bluuebunny/crossref_metadata_2025 huggingface dataset:
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

NMR 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

We 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.
Spinodal Decomposition and High-TC Superconductivity
Authors: Markiewicz Robert S.
Published: March 2011

The singularity in the density of states near a Lifshitz point makes a significant contribution to electron exchange and correlation energy, which does not show up in conventional band theory calculations. This paper discusses several consequences of this fact for high temperature superconductivity.
Critical Currentc Anisotropylc in Sintered Superconducting YBa2Cu3O7
Authors: Głowacki B. A. , Evetts J. E.
Published: March 2011

We 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

The 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

We 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

We 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

We 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

We 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

Via 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

Electron 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

We 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

The 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

We 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

Polycrystalline 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

The 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

We 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

The 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

Fluorine 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.
Simulation and Processing of High Resolution Images of Defects and Interfaces in Superconducting YBa2Cu3O7
Authors: Zandbergen H. W. , Gronsky R. , Wang K. , Thomas G.
Published: March 2011

The superconducting performance, in particular the critical current, of polycrystalline YBa2Cu3O7 will depend strongly on the structure of grain boundaries and the nature and number of defects in the microstructure. To characterize the atomic structure of defects and grain boundaries in these materials, a high resolution electron microscopy study has been initiated. Emphasis has been placed on the technique of phase contrast imaging with corresponding computer simulation and processing for optimum interpretation of results.
Determination of the Oxygen Content in Samples of YBa2Cu3O7−x with Variable Oxygen Content
Authors: Matacotta F. C. , Nobile G. , Serrini Gianna , Giardina M. D. , Merlini A. E.
Published: March 2011

Since the discovery of the new high Tc cuprate superconductors [1,2] the oxygen stoichiometry of the compounds was of principal importance for the occurrence of the superconductivity.
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

The 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

Enthalpies 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

Ordering 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

The 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

The 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.
X-Ray Absorption and Resistivity Studies of the Quinary-Compound Superconductor Y-Ba-Cu-O-S
Authors: Spagna S. , Althoff J. , Yao Y. D. , Xu F. , Jang L. Y. , Krol A. , Kao Y. H.
Published: March 2011

A quinary-compound system consisting of Y, Ba, Cu, O, and S has been prepared in our laboratory. The nominal composition of Y, Ba, Cu, and O is similar to the well known material YBa2Cu3O7-y; the addition of S is intended to partially substitute the O sites. X-ray absorption measurements show that the lattice is distorted with the presence of S atoms. The transition temperature is found to decrease from 93K to about 77K with an increasing S content up to a S/Cu concentration ratio near 0.25; further increase of S results in unstable superconducting behavior and very broad resistive transition.
Advantages of Barium Peroxide in the Powder Synthesis of Perovskite Superconductors
Authors: Hepp A. F. , Gaier J. R. , Philipp W. H. , Warner J. D. , Garlick R. G. , Pouch J. J. , Hambourger P. D.
Published: March 2011

The results of Bednorz and Muller [1] and Wu and Chu [2] have stimulated a tremendous volume of research on ceramic superconductors [3–7]. Despite a number of other synthetic techniques, the solid state reaction remains the choice of most workers due to its simplicity [4,5,7]: CuO, Y2O3and BaCO3are often used in the powder synthesis of Ba2YCu3O7−x. BaO2is known to be a useful reagent in the synthesis of compounds containing higher oxidation states of metals [8]. Therefore, in our study of the possible role of Cu3+in superconducting perovskites, we also use BaO2in the solid state reaction. This paper compares reaction chemistry, material processing and material characterization using BaCO3or BaO2in the solid state reaction. We obtain greater mass density, increased sample homogeneity, lower resistance, and improved reproducibility for material prepared using BaO2. We would like to point out that other groups have produced Ba2YCu3O7−xusing BaO2[4,7]; Calestani and Rizzoli have reported a one-step process for producing single crystals of Ba2YCu3O7−xusing BaO2[9].
High-Tc Superconducting Films of Y-Ba-Cu Oxide Prepared by a Low Pressure Plasma Spraying
Authors: Tachikawa K. , Watanabe I. , Kosuge S.
Published: March 2011

