bluuebunny/crossref_metadata_2025_split huggingface dataset:
Superconductivity in Pseudo-Quaternary System
Authors: Yao P. C. , Chiang C. I. , Hsieh C. W. , Chen J. W. , Lin I. N. , Yang S. J. , Hsu S. E. 
Published: March 2011

ABSTRACTThe superconductivity of pseudo-quternary system Y1−xMx Ba2 Cu3 O7-δ, YBa2 Cu3−xM x O7-δ, where M stands Co,Cr,&Zn and with x=0,0.001,0.005,0.01 & 0.02, has been investigated.The XRD analysis shows that the perovskite structure is preserved and a stabilization effect on orthorhombic structure by 3d elements addition was proposed. On the contrary, the microstructure has been modified prominently and it is determined by the sintering mechanism involved and/or diffusion process in each doped sample. Second phase precipitate can be found at grain surface. The superconductivity, however, has not been greatly affected.
On the Defect Structure of Grain Boundaries in Ba2YCu3O7−x
Authors: Nakahara S. , Fisanick G. J. , Yan M. F. , Van Dover R. B. , Boone T. , Moore R. 
Published: March 2011

ABSTRACTCorrelations between observed defect structures and the orientation of planes involved in grain boundary (GB) formation in single phase, near ideal density orthorhombic Ba2YCu3O7−x are presented. Coherent boundaries involving only a low energy network of dislocations at the interface are associated with boundaries not involving the (001) basal plane, while basal-plane-faced GBs are highly defective. These results are interpreted using a model for local stress based on the known anisotropie thermal contraction of the material during cooling from sintering temperatures. Scanning Auger microscopy of in situ fractured surfaces demonstrates that there is preferential segregation of carbon at the GBs as well.
Epr Spectroscopy on Zn-Substituted YBa2Cu3O7
Authors: Ponte Goncalves A. M. , Jee Chan-Soo , Nichols D. , Crow J. E. , Myer G. H. , Salomon R. E. , Schlottmann P. 
Published: March 2011

ABSTRACTThe temperature and concentration dependence of the electron paramagnetic resonance spectra of YBa2(Cu1−xZnx)3O7 has been measured for 0≤x≤0.16. Zn substituted on the Cu-site cause a rapid nearly linear depression of the superconducting transition temperature Tc with Tc going to zero in the vicinity of x=0.10. Only weak EPR spectra due to ≤1% of the Cu-ions are seen in the superconducting phase of YBa2Cu3O7. These spectra are most likely attributed to Cu-ions in the vicinity of grain boundaries and do not represent a bulk response. However, a strong asymmetric resonance is observed in the Zn-substituted samples with x>0.1. The EPR results obtained for YBa2(Cu1−xZnx)3O7 are discussed in terms of a possible localization of d-electrons.
Effect of Oxidizing Atmosphere on Superconductivity in RBa2Cu3−xMxOz
Authors: Robinsonem David A. , Maginnis Abbot , Morrobel-Sosa A. , Alexander Chester , Asavaroengchai C. , Metzger Robert M. , Stanley Donald A. 
Published: March 2011

ABSTRACTThe dependence of the superconducting properties of RBa2Cu3−xMxOz (R = Y, Gd, M = Cr, Mn, Fe, Co, Ni, and x = 0.0, 0.025, 0.05, 0.1, 1.0, 3.0) on the oxidizing environment used during the processing (sintering/annealing) of these materials has been investigated. Samples of nominal composition, YBa2Cu3Oz, were prepared from the same starting materials and subjected to two different controlled heat treatments, under both controlled oxygen and ozone atmospheres. Measurements of ac electrical resistance versus temperature indicate that the critical temperatures are increased, and the widths of the superconducting transitions are narrowed for identically heat-treated samples when processed under ozone atmosphere rather than under an oxygen environment. Thermogravimetric analysis data indicate this trend to be correlated with increased oxygen content and thermal stability. This effect is also observable for materials with metal substitution for Cu, although the measured Tc's are generally lower for increased values of x. X-ray powder diffraction analysis showed the materials to be mostly single phase.
Electron Diffraction and TEM Studies of Y1Ba2Cu3O7−x
Authors: Pérez R. , Pérez-Ramírez J. G. , Avalos M. , Reyes J. , Martinez L. , Orozco E. , Carrillo E. , Mendoza A. , Albarran J. , Fuentes Maya J. , Boldú J. L. , José-Yacamán M. 
Published: March 2011

