bluuebunny/crossref_metadata_2025_split huggingface dataset:
High Temperature Neutron Diffraction Study of the Formation Reaction of Bismuth Superconductors
Authors: Garbauskas Mary F. , Arendt Ronald H. , Jorgensen James D. , Hitterman Richard L. 
Published: March 2011

AbstractHigh temperature neutron powder diffraction has been used to study the formation of the 110K transition temperature material, Bi2Ca2Sr2Cu3Ox (2223), both from synthetic reaction mixtures and after partial melting. The results indicate that the 80K transition temperature material, Bi2CaSr2Cu2Ox (2122), is the precursor to the (2223) material. The reaction to form the (2122) occurs rapidly at 860°C, while the conversion of this material to the (2223) is much slower.
Phase Development in Ag-Clad Bscco Wires
Authors: Ray II R.D. , Hellstrom E.E. 
Published: March 2011

AbstractWe have studied phase evolution in Ag‐clad BSCCO wires with nominal composition Bi2.4.8Sr2.05Ca0.95Cu2.27Oy‐ The wires were initially processed at 920°C where the oxide was partiaily moiten, then subsequently annealed at 840° C. The microstructure and composition of the phases present were studied at different points in the processing using optical and scanning electron microscopy, and electron probe microanalysis. The microstructure became simpler during the anneal resulting in two oxide phases and Ag. Ag from the cladding had dissolved into the melt at 920° C and subsequently precipitated in the core of the wire on cooling to the annealing temperature.
Cation Disordering in the Tl-2122 Superconductors
Authors: Morosin B. , Ginley D. S. , Venturini E. L. , Baughman R. J. , Schirber J. E. , Tigges C. P. 
Published: March 2011

AbstractWe have examined several crystals belonging to the Tl‐2122 structure type (Tl2CaBa2Cu2O8 with c=29Å), and have shown that cation solid solution occurs. Such cation disorder appears to be responsible for the observed small differences in lattice parameters reported by various investigators and to contribute towards the substantial variation in the superconducting transition temperatures.
Superconducting and Structural Properties of the (Ba0.6K0.4) (Bi1-YSbY)O3 System
Authors: Dabrowski B. , Pei S. , Richards D.R. , Zheng Y. , Jorgensen J.D. , Hinks D.G. , Kimball C.D. , Mitchell A.W. 
Published: March 2011

AbstractSingle‐phase samples of (Ba1‐xKx)(Bi1‐xSby)O3 have been synthesized over a limited compositional range using a two‐step procedure: high‐temperature firing in a low oxygen partial pressure followed by low‐temperature oxygen annealing. For y=0 and 0.37<x<0.50, samples have a simple cubic structure and are bulk superconductors with Tc gradually decreasing from 30 to 22K as x increases to 0.50. For fixed x and y>0 samples are superconducting again with a simple cubic structure and with Tc gradually decreasing as y increases.
Oxygen Evolution from Yba2cu3o7‐δ Superconducting Powders Generated by Aerosol Routes
Authors: Biswas Pratim , Zhoul Derong , Grothaus Jeff , Boolchand Punit , McDaniel Darl 
Published: March 2011

AbstractThe oxygen desorption kinetics of the YBa2Cu3O7‐δ powders generated by an aerosol route was investigated and compared to that of solid state reacted powders. The oxygen content of the aerosol sample was determined using a thermogravimetric analyzer (at 990 C) and wet chemical methods, and δ was calculated to be ‐0.1. The activation energy and pre‐exponential factor were determined by regression for two peaks at 540 C and 850 C. Other activation parameters were also calculated. The calculated values of these parameters for aerosol samples and those reported for solid state reacted powders are in good agreement.
Ultrasonic Study of the Low Temperature Structural Phase Transition in Yba2Cu3O7-δ. and its Dependence on Oxygen Concentration
Authors: Toulouse J. , Wang X.Q. , Hong D.J.L. 
Published: March 2011

