WorldWideScience

Sample records for bulk high-tc superconductors

  1. Mechanical reliability of bulk high Tc superconductors

    International Nuclear Information System (INIS)

    Freiman, S.W.

    1990-01-01

    Most prospective applications for high T c superconductors in bulk form, e.g. magnets, motors, will require appreciable mechanical strength. Work at NIST [National Institute of Standards and Technology] has begun to address issues related to mechanical reliability. For example, recent studies on Ba-Y-Cu-O have shown that the intrinsic crack growth resistance, K IC , of crystals of this material is even smaller than was first reported, less than that of window glass, and is sensitive to moisture. Processing conditions, particularly sintering and annealing atmosphere, have been shown to have a major influence on microstructure and internal stresses in the material. Large internal stresses result from the tetragonal to orthorhombic phase transformation as well as the thermal expansion anisotropy in the grains of the ceramic. Because stress relief is absent, microcracks form which have a profound influence on strength

  2. Induction linear accelerators with high-Tc bulk superconductor lenses

    International Nuclear Information System (INIS)

    Matsuzawa, Hidenori; Wada, Haruhisa; Mori, Satoshi; Yamamoto, Tadashi

    1991-01-01

    Solenoidal coils in a one-stage induction accelerator were replaced by a high-T c bulk superconductor lens (Supertron). The accelerator postaccelerated injected electron beams to ∼ 400 keV, ∼ 0.35 kA, and ∼ 10 ns of duration time. (author)

  3. Proposal of Magnetic Circuit using Magnetic Shielding with Bulk-Type High Tc Superconductors

    Science.gov (United States)

    Fukuoka, Katsuhiro; Hashimoto, Mitsuo; Tomita, Masaru; Murakami, Masato

    Recently, bulk-type high Tc superconductors having a characteristic of critical current density over 104 A/cm2 in liquid nitrogen temperature (77K) on 1T, can be produced. They are promising for many practical applications such as a magnetic bearing, a magnetic levitation, a flywheel, a magnetic shielding and others. In this research, we propose a magnetic circuit that is able to use for the magnetic shield of plural superconductors as an application of bulk-type high Tc superconductors. It is a closed magnetic circuit by means of a toroidal core. Characteristics of the magnetic circuit surrounded with superconductors are evaluated and the possibility is examined. As the magnetic circuit of the ferrite core is surrounded with superconductors, the magnetic flux is shielded even if it leaked from the ferrite core.

  4. Development of application technique of bulk high-Tc superconductor

    International Nuclear Information System (INIS)

    Hong, Kye Won; Kim, Chan Joong; Kim, Kee Baek; Kwon, Sun Chil; Won, Dong Yun; Lee, Hoh Jin; Lee, Heui Kyoon; Jang, Kun Ik; Yang, Suk Woo

    1995-03-01

    YBCO-Ag composite superconductors were prepared by extrusion using inorganic binder materials. In the case of the undoped 1-2-3 sample with a dia. of 2.5 mm, critical current density (Jc) was 150 A/cm 2 and current density (Ic) was 10 amps. In the case of the sample with a die. of 4.5 mm, meanwhile, Jc and Ic were 50 A/cm 2 and 32 amps, respectively. Influence of BaCeO 3 addition on magnetization characteristics of melt-textured Y-Ba-Cu-O superconductor was investigated. The variation of magnetization behavior due to the addition of BaCeO 3 is discussed on the basis of the related microstructures. 37 figs, 1 tab, 56 refs. (Author)

  5. Surface flux density distribution characteristics of bulk high-Tc superconductor in external magnetic field

    International Nuclear Information System (INIS)

    Torii, S.; Yuasa, K.

    2004-01-01

    Various magnetic levitation systems using oxide superconductors are developed as strong pinning forces are obtained in melt-processed bulk. However, the trapped flux of superconductor is moved by flux creep and fluctuating magnetic field. Therefore, to examine the internal condition of superconductor, the authors measure the dynamic surface flux density distribution of YBCO bulk. Flux density measurement system has a structure with the air-core coil and the Hall sensors. Ten Hall sensors are arranged in series. The YBCO bulk, which has 25 mm diameter and 13 mm thickness, is field cooled by liquid nitrogen. After that, magnetic field is changed by the air-core coil. This paper describes about the measured results of flux density distribution of YBCO bulk in the various frequencies of air-core coils currents

  6. Surface flux density distribution characteristics of bulk high- Tc superconductor in external magnetic field

    Science.gov (United States)

    Torii, S.; Yuasa, K.

    2004-10-01

    Various magnetic levitation systems using oxide superconductors are developed as strong pinning forces are obtained in melt-processed bulk. However, the trapped flux of superconductor is moved by flux creep and fluctuating magnetic field. Therefore, to examine the internal condition of superconductor, the authors measure the dynamic surface flux density distribution of YBCO bulk. Flux density measurement system has a structure with the air-core coil and the Hall sensors. Ten Hall sensors are arranged in series. The YBCO bulk, which has 25 mm diameter and 13 mm thickness, is field cooled by liquid nitrogen. After that, magnetic field is changed by the air-core coil. This paper describes about the measured results of flux density distribution of YBCO bulk in the various frequencies of air-core coils currents.

  7. Flux Trapping Properties of Bulk HIGH-TC Superconductors in Static Field-Cooling Magnetization

    Science.gov (United States)

    Deng, Z.; Tsuzuki, K.; Miki, M.; Felder, B.; Hara, S.; Izumi, M.

    2013-06-01

    The trapping process and saturation effect of trapped magnetic flux of bulk high-temperature superconductors by static field-cooling magnetization (FCM) are reported in the paper. With a cryogenic Bell Hall sensor attached on the center of the bulk surface, the synchronous magnetic signals were recorded during the whole magnetization process. It enables us to know the flux trapping behavior since the removal of the excitation field, as well as the subsequent flux relaxation phenomenon and the flux dissipation in the quench process of the bulk sample. With the help of flux mapping techniques, the relationship between the trapped flux and the applied field was further investigated; the saturation effect of trapped flux was discussed by comparing the peak trapped field and total magnetic flux of the bulk sample. These studies are useful to understand the basic flux trapping properties of bulk superconductors.

  8. Magnetic torque transferring study for bulk High-Tc superconductors and permanent magnets

    International Nuclear Information System (INIS)

    Wongsatanawarid, A; Suzuki, A; Seki, H; Murakami, M

    2009-01-01

    The torque transferring mechanism taking place in a superconducting mixer design has been studied. Several coupling magnetic arrangements were investigated for more details in the engineering design. A bulk superconductor sample was used to study the torque forces for various cooling gaps, and the twist angle dependence was also monitored for the rotational stiffness in stability. The experimental data with four permanent magnet configurations have been studied in the present work. The maximum torque forces are summarized for usage of engineering design with various gaps. The torque/gap characteristics for four configurations were also measured for the optimisation of the torque at a designed operating gap.

  9. Measurement of the magnetic field inside the holes of a drilled bulk high-Tc superconductor

    Science.gov (United States)

    Lousberg, Gregory P.; Fagnard, Jean-François; Noudem, Jacques G.; Ausloos, Marcel; Vanderheyden, Benoit; Vanderbemden, Philippe

    2009-04-01

    We use macroscopic holes drilled in a bulk YBCO superconductor to probe its magnetic properties in the volume of the sample. The sample is subjected to an AC magnetic flux with a density ranging from 30 to 130 mT and the flux in the superconductor is probed by miniature coils inserted in the holes. In a given hole, three different penetration regimes can be observed: (i) the shielded regime, where no magnetic flux threads the hole; (ii) the gradual penetration regime, where the waveform of the magnetic field has a clipped sine shape whose fundamental component scales with the applied field; and (iii) the flux concentration regime, where the waveform of the magnetic field is nearly a sine wave, with an amplitude exceeding that of the applied field by up to a factor of two. The distribution of the penetration regimes in the holes is compared with that of the magnetic flux density at the top and bottom surfaces of the sample, and is interpreted with the help of optical polarized light micrographs of these surfaces. We show that the measurement of the magnetic field inside the holes can be used as a local characterization of the bulk magnetic properties of the sample.

  10. High-Tc superconductor applications

    International Nuclear Information System (INIS)

    Anon.

    1988-01-01

    There has been much speculation about new products and business opportunities which high-Tc superconductors might make possible. However, with the exception of one Japanese survey, there have not been any recognized forecasts suggesting a timeframe and relative economic impact for proposed high-Tc products. The purpose of this survey is to provide definitive projections of the timetable for high-Tc product development, based on the combined forecasts of the leading U.S. superconductivity experts. The FTS panel of experts on high-Tc superconductor applications, representing both business and research, forecast the commercialization and economic impact for 28 classes of electronic, magnetic, communications, instrumentation, transportation, industrial, and power generation products. In most cases, forecasts predict the occurrence of developments within a 90% statistical confidence limit of 2-to-3 years. The report provides background information on the 28 application areas, as well as other information useful for strategic planners. The panel also forecast high-Tc research spending, markets, and international competitiveness, and provide insight into how the industry will evolve

  11. Levitation force and magnetization in bulk and thin film high Tc superconductors

    International Nuclear Information System (INIS)

    Riise, A.B

    1998-04-01

    The authors present high-resolution measurements of the repulsive vertical force and its associated stiffness between a Nd-B-Fe magnet and a YBa 2 Cu 3 O 7-δ superconductor in cylindrical geometry. The results are compared with theoretical predictions. The calculations are based on a model in which the superconductor is assumed to be either a sintered granular material or consisting of grains embedded in a nonactive matrix so that only intragranular currents are important. The critical state model is applied to each grain individually and closed form expressions for both vertical force F z and stiffness are obtained in a configuration with cylindrical symmetry. The model explains all features of the experimental results in a consistent way. A good quantitative agreement has been obtained using only three adjustable parameters. Several central aspects of the phenomenon of magnetic levitation with high-T c superconductors are presented. High-resolution measurements are made of the repulsive vertical force and its associated stiffness as well as the horizontal stabilizing force and the stiffness governing lateral vibrations. The results obtained at 77 K using a granular YBa 2 Cu 3 O 7-δ sample and Nd-Fe-B magnet in a rectangular levitation configuration are compared with theoretical predictions. The calculations, which are based on the critical state model with the assumption that it applies to the grins individually, give closed-form expressions for all the measured quantities. It is concluded that the present model explains all features of the observations in a consistent way. Using only three adjustable parameters a good agreement exists also at a quantitative level. Experimental studies and theoretical modelling of the levitation force on a permanent magnet placed above a superconducting thin film are offered. It is shown that measurements of the levitation force is a simple and precise method to determine the critical current density in thin films

  12. Present Status and Future Prospects in Bulk Processing of HIGH-Tc Superconductors

    Science.gov (United States)

    Jin, S.; Chu, C. W.

    The following sections are included: * INTRODUCTION * HIGH SUPERCONDUCTING TRANSITION TEMPERATURE * HIGH CRITICAL CURRENT DENSITY * Grain Boundary Weak Links * Nature of Weak Links * Possible Processing Approaches for Weak Link Problem * Processing Techniques for Texture Formation * Flux Creep in HTSC * Desirable Pinning Defects * Processing for Flux Pinning Enhancement * PROSPECTS FOR BULK APPLICATIONS * Magnetic Field Gener * Energy Storage * Magnetic Shielding * Other Applications * CONCLUDING REMARKS * ACKNOWLEDGMENT * REFERENCES

  13. Feasibility of introducing ferromagnetic materials to onboard bulk high-Tc superconductors to enhance the performance of present maglev systems

    Science.gov (United States)

    Deng, Zigang; Wang, Jiasu; Zheng, Jun; Zhang, Ya; Wang, Suyu

    2013-02-01

    Performance improvement is a long-term research task for the promotion of practical application of promising high-temperature superconducting (HTS) magnetic levitation (maglev) vehicle technologies. We studied the feasibility to enhance the performance of present HTS Maglev systems by introducing ferromagnetic materials to onboard bulk superconductors. The principle here is to make use of the high magnetic permeability of ferromagnetic materials to alter the flux distribution of the permanent magnet guideway for the enhancement of magnetic field density at the position of the bulk superconductors. Ferromagnetic iron plates were added to the upper surface of bulk superconductors and their geometric and positioning effects on the maglev performance were investigated experimentally. Results show that the guidance performance (stability) was enhanced greatly for a particular setup when compared to the present maglev system which is helpful in the application where large guidance forces are needed such as maglev tracks with high degrees of curves.

  14. Feasibility of introducing ferromagnetic materials to onboard bulk high-Tc superconductors to enhance the performance of present maglev systems

    International Nuclear Information System (INIS)

    Deng, Zigang; Wang, Jiasu; Zheng, Jun; Zhang, Ya; Wang, Suyu

    2013-01-01

    Highlights: ► Ferromagnetic materials guide the flux distribution of the PMG to bulk positions. ► With ferromagnetic materials, guidance performance can be enhanced greatly. ► A new HTS Maglev system with onboard ferromagnetic materials is designed. ► The design can meet large guidance force requirements for practical applications. -- Abstract: Performance improvement is a long-term research task for the promotion of practical application of promising high-temperature superconducting (HTS) magnetic levitation (maglev) vehicle technologies. We studied the feasibility to enhance the performance of present HTS Maglev systems by introducing ferromagnetic materials to onboard bulk superconductors. The principle here is to make use of the high magnetic permeability of ferromagnetic materials to alter the flux distribution of the permanent magnet guideway for the enhancement of magnetic field density at the position of the bulk superconductors. Ferromagnetic iron plates were added to the upper surface of bulk superconductors and their geometric and positioning effects on the maglev performance were investigated experimentally. Results show that the guidance performance (stability) was enhanced greatly for a particular setup when compared to the present maglev system which is helpful in the application where large guidance forces are needed such as maglev tracks with high degrees of curves

  15. Magnetic levitation systems using a high-Tc superconducting bulk magnet

    Energy Technology Data Exchange (ETDEWEB)

    Ohsaki, Hiroyuki [Dept. of Electrical Engineering, Univ. of Tokyo (Japan); Kitahara, Hirotaka [Dept. of Electrical Engineering, Univ. of Tokyo (Japan); Masada, Eisuke [Dept. of Electrical Engineering, Univ. of Tokyo (Japan)

    1996-12-31

    Recent development of high-performance high-Tc bulk superconductors is making their application for electromagnetic force use feasible. We have studied electromagnetic levitation systems using high-Tc bulk superconducting material. In this paper, after an overview of superconducting magnetic levitation systems, with an emphasis on high-Tc bulk superconductor applications, experimental results of a high-Tc bulk EMS levitation and FEM analysis results of magnetic gradient levitation using bulk superconductor are described. Problems to be solved for their application are also discussed. (orig.)

  16. Influence of lateral displacement on the levitation performance of a magnetized bulk high-Tc superconductor magnet

    International Nuclear Information System (INIS)

    Liu, W.; Wang, J.S.; Ma, G.T.; Zheng, J.; Tuo, X.G.; Li, L.L.; Ye, C.Q.; Liao, X.L.; Wang, S.Y.

    2012-01-01

    Compared with the permanent magnet, the magnetized bulk high-T c superconductor magnet (MBSCM) can trap higher magnetic field due to its strong flux pinning ability, so it is a good candidate to improve the levitation performance of high-T c superconductive (HTS) maglev system. The trapped magnetic flux of a MBSCM is sustained by the inductive superconducting current produced by the magnetizing process and is susceptible to the current intensity as well as configuration. In the HTS maglev system, the lateral displacement is an important process to change the superconducting current within a MBSCM and then affects its levitation performance, which is essential for the traffic ability in curve-way, the loading capacity of lateral impact and so on. The research about influence of lateral displacement on the levitation performance of MBSCM is necessary when MBSCM is applied on the HTS maglev vehicle. The experimental investigations about the influence of lateral displacement on the levitation performance of a MBSCM with different trapped fluxes and applied fields are processed in this article. The analyses and conclusions of this article are useful for the practical application of MBSCM in HTS maglev system.

  17. AC losses in high Tc superconductors

    International Nuclear Information System (INIS)

    Campbell, A.M.

    1998-01-01

    Full text: Although in principle the AC losses in high Tc superconductors can be calculated from the critical current density, a number of complications make this difficult. The Jc is very field dependent, there are intergranular and intragranular critical currents, the material is anisotropic and there is usually a large demagnetising factor. Care must be taken in interpreting electrical measurements since the voltage depends on the position of the contacts. In spite of these complications the simple theory of Norris has proved surprisingly successful and arguments will be presented as to why this is the case. Results on a range of tapes will be compared with theory and numerical methods for predicting losses discussed. Finally a theory for coupling losses will be given for a composite conductor with high resistance barriers round the filaments

  18. Electronic properties of high Tc superconductors

    International Nuclear Information System (INIS)

    Rojo, A.G.

    1989-01-01

    Using analytical and numerical methods, the electronic properties of the copper-oxygen plane in the normal phase of high Tc superconductors are described. Using the slave-boson technique in the saddle point, a theory of the metal insulator transition which generalizes the notions of a Mott insulator to the case of more than a single band for those planes is presented. A phase-diagram is obtained in the parameter space and effective masses, optical gaps and metallization are calculated as a function of the number of carriers. Based on the experimental evidence, the theory permits classification of superconducting compounds as charge transfer insulators in the stoichiometric case. The insulator state is characterized by a non-zero optical gap and a divergent effective mass which corresponds to the breakage of a Fermi-liquid scheme. The results obtained are applicable to metal-transition-oxides whose behaviour has been traditionally controversial and it is concluded that it is necessary to broaden the meaning of a Mott insulator to the case of more than a single band to better understand them. Based on the ideas of group renormalization in a real space, a lattice approximation is presented, which allows: a) To complement the treatment of slave-bosons in phase diagrams and optical gaps; b) Identification of an attraction mechanism between carriers originating from purely repulsive interactions. Numerical calculations in small clusters show the existence of a pairing mechanism showing a superconducting instability from a charge transfer insulator. (Author) [es

  19. Critical current enhancement in high Tc superconductors

    International Nuclear Information System (INIS)

    Jin, S.; Graebner, J.E.; Tiefel, T.H.

    1990-01-01

    Progress toward major technological applications of the bulk, high T c superconductors has been hindered by two major barriers, i.e., the Josephson weak-links at grain boundaries and the lack of sufficient intragrain flux pinning. It has been demonstrated that the weak link problem can be overcome by extreme alignment of grains such as in melt-textured-growth (MTG) materials. Modified or improved processing by various laboratories has produced further increased critical currents. However, the insufficient flux pinning seems to limit the critical current density in high fields to about 10 4 --10 5 A/cm 2 at 77K, which is not satisfactory for many applications. In this paper, processing, microstructure, and critical current behavior of the MTG type superconductors are described, and various processing possibilities for flux pinning enhancement are discussed

  20. Pinning and creep in high-Tc superconductors

    International Nuclear Information System (INIS)

    Ovchinnikov, Yu.N.; Ivlev, B.I.

    1992-01-01

    The angular and magnetic field dependence of a critical current parallel to the layers in the layered superconductors is studied. The critical current value is found for a superconductor with strong pinning centers. Quantum flux creep in sufficiently perfect layered high-Tc superconductors is discussed. The cross-over temperature between activated and quantum creep is found. (orig.)

  1. Processing and critical currents of high-Tc superconductor wires

    International Nuclear Information System (INIS)

    Krauth, H.; Heine, K.; Tenbrink, J.

    1991-01-01

    High-Tc superconductors are expected to have a major impact on magnet and energy technology. For technical applications they have to fulfill the requirement of carrying sufficient current at a critical current density of the order of 10 5 A/cm 2 at operating temperature and magnetic field. At 77 K these values have not been achieved yet in bulk material or wires due to weak link problems and flux creep effects. Progress made so far and remaining problems will be discussed in detail concentrating on problems concerning development of technical wires. In Bi-based materials technically interesting critical current densities could be achieved at 4.2 K in fields above 20 T (1,2), rendering possible the use of such material for very high field application. (orig.)

  2. Quantum Monte Carlo simulations for high-Tc superconductors

    International Nuclear Information System (INIS)

    Muramatsu, A.; Dopf, G.; Wagner, J.; Dieterich, P.; Hanke, W.

    1992-01-01

    Quantum Monte Carlo simulations for a multi-band model of high-Tc superconductors are reviewed with special emphasis on the comparison of different observabels with experiments. It is shown that a give parameter set of the three-band Hubbard model leads to a consistent description of normal-state propteries as well as pairing correlation function for the copper-oxide superconductors as a function of doping and temperature. (orig.)

  3. Fast neutron induced flux pinning in Tl-based high-Tc single crystals and thin films, highly textured tapes and melt-textured bulk 123-superconductors

    International Nuclear Information System (INIS)

    Brandstaetter, G.; Samadi Hosseinalli, G.; Kern, C.; Sauerzopf, F.M.; Schulz, G.W.; Straif, W.; Yang, X.; Weber, H.W.; Hu, Q.Y.

    1999-01-01

    Various compounds (TI-2223, TI-1223, TI-2212) as well as material forms (single crystals, thin films, ceramics, tapes) of TI-based high temperature superconductors were investigated by magnetic and transport techniques. TI-2223 has a very 'low lying' irreversibility line (H parallel e) and negligible critical current densities J c at 77 K. However, the irreversibility line shifts to higher fields and temperatures and J c is strongly enhanced, even at 77 K, after fast neutron irradiation. In contrast, the related TI-1223 compound has a much steeper irreversibility line (H parallel c) similar to that of Y-123. J c is significant up to 77 K, even in the unirradiated state, and can be largely improved by neutron irradiation. Transport measurements made on TI-1223 tapes still show much lower critical current densities. TI-2212 and Tl-2223 thin films have J c 's at 77 K, which are comparable to those of TI-1223 single crystals. Transport measurements on highly textured Bi-2223 tapes as well as flux profile measurements on Nd-123 bulk superconductors confirm the beneficial effects of neutron induced defects (collision cascades) for flux pinning. (author)

  4. High-Tc ferroelectrics and superconductors

    International Nuclear Information System (INIS)

    Muller, K.A.

    1990-01-01

    The meaning of the title refers to transition temperatures T c in ferroelectrics (FE) and superconductors (S). The highest T c 's in either field are observed in oxides: 1770 K in the ferroelectric La 2 TiO 7 and 125 K in the superconductor Tl 2 Ca 2 Cu 3 O 10 . Therefore, the question can be asked whether the observed high T c 's in oxide FE and S are a pure coincidence or whether there may be an underlying reason for it. This question is addressed first by recalling recent advances concerning anharmonic FE-properties and then by reviewing S-findings in the new compounds related to these properties

  5. High-Tc superconductor quantum interference devices

    International Nuclear Information System (INIS)

    1991-01-01

    This patent describes a superconductive quantum interferometric device for sensing a characteristic of a magnetic field. It comprises a substrate having a surface, the substrate being selected from the group which consists of strontium titanate, aluminum oxide, sapphire, ZrO 2 and mixtures thereof; a coating of MgO on the surface of the substrate; two identical thin-strip films of a high-critical temperature superconductor on the coating, each of the films having a pair of mutually parallel arms in the form of superconductor strips extending toward and aligned with super conductor strips forming corresponding arms of the other thin-strip film, and a crossbar strip connecting the arms of each thin-strip film at right angles to the arms, the high-critical-temperature superconductor being selected from the group which consists of yttrium-barium-calcium-copper-oxides, bismuth-strontium-calcium-copper-oxides, thallium-barium-copper-oxides, thallium-barium-calcium-copper-oxides, barium oxide: potassium oxide: bismuth oxides, and calcium oxide: zinc oxide: iron oxides; and insulating films on the coating between corresponding free ends of the arms thin-strip films, the insulating films being composed of a material selected from the group which consists of silicon dioxide, silicon nitride, magnesium oxide and mixture thereof

  6. An infrared view of high Tc superconductors

    International Nuclear Information System (INIS)

    Tanner, D.B.; Timusk, T.; McMaster Univ., Hamilton, ON

    1989-01-01

    Studies of the infrared properties of the high T c superconductors are reviewed, with particular emphasis on attempts to determine the energy gap by far infrared spectroscopy and on the properties of the strong absorption that occurs in the mid infrared. The authors argue that this mid-infrared absorption is a direct particle-hole excitation rather than a Holstein emission process. In addition, they conclude that although the energy gap is not easily observed, several recent experiments place it in the weak to moderate strong coupling range

  7. High Tc superconductors using solution techniques

    International Nuclear Information System (INIS)

    Barboux, P.; Valente, I.; Henry, M.; Morineau, R.; Tarascon, J.M.; Khan, S.; Shokoohi, F.; Bagley, B.G.

    1989-01-01

    The authors have investigated different solution techniques to synthesize the Cu-based superconductors in the thick film form. Thick films of YBa 2 Cu 3 O 7 have been produced using controlled precipitation techniques. Bi-based and Tl-based materials have been deposited by spraying of ionic solutions. The numerous difficulties encountered during each process are analyzed in order to propose new synthesis procedures such as a new method, based on the precipitation of hydroxides only, which is described as a prospective for lowering the synthesis temperature and shortening the reaction time

  8. Infrared properties of high Tc superconductors

    International Nuclear Information System (INIS)

    Schlesinger, Z.; Rotter, L.D.; Collins, R.T.; Holtzberg, F.; Feild, C.

    1991-01-01

    Over the past several years a coherent phenomenology of the high T c cuprate superconductors has begun to emerge. Infrared measurements have contributed several important ingredients to this picture including: (1) the inference of a scattering rate that is linear in frequency for ω>T, and of order ω, (2) a characteristic energy scale in the superconducting state of 500 cm -1 (60 meV), which can be interpreted as a superconducting pair excitation threshold or energy gap, and (3) evidence for very unusual temperature dependence in the vicinity of T c . An attempt to describe these aspects of the data is presented here

  9. Oxygen diffusion in high-Tc superconductors

    International Nuclear Information System (INIS)

    Rothman, S.J.; Routbort, J.L.

    1992-07-01

    The cuprate superconductors are fascinating not only because of their technical promise, but also because of their structures, especially the anisotropy of the crystal lattice. There are some structural similarities among these compounds, but also significant differences. Measurements of the oxygen tracer diffusion coefficients have been carried out as a function of temperature, oxygen partial pressure, crystal orientation, and doping in the La-Sr-Cu-0, Y-Ba-Cu-0, and Bi-Sr-Ca-Cu-0 systems. These measurements have revealed a variety of defect mechanisms operating in these compounds; the exact nature of the mechanism depends on the details of the structure

  10. Charged vortices in high-Tc superconductors

    International Nuclear Information System (INIS)

    Matsuda, Y.; Kumagai, K.

    2002-01-01

    It is well known that a vortex in type II superconductors traps a magnetic flux. Recently the possibility that a vortex can accumulate a finite electric charge as well has come to be realized. The sign and magnitude of the vortex charge not only is closely related to the microscopic electronic structure of the vortex, but also strongly affects the dynamical properties of the vortex. In this chapter we demonstrate that a vortex in high-T c superconductors (HTSC) indeed traps a finite electronic charge, using the high resolution measurements of the nuclear quadrupole frequencies. We then discuss the vortex Hall anomaly whose relation with the vortex charging effect has recently received considerable attention. We show that the sign of the trapped charge is opposite to the sign predicted by the conventional BCS theory and deviation of the magnitude of the charge from the theory is also significant. We also show that the electronic structure of underlying system is responsible for the Hall sign in the vortex state and again the Hall sign is opposite to the sign predicted by the BCS theory. It appears that these unexpected features observed in both electrostatics and dynamics of the vortex may be attributed to the novel electronic structure of the vortex in HTSC. (orig.)

  11. Granularity effect on microwave surface resistance in high-Tc YBa2Cu3O7-x bulk and thin film superconductor

    International Nuclear Information System (INIS)

    Swarup, Ram; Gupta, A.K.

    2001-01-01

    We report the effect of variation of Josephson coupling strength in YBa 2 Cu 3 O 7-x (YBCO) superconductor due to grain enlargement, grain orientation and magnetic field on microwave surface resistance (R s ). The coupling strength in the bulk samples has been increased by increasing the sample density from 4.4 to 5.3 g/cm 3 , whereas in thin films, the same could be increased by increasing the c-axis orientation of the grains. The value of R s (10 GHz, 65 K) in bulk samples has been found to decrease from 52 to 4 mΩ with the increase of the coupling strength from 0.06 to 0.43 and in thin films from 930 to 600 μΩ with increase of the coupling strength from 0.92 to 2.43. The effect of grain decoupling on microwave surface resistance was studied under dc and microwave magnetic fields. The surface resistance increases gradually with the application of dc and microwave magnetic fields due to grain decoupling and finally gets saturated beyond a certain critical field. (author)

  12. High Tc superconductors at microwave frequencies

    International Nuclear Information System (INIS)

    Gruener, G.

    1991-01-01

    The author discusses various experiments conducted in the micro- and millimeter wave spectral range on thin film and single crystal specimens of the high temperature oxide superconductors. For high quality film the surface resistance R s is, except at low temperatures, due to thermally excited carriers, with extrinsic effects playing only a secondary role. Because of the low loss various passive microwave components, such as resonators, delay lines and filters, with performance far superior to those made of normal metals can be fabricated. The conductivity measured at millimeter wave frequencies displays a peak below T c . Whether this is due to coherence factors or due to the change of the relaxation rate when the materials enter the superconducting state remains to be seen

  13. Spectroscopic views of high-Tc superconductors

    International Nuclear Information System (INIS)

    Wendin, G.

    1989-01-01

    In this paper progress in the field of photoelectron spectroscopy, electron energy loss spectroscopy, inverse photoemission, and infrared- and optical reflectivity applied to high-T c superconductors in analyzed in terms of correlation effects, transport properties and Fermi liquid behavior. For the CuO 2 based materials, a picture emerges of localized holes in copper 3d levels and itinerant holes in oxygen 2p-like bands. A Fermi liquid picture and a superconducting gap is indicated by angle-resolved photoemission, infrared absorption, and NMR. A Fermi surface is indicated by positron annihilation. Infrared absorption revels strongly frequency and temperature dependent scattering and polaronic behavior for frequencies below 0.1 eV. Infrared absorption indicates a maximum superconducting gas of 2Δ/K B T c = 8 and suggests that ordinary samples may show a range of gaps 2 B T c B = 5

  14. Rugged Low-Resistance Contacts To High-Tc Superconductors

    Science.gov (United States)

    Caton, Randall; Selim, Raouf; Byvik, Charles E.; Buoncristiani, A. Martin

    1992-01-01

    Newly developed technique involving use of gold makes possible to fabricate low-resistance contacts with rugged connections to high-Tc superconductors. Gold diffused into specimen of superconducting material by melting gold beads onto surface of specimen, making strong mechanical contacts. Shear strength of gold bead contacts greater than epoxy or silver paste. Practical use in high-current-carrying applications of new high-Tc materials, including superconducting magnets, long-wavelength sensors, electrical ground planes at low temperatures, and efficient transmission of power.

  15. Optical properties of high-Tc superconductors

    International Nuclear Information System (INIS)

    Aspnes, D.E.; Kelly, M.K.

    1989-01-01

    The authors summarize the present status of optical spectroscopy of high-T c superconductors. The optical properties of these materials resemble those of the more common transition metal oxides except for being highly anisotropic in the infrared (IR). This large IR anisotrophy and a need to rely solely on reflectance techniques has hindered progress in obtaining accurate IR data and interpreting these data in terms of microscopic mechanisms. However, experimental consistency is now being approached with single-crystal samples, although interpretations of these data remain controversial and an unequivocal demonstration of a superconducting gap structure has not yet been achieved. The mid IR exhibits an absorption band whose systematics are neither well established nor understood. The situation in the visible-near-ultraviolet (V-NUV) is better, partly because of greatly reduced optical anisotropy and the availability of alternative measurement techniques that are not strongly affected by the lower optical quality of sintered material. As polycrystalline, sintered samples can be prepared relatively easily over wide ranges of composition, doping, and chemical substitution, most work on studying the chemical systematics of these materials has been done in this spectral range and some of the structure that appears here has been positively identified

  16. Doping effects in high-Tc superconductors

    International Nuclear Information System (INIS)

    Hessel Andersen, N.

    1996-11-01

    The purpose of the project has been to study how the superconducting and magnetic properties of the high temperature superconductors change as function of oxygen stoichiometry and cation doping. The primary system of investigation has been YBa 2 Cu 3 O 6+x , which has been studied as function of oxygen stoichiometry, 0 2 planes, that is necessary for superconductivity, is strongly depending on structural ordering. The static properties and the kinetics of the structural ordering process have been studied experimentally by neutron and high energy synchrotron x-ray diffraction, by Raman scattering, and by computer simulation technique. Not only the oxygen stoichiometry but also the cation doping has been shown to influence the magnetic phases, in some cases in an unexpected manner. Thus, by neutron diffraction experiments it has been shown that doping with non-magnetic Al gives rise to a new magnetic phase. A theoretical model, has been developed. The magnetic phases of the Cu and Nd ordering in NdBa 2 Cu 3 O 6+x , and of the Cu and Pr ordering in PrBa 2 Cu 3 O 6+x have been studied by neutron diffraction with the main purpose of understanding why PrBa 2 Cu 3 O 6+x is magnetic and non-superconducting for all oxygen stoichiometries. In NdBa:2Cu 3 O 6+x studies of the magnetic flux lattice have been carried out by Small Angle Neutron Scattering. Additional structural studies of the superconducting and magnetic phases of related materials, of RENi 2 B 2 C (RE = rare earth), and of oxidized and cation doped materials based on La 2 CuO 4+δ have been carried out. Methods for structural studies and analyses, and equipment for electrical and magnetic characterization have been developed. (EG) 5 tabs., 46 ills., 35 refs

  17. On the superconducting phase diagram of high Tc superconductors

    International Nuclear Information System (INIS)

    de la Cruz, F.

    1990-01-01

    The tendency of oxide superconductors to show granularity has been pointed out since the beginning of research on superconductivity in this type of materials. Nevertheless, only very recently the full phase diagram and characteristics of the grains have been determined. In this paper, the authors review and discuss the different critical fields and their relation to the transport of superconducting current. The superconducting response of single crystals of High Tc superconductors is discussed. Special attention is devoted to the behavior of the vortex lattice and, in particular, to the recent discovery of the quenching of H c1 in YBaCuO, several degrees below Tc

  18. Solidification processing of high-Tc superconductors

    CERN Document Server

    Shiohara, Y; Nakamura, Y; Izumi, T

    2001-01-01

    Recent progress in the solidification processing of RE-system (RE:Y, Sm, Nd etc.) oxide superconducting materials is reviewed. The superconducting YBa/sub 2/Cu/sub 3/O/sub y/(Y123) phase is solidified from Y/sub 2/BaCuO/sub 5/(Y211) and liquid phases, by a peritectic reaction. The solidified micro and macro structure can not be explained by the peritectic reaction with diffusion in the solid but rather by diffusion in the liquid. A solidification model for this reaction is developed. It is confirmed that the prediction from the model calculation is in good agreement with the experimental results. Furthermore, the basic idea is expanded to develop a novel single crystal pulling process. Y211 powders were placed at the bottom of the crucible as the solute source for the growth and a BaO-CuO composite (Ba to Cu cation ratio was 3 to 5) was placed on the layer of Y211 powders. Temperature gradient was provided in the melt. Large bulk single crystals were obtained by this technique, and the growth mechanism was al...

