Chemical nature of the barrier in Pb/YBa2Cu3O(7-x) tunneling structures

NASA Technical Reports Server (NTRS)

Vasquez, R. P.; Foote, M. C.; Hunt, B. D.; Bajuk, L.

1991-01-01

Several reports of reproducible tunneling measurements on YBa2Cu3O(7-x) thin films or single crystals with a Pb counterelectrode have recently appeared. The nature of the tunnel barrier, formed by air exposure, in these structures has been unknown. In the present work, the chemical nature of the tunnel barrier is studied with X-ray photoelectron spectroscopy (XPS). Laser-ablated films grown on LaAlO3 which have been chemically etched and heated in air are found to form nonsuperconducting surface Ba species, evident in an increase of the high binding energy Ba 3d and O 1s signals. A deposited Pb film about 10 A thick is found to be oxidized, and Cu(+2) is partially reduced to Cu(+1). The tunneling barrier thus appears to consist of species resulting from a combination of the air exposure and a reaction between the superconductor and the deposited Pb counterelectrode.

A two-dimensional ACAR study of untwinned YBa2Cu3O(7-x)

NASA Astrophysics Data System (ADS)

Smedskjaer, L. C.; Bansil, A.

1991-12-01

We have carried out 2D-ACAR measurements on an untwinned single crystal of YBa2Cu3O(sub 7-x) as a function of temperature, for five temperatures ranging from 30K to 300K. We show that these temperature-dependent 2D-ACAR spectra can be described to a good approximation as a superposition of two temperature independent spectra with temperature-dependent weighting factors. We show further how the data can be used to correct for the 'background' in the experimental spectrum. Such a 'background corrected' spectrum is in remarkable accord with the corresponding band theory predictions, and displays, in particular, clear signatures of the electron ridge Fermi surface.

Temperature and depth dependence of positron annihilation parameters in YBa2Cu3O7-x and La1.85Sr0.15CuO4

NASA Astrophysics Data System (ADS)

Lynn, K. G.; Usmar, S. G.; Nielsen, B.; van der Kolk, G. J.; Kanazawa, I.; Sferlazzo, P.; Moodenbaugh, A. R.

1988-02-01

The temperature dependence of the positron annihilation parameters for YBa2Cu3O7-x x=0.7, 0.4 and 0.0 and La1.85Sr0.15CuO4 were measured. The depth dependence of the YBa2Cu3O7 was studied using a variable-energy positron beam showing a strong depth dependence in the Doppler line-shape extending up to an average depth of ˜5.0 μm. It was found that a transition in the Doppler line-shape parameter, ``S'', was associated with the superconducting transition temperature (Tc) in YBa2Cu3O7-x x=0.4 and 0.0 while no transition was observed in the nonsuperconducting YBa2Cu3O6.3. Positron lifetime parameters in YBa2Cu3O7 were found to be consistent with positrons localized at open volume regions (probably unoccupied crystallographic sites) in this material with a lifetime of 210 psec at 300 K. These results indicate that the electron density at these unoccupied sites increases, using a free electron model, approximately 9% between 100 and 12 K.

Chemical durability of high-temperature superconductor YBa2Cu3O(7-x) in aqueous environments

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Sandkuhl, Ann L.

1988-01-01

The stability of YBa2Cu3O(7-x) in water and 100-percent humidity has been investigated at three temperatures, using pH measurements, X-ray diffraction, and scanning electron microscopy. The oxide-ceramic superconductor is highly unstable; it reacts rapidly with water and degrades in moisture. Dissolution of the oxide perovskite in water is highly incongruent. The corrosion products are found to be BaCO3, CuO, O2, etc. Barium hydroxide is first formed and further reacts with atmospheric CO2 to form needle-shaped crystals of BaCO3. For any practical applications, devices made from these materials would have to be protected with an impermeable coating to prevent deterioration from atmosphere.

Epitaxial growth and properties of YBa2Cu3O(x)-Pb(Zr(0.6)Ti(0.4))O3-YBa2Cu3O(x) trilayer structure by laser ablation

NASA Astrophysics Data System (ADS)

Boikov, Iu. A.; Esaian, S. K.; Ivanov, Z. G.; Brorsson, G.; Claeson, T.; Lee, J.; Safari, A.

1992-08-01

YBa2Cu3O(x)Pb(Zr(0.6)Ti(0.4))O3-YBa2Cu3O(x) multilayer structure has been grown on SrTiO3 and Al2O3 substrates using laser ablation. The deposition conditions for the growth of trilayers and their properties are studied in this investigation. Scanning electron microscope images and X-ray diffraction analyses indicate that all the constituent films in the trilayer grow epitaxially on SrTiO3 and were highly oriented on Al2O3. Transport measurements on these multilayers show that top YBa2Cu3O(x) films have good superconducting properties.

Heteroepitaxial growth of Ba1 - xSrxTiO3/YBa2Cu3O7 - x by plasma-enhanced metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Chern, C. S.; Liang, S.; Shi, Z. Q.; Yoon, S.; Safari, A.; Lu, P.; Kear, B. H.; Goodreau, B. H.; Marks, T. J.; Hou, S. Y.

1994-06-01

Epitaxial Ba1-xSrxTiO3(BST)/YBa2Cu3O7-x heterostructures with superior electrical and dielectric properties have been fabricated by plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD). Data of x-ray diffraction and high resolution transmission electron microscopy showed that <100> oriented Ba1-xSrxTiO3 layers were epitaxially deposited on epitaxial (001) YBa2Cu3O7-x layers. The leakage current density through the Ba1-xSrxTiO3 films was about 10-7 A/cm2 at 2 V (about 2×105 V/cm) operation. Moreover, the results of capacitance-temperature measurements showed that the PE-MOCVD Ba1-xSrxTiO3 films had Curie temperatures of about 30 °C and a peak dielectric constant of 600 at zero bias voltage. The Rutherford backscattering spectrometry and x-ray diffraction results showed that the BST film composition was controlled between Ba0.75Sr0.25TiO3 and Ba0.8Sr0.2TiO3. The structural and electrical properties of the Ba1-xSrxTiO3/YBa2Cu3O7-x heterostructure indicated that conductive oxide materials with close lattice to Ba1-xSrxTiO3 can be good candidates for the bottom electrode.

Ellipsometric study of YBa2Cu3O(7-x) laser ablated and co-evaporated films

NASA Technical Reports Server (NTRS)

Alterovitz, S. A.; Sieg, R. E.; Warner, J. D.; Stan, M. A.; Vitta, S.

1990-01-01

High temperature superconducting films of YBa2Cu3O(7-x) (YBCO were grown on SrTiO3, LaA1O3, and YSZ substrates using two techniques: excimer laser ablation with in situ annealing and co-evaporation of Y, Cu, and BaF2 with ex-situ annealing. Film thicknesses were typically 5000 A, with predominant c-axis alignment perpendicular to the substrate. Critical temperatures up to Tc(R=O)=90 K were achieved by both techniques. Ellipsometric measurements were taken in the range 1.6 to 4.3 eV using a variable angle spectroscopic ellipsometer. The complex dielectric function of the laser ablated films was reproducible from run to run, and was found to be within 10 percent of that previously reported for (001) oriented single crystals. A dielectric overlayer was observed in these films, with an index of refraction of approximately 1.55 and nearly zero absorption. For the laser ablated films the optical properties were essentially independent of substrate material. The magnitude of the dielectric function obtained for the co-evaported films was much lower than the value reported for single crystals, and was sample dependent.

Composition dependence of superconductivity in YBa2(Cu(3-x)Al(x))O(y)

NASA Technical Reports Server (NTRS)

Bansal, N. P.

1993-01-01

Eleven different compositions in the system YBa2(Cu(3-x)Al(x))O(y) (x = 0 to 0.3) have been synthesized and characterized by electrical resistivity measurements, powder X-ray diffraction, and scanning electron microscopy. The superconducting transition temperature T sub c (onset) was almost unaffected by the presence of alumina due to its limited solubility in YBa2Cu3O(7-x). However, T sub c(R = 0) gradually decreased, and the resistive tails became longer with increasing Al2O3 concentration. This was probably due to formation of BaAl2O4 and other impurity phases from chemical decomposition of the superconducting phase by reaction with Al2O3.

YBa2Cu3O x superconducting nanorods

NASA Astrophysics Data System (ADS)

Rieken, William; Bhargava, Atit; Horie, Rie; Akimitsu, Jun; Daimon, Hiroshi

2018-02-01

Herein, we report the synthesis of YBa2Cu3O x superconducting nanorods performed by solution chemistry. Initially, a mixture of fine-grained coprecipitated powder was obtained and subsequently converted to YBa2Cu3O x nanorods by heating to 1223 K in oxygen for 12 h. The nanorods are superconducting without the need for any further sintering or oxygenation, thereby providing an avenue for direct application to substrates at room temperature or direct use as formed nanorods. A critical superconducting transition temperature T c of about 92 K was achieved at a critical magnetic field of 10 Oe.

Electronic state and superconductivity of YBa2Cu3-xO7-y (M=Al,Zn and Sn) systems

NASA Technical Reports Server (NTRS)

Zhao, Y.; Zhang, Q. R.; Zhang, H.

1990-01-01

A series of YBa2Cu(3-x)MxO(7-y) (M=Al,Zn and Sn) single phase samples were prepared, and the measurements of the crystal structure, oxygen content, electric resistivity, thermoelectric power, Mossbauer spectrum, XPS and superconductivity were performed. The experimental results of X ray powder diffraction, Mossbauer spectrum and oxygen content show that the Zn(2+) and the Al(3+) occupy the Cu(2) site in Cu-O planes and the Cu(1) site in Cu-O chains respectively, but the Sn(4+) occupies both the Cu(1) sites. As regards the properties in superconducting state, both the Zn(2+) and the Al(3+) depress T(sub c) strongly, but the Sn(4+) does not. As for the electronic transport properties in normal state, the system doped by Al(3+) displays a rapid increase of resistivity and some electron localization-like effects, and the thermoelectric power enhances obviously; the series contained Zn(2+) almost shows no changes of electric resistivity but the sign of the thermoelectric power is reversed. Other results are given and briefly discussed.

Disappearance of the force-free current configuration at the first order vortex lattice phase transition in YBa 2Cu 3O 7-δ single crystals

NASA Astrophysics Data System (ADS)

van der Beek, C. J.; Indenbom, M. V.; Berseth, V.; Benoit, W.; Erb, A.; Flükiger, R.

1997-08-01

The anisotropy in the transverse AC susceptibility of YBa2Cu3O7-δ single crystals, induced by the periodic appearance of a force-free current configuration upon rotation of a superimposed DC field in the crystal plane, disappears at the vortex phase transition, indicating the loss of the vortex lines' stability against mutual cutting.

Subtle porosity variation in the YBa2Cu3O(7-x) high-temperature superconductor revealed by ultrasonic imaging

NASA Technical Reports Server (NTRS)

Roth, D. J.; Generazio, E. R.; Stang, D. B.; Hepp, A. F.

1990-01-01

The characterization of global porosity variation within a nominally 93-percent-dense specimen of YBa2Cu3O(7-x) high-temperature superconductor is reported. With a computer-controlled scanning system, precision ultrasonic velocity measurements were obtained at 100 micron increments over an 8- by 8-mm area of the YBa2Cu3O(7-x) specimen. The measurements were used to form a color map of velocity variation across the scanned region of the specimen. Subtle velocity variation on the order of 1 percent was observed. The specimen was shown by experimental methods to be single-phase, untextured, and free of nonuniform residual microstresses. From this knowledge and an established velocity-density relationship, a likely conclusion is that the observed velocity variations are solely due to porosity variations of similar magnitude. Locating these subtle porosity variations is critical since they can result in an order of magnitude variation in J(sub c) for dense YBCO specimens. Thus, mapping the global porosity distribution within YBa2Cu3O(7-x) may reveal regions that have poorer superconducting properties. Ultrasonic velocity results are translated into useful microstructural information for the material scientist.

Thermodynamic evidence for the Bose glass transition in twinned YBa 2 Cu 3 O 7 - δ crystals

DOE PAGES

Pérez-Morelo, D. J.; Osquiguil, E.; Kolton, A. B.; ...

2015-07-21

We used a micromechanical torsional o scillator to measure the magnetic response of a twinned YBaBa2Cu3O7-δ single crystal disk near the Bose glass transition. We observe an anomaly in the temperature dependence of the magnetization consistent with the appearance of a magnetic shielding perpendicular to the correlated pinning of the twin boundaries. This effect is related to the thermodynamic transition from the vortex liquid phase to a Bose glass state.

Near-edge study of gold-substituted YBa2Cu3O(7-delta)

NASA Technical Reports Server (NTRS)

Ruckman, Mark W.; Hepp, Aloysius F.

1991-01-01

The valence of Cu and Au in YBa2Au0.3Cu2.7O7-delta was investigated using X-ray absorption near edge structure (XANES). X-ray and neutron diffraction studies indicate that Au goes on the Cu(1) site and Cu K-edge XANES shows that this has little effect on the oxidation state of the remaining copper. The Au L3 edge develops a white line feature whose position lies between that of trivalent gold oxide and monovalent potassium gold cyanide, and whose height relative to the edge step is smaller than in the two reference compounds. The appearance of the Au L3 edge suggests that fewer Au 3d states are involved in forming the Au-O bond in YBa2Au0.3Cu2.7O7-delta than in trivalent gold oxide.

Near-edge study of gold-substituted YBa2Cu3O(7-delta)

NASA Technical Reports Server (NTRS)

Ruckman, Mark W.; Hepp, Aloysius F.

1991-01-01

The valence of Cu and Au in YBa2Au0.3Cu2.7O7-delta was investigated using x-ray absorption near edge structure (XANES). X-ray and neutron diffraction studies indicate that Au goes on the Cu(1) site and Cu K-edge XANES shows that this has little effect on the oxidation state of the remaining copper. The Au L3 edge develops a white line feature whose position lies between that of trivalent gold oxide and monovalent potassium gold cyanide, and whose height relative to the edge step is smaller than in the two reference compounds. The appearance of the Au L3 edge suggests that fewer Au 3d states are involved in forming the Au-O bond in YBa2Au0.3Cu2.7O7-delta than in trivalent gold oxide.

Forming YBa2Cu3O7-x Superconductors On Copper Substrates

NASA Technical Reports Server (NTRS)

Mackenzie, J. Devin; Young, Stanley G.

1991-01-01

Experimental process forms layer of high-critical-temperature ceramic superconductor YBa2Cu3O7-x on surface of copper substrate. Offers possible solution to problem of finishing ceramic superconductors to required final sizes and shapes (difficult problem because these materials brittle and cannot be machined or bent). Further research necessary to evaluate superconducting qualities of surface layers and optimize process.

Room-temperature annealing effects on the basal-plane resistivity of optimally doped YBa2Cu3O7-δ single crystals

NASA Astrophysics Data System (ADS)

Khadzhai, G. Ya.; Vovk, R. V.; Vovk, N. R.; Kamchatnaya, S. N.; Dobrovolskiy, O. V.

2018-02-01

We reveal that the temperature dependence of the basal-plane normal-state electrical resistance of optimally doped YBa2Cu3O7-δ single crystals can be with great accuracy approximated within the framework of the model of s-d electron-phonon scattering. This requires taking into account the fluctuation conductivity whose contribution exponentially increases with decreasing temperature and decreases with an increase of oxygen deficiency. Room-temperature annealing improves the sample and, thus, increases the superconducting transition temperature. The temperature of the 2D-3D crossover decreases during annealing.

Wet chemical techniques for passivation of YBa2Cu3O7(7-x)

NASA Technical Reports Server (NTRS)

Vasquez, R. P.; Foote, M. C.; Hunt, B. D.

1989-01-01

Wet chemical techniques are described for treatment of YBa2Cu3O(7-x) surfaces, resulting in the formation of native compounds with little or no reactivity to water. Promising native compounds include CuI, BaSO4, CuS, Cu2S, and the oxalates, all of which are either insoluble or have very low solubility in water. Treatment with dilute HI results in the formation of a native iodide film which is 80-90 percent CuI with small amounts of YI3 and BaI2. Treatment with dilute H2SO4 results in the formation of a film which is 95 percent BaSO4 and 5 percent Y2(SO4)3. Cu2S is formed on the surface with a dilute Na2S solution. An oxalate film with equal amounts of Y2(C2O4)3 and BaC2O4 results from treatment with dilute oxalic acid. X-ray photoelectron spectra show no significant changes when the sulfide, sulfate, or oxalate films are dipped in water, while the iodide film shows evidence of Cu(OH)2 formation.

Preparation of YBa2Cu3O7 High Tc Superconducting Coatings by Plasma Spraying

NASA Astrophysics Data System (ADS)

Danroc, J.; Lacombe, J.

The following sections are included: * INTRODUCTION * THE COMPOUND YBa2Cu3O7-δ * Structure * Critical temperature * Critical current density * Phase equilibria in the YBaCuO system * PREPARATION OF YBa2Cu3O7 COATINGS * General organisation of the preparation process * The powder * Hot plasma spraying of YBa2Cu3O7 * The post-spraying thermal treatment * CHARACTERISTICS OF THE YBa2Cu3O7-δ COATINGS * Chemical composition * Crystalline structure * Morphology of the coatings * Electrical and magnetic characteristics * Conclusion * REFERENCES

A new method for measuring low resistivity contacts between silver and YBa2Cu3O(7-x) superconductor

NASA Technical Reports Server (NTRS)

Hsi, Chi-Shiung; Haertling, Gene H.; Sherrill, Max D.

1991-01-01

Several methods of measuring contact resistivity between silver electrodes and YBa2Cu3O(7-x) superconductors were investigated; including the two-point, the three point, and the lap-joint methods. The lap-joint method was found to yield the most consistent and reliable results and is proposed as a new technique for this measurement. Painting, embedding, and melting methods were used to apply the electrodes to the superconductor. Silver electrodes produced good ohmic contacts to YBa2Cu3O(7-x) superconductors with contact resistivities as low as 1.9 x 10 to the -9th ohm sq cm.

Comparative study of flux pinning, creep and critical currents between YBaCuO crystals with and without Y2BaCuO5 inclusions

NASA Technical Reports Server (NTRS)

Murakami, Masato; Gotoh, Satoshi; Fujimoto, Hiroyuki; Koshizuka, Naoki; Tanaka, Shoji

1991-01-01

In the Y-Ba-Cu-O system, YBa2Cu3O(x) phase is produced by the following peritectic reaction: Y2BaCuO5 + liquid yields 2YBa2Cu3O(x). Through the control of processing conditions and starting compositions, it becomes possible to fabricate large crystals containing fine Y2BaCuO5(211) inclusions. Such crystals exhibit Jc values exceeding 10000 A/sq cm at 77 K and 1T. Recently, researchers developed a novel process which can control the volume fraction of 211 inclusions. Elimination of 211 inclusions is also possible. In this study, researchers prepared YBaCuO crystals with and without 211 inclusions using the novel process, and compared flux pinning, flux creep and critical currents. Magnetic field dependence of Jc for YBaCuO crystals with and with 211 inclusions is shown. It is clear that fine 211 inclusions can contribute to flux pinning. It was also found that flux creep rate could be reduced by increasing flux pinning force. Critical current density estimates based on the conventional flux pinning theory were in good agreement with experimental results.

Laser ablated YBa2Cu3O(7-x) high temperature superconductor coplanar waveguide resonator

NASA Technical Reports Server (NTRS)

Valco, G. J.; Blemker, A. R.; Bhasin, K. B.

1992-01-01

Several 8.8-GHz coplanar waveguide resonators are fabricated and tested that are made from laser ablated YBa2Cu3O(7-x) thin films on LaAlO3 substrates. A quality factor of 1250 at 77 K was measured. A correlation between the microwave performance of the resonators and the critical temperature and morphology of the films was observed.

Desorption of oxygen from YBa2Cu3O6+x films studied by Raman spectroscopy

NASA Astrophysics Data System (ADS)

Bock, A.; Kürsten, R.; Brühl, M.; Dieckmann, N.; Merkt, U.

1996-08-01

Phonons of laser-deposited YBa2Cu3O6+x films on MgO(100) substrates are investigated in a Raman setup as a function of laser power density. Investigations of YBa2Cu3O7 films allow us to study oxygen out-diffusion, where the onset of out-diffusion is indicated by the appearance of disorder-induced modes in the Raman spectra. At a pressure of 5×10-6 mbar the temperature threshold of the out-diffusion is (490+/-15) K. With increasing oxygen pressure the observed temperature thresholds rise only moderately in contrast to the behavior expected from the pox-T phase diagram of YBa2Cu3O6+x. Even at 1 bar oxygen partial pressure out-diffusion is observed and tetragonal sites with x=0 develop. These observations can be explained by photon-stimulated desorption of oxygen. Investigations of YBa2Cu3O6 films allow us to study oxygen in-diffusion. In 1 bar oxygen we observe competing oxygen fluxes due to thermally activated diffusion and photon-stimulated desorption. From these measurements we determine an upper bound of the thermal activation energy of the oxygen in-diffusion into YBa2Cu3O6 films of (0.19+/-0.01) eV.

High sensitivity of positrons to oxygen vacancies and to copper-oxygen chain disorder in YBa2Cu3O(7-x)

NASA Astrophysics Data System (ADS)

von Stetten, E. C.; Berko, S.; Li, X. S.; Lee, R. R.; Brynestad, J.

1988-05-01

Temperature-dependent positron-electron momentum densities have been studied by two-dimensional angular correlation of annihilation radiation from 10 to 320 K in YBa2Cu3O(7-x) samples. The positron ground-state charge density, computed by the linearized augmented-plane-wave method, indicates that in YBa2Cu3O7 delocalized positrons sample preferentially the linear copper-oxygen chains. Positron localization due to disorder in these chains is invoked to explain the striking differences observed between superconducting (x = about 0.02) and nonsuperconducting (x = about 0.70) samples.

Oxygen desorption from YBa2Cu3O(7-x) and Bi2CaSr2Cu2O(8 + delta) superconductors

NASA Technical Reports Server (NTRS)

Mesarwi, A.; Levenson, L. L.; Ignatiev, A.

1991-01-01

Oxygen desorption experiments from YBa2Cu3O(7-x) (YBCO) and Bi2CaSr2Cu2O(8 + delta) (BSCCO) superconductors were carried out using a quadrupole mass spectrometer for monitoring the desorbing species and X-ray photoemission spectroscopy for surface characterization. Molecular oxygen was found to desorb from both superconductors following photoirradiation with ultraviolet/optical radiation and subsequent heating at over 150 C. Both YBCO and BSCCO were found to have similar oxygen desorption rates and similar activation energies. The desorption data as well as the X-ray photoemission data indicate that the oxygen desorption is not intrinsic to the superconductors but rather due to molecular oxygen entrapped in the material.

Reduced reactivity to air on HF-treated YBa2Cu3O(7-x)surfaces

NASA Technical Reports Server (NTRS)

Vasquez, R. P.; Hunt, B. D.; Foote, M. C.

1989-01-01

Treatment of YBa2Cu3O(7-x) films with a nonaqueous solution of HF in absolute ethanol results in the formation of an oxyfluoride with relative Y:Ba:Cu concentrations of 1:4:3 on the surface, as determined by X-ray photoelectron spectroscopy. The passivation properties of chemically treated films were tested by monitoring the growth of the high binding energy O 1s peak, associated with nonsuperconducting surface species, as a function of air exposure time, for both HF-treated and untreated films. The native oxyfluoride is shown to reduce the reactivity of the superconductor to air.

Sequentially evaporated thin film YBa2Cu3O(7-x) superconducting microwave ring resonator

NASA Technical Reports Server (NTRS)

Rohrer, Norman J.; To, Hing Y.; Valco, George J.; Bhasin, Kul B.; Chorey, Chris; Warner, Joseph D.

1990-01-01

There is great interest in the application of thin film high temperature superconductors in high frequency electronic circuits. A ring resonator provides a good test vehicle for assessing the microwave losses in the superconductor and for comparing films made by different techniques. Ring resonators made of YBa2Cu3O(7-x) have been investigated on LaAlO3 substrates. The superconducting thin films were deposited by sequential electron beam evaporation of Cu, Y, and BaF2 with a post anneal. Patterning of the superconducting film was done using negative photolithography. A ring resonator was also fabricated from a thin gold film as a control. Both resonators had a gold ground plane on the backside of the substrate. The ring resonators' reflection coefficients were measured as a function of frequency from 33 to 37 GHz at temperatures ranging from 20 K to 68 K. The resonator exhibited two resonances which were at 34.5 and 35.7 GHz at 68 K. The resonant frequencies increased with decreasing temperature. The magnitude of the reflection coefficients was in the calculation of the unloaded Q-values. The performance of the evaporated and gold resonator are compared with the performance of a laser ablated YBa2Cu3O(7-x) resonator. The causes of the double resonance are discussed.

Defect ordering in YBa 2Cu 3O 6.5 and YBa 2Cu 3O 6.6: Synthesis and characterization by neutron and electron diffraction

NASA Astrophysics Data System (ADS)

Lin, Y. P.; Greedan, J. E.; O'Reilly, A. H.; Reimers, J. N.; Stager, C. V.; Post, M. L.

1990-02-01

Polycrystalline samples of YBa 2Cu 3O 6.5 and YBa 2Cu 3O 6.6 were prepared by oxygen titration of YBa 2 Cu 3O 6.0 at 450°C followed by slow cooling to room temperature. Both samples showed evidence for the a' = 2a supercell in individual grains by electron diffraction as reported previously. In addition the superlattice was observed in neutron powder diffraction indicating that the bulk material is also well ordered. In this study the YBa 2Cu 3O 6.6 phase showed longer correlation lengths for ordering along both a* and b* than YBa 2Cu 3O 6.5. For the former compound the powder-averaged, sample-averaged a* correlation distance is 26A˚from neutron diffraction. Analysis of electron diffraction profiles on selected single crystals give correlation lengths along a*, b*, and c* of 100, 200, and 50A˚, respectively. Dark field imaging discloses the presence of striped, ordered domains elongated along b* with a distribution of sizes. Both neutron diffraction and dark field imaging indicate that the volume fraction of the ordered domains is about 50%. A correlation is noted between the Meissner Effect and the extent of defect ordering in the bulk samples of the two phases.

Theoretical calculations of oxygen relaxation in YBa2Cu3O6+x ceramics

NASA Astrophysics Data System (ADS)

Mi, Y.; Schaller, R.; Sathish, S.; Benoit, W.

1991-12-01

A two-dimensional theoretical model of stress-induced point-defect relaxation in a layered structure is presented, with a detailed discussion of the special case of YBa2Cu3O6+x. The experimental results of oxygen relaxation in YBa2Cu3O6+x can be explained qualitatively by this model.

Composition dependence of the in-plane Cu-O bond-stretching LO phonon mode in YBa2Cu3O6+x

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stercil, F.; Egami, T.; Mook Jr, Herbert A

An inelastic pulsed neutron scattering study was performed on the dependence of the dispersion and spectral intensity of the in-plane Cu-O bond-stretching LO phonon mode on doped charge density. The measurements were made in the time-of-flight mode with the multiangle position sensitive spectrometer of the ISIS facility on single crystals of YBa{sub 2}Cu{sub 3}O{sub 6+x} (x=0.15, 0.35, 0.6, 0.7, and 0.95). The focus of the study is the in-plane Cu-O bond-stretching LO phonon mode, which is known for strong electron-phonon coupling and unusual dependence on composition and temperature. It is shown that the dispersions for the samples with x=0.35, 0.6,more » and 0.7 are similar to the superposition of those for x=0.15 and 0.95 samples, and cannot be explained in terms of the structural anisotropy. It is suggested that the results are consistent with the model of nanoscale electronic phase separation, with the fraction of the phases being dependent on the doped charge density.« less

Spectrophotometric Determination of the Hole Concentration in the Superconductor YBa2Cu3O(sub 7-x)

ERIC Educational Resources Information Center

Hoppe, Jack I.; Malati, Mounir A.