AbstractElastic and structural instability have been reported in YBa2Cu3O7‐δbetween 210K and 270K. We have carried out an ultrasonic study of these instabilities as a function of both oxygen concentration and annealing temperature. The results strongly indicate that an athermal (martensitic‐type) transition starts at a temperature Ts which decreases with decreasing oxygen concentration. A linear relationship between Ts and Tc suggests that the second phase formed is essential for the high Tc.
The Determination of the Oxygen Stoichiometry in High TC Superconducting Thin Films Using Nuclear Scattering of 3 Mev Protons
Authors: Jin H.-S. , Homma H. , Yan D. , Drehman A.J. , Wang G.-C. 
Published: March 2011

AbstractThe nuclear scattering of 3 MeV protons on oxygen is applied to determine the oxygen stoichiometry in high Tc superconducting (HTS) thin films. Their oxide substrates are used as reference standards. This is a nondestructive, absolute method, which is as simple as the traditional Rutherford Backscattering Spectrometry (RBS). However, the relative sensitivity to oxygen has been enhanced. To obtain the stoichiometry, one only needs the data on atomic stopping powers and the chemical composition of the substates.When the measurements on the thin film and on the substate are carried out simultaneously, the inaccuracy in charge integration can be avoided and the accuracy of the oxygen stoichiometry can be further improved.
The Effects of Metal Doping: Yba2(Cu1-XMX)3O7-δ (M=;Fe, Co, Ni, and Zn)
Authors: Yang C .Y. , Moodenbaugh A. R. , Wang Y. L. , Xu Youwen , Heald S. M. , Welch D. O. , Suenaga M. , Fischer D. A. , Kirkland J. P. 
Published: March 2011

AbstractIn this study, we describe X‐ray absorption measurements designed to determine the influence of subsitutents on the location of dopants, the valence of dopants, structural changes, and modifications of electronic densities of states. Several possible mechanisms are offered which may elucidate Tc suppression due to metal dopings.
Continuous Two-Dimensional Melting of Vortex-Solid in High Temperature Superconductors
Authors: Yeh N.-C. 
Published: March 2011

AbstractA model of continuous two-dimensional melting in the mixed state of high temperature superconductors is proposed. Two-dimensional melting sets in at a cross-over temperature Tx(H) below the three-dimensinal phase transition Tx(H) due to finite size effects, and Tx(H) is a function of the sample thickness (lc), applied magnetic field (H), and k(= λ/ξ) For a given zero-field transition temperature Tc0 and material properties, (such as defect density), the onset temperature of 2D-melting (Tx(H)) decreases with decreasing sample thickness and increasing magnetic field. In transport studies, thermally induced melting is further complicated by the depinning effect of high current densities.
Control of Microstructures in the YBA2CU3O7‐σ system: 1. Reaction with CO2
Authors: Kingon Angus I. , Davis Cheryl D. , Hare Thomas M. , Palmour III Hayne , Koch Carl C. , Haase D.G. 
Published: March 2011

AbstractControlled reactions have been undertaken between CO2 and polycrystalline YBa2Cu3O7‐σ in the temperature range 500°‐700°C. Typical reaction products are Y2BaCu05, BaC03 and CuO. Subsequent processing in O2 (e.g. sintering) results in the formation of liquid phases(s) by peritectic reaction at temperatures of 935‐975°C, well below the incongruent melting point of YBa2Cu3O7‐σ (∼1010°C). This “low temperature” liquid phase is shown to have a dramatic influence on the sintering process, and the resulting microstructures. The reactions are difficult to reverse even after extended times at temperatures >900°C. The results give an indication of the effect of adsorbed CO2 into YBa2Cu3O7‐σ powders, albeit on a more localized scale.
Texturing Crystal Growth in Vertical Thermal Gradients
Authors: Tan N. X. , Bourdillon A. J. , Sawides N. 
Published: March 2011

AbstractTexture growth in incongruently melting ceramic superconductor materials, such as YBa2Cu3O7‐χ can be combined with zone refinement in thermal gradients to increase critical current densities. In gravity aided texture growth (GATEG), a vertical thermal gradient is used with downward motion of the partially molten specimen (relative to the furnace) so that the molten phase recrystallizes with grain growth. The oxidation features of Y‐Ba‐Cu‐0 and Bi‐Sr‐Ca‐Cu‐0 can be explained by Madelung potentials.
Preparation of Bipbsrcacuo Superconductors by Laser Pedestal Growth Method
Authors: Hayashi K. , Nonoyama H. , Ueyama M. , Nagata M. , Hitotsuyanagi H. 
Published: March 2011