A low pressure plasma spraying technique for depositing high-Tc YBCO thick films has been developed. Films with thickness ranging 20–100 μm have been prepared using Y0.3Ba0.7CuOx powders. After post-annealing in oxygen for 1h at 930–950°C, the films, which were deposited on nimonic alloy substrate heated at 650°C during spraying, exhibited a zero resistance temperature of 90.6K with transition width (90%-10%) of 2K and a critical current density (77K, 0T) of 690 A/cm2.
A Hydroxycarbonate Route to Superconductor Precursor Powders
Authors: Voigt J. A. , Bunker B. C. , Doughty D. H. , Lamppa D. L. , Kimball K. M.
Published: March 2011

A precipitation process is described for the preparation of powders that can be thermally decomposed to form high critical temperature superconductors such as YBa2Cu3O7. In the process, a cationic solution (a concentrated chloride or nitrate solution) is instantaneously mixed with an anionie solution (a mixture of tetramethylammonium hydroxide and carbonate) to produce a metal-hydroxycarbonate precipitate having the metal stoichiometry of the desired superconducting oxide. The calcining and sintering of the precipitates is critical in controlling the structural integrity and morphology of the superconducting ceramics made from the chem-prep powders, as well as controlling superconducting properties. Under appropriate conditions, high density (>95%) materials that exhibit good superconducting characteristics can be prepared with the chem-prep powders.
Copper Mixed-Valency in a new Aluminum-Barium-Copper Oxide
Authors: VerNooy Paul D. , Dixon Michael A. , Stacy Angelica M.
Published: March 2011

Since their discovery last yearf[1], the high Tc super-conductors have been the subject of intense investigation. Most researchers have studied the material as ceramics--sintered masses of randomly oriented grains of the material. The materials, however, are anisotropie, so measurements made on ceramic pellets only result in averages over the crystallographic directions.
Superconductivity in Y-Ba-Cu-Ag-O and Y-Ba-Cu-Pt-O Systems
Authors: Kovachev V. T. , Gospodinov M. M. , Vlachov E. S. , Lovchinov V. A. , Svestarov P. K. , Nenkov K. A. , Stoianova A. K. , Dimitrov D. A. , Terziiska B. M. , Tinchev S. , Taslakov M. , Mydlarz T. , Czyczek M.
Published: March 2011

A STUDY OF THE Y-Ba-Cu-Ag-O SYSTEM: The specimens studied were produced using the standard ceramic technique. High purity source materials Y2O3, BaCO3CuO, and Ag2O were used. Solid state synthesis was carried out at 900 C for six hours in oxygen ambient. Pressed samples of 16 mm diameter and 2 mm thick were processed in an atmosphere of pure oxygen at 950 C for 12 hours. The transition temperature to the superconducting state was measured by the four point probe resistance technique. The ac magnetic susceptibility was determined by the method outlined in [1].
Effect of Uniaxial Strain on the Superconducting Transition Temperature in thin YBa2Cu3O7 Film
Authors: Park S. I. , Scheuermann M. R. , Chi C. C. , Tsuei C. C.
Published: March 2011

The effect of uniaxial strain e on superconducting transition temperature Tc of thin YBa2Cu3O7 film is presented. The value of TC increases linearly with compressional strain with a slope of -275K/e. Under tensile strain, Tc initially decreases to a value ∼ 0.3K below the zero-strain value and then remains constant with additional strain. In compression, the logarithmic strain derivative of Tc, (1/Tc)(dTc/de), is -3 per unit strain which is slightly less than 4–6 per unit strain observed in conventional superconductors.
Deposition of High Tc Superconductor thin Films by Pulsed Laser Ablation
Authors: Mashburn D. N. , Geohegan D. B. , Eres D. , Lowndes D. H. , Boatner L. A. , Sales B. C. , Pennycook S. J. , Culbertson R. J. , Sonder E. , Christen D. K.
Published: March 2011