2005-01-01

An experimental study of ceramic superconductors namely YBa2Cu3O(sub 7-x), which illustrates the use of spectrophotometry, based on the electronic spectra of complexes of Fe(II), Fe(III) and Cu(II) to better understand the stoichiometry of YBCO is described. The results from this experiment are in good agreement with those obtained by the…

Boson localization and universality in YBa2Cu(3-x)M(x)O(7-delta)

NASA Technical Reports Server (NTRS)

Kallio, A.; Apaja, V.; Poykko, S.

1995-01-01

We consider a two component mixture of charged fermions on neutralizing background with all sign combinations and arbitrarily small mass ratios. In the two impurity limit for the heavier component we show that the pair forms a bound state for all charge combinations. In the lowest order approximation we derive a closed form expression Veff(r) for the binding potential which has short-range repulsion followed by attraction. In the classical limit, when the mass of embedded particles is large m2 much greater than m, we can calculate from Veff(r) also the cohesive energy E and the bond length R of a metallic crystal such as lithium. The lowest order result is R = 3.1 A, E = -0.9 eV, not entirely different from the experimental result for lithium metal. The same interaction for two holes on a parabolic band with m2 greater than m gives the quantum mechanical bound state which one may interpret as a boson or local pair in the case of high-Te and heavy fermion superconductors. We also show that for compounds of the type YBa2Cu(3 - x)M(x)O(7 - delta) one can understand most of the experimental results for the superconducting and normal states with a single temperature dependent boson breaking function f(T) for each impurity content x governing the decay of bosons into pairing fermions. In the normal state f(T) turns out to be a linear, universal function, independent of the impurity content I and the oxygen content delta. We predict with universality a depression in Tc(x) with slight down bending in agreement with experiment. As a natural consequence of the model the bosons become localized slightly above Tc due to the Wigner crystallization, enhanced with lattice local field minima. The holes remain delocalized with a linearly increasing concentration in the normal state, thus explaining the rising Hall density. The boson localization temperature T(sub BL) shows up as a minimum in the Hall density R(sub ab)(exp -1). We also give explanation for very recently observed

Boson localization and universality in YBa2Cu(3-x)M(x)O(7-delta)

NASA Astrophysics Data System (ADS)

Kallio, A.; Apaja, V.; Poykko, S.

1995-04-01

We consider a two component mixture of charged fermions on neutralizing background with all sign combinations and arbitrarily small mass ratios. In the two impurity limit for the heavier component we show that the pair forms a bound state for all charge combinations. In the lowest order approximation we derive a closed form expression Veff(r) for the binding potential which has short-range repulsion followed by attraction. In the classical limit, when the mass of embedded particles is large m2 much greater than m, we can calculate from Veff(r) also the cohesive energy E and the bond length R of a metallic crystal such as lithium. The lowest order result is R = 3.1 A, E = -0.9 eV, not entirely different from the experimental result for lithium metal. The same interaction for two holes on a parabolic band with m2 greater than m gives the quantum mechanical bound state which one may interpret as a boson or local pair in the case of high-Te and heavy fermion superconductors. We also show that for compounds of the type YBa2Cu(3 - x)M(x)O(7 - delta) one can understand most of the experimental results for the superconducting and normal states with a single temperature dependent boson breaking function f(T) for each impurity content x governing the decay of bosons into pairing fermions. In the normal state f(T) turns out to be a linear, universal function, independent of the impurity content I and the oxygen content delta. We predict with universality a depression in Tc(x) with slight down bending in agreement with experiment. As a natural consequence of the model the bosons become localized slightly above Tc due to the Wigner crystallization, enhanced with lattice local field minima. The holes remain delocalized with a linearly increasing concentration in the normal state, thus explaining the rising Hall density. The boson localization temperature T(sub BL) shows up as a minimum in the Hall density R(sub ab)(exp -1). We also give explanation for very recently observed

Room temperature degradation of YBa2Cu3O(7-x) superconductors in varying relative humidity environments

NASA Technical Reports Server (NTRS)

Hooker, M. W.; Wise, S. A.; Carlberg, I. A.; Stephens, R. M.; Simchick, R. T.; Farjami, A.

1993-01-01

An aging study was performed to determine the stability of YBa2Cu3O(7-x) ceramics in humid environments at 20 C. In this study, fired ceramic specimens were exposed to humidity levels ranging from 30.5 to 100 percent for 2-, 4-, and 6-week time intervals. After storage under these conditions, the specimens were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrical resistance measurements. At every storage condition evaluated, the fired ceramics were found to interact with H2O present in the surrounding environment, resulting in the decomposition of the YBa2Cu3O(7-x) phase. XRD data showed that BaCO3, CuO, and Y2BaCuO5 were present after aging and that the peak intensities of these impurity phases increased both with increasing humidity level and with increasing time of exposure. Additionally, SEM analyses of the ceramic microstructures after aging revealed the development of needle-like crystallites along the surface of the test specimens after aging. Furthermore, the superconducting transition temperature T(sub c) was found to decrease both with increasing humidity level and with increasing time of exposure. All the specimens aged at 30.5, 66, and 81 percent relative humidity exhibited superconducting transitions above 80 K, although these values were reduced by the exposure to the test conditions. Conversely, the specimens stored in direct contact with water (100 percent relative humidity) exhibited no superconducting transitions.

Synthesis of YBa2CU3O7 using sub-atmospheric processing

DOEpatents

Wiesmann, Harold; Solovyov, Vyacheslav

2004-09-21

The present invention is a method of forming thick films of crystalline YBa.sub.2 Cu.sub.3 O.sub.7 that includes forming a precursor film comprising barium fluoride (BaF.sub.2), yttrium (Y) and copper (Cu). The precursor film is heat-treated at a temperature above 500.degree. C. in the presence of oxygen, nitrogen and water vapor at sub-atmospheric pressure to form a crystalline structure. The crystalline structure is then annealed at about 500.degree. C. in the presence of oxygen to form the crystalline YBa.sub.2 Cu.sub.3 O.sub.7 film. The YBa.sub.2 Cu.sub.3 O.sub.7 film formed by this method has a resistivity of from about 100 to about 600 .mu.Ohm-cm at room temperature and a critical current density measured at 77 K in a magnetic field of 1 Tesla of about 1.0.times.10.sup.5 Ampere per square centimeter (0.1 MA/cm.sup.2) or greater.

Flux Pinning Enhancement in YBa2Cu3O7-x Films with BaSnO3 Nanoparticles

DTIC Science & Technology

2008-10-01

SUPERCONDUCTOR SCIENCE AND TECHNOLOGY Supercond. Sci. Technol. 19 (2006) L37 –L41 doi:10.1088/0953-2048/19/10/L01 RAPID COMMUNICATION Flux pinning enhancement in...2006 Online at stacks.iop.org/SUST/19/ L37 Abstract Nanoparticles of BaSnO3 were incorporated into YBa2Cu3O7−x (YBCO) films on LaAlO3 substrates for...0953-2048/06/100037+05$30.00 © 2006 IOP Publishing Ltd Printed in the UK L37 1 Rapid Communication materials and sintered together to form a composite

Large single domain 123 material produced by seeding with single crystal rare earth barium copper oxide single crystals

DOEpatents

Todt, V.; Miller, D.J.; Shi, D.; Sengupta, S.

1998-07-07

A method of fabricating bulk YBa{sub 2}Cu{sub 3}O{sub x} where compressed powder oxides and/or carbonates of Y and Ba and Cu present in mole ratios to form YBa{sub 2}Cu{sub 3}O{sub x} are heated in the presence of a Nd{sub 1+x}Ba{sub 2{minus}x}Cu{sub 3}O{sub y} seed crystal to a temperature sufficient to form a liquid phase in the YBa{sub 2}Cu{sub 3}O{sub x} while maintaining the seed crystal solid. The materials are slowly cooled to provide a YBa{sub 2}Cu{sub 3}O{sub x} material having a predetermined number of domains between 1 and 5. Crack-free single domain materials can be formed using either plate shaped seed crystals or cube shaped seed crystals with a pedestal of preferential orientation material. 7 figs.

Method for preparation of textured YBa.sub.2 Cu.sub.3 O.sub.x superconductor

DOEpatents

Selvamanickam, Venkat; Goyal, Amit; Kroeger, Donald M.

1998-01-01

The present invention relate to textured YBa.sub.2 Cu.sub.3 O.sub.x (Y-123) superconductors and a process of preparing them by directional recrystallization of compacts fabricated from quenched YBCO powders at temperatures about 100.degree. C. below the peritectic temperature to provide a superconductor where more than 75% of the YBa.sub.2 Cu.sub.3 O.sub.x phase is obtained without any Y.sub.2 BaCuO.sub.5 .

Flux Pinning Enhancement in YBa2Cu3O7-x Films for Coated Conductor Applications (Postprint)

DTIC Science & Technology

2010-01-01

YBa2Cu3O7–x Films for Coated Conductor Applications Maiorov , B. , Civale , L. , Lin , Y. , Hawley , M.E. , Maley , M.P. , and Peterson , D.E...L. , Maiorov , B. , Hawley , M.E. , Maley , M.P. , and Peterson , D.E. ( 2004 ) Nat. Mater. , 3 , 439 . 30 Kang , S. , Goyal...1864 . 47 Civale , L. , Maiorov , B. , Serquis , A. , Willis , J.O. , Coulter , J.Y. , Wang , H. , Jia , Q.X. , Arendt , P.N

Processing of La(1.8)Sr(0.2)CuO4 and YBa2Cu3O7 superconducting thin films by dual-ion-beam sputtering

NASA Astrophysics Data System (ADS)

Madakson, P.; Cuomo, J. J.; Yee, D. S.; Roy, R. A.; Scilla, G.

1988-03-01

High-quality La(1.8)Sr(0.2)CuO4 and YBa2Cu3O7 superconducting thin films, with zero resistance at 88 K, have been made by dual-ion-beam sputtering of metal and oxide targets at elevated temperatures. The films are about 1.0 micron thick and are single phase after annealing. The substrates investigated are Nd-YAP, MgO, SrF2, Si, CaF2, ZrO2-(9 pct)Y2O3, BaF2, Al2O3, and SrTiO3. Characterization of the films was carried out using Rutherford backscattering spectroscopy, resistivity measurements, TEM, X-ray diffraction, and SIMS. Substrate/film interaction was observed in every case. This generally involves diffusion of the substrate into the film, which is accompanied by, for example, the replacement of Ba by Sr in the YBa2Cu2O7 structure, in the case of SrTiO3 substrate. The best substrates were those that did not significantly diffuse into the film and which did not react chemically with the film.

Investigation of Pb doping on electrical, structural and superconducting properties of YBa2-xPbxCu3O7-δ superconductors

NASA Astrophysics Data System (ADS)

Ezzatpour, S.; Sharifzadegan, L.; Sarvari, F.; Sedghi, H.

2018-06-01

In this study the high temperature superconductor YBa2-xPbxCu3O7-δ with doping x = ,0.05,0.1,0.15 were prepared by the standard solid-state reaction method. The effect of Pb substitution on Ba site of YBCO superconducting system, structural, electrical and superconducting properties of Y-based superconductor has been investigated. The measurements of dc resisitivity were performed on all samples with four-probe method using low frequency/lowAC current (4 mA) . The superconducting temperature, Tc, were determined from the resistivity versus temperature (R-T) curves. Results show that Pb doping reduced the cirtical temperature(Tc) and superconductivity properties of our samples. The maximum and the minimum Tc were observed for the samples with x = 0.15 and x = 0.1 respectively. The structure and phase purity of samples were examined by the X-ray powder diffraction technique (XRD) performed by means of D8 Advance Bruker diffractometer with Cu kα radiation. The grain morphology of surface of the samples was analyzed by sacanning electron microscopy (SEM). XRD patterns of polycrystalline materials of composition YBa2-xPbxCu3O7-δ revealed that all prepared samples are orthorhombic. All of the peaks of YBCO and YBa2-xPbxCu3O7-δ have been used for the estimation of volume fractions of the phases and ignored the void peaks.

Synthesis and characterization of YBaCu2O5-δ compound

NASA Astrophysics Data System (ADS)

Ehsandoust, A.; Sandoghchi, M.; Mokhtari, P.; Akhavan, M.

2018-05-01

YBaCu2O5 compound as one of the possible microstructures of Y3Ba5Cu8O19 has been synthesized. The X-ray diffraction analysis of this compound indicates that its formation is accompanied with the formation of YBa2Cu3O7-δ. The observed superconductivity around ∼92 K supports this. So, it seems that YBa2Cu3O7-δ is responsible for the observed superconductivity in YBaCu2O5, and this phase is not an independent superconducting phase. Consequently, the overall effect of the YBaCu2O5 formation during the Y3Ba5Cu8O19 fabrication process could be a reduction in Tc.

Critical current density enhancement by phase decomposition of YBa 2Cu 4O 8 into YBa 2Cu 3O 7-σ and CuO

NASA Astrophysics Data System (ADS)

Krelaus, J.; Heinemann, K.; Ullmann, B.; Freyhardt, H. C.

1995-02-01

Bulk YBa 2Cu 4O 8 (Y-124) is prepared from YBa 2Cu 3O 7-σ (Y-123) and CuO by a powder-metallurgical method. The superconducting features of the Y-124, in particular critical current densities and activation energies, are measured resistively using a four-probe technique and magnetically using a Faraday magnetometer. In a second step the Y-124 is decomposed at high temperatures. The intragranular critical current density is measured at different annealing times, tA, in order to determine and discuss the characteristics of the jc( tA) curves.

Large area ion beam sputtered YBa2Cu3O(7-delta) films for novel device structures

NASA Astrophysics Data System (ADS)

Gauzzi, A.; Lucia, M. L.; Kellett, B. J.; James, J. H.; Pavuna, D.

1992-03-01

A simple single-target ion-beam system is employed to manufacture large areas of uniformly superconducting YBa2Cu3O(7-delta) films which can be reproduced. The required '123' stoichiometry is transferred from the target to the substrate when ion-beam power, target/ion-beam angle, and target temperature are adequately controlled. Ion-beam sputtering is experimentally demonstrated to be an effective technique for producing homogeneous YBa2Cu3O(7-delta) films.

Positron annihilation study of Y 1- xPr xBa 2Cu 3O 7

NASA Astrophysics Data System (ADS)

Zhao, Y. G.; Cao, B. S.; Yu, W. Z.; Du, Z. H.; Wang, Y. J.; Luo, C. Y.; Hu, H.; Wang, S.; Yang, J. H.; He, A. S.; Gu, B. L.

1995-02-01

A positron annihilation study of Y 1- xPr xBa 2Cu 3O 7 was performed. The results showed that charge transfer between the CuO 2 planes and 1D CuO chains upon Pr doping, as proposed in the literature, did not occur. Pr doping suppressed the anomaly of positron annihilation lifetime near and below Tc which has been observed in YBa 2Cu 3O 7. The perfection of the 1D CuO chains was reduced by Pr doping and this may be partly responsible for the increase of resistivity with Pr doping, and finally the semiconducting behaviour of DC resistivity in Y 1- xPr xBa 2Cu 3O 7 with x > 0.6.

Study of Substitution of Zn FOR Cu in YBa2Cu3O7 System

NASA Astrophysics Data System (ADS)

Sharma, P. K.; Samariya, A.; Dhawan, M. S.; Singhal, R. K.

The polycrystalline YBa2(Cu1-XZnX)3O7-δ samples (x=0.0 to 0.06) were synthesized and studied using X Ray diffraction, titration, resistivity, magnetization and X ray photoelectron spectroscopy (XPS). Results show that O2 stoichiometry (δ) changes on Zn substitution which affects their normal state resistivity as well as the TC. Zn also induces local magnetic moment as evidenced from magnetization results. A combination of change in O2 stoichiometry and magnetic pair breaking is found to be responsible for a rapid suppression of superconductivity.

Dominant pinning mechanisms in YBa2Cu3O7-x films on single and polycrystalline yttria stabilized zirconia substrates

NASA Astrophysics Data System (ADS)

Harshavardhan, K. S.; Rajeswari, M.; Hwang, D. M.; Chen, C. Y.; Sands, T.; Venkatesan, T.; Tkaczyk, J. E.; Lay, K. W.; Safari, A.

1992-04-01

Critical-current densities have been measured in YBa2Cu3O7-x films deposited on (100) yttria stabilized zirconia (YSZ) and polycrystalline YSZ substrates as a function of temperature (4.5-88 K), magnetic field (0-1 T) and orientation relative to the applied field. The results indicate that in films on polycrystalline substrates, surface and interface pinning play a dominant role at high temperatures. In films on (100) YSZ, pinning is mainly due to intrinsic layer pinning as well as extrinsic pinning associated with the interaction of the fluxoids with point defects and low energy planar (2D) boundaries. The differences are attributed to the intrinsic rigidity of single fluxoids which is reduced in films on polycrystalline substrates thereby weakening the intrinsic layer pinning.

Shear at Twin Domain Boundaries in YBa2Cu3O7-x

NASA Astrophysics Data System (ADS)

Caldwell, W. A.; Tamura, N.; Celestre, R. S.; MacDowell, A. A.; Padmore, H. A.; Geballe, T. H.; Koster, G.; Batterman, B. W.; Patel, J. R.

2004-05-01

The microstructure and strain state of twin domains in YBa2Cu3O7-x are discussed based upon synchrotron white-beam x-ray microdiffraction measurements. Intensity variations of the fourfold twin splitting of Laue diffraction peaks are used to determine the twin domain structure. Strain analysis shows that interfaces between neighboring twin domains are strained in shear, whereas the interior of these domains are regions of low strain. These measurements are consistent with the orientation relationships of twin boundaries within and across domains and show that basal plane shear stresses can exceed 100MPa where twin domains meet. Our results support stress field pinning of magnetic flux vortices by twin domain boundaries.

Fermi surface ridge at second and third UMKLAPP positron annihilations in YBa 2Cu 3O 7- δ

NASA Astrophysics Data System (ADS)

Adam, Gh.; Adam, S.; Barbiellini, B.; Hoffmann, L.; Manuel, A. A.; Peter, M.; Massida, S.

1993-12-01

Results of statistical noise smoothing of the electron momentum distribution got by two-dimensional angular correlation of the electron-positron annihilation radiation technique on untwinned YBa 2Cu 3O 7- δ single crystals are reported. Two distinct signatures of the sheet of Fermi surface related to the CuO chains (the ridge) are resolved. The first occurs at second Umklapp processes, in agreement with previous evidence. The second one, identified for the first time, occurs at third Umklapp processes. Comparison with FLAPW calculations confirms this result.

Bulk modulus and its pressure derivative of YBa2Cu3O7-x

NASA Astrophysics Data System (ADS)

Cankurtaran, M.; Saunders, G. A.; Willis, J. R.; Al-Kheffaji, A.; Almond, D. P.

1989-02-01

Pressure dependences of the ultrasonic wave velocities in polycrystalline YBa2Cu3O7-x are reported. Porosity effects are taken into account using wave-scattering theory in a porous medium. The bulk modulus B0 at atmospheric pressure for the nonporous matrix is 65 GPa, much smaller than B(P) obtained at high pressures from lattice-parameter measurements. This discrepancy accrues from the large value of (∂B/∂P). The comparatively small B0 and large (∂B/∂P) are due to vacant anion sites in this defect perovskite.

Raman scattering spectra of superconducting Bi2Sr2CaCu2O8 single crystals

NASA Astrophysics Data System (ADS)

Kirillov, D.; Bozovic, I.; Geballe, T. H.; Kapitulnik, A.; Mitzi, D. B.

1988-12-01

Raman spectra of Bi2Sr2CaCu2O8 single crystals with superconducting phase-transition temperature of 90 K have been studied. The spectra contained phonon lines and electronic continuum. Phonon energies and polarization selection rules were measured. A gap in the electronic continuum spectrum was observed in a superconducting state. Noticeable similarity between Raman spectra of Bi2Sr2CaCu2O8 and YBa2Cu3O7 was found.

Cation disorder and gas phase equilibrium in an YBa 2Cu 3O 7- x superconducting thin film

NASA Astrophysics Data System (ADS)

Shin, Dong Chan; Ki Park, Yong; Park, Jong-Chul; Kang, Suk-Joong L.; Yong Yoon, Duk

1997-02-01

YBa 2Cu 3O 7- x superconducting thin films have been grown by in situ off-axis rf sputtering with varying oxygen pressure, Ba/Y ratio in a target, and deposition temperature. With decreasing oxygen pressure, increasing Ba/Y ratio, increasing deposition temperature, the critical temperature of the thin films decreased and the c-axis length increased. The property change of films with the variation of deposition variables has been explained by a gas phase equilibrium of the oxidation reaction of Ba and Y. Applying Le Chatelier's principle to the oxidation reaction, we were able to predict the relation of deposition variables and the resultant properties of thin films; the prediction was in good agreement with the experimental results. From the relation between the three deposition variables and gas phase equilibrium, a 3-dimensional processing diagram was introduced. This diagram has shown that the optimum deposition condition of YBa 2Cu 3O 7- x thin films is not a fixed point but can be varied. The gas phase equilibrium can also be applied to the explanation of previous results that good quality films were obtained at low deposition temperature using active species, such as O, O 3, and O 2+.

Selective interlayer ferromagnetic coupling between the Cu spins in YBa2Cu3O7−x grown on top of La0.7Ca0.3MnO3

PubMed Central

Huang, S. W.; Wray, L. Andrew; Jeng, Horng-Tay; Tra, V. T.; Lee, J. M.; Langner, M. C.; Chen, J. M.; Roy, S.; Chu, Y. H.; Schoenlein, R. W.; Chuang, Y.-D.; Lin, J.-Y.

2015-01-01

Studies to date on ferromagnet/d-wave superconductor heterostructures focus mainly on the effects at or near the interfaces while the response of bulk properties to heterostructuring is overlooked. Here we use resonant soft x-ray scattering spectroscopy to reveal a novel c-axis ferromagnetic coupling between the in-plane Cu spins in YBa2Cu3O7−x (YBCO) superconductor when it is grown on top of ferromagnetic La0.7Ca0.3MnO3 (LCMO) manganite layer. This coupling, present in both normal and superconducting states of YBCO, is sensitive to the interfacial termination such that it is only observed in bilayers with MnO2 but not with La0.7Ca0.3O interfacial termination. Such contrasting behaviors, we propose, are due to distinct energetic of CuO chain and CuO2 plane at the La0.7Ca0.3O and MnO2 terminated interfaces respectively, therefore influencing the transfer of spin-polarized electrons from manganite to cuprate differently. Our findings suggest that the superconducting/ferromagnetic bilayers with proper interfacial engineering can be good candidates for searching the theorized Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state in cuprates and studying the competing quantum orders in highly correlated electron systems. PMID:26573394

Method of producing superconducting fibers of YBa[sub 2]Cu[sub 3]O[sub x

DOEpatents

Schwartzkopf, L.A.; Ostenson, J.E.; Finnemore, D.K.

1990-11-13

Fibers of YBa[sub 2]Cu[sub 3]O[sub x] have been produce by pendant drop melt extraction. This technique involves the end of a rod of YBa[sub 2]Cu[sub 3]O[sub x] melted with a hydrogen-oxygen torch, followed by lowering onto the edge of a spinning wheel. The fibers are up to 10 cm in length with the usual lateral dimensions, ranging from 20 [mu]m to 125 [mu]m. The fibers require a heat treatment to make them superconducting.

Direct, experimental evidence of the Fermi surface in YBa2Cu3O(7-x)

NASA Astrophysics Data System (ADS)

Haghighi, H.; Kaiser, J. H.; Rayner, S. L.; West, R. N.; Liu, J. Z.; Shelton, R.; Howell, R. H.; Sterne, P. A.; Solal, F. R.; Fluss, M. J.

1991-04-01

We report new measurements of the electron positron momentum spectra of YBa2Cu3O(7-x) performed with ultra-high statistical precision. These data differ from previous results in two significant respects: They show the D(sub 2) symmetry appropriate for untwinned crystals and, more importantly, they show unmistakable, statistically significant, discontinuities that are evidence of a major Fermi surface section. These results provide a partial answer to a question of special significance to the study of high temperature superconductors i.e., the distribution of the electrons in the material, the electronic structure. Special consideration has been given both experimentally and theoretically to the existence and shape of a Fermi surface in the materials and to the superconducting gap. There are only three experimental techniques that can provide details of the electronic structure at useful resolutions. They are angular correlation of positron annihilation radiation, ACAR, angle resolved photo emission, PE, and de Haas van Alphen measurements.

Growth, patterning, and weak-link fabrication of superconducting YBa2Cu3O(7-x) thin films

NASA Astrophysics Data System (ADS)

Hilton, G. C.; Harris, E. B.; van Harlingen, D. J.

1988-09-01

Thin films of the high-temperature superconducting ceramic oxides have been grown, and techniques for fabricating weak-link structures have been investigated. Films of YBa2Cu3O(7-x) grown on SrTiO3 by a combination of dc magnetron sputtering and thermal evaporation from the three sources have been patterned into microbridges with widths down to 2 microns. Evidence is found that the bridges behave as arrays of Josephson-coupled superconducting islands. Further weak-link behavior is induced by in situ modification of the coupling by ion milling through the bridge.

Selective interlayer ferromagnetic coupling between the Cu spins in YBa 2Cu 3O 7–x grown on top of La 0.7Ca 0.3MnO 3

DOE PAGES

Huang, S. W.; Wray, L. Andrew; Jeng, Horng -Tay; ...

2015-11-17

Studies to date on ferromagnet/d-wave superconductor heterostructures focus mainly on the effects at or near the interfaces while the response of bulk properties to heterostructuring is overlooked. Here we use resonant soft x-ray scattering spectroscopy to reveal a novel c-axis ferromagnetic coupling between the in-plane Cu spins in YBa 2Cu 3O 7–x (YBCO) superconductor when it is grown on top of ferromagnetic La 0.7Ca 0.3MnO 3 (LCMO) manganite layer. This coupling, present in both normal and superconducting states of YBCO, is sensitive to the interfacial termination such that it is only observed in bilayers with MnO 2 but not withmore » La 0.7Ca 0.3O interfacial termination. Thus, such contrasting behaviors, we propose, are due to distinct energetic of CuO chain and CuO 2 plane at the La 0.7Ca 0.3O and MnO 2 terminated interfaces respectively, therefore influencing the transfer of spin-polarized electrons from manganite to cuprate differently. Our findings suggest that the superconducting/ferromagnetic bilayers with proper interfacial engineering can be good candidates for searching the theorized Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state in cuprates and studying the competing quantum orders in highly correlated electron systems.« less

ESR and nonresonant microwave absorption of ErBa2Cu3O(7-delta) and HoBa2Cu3O(7-delta) single crystals

NASA Astrophysics Data System (ADS)

Tagaya, Kimihito; Fukuoka, Nobuo; Nakanishi, Shigemitsu

1990-12-01

ESR measurements were performed for ErBa2Cu3O(7-delta) and HoBa2Cu3O(7-delta) single crystals from 77 K to room temperature. The ESR signals of Er2BaCuO5 and Ho2BaCuO5 were observed, and their temperature variations were investigated. Nonresonant microwave absorption was also observed below the superconducting critical temperature of 93 K. The principal values of lower critical field were determined.

