. - Graphical abstract: Ternary copper pnictides of barium Ba{sub 2}Cu{sub 3}P{sub 4} and BaCu{sub 2}Pn{sub 2} (Pn=As, Sb) show metallic and non-magnetic behavior. Highlights: Black-Right-Pointing-Pointer Synthesis of Ba{sub 2}Cu{sub 3}P{sub 4} and BaCu{sub 2}Pn{sub 2} (Pn=As, Sb). Black-Right-Pointing-Pointer A new form of BaCu{sub 2}Sb{sub 2} (CaBe{sub 2}Ge{sub 2}-type) obtained and characterized. Black-Right-Pointing-Pointer The phases are metallic and non-magnetic in agreement with theory. Black-Right-Pointing-Pointer The thermal conductivity and Seebeck coefficient of BaCu{sub 2}As{sub 2} are quite low.

  2. 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.

  3. 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.

  4. 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

  5. Ba 2Pr .34+Pr .73+Cu .73+Cu 2.32+O 7 : Crystal growth, structure and magnetic properties

    NASA Astrophysics Data System (ADS)

    Moran, E.; Amador, U.; Barahona, M.; Alario-Franco, M. A.; Vegas, A.; Rodriguez-Carvajal, J.

    1988-06-01

    Non-twinned, single crystals of Ba 2PrCu 3O 7 have been grown by a novel procedure. They are isostructural with the very well known Ba 2YCu 3O 7, but tetragonal and not superconducting down to 4.2 K, S.G. P4/mmm, a=3.8918(2)A,c=11.6484 (8)A. From crstaallochemical considerations and magnetic measurements their composition can be established as in the title. This appears to be the first case of a tetragonal member of the series with such a high oxygen contents.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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 °C. TEM/EDS and NBED results combined with SF calculation revealed the evidence of metastable θ'-CuAl2 IMC phase (tetragonal, space group: I4¯m2, 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 θ'-CuAl2 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 θ'-CuAl2, which can minimize lattice mismatch for θ'-CuAl2 to grow on Cu.

  7. New barium copper chalcogenides synthesized using two different chalcogen atoms: Ba2Cu(6-x)STe4 and Ba2Cu(6-x)Se(y)Te(5-y).

    PubMed

    Mayasree, Oottil; Sankar, Cheriyedath Raj; Assoud, Abdeljalil; Kleinke, Holger

    2011-05-16

    Ba(2)Cu(6-x)STe(4) and Ba(2)Cu(6-x)Se(y)Te(5-y) were prepared from the elements in stoichiometric ratios at 1123 K, followed by slow cooling. These chalcogenides are isostructural, adopting the space group Pbam (Z = 2), with lattice dimensions of a = 9.6560(6) Å, b = 14.0533(9) Å, c = 4.3524(3) Å, and V = 590.61(7) Å(3) in the case of Ba(2)Cu(5.53(3))STe(4). A significant phase width was observed in the case of Ba(2)Cu(6-x)Se(y)Te(5-y) with at least 0.17(3) ≤ x ≤ 0.57(4) and 0.48(1) ≤ y ≤ 1.92(4). The presence of either S or Se in addition to Te appears to be required for the formation of these materials. In the structure of Ba(2)Cu(6-x)STe(4), Cu-Te chains running along the c axis are interconnected via bridging S atoms to infinite layers parallel to the a,c plane. These layers alternate with the Ba atoms along the b axis. All Cu sites exhibit deficiencies of up to 26%. Depending on y in Ba(2)Cu(6-x)Se(y)Te(5-y), the bridging atom is either a Se atom or a Se/Te mixture when y ≤ 1, and the Te atoms of the Cu-Te chains are partially replaced by Se when y > 1. All atoms are in their most common oxidation states: Ba(2+), Cu(+), S(2-), Se(2-), and Te(2-). Without Cu deficiencies, these chalcogenides were computed to be small gap semiconductors; the Cu deficiencies lead to p-doped semiconducting properties, as experimentally observed on selected samples.

  8. 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.

  9. 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.

  10. 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.

  11. Enhanced flux pinning in GdBaCuO bulk superconductors by Zr dopants

    NASA Astrophysics Data System (ADS)

    Xu, C.; Hu, A.; Ichihara, M.; Sakai, N.; Izumi, M.; Hirabayashi, I.

    2007-10-01

    We, respectively, fabricated GdBa2Cu3O7-δ (Gd123) single domain superconductors by melt growth process in air with Gd2Ba4CuZrOx (GdZr2411) and nanosize ZrO2 dopants. The microstructures and superconducting properties were investigated by scanning/transmission electron microscopy (SEM/TEM) and SQUID. GdZr2411 and BaZrO3 particles with the average size of 50 nm were observed in the GdZr2411 and nanosize ZrO2 doped Gd123 bulks by TEM, respectively. Critical current density (Jc) was enhanced up to 100,000 A/cm2 at 77 K and self-field with 0.4 mol% nano-sized ZrO2. The present study also showed that small amount GdZr2411 dopants (8 mol%, ratio to Gd123) were effective to induce a δTc-type pinning.

  12. 2-D and Mott Transition Studies on Metal (M) Doped PrBa2Cu3O7

    NASA Astrophysics Data System (ADS)

    Chen, T.-P.; Wu, K.; Li, Q.; Chen, B.; Kandel, H.; Chen, J. C.; Mohammed, M.; Al-Hilo, A.

    2013-11-01

    We doped PrBa2Cu3O7 (PBCO) using various metals (M) to obtain PrBa2[Cu(1- x)M x ]O7 (PBCMO) ceramic samples and epitaxial thin films. As suggested in the above chemical composition, these samples were made by replacing some of the Cu ions in PBCO with its metallic neighbors (M) such as Al, Co, Fe, Ga, Ni, and Zn at four different doping concentrations ( x)—0.05, 0.10, 0.15, and 0.20. The epitaxial films were made by performing laser ablation on a ceramic disk target. We also present the results of our transport and Raman studies on the aforementioned PBCMO samples. From our Raman data, we were able to identify the doping sites used. Combined with the transport data, this enabled us to explain the abnormal increase in the electrical resistivity of our doped samples. Our transport property studies on PBCMO samples and the YBCO/PBCMO multilayer allowed us to deduce the superconducting coupling length, the finite-size effect, and the two-dimensional phase transition of YBCO.

  13. Anisotropic transport properties of PrBa 2Cu 3O 7

    NASA Astrophysics Data System (ADS)

    Goto, M.; Takenaka, K.; Eisaki, H.; Uchida, S.

    1997-08-01

    The in-plane resitivity is measured on the twin-free PrBa 2Cu 3O 7 crystals. The observal anisotropy indicates that dominant carrier conduction takes place in the CuO one-dimensional chain. By applying the pressure, ϱa, containing CuO 2 plane contribution increases more rapidly than ϱa, containing both and plane contributions. This is considered to be due to the increased the hybridization between Pr4f and O2p orbital at the plane site, consistent with the scenario proposed by Fehrenbacher and Rice.

  14. Effect of Cu Addition to Zn-12Al Alloy on Thermal Properties and Wettability on Cu and Al Substrates

    NASA Astrophysics Data System (ADS)

    Gancarz, Tomasz; Pstruś, Janusz; Mosińska, Sylwia; Pawlak, Sylwia

    2016-01-01

    The thermal properties, electrical resistivity, thermal linear expansion and tensile strength of a new high-temperature lead-free solder based on a eutectic Zn-Al alloy with 0.5, 1.0, or 1.5 at. pct Cu added were studied. Wettability studies on Cu substrate were performed with flux at 773 K (500 °C) for 60, 180, 240, 900, 1800, and 3600 seconds, and for 480 seconds at 733 K, 753 K, 773 K, 793 K, and 823 K (460 °C, 480 °C, 500 °C, 520 °C, and 550 °C, respectively). The experiment was designed to demonstrate the effect of the addition of Cu on the kinetics of the formation and growth of the CuZn, Cu5Zn8, CuZn4, and Al4Cu9 phases, which were identified by X-ray diffraction analysis. Wetting tests were also performed on the Al substrate, for 15 and 30 seconds at 773 K and 793 K (500 °C and 520 °C, respectively). Very low contact angles on Al pads were obtained. The electrical resistivity of Zn-Al-Cu alloys was slightly higher than that of the ZnAl eutectic alloy. The present results are discussed with respect to the available literature on Zn-Al and Zn-Al-Cu alloys.

  15. Synthesis of YBa2Cu3Oy superconductors via attrition-milled intermediate oxide precursor containing BaCuO2.5

    NASA Astrophysics Data System (ADS)

    Park, Haiwoong; Lee, Haigun

    2001-06-01

    YBa2Cu3Oy (Y123) phase was synthesized from the oxide precursor containing BaCuO2.5 in two distinct processes. in the first stage, a suitable amount of metallic Y, metallic Cu and barium nitrate (Ba(NO3)2) were mixed via attrition milling for 20 h. After 20 h of milling, the particle size of the powder was in the range of 0.05-0.2 μm. On subsequent heat treatment of the milled powder at 600°C for 5h with continuous argon flow, the intermediate precursor (IP) was synthesized. The IP contained BaCuO2.5, Y2O3 and CuO and the overall composition of the IP was Y:Ba:Cu:O=1:2:3:7.4. The oxygen content of the IP was higher than that of the corresponding orthorhombic Y123 superconductor. In the second stage, the synthesized IP was converted to the superconducting Y123 phase with heat treatment at 900-1020°C in air without any additional low temperature oxygenation process. A DTA experiment at 20°C/min in air and a series of rapid heat, soak, and quench experiments showed that the BaCuO2.5 constituent of the precursor decomposed at 838°C, which is higher than that of pure BaCuO2.5 (760°C). The results of the TGA experiments suggested that the heating rate had a strong influence on the decomposition temperature of the BaCuO2.5 of the IP. At a heating rate of>50°C/min, the BaCuO2.5 did not decompose completely during heating to 1020°C and form orthorhombic YBa2Cu3O7-x.

  16. Stability of Y-Ba-Cu-oxide phases in salt flux

    NASA Technical Reports Server (NTRS)

    Tao, Y. K.; Chen, H. C.; Lin, J. G.; Hor, P. H.; Chu, C. W.

    1991-01-01

    The results of an investigation into the possibility of growing YBa2Cu3O7 (or Y123) single crystals from a NaCl-KCl flux (salt flux) are presented. They are compared with results for Y123 crystals grown from a Ba-Cu-oxide flux system. The chosen salt flux composition was 1:1 (NaCl:KCl). The preparation method of the solutes is presented, with particular attention given to the compounds surrounding the Y123 phase, such as Y2BaCuO6 (Y211). Optical microscopy was introduced to study the morphology of the sample; X-ray diffraction was used for phase identification; and a chemical analysis was effected. The Y123, Y211, and BaCuO2 phases were shown to be dissociated in the NaCl-KCl flux, and could not be recrystallized. A small amount of the flux could be added to create large-grain Y123 crystals, but single-crystal growth was not possible in a top-seeded NaCl-KCl solution. This is attributed to significant differences in solubility of the crystal elements, and phase separation caused by CuO crystal formation.

  17. 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.

  18. Structural, optical and electrical properties of GdAlO3:Eu3+Ba2+

    NASA Astrophysics Data System (ADS)

    Selvalakshmi, T.; Tamilarasi, S.; Bose, A. Chandra

    2015-06-01

    Effect of Ba2+ ions concentration on the photoluminescence of GdAlO3:Eu3+ Ba2+ phosphor is investigated. The phosphors are synthesized by citrate-based sol-gel method and the formation of orthorhombic phase GdAlO3 is confirmed by XRD analysis. Kubelka-Munk function is used to estimate the band gap and the value varies with concentration of Ba2+ is observed. Photoluminescence spectra show a strong red emission peak at 616 nm corresponding to5D0→7F2 transition and its intensity increase with the addition of Ba2+ ions. The presence of Eu3+ and Ba2+ ions in GdAlO3 strongly influences the dielectric property of GdAlO3.

  19. 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.

  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. Formation and decomposition of BaCuO sub 2. 5 prepared from a mixture of nitrates

    SciTech Connect

    Machida, Masato; Yasuoka, Kiyoshi; Eguchi, Koichi; Arai, Hiromichi )

    1991-03-01

    Phase relationships in a Ba-Cu-O system prepared from nitrates or from acetates were determined as functions of calcination temperature. It was first proved that the BaCuO{sub 2.5} phase, which was known to be obtained only from peroxides, was produced in air at 650C when a Ba(NO{sub 3}){sub 2}/Cu(NO{sub 3}){sub 2} mixture was used as a precursor. From iodometric analysis, only the nitrate-derived sample was found to contain exclusively Cu{sup 3+} ions. This pseudobinary oxide of high oxidation state was decomposed easily into BaCuO{sub 2+{alpha}} ({alpha} = 0.07) by heating above 700C or by evacuating at 400C.

  2. Al-to-Cu Friction Stir Lap Welding

    NASA Astrophysics Data System (ADS)

    Firouzdor, Vahid; Kou, Sindo

    2012-01-01

    Recently, friction stir welding (FSW) has been used frequently to join dissimilar metals, for instance, Al to Mg, Cu, and steel. The formation of brittle intermetallic compounds often severely limits the strength and ductility of the resultant welds. In the present study, Al-to-Cu lap FSW was studied by welding 6061 Al to commercially pure Cu. Conventional lap FSW was modified by butt welding a small piece of Al to the top of Cu, with a slight pin penetration into the bottom of Al. At travel speeds up to 127 mm/min (5 ipm), the modified welds were about twice the joint strength and five to nine times the ductility of the conventional lap welds. In the conventional lap welds, voids were present along the Al-Cu interface, and fracture occurred along the interface in tensile testing. No such voids were observed in the modified lap welds, and fracture occurred through Cu. Thus, as in the case of Al-to-Mg lap FSW recently studied by the authors, modified lap FSW significantly improved the weld quality in Al-to-Cu lap FSW. At the relatively high travel speed of 203 mm/min (8 ipm), however, modified lap FSW was no longer superior because of channel formation.

  3. Two-dimensional behavior in (YBa 2Cu 3O 7- δ) 24/(PrBa 2Cu 3O 7- δ) 2 multilayer thin films

    NASA Astrophysics Data System (ADS)

    Wang, Z. H.; Wang, S. J.; Chen, J. L.; Zhang, H.; Cao, X. W.

    1999-04-01

    We have measured the field and angular dependencies of the resistive broadening of epitaxial (YBa 2Cu 3O 7- δ) 24/(PrBa 2Cu 3O 7- δ) 2 multilayer thin film. The results show that in low measuring current density regime, the resistive broadening induced by magnetic field depends mainly on the orientation of applied magnetic field with respect to the c-axis rather than the macroscopic Lorentz force. The field dependence of the activation energy for H‖ c follows a logarithmic law, U∝ln H, similar to the results reported by Brunner et al. [O. Brunner, L. Antognazza, J.-M. Triscone, et al., Phys. Rev. Lett. 67 (1991) 1354.], suggesting a 2D character in the multilayer thin film. The angular dependence of the activation energy U and the characteristic temperature T* can be scaled by 2D model proposed by Kes et al. [P.H. Kes, J. Aarts, V.M. Vinokur, et al., Phys. Rev. Lett. 64 (1990) 267]. The phenomenon may be attributed to the flux lines that are cut by the insulating PrBCO layers when the applied magnetic field is tilted away from the ab-plane.

  4. Frequency dependent dielectric properties of Cu0.5Tl0.5Ba2Ca2(Cu3-yMy)O10-δ superconductor

    NASA Astrophysics Data System (ADS)

    Mumtaz, M.; Khan, Nawazish A.; Khan, Sajid

    2012-01-01

    The frequency dependent dielectric properties such as dielectric constants (ɛ/r, ɛ//r), absolute dielectric loss |tanδ|, and ac-conductivity (σac) of Cu0.5Tl0.5Ba2Ca2(Cu3-yMy)O10-δ (M = Si, Ge, Sn, y = 0, 1) superconductor have been investigated by means of capacitance (C) and conductance (G) measurements with the test frequency (f) in the range of 10 KHz to 10 MHz at various temperatures from superconducting state to normal conducting state. The negative capacitance has been observed in all Cu0.5Tl0.5Ba2Ca2(Cu3-yMy)O10-δ samples. The large values of negative dielectric constant (ɛ/r) at lower frequencies and temperatures are linked with reduced thermal vibrations of the atoms due to which polarizability has been enhanced. The decreased value of dielectric constant observed in the Ge-doped samples may possibly be linked with its greater electronegativity (EN) and less polarization. The electronegativity of Si and Sn has approximately the same values as that of Cu, so almost all the dielectric properties do not vary significantly in Si-doped Cu0.5Tl0.5Ba2 Ca2(Cu2Si1)O10-δ and Sn-doped Cu0.5Tl0.5Ba2Ca2(Cu2Sn1)O10-δ samples. These experimental investigations on dielectric properties of Cu0.5Tl0.5Ba2Ca2(Cu3-yMy)O10-δ superconductor have shown lower dielectric loss and higher ac-conductivity at all frequencies and temperatures as compared to that of other high Tc superconductor families. The decreased dielectric loss in Cu0.5Tl0.5Ba2Ca2(Cu3-yMy)O10-δ samples suggests that the polarization is most likely arising from the charge carriers between Cu0.5Tl0.5Ba2O4-δ charge reservoir layer and conducting CuO2/MO2 planes; since the charge reservoir layer has localized charge carriers at Ba+2, Tl+3, and Cu+2 sites, whereas CuO2/MO2 planes contain mobile charge carriers, which are displaced from their equilibrium position by external applied ac-field.

  5. (Ba1-xKx)(Cu2-xMnx)Se2: A copper-based bulk form diluted magnetic semiconductor with orthorhombic BaCu2S2-type structure

    NASA Astrophysics Data System (ADS)

    Guo, Shengli; Man, Huiyuan; Gong, Xin; Ding, Cui; Zhao, Yao; Chen, Bin; Guo, Yang; Wang, Hangdong; Ning, F. L.

    2016-02-01

    A new copper-based bulk form diluted magnetic semiconductor (DMS) (Ba1-xKx)(Cu2-xMnx)Se2 (x=0.075, 0.10, 0.125, and 0.15) with TC ∼18 K has been synthesized. K substitution for Ba introduces hole-type carriers, while Mn substitution for Cu provides local spins. Different from previous reported DMSs, this material crystallizes into orthorhombic BaCu2S2-type crystal structure. No ferromagnetism is observed when only doping Mn, and clear ferromagnetic transition and hysteresis loop have been observed as K and Mn are codoped into the parent compound BaCu2Se2.

  6. Simultaneous thermogravimetry and evolved-gas analysis of YBa2Cu3O7 and LaBa2Cu3O7 superconductors

    NASA Astrophysics Data System (ADS)

    Wada, Takahiro; Yamauchi, Hisao; Tanaka, Shoji

    1992-06-01

    Results are presented from concurrent thermogravimetry (TG) an evolved-gas analysis (EGA) performed on YBa2Cu3O(7-z) and LaBa2Cu3O(7-z) superconductors. The evolved O2 and CO2 gases were monitored by quadruple mass spectrometer. Results showed that CO2 gas began to evolve from YBa2Cu3O(7-z) at 543 C and from LaBa2Cu3O(7-z) at 692 C (although the X-ray diffraction patterns of these samples did not disclose the presence of an impurity phase containing a carbonate group).

  7. Mercury embrittlement of Cu-Al alloys under cyclic loading

    NASA Technical Reports Server (NTRS)

    Regan, T. M.; Stoloff, N. S.

    1977-01-01

    The effect of mercury on the room temperature, high cycle fatigue properties of three alloys: Cu-5.5 pct Al, Cu-7.3 pct Al, and Cu-6.3 pct Al-2.5 pct Fe has been determined. Severe embrittlement under cyclic loading in mercury is associated with rapid crack propagation in the presence of the liquid metal. A pronounced grain size effect is noted under mercury, while fatigue properties in air are insensitive to grain size. The fatigue results are discussed in relation to theories of adsorption-induced liquid metal embrittlement.

  8. Growth of epitaxial Ba 2YCu 3O 7- x films on LaAlO 3 (001)

    NASA Astrophysics Data System (ADS)

    Siegal, Michael P.; Phillips, Julia M.; Hsieh, Yong-Fen; Marshall, J. H.

    1990-12-01

    We report the ex situ growth of 1000 and 2000 Å epitaxial Ba 2YCu 3O 7- x ( BYCO) filmsonLaAlO3 (001 with surface morphologies and crystallinity generally associated with high quality in situ films. Films are grown by co-depositing BaF 2, Y and Cu in a stoichiometric ratio within 1% of 2:1:3, followed by annealing in a two-stage process in a tube furnace. By optimizing the annealing conditions, excellent crystallinity is obtained, with χ min∼ 2-4] from Rutherford backscattering/channeling. These films have sharp superconducting resistance transitions at 90-91 K. Critical current densities at 77 K are ∼ 10 6 A/cm 2 in zero magnetic field and ⪅ 10 5 A/cm 2 in H=0.9 T oriented perpendicular to the ab plane of the films.

  9. Novel Pr-Cu Magnetic Phase at Low Temperature in PrBa{sub 2}Cu{sub 3}O{sub 6{ital +x}} Observed by Neutron Diffraction

    SciTech Connect

    Boothroyd, A.; Longmore, A.; Andersen, N.; Wolf, T.

    1997-01-01

    We have studied by neutron diffraction the magnetic ordering in Al-free crystals of PrBa{sub 2}Cu{sub 3}O{sub 6+x} (x=0.35 and 0.92) that do not display the AFII Cu magnetic phase. We find that the Pr ordering below 20K is accompanied by a counterrotation of the Cu antiferromagnetism on each plane of the bilayer. The maximum turn angle between the two planes is 60{degree}{plus_minus}9{degree} for the x=0.92 crystal, and 40{degree}{plus_minus}11{degree} for the x=0.35 crystal. This is the first observation of a noncollinear ordering of Cu moments in the bilayer, and is evidence for significant magnetic coupling between the Cu and Pr sublattices. {copyright} {ital 1996} {ital The American Physical Society}

  10. An impedance study of complex Al/Cu-Al2O3 electrode

    NASA Astrophysics Data System (ADS)

    Denisova, J.; Katkevics, J.; Erts, D.; Viksna, A.

    2011-06-01

    Electrochemical impedance spectroscopy (EIS) was used to investigate different Cu deposition regimes on Al surface obtained by internal electrolysis and to characterize properties of fabricated electrodes. EIS experimental data confirmed that Cu deposition by internal electrolysis is realized and the complex electrode system is obtained. The main difficulty in preparation of Al/Cu electrodes is to prevent aluminium oxidation before and during electrochemical deposition of Cu particles. In this work NaCl, CH3COONa, K2SO4, mono- and diammonium citrate electrolytes were examined to determine their suitability for impedance measurements. Al/Cu-Al2O3 electrode composition was approved by equivalent circuit analysis, optical and scanning electron microscope methods. The most optimal Cu deposition mode using internal electrolysis was determined. The obtained results are promising for future electrochemical fabrication of nanostructures directly on Al surfaces by internal electrolysis.

  11. Nonenzymatic detection of glucose using BaCuO2 thin layer

    NASA Astrophysics Data System (ADS)

    Ito, Takeshi; Asada, Tsuyoshi; Asai, Naoto; Shimizu, Tomohiro; Shingubara, Shoso

    2017-01-01

    A BaCuO2 thin layer was deposited on a glassy carbon electrode and used for the direct oxidation of glucose. The crystalline, electrochemical, and physicochemical properties that depend on the deposition temperature and deposition time were studied. X-ray diffraction (XRD) analysis showed that the thin layer was amorphous even at 400 °C. The current density of the glucose oxidation using the thin layer deposited at 200 °C was higher than those at other deposition temperatures. Under this condition, the current density increased with the glucose concentration and deposition time. These results indicate that a BaCuO2 thin layer has potential for measuring the blood glucose level without enzymes.

  12. 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.

  13. The Y 3-xBa 3+xCu 6O 14+δ system of superconductors

    NASA Astrophysics Data System (ADS)

    Umarji, A. M.; Somasundaram, P.; Ganapathi, L.; Rao, C. N. R.

    1988-04-01

    Members of the Y 3-xBa 3+xCu 6O 14+δ system prepared at relatively low temperatures by nitrate decomposition have a tetragonal structure and show superconducting transitions (zero-resistance) around 50K.

  14. 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.

  15. Hall effect in semiconducting epitaxial and amorphous Y-Ba-Cu-O thin films

    NASA Astrophysics Data System (ADS)

    Shan, Pao-Chuan; Jahanzeb, Agha; Butler, Donald P.; ćelik-Butler, Zeynep; Kula, Witold; Sobolewski, Roman

    1997-05-01

    An experimental study of the Hall effect in nonmetallic Y-Ba-Cu-O thin films is reported. Both epitaxial crystalline YBa2Cuoverflow="scroll">3O6+x (x⩽0.5) and multiphase/amorphous Y-Ba-Cu-O thin films were studied. The structure of the samples was measured by x-ray diffraction and Raman microprobe. The amorphous Y-Ba-Cu-O samples were found to have a grain size of about 100 Å. The conduction properties were studied and analyzed for the two types of samples over a wide temperature range including room temperature. The Hall effect measurements showed positive charge carriers with a concentration ranging from 1017 to 1020 cm-3 at room temperature. The mobility was found to decrease with higher Hall carrier concentration. The empirical relationship for the mobility dependence on impurity concentration agreed with the relationship between mobility and the experimental Hall carrier concentration, suggesting that the same localized states were responsible for both providing the carriers and reducing the mobility through scattering. It was also observed that the mobility values for both amorphous and crystalline samples followed the same empirical curve, a result which showed that the conduction mechanisms in the epitaxial (tetragonal) and amorphous Y-Ba-Cu-O materials are very likely to be similar despite the differences in the composition and structure of the films. The similarity is consistent with other work that concludes that the conduction mechanism occurs along the copper oxide planes. Our work implies that the conduction mechanism operates over a short range, less than the 100 Å grain size of the amorphous, such that the lack of order in the amorphous samples was essentially irrelevant to the charge transport.

  16. Piezoelectric properties and stabilities of CuO-modified Ba(Ti,Zr)O3 ceramics

    NASA Astrophysics Data System (ADS)

    Zheng, P.; Zhang, J. L.; Shao, S. F.; Tan, Y. Q.; Wang, C. L.

    2009-01-01

    Due to the orthorhombic-tetragonal polymorphic phase transition near room temperature, undesirable large temperature dependence of piezoelectric properties is observed over common usage temperature range in BaTiO3 ceramics with high d33 values. Whereas shifting the phase transition temperature upward by partially substituting Ti with Zr is effective in reducing the piezoelectric temperature dependence, serious long-term degradation occurs. However, it is found that this could be overcome by incorporating a small amount of CuO additive. CuO-modified Ba(Ti0.9625Zr0.0375)O3 ceramics possess excellent piezoelectric properties of d33=300 pC/N, kp=0.493, and k33=0.651 with tan δ=0.011, and its kp remains larger than 0.40 in the broad temperature range from -43 to 73 °C and is almost constant between -25 and 55 °C. The results indicate that CuO-modified Ba(Ti,Zr)O3 ceramics are a promising low-cost lead-free material for practical applications.

  17. High-pressure modifications of CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}, and BaAl{sub 2}: Implications for Laves phase structural trends

    SciTech Connect

    Kal, Subhadeep; Stoyanov, Emil; Belieres, Jean-Philippe; Groy, Thomas L.; Norrestam, Rolf; Haeussermann, Ulrich

    2008-11-15

    High-pressure forms of intermetallic compounds with the composition CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}, and BaAl{sub 2} were synthesized from CeCu{sub 2}-type precursors (CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}) and Ba{sub 21}Al{sub 40} by multi-anvil techniques and investigated by X-ray powder diffraction (SrAl{sub 2} and BaAl{sub 2}), X-ray single-crystal diffraction (CaZn{sub 2}), and electron microscopy (SrZn{sub 2}). Their structures correspond to that of Laves phases. Whereas the dialuminides crystallize in the cubic MgCu{sub 2} (C15) structure, the dizincides adopt the hexagonal MgZn{sub 2} (C14) structure. This trend is in agreement with the structural relationship displayed by sp bonded Laves phase systems at ambient conditions. - Graphical abstract: CeCu{sub 2}-type polar intermetallics can be transformed to Laves phases upon simultaneous application of pressure and temperature. The observed structures are controlled by the valence electron concentration.

  18. Composition dependence of the electronic properties of Al-Cu-Fe and Al-Cu-Ru-Si semimetallic quasicrystals

    NASA Astrophysics Data System (ADS)

    Pierce, F. S.; Bancel, P. A.; Biggs, B. D.; Guo, Q.; Poon, S. J.

    1993-03-01

    Electronic transport properties and specific heats of ordered icosahedral phase alloys in the Al-Cu-Ru-Si and Al-Cu-Fe systems are examined, and comparison with high-quality rhombohedral (3/2) approximant phase samples of Al-Cu-Fe is made. Strong temperature dependence and sensitivity to composition changes of these properties are observed. The similarity of transport properties between the icosahedral (i) and rhombohedral (r) phases of Al62.5Cu26.5Fe11 is noted. The results can be qualitatively interpreted in terms of band structure. There appears to be sufficient evidence for a rapidly varying conductivity spectrum σ(E) in the ordered i phases. However, important questions concerning the physics of these semimetallic quasicrystals remain to be answered.

  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. Hysteresis and relaxation in TlBa2Ca2Cu3Oy superconducting polycrystals

    NASA Astrophysics Data System (ADS)

    Batista-Leyva, A. J.; Cobas, R.; Orlando, M. T. D.; Altshuler, E.

    2003-08-01

    We study the hysteresis and relaxation of both intragranular and intergranular properties of TlBa2Ca2Cu3Oy (Tl-1223) superconducting polycrystals between 80 and 120 K. The samples have been prepared using a technique involving the mixing of grains of different sizes before the final sintering. The grains show a sizeable reversible magnetization, while vortices inside the grain behave as three-dimensional objects. The transport critical current is strongly hysteretic, with features that distinguish our Tl-1223 samples from 'standard' YBa2Cu3O7-delta (YBCO), (Hg, Re)Ba2Ca2Cu3O8+delta (HBCCO) and (Bi, Pb)2Sr2Ca2Cu3O10-delta (BSCCO) polycrystals. The preparation method improves the transport properties of the samples. The relaxation of the transport critical current density, in the presence of trapped fields, is reported here for the first time in this system, as far as we know. A phenomenological model can qualitatively describe the transport properties, where the intragrain magnetization affects the intergranular junctions, but a precise quantitative description is not achieved. The differences in the shape of the transport measurements, for different polycrystalline systems, are also well described by the model.

  1. Unusual Magnetic Properties or Unconventional Superconductivity in PrBa2Cu3O7?

    NASA Astrophysics Data System (ADS)

    Ku, H. C.; Lin, B. N.; Hsu, Y. Y.; Lin, Y. H.; Yang, H. B.

    2001-04-01

    Structural, transport and magnetic data were reported for the Pr1+xBa2-xCu3O7-y or 1212-type Cu(Ba2-xPrx)PrCu2O7+y system (-0.2 ≤ x ≤ 1, -0.4 ≤ y ≤ 1). The phase diagram shows two structural symmetry transitions, from orthorhombic 1212C (C for CuO chain) O(I)-phase (space group Pmmm) to tetragonal 1212 T-phase (P4/mmm), and then to a new type of orthorhombic 1212 O(II)-phase (Cmmm). Electrical resistivity data (represented by room temperature resistivity ρ(300 K)) indicate that this system is not favorable for metallic state and no superconductivity can be detected for these Mott-insulating cuprates. Magnetic susceptibility data show that, regardless of the structural transitions, antiferromagnetic Pr ordering with anomalous high Néel temperature TN(Pr) decreases monotonically and smoothly with increasing x and/or y parameter except in the O(II) phase region.

  2. Kinetic parameters and structural variations in Cu-Al-Mn and Cu-Al-Mn-Mg shape memory alloys

    NASA Astrophysics Data System (ADS)

    Canbay, Canan Aksu

    2017-02-01

    In this work polycrystalline Cu-Al-Mn and Cu-Al-Mn-Mg SMAs were fabricated by arc melting. The thermal analysis was made to determine the characteristic transformation temperatures of the samples and kinetic parameters. Also the effect of Mg on transformation temperatures and kinetic parameters detected. The structural analysis was made to designate the diffraction planes of martensite phase at room temperature and this was supported by optical measurement observations.

  3. Observation of Pr magnetic order in PrBa2Cu3O7

    NASA Astrophysics Data System (ADS)

    Skanthakumar, S.; Lynn, J. W.; Rosov, N.; Cao, G.; Crow, J. E.

    1997-02-01

    Neutron-diffraction experiments have been carried out to investigate the magnetic order in PrBa2Cu3O7. Our neutron data indicate that the Cu spins order above 300 K. This ordering is not significantly affected at low temperatures, where new magnetic Bragg peaks develop below 17 K that must be associated with the antiferromagnetic ordering of Pr spins, with an ordered moment of 0.79(5)μB. This rules out the possibility recently proposed by Nehrke and Pieper [Phys. Rev. Lett. 76, 1936 (1996)] that the new magnetic Bragg peaks arise from a spin reorientation of the Cu spins and that the Pr carries essentially no moment.

  4. Y 3-xBa 3+xCu 6O 14+δ system: A new family of superconductors

    NASA Astrophysics Data System (ADS)

    Umarji, A. M.; Somasundaram, P.; Rao, C. N. R.

    1988-06-01

    Compounds of the Y 3-x Ba 3+x Cu 6O 14+δ system, which YBa 2Cu 3O 7-δ (x = 1) is member, have been prepared. A relatively low temperature nitrate decomposition method gives almost single phase compounds with tetragonal structure. The phases are metastable and show superconducting transitions (zero-resistance) around 50K.

  5. 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.

  6. Syntheses, structures, and optical properties of Ba{sub 4}MInSe{sub 6} (M=Cu, Ag)

    SciTech Connect

    Yin Wenlong; Feng Kai; Hao Wenyu; Yao Jiyong; Wu Yicheng

    2012-08-15

    Two new quaternary chalcogenides, namely Ba{sub 4}MInSe{sub 6} (M=Cu, Ag), were synthesized by solid state reactions. These two isostructural compounds adopt the Ba{sub 2}MnS{sub 3} structure type in the orthorhombic space group Pnma. In the structure, the M and In atoms randomly occupy one crystallographic unique metal position with the molar ratio of 1:1 The (M/In)Se{sub 4} tetrahedra are connected to each other by corner-sharing to form one-dimensional chains along the b direction, which are separated by mono-capped trigonal prismatically coordinated Ba atoms. Based on the diffuse reflectance spectrum, the optical band gaps were determined to be 2.23(2) and 2.41(2) eV for Ba{sub 4}CuInSe{sub 6} and Ba{sub 4}AgInSe{sub 6}, respectively. - Graphical abstract: In the structure of Ba{sub 4}MInSe{sub 6} (M=Cu, Ag), the (M/In)Se{sub 4} tetrahedra are connected by corner-sharing to form chains along the b direction, which are separated by Ba atoms. Highlights: Black-Right-Pointing-Pointer Two new quaternary chalcogenides, Ba{sub 4}MInSe{sub 6} (M=Cu, Ag), were synthesized. Black-Right-Pointing-Pointer Ba{sub 4}MInSe{sub 6} (M=Cu, Ag) are isostructural and crystallize in the Ba{sub 2}MnS{sub 3} structure type Black-Right-Pointing-Pointer The (M/In)Se{sub 4} tetrahedra are connected by corner-sharing to form chains along the b direction. Black-Right-Pointing-Pointer The chains are separated by mono-capped trigonal prismatically coordinated Ba atoms. Black-Right-Pointing-Pointer The optical band gaps are 2.23(2) and 2.41(2) eV for Ba{sub 4}CuInSe{sub 6} and Ba{sub 4}AgInSe{sub 6}, respectively.

  7. 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.

  8. Formation and decomposition of BaCuO 2.5 prepared from a mixture of nitrates

    NASA Astrophysics Data System (ADS)

    Machida, Masato; Yasuoka, Kiyoshi; Eguchi, Koichi; Arai, Hiromichi

    1991-03-01

    Phase relationships in a BaCuO system prepared from nitrates or from acetates were determined as functions of calcination temperature. It was first proved that the BaCuO 2.5 phase, which was known to be obtained only from peroxides, was produced in air at 650°C when a {Ba(NO 3) 2}/{Cu(NO 3) 2} mixture was used as a precursor. From iodometric analysis, only the nitrate-derived sample was found to contain exclusively Cu 3+ ions. This pseudobinary oxide of high oxidation state was decomposed easily into BaCuO 2+α (α = 0.07) by heating above 700°C or by evacuating at 400°C.

  9. XPS study of the chemical stability of DyBa2Cu3O6+δ superconductor

    NASA Astrophysics Data System (ADS)

    Fetisov, A. V.; Kozhina, G. А.; Estemirova, S. Kh.; Fetisov, V. B.; Gulyaeva, R. I.

    2015-01-01

    The chemical stability of the powder DyBa2Cu3O6+δ has been studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and thermal analysis at ambient conditions. The powder was subjected to mechanical processing in a ball mill-activator to accelerate chemical degradation. The kinetic regularities of hydrolytic decomposition of DyBa2Cu3O6+δ under the influence of air moisture have been determined. The resistive properties of DyBa2Cu3O6+δ to water have been found to be better, but not much different from analogous properties of YBa2Cu3O6+δ which is unstable in a wet environment. Chemical degradation of the material is triggered by crucial concentrating of water particles near the free surface of the solid reactant (due to their low diffusibility in the bulk) leading to rapid chemical decomposition of the respective regions.

  10. S =1/2 quantum critical spin ladders produced by orbital ordering in Ba2CuTeO6

    NASA Astrophysics Data System (ADS)

    Gibbs, A. S.; Yamamoto, A.; Yaresko, A. N.; Knight, K. S.; Yasuoka, H.; Majumder, M.; Baenitz, M.; Saines, P. J.; Hester, J. R.; Hashizume, D.; Kondo, A.; Kindo, K.; Takagi, H.

    2017-03-01

    The ordered hexagonal perovskite Ba2CuTeO6 hosts weakly coupled S =1/2 spin ladders produced by an orbital ordering of Cu2 +. The magnetic susceptibility χ (T ) of Ba2CuTeO6 is well described by that expected for isolated spin ladders with exchange coupling of J ≈ 86 K but shows a deviation from the expected thermally activated behavior at low temperatures below T*≈25 K . An anomaly in χ (T ) , indicative of magnetic ordering, is observed at Tmag=16 K . No clear signature of long-range ordering, however, is captured so far in NMR 1 /T1 , specific heat or neutron diffraction measurements at and below Tmag. The marginal magnetic transition, indicative of strong quantum fluctuations, is evidence that Ba2CuTeO6 is in very close proximity to a quantum critical point between magnetically ordered and spin-gapped phases controlled by interladder couplings.

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

    DOE PAGES

    Selvamanickam, V.; Gharahcheshmeh, M. Heydari; Xu, A.; ...

    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

  12. 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.

  13. 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.

  14. Nanostripe structures in SmBa2Cu3Ox superconductors

    NASA Astrophysics Data System (ADS)

    Koblischka, M. R.; Winter, M.; Hartmann, U.

    2007-07-01

    Atomic force microscopy and scanning tunnelling microscopy scans of SmBa2Cu3Ox (Sm123) high-Tc superconductors (single crystals and melt-textured samples) prepared using different growth techniques revealed the presence of nanoscale stripe-like structures, which are found to be sometimes parallel over several micrometres and sometimes wavy. These structures consist of chemical compositional fluctuations inherent to the light rare earth high-Tc superconductors and may act as effective pinning centres due to their periodicity of typically 10-60 nm which is comparable to the ideal pinning centre size 2ξ (~10 nm for YBa2Cu3Ox in the ab-plane). Nanostripes are observed in Sm123 single crystals grown by the top-seed pulling technique and in melt-textured samples. The periodicity of the nanostripes is found to be much larger (~50 nm) in the former samples than in the melt-textured samples (10-25 nm). Detailed measurements reveal that the nanostripes are formed by chains of individual nanoclusters formed from unit cells of the Sm-rich phase, Sm1+xBa2-xCu3Oy. The control of these pinning structures running throughout the whole sample volume may be a key to improving critical current densities, especially at high external magnetic fields.