Thin superconducting films of YBa2Cu3O7 and HoBa2Cu3O7 have been obtained by ablating material from high-Tc bulk superconductor ceramics onto a nearby substrate using focused excimer laser radiation. Subsequent annealing in oxygen at elevated temperatures was necessary to achieve the superconducting phase. A range of deposition and annealing conditions was investigated to yield films of the desired stoi chiometry and phase.
Superconducting thin Films of (RE)Ba2Cu3(Ag)O7x Prepared by Pulsed Laser Ablation
Authors: Lynds L. , Weinberger B. R. , Peterson G. G. , Krasinski H. A.
Published: March 2011

Thin films of (RE)-Ba-Cu-O perovkites containing silver were prepared by pulsed Nd:YAG (wavelength 1064 nm) laser ablation. Presence of the 1:2:3 phase was verified by scanning Auger microscopy. Onset of the d.c. resistive superconducting transition of 85 K was observed. Films with and without silver were compared and the potential benefits of silver inclusion are discussed.
High Tc Superconducting Y-Ba-Cu-O Thick Fim by Screen Printing
Authors: Yen H. H. , Kung J. H. , Chen Y. C. , Wu P. T.
Published: March 2011

Superconducting film of ternary copper oxides from the Y-Ba-Cu-O system has been prepared by screen printing on 96% A1203 substrate with onset temperature at 95K and zero resistance at 85K. X-ray diffraction patterns show that film will react with the A1203 substrate. With decreasing film thickness the superconductivity is destroyed and may become a semiconductor.
The Morphology of YBa2Cu3O7−x Thin Films Grown on Ceramic Substrates
Authors: Tietz L. A. , De Cooman B. C. , Carter C. B. , Lathrop D. K. , Russek S. E. , Buhrman R. A.
Published: March 2011

The microstructure of thin films of the high Tc superconductor YBa2Cu3O7−x deposited on SrTiO3 and Y-stabilized cubic-zirconia (YSZ) single-crystal substrates has been characterized by transmission electron microscopy. Films on both substrates were polycrystalline. On {001 }-oriented SrTiO3, the grains are oriented with <110> normal to the substrate surface. On the same orientation of YSZ, two microstructures are observed: one in which grains have their c-axes normal to the substrate surface, the other in which grains have the a- (or b-) axis normal to the substrate surface. Both of these microstructures contain special grain boundaries. Annealing of ion-milled TEM specimens is presented as a means of removing ion-beam damage.
Preparation of Y-BA-CU Oxide Superconducting Composite Tapes by a Diffusion Process
Authors: Tachikawa K. , Sugimoto M. , Sadakata N. , Kohno O.
Published: March 2011

Since discovery of the Y-Ba-Cu oxide compound showing superconductivity above liquid nitrogen temperature, intensive study has been under way to clarify nature of the high Tc oxides[l-4]. Much efforts were also made in the field of superconductor applications. A number of studies have been carried out by a powder metallurgical process of Y-Ba-Cu oxide compound wires, although, obtained critical current densities were still low at liquid nitrogen temperature[5–6]. Other techniques for wire fabrication is also being attempted[7–9]. In this study, Y-Ba-Cu oxide superconducting composite tapes were prepared by a diffusion process, which is one of the promising methods to obtain a high critical current density.
Laser Induced Deposition of YBa2Cu3O7−x Thin Films
Authors: Kwok H. S. , Mattocks P. , Shaw D. T. , Shi L. , Wang X. W. , Witanachchi S. , Ying Q. Y. , Zheng J. P. , Bush P.
Published: March 2011

