bluuebunny/crossref_metadata_2025_split huggingface dataset:
YBa2Cu3O7-δ Superconductors Produced by Hot-Pressing of Freeze-Dried, Carbonate- and Oxalate-Coprecipitated Powders
Authors: Wang C. T. , Lin L. S. , Lin J. H. , Su J. Y. , Yang S. J. , Hsu S. E. 
Published: March 2011

ABSTRACTReactive YBa2Cu3O7-δ powders have been produced via freeze-drying, carbonate- and oxalate-coprecipitating methods. In the coprecipitating methods, sodium carbonate and sodium oxalate were used as precipitants. These powders were characterized by TGA, XRD, and SEM. The morphologies of the YBa2Cu3O7-δ powders produced from these methods are different from each other. The influence of hot-press process on the bulk density, micro-structure development and superconducting properties of YBa2Cu3O7-δ samples was also studied.
Theories of High Tc Superconductors
Authors: Bardeen John 
Published: March 2011

ABSTRACTMany theories have been given to account for the high transition temperatures in the oxide superconductors. While most are based on pairing, they differ as to the origin of the attractive interaction that gives rise to the pairs and whether the pairing is weak or strong. If weak(λ < ∼ 0.5), the energy range of the pairing interaction must be wider than is consistent with one mediated solely by phonons. With measurements on single crystals becoming available, giving data covering a wide range of frequencies and temperatures, it is possible to narrow down the possible options. The data show that anisotropie 3D models are required. Observed isotope shifts indicate that phonons must play a role, but additional mechanisms are likely necessary to account for the high T's. Thermal, magnetic and transport data are consistent with anisotropie Ginzburg-Landau theory near T, with expected departures at low temperatures.
Top Seeded Solution Growth of Lanthanum Copper Oxide
Authors: Picone P. J. , Jenssen H. P. , Gabbe D. R. , Tuller H. L. 
Published: March 2011

ABSTRACTSingle crystals of pure and Sr doped La2CuO4 have been grown with a top seeded solution growth technique. Crystals grown from a lithium borate flux incorporate impurities detrimental to superconductive properties while those grown from excess copper oxide are free from this difficulty.
Formation and Processing of High Tc Superconductor films with Pulsed Excimer Laser
Authors: Kawaiw Tomoji , Kanaiw Masaki , Kawai Maki 
Published: March 2011

ABSTRACTHigh Tc YBa2 Cu3 Oy and GdBa2 Cu3 Oy thin films can be made by a laser sputtering method using LnBa2 Cu3 Oy (Ln=Y and Gd) ceramics as targets and cubic zirconia as a substrate in a high vacuum system. The superconcucting onset temperature and the zero resistance temperature of the film are 95 and 80K, respectively. The surfaces of these films were subjected to an irradiation with a focused pulsed excimer laser. Scanning of the beam led to the etching of the surface to form a groove. Photochemical processes on these superconductor films were studied using dynamic mass-spectroscopic method.
Epitaxial Films of High Tc Oxide Superconductors Y1Ba2Cu3O7 Grown on SrTiO3 by Molecular Beam Epitaxy
Authors: Kwo J. , Hsieh T. C. , Hong M. , Fleming R. M. , Liou S. H. , Davidson B. A. 
Published: March 2011

ABSTRACTOrientation ordered high-Tc oxide films of Y1Ba2Cu3O7 were prepared by molecular beam epitaxy on SrTiO3 substrates. A combination of effusion cells and e-beam evaporators was used with the addition of an oxygen jet. The superconducting phase is formed by further O2 anneal at temperatures ≥800° C. For SrTiO3 (100), the Y1Ba2Cu3O7 films grow in the orientation of either the c-axis or the a-axis perpendicular to the film plane. Films with predominant “c⊥” orientation exhibit a high degree of crystalline order with a rocking curve 0.3° wide. The Jc is about two times higher than those with the “a⊥” orientation of a comparable Tc (R=0). For a typical film of 9000Å thickness, a Tc (R=O) of 87K, and a Jc of 7 × 104 A/cm2 at 77K were reproducibly achieved. For SrTiO3 (110), X-ray showed twinning of (110) and (103) orientations in Y1Ba2Cu3O7, thus precluding the observation of anisotropy expected for the in-plane axes of [001] and [110].
Photoemission Study of the Electronic Structure of Copper Oxide Superconductors
Authors: Shen Z.-X. , Allen J. W. , Yeh J. J. , Kang J.-S. , Ellis W. , Spicer W. E. , Lindau I. , Sun J. Z. , Geballe T. H. , Maple M. B. , Dalichaouch Y. D. , Torikachvei M. S. 
Published: March 2011

