bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sn and Fe Mossbauer Spectra of Y Ba Cu (O, N)
Authors: DeMarco M. , Wang X. W. , Trbovich G. , Naughton M.J. , Chaparala M. 
Published: March 2011

AbstractWe report new results on 119 Sn and 57 Fe Mossbauer spectra of Y1 Ba2 Cu3-z (O, N)7-x, where M is either Sn or Fe, O denotes oxygen and N denotes ni trogen, 0 ≤ X ≤ 0.5, and z = 0.05, 0.1, 0.15, 0.2. The oxygen annealed samples were superconductors, but nitrogen annealed samples were not. The Mossbauer measurements indicate four quadrupole pairs in Y Ba2 (Cu, Fe)3 O7-x, but only three pairs in Y1 Ba2 (Cu, Fe)3 N6.5. In the Sn Mossbauer spectra, the quadrupole splittings of nitrogen annealed samples are larger than that of oxygen annealed samples. In both Fe and Sn spectra, the isomer shifts of oxygen annealed samples are different from that of nitrogen annealed samples. Our study provides some information about the Cu(1) and Cu(2) sites and their surrounding environment in the Y Ba Cu system.
Characterization of High-Temperature Superconducting Materials in Y-Ba-Cu-0 Systems
Authors: Kezuka Hiroshi , Masaki Tomomi 
Published: March 2011

AbstractThe Y-Ba-Cu-0 systems have been reported to be a high temprature superconductor with above 90K. Optical Study would give us useful informations as a characterization for Y-Ba-Cu-0 systems with an analysis of energy dispersive X-ray system EDS. Optical constants of superconducting Y-Ba-Cu-0 systems are n*=1.6 92-j0.403 for 99.99%(4N) with Y1.00 Bal.90 Cu2.87 and n*=1.604-j 0.441 for 99.99%+ (4N+) with Y1.00 Ba2.18 Cu3.12.
Transport and Diamagnetic Properties of 2:2:1:2 and 2:2:2:3 (Bi-Pb)-Sr-Ca-Cu-O Superconducting Materials
Authors: Ibanez R. , Sanchis M. J. , Sapina F. , Beltran D. , Beltran A. , De La Fuente G.F. , Rillo C. , Bartolome J. , Lera F. , Navarro R. 
Published: March 2011

AbstractBismuth superconducting oriented fibers of the compositions 2:2:1:2: and 2:2:2:3 have been grown by the Laser Floating Zone (LFZ) method. Growth conditions have been optimized in order to improve the superconducting properties. The 108 K onset in susceptibility measurements (associated to the 2:2:2:3 phase) only appears well defined when starting from Sr-defective precursors.
Field and Temperature Dependent Suspension Studies of High Temperature Superconductors
Authors: Huang Y. , Solin S.A. 
Published: March 2011

AbstractWe have employed a novel variable-temperature, variable-field/field-gradient cryogenic levitometer, previously used in levitation experiments, to study the suspension properties of the thallium-based high temperature superconductors. Our results are compared and contrasted with the levitation studies and the singular features of the suspension properties are noted.
Expansion of Pb2Sr2Y1-xCaxCu3O8+δ and Ba2YCu3O6+δ
Authors: O'Bryan H. M. , Gallagher P. K. 
Published: March 2011

AbstractThe expansions of Pb2Sr2Y1-xCaxO8+δ for x=0, 0.2 and 0.4 and Ba2YCu3O6+δ have been determined during heating to 700°C. Thermal and compositional components of the expansion have been identified by using different atmospheres. In N2 only thermal expansion with a CTE~13 ppm/*C is noted, while in O2 compositional effects are domina nt. At 550* the incorporation of 1.2 atoms of oxygen by Pb2Sr2YCu3O8 produces an expansion -0.4%. This behavior contrasts to the -0.2% shrinkage which occurs for Ba2YCu3O6.2 when -0.6 atom of oxygen is added. The different expansion behaviors of the two compounds are explained in terms of their structures and the position of the removable oxygen.
Anomaly in Thermal Expansion of YB2Cu307-y Around 250K
Authors: Ramadass G.A. , Ramcahdnran V. , Srinivasan R. 
Published: March 2011