We describe here the deposition of the YBaCuO superconducting thin films by the laser evaporation technique. The characterization of this process, and possible optimization with regards to wavelength and pulse duration of the laser will be discus sed.
Thermal Conductivity of Single-Crystal and Sintered RBa2Cu3O7 at low Temperatures
Authors: Graebner J. E. , Schneemeyer L. F. , Cava R. J. , Waszczak J. V. , Rietman E. A.
Published: March 2011

The thermal conductivity k of micro-twinned single crystals of YBa2Cu3O7 and HoBa2Cu3O7 and a sintered sample of YBa2Cu3O7 has been measured for temperatures 0.03<T<5K. For the single crystals, k is small and varies as T1.8-1.9 This behavior resembles k for glassy insulators except for the lack of a plateau above IK. It is concluded that the thermal carriers are phonons with their mean free path limited by resonant scattering from tunneling entities, as in glasses. Suggestions for the location of tunneling systems are given. For the sinter, k is still smaller but does not follow a power law T-dependence. It is similar to other sintered ceramics with the same particle size, where the phonon mean free path is dominated by Rayleigh scattering from the particles. This strong scattering from the microstructure presumably masks the scattering from TS within each particle.
Electrical Conductivity and Thermogravimetric Studies of the High-7c Superconductor YBa2Cu3Ox
Authors: Han Y. H. , Monroe D. W.
Published: March 2011

Nonstoichiometry in YBa2Cu3Ox has been studied by means of equilibrium electrical conductivity and thermogravimetric method. We have observed a strong correlation between electrical resistivity and oxygen stoichiometry (x) at high temperature. Electrical resistivities increase linearly from the superconducting onset tcmperature(100 K) to 450 C where oxygen starts to evolve from this material, and then begin to deviate from linear temperature dependence. The experimental results indicate that electrical resistivity in this material is associated with the defect species (charge carrier) population due to oxygen stoichiometry. Electrical conductivities were also measured as a function of oxygen partial pressure (1 to 10−4 atm) at various temperatures. At P(OI) > 101 atm the conductivity shows a l/4th slope dependence on oxygen partial pressure while at P(0;) < 10 f atm the conductivity is proportional to P(O2)1/2- The conductivity behavior with oxygen stoichiometry suggests that the electron holes associated with Cu+ play an important role as charge carriers in this material, and even at x < 6.5 p-typc conduction is predominant.
Optical Reflectance Studies on YBa2Cu3O7−x and Related Compounds
Authors: KamaráS K. , Doss M. G. , Herr S. L. , Kim J. S. , Porter C. D. , Stewart G. R. , Tanner D. B. , Bonn D. A. , Greedan J. E. , O'reilly A. H. , Stager C. V. , Timusk T. , Keszei B. , Pekker S. , Hutiray Gy. , Míhaly L.
Published: March 2011

Optical reflectance spectra in the range 30–35000 cm-1 and 4–300 K are presented on several YBa2CuxOy phases, as well as different forms of the superconducting YBa2CuxO7−x (polycrystalline pellets, textured pellets with ab-plane oriented surface, and single crystals).
Mechanism of Je Enhancement of YBa2Cu3O7-α Due to Ag-Doping
Authors: Kung J. H. , Yen H. H. , Chen Y. C. , Wang C. M. , Wu P. T.
Published: March 2011

Ag-doping was found to enhance the critical current density of the ceramic superconductors by as much as a factor of 15. This Jc enhancement is due to both the increased amount of the superconducting phase and the resulting preferred crystal orientation. The optimum level of dopant may vary according to the chemical forms of Ag dopants.
Effect of Water and Iron on Slowly and Rapidly Cooled Y-1 Ba2Cu3O6+x Superconductors: An EPR/NMR Study
Authors: Brahme U. S. , Kordas G. , Kirkpatrick R. J.
Published: March 2011