ABSTRACTOptical microscopy and transmission electron microscopy show that most of the crystalline grains in Y1Ba2Cu3O7−x superconducting specimens have large number of twins. These bands of different image contrast have similar microdiffraction patterns. However the diffraction conditions are different and correspond to different tilts of the crystalline grains along one of the zone axis. HREM images of these twin boundaries indicate that the boundary area has appreciable dimensions and both matrix and twin crystals show the existence of a superstructure with double of the common periodicity obtained under [001] diffraction conditions.
Local Environment Around Barium Atoms in the Superconductor Y-Ba-Cu-O
Authors: Krol A. , Xu F. , Jang L. Y. , Sher C. J. , Spagna S. , Althoff J. , Kao Y. H. 
Published: March 2011

ABSTRACTThe local structure around Ba atoms in the compound superconductor Y-Ba-Cu-O has been studied by measuring the extended x-ray absorption fine structure (EXAFS) near the Ba K edge. This technique is used to investigate the changes in the short range order structure when the system is doped with impurities.
Possibility of High-Tc Copper Fluoride Oxide Superconductors
Authors: Wu P. T. , Liu R. S. , Sung H. M. , Rung J. H. 
Published: March 2011

ABSTRACTSuperconductivity of YBa2Cu3FxOy system prepared by using a mixed solid state and gel method. A consistent and non-zero resistance drop near 280K was achieved in the nominal YBa2Cu3FxOy system for x=l and 2, with complete loss of resistance at 90K. The metal-semiconductor transition occurs at x value between 2 and 3. Temporal room temperature superconductivity with zero resistance was observed in a YBa2Cu3F2Oy sample at 308K. The phenomenon lasted for three minutes and was not reproducible.
Processing Relationships in YBa2Cu3O7−x Superconductors
Authors: Heber W. J. , Pederson L. R. , Maupin G. D. , Leblanc E. J. 
Published: March 2011

ABSTRACTSamples of YBa2Cu3O7−x were prepared by solid state reaction of Y2O3, BaO2, and CuO powders mixed in stoichiometric proportions. Powders reacted at 900°C-925°C in air were pressed at 35 MPa into rectangular bars and sintered at 950°C in air for six hours. Slow cooling at 50°C/hour promoted complete transformation to the orthorhombic structure. The effects of subsequent oxidation processing on superconducting properties were also investigated. Oxidation anneals at one atmosphere pressure in flowing O2over the temperature range from 300 to 550°C were performed. Results indicate that oxidation at 450°C optimized the superconducting transition temperature at 91K with a 2-degree transition width. Subsequent high-pressure oxidation (2000 psi O2) at 200°C for one week significantly degraded the superconducting characteristics. Results based on i udometric titration, thermogravimetric analysis, and x-ray photoelectron spectroscopy suggest that the copper valency is about 2.3 and oxygen stoi chiometry is 6.94 (x = 0.06) in samples processed to optimize superconducting properties.
Laser Processing and Characterization of High-Tc Superconductors
Authors: Weber W. H. , Logothetis E. M. , Soiitis R. E. , Graham G. W. , Chen J. T. , Wenger L. E. 
Published: March 2011