AbstractThe linear thermal expansion coefficient of YBa2Cu307 as a function of temperature has been studied. An anomaly is observed at 250K. This temperature is found to be dependent on oxygen deficiency.
High Speed Infrared Detectors Using Y-Ba-Cu-O Thin Films
Authors: Zheng J.P. , Ying Q.Y. , Kwok H.S. 
Published: March 2011

AbstractY-Ba-Cu-O thin films were used for CO2 laser detection. Operation of the Y-Ba-Cu-O detector in both the bolometric and nonbolometric modes were studied. It was found that the detectivity of the superconducting detector was competitive with conventional detectors. The speed was within the instrument resolution of 10 ns. The superconducting film quality is critical to the performance of these detectors.
In-Situ Preparation and Characterization of Superconducting Thin Films and Related Materials by Mocvd for the Development of Three Terminal Switching Devices
Authors: Singh R. , Sinha S. , Narayan J. 
Published: March 2011

AbstractMetalorganic chemical vapor deposition (MOCVD) has the potential of emerging as a major technique for the fabrication of high temperature superconductor devices. In this paper, we present preliminary results of in-situ deposition of Y-Ba-Cu-0 thin films (Tc = 79K) by rapid isothermal processing assisted MOCVD on BaF2/silicon substrates.
Measurements of the Surface Resistance of Hts Thin Films From 0.5 to 40Ghz
Authors: Steinueck J. , Oates D.E. , Anderson A.C. 
Published: March 2011

AbstractWe have measured the surface resistance R, in polycrystalline films of YBCO and BSCCO deposited in our laboratory as well as oriented films made by other laboratories by codepostion techniques. The R, of YBCO and BSCCO has been measured in the frequency range between 0.5 and 40 GHz using a stripline resonator technique. R, for the films is nearly proportional to the square of the applied frequency over the entire measurement range. The magnitude of R, is, however, strongly dependent on the film microstructure. Our measurements at 1 GHz and 4 K show that randomly oriented films have R, ~ 10~3 Ω (close to Cu) while oriented large-grain films have markedly lower R, ~ 2 x 10-6 Ω, approaching the R, of superconducting Nb. The magnitude of R, rises to ~ 2 Ω and ~ 10-3 Ω at 40 GHz for the randomly oriented and preferentially oriented films, respectively. An effective penetration depth, λeff, has been determined from R, using local electrodynamics. We find that λeff is dependent on film microstructure and is ~ 5 µm for high-R, films, decreasing to ~ 5000 Å for low-R, films. The smaller values of Ωeff calculated for oriented films are of similar magnitude to values of the YBCO penetration depth (~ 2000 Å) reported in the literature. The use of the stripline resonator technique for temperature and magnetic field dependent i Measurements of R, will also be discussed.
Laser Interferometric Temperature Measurement of Heated Substrates Used for High Tc Superconductor Deposition
Authors: Saenger K. L. , Roy R. A. , Gupta J. , Doyle J. P. , Cuomo J.J. 
Published: March 2011

AbstractSubstrate temperature during film growth is an important processing parameter for vapor deposited films of the high Tc superconductors. In this paper we describe a novel, non-contact optical thermometry technique in which the temperature of a transparent substrate or “temperature sensor” is determined from its thermal expansion and refractive index change measured by laser interferometry. The technique is easy to implement and extremely accurate. Temperatures measured with this technique are reported for MgO substrates in varying degrees of thermal contact with a heated backing plate and compared to those measured conventionally by optical pyrometry or thermocouples in close proximity to the sample. The effect of the deposited film on the temperature of radiatively heated substrates will also be discussed.
Reactions at Ceramic Superconductor/Metal Interfaces
Authors: Oh Min-Seok , Notis Michael R. 
Published: March 2011