  15. Liquidus Diagram of the Ba-Y-Cu-O System in the Vicinity of the Ba2YCu3O6+x Phase Field

    PubMed Central

    Wong-Ng, Winnie; Cook, Lawrence P.

    1998-01-01

    This paper describes the melting equilibria in the vicinity of the high Tc phase Ba2YCu3O6+x, including evidence for two Ba-Y-Cu-O immiscible liquids. Melting equilibria have been investigated in purified air using a combination of differential thermal analysis (DTA), thermogravimetric analysis (TGA), powder x-ray diffraction (XRD), MgO wick entrapment of liquid for analysis, scanning electron microscopy (SEM) coupled with energy dispersive x-ray analysis (EDS), and hydrogen reduction for determination of copper oxidation state. For relatively barium-rich compositions, it was necessary to prepare the starting materials under controlled atmosphere conditions using BaO. A liquidus diagram was derived from quantitative data for the melts involved in various melting reactions. In general the 1/2(Y2O3) contents of the melts participating in these equilibria were low (mole fraction <4 %). The primary phase field of Ba2YCu3O6+x occurs at a mole fraction of <2.0 % 1/2Y2O3 and lies very close along the BaO-CuOx edge, extending from a mole fraction of ≈43 % CuO to a mole fraction of ≈76 % CuO. It is divided by a liquid miscibility gap and extends on either side about this gap. The topological sequence of melting reactions associated with the liquidus is presented as a function of temperature. Implications for the growth of Ba2YCu3O6+x crystals are discussed. PMID:28009382

  16. Phase diagram of the CuO3 chains in YBa2Cu3O6+x and PrBa2Cu3O6+x

    NASA Astrophysics Data System (ADS)

    Franco, R.; Aligia, A. A.

    2003-05-01

    We use a mapping of the multiband Hubbard model for CuO3 chains in R Ba2Cu3O6+x (R=Y or a rare earth) onto a t-J model and the description of the charge dynamics of the latter in terms of a spinless model, to study the electronic structure of the chains. We briefly review results for the optical conductivity and we calculate the quantum phase diagram of quarter filled chains including Coulomb repulsion up to that between next-nearest-neighbor Cu atoms V2, using the resulting effective Hamiltonian, mapped onto an XXZ chain, and the method of crossing of excitation spectra. The method gives accurate results for the boundaries of the metallic phase in this case. The inclusion of V2 greatly enhances the region of metallic behavior of the chains.

  17. 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.

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

    SciTech Connect

    Green, Tim 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)2•8H2O 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. Structure and physical properties of Y(La)-Ba(Sr)-Cu-O superconducting compounds

    NASA Astrophysics Data System (ADS)

    Verkin, B. I.; Bandurian, B. B.; Baryl'Nik, A. S.; Batrak, A. G.; Bobrov, N. L.

    1987-07-01

    The structure and physical properties of Y(La)-Ba(Sr)-Cu-O superconducting compounds prepared by the cryogenic dispersion of a mixture of oxides and carbonates are investigated experimentally in the temperature range from 21 mK to 300 K. In particular, attention is given to the electrical conductivity and critical current density of the superconductors. Attention is also given to the degradation of the critical parameters of the superconductors with time, their structural characteristics, magnetic suceptibility, specific heat, and acoustic properties; the volt-ampere characteristics of the superconducting compounds are determined.

  20. 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.

  1. 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.

  2. Chemistry and High Tc Superconductivity in the La-Ba-Cu-O System

    DTIC Science & Technology

    1988-07-15

    terbium 21 to form the same type of perovskite-like structure with the stoichiometry of ReBa 2Cu3076 (Re - Rare-earth). However, some of these rare...it has been shown to be present by other techniques, such as Raman spectroscopy. ( 7) We propose that at the preparative temperatures necessary for...greatfully acknowledge helpful discussions with Dr. S. Fine and Dr. KyV. Raman -ijachary This work was supported by the Office of Naval Research and by

  3. 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.

  4. 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.

  5. Induced thulium magnetisation in the `green phase' Tm 2BaCuO 5

    NASA Astrophysics Data System (ADS)

    Stewart, Glen A.; Gubbens, Paul C. M.

    1999-10-01

    A 169Tm Mössbauer investigation over the temperature range 0.3-300 K is reported for the orthorhombic Pnma phase of Tm 2BaCuO 5. The behaviour of the nuclear quadrupole splitting is shown to be consistent with significantly different crystal field schemes for the two Tm sites. Tm moments induced by the antiferromagnetically ordered Cu sub-lattice ( TN1=19 K) are observed to be very small with saturation values of just 0.503(6) μ B and 0.23(1) μ B. On the basis of the crystal field analysis, the moments are predicted to align with the b-axis and are able to be identified with their respective sites.

  6. Controlling Bulk Cu6Sn5 Nucleation in Sn0.7Cu/Cu Joints with Al Micro-alloying

    NASA Astrophysics Data System (ADS)

    Xian, J. W.; Belyakov, S. A.; Gourlay, C. M.

    2016-01-01

    We show that dilute Al additions can control the size of primary Cu6Sn5 rods in Sn-0.7Cu/Cu ball grid array joints. In Sn-0.7Cu-0.05Al/Cu joints, the number of primary Cu6Sn5 per mm2 is ˜7 times higher and the mean three-dimensional length of rods is ˜4 times smaller than in Al-free Sn-0.7Cu/Cu joints, while the area fraction of primary Cu6Sn5 is similar. It is shown that epitaxial nucleation of primary Cu6Sn5 occurs on δ-Cu33Al17 or γ 1-Cu9Al4 particles, which are stable in the Sn-0.7Cu-0.05Al melt during holding at 250°C. The observed facet relationships agree well with previously determined orientation relationships between δ-Cu33Al17 and Cu6Sn5 in hypereutectic Sn-Cu-Al alloys and result in a good lattice match with <˜2.5% lattice mismatch on two different interfacial planes.

  7. 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

  8. Preparation of 94 K-superconducting NdBa 2Cu 3O 7 - δ without post-anneal in oxygen

    NASA Astrophysics Data System (ADS)

    Fujihara, S.; Yoshida, N.; Kimura, T.

    1997-02-01

    The preparation of the polycrystalline NdBa 2Cu 3O 7 - δ superconductor using Ba 2Cu 3O 5 + x as a precursor has been studied. Ba 2Cu 3O 5 + x was prepared by the sol-gel process using metal acetates as starting materials, tartaric acid as an chelating reagent and water as solvent. The gel was heated at 780°C for 60 h in O 2 to form the Ba 2Cu 3O 5 + x precursor. The value of x in Ba 2Cu 3O 5 + x was determined to be 0.5; that is, copper was in a highly oxidized state over +2. NdBa 2Cu 3O 7 - δ was obtained by the solid-state reaction between Nd 2O 3 and Ba 2Cu 3O 5 + x heated at 900°C for 20 h in N 2. Although the sample did not undergo post-anneal in oxygen, it showed good superconducting properties; Tc of 94 K and the intragranular Jc of 3.7 × 10 5 A/cm 2 under a field of 50 kOe at 20 K. The advantage of using Ba 2Cu 3O 5 + x is considered to be its sufficient amount of oxygen as well as prevention of the Nd 3+/Ba 2+ substitution.

  9. Al substituted Ba ferrite films with high coercivity and excellent squareness for low noise perpendicular recording layer

    NASA Astrophysics Data System (ADS)

    Feng, J.; Matsushita, N.; Watanabe, K.; Nakagawa, S.; Naoe, M.

    1999-04-01

    Al substituted BaM (Al-BaM) ferrite films with composition of BaAlxFe12-xO19 (x=0,1,2) were deposited using facing targets sputtering apparatus on SiOx/Si wafers with a Pt seed layer. A postannealing process is necessary to crystallize the films. It was confirmed that the substrate temperature Ts is also one of the important parameters for the magnetic properties of the postannealed films. Al-BaM ferrite films exhibit the Ts dependence of magnetic properties different from that of simple BaM ones. With increase of the Al content x in Al-BaM ferrite films, 4πMs decreased, while Hc and the anisotropy field HA increased. It was found that acicular shape grains formed more easily in Al-BaM ferrite films than in simple BaM ones. The squareness S⊥ increased largely by substitution of Al for Fe. The Al-BaM ferrite films with high Hc⊥ (˜3 kOe) and large S⊥(˜0.9) may be applicable as perpendicular magnetic recording layers with low noise level.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Variation of structural and magnetic properties of La-doped PrBa 2Cu 3O 7 system

    NASA Astrophysics Data System (ADS)

    Luo, H. M.; Ding, S. Y.; Lu, G. X.; Chen, Z. Y.

    2001-11-01

    X-ray Rietveld refinement and magnetic susceptibility were performed to study the effects of La-doping on the structural and magnetic properties of polycrystalline Pr 1- xLa xBa 2Cu 3O 7 and PrBa 2- xLa xCu 3O z (0⩽ x⩽1) solid solution. The structure remains orthorhombic with space group Pmmm for Pr 1- xLa xBa 2Cu 3O 7. The antiferromagnetic (AFM) ordering temperature TN of Pr ions decreases monotonically from 18 K for x=0 to 6 K for x=0.8. Whereas, superconductivity (SC) was induced by La doping with 52 K for x=0.5, and 90 K for x=1. Thus there is a large range of coexistence of SC and AFM for 0.5⩽ x⩽0.8. While, Ba replacement by La in PrBa 2- xLa xCu 3O z system results in complex structural phase transitions from orthorhombic Pmmm to tetragonal P4/mmm around x=0.45, then to another orthorhombic Cmmm around x=0.7. No SC is detected and TN(Pr) decreases smoothly from 18 to 2.8 K for PrBa 1.3La 0.7Cu 3O 7.24. The results are interpreted by the wave function overlap between Pr-4f and O-2p π orbitals in the CuO 2 layers.

  16. 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.

  17. Pressure study of local tilts and their correlation to stripe order in single crystal La1.875Ba0.125CuO4

    NASA Astrophysics Data System (ADS)

    Fabbris, Gilberto; Hücker, Markus; Gu, Genda; Tranquada, John; Haskel, Daniel

    2012-02-01

    The strong Tc suppression in LaBaCuO at x=0.125 is widely believed to be related to formation of static stripes, at least partially driven by a strong electron-lattice coupling in a low temperature tetragonal (LTT) phase (Tranquada et al., Nature 375, 561 (1995)). A recent high-pressure experiment appears to challenge this view as it was observed that static stripe order persists to pressures higher than required to induce LTT to HTT transition (Hucker et al., PRL 104, 057004 (2010)). We carried out high-pressure La K-edge polarized XAFS measurements in LaBaCuO (x=0.125) single crystals in a diamond anvil cell to probe local CuO6 tilts. We observe that the local tilts remain LTT-like at high pressure, even though the macroscopic structure is HTT. The results suggest a significant order-disorder component to this pressure-induced phase transition, whereby the local LTT tilts remain present in the local scale but disorder over long range resulting in HTT symmetry seen by diffraction. The result may help explain why the stripe order is largely unaffected by the LTT to HTT pressure-induced transition. Work at Argonne (BNL) is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 (DE-AC02-98CH10886).

  18. Excitation Spectra of Plane Site Cu Spins of Y0.52Pr0.48Ba2Cu3O7 (T_c≃ 20 K)

    NASA Astrophysics Data System (ADS)

    Kodama, Katsuaki; Shamoto, Shin-ichi; Harashina, Hiroshi; Sato, Masatoshi; Nishi, Masakazu; Kakurai, Kazuhisa

    1994-12-01

    Neutron inelastic scattering measurements have been carried out on Y0.52Pr0.48Ba2Cu3O7 with the superconducting transition temperature T_c≃ 20 K. From the spectral weight function χ''(q, ω) of the Cu-spin excitations in the CuO2 planes, the reduction of the hole-carrier concentration and the degree of the randomness induced by the substitution of Pr for Y are estimated. These results present evidences that the model of a hole-trapping by the hybridized states of the Pr4f and O2pπ orbitals proposed by Fehrenbacher and Rice [Phys. Rev. Lett. 70 (1993) 3471] provides an appropriate explanation of the experimental results associated with the well-known T c-suppression of R1-xPrxBa2Cu3O7 (R=Y or various lanthanide elements) by the Pr-doping.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

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

    2016-01-08

    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.

  1. 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.

  2. 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.

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

    DOE PAGES

    Huang, Yuxiang; Huang, Li; Wang, C. Z.; ...

    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

  4. Thermoelectric, band structure, chemical bonding and dispersion of optical constants of new metal chalcogenides Ba4CuGa5Q12 (Q=S, Se)

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.; Azam, Sikander

    2014-08-01

    The electronic structure and dispersion of optical constants of the Ba4CuGa5S12 and Ba4CuGa5Se12 compounds were calculated by the first-principles full-potential linearized augmented plane wave (FPLAPW) method. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel-Vosko GGA (EVGGA) to calculate the electronic structures, Fermi surface, thermoelectric, chemical bonding and dispersion of optical constants of these compounds. By investigating the influence of replacing S by Se, it has been found that the charge density around 'Ga' is greater in Ba4CuGa5Se12 than Ba4CuGa5S12. Fermi surface of Ba4CuGa5S12 consists of an electronic sheet only because there is no empty region while Ba4CuGa5Se12 contains both holes and electronic sheets because this compound contains both empty and shaded region. As we replace S by Se the heights of the peaks decreases as a results the reflectivity also decreases. It is noticed that the reflectivity is over 68% (60%) for Ba4CuGa5S12 (Ba4CuGa5Se12) compounds within the energy range studied. This implies that the material will serve as a good reflector. By replacing S by Se the figure of merit values increases from 0.97 to 1.0, which shows the good thermoelectric behavior of both compounds.

  5. All high T sub c edge-geometry weak links utilizing Y-Ba-Cu-O barrier layers

    SciTech Connect

    Hunt, B.D.; Foote, M.C.; Bajuk, L.J. )

    1991-08-19

    High quality YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}}/normal-metal/YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} edge-geometry weak links have been fabricated using nonsuperconducting Y-Ba-Cu-O barrier layers deposited by laser ablation at reduced growth temperatures. Devices incorporating 25--100 A thick barrier layers exhibit current-voltage characteristics consistent with the resistively shunted junction model, with strong microwave and magnetic field response at temperatures up to 85 K. The critical currents vary exponentially with barrier thickness, and the resistances scale linearly with Y-Ba-Cu-O interlayer thickness and device area, indicating good barrier uniformity, with an effective normal metal coherence length of 20 A.

  6. The “irreversibility line” of a Tl 2Ba 2CaCu 2O 8 single crystal: Evidence for a phase transition

    NASA Astrophysics Data System (ADS)

    Giordanengo, B.; Genicon, J. L.; Sulpice, A.; Chaussy, J.; Tournier, R.; Frison, J. C.; Chaminade, J. P.; Pouchard, M.; Etourneau, J.

    1990-08-01

    The irreversibility line H *(T) of a Tl 2Ba 2CaCu 2O 8 single crystal varies as {ie1147-1} and diverges below 20 K. These phenomena could be related to a breakdown field of a weak superconductivity induced in BaO-TlO-TIO-BaO layer blocks by superconducting CuO layer blocks. The magnetization at the transition can be calculated assuming the existence of a second order phase transition.

  7. Preparation and Characterization of DyBa2Cu3Oy Thick Films with Dy2BaO4 Precursor

    NASA Astrophysics Data System (ADS)

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

    DyBa2Cu3Oy (Dy-123) thick films were fabricated from Dy2BaO4, BaCuO2, and CuO powders. We have added 0, 1, 2, and 4 wt% of Ag2O. Mixture of alpha-terpineol and 2-ethyl acetate was used as a solvent, to which 100nm-sized stoichiometric powdered mixture was added and grinded for several hours to form a highly dense paste. Thick film precursors were prepared by spreading the paste on MgO substrates with a screen printing technique. The films were sintered with a double-step annealing process. The Dy-123 thick films obtained were of good quality. XRD analyses confirmed the formation of a high-quality c-axis oriented Dy-123 for films annealed at 1070oC for 10 min and at 880oC for 2 h. Scanning electron microscopy showed the formation of large flat grains. Onset Tc was 91 K according to magnetization measurements. The present results suggest that this process might be useful for the preparation of large-area superconducting thick films on MgO substrates in a short processing time.

  8. 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.

  9. Investigation of Al/CuO multilayered thermite ignition

    NASA Astrophysics Data System (ADS)

    Nicollet, Andréa; Lahiner, Guillaume; Belisario, Andres; Souleille, Sandrine; Djafari-Rouhani, Mehdi; Estève, Alain; Rossi, Carole

    2017-01-01

    The ignition of the Al/CuO multilayered material is studied experimentally to explore the effects of the heating surface area, layering, and film thickness on the ignition characteristics and reaction performances. After the description of the micro-initiator devices and ignition conditions, we show that the heating surface area must be properly calibrated to optimize the nanothermite ignition performances. We demonstrated experimentally that a heating surface area of 0.25 mm2 is sufficient to ignite a multilayered thermite film of 1.6 mm wide by a few cm long, with a success rate of 100%. A new analytical and phenomenological ignition model based on atomic diffusion across layers and thermal exchange is also proposed. This model considers that CuO first decomposes into Cu2O, and then the oxygen diffuses across the Cu2O and Al2O3 layers before reaching the Al layer, where it reacts to form Al2O3. The theoretical results in terms of ignition response times confirm the experimental observation. The increase of the heating surface area leads to an increase of the ignition response time and ignition power threshold (go/no go condition). We also provide evidence that, for any heating surface area, the ignition time rapidly decreases when the electrical power density increases until an asymptotic value. This time point is referred to as the minimum response ignition time, which is a characteristic of the multilayered thermite itself. At the stoichiometric ratio (Al thickness is half of the CuO thickness), the minimum ignition response time can be easily tuned from 59 μs to 418 ms by tuning the heating surface area. The minimum ignition response time increases when the bilayer thickness increases. This work not only provides a set of micro-initiator design rules to obtain the best ignition conditions and reaction performances but also details a reliable and robust MicroElectroMechanical Systems process to fabricate igniters and brings new understanding of phenomena

  10. Superconducting Critical Temperature of Overdoped LnBa2Cu3Oy+Δy (Ln=La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm and Yb)

    NASA Astrophysics Data System (ADS)

    Okai, Bin; Ono, Akira

    1999-09-01

    A series of overdoped LnBa2Cu3Oy+Δy (Ln=La˜Yb) was synthesized at high oxygen pressure for investigating the relationship between the superconducting critical temperature Tc, overdoping oxygen content Δy, and Ln. Tc of 1-2-3 compound LnBa2Cu3Oy+Δy remains almost unchanged through various levels of overdoping for small ionic radii of Ln. As the ionic radus of Ln increases, Tc decreases with the level of overdoping. The decrease changes systematically from EuBa2Cu3Oy+Δy to LaBa2Cu3Oy+Δy; the decrease for LaBa2Cu3Oy+Δy is the steepest. Tc is also reduced probably by the mixing of Ln and Ba, as observed in NdBa2Cu3Oy+Δy and LaBa2Cu3Oy+Δy.

  11. 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.

  12. Effectiveness of BaTiO 3 dielectric patches on YBa 2 Cu 3 O 7 thin films for MEM switches

    DOE PAGES

    Vargas, J.; Hijazi, Y.; Noel, J.; ...

    2014-05-12

    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. Furthermore, the dielectric patch crystal structure and roughness affect the ability of repetitively switching cycles and lifetime. We performed a series of experiments using different deposition methods and RF magnetron sputtering was found to be the best deposition process for the BaTiO3 layer. The effect examination of surface morphology will be presented using characterization techniques as x-ray diffraction,more » SEM and AFM for an optimum switching device. The thin film is made of YBa2Cu3O7 deposited on LaAlO3 substrate by pulsed laser deposition. In our work, the dielectric material sputtering pressure is set at 9.5x10-6 Torr. The argon gas is released through a mass-flow controller to purge the system prior to deposition. RF power is 85 W at a distance of 9 cm. The behavior of Au membranes built on ultimate 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.« less

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

    DOE PAGES

    Vargas, J.; Hijazi, Y.; Noel, J.; ...

    2014-05-12

    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. Furthermore, the dielectric patch crystal structure and roughness affect the ability of repetitively switching cycles and lifetime. We performed a series of experiments using different deposition methods and RF magnetron sputtering was found to be the best deposition process for the BaTiO3 layer. The effect examination of surface morphology will be presented using characterization techniques as x-ray diffraction,more » SEM and AFM for an optimum switching device. The thin film is made of YBa2Cu3O7 deposited on LaAlO3 substrate by pulsed laser deposition. In our work, the dielectric material sputtering pressure is set at 9.5x10-6 Torr. The argon gas is released through a mass-flow controller to purge the system prior to deposition. RF power is 85 W at a distance of 9 cm. The behavior of Au membranes built on ultimate 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.« less

  14. Thermoelectric study of Y-Ba-Cu-O thin film on MgO substrate prepared by resistive evaporation

    NASA Astrophysics Data System (ADS)

    Pekala, M.; Pekala, K.; Lapsker, I.; Verdyan, A.; Azoulay, J.

    1993-04-01

    Thermoelectric measurements were carried out on Y-Ba-Cu-O thin film deposited on MgO substrate by resistive evaporation technique. A pulverized mixture of Y, BaF 2 and Cu weighed in the atomic proportion was evaporated from resistively heated source onto a MgO substrate kept at 400°C using a simple vacuum system. The substrate temperature was then raised to 700°C for insitu heat treatment. Oxygen was injected through a nozzle placed close to subtrate surface, thus raising the pressure to about 7 Pa during the heat treatment, which lasted for about 15 minutes. The film was then gradually cooled down to room temperature and the pressure raised to atmospheric pressure. The films thus obtained were measured and the values of thermoelectric power measurements in the plane of the film were found to be close to the typical thermoelectric power values of crystalline Y-Ba-Cu-O superconductors. As expected, vanishing values of the thermoelectric power have been observed below 80 K. If the relation observed for sintered Y-Ba-Cu-O is applied for thin films, it suggests an extremely low oxygen deficiency.

  15. Electromagnetic Properties of (Gd, Y)Ba2Cu3Ox Superconducting Tapes With High Levels of Zr Addition

    SciTech Connect

    Liu, Y; Yao, Y; Chen, Y; Khatri, ND; Liu, J; Galtsyan, E; Lei, C; Selvamanickam, V

    2013-06-01

    The dependence of the critical current density (J(c)) on the orientation of applied magnetic fields was studied in Zr-doped (Gd, Y)Ba2Cu3Ox tapes fabricated by metal organic chemical vapor deposition. The in-field performance of J(c) of (Gd, Y)Ba2Cu3Ox tapes with Zr-doping levels of 7.5-30 at.% was investigated up to 5 T over a temperature range of 40-77 K. The highest critical currents (I-c) at H parallel to c and the highest values of minimum Ic in angular dependence measurements were achieved in the tapes with 20% Zr doping over a broad range of temperature and magnetic field conditions measured. The electromagnetic properties have been related to the changes in BaZrO3 content and microstructure.

  16. Long range coupling in YBa2Cu3O7-δ/Y1-xPrxBa2Cu3O7-δ multilayers

    NASA Astrophysics Data System (ADS)

    Fivat, P.; Triscone, J.-M.; Fischer, Ø.

    1996-12-01

    YBa2Cu3O7-δ/(Y1-xPrx)Ba2Cu3O7-δ multilayers have been used to probe coupling through (Y1-x:Prx)Ba2Cu3O7-δ alloys. We observe that the coupling between ultrathin YBa2Cu3O7-δ layers, 12 or 24 Å thick, survives through several hundred Å of (Y1-xPrx)Ba2Cu3O7-δ with x=0.4 and 0.55. Tc versus the thickness of the spacer-alloy, and activation energies for flux motion, with fields parallel and perpendicular to the c-axis, have been used to probe this long range coupling. All these experiments point to an unusually large coupling length for these two alloy compositions. In the x=0.55 case this result is particularly surprising since the alloy material display a semiconducting behaviour for this composition. Tc measurements, activation energies, and a study of the vortex dynamics in these coupled multilayers is presented along with new results obtained on a series of multilayers built with a more insulating alloy, x=0.7.

  17. Transverse resistance in HoBa2Cu3O7-δ single crystals

    NASA Astrophysics Data System (ADS)

    Vovk, Ruslan V.; Khadzhai, Georgij Ya.; Dobrovolskiy, Oleksandr V.; Nazyrov, Zarif F.; Chroneos, Alexander

    2015-11-01

    The transverse electrical resistance of HoBa2Cu3O7-δ single crystals is investigated in the temperature range Tc - 300K for optimally-doped (Tc ≈ 91K) and oxygen-poor (Tc ≈ 51K) samples. With decreasing temperature, the resistivity of the optimally-doped samples has been found to transit from the regime of scattering on phonons and defects to the regime of “semiconductor” character and, near Tc, of the fluctuation conductivity. The oxygen-poor samples have been revealed to exhibit only a variable range hopping conductivity of “semiconductor” character, which near Tc transits into the fluctuation conductivity. A significant anisotropy of the residual resistivity and characteristics of the fluctuation conductivity is observed for samples of both types.

  18. 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.

  19. 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.

  20. Y1Ba2Cu3O7-δ thin films grown by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Takano, Satoshi; Hayashi, Noriki; Okuda, Shigeru; Hitosuyanagi, Hajime

    1989-12-01

    Y1Ba2Cu3O7-δ thin films were grown on (100)MgO and polycrystalline YSZ substrates by RF magnetron sputtering. We measured the magnetic field dependence of Jc of these films. The films grown on MgO with Jc of 4.0x106, 2.9 x106 and 1.5x104 A/cm2 at OT showed 7.1x105 A/cm2 at 8T, 1x104 A/cm2 at 20T and 1.1x103 A/cm2 at 5 T, respectively . We could attain a c-axis oriented film with a Jc of 1.2x104 A/cm2 on YSZ polycrystalline substrate, however, it showed greater degradation than the films grown on MgO in Jc with magnetic field.

  1. Y 1Ba 2Cu 3O 7-δ thin films grown by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Takano, Satoshi; Hayashi, Noriki; Okuda, Shigeru; Hitosuyanagi, Hajime

    1989-12-01

    Y 1Ba 2Cu 3O 7-δ thin films were grown on (100)MgO and polycrystalline YSZ substrates by RF magnetron sputtering. We measured the magnetic field dependence of Jc of these films. The films grown on MgO with Jc of 4.0x10 6, 2.9 x10 6 and 1.5x10 4 A/cm 2 at OT showed 7.1x10 5 A/cm 2 at 8T, 1x10 4 A/cm 2 at 20T and 1.1x10 3 A/cm 2 at 5 T, respectively . We could attain a c-axis oriented film with a Jc of 1.2x10 4 A/cm 2 on YSZ polycrystalline substrate, however, it showed greater degradation than the films grown on MgO in Jc with magnetic field.

  2. Temporal relaxation of nonequilibrium in Y-Ba-Cu-O measured from transient photoimpedance response

    SciTech Connect

    Bluzer, N. )

    1991-11-01

    Nonequilibrium in Y-Ba-Cu-O thin films biased with a dc current is photoinduced by exposure to 300-fsec 2-eV laser pulses. The photoinduced nonequilibrium transients were measured in the superconducting, transition, and normal states occurring between 7 and 200 K. The photoabsorption produced temporal changes in the sample's impedance, which manifest themselves as transient voltage signals occurring across the samples during the nonequilibrium's relaxation process. At and above {ital T}{sub {ital c}}, the observed photoresponse is thermal. Below {ital T}{sub {ital c}}, a quantum response is obtained corresponding to changes in the Cooper-pair populations. In the zero-resistance superconducting state, a positive signal corresponds to quasiparticle generation and a negative signal corresponds to quasiparticle recombination.

  3. Stripe correlations in La 1.875Ba 0.125CuO 4

    NASA Astrophysics Data System (ADS)

    Fujita, M.; Goka, H.; Tranquada, J. M.; Yamada, K.

    2004-08-01

    We have performed neutron scattering measurements on the single crystal of La 1.875Ba 0.125CuO 4 in order to study the melting sequence of stripe correlations. Low-energy incommensurate spin fluctuations clearly are observed around (π,π) at low temperatures and remain even above the stripe ordering temperature of 50 K. However, the peak intensity dramatically degrades toward the structural transition temperature between low-temperature tetragonal and low-temperature orthorhombic phases, Td2, of 60 K. No well-defined signal was observed above Td2. These results suggest that the charge fluctuations, which are closely related with the crystal structure, modify the magnetic correlations as expected from the stripe model.

  4. Manipulating stripes in La2-x Ba x CuO 4 in extreme environments

    NASA Astrophysics Data System (ADS)

    Huecker, Markus; Gu, Genda; Xu, Zhijun; Wen, Jinsheng; Tranquada, John M.; von Zimmermann, Martin

    2011-03-01

    Competing magnetic and electronic interactions in the copper-oxide high temperature superconductors often result in nanoscale inhomogeneity of the charge and spin density. Such observations motivated a proposal that dynamic electronic inhomogeneities are intrinsic to the copper-oxide planes, and can result in electronic states that break their four-fold symmetry. We have performed high-energy single-crystal X-ray diffraction in high magnetic fields and at high pressure to show that the charge and spin stripe phase in La 2-x Ba x Cu O4 constitutes such a state. In particular, our results provide strong evidence that charge stripe correlations in the cuprates are electronically driven and are enhanced within vortices. The work at Brookhaven was supported by the Office of Science, U.S. Department of Energy under Contract No. DE-AC02-98CH10886.

  5. Fabrication of Tri-axially Oriented RE-Ba-Cu-O Ceramics by Magnetic Alignment

    NASA Astrophysics Data System (ADS)

    Yamaki, M.; Furuta, M.; Doi, T.; Shimoyama, J.; Horii, S.

    Magnetic alignment is a new crystal alignment process which enables tri-axial orientation without epitaxial growth at room temperature. In order to investigate the effectiveness of this magnetic tri-axial alignment process, we attempted to fabricate tri-axially oriented ErBa2Cu4O8 (Er124) ceramics by a slip-casting technique under two different modulated rotation magnetic fields (MRFs); uni-directional rotation type and oscillation type. For improvement of the degrees of tri-axial orientation in the Er124 green compacts slip-casted under MRFs, appropriate choice of sample-rotation method, magnetic field condition, control of mean diameter of source powders, and viscosity of slurry was found to be important in the case of MRFs induced by the sample-rotation. At the current stage, the degree of inplane orientation with ∼10̊ in Er124 was achieved.

  6. 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.

  7. A superconducting conveyer system using multiple bulk Y-Ba-Cu-O superconductors and permanent magnets

    NASA Astrophysics Data System (ADS)

    Kinoshita, T.; Koshizuka, N.; Nagashima, K.; Murakami, M.

    Developments of non-contact superconducting devices like superconducting magnetic levitation transfer and superconducting flywheel energy storage system have been performed based on the interactions between bulk Y-Ba-Cu-O superconductors and permanent magnets, in that the superconductors can stably be levitated without any active control. The performances of noncontact superconducting devices are dependent on the interaction forces like attractive forces and stiffness. In the present study, we constructed a non-contact conveyer for which the guide rails were prepared by attaching many Fe-Nd-B magnets onto an iron base plate. Along the translational direction, all the magnets were arranged as to face the same pole, and furthermore their inter-distance was made as small as possible. The guide rail has three magnet rows, for which the magnets were glued on the iron plate such that adjacent magnet rows have opposite poles like NSN. At the center row, the magnetic field at zero gap reached 0.61T, while the field strengths of two rows on the side edges were only 0.48T due to magnetic interactions among permanent magnets. We then prepared a cryogenic box made with FRP that can store several bulk Y-Ba-Cu-O superconductors 25 mm in diameter cooled by liquid nitrogen. It was found that the levitation forces and stiffness increased with increasing the number of bulk superconductors installed in the box, although the levitation force per unit bulk were almost the same. We also confirmed that these forces are dependent on the configuration of bulk superconductors.

  8. 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

  9. 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.

  10. Theoretics-directed effect of copper or aluminum content on the ductility characteristics of Al-based (Al3Ti, AlTi, AlCu, AlTiCu2) intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Li, Yong; Ma, Xiao-Juan; Liu, Qi-Jun; Kong, Ge-Xing; Ma, Hai-Xia; Wang, Wen-Peng; Wang, Yi-Gao; Jiao, Zhen; Liu, Fu-Sheng; Liu, Zheng-Tang

    2016-11-01

    First-principle simulations have been applied to investigate the effect of copper (Cu) or aluminum (Al) content on the ductility of Al3Ti, AlTi, AlCu, and AlTiCu2 alloys. The mechanical stable and elastic properties of Al-based intermetallic compounds are researched by density functional theory with the generalized gradient approximation (DFT-GGA). The calculated lattice constants are in conformity with the previous experimental and theoretical data. The deduced elastic constants show that the investigated Al3Ti, AlTi, AlCu, and AlTiCu2 structures are mechanically stable. Shear modulus, Young’s modulus, Poisson’s ratio, and the ratio B/G have also been figured out by using reckoned elastic constants. A further analysis of Young’s modulus and Poisson’s ratio reveals that the third added element copper content has significant effects on the Al-Ti-based ICs ductile character. Project supported by the National Natural Science Foundation of China (Grant Nos. 41674088, 11574254, 11272296, and 11547311), the National Basic Research Program of China (Grant No. 2011CB808201), the Fundamental Research Fund for the Central Universities, China (Grant Nos. 2682014ZT30 and 2682014ZT31), and the Fund of the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University, China (Grant No. SKLSP201511).

  11. 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.

  12. 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.

  13. 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).

  14. Decoupling of superconducting planes of La1.905Ba0.095CuO4 in a transverse magnetic field

    NASA Astrophysics Data System (ADS)

    Tranquada, John; Stegen, Z.; Boebinger, G. S.; Han, Su Jung; Wu, Jie; Xu, Zhijun; Gu, Genda; Li, Qiang

    2012-02-01

    We have measured the resistivity parallel and perpendicular to the CuO2 planes in single crystals of La1.905Ba0.095CuO4 for magnetic fields up to 35 T applied along the c-axis. Below the zero-field superconducting transition temperature of 32 K, we observe that, above a threshold field, the c-axis resistivity grows with field, eventually reaching a maximum and then decreasing. At the resistivity maximum, interlayer pair tunneling becomes insignificant. Under the same field and temperature conditions, the in-plane resistivity remains quite low, reflecting robust superconductivity. We identify a regime in which the superconducting planes are effectively decoupled. At 20 K, a field much greater than 35 T would be required to destroy the in-plane pairing, despite the fact that the field also induces both charge and spin stripe order (J.S. Wen et al., arXiv:1009.0031).

  15. Crystallization kinetics of BaO-Al2O3-SiO2 glasses

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Hyatt, Mark J.

    1988-01-01

    Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt percent) 10BaO-38Al2O3-51SiO2-1MoO3 (glass A) and 39BaO-25Al2O3-35SiO2-1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3-2SiO2) and hexacelsian (BaO-Al2O3-2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 C. It undergoes structural transformation into the orthorhombic form at approximately 300 C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.

  16. Effects of Oxygen Deficiency and Dopping of pr in Gd1-x Prx Ba2Cu3O7-y

    NASA Astrophysics Data System (ADS)

    Zolfagharkhani, G.; Daadmehr, V.; Farzaneh, M.; Sedighiani, A.; Akhavan, M.

    2000-09-01

    Single phase crystalline samples of Gd1-x Prx Ba2Cu3O7-y with 0.0 ≤ x ≤ 0.2 have been prepared by standard solid state reaction technique and characterized by SEM and XRD. The electrical measurements show two plateaus in Tc versus y curve for GdBa2Cu3O7-y (0CuO2 planes. The experiments indicate that in GdPr-123 samples, presence of Pr causes the oxygen bond to become stronger than in undoped samples.

  17. Investigation of new type Cu-Hf-Al bulk glassy alloys

    NASA Astrophysics Data System (ADS)

    Nagy, E.; Rontó, V.; Sólyom, J.; Roósz, A.

    2009-01-01

    In the last years new type Cu-Hf-Al ternary alloys were developed with high glass forming ability and ductility. The addition of Al to Cu-Hf alloys results in improvements in glass formation, thermal stability and mechanical properties of these alloys. We have investigated new Cu-based bulk amorphous alloys in Cu-Hf-Al ternary system. The alloys with Cu49Hf42Al9, Cu46Hf45Al9, Cu50Hf42.5Al7.5 and Cu50Hf45Al5 compositions were prepared by arc melting. The samples were made by centrifugal casting and were investigated by X-ray diffraction method. Thermodynamic properties were examined by differential scanning calorimetry and the structure of the crystallising phases by scanning electron microscopy. The determination of liquidus temperatures of alloys were measured by differential thermal analysis.

  18. Structural properties of the copper oxide carbonate Ba 4CaCu 2O 6 + δCO 3 ( δ ≈ 0)

    NASA Astrophysics Data System (ADS)

    Kikuchi, Mami; Izumi, Fujio; Kikuchi, Masae; Ohshima, Eriko; Morii, Yukio; Shimojo, Yutaka; Syono, Yasuhiko

    1995-02-01

    The structure parameters of Ba 4CaCu 2O 6 + δCO 3 were refined by Rietveld analysis of angle-dispersive neutron powder diffraction data. The stoichiometric metal composition was confirmed by X-ray microanalysis. Iodometry showed that the amount of excess oxygen, δ, was nearly zero. The carbon content and infrared absorption spectrum of the compound gave evidence for the inclusion of CO 32- ions in its crystal lattice. Ba 4CaCu 2O 6CO 3 is tetragonal with the P4/mmm space group and lattice parameters of a = 5.7879(2) Å and c = 8.1409(3) Å. Ba atoms occupy positions corresponding to the A site in ABO 3 whereas Ca, Cu and C atoms are located at positions corresponding to the B site. Two copper sites are contained in the structure of Ba 4CaCu 2O 6CO 3: Cu(1) and Cu(2). If weak bonds between the Cu atoms and O atoms in the CO 32- ion are neglected, Cu(1) and Cu(2) are taken as coordinated to four O(1) atoms and two O(2) atoms, respectively. Bond-valence sum calculations showed that the oxidation state of Cu is 2.48 for Cu(1) and 1.66 for Cu(2). The splitting and large thermal parameters of O atoms contained in the CO 32- ion revealed its highly disordered orientation.

  19. 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.

  20. Flux Pinning Enhancement in YBa2Cu3O7-x Films with BaSnO3 Nanoparticles

    DTIC Science & Technology

    2008-10-01

    YBCO +BaSnO3 samples of different thickness (240, 317, 359 nm ) were compared with two standard ∼300 nm thick YBCO films on a ( 100 ... YBCO + BaSnO3 nanoparticle film. Films were deposited on ( 100 ) lanthanum aluminate single crystal substrates (LaAlO3) to investigate the flux pinning...LAO (Sample 3) YBCO /STO YBCO /LAO YBCO /LAO YBCO /STO YBCO +BaSnO 3 /LAO 106 105 104 1000 100 10 0 2 4 6 8 10 1 Magnetic Field H(T) J c

  1. 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.

  2. Flux Pinning and Properties of Solid-Solution (Y,Nd)1+xBa2-xCu3O7-delta Superconductors (Preprint)

    DTIC Science & Technology

    2012-02-01

    AFRL-RZ-WP-TP-2012-0095 FLUX PINNING AND PROPERTIES OF SOLID - SOLUTION (Y,Nd)1+xBa2-xCu3O7-δ SUPERCONDUCTORS (PREPRINT) Timothy J. Haugan...2001 – 01 April 2003 4. TITLE AND SUBTITLE FLUX PINNING AND PROPERTIES OF SOLID - SOLUTION (Y,Nd)1+xBa2-xCu3O7-δ SUPERCONDUCTORS (PREPRINT) 5a...FLUX PINNING and PROPERTIES OF SOLID - SOLUTION (Y,Nd)1+xBa2-xCu3O7- SUPERCONDUCTORS T. J. Haugan, M. E. Fowler, J. C. Tolliver, P. N. Barnes

  3. 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.