  19. The Goettingen high-Tc superconductivity research pool: the effects of structure and structural defects on the performance of high-Tc superconductors. Final reports

    International Nuclear Information System (INIS)

    1992-02-01

    The compilation presents the final reports prepared by the various teams of the Goettingen research pool for high-Tc superconductivity. The reports are entitled: Structure and phase transition in high-Tc superconductors (Krebs/Freyhardt). Preparation and critical properties of high-Tc superconductors (Freyhardt/Heinemann/Zimmermann). EMC measurements in high-Tc superconductors (Bormann/Noelting). Phase analysis of the various phases observed in the preparation of high-Tc superconductors (Faupel/Hehenkamp). Positron annihilation in high-Tc superconductors (Hehenkamp). Preparation and characterization of thin films consisting of superconducting oxide ceramics (v. Minnigerode/Samwer). High-Tc superconductivity in monocrystals (Winzer/Beuermann). Microwave conductivity in high-Tc superconductors (Helberg). High-resolution structural analyses in high-Tc superconductors (Kupcik/Bente). Synthesis, structural analyses and spectroscopy of high-Tc superconductors (Bente). Synthesis, monocrystal growing, crystal structure of high-Tc superconductors (Schwarzmann). Ion-beam-aided studies in high-Tc superconductors (Uhrmacher). (orig./MM) [de

  20. Non-equilibrium spectroscopy of high-Tc superconductors

    International Nuclear Information System (INIS)

    Krasnov, V M

    2009-01-01

    In superconductors, recombination of two non-equilibrium quasiparticles into a Cooper pair results in emission of excitation that mediates superconductivity. This is the basis of the proposed new type of 'non-equilibrium' spectroscopy of high T c superconductors, which may open a possibility for direct and unambiguous determination of the coupling mechanism of high T c superconductivity. In case of low T c superconductors, the feasibility of such the non-equilibrium spectroscopy was demonstrated in classical phonon generation-detection experiments almost four decades ago. Recently it was demonstrated that a similar technique can be used for high T c superconductors, using natural intrinsic Josephson junctions both for injection of non-equilibrium quasiparticles and for detection of the non-equilibrium radiation. Here I analyze theoretically non-equilibrium phenomena in intrinsic Josephson junctions. It is shown that extreme non-equilibrium state can be achieved at bias equal to integer number of the gap voltage, which can lead to laser-like emission from the stack. I argue that identification of the boson type, constituting this non-equilibrium radiation would unambiguously reveal the coupling mechanism of high Tc superconductors.

  1. Powder processing of high Tc oxide superconductors and their properties

    International Nuclear Information System (INIS)

    Vajpei, A.C.; Upadhyaya, G.S.

    1992-01-01

    Powder processing of ceramics is an established technology and in the area of high T c superconductors, its importance is felt even more significantly. The present monograph is an attempt in this direction to explore the perspectives and practice of powder processing routes towards control and optimization of the microstructure and pertinent properties of high T c oxide superconductors. The monograph consists of 6 chapters. After a very brief introduction (Chapter 1), Chapter 2 describes various classes of high T c oxide superconductors and their phase equilibria. Chapter 3 highlights the preparation of oxide superconductor powders through various routes and details their subtle distinctions. Chapter 4 briefly covers characterisation of the oxide superconductors, laying emphasis on the process-analysis and microstructure. Chapter 5 describes in detail various fabrication techniques for bulk superconductors through the powder routes. The last Chapter (Chapter 6) describing properties of bulk oxide superconductors, discusses the role of subtituents, compositional variations and processing methods on such properties. References are given at the end of each chapter. (orig.)

  2. Atomic hydrogen effects on high-Tc superconductors

    International Nuclear Information System (INIS)

    Frantskevich, N.V.; Ulyashin, A.G.; Alifanov, A.V.; Stepanenko, A.V.; Fedotova, V.V.

    1999-01-01

    The atomic hydrogen effects on the properties of bulk high-temperature superconductors were investigated. It is shown that the insertion of the atomic hydrogen into the bulk of these materials from a DC plasma leads to the increase of the critical current density J c for YBaCuO(123) as well as for BiSrCaCuO(2223) high-temperature superconductors. It is found that the hydrogenation of the He implanted samples with following annealing leads to the optically detected blistering on the surface. It means that the textured thin subsurface layers of high-temperature superconductors can be formed by this method. The improvement of superconductivity by atomic hydrogen can be explained by the passivation of dangling bonds and defects on grain boundaries of these materials

  3. Mechanical considerations in the processing of high Tc superconductors

    International Nuclear Information System (INIS)

    Wright, R.N.; German, R.M.; Knorr, D.B.; Maccrone, R.K.; Rajan, K.

    1990-01-01

    This paper presents a brief review of deformation processing concepts germane to high-Tc superconductor processing, and illustrates some available techniques with results from recent work. It is noted that YBa2Cu3O(7-x) powder/binder cold extrusion technique is quite sensitive to binder formulation and processing conditions. With appropriate technique, indefinite lengths of YBa2Cu3O(7-x) powder/binder composite can be extruded with sufficient workability to allow coiling and other forming operations. With heat treatment, the resulting prototype wire is electrically continuous and manifests critical current densities of a few hundred A/sq cm. The hot extrusion of YBa2Cu3O(7-x) powder results in a modest, but favorable, development of a texture involving preferential rotation of the c-axis toward the radial direction. Billet designs involving larger powder charge diameters, and thinner container walls, produce the favorable texture. Unfortunately, such billet designs reduce workability. 29 refs

  4. High-Tc Superconductors Based on FeAs Compounds

    CERN Document Server

    Izyumov, Yuri

    2010-01-01

    Physical properties and models of electronic structure are analyzed for a new class of high-TC superconductors which belong to iron-based layered compounds. Despite their variable chemical composition and differences in the crystal structure, these compounds possess similar physical characteristics, due to electron carriers in the FeAs layers and the interaction of these carriers with fluctuations of the magnetic order. A tremendous interest towards these materials is explained by the prospects of their practical use. In this monograph, a full picture of the formation of physical properties of these materials, in the context of existing theory models and electron structure studies, is given. The book is aimed at a broad circle of readers: physicists who study electronic properties of the FeAs compounds, chemists who synthesize them and specialists in the field of electronic structure calculations in solids. It is helpful not only to researchers active in the fields of superconductivity and magnetism, but also...

  5. Orbitals, correlation, valencies in high-Tc superconductors

    International Nuclear Information System (INIS)

    Khomskii, D.I.

    1990-09-01

    The survey is given of certain properties of high-Tc superconductors connected with the details of their electronic structure such as the kind of orbitals involved and the degree of correlation. Special attention is paid to the properties of cuprates at high doping level. The problem whether there exists a ''Mott transition'' at high electron or a hole concentration is discussed. We also discuss physical factors (d-p Coulomb interaction, orbital mixing) leading to the partial occupation of copper d x 2 -orbital. In particular we show that in localized picture (x 2 -y 2 ) and z 2 -levels in La 2-x Sr x CuO 4 may cross at x approx. 0.4 which may be responsible for a marked change of many properties at this doping. The possible role of x 2 -electrons in pairing is discussed in connection with some recent experiments. (author). 28 refs, 6 figs, 1 tab

  6. International Discussion Meeting on High-Tc Superconductors

    CERN Document Server

    1988-01-01

    In the past two years conferences on superconductivity have been characterized by the attendance of hundreds of scientists. Consequently, the organizers were forced to schedule numerous parallel sessions and poster presentations with an almost unsurveyable amount of information. It was, therefore, felt that a more informal get-together, providing ample time for a thourough discussion of some topics of current interest in high-temperature superconductivity, was timely and benefitial for leading scientists as well as for newcomers in the field. The present volume contains the majority of papers presented at the International Discussion Meeting on High-Tc Superconductors held at the Mauterndorf Castle in the Austrian Alps from February 7 to 11, 1988. Each subject was introduced in review form by a few invited speakers and then discussed together with the contributed poster presentations. These discussion sessions chaired by selected scientists turned out to be the highlights of the meeting, not only because all ...

  7. Magnetically-related properties of bismuth containing high Tc superconductors

    Science.gov (United States)

    Vezzoli, Gary C.; Chen, M. F.; Craver, F.; Safari, A.; Moon, B. M.; Lalevic, B.; Burke, Terence; Shoga, M.

    1990-08-01

    The effect of magnetic fields to 15 T on electrical resistance has been measured for the BiSrCaCuO superconductor at precise temperatures during the transition to the superconducting state from pre-onset conditions to essentially zero resistance conditions. The results show that the temperature at which the magnetic field causes a divergence in the resistance versus 1000/ T curve is approximately the same temperature as the value at which, during cooling, the positive Hall coefficient begins its abrupt descent to zero. This temperature gives the best measure of Tc. It is also shown that small oscillations of low frequency start near onset conditions, the amplitude of which at a given temperature is B-field dependent. Additionally, Hall effect studies as a function of temperature at 4 T in three separate experiments (including high Tc BiSrCaCu PbO of > 90% theoretical density) show that sharp delta-function-like peaks in + RH are observed near Tc and are superimposed on a broader maximum. The Hall data are explicable in terms of exciton formation and ionization. The bound holes associated with these excitons are believed to be the mediators producing Cooper-pairing, and scale very well with Tc for all the known high Tc oxides.

  8. Towards a complete Fermi surface in underdoped high Tc superconductors

    Science.gov (United States)

    Harrison, Neil

    The discovery of magnetic quantum oscillations in underdoped high Tc superconductors raised many questions, and initiated a quest to understand the origin of the Fermi surface the like of which had not been seen since the very first discovery of quantum oscillations in elemental bismuth. While studies of the Fermi surface of materials are today mostly assisted by computer codes for calculating the electronic band structure, this was not the case in the underdoped high Tc materials. The Fermi surface was shown to reconstructed into small pockets, yet there was no hint of a viable order parameter. Crucial clues to understanding the origin of the Fermi surface were provided by the small value of the observed Fermi surface cross-section, the negative Hall coefficient and the small electronic heat capacity at high magnetic fields. We also know that the magnetic fields were likely to be too weak to destroy the pseudogap and that vortex pinning effects could be seen to persist to high magnetic fields at low temperatures. I will show that the Fermi surface that appears to fit best with the experimental observations is a small electron pocket formed by connecting the nodal `Fermi arcs' seen in photoemission experiments, corresponding to a density-wave state with two different orthogonal ordering vectors. The existence of such order has subsequently been detected by x-ray scattering experiments, thereby strengthening the case for charge ordering being responsible for reconstructing the Fermi surface. I will discuss new efforts to understand the relationship between the charge ordering and the pseudogap state, discussing the fate of the quasiparticles in the antinodal region and the dimensionality of the Fermi surface. The author acknowledges contributions from Suchitra Sebastian, Brad Ramshaw, Mun Chan, Yu-Te Hsu, Mate Hartstein, Gil Lonzarich, Beng Tan, Arkady Shekhter, Fedor Balakirev, Ross McDonald, Jon Betts, Moaz Altarawneh, Zengwei Zhu, Chuck Mielke, James Day, Doug

  9. Electronic properties of high-Tc superconductors. The normal and the superconducting state of high-Tc materials. Proceedings

    International Nuclear Information System (INIS)

    Kuzmany, H.; Mehring, M.; Fink, J.

    1993-01-01

    The International Winter School on Electronic Properties of High-Temperature Superconductors, held between March 7-14, 1992, in Kirchberg, (Tyrol) Austria, was the sixth in a series of meetings to be held at this venue. Four of the earlier meetings were dedicated to issues in the field of conducting polymers, while the winter school held in 1990 was devoted to the new discipline of high-Tc superconductivity. This year's meeting constituted a forum not only for the large number of scientists engaged in high-Tc research, but also for those involved in the new and exciting field of fullerenes. Many of the issues raised during the earlier winter schools on conducting polymers, and the last one on high-Tc superconductivity, have taken on a new significance in the light of the discovery of superconducting C 60 materials. The Kirchberg meetings are organized in the style of a school where experienced scientists from universities, research laboratories and industry have the opportunity to discuss their most recent results, and where students and young scientists can learn about the present status of research and applications from some of the most eminent workers in their field. In common with the previous winter school on high-Tc superconductors, the present one focused on the electronic properties of the cuprate superconductors. In addition, consideration was given to related compounds which are relevant to the understanding of the electronic structure of the cuprates in the normal state, to other oxide superconductors and to fulleride superconductors. Contributions dealing with their preparation, transport and thermal properties, high-energy spectroscopies, nuclear magnetic resonance, inelastic neutron scattering, and optical spectroscopy are presented in this volume. The theory of the normal and superconducting states also occupies a central position. (orig.)

  10. Mechanochemical effects on high-Tc superconductor powders

    International Nuclear Information System (INIS)

    Yamada, Taichi; Nagai, Ryoji; Takeuchi, Manabu; Minehara, Eisuke.

    1991-03-01

    We have investigated the mechanochemical effects on high-Tc superconductor (YBa 2 Cu 3 O 7 -δ) powders. The powder was mechanically ground in air using an agate mortar with a pestle. The grinding time was varied from 2 to 100 min. The mean particle sizes of the powders were measured by a sedimentation method. The degradation of superconductivity was evaluated by the measurements of the crystallinity and volume fraction of the superconducting phase. The crystallinity was estimated from X-ray diffraction patterns. The volume fraction of the superconducting phase was estimated from the diamagnetization. The results of these changes of 2 min. and 100 min. grinding are respectively as follows; 1) mean particle size: 10.8 μm and 7.2 μm, 2) crystallinity: 40.0 % and 24.8 %, 3) volume fraction of superconducting phase: 91.5 % and 30.0 %. Recovery of the crystallinity and superconductivity of the ground specimens by re-sintering and re-annealing was also studied. It was found that the recovery of both of the characteristics was not complete. (author)

  11. Large area bulk superconductors

    Science.gov (United States)

    Miller, Dean J.; Field, Michael B.

    2002-01-01

    A bulk superconductor having a thickness of not less than about 100 microns is carried by a polycrystalline textured substrate having misorientation angles at the surface thereof not greater than about 15.degree.; the bulk superconductor may have a thickness of not less than about 100 microns and a surface area of not less than about 50 cm.sup.2. The textured substrate may have a thickness not less than about 10 microns and misorientation angles at the surface thereof not greater than about 15.degree.. Also disclosed is a process of manufacturing the bulk superconductor and the polycrystalline biaxially textured substrate material.

  12. How to determine Hc1 of high Tc oxide superconductors

    International Nuclear Information System (INIS)

    Cao Xiaowen; Huang Sunli

    1989-12-01

    The magnetizations of cylinder Bi 1.7 Pb 0.3 Sr 2 Ca 2 Cu 3 O y bulk superconductor whose length is shorten step by step has shown that H c1 is independent of the length of cylinder, i.e. independent of the demagnetic factor, as the length is larger than the diameter, whereas it is dependent of demagnetic factor, as the length is smaller than the diameter. But the demagnetization factor is a constant about 1/4 for l< d

  13. Phase Equilibria Relationships of High-Tc Superconductors

    International Nuclear Information System (INIS)

    Wong-Ng, Winnie

    2011-01-01

    As an integral part of a R and D program partially supported by the Electricity Delivery and Energy Reliability Office of DOE, we have determined phase equilibria data and phase diagrams for the three generations of superconductor materials: 1st generation, (Bi,Pb)-Sr-Ca- Cu-O systems; 2nd generation, Ba-R-Cu-O systems (R=lanthanides and yttrium); and 3rd generation, MgB2 systems. Our studies involved bulk materials, single crystals and thin films. This report gives a summary of our accomplishments, a list of publications, and 15 selected journal publications.

  14. On the application of High-Tc superconductors in power coils and transformers

    NARCIS (Netherlands)

    Chevtchenko, O.A.

    2002-01-01

    In this study, the electro-magnetic properties of high-Tc tapes and coils are investigated. The focus is on Bi-2223/Ag tapes with non-twisted superconducting filaments as these are the only high-Tc superconductors at present available in sufficient length for practical applications. The study is

  15. Plasma resonance and flux dynamics in layered high-Tc superconductors

    DEFF Research Database (Denmark)

    Pedersen, Niels Falsig; Sakai, S.

    2000-01-01

    Flux dynamics of layered high Tc superconductors are considered with special emphasis on the small oscillation modes. In particular we find the dispersion relation for the plasma modes and discuss the spectra to be observed in microwave experiments.......Flux dynamics of layered high Tc superconductors are considered with special emphasis on the small oscillation modes. In particular we find the dispersion relation for the plasma modes and discuss the spectra to be observed in microwave experiments....

  16. Atomic site tunneling spectroscopy on high-Tc superconductors

    International Nuclear Information System (INIS)

    Hasegawa, T.; Nantoh, M.; Takagi, A.; Yamaguchi, W.; Ogino, M.; Kawasaki, M.

    1994-01-01

    Superconducting gap structures of Bi 2 Sr 2 CaCu 2 O y (BSCCO) and YBa 2 Cu 3 O y (YBCO) have been probed by scanning tunneling microscopy (STM) at cryogenic temperatures. The tunneling conductance curves observed on bulk single crystals of BSCCO and epitaxial thin films of YBCO revealed clear obershooting peaks and flat bottom regions around V=0 with quite low zero-bias conductances of ∝1%. Since the electron tunneling process in STM is essentially incoherent, the present observation is favored by the s-wave pairing mechanism. However, the conductance curves were found to be substantially smeared in comparison with the conventional spectra predicted in the BCS (isotropic s-wave) superconductors, suggesting gap anisotropy. (orig.)

  17. Neutron depolarization effects in a high-Tc superconductor (abstract)

    Science.gov (United States)

    Nunes, A. C.; Pickart, S. J.; Crow, L.; Goyette, R.; McGuire, T. R.; Shinde, S.; Shaw, T. M.

    1988-11-01

    Using the polarized beam small-angle neutron scattering spectrometer at the Rhode Island Nuclear Science Center Reactor, we have observed significant depolarization of a neutron beam by passage through polycrystalline high-Tc superconductors, specifically 123 Y-Ba-Cu-O prepared and characterized at the IBM Watson Research Center. We believe that this technique will prove useful in studying aspects of these materials, such as the penetration depth of shielding currents, the presence and structure of trapped flux vortices, and grain size effects on the supercurrent distribution in polycrystalline samples. The two samples showed sharp transitions at 87 and 89 K, and have been studied at temperatures of 77 K; the second sample has also been studied at 4 K. The transition to the superconducting state was monitored by the shift in resonant frequency of a coil surrounding the sample. No measurable depolarization was observed in either sample at 77 K in both the field-cooled and zero-field-cooled states, using applied fields of 0 (nominal), 54, and 1400 Oe. This negative result may be connected with the fact that the material is still in the reversible region as indicated by susceptibility measurements, but it allows an estimate of the upper bound of possible inhomogeneous internal fields, assuming a distance scale for the superconducting regions. For the 10-μm grain size suggested by photomicrographs, this upper bound for the field turns out to be 1.2 kOe, which seems reasonable. At 4 K a significant depolarization was observed when the sample was cooled in low fields and a field of 1400 Oe was subsequently applied. This result suggests that flux lines are penetrating the sample. Further investigations are being carried out to determine the field and temperature dependence of the depolarization, and attempts will be made to model it quantitatively in terms of possible internal field distributions. We are also searching for possible diffraction effects from ordered vortex

  18. Electrochemical investigations of high-Tc superconductors - low-temperature electrochemistry

    International Nuclear Information System (INIS)

    Lorenz, W.J.

    1992-01-01

    This research report presents a summary of results obtained by electrochemical investigations of high-Tc superconductors at room temperature and below the critical temperature (Tc). The studies were to reveal the behaviour of the ceramic superconducting materials at the interface between superconductor and ionic conductor. (MM) With 4 tabs., 8 figs [de

  19. Point-contact electron tunneling into the high-Tc superconductor Y-Ba-Cu-O

    Science.gov (United States)

    Kirk, M. D.; Smith, D. P. E.; Mitzi, D. B.; Sun, J. Z.; Webb, D. J.

    1987-06-01

    Results are reported from a study of electron tunneling into bulk samples of the new high-Tc superconductor Y-Ba-Cu-O using point-contact tunneling. Based on a superconductive tunneling interpretation, the results show exceptionally large energy gaps in these materials (roughly 2Delta = 100 MeV), implying 2Delta/kBTc = about 13. Similar values were found for La-Sr-Cu-O. The structure in the I-V curves is also similar to that seen in La-Sr-Cu-O. From the asymmetries observed in the I-V characteristics, it is inferred that the natural tunneling barrier on this material is of the Schottky type.

  20. Changes of soft X-ray emission spectra of oxygen and copper in high Tc superconductors

    International Nuclear Information System (INIS)

    Fukushima, Sei; Gohshi, Yohichi; Kohiki, Shigemi; Saitoh, Naoki

    1989-01-01

    X-ray induced soft X-ray emission spectroscopy is one of the bulk analysis methods used to characterize high-Tc superconductor. In this report, some observations on the changes in O Kα and Cu L spectra of thin layer LnBa 2 Cu 3 O 7-δ (Ln=Er,Gd) samples are presented. From the measurement of O Kα, no discernible difference was found between those of Gd compounds which were composed single phase or not. It may be said that the electronic structure of p state localized on the O is not sensitive to the change of Tc or zero-resistance temperature. From the measurement of Cu L spectra, it was found that Cu Lα of only Gd containing compounds has a low energy shoulder

  1. Quantitative XPS analysis of high Tc superconductor surfaces

    International Nuclear Information System (INIS)

    Jablonski, A.; Sanada, N.; Suzuki, Y.; Fukuda, Y.; Nagoshi, M.

    1993-01-01

    The procedure of quantitative XPS analysis involving the relative sensitivity factors is most convenient to apply to high T c superconductor surfaces because this procedure does not require standards. However, a considerable limitation of such an approach is its relatively low accuracy. In the present work, a proposition is made to use for this purpose a modification of the relative sensitivity factor approach accounting for the matrix and the instrumental effects. The accuracy of this modification when applied to the binary metal alloys is 2% or better. A quantitative XPS analysis was made for surfaces of the compounds Bi 2 Sr 2 CuO 6 , Bi 2 Sr 2 CaCu 2 O 8 , and YBa 2 Cu 3 O Y . The surface composition determined for the polycrystalline samples corresponds reasonably well to the bulk stoichiometry. Slight deficiency of oxygen was found for the Bi-based compounds. The surface exposed on cleavage of the Bi 2 Sr 2 CaCu 2 O 8 single crystal was found to be enriched with bismuth, which indicates that the cleavage occurs along the BiO planes. This result is in agreement with the STM studies published in the literature

  2. On the electronegativity of the high-Tc oxide superconductor

    International Nuclear Information System (INIS)

    Zhang Liyuan.

    1991-08-01

    We employ a very useful quantity, the electronegativity, to classify the superconductor. The value of the group average electronegativity to separate superconductor into two categories is 2. Each category has unique chemical bond features. The high-T c oxide superconductor belongs to the second category with group average electronegativity being larger than 2. Their unusual bond nature also gives new insight into some essential factors beneficial to enhance superconductivity. (author). 9 refs, 2 tabs

  3. Filters for mobile radio from high Tc ceramic superconductors

    International Nuclear Information System (INIS)

    Peterson, G.E.; Wong, E.; Alford, N.McN.

    1990-01-01

    Mobile radio frequencies lie between 30 MHz and 1,000 MHz. This frequency range is ideal for ceramic high T c superconductors. We have designed Chebyshev, Butterworth and interdigital filters that can employ high T c superconductors in the form of rods, tubes and helices. In general, the performance of these filters at milliwatt power levels is excellent. We will describe fabrication of the superconductors and filter design

  4. Rapid solidification for preparation of high Tc superconductors

    International Nuclear Information System (INIS)

    Yavari, A.R.

    1988-01-01

    High Tc superconducting oxides are prepared in two different ways using rapid solidification: by oxidation of microcrystalline or amorphous tapes obtained by quenching the liquid alloy and via crystallisation of the amorphous oxide obtained by rapid quenching of the oxide melt. This technique is applied for the first time to the BiCaSrCuO family [fr

  5. Preparation and properties of high-Tc Bi-oxide superconductors

    International Nuclear Information System (INIS)

    Maeda, H.

    1989-01-01

    Bulk superconductors of Pb-doped Bi-oxide system (BSCCO) dominated with the high-Tc phase have the critical transition temperature, Tc of 110 K, and the upper critical fields, H c2 of 140 T at OK and 60 T at 77 K. A highly dense and a highly oriented microstructure is obtained by inserting an intermediate uniaxial pressing process. The critical current density, Jc at 77 K in zero field, Jc (77K,OT) of some 5000 A/cm 2 can be easily obtained by this process, and the field dependence of Jc is also improved. Flexible high-Tc BSCCO ribbons with a Jc (77K,Ot) of 1850 A/cm 2 have been successfully prepared by the combined process of doctor blade casting, cold rolling and sintering. Aq-sheeted multifilamentary wires with 1330 filaments and tapes with 30 filaments have also been successfully fabricated and the 36-filament tape shows a Jc(77K,OT) of 1050 A/cm 2 . (Auth.). 7 refs.; 7 figs

  6. A phenomenological approach to high Tc oxide superconductors

    International Nuclear Information System (INIS)

    Chela-Flores, J.; Das, M.P.; Saif, A.G.

    1987-06-01

    Oxide superconductors are described in terms of macroscopic wave functions Ψ and Φ corresponding, respectively, to electron pairs of the superconducting and insulating states. In terms of the total free energy of the system, including the effect of interaction, we discuss the electrodynamic responses of the oxide superconductors in relation with the experiments to data. (author). 10 refs

  7. Five-fold way to new high Tc superconductors

    Indian Academy of Sciences (India)

    Discovery of high c superconductivity in La2−BaCuO4 by Bednorz and Muller in 1986 was a breakthrough in the 75-year long search for new superconductors. Since then new high c superconductors, not involving copper, have also been discovered. Superconductivity in cuprates also inspired resonating valence ...

  8. Unconventional superconductivity in heavy fermionic and high-Tc superconductors

    International Nuclear Information System (INIS)

    Volovik, G.E.

    1989-01-01

    Splitting of the superconducting transition and glass spectrum in heavy fermion companies and oxide superconductors are discussed. The multicomponent order parameter leads to splitting of transition due to magnetic field, impurities, orthorhombic distortion, etc... Linear specific heat in oxide superconductors may be explained in terms of the Fermi-surface arising in superconducting state if interband is pairing strong enough

  9. Experimental constraints on theories of high Tc superconductors

    International Nuclear Information System (INIS)

    Little, W.A.

    1989-01-01

    Recent experiments on the high-T c superconductors have begun to narrow the possible theoretical explanations of the phenomenon. Experimental evidence on the size, structure and symmetry of the charge carriers will be reviewed; evidence for and against strong coupling; and, recent results on a search for direct evidence of magnetic signature in the coupling mechanism will be presented. The authors show how these experiments impose strong constraints on the theories of these superconductors. A new type of experiment is also discussed which appears capable of identifying the true nature of the coupling mechanism if the superconductors prove to be BCS-like in nature

  10. Study of flux flow in high Tc superconductors

    International Nuclear Information System (INIS)

    Takacs, S.; Gomory, F.

    1989-01-01

    The magnetic field distribution and the hysteresis losses in superconductors with very large viscous forces are calculated for field amplitudes below and above the penetration field. Both the magnetic field and frequency dependence of the losses are changing with respect to the critical state model. The results are qualitatively confirmed by AC susceptibility measurements on YBaCuO superconductors, but the quantitative differences indicate that the flux flow effects are not so strong as expected and supposed by some theories

  11. Bi-Polaron Condensation in High Tc Superconductors

    International Nuclear Information System (INIS)

    Ranninger, J.

    1995-01-01

    On the basis of optical measurements-, photoemission-, EXAFS- and neutron scattering-experiments we conclude that itinerant valence electrons coexist with localized bi-polarons.Entering the metallic phase upon chemical doping, a charge transfer between the two electronic subsystems is triggered off. We show that as the temperature is lowered towards Tc this process leads to a delocalization of bi-polarons due to a precursor effect of superfluidity of those bi-polarons. Upon entering the superconducting phase, these bipolarons ultimately condense into a superfluid state which is expected to largely determine the superconducting properties of high Tc materials. (authors)

  12. Plasma resonance in anisotropic layered high-Tc superconductors

    DEFF Research Database (Denmark)

    Sakai, Shigeki; Pedersen, Niels Falsig

    1999-01-01

    The plasma resonance is described theoretically by the inductive coupling model for a large stacked Josephson-junction system such as the intrinsic Josephson-junction array in anisotropic high- T-c superconductors. Eigenmodes of the plasma oscillation are analytically described and a numerical...

  13. On the electronic structure of high Tc superconductors

    International Nuclear Information System (INIS)

    Fink, J.; Nuecker, N.; Romberg, H.; Alexander, M.; Knupfer, M.; Mante, J.; Claessen, R.; Buslaps, T.; Harm, S.; Manzke, R.; Skibowski, M.

    1992-01-01

    Studies of the electronic structure of high-T c superconductors and related compounds by high-energy spectroscopies are reviewed. In particular, we report on investigations by electron energy-loss, angle-resolved photoemission, and inverse angle-resolved photoemission spectroscopy. Information on the symmetry and the character of states close to the Fermi level has been obtained. 25 refs., 8 figs

  14. On the role of doping in High-Tc superconductors

    International Nuclear Information System (INIS)

    Mei, C.; Smith, V.H. Jr.

    1994-01-01

    High-T c superconductors (HTSCS) are usually obtained by doping electron donors or acceptors into parent materials. The actual role played by doping is still uncertain with various interpretations. The present electronic structure study provides some hints which may help to solve the mystery

  15. Observation of magnetooptical effects in several high Tc superconductors

    International Nuclear Information System (INIS)

    Dillon, J.F. Jr; Lyons, K.B.

    1992-01-01

    Recent so called 'anyon' theories of high temperature superconductivity in layer structure materials suggested that at some temperature T TP ≥T c there is a symmetry breaking transition below which these materials may be in either of two distinct states related to each other by time reversal. The study of magneto-optical effects in superconductors reviewed here was undertaken to explore time reversal symmetry of these materials. Using novel technique with rotating λ/2 plate at 525 nm, 'circular dichroism' was observed on reflection from epitaxial films and single crystals of cuprate superconductor with layer structures. The onset of dichroism was at temperatures of ∼ 180K to ∼ 300K. These results appear to support the 'anyon' theories. However, circular dichroism was also seen in films and single crystals of bismuthate superconductors with cubic structure, to which the theories seem inapplicable. In sharp contrast, Spielman et al., at Stanford in a very sensitive experiment at 1060 nm have seen no evidence of non-reciprocal circular birefringence in epitaxial cuprate superconducting films. Weber et al. at Dortmund have recently reported the observation at 633 nm of non-reciprocal magneto-optical effects on single crystals of cuprate superconductors, but none on films. (author). 15 refs., 5 figs

  16. High pressure effect for high-Tc superconductors

    International Nuclear Information System (INIS)

    Takahashi, Hiroki; Tomita, Takahiro

    2011-01-01

    A number of experimental and theoretical studies have been performed to understand the mechanism of high-T c superconductivity and to enhance T c . High-pressure techniques have played a very important role for these studies. In this paper, the high-pressure techniques and physical properties of high-T c superconductor under high pressure are presented. (author)

  17. Comparative study of magnetization in conventional and high Tc superconductors

    International Nuclear Information System (INIS)

    Sarkissian, B.V.B.; Grover, A.K.; Balakrishnan, G.; Paulose, P.L.; Vijayaraghavan, R.

    1989-01-01

    Results of a comparative study of thermomagnetic history effects and anomalous variations in isothermal magnetization hysteresis curves in a High T compound (YBa 2 Cu 3 O 7 ) with two specimens of Nb are presented. They show that the former behaves like any hard type c II superconductor

  18. Electronic components with yttrium- and bismuth-based high-Tc superconductors

    International Nuclear Information System (INIS)

    Daginnus, M.; Guettler, B.

    1992-01-01

    This project investigates the fabrication of microwave components by use of high-Tc superconductors. Detailed descriptions are given of the manufacturing and use of active Y-Ba-Cu-O components. The surface resistance of thin films used in high-quality passive microwave components such as resonators and filters is measured and optimized. (orig./MM) [de

  19. High-Tc superconductors under very high pressure

    International Nuclear Information System (INIS)

    Wijngaarden, R.J.; Scholtz, J.J.; Eenige, E.N. van; Griessen, R.

    1991-01-01

    High pressure has played a crucial role in the short history of high T c superconductors. Soon after the discovery of superconductivity by Bednorz and Muller in La-Ba-Cu-O, Chu et al. showed that the critical temperature T c could be significantly increased by pressure. This observation led to the discovery of YBa 2 Cu 3 O 7 by Wu et al. with a T c above 90 K. Incidentally, this high T c is probably also due to the fact that YBa 2 Cu 3 O 7 has two CuO 2 layers per unit cell instead of a single one in La-Ba-Cu-O. The authors discuss the high pressure dependence of the oxide superconductors, particularly at pressures above 10 GPa, and the nonmonotonic dependence of transition temperature on pressure

  20. The defect structure of ceramic high Tc superconductors

    International Nuclear Information System (INIS)

    Van Tendeloo, G.; Amelinckx, S.; Zandbergen, H.W.; Verwerft, M.

    1989-01-01

    In this paper an overview is given of electron microscopy studies on the different ceramic superconductors: YBa 2 Cu 3 O 7 , Bi(Tl)-Sr(Ba)- Ca-Cu-O and Pb 2 Sr 2 Y 0.5 Ca 0.5 Cu 3 O x . Planar defects in these materials play an important role in the superconducting properties. Their structural characteristics are discussed

  1. Flux flow and flux dynamics in high-Tc superconductors

    International Nuclear Information System (INIS)

    Bennett, L.H.; Turchinskaya, M.; Swartzendruber, L.J.; Roitburd, A.; Lundy, D.; Ritter, J.; Kaiser, D.L.

    1991-01-01

    Because high temperature superconductors, including BYCO and BSSCO, are type 2 superconductors with relatively low H(sub c 1) values and high H(sub c 2) values, they will be in a critical state for many of their applications. In the critical state, with the applied field between H(sub c 1) and H(sub c 2), flux lines have penetrated the material and can form a flux lattice and can be pinned by structural defects, chemical inhomogeneities, and impurities. A detailed knowledge of how flux penetrates the material and its behavior under the influence of applied fields and current flow, and the effect of material processing on these properties, is required in order to apply, and to improve the properties of these superconductors. When the applied field is changed rapidly, the time dependence of flux change can be divided into three regions, an initial region which occurs very rapidly, a second region in which the magnetization has a 1n(t) behavior, and a saturation region at very long times. A critical field is defined for depinning, H(sub c,p) as that field at which the hysteresis loop changes from irreversible to reversible. As a function of temperature, it is found that H(sub c,p) is well described by a power law with an exponent between 1.5 and 2.5. The behavior of H(sub c,p) for various materials and its relationship to flux flow and flux dynamics are discussed

  2. Simulation of the vortex motion in the high Tc superconductors

    International Nuclear Information System (INIS)

    Dong Jinming.

    1992-11-01

    1d and 2d simulations of the single vortex dynamics in the presence of random pinning potential and periodical one have been carried out. It is shown that the randomness of the pinning sites distribution does not have considerable effect on the transport properties such as I-V characteristics of the high T c superconductors, which has been widely discussed in the approximation of a periodical pinning potential using analytical method. The randomness effect probably only reduces the vortex diffusing mobility more below the depinning current value, which is more obvious at lower temperature. (author). 12 refs, 4 figs

  3. Nuclear hyperfine interactions and chemical bonding in high TC superconductors

    International Nuclear Information System (INIS)

    Danon, J.

    1987-01-01

    Nuclear quadrupole resonances of Cu 63 and Fe 57 Moessbauer spectroscopy of the high temperature superconductor YBa 2 Cu 3 O 7-γ e described together with synchrotron radiation studies of the copper oxidation states in this material. The Moessbauer spectra of 57 Fe in the two distinct crystallographic sites of the Cu atoms in YBa 2 Cu 3 O 7-γ are very similar from the quadrupole coupling point of view although exhibiting markedly different values for the isomer shift. The role of oxygen vacancies in the hyperfine interactions is discussed. (author) [pt

  4. Microstructures and critical currents in high-Tc superconductors

    International Nuclear Information System (INIS)

    Suenaga, Masaki

    1998-01-01

    Microstructural defects are the primary determining factors for the values of critical-current densities in a high T c superconductor after the electronic anisotropy along the a-b plane and the c-direction. A review is made to assess firstly what would be the maximum achievable critical-current density in YBa 2 Cu 3 O 7 if nearly ideal pinning sites were introduced and secondly what types of pinning defects are currently introduced or exist in YBa 2 Cu 3 O 7 and how effective are these in pinning vortices

  5. Melted flux liquids in high-Tc superconductors

    International Nuclear Information System (INIS)

    Nelson, D.R.