ABSTRACTRaman spectra of several samples of YBa2Cu3O7 presented, correlated with resistivity and structural data, and compared with previous results. Laser heating to ∼1100°C in air is shown to produce a surface layer of Y2O3 and Y2BaCuO5. Similar heating of La2−x(Sr,Ba)xCuO4 produces a layer of La2O3. All of these compounds are readily identified by their Raman spectra.
Improved Magnetization for YBa2Cu3O7-δ Annealed in Oxygen Above 1000°C
Authors: Venturini E. L. , Ginley D. S. , Baughman R. J. , Morosin B. , Kwak J. F. 
Published: March 2011

ABSTRACTAir sintering and subsequent oxygen annealing at high temperatures are integral to the production of ceramic superconducting YBa2Cu3O7-δ. We present results directed toward optimizing the temperature for these two process steps, using static magnetization to determine the intragranular properties. Surprisingly, pure oxygen stabilizes the material against decomposition at temperatures near the melting point, allowing the production of significantly higher quality single phase material.
Effects and Behavior of Implanted Fluorine in High Temperature Superconductors
Authors: Tesmer J. R. , Maggiore C. J. , Nastasi M. , Cheong S-W. , Dick C-M. 
Published: March 2011

ABSTRACTThe effects of implanted fluorine on the resistivity of high temperature superconductors and its diffusion within the superconductors have been studied in an attempt to duplicate a recent report of enhanced critical temperatures. Implanted fluorine was found to have no effect on the critical temperature and, upon heating, the fluorine diffuses out of the near surface.
Gkowth of YBa2Cu3O7-δ Single Crystals and Films by a Flux and a Sputtering Methods
Authors: Takagi K. , Hirao M. , Hiratani M. , Kakibayashi H. , Aida T. , Takayama S. 
Published: March 2011

ABSTRACTYBa2Cu3O7-δ single crystals and epitaxial films are grown and characterized. In flux growth for bulk crystals, effects of growth conditions on yield and electric resistivity of crystals are examined. The yield of flaky crystals depends on the formation of cavities. The transition temperature is 86 K after annealing in an oxygen atmosphere. Films are prepared on SrTiO3 by sputtering and epitaxial growth is confirmed by high resolution electron microscopy. Periodic lattice defects are observed near the interface between the substrate and the film. It seems that these defects result from the diffusion of impurities from the substrate.
Preparation of Superconducting thin Films of High Tc Cuprates by a Novel Spin-on/Pyrolysis Technique
Authors: Rice C. E. , Van Dover R. B. , Fisanick G. J. 
Published: March 2011

ABSTRACTSuperconducting thin films of high Tc cuprates have been prepared using wet chemical precursors, which are spun on a substrate, pyrolyzed and heat-treated. This new method is simple and inexpensive, and is easily amenable to scale-up to cover large areas. No vacuum equipment is required. The technique allows easy manipulation of film stoichiometry and gives films having excellent compositional uniformity. A 1600 A film of Ba2YCu3O7 prepared by this method had a room temperature resistivity of 500/xfzcm, Tc/(onset) of 90K, and R=0 at 58K. The preparation and electrical and microstructural characterization of thin films of Ba2YCu3O7 and other high TC cuprates will be discussed.
Magnetism, Specific Heat, and Surface Topography of Oxide Superconductors
Authors: Jenny H. , Bretscher H. , Frey T. , Anselmetti D. , Heinzelmann H. , Wiesendanger R. , Leemann G. , Walz B. , Säckinger D. , Güntherodt H.-J. 
Published: March 2011

ABSTRACTSamples of the composition MBa2Cu3O7−x with M = Y, Eu, Er, and Gd have been prepared by the standard solid state reaction method. The magnetic susceptibility has been investigated above room temperature up to 187O K in vacuum. Specific heat measurements have been performed with a differential scanning calorimeter (DSC) working at low temperatures in a differential mode using superconducting and non-superconducting samples. The surface topography of the high-Tc superconductors has been investigated at room temperature by scanning tunneling microscopy (STM).
Grain Boundaries in YBa2Cu3O7−x
Authors: Tietz L. A. , Carter C. B. , Lathrop D. K. , Russek S. E. , Buhrman R. A. 
Published: March 2011