ABSTRACTWe report the photoemission spectra from a high quality thin film sample of Y1Ba2Cu3C7-δ at room temperature and bulk samples of Y1Ba2Cu3C7-δ at different temperatures. The experimental data are interpreted within the configuration interaction model of Anderson Hamiltonian. The experimental values for Δ, U and T are determined. We also give the reasons why we think PES data reflect the intrinsic property of the superconductors. Furthermore, we emphasize the importance of the presence of a 3d8-like satellite which signals the strong correlation among 3d electrons.
Electronic Structure and Antiferromagnetism in La2CuO4
Authors: Sterne P. A. , Wang C. S. , Stocks G. M. , Temmerman W. M. 
Published: March 2011

ABSTRACTSelf-consistent spin-polarized energy bands have been calculated for tetragonal and orthorhombic La2CuO4. No stable antiferromagnetic order is found in either the stoichiometric compound or oxygen deficient La2CuO3.75. Constraining the occupancy of Brillouin zone boundary states leads to a small antiferromagnetic moment in both systems which is rapidly quenched by Ba doping.
Magnetization of a Superconducting Glass
Authors: Tuominen M. , Goldman A. M. , MeCartney M. L. 
Published: March 2011

ABSTRACTThe time-dependent magnetization of single crystal samples of the high temperature superconductor YBa2Cu3O7 has been studied as a function of temperature and magnetic field. Long relaxation times have been found to persist up to the transition temperature, implying that the transition temperature is the upper bound on glass-like behavior.
63,65Cu NMR and NQR in YBa2Cu3O7-δ
Authors: Warren W. W. , Walstedt R. E. , Bell R. F. , Brennert G. F. , Cava R. J. , Espinosa G. P. , Remeika J. P. , Rietman E. A. 
Published: March 2011

ABSTRACTNMR and NQR results are reported for 63,65Cu in YBa2Cu3O7-δ. Analysis of the high-field NMR spectrum indicates substantial disorder in the copper-oxygen planes. Nuclear relaxation rates are significantly different for copper in the chains and planes both above and below Tc and yield sharply different electron pairing energies on these structural units in the superconducting state.
Synthesis Study of Superconducting YBa2Cu3O7−x Powders from Metal-Alkoxides
Authors: Wu K. , Kramer S. , Kordas G. 
Published: March 2011

ABSTRACTWe have synthesized orthorhombic phase YBa2Cu3O7−x superconductors by using metal alkoxides. Cu (II) ethoxide was first partially dissolved in toluene, followed by the addition of Ba-methoxyethoxide and Y-methoxyethoxide in methoxyethanol to further enhance the solution solubility. A homogeneous gel-like paste was obtained both by adding water to the stock solution and by exposing it to the atmosphere. The gels were then vacuum dried and fired at 800 and 850°C in flowing O2. The superconducting transition temperature was 90 +K.
Critical Currentc Anisotropylc in Sintered Superconducting YBa2Cu3O7
Authors: Głowacki B. A. , Evetts J. E. 
Published: March 2011

ABSTRACTWe report a pronounced critical current anisotropy in bar shaped samples formed from different particle sizes as a function of the magnetic field orientation. Anisotropy of the critical current in tape form wires confirms the measurements on bar samples. X-ray measurements indicate a c-axis preference parallel to the compression axis.
Measurement of the Magnetic form Factor of Cu in Antiferromagnetic La2CuO4
Authors: Mitsuda S. , Freltoft T. , Shirane G. , Remeika J. P. , Cooper A. S. 
Published: March 2011