AbstractJoining technology for ceramic superconductors is currently a major problem. The possible reactions which occur at ceramic superconductors/metal interfaces are discussed and examples are shown of interfaces between YBa2Cu3Ox and Nd1.85Ce0.15CuO4-x vs. a series of metals (Ag, Ni, Fe) now being considered for joining and cladding applications. Various characterization techniques, including EPMA and x-ray mapping, are utilized for analyzing the spatial distribution of reaction products. In a composite configuration, Ag interlayer is found to promote interfacial reactions.
Preparation of High Tc Oxide Superconducting Tape by Rf Magnetron Sputtering
Authors: Fukutomi M. , Tanaka Y. , Asano T. , Maeda H. , Takahara H. 
Published: March 2011

AbstractThe feasibility of preparing YBaCuO films on metallic substrates is discussed in an attempt to fabricate a superconducting tape. Deposition method employed was an rf magnetron sputtering. An amorphous MgO thin layer was found to be a promising buffer layer. The highest zero resistance temperature was 84.0 K in its as grown state, and a critical current density was 4.8x10 A/cm2 at zero field and 77.4 K. Preliminary experiments using laser ablation technique were also carried out to obtain YBaCuO films at a rather high deposition rate.
High Density Bulk Shape Rapid Consolidation of the Yba2Cu307-X Superconductor
Authors: Rele S. V. , Raman R. V. , Meeks H. S. , Anderson R. L. , Shelton R. N. , Lan M. D. 
Published: March 2011

AbstractA novel rapid densification technique for fabrication of bulk shape YBa2Cu307–xsuperconductor is presented. The Ceracon process is a one‐step, quasi‐isostatic consolidation route utilizing conventional P/M equipment and set‐up. The Ceracon technology has enabled successful fabrication of bulk, shapes such as discs, cylinders, hollow cylinders and spheres along with significant increases in the density up to 95‐98% of the theorertical. The superconducting volume fraction is preserved due to short hold times at the operating temperatures and avoidance of high processing temperatures. Results based on densities, microstructure, susceptibility measurements, X‐ray diffraction patterns and TGA measurements are discussed.
High-Temperature Deformation of Yba2Cu307-8 With Ag Additions
Authors: Routbort J.L. , Goretta K.C. , Singh J.P. 
Published: March 2011

AbstractThe steady‐state flow stress of YBa2Cu3O7‐δ containing 15 to 30 vol.% Ag has been measured in air at nearly constant compressive strain rates between 5 x 10‐6 and 1 x 10‐4 s‐1 from 830 to 900°C. Addition of Ag dramatically decreases the flow stress compared to that of the pure superconductor, but the stress exponents and the activation energy for deformation remain unchanged.
Crystallite Orientation in Ybco Ceramic Layers Sintered on Silver Substrates
Authors: Schüler Claus Chr. , Greuter Felix , Kluge-Weiss Petra 
Published: March 2011

AbstractStrongly c‐axis textured layers of YiBa2Cu307_xwere prepared by sintering a precursor powder on Ag‐foils. Critical current densities of layers with a few (Am thickness are presently jc∼ 5000‐8000 A/cm2(77 K, H = 0) over a few centimeters length.
The Fabrication and Magnetic Shielding Properties of Melt Cast Bi‐Sr‐Ca‐Cu‐O
Authors: Rayne R.J. , Toth L.E. , Bender B.A. , Lawrence S.H. , Soulen R.J. , Miller M.M. , Candella G. 
Published: March 2011

AbstractMagnetic shields for SQUID applications were successfully fabricated using high Tc superconducting BSCCO. To produce shields with appropriate superconducting properties and close dimensional control, it was necessary to develop new processing techniques. Shields were produced by casting liquid BSCCO into molds, heat treating and machining. This technique is applicable to fabricating other types of superconducting devices requiring bulk superconductors with complex shapes and close dimensional control.
Magnet Replica by High Tc Superconductors
Authors: Weinstein R. , Chen In-Gann , Liu J. , Parks D. 
Published: March 2011