We present here a study of the effect of Fe doping and hydration on the NMR, EPR spectra and Tc of slowly and rapidly cooled Y-1 Ba2Cu3O6+x Superconductor. The g-values of the EPR signals are related to Cu2+ ions in six-fold coordination. Tc is suppressed 10–20°C due to changes in processing conditions and the addition of Fe. The 89Y MAS-NMR spectra show that Y is more shielded (more ionically bonded) in the slowly cooled sample than in the rapidly cooled sample and the hydrated slowly cooled sample is less shielded. The effect of hydration on 89Y chemical shift is consistent with the presence of protons near the Y.
Grain Boundary Segregation and Thermal History Effects on Properties of La1.85Sr0.15CuO4-y Superconductors
Authors: Chiang Yet-Ming , Roshko Alexana , Fabes Brian D. , Leung Dominic K. , Ikeda Jeri Ann S. , Rudman David A. , Parker Michael J. , Martin John R.
Published: March 2011

The grain boundary segregation of Sr in the La1.85Sr0.15CuO4-y system, and its effects on polycrystalline diamagnetic properties, have been characterized. Equilibration at 1000°C reduces grain boundary segregation compared to that which is present at 700°C. Results indicate that critical currents in randomly oriented polycrystalline materials will be improved if annealing treatments can be optimized to minimize grain boundary segregation without degrading lattice oxygen stoichiometry.
Absorption Component of the Magnetic Susceptibility in Superconducting YBa2Cu3O7
Authors: Durny R. , Ducharme S. , Hautala J. , Symko O. G. , Taylor P. C. , Kulkarni Sudhir
Published: March 2011

Microwave absorption measurements from 20 to 80 K in magnetic fields up to 12 kG are reported. Below a certain characteristic temperature T* = 80 ± 2 K < Tc the absorption in magnetic-field-cooled samples is smaller and broader in comparison to the zero-field-cooled samples. The incident microwave radiation induces a dc voltage across the sample which is also magnetic field dependent and peaks at zero magnetic field.
Light-Induced Current Suppression of Superconducting YBa2Cu3O7-δ Weak Link
Authors: Kawabe U. , Nishino T. , Tarutani Y. , Hasegawa H.
Published: March 2011

The high-T oxide-superconductor YBa2Cu3O7-δ is expected to be a low carrier-density material having optical ana nonequilibrium properties. Light can penetrate the superconductor and can effectively excite the quasi-particles in it. To clarify the nonequilibrium phenomenon, we have studied this oxide superconductor exposed to light.
Preliminary Results on YBCO/Nb Bulk Junction
Authors: Barone A. , Di Chiara A. , Peluso G. , Pepe G. , Russo M. , Scotti Di Uccio U.
Published: March 2011

Current-voltage characteristics and dV/dI curves of a YBCO/Nb bulk junction at 4.2 K are reported. The presence of the Josephosn effect is clearly shown. The dV/dI spectrum shows sharp structures which can be related to the Niobium and the YBCO energy gaps Δnb and ΔNb and ΔYBCO. A value ΔYBCO = 26.2 ± 1.0 meV can be estimated, confirming the strong coupling character of such a compound.
Irradiation Effects Induced by 2.5 MeV-Electrons and 2.9 GeV-Krypton Ions in the High Tc Superconducting Oxides
Authors: Studer F. , Prouost J. , Groult D. , Raveau B. , Bouffard S. , Toulemonde M. , Jousset J. C.
Published: March 2011

The resistivity measurements of bulk super-conducting oxides La2−xSrxCuO4−x/2+ 〈0.15〈x〈0.2) irradiated by 2.5 Mev-electrons and YBa2Cu3O7-δ 〈0〈δ〈0.15) irradiated by 2.9 GeU-krypton ions have shown a regular and constant decrease of the critical temperature Tc as a function of the fluence.

On the contrary, an increase of Tc has been observed durino irradiation of super-conduct ino La2CuO4 compound by 2.9 GeV-krypton ions, which saturates at Tc/Tco = 0.1 for fluences hioher than 3.1012 Kr.cm−. The evolution of the R(T) curves during irradiation is very similar to the one observed under Dressure.