Influence of planar macrodefects on the anisotropy of magnetic-flux penetration in YBa 2Cu 3O 7-δ

NASA Astrophysics Data System (ADS)

Cuche, E.; Indenbom, M. V.; André, M.-O.; Richard, P.; Benoit, W.; Wolf, Th.

1996-02-01

The magnetic flux penetration in a high-quality YBa 2Cu 3O 7-δ single crystal with an external field applied perpendicular to the crystalline c axis is directly visualized by means of the magneto-optical technique. The observations show that the field penetrates preferentially along the ab planes. Scanning acoustic microscopy reveals macrodefects along ab planes which strongly affect this anisotropy of the field penetration.

Effects of oxygen stoichiometry on the scaling behaviors of YBa2Cu3O(x) grain boundary weak-links

NASA Technical Reports Server (NTRS)

Wu, K. H.; Fu, C. M.; Jeng, W. J.; Juang, J. Y.; Uen, T. M.; Gou, Y. S.

1995-01-01

The effects of oxygen stoichiometry on the transport properties of the pulsed laser deposited YBa2Cu3O(x) bicrystalline grain boundary weak-link junctions were studied. It is found that not only the cross boundary resistive transition foot structure can be manipulated repeatedly with oxygen annealing processes but the junction behaviors are also altered in accordance. In the fully oxygenated state i.e with x = 7.0 in YBa2Cu3O(x) stoichiometry, the junction critical current exhibits a power of 2 scaling behavior with temperature. In contrast, when annealed in the conditions of oxygen-deficient state (e.g with x = 6.9 in YBa2Cu3O(x) stoichiometry) the junction critical current switches to a linear temperature dependence behavior. The results are tentatively attributed to the modification of the structure in the boundary area upon oxygen annealing, which, in turn, will affect the effective dimension of the geometrically constrained weak-link bridges. The detailed discussion on the responsible physical mechanisms as well as the implications of the present results on device applications will be given.

Reaction of YBa2Cu3O(7-beta) with Gold, Silver, Bismuth and Lead: Substitution Chemistry and Composite Fabrication

NASA Technical Reports Server (NTRS)

Hepp, Aloysius F.; Gaier, James R.

1993-01-01

The reaction of YBa2Cu3O(7-beta) with Au, Ag, Bi, and Ph ions or metal is described. Three types of materials were produced: a well-defined series of homogeneous superconductors was obtained for Au ion substitution with little effect on T(sub c); attempted Ag and Bi ion substitution resulted in multi-phase samples with slightly enhanced T(sub c); finally, attempts to produce superconducting metal/superconducting ceramic composites with Pb and Bi powders resulted in multi-phase samples with drastically diminished superconducting properties. For Au- substituted superconductors, YBa2(Cu(l-x)Au(x))3O(7-beta), a substitution series (x = 0 - 0.1) has been synthesized. For x = 0.1 there was no change in the a and b lattice parameters (a = 3.826 A and b = 3.889 A) but a 0.06 A c axis expansion to 11.75 A was observed. The valence of Cu and Au in YBa2Au(0.3)Cu(2.7)O(7-beta) was investigated using X-ray Absorption Near-Edge Structure (XANES). X-ray studies indicate that Au goes into the Cu(l) site and Cu K edge XANES shows that this has little effect on the oxidation state of the remaining copper. A small effect on T(sub c) is observed (T(sub c) = 89 K for x = 0.10). Ag and Bi addition results in a rise in T(sub c) and a decrease in (delta)T(sub c) at low levels (x = 0.10 Ag, T(sub c) = 94 K and (delta)T(sub c) = 0.5 K; x = 0.02 Bi, T(sub c) = 94 K and (delta)T(sub c) = 1K) relative to typical values for YBa2Cu3O(7-beta) (T(sub c) = 91 K, (delta)T(sub c) = 2 K). Attempts at fabrication of Pb- and Pb(1-x)Bi(x)-superconductor composites are described. Cold pressing followed by low temperature (200 C) sintering resulted in a composite which excluded flux below 90 K but did not show zero electrical resistance until the metal (alloy) superconducting transition. X-ray diffraction showed the presence of pervoskite and metal. Processing at moderate (450 C) or high (950 C) temperatures resulted in oxygen-depleted pervoskite and/or metal oxides. These materials displayed greatly

Large single domain 123 material produced by seeding with single crystal rare earth barium copper oxide single crystals

DOEpatents

Todt, Volker; Miller, Dean J.; Shi, Donglu; Sengupta, Suvankar

1998-01-01

A method of fabricating bulk YBa.sub.2 Cu.sub.3 O.sub.x where compressed powder oxides and/or carbonates of Y and Ba and Cu present in mole ratios to form YBa.sub.2 Cu.sub.3 O.sub.x are heated in the presence of a Nd.sub.1+x Ba.sub.2-x Cu.sub.3 O.sub.y seed crystal to a temperature sufficient to form a liquid phase in the YBa.sub.2 Cu.sub.3 O.sub.x while maintaining the seed crystal solid. The materials are slowly cooled to provide a YBa.sub.2 Cu.sub.3 O.sub.x material having a predetermined number of domains between 1 and 5. Crack-free single domain materials can be formed using either plate shaped seed crystals or cube shaped seed crystals with a pedestal of preferential orientation material.

Magnetic flux relaxation in YBa2Cu3O(7-x) thin film: Thermal or athermal

NASA Technical Reports Server (NTRS)

Vitta, Satish; Stan, M. A.; Warner, Joseph D.; Alterovitz, Samuel A.

1992-01-01

The magnetic flux relaxation behavior of YBa2Cu3O(7-x) thin film on LaAlO3 for H parallel c was studied in the range of 4.2-40 k and 0.2-1.0 T. Both the normalized flux relaxation rate (S) and the net flux pinning energy (U) increase continuously from 1.3 x 10 exp -2 to 3.0 x 10 exp -2 and from 70-240 meV respectively, as the temperature (T) increases from 10 to 40 K. This behavior is consistent with the thermally activated flux motion model. At low temperatures, however, S is found to decrease much more slowly as compared with kT, in contradiction to the thermal activation model. This behavior is discussed in terms of the athermal quantum tunneling of flux lines. The magnetic field dependence of U, however, is not completely understood.

Epitaxial growth of YBa2Cu3O7 - delta films on oxidized silicon with yttria- and zirconia-based buffer layers

NASA Astrophysics Data System (ADS)

Pechen, E. V.; Schoenberger, R.; Brunner, B.; Ritzinger, S.; Renk, K. F.; Sidorov, M. V.; Oktyabrsky, S. R.

1993-09-01

A study of epitaxial growth of YBa2Cu3O7-δ films on oxidized Si with yttria- and zirconia-based buffer layers is reported. Using substrates with either SiO2 free or naturally oxidized (100) surfaces of Si it was found that a thin SiO2 layer on top of the Si favors high-quality superconducting film formation. Compared to yttria-stabilized ZrO2 (YSZ) single layers, YSZY2O3 double and YSZ/Y2O3YSZ triple layers allows the deposition of thin YBa2Cu3O7-δ films with improved properties including reduced aging effects. In epitaxial YBa2Cu3O7-δ films grown on the double buffer layers a critical temperature Tc(R=0)=89.5 K and critical current densities of 3.5×106 A/cm2 at 77 K and 1×107 A/cm2 at 66 K were reached.

Vibrational spectra and lattice instabilities in the high-Tc superconductors YBa2Cu3O7 and GdBa2Cu3O7

NASA Astrophysics Data System (ADS)

Bozović, I.; Mitzi, D.; Beasley, M.; Kapitulnik, A.; Geballe, T.; Perkowitz, S.; Carr, G. L.; Lou, B.; Sudharsanan, R.; Yom, S. S.

1987-09-01

The exceptionally high Tc of layered cuprates was proposed recently as originating from electronically driven structural instabilities. We have studied the infrared and Raman spectra of YBa2Cu3O7-δ and GdBa2Cu3O7-δ over a broad range of temperatures, from 10 to 300 K. We observed neither mode softening nor any other spectroscopic signature of lattice instabilities.

Dynamics of oxygen ordering in YBa2CU3O6+x studied by neutron and high-energy synchrotron x-ray diffiaction.

NASA Astrophysics Data System (ADS)

Frello, T.; Andersen, N. H.; Madsen, J.; Ka¨ll, M.; von Zimmermann, M.; Schmidt, O.; Poulsen, H. F.; Schneider, J. R.; Wolf, Th.

1997-08-01

The dynamics of the ortho-II oxygen structure in a high purity YBa 2Cu 3O 6+ x single crystal with x=0.50 has been studied by neutron and by X-ray diffraction with a photon energy of 100 keV. Our data show that the oxygen order develops on two different time-scales, one of the order of seconds and a much slower of the order of weeks and months. The mechanism dominating the slow time-scale is related to oxygen diffusion, while the fast mechanism may result from a temperature-dependent change in the average oxygen chain length.

Theoretical calculation of electron-positron momentum density in YBa 2Cu 3O 7-δ

NASA Astrophysics Data System (ADS)

Massidda, S.

1990-07-01

We present calculations of the electron-positron momentum density for the high- Tc superconductor YBa 2Cu 3O 7-δ for δ=0 and for the insulating parent compound YBa 2Cu 3O 6, based on first-principle electronic structure calculations performed within the local density approximation (LDA) using the full potential linearized augmented plane wave (FLAPW) method. Our results indicate a small overlap of the positron wave function with the CuO 2 plane electrons and, as a consequence, relatively small signals due to the related Fermi surfaces. By contrast, the present calculations show, after the folding of Umklapp terms according to Lock, Crisp and West, clear Fermi surface breaks arising from the Cu-O chain bands. No general agreement with existing experiments allows a clear definition of Fermi surface structures in the latter. A comparison of the calculated momentum with the experimental two-dimensional angular correlation of annihilation radiation (2D-ACAR) recently measured in Geneva shows an overall agreement for the insulating compound, despite the spurious LDA metallic state, and possibly suggests the importance of O vacancies in experiments performed on non-stoichiometric YBa 2Cu 3O 7-δ samples.

XANES and EXAFS study of Au-substituted YBa2Cu3O(7-delta)

NASA Technical Reports Server (NTRS)

Ruckman, Mark W.; Hepp, Aloysius F.

1990-01-01

The near-edge structure (XANES) of the Au L3 and Cu K edges of YBa2Au(0.3)Cu(2.7)O(7-delta) was studied. X ray diffraction suggests that Au goes on the Cu(1) site and XANES shows that this has little effect on the oxidation state of the remaining copper. The gold L3 edge develops a white line feature whose position lies between that of trivalent gold oxide (Au2O3) and monovalent potassium gold cyanide (KAu(CN)2) and whose intensity relative to the edge step is smaller than in the two reference compounds. The L3 EXAFS for Au in the superconductor resembles that of Au2O3. However, differences in the envelope of the Fourier filtered component for the first shell suggest that the local structure of the Au in the superconductor is not equivalent to Au2O3.

Superconductor-to-insulator transition and transport properties of underdoped YBa2Cu3O(y) crystals.

PubMed

Semba, K; Matsuda, A

2001-01-15

The carrier-concentration-driven superconductor-to-insulator (SI) transition as well as transport properties in underdoped YBa2Cu3O(y) twinned crystals is studied. The SI transition takes place at y approximately 6.3, carrier concentration n(SI)H approximately 3x10(20) cm(-3), anisotropy rho(c)/rho(ab) approximately 10(3), and the threshold resistivity rho(SI)ab approximately 0.8 mOmega cm which corresponds to a critical sheet resistance h/4e2 approximately 6.5 kOmega per CuO2 bilayer. The evolution of a carrier, nH infiniti y - 6.2, is clearly observed in the underdoped region. The resistivity and Hall coefficient abruptly acquire strong temperature dependence at y approximately 6.5 indicating a radical change in the electronic state.

Processing-property relations in YBa2Cu3O(6+x) superconductors

NASA Astrophysics Data System (ADS)

Safari, A.; Wachtman, J. B., Jr.; Parkhe, V.; Caracciolo, R.; Jeter, D.

Processing of YBa2Cu3O(6+x) superconducting samples by employing different precursor powder preparation techniques such as ball milling, attrition milling, and narrow particle size distribution powder preparation through coprecipitation by spraying will be discussed. CuO coated with oxalates shows the lowest resistance above Tc up to room temperature. The extent of corrosion by water has been studied by employing magnetic susceptibility, XPS, and X-ray diffraction. Superconducting samples are affected to a considerable extent when treated in water at 60 C and the severity of the attack increases with time.

Novel configuration of processing bulk textured YB 2Cu 3O 7-x superconductor by seeded infiltration growth method

NASA Astrophysics Data System (ADS)

Cao, Haitao; Moutalbi, Nahed; Harnois, Christelle; Hu, Rui; Li, Jinshan; Zhou, Lian; Noudem, Jacques G.

2010-01-01

Mono-domain YBa 2Cu 3O 7-x (Y123) bulk superconductors have been processed using seeded infiltration growth technique (SIG). The combination of melt infiltrated liquid source (Ba 3Cu 5O 8) into the Y 2BaCuO 5 (Y211) pre-form and the nucleation of Y123 domain from SmBa 2Cu 3O 7 crystal seed has been investigated. The different configurations of SIG process were compared in this study. In addition, the effect of the starting Y211 particles size has been studied. The results reveal that, the Y211 particle size and different configurations strongly influence the properties of the final bulk superconductor sample.

Evidence for three-dimensional XY critical properties in underdoped YBa2Cu3O7-δ

NASA Astrophysics Data System (ADS)

Schneider, T.

2007-05-01

We perform a detailed analysis of the reversible magnetization data of Salem-Sugui and Babíc of underdoped and optimally doped YBa2Cu3O7-δ single crystals. Near the zero field transition temperature we observe extended consistency with the properties of the three-dimensional XY universality class, even though the attained critical regime is limited by an inhomogeneity induced finite size effect. Nevertheless, as Tc falls from 93.5to41.5K , the critical amplitude of the in-plane correlation length ξab0 , the anisotropy γ=ξab0/ξc0 and the critical amplitude of the in-plane penetration depth λab0 increase substantially, while the critical amplitude of the c -axis correlation length ξc0 does not change much. As a consequence, the correlation volume Vcorr- increases and the critical amplitude of the specific heat singularity A- decreases dramatically, while the rise of λab0 reflects the behavior of the zero temperature counterpart. Conversely, although ξab0 and λab0 increase with reduced Tc , the ratio λab0/ξab0- , corresponding to the Ginzburg-Landau parameter κab , decreases substantially and YBa2Cu3O7-δ crosses over from an extreme to a weak type-II superconductor.

Study of photoirradiation for YBa 2Cu 3O 6+ x compounds and the electron structure by positron experiment

NASA Astrophysics Data System (ADS)

Guosheng, Cheng; Jiaxiang, Shang; Xigui, Li; xianqi, Dai; Xizhong, Wang; Jincang, Zhang

1997-08-01

We present positron lifetime data of YBa 2Cu 3O 6+ x (x=0.92, 0.43) compounds for different photo-irradiation time. It is given that change of the local electron density and vacancy concentration with photoirradiation time. It is found that there is transform at the electronic structure of CuO chains. We also have discussed the effect of photoirradiations time on the electronic structure of YBa 2Cu 3O 6+ x systems and their charge reservoir layer and CuO 2 plane conduction.layer. The positron experimental results support the model of photoinduced oxygen-diffusion mechanism.

Observation of a three-dimensional quasi-long-range electronic supermodulation in YBa 2Cu 3O 7-x/La 0.7Ca 0.3MnO 3 heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Junfeng; Shafer, Padraic; Mion, Thomas R.

Recent developments in high-temperature superconductivity highlight a generic tendency of the cuprates to develop competing electronic (charge) supermodulations. While coupled with the lattice and showing different characteristics in different materials, these supermodulations themselves are generally conceived to be quasi-two-dimensional, residing mainly in individual CuO 2 planes, and poorly correlated along the c axis. Here we observed with resonant elastic X-ray scattering a distinct type of electronic supermodulation in YBa 2Cu 3O 7–x (YBCO) thin films grown epitaxially on La 0.7Ca 0.3MnO 3 (LCMO). This supermodulation has a periodicity nearly commensurate with four lattice constants in-plane, eight out of plane, withmore » long correlation lengths in three dimensions. It sets in far above the superconducting transition temperature and competes with superconductivity below this temperature for electronic states predominantly in the CuO 2 plane. Our finding sheds light on the nature of charge ordering in cuprates as well as a reported long-range proximity effect between superconductivity and ferromagnetism in YBCO/LCMO heterostructures.« less

Observation of a three-dimensional quasi-long-range electronic supermodulation in YBa 2Cu 3O 7-x/La 0.7Ca 0.3MnO 3 heterostructures

DOE PAGES

He, Junfeng; Shafer, Padraic; Mion, Thomas R.; ...

2016-03-01

Recent developments in high-temperature superconductivity highlight a generic tendency of the cuprates to develop competing electronic (charge) supermodulations. While coupled with the lattice and showing different characteristics in different materials, these supermodulations themselves are generally conceived to be quasi-two-dimensional, residing mainly in individual CuO 2 planes, and poorly correlated along the c axis. Here we observed with resonant elastic X-ray scattering a distinct type of electronic supermodulation in YBa 2Cu 3O 7–x (YBCO) thin films grown epitaxially on La 0.7Ca 0.3MnO 3 (LCMO). This supermodulation has a periodicity nearly commensurate with four lattice constants in-plane, eight out of plane, withmore » long correlation lengths in three dimensions. It sets in far above the superconducting transition temperature and competes with superconductivity below this temperature for electronic states predominantly in the CuO 2 plane. Our finding sheds light on the nature of charge ordering in cuprates as well as a reported long-range proximity effect between superconductivity and ferromagnetism in YBCO/LCMO heterostructures.« less

RAPID COMMUNICATION: Large-area uniform ultrahigh-Jc YBa2Cu3O7-x film fabricated by the metalorganic deposition method using trifluoroacetates

NASA Astrophysics Data System (ADS)

Araki, Takeshi; Yamagiwa, Katsuya; Hirabayashi, Izumi; Suzuki, Katsumi; Tanaka, Shoji

2001-07-01

Ultrahigh-Jc YBa2Cu3O7-x (YBCO) films have been successfully fabricated by the metalorganic deposition method using a trifluoroacetate coating solution which is prepared by a newly developed purification technique, the solvent-into-gel (SIG) method. The prepared pure coating solution has less than 0.25% impurities and has a wide flexibility in process conditions to obtain high-Jc YBCO film. Using this feature, we have successfully formed 50 mm diameter YBCO films, which have a critical current density over 10 MA cm-2 (77 K, 0 T) on LaAlO3 single crystalline substrates.

Improved epitaxial texture of thick YBa2Cu3O7-δ/GdBa2Cu3O7-δ films with periodic stress releasing

NASA Astrophysics Data System (ADS)

Lin, Jianxin; Yang, Wentao; Gu, Zhaohui; Shu, Gangqiang; Li, Minjuan; Sang, Lina; Guo, Yanqun; Liu, Zhiyong; Cai, Chuanbing

2015-04-01

Thick high-Tc superconducting films consisting of a YBa2Cu3O7-δ/GdBa2Cu3O7-δ periodic architecture are developed on oxid-buffered Hastelloy tapes using a pulsed laser deposition process. It is revealed that multilayer intermittent structures for superconducting layers are effective to avoid the presence of a-axis grains and microcracks that occur with increasing thickness, which are frequently observed in monolayer films of REBa2Cu3O7-δ (RE = Y, Gd, or other rare earths), such grains and cracks being the significant challenge for obtaining high critical current in coated conductors. Presently, the thicknesses of multilayer films vary from 0.5 μm to 3 μm and, based on the SEM images and x-ray φ-scans, hardly show the influences on the microstructures and grain orientation of the c-axis. Also, the characteristic Raman spectrum patterns and their shifting with increasing the thickness of YBCO/GdBCO imply that the superior texture is obtained due to the evolution of stress dominated by the compressive stress rather than tensile stress.

Self-adjusted flux for the traveling solvent floating zone growth of YBaCuFeO5 crystal

NASA Astrophysics Data System (ADS)

Lai, Yen-Chung; Shu, Guo-Jiun; Chen, Wei-Tin; Du, Chao-Hung; Chou, Fang-Cheng

2015-03-01

A modified traveling solvent floating zone (TSFZ) technique was used to successfully grow a large size and high quality single crystal of multiferroic material YBaCuFeO5. This modified TSFZ growth uses a stoichiometric feed rod and pure copper oxide as the initial flux without prior knowledge of the complex phase diagram involving four elements, and the optimal flux for the growth of incongruently melt crystal is self-adjusted after a prolonged stable pulling. The wetting of the feed rod edge that often perturbs the molten zone stability was avoided by adding 2 wt% B2O3. The optimal flux concentration for the YBaCuFeO5 growth can be extracted to be near YBaCuFeO5:CuO=13:87 in molar ratio. The crystal quality was confirmed by the satisfactory refinement of crystal structure of space group P4mm and the two consecutive anisotropic antiferromagnetic phase transitions near 455 K and 170 K.

Single domain YBa2Cu3Oy thick films on metallic substrates

NASA Astrophysics Data System (ADS)

Reddy, E. S.; Noudem, J. G.; Goodilin, E. A.; Tarka, M.; Schmitz, G. J.

2003-03-01

The fabrication of single domain YBa2Cu3Oy (123) thick films (10-100 mum) on metallic substrates is reported. The process involves the formation of the 123 phase by a peritectic reaction between an air-brushed dense Y2BaCuO5 (211) layer on a Ag12Pd substrate and infiltrated liquid phases containing barium cuprates and copper oxides. Single domain growth is achieved by seeding the green films with a c-axis oriented NdBa2Cu3Oy crystal prior to processing. The maximum processing temperatures are lowered to 970 °C by modifying the characteristics of the liquid phases meant for infiltration by addition of Ag powder. The fabrication technique, processing conditions for single domain growth and the resulting microstructures are discussed.

Formation of high-Tc YBa2Cu3O(7-delta) films on Y2BaCuO5 substrate

NASA Astrophysics Data System (ADS)

Wang, W. N.; Lu, H. B.; Lin, W. J.; Yao, P. C.; Hsu, H. E.

1988-07-01

High-Tc superconducting YBa2Cu3O(7-delta) films have been successfully prepared on green Y2BaCuO5 (2115) ceramic substrate. The films have been formed by RF sputtering and screen printing with post annealing at 925 C. Regarding superconducting features, the sharp resistivity drop with Tc onset around 95 K (midpoint 84 K) and 99 K (midpoint 89 K) has been observed for RF sputtered and printed films respectively. Both films show the excellent adhesion towards the 2115 substrate. Powder X-ray diffraction profiles indicate a majority of 1237 phase with preferred orientation for RF sputtered thin film.

Disorder-controlled superconductivity at YBa2Cu3O7/SrTiO3 interfaces

NASA Astrophysics Data System (ADS)

Garcia-Barriocanal, J.; Perez-Muñoz, A. M.; Sefrioui, Z.; Arias, D.; Varela, M.; Leon, C.; Pennycook, S. J.; Santamaria, J.

2013-06-01

We examine the effect of interface disorder in suppressing superconductivity in coherently grown ultrathin YBa2Cu3O7 (YBCO) layers on SrTiO3 (STO) in YBCO/STO superlattices. The termination plane of the STO is TiO2 and the CuO chains are missing at the interface. Disorder (steps) at the STO interface cause alterations of the stacking sequence of the intracell YBCO atomic layers. Stacking faults give rise to antiphase boundaries which break the continuity of the CuO2 planes and depress superconductivity. We show that superconductivity is directly controlled by interface disorder outlining the importance of pair breaking and localization by disorder in ultrathin layers.

Uncovering a new quasi-2D CuO2 plane between the YBa2Cu3O7 and CeO2 buffer layer of coated conductors

NASA Astrophysics Data System (ADS)

Li, Zhi-Xin; Cao, Jin-Jin; Gou, Xiao-Fan; Wang, Tian-Ge; Xue, Feng

2018-01-01

We report a discovery of the quasi-two-dimensional (quasi-2D) CuO2 plane between the superconductor YBa2Cu3O7 (YBCO) and CeO2 buffer layer (mostly used in the fabrication) of coated conductors through the atomistic computer simulations with the molecular dynamics (MD) and first-principle calculations. For an YBCO coated conductor with multilayer structures, the buffer layers deposited onto a substrate are mainly considered to transfer a strong biaxial texture from the substrate to the YBCO layer. To deeply understand the tuning mechanism of the texture transfer, exploring the complete atomic-level picture of the structure between the YBa2Cu3O7/CeO2 interfaces is firstly required. However, the related observation data have not been available due to some big challenges of experimental techniques. With the MD simulations, having tested the accuracy of the potential functions for the YBa2Cu3O7/CeO2 interface, we constructed a total of 54 possible atom stacking models of the interface and identified its most appropriate and stable structure according to the criterion of the interface adhesion energy and the coherent characterization. To further verify the stability of the identified structure, we performed the first-principle calculations to obtain the adhesion energy and developed the general knowledge of the interface structure. Finally, a coherent interface formed with a new built quasi-2D CuO2 plane that is structurally similar to the CuO2 plane inside bulk YBCO was determined.

Calorimetric determination of the magnetic phase diagram of underdoped ortho II YBa2Cu3O6.54 single crystals

PubMed Central

Marcenat, C.; Demuer, A.; Beauvois, K.; Michon, B.; Grockowiak, A.; Liang, R.; Hardy, W.; Bonn, D. A.; Klein, T.

2015-01-01

The recent discovery of a charge order in underdoped YBa2Cu3Oy raised the question of the interplay between superconductivity and this competing phase. Understanding the normal state of high-temperature superconductors is now an essential step towards the description of the pairing mechanism in those materials and determining the upper critical field is therefore of fundamental importance. We present here a calorimetric determination of the field–temperature phase diagram in underdoped YBa2Cu3Oy single crystals. We show that the specific heat saturates in high magnetic fields. This saturation is consistent with a normal state without any significant superconducting contribution and a total Sommerfeld coefficient γN∼6.5±1.5 mJ mol−1 K−2 putting strong constraints on the theoretical models for the Fermi surface reconstruction. PMID:26294047

Fluctuation-induced conductivity in melt-textured Pr-doped YBa2Cu3O7-δ composite superconductor

NASA Astrophysics Data System (ADS)

Opata, Yuri Aparecido; Monteiro, João Frederico Haas Leandro; Siqueira, Ezequiel Costa; Rodrigues, Pedro Júnior; Jurelo, Alcione Roberto

2018-04-01

In this study, the effects of thermal fluctuations on the electrical conductivity in melt-textured YBa2Cu3O7-δ, Y0.95Pr0.05Ba2Cu3O7-δ and (YBa2Cu3O7-δ)0.95-(PrBa2Cu3O7-δ)0.05 composite superconductor were considered. The composite superconductor samples were prepared through the top seeding method using melt-textured NdBa2Cu3O7-d seeds. The resistivity measurements were performed with a low-frequency, low-current AC technique in order to extract the temperature derivative and analyze the influence of the praseodymium ion on the normal superconductor transition and consequently on the fluctuation regimes. The results show that the resistive transition is a two-step process. In the normal phase, above the critical temperature, Gaussian and critical fluctuation regimes were identified, while below the critical temperature, in the regime near the approach to the zero-resistance state, the fluctuation conductivity diverges as expected in a paracoherent-coherent transition.