AbstractA study of magnetic field trapping phenomenon in oriented grain YBa2Cu3O7‐x samples produced by liquid phase processing has been conducted. The magnetic field reproduced from the parent magnetic field allows the production of “magnet replicas”, which can be used in various instruments when large magnetic field is needed constant in time. This paper reports the magnetic field trapping capability and uniformity observed in these oriented grain samples. The feasibility of building large and uniform magnetic field by assembling small SC specimens has also been explored.
High Resolution Neutron Powder Diffraction Study of the Tubular Phase Bi4Sr8Cu5O19+x
Authors: Caldés M.T. , Navarro J.M. , Fuertes A. , Obradors X. , Miravitlles C. , Rodriguez - Carvajal J. , Vallet M. , Gonzâlez-Calbet J. 
Published: March 2011

AbstractA high resolution neutron powder diffraction experiment has been performed on Bi4Sr8Cu5O19+x. The structure is well described in the space group Fmmm with the oxygen atoms in the bismuth planes appearing disordered in intermediate positions between NaCl and bridging sites as occurs in the superconductors Bi2Sr2Can‐1CunO4n+2. Temperature dependence study of powder neutron diffraction patterns between 1.5K and 998K does not show any relevant structural change neither evidence of antiferromagnetic ordering in this sample.
Renormalization from Density Functional Theory to Strong Coupling Models for the Electronic Structure of La2CuO4
Authors: Hybertsen Mark S. , Schluter Michael , Stechel E.B. , Jennison D.R. 
Published: March 2011

AbstractStrong coupling models for the electronic structure of La2CuO4 are derived in two successive stages of renormalization. First, a three-band Hubbard model is derived using a constrained density functional approach. Second, exact diagonalization studies of finite clusters within the three band Hubbard model are used to select and map the low energy spectra onto effective one-band Hamiltonians. At each stage, some observables are calculated and found to be in quantitative agreement with experiment. The final results suggest the following models to be adequate descriptions of the low energy scale dynamics: (1) a spin 1/2 Heisenberg model for the insulating case with nearest neighbor J≈130 meV; (2) a "t–t'–J" model with nearly identical parameters for the electron and hole doped cases.
Oxidation and Reduction of Bi2Sr1.85Cuo6-Y Crystals
Authors: Sonder Edward , Chakoumakos B. C. , Sales B. C. 
Published: March 2011

AbstractThe effects of oxidizing and reducing atmospheres on the oxygen contents and electrical properties of Bi2Sr1.85CuO6‐y single crystals were investigated. As‐grown crystals were normally semiconducting but became metallic and superconducting after heating the crystals for several hours in oxygen at temperatures between 500 and 800°C Previously superconducting crystals were made semiconducting by heat treatments in helium at temperatures between 700 and 780°C. Changes in the oxygen content of the crystals as well as the oxidation and reduction kinetics during the various heat treatments were monitored using standard thermogravimetric techniques. A good correlation was found between the annealing temperatures in oxygen (helium) at which there was an uptake (loss) of oxygen by the crystals, 500°C (700°C), and the onset (loss) of metallic behavior and superconductivity. From isothermal measurents of the weight change as a function of time, it was found that the apparent activation energies for oxidation and reduction were about 0.5 eV and 2.7 eV, respectively. A partial decomposition of the crystals during the various heat treatments, however, precluded a quantitative analysis of the kinetic data.
A Systematic Study of the Effects of Metal Substitutions for Cu in Yba2(Cu1-XMX)3O7-δ, M=Fe, Co, Al, Ga, Cr, Ni, and Zn
Authors: Xu Youwen , Moodenbaugh A. R. , Wang Y. L. , Suenaga M. , Sabatini R. L. 
Published: March 2011

AbstractA series of polycrystalline YBa2(Cu1‐xMx)3O7‐δ (1:2:3) samples with a typical grain size > 10μm was prepared using well controlled and reproducible precedures. This relatively large grain size allowed microprobe studies of individual grains to determine M content of the 1:2:3 phase. Solubility limits of substitutions for Cu in these samples are estimated. Superconducting transition temperatures and lattice parameters are presented. In the case of Ga, microprobe studies show no evidence for Ga content of 1:2:3 above x=0.01. Preliminary studies show no evidence for solid solution above x=0.01 when substituting Mn, Cr, Zr, and Ti for Cu in 1:2:3.
Conversion of 124 into 123 + CuO: microstructure and phase diagram
Authors: Morris Donald E. , Nickel Janice H. , Markelz Andrea G. , Gronsky Ronald , Fendorf Mark , Burmester Christopher P. 
Published: March 2011