A comparison of the variations of Tc as a function of the number of di solacements oer atom for various particles (n. e−. He+. O. Kr) suggests that the hijjh electronic stoppino power of the heavy ions could be the main factor of damage.
A Study of the Tetragonal-To-Orthorhombic Transition of YBa2Cu3Ox by Dilatometry
Authors: Han S. C. , Wu Z. L.
Published: March 2011

An YBa2Cu3Ox bar specimen was air annealed at 930°C followed by water quenching under protection of a quartz sheath, then annealed at a series of temperatures between 300° -500°C. Isothermal dilatation curves were measured at each annealing temperature. An Avrami type plot of these data gave rise to an activation energy H=1.2eV for the tetragonal-to-orthorhombic reaction. It is suggested that this is the activation enthalpy of oxygen diffusion in the tetragonal phase which remains continuous and therefore rate controlling throughout the whole course of transition. Based upon this transition process, we expect a fully annealed specimen to be composed of numerous superconducting domains separated by a continuous film of semiconducting tetragonal phase, one or two molecular layers thick. At the points of contact, this film is highly strained by the impinging domains, rendering the material superconductive by S/N/S junctions.
LA1BA2CU3O9-γ: Structural Analysis as Determined by Neutron Diffraction
Authors: Golben J. P. , Song YI , Chittipeddi S. , Lee S. I. , Mcmichael R. D. , Chen X. D. , Gaines J. R. , Cox D. L. , Epstein A. J.
Published: March 2011

The La-Ba-Cu-O system contains several phases of special interest in the field of high Tc superconductivity. Specifically intriguing is the La3−xBa3+xCu6O4+y (“3–3–6”) phase [1,2], the La1·8 5Ba·1 5CuO4 (‘K2NiF4’) phase with a zero resistance temperature (Tc) of about 20 K [3,4], and the La1Ba2CU3O9–6 (“1–2–3”) phase with Tc's reported up to 75 K [5–7]. It has been suggested that the “3–3–6” phase may also be superconducting, especially in a Ba-doped version such that the stoichiometry is 2–4–6 [8–10]. In addition to defining a new high temperature superconducting phase, this latter suggestion would also rule out the possibility of Cu-0 “chains” being important to 90 K superconductivity since these chains are absent in the proposed configuration [1,2] of this phase.
X-Ray Study of Superconducting Y1Ba2Cu3−xFexOy Compounds
Authors: Gonzalez G. , Rios-Jara D. , Akachi T. , Barrio R. , BañOs L. , Escudero R.
Published: March 2011

Superconducting compounds of Y1B2C3−xFexOy, with x=0.125, 0.0625, 0.125 and 0.300, were studied using X-ray powder diffractometry. Two sets of samples were prepared. Samples quenched from 950°C to liquid nitrogen temperature showed a tetragonal non-superconducting phase, whose lattice parameters depend on the Fe content and differ from those of the yttrium 1:2:3 tetragonal phase. Samples oxygenated at 450°C showed an orthorhombic to tetragonal phase transition for Fe contents higher than x=0.0625. The lattice parameters of this tetragonal phase were different from those of both tetragonal phases mentioned above. All these observations allow us to conclude that C(l) sites are occupied at least partially by Fe impurities.
Neutron Diffraction Studies of High TC Superconductors
Authors: Hinks D. G. , Dabrowski B. , Zhang K. , Segre C. U. , Jorgensen J. D. , Soderholm L. , Beno M. A.
Published: March 2011