Effect of high pressure on the electrical resistivity of optimally doped YBa2Cu3O7-δ single crystals with unidirectional planar defects

NASA Astrophysics Data System (ADS)

Vovk, R. V.; Vovk, N. R.; Khadzhai, G. Ya.; Goulatis, I. L.; Chroneos, A.

2013-08-01

In the present work the effect of hydrostatic pressure up to 10 kbar on in-plane electrical resistivity of well-structured YBa2Cu3O7-δ (δ<0.15, Тс≈91 K, ΔТс≈0.3 K) single crystals was investigated. The influence of the twin boundaries on the electrical resistivity was minimized. The resistivities temperature dependences in the interval Тс up to 300 K can be approximated by taking into account the linear term at high temperatures and the fluctuation conductivity (Maki-Thompson model) near Тс. The parameters of the linear dependence of R(T) are decreasing as the pressure is increasing. Тс increases linearly when the pressure increases with the derivative dTc/dP≈0.080 K/kbar. Among the Maki-Thompson model parameters the inter-layer distance, d, can be considered to be independent from pressure, the transverse coherence length, ξc(0)∼0.1d.

Shaping and reinforcement of melt textured YBa2Cu3O7-δ superconductors

NASA Astrophysics Data System (ADS)

Meslin, S.; Harnois, C.; Chubilleau, C.; Horvath, D.; Grossin, D.; Suddhakar, E. R.; Noudem, J. G.

2006-07-01

From porous Y2BaCuO5 (Y211) with various grain sizes, single domain ceramic composites YBa2Cu3Oy/Y2BaCuO5 have been prepared by combination of the infiltration and top seed growth (ITSG) process. In addition, perforated Y123 has been prepared from Y211 by the ITSG method in order to magnify the specific surface and then increase oxygen diffusion into the core of the material. Magnetic and electrical properties were determined and correlate well with the microstructure of the composites and were compared to the conventional doped or undoped YBa2Cu3Oy (Y123). From magnetic measurements, high critical current densities, Jc, of 86 000 A cm-2 have been measured. Transport Jc values higher than 10 600 A cm-2 are reached at 77 K and 0 T, corresponding to the nominal critical currents of 325 A injected reproducibly through sections less than 3.082 mm2. This confirms the high quality of single domains obtained with a well controlled ITSG process. On the other hand, the perforated samples were reinforced using resin impregnation and the flux mapping has been investigated.

Characteristics of YBa2Cu3O7 high-Tc superconductor with KCl

NASA Astrophysics Data System (ADS)

Yoon, Ki Hyun; Chang, Sung Sik

1990-03-01

The lattice parameters, microstructural change, transition temperature, and electrical properties of the YBa2-xKxCu3O7 high-Tc superconductor in the range from x=0 to x=0.25 have been investigated. The high-Tc orthorhombic phase increases with increasing KCl up to x=0.20, above which it decreases. The lattice parameters decrease with increasing KCl up to x=0.10, and then become nearly uniform. The grain size increases with increasing KCl up to x=0.20 due to its role as sintering agent. The specimens with x=0.2 have transition temperatures of 96 K and high magnetic susceptibility due to the contraction of lattice parameters a and b and the increase of orthorhombic distortion.

Laser ablated high T(sub c) superconducting thin YBa2Cu3O(7-x) films on substrates suitable for microwave applications

NASA Astrophysics Data System (ADS)

Warner, J. D.; Meola, J. E.; Jenkins, K. A.; Bhasin, K. B.

1990-04-01

The development of high temperature superconducting YBa2Cu3O(7-x) thin films on substrates suitable for microwave applications is of great interest for evaluating their applications for space radar, communication, and sensor systems. Thin films of YBa2Cu3O(7-x) were formed on SrTiO3, ZrO2, MgO, and LaAlO3 substrates by laser ablation. The wavelength used was 248 nm from a KrF excimer laser. During deposition the films were heated to 600 C in a flowing oxygen environment, and required no post annealing. The low substrate temperature during deposition with no post annealing gave films which were smooth, which had their c-axis aligned to the substrates, and which had grains ranging from 0.2 to 0.5 microns in size. The films being c-axis aligned gave excellent surface resistance at 35 GHz which was lower than that of copper at 77 K. At present, LaAlO3 substrates with a dielectric constant of 22, appears suitable as a substrate for microwave and electronic applications. The films were characterized by resistance-temperature measurements, scanning electron microscopy, and x ray diffraction. The highest critical transition temperatures (T sub c) are above 89 K for films on SrTiO3 and LaAlO3, above 88 K for ZrO2, and above 86 K for MgO. The critical current density (J sub c) of the films on SrTiO3 is above 2 x 10(exp 6) amperes/sq cm at 77 K. The T(sub c) and J(sub c) are reported as a function of laser power, composition of the substrate, and temperature of the substrate during deposition.

COEXISTENCE OF DIFFERENT TYPES OF TRANSVERSE CONDUCTIVITY IN Y1-xPrxBa2Cu3 O7-δ SINGLE CRYSTALS WITH DIFFERENT PRASEODYMIUM CONCENTRATIONS

NASA Astrophysics Data System (ADS)

Vovk, R. V.; Vovk, N. R.; Goulatis, I. L.; Chroneos, A.

2013-10-01

In this paper, the influence of praseodymium doping on the conductivity across (transverse) the basal plane of high-temperature superconducting Y1-xPrxBa2Cu3O7-δ single crystals is investigated. It is determined that an increase of praseodymium doping leads to increased localization effects and the implementation of a metal-insulator transition Y1-xPrxBa2Cu3O7-δ, which always precedes the superconducting transition. The increase of the praseodymium concentration also leads to a significant displacement of the point of the metal-insulator transition to the low temperature region.

Effects of oxygen stoichiometry on the scaling behaviors of YBa{sub 2}Cu{sub 3}O{sub x} grain boundary weak-links

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, K.H.; Fu, C.M.; Jeng, W.J.

1994-12-31

The effects of oxygen stoichiometry on the transport properties of the pulsed laser deposited YBa{sub 2}Cu{sub 3}O{sub x} bicrystalline grain boundary weak-link junctions were studied. It is found that not only the cross boundary resistive transition foot structure can be manipulated repeatedly with oxygen annealling processes but the junction behaviors are also altered in accordance. In the fully oxygenated state i.e. with x=7.0 in YBa{sub 2}Cu{sub 3}O{sub x} stoichiometry, the junction critical current exhibits a power of 2 scaling behavior with temperature. In contrast, when annealed in the conditions of oxygen-deficient state (e.g. with x=6.9 in YBa{sub 2}Cu{sub 3}O{sub x}more » stoichiometry) the junction critical current switches to a linear temperature dependence behavior. The results are tentatively attributed to the modification of the structure in the boundary area upon oxygen annealing, which, in turn, will affect the effective dimension of the geometrically constrained weak-link bridges. The detailed discussion on the responsible physical mechanisms as well as the implications of the present results on device applications will be given.« less

La0.7Sr0.3MnO3: A single, conductive-oxide buffer layer for the development of YBa2Cu3O7-δ coated conductors

NASA Astrophysics Data System (ADS)

Aytug, T.; Paranthaman, M.; Kang, B. W.; Sathyamurthy, S.; Goyal, A.; Christen, D. K.

2001-10-01

Coated conductor applications in power technologies require stabilization of the high-temperature superconducting (HTS) layers against thermal runaway. Conductive La0.7Sr0.3MnO3 (LSMO) has been epitaxially grown on biaxially textured Ni substrates as a single buffer layer. The subsequent epitaxial growth of YBa2Cu3O7-δ (YBCO) coatings by pulsed laser deposition yielded self-field critical current densities (Jc) of 0.5×106A/cm2 at 77 K, and provided good electrical connectivity over the entire structure (HTS+conductive-buffer+metal substrate). Property characterizations of YBCO/LSMO/Ni architecture revealed excellent crystallographic and morphological properties. These results have demonstrated that LSMO, used as a single, conductive buffer layer, may offer potential for use in fully stabilized YBCO coated conductors.

Fabrication of Large Domain YBa2Cu3O(x) for Magnetic Suspension Applications

NASA Technical Reports Server (NTRS)

Sengupta, S.; Corpus, J.; Gaines, J. R., Jr.; Todt, V. R.; Zhang, X.; Miller, D. J.

1996-01-01

Large domain YBa2Cu3O(x) levitators have been fabricated using a seeded melt processing technique. Depending upon the seed, either a single or five domained sample can be obtained. The grain boundaries separating each domains in the five domain levitator are found to be 90 degrees. Similar levitation forces can be observed for single and five domained samples. After thermal cycling, however, a small decrease in the levitation force of the five domain levitator was observed as a function of thermal cycles while nearly no change in force was observed in the single domain levitator. Finally, it is shown that both, single and five domain YBCO, behave similarly as a function of sample thickness.

Phase compatibilities of YBa2Cu3O(9-delta) type structure in quintenary systems Y-Ba-Cu-O-X (impurity)

NASA Technical Reports Server (NTRS)

Karen, P.; Fjellvag, H.; Kjekshus, A.

1990-01-01

Electrical transport properties of the oxidic high T(sub c) superconductors are significantly affected by the presence of minor amounts of various elements adventing as impurities, e.g., from the chemical environment during manufacturing. YBa2Cu3O(9-delta) is prone to an extinction of the superconductivity on (partial) substitution of all four elemental components. E.g., Pr (for Y), La (for Ba), Zn (for Cu) or peroxygroup (for O) substituents will alter some of the superconductivity preconditions, like mixed valence state in Cu3O7/O(9-delta) network or structural distortion of the network. Although various pseudoternary chemical equilibrium phase diagrams of the Y(O)-Ba(O)-Cu(O) system now are available, no consensus is generally shown, however, this is partly due to lack of compatible definitions of the equilibrium conditions. Less information is available about the phase compatibilities in the appropriate quaternary phase diagram (including oxygen) and virtually no information exists about any pentenary phase diagrams (including one impurity). Unfortunately, complexity of such systems, stemming both from number of quaternary or pentenary compounds and from visualizing the five-component phase system, limits this presentation to more or less close surroundings of the YBa2Cu3O(9-delta) type phase in appropriate pseudoquaternary or pseudopseudoternary diagrams, involving Y-Ba-Cu and O, O-CO2, alkaline metals, Mg and alkaline earths, and Sc and most of the 3-d and 4-f elements. The systems were investigated by means of x ray diffraction, neutron diffraction and chemical analytical methods on samples prepared by sol-gel technique from citrates. The superconductivity was characterized by measuring the diamagnetic susceptibility by SQUID.

Magnetoresistivity of thin YBa2Cu3O7-δ films on sapphire substrate

NASA Astrophysics Data System (ADS)

Probst, Petra; Il'in, Konstantin; Engel, Andreas; Semenov, Alexei; Hübers, Heinz-Wilhelm; Hänisch, Jens; Holzapfel, Bernhardt; Siegel, Michael

2012-09-01

Magnetoresistivity of YBa2Cu3O7-δ films with thicknesses between 7 and 100 nm deposited on CeO2 and PrBa2Cu3O7-δ buffer layers on sapphire substrate has been measured to analyze the temperature dependence of the second critical magnetic field Bc2. To define Bc2, the mean-field transition temperature Tc was evaluated by fitting the resistive transition in zero magnetic field with the fluctuation conductivity theory of Aslamazov and Larkin. At T → Tc the Bc2(T) dependence shows a crossover from downturn to upturn curvature with the increase in film thickness.

Ten Ghz YBa2Cu3O(7-Delta) Superconducting Ring Resonators on NdGaO3 Substrates

NASA Technical Reports Server (NTRS)

To, H. Y.; Valco, G. J.; Bhasin, K. B.

1993-01-01

YBa2Cu3O(7-delta) thin films were formed on NdGaO3 substrates by laser ablation. Critical temperatures greater than 89 K and critical current densities exceeding 2 x 10(exp 8) Acm(sub -2) at 77 K were obtained. The microwave performance of films patterned into microstrip ring resonators with gold ground planes was measured. An unloaded quality factor six times larger than that of a gold resonator of identical geometry was achieved. The unloaded quality factor decreased below 70 K for both the superconducting and gold resonators due to increasing dielectric losses in the substrate. The temperature dependence of the loss tangent of NdGaO3 was extracted from the measurements.

YBa_2Cu_3O_{7-δ} : in pursuit of the ideal microstructure

NASA Astrophysics Data System (ADS)

Smith, D. S.; Suasmoro, S.; Lejeune, M.; Rabier, J.; Denanot, M. F.; Heintz, J. M.; Magro, C.; Bonnet, J. P.

1992-02-01

This paper examines the role of different factors in the microstructure of ceramic YBa2Cu3O{7-δ} with emphasis on its electrical response. In particular we discuss : 1. the effect of microstructural variations on j_c and ρ_{300}, 2. measurement of j_c, 3. the presence of minor phases and carbonates, 4. oxygen uptake and microcracks, 5. plastic deformation and related structural defects. Dans cet article, nous examinons d'une part la réponse électrique de céramiques supraconductrices massives de type YBa2Cu3O{7-δ} et d'autre part sa relation avec la microstructure. Nous présenterons successivement : 1. L'incidence de modifications microstructurales sur les valeurs de j_c et ρ_{300}, 2. les mesures expérimentales de j_c, 3. la présence de phases minoritaires et de carbonates, 4. la reprise d'oxygène et la microfissuration, 5. la déformation plastique et les défauts structuraux associés.

TOPICAL REVIEW: Importance of low-angle grain boundaries in YBa2Cu3O7-δ coated conductors

NASA Astrophysics Data System (ADS)

Durrell, J. H.; Rutter, N. A.

2009-01-01

Over the past ten years the perception of grain boundaries in YBa2Cu3O7-δ conductors has changed greatly. They are now not a problem to be eliminated, but an inevitable and potentially favourable part of the material. This change has arisen as a consequence of new manufacturing techniques which result in excellent grain alignment, reducing the spread of grain boundary misorientation angles. At the same time there is considerable recent evidence which indicates that the variation of properties of grain boundaries with mismatch angle is more complex than a simple exponential decrease in critical current. This is due to the fact that low-angle grain boundaries represent a qualitatively different system to high-angle boundaries. The time is therefore right for a targeted review of research into low-angle YBa2Cu3O7-δ grain boundaries. This article does not purport to be a comprehensive review of the physics of grain boundaries as found in YBa2Cu3O7-δ in general; for a broader overview we would recommend that the reader consult the comprehensive review of Hilgenkamp and Mannhart (2002 Rev. Mod. Phys. 74 485). The purpose of this article is to review the origin and properties of the low-angle grain boundaries found in YBa2Cu3O7-δ coated conductors both individually and as a collective system.

Preparation, Iodometric Analysis, and Classroom Demonstration of Superconductivity in YBa2Cu3O8-x.

ERIC Educational Resources Information Center

Harris, Daniel C.; And Others

1987-01-01

Described is a student preparation of YBa2Cu3O8-x, a classroom demonstration of its superconductivity, and an analytical chemistry experiment dealing with the oxidation state of copper in the material. (RH)

Magnetic flux relaxation in YBa2Cu3)(7-x) thin film: Thermal or athermal

NASA Technical Reports Server (NTRS)

Vitta, Satish; Stan, M. A.; Warner, J. D.; Alterovitz, S. A.

1991-01-01

The magnetic flux relaxation behavior of YBa2Cu3O(7-x) thin film on LaAlO3 for H is parallel to c was studied in the range 4.2 - 40 K and 0.2 - 1.0 T. Both the normalized flux relaxation rate S and the net flux pinning energy U increase continuously from 1.3 x 10(exp -2) to 3.0 x 10(exp -2) and from 70 to 240 meV respectively, as the temperature T increases from 10 to 40 K. This behavior is consistent with the thermally activated flux motion model. At low temperatures, however, S is found to decrease much more slowly as compared with kT, in contradiction to the thermal activation model. This behavior is discussed in terms of the athermal quantum tunneling of flux lines. The magnetic field dependence of U, however, is not completely understood.

Studies of iron impurities in YxPr1-xBa2Cu3O7-delta

NASA Technical Reports Server (NTRS)

Swartzendruber, L. J.; Bennett, L. H.; Ritter, J.; Rubinstein, M.; Harford, M. Z.

1990-01-01

Pr is the only rare earth which, when substituted for Y in YBa2Cu3O7, significantly alters the superconducting transition temperature T(sub c) without changing the crystal structure. For YxPr1-xBa2Cu3O7-delta with delta approx. equal to 0, T(sub c) is reduced rapidly as x is increased, reaching zero for x about 0.5. For x above 0.5 the compound is antiferromagnetic with a Neel temperature that increases with increasing x, rising to above room temperature for x near 1. A similar behavior is observed when the oxygen deficit delta is increased from zero to 1 with x=0. For the case of Pr substitution, the drop in T(sub c) is believed due to magnetic interactions. For the case of varying delta with x=0, the drop can be attributed to a combination of magnetic interactions, band filling, and changes in crystal structure. To study these effects, the Mossbauer effect of 57 Fe atoms substituted for the Cu atoms has been observed as a function of delta, x, and temperature. The observed spectra are all well described by a two quadrupole-split pairs, a central singlet, and a six-line magnetic hyperfine field pattern. For several Pr compositions both delta and temperature were varied, and the results support the hypothesis that a magnetic interaction exists between the Fe in the Cu lattice and the substitutional Pr atoms.

Influence of calcium on transport properties, band spectrum and superconductivity of YBa2Cu3O(y) and YBa(1.5)La(0.5)Cu3O(y)

NASA Technical Reports Server (NTRS)

Gasumyants, V. E.; Vladimirskaya, E. V.; Patrina, I. B.

1995-01-01

The comparative investigation of transport phenomena in Y(1-x)Ca(x)Ba2Cu3O(y) (0 is less than x is less than 0.25; 6.96 is greater than y is greater than 6.87 and 6.73 is less than x is less than 6.53); Y(1-x)Ca(x)Ba(1.5)La(0.5)Cu3O(y) (0 is less than x is less than 0.5; 7.12 is greater than y is greater than 6.96) and YBa(2-x)La(x)Cu3O(y) (0 is less than x is less than 0.5; 6.95 is less than y is less than 7.21) systems have been carried out. The temperature dependencies of resistivity and thermopower have been measured. It was found that the S(T) dependencies take some additional features with Ca content increase. The results obtained have been analyzed on the basis of the phenomenological theory of electron transport in the case of the narrow conductive band. The main parameters of the band spectrum (the band filling with electrons degree and the total effective band width) have been determined. The dependencies of these from contents of substituting elements are discussed. Analyzing the results obtained simultaneously with the tendencies in oxygen content and critical temperature change we have confirmed the conclusion that the oxygen sublattice disordering has a determinant effect on band structure parameters and superconductive properties of YBa2Cu3O(y). The results obtained suggest that Ca gives rise to some peculiarities in band spectrum of this compound.

In operando evidence of deoxygenation in ionic liquid gating of YBa2Cu3O7-X

PubMed Central

Perez-Muñoz, Ana M.; Schio, Pedro; Poloni, Roberta; Fernandez-Martinez, Alejandro; Rivera-Calzada, Alberto; Salas-Colera, Eduardo; Kinney, Joseph; Leon, Carlos; Santamaria, Jacobo; Garcia-Barriocanal, Javier; Goldman, Allen M.

2017-01-01

Field-effect experiments on cuprates using ionic liquids have enabled the exploration of their rich phase diagrams [Leng X, et al. (2011) Phys Rev Lett 107(2):027001]. Conventional understanding of the electrostatic doping is in terms of modifications of the charge density to screen the electric field generated at the double layer. However, it has been recently reported that the suppression of the metal to insulator transition induced in VO2 by ionic liquid gating is due to oxygen vacancy formation rather than to electrostatic doping [Jeong J, et al. (2013) Science 339(6126):1402–1405]. These results underscore the debate on the true nature, electrostatic vs. electrochemical, of the doping of cuprates with ionic liquids. Here, we address the doping mechanism of the high-temperature superconductor YBa2Cu3O7-X (YBCO) by simultaneous ionic liquid gating and X-ray absorption experiments. Pronounced spectral changes are observed at the Cu K-edge concomitant with the superconductor-to-insulator transition, evidencing modification of the Cu coordination resulting from the deoxygenation of the CuO chains, as confirmed by first-principles density functional theory (DFT) simulations. Beyond providing evidence of the importance of chemical doping in electric double-layer (EDL) gating experiments with superconducting cuprates, our work shows that interfacing correlated oxides with ionic liquids enables a delicate control of oxygen content, paving the way to novel electrochemical concepts in future oxide electronics. PMID:28028236

In operando evidence of deoxygenation in ionic liquid gating of YBa2Cu3O7-X.

PubMed

Perez-Muñoz, Ana M; Schio, Pedro; Poloni, Roberta; Fernandez-Martinez, Alejandro; Rivera-Calzada, Alberto; Cezar, Julio C; Salas-Colera, Eduardo; Castro, German R; Kinney, Joseph; Leon, Carlos; Santamaria, Jacobo; Garcia-Barriocanal, Javier; Goldman, Allen M

2017-01-10

Field-effect experiments on cuprates using ionic liquids have enabled the exploration of their rich phase diagrams [Leng X, et al. (2011) Phys Rev Lett 107(2):027001]. Conventional understanding of the electrostatic doping is in terms of modifications of the charge density to screen the electric field generated at the double layer. However, it has been recently reported that the suppression of the metal to insulator transition induced in VO 2 by ionic liquid gating is due to oxygen vacancy formation rather than to electrostatic doping [Jeong J, et al. (2013) Science 339(6126):1402-1405]. These results underscore the debate on the true nature, electrostatic vs. electrochemical, of the doping of cuprates with ionic liquids. Here, we address the doping mechanism of the high-temperature superconductor YBa 2 Cu 3 O 7-X (YBCO) by simultaneous ionic liquid gating and X-ray absorption experiments. Pronounced spectral changes are observed at the Cu K-edge concomitant with the superconductor-to-insulator transition, evidencing modification of the Cu coordination resulting from the deoxygenation of the CuO chains, as confirmed by first-principles density functional theory (DFT) simulations. Beyond providing evidence of the importance of chemical doping in electric double-layer (EDL) gating experiments with superconducting cuprates, our work shows that interfacing correlated oxides with ionic liquids enables a delicate control of oxygen content, paving the way to novel electrochemical concepts in future oxide electronics.

The effect of fluctuations on the electrical transport behavior in YBa2Cu3O(7-x)

NASA Technical Reports Server (NTRS)

Vitta, Satish; Alterovitz, S. A.; Stan, M. A.

1993-01-01

The excess conductivity behavior of highly oriented YBa2Cu3O(7-x) thin films prepared by both coevaporation and laser ablation was studied in detail in the reduced-temperature range 9 x 10(exp -4) is less than t is less than 1. The excess conductivity in all the films studied was found to diverge sharply near T(sub c), in agreement with the conventional mean-field theory. However, the detailed temperature dependence could not be fitted to either the power-law or the logarithmic functional forms as predicted by the theory. The excess conductivity of all the films was found to be exponentially dependent on the temperature over nearly three decades for 9 x 10(exp -4) is less than t is less than 10(exp -1), in contradiction to the mean-field theory.

Preparation and Physical Properties of Segmented Thermoelectric YBa2Cu3O7-x -Ca3Co4O9 Ceramics

NASA Astrophysics Data System (ADS)

Wannasut, P.; Keawprak, N.; Jaiban, P.; Watcharapasorn, A.

2018-01-01

Segmented thermoelectric ceramics are now well known for their high conversion efficiency and are currently being investigated in both basic and applied energy researches. In this work, the successful preparation of the segmented thermoelectric YBa2Cu3O7-x -Ca3Co4O9 (YBCO-CCO) ceramic by hot pressing method and the study on its physical properties were presented. Under the optimum hot pressing condition of 800 °C temperature, 1-hour holding time and 1-ton weight, the segmented YBCO-CCO sample showed two strongly connected layers with the relative density of about 96%. The X-ray diffraction (XRD) patterns indicated that each segment showed pure phase corresponding to each respective composition. Scanning electron microscopy (SEM) results confirmed the sharp interface and good adhesion between YBCO and CCO layers. Although the chemical analysis indicated the limited inter-layer diffusion near the interface, some elemental diffusion at the boundary was expected to be the source of this strong bonding.

YBa2Cu307 superconducting microbolometer linear arrays

NASA Astrophysics Data System (ADS)

Johnson, Burgess R.; Ohnstein, Thomas R.; Marsh, Holly A.; Dunham, Scott B.; Kruse, Paul W.

1992-09-01

Single pixels and linear arrays of microbolometers employing the high-T(subscript c) superconductor YBa(subscript 2)Cu(subscript 3)O(subscript 7) have been fabricated by silicon micromachining techniques. The substrates are 3 in. diameter silicon wafers upon which buffer layers of Si(subscript 3)N(subscript 4) and yttria-stabilized zirconia (YSZ) have been deposited. The YBa(subscript 2)Cu(subscript 3)O(subscript 7) was deposited by ion beam sputtering upon the yttria-stabilized zirconia (YSZ), then photolithographically patterned into serpentines 4 micrometers wide. Anisotropic etching in KOH removed the silicon underlying each pixel, thereby providing the necessary thermal isolation. When operated at 70 degree(s)K with 1 (mu) A dc bias, the D(superscript *) is 7.5 X 10(superscript 8) cm Hz(superscript 1/2)/Watt with a thermal response time of 24 msec.

Levitation of YBa2Cu3O(7-x) superconductor in a variable magnetic field

NASA Technical Reports Server (NTRS)

Terentiev, Alexander N.; Kuznetsov, Anatoliy A.

1992-01-01

The influence of both a linear alternating and rotational magnetic field component on the levitation behavior of a YBa2Cu3O(7-x) superconductor was examined. The transition from a plastic regime of levitation to an elastic one, induced by an alternating field component, was observed. An elastic regime in contrast to a plastic one is characterized by the unique position of stable levitation and field frequency dependence of relaxation time to this position. It was concluded that the vibrations of a magnet levitated above the superconductor can induce a transition from a plastic regime of levitation to an elastic one. It was found that a rotational magnetic field component induced rotations of a levitated superconductor. Rotational frictional motion of flux lines is likely to be an origin of torque developed. A prototype of a motor based on a levitated superconductor rotor is proposed.

Artificial in-plane ordering of textured YBa2Cu3O(7-x) films deposited on polycrystalline yttria-stabilized zirconia substrates

NASA Astrophysics Data System (ADS)

Harshavardhan, K. S.; Rajeswari, M.; Hwang, D. M.; Chen, C. Y.; Sands, T. D.; Venkatesan, T.; Tkaczyk, J. E.; Lay, K. W.; Safari, A.; Johnson, L.

1992-12-01

Anisotropic surface texturing of the polycrystalline yttria-stabilized zirconia substrates, prior to YBa2Cu3O(7-x) film deposition, is shown to promote in-plane (basal plane) ordering of the film growth in addition to the c-axis texturing. The Jc's of the films in the weak-link-dominated low-field regime are enhanced considerably, and this result is attributed to the reduction of weak links resulting from a reduction in the number of in-plane large-angle grain boundaries.

Method of producing superconducting fibers of YBA2CU30X

DOEpatents

Schwartzkopf, Louis A.; Ostenson, Jerome E.; Finnemore, Douglas K.