ABSTRACTThe magnetic form factor for Cu in the antiferromagnetic state of a single crystal La2CuO4 has been measured using neutron diffraction. Our result is consistent with Freeman and Watson's calculation for Cu2+, at least up to Q=4Å1, although a plateau between 1 and 3 Å-1 suggests a small contribution of magnetic moment at the out-of-plane oxygen sites. For larger values of Q the form factor for La2CuO4 seems to drop faster than for Cu2+. The sample ordered antiferromagnetically at TN ≃ 185K with an average ordered moment μ = 0.30/μB per Cu atom.
Far Infrared Measurements on Single Crystals, Films and Bulk Sintered High Temperature Superconductors
Authors: Noh T. W. , Sulewski P. E. , Kaplan S. G. , Sievers A. J. , Lathrop D. K. , Buhrman R. A. 
Published: March 2011

ABSTRACTWe report measurements of the reflectivity of bulk samples, films and single crystals of high Tc materials. The data are fitted with the Mattis-Bardeen theory to obtain gap values. For sintered samples we find 2Δ/kTc = 2.6, while for YBa2Cu3O7-y films and single crystals 2Δ/kTc = 6.4 and 7.7 respectively.
Anisotrop1C Behavior of a High Tc Superconductor
Authors: Otter F. A. , Budnick J. I. , Weinberger B. R. , Lynds L. , Yang D.-P. , Galasso S. F. , Filipkowski M. , Hines W. A. , Potrepka D. M. 
Published: March 2011

ABSTRACTWe report low and high field vibrating sample magnetometry results and resistance measurements on a highly oriented, single-phase sample of Y1Ba2Cu3O7−x. We find no anisotropy for the low-field (1mT) Meissner effect or trapped flux. Ratios for high field (to 1.9 T) and ρab/ρc are ∼ 2 and 3.6 respectively. Both are different from single-crystal results, a difference we attribute to grain boundary effects.
Tight-Binding Study of the Electronic Structure of the high Temperature Superconductor La2CuO4
Authors: Papaconstantopoulos D. A. , Deweert M. J. , Pickett W. E. 
Published: March 2011

ABSTRACTWe have fit our first principles LAPW band structure results for the high Tc superconductor La2CuO4 to a tight-binding Hamiltonian that contains s, p, and d interactions from the three components of these materials. Our fit reproduces very accurately the 17 lower bands of this material and especially the Fermi surface.
Specific Heat Linear Term in YBa2Cu3O7−x and a Survey of Related Compounds
Authors: Ramirez A. P. , Cava R. J. , Espinosa G. P. , Remeika J. P. , Batlogg B. , Zahurak S. , Rietman E. A. 
Published: March 2011

ABSTRACTWe have measured the specific heat, C, in the temperature range 0.3 to 20K and in magnetic fields up to 12 Tesla of several compounds related to the high-Tc superconductors. The linear term in C for YBa2Cu3O7−x is only weakly dependent on oxygen concentration in the range 0 ≤ × ≤ 0.7. The linear term in C changes by less than 10% at 10 Tesla for La1.98Sr.02CuO4, whereas for YBa2Cu3O7−x it is obscured by additional field-dependent structure. Magnetic ordering anomalies are observed in YBa2Cu2O5 at 10.6 K and in BaCuO2+6 at 9.3 K.
Copper Valence Via Small Polaron Analysis in Sinter-Forged YBa2Cu3O7-y at 700°C
Authors: Ahuja Deepak , Dorris S. E. , Su M.-Y. , Robinson Q. , Johnson D. L. , Mason T. O. 
Published: March 2011

ABSTRACTVia electrical property measurements (conductivity, thermopower) at 700°C on sinter-forged YBa Cu O, it was YBa2Cu3O7−x, it was determined that conduction occurs via small polaron conduction in the tetragonal phase. From the thermopower and oxygen content the distribution of copper valence states was determined.
Electron Scattering in Superconducting Oxides
Authors: Ruvalds J. , Ishu Y. 
Published: March 2011