  4. Dirac and Weyl Semimetal in XYBi (X = Ba, Eu; Y = Cu, Ag and Au)

    PubMed Central

    Du, Yongping; Wan, Bo; Wang, Di; Sheng, Li; Duan, Chun-Gang; Wan, Xiangang

    2015-01-01

    Weyl and Dirac semimetals recently stimulate intense research activities due to their novel properties. Combining first-principles calculations and effective model analysis, we predict that nonmagnetic compounds BaYBi (Y = Au, Ag and Cu) are Dirac semimetals. As for the magnetic compound EuYBi, although the time reversal symmetry is broken, their long-range magnetic ordering cannot split the Dirac point into pairs of Weyl points. However, we propose that partially substitute Eu ions by Ba ions will realize the Weyl semimetal. PMID:26399742

  5. Massive spalling of Cu-Zn and Cu-Al intermetallic compounds at the interface between solders and Cu substrate during liquid state reaction

    NASA Astrophysics Data System (ADS)

    Kotadia, H. R.; Panneerselvam, A.; Mokhtari, O.; Green, M. A.; Mannan, S. H.

    2012-04-01

    The interfacial intermetallic compound (IMC) formation between Cu substrate and Sn-3.8Ag-0.7Cu-X (wt.%) solder alloys has been studied, where X consists of 0-5% Zn or 0-2% Al. The study has focused on the effect of solder volume as well as the Zn or Al concentration. With low solder volume, when the Zn and Al concentrations in the solder are also low, the initial Cu-Zn and Al-Cu IMC layers, which form at the solder/substrate interface, are not stable and spall off, displaced by a Cu6Sn5 IMC layer. As the total Zn or Al content in the system increases by increasing solder volume, stable CuZn or Al2Cu IMCs form on the substrate and are not displaced. Increasing concentration of Zn has a similar effect of stabilizing the Cu-Zn IMC layer and also of forming a stable Cu5Zn8 layer, but increasing Al concentration alone does not prevent spalling of Al2Cu. These results are explained using a combination of thermodynamic- and kinetics-based arguments.

  6. Martensitic transformation in a Cu-Zn-Al alloy studied by 63Cu and 27Al NMR

    NASA Astrophysics Data System (ADS)

    Rubini, S.; Dimitropoulos, C.; Gotthardt, R.; Borsa, F.

    1991-08-01

    27Al and 63Cu line shape, Knight shift, and relaxation rates over a wide range of temperature and external magnetic field are reported for a Cu-Zn-Al alloy displaying a martensitic phase transformation (MPT) at MS=152 K. Changes in line shape, linewidth, and T-12 at the MPT are detected for both nuclei, and are found to be consistent with the local atomic rearrangement occurring at the transformation. A double structure for the 27Al NMR line is observed in a small range of temperature below MS, and interpreted as the superposition of the signals arising from the two coexisting phases. It is shown that the growth of the martensitic phase during the cooling can be monitored by means of the deconvolution of the 27Al spectrum into the two components. From the analysis, it is inferred that a sudden formation of extensive regions in the martensitic phase occurs at the transition. The Knight shift and the Korringa term (T1T)-1 are slightly different in the two phases, indicating a small increase of the density of s electrons at the Fermi surface at the nuclear sites. The enhancement factors of the susceptibility and of the spin-lattice relaxation rate do not seem to be affected by the MPT but are different when measured at the Al or Cu site, indicating a local nonuniform charge-density distribution in the unit cell. A small enhancement of T-11 is observed for both nuclei in the temperature interval in which the growth of the martensite within the austenite is detected. The anomalous contribution to the relaxation is interpreted as due to strong local charge-density fluctuations caused by atomic motion at the interfaces between the two phases. No precursor effects were detected on the NMR parameters above MS, indicating the absence of a static or long-lived microstructure of the product phase and of a static short-wavelength modulation of the lattice.

  7. Melt processing for strong flux pinning in RE-Ba-Cu-O (RE: Nd, Sm, Eu, Gd) superconductors

    NASA Astrophysics Data System (ADS)

    Yoo, S. I.; Murakami, M.; Sakai, N.; Ohyama, T.; Higuchi, T.; Watahiki, M.; Takahashi, M.

    1995-12-01

    Factors affecting a characteristic flux pinning in light rare earth (RE)-Ba-Cu-O (RE: Nd, Sm, Eu, Gd) superconductors fabricated by the oxygen-controlled-melt-growth (OCMG) process have been investigated through a comparative study. At 77K and for the applied field parallel to the c-axis of the sample (H//c), the flux pinning of all OCMG-processed REBa2Cu3O (RE123) samples studied was very sensitive to the oxygen partial pressure (PO2) controlled during the melt growth and thus, with lowering PO2, the peak field (Bpk) in the M-H loops shifted to a high field and the irreversibility line (IL) shifted to a high H-T region. For a Ndl23 sample, as the oxygen annealing temperature increased above 300‡C, both Bpk and IL were systematically depressed. However, Bpk for all systems was insensitive to the amount of the second phase (Nd4Ba2Cu2O10 (Nd422) and RE2BaCuO5 (RE211) for the other) inclusion in the superconducting RE123 matrix, supporting that the characteristic flux pinning is due to the superconducting matrix.

  8. 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.

  9. 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.

  10. Dependence of superconducting properties on the Cu-valence determined by iodometry in HgBa 2CuO 4+δ

    NASA Astrophysics Data System (ADS)

    Fukuoka, A.; Tokiwa-Yamamoto, A.; Itoh, M.; Usami, R.; Adachi, S.; Yamauchi, H.; Tanabe, K.

    1996-02-01

    We have synthesized nearly single-phase HgBa 2CuO 4+δ samples with various oxygen contents, and systematically investigated the relationship between the lattice parameters, the superconductivity transition temperature ( Tc) and the oxygen content determined by iodometry. Furthermore, the nominal copper valence values were calculated from the oxygen content data by assuming constant valence values of +2.00 and -2.00 for mercury and oxygen, respectively. Both the a and c lattice parameters were found to decrease monotonically with the Cu valence over a wide range of +2.05-2.28. The obtained Tc versus Cu valence curve exhibits a “bell shaped” correlation with the maximum in Tc at the Cu valence of ∼ +2.18.

  11. 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.

  12. 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.

  13. The effect of Al-substitution on superconducting type-I clathrate Ba8Si46

    NASA Astrophysics Data System (ADS)

    Liu, Lihua; Bi, Shanli; Chen, Ning; Li, Feng; Liu, Yang; Cao, Guohui; Li, Yang

    2014-11-01

    A series of samples with the chemical formula Ba8Si46-xAlx (x = 2, 3, 5, 6, 7 and 8) were prepared by arc melting, ball milling and washing with diluted HCl. The lattice parameter of Ba8Si46-xAlx increases linearly with the increase of nominal Al content x. The composition analysis by energy-dispersive X-ray spectroscopy (EDS) shown that the actual Al contents in clathrates are lager than the nominal compositions because the dilute Al-contained impurity phases were washed out. The experimental results show that the minimum incorporation of Al into clathrate structure is expected to be about 3 at ambient pressure, which is in agreement with a first-principle simulation. The Al substitution for Si results in the decrease of superconducting transition temperature TC, which can be explained on the BCS theoretical frame. The electron density of state at Fermi level N(EF) decreases with the increment of x except for an abnormal increase for the sample x = 6. Such sample has a higher spatial symmetry of the structure in which all the six Si atoms at 6c sites were substituted by Al atoms. Its higher N(EF) causes to a higher TC. In addition, we calculated the phonon-dispersion relations and vibrational density of states for Al-doped silicon clathrates. The high frequency acoustic branch has a red shift from 430 cm-1 to 420 cm-1 with the doping of Al. The decreased frequency of bond-stretching vibration modes is another reason for the suppression of TC induced by Al substitution.

  14. Tuning Porosity of YBa2Cu3O7-delta Vicinal Films by Insertion of Y2BaCuO5 Nanoparticles (Postprint)

    DTIC Science & Technology

    2012-02-01

    microstructure on Jc. By growing YBa2Cu3O7−δ YBCO films at a small vicinal angle, we have recently obtained a highly porous structure in these films...accompanied with a significantly enhanced Jc. This result raises a challenging question on whether the porosity can be tailored in YBCO films to allow a...higher Jc. In this study, we have explored the insertion of Y2BaCuO5 (211) nanoparticles in vicinal YBCO thick films to alter the strain at the

  15. 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.

  16. Fabrication of CdS/CdTe solar cells with transparent p-type conductive BaCuSeF back contact

    NASA Astrophysics Data System (ADS)

    Yamamoto, Koichi; Sakakima, Hiroshi; Ogawa, Yohei; Hosono, Aikyo; Okamoto, Tamotsu; Wada, Takahiro

    2015-08-01

    BaCuSeF films were applied to CdS/CdTe solar cells as back electrodes. The interfaces between the CdTe and BaCuSeF layers in the CdS/CdTe solar cells with BaCuSeF back contact deposited at substrate temperatures (TS) of 200 and 300 °C were analyzed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). We clearly observed many dislocations in the CdTe layer in the CdS/CdTe solar cell with the BaCuSeF layer deposited at TS = 300 °C. We also observed a reaction layer of Cu2.72Te2 between the BaCuSeF and CdTe layers in both solar cells. We concluded that (1) the substrate temperature for the pulsed laser deposition of the BaCuSeF layer and (2) the interface between the CdTe and BaCuSeF layers are important factors for the performance of the CdTe solar cells. We obtained high conversion efficiency of 8.31% for a solar cell with a BaCuSeF layer deposited at TS = 200 °C on a CdTe surface etched in a NH3 aqueous solution. The highest conversion efficiency of 9.91% was obtained for a solar cell with a CdTe surface etched in a bromide-bromate solution.

  17. Heavy-ions irradiation dependence of superconducting properties of the Cu-based (Cu,C)Ba 2Ca 3Cu 4O 11- δ

    NASA Astrophysics Data System (ADS)

    Kitô, Hijiri; Iyo, Akira; Hirai, Manabu; Crisan, A.; Tokumoto, Madoka; Okayasu, Satoru; Sasase, Masahito; Sataka, Masao; Ihara, Hideo; Tanaka, Yasumoto

    2003-10-01

    To further enhance the critical current density ( Jc) and irreversibility field ( Hirr) of (Cu 1- xC x)Ba 2Ca n-1 Cu nO 2 n+4- δ ( n=4; hereafter described as (Cu,C)-1234), pinning centers were introduced by heavy-ion irradiation. The polycrystalline samples were irradiated with Au 15+ ions (240 MeV energy) at various fluence of 3.5 × 10 10, 6.5 × 10 10, 1 × 10 11, 2.5 × 10 11 and 5 × 10 11 ions/cm 2. The intragrain Jc was determined from M- H curves using Bean’s critical state model. With increase of the fluence, Jc shows a rapid increase and reaches a maximum value, 4.1 × 10 6 A/cm 2 (77 K and 1 T) for the fluence of 1 × 10 11 ions/cm 2 and above which it decreases slowly. The maximum value of Hirr(77 K), determined by extrapolating Jc curves to a 10 3 A/cm 2 criterion, is about 14.5 T for the 2.5 × 10 11 ions/cm 2. The α value in equation Hirr( T)= Hirr(0)(1- T/ Tc) α decreases from 2.97 for un-irradiated sample to 1.87 for the fluence of 1 × 10 11 ions/cm 2. These results indicate the possibility of Jc(77 K and 1 T) enhancement and reaching a high Hirr(77 K) at the fluence of the 1.5 × 10 11 ions/cm 2.

  18. Vortex dynamics at subcritical currents at microwave frequencies in DyBa2Cu3O7-δ thin films

    NASA Astrophysics Data System (ADS)

    Banerjee, Tamalika; Bagwe, V. C.; John, J.; Pai, S. P.; Pinto, R.; Kanjilal, D.

    2004-03-01

    We have investigated the dynamics of vortices at subcritical microwave currents in dc magnetic fields (up to 0.8 T) in epitaxial DyBa2Cu3O7-δ (DBCO) thin films. Microwave measurements were performed using microstrip resonators as test vehicles at 4.88 GHz and 9.55 GHz on laser ablated DBCO thin films in the thickness range 1800 3800 Å. Experimental evidence indicates that the peak effect (PE) observed in surface resistance vs temperature (Rs vs T) plots in applied dc magnetic fields up to 0.8 T is primarily due to the extended defects in thinner films (1800 Å) such as twin boundaries at the substrate(LaAlO3)-film interface; whereas, the high density of point defect disorder in thicker (⩾3000 Å) films is responsible for low Rs and high depinning frequency ωp. This has been confirmed by generation of columnar defects using 200 MeV Ag ion irradiation which showed that even thicker DBCO films show PE in Rs after the introduction of columnar defects. Further, DBCO films grown on low-twinned LaAlO3 substrates (which cause low density of substrate-related extended defects in the film) have shown PE only at 9.55 GHz but not at 4.88 GHz. Values of ωp have been calculated from experimental Rs data. ωp vs T plots obtained for the thinner films show a peak which is a result of the peaks in Rs vs T plots of these films at 4.88 GHz and 9.55 GHz.

  19. 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)

  20. 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.

  1. Effect of Annealing Conditions on the Structural and Superconducting Properties of Y-Ba-Cu-O Films

    DTIC Science & Technology

    1989-05-01

    591768 (1987). 2 J. FKwo, T. C. Hsieh, R. M. Fleming, M. Hong, S. H . Liou, B. A. Davidson, and L. C. Feldman, Structure and Superconducting...Properties of Orien tat ion -Ordered B BajCu30- Films Prepared by Molecular-beam Epitaxy, Phys. Rev. B 36:4039 (1 87i 0 - 3. K_ Setsune, T. Kamada, H . Adachi...Yamamoto, Y. Bando, and H . Mazaki, Single-Crystal Y"Ba Cu ~0 7 Thin Films by Activated Reactive Evaporation, JDrI. J. Appl. Phys. 27:Ll (f88). 5. J

  2. Electronically driven instabilities and superconductivity in the layered La(2-x)Ba(x)CuO4 perovskites

    NASA Astrophysics Data System (ADS)

    Yu, Jaejun; Freeman, A. J.; Xu, J.-H.

    1987-03-01

    Body-centered tetragonal La2CuO4 is shown to have its electronic structure and properties dominated by the layered in-plane Cu-3d - O-2p interactions. A strong Fermi-surface instability along the 110 line with the absolute value of q = 2kF leads, via a soft-phonon mode, to the observed orthorhombic phase and accounts for its semiconducting properties. The addition of divalent metals (i.e., Ba or Sr) suppresses the instability and stabilizes the tetragonal phase where the same soft-phonon branch apparently contributes to a large electron-phonon interaction and a high Tc.

  3. Effects of Codoping with Ga and P on Thermoelectric Properties of Ba8Al16Si30 Clathrate System

    NASA Astrophysics Data System (ADS)

    Anno, Hiroaki; Ueda, Takahiro; Okamoto, Kazuya

    2017-01-01

    We have investigated the effects of Codoping With Ga and P on the thermoelectric properties of the Ba8Al16Si30 clathrate system, attempting to optimize the carrier concentration. The elastic properties, which are important for design of thermoelectric devices, were investigated by ultrasonic testing. Ga/P-codoped specimens with nominal compositions Ba8Al16Ga x Si30-2x P x (x = 1.0, 1.5, 2.0) were prepared by arc melting and spark plasma sintering and their Seebeck coefficient, electrical conductivity, and thermal conductivity were measured. Analytical studies revealed that the total content of Al and Ga, expressed as atoms per formula unit, increased to 15.65 at nominal x = 2.0, exceeding the maximum content (y = 15.16) of Al for the Ba8Al y Si46-y clathrate system. Ultrasonic tests determined the Young's modulus, shear modulus, bulk modulus, and Poisson's ratio to be 102.55 GPa, 40.14 GPa, 76.85 GPa, and 0.2775, respectively, for Ba8Al16Ga x Si30-2x P x (x = 2.0). The Hall carrier concentration decreased from ˜1.0 × 1021 cm-3 for Ba8Al y Si46-y to ˜6.3 × 1020 cm-3 for Ba8Al16Ga x Si30-2x P x (x = 2.0), suggesting that Ga/P codoping may be useful for tuning the carrier concentration. The value of the Seebeck coefficient at ˜320 K increased from -46 μV K-1 for Ba8Al y Si46-y to -67 μV K-1 for Ba8Al16Ga x Si30-2x P x (x = 2.0). The dimensionless thermoelectric figure␣of merit ZT at 900 K improved from ˜0.4 for Ba8Al y Si46-y to ˜0.47 for Ba8Al16Ga x Si30-2x P x (x = 2.0).

  4. Effects of Codoping with Ga and P on Thermoelectric Properties of Ba8Al16Si30 Clathrate System

    NASA Astrophysics Data System (ADS)

    Anno, Hiroaki; Ueda, Takahiro; Okamoto, Kazuya

    2017-03-01

    We have investigated the effects of Codoping With Ga and P on the thermoelectric properties of the Ba8Al16Si30 clathrate system, attempting to optimize the carrier concentration. The elastic properties, which are important for design of thermoelectric devices, were investigated by ultrasonic testing. Ga/P-codoped specimens with nominal compositions Ba8Al16Ga x Si30-2 x P x ( x = 1.0, 1.5, 2.0) were prepared by arc melting and spark plasma sintering and their Seebeck coefficient, electrical conductivity, and thermal conductivity were measured. Analytical studies revealed that the total content of Al and Ga, expressed as atoms per formula unit, increased to 15.65 at nominal x = 2.0, exceeding the maximum content ( y = 15.16) of Al for the Ba8Al y Si46- y clathrate system. Ultrasonic tests determined the Young's modulus, shear modulus, bulk modulus, and Poisson's ratio to be 102.55 GPa, 40.14 GPa, 76.85 GPa, and 0.2775, respectively, for Ba8Al16Ga x Si30-2 x P x ( x = 2.0). The Hall carrier concentration decreased from ˜1.0 × 1021 cm-3 for Ba8Al y Si46- y to ˜6.3 × 1020 cm-3 for Ba8Al16Ga x Si30-2 x P x ( x = 2.0), suggesting that Ga/P codoping may be useful for tuning the carrier concentration. The value of the Seebeck coefficient at ˜320 K increased from -46 μV K-1 for Ba8Al y Si46- y to -67 μV K-1 for Ba8Al16Ga x Si30-2 x P x ( x = 2.0). The dimensionless thermoelectric figure of merit ZT at 900 K improved from ˜0.4 for Ba8Al y Si46- y to ˜0.47 for Ba8Al16Ga x Si30-2 x P x ( x = 2.0).

  5. 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.

  6. 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.

  7. 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.

  8. Pinning enhancement by heterovalent substitution in Y1-xRExBa2Cu3O7-δ

    NASA Astrophysics Data System (ADS)

    Petrov, M. I.; Gokhfeld, Yu S.; Balaev, D. A.; Popkov, S. I.; Dubrovskiy, A. A.; Gokhfeld, D. M.; Shaykhutdinov, K. A.

    2008-08-01

    The intragrain pinning in high-Tc superconductor compounds Y1-xRExBa2Cu3O7-δ with low concentration of RE (La, Ce, Pr) was investigated. Magnetic and transport measurements reveal that the pinning is maximal for the concentration of heterovalent RE such that the average distance between the impurity ions in the plane of rare-earth elements is close to the diameter of Abrikosov vortices in YBCO.

  9. The conduction mechanism in Gd1-x-zCexCazBa2Cu3O7-δ

    NASA Astrophysics Data System (ADS)

    Mazaheri, M.; Mofakham, S.; Akhavan, M.

    2008-09-01

    We have investigated the substitution of Ce and divalent Ca with a radius similar to Gd in Gd1-x-zCexCazBa2Cu3O7-δ. We have prepared Gd1-x-zCexCazBa2Cu3O7-δ compounds with different concentrations of Ce and Ca by the standard solid-state reaction technique. X-ray diffraction (XRD) experiments are performed and the results are refined by the Rietveld method. XRD analysis shows a predominantly single-phase perovskite structure with orthorhombic Pmmm symmetry. In Gd1-x-zCexCazBa2Cu3O7-δ compounds, induced suppression of Tc due to Ce doping is compensated by hole doping with increasing Ca substitution for Gd. With the increase of Ca content, Tc increases up to an optimum value; thereafter it begins to decrease, and the resistivity curve has a bell shape. The transition temperature width also decreases for all x with the increase of z. In order to interpret the normal state electrical properties of the samples, the quantum percolation theory based on localized states is applied. Fitting the data with two-dimensional variable range hopping and three-dimensional variable range hopping models, and a Coulomb gap regime, shows that our results are consistent with the Coulomb gap regime. The results of the electrical and structural properties of Gd1-x-zCexCazBa2Cu3O7-δ-doped compounds suggest that Ca doping compensates the suppression of the superconducting state caused by the Ce content.

  10. Physical Characterization of Pure and Substituted Tetragonal LaBaCaCu3O7-δ Superconductor

    NASA Astrophysics Data System (ADS)

    Awana, V. P. S.; Narlikar, A. V.

    The high Tc superconductor, forming the focus of the present review, presents an interesting situation where, despite its oxygen content close to 7.0, the system prefers to crystallize in tetragonal structure, as distinct from exhaustively studied orthorhombic RE:123 (REBa2Cu3O7, RE = rare earth) compounds. Its optimum Tc is decided by the cation intermixing at various sites, unlike that in case of normal RE:123, where all cationic sites are fully occupied and fixed, leaving the anionic sites free for oxygen filling. In this, we review the rich crystal chemistry of this compound and discuss it in conjunction with its unusual superconducting properties. The article is divided in five parts: (1) first we discuss variously reported interesting finer structural details and superconductivity of pristine LaBaCaCu3O7-δ (La:1113) superconductor. The La, Ba and Ca sites are found to be intermixed with respect to their nominal sites of the standard RE:123 structure. (2) We examine the structural aspects and superconductivity of La1-xRExBaCaCu3O7 (RE = Nd, Dy, Sm and Pr). Unlike RE:123 and 124 compounds, the RE:1113 compounds form only with light rare earths such as La, Pr and Nd. Pr:1113 compound is found to be an insulator with Pr moments ordering magnetically at around 8 K, unlike at 17 K for Pr:123. (3) Studies of Pr substitution reveal that relative Tc depression due to Pr in the (La,Nd)1-xPrxBaCaCu3O7 system is less in comparison to that found for La or Nd site Pr substituted (La,Nd)1- xPrxBa2Cu3O7. (4) The results of superconductivity and structural details are reviewed for LaBaCaCu3-xMxO7 (M = Fe, Co, Ni, Ga and Zn) and finally (5) we summarize our conclusions. The results in terms of Tc depression due to these impurities in the parent La:1113 system are seen as similar to those observed for RE:124 (REBa2Cu4O8) and Nd:214 (Nd2-xCexCuO4), but are different from RE:123 and La:214. The results of structural details, superconductivity and magnetic ordering presented in

  11. Crystallographic analysis and conductivity fluctuations of the Y2Ba5Cu8O17 superconductor

    NASA Astrophysics Data System (ADS)

    Barrera, E. W.; Téllez, D. A. Landínez; Roa-Rojas, J.

    2015-02-01

    Synthesis of the Y2Ba5Cu8O17 superconducting material by the standard solid state reaction is reported. DC resistivity measurements reveal a bulk Tc = 104.95 K which was determined by the criterion of the maximum in the numerical temperature derivative of electrical resistivity. Structure characterization was performed by means of the X-ray diffraction (XRD) technique. A Rietveld refinement of XRD patterns shows that the material crystallizes in an orthorhombic structure, space group Pmm2 with cell parameters a = 3.8712(0) Å, b = 3.8481(4) Å and c = 27.1601(4) Å. In order to study the pairing mechanism close to Tc, conductivity fluctuation analysis was performed by the method of logarithmic temperature derivative of the conductivity excess. Close and above Tc, the conductivity fluctuation analysis reveal the occurrence of two fluctuation regimes characterized by the critical exponents λ3D = 0.52 and λ1D = 1.51, corresponding to 3D and 1D Gaussian regimes, respectively. The correlations of the critical exponents with the dimensionality of the fluctuation system for each Gaussian regime were performed by using the Aslamazov-Larkin theory.

  12. TOPICAL REVIEW: Melt-processed light rare earth element - Ba - Cu - O

    NASA Astrophysics Data System (ADS)

    Murakami, M.; Sakai, N.; Higuchi, T.; Yoo, S. I.

    1996-12-01

    Unlike Y123 which forms only a stoichiometric compound, the light rare earth elements (LREs: La, Nd, Sm, Eu, Gd) form a solid solution 0953-2048/9/12/001/img1. The presence of such solid solution caused a depression in the superconducting transition temperatures 0953-2048/9/12/001/img2, particularly for La123, Nd123 and Sm123 when they are melt processed in air. Recently, we have found that the 0953-2048/9/12/001/img3 of these LRE123 superconductors can greatly be enhanced when they are melt processed in a reduced oxygen atmosphere. Furthermore, 0953-2048/9/12/001/img4 values of these superconductors were larger than that of a good quality Y123 superconductor in high magnetic fields at 77 K. In this article, on the basis of our study over the last several years, the melt processes for LRE - Ba - Cu - O are described, the microstructural and superconducting properties of the superconductors are reviewed and the flux pinning mechanism is also discussed.

  13. Localization Effect and Pseudogap in Praseodymium Doped Y1-zPrzBa2Cu3O7-δ Single Crystals

    NASA Astrophysics Data System (ADS)

    Vovk, R. V.; Nazyrov, Z. F.; Goulatis, I. L.; Chroneos, A.

    2012-10-01

    In this paper, we investigate the temperature dependence of the transverse conductivity in Y1-zPrzBa2Cu3O7-δ single crystals with different praseodymium concentrations. It is determined that the increase of the praseodymium concentration in Y1-zPrzBa2Cu3O7-δ leads to the enhancement of localization effects. This in turn results to the transition from the pseudo-gap regime to the variable-range-hopping regime.

  14. 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.

  15. Thermoelectric, band structure, chemical bonding and dispersion of optical constants of new metal chalcogenides Ba4CuGa5Q12 (Q=S, Se)

    NASA Astrophysics Data System (ADS)

    Azam, Sikander; Reshak, A. H.

    2014-08-01

    The electronic structure and dispersion of optical constants of the Ba4CuGa5S12 and Ba4CuGa5Se12 compounds were calculated by the first-principles full-potential linearized augmented plane wave (FPLAPW) method. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel-Vosko GGA (EVGGA) to calculate the electronic structures, Fermi surface, thermoelectric, chemical bonding and dispersion of optical constants of these compounds. By investigating the influence of replacing S by Se, it has been found that the charge density around ‘Ga’ is greater in Ba4CuGa5Se12 than Ba4CuGa5S12. Fermi surface of Ba4CuGa5S12 consists of an electronic sheet only because there is no empty region while Ba4CuGa5Se12 contains both holes and electronic sheets because this compound contains both empty and shaded region. As we replace S by Se the heights of the peaks decreases as a results the reflectivity also decreases. It is noticed that the reflectivity is over 68% (60%) for Ba4CuGa5S12 (Ba4CuGa5Se12) compounds within the energy range studied. This implies that the material will serve as a good reflector. By replacing S by Se the figure of merit values increases from 0.97 to 1.0, which shows the good thermoelectric behavior of both compounds.

  16. Effet du traitement thermique sur la structure cristalline, la température critique et la ligne d'irréversibilité de Lm(SrBa)Cu 3O 6+ z (Lm=Sm, Nd)

    NASA Astrophysics Data System (ADS)

    Bellioua, Mohammed; Nafidi, Abdelhakim; El Kaaouachi, Abdelhamid; Nafidi, Ahmed

    2004-03-01

    We have studied the structural and superconducting properties of Lm(SrBa)Cu 3O 6+ z (Lm=Sm, Nd). Each of the two samples was submitted to two types of heat treatment: an annealing in oxygen [O] and a heated in argon followed by oxygen annealing [A, O]. Our iodometry measurements indicate the same total oxygen constant 6+ z, which was around 6.95±0.04 in each sample. In the case of SmSrBaCu 3O 6+ z, the treatment [A, O] increased the orthorhombicity ɛ= b- a/( b+ a) from 0 to 5.34×10 -3, indicating a tetragonal to orthorhombic structural phase transition, accompanied by an increase of 6 K in critical temperature Tc to Tc[A, O]=85 K. While in the case of NdSrBaCu 3O 6+ z, ɛ[O]= ɛ[A, O]=0 but the Tc[O]=68 K increase by 10 K. Further, there was an enhancement of the irreversibility Tp/ Tc line whatever Lm. A combination of several factors such as the change of the ionic size of the rare earth Lm, its disorder on the (Sr, Ba) site, chain oxygen ordering and increase in phase purity for the [A, O] samples may qualitatively account for the observed data. To cite this article: M. Bellioua et al., C. R. Physique 5 (2004).

  17. Aerosol flow reactor production of fine Y1Ba2Cu3O7 powder: Fabrication of superconducting ceramics

    NASA Astrophysics Data System (ADS)

    Kodas, T. T.; Engler, E. M.; Lee, V. Y.; Jacowitz, R.; Baum, T. H.; Roche, K.; Parkin, S. S. P.; Young, W. S.; Hughes, S.; Kleder, J.; Auser, W.

    1988-05-01

    An aerosol flow reactor operating at 900-1000 °C is used to prepare high-purity Y1Ba2Cu3O7 powders with a uniform chemical composition and a submicron to micron average particle size by thermally decomposing aerosol droplets of a solution consisting of the nitrate salts of Y, Ba, and Cu in a 1:2:3 ratio. The powders were at least 99% reacted based on thermogravimetric analysis, and the x-ray diffraction pattern is essentially that of Y1Ba2Cu3O7. Magnetic susceptibility measurements showed the powders to be superconducting with a transition at 90 K even for average reactor residence times as short as 20 s. Sintering cold-pressed pellets between 900 and 1000 °C provides dense, fine grained (average size on the order of 1 μm) superconducting ceramics with sharp 90 K transitions. The grain size and shape of a final sintered part could be varied depending on powder production, processing, and sintering conditions.

  18. 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.

  19. 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.

  20. Structure and physical properties of the new telluride BaAg{sub 2}Te{sub 2} and its quaternary variants BaCu{sub {delta}}Ag{sub 2-{delta}}Te{sub 2}

    SciTech Connect

    Assoud, Abdeljalil; Cui Yanjie; Thomas, Stephanie; Sutherland, Brodie; Kleinke, Holger

    2008-08-15

    The new materials BaCu{sub {delta}}Ag{sub 2-{delta}}Te{sub 2} (0{<=}{delta}{<=}2) were prepared from the elements at 800 deg. C in evacuated silica tubes. BaAg{sub 2}Te{sub 2} crystallizes in the {alpha}-BaCu{sub 2}S{sub 2} type, space group Pnma, with lattice parameters a=10.8897(3) A, b=4.6084(1) A, c=11.8134(3) A (Z=4). The structure consists of a three-dimensional network of vertex- and edge-condensed AgTe{sub 4} tetrahedra, which includes the Ba{sup 2+} cations in linear channels running along the short b-axis. Half of the Ag atoms participate in an Ag atom zigzag chain extended parallel to the channels. BaAg{sub 2}Te{sub 2} is a p-type semiconductor with large Seebeck coefficient. Within the series BaCu{sub {delta}}Ag{sub 2-{delta}}Te{sub 2}, the electrical conductivity increases and the Seebeck coefficient decreases strongly with increasing Cu content. - Graphical abstract: The tellurides BaCu{sub {delta}}Ag{sub 2-{delta}}Te{sub 2} all crystallize in the {alpha}-BaCu{sub 2}S{sub 2} type. The Ag atoms prefer the M2 sites with short M-M bonds (solid lines). The materials are (degenerate) p-type semiconductors. Higher Ag content reflects itself in higher Seebeck coefficient and lower electrical conductivity.

  1. Microstructure development in Al-Cu-Ag-Mg quaternary alloy

    NASA Astrophysics Data System (ADS)

    Zhou, Bin; Froyen, L.

    2012-01-01

    The solidification behaviour of multi-component and multi-phase systems has been largely investigated in binary and ternary alloys. In the present study, a quaternary model system is proposed based on the well known Al-Cu-Ag and Al-Cu-Mg ternary eutectic alloys. The quaternary eutectic composition and temperature were determined by EDS (Energy Dispersive Spectrometry) and DSC (Differential Scanning Calorimetry) analysis, respectively. The microstructure was then characterised by SEM (Scanning Electron Microscope). In the DSC experiments, two types of quaternary eutectics were determined according to their phase composition. For each type of eutectic, various microstructures were observed, which result in different eutectic compositions. Only one of the determined eutectic compositions was further studied by the controlled growth technique in a vertical Bridgeman type furnace. In the initial part of the directionally solidified sample, competing growth between two-phase dendrites and three-phase eutectics was obtained, which was later transformed to competing growth between three-phase and four-phase eutectics. Moreover, silver enrichment was measured at the solidification front, which is possibly caused by Ag sedimentation due to gravity and Ag rejection from dendritic and three-phase eutectic growth, and its accumulation at the solidification front.

  2. 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).

  3. Synthesis of Ca-substituted Y1-xCaxBa2Cu4O8 at ambient pressure using CuI

    NASA Astrophysics Data System (ADS)

    Zheng, X. G.; Suzuki, M.; Xu, C.; Kuriyaki, H.; Hirakawa, K.

    1996-02-01

    Ca-substituted Y124 superconductors Y 1- xCa xBa 2Cu 4O 8 ( x = 0.05, 0.1) were synthesized at ambient oxygen pressure by a solid-state reaction method which used CuI instead of the conventional CuO. Experimental results showed a promoting effect of copper iodide on the formation of the 124 phase at normal oxygen pressure. Tc determined from the Meissner effect was 88 K for x = 0.05 and 90 K for x = 0.1. For the same Ca-substitution rates Tc(zero-resistance) of 80.5 K and 82.0 K was obtained respectively.

  4. 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.

  5. A propos de la ferroeléctricité dans BaAl 2O 4

    NASA Astrophysics Data System (ADS)

    Huang, Sui-Yang; Von Der Mühll, Régnault; Ravez, Jean; Chaminade, Jean Pierre; Hagenmuller, Paul; Couzi, Michel

    1994-03-01

    Structural, ferroelectric, pyroelectric, and optical properties of ceramics and crystals of BaAl 2O 4 have been investigated. A refinement of the atomic positions has been carried out from the X-ray powder data. BaAl 2O 4 shows anomalous behavior of the dielectric and pyroelectric properties: the dielectric constant ɛ 'r is very weak; its maximal value at Curie temperature for a crystal oriented along the hexagonal c-axis is about 15 and that of a ceramic of compactness 0.89 is around 7.5. The Curie-Weiss constant is relatively weak ( C = 125). The behavior of the spontaneous polarization Ps is unexpected with respect to that of classical ferroelectric materials: Ps increases with decreasing temperature from Tc and decreases again after having reached a maximum at 200 K. A model based on ferrielectric behavior and supported by the Landau equation has been proposed. La structure et les propriétés ferroélectriques, pyroélectriques et optiques de céramiques et de cristaux du composé BaAl 2O 4 ont été étudiées. Un affinement des positions atomiques a été entrepris à partir du spectre de diffraction X sur poudre. BaAl 2O 4 présente un comportement anormal des propriétés diélectriques et pyroélectriques: la constante diélectrique ɛ' r est faible, sa valeur maximale à Tc est voisine de 15 pour les cristaux et de 7,5 pour des céramiques de compacité 0,89. La constante de Curie est aussi relativement faible ( C = 125). Le comportement de la polarisation spontaneé Ps diffère de celui des matériaux ferroélectriques "classiques": Ps augmente lorsque T décroı̂t en-dessous de Tc pour atteindre un maximum à T = 200 K suivi d'une décroissance. Un modèle de comportement ferriélectrique s'appuyant sur la relation de Landau pourrait justifier les propriétés observées.

  6. Characterization and Electrical Properties of Al-Doped Cu(In,Ga)Se2 Semiconductors with Various Cu Contents

    NASA Astrophysics Data System (ADS)

    Monsefi, Mehrdad; Kuo, Dong-Hau

    2014-04-01

    Cu(In,Ga)Se2 (CIGSe) semiconductor, which shows record photovoltaic conversion efficiencies near 20%, has become a leading material for thin-film solar cell applications. In this work, Al-doped CIGSe (Al-CIGSe) bulk material with different Cu contents has been prepared by a liquid-phase reactive sintering method at 650°C. Sintering of the Al-CIGSe bulk material has been carried out in the presence of Sb2S3 and Te. The bulk Cu x [(In0.6Al0.1)Ga0.3]Se2 semiconductor was n-type for x = 0.7 and p-type for higher Cu content. The defect chemistry of Al-CIGSe was studied by measuring the electrical properties as a function of copper content. The changes in the conductivity type and carrier concentration were related to defect states involving Cu vacancy and antisite defects of In Cu 2+ and Cu B 2 - in a Cu B IIISe2-type phase. The lattice parameters were in good agreement with other evidence for the existence of different defect states.

  7. Vanishing quasiparticle density in a hybrid Al/Cu/Al single-electron transistor

    NASA Astrophysics Data System (ADS)

    Saira, O.-P.; Kemppinen, A.; Maisi, V. F.; Pekola, J. P.

    2012-01-01

    The achievable fidelity of many nanoelectronic devices based on superconducting aluminum is limited by either the density of residual nonequilibrium quasiparticles nqp or the density of quasiparticle states in the gap, characterized by Dynes parameter γ. We infer upper bounds nqp<0.033μm-3 and γ<1.6×10-7 from transport measurements performed on Al/Cu/Al single-electron transistors, improving previous results by an order of magnitude. Owing to efficient microwave shielding and quasiparticle relaxation, a typical number of quasiparticles in the superconducting leads is zero.

  8. New insights into the application of the valence rules in Zintl phases—Crystal and electronic structures of Ba{sub 7}Ga{sub 4}P{sub 9}, Ba{sub 7}Ga{sub 4}As{sub 9}, Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 6}CaAl{sub 4}Sb{sub 9}, and Ba{sub 6}CaGa{sub 4}Sb{sub 9}

    SciTech Connect

    He, Hua; Stoyko, Stanislav; Bobev, Svilen

    2016-04-15

    Crystals of three new ternary pnictides—Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 7}Ga{sub 4}P{sub 9}, and Ba{sub 7}Ga{sub 4}As{sub 9} 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 Ba{sub 7}Ga{sub 4}Sb{sub 9}-type structure (space group Pmmn, Pearson symbol oP40, Z=2), for which only the prototype is known. The structure is based on TrPn{sub 4} tetrahedra (Tr=Al, Ga; Pn=P, As, Sb), connected in an intricate scheme into 1D-ribbons. Long interchain Pn–Pn bonds (d{sub P–P}>3.0 Å; d{sub As–As}>3.1 Å; d{sub Sb–Sb}>3.3 Å) account for the realization of 2D-layers, separated by Ba{sup 2+} cations. Applying the classic valance rules to rationalize the bonding apparently fails, and Ba{sub 7}Ga{sub 4}Sb{sub 9} 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 Ba{sub 6}CaTr{sub 4}Sb{sub 9} (Tr=Al, Ga). Single-crystal X-ray diffraction work confirms Ba{sub 6.145(3)}Ca{sub 0.855}Al{sub 4}Sb{sub 9} and Ba{sub 6.235(3)}Ca{sub 0.765}Ga{sub 4}Sb{sub 9}, 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 Ba{sub 7}Ga{sub 4}As{sub 9} is interrogated by tight-binding linear muffin-tin orbital calculations. - Graphical abstract: The new Zintl phases—Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 7}Ga{sub 4}P{sub 9}, and Ba{sub 7}Ga{sub 4}As{sub 9}, and their quaternary variants Ba{sub 6}CaTr{sub 4}Sb{sub 9} (Tr=Al, Ga)—crystallize in the Ba{sub 7}Ga{sub 4}Sb{sub 9} structure type. The structures are based

  9. Structural phase transitions and the effect on Pr anomalous ordering for the PrBa 2- xLa xCu 3O 7+ y system

    NASA Astrophysics Data System (ADS)

    Ku, H. C.; Luo, H. M.; Chi, Y. P.; Lin, B. N.; Hsu, Y. Y.; Lin, C. H.; Kao, H.-C. I.