1990-11-13

Fibers of YBa.sub.2 Cu.sub.3 O.sub.x have been produce by pendant drop melt extraction. This technique involves the end of a rod of YBa.sub.2 Cu.sub.3 O.sub.x melted with a hydrogen-oxygen torch, followed by lowering onto the edge of a spinning wheel. The fibers are up to 10 cm in length with the usual lateral dimensions, ranging from 20 .mu.m to 125 .mu.m. The fibers require a heat treatment to make them superconducting.

Elliptical flux vortices in YBa2Cu3O7

NASA Technical Reports Server (NTRS)

Hickman, H.; Dekker, A. J.; Chen, T. M.

1991-01-01

The most energetically favorable vortex in YBa2Cu3O7 forms perpendicular to an anisotropic plane. This vortex is elliptical in shape and is distinguished by an effective interchange of London penetration depths from one axis of the ellipse to another. By generalizing qualitatively from the isotropic to the anisotropic case, we suggest that the flux flow resistivity for the vortex that forms perpendicular to an anistropic plane should have a preferred direction. Similar reasoning indicates that the Kosterlitz-Thouless transition temperature for a vortex mediated transition should be lower if the vortex is elliptical in shape.

Modification of structural disorder by hydrostatic pressure in the superconducting cuprate YBa2Cu3O6.73

NASA Astrophysics Data System (ADS)

Huang, H.; Jang, H.; Fujita, M.; Nishizaki, T.; Lin, Y.; Wang, J.; Ying, J.; Smith, J. S.; Kenney-Benson, C.; Shen, G.; Mao, W. L.; Kao, C.-C.; Liu, Y.-J.; Lee, J.-S.

2018-05-01

Compelling efforts to improve the critical temperature (Tc) of superconductors have been made through high-pressure application. Understanding the underlying mechanism behind such improvements is critically important; however, much remains unclear. Here we studied ortho-III YBa2Cu3O6.73 (YBCO) using x-ray scattering under hydrostatic pressure (HP) up to ˜6.0 GPa . We found the reinforced oxygen order of YBCO under HP, revealing an oxygen rearrangement in the Cu-O layer, which evidently shows the charge-transfer phenomenon between the Cu O2 plane and Cu-O layer. Concurrently, we also observed no disorder-pinned charge-density-wave signature in Cu O2 plane under HP. This indicates that the oxygen rearrangement modifies the quenched disorder state in the Cu O2 plane. Using these results, we appropriately explain why pressure condition can achieve higher Tc compared with the optimal Tc under ambient pressure in YBa2Cu3O6 +x . As an implication of these results, finally we have discussed that the change in disorder could make it easier for YBa2Cu3O6 +x to undergo a transition to the nematic order under an external magnetic field.

Growth of single crystals, thermal dependency of lattice parameters and Raman scattering in the Nd 2- xCe xCuO 4- δ system

NASA Astrophysics Data System (ADS)

Sadowski, W.; Hagemann, H.; François, M.; Bill, H.; Peter, M.; Walker, E.; Yvon, K.

1990-09-01

We report on the growth of Nd 2- xCe xCuO 4- δ single crystals (0< x<0.2) from Cu 2O flux. Free separated crystals with maximum size of 5x8x0.15 nm 3 have been obtained. Magnetic AC susceptibility measurements show a sharp superconducting transition at temperatures up to 23 K. The temperature dependence of the lattice parameters has been measured by means of X-ray powder diffraction between 10 K ( a=3.9413(3) Å, c=12.0290(18) Å) and 290 K ( a=3.9482(3) Å, c=12.0590(18) Å). Room temperature Raman spectra reveal a new band at 320 cm -1 which is not observed in Nd 2CuO 4. Raman spectra of crystals with Tc ranging from 7 to 22 K show a systematic intensity change of the broad band at 590 cm -1.

Ultrasonic evaluation of oxidation and reduction effects on the elastic behavior and global microstructure of YBa2Cu3O7-x

NASA Technical Reports Server (NTRS)

Roth, Don J.; Deguire, Mark R.; Dolhert, Leonard E.

1991-01-01

Ultrasonic velocity measurement techniques were used to evaluate the effects of oxidation and reduction on the elastic properties, global microstructure and oxygen content of the YBa2Cu3O(7-x) ceramic superconductor for samples ranging from 70 to 90 pct. of theoretical density. Bulk density, velocity, and elastic modulus generally increased with increasing oxygen content upon oxidation, and this behavior was reversible. Velocity image patterns were similar after oxidation and reduction treatments for a 90 pct. dense sample, although the velocity value at any given point on the sample was changed following the treatments. The unchanging pattern correlated with destructive measurements showing that the spatial pore distribution (fraction and size) was not measurably altered after the treatments. Changes in superconducting behavior, crystal structure, and grain structure were observed consistent with changes in oxygen content.

Atomic layer epitaxy of YBaCuO for optoelectronic applications

NASA Technical Reports Server (NTRS)

Skogman, R. A.; Khan, M. A.; Van Hove, J. M.; Bhattarai, A.; Boord, W. T.

1992-01-01

An MOCVD-based atomic-layer epitaxy process is being developed as a potential solution to the problems of film-thickness and interface-abruptness control which are encountered when fabricating superconductor-insulator-superconductor devices using YBa2Cu3O(7-x). In initial studies, the atomic-layer MOCVD process yields superconducting YBa2Cu3O(7-x) films with substrate temperatures of 605 C during film growth, and no postdeposition anneal. The low temperature process yields a smooth film surface and can reduce interface degradation due to diffusion.

Electronic structures of the YBa2Cu3O7-x surface and its modification by sputtering and adatoms of Ti and Cu

NASA Astrophysics Data System (ADS)

Meyer, H. M., III; Hill, D. M.; Wagener, T. J.; Gao, Y.; Weaver, J. H.; Capone, D. W., II; Goretta, K. C.

1988-10-01

We present x-ray and inverse photoemission results for fractured surfaces of YBa2Cu3O6.9 before and after surface modification by Ar ion bombardment and the deposition of adatoms of Ti and Cu. Representative results are compared for samples prepared in three different ways. Two of the sample types exhibit substantial emission from grain-boundary phases because of both intergranular and transgranular fracture; they produce results that are very similar to those presented thus far in the literature. A third type was nearly free of contamination and clearly showed spectral features characteristic of the superconductor. Comparison of these nearly contamination-free valence-band results to those for clean La1.85Sr0.15CuO4 shows remarkably similar x-ray photoemission spectroscopy densities of states, with subtle differences near the Fermi level and at 3 eV. Inverse photoemission results show the top of the Cu-O hybrid orbitals to be 2 eV above EF and the empty states of Y and Ba at higher energy. Comparison with one-electron densities of states shows reasonable agreement, but there are large differences within the set of calculated results, and it is unclear from the valence bands alone how to account for final-state Cu d-d Coulomb correlation effects (satellite features show these effects very clearly). Argon sputtering for both types of samples shows destruction of the superconductor, with differences that can be related to sample surface quality. The deposition of adatoms of Ti and Cu results in reaction associated with oxygen withdrawal from the near-surface region. Studies of the Cu 2p3/2 line shape show that the deposition of as little as ~1 monolayer equivalent of Ti or Cu reduces the formal Cu2+ emission within the probed volume (30-50 Å deep). Core-level analysis shows that this chemical reduction of Cu is accompanied by crystal-structure modifications as well. Studies of Cu adatom interactions reveal the progression from Cu2+ to Cu1+ and ultimately, to Cu

Electron tunneling and the energy gap in Bi2Sr2CaCu2Ox

NASA Astrophysics Data System (ADS)

Lee, Mark; Mitzi, D. B.; Kapitulnik, A.; Beasley, M. R.

1989-01-01

Results of electron tunneling on single crystals of the Bi2Sr2CaCu2Ox superconductor are reported. The junctions show a gap structure with Δ~=25 meV, whose temperature dependence exhibits a qualitatively Bardeen-Cooper-Schrieffer-like behavior with a gap-closing Tc~=81-85 K. Comparisons of these tunneling spectra to those obtained on YBa2Cu3O7-x are made. Evidence that 2Δ/kTc~7 for both Ba2Sr2CaCu2Ox and YBa2Cu3O7-x is also discussed.

Electronic correlations in YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ from Auger spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balzarotti, A.; De Crescenzi, M.; Giovannella, C.

1987-12-01

Cu L/sub 3/VV Auger spectra of the superconducting compound YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ have been measured above and below the critical temperature T/sub c/ = 90 K and compared with those of CuO. In the superconductor a localized peak whose intensity increases with temperature is found. Such a structure, lacking in copper oxide, is attributed to electronic correlations in the Cu 3d/sup 8/ configuration.

Atomic scale real-space mapping of holes in YBa2Cu3O(6+δ).

PubMed

Gauquelin, N; Hawthorn, D G; Sawatzky, G A; Liang, R X; Bonn, D A; Hardy, W N; Botton, G A

2014-07-15

The high-temperature superconductor YBa2Cu3O(6+δ) consists of two main structural units--a bilayer of CuO2 planes that are central to superconductivity and a CuO(2+δ) chain layer. Although the functional role of the planes and chains has long been established, most probes integrate over both, which makes it difficult to distinguish the contribution of each. Here we use electron energy loss spectroscopy to directly resolve the plane and chain contributions to the electronic structure in YBa2Cu3O6 and YBa2Cu3O7. We directly probe the charge transfer of holes from the chains to the planes as a function of oxygen content, and show that the change in orbital occupation of Cu is large in the chain layer but modest in CuO2 planes, with holes in the planes doped primarily into the O 2p states. These results provide direct insight into the local electronic structure and charge transfers in this important high-temperature superconductor.

Orthorhombic YBaCo{sub 4}O{sub 8.4} crystals as a result of saturation of hexagonal YBaCo{sub 4}O{sub 7} crystals with oxygen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Podberezskaya, N. V., E-mail: podberez@niic.nsc.ru; Bolotina, N. B., E-mail: nb-bolotina@mail.ru; Komarov, V. Yu., E-mail: komarov-v-y@niic.nsc.ru

Hexagonal YBaCo{sub 4}O{sub 7} crystals (sp. gr. P6{sub 3}mc, a{sub h} = 6.3058(4) Å, c{sub h} = 10.2442(7) Å, Z = 2) are saturated with oxygen to the YBaCo{sub 4}O{sub 8.4} composition and studied by X-ray diffraction (XRD) analysis. The saturation is completed by a structural first-order phase transition to orthorhombic crystals (sp. gr. Pbc2{sub 1}, a{sub o} = 31.8419(2) Å, b{sub o} = 10.9239(5) Å, c{sub o} = 10.0960(5) Å, Z = 20). The connection of two lattices is expressed in terms of the action of matrix (500/120/001) on the hexagonal basis. Five structural fragments of the same typemore » but with different degrees of order alternate along the long axis of the oxygen-saturated orthorhombic structure. The XRD data on single crystals differ from the results obtained by other researchers on ceramic samples; possible causes of these differences are discussed.« less

Magnetic susceptibility of YBa2(Cu/1-x/Fe/x/)3O(y) prepared by various heat treatments

NASA Astrophysics Data System (ADS)

Shibata, Tomohiko; Katsuyama, Shigeru; Yoshimura, Kazuyoshi; Kosuge, Koji

1991-02-01

The magnetic susceptibility of YBa2(Cu/1-x/Fe/x/)3O(y) specimens was measured following a standard heat treatment and a special heat treament stabilizing the orthorhombic phase to higher Fe concentrations. The values of the effective magnetic moment per Fe in the Cu1 site, estimated from the magnetic susceptibility and Mossbauer effect measurements, were 4.4 and 2.2 muB for the standard and specially treated specimens, respectively. The smaller effective magnetic moment in the case of specially treated specimens is attributed to the antiferromagnetic coupling between Fe spins at high temperatures.

Modification of structural disorder by hydrostatic pressure in the superconducting cuprate YBa 2 Cu 3 O 6.73

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, H.; Jang, H.; Fujita, M.

Here, compelling efforts to improve the critical temperature (T c) of superconductors have been made through high-pressure application. Understanding the underlying mechanism behind such improvements is critically important; however, much remains unclear. Here we studied ortho-III YBa 2Cu 3O 6.73 (YBCO) using x-ray scattering under hydrostatic pressure (HP) up to ~6.0GPa. We found the reinforced oxygen order of YBCO under HP, revealing an oxygen rearrangement in the Cu-O layer, which evidently shows the charge-transfer phenomenon between the CuO 2 plane and Cu-O layer. Concurrently, we also observed no disorder-pinned charge-density-wave signature in CuO 2 plane under HP. This indicates thatmore » the oxygen rearrangement modifies the quenched disorder state in the CuO 2 plane. Using these results, we appropriately explain why pressure condition can achieve higher T c compared with the optimal T c under ambient pressure in YBa 2Cu 3O 6+x. As an implication of these results, finally we have discussed that the change in disorder could make it easier for YBa 2Cu 3O 6+x to undergo a transition to the nematic order under an external magnetic field.« less

Modification of structural disorder by hydrostatic pressure in the superconducting cuprate YBa 2 Cu 3 O 6.73

DOE PAGES

Huang, H.; Jang, H.; Fujita, M.; ...

2018-05-09

Here, compelling efforts to improve the critical temperature (T c) of superconductors have been made through high-pressure application. Understanding the underlying mechanism behind such improvements is critically important; however, much remains unclear. Here we studied ortho-III YBa 2Cu 3O 6.73 (YBCO) using x-ray scattering under hydrostatic pressure (HP) up to ~6.0GPa. We found the reinforced oxygen order of YBCO under HP, revealing an oxygen rearrangement in the Cu-O layer, which evidently shows the charge-transfer phenomenon between the CuO 2 plane and Cu-O layer. Concurrently, we also observed no disorder-pinned charge-density-wave signature in CuO 2 plane under HP. This indicates thatmore » the oxygen rearrangement modifies the quenched disorder state in the CuO 2 plane. Using these results, we appropriately explain why pressure condition can achieve higher T c compared with the optimal T c under ambient pressure in YBa 2Cu 3O 6+x. As an implication of these results, finally we have discussed that the change in disorder could make it easier for YBa 2Cu 3O 6+x to undergo a transition to the nematic order under an external magnetic field.« less

Investigation of flux penetration in YBa 2Cu 3O 7-δ filaments

NASA Astrophysics Data System (ADS)

Devos, P.; Buekenhoudt, A.; D'Anna, G.; André, M.-O.; Indenbom, M. V.; Benoit, W.; De Batist, R.; Cornelis, J.

1994-12-01

ac Susceptibility measurements using a low frequency torsion pendulum and an ac susceptometer were conducted on YBa 2Cu 3O 7-δ filaments in low magnetic dc fields (≤1T). Different dissipation peaks are observed, dependent on the temperature and the applied amplitude. The peak at low temperatures, which is of intergranular nature is studied in detail. The penetration follows the Bean model and the intergranular creep is observed.

Direct observation of vortex structure in a high-{Tc} YBa{sub 2}Cu{sub 3}O{sub 7{minus}y} thin film by Bitter decoration method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sugimoto, Akira; Yamaguchi, Tetsuji; Iguchi, Ienari

1999-12-01

The Bitter decoration technique is one of the most powerful techniques to study the vortex structure of superconductor. The authors report the observation of vortex structure in a high {Tc} YBa{sub 2}Cu{sub 3}O{sub 7{minus}y} (YBCO) thin film by Bitter decoration method. The image of vortex structure was monitored by SEM, AFM and high resolution optical microscope. For magnetic field about 4--6mT, a vortex structure is seen. The vortex image varied with changing magnetic field. As compared with the vortex image of a Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+y} single crystal, the observed image appeared to be more randomly distributed.

The study of ultrasonic irradiation effects on solid state powders of HTc superconductor YBa2Cu3O7-x

NASA Astrophysics Data System (ADS)

Kargar, Mahboubeh; Khoshnevisan, Bahram

2016-03-01

In this paper, an ultrasound assisted solid state synthesis method for high-temperature (HTc) YBa2Cu3O7-x (YBCO) superconductor nanostructures with different morphologies is presented. Here, the routine heat treatment of the powder mixture of as-prepared precursors is followed by the ultrasound irradiation inside various alcoholic solutions. Not only the influence of the ultrasound irradiation intensity and duration but also the influence of different solvents such as ethanol, methanol and 1-butanol with various vapor pressures and so various destruction powers were also studied on the morphology and particle size of the products. The various morphologies were studied by scanning electron microscope (SEM) which not only have been affected by intensity and type of alcoholic solvent but also sonication time and ultrasound power have significant role as well. Formation of the YBCO superconducting phase was examined by using Rietveld refinement of X-ray diffraction (XRD) which indicates the crystalline preferred growth in c-axis orientation in crystal. Magnetic susceptibility measurements showed the ultrasound waves had no important effect on the onset critical temperature of the prepared nanorods (about 91.64 K) which is compared with the bulk samples (Tc ˜ 92K).

Effectiveness of BaTiO 3 dielectric patches on YBa 2Cu 3O 7 thin films for MEM switches

DOE PAGES

Vargas, J.; Hijazi, Y.; Noel, J.; ...

2014-05-12

A micro-electro-mechanical (MEM) switch built on a superconducting microstrip filter will be utilized to investigate BaTiO 3 dielectric patches for functional switching points of contact. Actuation voltage resulting from the MEM switch provokes static friction between the bridge membrane and BaTiO 3 insulation layer. Furthermore, the dielectric patch crystal structure and roughness affect the ability of repetitively switching cycles and lifetime. We performed a series of experiments using different deposition methods and RF magnetron sputtering was found to be the best deposition process for the BaTiO 3 layer. The effect examination of surface morphology will be presented using characterization techniquesmore » as x-ray diffraction, SEM and AFM for an optimum switching device. The thin film is made of YBa 2Cu 3O 7 deposited on LaAlO 3 substrate by pulsed laser deposition. In our work, the dielectric material sputtering pressure is set at 9.5x10 -6 Torr. The argon gas is released through a mass-flow controller to purge the system prior to deposition. RF power is 85 W at a distance of 9 cm. The behavior of Au membranes built on ultimate BaTiO 3 patches will be shown as part of the results. These novel surface patterns will in turn be used in modelling other RF MEM switch devices such as distributed-satellite communication system operating at cryogenic temperatures.« less

Fabrication and characterization of La2Zr2O7 films on different buffer architectures for YBa2Cu3O7-δ coated conductors by RF magnetron sputtering.

PubMed

Xu, Da; Liu, Linfei; Xiao, Guina; Li, Yijie

2013-02-27

La2Zr2O7 (LZO) films were grown on different buffer architectures by radio frequency magnetron sputtering for the large-scale application of YBa2Cu3O7-x (YBCO)-coated conductors. The three different buffer architectures were cerium oxide (CeO2), yttria-stabilized zirconia (YSZ)/CeO2, and CeO2/YSZ/CeO2. The microstructure and surface morphology of the LZO film were studied by X-ray diffraction, optical microscopy, field emission scanning electron microscopy, and atomic force microscopy. The LZO films prepared on the CeO2, YSZ/CeO2, and CeO2/YSZ/CeO2 buffer architectures were preferentially c-axis-oriented and highly textured. The in-plane texture of LZO film on CeO2 single-buffer architecture was ∆ φ = 5.5° and the out-of-plane texture was ∆ ω = 3.4°. All the LZO films had very smooth surfaces, but LZO films grown on YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures had cracks. The highly textured LZO film grown on CeO2-seed buffered NiW tape was suitable for the epitaxial growth of YBCO film with high currents.

High-performance linear arrays of YBa2Cu3O7 superconducting infrared microbolometers on silicon

NASA Astrophysics Data System (ADS)

Johnson, Burgess R.; Foote, Marc C.; Marsh, Holly A.

1995-06-01

Single detectors and linear arrays of microbolometers utilizing the superconducting transition edge of YBa(subscript 2)Cu(subscript 3)O(subscript 7) have been fabricated by micromachining on silicon wafers. A D* of 8 +/- 2 X 10(superscript 9) cm Hz(superscript 1/2)/watt has been measured on a single detector. This is the highest D* reported on any superconducting microbolometer operating at temperatures higher than about 70 K. The NEP of this device was 1.5 X 10(superscript -12) watts/Hz(superscript HLF) at 2 Hz, at a temperature of 80.7 K. The thermal time constant was 105 msec, and the detector area was 140 micrometers X 105 micrometers . The use of batch silicon processing makes fabrication of linear arrays of these detectors relatively straightforward. The measured responsivity of detectors in one such array varied by less than 20% over the 6 mm length of the 64-element linear array. This measurement shows that good uniformity can be achieved at a single operating temperature in a superconductor microbolometer array, even when the superconducting resistive transition is a sharp function of temperature. The thermal detection mechanism of these devices gives them broadband response. This makes them especially useful at long wavelengths (e.g. (lambda) > 20 micrometers ), where they provide very high sensitivity at relatively high operating temperatures.

Superconducting YBa2Cu3O7- δ Thin Film Detectors for Picosecond THz Pulses

NASA Astrophysics Data System (ADS)

Probst, P.; Scheuring, A.; Hofherr, M.; Wünsch, S.; Il'in, K.; Semenov, A.; Hübers, H.-W.; Judin, V.; Müller, A.-S.; Hänisch, J.; Holzapfel, B.; Siegel, M.

2012-06-01

Ultra-fast THz detectors from superconducting YBa2Cu3O7- δ (YBCO) thin films were developed to monitor picosecond THz pulses. YBCO thin films were optimized by the introduction of CeO2 and PrBaCuO buffer layers. The transition temperature of 10 nm thick films reaches 79 K. A 15 nm thick YBCO microbridge (transition temperature—83 K, critical current density at 77 K—2.4 MA/cm2) embedded in a planar log-spiral antenna was used to detect pulsed THz radiation of the ANKA storage ring. First time resolved measurements of the multi-bunch filling pattern are presented.

Transport properties of ultrathin YBa2Cu3O7 -δ nanowires: A route to single-photon detection

NASA Astrophysics Data System (ADS)

Arpaia, Riccardo; Golubev, Dmitri; Baghdadi, Reza; Ciancio, Regina; Dražić, Goran; Orgiani, Pasquale; Montemurro, Domenico; Bauch, Thilo; Lombardi, Floriana

2017-08-01

We report on the growth and characterization of ultrathin YBa2Cu3O7 -δ (YBCO) films on MgO (110) substrates, which exhibit superconducting properties at thicknesses down to 3 nm. YBCO nanowires, with thicknesses down to 10 nm and widths down to 65 nm, have also been successfully fabricated. The nanowires protected by a Au capping layer show superconducting properties close to the as-grown films and critical current densities, which are limited by only vortex dynamics. The 10-nm-thick YBCO nanowires without the Au capping present hysteretic current-voltage characteristics, characterized by a voltage switch which drives the nanowires directly from the superconducting to the normal state. We associate such bistability to the presence of localized normal domains within the superconductor. The presence of the voltage switch in ultrathin YBCO nanostructures, characterized by high sheet resistance values and high critical current values, makes our nanowires very attractive devices to engineer single-photon detectors.

Atom-replaced pins in a Y-based superconductor—single-crystalline perovskite structure including both PrBa2Cu3O7‑x and YBa2Cu3O7‑y

NASA Astrophysics Data System (ADS)

Hayashi, Mariko; Araki, Takeshi; Ishii, Hirotaka; Nishijima, Gen; Matsumoto, Akiyoshi

2018-05-01

Metal organic deposition using trifluoroacetates (TFA-MOD) provides many uniform superconductors on long metal tapes. The large numbers of long wires have been applied for power grids or superconducting fault current limiters. The related applications worked for a long time without fatal trouble. The quasi-liquid produced during the firing process assisted the perfectly uniform structure in TFA-MOD. On the other hand, when it was desired to introduce artificial pinning centers, the quasi-liquid also enlarged the diameter of the artificial pinning centers to several tens of nanometers. In other words, due to the nature of TFA-MOD, there is very little chance of using TFA-MOD to prepare several nm-sized artificial pinning centers. By proposing atom-replaced pins (ARPs), we aim to overcome the impasse. ARPs are realized by replacing yttrium (Y) with praseodymium (Pr) whose valence number changes from 3+ to approximately 4+. Analytical results suggested that Pr makes pinning centers on a PrBa2Cu3O7‑x (PrBCO) unit cell, and the weak-linked superconductivity derived from PrBCO extends to the adjacent unit cells in the a/b-plane. J c decrease by Pr is five times as large as the volume fraction of Pr in the Y-site of the perovskite structure. On the other hand, T c does not show large degradation in YBCO including 10% PrBCO. These results suggest that PrBCO unit cells are fully dispersed in YBa2Cu3O7‑y matrix. With regard to J c in the magnetic field, (Y0.98, Pr0.02)BCO has been slightly improved compared with pure YBCO only in the region of high temperature and low magnetic field of less than 1 T.

Direct observation of twin deformation in YBa2Cu3O7-x thin films by in situ nanoindentation in TEM

NASA Astrophysics Data System (ADS)

Lee, Joon Hwan; Zhang, Xinghang; Wang, Haiyan

2011-04-01

The deformation behaviors of YBa2Cu3O7-x (YBCO) thin films with twinning structures were studied via in situ nanoindentation experiments in a transmission electron microscope. The YBCO films were grown on SrTiO3 (001) substrates by pulsed laser deposition. Both ex situ (conventional) and in situ nanoindentation were conducted to reveal the deformation of the YBCO films from the directions perpendicular and parallel to the twin interfaces. The hardness measured perpendicular to the twin interfaces is ˜50% and 40% higher than that measured parallel to the twin interfaces ex situ and in situ, respectively. Detailed in situ movie analysis reveals that the twin structures play an important role in deformation and strengthening mechanisms in YBCO thin films.

Method for making high-critical-current-density YBa.sub.2 Cu.sub.3 O.sub.7 superconducting layers on metallic substrates

DOEpatents

Feenstra, Roeland; Christen, David; Paranthaman, Mariappan

1999-01-01

A method is disclosed for fabricating YBa.sub.2 Cu.sub.3 O.sub.7 superconductor layers with the capability of carrying large superconducting currents on a metallic tape (substrate) supplied with a biaxially textured oxide buffer layer. The method represents a simplification of previously established techniques and provides processing requirements compatible with scale-up to long wire (tape) lengths and high processing speeds. This simplification has been realized by employing the BaF.sub.2 method to grow a YBa.sub.2 Cu.sub.3 O.sub.7 film on a metallic substrate having a biaxially textured oxide buffer layer.

Symmetry of the oxygen hole states in Bi 2Sr 2CaCu 2O 8 investigated by XAS

NASA Astrophysics Data System (ADS)

Kuiper, P.; Grioni, M.; Sawatzky, G. A.; Mitzi, D. B.; Kapitulnik, A.; Santaniello, A.; de Padova, P.; Thiry, P.

1989-02-01

We have observed strong polarization dependence in the X-ray absorption near the oxygen K edge in a single crystal of Bi 2Sr 2CaCu 2O 8 ( Tc=85 K). The results show that O-derived holes near the Fermi-level have p x, y (perpendicular to the c-axis) symmetry. Some consequences for models of superconductivity are discussed. The concentration of holes is estimated to be about equal to that in YBa 2Cu 3O 7.

Study on the photo-induced oxygen reordering in YBa2Cu3O6+x

NASA Astrophysics Data System (ADS)

Milić, M. M.; Lazarov, N. Dj.; Cucić, D. A.