    1989-01-01

    A theory of the entangles flux liquids which arise in the new high-T c superconductors is reviewed. New physics appears because of the weak interplanar couplings and high critical temperatures in these materials. Flux line wandering melts the conventional Abrikosov flux lattice over large portions of the phase diagram and leads to a novel entangled vortex state. The authors suggest that a heavily entangled flux liquid could exhibit glassy behavior on experimental time scales, in analogy with viscoelastic behavior in dense polymer melts

  6. Condensate localization by mesoscale disorder in high-Tc superconductors

    International Nuclear Information System (INIS)

    Kumar, N.

    1994-06-01

    We propose and solve approximately a phenomenological model for Anderson localization of the macroscopic wavefunction for an inhomogeneous superconductor quench-disordered on the mesoscale of the order of the coherence length ξ 0 . Our treatment is based on the non-linear Schroedinger equation resulting from the Ginzburg-Landau free-energy functional having a spatially random coefficient representing spatial disorder of the pairing interaction. Linearization of the equation, valid close to the critical temperature T c , or to the upper critical field H c2 (T c ) maps it to the Anderson localization problem with T c identified with the mobility edge. For the highly anisotropic high-T c materials and thin (2D) films in the quantum Hall geometry, we predict windows of re-entrant superconductivity centered at integrally spaced temperature values. Our model treatment also provides a possible explanation for the critical current J c perpendicular becoming non-zero on cooling before J c parallel does in some high-T c superconductors. (author). 18 refs

  7. HREM study of Bi-oxide based high Tc superconductors

    International Nuclear Information System (INIS)

    Hewat, E.A.

    1988-01-01

    A HREM study of the superstructure and structural defects in Bi 2-x Pb x Sr 2 CaCu 2 O 8 and Bi 2-x Pb x (SrCa) 2 CuO 6 (for x=0 and x=0.4) is presented. The superstructures are shown to involve waves of distortion along the b-axis. These waves are locked on to the lattice positions so that they have a local wave length of 4,5,6,7 or 8 times the basic unit cell. The superstructures are composed of roughly periodic combinations of these basic building blocks (waves). The lead doped superconductors show a less pronounced but more complicated superstructure along b where two distinct periodicities close to 4 and 7 times the basic unit cell predominate. In each of the compounds studied the superstructure, in the better ordered crystals, is shown to be commensurate with a unit cell between 5 and 23 times the basic unit cell. The superstructure in Bi 2-x Pb x Sr 2 CaCu 2 O 8 is orthorhombic where as the superstructure in Bi 2-x Pb x (SrCa) 2 CuO 6 is monoclinic. All these superconductors have a low ''twin'' density (ie density of 90 0 twist boundaries). They exhibit many dislocations and dislocation arrays associated with the weak bonding between BiO planes. They also form non-stoechiometric stacking faults with local changes in the c-axis spacing between layers

  8. Strong-coupling interaction in high-Tc superconductors

    International Nuclear Information System (INIS)

    Ray, D.K.

    1991-01-01

    Extensive experimental and theoretical work have been done to understand the mechanisms of superconductivity. Until 1986 when Bednorz and Muller discovered superconductivity in the copper oxide perovskite, the principal mechanism was found to be electron-phonon interaction and the characteristics of superconductivity vary depending on the strength of the electron-phonon interaction and the electronic structure. The essential characteristic of these conventional superconductors could be divided into two groups: wide band metals with low density of states N(E F ) at the Fermi energy E F and a rather weak electron-phonon coupling V obeying the universal characteristics of the BCS theory and narrow d band metals, compounds, and alloys with high values of N(E F ), electron-phonon coupling V and non negligible Coulomb interaction between the electrons. In this paper a short summary and the important results of these theories are discussed. The inherent limitations of these theories based on electron-phonon interaction will be discussed. The authors indicate the major characteristics of the new superconductors. These characteristics are difficult to explain on the basis of either the conventional electron-phonon theory or theories based on magnetic interactions alone

  9. High density high-TC ceramic superconductors by hot pressing

    International Nuclear Information System (INIS)

    Mak, S.; Chaklader, A.C.D.

    1989-01-01

    High density and high T C superconductor specimens, YBa 2 Cu 3 O x , have been produced by hot-pressing. The factors studied are the effect of hot pressing on the density, the oxygen stoichiometry, the crystal structure, and the critical temperature. Hot pressing followed by heat treatment increased the density of the specimen to 93%. The hot pressing itself did not significantly affect the oxygen content in the specimen, and although the crystal structure appeared to be orthorhombic, the specimens were not superconducting above liquid nitrogen temperature. The superconductivity was restored after head treatment in oxygen. The highest critical temperature (T C ) of the hot pressed pellets was 82K, which was slightly lower than the T C that could be obtained with the cold pressed/sintered pellets. (6 refs., 5 figs., tab.)

  10. Olson sees how they conduct (High Tc superconductors)

    International Nuclear Information System (INIS)

    Olson, C.

    1989-01-01

    Thanks to Cliff Olson's synchrotron radiation measurements of the surface of several of the new high-temperature superconducting materials, these ceramic-like crystals can now be classified as metals. This means their electronic band structure meets the criteria for a metal or conductor, rather than those of an insulator, or of a semiconductor. Working with graduate assistant Liu, Olson has now measured the energy gap in crystals of a bismuth-strontium-calcium-copper oxide with a 100K or 300K transition temperature. They determined that the superconductivity gap is isotropic, or independent of direction within the layer. This is significant, because the high temperature materials are all anisotropic, layered in flat sheets, a fact that had led to speculations about a very different kind of superconducting coupling in these materials. The superconducting mechanism now turns out to be the same as that in classical superconductors

  11. Low field scaling properties of high Tc superconductor glasses

    Science.gov (United States)

    Giovannella, C.; Fruchter, L.; Chappert, C.

    We show that the zero field cooling (ZFC) M/H curves of both the YBaCuO and the LaSrCuO granular superconductor glasses (SuG) are subjected to scaling when plotted against the reduced variable t/H1/ψ . The breaking of the scaling for too weak or too strong magnetic fields is discussed and justified by the introduction of a phenomenological fractal picture, describing the behaviour of the disordered intergranular junction network. Nous montrons que les courbes M/H caractéristiques des verres de supraconducteurs granulaires sont sujettes à une loi d'échelle lorsqu'elles sont tracées en fonction de la variable réduite t/H1/ψ. La brisure de la loi d'échelle pour des champs trop forts ou trop faibles est justifiée par l'introduction d'un modèle phénoménologique fractal capable de décrire le comportement d'un réseau désordonné des jonctions.

  12. Probe high-Tc Superconductors by neutron scattering

    International Nuclear Information System (INIS)

    Fauque, B.

    2007-10-01

    This research thesis explores two aspects of the phase diagram of high critical temperature superconductors: the evolution of AF correlations and the nature of the pseudo-gap phase. The author presents the problematic associated with these particular semiconductors, describes the neutron diffusion probe used in this study, and presents the three families of semiconductors investigated during this research: Bi 2 Sr 2 CaCu 2 O 8+x , YBa 2 Cu 3 O 6+x and La 2-x Sr x CuO 4 . He reports the results of the investigation of the spin dynamics in the Bi 2 Sr 2 CaCu 2 O 8+x . He reports a detailed investigation of the magnetic cross section associated with different types of non conventional magnetic orders proposed as candidates for the pseudo-gap phase. He reports and comments the results obtained for the pseudo-gap phase for the YBa 2 Cu 3 O 6+x and La 2-x Sr x CuO 4 families. Finally, the author discusses the consequences of the obtained results for the description of the diagram phase of high critical temperature semiconductors

  13. Phonon anomalies in trilayer high-Tc cuprate superconductors

    International Nuclear Information System (INIS)

    Dubroka, Adam; Munzar, Dominik

    2004-01-01

    We present an extension of the model proposed recently to account for dramatic chAes below T c (anomalies) of some c-axis polarized infrared-active phonons in bilayer cuprate superconductors, that applies to trilayer high-T c compounds. We discuss several types of phonon anomalies that can occur in these systems and demonstrate that our model is capable of explaining the spectral chAes occurring upon entering the superconducting state in the trilayer compound Tl 2 Ba 2 Ca 2 Cu 3 O 10 . The low-temperature spectra of this compound obtained by Zetterer and coworkers display an additional broad absorption band, similar to the one observed in underdoped YBa 2 Cu 3 O 7-δ and Bi 2 Sr 2 CaCu 2 O 8 . In addition, three phonon modes are strongly anomalous. We attribute the absorption band to the transverse Josephson plasma resonance, similar to that of the bilayer compounds. The phonon anomalies are shown to result from a modification of the local fields induced by the formation of the resonance. The spectral chAes in Tl 2 Ba 2 Ca 2 Cu 3 O 10 are compared with those occurring in Bi 2 Sr 2 Ca 2 Cu 3 O 10 , reported recently by Boris and coworkers

  14. Electronic properties of high Tc superconductors. Propiedades electronicas de los superconductores de alta temperatura critica

    Energy Technology Data Exchange (ETDEWEB)

    Rojo, A G

    1989-01-01

    Using analytical and numerical methods, the electronic properties of the copper-oxygen plane in the normal phase of high Tc superconductors are described. Using the slave-boson technique in the saddle point, a theory of the metal insulator transition which generalizes the notions of a Mott insulator to the case of more than a single band for those planes is presented. A phase-diagram is obtained in the parameter space and effective masses, optical gaps and metallization are calculated as a function of the number of carriers. Based on the experimental evidence, the theory permits classification of superconducting compounds as charge transfer insulators in the stoichiometric case. The insulator state is characterized by a non-zero optical gap and a divergent effective mass which corresponds to the breakage of a Fermi-liquid scheme. The results obtained are applicable to metal-transition-oxides whose behaviour has been traditionally controversial and it is concluded that it is necessary to broaden the meaning of a Mott insulator to the case of more than a single band to better understand them. Based on the ideas of group renormalization in a real space, a lattice approximation is presented, which allows: a) To complement the treatment of slave-bosons in phase diagrams and optical gaps; b) Identification of an attraction mechanism between carriers originating from purely repulsive interactions. Numerical calculations in small clusters show the existence of a pairing mechanism showing a superconducting instability from a charge transfer insulator. (Author).

  15. Quantum vortex motion in high-Tc superconductors

    International Nuclear Information System (INIS)

    Garcia, A.; Zhang, X.X.; Tejada, J.

    1996-01-01

    Magnetic relaxation experiments at low temperatures were performed in different zero-field-cooled (ZFC) and field-cooled (FC) high-T c superconductors (HTSCs): TlBaCaCuO (2212 and 2223 phases, polycrystalline and thin-film samples), (Hg,Tl)BaCaCuO (1223 phase, polycrystalline material), and (Bi,Pb)SrCaCuO (2212 phase, single crystal). For each system and in the whole temperature range investigated, the relaxation curves obtained after both cooling processes are linear with the logarithm of time. The temperature dependence of the relaxation rate normalized to the first magnetization value, R=parallel d(M/M 0 )/dln(t)parallel, follows a trend which is common to all systems: R decreases linearly with decreasing temperature down to a value, which is called the crossover temperature, below which it levels off to a T-independent plateau. This behavior gives evidence of a transition in the mechanism responsible for the relaxation process at low temperatures, from thermally activated (linear dependence on T) to quantum vortex motion (T-independent regime). The experimental values for the crossover temperatures and normalized relaxation rates compare fairly well to numerical estimates in the framework of the theories of quantum vortex motion in layered HTSCs. Finally, the transition from one regime into another was studied in two samples of the TlBaCaCuO, 2223 phase, system in order to investigate the influence of dissipation on the quantum process. A clear conclusion on this point could not be drawn from these kinds of measurements. copyright 1996 American Institute of Physics

  16. Grain boundary dissipation in high-Tc superconductors

    International Nuclear Information System (INIS)

    Gray, K.E.; Miller, D.J.; Field, M.B.; Kim, D.H.; Berghuis, P.

    2000-01-01

    Thin-film and bulk [001] tilt bicrystal grain boundaries (GBs) in YBa 2 Cu 3 O 7 exhibit a strong dependence of critical current density, J c on misorientation angle. What was initially difficult to understand was the 30x smaller J c in bulk GBs which are microscopically more perfect. The authors review an explanation of this zero-field data, which is based on the pinning of Josephson vortices by the meandering found in thin-film GBs. In addition, there is evidence that J c of GBs does not drop as quickly with applied magnetic field as expected by simple Josephson junction models. The long-wavelength pinning potential due to meandering is less effective at high fields, but Gurevich and Cooley (GC) proposed a new mechanism for an enhanced GB J c arising from pinned Abrikosov vortices in the banks of a GB which present a static, quasiperiodic pinning potential to pin GB vortices. They find a peak in J c and an unusual hysteresis which give considerable support to the GC concept. In low fields, the GBs exhibit a larger J c for field cooling, which is opposite to the usual hysteresis but agrees with GC due to the larger Abrikosov vortex density in the banks. Magnetization data on the same sample are consistent including the identification of the irreversibility field

  17. The disordered Bose condensate in two dimensions: application to high-Tc superconductors

    International Nuclear Information System (INIS)

    Gold, A.

    1992-01-01

    We calculate the dynamical conductivity for a weakly disordered Bose condensate in two dimensions. The disorder is due to neutral impurities. We compare the asymptotic laws (for small and large frequencies) for neutral impurities with the ones for charged impurities. Universal functions for the dynamical transport properties are derived. The plasmon density of states shows a linear increase with energy for intermediate energies and a peak structure at larger energies. Our theoretical results are compared with experimental results (far-infrared, electron-energy-loss and Raman spectroscopy) found in the high-Tc superconductor YBa 2 Cu 3 O 7-δ . The occurrence of a quasi-gap in a disordered Bose condensate is described and discussed in connection with experiments on high-Tc superconductors. (orig.)

  18. The Effect of Twins on Critical Currents of High Tc Superconductors

    Science.gov (United States)

    1989-01-01

    particles to stick together due to electrostatic forces. To overcome this we have formed a slurry of the material in liquid nitrogen and flash...can use and the liquid convection tends to counteract the separation process. We have-now designed a magnetic track which particles will slide down with...Currents of High Tc Superconductors" - A.M. Campbell and M.F. Ashby The initial work on levitation forces and separation of superconducting powders has

  19. Nonequilibrium states of high tc YBCO superconductors under tunnel injection of quasiparticles

    International Nuclear Information System (INIS)

    Iguchi, I.; Wang, Q.; Lee, K.; Yoshida, K.

    1995-01-01

    The nonequilibrium states of high Tc superconductors are investigated by means of tunnel injection of quasiparticles using Pb(or Au)/MgO/YBCO tunnel junctions. The effective critical-current reduction due to tunnel injection is observed, whose behaviour is different from simple heating. The observed results suggest that the resultant nonequilibrium states may also differ from those described by conventional nonequilibrium models

  20. Josephson junction between two high Tc superconductors with arbitrary transparency of interface

    Directory of Open Access Journals (Sweden)

    GhR Rashedi

    2010-03-01

    Full Text Available In this paper, a dc Josephson junction between two singlet superconductors (d-wave and s-wave with arbitrary reflection coefficient has been investigated theoretically. For the case of high Tc superconductors, the c-axes are parallel to an interface with finite transparency and their ab-planes have a mis-orientation. The physics of potential barrier will be demonstrated by a transparency coefficient via which the tunneling will occur. We have solved the nonlocal Eilenberger equations and obtained the corresponding and suitable Green functions analytically. Then, using the obtained Green functions, the current-phase diagrams have been calculated. The effect of the potential barrier and mis-orientation on the currents is studied analytically and numerically. It is observed that, the current phase relations are totally different from the case of ideal transparent Josephson junctions between d-wave superconductors and two s-wave superconductors. This apparatus can be used to demonstrate d-wave order parameter in high Tc superconductors.

  1. Development of superconductor bulk for superconductor bearing

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Chan Joong; Jun, Byung Hyuk; Park, Soon Dong (and others)

    2008-08-15

    Current carrying capacity is one of the most important issues in the consideration of superconductor bulk materials for engineering applications. There are numerous applications of Y-Ba-Cu-O (YBCO) bulk superconductors e.g. magnetic levitation train, flywheel energy storage system, levitation transportation, lunar telescope, centrifugal device, magnetic shielding materials, bulk magnets etc. Accordingly, to obtain YBCO materials in the form of large, single crystals without weak-link problem is necessary. A top seeded melt growth (TSMG) process was used to fabricate single crystal YBCO bulk superconductors. The seeded and infiltration growth (IG) technique was also very promising method for the synthesis of large, single-grain YBCO bulk superconductors with good superconducting properties. 5 wt.% Ag doped Y211 green compacts were sintered at 900 .deg. C {approx} 1200 .deg.C and then a single crystal YBCO was fabricated by an infiltration method. A refinement and uniform distribution of the Y211 particles in the Y123 matrix were achieved by sintering the Ag-doped samples. This enhancement of the critical current density was ascribable to a fine dispersion of the Y211 particles, a low porosity and the presence of Ag particles. In addition, we have designed and manufactured large YBCO single domain with levitation force of 10-13 kg/cm{sup 2} using TSMG processing technique.

  2. Transport phenomena in high Tc superconductors. Resume of Ph.D thesis

    International Nuclear Information System (INIS)

    Crisan, I.A.

    1994-01-01

    This is an extended abstract of the Ph. D. thesis devoted to the transport phenomena in high-Tc superconductors. There are three chapters. The first chapter presents an overview of the essential theoretical aspects concerning the vortex dynamics particularly in ceramic superconductors. The chapter two gives a description of the preparation methods of superconductor samples used by the author as well as the measurement devices for volt-ampere characteristics and the associated electronic circuitry. In the third chapter there are presented the experimental data obtained from different samples prepared in different temperature and magnetic field conditions. The obtained results are finally interpreted in the frame of existent or original models. (M.I.C.). 31 Refs

  3. Characteristics of YBa2Cu3O7 high-Tc superconductor with KCl

    Science.gov (United States)

    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.

  4. Experimental Set-Up for Evaluation of Electro-Magnetic Characteristics of High-Tc Superconductors Cooled by Liquid Hydrogen

    OpenAIRE

    Shirai, Yasuyuki; Hikawa, Kyosuke; Shiotsu, Masahiro; Tatsumoto, Hideki; Hata, Koichi; Kobayashi, Hiroaki; Nonaka, Satoshi; Naruo, Yoshihiro; Inatani, Yoshifumi

    2013-01-01

    Liquid hydrogen (LH2) has excellent properties as a coolant, such as large latent heat, low viscosity coefficient, etc. Not only MgB2 but also other high-Tc superconductors are expected to have excellent properties when cooled by LH2. It is necessary for a stability design of a high-Tc superconductor cooled by LH2 to make an electro-magnetic characteristic clear. However, due to the handling difficulties of LH2, there are only few papers on the properties of LH2-cooled superconductors, especi...

  5. Performance of ultrahigh resolution electron microscope JEM-4000EX and some applications of high Tc superconductors

    International Nuclear Information System (INIS)

    Honda, T.; Ibe, K.; Ishida, Y.; Kersker, M.M.

    1989-01-01

    The high resolution electron microscope is powerful for modern materials science because of its direct observation capability for the atomic structure of materials. the JEM-4000EX, a 400 kV accelerating voltage electron microscope whose objective lens has a 1 mm spherical aberration coefficient, has a 0.168 nm theoretical resolving power. Using this microscope, atomic structure images of high Tc superconductor such as Y-Ba-Cu-O, Bi-Ca-Sr-Cu-O and Tl-Ca-Ba-Cu-O are reported

  6. Positron annihilation studies of the electronic structure and fermiology of high-Tc superconductors

    International Nuclear Information System (INIS)

    Smedskjaer, L.C.; Bansil, A.

    1993-01-01

    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of high-Tc superconductors, with focus on the YBa 2 Cu 3 O 7 system where most of the experimental and theoretical work has to date been concentrated. Detailed comparisons between the measured 2D-ACAR positron spectra and the corresponding band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture. (orig.)

  7. Electromagnetic wave absorption in high-Tc superconductors and its application

    International Nuclear Information System (INIS)

    Porjesz, T.; Khatiashvili, N.; Kovacs, Gy.; Leppavuori, S.; Uusimaki, A.; Kokkomaki, T.; Hagberg, J.

    1995-08-01

    The experimental study of the electromagnetic wave absorption of high-Tc superconductors subjected to small magnetic fields has been extended to a wide frequency range. The results obtained show an almost frequency independent behaviour in the 4 MHz - 20 GHz region. The measurement technique for the high frequency regime was developed in such a way that the sensitivity increased so much that the sample under investigation could be used as a very sensitive magnetic field detector, too. (author). 4 refs, 8 figs, 1 tab

  8. Superconductive properties, interaction mechanisms, materials preparation and electronic transport in high-Tc superconductors

    International Nuclear Information System (INIS)

    Saemann-Ischenko, G.

    1993-01-01

    The final report is composed of eight chapters dealing with the following aspects: I. Mixed state, critical currents, anisotropy, intrinsic and extrinsic pinning. II. Microwave properties and far-infrared reflectivity of epitactic HTSC films. III. Hall effect at the states of normal conductivity and superconductivity, magnetoresistance, superconducting fluctuation phenomena. IV. Effects of the nuclear and the electronic energy loss. V. Scanning electron microscopy. VI. p- and n-doped high-Tc superconductors: Charge symmetry and magnetism. VII. Preparation methods. VIII. Electrochemical examinations of HTSC films and HTSC monocrystals at low temperatures. (orig./MM) [de

  9. Extended abstracts of the 12th JAERI workshop on high-Tc superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Hojou, Kiichi; Okayasu, Satoru; Sasase, Masato [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Ishida, Takekazu [Osaka Prefectual Univ., Sakai (JP)] (eds.)

    2001-03-01

    This workshop was held on December 7-8, 2000 at JAERI (Tokai). The research group at JAERI shares a responsibility for material modification of high-Tc superconductors by irradiation in 'the multi-core project II of the high temperature superconducting material research' organized by STA (Science and Technology Agency) of Japan. This report contains the extended abstracts of workshop presentations covering basic theories, various experimental results and material improvement studies of the superconductivity by high energy ion irradiation. The twelve presentations of the workshop were devoted to a mini symposium where the direct observations of vortices were discussed in view of the various sophisticated techniques. (author)

  10. Extended abstracts of the 12th JAERI workshop on high-Tc superconductors

    International Nuclear Information System (INIS)

    Hojou, Kiichi; Okayasu, Satoru; Sasase, Masato

    2001-03-01

    This workshop was held on December 7-8, 2000 at JAERI (Tokai). The research group at JAERI shares a responsibility for material modification of high-Tc superconductors by irradiation in 'the multi-core project II of the high temperature superconducting material research' organized by STA (Science and Technology Agency) of Japan. This report contains the extended abstracts of workshop presentations covering basic theories, various experimental results and material improvement studies of the superconductivity by high energy ion irradiation. The twelve presentations of the workshop were devoted to a mini symposium where the direct observations of vortices were discussed in view of the various sophisticated techniques. (author)

  11. Modelling of bulk superconductor magnetization

    International Nuclear Information System (INIS)

    Ainslie, M D; Fujishiro, H

    2015-01-01

    This paper presents a topical review of the current state of the art in modelling the magnetization of bulk superconductors, including both (RE)BCO (where RE = rare earth or Y) and MgB 2 materials. Such modelling is a powerful tool to understand the physical mechanisms of their magnetization, to assist in interpretation of experimental results, and to predict the performance of practical bulk superconductor-based devices, which is particularly important as many superconducting applications head towards the commercialization stage of their development in the coming years. In addition to the analytical and numerical techniques currently used by researchers for modelling such materials, the commonly used practical techniques to magnetize bulk superconductors are summarized with a particular focus on pulsed field magnetization (PFM), which is promising as a compact, mobile and relatively inexpensive magnetizing technique. A number of numerical models developed to analyse the issues related to PFM and optimise the technique are described in detail, including understanding the dynamics of the magnetic flux penetration and the influence of material inhomogeneities, thermal properties, pulse duration, magnitude and shape, and the shape of the magnetization coil(s). The effect of externally applied magnetic fields in different configurations on the attenuation of the trapped field is also discussed. A number of novel and hybrid bulk superconductor structures are described, including improved thermal conductivity structures and ferromagnet–superconductor structures, which have been designed to overcome some of the issues related to bulk superconductors and their magnetization and enhance the intrinsic properties of bulk superconductors acting as trapped field magnets. Finally, the use of hollow bulk cylinders/tubes for shielding is analysed. (topical review)

  12. Trapped magnetic field of a superconducting bulk magnet in high- Tc RE-Ba-Cu-O

    International Nuclear Information System (INIS)

    Fujimoto, Hiroyuki; Yoo, Sang Im; Higuchi, Takamitsu; Nakamura, Yuichi; Kamijo, Hiroki; Nagashima, Ken; Murakami, Masato

    1999-01-01

    Superconducting magnets made of high-T c superconductors are promising for industrial applications. It is well known that REBa 2 Cu 3 O 7-x and LRE (light rare-earth) Ba 2 Cu 3 O 7-x superconductors prepared by melt processes have a high critical current density, J c , at 77 K and high magnetic fields. Therefore, the materials are very prospective for high magnetic field application as a superconducting permanent/bulk magnet with liquid-nitrogen refrigeration. LREBaCuO bulks, compared with REBaCuO bulks, exhibit a larger J c in high magnetic fields and a much improved irreversibility field, H irr , at 77 K. In this study, we discuss the possibility and trapped field properties of a superconducting bulk magnet, as well as the melt processing for bulk superconductors and their characteristic superconducting properties. One of the applications is a superconducting magnet for the future magnetically levitated (Maglev) train

  13. The evidence of unconventional pairing in heavy fermion superconductors and high-Tc superconductors

    International Nuclear Information System (INIS)

    Tien, C.; Wur, C.S.; Jiang, I.M.

    1989-01-01

    Recently there has been a great deal of interest in two classes of superconductors, heavy fermion superconductors and high T c copper oxide superconductors. The behavior and nature of superconductivity in these two classes of materials are very similar. The temperature dependences of spin-lattice relaxation time (T 1 ) and spin-spin relaxation time (T 2 ) of 9 Be in UBe 13 are quite similar to those of 63 Cu and 89 Y in YBa 2 Cu 3 O 7-δ . The Knight shift of UBe 13 is unchanged during the superconducting phase transition. The Knight shift of YBa 2 Cu 3 O 7-δ changes from the value in the normal state K n /K s = 1 at T ≥ T c to K n /K s = 0.5 at T = 6 K. Both do not approach zero as expected in BCS theory. The acoustic attenuation is enhanced just below T c instead of rapid drop near T c for these two superconducting system. Neither the enhancement, the temperature variation, nor any other anomalous behaviors appear to be mirrored in EPR data for heavy Fermion superconductors and high T c superconductors. This strongly suggests that the unconventional pairing mechanism which induces superconductivity in heavy fermion materials might also involve in high T c superconductors

  14. Report on neutron beam utilization and study of high Tc superconductors at NRI

    Energy Technology Data Exchange (ETDEWEB)

    Tan, Vuong Huu [Nuclear Physics Dept., Nuclear Research Inst. (NRI), Dalat (Viet Nam)

    1998-10-01

    Utilization of reactor neutron beams at NRI for research and applications up to November 1996 had been presented at the last Workshop in Jakarta (25-28 Nov., 1996). This paper describes new research and applications carried out at Nuclear Physics Department of NRI after that time. They consist of neutron beam developments, neutron activation cross section measurements for waste disposal assessment and in-vivo prompt gamma neutron activation analysis for Cd determination in organs. After the last Sub-Workshop on Neutron Scattering in Serpong (21-23 Nov., 1996), we were accepted to participate in the Regional Program on Study of High Tc Superconductors with the topic `The mechanism of Pb and Sb dopant role on superconductivity of 2223 phase of Bi-Sr-Ca-Cu-O system`. Indeed, this study has begun at NRI only since August, 1997 due to the problem of materials. The study has been carried out in collaboration with the Hanoi State University (Superconductors Department) where experts and equipment for superconductors research have been considered as the best ones in Vietnam. Primary results in this study are presented in this workshop. (author)

  15. Internal friction and ultrasonic attenuation in solids, including high Tc superconductors

    International Nuclear Information System (INIS)

    Magalas, L.B.; Gorczyca, S.

    1993-01-01

    This volume contains seven invited papers and about eighty refereed contributions from the main sessions of the Sixth European Conference on Internal Friction and Ultrasonic Attenuation in Solids (ECIFUAS-6) held at the Academy of Mining and Metallurgy (Akademia Gorniczo-Hutnicza, AGH) in Krakow, Poland, 5-7 September, 1991. In addition, this volume contains six invited lectures and eight contributed papers presented at the Workshop on High Tc Superconductors on 5 September, 1991. Together these documents constitute the Proceedings of the ECIFUAS-6 Conference. A total of 140 scientists from 20 countries participated in the Conference. The programme of the Conference and the Workshop consisted of 16 invidet papers and 119 contributed papers. 107 papers were presented during 8 poster sessions. (orig.)

  16. Internal friction of flux motion in Hg-system high-Tc superconductors

    International Nuclear Information System (INIS)

    Tian, W.; Zhu, J.S.; Shao, H.M.; Li, J.; Wang, Y.N.

    1996-01-01

    The internal friction(IF) and modulus as functions of temperature were measured for several Hg-system high-Tc superconductors(Hg1201, Hg1223, Hg1223 doped with Fe and Pb), under the applied magnetic field, with vibrating reed technique. An IF peak associated with flux motion can be found below Tc for all samples. The temperature of the IF peak increases with reducing vibrating amplitude. This amplitude dependence of IF indicates that the flux motion is characterized by nonlinear behavior. No apparent shift of IF peak position can be detected by varying the frequency in the range from 10 2 Hz to 10 3 Hz. Furthermore, the IF peak height satisfies a scaling law Q -1 ∝ω -n . This may be originated from phase transition of flux line lattice(FLL) rather than a thermally activated diffusion process. (orig.)

  17. Electrical and microstructural characterization of silver sheathed high Tc superconductors wires and ribbons

    International Nuclear Information System (INIS)

    Chaffron, L.; Regnier, P.; Schmirgeld, L.; Maurice, F.; Aguillon, C.; Senoussi, S.

    1991-01-01

    High Tc superconductors wires and ribbons were prepared according to the powder in tube method. It is shown that the electrical performances of the so prepared superconductors can be considerably improved, first by increasing as much as possible the density of the green body before sintering, and afterwards by melt texturing the sintered conductors. Some measurements of the transport critical current density of our conductors as a function of their diameter or their thickness are then presented and compared with indirect values obtained via the Bean method. The highest transport Jc measured in the present study, before melt texturing, are: 2250 and 5100 A/cm 2 at 77 and 63 K respectively, for a 50 μm thick silver sheathed ribbon. These figures compare nicely with the values of the intergranular critical current densities determined from magnetic measurements which are: 2100 and 5000 A/cm 2 at the same temperatures, and 40000 A/cm 2 at 4.2 K. Much higher intergranular values, in the range of 10 5 A/cm 2 were obtained after melt texturing the wires. Finally, microstructural characterizations carried out by X-ray diffraction, electron microprobe analysis and transmission electron microscopy are reported and discussed

  18. Transport measurements in superconductors: critical current of granular high TC ceramic superconductor samples

    International Nuclear Information System (INIS)

    Passos, W.A.C.

    2016-01-01

    This work presents a method to obtain critical current of granular superconductors. We have carried out transport measurements (ρxT curves and VxI curves) in a YBa_2Cu_3O_7_-_δ sample to determine critical current density of it. Some specimens reveal a 'semiconductor-like' behavior (electrical resistivity decreases with increasing temperatures above critical temperature T_c of material) competing with superconductor behavior. Due to high granular fraction of the sample, these competition is clearly noted in ρxT curves. Measurements carried out from 0 to 8500 Oe of applied field show the same behavior, and the critical current density of the samples is shown. (author)

  19. Vortex properties in a strongly textured Bi(2212) high Tc superconductor

    International Nuclear Information System (INIS)

    Verhoeven, P.F.M.

    1993-08-01

    The research described in this report was aimed at obtaining more information about the behaviour of vortices in a textured type II Bi 2 Sr 2 CaCu 2 O 8 high Tc superconductor. With the neutron depolarization technique used, it is possible to determine the mean magnetic induction in the sample and the magnetic disorder in the vortex system in one measurement. If the mean induction is directed along one of the main axes, it is possible to determine the local orientation of the vortices. The vortex distribution can in first order approximation be described by the Bean-model. This model claims a constant gradient in the vortex distribution from the edges toward the centre of the superconductor. In order to investigate this gradient, a scan method is used to measure the mean induction as a function of the position in the superconductor. From these measurements a non homogeneous vortex distribution at the edges could be concluded, although it could not be determined whether the gradient of the vortex distribution near the edges is constant. In order to investigate the relaxation of the vortex distribution after a magnetic field pulse, time dependent measurements were carried out. It appeared that the relaxation of the vortex system on short time scale (ms) is not only due to flux creep, but also to a collective expulsion of vortices because of the repulsive force between the vortices which are very closely packed together right after the pulse. Large remanence (>20 Gauss) after a large applied field pulse (>1 T) was observed, perpendicular to the applied field. This perpendicular remanence was investigated as a function of time, as a function of position, as a function of temperature and as a function of the applied field pulse. These large perpendicular fields can be explained if the texture of the sample is taken into account. (orig.)

  20. High pressure studies up to 50 GPa of Bi-based high-Tc superconductors

    International Nuclear Information System (INIS)

    Staun Olsen, J.; Steenstrup, S.; Gerward, L.; Sundqvist, B.

    1991-01-01

    The high-T c superconductor with nominal composition BiSrCaCu 2 O x has been studied at high pressure, i.e. up to 50 GPa. A tetragonal structure was compatible with the measurements at all pressures, and no phase change was observed. The bulk modulus, B o =62.5 GPa, obtained has a somewhat smaller value than the one estimated earier. (orig.)

  1. Far infrared spectroscopy of high-Tc superconductors at the National Synchrotron Light Source

    International Nuclear Information System (INIS)

    Perkowitz, S.; Williams, G.P.

    1989-01-01

    This paper reports the first far infrared transmission spectra for micron-thick films of high-T c rare-earth superconductors such as DyBaCuO, with implications for the superconducting gap. Spectra were obtained at Brookhaven's National Synchrotron Light Source, a new high-intensity, broad-band millimeter to infrared source. The National Synchrotron Light Source at Brookhaven National Laboratory, known for powerful X-ray and UV output, is also a high-intensity (10 to 1000 times above a black body), high-brightness (intensity per solid angle), broad-band, picosecond, millimeter to infrared source. These features make it valuable for far-infrared condensed matter experiments, especially those in highly absorbing or extremely small systems. A first application has been to measure very small infrared transmissions through thick bulk-like high-T c superconducting films. Preliminary measurements through films of the conventional superconductor Nb 3 Ge established techniques. These were followed by the first measurements (to the author's knowledge) through micron-thick films of high-T c rare-earth superconductors such as DyBaCuO over 10-300 cm -1 , which includes the superconducting gap according to BCS or moderately strong-coupled theory. The authors discuss the transmission evidence bearing on the existence of a gap and other important features of high-T c superconductors, and describe the synchrotron and instrumentation features which make possible these unusual measurements

  2. Predicted midgap states in unconventional superconductors and their numerous implications for high-Tc superconductors

    International Nuclear Information System (INIS)

    Hu, C.R.