ABSTRACTElectron energy loss measurements on superconducting oxides are correlated with an acoustic plasm on branch whose energy and width is highly sensitive to the alloy composition. Changing oxygen content reveals structure in the electron cross section which tracks the changes in the superconducting transition temperature.
Pressure Dependence of the Tetragonal-Orthorhombic Transition in La1.88 Sr0.12 Cu O4-δ: A Single Crystal X-Ray Study
Authors: Moret R. , Collin G. 
Published: March 2011

ABSTRACTWe report the first combined high pressure (up to 30 kbar) and low temperature (10 K - 300 K) single crystal X-ray diffraction study of the tetra-gonal-orthorhombic transition in La2−xCuO4-δ(x=0.12). Superstructure reflections of the orthorhombic phase were used to characterize the transition. The transition temperature, TT–O, is found to decrease under pressure and the orthorhombic phase is suppressed above about 15 kbar. These results confirm that both phases are superconducting and suggest to attribute a previously reported kink in dTc/dP to different rates of increase of Tc for the tetragonal and orthorhombic phases.
Superconducting Properties of YBa2Cu3O7-δ Doped with Various Metals and Oxides
Authors: Sherwood R. C. , Jin S. , Tiefel T. H. , Van Dover R. B. , Fastnacht R. A. , Yan M. F. , Rhodes W. W. 
Published: March 2011

ABSTRACTThe interactions of YBa2Cu3O7-δ type high Tc superconductors with other metals and oxides are of significant technical importance because of the need for i) proper stabilizing normal metal for composite superconductor wire, ii) nonreactive crucible materials for melt processing or crystal growth, and iii) suitable nonpoisonous substrate materials for thin film/thick film superconducting devices. For these reasons, and also for the purpose of exploring possible improvements in Tc, Jc and mechanical properties, the effects of various metal and oxide additions (1–40% by weight) have been investigated. It is shown that many of the elements in the periodic table deteriorate the superconducting properties to a various degree ranging from a broadened transition or reduced Tc to a complete elimination of the superconducting behavior. However, silver, gold and cadmium were relatively benign or slightly improved the properties. These benign materials have potential for practical application in superconducting composites.
Ion Channeling Studies of Crystallinity, Amorphization, and Thermal Annealing in Single-Crystal YBa2Cu3Ox.
Authors: Stoffel N. G. , Bonner W. A. , Morris P. A. , Wilkens B. J. 
Published: March 2011

ABSTRACTWe have performed Rutherford backscattering spectroscopy (RBS) and axial channeling on single crystals of the high-temperature superconductor YBa2Cu3Ox. The results demonstrate good crystal quality and cation stoichiometry in the as-grown samples. We observe some surface disorder, and estimate from the surface-peak intensities that there is roughly one formula unit of misregistered atoms per unit cell, or one molecular monolayer of surface disorder.We have studied the surface disorder induced in these crystals by various surface processing treatments, and have tried to achieve solid-phase epitaxial regrowth of disordered surface layers. Preliminary results have been obtained on the annealing of 100 nm amorphous layers formed on the surface of single crystals by 30 keV oxygen ion implantation. The Ba in the amorphous layer was found to segregate strongly to the surface for annealing temperatures as low as 500°C, although the crystalline phase does not decompose even at much higher temperatures.
Grain Boundaries, Planar Defects and Superconducting Properties of YBa2Cu3O7
Authors: Tafto J. , Suenaga M. , Wang T. , Sabatini R. L. , Moodenbaugh A. R. , Levine S. 
Published: March 2011

ABSTRACTPolycrystalline samples of tetragonal YBa2Cu3O6.25 were transformed into the superconducting orthorhombic phase by annealing in an oxygen atmosphere at temperatures ranging from 400–850°C and then slowly cooled to room temperature (15°C/h). Transmission electron microscopy (TEM) images of these samples and samples prepared in the usual way show layers of amorphous or highly disordered material, several 100 nm thick, at a large fraction of the grain boundaries. Also all samples contain 10–100 nm thick sheets of disordered material which lie in the a-b planes and tend to run through the entire crystal grain. In the a-b planes we also observe dislocation loops, particularly in the as-quenched tetragonal samples and stacking faults in the heat-treated samples. We also frequently observe set of twins with orthogonal habit planes within a crystal grain. We attribute the low critical current density in YBa2Cu3O7 to these planar faults and the disordered grain boundary regions, and discuss the TEM observations with reference to resistivity and inductive measurements.
On the Existence of (O2)2- in YBa2Cu3-yMyO7+x, M=Co and Fe
Authors: Tao Y. K. , Swinnea J. S. , Manthiram A. , Kim J. S. , Goodenough J. B. , Steinfink H. 
Published: March 2011