2012-05-01

Effect of the long term illumination of the YBa2Cu3O6+x with visible light or ultraviolet irradiation on its superconducting properties was studied in the frame of a simple theoretical model, which assumes that photodoping triggers rearrangement of oxygen monomers in the chain layers thus causing the enhancement of the average chain length, lav. Since, according to the model of charge transfer mechanism, long CuO chains are better electronic hole donors than the short ones, increase of the average chain length induces additional holes transfer from chain layers to the superconducting CuO2 planes which in turn leads to the increase of the superconducting transition temperature Tc. By the use of the expression for the chain length probability distribution and numerically calculated values for the average chain length in the non-excited system, we were able to estimate the doping p (number of holes per one Cu atom in the superconducting CuO2 planes) and Tc enhancement due to photo-induced oxygen reordering. The theoretical results are compared with available experimental data.

Microscopic adaptation of BaHfO3 and Y2O3 artificial pinning centers for strong and isotropic pinning landscape in YBa2Cu3O7-x thin films

NASA Astrophysics Data System (ADS)

Gautam, Bibek; Sebastian, Mary Ann; Chen, Shihong; Haugan, Timothy; Zhang, Wenrui; Huang, Jijie; Wang, Haiyan; Wu, Judy Z.

2018-07-01

A study of 3 vol% Y2O3 + 2-6 vol% BaHfO3 double-doped YBa2Cu3O7-x (BHO DD) epitaxial thin films was carried out to explore the morphology adaption of c-axis aligned one-dimensional BHO artificial pinning centers (1D APCs) to secondary Y2O3 nanoparticles (3D APCs). BHO 1D APCs have been predicted to have the least rigidity in an elastic strain energy model in APC/YBa2Cu3O7-x nanocomposite films. Consequently, they could be best ‘tuned’ away from the c-axis alignment by local strains generated by the Y2O3 3D APCs. This provides an opportunity to generate mixed-morphology APCs, especially at high BHO concentrations. Motivated by this, we have carried out a systematic study of the transport critical current density J c(H, T, θ) on the BHO DD samples in magnetic fields (H) up to 90 kOe at different H orientations from H//c-axis (θ = 0), to θ = 45°, and to H//ab-plane (θ = 90°). Enhanced pinning at all three orientations was observed as illustrated in the comparable low alpha (α) values in the range of 0.13-0.25 at 65 K, which is consistent with the mixed 1D (in c-axis) + 2D (in ab-plane) + 3D APCs observed in transmission electron microscopy (TEM). Upon increasing BHO concentration from 2 to 4 vol%, a monotonic increase of the accommodation field H* at θ = 0°, 45° and 90° was observed, indicative of the APC concentration increase of the mixed morphologies. At 6 vol% BHO, the H* continues the increase to 85 kOe at H//c-axis (θ = 0), and >90 kOe H//ab-plane (θ = 90°), while it decreases from 80 to 85 kOe at 2-4 vol% to 60 kOe at 6 vol% at θ = 45°, which is consistent with the TEM observation of the connection of 3D APCs, appeared at lower BHO concentration into 2D ones in ab-plane at the higher BHO concentrations. These results shed light on the quantitative adaptation of APCs of mixed morphologies with increasing BHO doping in the BHO DD thin films and are important for controlling the APC pinning landscape towards minimal angular dependence.

Epitaxial Growth of YBa2Cu3O7 Films onto LaAlO3 (100) by Using Oxalates

NASA Astrophysics Data System (ADS)

Dominguez, A. Bustamante; Felix, L. León; Garcia, J.; Santibañez, J. Flores; Valladares, L. De Los Santos; Gonzalez, J. C.; Anaya, A. Osorio; Pillaca, M.

Due to the current necessity to obtain epitaxial superconductor films at low cost, we report the growth of YBa2Cu3O7 (Y123) films by chemical deposition. The procedure involved simple steps such as precipitation of stoichiometric amounts of yttrium, barium and copper acetates in oxalic acid (H2C2O4). The precursor solution was dripped onto LaAlO3 (100) substrates with the help of a Fisher pipette. The films were annealed in oxygen atmosphere during 12 h at three different temperatures: 820 °C, 840 °C and 860 °C. After 820 °C and 860 °C annealing, X-ray diffraction (XRD) analysis revealed high intensity of the (00l) reflections denoting that most of the Y123 grains were c-axis oriented. In addition, we also observed a-axis oriented grains ((h00) reflexion), minor randomly oriented grains and other phases (such as Y2BaCuO5 and CuO). In contrast, the sample treated at 840 °C, we noticed c - and a-axis oriented grains, very small amounts of randomly oriented grains without formation of other phases. From the magnetization versus temperature measurements, the critical temperatures were estimated at 70K and 90K for the samples annealed at 820 °C and 860 °C respectively.

Epitaxial YBa2Cu3O7-x nanocomposite films and coated conductors from BaMO3 (M = Zr, Hf) colloidal solutions

NASA Astrophysics Data System (ADS)

Obradors, X.; Puig, T.; Li, Z.; Pop, C.; Mundet, B.; Chamorro, N.; Vallés, F.; Coll, M.; Ricart, S.; Vallejo, B.; Pino, F.; Palau, A.; Gázquez, J.; Ros, J.; Usoskin, A.

2018-04-01

Superconducting nanocomposites are the best material choice to address the performance required in power applications and magnets working under high magnetic fields. However, it is still challenging to sort out how to achieve the highest superconducting performance using attractive and competitive manufacturing processes. Colloidal solutions have been recently developed as a novel and very promising low cost route to manufacture nanocomposite coated conductors. Well dispersed and stabilized preformance nanoparticle solutions are first prepared with high concentrations and then mixed with the YBa2Cu3O7 metalorganic precursor solutions to generate colloidal solutions to grow the nanocomposite films. Here we demonstrate, for the first time, that non-reactive BaZrO3 and BaHfO3 perovskite preformed nanoparticles are suitable for growing high quality thin and thick films, and coated conductors with a homogeneous distribution and controlled particle size using this fabrication method. Additionally, we extend the nanoparticle content of the nanocomposites up to 20%-25% mol without any degradation of the superconducting properties. Thick nanocomposite films, up to 0.8 μm, have been prepared with a single deposition of low-fluorine solutions using an ink jet printing dispenser and we demonstrate that the preformed nanoparticles display only a very limited coarsening during the growth process and so high critical current densities J c (B) under high magnetic fields. These films show the highest critical currents achieved so far based on the colloidal solution approach, I c = 220 A/cm-w at 77 K and self-field, and they still have a high potential for further increase in the film thickness. Finally, we also show that nanocomposite YBa2Cu3O7-BaZrO3 coated conductors based on an alternating beam assisted deposited YSZ buffer layer on stainless steel metallic substrates can be developed based on these novel colloidal solutions. Non-reactive preformed oxide perovskite

Induced Ferromagnetism at BiFeO 3/YBa 2Cu 3O 7 Interfaces

DOE PAGES

Zhu, Jian-Xin; Wen, Xiao-Dong; Haraldsen, J. T.; ...

2014-06-20

We report that transition metal oxides (TMOs) exhibit many emergent phenomena ranging from high-temperature superconductivity and giant magnetoresistance to magnetism and ferroelectricity. In addition, when TMOs are interfaced with each other, new functionalities can arise, which are absent in individual components. Here, we report results from first-principles calculations on the magnetism at the BiFeO 3/YBa 2Cu 3O 7 interfaces. By comparing the total energy for various magnetic spin configurations inside BiFeO 3, we are able to show that a metallic ferromagnetism is induced near the interface. We further develop an interface exchange-coupling model and place the extracted exchange coupling interactionmore » strengths, from the first-principles calculations, into a resultant generic phase diagram. Our conclusion of interfacial ferromagnetism is confirmed by the presence of a hysteresis loop in field-dependent magnetization data. Lastly, the emergence of interfacial ferromagnetism should have implications to electronic and transport properties.« less

High Tc screen-printed YBa2Cu3O(7-x) films - Effect of the substrate material

NASA Astrophysics Data System (ADS)

Bansal, Narottam P.; Simons, Rainee N.; Farrell, D. E.

1988-08-01

Thick films of YBa2Cu3O(7-x) have been deposited on highly polished alumina, magnesia spinel, nickel aluminum titanate (Ni-Al-Ti), and barium tetratitanate (Ba-Ti) substrates by the screen printing technique. Properties of the films were found to be highly sensitive to the choice of the substrate material. The film on Ba-Ti turned green after firing, due to a reaction with the substrate and were insulating. A film on Ni-Al-Ti had a Tc (onset) of about 95 K and lost 90 percent of its resistance by about 75 K. However, even at 4 K it was not fully superconducting, possibly due to a reaction between the film and the substrate and interdiffusion of the reaction products. The film on alumina had Tc (onset) of about 96 K, Tc (zero) of about 66 K, and Delta Tc of about 10 K. The best film was obtained on spinel and had Tc (onset) of about 94 K, zero resistance at 81 K, and a transition width of about 7 K.

High Tc screen-printed YBa2Cu3O(7-x) films - Effect of the substrate material

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Simons, Rainee N.; Farrell, D. E.

1988-01-01

Thick films of YBa2Cu3O(7-x) have been deposited on highly polished alumina, magnesia spinel, nickel aluminum titanate (Ni-Al-Ti), and barium tetratitanate (Ba-Ti) substrates by the screen printing technique. Properties of the films were found to be highly sensitive to the choice of the substrate material. The film on Ba-Ti turned green after firing, due to a reaction with the substrate and were insulating. A film on Ni-Al-Ti had a Tc (onset) of about 95 K and lost 90 percent of its resistance by about 75 K. However, even at 4 K it was not fully superconducting, possibly due to a reaction between the film and the substrate and interdiffusion of the reaction products. The film on alumina had Tc (onset) of about 96 K, Tc (zero) of about 66 K, and Delta Tc of about 10 K. The best film was obtained on spinel and had Tc (onset) of about 94 K, zero resistance at 81 K, and a transition width of about 7 K.

Valence charge fluctuations in YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ from core-level spectroscopies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balzarotti, A.; De Crescenzi, M.; Motta, N.

1988-10-01

From x-ray photoemission and Auger measurements of the Cu 2p and O 1s core levels of YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ as a function of the oxygen concentration delta, the average copper charge is determined. Evidence is found of dynamic charge fluctuations on the oxygen sublattice giving rise to a greater concentration of trivalent copper at the Cu(1) sites with respect to that determined by the analysis of neutron-diffraction data. On the basis of our experimental results, we introduce a molecular cluster description for the Cu states. The lowest final-states configurations of Cu/sup 2+/ and Cu/sup 3+/ are c3d/sup 10/Lmore » and c3d/sup 10/L/sup 2/, respectively, where c and L denote core holes on copper and oxygen atoms. Oxygen holes have high mobility and a Hubbard correlation energy less than 2 eV, a signature of their delocalization. The effect of temperature on the spectra is minor. Surface degradation modifies the relative intensity of the structures, particularly those of the O spectrum.« less

Macroscopic shape change of melt-processed YBa{sub 2}Cu{sub 3}O{sub x-}Y{sub 2}BaCuO{sub 5} bulk superconductors.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Diko, P.; Goretta, K. C.; Energy Technology

A macroscopic change in the shape of five-domain melt-processed YBa{sub 2}Cu{sub 3}O{sub x}/Y{sub 2}BaCuO{sub 5} bulk superconductors is reported and explained. The change, a distortion from circular cross-section, is attributed to liquid transport from a slower growth front in an a-axis direction to a faster growth front in a c-axis direction at the edge between the a- and c-growth fronts, a phenomenon that we call the edge melt distribution (EMD) effect. Formation of bands of higher Y{sub 2}BaCuO{sub 5} particle density along the a/c growth boundaries, which nearly coincide with {l_brace}110{r_brace}-type planes, is explained by the EMD effect.

Compatibilities of YBa2Cu3O(9-delta) type phase in quintenary systems Y-Ba-Cu-O-X (impurity)

NASA Technical Reports Server (NTRS)

Karen, P.; Braaten, O.; Fjellvag, H.; Kjekshus, A.

1991-01-01

Isothermal phase diagrams at various oxygen pressures were studied by powder diffraction and chemical analytical methods. The components, Y, Ba, Cu, and O (specifically O2, O2-, and O2 sup 2-) are treated, together with C (specifically CO2 and CO2 sup 2-), alkaline metals, Mg, alkaline earths, Sc, 3-d and 4-f elements. Effects of the substitutions at the structural sites of YBa2Cu3O(9-delta) on T sub c are discussed with respect to changes in crystallochemical characteristics of the substituted phase and to the nature of the substituents.

Comparison of the Microstructure and Flux Pinning Properties of Polycrystalline YBa2Cu3O7-d Containing Zn0.95Mn0.05O or Al2O3 Nanoparticles

NASA Astrophysics Data System (ADS)

Al-Mohsin, R. A.; Al-Otaibi, A. L.; Almessiere, M. A.; Al-badairy, H.; Slimani, Y.; Ben Azzouz, F.

2018-07-01

Here we compare the microstructure and flux pinning properties of polycrystalline YBa2Cu3O7-d (Y-123 or YBCO) containing either Al2O3 or Zn0.95Mn0.05O nanoparticles. Samples were prepared using a standard solid-state reaction process, and nanoparticles were added up to a concentration of 0.1 wt%. The crystal structure, microstructure, electrical and magnetic properties were analyzed using X-ray diffraction, scanning electron microscopy and transmission electron microscopy (TEM), and electrical resistivity and DC magnetization measurements, respectively. TEM observations showed that the addition of Zn0.95Mn0.05O resulted in a high density of fine twins and a variety of interacting microstructures, while Al2O3 addition resulted in a high density of Al-rich nanoscale inhomogeneities embedded in the Y-123 matrix. Flux pinning forces were determined, and predominant pinning mechanisms in the prepared samples were proposed. We evaluated the superconducting properties of YBCO considering the effects of adding insulating or magnetic nanoparticles.

Comparison of the Microstructure and Flux Pinning Properties of Polycrystalline YBa2Cu3O7-d Containing Zn0.95Mn0.05O or Al2O3 Nanoparticles

NASA Astrophysics Data System (ADS)

Al-Mohsin, R. A.; Al-Otaibi, A. L.; Almessiere, M. A.; Al-badairy, H.; Slimani, Y.; Ben Azzouz, F.

2018-03-01

Here we compare the microstructure and flux pinning properties of polycrystalline YBa2Cu3O7-d (Y-123 or YBCO) containing either Al2O3 or Zn0.95Mn0.05O nanoparticles. Samples were prepared using a standard solid-state reaction process, and nanoparticles were added up to a concentration of 0.1 wt%. The crystal structure, microstructure, electrical and magnetic properties were analyzed using X-ray diffraction, scanning electron microscopy and transmission electron microscopy (TEM), and electrical resistivity and DC magnetization measurements, respectively. TEM observations showed that the addition of Zn0.95Mn0.05O resulted in a high density of fine twins and a variety of interacting microstructures, while Al2O3 addition resulted in a high density of Al-rich nanoscale inhomogeneities embedded in the Y-123 matrix. Flux pinning forces were determined, and predominant pinning mechanisms in the prepared samples were proposed. We evaluated the superconducting properties of YBCO considering the effects of adding insulating or magnetic nanoparticles.

Fermi Surface Studies and Temperature Dependence of the Electron-Positron Momentum Density in the High Critical Temperature Superconducting Yttrium BARIUM(2) COPPER(3) OXYGEN(7-X) System by Two-Dimensional Acar

NASA Astrophysics Data System (ADS)

von Stetten, Eric Carl

The electron-positron momentum density has been measured by the two dimensional angular correlation of annihilation radiation (2D ACAR) technique for single crystal and polycrystalline (sintered powder) YBa_2 Cu_3O_{7-x} samples. For sintered superconducting and nonsuperconducting samples, the shape and temperature variation of the momentum density was investigated using the high sensitivity 2D ACAR technique. The possible existence of Fermi surfaces (FS's) in the YBa_2Cu _3O_{7-x} system was investigated in high precision 2D ACAR experiments on an oriented (twinned) single crystal superconducting YBa_2Cu _3O_{7-x} (x ~ 0.1) sample, at temperatures above and below the superconducting transition temperature (~85 K). These experiments were performed in the c-axis projection, in order to observe the theoretically predicted cylindrical FS's (if they exist) in a single experiment, without a full reconstruction of the three dimensional momentum density. Large differences were observed between the room temperature 2D ACAR spectra for superconducting and nonsuperconducting sintered powder samples, and smaller differences were observed between the spectra for similarly prepared superconducting samples. For sintered superconducting samples, complex sample dependent temperature variations of the momentum density were observed, in contrast to the small linear temperature variation observed for a sintered powder nonsuperconducting sample. These results are interpreted as manifestations of the theoretically predicted preferential sampling of the linear Cu-O chain region by the positron in the YBa _2Cu_3O _{7-x} system. High precision experiments on the single crystal superconducting sample revealed a nearly isotropic 2D ACAR spectrum, with only four small (~3% of the height at p_{x} = p _{y} = 0) peaks centered along the (110) symmetry lines. A small narrowing of the 2D ACAR spectrum was observed above T_{c}. The Brillouin-zone-reduced momentum density was formed using the "Lock

Transformational dynamics of BZO and BHO nanorods imposed by Y2O3 nanoparticles for improved isotropic pinning in YBa2Cu3O7 -δ thin films

NASA Astrophysics Data System (ADS)

Gautam, Bibek; Sebastian, Mary Ann; Chen, Shihong; Shi, Jack; Haugan, Timothy; Xing, Zhongwen; Zhang, Wenrui; Huang, Jijie; Wang, Haiyan; Osofsky, Mike; Prestigiacomo, Joseph; Wu, Judy Z.

2017-07-01

An elastic strain model was applied to evaluate the rigidity of the c-axis aligned one-dimensional artificial pinning centers (1D-APCs) in YBa2Cu3O7-δ matrix films. Higher rigidity was predicted for BaZrO3 1D-APCs than that of the BaHfO3 1D-APCs. This suggests a secondary APC doping of Y2O3 in the 1D-APC/YBa2Cu3O7-δ nanocomposite films would generate a stronger perturbation to the c-axis alignment of the BaHfO3 1D-APCs and therefore a more isotropic magnetic vortex pinning landscape. In order to experimentally confirm this, we have made a comparative study of the critical current density Jc (H, θ, T) of 2 vol.% BaZrO3 + 3 vol.%Y2O3 and 2 vol.%BaHfO3 + 3 vol.%Y2O3 double-doped (DD) YBa2Cu3O7-δ films deposited at their optimal growth conditions. A much enhanced isotropic pinning was observed in the BaHfO3 DD samples. For example, at 65 K and 9.0 T, the variation of the Jc across the entire θ range from θ=0 (H//c) to θ=90 degree (H//ab) is less than 18% for BaHfO3 DD films, in contrast to about 100% for the BaZrO3 DD counterpart. In addition, lower α values from the Jc(H) ˜ H-α fitting were observed in the BaHfO3 DD films in a large θ range away from the H//c-axis. Since the two samples have comparable Jc values at H//c-axis, the improved isotropic pinning in BaHfO3 DD films confirms the theoretically predicted higher tunability of the BaHfO3 1D-APCs in APC/YBa2Cu3O7-δ nanocomposite films.

YBa2Cu3O7 thin films on nanocrystalline diamond films for HTSC bolometer

NASA Technical Reports Server (NTRS)

Cui, G.; Beetz, C. P., Jr.; Boerstler, R.; Steinbeck, J.

1993-01-01

Superconducting YBa2Cu3O(7-x) films on nanocrystalline diamond thin films have been fabricated. A composite buffer layer system consisting of diamond/Si3N4/YSZ/YBCO was explored for this purpose. The as-deposited YBCO films were superconducting with Tc of about 84 K and a relatively narrow transition width of about 8 K. SEM cross sections of the films showed very sharp interfaces between diamond/Si3N4 and between Si3N4/YSZ. The deposited YBCO film had a surface roughness of about 1000 A, which is suitable for high-temperature superconductive (HTSC) bolometer fabrication. It was also found that preannealing of the nanocrystalline diamond thin films at high temperature was very important for obtaining high-quality YBCO films.

Phonon Dispersion Measurements of YBa 2Cu 3O 6.15 and YBa 2Cu 3O 6.95 by Time-of-Flight Neutron Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chung, J.-H.; Egami, T.; McQueeny, R. J.

We measured the phonon dispersions of YBa{sub 2}Cu{sub 3}O{sub 6.15} and YBa{sub 2}Cu{sub 3}O{sub 6.95} by time-of-flight inelastic neutron scattering. The in-plane bond-stretching modes in the metallic phase showed a distinct a-b plane anisotropy beyond what is expected for structural origin. Such anisotropy in the longitudinal optical modes, which is absent in the TO, suggests strong in-plane anisotropy in the underlying electronic structure. Apical oxygen bond-stretching modes showed a large frequency change between the insulating and the metallic phases. This large softening also is beyond structural origin, and suggests the effect of local electronic environment.

Studies of anisotropic in-plane aligned a-axis oriented YBa(2)Cu(3)O(7-x) thin films

NASA Astrophysics Data System (ADS)

Trajanovic, Zoran

1997-12-01

Due to their layered planar structure, cuprate oxide superconductors possess remarkable anisotropic properties which may be related to their high transition temperatures. In-plane aligned a-axis YBa2Cu3O7 (YBCO) films are good candidates for such anisotropic studies. Furthermore, the full advantage of favorable material characteristics can be then utilized in applications such as vertical SNS junctions with the leads along the b-direction of YBCO and other novel junction configurations. High quality, smooth, in-plane aligned films are obtained on (100) LaSrGaO4. Form x-ray data, the films show complete b- and c-axes separation for the measured a-axis orientation. The anisotropic resistivity ratio (ρ c/ρ b), measured along the two crystallographic axes of single films gives ρ c/ρ b of ≈20 near the transition, with T cs near 90 K. In such films the grain boundary effects can be decoupled from the intrinsic anisotropic properties of YBCO. From oxygen annealing studies it was estimated that the CuO chains supply about 60% of the carriers. From J c measurements it is determined that the orientation of magnetic field with respect to the crystallographic film axes is the primary factor governing the J c values. The angular dependence of J c on the applied magnetic field is compared against various theoretical models showing the best agreement with the modified Ginzburg-Landau's anisotropic mass model (at T ≈ T c) and Tinkham's thin film model (at T < T c). By utilizing the Co-dopant, the coupling between CuO2 planes and the resulting enhancement of the intrinsic anisotropy of YBCO can be studied. Deposition and cooling conditions are shown to be the primary factor that influence the quality of dopant incorporation and the resulting oxygen ordering within the YBCO lattice. Various complex structures and devices utilizing in-plane aligned, a-axis films are presented. Other materials exhibiting in-plane alignment and a-axis growth are described. Optional substrates

Ultrafast relaxation dynamics in BiFeO 3/YBa 2Cu 3O 7 bilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Springer, D.; Nair, Saritha K.; He, Mi

The temperature dependence of the relaxation dynamics in the bilayer thin film heterostructure composed of multiferroic BiFeO 3 (BFO) and superconducting YBa 2Cu 3O 7 (YBCO) grown on (001) SrTiO 3 substrate is studied by time-resolved pump-probe technique, and compared with that of pure YBCO thin film grown under the same growth conditions. The superconductivity of YBCO is found to be retained in the heterostructure. We observe a speeding up of the YBCO recombination dynamics in the superconducting state of the heterostructure, and attribute it to the presence of weak ferromagnetism at the BFO/YBCOinterface as observed inmagnetization data. An extensionmore » of the Rothwarf-Taylor model is used to fit the ultrafast dynamics of BFO/YBCO, that models an increased quasiparticle occupation of the ferromagnetic interfacial layer in the superconducting state of YBCO.« less

Ultrafast relaxation dynamics in BiFeO 3/YBa 2Cu 3O 7 bilayers

DOE PAGES

Springer, D.; Nair, Saritha K.; He, Mi; ...

2016-02-12

The temperature dependence of the relaxation dynamics in the bilayer thin film heterostructure composed of multiferroic BiFeO 3 (BFO) and superconducting YBa 2Cu 3O 7 (YBCO) grown on (001) SrTiO 3 substrate is studied by time-resolved pump-probe technique, and compared with that of pure YBCO thin film grown under the same growth conditions. The superconductivity of YBCO is found to be retained in the heterostructure. We observe a speeding up of the YBCO recombination dynamics in the superconducting state of the heterostructure, and attribute it to the presence of weak ferromagnetism at the BFO/YBCOinterface as observed inmagnetization data. An extensionmore » of the Rothwarf-Taylor model is used to fit the ultrafast dynamics of BFO/YBCO, that models an increased quasiparticle occupation of the ferromagnetic interfacial layer in the superconducting state of YBCO.« less

Atomic-scale identification of novel planar defect phases in heteroepitaxial YBa2Cu3O7-δ thin films

NASA Astrophysics Data System (ADS)

Gauquelin, Nicolas; Zhang, Hao; Zhu, Guozhen; Wei, John Y. T.; Botton, Gianluigi A.

2018-05-01

We have discovered two novel types of planar defects that appear in heteroepitaxial YBa2Cu3O7-δ (YBCO123) thin films, grown by pulsed-laser deposition (PLD) either with or without a La2/3Ca1/3MnO3 (LCMO) overlayer, using the combination of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging and electron energy loss spectroscopy (EELS) mapping for unambiguous identification. These planar lattice defects are based on the intergrowth of either a BaO plane between two CuO chains or multiple Y-O layers between two CuO2 planes, resulting in non-stoichiometric layer sequences that could directly impact the high-Tc superconductivity.

Structural investigation of Y1-xNixBa2Cu3O7-δ superconductor

NASA Astrophysics Data System (ADS)

Hadi-Sichani, Behnaz; Shakeripour, Hamideh; Salamati, Hadi

2018-07-01

Y1-xNixBa2Cu3O7-δ superconducting samples with 0 ≤ x ≤ 0.02 were synthesized by standard solid-state reaction and characterized by the X-ray powder diffraction technique. The Rietveld fitted XRD refinements show that all samples are crystallized in single phase, having orthorhombic structure with Pmmm space group. We investigated the effect of adding a magnetic element on the structure of this superconductor. The c cell parameter increases by doping of Ni until to an optimal value of Ni content, x ∼ 0.004, and then starts to decrease by higher value of Ni substitution. Moreover, it is seen that Cu(2)sbnd O(2) bond length decreases with increasing Ni up to the optimal concentration of Ni, too. The CuO2 planes become more distorted and hence charge carriers may have better chances of transportation to the CuO2 planes. By further increasing of Ni content than the optimal value, the Cu(2)sbnd O(2) bond lengths start to increase, and cause CuO2 planes to be flatten. We suggest, besides affecting the magnetic characteristic of Ni impurity, the Ni substitution leads to interesting crystallographic changes.

Investigation of magnetic properties of superconductors Y0.98 - x Cax Co0.02 Ba2 Cu3O7 - δ

NASA Astrophysics Data System (ADS)

Pourasad, Sepideh; Shakeripour, Hamideh; Hosseini, SeyedSajad; Salamati, Hadi

2018-06-01

The effect of Co2+, 3+ and Ca2+ substitution in Y3+ site in YBa2Cu3O7-δ superconductor has been studied. The series of high temperature superconducting samples of Y1-y-xCoyCaxBa2Cu3O7-δ with 0 ≤ x ≤ 0.015 and y = 0.020 were prepared by solid-state reaction method. The samples were characterized for phase purity and lattice parameter variations by X-ray diffraction. The AC susceptibility curves, χ'(T), show that in reserving cobalt fixed sample with the optimum Tc, by substitution of divalent Ca2+ at the trivalent Y3+ site no sensitive increasing happen in the superconducting transition temperature.