We have investigated the structure and composition of La2CuO4 (both pure and Sr-doped) and Nd(Ba2−xNdx)Cu3O7 using powder neutron diffraction. In La2−xSrxCuO4, Tc reacnes its maximum at x=0.15, after which vacancies are introduced in the 2D planes and superconductivity is destroyed. Superconductivity in La2CuO4 is not bulk. No evidence for nonstoichlometry in this material can be observed. In the Nd(Ba2−xNdx)Cu3O7 system, Tc is a complex function of oxygen ordering and electronic effects.
Thermal Cycling Degradation of YBa2Cu3O9−x Superconductors
Authors: Kinser Donald L. , Magruder Robert H. , Quarles Ronald A. , Dora Schaefer J.
Published: March 2011

Thermal cycling for four cycles between 294 and 78°K has been observed to shift the superconducting transition temperature from 85 to 28°K. Samples cycled for 12 cycles between 373 and 78°K do not display superconductivity at temperatures down to 37°K. Guinier de Wolff X-ray diffraction observations of these samples reveal no crystallography changes during thermal cycling up to 12 cycles. Scanning electron microscopy studies of polished samples of the thermally cycled material revealed the presence of cracks in individual grains within each sample. The percentage of grains displaying cracks climbs rapidly with thermal cycling. We conclude that the loss of superconducting behavior is a consequence of removal of continuous paths but we are not, at this time, able to rationalize the shift of Tc with thermal cycling. We conclude that the thermal expansion anisotropy produces strains which lead to destructive fractures within the material.
The Microscopic Study of Y-Ba-Cu-O Compound
Authors: Lin W. T. , Chu H. C. , Chen B. H. , Chang Y. H. , Chin T. S. , Wu P. T.
Published: March 2011

The microstructure of Y-Ba-Cu-O compound, sintered at 950°C for 16h, was examined by using transmission electron microscope(TEM). For the furnace cooling sample, two variants of–orthorhombic YBa2-Cu3O7−x (O-Y123) twins, grown on (110) and (110) planes, respectively, are crystallographically related to the matrix and produce a Widmanstatten morphology. The orientation relationship between the lath twin and the matrix is (001)T//(001) and [100]T//[010]M. The O-Y123 compound is unstable under tne electron irradition. Twin boundaries are identified as S-boundaries. The minor phases as Y2BaCuO5 (Y211) and BaCuO2 were also observed. For the air cooling sample, no superconductivity above 77K was found. The major phase is tetragonal Y123 (T-Y123), while small amount of 0-Y123 is also existent.
Atom Probe Microanalysis of Superconducting YBa2Cu3O7−x
Authors: Brenner S. S. , Kellogg G. L.
Published: March 2011

Superconducting YBa2Cu3O7−x needles prepared from hot-pressed discs of oxide powders were analyzed in a long drift-tube type atom probe. An analyses was made from a randomly located area about 2 nm in diameter. Most of the oxygen field-evaporated as O2+ ions. The measured composition agreed well with that of YBa2Cu3O6.5 except for yttrium which was found to be too high. The oxygen concentration profile showed fluctuations about 2.5 nm apart which must still be clarified.
Theoretical Studies of Copper Oxide Clusters: Prediction of an Electronically Driven Phase Separation in YBa2Cu3Ox
Authors: Curtiss L. A. , Brun T. O. , Gruen D. M.
Published: March 2011

On the basis of semi-empirical extended Hiickel molecular orbital calculations of copper-oxide clusters representing the new superconducting material YBa2Cu3Ox, a phase diagram is proposed which suggests that the 94 K high temperature superconducting phase of YBa2Cu3Ox is characterized by an oxygen stoichiometry near 7.0. The phase diagram predicts that a plateau should exist for Tc in the region x = 0.0 – 0.25 and that in this region two phases are present which are characterized by compositions having oxygen stoichiometries 6.5–6.75 and ca. 7.0.
Properties and Structures of Copper Rich Y-Ba-Cu-O Superconductors
Authors: Drehman A. J. , Horrigan J. A. , Dumais M. W.
Published: March 2011