ABSTRACTThe limiting substitution of Co or Fe for Cu in the orthorhombic superconducting phase YBa2Cu3O7−x yields the tetragonal, semiconducting compositions YBa2Cu2CoO7.25 and YBa2Cu2.5Fe0.5O7.19 after annealing at 400°C and slow-cooling in O2. Single-crystal x-ray structural analyses, conductivity and magnetic-susceptibility measurements, and TGA data provide evidence for Co or Fe substitution at the Cu(1) position and intercalation of peroxide ions (O2)2-. The two compositions decompose for disintercala-tion of oxygen beyond O6.7 for M=Co and O6.4 for M=Fe when heated in N2. The Cu(2) atoms of tetragonal YBa2Cu3O6 appear to be antiferromagnetic below a TN = 240 K, which is similar to comparable Cu-O planar nets in stoichiometric La2LnO4.
Oxygen Absorption and Structural Transition in a Model YBa2 Cu3 O7-y
Authors: Varea C. , Robledo A. 
Published: March 2011

ABSTRACTWe describe the properties of a model for the absorption of oxygen in the basal planes of YBa2 Cu3 O7-y. The model consists of a layered oxygen lattice gas in equilibrium with an external source of O2 wherethe Cu-mediated oxygen-oxygen interactions are coupled to the elastic energy of the crystal. Our predictions for the dependence of oxygen-ordering, and unit cell dimensions with temperature and oxygen partial pressure are in quantitative agreement with experiment.
Vacancy Ordering in the Basal Plane of YB2Cu3Oz
Authors: Wille L. T. , Berera A. , De Fontaine D. , Moss S. C. 
Published: March 2011

ABSTRACTThe ordering in the Cu-O basal plane of the high Tc superconductor YBa2Cu3Oz is investigated. Asymmetric pairwise interactions between nearest and next nearest neighbors are assumed. Ordering instabilities in two-dimensional k-space are mapped out as a function of the interactions and the ordered ground state superstructures consisting of occupied and empty oxygen sites are determined. A temperature-composition phase diagram is calculated by means of the Cluster Variation Method. The thermodynamic behavior of the superconducting compound is discussed in the light of these results.
Superconductivity in the Fluorinated YBaCuO
Authors: Young R. T. , Ovshinsky S. R. , Chao B. S. , Fournier G. , Pawlik D. A. 
Published: March 2011

ABSTRACTFluorine substitution for oxygen in the high Tc superconducting ceramic oxides is not only fundamentally but also technologically interesting. We have previously reported the observation of superconducting zero resistance transition at 155–168K, subsequently confirmed by several other groups. We have also observed diamagnetic signals and flux trapping at temperatures as high as 305K. The samples were made from solid-state reaction in a pressed pellet form. Because of the BaF2 formation and the small volume fraction, we have not yet been able to identify the specific high Tc phases.In the course of elucidating and optimizing the fluorination effect, we have carried out other means of low-temperature fluorination experiments. The zero resistance at 154K was repeated.In addition to the observation of these high 1c results, we found that a dopant amount of fluorine promotes the oriented crystal growth. We also found that the replacement of weakly bonded oxygen by fluorine can greatly enhance the material's stability by eliminating the serious problem of oxygen diffusion.
Fermi Surface in La2CuO4-σ Determine by Positron 2D-ACAR
Authors: Tanigawa Shoichiro , Mizuhara Yoji , Hidaka Yoshikazu , Oda Migaku , Suzuki Minoru , Murakami Toshiaki 
Published: March 2011