ABSTRACTGrain boundaries in YBa2Cu3O7−x. thin films deposited on yttria-stabilized cubic zirconia have been characterized using selected-area diffraction. In addition to twin boundaries, several types of low-angle and high-angle grain boundaries are frequently found in these films. The high-angle boundaries include 23.5°, 29°, and 45° rotations about [001] and 90° rotations about [100] or [010]. These boundaries are compared to special high-angle grain boundaries in cubic materials.
High-Tc Superconducting Films of Y-Ba-Cu Oxide Prepared by a CO2 Laser Beam Evaporation
Authors: Tachikawa K. , Atanabe I. , Kosuge S. , Ono M. 
Published: March 2011

ABSTRACTThe high-Tc YBCO superconducting films have been prepared using a cw CO2 laser evaporation from a single bulk target. The adjustment of the target composition, especially the yttrium concentration, was found to be a key factor to achieve a desired film composition. After post-annealing at 930°C, the films deposited on YSZ substrate exhibited a zero resistance temperature of 85K. The deposition rate of the films was about lOOA/sec.
A Versatile new Metallo-Organic Spin-on Process for Preparing Superconducting Thin films
Authors: Gross M. E. , Hong M. , Liou S. , Gallagher P. K. 
Published: March 2011

ABSTRACTA new metallo-organic spin-on technique is described for producing thin films of the high temperature perovskite superconductors, LnBa2Cu3O7−x, where Ln represents a rare earth element. Pyrolysis of the spin-coated films leads to black films up to several microns thick whose degree of orientation is a function of the processing temperature and duration. Representative films of YBa2Cu3O7−x on MgO begin to exhibit orientation with the c-axis perpendicular to the film at heat treatments above 900 'C. The superconducting behavior of a highly oriented film produced at 990 ° C is characterized by Tc (onset) = 89 K, Tc (R=0) = 77 K and Jc = 104 amp cm-2 at 65 K.
External and Internal Diffusion of Oxygen in Superconducting YBa2Cu3O7−x Composite Conductors
Authors: Gaowacki B. A. , Evetts J. E. 
Published: March 2011

ABSTRACTWe report a systematic investigation of the critical current at 77K for a number of different composite conductors based on the high critical temperature superconductor YBa2 Cu3 O7. Results are reported for an ‘external’ diffusion composite where the oxygen diffuses through an outer cladding of silver, and for an ‘internal’ diffusion design where the composite is clad externally with an oxygen impermeable layer and oxygen diffuses internally from a channel within the conductor. Measurements are reported of the dependence of the critical current on i) the preparation route for the superconducting powder, ii) the preform particle size, iii) the presence of air or vacuum during compaction, iv) the time of the sintering anneal and v) the applied load on the conductor during a critical current test.
Crystal Structures and Superconductivity in the La1.5−xBa1.5+Cu7+ySystem
Authors: Greedan JE. , O'Reilly A. H. , Stager C. V. , Razavi F. , Abriel W. 
Published: March 2011

ABSTRACTMembers of the solid solution system La1.5−xBa1.5+Cu7+ywith x = 0, 0.125, 0.25. 0.375 and 0.5 have been prepared both in air and under one atmosphere of flowing oxygen. In general, except for x =0, the oxygen annealed compounds are superconducting while the air-annealed samples are semiconductors. Tc's measured by Meissner effect and resistivity data range to 70K. The crystal symmetry in all cases is apparently tetragonal as verified for x = 0.375 by variable temperature Guinier x-ray experiments at temperatures down to 8K. Crystal structures have been refined from neutron powder diffraction data. A correlation is noted between Cu-0 distances which connect adjacent Cu planes - the average copper valence and the occurrence of superconductivity.
Evidence for d-Electron Localization in YBa2(Cu1−xZnx)3O7 for 0<x<0.16
Authors: Jee C. , Nichols D. , Ciasullo J. , Crow J. E. , Mihalisin T. , Myer G. N. , Kuric M. V. , Bloom S. H. , Guertin R. P. 
Published: March 2011