AbstractBi‐Pb‐Sr‐Ca‐Cu‐0 superconductors were prepared by the laser pedestal growth method. The high Tc phase was created only by post annealing. As the growing speed increased, the annealing time necessary to obtain a Tc above 100K decreased. When the low Tc phase was aligned with the growing direction, Tc was under 100K, but a Jc of 15B0A/cm2(77.3K, OT) was obtained. In this case, magnetic field dependence below 300 gauss was superior to that of Pb‐free materials.
Sandwich Excitons as the Mechanism of High-TC Superconductivity
Authors: Richert Brent A. , Schachinger Ewald , Allen Roland E. 
Published: March 2011

AbstractOne potential objection to virtual “sandwich excitons” as a pairing mechanism is that the transition densities may not be large enough to overcome the inherent disadvantage of a large energy denominator . In model calculations, we find that some of the transition densities and matrix elements can be large even if the dielectric constant is sizeable for, e.g., LaO excitons in La2‐xSrxCuO4
Solid State Formation of Superconducting Phases in the T1-Ca-Ba-Cu-O System
Authors: Huang T.W. , Hung M.P. , Chin T.S. , Ku H.C. , Yang S.C. , Hsu S.E. 
Published: March 2011

AbstractDifferential thermal analysis (DTA) and thermal gravitometry analysis (TG A) under flowing oxygen show that the formation temperatures of the high Tc T12Ca2Ba2Cu3Ox (2223) and the low Tc T12CaBa2Cu2Ox (2212) phases lie at around 910 °C and 840 °C, respectively. The activation energies are as low as 50 kcal/mole for the 2223 phase and 35 kcal/mole for the 2122 phase. Thus the time for the formation of these phases can be within 30 minutes.Two preparation methods were tried, and the one with Ca3BaCu3O7 as a precursor was easier to attain pure high Tc 2223 phase than that prepared directly from component oxides and carbonates.
Microanalysis of Cuprate Superconductors Using the Color of Polarization
Authors: Hoff H.A. , Lechter W.L. , Osofsky M.S. , Candela G.A. 
Published: March 2011

AbstractA technique for the identification of individual anisotropic grains in a heterogeneous and opaque material involves the observation of grain color in a reflecting light optical microscope. Such colors are generally characteristic of particular phases. We have studied the presence of color in many superconducting cuprates and found a strong correlation between color and the existence of superconductivity. The change in color from insulator to superconductor facilitates the selection of grains for microanalysis. Color variations in a Tl-Sr-Ca-Cu-O material are investigated using quantitative energy dispersive x-ray spect-roscopy. Cation concentrations are found not to correlate with the changes in color. This apparent lack of correlation of color with composition is discussed.
Electronic Structure Calculations of the Copper Oxygen Planes in Yba2Cu3O6+δ, for 0 < δ < 1
Authors: Cogordan J. A. 
Published: March 2011

AbstractMolecular ab initio seIf-consistent calculations on clusters simulating the
copper-oxygen layers in the Yba2Cu3O6;δ are reported. The electronic structure, of this layer, was computed for different sets of values of the lattice parameters (a,b,c), according to their dependence on the oxygen stiochiometry. For the molecular orbitals , two different electronic occupations are considered, a closed shell and an open shell. For the open shell, an electron has been excited to the first virtual molecular orbital. It is found that this excited state has lower energy than the closed shell configuration for 0 < δ < 1. Molecular energies an electronic population are reported.
Processing and Fabrication of YBa2Cu4O8 and YBa2Cu4O8/YBa2Cu3Ox Composites
Authors: Balachandran U. , Biznek M. E. , Goretta K. C. , Veal B. W. , Poeppel R. B. 
Published: March 2011