    1998-01-01

    A fundamental topological consequence of the unconventional (i.e., non-s-wave) pairing symmetry of high-T c superconductors (HTSC's) is the existence of midgap (quasi-particle) states (MS's) bound to surface,m interfaces and other locations. This prediction by the author has most-likely solved a decade-old puzzle, viz., the ubiquitous observation of a zero-bias conductance peak (ZBCP) in tunneling experiments performed on HTSC's. There are also numerous other novel consequences of these MS's, predicted by various researchers, including a new Josephson critical current term; an (already observed) low-temperature splitting of the ZBCP due possibly to a spontaneous breaking of the time-reversal symmetry at a sample surface; a new explanation of the paramagnetic Meissner effect; and a giant magnetic moment, etc. Here the author will review the physical origin of the MS's, the several extensions of the original idea and the many novel consequences of these MS's, some of which have been investigated quantitatively and some others only deduced in qualitative terms so far

  3. What is the role of Pb(II) in high Tc superconductors

    International Nuclear Information System (INIS)

    Raveau, B.; Hervieu, M.; Michel, C.; Groult, D.; Provost, J.

    1990-01-01

    An overview of the layered lead cuprates is presented here. The structure of these oxides and their non-stoichiometry are studied in connection with their superconducting properties. The phenomena involving a modulation of the structure, characterized by the presence of satellites on E.D. patterns are described and the particular role of the 6s 2 lone pair of Pb(II) is discussed. Divalent lead is, owing to its size intermediate between that of strontium and barium, a potential cation for superconductive cuprates. Moreover, this interest for Pb(II), is supported by its electronic structure which involves an electronic 6s 2 lone pair well known for its ability to form layered structures. In spite of these characteristics, few superconductive layered suprates were isolated at the beginning of the rush to high Tc superconductors. This is probably due to the possibility of existence of redox reactions involving the couple Pb(II)/Pb(IV), which require very particular experimental conditions. The authors report here on the recent development of the crystal chemistry of those materials and on their corresponding superconducting properties

  4. Singularity in the positive Hall coeffcient near pre-onset temperatures in high-Tc superconductors

    Science.gov (United States)

    Vezzoli, G. C.; Chen, M. F.; Craver, F.; Moon, B. M.; Safari, A.; Burke, T.; Stanley, W.

    1990-10-01

    Hall measurements using continuous extremely slow cooling and reheating rates as well as employing eqiulibrium point-by-point conventional techniques reveals a clear anomally in RH at pre-onset temperatures near Tc in polycrystalline samples Y1Ba2Cu3O7 and Bi2Sr2Ca2Cu3O10. The anomaly has the appearance of a singularity of Dirac-delta function which parallels earlier work on La1-xSrxCuO4. Recent single crystal work on the Bi-containing high-Tc superconductor is in accord with a clearcut anomaly. The singularity is tentatively interpreted to be associated (upon cooling) with initially the removal of positive holes from the hopping conduction system of the normal state such as from the increased concentration of bound virtual excitons due to increased exciton and hole lifetimes at low temperature. Subsequently the formation of Cooper pairs by mediation from these centers (bound-holes) and/or bound excitons) may cause an ionization of these bound virtual excitons thereby re-introducing holes and electrons into the conduction system at Tc.

  5. Correlation effects in high-Tc superconductors and heavy fermion compounds

    International Nuclear Information System (INIS)

    Kuzemsky, A.L.

    1993-10-01

    This paper describes certain aspects of Highly Correlated Systems (HCS) such as high Tc superconductors (HTSC) and some new class of Heavy Fermion (HF) systems which have been studied recently. The problem is discussed on how the charge and spin degrees of freedom participate in the specific character of superconductivity in the copper oxides and competition of the magnetism and Kondo screening in heavy fermions. The electronic structure and possible superconducting mechanisms of HTSC compounds are discussed. The similarity and dissimilarity with HF compounds is pointed out. It is shown that the spins and carriers in the copper oxides are coupled in a very nontrivial way in order to introduce the discussion and the comparison of the Emery model, the t - J-model and the Kondo-Heisenberg model. It concerns attempts to derive from fundamental multi-band Hamiltonian the reduced effective Hamiltonians to extract and separate the relevant low-energy physics. A short review of the arguments which seem to support the spin-polaron pairing mechanism in HTSC are presented. Many other topics like the idea of mixed valence states in oxides, the role of charge transfer (CT) excitations, phase separation, self-consistent nonperturbative technique, etc. are also discussed. (author). 161 refs

  6. Critical current density and wire fabrication of high-TC superconductors

    International Nuclear Information System (INIS)

    Schlabach, T.D.; Jin, S.; Sherwood, R.C.; Tiefel, T.H.

    1989-01-01

    In this paper, some of the recent investigations of wire fabrication techniques and critical current behavior in high T c superconductors will be reviewed. In spite of the tremendous interest and research effort, the progress toward major applications of the bulk high-temperature superconductors has been impeded by, among other thins, the low critical currents and their severe deterioration in weak magnetic fields. Significant advances, however, have been made in understanding the causes of the problem as well as in improving the current-carrying capacity through proper microstructural control such as the melt-textured-growth in Y-Ba-Cu-O. The low density of effective flux-pinning sites in bulk Y-Ba-Cu-O limits J c at 77K in high magnetic fields to about 10 4 A/cm 2 even in the absence of weak links. Magnetization measurements on Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O at 77K by various researchers indicate even weaker flux pinning capabilities in these materials than in Y-Ba-Cu-O. The challenge in the future is to obtain suitable flux-pinning defects by choosing the right processing and chemistry changes

  7. Bulk Superconductors in Mobile Application

    Science.gov (United States)

    Werfel, F. N.; Delor, U. Floegel-; Rothfeld, R.; Riedel, T.; Wippich, D.; Goebel, B.; Schirrmeister, P.

    We investigate and review concepts of multi - seeded REBCO bulk superconductors in mobile application. ATZ's compact HTS bulk magnets can trap routinely 1 T@77 K. Except of magnetization, flux creep and hysteresis, industrial - like properties as compactness, power density, and robustness are of major device interest if mobility and light-weight construction is in focus. For mobile application in levitated trains or demonstrator magnets we examine the performance of on-board cryogenics either by LN2 or cryo-cooler application. The mechanical, electric and thermodynamical requirements of compact vacuum cryostats for Maglev train operation were studied systematically. More than 30 units are manufactured and tested. The attractive load to weight ratio is more than 10 and favours group module device constructions up to 5 t load on permanent magnet (PM) track. A transportable and compact YBCO bulk magnet cooled with in-situ 4 Watt Stirling cryo-cooler for 50 - 80 K operation is investigated. Low cooling power and effective HTS cold mass drives the system construction to a minimum - thermal loss and light-weight design.

  8. Reply to the ''Comment on 'Observation of trapped O2 in high-Tc metal oxide superconductors' ''

    International Nuclear Information System (INIS)

    Chen, C.H.; Phillips, R.C.; Payne, M.G.

    1990-01-01

    Desorption of O 2 in certain high-T c superconductors was observed from scraping the surfaces of superconductors by Rosenberg and Wen. Their conclusion agrees with the results from the observation of O 2 trapping by a laser ablation of superconductors. However, the local heating due to the scraping process can possibly raise the local surface temperature significantly higher than the temperature of the bulk

  9. Josephson effect in high-Tc superconductors and in structures using them

    International Nuclear Information System (INIS)

    Kupriyanov, M.Yu.; Likharev, K.K.

    1990-01-01

    A review of the investigations of the Josephson effect in HTS materials and HTS Josephson structures is represented. The influence of the synthesis conditions and a surface etching on the surface properties of the HTS/Ag(Au) are briefly discussed. On the basis of these results the experimental data obtained in various types of the Josephson junctions (point contacts, tunnel junctions, weak links, break and bulk junctions and crystal type break junctions) are considered. These data are compared with theoretical results obtained from different BCS models of the Josephson junctions. It is concluded that now it is impossible to make either the conclusion on the applicability of the BCS theory for HTS superconductors or the unambiguous identification of the principal physical structure of the junctions. The directions of the future experimental investigations of the Josephson effect in HTS tunnel junctions and weak links are discussed

  10. Microwave superconductivity for particle accelerators - How the high TC superconductors measure up

    International Nuclear Information System (INIS)

    Padamsee, H.; Green, K.; Gruschus, J.

    1988-01-01

    Application of superconducting niobium cavities to accelerators for high energy physics, nuclear physics and free electron laser is growing rapidly. Cornell has a long standing effort in the development of superconducting RF accelerator technology. Nb cavities developed here from the basis for constructing the world's highest energy electron accelerator for nuclear physics. These cavities have set a standard against which the behavior of the new superconductors must be compared. From available results on dc critical fields, and the energy gap, it appears that the new materials could make a significant impact on the capabilities of future accelerators. Crucial to this assessment, however, are direct microwave loss measurements, together with measurements of the energy gap and RF frequency dependence as well as the behavior at high RF fields. Latest results on these properties for bulk sintered ceramics, thin films and single crystals at RF frequencies of 1.5 and 6 Ghz are presented

  11. Towards novel organic high-Tc superconductors: Data mining using density of states similarity search

    Science.gov (United States)

    Geilhufe, R. Matthias; Borysov, Stanislav S.; Kalpakchi, Dmytro; Balatsky, Alexander V.

    2018-02-01

    Identifying novel functional materials with desired key properties is an important part of bridging the gap between fundamental research and technological advancement. In this context, high-throughput calculations combined with data-mining techniques highly accelerated this process in different areas of research during the past years. The strength of a data-driven approach for materials prediction lies in narrowing down the search space of thousands of materials to a subset of prospective candidates. Recently, the open-access organic materials database OMDB was released providing electronic structure data for thousands of previously synthesized three-dimensional organic crystals. Based on the OMDB, we report about the implementation of a novel density of states similarity search tool which is capable of retrieving materials with similar density of states to a reference material. The tool is based on the approximate nearest neighbor algorithm as implemented in the ANNOY library and can be applied via the OMDB web interface. The approach presented here is wide ranging and can be applied to various problems where the density of states is responsible for certain key properties of a material. As the first application, we report about materials exhibiting electronic structure similarities to the aromatic hydrocarbon p-terphenyl which was recently discussed as a potential organic high-temperature superconductor exhibiting a transition temperature in the order of 120 K under strong potassium doping. Although the mechanism driving the remarkable transition temperature remains under debate, we argue that the density of states, reflecting the electronic structure of a material, might serve as a crucial ingredient for the observed high Tc. To provide candidates which might exhibit comparable properties, we present 15 purely organic materials with similar features to p-terphenyl within the electronic structure, which also tend to have structural similarities with p

  12. Rigid levitation, flux pinning, thermal depinning, and fluctuation in high-Tc superconductors

    International Nuclear Information System (INIS)

    Brandt, E.H.

    1991-01-01

    Here, the author shows that the strong velocity-independent frictional force on a levitating superconductor and on any type-II superconductor moving in a homogeneous magnetic field is caused by pinning and depinning of the magnetic flux lines in its interior. Levitation may thus be used to investigate the pinning properties of a superconductor, and friction in a superconductor bearing may be minimized by choosing appropriate materials and geometries

  13. Boundary conditions in Ginsburg-Landau theory and critical temperature of high-Tc superconductors

    International Nuclear Information System (INIS)

    Lykov, A.N.

    2008-01-01

    New mixed boundary conditions to the Ginsburg-Landau equations are found to limit the critical temperature (T c ) of high-T c superconductors. Moreover, the value of the pseudogap in these superconductors can be explained by using the method. As a result, the macroscopic approach is proposed to increase T c of cuprate superconductors

  14. Force measurements for levitated bulk superconductors

    International Nuclear Information System (INIS)

    Tachi, Y.; Sawa, K.; Iwasa, Y.; Nagashima, K.; Otani, T.; Miyamoto, T.; Tomita, M.; Murakami, M.

    2000-01-01

    We have developed a force measurement system which enables us to directly measure the levitation force of levitated bulk superconductors. Experimental data of the levitation forces were compared with the results of numerical simulation based on the levitation model that we deduced in our previous paper. They were in fairly good agreement, which confirms that our levitation model can be applied to the force analyses for levitated bulk superconductors. (author)

  15. Force measurements for levitated bulk superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Tachi, Y. [Department of Electrical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama (Japan); ISTEC, Superconductivity Research Laboratory, 1-16-25 Shibaura, Minato-ku, Tokyo (Japan). E-mail: tachi at istec.or.jp; Uemura, N. [Department of Electrical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama (Japan); ISTEC, Superconductivity Research Laboratory, 1-16-25 Shibaura, Minato-ku, Tokyo (Japan); Sawa, K. [Department of Electrical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama (Japan); Iwasa, Y. [Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA (United States); Nagashima, K. [Railway Technical Research Institute, Hikari-cho, Kokubunji-shi, Tokyo (Japan); Otani, T.; Miyamoto, T.; Tomita, M.; Murakami, M. [ISTEC, Superconductivity Research Laboratory, 1-16-25 Shibaura, Minato-ku, Tokyo (Japan)

    2000-06-01

    We have developed a force measurement system which enables us to directly measure the levitation force of levitated bulk superconductors. Experimental data of the levitation forces were compared with the results of numerical simulation based on the levitation model that we deduced in our previous paper. They were in fairly good agreement, which confirms that our levitation model can be applied to the force analyses for levitated bulk superconductors. (author)

  16. Temperature Dependence of Quasiparticle Spectral Weight and Coherence in High Tc Superconductors

    Science.gov (United States)

    He, Yang; Zhang, Jessie; Hoffman, Jennifer; Hoffman Lab Team

    2014-03-01

    Superconductivity arises from the Cooper pairing of quasiparticles on the Fermi surface. Understanding the formation of Cooper pairs is an essential step towards unveiling the mechanism of high Tc superconductivity. We compare scanning tunneling microscope investigations of the temperature dependence of quasiparticle spectral weight and quasiparticle interference in several families of high Tc materials. We calculate the coherent spectral weight related to superconductivity, despite the coexistence of competing orders. The relation between pairing temperature and coherent spectral weight is discussed. We acknowledge support by the New York Community Trust-George Merck Fund.

  17. On characteristic voltage of the high Tc superconductor. [Y-Ba-Cu-O

    Energy Technology Data Exchange (ETDEWEB)

    Vasiliev, B V; Uchaikin, S V [Joint Inst. for Nuclear Research, Low Temperature Physics Dept., Dubna (USSR)

    1991-12-01

    The critical currents and normal resistances of the small bridges from yttrium-based high-Tc superconducting ceramics have been measured. The characteristic voltage of these bridges was found to be approximately 20{mu}V. This effect can be explained if between the ceramic grains there are contacts of an order of one crystalline cell in size. (orig.).

  18. High temperature superconductivity: Concept, preparation and testing of high Tc superconductor compounds, and applications

    International Nuclear Information System (INIS)

    Harara, Wafik

    1992-06-01

    Many studies have been carried out on high temperature superconductors with transition temperature above that of the liquid nitrogen. In this scientific study the concept and the mechanism of this phenomena are discussed, in addition the examples of preparation and testing of high temperature superconductors compounds are shown. Also the most important applications in industry are explained. (author). 15 refs., 2 tabs., 18 figs

  19. Anomalous Hall effect from vortex motion in high-Tc superconductors

    International Nuclear Information System (INIS)

    Chen, J.L.; Yang, T.J.

    1994-01-01

    In this work, the unusual Seebeck effect is taken into consideration in explaining the possible origin of the anomalous Hall effect for high-T c superconductors. Combining Maki's theory of transport entropy and Tinkham's theory of resistive transition, we explain why the anomalous Hall effect can be observed in high-T c superconductors, but is absent in most conventional superconductors. The behavior of ρ xy (H,T) in our theory is qualitatively consistent with experiments. In addition, our theory not only predicts that ρ xy will become positive from ρ xy xy |∝ρ xx 2 in the region of ρ xy xy will diminish with increasing defect concentration

  20. Can positron 2D-ACAR resolve the electronic structure of high-Tc superconductors

    International Nuclear Information System (INIS)

    Chan, L.P.; Lynn, K.G.; Harshman, D.R.

    1992-01-01

    In this paper, the authors examine the ability of the positron Two-Dimensional Angular Correlation Annihilation Radiation (2D-ACAR) technique to resolve the electronic structures of high-T c cuprate superconductors. Following a short description of the technique, discussions of the theoretical assumptions, data analysis and experimental considerations, in relation to the high-T c superconductors, are given. The authors briefly review recent 2D-ACAR experiments on YBa 2 Cu 3 O 7-x , Bi 2 Sr 2 CaCuO 8+δ and La 2-x Sr x CuO 4 . The 2D-ACAR technique is useful in resolving the band crossings associated with the layers of the superconductors that are preferentially sampled by the positrons. Together with other Fermi surface measurements (namely angle-resolved photoemission), 2D-ACAR can resolve some of the electronic structures of high-T c cuprate superconductors

  1. Bearing design for flywheel energy storage using high-TC superconductors

    Science.gov (United States)

    Hull, John R.; Mulcahy, Thomas M.

    2000-01-01

    A high temperature superconductor material bearing system (38) This system (38) includes a rotor (50) having a ring permanent magnet (60), a plurality of permanent magnets (16, 20 and 70) for interacting to generate levitation forces for the system (38). This group of magnets are a push/pull bearing (75). A high temperature superconductor structure (30) interacts with the ting permanent magnet (60) to provide stabilizing forces for the system (38).

  2. High precision determination of 16O in high Tc superconductors by DIGME

    International Nuclear Information System (INIS)

    Vickridge, I.; Tallon, J.; Presland, M.

    1994-01-01

    A method is described for measuring the 16 O content of high T c superconductors with better than 1% precision by exploiting the detection of gamma rays emitted when they are irradiated by an MeV deuterium beam. The method is presently less accurate than the widely used titration and thermogravimetric methods, however it is rapid, and may be applied to materials such as Tl-containing high T c superconductors which pose serious problems for the usual analytical methods. (orig.)

  3. Asymmetry in the normal-metal to high-Tc superconductor tunnel junction

    International Nuclear Information System (INIS)

    Flensberg, K.; Hedegaard, P.; Brix, M.

    1988-01-01

    We show that the observed asymmetry in the I-V characteristics of high-T c material to normal metal junctions can be explained within the Resonating-Valence-Bond model. For a bias current with electrons moving from the superconductor to the normal metal the current is quadratic in the bias voltage, and in the opposite case with electrons moving from the normal metal to the superconductor the current is linear in V. (orig.)

  4. Crossover from three - to two-dimensional behavior of the vortex energies in layered XY-models for high Tc superconductors

    International Nuclear Information System (INIS)

    Weber, H.; Jensen, H.J.

    1992-01-01

    We use Monte Carlo simulations of a layered XY-model to study the phase fluctuations in high Tc superconductors. A vortex-antivortex interaction dominated by a term linear in the vortex separation is found in the low temperature regime. This is in agreement with a zero temperature variational calculation. At temperature just above the 2D vortex unbinding temperature the linear term vanishes and an ordinary 2D vortex behaviour is found. This explains the finding that the High Tc superconductors show 2D properties in the vortex fluctuations responsible for the resistivity transition close to the critical temperature. (orig.)

  5. Finding new superconductors: the spin-fluctuation gateway to high Tc and possible room temperature superconductivity.

    Science.gov (United States)

    Pines, David

    2013-10-24

    We propose an experiment-based strategy for finding new high transition temperature superconductors that is based on the well-established spin fluctuation magnetic gateway to superconductivity in which the attractive quasiparticle interaction needed for superconductivity comes from their coupling to dynamical spin fluctuations originating in the proximity of the material to an antiferromagnetic state. We show how lessons learned by combining the results of almost three decades of intensive experimental and theoretical study of the cuprates with those found in the decade-long study of a strikingly similar family of unconventional heavy electron superconductors, the 115 materials, can prove helpful in carrying out that search. We conclude that, since Tc in these materials scales approximately with the strength of the interaction, J, between the nearest neighbor local moments in their parent antiferromagnetic state, there may not be a magnetic ceiling that would prevent one from discovering a room temperature superconductor.

  6. The design of high-Tc superconductors - Room-temperature superconductivity?

    International Nuclear Information System (INIS)

    Tallon, J.L.; Storey, J.G.; Mallett, B.

    2012-01-01

    This year is the centennial of the discovery of superconductivity and the 25th anniversary of the discovery of high-T c superconductors (HTS). Though we still do not fully understand how HTS work, the basic rules of design can be determined from studying their systematics. We know what to do to increase T c and, more importantly, what to do to increase critical current density J c . This in turn lays down a challenge for the chemist. Can the ideal design be synthesized? More importantly, what are the limits? Can one make a room-temperature superconductor? In fact fluctuations place strict constraints on this objective and provide important guidelines for the design of the ideal superconductor.

  7. Pseudogap and the specific heat of high Tc superconductors: a Hubbard model in a n-pole approximation

    Science.gov (United States)

    Calegari, E. J.; Lausmann, A. C.; Magalhaes, S. G.; Chaves, C. M.; Troper, A.

    2015-03-01

    In this work the specific heat of a two-dimensional Hubbard model, suitable to discuss high-Tc superconductors (HTSC), is studied taking into account hopping to first (t) and second (t2) nearest neighbors. Experimental results for the specific heat of HTSC's, for instance, the YBCO and LSCO, indicate a close relation between the pseudogap and the specific heat. In the present work, we investigate the specific heat by the Green's function method within a n-pole approximation. The specific heat is calculated on the pseudogap and on the superconducting regions. In the present scenario, the pseudogap emerges when the antiferromagnetic (AF) fluctuations become sufficiently strong. The specific heat jump coefficient Δγ decreases when the total occupation per site (nT) reaches a given value. Such behavior of Δγ indicates the presence of a pseudogap in the regime of high occupation.

  8. Inter plane coupling and magnetic properties in a high Tc superconductor

    International Nuclear Information System (INIS)

    Malacarne, L.C.; Mendes, R.S.; Veroneze, P.R.

    1997-01-01

    We investigate if besides an increasing in T c , an interaction favoring pair tunneling reproduces some characteristic properties of the superconductors, in the presence of a magnetic field. With this objective, we use a sufficiently simple Hamiltonian which maintains the main qualitative aspects of the inter plane interaction through pairs. We also apply an functional integration method for obtaining the Landau-Ginzburg (L G) equations in presence of magnetic field. From these equations, we verify that the applied model presents the properties expected for a superconductor, e.g. magnetic flux quantization, Meissner effect and possible existence of vortex and vortex lattice

  9. Fermi velocity mismatch effects in the tunneling characteristics of high-Tc superconductors

    International Nuclear Information System (INIS)

    Aponte, J.M.; Nunez-Regueiro, J.E.; Bellorin, A.; Octavio, M.

    1994-01-01

    We present a comparative study of the tunneling characteristics of point contacts in which one electrode was a superconducting single crystal of Bi 2 Sr 2 CaCu 2 O x and the other electrode was either a normal metal (N-HTSC point contact), or a non-superconducting rare earth metallic oxide (REMO-HTSC point contact), or another crystal of the same superconductor (HTSC'-HTSC point contact). We show that the mismatch of the Fermi velocities of the electrodes is in part responsible for the irreproducibility of most of the tunneling conductance curves observed in high temperature superconductors. (orig.)

  10. Magnetic-flux dynamics of high-Tc superconductors in weak magnetic fields

    DEFF Research Database (Denmark)

    Il’ichev, E. V.; Jacobsen, Claus Schelde

    1994-01-01

    Aspects of magnetic-flux dynamics in different types of samples of the high-temperature superconductor YBa2Cu3Ox have been investigated in magnetic fields below 1 Oe and at 77 K. The experiments were carried out in an arrangement including a field coil, a flat sample perpendicular to the field...

  11. Basic technology of high-Tc superconductors. Project: Preparation, microstructure, contacts

    International Nuclear Information System (INIS)

    Arlt, G.; Bonnenberg, D.; Kliem, H.

    1991-01-01

    By conventional mixed oxide sintering technique some hundred samples of polycrystalline BYaCuO were prepared. Their physical properties were measured here and in some other research organizations. We investigated mainly: The origin of domain configuration, the contact resistances metal-superconductor, the critical current. All problems were solved satisfactorily. (orig.) With 30 refs [de

  12. Positron annihilation study on Y-Ba-Cu-O high Tc superconductors

    International Nuclear Information System (INIS)

    Balogh, A.G.; Liszkay, L.; Molnar, B.; Puff, W.

    1987-08-01

    First positron annihilation measurements are reported on high T c superconductor YBa 2 Cu 3 O 7-x . The lifetime and Doppler broadening spectra show a slight but significant change about 240K suggesting a deviation from the normal structure far above 90K where the resistance falls to zero. (author)

  13. Operating modes of high-Tc composite superconductors and thermal runaway conditions under current charging

    International Nuclear Information System (INIS)

    Romanovskii, V R; Watanabe, K

    2006-01-01

    The operating thermal and electric modes of a high-T c superconducting composite in partially and fully penetrated states induced by the charging current are investigated. They were studied under conditions in which the current charging rate, the volume fraction of the superconductor in a composite or the temperature of the cooling bath were changed. The transient behaviour of the voltage-current dependence, which is characteristic during stable and unstable increases in electric field inside the composite under a continuous current charging, is discussed. Simulations were done using zero- and one-dimensional steady and unsteady thermoelectric models with a power equation describing the virgin voltage-current characteristic of a superconductor. It is found that some thermoelectric trends underlie the shape of the voltage-current characteristic of the high-T c superconducting composite. These have to be considered during experiments in which the critical or quench currents are defined. First, in the initial stage of the fully penetrated regime (in the low voltage range), the electric field distribution does not have a uniform character. These states depend on the volume fraction of the superconductor and the current charging rate: the higher these quantities, the higher the heterogeneity of the electric field. Second, during the stable over-critical regime (in the high voltage range) occurring in complete penetration modes, the evolution of the electric field may depend on the relevant temperature increase of a composite according to the corresponding increase in its temperature-dependent heat capacity. Consequently, the shape of the voltage-current characteristic of a composite high-T c superconductor during continuous current charging, both before and after thermal runaway, has only a positive slope. Moreover, it is proved that the growth of the fully penetrated part of the voltage-current characteristic becomes less intensive when the current charging rate or the

  14. Quality criteria for high Tc superconductors and on the clarification of the superconducting mechanism

    International Nuclear Information System (INIS)

    Haase, E.L.; Ruzicka, J.

    1992-03-01

    After the successful basic solution of the Nb 3 Ge and Nb 3 Si problems, optimization strategies and quality criteria were developed for high Tc superconducting (HTCS) samples in analogy. After improvements of the sputtering system, the preparation parameters were tightly controlled, leading to samples with a reproducible linear slope of the specific resistance ρ(T). Further improvements by us and Poppe et al. lead to the preparation of 123 films with non-linear ρ(T) curves above 120K. A generalization to a T 2 behavior of ρ(T) leads to the further generalization that defect free HTCS are essentially two dimensional in nature, with all ensuing consequences. The momentum transport of the moving charge cariers requires, because of momentum conservation, a mechanism to transfer momentum to the lattice (momentum relaxation). The qualitative theory developed for two dimensional (2D) systems shows that the electron-phonon interaction is strongly suppressed and hence that the weaker electron-electron interaction dominates. That theory makes numerous predictions, which so far are confirmed by experiments. In particular, it accounts for the extreme temperature dependence of the mean free path and the Hall effect. It is inferred that the mechanism of HTCS is predominantly due to electron-electron interaction - probably of bipolaron nature, as indicated by experiment. At this point experiment meets just a few theories, that conform with the experimental facts and above theory, all based on the quasi-particle theory of electron-electron interaction. The theory of Newns, Pattnaik and Tsuei should have a T 2 shape of ρ(T) and, because E F lies near a nearly logarithmic van Hove singularity, accounts for the high Tc. Ruvalds and Virosztek's theory predicts the T 2 shape of ρ(T). (orig./GSCH)

  15. Magnetic Signals of High-Temperature Superconductor Bulk During the Levitation Force Measurement Process

    Science.gov (United States)

    Huang, Huan; Zheng, Jun; Qian, Nan; Che, Tong; Zheng, Botian; Jin, Liwei; Deng, Zigang

    2017-05-01

    In order to study the commonly neglected magnetic field information in the course of levitation force measurement process in a superconducting maglev system, a multipoint magnetic field measurement platform was employed to acquire magnetic signals of a bulk high-Tc superconductor on both the top and the bottom surface. Working conditions including field cooling (FC) and zero field cooling were investigated for these vertical down and up motions above a permanent magnet guideway performed on a HTS maglev measurement system. We have discussed the magnetic flux variation process based on the Bean model. A magnetic hysteresis effect similar to the levitation force hysteresis loop of the bulk superconductor was displayed and analyzed in this paper. What is more valuable, there exists some available magnetic flux on the top surface of the bulk superconductor, and the proportion is as high as 62.42% in the FC condition, which provides an experimental hint to design the superconductor bulk and the applied field for practical use in a more efficient way. In particular, this work reveals real-time magnetic flux variation of the bulk superconductor in the levitation application, which is the other important information in contrast to the macroscopic levitation and guidance force investigations in previous studies, and it enriches the existing research methods. The results are significant for understanding the magnetic characteristic of superconductors, and they can contribute to optimize the present HTS maglev system design.

  16. Electronic bound states in parity-preserving QED3 applied to high-Tc cuprate superconductors

    International Nuclear Information System (INIS)

    Christiansen, H.R.; Cima, O.M. Del; Ferreira Junior, M.M.; Maranhao Univ., Sao Luis, MA; Helayel-Neto, J.A.; Centro Brasileiro de Pesquisas Fisicas

    2001-08-01

    We consider a parity-preserving QED 3 model with spontaneous breaking of the gauge symmetry as a framework for the evaluation of the electron-electron interaction potential underlying high-T e superconductivity. The fact that resulting potential, - C s K o (Mr), is non-confining and weak (in the sense of Kato) strongly suggests the mechanism of pair-condensation. This potential, compatible with an s-wave order parameters, is then applied to the Schrodinger equation for the sake of numerical calculations, thereby enforcing the existence of bound states. The results worked out by means of our theoretical framework are checked by considering a number of phenomenological data extracted from different copper oxide superconductors. The agreement may motivate a deeper analysis of our model viewing an application to quasi-planar cuprate superconductors. The data analyzed here suggest an energy scale of 1-10 meV for the breaking of the U(1)-symmetry. (author)

  17. Disorder and non-linear magnetic response of high Tc superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Burin, J.P. (Lab. de Physique des Solides, INSA, 35 - Rennes (France)); Fouad, Y. (Lab. de Physique des Solides, INSA, 35 - Rennes (France)); Raboutou, A. (Lab. de Physique des Solides, INSA, 35 - Rennes (France)); Peyral, P. (Lab. de Physique des Solides, INSA, 35 - Rennes (France)); Lebeau, C. (Lab. de Physique des Solides, INSA, 35 - Rennes (France)); Rosenblatt, J. (Lab. de Physique des Solides, INSA, 35 - Rennes (France)); Mokhtari, M. (Lab. de Chimie du Solide et inorganique Moleculaire, Univ. Rennes 1, 35 (France)); Pena, O. (Lab. de Chimie du Solide et inorganique Moleculaire, Univ. Rennes 1, 35 (France)); Perrin, C. (Lab. de Chimie du Solide et inorganique Moleculaire, Univ. Rennes 1, 35 (France))

    1993-05-10

    We measure the low frequency magnetic response of YBa[sub 2]Cu[sub 3]O[sub 6.7]F[sub x] (0 [<=] x < 0.2) ceramics in a wide range of a.c. fields (10[sup -7] T [<=] [mu][sub 0]H[sub 0] [<=] 10[sup -4]). When changing the amount of disorder (varying x) on the microscopic level we find the same non linear response with field amplitude H[sub 0] as in granular conventional superconductors. The real part of the susceptibility appears as a universal function of H[sub 1](T)/H[sub 0] where H[sub 1](T) is the field of first flux penetration. The power law dependence found for H[sub 1](T) can be understood in the framework of the coherence transition of granular superconductors with random couplings. (orig.)

  18. Three-terminal devices of high-Tc superconductors: A status report and future challenges

    International Nuclear Information System (INIS)

    Kung, Pang-Jen; Carnegie-Mellon Univ., Pittsburgh, PA

    1992-01-01

    A study has been conducted on the recent progress of the three-terminal devices with transistor-like characteristics fabricated from the high-T c superconducting materials. This study explored the operating principles and characteristics of these devices in relation to the relevant materials and techniques. A comparison of a variety of techniques for superconducting thin film deposition will be given. This study indirates that the feasibility of fabricating hybrid devices composed of semiconductors and superconductors appear to be the key issue to push forward the applications of high-T c superconductors in microelectronics. The junction field-effect transistors with a semiconductor base controlled by the proximity effect are likely to be more manufacturable. The factors that influence the operating reliability of devices and the problems arising from integrating and packaging the devices will also be discussed

  19. Magnetic field and force analysis of high Tc superconductor with flux flow and creep

    International Nuclear Information System (INIS)

    Yoshida, Yoshikatsu; Uesaka, Mitsuru; Miya, Kenzo

    1994-01-01

    This paper describes a new method for the magnetic force analysis of high T c superconductor based on the flux flow and creep model. The introduction of the artificial conductivity, which is used in the conventional method, is not needed. The CPU time requirement of the calculations is considerably lower than that in the case of the conventional method. Thereby the vibration of a levitated permanent magnet was numerically analyzed by taking into account the flux flow and creep

  20. Electron-gamma perturbed angular correlation studies on high-TC superconductors

    International Nuclear Information System (INIS)

    Correia, J.G.; Araujo, J.P.; Marques, J.G.; Ramos, A.R.; Lourenco, A.A.; Amaral, V.; Galindo, V.; Senateur, J.P.; Weiss, F.; Wahl, U.; Melo, A.A.; Soares, J.C.; Sousa, J.B.

    2000-01-01

    Recent results on the study of high-T C superconductors using the e - -γperturbed angular correlation technique are presented. The basic features of the experimental equipment and its installation at the ISOLDE facility are briefly described. Results obtained from 197m Hg implanted into high quality Y 1 Ba 2 Cu 3 O 6+δ epitaxy thin films are presented and discussed

  1. Limiting stable states of high-Tc superconductors in the alternating current modes

    International Nuclear Information System (INIS)

    Romanovskii, V.R.; Watanabe, K.; Awaji, S.

    2014-01-01

    The limiting current-carrying capacity of high-T c superconductor and superconducting tape has been studied in the alternating current states. The features that are responsible for their stable formation have been investigated under the conduction-cooled conditions when the operating peak values of the electric field and the current may essentially exceed the corresponding critical values of superconductor. Besides, it has been proved that these peak values are higher than the values of the electric field and the current, which lead to the thermal runaway phenomenon when the current instability onset occurs in the operating modes with direct current. As a result, the stable extremely high heat generation exists in these operating states, which can be called as overloaded states. The limiting stable peak values of charged currents and stability conditions have been determined taking into account the flux creep states of superconductors. The analysis performed has revealed that there exist characteristic times defining the corresponding time windows in the stable development of overloaded states of the alternating current. In order to explain their existence, the basic thermo-electrodynamics mechanisms have been formulated, which have allowed to explain the high stable values of the temperature and the induced electric field before the onset of alternating current instability. In general, it has been shown that the high-T c superconductors may stably operate in the overloaded alternating current states even under the not intensive cooling conditions at a very high level of heat generation, which is not considered in the existing theory of losses. (authors)

  2. Studies of the interaction between a magnet and a High Tc Superconductor

    International Nuclear Information System (INIS)

    Yang, Z.