Distribution of flux-pinning energies in YBa2Cu3O(7-delta) and Bi2Sr2CaCu2O(8+delta) from flux noise

NASA Astrophysics Data System (ADS)

Ferrari, M. J.; Johnson, Mark; Wellstood, Frederick C.; Clarke, John; Mitzi, D.

1990-01-01

The spectral density of the magnetic flux noise measured in high-temperature superconductors in low magnetic fields scales approximately as the inverse of the frequency and increases with temperature. The temperature and frequency dependence of the noise are used to determine the pinning energies of individual flux vortices in thermal equilibrium. The distribution of pinning energies below 0.1 eV in YBa(2)Cu(3)O(7-delta) and near 0.2 eV in Bi(2)Sr(2)CaCu(2)O(8+delta). The noise power is proportional to the ambient magnetic field, indicating that the vortex motion is uncorrelated.

Knight shift and spin-echo decay time of YBa{sub 2}Cu{sub 4}O{sub 8} and YBa{sub 2}Cu{sub 3}O{sub 7} in the superconducting state

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pines, D.; Wrobel, P.

1996-03-01

We report on calculations of the Knight shift and spin-echo decay time, {ital T}{sub 2{ital G}}, in the superconducting state which are based on a nearly antiferromagnetic Fermi-liquid description of the spin-fluctuation spectrum, in which a single spin component is responsible for the dynamic spin behavior and the magnetic interaction between the planar quasiparticles brings the system close to antiferromagnetic behavior. The dynamic spin susceptibility is described by a random-phase-approximation-like expression, with a restoring force which is unchanged from the normal state, and an irreducible particle-hole susceptibility which reflects the {ital d}{sub {ital x}{sup 2}{minus}{ital y}{sup 2}} symmetry of themore » gap parameter and a quasiparticle Fermi surface consistent with photoemission experiments. We obtain a quantitative fit to the Knight shift results for YBa{sub 2}Cu{sub 4}O{sub 8} with a {ital d}{sub {ital x}{sup 2}{minus}{ital y}{sup 2}} strong coupling gap of maximum magnitude 2.8{ital k}{sub {ital BT}}{sub {ital c}}, and show that quantitative agreement with the recent measurements of {ital T}{sub 2{ital G}} by Corey {ital et al}. may be obtained with this {ital d}{sub {ital x}{sup 2}-{ital y}{sup 2}} pairing state and a quite substantial antiferromagnetic enhancement ({approximately}140) of the static {open_quote}{open_quote}band structure{close_quote}{close_quote} spin susceptibility at wave vectors in the vicinity of {bold Q}=({pi},{pi}). We demonstrate that the experimental results of Corey {ital et al}. rule out an anisotropic {ital s}-wave state. Analogous calculations for the Knight shift of YBa{sub 2}Cu{sub 3}O{sub 7} suggest that the {ital d}{sub {ital x}{sup 2}-{ital y}{sup 2}} strong coupling gap possesses a maximum magnitude, 2.6{ital k}{sub {ital BT}}{sub {ital c}}, and on this basis, we predict a reduction in {ital T}{sup -1}{sub 2{ital G}} of some 5% for the smaller antiferromagnetic enhancement ({approximately}38) expected for this

Impact of oxygen diffusion on superconductivity in YBa2Cu3O7 -δ thin films studied by positron annihilation spectroscopy

NASA Astrophysics Data System (ADS)

Reiner, M.; Gigl, T.; Jany, R.; Hammerl, G.; Hugenschmidt, C.

2018-04-01

The oxygen deficiency δ in YBa2Cu3O7 -δ (YBCO) plays a crucial role for affecting high-temperature superconductivity. We apply (coincident) Doppler broadening spectroscopy of the electron-positron annihilation line to study in situ the temperature dependence of the oxygen concentration and its depth profile in single crystalline YBCO film grown on SrTiO3 (STO) substrates. The oxygen diffusion during tempering is found to lead to a distinct depth dependence of δ , which is not accessible using x-ray diffraction. A steady state reached within a few minutes is defined by both, the oxygen exchange at the surface and at the interface to the STO substrate. Moreover, we reveal the depth-dependent critical temperature Tc in the as prepared and tempered YBCO film.

Crossover between superconductivity and magnetism in SrRuO3 mesocrystal embedded YBa2Cu3O7-x heterostructures.

PubMed

Suresh, Vandrangi; Lin, Jheng-Cyuan; Liu, Heng-Jui; Zhang, Zaoli; Chiang, Ping-Chih; Hsun, Yu-Ching; Chen, Yi-Chun; Lin, Jiunn-Yuan; Chu, Ying-Hao

2016-11-03

The competition between superconductivity and ferromagnetism poses great challenges and has attracted renewed interest for applications in novel spintronic devices. In order to emphasize their interactions, we fabricated a heterostructure composed of superconducting YBa 2 Cu 3 O 7-δ (YBCO) film embedded with itinerant ferromagnetic SrRuO 3 (SRO) mesocrystals. Starting from a doping concentration of 10 vol% of SRO mesocrystal in a YBCO matrix, corresponding to the density of SRO nanocrystals ∼5 × 10 9 cm -2 , which exhibits the typical characteristic of a metal-superconductor transition, and then increasing the magnetic interactions as a function of SRO embedment, the electronic correlation and the interplay between superconductivity and magnetism throughout the temperature regime were investigated. A metal-insulator transition in the normal state of YBCO and a crossover between superconductivity and magnetism at low temperatures were found upon increasing the density of nano-size SRO crystallites in the YBCO matrix as a consequence of competing interactions between these two ordered phases.

Millimeter-wave surface resistance of laser-ablated YBa2Cu3O(7-delta) superconducting films

NASA Technical Reports Server (NTRS)

Miranda, F. A.; Gordon, W. L.; Bhasin, K. B.; Warner, J. D.

1990-01-01

The millimeter-wave surface resistance of YBa2Cu3O(7-delta) superconducting films was measured in a gold-plated copper host cavity at 58.6 GHz between 25 and 300 K. High-quality laser-ablated films of 1.2-micron thickness were deposited on SrTiO3 and LaGaO3 substrates. Their transition temperatures were 90.0 and 88.9 K, with a surface resistance at 70 K of 82 and 116 milliohms, respectively. These values are better than the values for the gold-plated cavity at the same temperature and frequency.

Fermi surface ridge at second and third Umklapp positron annihilations in Y Ba2Cu3O(7-delta)

NASA Astrophysics Data System (ADS)

Adam, G.; Adam, S.; Barbiellini, B.; Hoffmann, L.; Manuel, A. A.; Massidda, S.; Peter, M.

1993-06-01

Results of statistical noise smoothing of the electron momentum distribution obtained by two-dimensional angular correlation of the electron-positron annihilation radiation technique on untwinned YBa2Cu3O(7-delta) single crystals are reported. Two distinct signatures of the sheet of Fermi surface related to the CuO chains (the ridge) are resolved. The first occurs at second Umklapp processes, in agreement with previous evidence. The second one, identified for the first time, occurs at third Umklapp processes. Comparison with FLAPW calculations confirms this result.

Phase Equilibria and Crystal Chemistry in Portions of the System SrO-CaO-Bi2O3-CuO, Part II—The System SrO-Bi2O3-CuO

PubMed Central

Roth, R. S.; Rawn, C. J.; Burton, B. P.; Beech, F.

1990-01-01

New data are presented on the phase equilibria and crystal chemistry of the binary systems Sr0-Bi203 and SrO-CuO and the ternary system SrO-Bi2O3-CuO. Symmetry data and unit cell dimensions based on single crystal and powder x-ray diffraction measurements are reported for all the binary SrO-Bi2O3 phases, including a new phase identified as Sr6Bi2O9. The ternary system contains at least four ternary phases which can be formed in air at ~900 °C. These are identified as Sr2Bi2CuO6, Sr8Bi4Cu5O19+x, Sr3Bi2Cu2O8 and a solid solution (the Raveau phase) which, for equilibrium conditions at ~900 °C, corresponds approximately to the formula Sr1.8−xBi2.2+xCu1±x/2Oz.(0.0⩽x⩽~0.15). Superconductivity in this phase apparently occurs only in compositions that correspond to negative values of x. Compositions that lie outside the equilibrium Raveau-phase field often form nearly homogeneous Raveau-phase products. Typically this occurs after relatively brief heat treatments, or in crystallization of a quenched melt. PMID:28179779

Controlling particle properties in {{YBa}}_{2}{{Cu}}_{3}{{\\rm{O}}}_{7-\\delta } nanocomposites by combining PLD with an inert gas condensation system

NASA Astrophysics Data System (ADS)

Sparing, M.; Reich, E.; Hänisch, J.; Gottschall, T.; Hühne, R.; Fähler, S.; Rellinghaus, B.; Schultz, L.; Holzapfel, B.

2017-10-01

The critical current density {J}{{c}} in {{YBa}}2{{Cu}}3{{{O}}}7-δ thin films, which limits their application in external magnetic fields, can be enhanced by the introduction of artificial pinning centers such as non-superconducting nanoparticles inducing additional defects and local strain in the superconducting matrix. To understand the correlation between superconductivity, defect structures and particles, a controlled integration of particles with adjustable properties is essential. A powerful technique for the growth of isolated nanoparticles in the range of 10 nm is dc-magnetron sputtering in an inert gas flow. The inert gas condensation (IGC) of particles allows for an independent control of both the particle diameter distribution and the areal density. We report on the integration of such gas-phase-condensed {{HfO}}2 nanoparticles into pulsed laser deposited (PLD) {{YBa}}2{{Cu}}3{{{O}}}7-δ thin film multilayers with a combined PLD-IGC system. The particles and the structure of the multilayers are analyzed by transmission electron microscopy on cross-sectional FIB lamellae. As a result of the IGC particle implementation, randomly as well as biaxially oriented {{BaHfO}}3 precipitates are formed in the {{YBa}}2{{Cu}}3{{{O}}}7-δ thin films. With as few as three interlayers of nanoparticles, the pinning force density is enhanced in the low-field region.

The YBa2Cu3O7- anomalous second peak and irreversible magnetic field in the magnetization hysteresis cycles

NASA Astrophysics Data System (ADS)

Taoufik, A.; Ramzi, A.; Senoussi, S.; Labrag, A.

2004-05-01

The flux jumps, the second peak and the irreversible magnetic field in the magnetization hysteresis cycles have been investigated in the high temperature superconductor YBa2Cu3O7- single crystals. These cycles were obtained for different temperature values, the applied magnetic fields up to 6 T and the angle between the applied magnetic field and c-axis. The magnetization curves exhibit a remarkable second peak fishtail, this second peak was not observed for the low temperature, but we observed the flux jumps saw tooth. The temperature dependence of the irreversible magnetic field, Hirr, for the applied magnetic field perpendicular to the ab planes is given by an extended expression, Hirr α (1-T/Tc )α, where α is a constant, the Abrikosov flux dynamics can explain this behavior. The Hirr as a function of has been strongly influenced by the flux pinning and the thermally assisted flux motion.

Two superconducting transitions in single-crystal La 2 - x Ba x CuO 4

DOE PAGES

Tee, X. Y.; Ito, T.; Ushiyama, T.; ...

2017-02-27

Here, we use spatially-resolved transport techniques to investigate the superconducting properties of single crystals La 2-xBa xCuO 4. We also found a superconducting transition temperature T cs associated with the ab-plane surface region which is considerably higher than the bulk T c. This effect is pronounced in the region of charge carrier doping x with strong spin-charge stripe correlations, reaching T cs = 36 K or 1.64T c.

The effect of temperature cycling typical of low earth orbit satellites on thin films of YBa2Cu3O(7-x)

NASA Technical Reports Server (NTRS)

Mogro-Campero, A.; Turner, L. G.; Bogorad, A.; Herschitz, R.

1991-01-01

Thin films of YBa2Cu3O(7-x) (YBCO) were temperature cycled to simulate conditions of a low earth orbit satellite. In one series of tests, epitaxial and polycrystalline YBCO films were cycled between temperatures of +/- 80 C in vacuum and in nitrogen for hundreds of cycles. The room temperature resistance of an epitaxial YBCO film increased by about 10 percent, but the superconducting transition temperature was unchanged. The largest changes were for a polycrystalline YBCO film on oxidized silicon with a zirconia buffer layer, for which the transition temperature decreased by 3 K. An extended test was carried out for epitaxial films. After 3200 cycles (corresponding to about 230 days in space), transition temperatures and critical current densities remained unchanged.

Strongly suppressed proximity effect and ferromagnetism in topological insulator/ferromagnet/superconductor thin film trilayers of Bi2Se3/SrRuO3/underdoped YBa2Cu3O x : a possible new platform for Majorana nano-electronics

NASA Astrophysics Data System (ADS)

Koren, Gad

2018-07-01

We report properties of a topological insulator–ferromagnet–superconductor trilayers comprised of thin films of 20 nm thick {Bi}}2{Se}}3 on 10 nm SrRuO3 on 30 nm {YBa}}2{Cu}}3{{{O}}}x. As deposited trilayers are underdoped and have a superconductive transition with {{T}}{{c}} onset at 75 K, zero resistance at 65 K, {{T}}Cueri} at 150 K and {{T}}* of about 200 K. Further reannealing under vacuum yields the 60 K phase of {YBa}}2{Cu}}3{{{O}}}x which still has zero resistance below about 40 K. Only when 10 × 100 microbridges were patterned in the trilayer, some of the bridges showed resistive behavior all the way down to low temperatures. Magnetoresistance versus temperature of the superconductive ones showed the typical peak due to flux flow against pinning below {{T}}{{c}}, while the resistive ones showed only the broad leading edge of such a peak. All this indicates clearly weak-link superconductivity in the resistive bridges between superconductive {YBa}}2{Cu}}3{{{O}}}x grains via the topological and ferromagnetic cap layers. Comparing our results to those of a reference trilayer (RTL) with the topological {Bi}}2{Se}}3 layer substituted by a non-superconducting highly overdoped {La}}1.65{Sr}}0.35{CuO}}4, indicates that the superconductive proximity effect as well as ferromagnetism in the topological trilayer are actually strongly suppressed compared to the non-topological RTL. This strong suppression could originate in lattice and Fermi levels mismatch as well as in short coherence length and unfavorable effects of strong spin–orbit coupling in {Bi}}2{Se}}3 on the d-wave pairing of {YBa}}2{Cu}}3{{{O}}}x. Proximity induced edge currents in the SRO/YBCO layer could lead to Majorana bound states, a possible signature of which is observed in the present study as zero bias conductance peaks.

High T c superconductivity in YBa2Cu3O7- x studied by PAC and PAS

NASA Astrophysics Data System (ADS)

Zhu, Shengyun; Li, Anli; Zheng, Shengnan; Huang, Hanchen; Li, Donghong; Din, Honglin; Du, Hongshan; Sun, Hancheng

1993-03-01

High T c superconductivity has been investigated in YBaCuO by both perturbed angular correlation and positron annihilation spectroscopy techniques as a function of temperature from 77 to 300 K. An abrupt change has been observed in the positron lifetime and Doppler broadening and the electric field gradient and its asymmetry parameter across T c, indicating a transition of two- to one-dimensional Cu-O-Cu chain structure and a charge transfer from CuO layers to CuO chains. An anomaly of the normal state has been demonstrated around 125 K, which is attributed to the structural instability.

Detection and imaging of the oxygen deficiency in single crystalline YBa{sub 2}Cu{sub 3}O{sub 7−δ} thin films using a scanning positron beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reiner, M.; Gigl, T.; Hugenschmidt, C.

2015-03-16

Single crystalline YBa{sub 2}Cu{sub 3}O{sub 7−δ} (YBCO) thin films were grown by pulsed laser deposition in order to probe the oxygen deficiency δ using a mono-energetic positron beam. The sample set covered a large range of δ (0.191 < δ < 0.791) yielding a variation of the critical temperature T{sub c} between 25 and 90 K. We found a linear correlation between the Doppler broadening of the positron electron annihilation line and δ determined by X-ray diffraction. Ab-initio calculations have been performed in order to exclude the presence of Y vacancies and to ensure the negligible influence of potentially present Ba or Cu vacancies tomore » the found correlation. Moreover, scanning with the positron beam allowed us to analyze the spatial variation of δ, which was found to fluctuate with a standard deviation of up to 0.079(5) within a single YBCO film.« less

Disentangling vortex pinning landscape in chemical solution deposited superconducting YBa2Cu3O7-x films and nanocomposites

NASA Astrophysics Data System (ADS)

Palau, A.; Vallès, F.; Rouco, V.; Coll, M.; Li, Z.; Pop, C.; Mundet, B.; Gàzquez, J.; Guzman, R.; Gutierrez, J.; Obradors, X.; Puig, T.

2018-07-01

In-field angular pinning performances at different temperatures have been analysed on chemical solution deposited (CSD) YBa2Cu3O7-x (YBCO) pristine films and nanocomposites. We show that with this analysis we are able to quantify the vortex pinning strength and energies, associated with different kinds of natural and artificial pinning defects, acting as efficient pinning centres at different regions of the H-T phase diagram. A good quantification of the variety of pinning defects active at different temperatures and magnetic fields provides a unique tool to design the best vortex pinning landscape under different operating conditions. We have found that by artificially introducing a unique defect in the YBCO matrix, the stacking faults, we are able to modify three different contributions to vortex pinning (isotropic-strong, anisotropic-strong, and isotropic-weak). The isotropic-strong contribution, widely studied in CSD YBCO nanocomposites, is associated with nanostrained regions induced at the partial dislocations surrounding the stacking faults. Moreover, the stacking fault itself acts as a planar defect which provides a very effective anisotropic-strong pinning at H//ab. Finally, the large presence of Cu-O cluster vacancies found in the stacking faults have been revealed as a source of isotropic-weak pinning sites, very active at low temperatures and high fields.

Fluctuation conductivity of oxygen underdoped YBa2Cu3O7-δ single crystals

NASA Astrophysics Data System (ADS)

Vovk, R. V.; Khadzhai, G. Ya.; Goulatis, I. L.; Chroneos, A.

2014-03-01

The electrical resistance in the range of ТC-300 K in the layer planes of YВа2Сu3О7-δ single crystals with a range of oxygen deficiency (providing a range of TC from 78 to 92 K) was investigated. The experimental data is approximated by an expression that accounts for the scattering of electrons on phonons, as well as on defects and the fluctuation conductivity in a 3-D model of the Aslamazov-Larkin theory. According to this approximation, depending upon the oxygen deficiency, the Debye temperature varies from 245 to 400 K, coherence length ξС(0)≈0.5 Å.

Comparative study of electrical transport and magnetic measurements of Y3Ba5Cu8O18±δ and YBa2Cu3O7-δ compounds: intragranular and intergranular superconducting properties

NASA Astrophysics Data System (ADS)

Slimani, Y.; Hannachi, E.; Ben Salem, M. K.; Ben Azzouz, F.; Ben Salem, M.

2018-02-01

We compare the superconducting properties and flux pinning characteristics between YBa2Cu3O7-δ (called Y-123) and Y3Ba5Cu8O18±δ (called Y-358) compounds. Both samples were synthesized through the solid-state reaction. The samples were examined by X-ray diffraction, and scanning electron microscope coupled with energy dispersive spectrometry. The critical current densities of the prepared samples were investigated using current-voltage, magnetization measurements and ac-susceptibility. It is demonstrated that the Y-358 exhibits better superconducting and pinning properties than the Y-123 one. This may be ascribed to the layered structure and the occurrence of a greater number of insulating layers between the CuO2 planes that act as effective pinning sites and consequently conduce to a better fundamental pinning capacity in Y-358.

Structural transition of secondary phase oxide nanorods in epitaxial YBa2Cu3O7-δ films on vicinal substrates

NASA Astrophysics Data System (ADS)

Shi, Jack J.; Wu, Judy Z.

2012-12-01

A theoretical study of a structural transition of secondary phase oxide nanorods in epitaxial YBa2Cu3O7-δ films on vicinal SrTiO3 substrates is presented. Two possible types of film/substrate interface are considered, with one assuming complete coherence, while the other is defective as manifested by the presence of antiphase grain boundaries. Only in the former case does the increase of the vicinal angle of the substrate lead to a substantial change of the strain field in the film, resulting in a transition of the nanorod orientation from the normal to the in-plane direction of the film. The calculated threshold vicinal angle for the onset of the transition and lattice deformation of the YBa2Cu3O7-δ film due to the inclusion of the nanorods is in very good agreement with experimental observations. This result sheds lights on the understanding of the role of the film/substrate lattice mismatch in controlling self-assembly of dopant nanostructures in matrix films.

Low-pressure large-area magnetron sputter deposition of YBa2Cu3O7-δ films for industrial applications

NASA Astrophysics Data System (ADS)

Wördenweber, Roger; Hollmann, Eugen; Poltiasev, Michael; Neumüller, Heinz-Werner

2003-05-01

This paper addresses the development of a technically relevant sputter-deposition process for YBa2Cu3O7-delta films. First, the simulation of the particle transport from target to substrate indicates that only at a reduced pressure of p approx 1-10 Pa can a sufficiently large deposition rate and homogeneous stoichiometric distribution of the particles during large-area deposition be expected. The results of the simulations are generally confirmed by deposition experiments on CeO2 buffered sapphire and LaAlO3 substrates using a magnetron sputtering system suitable for large-area deposition. However, it is shown that in addition to the effect of scattering during particle transport, the conditions at the substrate lead to a selective growth of Y-Ba-Cu-O phases that, among others, strongly affect the growth rate. For example, the growth rate is more than three times larger for optimized parameters compared to the same set of parameters but at 100 K lower substrate temperature. Stoichiometrical and structural perfect films can be grown at low pressure (p < 10 Pa). However, the superconducting transition temperature of these films is reduced. The Tc reduction seems to be correlated with the c-axis length of YBa2Cu3O7-delta. Two possible explanations for the increased c-axis length and the correlated reduced transition temperature are discussed, i.e. reduced oxygen content and strong cation site disorder due to the heavy particle bombardment.

Effects of process variables on the properties of YBa2Cu3O(7-x) ceramics formed by investment casting

NASA Technical Reports Server (NTRS)

Hooker, M. W.; Taylor, T. D.; Leigh, H. D.; Wise, S. A.; Buckley, J. D.; Vasquez, P.; Buck, G. M.; Hicks, L. P.

1993-01-01

An investment casting process has been developed to produce net-shape, superconducting ceramics. In this work, a factorial experiment was performed to determine the critical process parameters for producing cast YBa2Cu3O7 ceramics with optimum properties. An analysis of variance procedure indicated that the key variables in casting superconductive ceramics are the particle size distribution and sintering temperature. Additionally, the interactions between the sintering temperature and the other process parameters (e.g., particle size distribution and the use of silver dopants) were also found to influence the density, porosity, and critical current density of the fired ceramics.

Single crystal X-ray diffraction study of the HgBa2CuO4+δ superconducting compound

NASA Astrophysics Data System (ADS)

Bordet, P.; Duc, F.; Lefloch, S.; Capponi, J. J.; Alexandre, E.; Rosa-Nunes, M.; Antipov, E. V.; Putilin, S.

1996-02-01

A high precision X-ray diffraction analysis up to sin θ/λ = 1.15 of a HgBa2CuO4+δ single crystal having a Tc of ~ 90 K is presented. The cell parameters are a = 3.8815(4), c = 9.485 (7) Å. The refinements indicate the existence of a split barium site due to the presence of excess oxygen in the mercury layer. The position of this excess oxygen might be slightly displaced from the (1/2 1/2 0) position. A 6% mercury deficiency is observed. Models, including mercury defects, substitution by copper cations, or carbonate groups, are compared. However, we obtain no definite evidence for either of the three models. A possible disorder of the Hg position, due to the formation of chemical bonds with neighbouring extra oxygen anions, could correlate to the refinements of mixed species at the Hg site. A low temperature single crystal x-ray diffraction study, and comparison of refinements for the same single crystal with different extra oxygen contents, are in progress to help clarify this problem.

Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures.

PubMed

Gray, B A; Middey, S; Conti, G; Gray, A X; Kuo, C-T; Kaiser, A M; Ueda, S; Kobayashi, K; Meyers, D; Kareev, M; Tung, I C; Liu, Jian; Fadley, C S; Chakhalian, J; Freeland, J W

2016-09-15

The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.

Temperature dependence of superfluid density in YBa 2Cu 3O 7- δ and Y 0.7Ca 0.3Ba 2Cu 3O 7- δ thin films: A doping dependence study of the linear slope

NASA Astrophysics Data System (ADS)

Lai, L. S.; Juang, J. Y.; Wu, K. H.; Uen, T. M.; Gou, Y. S.

2005-11-01

By using a microstrip ring resonator to measure the temperature dependence of the in-plane magnetic penetration depth λ(T) in YBa2Cu3O7-δ (YBCO) and Y0.7Ca0.3Ba2Cu3O7-δ (Ca-YBCO) epitaxially grown thin films, the linear temperature dependence of the superfluid density ρs/m∗ ≡ 1/λ2(T) was observed from the under- to the overdoped regime at the temperatures below T/Tc ≈ 0.3 . For the underdoped regime of YBCO and Ca-YBCO thin films, the magnitude of the slope d(1/λ2(T))/dT is insensitive to doping, and it can be treated in the framework of projected d-density-wave model. Combining these slope values with the thermal conductivity measurements, the Fermi-liquid correction factor α2 from the Fermi-liquid model, suggested by Wen and Lee, was revealed here with various doping levels.

The microscopic structure of charge density waves in underdoped YBa2Cu3O6.54 revealed by X-ray diffraction

NASA Astrophysics Data System (ADS)

Forgan, E. M.; Blackburn, E.; Holmes, A. T.; Briffa, A. K. R.; Chang, J.; Bouchenoire, L.; Brown, S. D.; Liang, Ruixing; Bonn, D.; Hardy, W. N.; Christensen, N. B.; Zimmermann, M. V.; Hücker, M.; Hayden, S. M.

2015-12-01

Charge density wave (CDW) order appears throughout the underdoped high-temperature cuprate superconductors, but the underlying symmetry breaking and the origin of the CDW remain unclear. We use X-ray diffraction to determine the microscopic structure of the CDWs in an archetypical cuprate YBa2Cu3O6.54 at its superconducting transition temperature ~60 K. We find that the CDWs in this material break the mirror symmetry of the CuO2 bilayers. The ionic displacements in the CDWs have two components, which are perpendicular and parallel to the CuO2 planes, and are out of phase with each other. The planar oxygen atoms have the largest displacements, perpendicular to the CuO2 planes. Our results allow many electronic properties of the underdoped cuprates to be understood. For instance, the CDWs will lead to local variations in the electronic structure, giving an explicit explanation of density-wave states with broken symmetry observed in scanning tunnelling microscopy and soft X-ray measurements.

Crystal structure, Raman scattering and magnetic properties of CuCr2-xZrxSe4 and CuCr2-xSnxSe4 selenospinels

NASA Astrophysics Data System (ADS)

Pinto, C.; Galdámez, A.; Barahona, P.; Moris, S.; Peña, O.