AbstractPowders of YBa2Cu4O8 (“124”) were prepared via solid state reaction of Y2O3, BaCO3, and CuO. The mixed precursors were heated in flowing oxygen of reduced total pressure, followed by cooling and annealing at 750°C under ambient pressure oxygen. The procedure produced orthorhombic 124 as the main phase, with YBa2Cu3Ox (“123”) as a minor impurity phase. Phase purity improved, and nearly phase-pure 124 was obtained, upon annealing the as-calcined powder in flowing oxygen at 800°C.
Flux-Assisted Preparation of Powdered Bismuth Superconductors
Authors: Arendt R. H. , Garbauskas M. F. , Schilling L. L. 
Published: March 2011

AbstractResults are presented on efforts to prepare both the 80K, Bi2CaSr2Cu2Oz (2122), and 11 OK, (Bi,Pb)2Ca2Sr2Cu3Oz (2223), transition temperature bismuth superconducting species in either phase pure or nearly phase pure, powdered form using either equimolar NaCI-KCI or NaBiOz as molten fluxes. Data are presented on the effects of variation of the reaction temperature and duration, solvent content, relative CaO and CuO contents, and of post-synthesis anneals of the product materials.
The Preparation of Bi-Pb-Sr-Ca-Cu-O Superconducting Powder for Thick Film Pastes
Authors: Hagberg J. , Uusimäki A. , Levoska J. , Leppävuori S , Rautioaho R 
Published: March 2011

AbstractThe oxalate route was used to prepare (Bi-Pb) -Sr-Ca-Cu-O powder with the nominal composition Bi1.75Pb0.4Sr1.3Ca2.1Cu3.2Oy. This powder was decomposed/annealed at different temperatures between 434 and 795°C. They were investigated by thermogravimetric analysis, X-ray diffraction and transmission electron microscopy. Particle size distribution and surface area were also determined. The specific surface area decreased from a value of 16.5 m2/g for powder decomposed at 434 °C to 1.0 m2/g for powder decomposed at 795 °C. The measured mean particle size reached a minimum of 0.52 juri for powder decomposed at 589 °C.
Preparation of High-Purity T12CanBa2Cun+1O6+2n (n=1,2) Powders from Stoichiometric Reactant Mixtures
Authors: Wu Nae-Lih , Yao Yeong Der 
Published: March 2011

AbstractNew powder synthesis Methods have been developed for preparing the single-phase T12CaBa2Cu2O8 (the 2122 coapound) and T12CaBa2Cu3O10 (the 2223 coapound) powders froa stoichioaetric reactant mixtures. The 2122 coapound was prepared froa a stoichioaetric Mixture of T12O3, CuO, and CaBa2CuO4, while the 2223 coapound was prepared froa the same aixture but with additional CaO and CuO to Batch the correct (T1:Ca:Ba:Cu=2:2:2:3) stoichioaetry. The single-phase 2122 saaples with Tc above 110 K were obtained by using one-step calcination at 830°C, while the 2223 saaples with Tc ranging between 115 and 120 K were obtained by employing a first calcination at 830°C for 5 hrs and a second calcination at 870°C. Powder aelting, which is strongly associated with the conventional aethods, was significantly suppressed in the new aethods.
Effects of Processing Parameters on the Excimer Laser Deposition of Yba2Cu3O7-δ Thin Films
Authors: Muenchausen R. E. , Wu X. D. , Dye R. C. , Hubbard K. M. , Estler R. C. , Flamme C. , Brainard R. , Foltyn S. , Tesmer J. , Maley M. , Martin J. , Nogar N. S. 
Published: March 2011

AbstractSystematic studies of the effects of pulsed laser deposition processing parameters on plume dynamics and resultant film properties have been performed. Plume angular distributions, cosm(θ), were observed to be variable between 1 > m > 15 depending on laser energy density and spot size. Under optimized conditions, epitaxial, superconducting thin films could be grown in‐situ on a variety of single‐crystal substrates. High quality, 2000 Å  ss thick films were obtained at deposition rates approaching 150 Å/sec.
In Situ Growth of Epitaxial Superconducting Yba2Cu3O7-X Films on Insulating, Semiconducting and Ferroelectric K(Ta,Nb)O3 by Pulsed Laser Ablation
Authors: McCAMY J. W. , Norton David P. , Lowndes Douglas H. , Boatner L. A. , Christen D. K. , Feenstra R. , Sonder E. 
Published: March 2011