AbstractConversion of 124 into 123 + CuO is interesting because it can produce non‐superconducting CuO islands and highly strained local regions, both of which may act as flux pinning centers. Microstructural studies (TEM) show localized regions with high strain fields resulting from the lattice mismatch between 124 and 123 along the c axis. Enhanced Tc (95 K) was found in partly converted samples. The partial pressure of oxygen necessary for conversion from YBa2Cu4O8 (124) to YBa2Cu307 (123) decreases with decreasing temperatures, and below 850°C the boundary between 123 and 124 phase regions is found to fall approximately as log ρ(θ2) = 19.3 ‐22000/T. The phase diagram of the Y‐Ba‐Cu‐O system is given as a function of temperature and partial pressure of oxygen over the range between 500°C and 1000°C and 10‐6< P[O2] < 102 bar.
Two Fluid superconductors
Authors: Bar-Yam Y. 
Published: March 2011

AbstractAn approach to the theory of high‐Tc superconductivity is discused in which the semiconductor‐like layers between the copper‐oxide planes are more active participants in the superconductivity. Two types of states appear in the theory, a lattice of negative‐U sites and single particle (positive‐U) dispersive states. The negative‐U sites originate in oxygen vacancies and the single particle states in the copper‐oxide planes. The coupling between these two types of states lead to a two‐fluid superconductivity where the negative‐U sites give rise to a charged Bosonic fluid and the single particle states are a Cooper‐paired superconductor. The coupled Fermion‐Boson model for superconductivity is related both to theories of superconductivity in semiconductor‐metal eutectic alloys, and recent suggestions of s‐channel superconductivity of R. Freidberg and T. D. Lee. Basic aspects of general phenomenology are described. The breakdown of Fermi liquid theory in the normal state results from mixing of Fermions and Bosons at the Fermi energy. When the two‐particle states are filled, anti‐ferromagnetism arises from the positive‐U of the single particle states with a contribution from virtual excitation of two‐particle states. Prediction is made of a large class of superconducting materials based on metal‐semiconductor layering.
Preparation of High Tc Bi‐Pb‐Sr‐Ca‐Cu‐O Superconducting Fibers by Laser Heated Pedestal Growth Method
Authors: Tomomatsu K. , Kume A. , Tominaga H. 
Published: March 2011

AbstractHighly oriented Bi‐Pb‐Sr‐Ca‐Cu‐O superconducting fibers have been prepared by the laser heated pedestal growth method. The annealed fiber showed both the high Tc (≃K) phase's and the low Tc (≃80K) phase's superconducting transition. The fiber grown at 2mm/h had the Jc value as high as l.0x103A/cm2. The misalignment of the high Tc phase's a‐b plane was measured by XRD less than ± 2°. It was found that the high Tc phase formed during the annealing was highly oriented as well as the low Tc phase.
Preparation of Fibrous Bi(Pb)-Sr-Ca-Cu-O Crystals Containing the High-Tc Phase
Authors: Matsubara I. , Tanigawa H. , Ogura T. , Yamashita H. , Kinoshita M. , Kawai T. 
Published: March 2011

AbstractFibrous crystals containing the high-Tc phase (2223 phase) of the Bi(Pb)-Sr-Ca-Cu-O superconductor have been prepared by heating a glassy melt-quenched plate in a stream of oxygen gas. Each fiber is composed of several platelike single crystals which are stacked in a layered structure. The fibers show two stepdrops in resistance at 105K and 73K, and a zero-resistance state around 70K. From the results of SQUID measurements, the volume fraction of the high-T phase is found to be about 0.6%. The high-Tc phase is also detected with a microarea X-ray diffractometer, and it is stacked in the interlayer between the low-Tc platelike crystals. For the fibrous Bi-Sr-Ca-Cu-Li-O crystals, the volume fraction of the high-Tc phase increases to 1.5% and a zero resistance state is achieved at 81K. The Jc value of the Li doped fiber is 30,000A/cm2 at 77K and 300,000A/cm2 at 66K in a zero magnetic field.
The Effects of Seeding on the Formation of High-Tc Bi-Pb-Sr-Ca-Cu-O Compounds
Authors: Kim Cheol J. , DeGuire Mark R. , Bansal Narottam P. 
Published: March 2011