    2000-06-01

    Complex crystal symmetry variation is observed for the oxygenated PrBa 2- xLa xCu 3O 7+ y system (0⩽ x⩽1, -0.12⩽ y⩽0.39). Powder X-ray Rietveld analysis indicates that the crystal structure changes from the PrBa 2Cu 3O 7 or CuBa 2PrCu 2O 7 1212C-type (C for chain) orthorhombic O(I)-phase (space group Pmmm) to 1212-type tetragonal T-phase (P4/mmm) around x=0.45, and then to a new 1212-type of orthorhombic O(II)-phase (Cmmm) around x=0.65. However, regardless of the structural change, anomalous Pr ordering temperature TN(Pr) decreases monotonically from 18 K for PrBa 2Cu 3O 6.88 to 2.8 K for PrBa 1.3La 0.7Cu 3O 7.24. The increasing Pr-O bond length with decreasing TN indicates that Pr ordering is closely correlated with the wave function overlap between Pr-4f orbital and O-2p π orbital in the CuO 2 bi-layers.

  10. Temperature and Frequency Dependent Dielectric Properties of Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ Bulk Superconductor

    NASA Astrophysics Data System (ADS)

    Rahim, M.; Khan, Nawazish A.; Mumtaz, M.

    2013-07-01

    The temperature and frequency dependent dielectric properties of polycrystalline Cd-doped Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ ( y=0,0.25,0.5,0.75) bulk superconductor samples are investigated. The zero resistivity critical temperature { T c( R=0)} has decreased and normal state resistivity has increased with the increase of Cd-doping in Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ samples. The dielectric properties such as dielectric constants ( ɛ', ɛ″), dielectric loss tangent (tan δ) and ac-conductivity ( σ ac ) are investigated by measuring the capacitance (C) and conductance (G) in the frequency range of 10 KHz to 10 MHz at different temperature from 80 K to 300 K. The negative capacitance (NC) is observed in all Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ samples. The large values of NC observed at lower frequencies and temperatures may be due to reduced thermal vibrations and enhanced polarizability of the material. The effect of Cd-doping on bulk properties, dc-resistivity ( ρ) and ac-electrical conductivity ( σ ac ) of these superconductor samples are investigated. The polarization in Cu0.5Tl0.5Ba2Ca3(Cu4- y Cd y )O12- δ samples is most likely arising from the displacement of charges in CuO2/CdO2 planes relative to the static charges at Ba2+, Tl3+, and Cu2+ sites in Cu0.5Tl0.5Ba2O4- δ charge reservoir layers by external applied field.

  11. Evaluation of intermediate phases formed on the bonding interface of hot pressed Cu/Al clad materials

    NASA Astrophysics Data System (ADS)

    Lee, Kwang Seok; Lee, Sangmok; Lee, Jong-Sup; Kim, Yong-Bae; Lee, Geun-An; Lee, Sang-Pill; Bae, Dong-Su

    2016-09-01

    The aim of the present study is to identify the properties of intermediate phases formed on the bonding interface of hot pressed Cu/Al clad materials by transmission electron microscopy and nano-indentation analyses. Cu/Al clad materials were fabricated by hot pressing under 200 MPa at 250 °C for 1 h and then heat treated at 400 °C for 1 h. Nano-indentation measurement was conducted to evaluate the nanohardness and modulus of the intermediate phases formed between the Cu/Al interfaces. A 3-tier diffusion layer was observed at the Cu/Al interfaces. Knoop microhardness values at the bonding interface were 7 to 11 times that of the Cu and Al matrix metals. The intermediate phases formed at the bonding interface were Al4Cu9, AlCu, and Al2Cu. A mapping analysis confirmed that the Al and Cu particles moved via mutual diffusion toward the intermediate phases formed at the bonding interface. The nanohardness values of η2-AlCu and γ1-Al4Cu9 were 4 to 7 times that of the Cu and Al matrix metals. Nanohardness and Knoop microhardness measurement curves exhibited similar tendencies. The rigidity values of the respective intermediate phases can be arranged in descending order as follows: γ1-Al4Cu9 > η2-AlCu > θ-Al2Cu.

  12. 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)

  13. Diffusion Brazing of Al6061/15 Vol. Pct Al2O3p Using a Cu-Sn Interlayer

    NASA Astrophysics Data System (ADS)

    Cooke, Kavian O.; Khan, Tahir I.; Oliver, Gossett D.

    2013-06-01

    Diffusion brazing of Al-6061 alloy containing 15 vol. pct Al2O3 particles was attempted using Cu-Sn interlayer. Joint formation was attributed to the solid-state interdiffusion of Cu and Sn followed by eutectic formation and subsequent isothermal solidification. Examination of the joint region using scanning electron microprobe analyzer (EPMA), wavelength dispersive spectroscopy (WDS) and X-ray diffraction (XRD) showed the formation of intermetallic phases such as Al7Cu3Mg3, Mg2Cu6Al5, Cu3Sn, and Mg2Sn. The results indicated an increase in joint strength with increasing bonding time giving the highest joint shear strength of 94 MPa at a bonding duration of 3 hours.

  14. 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-SiO2, has a density of 3.39 g/cu cm, a thermal expansion coefficient of 6.6 x 10 to the -6th/C, a glass-transition temperature of 910 C, and a 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 have been studied. CIP'd samples, after appropriate heat treatments, always crystallized out as celsian, whereas presence of 5-10 wt pct 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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}.

  19. Physical properties of CuAlO 2 single crystal

    NASA Astrophysics Data System (ADS)

    Brahimi, R.; Bellal, B.; Bessekhouad, Y.; Bouguelia, A.; Trari, M.

    2008-09-01

    CuAlO 2 single crystal elaborated by the flux method is a narrow band gap semiconductor crystallizing in the delafossite structure (SG R3¯m). Oxygen insertion in the layered lattice generates p-type conductivity where most holes are trapped in surface-polaron states. The detailed photoelectrochemical characterization and electrochemical impedance spectroscopy (EIS) have been reported for the first time on the single crystal. The study is confined in the basal plan and reversible oxygen insertion is evidenced from the intensity potential characteristics. The oxide is characterized by an excellent chemical stability; the semi-logarithmic plot gave a corrosion potential of-0.82 V SCE and an exchange current density of 0.022 μA cm -2 in KCl (0.5 M) electrolyte. The capacitance measurement ( C-2- V) shows a linear behavior from which a flat band potential of +0.42 V SCE and a doping density NA of 10 16 cm -3 have been determined. The valence band, located at 5.24 eV (0.51 V SCE) below vacuum, is made up of Cu-3d orbital. The Nyquist plot exhibits a pseudo-semicircle whose center is localized below the real axis with an angle of 20°. This can be attributed to a single relaxation time of the electrical equivalent circuit and a constant phase element (CPE). The absence of straight line indicates that the process is under kinetic control.

  20. First-principles study of Al-Cu energetics and consequences on athermal formation of Cu-rich compounds

    NASA Astrophysics Data System (ADS)

    Besson, R.; Kwon, J.; Thuinet, L.; Avettand-Fènoël, M.-N.; Legris, A.

    2014-12-01

    In spite of its practical interest, the Al-Cu system remains largely unexplored, especially on its Cu-rich side. In order to improve the knowledge of this system, we perform a thorough ab initio study of fcc-based Al-Cu energetics, using the recently proposed M2BCE reciprocal-space cluster expansion approach. We demonstrate the existence of two clearly distinct composition domains, revealing complex ground-state properties. Below 50% Cu, the GP 2 -A l3Cu compound appears as highly favored, in agreement with the well-documented transformation sequence in Al-based alloys. Conversely, the domain between 50% and 80% Cu displays a much shallower landscape, characterized by the existence of a wealth of compounds undergoing fcc →bcc structural instabilities. While such "Bain paths" have been identified for a long time in iron-based alloys, our work gives evidence for their existence in the Al-Cu system. As a striking application, these instabilities provide plausible athermal mechanisms for the formation of Cu-rich phases, in particular for the unexpected emergence of γ1-A l4C u9 , a Hume-Rothery compound observed in various nonequilibrium conditions.

  1. Characterization of Y2BaCuO5 nanoparticles synthesized by nano-emulsion method

    NASA Astrophysics Data System (ADS)

    Li, Fang; Vipulanandan, Cumaraswamy

    2007-10-01

    Nanoscale yttrium-barium-copper oxide (Y2BaCuO5, Y211) particles were synthesized using the emulsion method and the solution method. The basic water-in-oil (w/o) emulsion system consisted of n-octane (continuous oil phase), cetyltrimethylammonium bromide (cationic surfactant), butanol (cosurfactant) and water. The composition of the emulsion system was varied and characterized by measuring the conductivity of the solutions and droplet size. The droplet size of emulsion was determined by using the dynamic light scattering method. The water content, cosurfactant content, and surfactant/ n-octane ratio affected the droplet size which was in the range of 3-8 nm, and hence the w/o emulsion system was referred to as a nano-emulsion system. A model was used to verify the droplet size. The influence of salt (Y2(NO3)3) content on the droplet size was investigated and the addition of salt reduced the droplet size. The effects of reaction time and temperature on the Y211 particle sizes were also investigated. The particles were characterized using the TEM, SEM, and XRD. Nanoparticles produced by the nano-emulsion method were calcined at 850°C to form the Y211 phase as compared to solid state processing temperature of 1050°C. Based on the TEM analysis, the average diameter of the Y211 particles produced using the nano-emulsion method was in the range of 30-100 nm. The effect of adding 15% Y211 nanoparticles to the superconductor YBCO-123 as flux pinning centers, was investigated, and the transition temperature was reduced by 3 K.

  2. Fracture toughness of an Al-Li-Cu-In alloy

    NASA Technical Reports Server (NTRS)

    Wagner, John A.; Gangloff, Richard P.

    1992-01-01

    The crack initiation and growth fracture toughness of select AL-Li-Cu alloy variants are characterized and elucidated. Conventionally processed plates form large DC cast ingots are investigated to eliminate the variation in microstructure associated with laboratory scale and SPF-processed material. Fracture resistance is characterized using the J-integral method to establish crack initiation and growth behavior at 25 and -185 C. It is shown that state-of-the-art 2090-T81 has superior toughness compared to 2090 + In-T6 at both test temperatures, with the low toughness of 2090 + In-T6 associated with intersubgranular fracture attributed to a high density of subboundary precipitates.

  3. 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.

  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. 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.

  6. 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.

  7. 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.

  8. The crystal chemistry of the alkaline-earth apatites A(10)(PO(4))(6)Cu(x)O(y)(H)(z) (A = Ca, Sr and Ba).

    PubMed

    Baikie, Tom; Ng, George M H; Madhavi, S; Pramana, Stevin S; Blake, Kevin; Elcombe, Margaret; White, T J

    2009-09-14

    The crystal chemistry of the cuprate apatites A(I)(4)A(II)(6)(PO(4))(6)Cu(x)O(y)(H)(z) (A = Ca, Sr and Ba) was investigated by powder X-ray (PXRD) and neutron diffraction (PND) and X-ray photoelectron spectroscopy (XPS). The refined crystal structures confirmed earlier X-ray diffraction studies that showed copper resides in the apatite channels and additionally, located hydrogen. For all materials copper is primarily divalent (Cu(2+)) but in the calcium and strontium analogues co-exists with minor Cu(3+). This is in contrast with a previous work where Cu(1+) and Cu(2+) were reported.

  9. A practical route for the fabrication of large single-crystal (RE)-Ba-Cu-O superconductors.

    PubMed

    Babu, Nadendla Hari; Shi, Yunhua; Iida, Kazumasa; Cardwell, David A

    2005-06-01

    Single-crystal superconductors of the general formula (LRE)-Ba-Cu-O (light rare earth, LRE = Nd, Sm, Eu and Gd) have considerable potential for engineering applications because of their ability to trap magnetic fields significantly higher than those achievable with permanent magnets. But the lack of a process by which these materials can be fabricated reliably and economically in the form of large single grains has severely hindered their development. We report a practical processing method for the fabrication in air of single-crystal (RE)BCO. The technique is economical and offers considerable freedom in terms of the processing parameters and reproducibility in growth of oriented single grains. The process is based primarily on the development of a new type of generic seed crystal that can effectively promote the epitaxial nucleation of any (RE)BCO system, and secondly on suppressing the formation of RE-Ba solid solution in a controlled manner within large grains processed in air.

  10. Structural and electronic properties of CuI doped with Zn, Ga and Al

    NASA Astrophysics Data System (ADS)

    Zhu, Jiajie; Gu, Mu; Pandey, Ravindra

    2013-08-01

    The structural and electronic properties of CuI doped with Zn, Ga and Al are investigated using density functional theory. The calculated results find that the solubility of the cation dopants considered is primarily determined by the difference in the electronic configurations between host and dopants. The order of the formation energy of the dopants is predicted to be E(ZnCu)>E(AlCu)>E(GaCu) in CuI. Furthermore, dopants at the octahedral interstitial sites have lower formation energies as compared to dopants located at the tetrahedral interstitial sites in the lattice. The defect complex consisting of ZnCu and the copper vacancy (ZnCu+VCu) is predicted to be preferred in the lattice, suggesting that incorporation of Zn is expected to enhance the concentration of copper vacancies in CuI.

  11. 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

  12. 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.

  13. 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.

  14. The Low-Lying States of AlCu and AlAg

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    The singlet and triplet states of AlCu and AlAg below about 32 000/cm are studied using the internally contracted multireference configuration-interaction method. A more elaborate study of the X(sup 1)Sum(sup +) ground state of AlCu is undertaken using extended Gaussian basis sets, including the effect of inner-shell correlation and including a perturbational estimate of relativistic effects. Our best estimate of the spectroscopic constants (r(sub 0), DeltaG(sub 1/2), and D(sub 0)) for the X(sup 1)Sum(sup+) state with the experimental values in parentheses are: 4.416(4.420) a(sub 0), 295 (294) /cm, and 2.318 (2.315) eV. The calculations definitively assign the upper state in the observed transition at 14 892/cm to the lowest (sup 1)Prod state. The calculated spectroscopic constants and radiative lifetime for the (sup 1)Prod state are in good agreement with experiment. The calculations support the tentative assignments of Behm et al. for three band systems observed in the visible region between 25 000 and 28 000 / cm. However, the computed spectroscopic constants are in very poor agreement with those deduced from an analysis of the spectra. Analogous theoretical results for AlAg suggest that the (2)(sup 3)Prod, (3)(sup 3)Prod, and (3)(sup 1)Sum(sup +) states account for the bands observed, but not assigned, by Duncan and co-workers.

  15. Effects of selective lattice deformation on YbBa2Cu4O8 and YBa2Cu3O7 epitaxial films

    NASA Astrophysics Data System (ADS)

    Mito, M.; Matsui, H.; Imakyurei, T.; Deguchi, H.; Horide, T.; Matsumoto, K.; Ichinose, A.; Yoshida, Y.

    2014-03-01

    Alternating current magnetic measurements of YbBa2Cu4O8 (Yb-124) and YBa2Cu3O7 (Y-123) epitaxial films were performed under hydrostatic pressure (HP). Here, the strain under HP results in uniaxial strain along the c-axis, in addition to the biaxial strain due to mismatching with the substrate. This uniaxial effect on Yb-124 film brings about a prominent increase in the superconducting transition temperature (Tc) against the initial strain. However, a nearly optimal Y-123 film hardly exhibits an initial change in Tc, and even an underdoped one only exhibits an increase in Tc, that is, one-third as much as that in the Yb-124 film. Effective carrier doping by the use of effective out-of-plane contraction prominently appears in the 124-structure rather than in the 123-structure.

  16. Effects of processing variables on the Y2BaCuO5 size and magnetic properties of melt-processed YBa2Cu3Ox

    NASA Astrophysics Data System (ADS)

    Yang, H. F.; Varanasi, C.; Ginn, P. J. M. C.

    1995-12-01

    Samples of YBa2Cu3Ox (123) with excess Y2BaCuO5 (211) in the molar ratio of 5:1 ( 123/211) were processed using the “solid liquid melt growth” (SLMG) technique. The effect of hold time above the peritectic on the magnetic properties was examined. Extended hold times above the peritectic during processing degrade the magnetic properties of SLMG processed 123. In SLMG 123, the very fine (>100 nm) 211 particles produced by this processing route are the primarymagnetic flux pinners. Extended hold periods reduce the number and/or coarsen the average size of these fine precipitates, resulting in a reduced magnetization. These results were compared to undoped Y123 processed by the more traditional melt texture growth (MTG). In MTG processing, extended hold times above the peritectic are found to result in improved magnetic behavior because of increased defect densities.

  17. Preparation of Al-Cu-Fe-(Sn,Si) quasicrystalline bulks by laser multilayer cladding

    NASA Astrophysics Data System (ADS)

    Feng, Li-ping; Fleury, Eric; Zhang, Guo-sheng

    2012-05-01

    (Al65Cu20Fe15)100- x Sn x ( x=0, 12, 20, 30) and Al57Si10Cu18Fe15 powders were cladded on a medium carbon steel (45# steel) substrate by laser multilayer cladding, respectively. The phases and properties of the produced quasicrystalline bulks were investigated. It was found that the main phases in the Al65Cu20Fe15 sample were crystalline λ-Al13Fe4 and icosahedral quasicrystal together with a small volume fraction of θ-Al2Cu phase. The volume fraction of icosahedral phase decreased as the Sn content in the (Al65Cu20Fe15)100- x Sn x samples increased owing to the formation of β-CuSn phase. The increase of Sn content improved the brittleness of the quasicrystal samples. The morphology of the solidification microstructure in the Al57Si10Cu18Fe15 sample changed from elongated shape to spherical shape due to the addition of Si. The nanohardness of the laser multilayer cladded quasicrystal samples was equal to that of the as-cast sample prepared by vacuum quenching. In terms of hardness, the laser cladded Al57Si10Cu18Fe15 quasicrystalline alloy has the highest value among all the investigated samples.

  18. 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.

  19. 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.

  20. Anisotropy and hysteresis of transport critical currents in high temperature Ln-Y-Ba-Cu-O superconductors

    NASA Astrophysics Data System (ADS)

    Watanabe, K.; Noto, K.; Morita, H.; Fujimori, H.; Mizuno, K.; Aomine, T.; Ni, B.; Matsushita, T.; Yamafuji, K.; Muto, Y.

    1989-03-01

    Following the measurements of anisotropy and hysteresis in transport critical currents with changing temperature and polarity of magnetic field, a.c. magnetic measurements by the Campbell method were performed for sintered Ln-Y-Ba-Cu-O superconductors. The information derived from them indicated that hysteresis does not occur in the intragrain current but in the intergrain one. The results are interpreted in terms of flux pinning, where the anisotropy originates from the texture structure and hysteresis is associated with the superconducting weak links of the sintered oxide pellets.

  1. 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.

  2. Neutron Diffraction Study of Nonstoichiometry in Ba1.5La1.5Cu3Oy

    NASA Astrophysics Data System (ADS)

    Izumi, Fujio; Takayama-Muromachi, Eiji; Kobayashi, Michiko; Uchida, Yoshishige; Asano, Hajime; Ishigaki, Tōru; Watanabe, Noboru

    1988-05-01

    The structure parameters of annealed and quenched samples of Ba1.5La1.5Cu3Oy were refined by the Rietveld analysis of TOF neutron powder diffraction data. Partial occupation of an oxygen site at (0, 1/2, 0) causes nonstoichiometry in the oxide. The y values calculated from the occupation factors of oxygen at this site are 7.20 (annealed) and 6.76 (quenched), which are in fair agreement with those determined by iodometry: 7.15 (annealed) and 6.74 (quenched).

  3. 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.

  4. Electronic structure of Ba3CuSb2O9: A candidate quantum spin liquid compound

    NASA Astrophysics Data System (ADS)

    Shanavas, K. V.; Popović, Z. S.; Satpathy, S.

    2014-02-01

    Using density-functional methods, we study the electronic structure of Ba3CuSb2O9, a candidate material for the quantum spin liquid behavior. We study both the triangular lattice as well as the recently proposed hexagonal lattice structures with flipped Cu-Sb dumbbells. The band structure near the Fermi energy is described very well by a tight-binding Hamiltonian involving the Cu (eg) orbitals, confirming their central role in the physics of the problem. A minimal tight-binding Hamiltonian for the triangular structure is presented. The Cu (d9) ions (a single eg hole in the band structure) present in the compound are expected to be Jahn-Teller centers, while the nature of the Jahn-Teller distortions in this material is still under debate. Solving a simple model by exact diagonalization, we show that electronic correlation effects in general enhance the tendency towards a Jahn-Teller distortion by reducing the kinetic energy due to correlation effects. Our density-functional calculations do indeed show a significant Jahn-Teller distortion of the CuO6 octahedra when we include the correlation effects within the Coulomb-corrected GGA+U method, so that the Jahn-Teller effect is correlation driven. We argue for the presence of a random static Jahn-Teller distortion in the hexagonal structure rather than a dynamical one because of the broken octahedral symmetry around the CuO6 octahedra and the potential fluctuations inherently present in the system caused by a significant disorder, which is believed to be present, in particular, due to the flipped Cu-Sb dumbbells.

  5. Friction Stir Welding of Al-Cu Bilayer Sheet by Tapered Threaded Pin: Microstructure, Material Flow, and Fracture Behavior

    NASA Astrophysics Data System (ADS)

    Beygi, R.; Kazeminezhad, M.; Kokabi, A. H.; Loureiro, A.

    2015-06-01

    The fracture behavior and intermetallic formation are investigated after friction stir welding of Al-Cu bilayer sheets performed by tapered threaded pin. To do so, temperature, axial load, and torque measurements during welding, and also SEM and XRD analyses and tensile tests on the welds are carried out. These observations show that during welding from Cu side, higher axial load and temperature lead to formation of different kinds of Al-Cu intermetallics such as Al2Cu, AlCu, and Al4Cu9. Also, existence of Al(Cu)-Al2Cu eutectic structures, demonstrates liquation during welding. The presence of these intermetallics leads to highly brittle fracture and low strength of the joints. In samples welded from Al side, lower axial load and temperature are developed during welding and no intermetallic compound is observed which results in higher strength and ductility of the joints in comparison with those welded from Cu side.

  6. Plasmon-exciton couplings in Al-CuCl nanoshells and the effects of oxidation

    NASA Astrophysics Data System (ADS)

    Yao, Jie; Ji, WenQian; Wu, DaJian; Cheng, Ying; Liu, XiaoJun

    2017-04-01

    The plasmon-exciton couplings in the Al-CuCl nanoshells have been investigated by using the Mie scattering theory. It is found that the bright dipole mode of the Al nanosphere can couple well with the exciton mode of the outer CuCl shell in the UV region by changing the geometry. The strong plasmon-exciton couplings in the Al-CuCl nanoshell lead to two hybrid plexcitonic modes and hence the Rabi splitting. We study the dispersion curves of the plexcitonic modes of the Al-CuCl nanoshells and obtain the splitting energy of about 135 meV. Furthermore, the influences of the metal oxide on the plasmon-exciton couplings in the Al-CuCl nanoshells have been studied. It is found that the Rabi splitting energy will shrink with the oxide.

  7. Three-dimensional characterization of BaHfO3 precipitates in GdBa2Cu3O7-y flim using STEM tomography.

    PubMed

    Nishiyama, T; Kaneko, K; Yamada, K; Teranishi, R; Kato, T; Hirayama, T; Tobita, H; Izumi, T; Shiohara, Y

    2014-11-01

    IntroductionSince the discovery of REBa2Cu3O7-y (RE: Rare Earth element, REBCO) superconductors, they have been expected as the best candidates for the power cable application due to its high critical temperature (Tc) and critical current density (Jc). Among those REBCO superconductors, GdBa2Cu3O7-y (GdBCO) have been receiving great interest because they have higher Tc and Jc than YBa2Cu3O7-y [1].GdBCO with various types of precipitates as artificial pinning centers (APCs) have been proposed to minimize the anisotropy of Jc characteristics under the magnetic field. Among those precipitates, BaHfO3 (BHO) was found most effective precipitates as APCs in GdBCO film prepared by pulsed laser deposition (PLD) method [2]. It is therefore necessary to investigate not only the morphologies but also the dispersion of BHO precipitates within the GdBCO, to understand the role of BHO for the superconducting characteristics. In this study, morphologies and dispersions of BHO precipitates were characterized three-dimensional by scanning transmission electron tomography ExperimentalBHO dispersed GdBCO films were fabricated on Hastelloy C-276TM substrates with buffer layers of CeO2/LaMnO3/MgO/ Gd2ZrO7 by PLD method.To observe microstructure of GdBCO film with BHO precipitates, cross-section TEM specimens were prepared by FIB method using Quanta 3D-200 (FEI, USA) with acceleration voltage from 2 to 30 kV. Three-dimensional information such as morphology and dispersion, of BHO precipitates were characterized by electron tomography using STEM-HAADF. Result and discussionFigure 1 shows three-dimensional reconstructed volume of BHO precipitates in GdBCO, which revealed that fine BHO precipitates have rod- and plate-like morphologies with homogeneous dispersion in GdBCO. In addition, growth directions of these precipitates were found with wide angular distributions from growth direction of GdBCO. Anisotropy of Jc in the magnetic fields was probably enhanced by various growth directions

  8. 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.

  9. 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.

  10. Ultraslow fluctuations in the pseudogap states of HgBa2CaCu2O6 +δ

    NASA Astrophysics Data System (ADS)

    Itoh, Yutaka; Machi, Takato; Yamamoto, Ayako

    2017-03-01

    We report the transverse relaxation rates 1 /T2 's of the 63Cu nuclear spin-echo envelope for double-layer high-Tc cuprate superconductors HgBa2CaCu2O6 +δ from underdoped to overdoped. The relaxation rate 1 /T2 L of the exponential function (Lorentzian component) shows a peak at 220 -240 K in the underdoped (Tc=103 K) and the optimally doped (Tc=127 K) samples but no peak in the overdoped (Tc=93 K) sample. The enhancement in 1 /T2 L suggests a development of the zero frequency components of local field fluctuations. Ultraslow fluctuations are hidden in the pseudogap states.

  11. Synthesis and characterization of the new two-dimensional Heisenberg antiferromagnet double perovskite BaLaCuSbO6.

    PubMed

    Blanco, M Cecilia; Paz, Sergio Alexis; Nassif, Vivian M; Guimpel, Julio J; Carbonio, Raúl E

    2015-06-21

    The BaLaCuSbO(6) double perovskite has been successfully synthesized by solid state reaction under an air atmosphere. Its structure was refined using powder neutron diffraction in the monoclinic space group I2/m with a 4% antisite disorder on the B cations. Magnetic measurements give signs of 2D-antiferromagnetic behaviour with TN around 64 K. The Jahn-Teller distortion produced by Cu(2+) ions favours a crystallographic tetragonal distortion and consequently the in-plane super-superexchange antiferromagnetic interactions, J(90°), are favoured over the in-plane J(180°) antiferromagnetic exchange interactions. Both, J and J' magnetic interactions have been evaluated according to a Heisenberg antiferromagnetic rectangular model using an approximation to Curie's law in powers of J/T, being |J| around 10 times stronger than |J'|.

  12. Remarkable Stability of Charge Density Wave Order in La_{1.875}Ba_{0.125}CuO_{4}.

    PubMed

    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

    2016-10-14

    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 La_{1.825}Ba_{0.125}CuO_{4} by using x-ray photon correlation spectroscopy at the CDW wave vector, detected resonantly at the Cu L_{3} 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.

  13. Remarkable Stability of Charge Density Wave Order in La1.875Ba0.125CuO4

    DOE PAGES

    Chen, X. M.; Thampy, V.; Mazzoli, C.; ...

    2016-10-11

    The occurrence of charge-density-wave (CDW) order in underdoped cuprates is now well established, although the precise nature of the CDW and its relationship with superconductivity is not. Theoretical proposals include contrasting ideas such as that pairing may be driven by CDW uctuations or that static CDWs may intertwine with a spatially-modulated superconducting wave function. We test the dynamics of CDW order in La1.875Ba0.125CuO4 by using x-ray photon correlation spectroscopy (XPCS) at the CDW wave vector, detected resonantly at the Cu L3-edge. We nd that the CDW domains are strikingly static, with no evidence of signi cant uctuations up to 2more » 3/4 hours. We discuss the implications of these results for some of the competing theories.« less

  14. Millimeter wave surface resistance of grain-aligned Y1Ba2Cu3O(x) bulk material

    NASA Technical Reports Server (NTRS)

    Wosik, J.; Kranenburg, R. A.; Wolfe, J. C.; Selvamanickam, V.; Salama, K.

    1990-01-01

    Measurements are reported of the millimeter-wave surface resistance of grain-aligned YBa2Cu3O(x) bulk material grown by a liquid-phase process. The measurements were performed by replacing the endplate of a TE(011) cylindrical copper cavity with the superconducting sample. Surface resistance was measured for samples with surfaces oriented perpendicular and parallel to the c-axis of the grains. For the parallel configuration, the surface resistance at 77 K and 80 GHz is given. For a very well-aligned sample with a very low density of Y2BaCuO(y) precipitates, measured in the perpendicular configuration, the transition width (10-90 percent) is about 2 K and the surface resistance is derived at 88 K. The effect of microstructure on surface resistance is discussed.

  15. Millimeter wave surface resistance of grain-aligned Y1Ba2Cu3O(x) bulk material

    NASA Technical Reports Server (NTRS)

    Wosik, J.; Kranenburg, R. A.; Wolfe, J. C.; Selvamanickam, V.; Salama, K.

    1991-01-01

    Measurements of the millimeter wave surface resistance of grain-aligned YBa2Cu3O(x) bulk material grown by a liquid phase process are reported. The measurements were performed by replacing the endplate of a TE011 cylindrical copper cavity with the superconducting sample. Surface resistance was measured for samples with surfaces oriented perpendicular and parallel to the c-axis of the grains. It is shown that, for the parallel configuration, the surface resistance at 77 K and 80 GHz is typically near 100 milliohms. For a very well-aligned sample with a very low density of Y2BaCuO(y) precipitates, measured in the perpendicular configuration, the transition width (10-90 percent) is about 2 K, and the surface resistance is less than 50 milliohms at 88 K. The effect of microstructure on surface resistance is discussed.

  16. Crystallographic and physical properties of new orthorhombic Cu-1212 R(Ba 2-xR‧ x)Cu 3O 7+y system (R, R‧La, Pr, Nd; 0.65

    NASA Astrophysics Data System (ADS)

    Lin, B. N.; Lin, Y. H.; Luo, H. M.; Lee, T. J.; Ho, J. C.; Ku, H. C.

    Structural, magnetic, calorimetric and transport results are reported for the new orthorhombic Cu-1212 R(Ba 2-xR‧ x)Cu 3O 7+y cuprates (R, R‧La, Pr, Nd; 0.65 < x < 1). Powder X-ray Rietveld refinement analysis for oxygenated R 1.7Ba 1.3Cu 3O 7+y (RLa, Pr, Nd; y ∼ 0.3) indicates that the new orthorhombic O(II)-phase with space group Cmmm and lattice parameters a 0 < b o ∼ 0.55 nm, c ∼ 1.16 nm is very similar to the Bi-2212 structure except that (BiO) 2 bi-layer is replaced by a single CuO 1+y plane. For the oxygenated Pr(Ba 2-xR x)Cu 3O 7+y O(II)-phase cuprates (RLa, Pr; y > 0.2), anomalous Pr ordering temperature T N(Pr) decreases sharply from 18 K for O(I)-phase PrBa 2Cu 3O 7 (space group Pmmm, a o < b o ∼ 0.39 nm and c ∼ 1.17 nm), to 5.5 K for Pr(Ba 1.3Pr 0.7)Cu 3O 7.25 and 6 K for Pr(Ba 1.3La 0.7)Cu 3O 7.29. The dramatically decreasing T N(Pr) is closely related with longer PrO bond length in the O(II)-phase which effectively decreases Pr 4f-O 2p π orbital hybridization. No superconductivity was observed for these new insulating cuprates.

  17. A new layered copper oxide - LaSrCuAlO5

    NASA Astrophysics Data System (ADS)

    Wiley, J. B.; Markham, L. M.; Vaughey, J. T.; McCarthy, T. J.; Sabat, M.

    This paper describes the synthesis, crystal structure, and conductivity of a new layered copper oxide, LaSrCuAlO5. The compound was prepared by solid state reaction of Aldrich cupric oxide, strontium carbonate, lanthanum oxide, and aluminum nitrate. The results of XRD studies showed that, although the crystal structure of LaSrCuAlO5 is similar to Ca2Fe2O5 and Ca2AlFeO5, there are significant differences in the ordering of oxygen vacancies. The LaSrCuAlO5 prepared was found to be semiconducting, with a resistivity at room temperature of 0.065 ohm cm.

  18. Irreversibility line and flux pinning properties in a multilayered cuprate superconductor of Ba2Ca3Cu4O8(O,F)2 (Tc = 105 K)

    NASA Astrophysics Data System (ADS)

    Shirage, P. M.; Iyo, A.; Shivagan, D. D.; Tanaka, Y.; Kito, H.; Kodama, Y.

    2008-07-01

    Irreversibility line (IL) and flux pinning properties were investigated for a Ba2Ca3Cu4O8(O,F)2 (F-0234) multilayered cuprate superconductor with a Tc of 105 K. The intragrain critical current density (Jc) and irreversibility field (Birr) were determined by using Bean's critical state model for the grain-aligned sample (nominal composition Ba2Ca3Cu4O8.7F1.3). The irreversibility line (IL) of F-0234 is much lower than that of (Cu,C)Ba2Ca3Cu4Oy ((Cu, C)-1234) and HgBa2Ca3Cu4Oy (Hg-1234) in spite of the spacing between the superconducting blocks of F-0234 (7.3 Å) being much thinner. The double logarithmic plot of Birr field versus [1-(T/Tc) ] analysis hints that the flux line melting model has been adopted. An anisotropy factor of 65 was calculated from a 3D to 2D crossover field of about 0.95 T. Due to the high anisotropy of this system, a low IL has resulted. The flux pinning force density Fp ( ≈JcB) exhibits scaling behaviour when the magnetic field B is normalized by the Birr field. Analysis of the normalized pinning force reveals that a surface pinning mechanism is dominant and the reduced magnetic field bmax = 0.2 agrees with surface pinning mechanism with closely spaced pins.

  19. 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.

  20. 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.

  1. New investigation of phase equilibria in the system Al-Cu-Si.

    PubMed

    Ponweiser, Norbert; Richter, Klaus W

    2012-01-25

    The phase equilibria and invariant reactions in the system Al-Cu-Si were investigated by a combination of optical microscopy, powder X-ray diffraction (XRD), differential thermal analysis (DTA) and electron probe micro analysis (EPMA). Isothermal phase equilibria were investigated within two isothermal sections. The isothermal section at 500 °C covers the whole ternary composition range and largely confirms the findings of previous phase diagram investigations. The isothermal section at 700 °C describes phase equilibria only in the complex Cu-rich part of the phase diagram. A new ternary compound τ was found in the region between (Al,Cu)-γ(1) and (Cu,Si)-γ and its solubility range was determined. The solubility of Al in κ-CuSi was found to be extremely high at 700 °C. In contrast, no ternary solubility in the β-phase of Cu-Al was found, although this phase is supposed to form a complete solid solution according to previous phase diagram assessments. Two isopleths, at 10 and 40 at.% Si, were investigated by means of DTA and a partial ternary reaction scheme (Scheil diagram) was constructed, based on the current work and the latest findings in the binary systems Al-Cu and Cu-Si. The current study shows that the high temperature equilibria in the Cu-rich corner are still poorly understood and additional studies in this area would be favorable.

  2. 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.

  3. Comparison of stripe modulations in La1.875Ba0.125CuO4 and La1.48Nd0.4Sr0.12CuO4

    NASA Astrophysics Data System (ADS)

    Wilkins, S. B.; Dean, M. P. M.; Fink, Jörg; Hücker, Markus; Geck, J.; Soltwisch, V.; Schierle, E.; Weschke, E.; Gu, G.; Uchida, S.; Ichikawa, N.; Tranquada, J. M.; Hill, J. P.

    2011-11-01

    We report combined soft and hard x-ray scattering studies of the electronic and lattice modulations associated with stripe order in La1.875Ba0.125CuO4 and La1.48Nd0.4Sr0.12CuO4. We find that the amplitude of both the electronic modulation of the hole density and the strain modulation of the lattice is significantly larger in La1.875Ba0.125CuO4 than in La1.48Nd0.4Sr0.12CuO4 and is also better correlated. The in-plane correlation lengths are isotropic in each case; for La1.875Ba0.125CuO4, ξhole=255±5 Å, whereas for La1.48Nd0.4Sr0.12CuO4, ξhole=111±7 Å. We find that the modulations are temperature independent in La1.875Ba0.125CuO4 in the low temperature tetragonal phase. In contrast, in La1.48Nd0.4Sr0.12CuO4, the amplitude grows smoothly from zero, beginning 13 K below the LTT phase transition. We speculate that the reduced average tilt angle in La1.875Ba0.125CuO4 results in reduced charge localization and incoherent pinning, leading to the longer correlation length and enhanced periodic modulation amplitude.

  4. 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.

  5. Transverse conductivity in Y_{1-y}Pr_{y}Ba_{2}Cu_{3}O_{7-\\delta } single crystals

    NASA Astrophysics Data System (ADS)

    Vovk, R. V.; Khadzhai, G. Ya; Dobrovolskiy, O. V.; Nazyrov, Z. F.; Goulatis, I. L.

    2014-04-01

    The out-of-plane resistivity of high-quality Y_{1-y}Pr_{y}Ba_{2}Cu_{3}O_{7-\\delta } single crystals was measured and analyzed within the range {{T}_{{\\rm{c}}}}-300 K. The temperature dependence of the resistivity \\rho \\left( T \\right) can be described well by a model that takes into account scattering of electrons by phonons and defects, in conjunction with a transition to the ‘semiconductor’-type behavior with increasing praseodymium concentration. The effect of fluctuations is described well by the 3D Aslamazov-Larkin model. The electron-phonon interaction in the Y_{1-y}PryBa_{2}Cu_{3}O_{7-\\delta } is strong, but it is weakened with increasing praseodymium concentration. A parabolic correlation between the critical temperature {{T}_{{\\rm{c}}}} and the parameter characterizing the volume fraction of the ‘semiconductor’ phase was observed. The quantified scattering and fluctuation parameters in the investigated interval of praseodymium concentrations (y<0.35) are reported.

  6. 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.

  7. Fabrication and properties of (Hg,Pb)Ba2Ca2Cu3O8+δ silver-sheathed tapes

    NASA Astrophysics Data System (ADS)

    Su, J. H.; Sastry, P. V. P. S. S.; van der Laan, D. C.; Schwartz, J.

    2002-05-01

    (Hg,Pb)Ba2Ca2Cu3O8+δ (HgPb1223) samples have been fabricated by wrapping Pb0.2Ba2Ca2Cu3Oy precursor powder within Ag foil and pressing or rolling. The precursor/Ag composite is then reacted with CaHgO2 in sealed reaction quartz glass tubes. The XRD pattern of as-prepared tapes shows only one superconducting phase, HgPb1223, was obtained, in agreement with the Tc measurements showing an onset critical temperature (Tc) of about 132 K. The microstructures of these tapes examined by ESEM show defects such as cracks, voids, sausaging, and non-superconducting phases, resulting from mechanical deformation and sintering. Although the localized grain alignment of the silver interface has been observed, globally the HgPb1223 grains are almost randomly aligned, in agreement with magneto-optical images. The irreversibility behavior and the temperature dependence of magnetic (intragrain) critical current density Jc,m, estimated by using Bean's model, are also reported. The average transport Jc,t of the HgPb1223 tapes was ˜103A/cm2 at 4.2 K and self-field, only 1/1000 of Jc,m, which was ˜106A/cm2. The much lower transport Jc,t is explained in terms of grain-linking and defects mentioned above.

  8. 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.

  9. Research of Mechanical Property Gradient Distribution of Al-Cu Alloy in Centrifugal Casting

    NASA Astrophysics Data System (ADS)

    Sun, Zhi; Sui, Yanwei; Liu, Aihui; Li, Bangsheng; Guo, Jingjie

    Al-Cu alloy castings are obtained using centrifugal casting. The regularity of mechanical property gradient distribution of Al-Cu alloy castings with the same centrifugal radius at different positions is investigated. The result shows that the tensile strength, yield strength, elongation and microscope hardness exhibit the following gradient distribution characteristic — high on both sides and low on the center. The trend of mechanical property gradient distribution of Al-Cu alloy increases with the increase in the rotation speed. Moreover, the mechanical properties of casting centerline two sides have asymmetry. The reason is that the grain size of casting centerline two sides and Al2Cu phase and Cu content change correspondingly.