ABSTRACTZn substitution for Cu in YBa2Cu3O7 rapidly reduces the superconducting transition temperature, Tc. Superconductivity is quenched between x=0.08 (T =30 K) and x=0.10. The normal state paramagnetism grows with Zn substu-tition, presumably due to increased localization on the Cu sublattice. Susceptibility studies of oxygen depleted (nonsuperconducting) Zn-substituted samples support this. Strong non-linear isothermal magnetization suggesting an internal magnetic field is found at T=4.2 K in samples with Zn concentration near to the critical value for suppression of superconductivity. The results are discussed in terms of increased localization of d-electrons on the Cu sites with increasing Zn concentration, which is consistent with recent EPR data.
The Effects of Oxygen Stoichiometry and Oxygen Ordering on Superconductivity in Y1Ba2Cu3O9−x
Authors: Beyers R. , Engler E. M. , Grant P. M. , Parkin S. S. P. , Lim G. , Ramirez M. L. , Roche K. P. , Vazquez J. E. , Lee V. Y. , Jacowitz R. D. , Ahn B. T. , Gür T. M. , Huggins R. A. 
Published: March 2011

ABSTRACTThis paper reports on the structures and properties of Y1Ba2Cu3O9−x samples prepared in precisely controlled oxygen environments using a solid-state ionic technique. By titrating out oxygen at low temperatures, orthorhombic Y1Ba2Cu3O9−x samples were prepared with oxygen contents below 6.50. Resistivity and magnetometry studies indicated that these reduced, orthorhombic samples were marginally superconducting, with their superconductivity probably arising from local regions of higher oxygen content.
Critical Current Density of the YBa2Cu3O7-δ Superconductor as Affected by Microstructuralxontrol
Authors: Jin S. , Sherwood R. C , Tiefel T. H. , van Dover R. B. , Kammlott G. W. , Davis M. E. , Fastnacht R. A. , Nakahara S. , Yan M. F. , Johnson D. W. 
Published: March 2011

ABSTRACTThe recent discovery of the YBa2Cu3O7-δ type high Tc superconductors stimulated worldwide R&D interest in this field. However, the relatively low critical current density (Jc) in the polycrystalline, bulk superconductors (as well as its significant deterioration in weak magnetic fields) has been a major roadblock to the rapid technical advancement toward applications. In this paper, we investigated the effect of processing and microstructural control on Jc of the superconductor. Improved Jc values of -3100 A/cm2 at 77K with somewhat reduced field dependence have been obtained through appropriate microstructural modifications.
Evaluation of Critical Current Density in Ba2Y1Cu3O7-y, Compound
Authors: Kumakura Hiroaki , Uehara Mitsuru , Takahashi Kazuhiko , Togano Kazumasa 
Published: March 2011

ABSTRACTMagnetization measurement was carried out for Ba2Y1Cu3O7-y bulk and powder samples at 77K and 4.2K in order to evaluate intrinsic Jc. Excellent Jc values above 10 A/cm were obtained for powder samples at 77K and lOkOe. These Jc values were somewhat increased by substiution of Er for Y. High temperature sintering at 1030°C brings about drastic increase in magnetization which can be explained by the grain coarsening.
L3 White line Splitting of Copper in the Electron Energy loss Spectrum of YBa2Cu3O7−x
Authors: Ahn Charming C. , Lee David S. , Samwer Konrad 
Published: March 2011