    1991-01-01

    This dissertation consists of two parts. The last part is eight research papers which involve topics related to High T c superconductor (HTSC) studies. The main topic describes the interaction between a permanent magnet and a HTSC studied by a mechanical pendulum. The first part of the dissertation has two purposes. One is to give a brief introduction and background to the research papers, and the other is to outline the scientific findings from the HTSC studies. 94 refs., 2 figs

  3. Assessment of potential advantages of high Tc-superconductors for technical application of superconductivity

    International Nuclear Information System (INIS)

    Schauer, F.; Juengst, K.P.; Komarek, P.; Maurer, W.

    1987-09-01

    A first assessment of the technical and economical consequences of liquid nitrogen cooling of new superconductors is given. For the investigation the applications of superconductivity are classified in two categories: First, systems where superconductors are practically indispensable for achieving the system's objectives; second, superconductor applications in competition with highly developed conventional technologies. Further development of those superconducting systems in the first category for which the cost of cryogenic equipment is a smaller fraction of the total system cost (e.g. fusion reactor or MHD generator) will hardly be affected. However, for systems like particle accelerators, research magnets, and NMR spectroscopy and imaging systems, the cryogenic equipment expenditures are significant and LN 2 cooling leads here to a reduction of investment and operating costs, to simplified handling and maintenance, to better reliability and availability, and will thereby improve the acceptance and further spread of these systems. In the second category each application of superconductivity has to be compared with its conventional counterpart, separately. Here, electonic components, power switches, resistive current limiters, and especially the power transmission cables are those applications which look most promising. For magnet applications the main advantageous arguments are less the cost saving aspect but more the higher reliability, simplicity, N 2 -availability, and ease of handling. (orig.) [de

  4. Junction structures based on the high-Tc superconductor YBa2Cu3O7-δ

    International Nuclear Information System (INIS)

    Gijs, M.A.M.

    1993-01-01

    An overview is given of the investigations of the Josephson effect in junction structures based on the high-T c superconductor YBa 2 Cu 3 O 7-δ , which were carried out at the Philips Research Laboratories in Eindhoven in the 1988-1990 period. The reported results are presented in their international scientific context, without attempting a complete review of the subject. However, the various junction types studied give a good idea of the scientific pursuits of high-T c junction researchers in this period. The following junctions are considered: in the category of 'weak link'-type junctions we have investigated YBa 2 Cu 3 O 7-δ -Ag-Nb point contact junctions, YBa 2 Cu 3 O 7-δ Dayem bridges and YBa 2 Cu 3 O 7-δ -Ag(-Al)-Pb proximity junctions. In these structures we combine a high-T c with a low-T c superconductor. We also fabricated planar 'all high-T c ' YBa 2 Cu 3 O 7-δ -Ag-YBa 2 Cu 3 O 7-δ junctions using a submicron structuring process. Next we have made tunnel junctions to study density of states effects of the high-T c superconductor : YBa 2 Cu 3 O 7-δ -Pb junctions using the degraded YBa 2 Cu 3 O 7-δ -Pb interface as a tunnel barrier, and YBa 2 Cu 3 O 7-δ -Ag-Al/Al 2 O 3 /Pb tunnel junctions based on the superconducting proximity effect. Our junction structures are electrically characterized and mostly studied in microwave and magnetic fields. Results are compared with current theoretical models. (orig.)

  5. Nodal quasi-particles of the high-Tc superconductors as carriers of heat

    Directory of Open Access Journals (Sweden)

    K. Behnia

    2006-09-01

    Full Text Available   In the quest for understanding correlated electrons, high-temperature superconductivity remains a formidable challenge and a source of insight. This paper briefly recalls the central achievement by the study of heat transport at low temperatures. At very low temperatures, nodal quasi-particles of the d-wave superconducting gap become the main carriers of heat. Their thermal conductivity is unaffected by disorder and reflects the fine structure of the superconducting gap. This finding had led to new openings in the exploration of other unconventional superconductors

  6. Direct imaging of fractional oxygen Oδ in Hg-based high-Tc superconductors

    International Nuclear Information System (INIS)

    Papoular, R.J.; Collin, G.; Colson, D.; Viallet, V.

    2002-01-01

    Maximum Entropy is applied to the crystallographic imaging of x-ray diffraction data in order to reveal reliable model-free weak electron density features (if any) in newly discovered high-T c superconductors. The use of suitably computed non-uniform priors turns out to be essential. The suggested maxentropic procedure shows that about .2 oxygen atoms [1.6 electrons] can unambiguously be evidenced near the much heavier mercury atoms [harboring 80 electrons each], and this from standard laboratory [non-synchrotron] x-ray data

  7. Of the crystal chemistry of Ruddlesden-Porter type structures in high Tc ceramic superconductors

    International Nuclear Information System (INIS)

    Dwivedi, A.; Cormack, A.N.

    1990-01-01

    This paper reports on atomistic computer simulation employed to examine the energetics and crystal chemistry of some Ruddlesden-Popper type oxide superconductors. Similar structural patterns have been noticed in the superconducting oxides. The formation of Ruddlesden-Popper type layers (alternating slabs of rocksalt and perovskite structures) is similar in many respects to that seen in the system Sr-Ti-O. However, there are some significant differences, for example, the rocksalt and perovskite blocks in the new superconducting compounds are not necessarily electrically neutral unlike in the Sr-Ti-O system and this may well lead to significant differences in their structural chemistry

  8. Spinning rate decay of levitated high-Tc superconductors in rotational magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Terentiev, A.N.; Kutukova, E.O.; Kuznetsov, A.A. (Inst. of Chemical Physics, Academy of Sciences, Moscow (Russia)); Mozhaev, A.P. (Moscow State Univ., Dept. of Chemistry (Russia))

    1992-04-01

    The rotation damping of a levitated superconductor was examined in the static field of a ring-shaped magnet and in the rotating field of coils. It was demonstrated that the pinning force mainly contributed to magnetic friction while the influence of a viscous component was negligible. The rotating magnetic field created a torque, reducing the angular deceleration under relaxation. Dependence of the rotational field-induced torque on the field-intensity was step-like. A relationship between the step-like behavior of rotational field-induced torque and pinning center distribution is discussed. The origins of friction torque and rotational field-produced torque are discussed. (orig.).

  9. Magnetic field dependence of ultrasound velocity in high-Tc superconductors

    International Nuclear Information System (INIS)

    Higgins, M.J.; Goshorn, D.P.; Bhattacharya, S.; Johnston, D.C.

    1989-01-01

    The magnetic field dependence of ultrasound velocity in the superconductor La 1.8 Sr 0.2 CuO 4-y is studied. The sound velocity anomaly near T c is shown to be unambiguously related to superconductivity. Below T c , the sound velocity is found to be sensitive to the dynamics of a pinned flux lattice. A combination of sound velocity and magnetization measurements suggests three regimes of pinning behavior. A generic pinning ''phase diagram'' is obtained in the superconducting state. An anomalous peak effect in the magnetization is also observed at intermediate field strengths

  10. On the force relaxation in the magnetic levitation system with a high-Tc superconductor

    International Nuclear Information System (INIS)

    Smolyak, B M; Zakharov, M S

    2014-01-01

    The effect of magnetic flux creep on the lift force in a magnet/superconductor system was studied. It was shown experimentally that in the case of real levitation (when a levitating object bears only on a magnetic field) the suspension height and consequently the lift force did not change over a long period of time. When the levitating object is fixed for some time (i.e. a rigid constraint is imposed on it), the levitation height decreases after removal of the external constraint. It is assumed that free oscillations of the levitating object slow down the flux creep process, which is activated when these oscillations are suppressed. (paper)

  11. Phonon characteristics of high Tc superconductors from neutron Doppler broadening measurements

    International Nuclear Information System (INIS)

    Trela, W.J.; Kwei, G.H.; Lynn, J.E.; Meggers, K.

    1994-01-01

    Statistical information on the phonon frequency spectrum of materials can be measured by neutron transmission techniques if they contain nuclei with low energy resonances, narrow enough to be Doppler-broadened, in their neutron cross sections. The authors have carried out some measurements using this technique for materials of the lanthanum barium cuprate class, La 2-x Ba x CuO 4 . Two samples with slightly different concentrations of oxygen, one being superconductive, the other not, were examined. Pure lanthanum cuprate was also measured. Lanthanum, barium and copper all have relatively low energy narrow resonances. Thus it should be possible to detect differences in the phonons carried by different kinds of atom in the lattice. Neutron cross section measurements have been made with high energy resolution and statistical precision on the 59m flight path of LANSCE, the pulsed spallation neutron source at Los Alamos National Laboratory. Measurements on all three materials were made over a range of temperatures from 15K to 300K, with small steps through the critical temperature region near 27K. No significant changes in the mean phonon energy of the lanthanum atoms were observed near the critical temperature of the super-conducting material. It appears however that the mean phonon energy of lanthanum in the superconductor is considerably higher than that in the non-superconductors. The samples used in this series of experiments were too thin in barium and copper to determine anything significant about their phonon spectra

  12. Appearance of ferroelectricity by suppressing superconductivity in nanoparticle dispersed glassy precursor for high Tc superconductor

    International Nuclear Information System (INIS)

    Mukherjee, Soma; Chaudhuri, B.K.; Sakata, H.

    2003-01-01

    The multicomponent Bi 1.8 Pb 0.3 Sr 2 Ca 2 Cu 2.8 K 0.2 O δ (FG) glass is found to show ferroelectric (FE) transition around T fc = 530K. Microstructural (TEM) studies of these glasses indicated the presence of nano-crystalline particles/ clusters (∼10-30 nm size). In this glass-nanoparticle composite (GNC), presence of ferroelectric nano-particles/ islands is considered to be responsible for the FE behavior. The K-free FG type glasses showing no dielectric anomaly (or ferroelectricity) are precursors of high T c superconductors which become superconductors (T c ∼80K) by annealing around 840 degC. The K-doped (FG) GNC is, however, not superconducting in the corresponding annealed phase which indicates suppression of superconductivity due to the presence of K or by the appearance of ferroelectricity. Transport and dielectric properties of both K doped and undoped GNC have been studied and they are found to be semiconducting and follow non-adiabatic small polaron hopping conduction mechanism. (author)

  13. Visualizing pair formation on the atomic scale in high-Tc superconductors

    International Nuclear Information System (INIS)

    Pasupathy, A.

    2008-01-01

    Full text: Unlike traditional superconductors, the density of states (DOS) of the high-T c superconductor Bi-2212 shows large nanoscale variations that have been detected using scanning tunneling microscopy (STM). Such variations are seen in the low temperature superconducting gap and in features associated with the coupling of pairs to boson modes. In order to understand these variations in the spectra, we perform atomic resolution STM measurements of Bi-2212 as a function of temperature. Using newly developed experimental techniques, we measure the evolution of the DOS from low temperature (T c ) to temperatures where all gaps in the spectrum have disappeared (T>T*). Such measurements show that the pairing gap nucleates in nanoscale regions at temperatures between T c and T*. By normalizing the low temperature DOS (T c ) to the DOS at high temperature, we are able to fit the superconducting DOS to the d-wave BCS form. We find that the experimental spectrum deviations from a simple d-wave fit indicating a strong coupling between electrons and bosonic modes. We will discuss the temperature evolution of these as well as other features in the DOS and correlate such measurements with the inhomogeneity seen in the gap magnitude at low temperature

  14. Symmetry of order-parameters in high-Tc layered superconductors

    International Nuclear Information System (INIS)

    Rajagopal, A.K.; Jha, Sudhanshu S.

    1997-01-01

    It is well known that the anisotropy and wave-vector dependence of the energy-gap function determine many important properties of a superconductor which are relevant for device applications. Apart from a weak dependence on the wave-vector k - > in the direction perpendicular to the reciprocal layer-plane of a high-T c layered superconductor, it is shown that anisotropic superconducting order parameters for intra-layer pairing in the class of such materials with orthorhombic crystal structures, can have either pure s-wave like symmetry or mixed d-wave and anisotropic extended s-wave like symmetries in the reciprocal layer-plane. However, in such materials with tetragonal crystal structures, it is possible to have a pure s-wave like symmetry, which may be either isotropic or anisotropic in the layer k - >-space, or a pure d-wave like symmetry, as far the k - >-dependence in the reciprocal layer plane is concerned. In view of this, some suggestions for analysing experimental data will also be presented. (author)

  15. Phonon characteristics of high {Tc} superconductors from neutron Doppler broadening measurements

    Energy Technology Data Exchange (ETDEWEB)

    Trela, W.J.; Kwei, G.H.; Lynn, J.E. [Los Alamos National Lab., NM (United States); Meggers, K. [Univ. of Kiel (Germany)

    1994-12-01

    Statistical information on the phonon frequency spectrum of materials can be measured by neutron transmission techniques if they contain nuclei with low energy resonances, narrow enough to be Doppler-broadened, in their neutron cross sections. The authors have carried out some measurements using this technique for materials of the lanthanum barium cuprate class, La{sub 2{minus}x}Ba{sub x}CuO{sub 4}. Two samples with slightly different concentrations of oxygen, one being superconductive, the other not, were examined. Pure lanthanum cuprate was also measured. Lanthanum, barium and copper all have relatively low energy narrow resonances. Thus it should be possible to detect differences in the phonons carried by different kinds of atom in the lattice. Neutron cross section measurements have been made with high energy resolution and statistical precision on the 59m flight path of LANSCE, the pulsed spallation neutron source at Los Alamos National Laboratory. Measurements on all three materials were made over a range of temperatures from 15K to 300K, with small steps through the critical temperature region near 27K. No significant changes in the mean phonon energy of the lanthanum atoms were observed near the critical temperature of the super-conducting material. It appears however that the mean phonon energy of lanthanum in the superconductor is considerably higher than that in the non-superconductors. The samples used in this series of experiments were too thin in barium and copper to determine anything significant about their phonon spectra.

  16. Magneto-optical imaging of magnetic flux distribution in high-Tc superconductors

    International Nuclear Information System (INIS)

    Ueno, K.; Murakamia, H.; Kawayama, I.; Doda, Y.; Tonouchi, M.; Chikumoto, N.

    2004-01-01

    Prototype systems of home-made magneto-optical microscopes were fabricated, and preliminary studies were carried out using Bi 2 Sr 2 CaCu 2 O 8+δ single crystals and an YBa 2 Cu 3 O 7-δ superconductor vortex flow transistor. In the study using BSCCO crystals, we succeeded in the observation of magnetic flux penetration into half-peeled thin flake region on the crystal surface, and it was found that the magnetic fluxes penetrate in characteristic one-dimensional alignment almost along the crystal a-axis. On the other hand, in the study using the YBCO device clear changes in the generated magnetic field distribution could be detected corresponding to the current direction

  17. Random phase approximations for the screening function in high Tc superconductors

    International Nuclear Information System (INIS)

    Lopez-Aguilar, F.; Costa-Quintana, J.; Sanchez, A.; Puig, T.; Aurell, M.T.; Martinez, L.M.; Munoz, J.S.

    1990-01-01

    This paper reports on the electronic transferences from the CuO 2 sheets toward the CuO 3 linear chain, which locate electrons in the orbitals p y /p z of O4/O1 and d z 2 -y 2 of Cu1, and holes in the orbitals d x 2 -y 2 - P z /p y of Cu2 - P2/O3. These holes states present large interatomic overlapping. In this paper, we determine the screening function within the random phase approximation applied to the high-T c superconductors. This screening function is vanishing for determined values of the frequency which correspond to renormalized plasmon frequencies. These frequencies depends on the band parameters and their knowledge is essential for determining the self energy. This self energy is deduced and it contain independent terms for each of the channels for the localization

  18. Determination of oxygen content in high Tc superconductors by deuteron particle activation analysis

    International Nuclear Information System (INIS)

    Tao Zhenlan; Yao, Y.D.; Kao, Y.H.

    1993-01-01

    The experimental method for determining the oxygen content in high T c superconductors is described in detail. This method is applied to determination of oxygen content in high T c Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O samples in which the stoichiometry is varied by reducing the copper and bismuth concentrations. The oxygen concentration is found to vary linearly with Cu(x = 0-0.2) and Bi (x = 0-0.4) deficiencies in YBa 2 Cu 3(1-x )O y and Bi 2(1-x) Sr 2 CaCu 2 O y respectively. X-ray powder diffraction measurements show that the compound of YBa 2 Cu 3(1-x) O y is orthorhombic in the variation range of x = 0-0.2

  19. Strong electron-phonon interaction in the high-Tc superconductors: Evidence from the infrared

    International Nuclear Information System (INIS)

    Timusk, T.; Porter, C.D.; Tanner, D.B.

    1991-01-01

    We show that low-frequency structure in the infrared reflectance of the high-temperature superconductor YBa 2 Cu 3 O 7 results from the electron-phonon interaction. Characteristic antiresonant line shapes are seen in the phonon region of the spectrum and the frequency-dependent scattering rate of the mid-infrared electronic continuum has peaks at 150 cm -1 (19 meV) and at 360 cm -1 (45 meV) in good agreement with phonon density-of-states peaks in neutron time-of-flight spectra that develop in superconducting samples. The interaction between the phonons and the charge carriers can be understood in terms of a charged-phonon model

  20. Numerical evaluation of electromagnetic force induced in high Tc superconductor with grain boundary

    International Nuclear Information System (INIS)

    Hashizume, Hidetoshi; Toda, Saburo; Maeda, Koutaro

    1996-01-01

    After high T c superconducting material was discovered, its superconducting characteristic has been improved so that its critical current density becomes comparable with that of metal alloy superconductors. Together with this progress of the high T c material, it is considered to apply the materials to generating levitation force in combination with permanent magnets. In this case, it becomes very important to evaluate quantitatively the electromagnetic force for designing of the devices. Some researches have used numerical analysis to evaluate the force, where the grain boundary was ignored or treated as nonconducting. In the real materials, however, some part of the screening current can pass through the grain boundary. In this paper, therefore, two dimensional electromagnetic analysis was performed with a new method to treat the grain boundaries, and its effect on the levitation force was discussed

  1. Temperature dependence of velocity of sound in high-Tc superconductors in normal state

    International Nuclear Information System (INIS)

    Bishoyi, K.C.; Rout, G.C.; Behera, S.N.

    2002-01-01

    A microscopic theoretical calculation of temperature dependence of velocity of sound in high temperature superconductors is addressed in this paper. The influence of model parameters of the system in its normal phase is investigated through numerical calculations. The results at the room temperature as well as low temperatures (∼ 25 K), are discussed. The dimensionless parameters involved in the calculations are the electron-phonon coupling (g), staggered magnetic field (h), hybridization (V), position of the f-level (d), temperature (t) and the conduction band width (ω). The model Hamiltonian contains the antiferromagnetism in conduction electrons of cooper and the electron-phonon interaction through the hybridization between conduction electrons and f-electrons of impurity atoms. The phonon Green's functions are calculated by Zubarev's technique. The velocity of sound is calculated in the long wavelength and finite temperature limit. (author)

  2. Development of software in LabVIEW for measurement of transport properties of high Tc superconductors

    International Nuclear Information System (INIS)

    Reilly, D.; Savvides, N.

    1996-01-01

    Full text: The gathering of data and their analysis are vital processes in experiments. We have used LabVIEW (National Instruments) to develop programs to measure transport properties of high - T c superconductors, eg. resistivity, ac susceptibility, I-V characteristics. Our systems make use of GPIB (IEEE - 488.2) programmable instruments and a personal computer. LabVIEW is a graphical programming system for instrument control and data acquisition, data analysis and presentation. A key feature of LabVIEW is the ability to graphically assemble software modules or virtual instruments (VIs) and 'wire' them together. In this paper we describe the development of several programs and will offer advice to colleagues wanting to explore LabVIEW

  3. Nanometer-scale patterning of high-Tc superconductors for Josephson junction-based digital circuits

    International Nuclear Information System (INIS)

    Wendt, J.R.; Plut, T.A.; Corless, R.F.; Martens, J.S.; Berkowitz, S.; Char, K.; Johansson, M.; Hou, S.Y.; Phillips, J.M.

    1994-01-01

    A straightforward method for nanometer-scale patterning of high-T c superconductor thin films is discussed. The technique combines direct-write electron beam lithography with well-controlled aqueous etches and is applied to the fabrication of Josephson junction nanobridges in high-quality, epitaxial thin-film YBa 2 Cu 3 O 7 . We present the results of our studies of the dimensions, yield, uniformity, and mechanism of the junctions along with the performance of a representative digital circuit based on these junctions. Direct current junction parameter statistics measured at 77 K show critical currents of 27.5 μA±13% for a sample set of 220 junctions. The Josephson behavior of the nanobridge is believed to arise from the aggregation of oxygen vacancies in the nanometer-scale bridge

  4. Weakening of flux-pinning strength for high-Tc superconductors in an alternating magnetic field

    International Nuclear Information System (INIS)

    Chen, Q.Y.

    1992-01-01

    This paper reports on the flux-pinning forces in high temperature superconductors which were found to be weakened in an ac field as the applied field strength or the frequency increases. In the weakly pinned regime, flux dynamics could be described with the concept of magnetic diffusion. Flux-motion-induced finite resistivity could lead to significant skin-effect which was reflected in the ac screening effectiveness. The frequency dependence of the relative local field within a superconducting hollow cylinder were used to deduce the flux-motion resistivity ρ. For superconducting YB 2 Cu 3 O 7 - x compounds at 77K it was found that ρ ∼(mu, Omega)-cm. The corresponding magnetic diffusion coefficient was ∼ 224 cm 2 /s. At 750 Hz the skin depth is around 1.54 mm as compared with the 2-mm sample wall thickness

  5. Behavior of high Tc-superconductors and irradiated defects under reactor irradiation

    International Nuclear Information System (INIS)

    Atobe, Kozo; Honda, Makoto; Fukuoka, Noboru; Yoshida, Hiroyuki.

    1991-01-01

    It has been well known that the lattice defects of various types are introduced in ceramics without exception, and exert large effect to the function of these materials. Among oxides, the electronic materials positively using oxygen defect control have been already put in practical use. Also in the oxide high temperature superconductors which are Perovskite type composite oxides, the superconductive characteristics are affected largely by the concentration of the oxygen composing them. This is regarded as an important factor for causing superconductivity, related with the oxygen cavities arising at this time and the carriers bearing superconductivity. In this study, the irradiation effect with relatively low dose, the measurement under irradiation, the effect of irradiation temperature, and the effect of radiation quality were evaluated by the irradiation of YBCO, EBCO and LBCO. The experimental method, and the irradiation effect at low temperature and normal temperature, the effect of Co-60 gamma ray irradiation instead of reactor irradiation are reported. (K.I.)

  6. The Hall effect: An acid test for the Luttinger liquid theory of high Tc superconductors

    International Nuclear Information System (INIS)

    Anderson, P.W.

    1992-01-01

    The temperature dependence of the Hall effect has been one of the most intriguing puzzles of the 'normal' metallic state in cuprate superconductors. It is shown that the Luttinger liquid theory provides a quantitative picture of the data, in particular showing that relaxation time τ perpendicular defined by the Hall angle tan θ H ω c τ perpendicular is the relaxation rate of the spinon elementary excitations and that θ H has a simple and characteristic temperature dependence (A+BT 2 ) -1 . Observed magnitudes of θ H are incompatible with Fermi liquid theory. A discussion is added of the interlayer mechanism for superconductivity and the new form of BCS gap equation which results from it. (author). 12 refs.; 4 figs

  7. Critical current measurements of high Tc superconductors in a scanning low temperature cryostat

    International Nuclear Information System (INIS)

    Telschow, K.L.; O'Brien, T.K.

    1991-01-01

    Maintaining uniformity of properties over long distances is one of the fabrication problems encountered with the new high T c superconductors. Uniform properties are crucial in long tapes or wires with high critical current since local nonuniformities can limit the current carrying capacity of the whole piece. Transport critical currents in high T c superconductors are conventionally measured with the contact 4-point probe DC current-voltage technique. This technique requires contact with the sample and and spatially averages over the region between the two voltage contacts. Two techniques have been used to infer the critical state model. The first uses the net magnetization of a suitably shaped sample in an external magnetic field. The second combines a DC magnetic field with AC induced currents to infer spatial flux profiles. The AC magnetization technique offers an advantage in that it is noncontacting; however, it also averages the measurement over a large area and requires that the sample be shaped and positioned such that it exhibits zero demagnetizing factor. This paper describes a measurement technique and a scanning cryostat assembly that are capable of determining local critical current in a tape or wire with high resolution and without any direct sample electrical contact. A small compensated coil was used to induce AC currents in slab-shaped samples. The coil was situated near the surface on one side of the slab. With this method, the AC probe can be used as a noncontacting dissipation probe, replacing the voltage probe in the 4-point contact method, when an externally driven transport current is used, or by itself as a local critical state generator and dissipation detector. The results are shown to be meaningful even when the internal magnetic field is not uniform due to shape demagnetizing effects. 10 refs., 5 figs

  8. Structural studies of metal oxides related to High-Tc superconductors

    International Nuclear Information System (INIS)

    Hjorth, M.

    1990-02-01

    The project was started in order to investigate metal oxide structures related in some way to high-T c superconductors, using the crystallographic methods available; and in order to be able to use crystallographic methods in ways that go beyond routine applications in order to contribute to the crystallographic knowledge concerning these oxides. The project goes a step outside the boarders normally defined by using the term ''high-T c superconductors'', thus studying metal oxides from a more general crystallographic viewpoint. The methods used are the expansions of the spherical atom model, and of the thermal probability density function, and combination of X-ray work with high resolution electron microscopy. The use of the expanded diffraction models presents problems such as bad convergence in least squares refinement, physical unreasonable parameters, problems with interpretation of the results and difficulties due to missing or insufficient computer programs. The use of these models is discussed. Dynamical theory is applied when considering electron diffraction results. The theory is presented, focusing on the modifications of the standard theory used for some of the structures considered in the thesis, and in overview on other theoretical topics is given. A presentation is given of the structures which have been considered and of earlier work on related compounds, of the problems and solutions applied to the compound discussed and of the results obtained. The results are discussed. The appendices describe published papers and the work not directly connected to the main topics, e.g. implementation and development of computer programs. (AB) 172 refs

  9. Development of fabrication technique of bulk high superconductor

    International Nuclear Information System (INIS)

    Hong, Gye Won; Kim, Chang Joong; Kim, Ki Baik; Lee, Ho Jin; Lee, Hee Gyoun; Kwon, Sun Chil.

    1997-05-01

    In order to realize the commercial application of HTSC materials, it is necessary to develop the fabrication process of high Tc oxide superconductor materials with desired shape and for practical application and high critical current density as well as good mechanical strength which critical current density as well as good mechanical strength which can withstand high lorenz force generated at high magnetic field. Much studies have been concentrated to develop the fabrication technique for high critical current density but still there are a lot of gap which should be overcome for large scale application of HTSC materials at liquid nitrogen temperature. Recently some new fabrication techniques have been developed for YBCO bulk superconductor with high mechanical strength and critical current density. In this project, plastic extrusion and melt process techniques were studied. The components materials for the current lead and the flywheel application were fabricated and their characteristics were investigated from the view point of microstructure and phase formation during heat treatment process. (author). 64 refs., 59 figs

  10. Internal resonance of an elastic body levitated above high-Tc superconducting bulks

    International Nuclear Information System (INIS)

    Kokuzawa, T; Toshihiko, S; Yoshizawa, M

    2010-01-01

    In high-Tc superconducting magnetic levitation systems, levitated bodies can keep stable levitation with no contact and no control and thus their damping is very small. Thanks to these features, their applications to various apparatus are expected. However, on account of their small damping, the nonlinearity of electromagnetic levitation force can give notable effects upon motion of the levitated bodies. Therefore this nonlinearity must be taken into account to accurately analyze the dynamical behavior of the levitated bodies. Structures of such a levitated body can show elastic deformation if the large electromagnetic force acts on it. Therefore, we need to deal with the model as an elastic body. As mentioned above, nonlinear characteristics easily appear in this elastic vibration on account of the small damping. Especially when the ratio of the natural frequencies of the eigenmodes is integer, internal resonance can occur. This nonlinear resonance is derived from nonlinear interactions among the eigenmodes of the elastic levitated body. This kind of internal resonance of an elastic body appearing in high-Tc superconducting levitation systems has not been studied so far. This research especially deals with internal resonance of a beam supported at both its ends by electromagnetic forces acting on permanent magnets. The governing equation with the nonlinear boundary conditions for the dynamics of a levitated beam has been derived. Numerical results show internal resonance of the 1st mode and the 3rd mode. Experimental results are qualitatively in good agreement with numerical ones.

  11. Neutron scattering studies on the high Tc superconductor YBa2Cu306+x

    International Nuclear Information System (INIS)

    Jurgens, M.J.G.M.

    1990-01-01

    The aim of the work described in this thesis is to clarify some of the magnetic aspects of high T c superconductors across the phase diagram as a function of doping and temperature, for which YBa 2 Cu 3 o 6+x has been chosen. Mainly the neutron scattering technique has been employed, which supplies a very powerful tool for this kind of research, for it directly shows the microscopic phenomena of the magnetism involved. First an introduction to the neutron scattering technique is given and a description of the spectrometers employed (ch. 2). The determination of the crystal structure of YBa 2 Cu 3 o 6+x is described, and the single crystals which were used during all the experiments on the magnetic properties as described in this thesis, are characterized (ch. 3). Ch. 4 deals with the phase diagram of the insulating antiferromagnetic phase in YBa 2 Cu 3 o 6+x , as obtained with neutron scattering. The inelastic scattering experiments on the magnetic excitations in this system are presented in ch. 5. In ch. 6 the total susceptibility, measure with a AQUID, is discussed. The local magnetizations, as determined with a polarized neutron scattering technique are the subject of ch. 7. (author). 254 refs.; 77 figs.; 25 tabs

  12. Critical temperatures Tc estimated by Josephson-junction array model of layered high Tc superconductors

    International Nuclear Information System (INIS)

    Kawabata, C.; Shenoy, S.R.; Bishop, A.R.

    1994-11-01

    We model high T c superconductors (HTS) by quantum capacitive Josephson junction arrays (JJA), with Angstrom-scale parameters, to obtain an estimate of Tc trends. The basic idea is as follows. Number (or change) and phase are conjugate variables, with the uncertainty products obeying ΔN · Δ Θ > 1. Thus, in HTS, global phase coherence is opposed by charging-energy induced quantum phase fluctuations, especially across Josephson-coupled CuO 2 planes. These have separation d 1 and effective interplanar dielectric constant ε, e.g. from Y atoms in YBaCuO. Decreasing the interplane charging energy E 0 perpendicular to ∼ d 1 /ε, raises Tc. In Section 1, we motivate a modelling of HTS phase excitations by a quantum capacitive 3D JJA model, with XY planar phases. Section 2 gives a physical picture of the HTS transition, relating the complex layered HTS structure to a simpler ''intermediate level'' quantum 3D JJA/XY model. Section 3 sets up a path integral (3+1)D model that reduces to a previously studied anisotropic 3D XY/JJA model, with constants renormalized in some way, by the capacitance. Postponing a detailed analysis to elsewhere, we make a heuristic estimate for the reduction of the previous Tc, by the charging energy. (author). 30 refs, 8 figs

  13. Magnetic properties of Bi- and Tl- based new high-Tc superconductors

    International Nuclear Information System (INIS)

    Togano, K.; Kumakura, H.; Dietderich, D.H.

    1988-01-01

    Upper critical field H c2 and Magnetization curve were measured for new high-T c oxide superconductors of Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O systems. H c2 values at 77K for the high-T phase of Bi-Sr-Ca-Cu-O, low-T c (T c (ρ = 0) = 105K) phase of Tl-Ba-Ca-Cu-O, and high-T c (T c (ρ = 0)=115K) phase of Tl-Ba-Ca-Cu-O are 41T, 50T, and 100T, respectively. The magnetization curve of the Bi-Sr-Ca-Cu-O shows a relatively small hysterisis, suggesting a weak pinning force compared to Tl-Ba-Ca-Cu-O as well as Ba 2 YCU 3 O x . Critical current density J c of 600A/Cm 2 at 77K and zero-magnetiac field was attained for the high-T c sample of Tl-Ba-Ca-Cu-O

  14. Fluctuational phenomenological model for the magnetodissipation in high-Tc superconductors

    International Nuclear Information System (INIS)

    Sarti, S.; Fastampa, R.; Giura, M.; Silva, E.; Marcon, R.

    1995-01-01

    We develop a phenomenological model for the magnetoresistivity in high-T c superconductors that includes the contribution of the fluctuation excess conductivity and the effects of the phase slip due to thermal motion of vortices above the irreversibility line over local depressions of the order parameter. The fluctuation conductivity in the proximity of the mean-field transition is inserted into the final expression for the resistivity through a scaling function, obtained theoretically by Ullah and Dorsey. The behavior of the system of vortices is taken into account assuming that below the irreversibility line the solid phase is a glass phase. Crossing the irreversibility line, the vortex system becomes a viscous fluid and, finally, a liquid. It is possible to fully describe the resistivity by recalling some of the main concepts of the conventional glass transitions. We obtain a compact expression for the resistivity that we compare to previously reported experimental data in twinned and untwinned Y-Ba-Cu-O single crystals. With very few parameters we can fit extremely well the resistive transitions in the full temperature and field range. Also, the transitions in very pure, untwinned crystals can be entirely fitted, including the ''kink' at the so-called melting transition. Moreover, the resistivity is shown to be heavily influenced by fluctuations

  15. Microscopic theory of ultrasonic attenuation in high-Tc superconductors in normal state

    International Nuclear Information System (INIS)

    Bishoyi, K.C.; Rout, G.C.; Behera, S.N.

    2001-01-01

    The mechanism of the ultrasonic attenuation in high temperature superconductors is not yet studied thoroughly both experimentally and theoretically. A microscopic theoretical model is proposed here to study the attenuation in the electron doped and hole doped compounds like L 2-x M x CuO 4 (L=La,Nd; M=Sr,Ca,Ce). The model Hamiltonian contains the staggered magnetic field in the d-electrons of copper, the doped f-electrons term and the hybridisation between d- and f-electrons. The electron-phonon interaction arises due to the volume strain dependence of the hybridisation. The phonon Green's function is calculated by equations of motion of Zubarev technique. The temperature dependence of the ultrasonic attenuation coefficient (α) is calculated from the imaginary part of the phonon self energy and the velocity of sound in the dynamic and long wavelength limit. The dimensionless parameters involved in the calculations are the electron-phonon coupling (g), staggered magnetic field (h) , hybridization (υ), position of the f-level (d), frequency (ω), and temperature (t). The results are discussed. (author)

  16. Thermal depinning and melting of the flux-line lattice in high-Tc superconductors

    International Nuclear Information System (INIS)

    Brandt, E.H.

    1991-01-01

    In high-T c superconductors (HTSC) the thermal fluctuation of the vortex lattice (VL) may become large since the vortex lattice is soft due to the strong overlap of the vortex fields and since the temperature T and b high. It was thus argued that the three-dimensional (3D) vortex lattice is thermally entangled and may melt. This type of transition and the consequences of melting are not clear as yet since the always present pinning of the vortex ores by material inhomogeneities may cause similar disorder. In HTSC the pinning energy may become comparable with k B T because the coherence length ξ(vortex radius) is small and t may be high. Therefore, thermally activated depinning competes with possible effects of flux melting, and the irreversibility line in the B-T-plane (B = magnetic field) should better be called depinning line. In this paper it is argued that theories predicting new phases of vortex matter (flux solid, flux liquid, vortex plasma, vortex glass, and hexatic vortex glass) may be improved by replacing the 2D straight-vortex interaction by the correct 3D interaction between all vortex segments

  17. Stabilization of high Tc phase in bismuth cuprate superconductor by lead doping

    Science.gov (United States)

    Gupta, Ram. P.; Pachauri, J. P.; Khokle, W. S.; Nagpal, K. C.; Date, S. K.