  10. Structural and superconducting properties of co-doped YBa2-xLaxCu3-xMxOz and La-free YBa2Cu3-xMxOz (M = Al, Zn) high-TC superconductors

    NASA Astrophysics Data System (ADS)

    Hao, S. J.; Jin, W. T.; Guo, C. Q.; Zhang, H.

    2012-05-01

    Two co-doped high-Tc superconducting systems, YBa2-xLaxCu3-xAlxOz and YBa2-xLaxCu3-xZnxOz (0 ⩽ x ⩽ 0.3), both of which have not been reported up to the present, were synthesized. The structural and superconducting properties have been investigated by X-ray diffraction (XRD) and DC magnetization measurement. Comparing the properties of these co-doped systems with single-doped systems YBa2Cu3-xAlxOz and YBa2Cu3-xZnxOz, it shows that in the Al-single-doped YBCO system, the depression of the critical temperature (Tc) with doping is stronger than that in (La, Al)-co-doped system, however, in the Zn-single-doped system, the Tc descends slower than that in (La, Zn)-co-doped system. This is possibly due to the opposite change of the distance between the Ba site and the CuO2 plane induced by the La doping. Besides, the La doping has another effect of improving the solid solubility compared with the Al- or Zn-single-doped system.

  11. 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.

  12. Crystal structure of novel compounds in the systems Zr-Cu-Al, Mo-Pd-Al and partial phase equilibria in the Mo-Pd-Al system.

    PubMed

    Khan, Atta U; Rogl, P; Giester, G

    2012-02-28

    The crystal structures of three Al-rich compounds have been solved from X-ray single crystal diffractometry: τ(1)-MoPd(2-x)Al(8+x) (x = 0.067); τ(7)-Zr(Cu(1-x)Al(x))(12) (x = 0.514) and τ(9)-ZrCu(1-x)Al(4) (x = 0.144). τ(1)-MoPd(2-x)Al(8+x) adopts a unique structure type (space group Pbcm; lattice parameters a = 0.78153(2), b = 1.02643(3) and c = 0.86098(2) nm), which can be conceived as a superstructure of the Mo(Cu(x)Al(1-x))(6)Al(4) type. Whereas Mo-atoms occupy the 4d site, Pd(2) occupies the 4c site, Al and Pd(1) atoms randomly share the 4d position and the rest of the positions are fully occupied by Al. A Bärnighausen tree documents the crystallographic group-subgroup relation between the structure types of Mo(Cu(x)Al(1-x))(6)Al(4) and τ(1). τ(7)-Zr(Cu(1-x)Al(x))(12) (x = 0.514) has been confirmed to crystallize with the ThMn(12) type (space group I4/mmm; lattice parameters a = 0.85243(2) and c = 0.50862(3) nm). In total, 4 crystallographic sites were defined, out of which, Zr occupies site 2a, the 8f site is fully occupied by Cu, the 8i site is entirely occupied by Al, but the 8j site turned out to comprise a random mixture of Cu and Al atoms. The compound τ(9)-ZrCu(1-x)Al(4) (x = 0.144) crystallizes in a unique structure type (space group P4/nmm; lattice parameters a = 0.40275(3) and c = 1.17688(4) nm) which exhibits full atom order but a vacancy (14.4%) on the 2c site, shared with Cu atoms. τ(9)-ZrCu(1-x)Al(4) is a superstructure of Cu with an arrangement of three unit cells of Cu in the direction of the c-axis. A Bärnighausen tree documents this relationship. The ZrCu(1-x)Al(4) type (n = 3) is part of a series of structures which follow this building principle: Cu (n = 1), TiAl(3) (n = 2), τ(5)-TiNi(2-x)Al(5) (n = 4), HfGa(2) (n = 6) and Cu(3)Pd (n = 7). A partial isothermal section for the Al-rich part of the Mo-Pd-Al system at 860 °C has been established with two ternary compounds τ(1)-MoPd(2-x)Al(8+x) and τ(2) (unknown structure). The

  13. 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.

  14. Insulator-metal transition by the substitution of Ho, Y or Ca for Pr in PrBa 2Cu 3O 7- δ

    NASA Astrophysics Data System (ADS)

    Tomkowicz, Z.; Lunkenheimer, P.; Knebel, G.; Bałanda, M.; Pacyna, A. W.; Zaleski, A. J.

    Comparative studies of electrical transport in the non-superconducting part of the R 1- xPr xBa 2Cu 3O 7- δ system (R=Ho, Y; x>0.60) and in the Pr 1- xCa xBa 2Cu 3O 7- δ system ( x≤0.5) have been carried out for ceramic samples. Electrical conduction of all samples at low temperatures can be described by the formula σ= σ0+ axTn, where n≅1 for the Ho- and Y-systems and 1≤ n≤1.88 for the Ca-system. For Ho 1- xPr xBa 2Cu 3O 7- δσ0≠0 and σ0→0 as x→1, but for Pr 1- xCa xBa 2Cu 3O 7- δσ0=0. Selected samples of the Ho 1- xPr xBa 2Cu 3O 7- δ system were substituted with gold, which blocks the conduction of chains. For gold substituted Ho 1- xPr xBa 2Cu 2.92Au 0.08O 7- δ samples σ0=0. We conclude that the suppression of superconductivity in the Ho 1- xPr xBa 2Cu 3O 7- δ system is connected with a metal-insulator (M-I) transition in planes (at x≈0.6), but chains are still conducting and become insulating only in the limit x=1. The electrical conduction of chains is dominated by tunneling, being possible due to the pronounced texture of samples. To get further insight into the mechanism of suppression, we studied also Sr- and Ca-substituted, oxygenated and deoxygenated samples. No superconductivity was obtained although it is known that Pr loses its anomalous properties in deoxygenated samples and Ca induces superconductivity in the deoxygenated Y 1- xCa xBa 2Cu 3O 7- δ system.

  15. Tl 2Ba 2CaCu 2O 8- x superconducting films deposited by aerosol and their hysteretic ac losses

    NASA Astrophysics Data System (ADS)

    Conde-Gallardo, A.; Klein, T.; Escribe-Filippini, C.; Marcus, J.; Lopez-Rios, T.; Jergel, M.

    1998-04-01

    ac susceptibility measurements have been performed on Tl 2Ba 2CaCu 2O 8- x superconducting films. The films were grown in two steps: first Ba-Ca-Cu-Ag-O precursor films have been prepared by spraying an aerosol on MgO substrates and the Tl was then subsequently introduced by diffusion into the precursor films. The most favourable preparation conditions have been determined by comparing the structural and magnetic properties of the films. A detailed study of the ac susceptibility shows that the ac losses are due to intragrain bulk hysteretic pinning eventhough small geometrical barriers contributions could also be observed.

  16. Effect of Sn substitution on the para-conductivity of polycrystalline Cu0.5Tl0.5Ba2Ca2Cu3-ySnyO10-δ superconductors

    NASA Astrophysics Data System (ADS)

    Khan, Nawazish Ali; Hassan, Najmul; Nawaz, Sana; Shabbir, Babar; Khan, Sajid; Rizvi, Azhar A.

    2010-04-01

    High quality electrical resistivity ρ(T) versus temperature data of as-prepared and O2-annealed Cu0.5Tl0.5Ba2Ca2Cu3-ySnyO10-δ (y=0, 0.25, 0.5, 0.75, 1.0, 1.25, and 1.5) superconductors has been studied for fluctuation-induced phenomena setting in at temperatures well above the critical temperature [Tc(R=0)]. The analysis of the data is done by using Aslamazov-Larkin (AL) and Lawrence-Doniach models for the excess conductivity. We have estimated several physical parameters, including coherence length, interplane coupling strength, exponents, and dimensionality of the fluctuations. The as-prepared and oxygen postannealed samples have shown a cross-over temperature associated with two distinct exponents and the excess conductivity data fits well with the two-dimensional and three-dimensional AL equations. The coherence length along the c-axis [ξc(0)] and the interlayer coupling strength (J) are found to decrease with increased Sn doping. These values are increased after annealing the samples in oxygen atmosphere, which is most likely associated with the approach of carrier concentration in the conducting CuO2/SnO2 planes to the optimum value. The Tc(R=0) and the peak temperature (TP) as determined from the dρ /dT versus temperature plots are also found to decrease with increased Sn substitution, however, these temperatures are improved to higher values after annealing the samples in oxygen atmosphere. The decreased values of Tc(R=0) and TP with increased Sn substitution in the as-prepared samples are most likely arising from the suppression of carrier's density promoted by the increased volume of unit cell and the localization of the carriers at the Sn4+ sites.

  17. Luminescence of delafossite-type CuAlO2 fibers with Eu substitution for Al cations

    PubMed Central

    Liu, Yin; Gong, Yuxuan; Mellott, Nathan P.; Wang, Bu; Ye, Haitao; Wu, Yiquan

    2016-01-01

    Abstract CuAlO2 has been examined as a potential luminescent material by substituting Eu for Al cations in the delafossite structure. CuAlO2:Eu3+ nanofibers have been prepared via electrospinning for the ease of mitigating synthesis requirements and for future optoelectronics and emerging applications. Single-phase CuAlO2 fibers could be obtained at a temperature of 1100 °C in air. The Eu was successfully doped in the delafossite structure and two strong emission bands at ~405 and 610 nm were observed in the photoluminescence spectra. These bands are due to the intrinsic near-band-edge transition of CuAlO2 and the f-f transition of the Eu3+ activator, respectively. Further electrical characterization indicated that these fibers exhibit semiconducting behavior and the introduction of Eu could act as band-edge modifiers, thus changing the thermal activation energies. In light of this study, CuAlO2:Eu3+ fibers with both strong photoluminescence and p-type conductivity could be produced by tailoring the rare earth doping concentrations. PMID:27877870

  18. Structural properties of the superconductor LaBa sub 2 Cu sub 3 minus y O sub 7 minus z in the solid solution system La sub 1+ x Ba sub 2 minus x Cu sub 3 minus y O sub 7 minus z

    SciTech Connect

    Izumi, M. ); Yabe, T.; Wada, T.; Maeda, A.; Uchinokura, K.; Tanaka, S.; Asano, H.

    1989-10-01

    We present time-of-flight (TOF) neutron-powder-diffraction results of four samples in the solid-solution orthorhombic La{sub 1+{ital x}}Ba{sub 2{minus}{ital x}}Cu{sub 3{minus}{ital y}}O{sub 7{minus}{ital z}} system. The data for all of the samples were taken at room temperature. The average crystal structures of LaBa{sub 2}Cu{sub 2.90}O{sub 6.82} ({ital T}{sub {ital c}}=45 K), La{sub 1.56}Ba{sub 1.44}Cu{sub 2.86}BO{sub 6.98} (nonsuperconductor), and the impurity-free LaBa{sub 2}Cu{sub 3}O{sub 6.85} ({ital T}{sub {ital c}}=93 K) were refined by the Rietveld analysis which includes the refinement of the occupancies of the La and/or Ba atoms. The remaining sample was imhomogeneous LaBa{sub 2}Cu{sub 3{minus}{ital y}}O{sub 7{minus}{ital z}} ({ital T}{sub {ital c}}=85 K).

  19. 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.

  20. 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.

  1. Further Precipitation Reactions Associated with Beta’ (Al3Zr) Particles in Al-Li-Cu-Mg-Zr Alloys

    DTIC Science & Technology

    1988-12-01

    Gregson 8’ precipitation in Al-Li-Mg-Cu-Zr alloys. H.M. Flower J. Mater. Sci. Lett., 3, 829 (1984) 5 P.L. Makin On the ageing of an aluminium-lithium...Technol., 2, 349 (1986) 8 H.M. Flower The effect of composition and heat treatment upon the et al microstructure/property relationships in Al-Li-Cu-Mg...1119 REFERENCES concluded) No. Author Title, etc 10 P.J. Gregon Microstructural control of toughness in aluminium- H.M. Flower lithium alloys. Acta

  2. 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.

  3. The shape memory capability and life of Cu-Al-Be-X alloys

    SciTech Connect

    Dong, Y.Y.; Dar, K.Z. ); Wang, T.M. ); Zin, S.J. )

    1994-09-01

    The shape memory capacity and the shape memory life of three alloys of the Cu-11.6Al-0.4Be-X type have been investigated using the strain angle restoration method and compared with the alloy Cu-25Zn-4Al. The alloys were subjected to various normalizing and normalizing plus aging treatments, and all were found to possess excellent shape memory properties. The alloy Cu-11.6Al-0.4Be-0.2Cr demonstrated the best shape memory capacity and life.

  4. Electrical transport properties of (110)-oriented PrBa2(Cu0.8Ga0.2)3O7 thin films

    NASA Astrophysics Data System (ADS)

    Kandel, Hom; Chen, Tar-Pin; Bourdo, Shawn; Iliev, Milko N.; Watanabe, Fumiya; Seo, Hye-Won; Viswanathan, Tito

    2012-06-01

    The electrical transport properties of (110)-oriented PrBa2(Cu0.8Ga0.2)3O7 (PBCGO) thin films have been investigated. The electrical resistivity, ρ(T), of (110)-oriented PBCGO thin films is 8.91 × 105 Ω-cm at 77 K, about five orders of magnitude higher than that of the (110)-oriented PrBa2Cu3O7 thin films and follows Mott's T-1/4 law up to room temperature. Our experimental results suggest filling and localization of holes in Cu-O chains of (110)-oriented PBCGO thin films. We observed very less proximity effect on YBa2Cu3O7 (YBCO)/PBCGO multilayers indicating that the (110)-oriented PBCGO thin films may serve as effective insulators in YBCO SIS tunneling Josephson junction.

  5. 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.

  6. 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; ...

    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

  7. Luminescent properties of BaAl2Si2O8:Eu2+, Mn2+ phosphor for white LED

    NASA Astrophysics Data System (ADS)

    Shen, Changyu; Li, Ke

    2010-10-01

    BaAl2Si2O8:xEu2+, yMn2+ was prepared by high-temperature solid state reaction and X-ray powder diffraction analysis confirmed the formation of it. It was found experimentally that, its emission peaks situated at 420 nm and 570 nm respectively under excitation of 380 nm irradiation. The emission peaks at 420 nm originate from the transition 5d to 4f of Eu2+ ions that occupy the Ba2+ sites in the crystal of BaAl2Si2O8, while the 580nm emission is attributed to the energy transfer from Eu2+ ions to Mn2+ ions. The white light can be obtained by combining the 380 nm chip with the phosphor. When the concentrations of the Eu2+ ions and Mn2+ ions were 0.05 mol and 0.35 mol respectively, the sample presented intense white emitting. The near-ultraviolet InGaN-based BaAl2Si2O8:0.05Eu2+, 0.35Mn2+ LED achieves good color rendering of 85 with the CIE coordinate of (0.3183, 0.3036).

  8. Unusual magnetic order in the pseudogap region of the superconductor HgBa2CuO4+delta.

    PubMed

    Li, Y; Balédent, V; Barisić, N; Cho, Y; Fauqué, B; Sidis, Y; Yu, G; Zhao, X; Bourges, P; Greven, M

    2008-09-18

    The pseudogap region of the phase diagram is an important unsolved puzzle in the field of high-transition-temperature (high-T(c)) superconductivity, characterized by anomalous physical properties. There are open questions about the number of distinct phases and the possible presence of a quantum-critical point underneath the superconducting dome. The picture has remained unclear because there has not been conclusive evidence for a new type of order. Neutron scattering measurements for YBa(2)Cu(3)O(6+delta) (YBCO) resulted in contradictory claims of no and weak magnetic order, and the interpretation of muon spin relaxation measurements on YBCO and of circularly polarized photoemission experiments on Bi(2)Sr(2)CaCu(2)O(8+delta)(refs 12, 13) has been controversial. Here we use polarized neutron diffraction to demonstrate for the model superconductor HgBa(2)CuO(4+delta) (Hg1201) that the characteristic temperature T* marks the onset of an unusual magnetic order. Together with recent results for YBCO, this observation constitutes a demonstration of the universal existence of such a state. The findings appear to rule out theories that regard T* as a crossover temperature rather than a phase transition temperature. Instead, they are consistent with a variant of previously proposed charge-current-loop order that involves apical oxygen orbitals, and with the notion that many of the unusual properties arise from the presence of a quantum-critical point.

  9. Magnetic-field-induced vortex-lattice transition in HgBa2CuO4 +δ

    NASA Astrophysics Data System (ADS)

    Lee, Jeongseop A.; Xin, Yizhou; Stolt, I.; Halperin, W. P.; Reyes, A. P.; Kuhns, P. L.; Chan, M. K.

    2017-01-01

    Measurements of the 17O nuclear magnetic resonance (NMR) quadrupolar spectrum of apical oxygen in HgBa2CuO4 +δ were performed over a range of magnetic fields from 6.4-30 T in the superconducting state. Oxygen-isotope-exchanged single crystals were investigated with doping corresponding to superconducting transition temperatures from 74 K underdoped, to 78 K overdoped. The apical oxygen site was chosen since its NMR spectrum has narrow quadrupolar satellites that are well separated from any other resonance. Nonvortex contributions to the spectra can be deconvolved in the time domain to determine the local magnetic field distribution from the vortices. Numerical analysis using Brandt's Ginzburg-Landau theory was used to find structural parameters of the vortex lattice, penetration depth, and coherence length as a function of magnetic field in the vortex solid phase. From this analysis we report a vortex structural transition near 15 T from an oblique lattice with an opening angle of 73∘ at low magnetic fields to a triangular lattice with 60∘ stabilized at high field. The temperature for onset of vortex dynamics has been identified from spin-spin relaxation. This is independent of the magnetic field at sufficiently high magnetic field similar to that reported for YBa2Cu3O7 and Bi2Sr2CaCu2O8 +δ and is correlated with mass anisotropy of the material. This behavior is accounted for theoretically only in the limit of very high anisotropy.

  10. 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

    2016-06-03

    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.

  11. Raman phonon study of Jahn-Teller distortion in Ba3CuSb2O9

    NASA Astrophysics Data System (ADS)

    Drichko, Natalia; Broholm, Collin; Kimura, Kenta; Ishii, Rieko; Nakatsuju, Satoru

    2013-03-01

    The frustrated magnet Ba3CuSb2O9 does not exhibit either structural or magnetic ordering down to the lowest measured temperatures and is of great current interest as a spin-liquid candidate. It has been proposed recently that the lack of ordering is due to a static or dynamic Jahn-Teller distortion that leads to orbital disorder. We use phonon Raman scattering at temperatures between 20 and 380 K to investigate Jahn-Teller distortion in crystals with different Sb:Cu stoichiometry. We focus on phonons in the range of 500-800 cm-1 attributable to oxygen vibrations. In addition to signatures of the strong disorder due to Cu-Sb site mixing present in these materials, we observe mode-splitting due to a static Jahn-Teller distortion below 200 K in samples that undergo a transition to an orthorhombic phase. In contrast, samples that remain hexagonal to the lowest temperatures do not show such mode splitting. We are thankful to O. Tchernyshyov and Zihao Hao for discussions. This work was supported in part by the U.S. DoE, Office of Basic Energy Science, DMSE under Award DE-FG02-08ER46544 and H. Blewett Fellowship from APS

  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. Hyperfine fields at the Ba site in the antiferromagnet YBa{sub 2}Cu{sub 3}O{sub 6.05}

    SciTech Connect

    Lombardi, A.; Mali, M.; Roos, J.; Brinkmann, D.

    1996-06-01

    We report a Ba nuclear quadrupole resonance (NQR) study of the antiferromagnetic state of YBa{sub 2}Cu{sub 3}O{sub 6.05} (N{acute e}el temperature {ital T}{sub {ital N}} = 415 K) performed between 16 and 402 K. The Zeeman perturbed {sup 137}Ba NQR spectrum yields information on two hyperfine fields present at the Ba site: the electric field gradient (EFG) and the internal magnetic field arising from the Cu(2) sublattice magnetization. The absolute value of the EFG is in remarkable agreement with cluster and band structure calculations thus demonstrating again that both methods provide a satisfying electronic bond picture for the Y-Ba-Cu-O compounds [except for the planar Cu(2) site]. The temperature dependence of the EFG arises from thermal expansion only. The internal field, {ital B}({ital T}), has been deduced from the modulation of the Ba spin-echo intensity. A calculation of the dipolar field at the Ba site produced by Cu(2) {ital d} electrons yields a value that is about three times larger than the experimental result. The discrepancy could be explained by assuming that part of the magnetic moment is located at oxygen ions. The temperature variation of {ital B}({ital T}) follows, up to 402 K, a power law [{ital B}(0){minus}{ital B}({ital T})]/{ital B}(0)={ital AT}{sup {alpha}} with {alpha} = 1.82(22) which agrees quite well with the result of a Cu(2) in-plane determination of the sublattice magnetization. Furthermore, this result is in accord with a spin-wave model for a quasi-two-dimensional (2D) antiferromagnet. The {open_quote}{open_quote}critical exponent{close_quote}{close_quote} {beta} is estimated to be {le} 0.18 which is in accord with values proposed by models for 2D ordered magnetic systems. Thus YBa{sub 2}Cu{sub 3}O{sub 6.05} behaves, in terms of its spin dynamics, as a quasi-2D antiferromagnet and this character can be studied either at out-of-plane Ba or at in-plane Cu(2) sites. {copyright} {ital 1996 The American Physical Society.}

  14. 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.

  15. Suppressed 3D conductivity in Mn doped Cu0.5Tl0.5Ba2Ca2-yMnyCu3O10-δ superconductors

    NASA Astrophysics Data System (ADS)

    Qurat-ul-Ain, Khan, Nawazish A.

    2013-04-01

    We have synthesised Mn-doped Cu0.5Tl0.5Ba2(Ca2-yMny)Cu3O10-δ superconducting samples and studied their Fluctuation Induced Conductivity (FIC) analysis. The Tc(R = 0) and magnitude of diamagnetism are suppressed with increased Mn-doping in the final compound. FIC analyses have shown a suppression of 3D Lawrence and Doniach (LD) regime and a significant enhancement of 2D LD regime of Mn-doping of y = 0.35. In the sample with Mn-doping of y = 0.5, the 3D LD regime vanishes altogether and only 2D LD regime is observed, showing the confinement of superconductivity in the two dimensional planes. The coherence length along the c-axis and the Fermi velocity of the carriers are suppressed with increased Mn doping. Using the Ginzburg-Landau (GL) number [NG] and GL equations, the thermodynamic critical magnetic field Bc(0), the lower critical field Bc1(0), the upper critical field Bc2(0), the critical current density Jc(0), and penetration depth λp.d are determined. The values of critical fields Bc(0) and Bc1(0) increases, despite suppression in the Tc(R = 0) with increased Mn-doping. The values of Jc(0), the penetration depth Λp.d, and inter-layer coupling are suppressed with enhanced Mn-doping. These observations suggested that Mn ions act as sub-nano-scale pinning centers between the CuO2 planes and their presence at the Ca-sites promote the de-coupling of CuO2 planes.

  16. 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.

  17. Structure, spin-stripe order, and superconductivity in La1.905 Ba 0.095 CuO 4 with and without 1% Zn substitution of Cu

    NASA Astrophysics Data System (ADS)

    Wen, Jinsheng; Xu, Z.; Xu, G.; Jie, Q.; Hucker, M.; Zheludev, A.; Tian, W.; Winn, B.; Zarestky, J.; Singh, D.; Hong, T.; Li, Q.; Gu, G.; Tranquada, J.

    2011-03-01

    We have performed susceptibility, thermal transport, and neutron scattering measurements to study the effect of Zn and magnetic field on the structure, spin-stripe order and superconductivity, and the interplay between them in La 1.905 Ba 0.095 Cu O4 with and without 1% Zn. It is shown that the bulk superconductivity is depressed by either the Zn doping or the magnetic field, spin stripe order is enhanced, and the structure is unaffected. For a range of magnetic field, the spin stripe order appears to stabilize a quasi-two-dimensional vortex glass phase. Supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC02-98CH10886.

  18. Effect of current reversal on the failure mechanism of Al-Cu-Si narrow interconnects

    SciTech Connect

    Kim, C.U.; Kang, S.H.; Morris, J.W. Jr. |

    1996-02-01

    The work reported here concerns the effect of a brief exposure to a reversed current on the electromigration failure of narrow Al-Cu thin-film conducting lines. While the precise mechanism by which Cu retards electromigration in Al-Cu alloys is not fully understood, the consistent observation that electromigration failure is preceded by the sweeping of Cu from the failure site can be used to improve electromigration resistance by stabilizing the distribution of Cu. One way of doing this is to expose the Al-Cu line to a reverse current for some period of time. The present work shows that this method is particularly effective in thin lines with `quasi-bamboo` microstructures. It has the effect of building a reservoir of Cu at the upstream ends of the polygranular segments that are the preferred failure sites, and significantly increases both the mean time of failure, and the time to first failure of a distribution of lines. It can be inferred from these results that Al-Cu lines that conduct alternating current should be exceptionally resistant to electromigration failure. 11 refs., 8 figs.

  19. 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.

  20. Stripe order, depinning, and fluctuations in La1.875 Ba0.125 CuO4 and La1.875 Ba0.075 Sr0.050 CuO4

    NASA Astrophysics Data System (ADS)

    Fujita, M.; Goka, H.; Yamada, K.; Tranquada, J. M.; Regnault, L. P.

    2004-09-01

    We present a neutron scattering study of stripe correlations measured on a single crystal of La1.875Ba0.125CuO4 . Within the low-temperature-tetragonal (LTT) phase, superlattice peaks indicative of spin and charge stripe order are observed below 50K . For excitation energies ℏω⩽12meV , we have characterized the magnetic excitations that emerge from the incommensurate magnetic superlattice peaks. In the ordered state, these excitations are similar to spin waves. Following these excitations as a function of temperature, we find that there is relatively little change in the Q -integrated dynamical spin susceptibility for ℏω˜10meV as stripe order disappears and then as the structure transforms from LTT to the low-temperature-orthorhombic phase. The Q -integrated signal at lower energies changes more dramatically through these transitions, as it must in a transformation from an ordered to a disordered state. We argue that the continuous evolution through the transitions provides direct evidence that the incommensurate spin excitations in the disordered state are an indicator of dynamical charge stripes. An interesting feature of the thermal evolution is a variation in the incommensurability of the magnetic scattering. Similar behavior is observed in measurements on a single crystal of La1.875Ba0.075Sr0.050CuO4 ; maps of the scattered intensity in a region centered on the antiferromagnetic wave vector and measured at ℏω=4meV are well reproduced by a model of disordered stripes with a temperature-dependent mixture of stripe spacings. We discuss the relevance of our results to understanding the magnetic excitations in cuprate superconductors.

  1. Mixed oxide semiconductor CuInAlO4 nanoparticles: synthesis, structure and photocatalytic properties

    NASA Astrophysics Data System (ADS)

    Xu, Jian; Qin, Chuanxiang; Bi, Shala; Wan, Yingpeng; Huang, Yanlin; Wang, Yaorong; Seo, Hyo Jin

    2017-01-01

    CuInAlO4 nanoparticles were synthesized via the facile sol-gel route. The phase formations were investigated by x-ray powder diffraction and structure refinements. The morphological characteristic of the nano-oxides was tested with scanning electron microscopy, transmission electron microscopy, energy-dispersive spectra, N2-adsorption-desorption isotherms and the x-ray photoelectron spectrum. The optical absorption, band energy and structures of the nanoparticles were measured. CuInAlO4 has wide optical absorption from UV to visible wavelength. The nano-oxides have a narrow band energy of 2.191 eV. The photocatalysis ability of CuInAlO4 nanoparticles was confirmed by its efficient photodegradation on methylene blue (MB) dye under the excitation of the visible wavelengths: CuInAlO4 demonstrates efficient photocatalysis on MB photodegradation.

  2. 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.

  3. Complex metallic surface phases in the Al/Cu(111) system: An experimental and computational study

    NASA Astrophysics Data System (ADS)

    Duguet, T.; Gaudry, E.; Deniozou, T.; Ledieu, J.; de Weerd, M. C.; Belmonte, T.; Dubois, J. M.; Fournée, V.

    2009-11-01

    The growth of complex intermetallics as surface alloys is investigated by annealing Al thin films deposited on Cu(111) substrate in ultrahigh vacuum. Already at room temperature, the large lattice mismatch between Al and Cu results in interfacial intermixing. Upon annealing, various phases are formed by diffusion depending on the thickness of the Al films and the annealing temperature. The surface structures are characterized by scanning tunneling microscopy, low-energy electron diffraction, and x-ray photoelectron spectroscopy. Three different superlattice phases are identified as well as the complex Hume-Rothery γ-Al4Cu9 phase. The epitaxial relationships between the surface phases and the Cu(111) substrate are determined. We further investigate the electronic structure of the γ phase by density functional calculations. Experimental valence bands are compared to calculated density of states and simulated STM images are used to identify possible bulk planes appearing as surface termination.

  4. 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

  5. The Structural Evolution of (Gd, Y)Ba2Cu3Ox Tapes With Zr Addition Made by Metal Organic Chemical Vapor Deposition

    SciTech Connect

    Lei, CH; Galstyan, E; Chen, YM; Shi, T; Liu, YH; Khatri, N; Liu, JF; Xiong, XM; Majkic, G; Selvamanickam, V

    2013-06-01

    Structural analysis of (Gd, Y) Ba2Cu3Ox tapes with Zr addition made by metal organic chemical vapor deposition has been conducted with transmission electron microscopy and X-ray diffraction. Zr content in the films was varied from 0 to 25% in the precursor. In all Zr-doped films, self-assembled nanocolumnar structures of BaZrO3 (BZO) were observed along the c-axis. The amount of BaZrO3 was found to increase steadily with Zr content. Additionally, planar BZO plates were found on the (001) plane of (Gd, Y) Ba2Cu3Ox film. The size and thickness of BZO plates were seen to increase with Zr doping level. Rare-earth copper oxide phases were observed to begin to emerge in the 20% Zr-doped film. Cross-sectional study of the interface between (Gd, Y)Ba2Cu3Ox and LaMnO3 cap layer revealed a thin discrete BZO layer on the LaMnO3 in the 20% Zr doped film.

  6. 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

  7. Spin pseudogap and interplane coupling in Y{sub 2}Ba{sub 4}Cu{sub 7}O{sub 15}: A {sup 63}Cu nuclear spin-spin relaxation study

    SciTech Connect

    Stern, R.; Mali, M.; Roos, J.; Brinkmann, D.

    1995-06-01

    We report measurements of the Gaussian contribution {ital T}{sub 2{ital G}} to the plane {sup 63}Cu nuclear spin-spin relaxation time in the YBa{sub 2}Cu{sub 3}O{sub 7} and YBa{sub 2}Cu{sub 4}O{sub 8} blocks of normal and superconducting Y{sub 2}Ba{sub 4}Cu{sub 7}O{sub 15}. The data confirm our previous results that adjacent CuO{sub 2} planes have different doping levels and that these planes are strongly coupled. The static spin susceptibility at the antiferromagnetic wave vector exhibits a Curie-Weiss-like temperature dependence in the normal state. The Y{sub 2}Ba{sub 4}Cu{sub 7}O{sub 15} data are incompatible with a phase diagram based on a single CuO{sub 2} plane theory but point to the importance of the interplane coupling in the spin-gap formation. Additional data for YBa{sub 2}Cu{sub 4}O{sub 8} and YBa{sub 2}Cu{sub 3}O{sub 6.982} are in acord with the single-plane theory. The temperature dependence of {ital T}{sub 2{ital G},ind} below {ital T}{sub {ital c}} excludes isotropic {ital s}-wave superconductivity in all three compounds.

  8. Ba'id al Jimalah tungsten prospect, Najd region, Kingdom of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Lofts, P. G.

    The Ba'id al Jimalah tungsten prospect is located in the NE of the Arabian Shield, at 25°09'N, 42°41'E. Mineralization is associated with a late-Proterozoic, porphyritic microgranite emplaced in folded, fine-grained clastic rocks of the Murdama group, within an aureole of biotite-rich hornfels. The microgranite forms a 30 m-thick sill and numerous smaller sills and dikes cropping out along two low, sub-parallel ridges and several small hills in an area 700 m square. The form of the intrusion at depth is uncertain. It is slightly to intensely sericitized, in places greisenized, and is enriched in Li, F and Rb. Wolframite occurs with minor cassiterite, scheelite and sulfides in quartz veins cutting both microgranite and hornfelsed wall-rock. The veins have a dominant trend of 110-115°, and are thicker and more numerous in the microgranite. Gangue minerals include plagioclase and potassium feldspar, muscovite, sericite, fluorite and minor siderite. A major Najd fault trending 130-135° probably controlled magma emplacement and subsequent hydrothermal and pneumatolytic activity. A percussion drilling program, restricted to the outcrop of the sill on the north ridge, has outlined 800,000 tonnes grading 0.10% WO 3 and 0.01% Sn.

  9. 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.

  10. 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.

  11. Synthesis of Y3Ba5Cu8O18 superconductor powder by auto-combustion reaction: Effects of citrate-nitrate ratio

    NASA Astrophysics Data System (ADS)

    Suan, Mohd Shahadan Mohd; Johan, Mohd Rafie; Chua Siang, Tat

    2012-10-01

    In this experiment, nanocrystalline Y3Ba5Cu8O18 superconductor powder was prepared by citrate-nitrate auto-combustion reaction. A series of Y3Ba5Cu8O18 precursor gels with different citrate-nitrate ratio ranged from 0.3 to 1.0 have been prepared by varying the amount of citric acid added. The auto-combustion reaction during drying process transformed the precursor gels into ashes powder that upon calcinations at 900 °C yield Y3Ba5Cu8O18 nanocrystalline powders. The TG/DTA analysis reveals that the precursor gels with 0.3 ⩽ c/n < 1.0 decomposed in a single-step reaction combusted at temperature of around 230 °C. Established from XRD and SEM characterization, the Y3Ba5Cu8O18 calcined powder prepared from c/n = 0.7 precursor gels has got the orthorhombic structure with smallest particle size (∼10 nm) compared to the rest of the batches. Samples with c/n = 0.5 and 0.7 appeared in this work to be electrically superconducting at temperature above 100 K as measured using standard four-probe technique. This emphasized on maintaining a stoichiometric or near stoichiometric reaction for the analysis.

  12. 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.; ...

    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

  13. Quasi-two-dimensional Bose-Einstein condensation of spin triplets in the dimerized quantum magnet Ba2CuSi2O6Cl2

    DOE PAGES

    Okada, Makiko; Tanaka, Hidekazu; Kurita, Nobuyuki; ...

    2016-09-20

    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 onmore » 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. Lastly, the magnetic-field-induced spin ordering in Ba2CuSi2O6Cl2 is described as the quasi-2D Bose-Einstein condensation of triplets.« less

  14. 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.

  15. 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.

  16. O-2p holes in tetravalent oxides of Ce and Pr and the Fehrenbacher-Rice hybrid in PrBa2Cu3O7-δ

    NASA Astrophysics Data System (ADS)

    Hu, Z.; Meier, R.; Schüßler-Langeheine, C.; Weschke, E.; Kaindl, G.; Felner, I.; Merz, M.; Nücker, N.; Schuppler, S.; Erb, A.

    1999-07-01

    We report on an x-ray absorption near-edge structure (XANES) study of O-2p holes induced by Ln-4f/O-2p covalence in LnO2 (Ln=Ce,Pr) and BaLnO3 (Ln=Ce,Pr,Tb). The pre-edge peak in the O-1s XANES spectra, associated with O-2p holes, shifts to lower energy from Ce to Pr, in agreement with theoretical expectation, and its intensity scales with the strength of the 4f/2p covalence. In Pr(IV) oxides, the pre-edge peak is at the energy of the ``Fehrenbacher-Rice'' state in PrBa2Cu3O7-δ , supporting the view that the suppression of superconductivity in PrBa2Cu3O7-δ is due to Pr-4f/O-2p hybridization.

  17. 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.

  18. Effects of pressure and distortion on superconductivity in Tl2Ba2CaCu2O8+δ

    NASA Astrophysics Data System (ADS)

    Zhang, Jian-Bo; Struzhkin, Viktor V.; Yang, Wenge; Mao, Ho-Kwang; Lin, Hai-Qing; Ma, Yong-Chang; Wang, Nan-Lin; Chen, Xiao-Jia

    2015-11-01

    The systematic evolution of the structural, vibrational, and superconducting properties of nearly optimally doped Tl2Ba2CaCu2O8+δ with pressure up to 30 GPa is studied by x-ray diffraction, Raman scattering, and magnetic susceptibility measurements. No phase transformation is observed in the studied pressure regime. The obtained lattice parameters and unit-cell volume continuously decrease with pressure by following the expected equation of state. The axial ratio of c/a exhibits an anomaly starting from 9 GPa. At such a pressure level, the deviation from the nonlinear variation of the phonon frequencies is detected. Both the above observations indicate the enhancement of the distortion upon compression. The superconducting transition temperature is found to exhibit a parabolic behavior with a maximum of 114 K around 7 GPa. We demonstrate that the interplay between the intrinsic pressure variables and distortion controls the superconductivity.

  19. (Hg, Sb)Ba2Ca2Cu3O8+δ thick films on YSZ substrates

    NASA Astrophysics Data System (ADS)

    Li, J. Q.; Lam, C. C.; Peacock, G. B.; Hyatt, N. C.; Gameson, I.; Edwards, P. P.; Shields, T. C.; Abell, J. S.

    2000-02-01

    Superconducting thick films of (Hg, Sb)Ba2Ca2Cu3O8+icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> have been fabricated on polycrystalline yttria-stabilized-zirconia substrates utilizing an Hg-free precursor film reacted with Hg vapour, released from a solid Hg source, in a sealed quartz tube. The resulting films have been studied by x-ray diffraction, scanning electron microscopy, ac susceptibility and resistance measurement techniques. A high quality Hg(Sb)-1223 superconducting thick film on YSZ can be fabricated by using a pre-melted Hg-free precursor film. The zero resistance superconducting transition temperature in the post-growth oxygenated thick film is in excess of 130 K and the transport critical current density for the film is 510 A cm-2 at 77 K.

  20. 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.

  1. The photo-catalytic activities of MP (M = Ba, Ca, Cu, Sr, Ag; P = PO43-, HPO42-) microparticles

    NASA Astrophysics Data System (ADS)

    Zhang, Fan; Shi, Yuanji; Zhao, Zongshan; Song, Weijie; Cheng, Yang

    2014-02-01

    For the good performance of apatite-based materials in the removal of dyes and their environment-friendly advantage, five kinds of apatite microparticles of MP (M = Ba, Ca, Cu, Sr, Ag; P = PO43-, HPO42-) were synthesized by a simple precipitation method and their photo-catalytic properties were invested. Better performance in the decolorization of methyl orange (MO) under the assistance of H2O2 than that of TiO2 were obtained for all the MPs. The photo-catalytic activity was mainly affected by surface area, energy band, impurity, crystallinity and crystal structure. The DFT calculation results demonstrated that the 2p of O and 3p of P in PO43- played the main role in the photo-catalytic process. This work would be helpful to design and synthesize low cost apatite materials with good photo-catalytic performance.

  2. Frequency dependence of the absorption component of the magnetic susceptibility in superconducting Y1Ba2Cu3O7

    NASA Astrophysics Data System (ADS)

    Ducharme, S.; Durny, R.; Hautala, J.; Symko, O. G.; Taylor, P. C.

    Measurements of an apparent magnetic-field-dependent absorption (imaginary part of the a.c. magnetic susceptibility) in superconducting Y1Ba2Cu3O7 ceramics and crystals are reported. The absorption, which is observed over a wide range of frequencies but only when the material is below the superconducting transition temperature, is characterized by a narrow (about 30 Gauss FWHM at 6 MHz) peak and a wide (greater than 10 kG) feature, both of which are maximum at zero magnetic field. The absorption strength varies approximately as one over the square root of the frequency. The unusual magnetic-field-dependent peaks in the magnetic susceptibility are inherent in single grains and therefore do not originate from intergrain Josephson currents or multigrain (i.e., percolative) loops. The susceptibility peaks must be due to bulk behavior, interactions at grain surfaces, intragrain current loops, or intragrain Josephson junctions.

  3. 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.