ABSTRACTThe topology of the Fermi surface in La2CuO4-σ is determined by two dimensional angular correlation measurements of annihilation radiations (2D-ACAR) at room temperature. The determined Fermi surface is two dimensional and has a slender electron pillar along ΓZ and two kinds of hole pillars along PX and along NN direction parallel to ΓZ, respectively, in the Bradley and Cracknell notation modified by Yu, Freeman and Xu. It is concluded that the Fermi surface is not a simple half filled one and this compound should be metallic at least at room temperature in the band picture.
Thermochemistry and High Temperature Thermodynamic Properties of Rare Earth-Alkaline Earth-Copper Oxide Superconductors
Authors: Morss Lester R. , Sonnenberger David C. , Thorn R. J. 
Published: March 2011

ABSTRACTEnthalpies of formation of the perovskite-related oxides, La1.85 Sr0.15CuO4, YBa2Cu3Oy, with y = 6.93, 6.69, and 6.47 have been determined at 298.15 K by perchloric acid solution calorimetry. Enthalpies of formation and free energies of reactions with H2 O(g) and CO2 (g) have been evaluated. The partial molar enthalpy of solution of oxygen in YBa2 Cu3Oy has been determined and compared with values derived from measurements or the equilibrium partial vapor pressures of oxygen. The significance of the defect state thermochemistry in conductivity is identified.
Ordering of Oxygen Atoms in YBA2CU3O6+X and its Effects on Superconducting Properties
Authors: Nakamura Keikichi , Hatano Takeshi , Ikeda Shozo , Ogawa Keiichi 
Published: March 2011

ABSTRACTOrdering of oxygen atoms in YBa2Cu3O6+x has been analysed by employing statistical thermodynamics ana the results are compared with the experimental data. The axial lengths a and b at room temperature were determined experimentally as a function of oxygen content and were found to show good agreement with the calculated lengths a and b. Special care was taken in the above experiment to dope oxygen atoms into the sample at low temperatures, typically 400° C. The superconducting transition temperature of the sample doped with oxygen at 400°C(starting material:YBa2Cu3O6.1.(decreases linearly with decreasing the oxygen content from 6+x=6.9(92 K) to 6.38(30 K) and decreased sharply around 6+x=6.35(5 K). No distinct superconducting phase corresponding to further ordered orthorhombic phase has been observed in this case.
Oxygen Stoichiometry and Superconductivity in Ho1Ba2Cu3O7−x
Authors: Sales B. C. , Kim Y. C. , Thompson J. R. , Christen D. K. , Boatner L. A. , Sekula S. T. 
Published: March 2011

ABSTRACTThe effects of varying oxygen content on the superconducting transition temperature Tc, resistivity, and crystal structure of HoBa2Cu3O7−x (0 < x < 1) have been investigated. The variation of Tc wltn 8 is very similar to that previously reported by several authors for YBa2Cu3O7−x [1,2]. In particular a plateau in the Tc vs x curve is observed for values of x between 0.3 and 0.4 witfi the value of Tc,(10 % onset measured magnetically) remaining relatively constant at about 55 K. The width of the superconducting transition, as measured both resistively and magnetically, is substantially narrower for x= 0.35 + 0.05 than for slightly larger or smaller values of x. High resolution powder x-ray diffraction analysis was used to measure the lattice constants of both the orthorhombic and tetragonal phases as x was varied. With increasing x the temperature coefficient of the resistivity changed from positive (metallic) for x ≤0.2 to negative (semiconducting) for x ≥, 0.3. Since the general shape of the Tc vs x curve was unaffected by the complete substitution of magnetic Ho for Y, these results suggest an ordering of the oxygen vacancies in the a-b plane and the existence of an ordered compound with a Tc of 55 K.
Growth of Separated YBa2Cu3O7−x Crystals
Authors: Scheel Hans J. , Licci F. 
Published: March 2011

ABSTRACTThe problem of separating YBCO crystals from solidified residual melts could be solved by systematic growth experiments. Free crystals up to 7×7 mm2 area and about 0.1 mm thickness could by obtained from a BaO-CuO solvent and small alumina crucibles. Superconductivity was revealed by levitation and Meissner effect.