    1991-01-01

    It has been widely ascertained that doping of lead in Bi-Sr-Ca-Cu-O systems promotes the growth of high T sub c (110 K) phase, improves critical current density, and lowers processing temperature. A systematic study was undertaken to determine optimum lead content and processing conditions to achieve these properties. A large number of samples with cationic compositions of Bi(2-x)Pb(x)Sr2Ca2Cu3 (x = 0.2 to 2.0) were prepared by conventional solid state reaction technique. Samples of all compositions were annealed together at a temperature and characterized through resistance temperature (R-T) measurements and x ray diffraction to determine the zero resistance temperature, T sub c(0) and to identify presence of phases, respectively. The annealing temperature was varied between 790 and 880 C to optimize processing parameters. Results are given. In brief, an optimum process is reported along with composition of leaded bismuth cuprate superconductor which yields nearly a high T sub c single phase with highly stable superconducting properties.

  18. Microstructure and critical current density in high-Tc metal oxide superconductors

    International Nuclear Information System (INIS)

    Johnson, S.M.; Gusman, M.I.

    1992-03-01

    Superconductor powders in the U-Ba-Cu-O (YBCO) and Bi-Pb-Sr-Ca-Cu-O (BSCCO) systems were synthesized by freeze-drying. Powders were characterized, and processed into samples for evaluation of superconducting behavior. Freeze-drying is attractive because the powders have high purity, are homogeneous, have a small size and are active. YBCO powders can be sintered to high density at 890 degrees C. Many compositions, processing approaches and heat treatments were explored in an effort to understand relations between microstructure and critical density, and to improve the critical current density. Powders were also formed into sputtering targets for coating preparation at Stanford University. The highest critical current density achieved with the YBCO powders was ∼15,000 A/cm 2 at 4.2K and 0.5T using powders treated to prevent carbon contamination. The BSCCO materials with the highest critical current density, ∼30,000 A/cm 2 at the same conditions were formed by heat treating melted and quenched samples. All critical current density measurements were made by Stanford University, a subcontractor to this effort. Stanford University also prepared coatings by off-axis magnetron sputtering

  19. Reentrance of a flux liquid near Hc1 in high-Tc superconductors

    International Nuclear Information System (INIS)

    Xing, L.

    1992-01-01

    Previous studies by D. R. Nelson have demonstrated that flux-line wandering in high-T c oxides in fields slightly above H c1 leads to an entangled flux liquid. The statistical mechanics of the flux lines is isomorphic to a two-dimensional (2D) interacting quantum particle system with pairwise interaction potential V(r)=(φ 0 2 /8π 2 λ 2 )K 0 (r/λ), where λ is the magnetic penetration length and K 0 (x) is a modified Bessel function. We have performed a Monte Carlo simulation on the 2D interacting Bose system. The existence of a flux-liquid phase has been observed and the transtion line between flux liquid and flux solid has been identified for a crystalline sample of Y-Ba-Cu-O on the H-T phase diagram over a wide range of temperature. The width of the liquid phase increases with temperature as T 2 at low temperatures, in agreement with the prediction of D. R. Nelson. At high temperatures the width of the liquid phase increases faster than T 2 . We argue that the melting curve eventually crosses over to the high-field vortex-lattice melting curve. Relevance to experiments on high-T c superconductors is mentioned

  20. Muon and neutron investigations of vortex correlations in high-Tc superconductors

    International Nuclear Information System (INIS)

    Aeppli, G.

    1991-01-01

    The muon spin relaxation (μSR) and neutron scattering techniques have made the following contributions to the author's understanding of copper oxide superconductors: (1) determination in absolute units of the magnetic length λ(T); (2) observation in YBa 2 Cu 3 O 7 of well ordered flux lattices, composed of straight flux lines, at low T and intermediate fields; (3) demonstration that sample multiphase coexistence is the most likely cause of reduced Meissner fractions found for La 2-x Sr x CuO 4 ceramics with non-optimal (i.e. x ≠ 0.15); (4) finding that microscopic irreversibility sets in at surprisingly low T; (5) observation of microscopic vortex motion in BiSrCaCuO single crystals. While studies of type (1) have been extensively performed, there have been relatively few experiments of the other four varieties. Therefore, he concludes that both μSR and neutron diffraction still have the potential to provide new information about the magnetic correlations in high-T c materials

  1. Resonant two-magnon Raman scattering in parent compounds of high-Tc superconductors

    International Nuclear Information System (INIS)

    Chubukov, A.V.; Frenkel, D.M.

    1995-01-01

    We propose a theory of two-magnon Raman scattering from the insulating parent compounds of high-T c superconductors, which contains information not only on magnetism, but also on the electronic properties in these materials. We use spin-density-wave formalism for the Hubbard model, and study diagrammatically the profile of the two-magnon scattering and its intensity dependence on the incoming photon frequency ω i both for ω i much-lt U and in the resonant regime, in which the energy of the incident photon is close to the gap between conduction and valence bands. In the nonresonant case, we identify the diagrams which contribute to the conventional Loudon-Fleury Hamiltonian. In the resonant regime, where most of the experiments have been done, we find that the dominant contribution to Raman intensity comes from a different diagram, one which allows for a simultaneous vanishing of all three of its dominators (i.e., a triple resonanc). We study this diagram in detail and show taht the triple resonance, combined with the spin-density-wave dispersion relation for the carriers, explains the unusual features found in the two-magnon profile and in the two-magnon peak intensity dependence on the incoming photon frequency. In particular, our theory predicts a maximum of the two-magnon peak intensity right at the upper edge of the features in the optical data, which has been one of the key experimental puzzles

  2. Entropy transport in high-Tc superconductors in the fluctuation regime

    International Nuclear Information System (INIS)

    Maki, K.

    1991-01-01

    Making use of the expression for the heat current associated with the space-time-dependent order parameter for the s-wave superconductor, we calculate, in the clean limit, the heat current induced by an electric field. In the absence of a magnetic field we find an extra Peltier coefficient associated with the fluctuations, which diverges logarithmically as the temperature T approaches the transition temperature T c . In the presence of a magnetic field perpendicular to the ab plane, the fluctuation gives rise to the Ettingshausen effect. In a small magnetic field, the corresponding entropy transported by magnetic flux is calculated: left-angle S φ right-angle f =[2π 3 τT/21ζ(3)d](h/var-epsilon)(1 +2α) -1/2 where τ and d are the transport lifetime and the interlayer spacing, ζ(3)=1.202. . ., h=2eξ a 2 B, var-epsilon=ln(T/T c ), and α=2(ξ c /d) 2 var-epsilon -1 . The result is compared with a recent observation of the Ettinghausen effect in a single crystal of YBa 2 Cu 3 O 7

  3. Differential conductivity mapping of solar panels using a high-TC superconductor SQUID

    International Nuclear Information System (INIS)

    Kiwa, T.; Maeda, S.; Miyake, K.; Kataoka, N.; Tsukamoto, A.; Adachi, S.; Tanabe, K.; Kandori, A.; Tsukada, K.

    2011-01-01

    To visualise the distribution of the electric property of solar cells, we developed a differential conductivity mapping system using high-T C (HTS-) superconductor SQUID with a normal conducting pick-up coil. The bias ac voltage with an offset voltage was applied to a solar panel made from amorphous silicon, and the normal component of the generated magnetic field was lock-in-detected. Thus the measured signal was converted to dB/dV properties, which are inverse-proportional to the differential resistivity, as the function of the offset voltage. By scanning the pick-up coil across the panel surface, we obtained the distribution of dB/dV properties across the solar panel was obtained by scanning the pick-up coil across the panel surface. The distribution of dB/dV on the panel differed between when the light source was on and when it was off. This result suggests that the proposed system is a potential tool for diagnosing the electric properties of solar cells.

  4. Investigations into the electronic structure of the high-Tc superconductors by means of photoelectron spectroscopy

    International Nuclear Information System (INIS)

    Dauth, B.H.

    1989-08-01

    The electronic structure of various polycrystalline samples including the new YBaCuO- and BiCaSrCuO- high T c superconductors (HTSC) and related systems is investigated by photoelectron spectroscopy. Additional characterization is performed by conductivity measurements. In particular, the binding energy of the Cu-2p 3/2 - and the O-1s-levels of various HTSC is determined. For the first time the controversial 531 eV oxygen line was shown to be an intrinsic electronic structure effect. Sintered CuO-samples are obtained for the first time. The electronic structure of the sintered CuO turns out to be drastically different with respect to pressed CuO powder. For the first time a crossover resonance from a O-1s- into a Cu-3d-level was observed with synchrotron radiation. This is additional evidence for the strong hybridization between the Cu-3d and the O-2p states. Photoemission spectroscopy shows that the holes in the HTSC's are located at the oxygen p-band. Fe and Al overlayers on the HTSC-samples induce a drastic change in the electronic properties of the interface: apparently oxygen is removed from the HTSC to the overlayer. (orig./BHO)

  5. 3D modeling of high-Tc superconductors by finite element software

    International Nuclear Information System (INIS)

    Zhang Min; Coombs, T A

    2012-01-01

    A three-dimensional (3D) numerical model is proposed to solve the electromagnetic problems involving transport current and background field of a high-T c superconducting (HTS) system. The model is characterized by the E–J power law and H-formulation, and is successfully implemented using finite element software. We first discuss the model in detail, including the mesh methods, boundary conditions and computing time. To validate the 3D model, we calculate the ac loss and trapped field solution for a bulk material and compare the results with the previously verified 2D solutions and an analytical solution. We then apply our model to test some typical problems such as superconducting bulk array and twisted conductors, which cannot be tackled by the 2D models. The new 3D model could be a powerful tool for researchers and engineers to investigate problems with a greater level of complicity.

  6. Theory of novel normal and superconducting states in doped oxide high-Tc superconductors

    International Nuclear Information System (INIS)

    Dzhumanov, S.

    2001-10-01

    A consistent and complete theory of the novel normal and superconducting (SC) states of doped high-T c superconductors (HTSC) is developed by combining the continuum model of carrier self-trapping, the tight-binding model and the novel Fermi-Bose-liquid (FBL) model. The ground-state energy of carriers in lightly doped HTSC is calculated within the continuum model and adiabatic approximation using the variational method. The destruction of the long-range antiferromagnetic (AF) order at low doping x≥ x cl ≅0.015, the formation of the in-gap states or bands and novel (bi)polaronic insulating phases at x c2 ≅0.06-0.08, and the new metal- insulator transition at x≅x c2 in HTSC are studied within the continuum model of impurity (defect) centers and large (bi)polarons by using the appropriate tight-binding approximations. It is found that the three-dimensional (3d) large (bi)polarons are formed at ε ∞ /ε 0 ≤0.1 and become itinerant when the (bi)polaronic insulator-to-(bi)polaronic metal transitions occur at x x c2 . We show that the novel pseudogapped metallic and SC states in HTSC are formed at x c2 ≤x≤x p ≅0.20-0.24. We demonstrate that the large polaronic and small BCS-like pairing pseudogaps opening in the excitation spectrum of underdoped (x c2 BCS =0.125), optimally doped (x BCS o ≅0.20) and overdoped (x>x o ) HTSC above T c are unrelated to superconductivity and they are responsible for the observed anomalous optical, transport, magnetic and other properties of these HTSC. We develop the original two-stage FBL model of novel superconductivity describing the combined novel BCS-like pairing scenario of fermions and true superfluid (SF) condensation scenario of composite bosons (i.e. bipolarons and cooperons) in any Fermi-systems, where the SF condensate gap Δ B and the BCS-like pairing pseudogap Δ F have different origins. The pair and single particle condensations of attracting 3d and two- dimensional (2d) composite bosons are responsible for

  7. Oxygen ordering and superconductivity in the high Tc superconductor YBa2Cu3O6+x

    International Nuclear Information System (INIS)

    Friis Poulsen, H.

    1991-12-01

    This report contains the result of an experimental and theoretical investigation of the oxygen ordering process in the High T c superconductor Y Ba 2 Cu 3 O 6+x . Neutron scattering is used in connection with in situ monitoring of the oxygen in-diffusion in a gas-volumetric equipment. Information on the variations of the structural phases, the twin domain sizes, the elastic forces, the chemical potential og oxygen as well as diffusion are provided. Using Monte Carlo simulations we find that a simple two-dimentional lattice gas model of the oxygen ordering process, the ASYNNNI model, gives an excellent description of the vast majority of these data. A systematic study of the relationship between the static and dynamic variations of the superconducting transition temperature, T c , and the corresponding variations of the low temperature oxygen ordering process is performed. Statistics from Monte Carlo simulations based on the ASYNNNI model are combined with experimental data from the literature. The combined static and dynamic analysis makes it evident that within a charge transfer model, a linear T c versus charge transfer relationship can only be rationalized if the description is based on extended coherent ordered domains and if the dynamic co-existence between the Ortho-I and the Ortho-II type of domains inherent to the ASYNNNI model is taken into account. A minimal model is proposed, where the total charge transfer is found as a weighted sum over the areas of the Ortho-I and the Ortho-II domains, and the minimal size of the two types of domains are given by a doubling og their unit cells in both directions. (au) 5 tabs., 35 ills., 108 refs

  8. Neutron spectroscopic investigations on crystalline-electric-field and exchange interactions on high-Tc superconductors

    International Nuclear Information System (INIS)

    Staub, U.

    1993-05-01

    It is well known that in the high temperature superconductors of the type RBa 2 Cu 3 O x (123), with R=Y and most of the rare earths, superconductivity is believed to be controlled by the density of mobile charges in the copper oxide (CuO 2 ) planes. In particular, the charge transfer process from the chains to the planes seems to play an important role. In the 123, RBa 2 Cu 4 O 8 (1248) and the Bi 2 Sr 2 Ca 1-x Ho x Cu 2 O 8+δ (Bi2212) systems, the R ions are sandwiched between the CuO 2 planes, thus the crystalline electric field (CEF) interaction at the R sites constitutes an ideal probe of the local symmetry and the charge distribution of the superconducting planes. The (2J+1)-fold degeneracy of the ground-state J-multiplet of the rare earth ions will be partially lifted under the action of the CEF potential. By means of inelastic neutron scattering experiments it is possible to observe directly the transitions between the CEF states. Therefrom we obtain useful information on both the structure and the charge distribution in the vicinity of the R ion. In order to quantify the charge transfer process from the chains to the planes, we performed a detailed analysis of the CEF of Ho 3+ in the 123, 1248 and Bi2212 systems. In addition, we present some experiments on a Cl doped 123 sample and some external pressure experiments on the 123 system. In nearly all high-T c compounds RBa 2 Cu 3 O 7-δ superconductivity and magnetic ordering of the R ion sublattice coexist at low temperatures. In order to understand the interplay of magnetism and superconductivity in these systems, information on both the electronic ground state of the R 3+ ions and the coupling mechanisms between the R 3+ ions is highly desirable. (author) figs., tabs., 73 refs

  9. μSR-investigation of high-Tc superconductors at the LNP JINR phasotron

    International Nuclear Information System (INIS)

    Bezhitadze, D.T.; Borovinskaya, I.P.; Burianek, J.

    1989-01-01

    High-T c superconductors La 2-x Sr x CuO 4 (x=0+0.25), Ho(Er)Ba 2 Cu 3 O 7-y and Bi-Sr-Ca-Cu-O (the main phase 2212 with a small admixture of the 2223-phase) were investigated in the zero and 100+400 Oe transverse external magnetic fields in the temperature interval 4.2+300 K. The magnetic ordering for the La 2-x Sr x CuO 4 samples with x=0.00 and x=0.01 occurs below T N ∝250 K and T N ∝170 K respectively. A considerable increase in the distribution width of the magnetic field on the muon with an increase in the Sr-content indicates an enhancement of the Cu 2+ magnetic moment deviation from the magnetic ordering axis. The results of the analysis of the μSR spectra indicate the formation of the spin glass state in the La 1.93 Sr 0.07 CuO 4 sample. In contrast to the behaviour of the HoBa 2 Cu 3 O 7-y ceramic the magnetic ordering of the Er-atoms in the ErBa 2 Cu 3 O 7-y sample is not observed in the conparable temperature interval. Our data has also allowed the magnetic field penetration depth λ perpendicular (0) to be determined: 3200±70 A for La 1.9 Sr 0.1 CuO 4 , 2420±60 A for La 1.85 Sr 0.15 CuO 4 , 2000±50 A for Bi-Sr-Ca-Cu-O (phase 2212), 1600±50 A for ErBa 2 Cu 3 O 7-y . 20 refs.; 8 figs

  10. Chemical equilibrium model for high- Tc and heavy fermion superconductors: the density of states

    International Nuclear Information System (INIS)

    Kallio, A.; Hissa, J.; Hayrynen, T.; Braysy, V.; Sakkinen, T.

    1998-01-01

    The chemical equilibrium model is based on the idea of correlated electron pairs, which in singlet state can exist as quasimolecules in the superfluid and normal states of a superconductor. These preformed pairs are bosons which can undergo a Bose-Einstein condensation in analogy with the superfluidity of 4 He+ 3 He-mixture. The bosons (B ++ ) and the fermions (h + ) are in chemical equilibrium with respect to the reaction B ++ ↔ 2h + , at any temperature. The mean densities of bosons and fermions (quasiholes) n B (T) and n h (T) are determined from the thermodynamics of the equilibrium reaction in terms of a single function f(T). By thermodynamics the function f(T) is connected to equilibrium constant φ(T) by 1-f(T) = [1 + φ(T)] -1/2 . Using a simple power law, known to be valid near T = 0, for the chemical constant φ(T) α/t 2γ , t = T/T*, the mean density of quasiholes is given in closed form. This enables one to calculate the corresponding density of states (DOS) D(E) N s /N(0), by solving an integral equation. The NIS- tunneling conductivity near T = 0, given by D(E) compares well with the most recent experiments: D(E) ∼ E γ , for small E and a finite maximum of right size, corresponding to 'finite quasiparticle lifetime'. The corresponding SIS-tunneling conductivity is obtained from a simple convolution and is also in agreement with recent break junction experiments of Hancotte et al. The position of the maximum can be used to obtain the scaling temperature T*, which comes close to the one measured by Hall coefficient in the normal state. A simple explanation for the spingap effect in NMR is given. (Copyright (1998) World Scientific Publishing Co. Pte. Ltd)

  11. Compensated electron and hole pockets in an underdoped high- Tc superconductor

    Science.gov (United States)

    Sebastian, Suchitra E.; Harrison, N.; Goddard, P. A.; Altarawneh, M. M.; Mielke, C. H.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Andersen, O. K.; Lonzarich, G. G.

    2010-06-01

    We report quantum oscillations in the underdoped high-temperature superconductor YBa2Cu3O6+x over a wide range in magnetic field 28≤μ0H≤85T corresponding to ≈12 oscillations, enabling the Fermi surface topology to be mapped to high resolution. As earlier reported by Sebastian [Nature (London) 454, 200 (2008)10.1038/nature07095], we find a Fermi surface comprising multiple pockets, as revealed by the additional distinct quantum oscillation frequencies and harmonics reported in this work. We find the originally reported broad low-frequency Fourier peak at ≈535T to be clearly resolved into three separate peaks at ≈460 , ≈532 , and ≈602T , in reasonable agreement with the reported frequencies of Audouard [Phys. Rev. Lett. 103, 157003 (2009)10.1103/PhysRevLett.103.157003]. However, our increased resolution and angle-resolved measurements identify these frequencies to originate from two similarly sized pockets with greatly contrasting degrees of interlayer corrugation. The spectrally dominant frequency originates from a pocket (denoted α ) that is almost ideally two-dimensional in form (exhibiting negligible interlayer corrugation). In contrast, the newly resolved weaker adjacent spectral features originate from a deeply corrugated pocket (denoted γ ). On comparison with band structure, the d -wave symmetry of the interlayer dispersion locates the minimally corrugated α pocket at the “nodal” point knodal=(π/2,π/2) , and the significantly corrugated γ pocket at the “antinodal” point kantinodal=(π,0) within the Brillouin zone. The differently corrugated pockets at different locations indicate creation by translational symmetry breaking—a spin-density wave has been suggested from the suppression of Zeeman splitting for the spectrally dominant pocket. In a broken-translational symmetry scenario, symmetry points to the nodal (α) pocket corresponding to holes, with the weaker antinodal (γ) pocket corresponding to electrons—likely responsible

  12. Thermodynamics, stability and processes of transport in high-Tc-superconductors

    International Nuclear Information System (INIS)

    Goepel, W.

    1993-01-01

    The aim of this paper is: Characterisation of oxygen nonstoichiometry (7-x) and oxygen diffusion (D o ) in YBa 2 Cu 3 O 7-x -ceramics. Separation of electronic (σ e ) and ionic (σ o2- ) conductivities. Determination of the electronic structure at the surface and in the bulk of epitaxial YBa 2 Cu 3 O 7-x -films. Analysis of chemical reactions between YBa 2 Cu 3 O 7-x -films and substrates, electrodes, pasivation layers etc. with the aim of preparing epitaxial YBa 2 Cu 3 O 7-x -films on Si-substrates with high values for T c and J c . The results make it possible to prepare longterm stable epitaxial YBa 2 Cu 3 O 7-x -films on Si and to control the oxygen content in YBa 2 Cu 3 O 7-x thermodynamically or kinetically by controlled solid state diffusion. (orig./MM) [de

  13. Measurement of mesoscopic high-Tc superconductors using Si mechanical micro-oscillators

    International Nuclear Information System (INIS)

    Dolz, M.; Antonio, D.; Pastoriza, H.

    2007-01-01

    In a superconducting mesoscopic sample, with dimensions comparable to the London penetration depth, some properties are qualitatively different to those found in the bulk material. These properties include magnetization, vortex dynamics and ordering of the vortex lattice. In order to detect the small signals produced by this kind of samples, new instruments designed for the microscale are needed. In this work we use micromechanical oscillators to study the magnetic properties of a Bi 2 Sr 2 CaCu 2 O 8+δ disk with a diameter of 13.5μm and a thickness of 2.5μm. The discussion of our results is based on the existence and contribution of inter and intra layer currents

  14. Thallium 2223 high Tc superconductor in a silver matrix and its magnetic shielding, hermal cycle and time aging properties

    Energy Technology Data Exchange (ETDEWEB)

    Fei, X.; He, W.S.; Havenhill, A. [and others

    1994-12-31

    Superconducting Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} (Tl2223) was ground to powder. Mixture with silver powder (0--80% weight) and press to desired shape. After proper annealing, one can get good silver-content Tl2223 bulk superconductor. It is time-stable and has good superconducting property as same as pure Tl2223. It also has better mechanical property and far better thermal cycle property than pure Tl2223.

  15. Nonlinear vibration behaviors of high-Tc superconducting bulks in an applied permanent magnetic array field

    Science.gov (United States)

    Li, Jipeng; Li, Haitao; Zheng, Jun; Zheng, Botian; Huang, Huan; Deng, Zigang

    2017-06-01

    The nonlinear vibration of high temperature superconducting (HTS) bulks in an applied permanent magnetic array (Halbach array) field, as a precondition for commercial application to HTS maglev train and HTS bearing, is systematically investigated. This article reports the actual vibration rules of HTS bulks from three aspects. First, we propose a new numerical model to simplify the calculation of levitation force. This model could provide precise simulations, especially the estimation of eigenfrequency. Second, an approximate analytic solution of the vibration of the HTS bulks is obtained by using the method of harmonic balance. Finally, to verify the results mentioned above, we measure the vertical vibration acceleration signals of an HTS maglev model, consisting of eight YBaCuO bulks, oscillating freely above a Halbach array with large displacement excitation. Higher order harmonic components, which indicate the nonlinear vibration phenomenon, are detected in the responses. All the three results are compared and agreed well with each other. This study combines the experimental and theoretical analyses and provides a deep understanding of the physical phenomenon of the nonlinear vibration and is meaningful for the vibration control of the relevant applications.

  16. Study on magnetic separation system using high Tc superconducting bulk magnets for water purification technique

    International Nuclear Information System (INIS)

    Oka, T; Kanayama, H; Tanaka, K; Fukui, S; Ogawa, J; Sato, T; Ooizumi, M; Yamaguchi, M; Yokoyama, K; Noto, K

    2009-01-01

    The application of superconducting bulk magnets to the magnetic separation techniques has been investigated for the Mn-bearing waste water drained from the university laboratories. The research has been conducted in comparison with the electromagnets, and the cryo-cooled superconducting solenoid magnet. The separation ratios of ferrite precipitates including Mn element in the waste slurry were estimated by means of the high gradient magnetic separation method with ferromagnetic iron filters in the water channel and open gradient magnetic separation without them. As the magnetic force acting on the particles is given by the product of a magnetization of particles and a gradient of magnetic field, and a superconducting bulk magnet shows a sharp gradient of the magnetic field on the surface, the performances of the bulk magnet system were almost equivalent to those of the superconducting solenoid magnet with wide bore with respect to the magnetic separation ratios. The separation ratios for Mn have reached over 80 % for HGMS and 10 % for OGMS under the flow rates less than 3 liter/min.

  17. Simulation of Field Dependence of Critical Current Densities of Bulk High Tc Superconducting Materials regarding Thermally Activated Flux Motion

    Science.gov (United States)

    Santosh, M.; Naik, S. Pavan Kumar; Koblischka, M. R.

    2017-07-01

    In the upcoming generation, bulk high temperature superconductors (HTS) will play a crucial and a promising role in numerous industrial applications ranging from Maglev trains to magnetic resonance imaging, etc. Especially, the bulk HTS as permanent magnets are suitable due to the fact that they can trap magnetic fields being several orders of magnitude higher than those of the best hard ferromagnets. The bulk HTS LREBa2Cu3O7-δ (LREBCO or LRE-123, LRE: Y, Gd, etc.,) materials could obtain very powerful compact superconducting super-magnets, which can be operated at the cheaper liquid nitrogen temperature or below due to higher critical temperatures (i.e., ∼90 K). As a result, the new advanced technology can be utilized in a more attractive manner for a variety of technological and medical applications which have the capacity to revolutionize the field. An understanding of the magnetic field dependence of the critical current density (J c(H)) is important to develop better adapted materials. To achieve this goal, a variety of Jc (H) behaviours of bulk LREBCO samples were modelled regarding thermally activated flux motion. In essence, the Jc (H) curves follows a certain criterion where an exponential model is applied. However, to fit the complete Jc (H) curve of the LRE-123 samples an unique model is necessary to explain the behavior at low and high fields. The modelling of the various superconducting materials could be understood in terms of the pinning mechanisms.

  18. High-Tc copper oxide superconductors and related novel materials dedicated to prof K. A. Müller on the occasion of his 90th birthday

    CERN Document Server

    Keller, Hugo; Bianconi, Antonio

    2017-01-01

    Authored by many of the world's leading experts on high-Tc superconductivity, this volume presents a panorama of ongoing research in the field, as well as insights into related multifunctional materials. The contributions cover many different and complementary aspects of the physics and materials challenges, with an emphasis on superconducting materials that have emerged since the discovery of the cuprate superconductors, for example pnictides, MgB2, H2S and other hydrides. Special attention is also paid to interface superconductivity. In addition to superconductors, the volume also addresses materials related to polar and multifunctional ground states, another class of materials that owes its discovery to Prof. Müller's ground-breaking research on SrTiO3.

  19. Effects of magnetic field on the cuprate high-Tc superconductor La2-xSrxCuO4

    DEFF Research Database (Denmark)

    Lake, B.; Aeppli, G.; Christensen, N.B.

    2004-01-01

    This article discusses neutron scattering measurements on the cuprate, high transition temperature superconductor La2-xSrxCuO4 (LSCO) in an applied magnetic field. LSCO is a type-II superconductor and magnetic flux can penetrate the material via the formation of vorticies. Phase coherent...

  20. Fault current limiter using bulk oxides superconductors

    International Nuclear Information System (INIS)

    Belmont, O.; Ferracci, P.; Porcar, L.; Barbut, J.M.; Tixador, P.; Noudem, J.G.; Bourgault, D.; Tournier, R.

    1998-01-01

    We study the limitation possibilities of bulk Bi high T c materials. For this we test these materials with AC or DC currents above their critical currents. We study particularly the evolution of the voltage with time or with current. The material, the value of the current and the time duration play important parts. For sintered Bi samples the voltage depends only on the current even for values much larger than the critical current. With textured samples the V(I) curves shows an hysteretic behaviour due to a warming up. The textured materials are more interesting than sintered ones in terms of required volume for the current limitation. In both cases the superconductors are in a dissipative state but not in the normal state. This state is nevertheless reached if the dissipated energy inside the sample is sufficient. We have tried to apply a magnetic field on the samples in order to trigger a more effective limitation. The voltage increases but with a limited effect for currents much higher (3-4 times) than the critical zero field current. We think that the dissipative state is due mainly to the grain boundaries which become resistive above the critical current. (orig.)

  1. Electrical Transport Through Tunnel Barriers and Thin Dielectric Layers and Physical Properties of the High Tc Oxide Superconductors

    Science.gov (United States)

    1990-03-26

    Josephson Tipo Emparedado con Barrera de (Nb-Si)-Amorto," PhD. Thesis, Universidad Nacional Autonoma de Mexico, May 1989. 17. E.S. Hellman, D.G...A15 Nb-Sn," Phys. Rev. B 30, p. 2590 (1984). 4. S.J. Bending, R.H. Hammond, and M.R. Beasley, "Superconductivity in the High-Tc A15 V-6a System," Bull

  2. Current sharing effect on the current instability and allowable temperature rise of composite high-TC superconductors

    International Nuclear Information System (INIS)

    Romanovskii, V.R.; Watanabe, K.; Awaji, S.; Nishijima, G.; Takahashi, Ken-ichiro

    2004-01-01

    To understand the basic mechanisms of the thermal runaway phenomenon, the limiting margin of the current instability, which may spontaneously occur in composite high-T C superconductors like multifilament Bi-based wire or tape, is derived under DC magnetic field. The current sharing and allowable temperature rise effects were considered. A static zero-dimensional model was utilized to describe the basic formulae dealing with the peculiarities of the non-isothermal change of superconducting composite voltage-current characteristic. The boundary of allowable stable values of the temperature, electric field and current are derived analytically. It was shown that permissible values of the current and electric field might be higher than those determined by use of the standard critical current criterion. In consequence of this feature, the noticeable allowable temperature rise of the composite superconductor before its transition to the normal state may be seen. The criterion for complete thermal stability condition is written describing the state when temperature of the composite equals critical temperature of a superconductor and the transport current flows stably only in matrix. The performed analysis also proves the existence of value of the volume fraction of a superconductor in composite at which its current-carrying capacity has minimum. These peculiarities are due to the stable current redistribution between superconductor and stabilizing matrix. Therefore, the current sharing not only leads to the matrix/superconductor ratio effect on the stable operating characteristics of the composite high-T C superconductors but also becomes important in the adequate description of quench process in the high-T C superconducting magnets

  3. Electronic-structure Fermi-liquid theory of high-Tc superconductors: Comparison of predictions with experiments

    International Nuclear Information System (INIS)

    Yu, Jaejun; Freeman, A.J.

    1991-01-01

    Predictions of local density functional (LDF) calculations of the electronic structure and transport properties of high T(sub c) superconductors are presented. As evidenced by the excellent agreement with both photoemission and positron annihilation experiments, a Fermi liquid nature of the 'normal' state of the high T(sub c) superconductors become clear for the metallic phase of these oxides. In addition, LDF predictions on the normal state transport properties are qualitatively in agreement with experiments on single crystals. It is emphasized that the signs of the Hall coefficients for the high T(sub c) superconductors are not consistent with the types of dopants (e.g., electron-doped or hole-doped) but are determined by the topology of the Fermi surfaces obtained from the LDF calculations

  4. Physical characterization and study of the electrical magnetic and thermal properties of the ceramic high Tc superconductor Y1Ba2Cu3O7-x

    International Nuclear Information System (INIS)

    Azeredo Orlando, M.T. de.

    1991-01-01

    It was built four systems for physical characterization of high Tc superconductors, with data acquisition by computer, and recent results on AC susceptibility, AC resistivity, specific heat and thermal diffusivity of the YBa 2 Cu 3 O 7-x (x ≅ 0.15) compound, in a ceramic form, could be reproduced. Our study pointed that those ceramics exhibit a preferential orientation of the grains, being the c axis of the compound parallel to the compression direction. The study of this material in the four different technics, for samples with same density and oxygen stoichiometry, has pointed also that its magnetic behavior is strongly influenced by the intergrain region. This influence can be described by the clem model for the intergrain region and by the Malozemoff proposition for the fluxoids collective behavior. (author)

  5. On the combination of the Cooper pair and the Ogg pair in the high-Tc oxide superconductor

    International Nuclear Information System (INIS)

    Zhang Liyuan.

    1991-08-01

    In this paper it is argued that the superconductivity of the high-T c oxide superconductor (HTOS) can be explained by the combinating mechanism of the Cooper pair and the Ogg pair. The properties of the superconducting state of the HTOS have been calculated under this mechanism, and the theoretical results are overall consistent with the experiment. (author). 37 refs

  6. Fabrication and properties of Y-Ba-Cu-O high Tc superconductor by upset-forging method

    International Nuclear Information System (INIS)

    Chang, Ho Jung; Kang, Kae Myung; Song, Jin Tae

    1990-01-01

    YBa 2 Cu 3 O 7-x oxide superconductors was fabricated by sintering process and upset-forging method, respectively, and microstructures and conduction properties were compared. There was no difference in crystal structure the (001) x-ray reflection presumably due to preferred crystal orientation of the YBa 2 Cu 3 O 7-x superconductor. Furthermore, the grain size of the 123-phase increased as the reduction ratio became larger during the upset-forging. The critical temperature for zero resistivity of both samples was almost the same, i.e., about 90K. These results have demonstrated the potential of producing YBa 2 Cu 3 O 7-x superconducting wire or tape effectively using a upset-forging method. The critical current density of the upset-forged sample, however, was lower than that of the sintered one, which fact might be ascribed to microcrack formation during fast upset-forging. (Author)

  7. Evolution of magnetic and superconducting fluctuations with doping of high-Tc superconductors. An electronic Raman scattering study

    International Nuclear Information System (INIS)

    Blumberg, G.

    1998-01-01

    For YBa 2 Cu 3 O 6+δ and Bi 2 Sr 2 CaCu 2 O 3±δ superconductors, electronic Raman scattering from high- and low-energy excitations has been studied in relation to the hole doping level, temperature, and energy of the incident photons. For underdoped superconductors, it is concluded that short range antiferromagnetic (AF) correlations persist with hole doping and doped single holes are incoherent in the AF environment. Above the superconducting (SC) transition temperature T c the system exhibits a sharp Raman resonance of B 1g symmetry and about 75 meV energy and a pseudogap for electron-hole excitations below 75 meV, a manifestation of a partially coherent state forming from doped incoherent quasi-particles. The occupancy of the coherent state increases with cooling until phase ordering at T c produces a global SC state

  8. On the applicability of the layered sine-Gordon model for Josephson-coupled high-Tc layered superconductors

    International Nuclear Information System (INIS)

    Nandori, I; Jentschura, U D; Nagy, S; Sailer, K; Vad, K; Meszaros, S

    2007-01-01

    We find a mapping of the layered sine-Gordon model to an equivalent gas of topological excitations and determine the long-range interaction potentials of the topological defects. This enables us to make a detailed comparison to the so-called layered vortex gas, which can be obtained from the layered Ginzburg-Landau model. The layered sine-Gordon model has been proposed in the literature as a candidate field-theoretical model for Josephson-coupled high-T c superconductors, and the implications of our analysis for the applicability of the layered sine-Gordon model to high-T c superconductors are discussed. We are led to the conjecture that the layered sine-Gordon and the layered vortex gas models belong to different universality classes. The determination of the critical temperature of the layered sine-Gordon model is based on a renormalization-group analysis

  9. On the applicability of the critical state model to the description of electromagnetic properties of high-Tc superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Fisher, L.M.; Il' in, N.V.; Voloshin, I.F. (All-Russian Electrical Engineering Inst., Moscow (Russia)); Makarov, N.M.; Yampol' skii, V.A. (Inst. for Radiophysics and Electronics, Ukr. Acad. Sci., Karkov (Ukraine)); Perez Rodriguez, F. (Inst. de Fisica, Univ. Autonoma de Puebla, Rue (Mexico)); Snyder, R.L. (New York State Coll. of Ceramics, Alfred Univ. (United States))

    1993-02-20

    The frequency dependence of the surface impedance of superconductors have been studied experimentally and theoretically in the radio frequency range. Its essential deviation was found from the linear law predicted by the usual critical state model. The character of this deviation depends qualitatively on the amplitude of the radio wave. We have established the frequency limits of applicability of the traditional critical state model. Results obtained print out an explanation in the frame of the modified model where we take into account the contribution of a dissipative term to the screening current. The value of this is connected with the V-I plot of the superconductor, so it is possible to obtain information about the V-I characteristics by the contactless method. (orig.).