  4. Magnetic properties of the TlBa2Ca2Cu3Oy with TC ~130K

    NASA Astrophysics Data System (ADS)

    Mikusu, S.; Watanabe, G.; Tokiwa, K.; Tanaka, Y.; Iyo, A.; Watanabe, T.

    2009-03-01

    We reported that maximum TC values for Tl system superconductors TlBa2Ca2Cu3Oy (Tl-1223) can be controlled by slightly varying the starting composition. From the DC magnetization measurements, we estimated intragrain critical current densities (JC) and irreversibility fields (Birr) of Tl-1223 samples with different maximum TC values (~130 K and 120 K). These results were compared with those values for previously reported optimally-doped Hg-1223. It is found that, in the Birr -T curve at temperatures above 77K, Birr values of the Tl-1223 samples with TC~130K shows slightly higher values than that of the Tl-1223 samples with low TC and Hg-1223 samples.

  5. Development of YBa2Cu3O7-Ba2YTaO6 nanocomposites by chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Garcés, P.; Coll, M.; Castro, H.; Puig, T.; Obradors, X.

    2014-12-01

    In this work we report the study of chemical solution deposited (CSD) YBa2Cu3O7-δ (YBCO) nanocomposite thin films, with diluted Ba2YTaO6 (BYTO) nanoparticles. We studied the influence of thermal treatment on the properties of nanocomposites, with different content of secondary phases (6%, 10% and 20%). We measured the film microstructure, nanostrain and the superconducting properties: critical temperature (Tc) and critical current density (Jc). The films were characterized using X-rays diffraction and SQUID inductive measurements. The use of two steps in the thermal treatment allowed to increase the nanostrain up to 0.30% for high nanoparticle loads (20%BYTO), decrease the nanoparticle size down to 15 nm and lead a smoother Jc(H) dependence, compared with the standard (single-step) thermal process and the pristine YBCO films.

  6. Composition variations in pulsed-laser-deposited Y-Ba-Cu-O thin films as a function of deposition parameters

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    The composition of pulsed-ultraviolet-laser-deposited Y-Ba-Cu-O films was examined as a function of position across the substrate, laser fluence, laser spot size, substrate temperature, target conditioning, oxygen pressure and target-substrate distance. Laser fluence, laser spot size, and substrate temperature were found to have little effect on composition within the range investigated. Ablation from a fresh target surface results in films enriched in copper and barium, both of which decrease in concentration until a steady state condition is achieved. Oxygen pressure and target-substrate distance have a significant effect on film composition. In vacuum, copper and barium are slightly concentrated at the center of deposition. With the introduction of an oxygen background pressure, scattering results in copper and barium depletion in the deposition center, an effect which increases with increasing target-substrate distance. A balancing of these two effects results in stoichiometric deposition.

  7. 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.

  8. The effects of processing sequences on the microwave surface resistance of TlCaBaCuO

    NASA Astrophysics Data System (ADS)

    Martens, J. S.; Zipperian, T. E.; Ginley, D. S.; Hietala, V. M.; Tigges, C. P.

    1991-06-01

    The effects of several microelectronic processing sequences on the high-frequency surface resistance of the high-temperature superconducting thin films in the TlCaBaCuO system have been examined. These processes include an acid etch, Br/alcohol etches, positive and negative photoresist sequences, and exposure to de-ionized water. The surface resistance decreases during the Br etch, remains constant during the negative photoresist process, and increases moderately during the positive photoresist sequence and on exposure to water. The surface resistance increases dramatically on exposure to the acid solution as might be expected from other work. The effects of extended exposures to de-ionized water and to Br etches on surface resistance are also presented.

  9. Pairing symmetry from in-plane torque anisotropy in Tl2Ba2CuO6+δ thin films

    NASA Astrophysics Data System (ADS)

    Willemin, M.; Rossel, C.; Hofer, J.; Keller, H.; Ren, Z. F.; Wang, J. H.

    1998-03-01

    The in-plane torque anisotropy of high-quality epitaxial Tl2Ba2CuO6+δ thin films patterned into disks has been investigated. We have found that the angular dependence of the reversible torque displays a clear fourfold symmetry added to a twofold one. Excluding all experimental artifacts due to geometry or magnetic-field misalignment, we propose in the frame of a model by Beal-Monod and Maki that this is real bulk evidence for a d+s pairing state allowed by the possible breaking of the tetragonal symmetry at low temperature. Identical measurements on a NbN thin film and a NbSe2 single crystal show no anisotropy, in agreement with the expected symmetry for these classical superconductors.

  10. 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.

  11. Incommensurate magnetism in PrBa{sub 2}Cu{sub 3}O{sub 6.92}

    SciTech Connect

    Hill, J.P.; Boothroyd, A.T.; Andersen, N.H.; Wolf, T.

    1998-11-01

    We report resonant x-ray magnetic scattering and high-resolution neutron-diffraction studies of the Pr site magnetism in high quality single crystals of PrBa{sub 2}Cu{sub 3}O{sub 6.92}. These studies reveal that the Pr sublattice orders at 19thinspK in a well correlated, long period incommensurate structure with probable wave vector (0.5{plus_minus}{delta},0.5,0) or (0.5,0.5{plus_minus}{delta},0) with {delta}=0.006 r.l.u. The observed x-ray scattering results from dipole transitions, demonstrating the existence of an ordered 5d Pr moment and implying a large 4f moment at the Pr site. A spin reorientation transition to a commensurate antiferromagnetic structure of wave vector (0.5,0.5,0.5) is observed at lower temperatures. {copyright} {ital 1998} {ital The American Physical Society}

  12. 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.

  13. Optical Measurement of Forming Limit and Formability of Cu/Al Clad Metals

    NASA Astrophysics Data System (ADS)

    Sun, Tao; Liang, Jin; Guo, Xiang; Ren, Maodong; Wang, Lizhong

    2015-04-01

    A digital image deformation measurement and analysis control system (XJTUDIC 8.0) was employed to measure the forming limit strain for Cu/Al clad metals produced via explosive welding technique. A contrast test between the digital image correlation (DIC) method and the conventional grid method was also implemented using the SPCC sheet metal forming limit test. The effect of heat treatment and contact status on forming limit was discussed based on the forming limit strain of Cu/Al clad metals. The interfacial and fracture structures were analyzed using scanning electron microscopy. The fracture site was predicted by finite element method. Results demonstrate that the forming limit curve of Cu/Al clad metals through DIC is more likely to reflect the formability of SPCC accurately. The forming limit of the clad with Al in the inner layer is higher than that of the clad with Cu in the inner layer. The formability of the annealed clads is superior to that of the non-annealed clads. The local interface failure induces the microcracks in Cu/Al clad metals during the forming process, which could be the main failure mode. With the finite element method, the fracture location of Cu/Al clad metals caused by uniaxial tensile during the forming limit test using DIC method is predicted accurately.

  14. 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.

  15. 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).

  16. Azide SHS of aluminium nitride nanopowder and its application for obtaining Al-Cu-AlN cast nanocomposite

    NASA Astrophysics Data System (ADS)

    Titova, Y. V.; Sholomova, A. V.; Kuzina, A. A.; Maidan, D. A.; Amosov, A. P.

    2016-11-01

    Method of azide self-propagating high-temperature synthesis (SHS-Az), using sodium azide (NaN3) as a nitriding reagent, was used for obtaining the nanopowder of aluminum nitride (AlN) from precursor that was sodium hexafluoroaluminate (Na3AlF6). The product of burning the mixture of Na3AlF6 + 3NaN3 after water rinsing consisted of micro - and nanoparticles of AlN (65%) and the residue of salt Na3AlF6 (35%). This product of SHS-Az was mixed with copper powder and pressed into a briquette of nanopowdery master alloy Cu- 4%(65%AlN+35%Na3AlF6), which was successfully introduced into aluminium melt at a temperature of 850°C. The salt Na3AlF6 in the product of combustion played a role of flux during introducing into the aluminum melt and was not included in the final composition of the composite alloy. The microstructure of the obtained cast composite aluminum alloy with the calculated composition of Al-1.2%Cu-0.035%AlN showed that the reinforcing particles of AlN of different sizes, including nanoparticles, were distributed mainly along the grain boundaries of the aluminum alloy.

  17. Investigation of SmBaCuCoO{sub 5+{delta}} double-perovskite as cathode for proton-conducting solid oxide fuel cells

    SciTech Connect

    Zhu, Zhiwen; Tao, Zetian; Bi, Lei; Liu, Wei

    2010-11-15

    SmBaCuCoO{sub 5+{delta}}, a double-perovskite oxide, was synthesized by the modified Pechini method and developed as cathode material for proton-conducting solid oxide fuel cells. The SmBaCuCoO{sub 5+{delta}} powders calcined at 800 {sup o}C, show the double-perovskite structure in powder XRD pattern. SmBaCuCoO{sub 5+{delta}} has a more suitable thermal expansion coefficient than SmBaCo{sub 2}O{sub 5+{delta}} for BaCe{sub 0.7}Zr{sub 0.1}Y{sub 0.2}O{sub 3-{delta}} electrolyte-based solid oxide fuel cells. The single cell was tested with humidified hydrogen ({approx}3% H{sub 2}O) as the fuel and static air as the oxidant. The performance of the cell was characterized by DC Electronic Load and AC impedance spectroscopy. The peak power densities reached 355-86 mW cm{sup -2} in the range of 700-550 {sup o}C and the interfacial polarization resistance decreased with increasing operation temperature, from 3.1 {Omega} cm{sup 2} at 550 {sup o}C to 0.22 {Omega} cm{sup 2} at 700 {sup o}C. The high power density and low polarization demonstrate that SmBaCuCoO{sub 5+{delta}} is a potential candidate for proton-conducting solid oxide fuel cells.

  18. Neutron-scattering evidence for a periodically modulated superconducting phase in the underdoped cuprate La1.905Ba0.095CuO4

    DOE PAGES

    Xu, Zhijun; Stock, C.; Chi, Songxue; ...

    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.

  19. Neutron-Scattering Evidence for a Periodically Modulated Superconducting Phase in the Underdoped Cuprate La1.905Ba0.095CuO4

    NASA Astrophysics Data System (ADS)

    Xu, Zhijun; Stock, C.; Chi, Songxue; Kolesnikov, A. I.; Xu, Guangyong; 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.

  20. Neutron-scattering evidence for a periodically modulated superconducting phase in the underdoped cuprate La1.905Ba0.095CuO4.

    PubMed

    Xu, Zhijun; Stock, C; Chi, Songxue; Kolesnikov, A I; Xu, Guangyong; Gu, Genda; Tranquada, J M

    2014-10-24

    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 La(2-x)Sr(x)CuO(4) and YBa(2)Cu(3)O(6+x).

  1. Wetting of TiC by Al-Cu alloys and interfacial characterization.

    PubMed

    Contreras, A

    2007-07-01

    The wetting behavior and the interfacial reactions that occurred between molten Al-Cu alloys (1, 4, 8, 20, 33, and 100 wt% Cu) and solid TiC substrates were studied by the sessile drop technique in the temperature range of 800-1130 degrees C. The effect of wetting behavior on the interfacial reaction layer was studied. All the Al-Cu alloys react with TiC at the interface forming an extensive reaction layer. The interface thickness varied with the samples, and depends on the temperature, chemical composition of the alloy and the time of the test. Wetting increases with increasing concentration of copper in the Al-Cu alloy at 800 and 900 degrees C. In contrast, at higher temperature such as 1000 degrees C wetting decreases with increasing copper content. The spreading kinetics and the work of adhesion were evaluated. The high values of activation energies indicated that spreading is not a simple viscosity controlled phenomenon but is a chemical reaction process. The spreading of the aluminum drop is observed to occur according to the formation of Al4C3, CuAl2O4, CuAl2, TiCux mainly, leading to a decreases in the contact angle. As the contact angle decreases the work of adhesion increases with increasing temperature. Al-Cu/TiC assemblies showed cohesive fracture corresponding to a strong interface. However, using pure Cu the adhesion work is poor, and the percentage of cohesion work is also too low (27-34%).

  2. Synthesis of YBa2Cu3O(7-δ) and Y2BaCuO5 nanocrystalline powders for YBCO superconductors using carbon nanotube templates.

    PubMed

    Shi, Yunhua; Hasan, Tawfique; Babu, Nadendla H; Torrisi, Felice; Milana, Silvia; Ferrari, Andrea C; Cardwell, David A

    2012-06-26

    We fabricate nanosized superconducting YBa(2)Cu(3)O(7-δ) (Y-123) and nonsuperconducting Y(2)BaCuO(5) (Y-211) powders using carbon nanotubes as template. The mean particle size of Y-123 and Y-211 is 12 and 30 nm, respectively. The superconducting transition temperature of the Y-123 nanopowder is 90.9 K, similar to that of commercial, micrometer-scale powders fabricated by conventional processing. The elimination of carbon and the formation of a high purity superconducting phase both on the micro- and macroscale is confirmed by Raman spectroscopy and X-ray diffraction. We also demonstrate improvement in the superconducting properties of YBCO single grain bulk samples fabricated using the nanosize Y-211 powder, both in terms of trapped field and critical current density. The former reaches 553 mT at 77 K, with a ∼20% improvement compared to samples fabricated from commercial powders. Thus, our processing method is an effective source of pinning centers in single grain superconductors.

  3. 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.

  4. 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.

  5. Length scale of the dendritic microstructure affecting tensile properties of Al-(Ag)-(Cu) alloys

    NASA Astrophysics Data System (ADS)

    Duarte, Roberto N.; Faria, Jonas D.; Brito, Crystopher; Veríssimo, Nathalia C.; Cheung, Noé; Garcia, Amauri

    2016-12-01

    The dependence of tensile properties on the length scale of the dendritic morphology of Al-Cu, Al-Ag and Al-Ag-Cu alloys is experimentally investigated. These alloys were directionally solidified (DS) under a wide range of cooling rates (Ṫ), permitting extensive microstructural scales to be examined. Experimental growth laws are proposed relating the primary dendritic arm spacing, λ1 to Ṫ and tensile properties to λ1. It is shown that the most significant effect of the scale of λ1 on the tensile properties is that of the ternary alloy, which is attributed to the more homogeneous distribution of the eutectic mixture for smaller λ1 and by the combined reinforcement roles of the intermetallics present in the ternary eutectic: Al2Cu and nonequilibrium Ag3Al.

  6. Synthesis and analysis of nanocrystalline β1-Cu3Al and β2-NiAl intermetallic-reinforced aluminum matrix composite by high energy ball milling

    NASA Astrophysics Data System (ADS)

    Nguyen, Hong-Hai; Nguyen, Minh-Thuyet; Kim, Won Joo; Kim, Jin-Chun

    2017-01-01

    Nanocrystalline β1-Cu3Al and β2-NiAl intermetallic compounds were in-situ reinforced in the aluminum matrix with the atomic composition of Al67Cu20Ni13 by the mechanical alloying of elemental powders. Both β1-Cu3Al, β2-NiAl phases that can be only co-synthesized in Cu base alloys have been obtained after 15h milling in this study. The phase evolution during milling process was investigated by X-ray diffraction. The β1-Cu3Al, β2-NiAl phases were metastable with further milling time up to 40 h. Specially, unreacted Al matrix has been totally transformed to amorphous state in the final powder. A remarkable crystalline size of 6.5 nm was reached after 15 h milling time. Thermal stability of the milled powder was also studied by differential thermal analysis. It is shown that β1-Cu3Al, β2-NiAl phases were stable up to higher than 550 °C. Moreover, the inter-diffusion between Al matrix and Cu3Al within the temperature range of 620-740 °C led to the formation of superstructure ζ1-Al3Cu4 phase.

  7. 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.

  8. Measurement of the mass attenuation coefficient from 81 keV to 1333 keV for elemental materials Al, Cu and Pb

    NASA Astrophysics Data System (ADS)

    Gjorgieva, Slavica; Barandovski, Lambe

    2016-03-01

    The mass attenuation coefficients (μ/ρ) for 3 high purity elemental materials Al, Cu and Pb were measured in the γ-ray energy range from 81 keV up to 1333 keV using 22Na, 60Co 133Ba and 133Cs as sources of gamma radiation. Well shielded detector (NaI (Tl) semiconductor detector) was used to measure the intensity of the transmitted beam. The measurements were made under condition of good geometry, assuring that any photon absorbed or deflected appreciably does not reach the detector. The measured values are compared with the theoretical ones obtained by Seltzer (1993).

  9. Critical current densities and irreversibility field of high-Tc Ba2Ca3Cu4O(O,F)2 superconductor

    NASA Astrophysics Data System (ADS)

    Shirage, P. M.; Iyo, A.; Shivagan, D. D.; Tanaka, Y.

    2008-03-01

    The superconductivity in apical fluorine system of Ba2Ca3Cu4O10-yFy: the fourth member of Ba2Can-1CunO2n(O,F)2 homologous series is significant to study as it deals with the novel phenomenon of superconductivity like co-existence of superconductivity and antiferromagnetism, in-equivalent and non-similar charge distribution in the CuO2 planes in a unit cell etc. The polycrystalline samples of Ba2Ca3Cu4O8(O,F)2 (F-0234) were synthesized under high pressure and showed sharp superconducting transitions temperature at 105 K. From the DA magnetization hysteresis loops, we determined the intragrain critical current density (Jc) and irreversibility field (Birr) using Bean's critical state model. The irreversibility line(IL) of F-0234 is higher than that for optimally-doped Bi-2212. However, IL much lower than that of Cu-1212 (Y-123) although the spacing of F-0234 (7.3 Å) is much thinner than that of Cu-1212.

  10. First-principles study of Be doped CuAlS2 for p-type transparent conductive materials

    NASA Astrophysics Data System (ADS)

    Huang, Dan; Zhao, Yu-Jun; Tian, Ren-Yu; Chen, Di-Hu; Nie, Jian-Jun; Cai, Xin-Hua; Yao, Chun-Mei

    2011-06-01

    CuAlS2 has attracted much attention recently as a p-type transparent conductive material. In this paper, we investigate the site preference of substitutional Be in CuAlS2 and the transition level of BeAl using the first-principles calculation. We find that Be would be doped effectively at Al sites in CuAlS2 as a good p-type dopant. In addition, we speculate that Be-Mg or Be-Zn codoped CuAlS2 could have a mobility enhancement and thus a good p-type conductivity due to low lattice distortion.

  11. Two-dimensional superconducting fluctuations in stripe-ordered La1.875Ba0.125CuO4.

    PubMed

    Li, Q; Hücker, M; Gu, G D; Tsvelik, A M; Tranquada, J M

    2007-08-10

    Recent spectroscopic observations of a d-wave-like gap in stripe-ordered La(2-x)Ba(x)CuO(4) with x=1/8 have led us to critically analyze the anisotropic transport and magnetization properties of this material. The data suggest that concomitant with the spin ordering is an electronic decoupling of the CuO(2) planes. We observe a transition (or crossover) to a state of two-dimensional (2D) fluctuating superconductivity, which eventually reaches a 2D superconducting state below a Berezinskii-Kosterlitz-Thouless transition. Thus, it appears that the stripe order in La(2-x)Ba(x)CuO(4) frustrates three-dimensional superconducting phase order, but is fully compatible with 2D superconductivity and an enhanced T(c).

  12. Effect of hydrogen on Al2O3/Cu interfacial structure and adhesion

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Gang; Smith, John R.; Scheffler, Matthias

    2002-08-01

    We have carried out an ab initio investigation of the effect of hydrogen on the Al2O3/Cu interface. H on the Al2O3 surface can play a bridging role in the formation of the interface. The interfacial OH bond is stable in the presence of two atomic layers of Cu. In contrast, an Al monolayer would dissociate the surface OH bond. For thicker Cu, one-third of a monolayer of H remains stable in the interface, lowering the work of separation by 2.3 J/m2. The interfacial work of separation remains larger than that of bulk Cu, however. These results are consistent with available experimental data.

  13. Cyclic Oxidation Behavior of CuCrAl Cold-Sprayed Coatings for Reusable Launch Vehicles

    NASA Technical Reports Server (NTRS)

    Raj, Sai; Karthikeyan, J.

    2009-01-01

    The next generation of reusable launch vehicles is likely to use GRCop-84 [Cu-8(at.%)Cr-4%Nb] copper alloy combustion liners. The application of protective coatings on GRCop-84 liners can minimize or eliminate many of the environmental problems experienced by uncoated liners and significantly extend their operational lives and lower operational cost. A newly developed Cu- 23 (wt.%) Cr-5% Al (CuCrAl) coating, shown to resist hydrogen attack and oxidation in an as-cast form, is currently being considered as a protective coating for GRCop-84. The coating was deposited on GRCop-84 substrates by the cold spray deposition technique, where the CuCrAl was procured as gas-atomized powders. Cyclic oxidation tests were conducted between 773 and 1,073 K to characterize the coated substrates.

  14. Direct observation of atomic-scale origins of local dissolution in Al-Cu-Mg alloys

    NASA Astrophysics Data System (ADS)

    Zhang, B.; Wang, J.; Wu, B.; Oguzie, E. E.; Luo, K.; Ma, X. L.

    2016-12-01

    Atomistic chemical inhomogeneities are anticipated to induce dissimilarities in surface potentials, which control corrosion initiation of alloys at the atomic scale. Precise understanding of corrosion is therefore hampered by lack of definite information describing how atomistic heterogeneities regulate the process. Here, using high-angle annular dark-field (HAADF) scanning transmission electron microscope (STEM) and electron energy loss spectroscopy (EELS) techniques, we systematically analyzed the Al20Cu2Mn3 second phase of 2024Al and successfully observed that atomic-scale segregation of Cu at defect sites induced preferential dissolution of the adjacent zones. We define an “atomic-scale galvanic cell”, composed of zones rich in Cu and its surrounding matrix. Our findings provide vital information linking atomic-scale microstructure and pitting mechanism, particularly for Al-Cu-Mg alloys. The resolution achieved also enables understanding of dealloying mechanisms and further streamlines our comprehension of the concept of general corrosion.

  15. Direct observation of atomic-scale origins of local dissolution in Al-Cu-Mg alloys

    PubMed Central

    Zhang, B.; Wang, J.; Wu, B.; Oguzie, E. E.; Luo, K.; Ma, X. L.

    2016-01-01

    Atomistic chemical inhomogeneities are anticipated to induce dissimilarities in surface potentials, which control corrosion initiation of alloys at the atomic scale. Precise understanding of corrosion is therefore hampered by lack of definite information describing how atomistic heterogeneities regulate the process. Here, using high-angle annular dark-field (HAADF) scanning transmission electron microscope (STEM) and electron energy loss spectroscopy (EELS) techniques, we systematically analyzed the Al20Cu2Mn3 second phase of 2024Al and successfully observed that atomic-scale segregation of Cu at defect sites induced preferential dissolution of the adjacent zones. We define an “atomic-scale galvanic cell”, composed of zones rich in Cu and its surrounding matrix. Our findings provide vital information linking atomic-scale microstructure and pitting mechanism, particularly for Al-Cu-Mg alloys. The resolution achieved also enables understanding of dealloying mechanisms and further streamlines our comprehension of the concept of general corrosion. PMID:28000750

  16. Microstructure evolution and strain localization in Cu and Cu-8Al single crystals subjected to channel-die compression.

    PubMed

    Lewandowska, Małgorzata; Swiatnicki, Wiesław; Piatkowski, Andrzej; Jasienski, Zdzisław

    2006-09-01

    Single crystals of pure Cu and Cu-8%Al with two initial orientations, {112}111 and {112}110, were subjected to monotonic compression in channel-die at room temperature (293 K). The dislocation microstructure and local crystallography were investigated by transmission electron microscopy after different amounts of deformation. Various factors, such as initial single crystal orientation, chemical composition and amount of plastic deformation, were analysed in order to determine their influence on the microstructure evolution, local orientation variations and strain localization phenomena.

  17. 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.

  18. A low-cost batch process for high-performance melt-textured GdBaCuO pellets

    NASA Astrophysics Data System (ADS)

    Muralidhar, M.; Tomita, M.; Suzuki, K.; Jirsa, M.; Fukumoto, Y.; Ishihara, A.

    2010-04-01

    High-Tc superconducting magnets promise a variety of industrial, medical, public, and research applications. However, the potential large-scale applications of these materials need excellent and uniform properties and a cheap production method. The batch process developed for the fabrication of GdBa2Cu3Oy pellets in air fulfils all of these requirements. The samples were melt-processed using a cold seeding method with thin film Nd-123 seeds grown on MgO crystals. We used self-made Gd-123 and Gd-211 powders mixed with 0.1 wt% of Pt. Up to 1-1.5 kg of melt-grown Gd-123 bulks could be prepared in one run. XRD analysis confirmed that all of the bulks were c-axis oriented. The superconducting and magnetic performance of the pellets was checked on several small test samples cut out at various standard positions within the bulk. The values were reasonably uniform and the performance was similar to the oxygen-controlled melt-grown Gd-123 samples. The average trapped field at 77 K in the 24 mm diameter batch samples was between 0.8 and 0.9 T, close to the maximum value of 1 T reported so far for Gd-123 single grains processed in air. The present results prove that a high-performance good-quality LREBa2Cu3Oy material can be scaled up from laboratory to industrial production.

  19. Two-dimensional mechanism of electrical conductivity in Gd1-xCexBa2Cu3O7-δ

    NASA Astrophysics Data System (ADS)

    Mofakham, S.; Mazaheri, M.; Akhavan, M.

    2008-08-01

    Partial substitutions of Pr and Ce are known to suppress the superconducting state in REBa2Cu3O7-δ systems. We have substituted Ce for Gd in Gd1-xCexBa2Cu3O7-δ compounds with x = 0.0-0.6 by the standard solid-state reaction technique. X-ray diffraction (XRD) experiments are performed and their results are refined by the Rietveld method. XRD analysis shows a predominantly single-phase perovskite structure with few impurity phases. Our resistivity results show that, by increasing the Ce content, Tc decreases, the transition temperature width increases, and in the normal state a metal-insulator transition (MIT) occurs at xc = 0.12. The normal state resistivity of the samples and their slopes change at this point. The normal state resistivity of the samples is fitted with the variable range hopping (VRH) and the Coulomb gap (CG). Our results are most consistent with the two-dimensional VRH model.

  20. 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.

  1. 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.

  2. Coherent charge and spin density waves in underdoped HgBa2CuO4+δ

    NASA Astrophysics Data System (ADS)

    Lee, Jeongseop A.; Xin, Yizhou; Halperin, W. P.; Reyes, A. P.; Kuhns, P. L.; Chan, M. K.

    2017-03-01

    Charge order in cuprate superconductors appears to be a universal characteristic, often associated with pseudogap behavior in the normal state. The central question is whether such charge ordering or the pseudogap are required for the existence of high temperature superconductivity and embody its mechanism. An important but phenomenological approach to this question is to examine whether these phenomena extend over various members of the cuprate family. Recent nuclear magnetic resonance (NMR) measurements on oxygen chain-ordered single crystals of YBa2Cu3O6+y (Y123) have demonstrated temperature and magnetic field induced charge ordering that was confirmed in x-ray experiments. In the present work on high-quality single crystals of the tetragonal compound, HgBa2CuO4+δ , we use 17O NMR to investigate the interplay between charge and spin order deduced from the full quadrupolar-split NMR spectrum over a wide range of temperature and magnetic field. We have found evidence for a coherent modulation of charge and spin order in this compound. However, neither temperature nor magnetic field induced ordering was observed and we infer that this aspect of high temperature superconductivity is not universal.

  3. Coexisting charge and magnetic orders in the dimer-chain iridate Ba5AlIr2O11

    DOE PAGES

    Terzic, J.; Wang, J. C.; Ye, Feng; ...

    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

  4. A new type of Cu-Al-Ta shape memory alloy with high martensitic transformation temperature

    NASA Astrophysics Data System (ADS)

    Wang, C. P.; Su, Y.; Y Yang, S.; Shi, Z.; Liu, X. J.

    2014-02-01

    In this study, a new type of Cu-Al-Ta (Cu86Al12Ta2 wt%) shape memory alloy with high martensitic transformation temperature is explored. The microstructure, reversible martensitic transformation and shape memory properties are investigated by means of optical microscopy, back-scattered electron, electron probe microanalysis, x-ray diffraction, differential scanning calorimetry and tensile tests. It is proposed that Cu86Al12Ta2 alloy consists of a mixture of primarily {\\beta }_{1}^{\\prime} martensite and a little {\\gamma }_{1}^{\\prime} martensite and some different precipitates. The tiny thin-striped Ta2(Al,Cu)3 precipitate is predominant in the as-quenched condition, whereas the particle-shaped Cu(Al, Ta) precipitate is dominant after hot-rolling. Additionally, the dendritic-shaped γ1(Cu9Al4) phase begins to appear after hot-rolling, but it disappears when the sample is re-quenched. All studied samples have reversible martensitic transformation temperatures higher than 450 ° C. The results show that two-step martensitic transformation behavior is observed for Cu86Al12Ta2 alloy in all three different conditions due to the transformations between ({\\beta }_{1}^{\\prime}+{\\gamma }_{1}^{\\prime}) martensites and the austenite parent phase. The results further show that the recovery ratios are almost 100% when the pre-strains are ≤2.5%, then they gradually decrease with further increase of the pre-strains. The shape memory effects clearly increase as a result of increase of the pre-strains, up to a maximum value of 3.2%.

  5. Microstructural Observations in a Cast Al-Si-Cu/TiC Composite

    NASA Astrophysics Data System (ADS)

    Karantzalis, A. E.; Lekatou, A.; Georgatis, E.; Poulas, V.; Mavros, H.

    2010-06-01

    A 3-5 vol.% TiC particulate Al-Si-Cu composite was prepared by diluting Al/20 vol.% TiC composite in an Al-7Si-4Cu alloy matrix. TiC particle distribution consists of isolated and clustered particles which are both located at the primary-α grain boundaries and at the areas of the last solidified liquid. Particle pushing by the solidification front is responsible for the final particle location. The solidified microstructure consists of primary and intermetallic phases formed by a sequence of possible eutectic reactions. No evidence of TiC particle degradation was observed.

  6. Superconducting properties and their relation with the hole concentration of La 1+ xBa 2- xCu 3O 7- δ system

    NASA Astrophysics Data System (ADS)

    Akinaga, H.; Takita, K.; Asano, H.; Masuda, K.

    1989-12-01

    The relation between superconducting transition temperature Tc and the hole concentration was investigated in single-phase samples of the La 1+ xBa 2- xCu 3O 7- δ solid solution system, where the hole concentration was changed by La-substitution for Ba ion. Hole concentration was determined by two different methods: Hall effect measurement and iodometry. T c decreased with decreased of pH(= {1}/{R He }). The hole concentration 3 p determined by the iodometry, where p is the average charge of [ shows no correlation with Tc. The hole concentration (2 ps in Cu-O sheets between La and Ba sites calculated based on Tokura's assumption gives a similar value to p H. This Tc-2 ps relation is almost the same to that of Ln 1+ xBa 2- xCu 3O 7- δ (Ln = Nd, Sm and Eu) reported previously. In spite of that the x-dependence of p in the present system is rather different from those of Nd-, Sm-and Eu-systems.

  7. AlCu alloy films prepared by the thermal diffusion technique

    SciTech Connect

    Oliva, A.I.; Corona, J.E.; Sosa, V.

    2010-07-15

    100-nm thick films of Al{sub 1-x}Cu{sub x} alloys were prepared on glass substrates by thermal diffusion technique. The Cu atomic concentration was varied from 10% to 90%. Alloys were prepared at different temperatures into a vacuum oven with Argon atmosphere. Two thermal processes were used: i) heating the film at 400 deg. C in a single step, and ii) heating the films in sequential steps at 100, 200, 300 and 400 deg. C. Morphology, electrical resistivity, and crystalline orientation of the alloys were studied. The electrical resistivity and surface roughness of the alloys were found to depend strongly on the atomic composition and the diffusion temperature. However, we did not find differences between samples prepared under the two thermal processes. Alloys prepared with x = 0.6 and x = 0.1-0.3 as Cu at concentration exhibited values on electrical resistivity and surface roughness lower than pure Al. Different phases of the Al{sub 1} {sub -} {sub x}Cu{sub x} films were observed as a function of Cu concentration showing a good agreement with the AlCu phase diagram.

  8. 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

  9. X-ray emission study of ion beam mixed Cu/Al films on polyimide

    SciTech Connect

    Kurmaev, E.Z.; Zatsepin, D.A.; Winarski, R.P.; Stadler, S.; Ederer, D.L.; Moewes, A.; Fedorenko, V.V.; Shamin, S.N.; Galakhov, V.R.; Chang, G.S.; Whang, C.N.

    1999-03-01

    Cu (40 nm)/Al/polyimide/Si was mixed with 80 keV Ar{sup +} and N{sub 2}{sup +} from 5.0{times}10{sup 15} to 15{times}10{sup 15} ions/cm{sup 2}. Ultrasoft x-ray emission valence spectra (XES) of Cu, C, N and O excited by electron and photon radiation were used for study of chemical reactions in Cu/Al/PI/Si and PI/Si systems induced by ion beam mixing in dependence of type of ions and dose. It is found that ion beam mixing changes the chemical state of Cu atoms with respect to that of pure metal. These changes depend on the dose of ion beam bombardment and type of ions and are attributed to a formation of CuAl{sub 2}O{sub 4} interfacial layer, which can be responsible for enhanced interfacial adhesion strength. On the other hand, it is shown that the shape of C {ital K}{alpha}, N {ital K}{alpha} and O {ital K}{alpha} XES of ion beam mixed polyimide layer (PI/Si) is modified with ion bombardment. This means that the ion-beam mixing process is able to break the bonding of constituent atoms of irradiated PI layers and can induce the formation of chemically bonded complexes linking atoms in the Cu, Al and PI layers.{copyright} {ital 1999 American Vacuum Society.}

  10. 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.

  11. Mössbauer spectroscopy study of Al distribution in BaAlxFe12-xO19 thin films

    NASA Astrophysics Data System (ADS)

    Przybylski, M.; Żukrowski, J.; Harward, I.; Celiński, Z.

    2015-05-01

    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.

  12. Processing of large YBa2 Cu3Ox domains for levitation applications by a Nd1+x Ba2-x Cu3 Oy-Seeded melt-growth technique

    NASA Astrophysics Data System (ADS)

    Todt, V. R.; Sengupta, S.; Shi, Donglu; Sahm, P. R.; McGinn, P. J.; Poeppel, R. B.; Hull, J. R.

    1994-11-01

    YBa2Cu3Ox domains for levitation applications have been produced by a seeding technology that includes Nd1+x Ba2-x Cu3Oy seeds and melt-processing technologies such as conventional melt-textured growth, melt-texturing with PtO2 and Y2BaCuO5 additions, and the new solid-liquid-melt-growth technology. Large domains (˜20 mm) with high levitation forces (F1 up to 8.2 N) have been produced. The reproducibility of the results is good, and the capability of producing a large number of pellets in a single batch indicates good potential for the production of large amounts of this material.

  13. Crystallization kinetics of rapidly quenched Cu50Zr50 and Cu46Zr46Al8 glass-forming alloys

    NASA Astrophysics Data System (ADS)

    Kulikova, T. V.; Ryltseva, A. A.; Bykov, V. A.; Estemirova, S. Kh; Shuhyaev, K. Yu

    2017-01-01

    We studied the crystallization processes, the structure and thermal properties of amorphous alloys Cu50Zr50 and Cu46Zr46Al8 in a wide temperature range. Comparative study of the crystallization kinetics of these amorphous alloys was carried out for the first time using multivariate non-linear regression. It was found that mechanisms of the crystallization of studied metallic glasses are substantially different. The binary alloy is crystallized by branched reaction complex in four steps. For the ternary system was proposed two-step kinetic model of the crystallization process with consecutive reactions. The values of the total energy of activation for each crystallization stage reach to Cu50Zr50: E1 (345.2 kJ/mol); E2 (307.9 kJ/mol), E3 (281.1 kJ/mol), E4 (259.51 kJ/mol) and Cu46Zr46Al8: E1 (350.7 kJ/mol); E2 (150.4 kJ/mol).

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. A combined powder melt and infiltration growth technique for fabricating nano-composited Y-Ba-Cu-O single-grain superconductor

    NASA Astrophysics Data System (ADS)

    Li, Guo-Zheng; Li, Jia-Wei; Yang, Wan-Min

    2015-10-01

    The top-seeded melt growth (MG) and infiltration growth (IG) techniques are the two most popular methods of fabricating single-grain Y-Ba-Cu-O (YBCO) bulk superconductors, which are also considered as two distinctly different processes. In this study, we report a combined powder melt and infiltration growth (PM-IG) technique for fabricating nano-composited YBCO single-grain superconductors using raw metallic oxides. In this new technique, a solid source pellet (SSP) of composition nano-Y2O3 + BaO + CuO + 1 wt.%CeO2 and a liquid source pellet (LSP) of composition nano-Y2O3 + 10BaO + 16CuO are employed, thus during heat treatment process the powder melt in SSP (corresponding to the final YBCO bulk) and liquid infiltration from LSP to SSP coexist. Because the process of precursor powder synthesis is avoided, the fabrication flow is much simplified and the experimental efficiency is increased significantly. Microstructural observation indicates that a large number of Y2BaCuO5 nano-inclusions (around 100 nm) are trapped in the YBa2Cu3O7-δ superconducting matrix. Measurements of levitation force and trapped field prove the superior performance of the nano-composited YBCO sample. The calculated zero-field J c at 77 K reaches 6.98 × 104 A cm-2, nearly 23% higher than the sample fabricated by the conventional IG technique. Thus, this study supplies a practical method for fabricating nano-composited YBCO bulk superconductors with high performance.

  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. 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.

  1. 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.

  2. Real-time x-ray microbeam characterization of electromigration effects in Al(Cu) wires

    SciTech Connect

    Wang, P.-C.; Noyan, I. C.; Kaldor, S. K.; Jordan-Sweet, J. L.; Liniger, E. G.; Hu, C.-K.

    2001-04-30

    We report real-time, in situ x-ray microbeam measurements of electromigration-induced Cu redistribution, and the concurrent local stress variation in Al(Cu) wires. The data, which were obtained by combining x-ray microtopography with energy-dispersive fluorescence analysis, encompass both the early and late stages of electromigration as well as the postrelaxation stage at high temperature with the current turned off. We observe that both Cu concentration and stress values show unexpected local variations that may reflect the effect of local configuration such as film--substrate interface integrity or microstructure.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. Variation of anomalous Pr ordering and crystal symmetry for the oxygenated Pr1+xBa2-xCu3O7+y system

    NASA Astrophysics Data System (ADS)

    Luo, H. M.; Lin, B. N.; Lin, Y. H.; Chiang, H. C.; Hsu, Y. Y.; Hsu, T. I.; Lee, T. J.; Ku, H. C.; Lin, C. H.; Kao, H.-C. I.; Shi, J. B.; Ho, J. C.; Chang, C. H.; Hwang, S. R.; Li, W.-H.

    2000-06-01

    Structural, transport, magnetic, calorimetric, and neutron data were reported for the oxygen-annealed Pr1+xBa2-xCu3O7+y or 1212-type Cu(Ba2-xPrx)PrCu2O7+y system (0<=x<=1, -0.11<=y<=0.31). Powder x-ray Rietveld analysis indicates that due to subtle oxygen distribution in the CuO1+y plane for these oxygenated cuprates, two structural symmetry transitions were observed, from orthorhombic 1212C (CuO chain) O(I) phase (space group Pmmm) for 0<=x<=0.4, to tetragonal 1212 T phase (P4/mmm) for 0.4<=x<=0.65, and then to a different type of orthorhombic 1212 O(II) phase (Cmmm) for 0.65Ba is not favorable for metallic state and no superconductivity can be detected for these insulating cuprates. Magnetic-susceptibility, heat-capacity, and neutron-diffraction data show that, regardless of the structural transitions, the anomalous Néel temperature TN(Pr) decreases monotonically and smoothly from 18 K for x=0 to 2.5 K for x=0.8, with the same c-axis antiferromagnetic Pr spin alignment. The increasing Pr-O bond length observed with decreasing TN(Pr) indicates that this unusual Pr magnetic ordering is closely correlated with the wave-function overlap between Pr-4f orbital and eight O-2pπ orbital in the CuO2 bilayer.

  8. 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.

  9. 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.