Copper rich Y-Ba-Cu-O samples were prepared by reacting and sintering powders. The resultant material is composed of YBa2Cu3Oy and CuO. Proper processing results in a 85% dense, well interconnected material with a superconducting transition temperature of 92K. Zero resistance is observed even though a quarter of the volume is the CuO phase. This is because the CuO phase is in the form of isolated grains and not at the grain boundaries of the superconducting matrix.
Twins in YBa2Cu3O7-δ
Authors: Gibbons P. C , Kelton K. F. , Li Z.-Y. , Mantese L. , Sobotka L.
Published: March 2011

High-resolution TEM images of well-characterized YBa2Cu3O7-δ prove that atomic disorder in the {110} twin boundaries is confined to within 20 A of the boundaries, and suggest that there is disorder within those regions.
Kinetics and Thermodynamics of the Reaction of Molecular Oxygen with YBa3Cu3Ox
Authors: Farneth W. E. , Bordia R. K. , Crawford M. K. , Abrams L. , Subramanian M. A. , McCarronIII E. M.
Published: March 2011

The sensitivity of the properties of RBa2Cu3Ox materials to oxygen stoichiometry has been widely reported.1 This is a serious problem in the synthesis and processing of these compounds since many operations must be carried out at temperatures and oxygen partial pressures where bulk oxygen is in dynamic equilibrium with gas phase molecular oxygen. Therefore it is crucial for the rational design of processing strategies to understand how the equilibria and kinetics of oxygen stoichiometry in this material vary with temperature and pressure. In this paper we report work on two problems in this area: first, we describe the development of accurate methods for the determination of oxygen stoichiometry in experimental samples, and second, the use of these methods to investigate and analyze equilibrium oxygen contents over a range of temperatures and oxygen partial pressures. Equilibrium oxygen contents from 350 – 900°C at oxygen pressures of. 05, .21, and 1.00 atmospheres have been determined. The pressure dependence has also been examined over a wider range at selected temperatures. Most of this data can be adequately fit to a model which assumes that a single chemical equilibrium constant can describe the entire stoichiometry range from x=6 to 7. However, kinetic data suggests that the detailed mechanism must be more complex, and that the overall thermochemistry may reflect contributions from a number of interacting processes rather than any single elementary step. In concurrent work we have used these methods to develop sample series that can be used to examine magnetic properties2 and far IR spectra3 of these materials as a systematic function of oxygen content.
The Granular Behavior of LaSrCuO: Oxygen Concentration Effects on the Electrical Resistivity
Authors: Osquiguil E. , Civale L. , Decca R. , Safar H. , Martinez E. , Nieva G. , De La Cruz F.
Published: March 2011

Electrical resistivity measurements of the superconductor La1.80sr0.20CuO4-δ over a Wide range of temperatures and oxygen concentration, together with the analysis of superconducting properties of the material, indicate that the ceramic superconductors are high < materials in the clean limit. The granular superconducting behavior is determined by the oxygen content.
Prisioneiros do discurso: o caso da indústria brasileira de transporte aéreo
Authors: Wood Jr. Thomaz , Binder Marcelo Pereira
Published: March 2011

Este artigo examina as mudanças ocorridas na indústria brasileira de transporte aéreo no período de 1970 a 2005. O objeto de estudo foram três empresas - Varig, Tam e Gol -, líderes de mercado no decorrer do período estudado. Como referencial teórico, foi empregada uma combinação "não ortodoxa" com conceitos de discurso e narrativa, nostalgia e memória organizacional, comprometimento estratégico e visão baseada em recursos (RBV). Mostramos como são formados certos discursos associados a determinadas lógicas dominantes, as quais por sua vez condicionam a definição de modelos de negócios e a utilização de competências e recursos estratégicos. Mostramos também que tais discursos alinham-se à memória organizacional, fomentam a nostalgia e estimulam a inércia organizacional, dificultando processos adaptativos de mudança e alteração do conjunto de recursos necessários a novas dinâmicas do mercado.