  10. Conductive polymer/high-TC superconductor sandwich structures: An example of a molecular switch for controlling superconductivity

    International Nuclear Information System (INIS)

    McDevitt, J.T.; Haupt, S.G.; Lo, R.K.

    1994-01-01

    The preparation of a hybrid conducting polymer/high-temperature superconductor device consisting of a polypyrrole coated YBa 2 Cu 3 O 7-x microbridge is reported. Electrochemical techniques are exploited to alter the oxidation state of the polymer and, in doing so, it is found for the first time that superconductivity can be modulated in a controllable and reproducible fashion by a polymer layer. Whereas the neutral (insulating) polypyrrole only slightly influences the electrical properties of the underlying YBa 2 Cu 3 O 7- film, the oxidized (conductive) polymer depresses T c by up to 50K. In a similar fashion, the oxidation state of the polymer is found to modulate reversibly the magnitude of J c , the superconducting critical current. Thus, a new type of molecular switch for controlling superconductivity is demonstrated. Electrochemical, resistance vs. temperature, atomic force microscopy and scanning electron microscopy measurements are utilized to explore the polymer/superconductor interactions

  11. International Workshop on Ion Beam Modification and Processing of High Tc- Superconductors: Physics and Devices: Program and Abstracts

    Science.gov (United States)

    1989-04-12

    that a train levitated by superconductivity magnets will be used routinely in Japan around the end of the century. All this has been achieved without...study of the effect of irradiation temperature on radiation damage. This study demonstrated that films or devices operating at liquid nitrogen ...April 1989 us Allpy R. i A- Ua NY 5510 1"~l HARWELL UK ATOMIC ENERGY AUTHORITY ION BEAM MODIFICATION AND PROCESSING IN HIGH-T, SUPERCONDUCTORS: PHYSICS

  12. Deposition of high Tc superconductor thin films by pulsed excimer laser ablation and their post-synthesis processing

    International Nuclear Information System (INIS)

    Ogale, S.B.

    1992-01-01

    This paper describes the use of pulsed excimer laser ablation technique for deposition of high quality superconductor thin films on different substrate materials such as Y stabilized ZrO 2 , SrTiO 3 , LiNbO 3 , Silicon and Stainless Steels, and dopant incorporation during the film depositions. Processing of deposited films using ion and laser beams for realisation of device features are presented. 28 refs., 16 figs

  13. Intermediate phases in the formation of the Cu-Ba-Y high-Tc superconductor from xerogel

    International Nuclear Information System (INIS)

    Arcon, I.; Bele, M.; Hribar, M.; Kodre, A.; Stuhec, M.; Pejovnik, S.; Frahm, R.

    1995-01-01

    In the synthesis of YBa 2 Cu 3 O 7-x superconductor ceramics by the sol-gel method, yttrium K EXAFS spectra of the intermediate products give evidence of the dynamics of the Y ion in the reaction. Together with previous data on Cu K and Ba L 3 EXAFS, the results give information on the processes in the amorphous phase, complementing the diffraction data on crystallite growth. ((orig.))

  14. Detailed investigation of the bifurcation diagram of capacitively coupled Josephson junctions in high-Tc superconductors and its self similarity

    Science.gov (United States)

    Hamdipour, Mohammad

    2018-04-01

    We study an array of coupled Josephson junction of superconductor/insulator/superconductor type (SIS junction) as a model for high temperature superconductors with layered structure. In the current-voltage characteristics of this system there is a breakpoint region in which a net electric charge appear on superconducting layers, S-layers, of junctions which motivate us to study the charge dynamics in this region. In this paper first of all we show a current voltage characteristics (CVC) of Intrinsic Josephson Junctions (IJJs) with N=3 Junctions, then we show the breakpoint region in that CVC, then we try to investigate the chaos in this region. We will see that at the end of the breakpoint region, behavior of the system is chaotic and Lyapunov exponent become positive. We also study the route by which the system become chaotic and will see this route is bifurcation. Next goal of this paper is to show the self similarity in the bifurcation diagram of the system and detailed analysis of bifurcation diagram.

  15. Review of progress in pulsed laser deposition and using Nd:YAG laser in processing of high Tc superconductors

    International Nuclear Information System (INIS)

    Chen, C.W.; Mukherjee, K.

    1993-01-01

    The current progress in pulsed laser ablation of high-temperature superconductors is reviewed with emphasis on the effect of pulse-width and wavelength, nature of the plasma plume, post-annealing and methods to improve quality of films grown at low temperature. An ion beam assisted millisecond pulsed laser vapor deposition process has been developed to fabricate YBa 2 Cu 3 O x high T. superconductor thin films. Solution to target overheating problem, effects of oxygen ion beam, properties of deposited films, and effect of silver buffer layer on YSZ substrate are presented. A new laser calcining process has been used to produce near single phase high T c superconductors of Bi-Pb-Sr-Ca-Cu-0 system. The total processing time was reduced to about 100 hours which is about half of that for conventional sintering. For this compound both resistance and magnetic susceptibility data showed an onset of superconducting transition at about 110K. A sharp susceptibility drop was observed above 106K. The zero resistance temperature was about 98K. High T c phase was formed via a different kinetic path in laser calcined sample compare with the conventionally processed sample

  16. Temperature measurement of RE123 bulk superconductors on magnetizing process

    International Nuclear Information System (INIS)

    Yokoyama, K.; Kaneyama, M.; Oka, T.; Fujishiro, H.; Noto, K.

    2004-01-01

    We study on the magnetization behavior of to magnetize RE123 bulk superconductors to apply it as strong magnets. Through magnetizing process, the temperature of bulk superconductors is raised by pinning loss caused by the magnetic fluxes motion (e.g. flux jump of flux flow), and the trapped field is decreased. This paper presents the measurement of temperature changes of Sm123 bulk superconductors during the exciting process by iteratively magnetizing pulsed-field operation with reducing amplitudes (IMRA) method. Five thermocouples are put on the surface of Sm123 bulk superconductor of 46 mm in diameter. The temperatures at the center, on the growth sector boundary (GSB) line and in the sector region surrounded by GSB's line (inter-GSB region) are monitored. The temperature at a cold stage is also measured. A Hall sensor is attached near the center thermocouple to measure the trapped field. After a bulk superconductor is cooled by the GM type refrigerator until 40 K, iterative pulsed-fields of 2.32-5.42 T are applied by a magnetizing coil. When high magnetic field of 5.42 T is applied, a temperature of bulk superconductor reaches to 72.4 K and the magnetic field distribution has C form with which a part of circle is dented, and then, a trapped field is 2.28 T. When a lower magnetic field of 4.64 T is applied, a maximum temperature is 68.3 K and a trapped field is raised to 2.70 T, and moreover, the distribution becomes round shape like field-cooling method (FC). We showed clearly that heat generation by pinning loss was related to the mechanism of magnetic field capture

  17. Peeling stress analysis for an inhomogeneous high-Tc superconductor with a discontinuous interface at the substrate

    International Nuclear Information System (INIS)

    Gao Zhiwen; Lee, Kang Yong; Zhou Youhe

    2011-01-01

    Research highlights: → The thermal stress generated in the inhomogeneous HTS is larger on a SiTiO 3 substrate than on a MgO substrate. → The maximum thermal stresses, i.e., the peeling stresses, occur near the bottom corner of the inhomogeneous HTS and may induce fracture behavior at the bi-material interface. → The inhomogeneous HTS cools at a slower pace than the homogeneous HTS from the room temperature to the operating temperature. → The magnitude of the peeling stress for a homogeneous HTS is larger than that for an inhomogeneous HTS. - Abstract: This paper presents an analysis of a superconductor-substrate system to calculate the peeling stress of a high temperature superconductor (HTS) when the temperature decreases from ambient to operating conditions (cryogenic temperatures). Firstly, the values for the material properties of the inhomogeneous high temperature superconductor (HTS) were obtained by fitting a second order polynomial to the experimental data. It is assumed that the material properties of the inhomogeneous HTS vary with varying height coordinate and temperature. Then, through the proposed graded finite element method, the coupled thermo-mechanical equations were solved numerically. The numerical results show that the thermal stress generated in the inhomogeneous HTS is larger on a SiTiO 3 substrate than on a MgO substrate. The maximum thermal stresses, i.e., the peeling stresses, occur near the bottom corner of the inhomogeneous HTS and may induce fracture behavior at the bi-material interface. The inhomogeneous HTS cools at a slower pace than the homogeneous HTS from the room temperature to the operating temperature. It is also shown that the magnitude of the peeling stress for a homogeneous HTS is larger than that for an inhomogeneous HTS. It is intended that the model presented here be useful to researchers who are interested in the mechanical properties of an inhomogeneous HTS.

  18. D-wave condensate and essential phenomenological description of some properties of high-Tc cuprate superconductors

    International Nuclear Information System (INIS)

    Dunne, L.J.; Univ. of Sussex, Falmer; Braendas, E.J.; Murrell, J.N.

    1999-01-01

    The discovery of high T c superconducting cuprates occurred over a decade ago but the cause of the superconducting condensation and electronic structure of such compounds is still a matter of considerable debate. While there is no agreement as to the pairing mechanism, there is, on the other hand, a wide consensus about the main properties which a theoretical description should provide. In this article, a theory is presented which accounts in a straightforward way for many of the essential properties of the high T c cuprate superconductors. Some further developments of the model are suggested, particularly relating to the normal state spin-gap which the model does not currently describe

  19. Device-quality tunnel junctions on the high Tc superconductor HgBa2CuO4+δ

    International Nuclear Information System (INIS)

    Zasadzinski, J.; Chen, J.; Romano, P.; Gray, K.E.; Wagner, J.L.; Hinks, D.G.

    1995-01-01

    SIN and SIS tunnel junction devices (e.g. photon detectors, logic elements) require quasiparticle characteristics that exhibit sharp current onsets at the gap voltage and very low sub-gap conductances. Progress is reported on the development of such junctions on High Tc cuprates using mechanical point contacts. In general, these contacts display the optimum characteristics that can be obtained from HTS native-surface tunnel barriers. Most cuprates display a sub-gap conductance which monotonically increases with voltage about the minimum value at zero bias. However, tunneling data of unusually high quality have been obtained for the recently discovered Hg-based cuprate, HgBa 2 CuO 4 (T c =96K). SIS' tunneling data using a Nb tip are presented which exhibit very low and flat sub-gap conductances and sharp conductance peaks as expected from a BCS density of states. These results are slightly improved over earlier published results with SIN junctions. Use of the experimental data to simulate the performance of a quasiparticle mixer demonstrates that noise temperatures approaching the quantum limit are possible for SIS and SIN mixers in the range 1-5 THz

  20. Least momentum space frustration as a condition for a ‘high Tc sweet spot’ in iron-based superconductors

    International Nuclear Information System (INIS)

    Usui, Hidetomo; Suzuki, Katsuhiro; Kuroki, Kazuhiko

    2012-01-01

    In the present paper, we describe how the band structure and the Fermi surface of iron-based superconductors vary as the Fe–As–Fe bond angle changes. We discuss how these Fermi surface configurations affect the superconductivity mediated by spin fluctuations, and show that, in several situations, frustration in the sign of the gap function arises due to the repulsive pairing interactions that requires a sign change of the order parameter. Such a frustration can result in nodes or very small gaps, and generally works destructively against superconductivity. Conversely, we propose that the optimal condition for superconductivity is realized for the Fermi surface configuration that gives the least frustration while maximizing the Fermi surface multiplicity. This is realized when there are three hole Fermi surfaces, where two of them have d XZ/YZ orbital character and one has d X 2 −Y 2 for all k z in the three-dimensional Brillouin zone. Looking at the band structures of various iron-based superconductors, the occurrence of such a ‘sweet spot’ situation is limited to a narrow window. (paper)

  1. Positron annihilation study of the high-Tc (Bi, Pb)2Sr2Ca2Cu3Ox superconductor

    International Nuclear Information System (INIS)

    Lim, H.J.; Byrne, J.G.

    1997-01-01

    Positron lifetime spectroscopy (PLS) and positron Doppler-broadening spectroscopy (PDBS) were applied to the high-T c lead-doped Bi 2 Sr 2 Ca 2 Cu 3 O x (BPSCCO 2223) superconductor as a function of temperature. Neither positron lifetimes nor Doppler parameters (S, W, and S/W) showed significant change through T c . This may result from having the highest positron density in the open BiO 2 double layers and no significant positron density in the superconducting CuO 2 layers where positrons, if mainly present, are known to be sensitive to the transition in other high-T c superconductors. Doppler parameters showed that the probability of positron annihilations with core electrons in the lattice slightly increased and that the probability of positron annihilations with conduction electrons slightly decreased as temperature decreased from ambient temperature to 20 K. The lifetime associated with positron annihilations in the perfect lattice of the sample (τ 1 ) was 209 ps and, due to the annihilations at internal surfaces or voids in the sample (τ 2 ) was about 540 ps, independent of temperature. Finally, the mean lifetime for BSCCO 2223 was about 307 ps. (orig.)

  2. Synthesis, thermal properties and recrystallization of ball-milled high Tc superconductors. (Topological stabilization of metastable phases)

    International Nuclear Information System (INIS)

    Schulz, R.; Lanteigne, J.; Simoneau, M.; Tessier, P.; Neste, A. van; Strom Olsen, J.O.

    1995-01-01

    Amorphous and nanocrystalline phases have been formed by ball-milling Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O. The strong mechanical deformations induce disorder on the oxygen sublattice and on the cation sites. These order-disorder transformations often produce simple cubic perovskite structures. During recrystallization, the chemical order is restored. Small ordered regions nucleate, grow and produce particular metastable configurations which minimize the total elastic strain energy. The sequence of events giving rise to the various metastable phases has been followed by x-ray diffraction and differential scanning calorimetry and is explained in terms of free energy diagrams. The stress and strain fields associated with the Y-Ba disorder are calculated using the elastic properties of the Y-Ba-Cu-O superconductor. A simple model is proposed to explain the stability of the structures observed after thermal treatments. (orig.)

  3. Influence of Three-square-well Interaction Potential on Isotope Effect Coefficient of High-TC Superconductors

    International Nuclear Information System (INIS)

    Udomsamuthirun, P.; Dokkaemklang, S.; Kumvongsa, C.; Maneeratanakul, S.

    2005-10-01

    In this research, the exact formula of the isotope effect coefficient of s wave and d-wave superconductor in weak-coupling limit are derived by using a three square- well interaction potential that pairing interaction consists of 3 parts : an attractive electron-phonon interaction, an attractive non-electron-phonon interaction , and a repulsive Coulomb interaction . op ac , w w and c w is the characteristic energy cutoff of the Debye phonon , non-phonon ,and Coulomb respectively and 2 / 1 ac M- a w , and c op , w w do not depend on isotope mass(M). We find that, in all case of consideration, the isotope coefficient converges to 0.5 at lower value of Coulomb coupling constant and larger values of phonon and non-phonon coupling constant

  4. Pseudogap and the specific heat of high Tc superconductors: a Hubbard model in a n-pole approximation

    International Nuclear Information System (INIS)

    Calegari, E J; Lausmann, A C; Magalhaes, S G; Chaves, C M; Troper, A

    2015-01-01

    In this work the specific heat of a two-dimensional Hubbard model, suitable to discuss high-T c superconductors (HTSC), is studied taking into account hopping to first (t) and second (t 2 ) nearest neighbors. Experimental results for the specific heat of HTSC's, for instance, the YBCO and LSCO, indicate a close relation between the pseudogap and the specific heat. In the present work, we investigate the specific heat by the Green's function method within a n-pole approximation. The specific heat is calculated on the pseudogap and on the superconducting regions. In the present scenario, the pseudogap emerges when the antiferromagnetic (AF) fluctuations become sufficiently strong. The specific heat jump coefficient Δγ decreases when the total occupation per site (n T ) reaches a given value. Such behavior of Δγ indicates the presence of a pseudogap in the regime of high occupation

  5. Contamination of YBCO bulk superconductors by samarium and ytterbium

    Czech Academy of Sciences Publication Activity Database

    Volochová, D.; Jurek, Karel; Radušovská, M.; Piovarči, S.; Antal, V.; Kováč, J.; Jirsa, Miloš; Diko, P.

    2014-01-01

    Roč. 496, JAN (2014), s. 14-17 ISSN 0921-4534 Institutional support: RVO:68378271 Keywords : YBCO bulk superconductors * critical temperature * critical current density * peak effect Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.942, year: 2014

  6. SHMUTZ & PROTON-DIAMANT H + Irradiated/Written-Hyper/Super-conductivity(HC/SC) Precognizance/Early Experiments Connections: Wet-Graphite Room-Tc & Actualized MgB2 High-Tc: Connection to Mechanical Bulk-Moduli/Hardness: Diamond Hydrocarbon-Filaments, Disorder, Nano-Powders:C,Bi,TiB2,TiC

    Science.gov (United States)

    Wunderman, Irwin; Siegel, Edward Carl-Ludwig; Lewis, Thomas; Young, Frederic; Smith, Adolph; Dresschhoff-Zeller, Gieselle

    2013-03-01

    SHMUTZ: ``wet-graphite''Scheike-....[Adv.Mtls.(7/16/12)]hyper/super-SCHMUTZ-conductor(S!!!) = ``wet''(?)-``graphite''(?) = ``graphene''(?) = water(?) = hydrogen(?) =ultra-heavy proton-bands(???) = ...(???) claimed room/high-Tc/high-Jc superconductOR ``p''-``wave''/ BAND(!!!) superconductIVITY and actualized/ instantiated MgB2 high-Tc superconductors and their BCS- superconductivity: Tc Siegel[ICMAO(77);JMMM 7,190(78)] connection to SiegelJ.Nonxline-Sol.40,453(80)] disorder/amorphous-superconductivity in nano-powders mechanical bulk/shear(?)-moduli/hardness: proton-irradiated diamond, powders TiB2, TiC,{Siegel[Semis. & Insuls.5:39,47, 62 (79)])-...``VS''/concommitance with Siegel[Phys.Stat.Sol.(a)11,45(72)]-Dempsey [Phil.Mag. 8,86,285(63)]-Overhauser-(Little!!!)-Seitz-Smith-Zeller-Dreschoff-Antonoff-Young-...proton-``irradiated''/ implanted/ thermalized-in-(optimal: BOTH heat-capacity/heat-sink & insulator/maximal dielectric-constant) diamond: ``VS'' ``hambergite-borate-mineral transformable to Overhauser optimal-high-Tc-LiBD2 in Overhauser-(NW-periodic-table)-Land: CO2/CH4-ETERNAL-sequestration by-product: WATER!!!: physics lessons from

  7. Glassy spin freezing and NMR wipeout effect in the high-Tc superconductor La1.90Sr0.10CuO4: Critical discussion of the role of stripes

    Science.gov (United States)

    Julien, M.-H.; Campana, A.; Rigamonti, A.; Carretta, P.; Borsa, F.; Kuhns, P.; Reyes, A. P.; Moulton, W. G.; Horvatić, M.; Berthier, C.; Vietkin, A.; Revcolevschi, A.

    2001-04-01

    We report on 139La and 63Cu NMR/NQR measurements in the high-Tc superconductor La1.90Sr0.10CuO4, with Tc=26.5 K. Spin fluctuations probed by 139La spin-lattice relaxation (T1) continuously slow down on cooling through Tc. We argue that spin freezing and superconductivity are bulk effects in this sample. Thus both phenomena have to coexist microscopically. The distribution of 139La T1 values at low temperature reveals a wide spread of spin fluctuation frequencies in CuO2 planes. A simple estimate shows that 63Cu nuclei at sites where electronic fluctuations are the slowest are not observable (wipeout effect) because relaxation times are too short. This means that the 63Cu NQR wipeout, observed in this sample, can be explained primarily by slow magnetic, rather than charge, fluctuations. The magnetic origin of the wipeout is still compatible with a connection between wipeout and charge order [as proposed by Hunt et al., Phys. Rev. Lett. 82, 4300 (1999)], but this connection is indirect. On the other hand, since the wipeout fraction is not an intensive quantity it cannot define a proper order parameter and cannot be used by itself as a criterion for the existence of a stripe phase.

  8. Effect of strong correlations on the high energy anomaly in hole- and electron-doped high-Tc superconductors

    International Nuclear Information System (INIS)

    Moritz, B; Johnston, S; Greven, M; Shen, Z-X; Devereaux, T P; Schmitt, F; Meevasana, W; Motoyama, E M; Lu, D H; Kim, C; Scalettar, R T

    2009-01-01

    Recently, angle-resolved photoemission spectroscopy (ARPES) has been used to highlight an anomalously large band renormalization at high binding energies in cuprate superconductors: the high energy 'waterfall' or high energy anomaly (HEA). This paper demonstrates, using a combination of new ARPES measurements and quantum Monte Carlo simulations, that the HEA is not simply the by-product of matrix element effects, but rather represents a cross-over from a quasi-particle band at low binding energies near the Fermi level to valence bands at higher binding energy, assumed to be of strong oxygen character, in both hole- and electron-doped cuprates. While photoemission matrix elements clearly play a role in changing the aesthetic appearance of the band dispersion, i.e. the 'waterfall'-like behavior, they provide an inadequate description for the physics that underlies the strong band renormalization giving rise to the HEA. Model calculations of the single-band Hubbard Hamiltonian showcase the role played by correlations in the formation of the HEA and uncover significant differences in the HEA energy scale for hole- and electron-doped cuprates. In addition, this approach properly captures the transfer of spectral weight accompanying both hole and electron doping in a correlated material and provides a unifying description of the HEA across both sides of the cuprate phase diagram.

  9. On the limits of consistency of Eliashberg theory and the density of states of high-Tc superconductors

    International Nuclear Information System (INIS)

    Varelogiannis, G.

    1997-01-01

    We make a detailed study of the Eliashberg theory in the coupling region where some fundamental qualitative deviations from the conventional BCS- like behavior begin to appear. These deviations are identified as the onset of a cross-over from BCS superconductivity to Bose condensation. We point out that the beginning of this cross-over occurs when the gap Δ g becomes comparable to the boson energies Ω ph . This condition traduces the physical constraint that the distance the paired electron covers during the absorption of the virtual boson, cannot be larger than the coherence length. The frontier region of couplings is of the order of λ∼3, and high-T c , materials are concerned. A clear qualitative indication of the occurrence of a cross-over regime should be a dip structure above the gap in the density of states of excitations, and this is one of the most robust characteristics of the high-T c , superconducting state. Comparing our results with tunneling and photoemission experiments we conclude that high-T c materials (cuprates and fullerides) are indeed at the beginning of a cross-over from BCS superconductivity to Bose condensation, even though the fermionic nature still prevails. If the Uemura plot is relevant, then the dip should also be present in the other materials that are close to the cross-over regime like heavy Fermion and organic superconductors. In all these materials Ginzburg Landau equations are irrelevant. (orig.)

  10. Direct images and unconventional dynamics of vortices in the high-Tc superconductors YBCO (123) and BSCCO (2212)

    International Nuclear Information System (INIS)

    Gammel, P.L.; Bishop, D.; Murray, C.; Huse, D.

    1991-01-01

    Static imaging has been used to complement transport I-V measurements in inferring the phase diagram and structure of the mixed state of the high T c superconductors YBCO(123) and BSCCO (2212). High resolution Bitter patterns reveal the static structure of the flux lattice in the low field mixed state of BSCCO (2212). For B parallel c, the in-plane effective mass anisotropy is found to distort the lattice. Rotation of the field away from the c axis results in the appearance of a unique structure: a striking array of vortex chains. At low fields, the pattern is otherwise amorphous. Increasing the field above ∼ 20G results in an abrupt transition into an hexatic phase. At high fields, I-V curves with picovolt resolution imply critical behavior within the mixed state, consistent in both 123 and 2212 with a three-dimensional vortex glass transition well below T c . In 2212, a field and temperature dependent crossover in the effective dimensionality of the vortex lattice is also found

  11. Determining the in-plane Fermi surface topology in high Tc superconductors using angle-dependent magnetic quantum oscillations

    International Nuclear Information System (INIS)

    Harrison, N; McDonald, R D

    2009-01-01

    We propose a quantum oscillation experiment by which the rotation of an underdoped YBa 2 Cu 3 O 6+x sample about two different axes with respect to the orientation of the magnetic field can be used to infer the shape of the in-plane cross-section of corrugated Fermi surface cylinder(s). Deep corrugations in the Fermi surface are expected to give rise to nodes in the quantum oscillation amplitude that depend on the magnitude and orientation of the magnetic induction B. Because the symmetries of electron and hole cylinders within the Brillouin zone are expected to be very different, the topology can provide essential clues as to the broken symmetry responsible for the observed oscillations. The criterion for the applicability of this method to the cuprate superconductors (as well as other layered metals) is that the difference in quantum oscillation frequency 2ΔF between the maximum (belly) and minimum (neck) extremal cross-sections of the corrugated Fermi surface exceeds |B|. (fast track communication)

  12. Far infrared conductivity of charge density wave materials and the oxygen isotope effect in high-Tc superconductors

    International Nuclear Information System (INIS)

    Creager, W.N.

    1991-09-01

    The far infrared reflectance and conductivity of (Ta 1-x Nb x Se 4 ) 2 I and TaS 3 have been measured to determine the origin of a huge infrared resonance that dominates the charge density wave (CDW) dynamics along with the pinned acoustic phason mode in the related materials (TaSe 4 ) 2 I and K 0. 3 MoO 3 . The measurements cover frequencies from 3 to 700cm -1 and the temperature range from 15K to 300K. In the niobium-doped alloys (Ta 1-x Nb x Se 4 ) 2 I, the size and frequency of the giant infrared mode remain nearly constant as the impurity concentration x is increased. For TaS 3 , the pinned acoustic phason near 0.5cm -1 dominates var-epsilon(ω) and an additional small mode lies near 9cm -1 . The latter mode is much smaller than the infrared mode in other CDW materials. These results rule out several models of a ''generic infrared mode'' in CDW excitations. They are compared in detail to the predictions of a recent theory attributing the infrared mode to a bound collective mode localized at impurity sites within the crystal. The transmittance of K 0.3 MoO 3 has been measured at 1.2K with a strong dc electric field applied across the crystal. Under these conditions, the charge density wave depins abruptly and carries large currents with near-zero differential resistance. For some samples, the low-frequency transmittance is enhanced slightly when the CDW depins. The magnitude of the oxygen isotope effect in the high-T c superconductor YBa 2 Cu 3 O 7 has been determined by substitution of 18 O for 16 O. A series of cross-exchanges was performed on high-quality polycrystalline specimens to eliminate uncertainties due to sample heat treatments and sample inhomogeneities

  13. Spectroscopic Imaging Scanning Tunneling Microscopy Studies of Electronic Structure in the Superconducting and Pseudogap Phases of Cuprate High-Tc Superconductors

    Science.gov (United States)

    Fujita, Kazuhiro; Schmidt, Andrew R.; Kim, Eun-Ah; Lawler, Michael J.; Lee, Dung Hai; Davis, J. C.; Eisaki, Hiroshi; Uchida, Shin-ichi

    2012-01-01

    phase diagram and the mechanism of high-Tc superconductivity, represents one of a key challenges for cuprate studies.

  14. Prospects for the use of high-Tc superconductors in fusion magnets and options for their test in SULTAN

    International Nuclear Information System (INIS)

    Wesche, Rainer; Bruzzone, Pierluigi; March, Stephen; Marinucci, Claudio; Stepanov, Boris; Uglietti, Davide

    2013-01-01

    Highlights: ► RE-123 tapes j c ≥ 500 A/cm (77 K) would enable fusion magnets operating above 20 K. ► Quench studies indicate that the protection of RE-123 fusion magnets is a challenge. ► Possibilities to test 50 kA class HTS conductors in SULTAN have been identified. ► HTS bus bar of large thermal resistance needed to connect sample and NbTi flux pump. ► Tests in the 20–50 K range require additional changes in the SULTAN cryogenics. -- Abstract: In the last few years, the critical current densities of long commercially available REBa 2 Cu 3 O 7−x (RE-123, where RE represents Y or a rare earth element) coated conductors have reached values of 250 A/cm-width at 77 K and zero applied field. Even higher values of 600 A/cm-w (77 K, B = 0) have been demonstrated in shorter lengths. The attractive features of the use of these high-T c superconductors (HTS) are operation temperatures above 20 K and/or magnetic fields higher than those envisaged for the ITER TF coils. Possible operation conditions for HTS fusion magnets have been studied taking into consideration the possible further improvements of RE-123 coated conductors. Investigations of stability and quench behavior indicate that stability is not a problem, whereas quench detection and protection need attention. Because of the high currents necessary for fusion magnets, many tapes need to be assembled into a transposed conductor. The qualification of HTS conductors for fusion magnets would require their test at magnetic fields of 11 T and currents well above 10 kA. The possibilities to test straight HTS conductor samples in SULTAN have been considered. For a test at 4.5 K, only the development of a low resistance joint between the HTS conductor under test and the NbTi transformer of SULTAN would be necessary. Tests up to 20 K would require that the HTS sample is connected with the NbTi transformer by a conduction-cooled HTS bus bar of large thermal resistance similar to the HTS module of a current

  15. Transport measurements in superconductors: critical current of granular high TC ceramic superconductor samples; Medidas de transporte em supercondutores: corrente critica de supercondutores granulares de alta temperatura critica

    Energy Technology Data Exchange (ETDEWEB)

    Passos, W.A.C., E-mail: wagner.passos@univasf.edu.br [Universidade Federal do Vale do Sao Francisco (IPCM/UNIVASF), Juazeiro do Norte, BA (Brazil). Instituto de Pesquisas em Ciencia dos Materiais; Silva, E.B. [Companhia Energetica do Sao Francisco (CHESF), Recife, PE (Brazil)

    2016-07-01

    This work presents a method to obtain critical current of granular superconductors. We have carried out transport measurements (ρxT curves and VxI curves) in a YBa{sub 2}Cu{sub 3}O{sub 7-δ} sample to determine critical current density of it. Some specimens reveal a 'semiconductor-like' behavior (electrical resistivity decreases with increasing temperatures above critical temperature T{sub c} of material) competing with superconductor behavior. Due to high granular fraction of the sample, these competition is clearly noted in ρxT curves. Measurements carried out from 0 to 8500 Oe of applied field show the same behavior, and the critical current density of the samples is shown. (author)

  16. Growth and characterization of bulk superconductor material

    CERN Document Server

    Chen, Dapeng; Maljuk, Andrey; Zhou, Fang

    2016-01-01

    This book focuses on recently developed crystal growth techniques to grow large and high quality superconducting single crystals. The techniques applied are traveling solvent floating zone (TSFZ) with infrared image furnace, Bridgeman, solution/flux and top seeded solution growth (TSSG) methods. The materials range from cuprates, cobaltates to pnictides including La2CuO4-based (LCO), YBa2Cu3O7-d (YBCO), Bi2Sr2Can−1CunO2n+4+δ (n=1,2,3) (BSCCO) to NaxCoO2. The modified Bridgman “cold finger” method is devoted to the pnictide system with the best quality (transition width DTc~0.5 K) with highest Tc~38.5 K of Ba0.68K0.32Fe2A2. The book presents various iron-based superconductors with different structures, such as 1111, 122, 111, 11 and 42622,10-3-8. Detailed single crystal growth methods (fluxes, Bridgman, floating zone), the associated procedures and their impact to crystal size and quality are presented. The book also describes the influence of doping on the structure and the electric, magnetic, and supe...

  17. Flux-pinning-induced stress and magnetostriction in bulk superconductors

    International Nuclear Information System (INIS)

    Johansen, Tom H.

    2000-01-01

    The development of bulk high-temperature superconductors (HTSs) and their applications has today come to a point where the mechanical response to high magnetic fields may be more important than their critical-current density and large-grain property. Reviewed in this article are the recent studies of the magneto-elastic effects which are caused by flux pinning in the superconductors. This includes the work on the giant irreversible magnetostriction and internal stress, which often cause fatal cracking of the HTS bulks as they become magnetized. The cracking is a problem that today accompanies the quest for the highest trapped field values, and the latest development in this area is also presented. While the first part is an overview of experimental efforts, the second summarizes the work done to model the pinning-induced stress and strain under various magnetic and geometrical conditions. (author)

  18. High trapped fields in bulk YBCO superconductors

    Science.gov (United States)

    Fuchs, Günter; Gruss, Stefan; Krabbes, Gernot; Schätzle, Peter; Verges, Peter; Müller, Karl-Hartmut; Fink, Jörg; Schultz, Ludwig

    The trapped field properties of bulk melt-textured YBCO material were investigated at different temperatures. In the temperature range of liquid nitrogen, maximum trapped fields of 1.1 T were found at 77 K by doping of YBCO with small amounts of zinc. The improved pinning of zinc-doped YBa2Cu3O7-x (YBCO) results in a pronounced peak effect in the field dependence of the critical current density. the trapped field at lower temperatures increases due to the increasing critical current density, however, at temperatures around 50 K cracking of the material is observed which is exposed to considerably tensile stresses due to Lorentz forces. Very high trapped fields up to 14.4 T were achieved at 22.5 K for a YBCO disk pair by the addition of silver improving the tensile strength of YBCO and by using a bandage made of a steel tube. The steel tube produces a compressive stress on YBCO after cooling down from 300 K to the measuring temperature, which is due to the higher coeeficient of thermal expansion of steel compared with that of YBCO in the a,b plane. The application of superconducting permanent magnets with trapped fields of 10 T and more in superconducting bearings would allow to obtain very high levitation pressures up to 2500 N/cm2 which is two orders of magnitude higher than the levitation pressure achievable in superconducting bearings with conventional permanent magnets. The most important problem for the application of superconducting permanent magnets is the magnetizing procedure of the YBCO material. Results of magnetizing YBCO disks by using of pulsed magnetic fields will be presented.

  19. Permanent magnet with MgB{sub 2} bulk superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Yamamoto, Akiyasu, E-mail: yamamoto@appchem.t.u-tokyo.ac.jp [The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); JST-PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Ishihara, Atsushi; Tomita, Masaru [Railway Technical Research Institute, 2-8-38 Hikari, Kokubunji, Tokyo 185-8540 (Japan); Kishio, Kohji [The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan)

    2014-07-21

    Superconductors with persistent zero-resistance currents serve as permanent magnets for high-field applications requiring a strong and stable magnetic field, such as magnetic resonance imaging. The recent global helium shortage has quickened research into high-temperature superconductors (HTSs)—materials that can be used without conventional liquid-helium cooling to 4.2 K. Herein, we demonstrate that 40-K-class metallic HTS magnesium diboride (MgB{sub 2}) makes an excellent permanent bulk magnet, maintaining 3 T at 20 K for 1 week with an extremely high stability (<0.1 ppm/h). The magnetic field trapped in this magnet is uniformly distributed, as for single-crystalline neodymium-iron-boron. Magnetic hysteresis loop of the MgB{sub 2} permanent bulk magnet was determined. Because MgB{sub 2} is a simple-binary-line compound that does not contain rare-earth metals, polycrystalline bulk material can be industrially fabricated at low cost and with high yield to serve as strong magnets that are compatible with conventional compact cryocoolers, making MgB{sub 2} bulks promising for the next generation of Tesla-class permanent-magnet applications.