ABSTRACTWe have used electron energy loss spectroscopy (EELS) in a transmission electron microscope (TEM) to probe the L23 excitation of the 930 eV copper 2p to 3d transition in YBa2Cu3O7−x. Unlike UPS and XPS which are surface sensitive, EELS permits analysis of bulk properties from submicron regions of a single crystal. In addition, EELS probes the lowest unoccupied states and is particularly suited to the analysis of Cu valance states in YBa2Cu3O7−x We observe a splitting of the L33 peak of ∼2.7 eV, which we attribute to contributions from both Cu 2+ and Cu 3+. The intensity contribution Cu 3+ is maximized when a two beam condition is used to enhance channeling of the electrons between the {033} planes of the crystal near a [100] orientation. Upon prolonged exposure of the compound to the incident electron beam, the splitting disappears and the only contribution to the L3 white line is from divalent copper.
Magnetic Transitions in High-Tc Superconductors
Authors: Barrio R. A. , Wang C. , Tagüeña-Martinez J. , Rios-Jara D. , Akachi T. , Escudero R. 
Published: March 2011

ABSTRACTBased on very recent experimental evidence about magnetic transitions in high-Tc superconductors the role of superconductivity and magnetism is analyzed. A model of interacting electrons in a one-dimensional system is constructed, taking into account that antiferromagnetic interactions in the underlying lattice are present. The origin of this antiferromagnetism could be due to local Y d-electrons or rare earth f-electrons, related to the structure. Self-consistent calculations in this model show the possibility of a new state, with a gap, in which there are electron pairs. The characteristics of this new state are discussed in relation to superconductivity. The results of this model suggest that an extension of it could be applied to the new superconducting ceramics.
Raman and Infrared Studies of Sr2TiO4 - an Isomorph of (La,Sr)2CuO4
Authors: Burns Gerald , Dacol F. H. , Kliche G. , König W. , Shafer M. W. 
Published: March 2011

ABSTRACTIn order to better understand the phonon spectra obtained from ceramic (La,Sr)2CuO4 superconductors, we have studied the infrared and Raman spectra of the isomorphic material Sr2TiO4 (as well as related materials). As a consequence, various aspects of the spectra of both materials are better understood, and this is discussed.
Magnetic Measurements on YBa(2)Cu(3)O(x) Ceramic High Temperature Superconductors
Authors: Cornelis J. , Van Den Bosch A. , Vansummeren J. , Ooms H. , Gilissen R. , Cooymans J. , Maene N. , Biermans F. 
Published: March 2011

ABSTRACTStatic magnetic susceptibilities have been measured, following the Faraday method, on a disc of home-made YBa(2)Cu(3)O(x). The superconducting ceramic disc was oriented perpendicular to the applied magnetic induction field < 10 mT. On cooling the sample in a constant field from above to below the critical temperature a Meissner-Ochsenfeld effect is observed. The interpretation of the data yields partial flux expulsion. That the flux is not completely expelled from the sample is understood on the basis of the flatness of the disc. Part of the flux which had not been expelled by the Meissner-Ochsenfeld effect remains trapped in the cooled superconducting material.
Far Infrared Spectroscopy of RBa2Cu3Ox with Variations in R and x
Authors: Crawford M. K. , Farneth W. E. , Bordia R. , Mc Carron E. M. 
Published: March 2011

ABSTRACTWe report far infrared reflectance measurements of RBa2Cu3Ox, where R-Y, Er and Nd and 6<×<7 for YBa2Cu3Ox. Based on these measurements we assign the observed phonon features. In particular, one vibration is clearly identified as an R vibration, while the lowest energy mode (near 151 cm-1) is associated with the linear Cu-O chains.
Ultra-Low-Field Squid Magnetic Measurements on High Temperature Ceramic YBaCuO Superconductors
Authors: Cronemeyer D. C. , Malozemoff A. P. , Mcguire T. R. 
Published: March 2011

ABSTRACTWe report ultra-low-field (5 mOe - 1 Oe) magnetic measurements on a ceramic sample of YBaCuO. A positive remanent moment is observed which accurately equals the difference of the field-cooled and zero-field-cooled moments throughout the temperature range. At higher fields this relationship breaks down. A reversible region is observed near the superconducting transition temperature which is independent of field. These results are discussed in the context of recent models.