  10. Joule-Heating-Induced Damage in Cu-Al Wedge Bonds Under Current Stressing

    NASA Astrophysics Data System (ADS)

    Yang, Tsung-Han; Lin, Yu-Min; Ouyang, Fan-Yi

    2014-01-01

    Copper wires are increasingly used to replace gold wires in wire-bonding technology owing to their better electrical properties and lower cost. However, not many studies have been conducted on electromigration-induced failure of Cu wedge bonds on Al metallization. In this study, we investigated the failure mechanism of Cu-Al wedge bonds under high current stressing from 4 × 104 A/cm2 to 1 × 105 A/cm2 at ambient temperature of 175°C. The resistance evolution of samples during current stressing and the microstructure of the joint interface between the Cu wire and Al-Si bond pad were examined. The results showed that abnormal crack formation accompanying significant intermetallic compound growth was observed at the second joint of the samples, regardless of the direction of electric current for both current densities of 4 × 104 A/cm2 and 8 × 104 A/cm2. We propose that this abnormal crack formation at the second joint is mainly due to the higher temperature induced by the greater Joule heating at the second joint for the same current stressing, because of its smaller bonded area compared with the first joint. The corresponding fluxes induced by the electric current and chemical potential difference between Cu and Al were calculated and compared to explain the failure mechanism. For current density of 1 × 105 A/cm2, the Cu wire melted within 0.5 h owing to serious Joule heating.

  11. Mechanism of resistive switching in Cu/AlOx/W nonvolatile memory structures

    NASA Astrophysics Data System (ADS)

    Sleiman, A.; Sayers, P. W.; Mabrook, M. F.

    2013-04-01

    The mechanism for resistive switching in aluminum oxide (AlOx) based electrochemical metallization memory cells is presented. Copper/AlOx/tungsten (Cu/AlOx/W) cells show reproducible resistive switching with an ON/OFF ratio of about 5 × 102 at a reading voltage of 0.1 V and reliable retention characteristics. Resistive switching occurs due to the formation and rupture of a Cu filament between the active electrode (Cu) and the counter electrode (W). The conduction of the devices was explained through back-to-back Schottky contacts in the OFF state, while it exhibits ohmic behavior in the ON state. Thermionic emission model was used to calculate the barrier heights of the Schottky contacts. The rupture of the Cu filament proved to occur at the weakest point of the filament inside the AlOx. Using Ohms Law, the slope of the linear I-V characteristics in the ON state was used to extract the Cu filament resistance and its diameter was estimated to be between 6 and 23 nm.

  12. Corrosion behaviors of Al-Si-Cu-based filler metals and 6061-T6 brazements

    NASA Astrophysics Data System (ADS)

    Su, T. L.; Wang, S. S.; Tsao, L. C.; Chang, S. Y.; Chuang, T. H.; Yeh, M. S.

    2002-04-01

    The corrosion behaviors of a series of Al-Si-Cu-based filler metals and the 6061-T6 butt joints brazed with these filler metals are evaluated by polarization tests and immersion tests in a 3.5% NaCl aqueous solution. For comparison, a traditional Al-12Si filler metal is also employed. The results indicate that the Al-Si-Cu-based filler metals before brazing possess much higher corrosion current densities and pitting tendencies than the Al-12Si filler metal. However, brazing of the 6061-T6 alloy with an Al-12Si filler metal produces a wider butt joint, which, in this case, creates a more extensive corrosion region. Severe galvanic corrosion occurs at the 6061-T6 joints when brazed with Al-Si-Cu-based filler metals. However, in the case of the 6061-T6/Al-12Si brazements, selective corrosion of the Al-12Si eutectic phase can be observed. The bonding strengths of the 6061-T6 butt joints brazed with various filler metals are also measured before and after the immersion tests.

  13. Growth of intermetallic phases in Al/Cu composites at various annealing temperatures during the ARB process

    NASA Astrophysics Data System (ADS)

    Hsieh, Chih-Chun; Shi, Ming-Shou; Wu, Weite

    2012-02-01

    The purpose of this study is to discuss the effect of annealing temperatures on growth of intermetallic phases in Al/Cu composites during the accumulative roll bonding (ARB) process. Pure Al (AA1100) and pure Cu (C11000) were stacked into layered structures at 8 cycles as annealed at 300 °C and 400 °C using the ARB technique. Microstructural results indicate that the necking of layered structures occur after 300 °C annealing. Intermetallic phases grow and form a smashed morphology of Al and Cu when annealed at 400 °C. From the XRD and EDS analysis results, the intermetallic phases of Al2Cu (θ) and Al4Cu9 (γ2) formed over 6 cycles and the AlCu (η2) precipitated at 8 cycles after 300 °C annealing. Three phases (Al2Cu (θ), Al4Cu9 (γ2), and AlCu (η2)) were formed over 2 cycles after 400 °C annealing.

  14. Nd substitution in y/ba sites in melt processed YBa2Cu3O7- δ through Nd2O3 additions

    NASA Astrophysics Data System (ADS)

    Varanasi, Chakrapani; Mc Ginn, Paul J.; Blackstead, Howard A.; Pulling, David B.

    1995-12-01

    YBa2Cu3O7- δ (Y123) samples with excess Nd2O3 and Y2O3 additions in the same molar ratios were melt textured in air. In the Nd-doped samples, in addition to Y ion site substitution, partial substitution into the Ba2+ sites is anticipated because of the similar ionic sizes of Nd3+ and Ba2+. The microstructure, Tc, and magnetic properties of Nd-doped samples were analyzed and compared with undoped Y123 and samples with excess Y2O3. The Nd2O3 additions lead to significant magnetization improvements, likely due to both rare earth- and Ba-site substitution by the doped Nd3+ ions, and to increases in Tc. Y2O3 additions resulted in no marked property enhancement.

  15. Tensile fatigue behavior and crack growth in GdBa2Cu3O7‑x /stainless-steel coated conductor grown via reactive co-evaporation

    NASA Astrophysics Data System (ADS)

    Rogers, Samuel; Schwartz, Justin

    2017-04-01

    (RE)Ba2Cu3O7‑x (REBCO) conductors have the potential to enable a wide range of superconducting applications over a range of temperatures and magnetic fields (Vincent et al 2013 IEEE Trans. Appl. Supercond. 23 5700805), yet AC applications and devices with a charge/discharge cycle may be limited by the conductor fatigue properties. Here the fatigue behavior of GdBa2Cu3O7‑x (GdBCO) conductors grown by reactive co-evaporation on stainless-steel substrates is reported for axial tensile strains, ε, up to 0.5% and 100 000 cycles. Failure mechanisms are investigated via microstructural studies and compared with a commercially available IBAD/MOCVD REBCO conductor. Results show that GdBCO/stainless-steel conductors retain their transport critical current for 10 000 cycles at ε = 0.35% and ε = 0.45%, and for 1000 cycles at ε = 0.50%. The main cause of fatigue degradation in GdBCO conductors is crack propagation and delamination that initiates at the edge of the conductor due to manufacturing defects.

  16. 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

  17. Sol-gel processing of precursor for high- Tc superconductors: influence of rhenium on the synthesis of Ba 2Ca 2Cu 3O x

    NASA Astrophysics Data System (ADS)

    Sin, A.; Odier, P.; Núñez-Regueiro, M.

    2000-03-01

    A sol-gel method for processing precursors of mercury-cuprates is described. It uses the gelification of a solution by acrylamide polymerisation and may be applied to concentrated solutions if a proper stabilisation of the cations is ensured. The method is described here for Ba 2Ca 2Cu 3O x and Re 0.25Ba 2Ca 2Cu 3O x but may serve to other precursors. Barium carbonate contamination is avoided in a large extent and Re-addition even helps by its efficient combination at low temperature with barium species. The precursor, with Re, might be handled without complicated precautions. Superconductors have been prepared in this way with an excellent homogeneity and high Tc.

  18. 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.

  19. 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.

  20. 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.; ...

    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

  1. 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.

  2. 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.

  3. Orthogonal spin arrangement as possible ground state of three-dimensional Shastry-Sutherland network in Ba3Cu3In4O12

    NASA Astrophysics Data System (ADS)

    Volkova, O. S.; Maslova, I. S.; Klingeler, R.; Abdel-Hafiez, M.; Arango, Y. C.; Wolter, A. U. B.; Kataev, V.; Büchner, B.; Vasiliev, A. N.

    2012-03-01

    The Ba3Cu3In4O12 stands for unique topology of the magnetic subsystem. It consists of rotated by 90° relative to each other “paper-chain” columns made of vertex-sharing CuIO4 and CuIIO4 planar units. The overall pattern of the copper ions is that of a three-dimensional Shastry-Sutherland network. At high temperatures, the magnetic susceptibility follows the Curie-Weiss law with positive Weiss temperature indicating strong predominance of ferromagnetic coupling. At low temperatures, however, this compound exhibits a long-range antiferromagnetically ordered state that reaches saturation magnetization by a nontrivial succession of two spin-flop and two spin-flip transitions already in modest magnetic fields. We show that the ground state in Ba3Cu3In4O12 may be a three-dimensional orthogonal arrangement of the Cu2+ (S = 1/2) magnetic moments forming three virtually independent antiferromagnetic subsystems. In this arrangement, favored by anisotropic exchange interactions, the quantum fluctuations provide the coupling between three mutually orthogonal magnetic subsystems resulting in an impressive “order by disorder” effect.

  4. Spontaneous symmetry breaking by charge stripes in the high pressure phase of superconducting La1.875Ba0.125CuO4.

    PubMed

    Hücker, M; Zimmermann, M V; Debessai, M; Schilling, J S; Tranquada, J M; Gu, G D

    2010-02-05

    In those cases where charge-stripe order has been observed in cuprates, the crystal structure is such that the average rotational symmetry of the CuO2 planes is reduced from fourfold to twofold. As a result, one could argue that the reduced lattice symmetry is essential to the existence of stripe order. We use pressure to restore the average fourfold symmetry in a single crystal of La1.875Ba0.125CuO4, and show by x-ray diffraction that charge-stripe order still occurs. Thus, electronically driven stripe order can spontaneously break the lattice symmetry.

  5. Spontaneous Symmetry Breaking by Charge Stripes in the High Pressure Phase of Superconducting La1.875Ba0.125CuO4

    NASA Astrophysics Data System (ADS)

    Hücker, M.; v. Zimmermann, M.; Debessai, M.; Schilling, J. S.; Tranquada, J. M.; Gu, G. D.

    2010-02-01

    In those cases where charge-stripe order has been observed in cuprates, the crystal structure is such that the average rotational symmetry of the CuO2 planes is reduced from fourfold to twofold. As a result, one could argue that the reduced lattice symmetry is essential to the existence of stripe order. We use pressure to restore the average fourfold symmetry in a single crystal of La1.875Ba0.125CuO4, and show by x-ray diffraction that charge-stripe order still occurs. Thus, electronically driven stripe order can spontaneously break the lattice symmetry.

  6. Microstructure properties and microhardness of rapidly solidified Al64Cu20Fe12Si4 quasicrystal alloy

    NASA Astrophysics Data System (ADS)

    Karaköse, Ercan; Keskin, Mustafa

    2012-04-01

    This paper presents differences in the microstructure and microhardness properties of conventional casting (ingot) and rapidly solidified Al64Cu20Fe12Si4 quasicrystal (QC) alloys. The phases present in the Al64Cu20Fe12Si4 ingot alloy were determined to be icosahedral quasicrystalline (IQC) Ψ-Al65Cu20Fe15, cubic β-AlFe, tetragonal θ-Al2Cu, and monoclinic λ-A13Fe4 phases, whereas only IQC Ψ-Al65Cu20Fe15 and cubic β-AlFe phases were identified in the rapidly solidified alloy. The microhardness value of the melt spun alloy was measured to be approximately 790 kg/mm2. Microhardness increases with increasing solidification rates.

  7. Resistance to Fracture, Fatigue and Stress-Corrosion of Al-Cu-Li-Zr Alloys

    DTIC Science & Technology

    2007-11-02

    Zr alloyý, 4 Heat treatment and hot rolling schedules fur 66 the Al-Cu-Li-Zr alloys 5 Laue transmission analysis of Al-Cu-Li-Zr alloys 67 6 X-ray...ratio, there appears to be an increase in amount of matrix 6 ’ as well as grain boundary precipitates ( 6 , T-phase) (? 4 ). As a result, there is a...containing 6 ’ precipitates that enhance slip planarity and certain titanium alloys (e.g. alloys with acicular astructure), will be expected to have a

  8. Equation of State of an AlCoCrCuFeNi High-Entropy Alloy

    NASA Astrophysics Data System (ADS)

    Li, Gong; Xiao, Daihong; Yu, Pengfei; Zhang, Lijun; Liaw, Peter K.; Li, Yanchun; Liu, Riping

    2015-08-01

    The pressure-volume (P-V) relationship of the AlCoCrCuFeNi high-entropy alloy (HEA) at room temperature has been studied using in situ high-pressure energy-dispersive x-ray diffraction with synchrotron radiation at high pressures. The equation of state of the AlCoCrCuFeNi HEA is determined by the calculation of the radial distribution function. The experimental results indicate that the HEA keeps a stable face-centered-cubic + body-centered-cubic structure in the experimental pressure range from 0 GPa to 24 GPa.

  9. 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

  10. Re-investigation of phase equilibria in the system Al-Cu and structural analysis of the high-temperature phase η1-Al1-δCu.

    PubMed

    Ponweiser, Norbert; Lengauer, Christian L; Richter, Klaus W

    2011-11-01

    The phase equilibria and reaction temperatures in the system Al-Cu were re-investigated by a combination of optical microscopy, powder X-ray diffraction (XRD) at ambient and elevated temperature, differential thermal analysis (DTA) and scanning electron microscopy (SEM). A full description of the phase diagram is given. The phase equilibria and invariant reactions in the Cu-poor part of the phase diagram could be confirmed. The Cu-rich part shows some differences in phase equilibria and invariant reactions compared to the known phase diagram. A two phase field was found between the high temperature phase η1 and the low temperature phase η2 thus indicating a first order transition. In the ζ1/ζ2 region of the phase diagram recent findings on the thermal stability could be widely confirmed. Contrary to previous results, the two phase field between δ and γ1 is very narrow. The results of the current work indicate the absence of the high temperature β0 phase as well as the absence of a two phase field between γ1 and γ0 suggesting a higher order transition between γ1 and γ0. The structure of γ0 (I-43m, Cu5Zn8-type) was confirmed by means of high-temperature XRD. Powder XRD was also used to determine the structure of the high temperature phase η1-Al1-δCu. The phase is orthorhombic (space group Cmmm) and the lattice parameters are a = 4.1450(1) Å, b = 12.3004(4) Å and c = 8.720(1) Å; atomic coordinates are given.

  11. 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).

  12. 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.

  13. Josephson effects in a Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ break junction at 77 K

    SciTech Connect

    Zhao, S.P.; Tao, H.J.; Chen, Y.F.; Che, G.C.; Yang, Q.S.

    1989-03-10

    Josephson effects in a Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ break junction at 77 K are reported. The I-V characteristics show clear Shapiro steps under microwave radiation and magnetic dependence of the critical current is of the typical Fraunhofer diffraction pattern. Estimate of the magnetic penetration depth is given. Discussions of the I-V curve concerning nonstationary processes are presented.

  14. 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.

  15. 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.

  16. Thermal Analysis of the Effect of Oxygen Contamination on Undercooling of Zr-Al-Ni-Cu, Cu-Zr-Ti, and Cu-Ni-Zr-Ti Metallic Glasses (Preprint)

    DTIC Science & Technology

    2009-04-01

    been done on systems other than Zr65Al7.5(Cu17.5Ni10). Zr55Al10(Cu30Ni5) was found to be less sensitive to oxygen content than Zr65Al7.5(Cu17.5Ni10...Zr11Ti34 by arc-melting each of the pure elements under a titanium - gettered atmosphere. Starting materials used were: Al pellets, 99.999%; Cu shot...produce 2-6 g alloyed ingots of each composition. Each ingot was flipped typically 4-5 times in a titanium -gettered, high-purity argon atmosphere

  17. Laser drilling: enhancing superconducting joint of GdBa2Cu3O7 - δ coated conductors

    NASA Astrophysics Data System (ADS)

    Park, Y. J.; Lee, M. W.; Oh, Y. K.; Lee, H. G.

    2014-08-01

    While GdBa2Cu3O7 - δ (GdBCO) coated conductors (CCs) have been proposed for superconducting applications, they have not been used in devices with persistent current mode (PCM) operation because of a lack of joining techniques. A superconducting joint of CCs, formed via melting diffusion and oxygenation annealing, offers no electrical resistance between the CCs, thus establishing a superconducting closed loop for PCM operation. Because superconductivity degrades with oxygen out-diffusion during melting diffusion, oxygenation annealing allows oxygen diffusion into the GdBCO lattices. As effective oxygenation annealing requires oxygen pathways in the joint, low solubility and diffusivity of oxygen in the buffer and CC substrate hinder full superconductivity recovery. Here we show a laser-drilling technique to produce microholes as conduits on the surfaces of GdBCO CCs’ to promote oxygen in-diffusion, which resulted in reduced superconductivity recovery time. Superconductivity was fully recovered after laser drilling, melting diffusion at 850 °C for 1 min, and oxygenation annealing at 500 °C for 350 h.

  18. Transverse resistance in Y1-yPryBa2Cu3O7-δ at large praseodymium concentrations

    NASA Astrophysics Data System (ADS)

    Vovk, Ruslan V.; Khadzhai, Georgij Ya.; Dobrovolskiy, Oleksandr V.

    2014-10-01

    The effect of praseodymium doping on the transverse electrical resistance of Y1-yPryBa2Cu3O7-δ single crystals is investigated by electrical resistance measurements. The resistance curves can be fitted well to an expression accounting for the thermo-activated variable-range hopping charge transfer in conjunction with the fluctuation conductivity in the 3D Aslamazov-Larkin model. Our analysis of the Pr concentration dependence of the fitting parameters shows that in the concentration range 0.34

  19. Tl 2Ba 2CaCu 2O 8 thin film high frequency filters on 3 inch sapphire substrates

    NASA Astrophysics Data System (ADS)

    Schneidewind, H.; Manzel, M.; Stelzner, T.

    2002-08-01

    Modern communication systems require densely packed frequency channels in the expensive frequency bands. Therefore high temperature superconducting (HTS) high frequency filters are of increasing importance, taking advantage of their outstanding properties namely steep filter skirts, low insertion loss, and furthermore reduced mass and volume compared to conventional cavity or dielectric resonator systems. Within the framework of a German BMBF pilot project a HTS equiped satellite repeater will be developed to demonstrate the performance advantage of HTS. For that purpose we prepare filters on double-sided Tl 2Ba 2CaCu 2O 8 thin films on CeO 2 buffered 3 inch sapphire substrates. The HTS films are prepared in the two-step process by sputtering an amorphous thallium free precursor and following oxythallination. The critical temperature and spatial distribution of critical current density at 77 K, both measured by inductive techniques, show values above 100 K or 1 MA/cm 2, respectively. We use a dielectric resonator technique at 3.9 GHz and power levels up to some mT to determine the films surface resistance. We present measurements of input filters made from our double-sided 3 inch films.

  20. Improvement of superconducting properties of old Y Ba Cu O specimens by high-energy heavy ion irradiation

    NASA Astrophysics Data System (ADS)

    Kirschner, I.; Balogh, A.; Peurla, M.; Laiho, R.; Mészáros, Cs.; Pintér-Csordás, A.

    2006-12-01

    Superconducting parameters of different, almost 20 years old Y-Ba-Cu-O samples, prepared in 1987-1988 are investigated. The aim of this research is to find out how a heavy ion beam can enhance the superconducting features of very old and originally not always perfect Y-based specimens. As is observed, their electrical and magnetic characteristics are very sensitive to high-energy Bi-ion irradiation, which results in significant increase of the superconducting parameters. The most important one of them is the global critical current density which is calculated with the help of a new method on the basis of experiments. It can be increased by 18-39%, depending on the original, starting conditions of the samples before the irradiation. At the same time, the average values of intragrain critical current density grows by 37-51%. A slight increase in the critical temperature of 1-2 K was also observed. The experiments on AC susceptibility demonstrate that this irradiation causes to develop faster the total diamagnetic state and decreases the loss. The reason of these effects can be found in the better orientation of crystals, enlargement of microcrystalline aggregates, higher homogenization of the material, thus, in the increase of the superconducting component of samples due to the irradiation.

  1. Quasiparticle recombination dynamics in the model cuprate superconductor HgBa2CuO4+δ

    NASA Astrophysics Data System (ADS)

    Hinton, J. P.; Thewalt, E.; Koralek, J. D.; Orenstein, J.; Barisic, N.; Xhao, X.; Chan, M.; Dorow, C.; Veit, M.; Ji, L.; Greven, M.

    2014-03-01

    The cuprate family of high temperature superconductors is characterized by a variety of electronic phases which emerge when charge carriers are added to the antiferromagnetic parent compound. The structural simplicity of the single layer cuprate system HgBa2CuO4+δ (Hg1201) is advantageous for experimentally detecting subtle features of these phases. In this work, we investigate the recombination dynamics of photo-excited quasiparticles in Hg1201 as a function of doping, temperature, and magnetic field using pump-probe optical reflectivity. We observe two distinct onset temperatures above TC in the underdoped part of the phase diagram, corresponding to T* and T** as observed in transport and neutron scattering experiments. We also measure a suppression of the recombination rate near TC which peaks at 8% hole concentration. We associate this suppression with coherence effects. Lastly, we observe a complex, non-monotonic temperature dependence in the dynamics around optimal doping, providing evidence for reentrant phase transitions near the apex of the superconducting dome. Work supported by DOE-BES

  2. Paramagnetic moments and time effects in melt-textured NdBaCuO system with Nd422 inclusions

    NASA Astrophysics Data System (ADS)

    Dias, F. T.; Vieira, V. N.; Silva, D. L.; Wolff-Fabris, F.; Kampert, E.; Almeida, M. L.; Mesquita, F.; Hneda, M.; Roa, J. J.

    2015-03-01

    We have performed magnetic measurements in two melt-textured NdBa2Cu3O7-δ samples with Nd422 inclusions under magnetic fields from 0.05 up to 14 T, applied parallel to the ab planes. The measurements were made with a superconducting quantum interference device (SQUID) and a vibrating sample magnetometer (VSM). Paramagnetic moments could be observed during FCC (field-cooled cooling) and FCW (field-cooled warming) experiments. This effect, known as Paramagnetic Meissner Effect (PME), persisted up to 14 T and strong irreversibilities were observed among FCC and FCW experiments, revealing the presence of time effects. These time effects were confirmed by specific magnetic relaxation experiments in different cooling rates and temperatures, showing an anomalous and curious paramagnetic behavior. We explain our results based on the flux-compressed state generated within nonsuperconducting regions of the sample, such as the Nd422 inclusions dispersed into the superconducting matrix. These inclusions may produce a strong vortex pinning that stabilize the paramagnetic state, allowing the admission of extra vortices into the sample responsible for the positive moments during the relaxation experiments.

  3. 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.

  4. Epitaxial Tl2Ba2CaCu2OX thin film dc SQUIDs operating at 99 K

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Han, Bing; Xu, Fengzhi; Chen, Genghua; Yang, Qiansheng; Lu, Rongtao; He, Ming; Yan, Shaolin

    2004-10-01

    Epitaxial Tl2Ba2CaCu2OX thin film dc superconducting quantum interference devices (dc SQUIDs) have been fabricated on bicrystal SrTiO3 (STO) substrates. By using the Tl-2212 single phase film, a flux noise density, SPHgr1/2, of 2.0 × 10-5PHgr0 Hz-1/2 at liquid nitrogen temperature was obtained in the white noise region, which is more than one order of magnitude lower than previous Tl-based SQUIDs made by multiphase thin films. The Tl-2212 thin film bicrystal grain boundary Josephson junctions have demonstrated resistively shunted junction (RSJ) behaviour. The characteristic voltage, VC, which is the product of critical current IC and junction resistance RN, was 45 µV at 95 K. The dependence of the critical current on temperature near TC (105 K) was measured as I_{\\mathrm {C}} (T)\\sim (1-T / T_{\\mathrm {C}})^{1.5\\mbox {--} 1.98} . The dc SQUIDs can operate at temperatures up to 99 K.

  5. Structure change via partial Se/Te substitution: crystal structure and physical properties of the telluride Ba(2)Cu(4-x)Te(5) in contrast to the selenide-telluride Ba(2)Cu(4-x)Se(y)Te(5-y).

    PubMed

    Mayasree, Oottil; Cui, Yanjie; Assoud, Abdeljalil; Kleinke, Holger

    2010-07-19

    The chalcogenides Ba(2)Cu(4-x)Se(y)Te(5-y) were synthesized from the elements in stoichiometric ratios at 700 degrees C, followed by annealing at 600 degrees C. The ternary telluride Ba(2)Cu(4-x)Te(5) crystallizes in a new structure type, space group C2/c, with lattice dimensions of a = 9.4428(6) A, b = 9.3289(6) A, c = 13.3028(8) A, beta = 101.635(1) degrees , V = 1147.8(1) A(3), for x = 0.75(1) (Z = 4). The corresponding selenide-telluride adopts another new, but strongly related, structure type, space group P4(1)2(1)2, with a = 6.5418(3) A, c = 25.782(2) A, V = 1103.3(1) A(3), for Ba(2)Cu(3.26(2))Se(0.729(8))Te(4.271) (Z = 4). Between 0.13 and 1.0 Te per formula unit can be replaced with Se, while the Cu content appears to vary only within 0.67 Ba(2)Cu(4-x)Se(y)Te(5-y). Despite crystallizing in different crystal systems, the telluride and the selenide-telluride exhibit topologically equivalent structure motifs, namely, chains of Cu(Se,Te)(4) tetrahedra with a Cu atom cis/trans chain as well as an almost linear Te atom chain. All these chalcogenides, as far as measured, are p-doped semiconductors, as determined by Seebeck coefficient and electrical conductivity measurements.

  6. Characteristics of quenched Y-Ba-Cu-O thin films on SrTiO/sub 3/ (100),(110) grown by organometallic chemical vapor deposition

    SciTech Connect

    Tsuruoka, T.; Takahashi, H.; Kawasaki, R.; Kanamori, T.

    1989-05-01

    A thin Y-Ba-Cu-O film was formed by the organometallic chemical vapor deposition (OMCVD) method. The substrates used were (100) and (110) SrTiO/sub 3/. After forming Y-Ba-Cu-O at 800 /sup 0/C, it was cooled at a rate of 100 /sup 0/C/min in O/sub 2/ under 1 atm. This film was c-axis oriented, with its (001) surface grown in parallel to the (100) surface of SrTiO/sub 3/ and T/sub c/ = 88 K. The (110) surface of Y-Ba-Cu-O was grown in parallel to the substrate crystal and T/sub c/ = 84 K on the (110) surface of SrTiO/sub 3/. After forming, these films were quenched in air from 800 /sup 0/C to room temperature. The change in resistance of the quenched sample with temperature was metallic, T/sub onset/ = 75 K, and T/sub c/ = 60 K.

  7. Influence of simultaneous doping of Sb and Pb on phase formation, superconducting and microstructural characteristics of HgBa 2Ca 2Cu 3O 8+ δ

    NASA Astrophysics Data System (ADS)

    Giri, Rajiv; Tiwari, R. S.; Srivastava, O. N.

    2007-01-01

    We report systematic studies of structural, microstructural and transport properties of (Hg 0.80Sb 0.2- xPb x)Ba 2Ca 2Cu 3O 8+ δ (where x = 0.0, 0.05, 0.1, 0.15, 0.2) compounds. Bulk polycrystalline samples have been prepared by two-step solid-state reaction route at ambient pressure. It has been observed that simultaneous substitution of Sb and Pb at Hg site in oxygen deficient HgO δ layer of HgBa 2Ca 2Cu 3O 8+ δ cuprate high- Tc superconductor leads to the formation of Hg-1223 as the dominant phase. Microstructural investigations of the as grown samples employing scanning electron microscopy reveal single crystal like large grains embodying spiral like features. Superconducting properties particularly transport current density ( Jct) have been found to be sensitive to these microstructural features. As for example (Hg 0.80Sb 0.05Pb 0.15)Ba 2Ca 2Cu 3O 8+ δ compound which exhibits single crystal like large grains (∼50 μm) and appears to result through spiral growth mechanism, shows highest Jct (∼1.85 × 10 3 A/cm 2) at 77 K. A possible mechanism for the generation of spiral like features and correlation between microstructural features and superconducting properties have been put forward.

  8. Oxygen nonstoichiometry, structural phase transitions and anomalous Pr ordering for PrBa2- xLaxCu3Oz solid solution

    NASA Astrophysics Data System (ADS)

    Luo, H. M.; Ding, S. Y.; Lu, G. X.; Lin, B. N.; Ku, H. C.; Lin, C. H.; Kao, H.-C. I.; Ho, J. C.

    2001-06-01

    The oxygen nonstoichiometry, structure, magnetic and calorimetric data for La doped Ba-site PrBa2-xLaxCu3Oz systems (0≤x≤1 and 6.881≤z≤ 7392) are reported. The x-dependence of the oxygen content increases monotonically and two structural phase transitions are observed, confirmed by powder x-ray Rietveld analysis, from the orthorhombic 1212C-phase (space group: Pmmm) to tetragonal 1212 (P4/mmm) at x = 0.45, and then to another orthorhombic (Cmmm) phase around x = 0.7. Magnetic susceptibility and heat capacity measurements show that the anomalous Néel temperature TN(Pr) decreases monotonically from 18 K for x = 0 to 2.8 K for PrBa1.3La0.7Cu3O7.236 and to below 2 K for x≥0.8 for samples prepared under the same conditions, while TN(Pr) increases with an increase of oxygen content for the same compound. The increasing Pr-O bond length observed with decreasing TN(Pr) indicates that this unusual Pr magnetic ordering is closely related to the wave-function overlap between the Pr-4f orbital and eight O-2pπ orbital in the CuO2 bi-layer. No superconductivity has been detected for these insulating cuprates.

  9. Comparison of the effects of platinum and CeO2 on the properties of single grain, Sm-Ba-Cu-O bulk superconductors

    NASA Astrophysics Data System (ADS)

    Zhao, Wen; Shi, Yunhua; Radušovská, Monika; Dennis, Anthony R.; Durrell, John H.; Diko, Pavel; Cardwell, David A.

    2016-12-01

    SmBa2Cu3O7-δ (Sm-123) is a light-rare-earth barium-cuprate (LRE-BCO) high-temperature superconductor (HTS) with significant potential for high field industrial applications. We report the fabrication of large, single grain bulk [Sm-Ba-Cu-O (SmBCO)] superconductors containing 1 wt% CeO2 and 0.1 wt% Pt using a top-seeded melt growth process. The performance of the SmBCO bulk superconductors containing the different dopants was evaluated based on an analysis of their superconducting properties, including critical transition temperature, T c and critical current density, J c , and on sample microstructure. We find that both CeO2 and Pt dopants refine the size of Sm2BaCuO5 (Sm-211) particles trapped in the Sm-123 superconducting phase matrix, which act as effective flux pinning centres, although the addition of CeO2 results in broadly improved superconducting performance of the fully processed bulk single grain. However, 1 wt% CeO2 is significantly cheaper than 0.1 wt% Pt, which has clear economic benefits for use in medium to large scale production processes for these technologically important materials. Finally, the use of CeO2 results generally in the formation of finer Sm-211 particles and to the generation of fewer macro-cracks and Sm-211 free regions in the sample microstructure.

  10. 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.

  11. Relationship between microstructure, cytotoxicity and corrosion properties of a Cu-Al-Ni shape memory alloy.

    PubMed

    Colić, Miodrag; Rudolf, Rebeka; Stamenković, Dragoslav; Anzel, Ivan; Vucević, Dragana; Jenko, Monika; Lazić, Vojkan; Lojen, Gorazd

    2010-01-01

    Cu-Al-Ni shape memory alloys (SMAs) have been investigated as materials for medical devices, but their biomedical application is still limited. The aim of this work was to compare the microstructure, corrosion and cytotoxicity in vitro of a Cu-Al-Ni SMA. Rapidly solidified (RS) thin ribbons, manufactured via melt spinning, were used for the tests. The control alloy was a permanent mould casting of the same composition, but without shape memory effect. The results show that RS ribbons are significantly more resistant to corrosion compared with the control alloy, as judged by the lesser release of Cu and Ni into the conditioning medium. These results correlate with the finding that RS ribbons were not cytotoxic to L929 mouse fibroblasts and rat thymocytes. In addition, the RS ribbon conditioning medium inhibited cellular proliferation and IL-2 production by activated rat splenocytes to a much lesser extent. The inhibitory effects were almost completely abolished by conditioning the RS ribbons in culture medium for 4 weeks. Microstructural analysis showed that RS ribbons are martensitic, with boron particles as a minor phase. In contrast, the control Cu-Al-Ni alloy had a complex multiphase microstructure. Examination of the alloy surfaces after conditioning by energy dispersive X-ray and Auger electron spectroscopy showed the formation of Cu and Al oxide layers and confirmed that the metals in RS ribbons are less susceptible to oxidation and corrosion compared with the control alloy. In conclusion, these results suggest that rapid solidification significantly improves the corrosion stability and biocompatibility in vitro of Cu-Al-Ni SMA ribbons.

  12. Morphology and photoluminescence of BaAl12O19:Mn2+ green phosphor prepared by flux method

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Wang, Yu-Hua; Liu, Bi-Tao; Liu, Ji-Di

    2010-12-01

    This paper reports that the green phosphor BaAl11.9O19:0.1Mn2+ is prepared by a flux assisted solid state reaction method. The effect of flux systems on the crystal structure, morphology and luminescent properties of the phosphor are studied in detail. The samples are characterized by the application of x-ray diffraction patterns, scanning electron microscopy patterns, luminescent spectra and decay curves. The results show that a pure phase BaAl12O19 can be achieved at the firing temperature above 1300 °C by adding the proper flux system, the firing temperature is reduced at least 200 °C in comparison with the conventional solid state reaction method. Maximum photoluminescence emission intensity is observed at 517 nm for (AlF3+Li2CO3) flux system under vacuum ultraviolet region (147 nm) excitation. The photoluminescence emission intensity and the decay time of these phosphor is found to be more superior to that of the corresponding sample prepared by the conventional solid state reaction method implying the suitability of this route for the preparation of display device worthy phosphor materials.

  13. Chemical-mechanical planarization of Al and Cu thin films for the damascene process

    NASA Astrophysics Data System (ADS)

    Wrschka, Peter Thomas

    In this thesis, the chemical-mechanical planarization (CMP) of Al and Cu thin films is investigated. Our results are obtained by polishing blanket and patterned wafers covered with either Al or Cu utilizing various pads and slurries. Removal rates and metal to SiO2 selectivity values at different pressures and velocities are measured. Furthermore, the results of the successful planarization of Al and Cu damascene structures are reported here. We analyze the surface oxidation of Al before and immediately after the polishing of blanket wafers by X-ray photoelectron spectroscopy. The results show that the CMP of Al proceeds by the growth and removal of the metal passivation layer, i.e. Al2O3. A model for the Al removal mechanism is proposed, which states that the in-situ passivation layer thickness is inversely proportional to the removal rate. The CMP of Cu damascene structures found that the Cu line recess, metal line corrosion and the adherence of slurry particles is determined by the slurry formulation. Cu line dishing, comer rounding of the SiO2 spacer and the pattern density dependence of the removal rate is controlled by the type of pad utilized. We found that moderate etch rates (~10 nm/min) yield high removal rates (~1 μm/min) and low Cu line recess (<10% of Cu line thickness). The occurrence of corrosion is favored at small feature sizes in low pattern density areas. However, this can be avoided by employing passivating agents. The dishing of metal lines and the comer rounding of dielectric spacers is prevented by employing a sufficiently hard pad. The diffusion barrier layer removal (Ta), which shows no chemical etching in the slurry, is affected by the pad and the slurry particle type. A hard pad and especially the use of silica particles enhances the liner removal significantly. Silica particles also adhere less to the metal lines and settle at a substantially slower rate in the slurry than alumina particles.

  14. Influence of Al2O3 sol concentration on the microstructure and mechanical properties of Cu-Al2O3 composite coatings

    NASA Astrophysics Data System (ADS)

    Wei, Xiaojin; Yang, Zhendi; Tang, Ying; Gao, Wei

    2015-03-01

    Copper (Cu) is widely used as electrical conducting and contacting material. However, Cu is soft and does not have good mechanical properties. In order to improve the hardness and wear resistance of Cu, sol-enhanced Cu-Al2O3 nanocomposite coatings were electroplated by adding a transparent Al oxide (Al2O3) sol into the traditional electroplating Cu solution. It was found that the microstructure and mechanical properties of the nanocomposite coatings were largely influenced by the Al2O3 sol concentration. The results show that the Al2O3 nanoparticle reinforced the composite coatings, resulting in significantly improved hardness and wear resistance in comparison with the pure Cu coatings. The coating prepared at the sol concentration of 3.93 mol/L had the best microhardness and wear resistance. The microhardness has been improved by 20% from 145.5 HV (Vickers hardness number) of pure Cu coating to 173.3 HV of Cu-Al2O3 composite coatings. The wear resistance was also improved by 84%, with the wear volume loss dropped from 3.2 × 10-3 mm3 of Cu coating to 0.52 × 10-3 mm3 of composite coatings. Adding excessive sol to the electrolyte deteriorated the properties.

  15. HPHT synthesis, structure and electrical properties of type-I clathrates Ba{sub 8}Al{sub x}Si{sub 46−x}

    SciTech Connect

    Liu, Binwu; Jia, Xiaopeng; Sun, Hairui; Sun, Bing; Zhang, Yuewen; Liu, Haiqiang; Kong, Lingjiao; Huo, Dexuan; Ma, Hongan

    2016-01-15

    Clathrate compounds Ba{sub 8}Al{sub x}Si{sub 46−x} were successfully synthesized using the method of high-pressure and high-temperature (HPHT). In this process, we used BaSi{sub 2} as one of the starting materials in place of Ba metals, which reduces the complexity of the program caused by the extremely high chemical reactivity. By using this method, the processing time was reduced from few days to an hour. X-ray diffraction and structural refinement indicated this composition crystallized in type-I clathrate phase. Bond length analysis showed the Ba atoms in small dodecahedron had spherical thermal ellipsoids while those in large tetrakaidecahedron displayed anisotropic thermal ellipsoids. The negative Seebeck coefficient indicated transport processes were dominated by electrons as carriers, and increased with the increasing temperature. The electrical properties, including Seebeck coefficient and Power factor, were greatly enhanced by Al substitution. - Graphical abstract: Left: The cavity structure diagram of a China-type large volume cubic high-pressure apparatus, and the Type-I clathrate structure of sample synthesized using HPHT. Middle: X-ray Rietveld refinement profile for Ba{sub 8}Si{sub 46} and element mapping for Ba{sub 8}Al{sub 16}Si{sub 30}. Right: Temperature dependence of Seebeck coefficient for Ba{sub 8}Al{sub x}Si{sub 46−x} prepared by HPHT. - Highlights: • HPHT is a simple and rapid synthetic approach. • We use BaSi{sub 2} as one of the starting materials replacing Ba metals. • The processing time reduces from few days to an hour. • Structure determination is refined by Rietveld analysis of XRD data. • Variable temperature electrical properties are characterized.

  16. Numerical investigation on thermal properties at Cu-Al interface in micro/nano manufacturing

    NASA Astrophysics Data System (ADS)

    Zhang, Liqiang; Yang, Ping; Chen, Min; Liao, Ningbo

    2012-02-01

    A hybrid model by integrating TTM (two-temperature model) and MD (molecular dynamics) is proposed to investigate the properties on interface of dissimilar materials under thermal flux conditions. This model can describe the electron phonon coupling and phonon scattering at the interface of different metals easily. By comparing the Cu-Cu interface and Cu-Al interface, the atoms of the Cu-Cu interface at different sides tend to move together; while, the atoms displacements of Cu and Al are opposite along the interface, which may cause stress and voids at the interface. Moreover, the propagation mechanisms of nanocracks and the corresponding change of temperature distribution and thermal flux are investigated. The results show that the interfaces of dissimilar materials are prone to crack initiations, leading to delaminations because of the high temperature. All these are useful for understanding the deformation and failure of the interfaces structures. It implies a potential method for design and analysis of interface structure in micro/nano manufacturing.