AbstractThe effect of adding of Bi1.80Pb1.33Sr1.87Ca2Cu3O2 seeds(the 37Å phase) to the polycrystalline and glassy Bi-(Pb)-Sr-Ca-Cu-O materials was studied using XRD and SEM. The seeding effect was observed at 835 °C, 855 °C, and 870 °C in several compositions. Adding pre-synthesized 37Å phase powder to a mixture of unreacted starting materials accelerates the formation of additional 37Å phase.
Comparison of Barium Carbonate and Nitrate Used in the Preparation of YBa2Cu3O7-x Superconductors
Authors: Wahlbeck Phillip G. , Myers Dwight L. , Ronald Richards R. 
Published: March 2011

AbstractSamples of YBa2Cu3O7-x were prepared by the solid state reaction method using Y2O3, CuO, and either BaCO3 or Ba(NO3)2. The samples were studied using DTA-TGA, Knudsen cell mass spectrometry, and SEM-EDAX. The results indicated that C was more abundant in samples prepared from the carbonate than from the nitrate. In both samples, C was more abundant than N which was at low levels in both samples. Knudsen cell mass spectrometry has proven to be an experimental technique which is sensitive to volatile impurities at low levels.
Electronic Structures of Ga- and Zn- Substituted Yba2Cu3O7 Superconductors
Authors: Xu Yong-Nian , Ching W.Y. , Wong K.W. 
Published: March 2011

AbstractThe band structures of YBa2Cu307 superconductors in which one of the Cu atoms was replaced by Ga or Zn have been studied by the first‐principles orthogonalized LCAO method. Substitutions involving Cu on the chain site and Cu on the plane site were investigated. Results show significant modifications in the electronic structure due to the dopant‐specific and site‐specific substitutions. These results are discussed in light of some recent experimental observations.
Superconducting High TC Thin Films Prepared by Laser Deposition: Comparison of Laser Sources
Authors: Lynds L. , Weinberger B. R. , Lindsay M. P. , Potrepka D. M. 
Published: March 2011

AbstractA comparison of the energetics and stoichiometry of effluents from YBa2CU307‐x targets ablated by Nd:YAG (1064 nm) and excimer (248 nm) lasers is presented. NdrYAG ablative processes are characterized by specularly directed neutral atom/cluster formation with translational energies in the range of 2 ‐ 20 eV. In sharp contrast, excimer ablation leads mainly to highly forward directed atomic ions with centroid energies between 200 and 400 eV. Analysis of the energetics indicates that different mechanisms are at play but both processes are non‐equilibrium in nature.
In-Situ Pulsed Laser Deposition of High-TC Yba2Cu3O7 Superconducting Thin Films on (100) LaAlO3 Substrates
Authors: Tiwari P. , Sharan S. , Singh R. K. , Holland O. W. , Narayan J. 
Published: March 2011

AbstractThe formation of superconducting thin films on lanthanum aluminate substrates is very important for high‐frequency applications. In this paper, we discuss the fabrication of epitaxial superconducting YBa2Cu3O7 thin films on (100)LaAlO3 substrates, which exhibit excellent dielectric properties required for high frequency applications. The films were deposited by the biased pulsed laser evaporation technique (PLE) at substrate temperatures between 500‐650°C and exhibit excellent crystallinity with best minimum ion channeling yields corresponding to approximately 3%. The superconducting transition temperatures varied from 88‐92 K with critical current densities at 77K and zero magnetic field greater than 4 ‐ 5 x 106 Amps/cm2.