AbstractK(Ta,Nb)O3 (KTN) is an interesting substrate for use in studies of epitaxial superconducting film‐substrate interactions because of a moderate lattice parameter mismatch with YBa2Cu3O7‐x and great versatility in electrical properties. KTN's properties are easily modified by doping to form an n‐type semiconductor and/or a ferroelectric with variable ferroelectric Tp. As an initial step in exploring such studies we have carried out what are believed to be the first epitaxial growth experiments of YBa2Cu3O7‐x films on insulating, semiconducting and ferroelectric KTN single crystals by pulsed laser ablation. We find that c‐axis‐normal epitaxial films can be consistently grown with TSc(R = 0) > 90K , △TSC ~1.5K, and Jc > IMA/cm2 on semiconducting and/or insulating KTaO3. However, growth on KNDO3 is problematic because of stresses generated by cooling the substrate through first order structural transitions, at even moderate cooling rates.
Growth and Properties of Epitaxial YBa2Cu3O7 thin Films on{1102}Al2O3
Authors: Fork D. K. , Geballe T. H. , Char K. , Laderman S. S. , Taber R. , Bridges F. , Ponce F. , Boyce J. B. , Connell G. A. N. 
Published: March 2011

AbstractEpitaxial YBa2Cu3O7 (YBCO) films were grown on r‐plane A12O3 {1102} by laser ablation. X‐ray diffraction shows that films are epitaxial with the c‐axis perpendicular to the substrate and the a or b axes parallel to (2201), although the full width at half maximum of the rocking curve is larger compared to those of epitaxial films on SrTiO3. The critical temperatures (zero resistance) are between 85 K and 88 K with transition widths between 0.5 K and 3 K. The 300 K resistivity of 250 μΩextrapolates to zero at zero temperature and the critical current is as high as 5 x 106 A/cm2 at 4.2 K according to magnetization hysteresis measurements. Surface resistance data shows that 2000 Å thick epitaxial films on {1102} have about 1 mΩ at 13 GHz at 4.2 K.
In Situ Preparation of Y‐Ba‐Cu‐O Thin Films on Silicon Single Crystals
Authors: Habermeier Hanns—Ulrich , Wagner Gunter , Mertens Günter 
Published: March 2011

AbstractSuperconducting Y—Ba—Cu—O thin films with critical temperatures exceeding 80 K are deposited on silicon single crystal substrates using the pulsed laser deposition technique. Deposition from a sintered Y1 Ba2Cu3O7‐ target in oxygen ambient of 0.1 — 5 mbar onto substrates kept at 700°C to 820°C results in crystalline films in which the target composition of the metallic constituents is preserved. No post deposition treatments are required to obtain high values for the zero resistance. X— ray analysis as well as Raman spectroscopy reveal that specimens prepared at optimum conditions are single phase c—axis oriented. In contrast to films prepared on LaAlO3 or SrTiO3 the surface morphology shows a granular structure. The films prepared by this technique are quite stable against chemicals used in conventional lithographic patterning, however, a strong correlation between film quality before patterning and some degradation after patterning is observed.
In‐Situ Fabrication of YBa2Cu3O7‐x Superconducting Thin Films Directly on Silicon Substrates with Tc0 > 77K
Authors: Lee C. B. , Singh R. K. , Sharan S. , Singh A. K. , Tiwari P. , Narayan J. 
Published: March 2011