  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. The fabricability and corrosion resistance of several Al-Cu-Li aerospace alloys

    SciTech Connect

    Walsh, D.W.; Danford, M.; Sanders, J.

    1996-12-31

    Al-Li-Cu alloys are attractive to the aerospace industry. The high specific strength and stiffness of these alloys will improve lift efficiency, fuel economy, performance and increase payload capabilities. The objectives of this study were to measure the fabricability of Al 2195 (Al-4Cu-1Li) and to assess the effect of welding on corrosion behavior. Al 2219 samples were used in parallel tests to provide a baseline for the data generated. In this study samples were exposed to 3.5% NaCl and mild corrosive water solutions in both the as received and as welded conditions. Fabricability was assessed using Gleeble testing, Varestraint testing and differential scanning calorimetry (DSC). Results indicate that Alloy 2195 is much more susceptible to hot cracking than Al 2219, and that cracking sensitivity is a strong function of chemical composition within specification ranges for Al 2195. Furthermore, for base metal samples, corrosion in mild corrosive water was more severe than corrosion in salt water. In addition, welding increases the corrosion rate in Al 2195 and 2219, and causes severe localization in Al 2195. Furthermore, autogenously welded Al 2195 samples were more susceptible to attack than heterogeneously welded Al 2195 samples and autogenously welded Al2219 samples were less susceptible to corrosion than autogenously welded Al 2195 samples. Heterogeneously welded samples in both materials had high corrosion rates, but only the Al 2195 material was subject to localization of attack. The partially melted zones of Al 2195 samples were subject to severe, focused attack. In all cases, interdendritic constituents in welded areas and intergranular constituents in base material were cathodic to the Al rich matrix materials. Fabricability and corrosion resistance were correlated to material microstructure using optical microscopy, scanning electron microscopy, electron probe microanalysis, polarization resistance and environmental scanning electron microscopy.

  19. Angle-Resolved photoemission spectroscopy on Tl2Ba2CuO6+δ

    NASA Astrophysics Data System (ADS)

    Levy, G.; Raichle, M.; Fournier, D.; Mottershead, J.; Veenstra, C.; Rosen, J.; Bostwick, A.; Rotenberg, E.; Liang, R.; Hardy, W.; Bonn, D.; Damascelli, A.

    2010-03-01

    Tl2201 is characterized by a simple and undistorted crystal structure, as well as less disorder than other high-Tc cuprate-based materials. On the very overdoped side of the phase diagram, a remarkable agreement has already been achieved between transport (i.e., AMRO and dHvA) and ARPES studies [1-3]. We here will present ARPES data on high-quality Tl2201 single crystals and compare them with transport results from the same material across the phase diagram, with emphasis on the evolution of Fermi surface volume, Fermi velocity, and many-body renormalization. We will also discuss the possibility of driving the doping on this material into the underdoped regime by in-situ potassium evaporation.[4pt] [1] N. E. Hussey et al., Nature 425, 814 (2003).[0pt] [2] M. Plat'e et al., Phys. Rev. Lett. 95, 077001 (2005).[0pt] [3] B. Vignolle et al., Nature 455, 952 (2008).

  20. Electronic structure and the van Hove singularity scenario in high-T(sub c)H(g)Ba2CuO(4+delta) superconductors

    NASA Technical Reports Server (NTRS)

    Agrawal, Bal K.; Agrawal, Savitri

    1995-01-01

    The electronic structure and the hole concentrations in the high Tc superconductor HgBa2CuO(4+delta) (delta = O, 1) has been investigated by employing a first principles full potential self-consistent LMTO method with the local density functional theory. The scalar relativistic effects have been considered. The hole concentrations of the Cu-d and O-p(x,y) orbitals are seen to be larger for the HgBaCuO5 system than those of the HgBaCuO4 solid. However, the van Hove singularity (vHs) induced Cu-d and O-p peak which is seen to lie comparatively away and above the Fermi level in the delta = 1 system shifts towards the Fermi level in the delta = 0 system. Thus, the superconducting behavior appears to originate from the occurrence of the vHs peak at the Fermi level. The Fermi surface nesting area in the delta = 0 compound is seen to be larger than in the delta = 1 compound. The calculation reveals that the increase in pressure on the crystal enhances the hole concentrations but without showing any optimum value, On the other hand, the vHs peak approaches to-wards the Fermi level with pressure and crosses the Fermi surface near V/Vo approximately equals 0.625 (V and Vo are the crystal volumes at high and normal pressures, respectively). Our calculated value of the bulk modulus equal to 0.626 Mbar predicts the occurrence of this crossover at about 24 GPa which is in complete agreement with the experimental value. At this pressure the compound has maximum nesting area and self-doped behavior.

  1. 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.

  2. Cu-doping effect on dielectric properties of organic gel synthesized Ba{sub 4}YMn{sub 3−x}Cu{sub x}O{sub 11.5±δ}

    SciTech Connect

    Barbier, Tristan; Autret-Lambert, Cécile; Andreazza, Pascal; Ruyter, Antoine; Honstettre, Christophe; Lambert, Sébastien; Gervais, François; Lethiecq, Marc

    2013-10-15

    Copper doped-Ba{sub 4}YMn{sub 3−x}Cu{sub x}O{sub 11.5±δ} samples were synthesized by an organic gel assisted citrate process. X-ray diffraction of compositions with x=0.002, 0.005, 0.01, 0.02 and 0.04 does not reveal any change of hexagonal perovskite structure on doping. The effects of Cu-doping on the microstructure and dielectric properties were investigated. Cu doping modifies the electrical properties at the level of the impedance characteristics of both grain and grain boundary and to understand these different behaviours, we have carried out high-resolution transmission electron microscopy analysis. Among the Ba{sub 4}YMn{sub 3−x}Cu{sub x}O{sub 11.5±δ} specimens studied, the composition x=0.002 shows a permittivity (ε′{sub r}) higher than the undoped compound and a lower loss tangent (tanδ) over several orders of magnitude of frequency. - Graphical abstract: Highlighting of many stacking faults (intergrowths) in substituted compounds with x>0.01 (right picture), which could explain the different dielectric properties observed in these compounds. However compounds with x>0.01 remain with a better stacking sequence as we can see on the left picture. Display Omitted - Highlights: • High permittivity of the Ba{sub 4}YMn{sub 3−x}Cu{sub x}O{sub 11.5±δ}. • Substitution leads to a mixed oxidation state for manganese: Mn{sup 4+}/Mn{sup 3+}. • Creation of oxygen vacancies which are responsible for stacking faults. • Highlighting relationship between Cu substitution and dielectric properties.

  3. Superconducting properties of the heavy-ions and neutron irradiated (Cu,C)Ba 2Ca n-1 Cu nO 2 n+4- δ ( n=3, 4 and 5)

    NASA Astrophysics Data System (ADS)

    Kitô, Hijiri; Iyo, Akira; Hirai, Manabu; Crisan, A.; Tokumoto, Madoka; Okayasu, Satoru; Sasase, Masahito; Ihara, Hideo

    2002-10-01

    For further enhancement of critical currents density Jc and irreversibility field Hirr of (Cu 1- xC x) Ba 2Ca n-1 Cu nO 2 n+4- δ ((Cu,C)-( n-1) n, n=3, 4 and 5) family, pinning centers were introduced by ion and neutron irradiation in these compounds. The polycrystalline samples were irradiated with 3.6×10 17 neutrons/cm 2 or with Au 15+ ions (240 MeV energy) at a fluence of 1×10 11 ions/cm 2. Jc and Hirr were determined for the irradiated samples as well as unirradiated samples. The intragrain Jc was evaluated from M- H curves using Bean's critical state model. In (Cu,C)-12( n-1) n, Jc (77 K, 1 T) shows a remarkable increase from 3.9×10 4 to 9.1×10 5 A/cm 2 for neutron irradiated (Cu,C)-1234 and from 3.9×10 4 to 4.1×10 6 A/cm 2 for heavy-ion irradiated (Cu,C)-1234. These results indicate the possibility of further enhancement of Jc and of achieving a very high Hirr of (Cu,C)-1234 in (Cu,C)-12( n-1) n family.

  4. Growth of large-domain YBa 2Cu 3O x with new seeding crystals of CaNdAlO 4 and SrLaGaO 4

    NASA Astrophysics Data System (ADS)

    Shi, Donglu; Lahiri, K.; Hull, J. R.; LeBlanc, D.; LeBlanc, M. A. R.; Dabkowski, Antoni; Chang, Y.; Jiang, Y.; Zhang, Z.; Fan, H.

    1995-02-01

    Single crystals of CaNdAlO 4 and SrLaGaO 4 were used as seeds to grow large domains of YBa 2Cu 3O x for levitation applications. These crystals have high melting temperatures (> 1500°C) and similar lattice structures to that of YBa 2Cu 3O x. In a seeded melt-texturing method developed previously, the single crystals of CaNdAlO 4, SrLaGaO 4, and NdBa 2Cu 3O x were used as seeds for comparison. After melt processing, scanning electron microscopy analysis did not reveal any major differences in all these seeded melt-textured samples. However, the levitation forces in the samples seeded with single crystals of CaNdAlO 4 and SrLaGaO 4 increased considerably compared to that of the sample seeded with NdBa 2Cu 3O x. A model is proposed to describe the domain growth mechanism during seeded melt processing.

  5. Oxygen nonstoichiometry and phase transitions of the neodymium-rich Nd 1+ xBa 2- xCu 3O z solid solution

    NASA Astrophysics Data System (ADS)

    Goodilin, E.; Limonov, M.; Panfilov, A.; Khasanova, N.; Oka, A.; Tajima, S.; Shiohara, Y.

    1998-05-01

    On the basis of chemical, thermal analysis and Cu K-edge X-ray absorption measurements, oxygen content in the Nd 1+ xBa 2- xCu 3O z solid solution was determined between 1000°C in air and 400°C in oxygen for x=0.05-0.9 compositions. It has been observed that the oxygen nonstoichiometry Δ z of the Nd 1+ xBa 2- xCu 3O 7+ x/2-Δ z solid solution decreases 2-2.5 times for a large substitution (Δ z≈0.3-0.33 for x=0.9), despite of the acclaimed higher total oxygen content. The difference in nonstoichiometry is explained by a higher average value of the copper oxidation state (ACV), which is vital for the solid solution with large x even at elevated temperatures (ACV≈2-2.05 for x>0.3 at 1000°C, PO 2=0.21 atm). On the contrary, the ACV after complete oxygenation is almost constant (about 2.25-2.3) for the whole series. The x-dependence of the oxygen content is not monotonous and structural phase transitions can be observed at x=0.3 and x=0.6, as confirmed by the X-ray diffraction and the Raman scattering spectroscopy. The first well-known transition is connected with the oxygen disorder due to the Nd substitution for Ba at random Ba-sites. In the present work, it is proved by the apical oxygen mode broadening in Raman spectra. Ordering of the Nd and Ba atoms with a subsequent orthorhombic distortion of the lattice may occur even at 1000°C in air due to the second transformation at x≈0.6. The invariable orthorhombicity of the Nd-rich solid solution with x>0.6 is not caused by the oxygen absorption as in the x=0.05 case. Existence of high- and low-temperature orthorhombic modifications of this solid solution has been observed for the first time. Finally, a tentative 3D ( z- x- T) diagram is suggested for the Nd 1+ xBa 2- xCu 3O z solid solution up to 1000°C in air, including the new x=0.6-0.9 region.

  6. 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.

  7. Electron transport in Al-Cu co-doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    Serin, T.; Atilgan, A.; Kara, I.; Yildiz, A.

    2017-03-01

    To investigate the influence of varying Al content on structural, optical, and electrical properties of ZnO thin films, Al-Cu co-doped ZnO thin films with fixed Cu content at 1 wt. % and different Al contents (1, 3, and 5 wt. %) were successfully synthesized on glass substrates using a sol-gel process. The results indicated that the varying Al content affects not only the grain size and band gap but also the electrical conductivity of the films, and a linear relationship was found between the band gap and strain values of the films. The temperature-dependent electrical conductivity data of the films demonstrated that electron transport was mainly controlled by the grain boundaries at intermediate and high temperatures, whereas it was governed by Mott-variable range hopping at low temperatures. Additionally, 3 wt. % Al content improved the electrical conductivity of Al-Cu co-doped ZnO by lowering the trap density and enhancing the hopping probability.

  8. Two-component uniform spin susceptibility of superconducting HgBa2CuO4+δ single crystals measured using 63Cu and 199Hg nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Haase, Jürgen; Rybicki, Damian; Slichter, Charles P.; Greven, Martin; Yu, Guichuan; Li, Yuan; Zhao, Xudong

    2012-03-01

    63Cu and 199Hg nuclear magnetic resonance shifts for an optimally doped and underdoped HgBa2CuO4+δ single crystal are reported, and the temperature dependence dictates a two-component description of the uniform spin susceptibility. The first component, associated with the pseudogap phenomenon in the NMR shifts, decreases at room temperature and continues to drop as the temperature is lowered, without a drastic change at the transition temperature into the superconducting state. The second component is temperature independent above the superconducting transition temperature and vanishes rapidly below it. It is a substantial part of the total T-dependent susceptibility measured at both nuclei.

  9. Angular dependence of the flux pinning for YBa{sub 2}Cu{sub 3}O{sub y}/PrBa{sub 2}Cu{sub 3}O{sub y} superlattice

    SciTech Connect

    Horng, H.E.; Wu, J.M.; Yang, H.C.

    1997-06-01

    The angular dependence of the magnetic relaxation for YBa{sub 2}Cu{sub 3}O{sub y}/PrBa{sub 2}Cu{sub 3}O{sub y} (YBCO/PBCO) superlattice was measured under magnetic field to investigate the flux pinning. The applied magnetic field was 0.1 Tesla. The direction of the applied magnetic field makes an angle of 10{degrees}, 20{degrees}, 30{degrees}, 45{degrees}... with the c-axis of YBCO/PBCO superlattice. Based on the Anderson-Kim model the authors derive the pinning energy of this film. The pinning energy is angular independent. The results are discussed.

  10. 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.

  11. Complete oxidation of volatile organic compounds over Ce/Cu/gamma-AL2O3 catalyst.

    PubMed

    Kim, S C; Shim, W G

    2008-05-01

    The effect of cerium (Ce) addition into Cu (5, 10 or 15 wt%)/gamma-Al2O3 catalysts on the catalyst properties and catalytic activity was investigated for the complete oxidation of volatile organic compounds (VOCs). X-ray diffraction (XRD), the Brunauer Emmett Teller method (BET), temperature programmed reduction (TPR) by H2, and N2O pulse titration were used to characterize a series of supported copper catalysts modified with cerium. Cerium was observed to be an inhibitor for 5 wt% and promoter for 10 or 15 wt% Cu/gamma-Al2O3 catalyst. The results of TPR, average crystallite size and dispersion indicated that even though Ce loadings on 10 and 15 wt% Cu/gamma-Al2O3 caused a reduction in BET surface area of the catalysts, the loaded amounts of Ce enhanced the catalytic activity through the formation of highly dispersed copper clusters. Kinetic parameters were developed for individual benzene, toluene and o-xylene (BTX) for 5 wt% Ce/10 wt% Cu/gamma-Al2O3 catalyst at temperatures ranging from 210 to 240 degrees C. The Mars and Van Krevelen model was found to be an adequate description of the catalytic oxidation of BTX for this study. The activity sequence with respect to the BTX molecules was found to be benzene > toluene > o-xylene under the surface-reaction-controlled region.

  12. 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.

  13. X-ray imaging and controlled solidification of Al-Cu alloys toward microstructures by design

    SciTech Connect

    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.; Clarke, Kester D.; Field, Robert D.; Smith, James L.

    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.

  14. Real-time investigations of selenization reactions in the system Cu-In-Al-Se

    NASA Astrophysics Data System (ADS)

    Jost, Stefan; Hergert, Frank; Hock, Rainer; Purwins, Michael; Enderle, Ralph

    2006-09-01

    In this article we present results of a detailed study of selenization reactions in the quaternary system Cu-In-Al-Se and of the binary subsystem aluminum-selenium. The investigation of solid-state reactions involved in the formation of the compound semiconductor Cu(In,Al)Se2 was performed using real-time X-ray diffraction (XRD) with a time resolution of 22.5 s while annealing an elemental layer stack of the metals covered with selenium. A temperature-resolved phase analysis shows that the formation of the semiconductor takes place via metal-selenides. Ex-situ XRD measurements of the processed thin films show a phase segregation concerning the aluminum content of the formed chalcopyrite. Subsequent Rietveld-refinement of real-time measurements reveals a formation reaction of the quaternary semiconductor Cu(In,Al)Se2 from the -In2Se3 related crystal structure of (Al,In)2Se3 and Cu2Se as educts.

  15. 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.

  16. Thermal and electronic properties of rare-earth Ba2Cu3Ox superconductors

    NASA Astrophysics Data System (ADS)

    Heremans, J.; Morelli, D. T.; Smith, G. W.; Strite, S. C., III

    1988-02-01

    We have measured the electrical resistivity, thermal conductivity, and specific heat of a series of high-temperature superconducting compounds of the form RBa2Cu3O7, with R=Y, Eu, Gd, Dy, and Er. Our results show that the afore-mentioned physical properties are virtually identical for all samples considered. In particular, the molar specific heats are identical to within +/-2% and exhibit Debye-type behavior. We observe a nearly constant thermal conductivity above Tc, but a rather sudden increase developes as the temperature is lowered below the critical temperature. The electrical resistivity is nearly linear in the normal state. Thermal and electrical conductivities indicate that for T>Tc, the predominant electron scattering mechanism is due to phonon interactions. Using electrical resistivity data and the Wiedemann-Franz law, we estimate the magnitude of the electronic component of the thermal conductivity to be an order of magnitude smaller than the measured thermal conductivity. We thus conclude that heat transport is predominantly by phonons. The enhancement of the lattice conduction below the critical temperature is understood as a reduction of carrier-phonon scattering as electrons condense into Cooper pairs. This lends support to standard Bardeen-Cooper-Schrieffer-type superconductivity. An estimate of the superconducting transition temperatures is made using the electron-phonon coupling constants and Debye temperatures deduced from the data which brackets the observed Tc quite well. We discuss the thermal conductivity at very low temperature in terms of a phonon mean-free path limited by pores in the samples.

  17. Materials Data on Ba2AlCu3O7 (SG:47) by Materials Project

    SciTech Connect

    Kristin Persson

    2014-09-30

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  18. Materials Data on BaAlCuSbO5 (SG:99) by Materials Project

    SciTech Connect

    Kristin Persson

    2014-09-30

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  19. Materials Data on Ba3Al2Cu2F16 (SG:4) by Materials Project

    SciTech Connect

    Kristin Persson

    2016-02-04

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  20. Materials Data on BaAlCuAgO5 (SG:99) by Materials Project

    SciTech Connect

    Kristin Persson

    2016-04-14

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  1. 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.

  2. 1D polymeric copper(I) complex [Cu2(μ-(2,6-Cl-ba)2en)(μ-I)2]n with exceptionally short Cusbnd Cu distance: Synthesis, characterization, thermal study and crystal structure

    NASA Astrophysics Data System (ADS)

    Khalaji, Aliakbar Dehno; Peyghoun, Seyyed Javad; Akbari, Alireza; Feizi, Nourollah; Dusek, Michal; Eigner, Vaclav

    2017-01-01

    A new 1D polymeric three coordinated copper(I) complex, [Cu2(μ-(2,6-Cl-ba)2en)(μ-I)2]n, with the bidentate Schiff base ligand N,N‧-bis(2,6-dichlorobenzylidene)ethane-1,2-diamine containing a flexible spacer (dbnd NCH2sbnd CH2sbnd Ndbnd) was synthesized and characterized by elemental analyses, UV-Vis, FT-IR and 1H NMR spectroscopy and thermal analaysis. Its molecular structure was determined by single-crystal X-ray diffraction and shows the (2,6-Cl-ba)2en acts as a bis-monodentate bridging ligand forming the dinuclear [Cu2(μ-(2,6-Cl-ba)2en)] groups. Such dinuclear groups are bridged by two iodine anions [(μ-I)2] to form a 1D polymeric copper(I) complex. The copper(I) ions are coordinated in a distorted trigonal planar geometry by two I atoms and one nitrogen atom of Schiff base ligand (2,6-Cl-ba)2en.

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

    SciTech Connect

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

    2014-05-12

    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. Furthermore, the dielectric patch crystal structure and roughness affect the ability of repetitively switching cycles and lifetime. We performed a series of experiments using different deposition methods and RF magnetron sputtering was found to be the best deposition process for the 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. In our work, the dielectric material sputtering pressure is set at 9.5x10-6 Torr. The argon gas is released through a mass-flow controller to purge the system prior to deposition. RF power is 85 W at a distance of 9 cm. The behavior of Au membranes built on ultimate 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.

  4. 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.

  5. Unusual Solidification Behavior of the Suction-Cast Cu-Zr-Al-Y Alloy Doped with Fe

    NASA Astrophysics Data System (ADS)

    Kozieł, Tomasz; Cios, Grzegorz; Latuch, Jerzy; Pajor, Krzysztof; Bała, Piotr

    2017-04-01

    The effect of iron addition on the microstructure of the Cu-Zr-Al-Y glass-forming alloy was studied. Despite a high superficial cooling rate, small Fe additions (1.5 and 3 pct) induced formation of crystalline CuZr and AlCu2Zr phases on the outer layers of suction-cast rods. As the melt composition near the solid/liquid interface was depleted in Fe, the remaining melt vitrified at a relatively low cooling rate.

  6. Unusual layer-dependent charge distribution, collective mode coupling, and superconductivity in multilayer cuprate Ba2Ca3Cu4O8F2.

    PubMed

    Chen, Yulin; Iyo, Akira; Yang, Wanli; Ino, Akihiro; Arita, M; Johnston, Steve; Eisaki, Hiroshi; Namatame, H; Taniguchi, M; Devereaux, Thomas P; Hussain, Zahid; Shen, Z-X

    2009-07-17

    Low energy ultrahigh momentum resolution angle resolved photoemission spectroscopy study on four-layer self-doped high Tc superconductor Ba2Ca3Cu4O8F2 (F0234) revealed fine structure in the band dispersion, identifying the unconventional association of hole and electron doping with the inner and outer CuO2 layers, respectively. For the states originating from two inequivalent CuO2 layers, different energy scales are observed in dispersion kinks associated with the collective mode coupling, with the larger energy scale found in the electron (n-) doped state which also has stronger coupling strength. Given the earlier finding that the superconducting gap is substantially larger along the n-type Fermi surface, our observations connect the mode coupling energy and strength with magnitude of the pairing gap.

  7. Unusual Layer-Dependent Charge Distribution, Collective Mode Coupling, and Superconductivity in Multilayer Cuprate Ba2Ca3Cu4O8F2

    SciTech Connect

    Chen, Yulin; Iyo, Akira; Yang, Wanli; Ino, Akihiro; Arita, M.; Johnston, Steve; Eisaki, Hiroshi; Namatame, H.; Taniguchi, M.; Devereaux, Thomas P.; Hussain, Zahid; Shen, Z.-X.; /SLAC /Stanford U., Phys. Dept.

    2011-08-12

    Low energy ultrahigh momentum resolution angle resolved photoemission spectroscopy study on four-layer self-doped high T{sub c} superconductor Ba{sub 2}Ca{sub 3}Cu{sub 4}O{sub 8}F{sub 2} (F0234) revealed fine structure in the band dispersion, identifying the unconventional association of hole and electron doping with the inner and outer CuO{sub 2} layers, respectively. For the states originating from two inequivalent CuO{sub 2} layers, different energy scales are observed in dispersion kinks associated with the collective mode coupling, with the larger energy scale found in the electron (n-) doped state which also has stronger coupling strength. Given the earlier finding that the superconducting gap is substantially larger along the n-type Fermi surface, our observations connect the mode coupling energy and strength with magnitude of the pairing gap.

  8. Al-Cu-Fe quasicrystal/ultra-high molecular weight polyethylene composites as biomaterials for acetabular cup prosthetics.

    PubMed

    Anderson, Brian C; Bloom, Paul D; Baikerikar, K G; Sheares, Valerie V; Mallapragada, Surya K

    2002-04-01

    Polymer composites of Al-Cu-Fe quasicrystals and ultra-high molecular weight polyethylene (UHMWPE) were investigated for use in acetabular cup prosthetics. The wear properties of the Al-Cu-Fe/UHMWPE samples and a 440 steel ball counterface were measured. The mechanical strength of the Al-Cu-Fe/UHMWPE composites was compared to UHMWPE and alumina/UHMWPE. The biocompatibility of the composite material was tested using a direct contact cytotoxicity assay. Al-Cu-Fe/UHMWPE demonstrated lower volume loss after wear and higher mechanical strength than UHMWPE. This composite material also showed no increase in counterface wear or cytotoxicity relative to UHMWPE. These combined results demonstrate that Al-Cu-Fe/UHMWPE composites are promising candidate materials for acetabular cup prosthetics.

  9. Consistency in Al/CuPc/ n-Si Heterojunction Diode Parameters Extracted Using Different Techniques

    NASA Astrophysics Data System (ADS)

    Ullah, Irfan; Shah, Mutabar; Khan, Majid; Wahab, Fazal

    2016-02-01

    This paper reports fabrication and characterization of an Al/CuPc/ n-Si heterojunction diode. The heterojunction was fabricated by depositing the active organic semiconducting material copper phthalocyanine (CuPc) on the n-Si substrate using the thermal vacuum evaporation technique. Electrical characterization of the fabricated heterojunction was carried out at ambient conditions. Various diode parameters, such as the ideality factor ( n), barrier height (Φ_{{b}}), and series resistance ( R s), were extracted from the current-voltage ( I- V) characteristic curve. These parameters are consistent with techniques used by Cheung, Norde and Hernandez et al. Furthermore these parameters are consistent with capacitance-voltage (C-V) characterization method. The conduction mechanism at the interface of CuPc and n-Si was also investigated. The surface morphology of the CuPc film was studied using atomic force microscopy and scanning electron microscopy. The optical bandgap of the CuPc film was calculated from the absorption spectrum using Tauc's law.

  10. Enhanced piezoelectric and mechanical properties of AlN-modified BaTiO3 composite ceramics.

    PubMed

    Xu, Dan; Wang, Lidong; Li, Weili; Wang, Wei; Hou, Yafei; Cao, Wenping; Feng, Yu; Fei, Weidong

    2014-07-14

    BaTiO3-xAlN (BT-xAlN) composite ceramics were prepared by conventional solid state reaction sintering. The effects of the AlN content on the crystalline structures, densities, and electrical and mechanical properties of the BT ceramics were investigated. The BT-1.5%AlN ceramic exhibits a good piezoelectric constant of 305 pC N(-1) and an improved Vickers hardness of 5.9 GPa. The enhanced piezoelectricity originates from interactions between defect dipoles and spontaneous polarization inside the domains due to the occurrence of local symmetry, caused by the preferential distribution of the Al(3+)-N(3-) pairs vertical to the c axis. The hardening of the material is attributed to the improved density, and particle and grain boundary strengthening. Our work indicates that if a suitable doping ion pair is designed, lead-free ceramic systems prepared from ordinary raw materials by a conventional sintering method have a high probability of exhibiting good piezoelectric and mechanical properties simultaneously.

  11. Scanning Tunneling Microscopy Studies of Surface Structures of Icosahedral Al-Cu-Fe Quasicrystals

    SciTech Connect

    Cai, Tanhong

    2001-01-01

    Three papers are included in this dissertation. The first paper: ''Structural aspects of the fivefold quasicrystalline Al-Cu-Fe surface from STM and dynamical LEED studies'', is in press with ''Surface Science''. The second paper: ''An STM study of the atomic structure of the icosahedral Al-Cu-Fe fivefold surface'' is submitted to ''Physical Review B, Rapid Communication''. The third paper: ''Pseudomorphic starfish: arrangement of extrinsic metal atoms on a quasicrystalline substrate'' is submitted to ''Nature''. Following the third paper are general conclusions and appendices that document the published paper ''Structural aspects of the three-fold surface of icosahedral Al-Pd-Mn'' (appearing in volume 461, issue 1-3 of ''Surface Science'' on page L521-L527, 2000), the design as well as the specifications of the aluminum evaporator used in the aluminum deposition study in this dissertation, an extended discussion of the aluminum deposition on the quasicrystalline surface, and the STM database.

  12. Tensile strength of Al matrix with nanoscale Cu, Ti and Mg inclusions

    NASA Astrophysics Data System (ADS)

    Pogorelko, V. V.; Mayer, A. E.

    2016-11-01

    Molecular-dynamic investigations of Al+Cu, Al+Ti and Al+Mg nanocomposite strength under high-rate uniaxial tension were carried out in this work. We consider two different mechanisms of reduction of the tensile strength of a material with inclusions in comparison with a pure material of matrix. The first mechanism is connected with a stress concentration in matrix near a stiff and strong inclusion (Ti, Cu); in this case, the fracture occurs inside the matrix and does not touch the inclusion. The second mechanism acts in the case of a soft and weak inclusion (Mg); the fracture begins inside the inclusion and thereafter propagates into the matrix. The tensile strength of the systems is determined at varied strain rates (in the range from 0.1/ns to 30/ns at the temperature 300 K) and varied temperatures (in the range from 300 K to 900 K at the strain rate 1/ns).

  13. Ordered state of magnetic charge in the pseudo-gap phase of a cuprate superconductor (HgBa2CuO(4+δ)).

    PubMed

    Lovesey, S W; Khalyavin, D D

    2015-12-16

    A symmetry-based interpretation of published experimental results demonstrates that the pseudo-gap phase of underdoped HgBa2CuO(4+δ) (Hg1201) possesses an ordered state of magnetic charge epitomized by Cu magnetic monopoles. Magnetic properties of one-layer Hg1201 and two-layer YBa2Cu3O(6+x) (YBCO) cuprates have much in common, because their pseudo-gap phases possess the same magnetic space-group, e.g. both underdoped cuprates allow the magneto-electric (Kerr) effect. Differences in their properties stem from different Cu site symmetries, leaving Cu magnetic monopoles forbidden in YBCO. Resonant x-ray Bragg diffraction experiments can complement the wealth of information available from neutron diffraction experiments on five Hg1201 samples on which our findings are based. In the case of Hg1201 emergence of the pseudo-gap phase, with time-reversal violation, is accompanied by a reduction of Cu site symmetry that includes loss of a centre of inversion symmetry. In consequence, parity-odd x-ray absorption events herald the onset of the enigmatic phase, and we predict dependence of corresponding Bragg spots on magneto-electric multipoles, including the monopole, and the azimuthal angle (crystal rotation about the Bragg wavevector).

  14. DSC and optical studies on BaO-Li2O-B2O3-CuO glass system

    NASA Astrophysics Data System (ADS)

    Bhogi, Ashok; Kumar, R. Vijaya; Ahmmad, Shaik Kareem; Kistaiah, P.

    2016-05-01

    Glasses with composition 15BaO-25Li2O-(60-x)B2O3 -xCuO (x= 0, 0.2, 0.4, 0.6, 0.8 and 1 mol%) were prepared by the conventional melt quenching technique. These glasses were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and density measurements. Optical absorption studies were carried out as a function of copper ion concentration. The optical absorption spectra of studied glasses containing copper oxide exhibit a single broad band around 761nm which has been assigned to the 2B1g→2B2g transition. From these studies, the variations in the values of glass transition temperature (Tg) have been observed. The fundamental absorption edge has been determined from the optical absorption spectra. The values of optical band gap and Urbach energy were determined with increase in concentration of CuO. The variations in density, glass transition temperature, optical band gap and Urbach energy with CuO content have been discussed in terms of changes in the glass structure. The analysis of these results indicated that copper ions mostly exist in Cu2+ state in these glasses when the concentration of CuO ≤ 0.8 mol% and above this concentration copper ions seem to subsist in Cu1+ state.

  15. Crystal structures of the four new quaternary copper(I)-selenides A0.5CuZrSe3 and ACuYSe3(A=Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Maier, Stefan; Prakash, Jai; Berthebaud, David; Perez, Olivier; Bobev, Svilen; Gascoin, Franck

    2016-10-01

    The four new quaternary copper(I)-selenides, Sr0.5CuZrSe3 (a=3.8386(7), b=14.197(2), c=10.1577(17) Å), Ba0.5CuZrSe3 (a=3.8386(7), b=14.196(2), c=10.1577(17) Å), SrCuYSe3 (a=10.620(2), b=4.1000(8), c=13.540(3) Å) and BaCuYSe3 (a=4.1800(7), b=13.940(2), c=10.6200(17) Å) were synthesized by high-temperature solid state reactions and their crystal structures were determined using single-crystal X-ray diffraction. A0.5CuZrSe3 (A= Sr, Ba) and BaCuYSe3 crystallize in the KCuZrS3 structure type (Cmcm), while SrCuYSe3 is isostructural to Eu2CuS3 (Pnma). All compounds form layered structures in which the charge of the - ∞ 2[CuZrSe3 and 2 - ∞ 2[CuYSe3 ] layers as well as the site occupancy of the A cations depend on the transition metal. Combining the alkaline earth metals Sr and Ba with tetravalent Zr leads to the formation of cation vacancies between the - ∞ 2[CuZrSe3 ] layers and structure type as well as symmetry are determined by the ratio between the cation and transition metal ionic radii r(A2+)/r(M3+/4+).

  16. Depth-dependent critical-current density of melt-processed Y-Ba-Cu-O discs determined by the third-harmonic technique: Surface barrier and intrinsic pinning

    NASA Astrophysics Data System (ADS)

    Chen, D.-X.; He, T.-F.; Zhang, M.-J.; Wang, S.-S.; Shi, Y.-H.; Cardwell, D. A.

    2016-08-01

    The critical-current density Jc of three Y-Ba-Cu-O (YBCO) discs, each cut from the upper section of a melt-processed single grain, has been determined as a function of the depth from the top (seeded) and bottom surfaces of the sample by a modified version of the inductive third-harmonic technique proposed originally by Mawatari et al. It is shown that local Jc in the vicinity of the bottom surface of the sample is lower than that in the vicinity of the top surface for thicker discs and there are reduced effect of surface barrier and intrinsic pinning and important surface damage. The technique employed is recommended as a tool for detecting the imperfection within superconducting structure in bulk YBCO.

  17. Improvement of critical current density in thallium-based (Tl,Bi)Sr{sub 1.6}Ba{sub 0.4}Ca{sub 2}Cu{sub 3}O{sub x} superconductors

    SciTech Connect

    Ren, Z.F.; Wang, C.A.; Wang, J.H.

    1994-12-31

    Epitaxial (Tl,Bi)Sr{sub 1.6}Ba{sub 0.4}Ca{sub 2}Cu{sub 3}O{sub x} (Tl,Bi)-1223 thin films on (100) single crystal LaAlO{sub 3} 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 > 2 x 10{sup 6} A/cm{sup 2}. The films exhibited good flux pinning properties.

  18. Absence of Jahn-Teller transition in the hexagonal Ba3CuSb2O9 single crystal

    DOE PAGES

    Katayama, Naoyuki; Kimura, Kenta; Han, Yibo; ...

    2015-07-13

    With decreasing temperature, liquids generally freeze into a solid state, losing entropy in the process. However, exceptions to this trend exist, such as quantum liquids, which may remain unfrozen down to absolute zero owing to strong quantum entanglement effects that stabilize a disordered state with zero entropy. Examples of such liquids include Bose-Einstein condensation of cold atoms, superconductivity, quantum Hall state of electron systems, and quantum spin liquid state in the frustrated magnets. Furthermore, recent studies have clarified the possibility of another exotic quantum liquid state based on the spin-orbital entanglement in FeSc2S4. To confirm this exotic ground state, experimentsmore » based on single-crystalline samples are essential. However, no such single-crystal study has been reported to date. Here, we report, to our knowledge, the first single-crystal study on the spin-orbital liquid candidate, 6H-Ba3CuSb2O9, and we have confirmed the absence of an orbital frozen state. In strongly correlated electron systems, orbital ordering usually appears at high temperatures in a process accompanied by a lattice deformation, called a static Jahn-Teller distortion. By combining synchrotron X-ray diffraction, electron spin resonance, Raman spectroscopy, and ultrasound measurements, we find that the static Jahn-Teller distortion is absent in the present material, which indicates that orbital ordering is suppressed down to the lowest temperatures measured. Lastly, we discuss how such an unusual feature is realized with the help of spin degree of freedom, leading to a spin-orbital entangled quantum liquid state.« less

  19. Magnetic characterisation of large grain, bulk Y-Ba-Cu-O superconductor-soft ferromagnetic alloy hybrid structures

    NASA Astrophysics Data System (ADS)

    Philippe, M. P.; Fagnard, J.-F.; Kirsch, S.; Xu, Z.; Dennis, A. R.; Shi, Y.-H.; Cardwell, D. A.; Vanderheyden, B.; Vanderbemden, P.

    2014-07-01

    Large grain, bulk Y-Ba-Cu-O (YBCO) high temperature superconductors (HTS) have significant potential for use in a variety of practical applications that incorporate powerful quasi-permanent magnets. In the present work, we investigate how the trapped field of such magnets can be improved by combining bulk YBCO with a soft FeNi, ferromagnetic alloy. This involves machining the alloy into components of various shapes, such as cylinders and rings, which are attached subsequently to the top surface of a solid, bulk HTS cylinder. The effect of these modifications on the magnetic hysteresis curve and trapped field of the bulk superconductor at 77 K are then studied using pick-up coil and Hall probe measurements. The experimental data are compared to finite element modelling of the magnetic flux distribution using Campbell’s algorithm. Initially we establish the validity of the technique involving pick-up coils wrapped around the bulk superconductor to obtain its magnetic hysteresis curve in a non-destructive way and highlight the difference between the measured signal and the true magnetization of the sample. We then consider the properties of hybrid ferromagnet/superconductor (F/S) structures. Hall probe measurements, together with the results of the model, establish that flux lines curve outwards through the ferromagnet, which acts, effectively, like a magnetic short circuit. Magnetic hysteresis curves show that the effects of the superconductor and the ferromagnet simply add when the ferromagnet is saturated fully by the applied field. The trapped field of the hybrid structure is always larger than that of the superconductor alone below this saturation level, and especially when the applied field is removed. The results of the study show further that the beneficial effects on the trapped field are enhanced when the ferromagnet covers the entire surface of the superconductor for different ferromagnetic components of various shapes and fixed volume.

  20. Absence of Jahn−Teller transition in the hexagonal Ba3CuSb2O9 single crystal

    PubMed Central

    Katayama, Naoyuki; Kimura, Kenta; Han, Yibo; Nasu, Joji; Drichko, Natalia; Nakanishi, Yoshiki; Halim, Mario; Ishiguro, Yuki; Satake, Ryuta; Nishibori, Eiji; Yoshizawa, Masahito; Nakano, Takehito; Nozue, Yasuo; Wakabayashi, Yusuke; Ishihara, Sumio; Hagiwara, Masayuki; Sawa, Hiroshi; Nakatsuji, Satoru

    2015-01-01

    With decreasing temperature, liquids generally freeze into a solid state, losing entropy in the process. However, exceptions to this trend exist, such as quantum liquids, which may remain unfrozen down to absolute zero owing to strong quantum entanglement effects that stabilize a disordered state with zero entropy. Examples of such liquids include Bose−Einstein condensation of cold atoms, superconductivity, quantum Hall state of electron systems, and quantum spin liquid state in the frustrated magnets. Moreover, recent studies have clarified the possibility of another exotic quantum liquid state based on the spin–orbital entanglement in FeSc2S4. To confirm this exotic ground state, experiments based on single-crystalline samples are essential. However, no such single-crystal study has been reported to date. Here, we report, to our knowledge, the first single-crystal study on the spin–orbital liquid candidate, 6H-Ba3CuSb2O9, and we have confirmed the absence of an orbital frozen state. In strongly correlated electron systems, orbital ordering usually appears at high temperatures in a process accompanied by a lattice deformation, called a static Jahn−Teller distortion. By combining synchrotron X-ray diffraction, electron spin resonance, Raman spectroscopy, and ultrasound measurements, we find that the static Jahn−Teller distortion is absent in the present material, which indicates that orbital ordering is suppressed down to the lowest temperatures measured. We discuss how such an unusual feature is realized with the help of spin degree of freedom, leading to a spin–orbital entangled quantum liquid state. PMID:26170280