2018-06-01

Selenospinels, CuCr2-xMxSe4 (M = Zr and Sn), were synthesized via conventional solid-state reactions. The crystal structure of CuCr1.5Sn0.5Se4, CuCr1.7Sn0.3Se4, CuCr1.5Zr0.5Se4, and CuCr1.8Zr0.2Se4 were determined using single-crystal X-ray diffraction. All the phases crystallized in a cubic spinel-type structure. The chemical compositions of the single-crystals were examined using energy-dispersive X-ray analysis (EDS). Powder X-ray diffraction patterns of CuCr1.3Sn0.7Se4 and CuCr1.7Sn0.3Se4 were consistent with phases belonging to the Fd 3 bar m Space group. An analysis of the vibrational properties on the single-crystals was performed using Raman scattering measurements. The magnetic properties showed a spin glass behavior with increasing Sn content and ferromagnetic order for CuCr1.7Sn0.3Se4.

No evidence for orbital loop currents in charge-ordered YBa2Cu3O6 +x from polarized neutron diffraction

NASA Astrophysics Data System (ADS)

Croft, T. P.; Blackburn, E.; Kulda, J.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Hayden, S. M.

2017-12-01

It has been proposed that the pseudogap state of underdoped cuprate superconductors may be due to a transition to a phase which has circulating currents within each unit cell. Here, we use polarized neutron diffraction to search for the corresponding orbital moments in two samples of underdoped YBa2Cu3O6 +x with doping levels p =0.104 and 0.123. In contrast to some other reports using polarized neutrons, but in agreement with nuclear magnetic resonance and muon spin rotation measurements, we find no evidence for the appearance of magnetic order below 300 K. Thus, our experiment suggests that such order is not an intrinsic property of high-quality cuprate superconductor single crystals. Our results provide an upper bound for a possible orbital loop moment which depends on the pattern of currents within the unit cell. For example, for the CC-θI I pattern proposed by Varma, we find that the ordered moment per current loop is less than 0.013 μB for p =0.104 .

Pulsed laser deposition of {CeO_2} and {Ce_{1-x}M_xO_2} (M = La, Zr): Application to insulating barrier in cuprate heterostructures

NASA Astrophysics Data System (ADS)

Berger, S.; Contour, J.-P.; Drouet, M.; Durand, O.; Khodan, A.; Michel, D.; Régi, F.-X.

1998-03-01

SrTiO_3 had been often tentatively used as an insulating barrier for HT superconductor/insulator heterostructures. Unfortunately, the deposition of SrTiO_3 on the YBa_2Cu_3O_7 inverse interface results in a poor epitaxial regrowth producing a high roughness dislocated titanate layer. Taking into account the good matching with YBa_2Cu_3O_7 and LaAlO_3, CeO_2 and Ce_{1-x}M_xO_2 (M = La, Zr), epitaxial layers were grown by pulsed laser deposition on LaAlO_3 substrates and introduced into YBa_2Cu_3O_7 based heterostructures as insulating barrier. After adjusting the growth parameters from RHEED oscillations, epitaxial growth is achieved, the oxide crystal axes being rotated by 45^circ from those of the substrate. The surface roughness of 250 nm thick films is very low with a rms value lower than 0.5 nm over 1;μ m^2. The YBa_2Cu_3O_7 layers of a YBa_2Cu_3O_7/CeO_2 /YBa_2Cu_3O_7 heterostructures grown using these optimized parameters show an independent resistive transition, when the thickness is larger than 25 nm, respectively at T_c_1 = 89.6;K and T_c_2 = 91.4;{K}. SrTiO3 est souvent utilisé comme barrière isolante dans des hétérostructures SIS de cuprates supraconducteurs, cependant les défauts générés lors de la croissance de ce titanate sur l'interface inverse de YBa2Cu3O7 conduisent à un matériau dont la qualité cristalline et les propriétés physiques sont médiocres. L'oxyde de cérium CeO2 est également une barrière isolante potentielle intéressante pour ces structures SIS basées sur YBa2Cu3O7 car cet oxyde cubique (a = 0,5411 nm, asqrt{2}/2 = 0,3825 nm) qui est peu désaccordé par rapport au plan ab du cuprate (Δ a/a = - 0,18 %, Δ b/a = 1,6 %) présente de plus un coefficient de dilatation thermique (10,6 × 10^{-6 circ}C^{-1}) très voisin de celui de YBa2Cu3O7 (13 × 10^{-6 circ}C^{-1}). Nous avons donc étudié l'épitaxie de CeO2 et des oxydes de type Ce{1-x}MxO2 (M = La, Zr) en ablation laser pulsée afin de définir des conditions de

Superconducting YBa2Cu3O7 Powder: Reduction of Carbon, Moisture, and Impurity Phase Concentrations in Commercial Powders and the Reactivity with Moisture and Carbon Dioxide

NASA Technical Reports Server (NTRS)

Stecura, Stephan

1994-01-01

The purpose of this study was to determine the experimental parameters under which commercially pure YBa2Cu3O7 (1237) powders would be converted into a single phase (1237) powder only. Carbon (present as carbonate) and impurity phase concentrations in the (1237) powder are very dependent upon the firing temperatures, heat-treating temperatures and times, and atmosphere, while the moisture concentration is not. YBa2Cu3O7 powder with about 0.03 wt/%, carbon, 0.03 wt% moisture, and low impurity phase concentrations was obtained. Moisture and carbon concentrations in heat-treated powders did not increase significantly after 48 and 72 h of exposure to air, respectively, and after 144 h of exposure they were less than 0.26 and 0.08 wt/%, respectively. The (1237) powder first reacts with moisture and then hydroxide reacts with CO2. Firing the as received powders in air led to the decomposition of the superconducting (1237) phase.

Phase Equilibria and Crystal Chemistry in Portions of the System SrO-CaO-Bi2O3-CuO, Part IV— The System CaO-Bi2O3-CuO

PubMed Central

Burton, B. P.; Rawn, C. J.; Roth, R. S.; Hwang, N. M.

1993-01-01

New data are presented on the phase equilibria and crystal chemistry of the binary systems CaO-Bi2O3 and CaO-CuO and the ternary CaO-Bi2O3-CuO. Symmetry data and unit cell dimensions based on single crystal and powder x-ray diffraction measurements are reported for several of the binary CaO-Bi2O3 phases, including corrected compositions for Ca4Bi6O13 and Ca2Bi2O5. The ternary system contains no new ternary phases which can be formed in air at ~700–900 °C. PMID:28053484

Controlling BaZrO3 nanostructure orientation in YBa2Cu3O{}_{7-\\delta } films for a three-dimensional pinning landscape

NASA Astrophysics Data System (ADS)

Wu, J. Z.; Shi, J. J.; Baca, F. J.; Emergo, R.; Wilt, J.; Haugan, T. J.

2015-12-01

The orientation phase diagram of self-assembled BaZrO3 (BZO) nanostructures in c-oriented YBa2Cu3O{}7-δ (YBCO) films on flat and vicinal SrTiO3 substrates was studied experimentally with different dopant concentrations and vicinal angles and theoretically using a micromechanical model based on the theory of elasticity. The organized BZO nanostructure configuration was found to be tunable, between c-axis to ab-plane alignment, by the dopant concentration in the YBCO film matrix strained via lattice mismatched substrates. The correlation between the local strain caused by the BZO doping and the global strain on the matrix provides a unique approach for controllable growth of dopant nanostructure landscapes. In particular, a mixed phase of the c-axis-aligned nanorods and the ab-plane-aligned planar nanostructures can be obtained, leading to a three-dimensional pinning landscape with single impurity doping and much improved J c in almost all directions of applied magnetic field.

Influence of γ-Irradiation on the Optical Properties of the Polyimide-YBa2Cu3O6.7 System

NASA Astrophysics Data System (ADS)

Muradov, A. D.; Korobova, N. E.; Kyrykbaeva, A. A.; Yar-Mukhamedova, G. Sh.; Mukashev, K. M.

2018-05-01

Influence of γ-irradiation on the optical properties of a polyimide film and its polymer compositions with fillers of a dispersed powder of a high-temperature superconductor ҮBa2Cu3O6.7 (YBaCuO) with concentrations of 0.05, 0.10, and 0.50 wt.% was studied. It was established that γ-irradiation with a dose up to 600 kGy does not affect the transparency of polyimide films in the visible region of the spectrum. However, at irradiation doses of 250 and 600 kGy, a weakly expressed fine structure appears in the spectra of polyimide films in the range of 220-300 nm due to the contribution of the resulting diene structures to the optical transmission and the increased content of oxygen atoms. The YBaCuO filler and γ-irradiation cause the polyimide transition from the amorphous state to the crystalline state, which is manifested in a sharp change in the spectrum in the range of 2.3-3.9 eV. A significant increase in the extinction coefficient was found in the composite containing 0.50 wt.% of the filler that is associated with an increase in the radius of action of structurally active fillers on the macromolecules of the matrix.

Optically induced lattice deformations, electronic structure changes, and enhanced superconductivity in YBa 2Cu 3O 6.48

DOE PAGES

Mankowsky, R.; Fechner, M.; Forst, M.; ...

2017-02-28

Resonant optical excitation of apical oxygen vibrational modes in the normal state of underdoped YBa 2Cu 3O 6+x induces a transient state with optical properties similar to those of the equilibrium superconducting state. Amongst these, a divergent imaginary conductivity and a plasma edge are transiently observed in the photo-stimulated state. Femtosecond hard x-ray diffraction experiments have been used in the past to identify the transient crystal structure in this non-equilibrium state. Here, we start from these crystallographic features and theoretically predict the corresponding electronic rearrangements that accompany these structural deformations. Using density functional theory, we predict enhanced hole-doping of themore » CuO 2 planes. The empty chain Cu dy2-z2 orbital is calculated to strongly reduce in energy, which would increase c-axis transport and potentially enhance the interlayer Josephson coupling as observed in the THz-frequency response. From these results, we calculate changes in the soft x-ray absorption spectra at the Cu L-edge. As a result, femtosecond x-ray pulses from a free electron laser are used to probe changes in absorption at two photon energies along this spectrum and provide data consistent with these predictions.« less

Coaxial line configuration for microwave power transmission study of YBa2Cu3O(7-delta) thin films

NASA Technical Reports Server (NTRS)

Chorey, C. M.; Miranda, F. A.; Bhasin, K. B.

1991-01-01

Microwave transmission measurements through YBa2Cu3O(7-delta) (YBCO) high-transition-temperature superconducting thin films on lanthanum aluminate (LaAlO3) have been performed in a coaxial line at 10 GHz. LaAlO3 substrates were ultrasonically machined into washer-shaped discs, polished, and coated with laser-ablated YBCO. These samples were mounted in a 50-ohm coaxial air line to form a short circuit. The power transmitted through the films as a function of temperature was used to calculate the normal state conductivity and the magnetic penetration depth for the films.

Trimming the electrical properties on nanoscale YBa2Cu3O7-x constrictions by focus ion beam technique

NASA Astrophysics Data System (ADS)

Lam, Simon K. H.; Bendavid, Avi; Du, Jia

2017-09-01

High temperature superconducting (HTS) nanostructure has a great potential in photon sensing at high frequency due to its fast recovery time. For maximising the coupling efficiency, the normal resistance of the nanostructure needs to be better matched to that of the thin-film antenna, which is typically few tens of ohm. We report on the fabrication of nanoscale high temperature superconducting YBa2Cu3O7-x (YBCO) constrictions using Gallium ion focus ion beam (FIB) technique. The FIB has been used to both remove the YBCO in lateral dimension and also tune its critical current and normal resistance by a combination of surface etching and implantation on the YBCO top layer. High critical current density of 2.5 MA/cm2 at 77 K can be obtained on YBCO nanobridges down to 100 nm in width. Subsequent trimming of the naobridges can lead to a normal resistance value over 50 Ω. Simulation of the Ga ion trajectory has also been performed to compare the measurement results. This method provides a simple step of fabricating nanoscale superconducting detectors such as hot electron bolometer.

Correlation between superfluid density and T(C) of underdoped YBa2Cu3O6+x near the superconductor-insulator transition.

PubMed

Zuev, Yuri; Kim, Mun Seog; Lemberger, Thomas R

2005-09-23

We report measurements of the ab-plane superfluid density n(s) (magnetic penetration depth lambda) of heavily underdoped films of YBa2Cu3O6+x, with T(C)'s from 6 to 50 K. We find the characteristic length for vortex unbinding transition equal to the film thickness, suggesting strongly coupled CuO2 layers. At the lowest dopings, T(C) is as much as 5 times larger than the upper limit set by the 2D Kosterlitz-Thouless-Berezinskii transition temperature calculated for individual CuO2 bilayers. Our main finding is that T(C) is not proportional to n(s)(0); instead, we find T(C) proportional to ns(1/2.3+/-0.4). This conflicts with a popular point of view that quasi-2D thermal phase fluctuations determine the transition temperature.

Effect of Load-Induced Oxygen Absorption in YBa2Cu3O6 + x on Mechanical Properties of the "Polyimide-YBa2Cu3O6 + x " System

NASA Astrophysics Data System (ADS)

Muradov, A. D.; Kyrykbaeva, A. A.

2018-05-01

We have studied the effect of oxygen absorption by disperse powder fillers made of high-temperature superconductor YBa2Cu3O6 + x (YBCO) with concentrations of 0.05, 0.1, and 0.5 mass % on mechanical properties of polyimide composite materials (PCMs) in the form of films. It has been established that an adsorption boundary layer consisting of an aggregate of several transition layers with a varying structure is formed between filler particles and the matrix. A sharp increase in relative elongation (strain) Δɛ c , which is observed for a PCM with YBCO fillers in the form of a jump in the region of loads of 40-47 MPa, is due to the fact that the bonds between the matrix macromolecules and the molecules in the vicinity of the upper boundary layer are ruptured, leading to a strain jump. An increase in the filler concentration increases the rigidity of the bonds between macromolecules in the boundary layers, leads to a shift of Δɛ c to the region of low stresses, and reduces its value.

Scanning micro-Hall probe mapping of magnetic flux distributions and current densities in YBa2Cu3O7 thin films

NASA Technical Reports Server (NTRS)

Xing, W.; Heinrich, B.; Zhou, HU; Fife, A. A.; Cragg, A. R.; Grant, P. D.

1995-01-01

Mapping of the magnetic flux density B(sub z) (perpendicular to the film plane) for a YBa2Cu3O7 thin-film sample was carried out using a scanning micro-Hall probe. The sheet magnetization and sheet current densities were calculated from the B(sub z) distributions. From the known sheet magnetization, the tangential (B(sub x,y)) and normal components of the flux density B were calculated in the vicinity of the film. It was found that the sheet current density was mostly determined by 2B(sub x,y)/d, where d is the film thickness. The evolution of flux penetration as a function of applied field will be shown.

Spatial variations in ac susceptibility and microstructure for the YBa2Cu3O(7-x) superconductor and their correlation with room-temperature ultrasonic measurements

NASA Technical Reports Server (NTRS)

Roth, Don J.; Deguire, Mark R.; Dolhert, Leonard E.; Hepp, Aloysius F.

1991-01-01

The spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu3O(7-x) specimens over the pore fraction range of 0.10 to 0.25 was examined. The viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability was determined. Spatial variations in superconductor properties were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in alternating-current shielding and loss behavior. Optical quantitative image analysis on sample cross-sections revealed pore fraction to be the varying microstructural feature.

Superconductor to Mott insulator transition in YBa 2Cu 3O 7/LaCaMnO 3 heterostructures

DOE PAGES

Gray, B. A.; Middey, S.; Conti, G.; ...

2016-09-15

The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In this paper, in pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa 2Cu 3O 7 (YBCO) and colossal magnetoresistance ferromagnet La 0.67Ca 0.33MnO 3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping inmore » cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Finally, such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.« less

Diffusion coalescence in НоBa2Cu3O7-x single crystals under the application of hydrostatic pressure

NASA Astrophysics Data System (ADS)

Boiko, Y. I.; Bogdanov, V. V.; Vovk, R. V.; Khadzhaj, G. Ya; Kamchatnaya, S. N.; Goulatis, I. L.; Chroneos, A.

2017-09-01

Experimental results on the effect of external hydrostatic pressure up to 5 kbar on the ρ(T) dependence in the ab plane of HoBa2Cu3O7-x single crystals (x  ≈  0.35) in the temperature range from 300 K to the superconducting transition temperature T c are presented and discussed. It was established that the application of external hydrostatic pressure P  =  5 kbar significantly intensified the process of diffusion coalescence of oxygen clusters, causing the growth of their average size. This leads to an increase in the number of negative U-centers, the presence of which results to the appearance of a phase capable of generating paired carriers of electric charge and, correspondingly, characterized by a higher transition temperature T c. Employing this hypothesis that concerns the mechanism of the diffusion coalescence of oxygen clusters, the change in the form of the temperature and time dependences of the electrical resistivity under the application of external hydrostatic pressure is discussed.

The microscopic structure of charge density waves in underdoped YBa 2Cu 3O 6.54 revealed by x-ray diffraction

DOE PAGES

E. M. Forgan; Huecker, M.; Blackburn, E.; ...

2015-12-09

Charge density wave (CDW) order appears throughout the underdoped high-temperature cuprate superconductors, but the underlying symmetry breaking and the origin of the CDW remain unclear. We use X-ray diffraction to determine the microscopic structure of the CDWs in an archetypical cuprate YBa 2Cu 3O 6.54 at its superconducting transition temperature ~60 K. We find that the CDWs in this material break the mirror symmetry of the CuO 2 bilayers. The ionic displacements in the CDWs have two components, which are perpendicular and parallel to the CuO 2 planes, and are out of phase with each other. The planar oxygen atomsmore » have the largest displacements, perpendicular to the CuO 2 planes. Our results allow many electronic properties of the underdoped cuprates to be understood. For example, the CDWs will lead to local variations in the electronic structure, giving an explicit explanation of density-wave states with broken symmetry observed in scanning tunnelling microscopy and soft X-ray measurements.« less

Spin glass freezing and superconductivity in YBa2(Cu(1-x)Fe(x))3O7 alloys

NASA Technical Reports Server (NTRS)

Mirebeau, I.; Hennion, M.; Dianoux, J.; Caignaert, V.; Phillips, T. E.; Moorjani, K.

1991-01-01

The dynamics were studied of the iron spins in superconducting YBa2(Cu(0.94)Fe(0.06))3O7 by neutron time of flight measurements. Two samples were studied with slightly different characteristics, as shown by resistivity and neutron diffraction measurements. The same dynamical anomalies are observed by neutrons in both samples. Differences appear qualitative but not quantitative. In the whole temperature range, the q-dependence of the magnetic intensity mainly reflects the magnetic form factor of iron which shows that the iron spins are almost uncorrelated. The elastic and quasielastic intensities strongly vary with temperature. A spin glass like freezing is revealed at low temperature by a sharp decrease of the quasielastic intensity, an increase of the 'elastic' or resolution limited intensity and a minimum in the quasielastic width. The freezing temperature (T sub f - 18 K) corresponds to that already determined by a magnetic splitting in Mossbauer experiments. Above T sub f, the relaxation of the iron spins in the paramagnetic state is modified by the occurrence of superconductivity. An increase was observed of the quasielastic intensity and of the quasielastic width at the superconducting transition.

Effects of graphene oxide doping on the structural and superconducting properties of YBa2Cu3O7-δ

NASA Astrophysics Data System (ADS)

Dadras, S.; Falahati, S.; Dehghani, S.

2018-05-01

In this research we reported the effects of graphene oxide (GO) doping on the structural and superconducting properties of YBa2Cu3O7-δ (YBCO) high temperature superconductors. We synthesized YBCO powder by sol-gel method. After calcination, the powder mixed with different weight percent (0, 0.1, 0.3, 0.7, 1 wt.%) of GO. Refinement of X-ray diffraction (XRD) was carried out by material analysis using diffraction (MAUD) program to obtain the structural parameters such as lattice parameters, site occupancy of different atoms and orthorhombicity value for the all samples. Results show that GO doping does not change the structure of YBCO compound, Cu (1), Cu (2) and oxygen sites occupancy. It seems that GO remains between the grains and can play the role of weak links. We found that GO addition to YBCO compound increases transition temperature (TC). The oxygen contents of the all GO-doped samples are increased with respect to the pure one. The strain (ɛ) of the samples obtained from Williamson-Hall method, varies with increasing of GO doping. The scanning electron microscopy (SEM) images of the samples show better YBCO grain connections by GO doping.

Secondary ion mass spectroscopy study of Au trapping and migration in the Au-irradiated YBa2Cu3O7 - delta film

NASA Astrophysics Data System (ADS)

Li, Yupu; Kilner, J. A.; Liu, J. R.; Chu, W. K.; Wagner, G. A.; Somekh, R. E.

1996-05-01

The range data and migration of Au in YBa2Cu3O7-δ film were studied with implanted 197Au (1.5 MeV 5×1015 Au+/cm2) as a tracer. The film was a c-axis oriented film, ˜750 nm thick, deposited by high-pressure planar dc sputtering on <100> LaAlO3. Analysis by secondary ion mass spectroscopy shows that the as-implanted Au concentration distribution is essentially Gaussian-like and the depth (R̂p) of maximum Au concentration (˜1.2 wt %) is 201 nm. The projected range (R¯p) and (R̂p) are found to be in very good agreement with the simulated data by TRIM-95, whereas the measured ``straggle'' (ΔRp*) is about 20% larger than that by TRIM-95 simulation. It has also been found that the implanted 197Au starts to migrate within the film at a temperature between 650 and 700 °C, which is much higher than that for the implanted 2H (˜175 °C) and the implanted 18O (between 250 and 300 °C) in c-oriented YBa2Cu3O7-δ films.

Single crystals of the 96 K superconductor (Hg,Cu)Ba2CuO4+δ: Growth, structure and magnetism

NASA Astrophysics Data System (ADS)

Pelloquin, D.; Hardy, V.; Maignan, A.; Raveau, B.

1997-02-01

Single crystals of the 1201 (n = 1) (Hg,Cu)Ba2CuO4+δ mercury based cuprate have been grown by using a simple process without dry box. The as-synthesized crystals exhibit constant Tc(onset) of 96 K with sharp superconducting transitions. The electron microscopy coupled with EDX analyses evidence a ``1201''-type structure while a mercury deficiency is observed balanced by an excess of copper. The structural refinements based on single-crystal X-ray diffraction data confirm the electron deficiency on the Hg site (0,0,0) and show a splitting of the latter along the c axis correlated to the partial substitution of Cu for Hg. This structural study leads to the following formula Hg0.84Cu0.16Ba2CuO4.19. The magnetic study of a large crystal (1.1 × 0.38 × 0.065 mm3) shows that the (Hg,Cu)-1201 crystals exhibit an irreversibility line higher than that of the 1201 Hg0.8Bi0.2Ba2CuO4+δ crystal (Tc = 75 K). From the reversible magnetization, a λab(0) = 2470 Å value can be extrapolated. Using a 3D-2D decoupling formula, we obtain γ = 29 for the electronic anisotropy of this phase.

Low temperature internal friction spectrum of YBa 2Cu 3O x

NASA Astrophysics Data System (ADS)

Mi, Y.; Schaller, R.; Berger, H.; Benoit, W.; Sathish, S.

1991-01-01

The elastic and anelastic behaviours of polycrystalline YBa 2Cu 3O x specimens have been studied between 80 and 300 K, by means of a resonant bar technique. Three damping peaks have been observed at 90, 115 and 220 K. The stability of these peaks during annealing in vacuum has been carefully examined. The 90 K peak is not related to the superconducting transition because it is still observed after thermal treatments leading to the disappearance of superconductivity. The 115 K is due to a relaxation mechanism. The activation energy is ∼0.17 eV and the frequency factor is ∼10 12s -1. Also this peak is certainly correlated with the excess oxygen atoms, because it disappears with annealing in vacuum. The 220 K maximum, which was also observed by ultrasonic measurements, seems to be affected by the sample preparation, i.e. by the sintering conditions. Finally, a frequency hysteresis has been observed in every superconducting sample, which accounts for an anomalous behaviour of the elastic modulus.

Environment-resistive coating for the thin-film-based superconducting fault-current limiter Ag/Au-Ag/YBa 2Cu 3O 7/CeO 2/Al 2O 3

NASA Astrophysics Data System (ADS)

Matsui, H.; Kondo, W.; Tsukada, K.; Sohma, M.; Yamaguchi, I.; Kumagai, T.; Manabe, T.; Arai, K.; Yamasaki, H.

2010-02-01

We have studied environment-resistive coatings (ERC) for the thin-film-based superconducting fault-current limiter (SFCL) Ag/Au-Ag/YBa 2Cu 3O 7/CeO 2/Al 2O 3. We evaluated nine candidate ERC materials by two accelerating-environment tests, and revealed that the shellac- and the fluorine-resin have a high environmental resistance. Especially, the shellac resin almost completely protected Jc of an element exposed to 60 °C saturated water vapor for 2 h (3.4->3.2 MA/cm 2). We also performed a practical operation test of SFCL using an element half covered by shellac, and found that the ERC does not diminish the current limiting properties similarly to the previous results of the Teflon-coated SFCL [1].

Defects and anharmonicity induced electron spectra of YBa2Cu3O7-δ superconductors

NASA Astrophysics Data System (ADS)

Singh, Anu; Indu, B. D.

2018-05-01

The effects of defects and anharmonicities on the electron density of states (EDOS) have been studied in high-temperature superconductors (HTS) adopting the many body quantum dynamical theory of electron Green's functions via a generalized Hamiltonian that includes the effects of electron-phonon interactions, anharmonicities and point impurities. The automatic emergence of pairons and temperature dependence of EDOS are appear as special feature of the theory. The results thus obtained and their numerical analysis for YBa2Cu3O7-δ superconductors clearly demonstrate that the presence of defects, anharmonicities and electron-phonon interactions modifies the behavior of EDOS over a wide range of temperature.

Orbital symmetry of charge-density-wave order in La 1.875Ba 0.125CuO 4 and YBa 2Cu 3O 6.67

DOE PAGES

A. J. Achkar; He, F.; Sutarto, R.; ...

2016-02-15

Recent theories of charge density wave (CDW) order in high temperature superconductors have predicted a primarily d CDW orbital symmetry. Here, we report on the orbital symmetry of CDW order in the canonical cuprate superconductors La 1.875Ba 0.125CuO 4 (LBCO) and YBa 2Cu 3O 6.67 (YBCO), using resonant soft x-ray scattering and a model mapped to the CDW orbital symmetry. From measurements sensitive to the O sublattice, we conclude that LBCO has predominantly s0 CDW orbital symmetry, in contrast to the d orbital symmetry recently reported in other cuprates. Additionally, we show for YBCO that the CDW orbital symmetry differsmore » along the a and b crystal axes and that these both differ from LBCO. This work highlights CDW orbital symmetry as an additional key property that distinguishes the di erent cuprate families.« less

Electronic structure of the La 1 + xBa 2 - xCu 3O 7 + δ system studied by photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Lindberg, P. A. P.; Shen, Z.-X.; Hwang, J.; Shih, C. K.; Lindau, I.; Spicer, W. E.; Mitzi, D. B.; Kapitulnik, A.

1989-01-01

Photoemission experiments utilizing synchrotron radiation have been carried out on the high temperature superconductor La 1.075Ba 1.925Cu 3O 7.0. The valence band spectra show similar spectral features as those of YBa 2Cu 3O 6.9, even though large differences in relative peak intensities are observed. Oxygen-related states are identified by scanning the photon energy through the O2 s → O2 p absorption edge. The stability of the sample surface, and changes in the valence band spectra after annealing in ultrahigh vacuum are also briefly discussed.