AbstractWe report in‐situ fabrication of c‐axis textured YBa2Cu3O7‐x superconducting thin films with Tco > 77K on unbuffered silicon substrates by the biased pulsed laser evaporation (PLE) technique in the temperature range of 550‐650°C. At substrate temperatures below 550°C, no c‐axis texturing of the superconducting film was observed. The YBa2Cu3O7‐x superconducting films were fabricated by ablating a bulk YBa2Cu3O7 target by a XeCl excimer laser (λ = 308 nm, τ = 45 × 10‐9 sec) in a chamber maintained at an oxygen pressure of 0.2 torr . The thickness of the films was varied from 0.3 to 0.5 nm depending on the number of laser pulses. Extensive diffusion was observed in thin films deposited at substrate temperatures above 550°C. However, microstructurally, with increase in the substrate temperature the films exhibited larger grain size and greater degree of c‐axis texturing (measured by the ratio of the (005) and (110) X‐ray diffraction peaks). This was found to give rise to better superconducting properties with Tco exceeding 77 K for YBa2Cu3O7‐x films deposited on Si substrates at 650°C.
Direct Observation by Transmission Electron Microscopy of the Early Stages of Growth of Superconducting Thin Films
Authors: Norton M. Grant , Tietz Lisa A. , Summerfelt Scott R. , Carter C. Barry 
Published: March 2011

AbstractThe fabrication of high quality thin films often depends on the early stages of the growth process during which epitaxy is established. The substrate surface structure generally plays a critical role at this stage. Many observations of the high‐Tc superconductor film‐substrate interface structure and chemistry have been made by transmission electron microscopy (TEM) of cross‐section samples. Ion‐milling induced damage, however, can be severe in these specimens. In the present study, the early stages of the growth of high Tc superconducting thin films of YBa2Cu3O7&#X03B4; have been studied by TEM using a technique which requires no post‐deposition specimen preparation.
Crystal Chemistry and Sub-Solidus Phase Relations in (La,Re)2CuO4 Systems
Authors: Bringley Joseph F. , Trail Steven S. , McElfresh Michael , Scott Bruce A. 
Published: March 2011

AbstractLa2‐xRExCuO4 (RE = Nd‐Y) solid solution systems have been investigated to determine the factors stabilizing the T (La2CuO4), T’ (Nd2CuO4) and hybrid T*‐type structures. A simple ionic model with a perovskite‐like tolerance factor is found to accurately define the existence field of each. Metastable T* phases are observed for the larger RE cations Nd, Gd, Eu. The structure is quite stable for RE = Dy, Tb, but does not occur at all for the smallest rare earths. Oxygen activity plays a role in T’ and T* phase formation.
Epitaxial Growth and Superconducting Properties of Yba2Cu3O7 Thin Films and Yba2Cu3O7/Dy(Pr)Yba2Cu3O7 Superlattices
Authors: Triscone J.-M. , Karkut M.G. , Brunner O. , Antognazza L. , Kent A.D. , Fischer ø. 
Published: March 2011

AbstractWe have prepared in situ REBa2Cu3O7 (REBCO) (RE= Y, Pr, Dy) thin films and YBC0/Dy(Pr)BC0 superlattices by single target dc planar magnetron sputtering. YBCO/DyBCO superlattices have been realized with modulation wavelength as short as 24Å, i.e., a unit cell of YBCO alternates with a unit cell of DyBCO, on average. The superconducting properties of such superlattices are indistinguishable from those of single layers. Tco's (zero resistance) are between 85 and 89K, and the residual resistivity ratios are between 2.5 and 3. In contrast to these results, when YBCO is layered with PrBCO, which is insulating, a dramatic change in the superconducting properties is observed. We have been able to artificially vary the coupling between single 12Å unit cell of YBCO by interposing insulating planes of PrBCO. As the YBCO layer separation increases, T is reduced and the transition broadens showing evidence of 2‐D superconducting fluctuations.
Effects of Oxygen Stoichiometry on The Magnetic Ordering of La2Ni1-YCuY04+δ
Authors: Zhao J. , Suresh Babu V. , Seehra Mohindar S. , Hepp Aloysius F. , Gaier James R. , Richman Robert M. 
Published: March 2011

AbstractAnnealing and quenching experiments in a thermogravimetric analysis apparatus are used to vary the oxygen content in La2Ni1‐yCuy04+δ, followed by magnetic susceptibility and x‐ray diffraction experiments. These studies show that for certain δ, transition to antiferromagnetism occurs with TN < 20 K. The effect of Cu doping (y = 0.01 and 0.05) on TN is negligible.