  20. Processing of bulk Bi-2223 high-temperature superconductor

    Directory of Open Access Journals (Sweden)

    Alexander Polasek

    2005-12-01

    Full Text Available The Bi2Sr2Ca2Cu3 O10+x (Bi-2223 is one of the main high temperature superconductors for applications. One of these applications is the Superconductor Fault Current Limiter (SCFCL, which is a very promising high temperature superconducting device. SCFCL's can be improved by using bulk superconductors with high critical currents, which requires a sufficiently dense and textured material. In the present work, a process for improving the microstructure of Bi-2223 bulk samples is investigated. Pressed precursor blocks are processed by sintering with a further partial melting step, in order to enhance the Bi-2223 grain texture and to healing cracks induced by pressing. In order to improve the microstructure, the precursor is mixed with silver powder before pressing. Samples with and without silver powder have been studied, with the aim of investigating the influence of silver on the microstructure evolution. The phase contents and the microstructure obtained have been analyzed through XRD and SEM/EDS. The electromagnetic characterization has been performed by Magnetic Susceptibility Analysis. We present and discuss the process and the properties of the superconducting blocks. High fractions of textured Bi-2223 grains have been obtained.

  1. Improvement of critical currents in Bi-2223 bulk superconductors

    International Nuclear Information System (INIS)

    Eujen, R.; Brauer, D.J.; Huedepohl, J.

    1991-01-01

    Potential applications of the high-Tc superconductors for energy transport or high-field magnets require high critical current densities. A limiting factor in polycrystalline oxidic materials is the quality of the grain boundaries. Weak links have been made responsible for the steep decrease in the critical current density j c upon application of even weak magnetic fields of YBa CuO whereas flux creep seems to dominate the obtainable j c values for the Bi-Sr-Ca-Cu-O system (BSCCO) at 77 K. In the lead containing material (BPSCCO) the formation of a porous microstructure is enhanced by the platelike shape of the crystals. Special techniques such as powder-in-tube, hot isostatic pressing, zone melting or application of fluxes have been used in order to improve the grain contacts. A positive influence of fluxes on j c , e.g. by addition of Ca 2 CuO 3 or Ag 2 O, has been reported. In this study we have investigated the influence of various compositions and conditions on the formation of the BSCCO-2223 phase (T c ca. 107 K), the critical current density j c , and the magnet field dependence of the a.c. susceptibility. (orig.)

  2. Possible charge analogues of spin transfer torques in bulk superconductors

    Science.gov (United States)

    Garate, Ion

    2014-03-01

    Spin transfer torques (STT) occur when electric currents travel through inhomogeneously magnetized systems and are important for the motion of magnetic textures such as domain walls. Since superconductors are easy-plane ferromagnets in particle-hole (charge) space, it is natural to ask whether any charge duals of STT phenomena exist therein. We find that the superconducting analogue of the adiabatic STT vanishes in a bulk superconductor with a momentum-independent order parameter, while the superconducting counterpart of the nonadiabatic STT does not vanish. This nonvanishing superconducting torque is induced by heat (rather than charge) currents and acts on the charge (rather than spin) degree of freedom. It can become significant in the vicinity of the superconducting transition temperature, where it generates a net quasiparticle charge and alters the dispersion and linewidth of low-frequency collective modes. This work has been financially supported by Canada's NSERC.

  3. A small Maglev car model using YBCO bulk superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Yang, W M [Department of Physics, Shaanxi Normal University, Xi' an, Shaanxi 710016 (China); Zhou, L [Northwest Institute for Nonferrous Metal Research, PO Box 51, Xi' an, Shaanxi 710016 (China); Yong, Feng [Northwest Institute for Nonferrous Metal Research, PO Box 51, Xi' an, Shaanxi 710016 (China); Zhang, P X [Northwest Institute for Nonferrous Metal Research, PO Box 51, Xi' an, Shaanxi 710016 (China); Chao, X X [Department of Physics, Shaanxi Normal University, Xi' an, Shaanxi 710016 (China); Bian, X B [Department of Physics, Shaanxi Normal University, Xi' an, Shaanxi 710016 (China); Zhu, S H [Department of Physics, Shaanxi Normal University, Xi' an, Shaanxi 710016 (China); Wu, X L [Department of Physics, Shaanxi Normal University, Xi' an, Shaanxi 710016 (China); Liu, P [Department of Physics, Shaanxi Normal University, Xi' an, Shaanxi 710016 (China)

    2006-07-15

    Models of two small Maglev cars have been made. The track was paved with NdFeB magnets. The arrangement of the magnets made it easy to get a uniform magnetic field distribution along the length of the track and a magnetic field gradient in the lateral direction. When the car with YBCO bulk superconductors was field cooled to LN{sub 2} temperature at a certain distance above the track, the car could be automatically levitated over the track and moved along the track without any obvious friction. The model can be used to demonstrate the Meissner effect and a fast transportation system to students and adults.

  4. A small Maglev car model using YBCO bulk superconductors

    International Nuclear Information System (INIS)

    Yang, W M; Zhou, L; Yong, Feng; Zhang, P X; Chao, X X; Bian, X B; Zhu, S H; Wu, X L; Liu, P

    2006-01-01

    Models of two small Maglev cars have been made. The track was paved with NdFeB magnets. The arrangement of the magnets made it easy to get a uniform magnetic field distribution along the length of the track and a magnetic field gradient in the lateral direction. When the car with YBCO bulk superconductors was field cooled to LN 2 temperature at a certain distance above the track, the car could be automatically levitated over the track and moved along the track without any obvious friction. The model can be used to demonstrate the Meissner effect and a fast transportation system to students and adults

  5. Mechanical properties of Nd-Ba-Cu-O bulk superconductors

    International Nuclear Information System (INIS)

    Matsui, Motohide; Sakai, Naomichi; Murakami, Masato; Osamura, Kozo

    2003-01-01

    We investigated the effects of Nd422 and Ag particles on the mechanical properties in Nd-Ba-Cu-O bulk superconductors. Both Nd422 and Ag particles were effective in decreasing the amount of microcracks running along the c direction. In the case of Nd422, however, excessive Nd422 addition enhanced the crack propagation, resulting in the degradation of mechanical strength. In the case of Ag addition, the beneficial effect of its ductile mechanical property was not observed. This was due to a relatively large size of Ag particles and low interfacial strength between Ag and Nd123 matrix. It was remarkable that the Weibull coefficient of the sample with Ag 2 O addition exceeded 13, which is reliable enough for practical engineering applications

  6. Acoustic emission behavior under bending deformation of YBCO bulk superconductor

    International Nuclear Information System (INIS)

    Yoneda, K.; Ye, J.; Tomita, M.

    2005-01-01

    Bending tests were conducted on U-notched specimens cut from a YBCO bulk superconductor. Acoustic emission (AE) signals obtained under loading parallel or perpendicular to the c-axis were analyzed to investigate the correlation between crack growth behavior and the AE signals. As a result of analyzing log-log plots of strength (σ B ) versus total AE energy (ΣE AE ), a linear relationship was found between ΣE AE and σ B n . Cracks could be broadly divided into two types based on the value of n as an index of crack growth behavior. One type consisted of microcracks originating from cleavage planes and gas holes; these crack propagated parallel to the c-axis and had an n index value of approximately 0.7. The other type was a main crack that originated from the U-notch and had an n index value of approximately 6.5. A sample (A) loaded parallel to the c-axis showed mean bending strength of 74.8MPa. Cracks displaying two different growth patterns of n=0.7 and 6.5 were presented in this sample. Microcracks parallel to the c-axis occurred in the vicinity of 5-10MPa. This sample was characterized by mixed crack growth of a main crack and microcracks. A sample (B) loaded perpendicular to the c-axis displayed mean bending strength of 43MPa. A main crack occurred in the vicinity of 20MPa and displayed a single growth pattern of n=6.5. By analyzing AE signals in this way in the process of conducting a strength evaluation, it was possible to evaluate the failure process of the bulk superconductor in relation to the strength level induced by the applied load

  7. Observation of an hexatic vortex glass in flux lattices of the high-Tc superconductor Bi2.1Sr1.9Ca0.9Cu2O8+δ

    International Nuclear Information System (INIS)

    Bishop, D.J.; Gammel, P.L.; Murray, C.A.; Mitzi, D.B.; Kapitulnik, A.

    1991-01-01

    We report observation of hexatic order in Abrikosov flus lattices in very clean crystals of the high-Tc superconductor Bi 2.1 Sr 1.9 Ca 0.9 Cu 2 O 8+δ (BSCCO). Our experiments consist of in situ magnetic decoration of the flux lattice at 4.2 K. Analysis of the decoration images shows that the positional order decays exponentially with a correlation length of a few lattice constants while the orientational order persists for hundreds of lattice constants and decays algebraically with an exponent η 6 =0.6±0.01. Our results confirm recent theoretical speculation that the positional order should be far more sensitive to disorder than the orientational order and that the low-temperature ordered phase of the flux lines in these systems might be an hexatic glass. (orig.)

  8. Observation of an hexatic vortex glass in flux lattices of the high-Tc superconductor Bi sub 2. 1 Sr sub 1. 9 Ca sub 0. 9 Cu sub 2 O sub 8+. delta

    Energy Technology Data Exchange (ETDEWEB)

    Bishop, D J; Gammel, P L; Murray, C A [AT and T Bell Labs., Murray Hill, NJ (USA); Mitzi, D B; Kapitulnik, A [Stanford Univ., CA (USA)

    1991-02-01

    We report observation of hexatic order in Abrikosov flus lattices in very clean crystals of the high-Tc superconductor Bi{sub 2.1}Sr{sub 1.9}Ca{sub 0.9}Cu{sub 2}O{sub 8+{delta}} (BSCCO). Our experiments consist of in situ magnetic decoration of the flux lattice at 4.2 K. Analysis of the decoration images shows that the positional order decays exponentially with a correlation length of a few lattice constants while the orientational order persists for hundreds of lattice constants and decays algebraically with an exponent {eta}{sub 6}=0.6{+-}0.01. Our results confirm recent theoretical speculation that the positional order should be far more sensitive to disorder than the orientational order and that the low-temperature ordered phase of the flux lines in these systems might be an hexatic glass. (orig.).

  9. Observation of a hexatic vortex glass in flux lattices of the High-Tc superconductor Bi(2.1)Sr(1.9)Ca(0.9)Cu2O(8 + delta)

    Science.gov (United States)

    Murray, C. A.; Gammel, P. L.; Bishop, D. J.; Mitzi, D. B.; Kapitulnik, A.

    1990-05-01

    Hexatic order is observed in Abrikosov flux lattices in very clean crystals of the high-Tc superconductor Bi(2.1)Sr(1.9)Ca(0.9)Cu2O(8 + delta) by in situ magnetic decoration of the flux lattice at 4.2 K. Analysis of the decoration images shows that the positional order decays exponentially with a correlation length of a few lattice constants, while the orientational order persists for hundreds of lattice constants and decays algebraically with an exponent eta6 = 0.06 + or - 0.01. These results confirm recent theoretical speculation that the positional order should be far more sensitive to disorder than the orientational order, and that the low-temperature ordered phase of the flux lines in these systems might be a hexatic glass.

  10. Observation of an hexatic vortex glass in flux lattices of the high- Tc superconductor Bi 2.1Sr 1.9Ca 0.9Cu 2O 8+δ

    Science.gov (United States)

    Bishop, D. J.; Gammel, P. L.; Murray, C. A.; Mitzi, D. B.; Kapitulnik, A.

    1991-02-01

    We report observation of hexatic order in Abrikosov flux lattices in very clean crystals of the high- Tc superconductor Bi 2.1Sr 1.9Ca 0.9Cu 2O 8+δ (BSCCO). Our experiments consist of in situ magnetic decoration of the flux lattice at 4.2 K. Analysis of the decoration images shows that the positional order decays exponentially with a correlation length of a few lattice constants while the orientational order persists for hundreds of lattice constants and decays algebraically with an exponent η 6 = 0.6 ± 0.01. Our results confirm recent theoretical speculation that the positional order should be far more sensitive to disorder than the orientational order and that the low-temperature ordered phase of the flux lines in these systems might be an hexatic glass.

  11. Observation of an hexatic vortex glass in flux lattices of the high Tc superconductor Bi2.1Sr1.9Ca0.9Cu2O8+δ

    Science.gov (United States)

    Bishop, D. J.; Gammel, P. L.; Murray, C. A.; Mitzi, D. B.; Kapitulnik, A.

    1990-10-01

    We report observation of hexatic order in Abrikosov flux lattices in very clean crystals of the high Tc superconductor Bi2.1Sr1.9Ca0.9Cu2O8+δ (BSCCO). Our experiments consist of in situ magnetic decoration of the flux lattice at 4.2 K. Analysis of the decoration images shows that the positional order decays exponentially with a correlation length of a few lattice constants while the orientational order persists for hundreds of lattice constants and decays algebraically with an exponent η6=0.06±0.01. Our results confirm recent theoretical speculation that the positional order should be far more sensitive to disorder than the orientational order and that the low temperature ordered phase of the flux lines in these systems might be an hexatic glass.

  12. Crossover from three- to two-dimensional behavior of the vortex energies in layered XY-models for high Tc superconductors

    International Nuclear Information System (INIS)

    Weber, H.; Tekniska Hoegskolan, Luleaa; Jeldtoft Jensen, H.

    1991-01-01

    We use Monte Carlo simulations of a layered XY-model to study the phase fluctuations in high T c superconductors. A vortex-antivortex interaction dominated by a term linear in the vortex separation is found in the low temperature region. This is in agreement with a zero temperature variational calculation. At temperature just above the 2D vortex unbinding temperature the linear term vanishes and an ordinary 2D vortex behaviour is found. This explains the finding that the High T c superconductors show 2D properties in the vortex fluctuations responsible for the resistivity transition close to the critical temperature. (orig.)

  13. Improvement of the mechanical properties of bulk superconductors; Jushiganshin niyoru baruku chodendotai no kikaitekitokusei no kaizen

    Energy Technology Data Exchange (ETDEWEB)

    Tomita, M; Murakami, M [Superconductivity Research Laboratory, Tokyo (Japan)

    1999-11-25

    Large single-grain bulk rare earth element (RE)-Ba-Cu-O superconductors can trip large fields exceeding several teslas and thus can function as very strong quasi-permanent magnets. However, the maximum trapped field is essentially limited by the mechanical strength of the bulk superconductors. The stress produced by refrigeration sometimes causes cracking. A large electromagnetic force also acts on superconductors when they trap large magnetic fields, and this occasionally leads to device failure. We have recently found that epoxy resin can penetrate into bulk superconductors under certain conditions. Microstructural observation revealed that microcracks as well as porosities can be impregnated with epoxy resin, which greatly improves the mechanical properties of bulk RE-Ba-Cu-O and thus results in the improvement of field trapping capability. (author)

  14. Ceramic superconductors II

    International Nuclear Information System (INIS)

    Yan, M.F.

    1988-01-01

    This volume compiles papers on ceramic superconductors. Topics include: structural patterns in High-Tc superconductors, phase equilibria of barium oxide superconductors, localized electrons in tetragonal YBa/sub 2/Cu/sub 3/O/sub 7-δ/, lattice and defect structure and properties of rare earth/alkaline earth-copper-oxide superconductors, alternate candidates for High-Tc superconductors, perovskite-structure superconductors; superconductive thin film fabrication, and superconductor/polymer composites

  15. Disclosure of hidden magnetic moments in low and high Tc hysteretic and semi-reversible type II superconductors during warming to Tc

    International Nuclear Information System (INIS)

    LeBlanc, M.A.R.; LeBlanc, D.; Cameron, D.S.M.; Celebi, S.

    2000-01-01

    We report on measurements of the evolution of the magnetization upon warming from T 0 (4.2 or 77 K) to T c for type II superconductors with the locus of initially situated along bridges between the envelopes of the major hysteresis curves. Strongly hysteretic and semi-reversible specimens of low and high T c type II superconductors have been studied (Nb 3 Zr, VTi, YBCO, Nb and BiSCCO). Concentric, oppositely directed magnetic moments coexist in the specimens when lies along the bridges. We focused on the cases where =0, hence, before warming, the constituent moments cancel each other exactly. Since they diminish in magnitude at different rates as T is increased to T c , their sequential 'release' leads to a rich variety of phenomena. A simple model exploiting the critical state, an equilibrium Meissner current and conservation of flux accounts for all the intricate behaviour encountered. (author)

  16. Structural changes between 100 and 300 K of the high-Tc superconductor Y-Ba-Cu-O studied by positron annihilation

    International Nuclear Information System (INIS)

    Wang, S.J.; Li, X.H.; Chen, Y.L.; Li, S.Q.; Fong, G.H.; Wang, Z.

    1989-01-01

    The structural changes of the high-T c superconductor Y-Ba-Cu-O between 100 and 300 K are studied by positron lifetime and Doppler broadening measurements as a function of temperature. There are anomalous changes in the positron lifetimes and Doppler broadening S-parameters near 130 and 260 K, which is consistent with some reported experimental results. These anomalies may be caused by the lattice instabilities, such as the ordering readjustment of oxygen vacancies. (author)

  17. Technique of Critical Current Density Measurement of Bulk Superconductor with Linear Extrapolation Method

    International Nuclear Information System (INIS)

    Adi, Wisnu Ari; Sukirman, Engkir; Winatapura, Didin S.

    2000-01-01

    Technique of critical current density measurement (Jc) of HTc bulk ceramic superconductor has been performed by using linear extrapolation with four-point probes method. The measurement of critical current density HTc bulk ceramic superconductor usually causes damage in contact resistance. In order to decrease this damage factor, we introduce extrapolation method. The extrapolating data show that the critical current density Jc for YBCO (123) and BSCCO (2212) at 77 K are 10,85(6) Amp.cm - 2 and 14,46(6) Amp.cm - 2, respectively. This technique is easier, simpler, and the use of the current flow is low, so it will not damage the contact resistance of the sample. We expect that the method can give a better solution for bulk superconductor application. Key words. : superconductor, critical temperature, and critical current density

  18. Surface barrier and bulk pinning in MgB$_2$ superconductor

    OpenAIRE

    Pissas, M.; Moraitakis, E.; Stamopoulos, D.; Papavassiliou, G.; Psycharis, V.; Koutandos, S.

    2001-01-01

    We present a modified method of preparation of the new superconductor MgB$_2$. The polycrystalline samples were characterized using x-ray and magnetic measurements. The surface barriers control the isothermal magnetization loops in powder samples. In bulk as prepared samples we always observed symmetric magnetization loops indicative of the presence of a bulk pinning mechanism. Magnetic relaxation measurements in the bulk sample reveal a crossover of surface barrier to bulk pinning.

  19. The effect of processing parameters during heat treatment of bulk high-T(sub c) superconductors

    Science.gov (United States)

    Cha, Y. S.; Dorris, S. E.; Hull, J. R.; Poeppel, R. B.

    1991-04-01

    Plastic extrusion is a promising method for producing the long lengths of high-Tc superconductor that will be necessary to meet many potential applications. A crucial phase of the extrusion method is removal of organic constituents. Incomplete removal can leave residual carbon at grain boundaries, which can adversely affect the superconducting properties, whereas excessively rapid removal of the organics can cause the extruded superconductor to disintegrate completely. In this paper, we analyze the effects of the following aspects of organics removal, as they apply to the firing of extruded YBa2Cu3O(x) coils: (1) total pressure in the furnace, (2) oxygen flow, (3) heat conduction, and (4) diffusion of volatile components during removal of organics.

  20. High temperature superconductor bulk materials. Fundamentals - processing - properties control - application aspects

    International Nuclear Information System (INIS)

    Krabbes, G.; Fuchs, G.; Canders, W.R.; May, H.; Palka, R.

    2006-01-01

    This book presents all the features of bulk high temperature superconducting materials. Starting from physical and chemical fundamentals, the authors move on to portray methods and problems of materials processing, thoroughly working out the characteristic properties of bulk superconductors in contrast to long conductors and films. The authors provide a wide range of specific materials characteristics with respect to the latest developments and future applications guiding from fundamentals to practical engineering examples. This book contains the following chapters: 1. Fundamentals 2. Growth and melt processing of YBCO 3. Pinning-relevant defects in bulk YBCO 4. Properties of bulk YBCO 5. Trapped fields 6. Improved YBCO based bulk superconductors and functional elements 7. Alternative systems 8. Peak effect 9. Very high trapped fields in YBCO permanent magnets 10. Engineering aspects: Field distribution in bulk HTSC 11. Inherently stable superconducting magnetic bearings 12. Application of bulk HTSCs in electromagnetic energy converters 13. Applications in magnet technologies and power supplies

  1. Recent progress in material technology on RE-Ba-Cu-O bulk superconductors

    International Nuclear Information System (INIS)

    Teshima, Hidekazu; Morita, Mitsuru

    2011-01-01

    The current status of large-grained RE-Ba-Cu-O (RE: Y or rare earth elements) bulk superconductors with excellent superconducting properties is described. Gd-Ba-Cu-O bulk superconductors can trap a very high magnetic field even if they are melt-processed in air. Although the electromagnetic force caused by the trapped field is larger for a larger sample and may break the sample, a large sample of Gd-Ba-Cu-O 46 mm in diameter has the potential of trapped magnetic fields greater than 10 T at around 40 K. In addition, single-grained bulk superconductors as large as 150 mm can be obtained using the RE compositional gradient method. Dy-Ba-Cu-O is an ideal material for current leads because it has low thermal conductivity and high critical current density at 77 K in high magnetic fields. Eu-Ba-Cu-O has low magnetic permeability, and is therefore suitable for bulk NMR applications. Progress in machining technology has made possible various bulk superconductors with complicated shapes such as coils, leading to small and strong electromagnets by stacking several coil-shaped bulk superconductors together. (author)

  2. Surface flux density distribution characteristics of bulk high-T c superconductor in external magnetic field

    International Nuclear Information System (INIS)

    Nishikawa, H.; Torii, S.; Yuasa, K.

    2005-01-01

    This paper describes the measured results of the two-dimensional flux density distribution of a YBCO bulk under applied AC magnetic fields with various frequency. Melt-processed oxide superconductors have been developed in order to obtain strong pinning forces. Various electric mechanical systems or magnetic levitation systems use those superconductors. The major problem is that cracks occur because the bulk superconductors are brittle. The bulk may break in magnetizing process after cracks make superconducting state instable. The trapped flux density and the permanent current characteristics of bulk superconductors have been analyzed, so as to examine the magnetizing processes or superconducting states of the bulk. In those studies, the two-dimensional surface flux density distributions of the bulk in static fields are discussed. On the other hand, the distributions in dynamic fields are little discussed. We attempted to examine the states of the bulk in the dynamic fields, and made a unique experimental device which has movable sensors synchronized with AC applied fields. As a result, the two-dimensional distributions in the dynamic fields are acquired by recombining the one-dimensional distributions. The dynamic states of the flux of the bulk and the influences of directions of cracks are observed from the distributions. In addition, a new method for measuring two-dimensional flux density distribution under dynamic magnetic fields is suggested

  3. Bulk superconductivity in Type II superconductors near the second critical field

    DEFF Research Database (Denmark)

    Fournais, Søren; Helffer, Bernard

    2010-01-01

    We consider superconductors of Type II near the transition from the ‘bulk superconducting’ to the ‘surface superconducting’ state. We prove a new L∞ estimate on the order parameter in the bulk, i.e. away from the boundary. This solves an open problem posed by Aftalion and Serfaty [AS]....

  4. Improvement of maglev model using high Tc superconductors and soft magnetic materials; Koon chodendotai to nanjiseitai wo kumiawaseta jiki fujo kiko no kairyo

    Energy Technology Data Exchange (ETDEWEB)

    Tsutsui, Y [Yasukawa Electric Corp., Kitakyushu (Japan). Basic Research Lab.; Higuchi, T [Kanagawa Academy of Science and Technology, Kawasaki (Japan); Kondo, N [Univ. of Tokyo, Tokyo (Japan)

    1995-02-25

    In this study, in a magnetic levitation system using pinning force of high temperature superconductors, for a propose of magnification of the stable contactless gap length and exclusion of mass regulation of a floater, a magnetic levitation model was improved. That is, the tangential component of an attractive force between a high temperature superconductor where magnetic flux was pinned and magnetic material is used for levitation and stable force in up and down directions, and restoring force generated due to pinned flux gathering was used for horizontal stabilization. For a floater made by using this principle, weight addition was necessary for letting the center of gravity down, however self-weight regulation of a floater is originally unnecessary. Thus, a magnetic levitation apparatus can be made without self-weight regulation of suspension and having a wide stable gap by using this levitation method. Since the floater was constructed under two rails, there are good points on easily dealing with the safety countermeasure in cases of which levitation would reduce or disappear. 4 refs., 7 figs.

  5. Hysteretic Vortex-Matching Effects in High-Tc Superconductors with Nanoscale Periodic Pinning Landscapes Fabricated by He Ion-Beam Projection

    Science.gov (United States)

    Zechner, G.; Jausner, F.; Haag, L. T.; Lang, W.; Dosmailov, M.; Bodea, M. A.; Pedarnig, J. D.

    2017-07-01

    Square arrays of submicrometer columnar defects in thin YBa2 Cu3 O7 -δ (YBCO) films with spacings down to 300 nm are fabricated by a He ion-beam projection technique. Pronounced peaks in the critical current and corresponding minima in the resistance demonstrate the commensurate arrangement of flux quanta with the artificial pinning landscape, despite the strong intrinsic pinning in epitaxial YBCO films. While these vortex-matching signatures are exactly at the predicted values in field-cooled experiments, they are displaced in zero-field-cooled, magnetic-field-ramped experiments, conserving the equidistance of the matching peaks and minima. These observations reveal an unconventional critical state in a cuprate superconductor with an artificial, periodic pinning array. The long-term stability of such out-of-equilibrium vortex arrangements paves the way for electronic applications employing fluxons.

  6. Microstructural analyses and critical current densities in the high-Tc superconductor system ReBa2Cu3OX, with RE = Y, Sm, Eu, Gd, Dy, Ho

    International Nuclear Information System (INIS)

    Schindler, G.; Seebacher, B.

    1989-01-01

    The authors report on investigations into the impact of the rare earths (RE) as given in the title on the ceramic microstructure and the critical current density j c in the superconductor system REBa 2 Cu 3 O x . With RE = Sm, Eu, or Gd, the material is homogeneous in phase and crystallizes in platelets with maximum sizes of up to 350 μm. Material with RE = Y, Dy, or Ho exhibits grain sizes up to 500 μm, and a low amount of phase inhomogeneities. The critical currents measured are between 25 Acm -2 and 290 Acm -2 at 77 K, without external field. The highest values are found in systems with RE = Eu or Gd. (orig.) [de

  7. 17O knight shifts of the various types of CuO2 planes in Bi-cuprates high-Tc superconductors

    International Nuclear Information System (INIS)

    Le Noc, L.; Trokiner, A.; Schneck, J.; Pougnet, A.M.; Mellet, R.; Primot, J.; Savary, H.

    1992-01-01

    A 17 O NMR study has been performed on a 17 O enriched powder sample of (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O y , also called n=3 phase (with Tc=110K) which belongs to the Bi-based superconductors family (Bi,Pb) 2 Sr 2 Ca n-1 Cu n O 2n+4 . The n=3 compound which contains in its unit cell two types of CuO 2 planes (labelled type I and II), is compared to the n=2 compound where only one type of CuO 2 planes (type I) is present. 17 O Knight shift measurements versus temperature, in the normal phase, have allowed us to evidence the distinct behaviours of the two types of planes present in the n=3 compound. The results are consistent with the existence of stronger electron correlations, or smaller charge carrier density in the type II planes. 14 refs., 3 figs

  8. Intralayer and interlayer spin-singlet pairing and energy gap functions with different possible symmetries in high-Tc layered superconductors

    International Nuclear Information System (INIS)

    Jha, S.S.; Rajagopal, A.K.

    1997-01-01

    Anisotropy and the wave-vector dependence of the energy gap function determine many important properties of a superconductor. Starting from first principles, we present here a complete analysis of possible symmetries of the superconducting gap function E g (k) at the Fermi surface in high-T c layered superconductors with either a simple orthorhombic or a tetragonal unit cell. This is done within the framework of Gorkov close-quote s mean-field theory of superconductivity in the so-called open-quotes layer representationclose quotes introduced by us earlier. For N conducting cuprate layers, J=1,2,hor-ellipsis,N, in each unit cell, the spin-singlet order parameters Δ JJ (k) can be expanded in terms of possible basis functions of all the irreducible representations relevant to layered crystals, which are obtained here. In layered materials, the symmetry is restricted to the translational lattice periodicity in the direction perpendicular to the layers and the residual point group and translational symmetries for the two-dimensional unit cell in each layer of the three-dimensional unit cell. We derive an exact general relation to determine different branches of the energy gap function E g (k) at the Fermi surface in terms of Δ JJ (k), which include both intralayer and interlayer order parameters. For N=2, we also obtain an exact expression for quasiparticle energies E p (k), p=1,2, in the superconducting state in the presence of intralayer and complex interlayer order parameters as well as complex tunneling matrix elements between the two layers in the unit cell, which need not be equivalent. The form of the possible basis functions are also listed in terms of cylindrical coordinates k t ,φ,k z to take advantage of the orthogonality of functions with respect to φ integrations. (Abstract Truncated)

  9. The effect of long annealing on Pb-doped high-Tc Bi-Sr-Ca-Cu-O systems

    Energy Technology Data Exchange (ETDEWEB)

    Chandra, S.; Agnihotry, S.A.; Asthana, P.; Nagpal, K.C.; Saini, K.K.; Chanderkant; Sharma, C.P.; Ekbote, S.N. (National Physical Lab., New Delhi (India))

    1991-01-16

    The lead doped Bi based copper oxide high-Tc superconductors with different nominal compositions and with different annealing time periods are studied. The highest Tc (zero) achieved is 112 K in bulk phase 2223. The varying intensity of the low angle line at 2{theta}{approx equal}4.7deg suggests the gradual formation of the high-Tc phase due to the long annealing of nearly 200 to 250 h. It is also found that the high-Tc phase starts degrading after 250 h of annealing and Tc reduces. The distortion of the 2223 phase is suggested by the broadening of different XRD peaks, also the SEM studies support the above contention. The EDAX studies show no presence of Pb in the crystallites. (orig.).

  10. Superconductors, analysis and applications, with special reference to the utilisation of bulk (Re)BCO materials

    Energy Technology Data Exchange (ETDEWEB)

    Coombs, T.A., E-mail: tac1000@cam.ac.u [University of Cambridge, Department of Engineering, Trumpington Street, Cambridge CB2 1PZ (United Kingdom)

    2010-11-01

    The Electrical Power and Energy Conversion (EPEC) superconductivity group at Cambridge University has been working on the application of superconductivity to large scale devices. This work is taking place over a range of areas which cover FCLs, motors and generators, SMES, accelerator magnets and MRI. The research is underpinned by advanced modelling techniques using both pure Critical State models and E-J models to analyse the behaviour of the superconductors. As part of the device design we are concentrating on the analysis of AC losses in complicated geometries such as are found in motor windings and the magnetisation of bulk superconductors to enable their full potential to be realised. We are interested in the full range of high-temperature superconductors and have measured and predicted the performance of YBCO, MgB{sub 2} and BSCCO at a range of temperatures and in wire, tape and bulk forms. This paper concentrates on recent work which includes: modelling of coils using formulations based on H and A. A critical state model for the analysis of coils in SMES; crossed field effects in bulk superconductors; a magnetic model together with experimental results which explain and describe the method of flux pumping whereby a bulk superconductor can be magnetised to a high flux density using a repeatedly applied field of low flux density and finally a new configuration for MRI magnets

  11. Preparation and physical properties of polycrystalline (Bi1-xPbx)2Sr2Ca2Cu3Oy high Tc superconductors

    International Nuclear Information System (INIS)

    Awan, M.S.; Maqsood, M.; Mirza, S.A.; Yousaf, M.; Maqsood, A.

    1995-01-01

    (Bi 1-x Pb x ) 2 Sr 2 Ca 2 Cu 3 O y (x = 0.3) high critical transition temperature (T c ) superconductors are synthesized by the solid-state reaction method in polycrystalline form. X-ray diffraction (XRD) studies, direct current (dc) electrical resistivity measurements, scanning electron microscopic (SEM) studies, critical current density measurements and zero-field alternating current (ac) susceptibility measurements are performed to investigate the physical changes, structural changes, and magnetic behavior of the superconducting samples. X-ray diffraction studies show that a high T c phase exists with orthorhombic symmetry in the specimen. According to the XRD data, the lattice parameters of the high T c phase were determined as a = 0.537(1) nm, b = 0.539(1) nm, and c = 3.70(1) nm. The compound exhibits a superconducting transition at 106 ± 1 K for zero resistance. The ac susceptibility measurements in zero field confirm the dc electrical resistivity results; hence both support the XRD results. The particle size and structural changes as a function of the cold-pressing and aging effect are also reported

  12. Effect of particle size and particle size distribution on physical characteristics, morphology and crystal strucutre of explosively compacted high-Tc superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kotsis, I.; Enisz, M.; Oravetz, D. [Univ. of Veszprem (Hungary)] [and others

    1994-12-31

    A superconductor, of composition Y(Ba,K,Na){sub 2}Cu{sub 3}O{sub x}/F{sub y} and a composite, of composition Y(Ba,K,Na){sub 2}Cu{sub 3}O{sub x}/F{sub y}+Ag, with changing K, Na and F content, but a constant silver content (Ag=10 mass per cent) was prepared using a single heat treatment. The resulting material was ground in a corundum lined mill, separated to particle size fractions of 0-40 {mu}m, 0-63 {mu}m and 63-900 {mu}m and explosively compacted, using an explosive pressure of 10{sup 4} MPa and a subsequent heat treatment. Best results were obtained with the 63-900 {mu}m fraction of composition Y(Ba{sub 1,95}K{sub 0,01})Cu{sub 3}O{sub x}F{sub 0,05}/Ag: porosity <0.01 cm{sup 3}/g and current density 2800 A/cm{sup 2} at 77 K.

  13. Project of RE123 bulk superconductors fabrication in a microgravity environment; Bishojuryokuka chodensotai seizo purojekuto

    Energy Technology Data Exchange (ETDEWEB)

    Sakai, N; Murakami, M [International Superconductivity Technology Center, Tokyo (Japan); Shisa, A [Ishikawajima-Harima Heavy Industries Co., Ltd., Toky o(Japan); Hirata, H [Institute for Unmanned Space Experiment Free Flyer, Tokyo (Japan)

    1999-11-25

    Large single-grain bulk rare earth element (RE)-Ba-Cu-O superconductors can be used for various applications such magnetic bearings, load trapped field magnets. The magnetic field generated by bulk RE-Ba-Cu-O superconductors is proportional to its radius, however, the growth of a large single-grain bulk with good quality is difficult due to contamination from the substrate or the crucible and also due to liquid loss. Such problems can be solved by growing RE-Cu-O bulk in a microgravity environment, where the bulk can be supported by a seed crystal alone during crystal growth. Such experiments will be conducted in the Unmanned Space Experiment Recovery System (USERS) project. In this paper, the experiment plan and the present status of the system development are reported. (author)

  14. Infrared studies of the superconducting energy gap and normal-state dynamics of the high-Tc superconductor YBa2Cu3O7

    International Nuclear Information System (INIS)

    Schlesinger, Z.; Collins, R.T.; Holtzberg, F.; Feild, C.; Koren, G.; Gupta, A.

    1990-01-01

    A detailed study of infrared properties (reflectivity, conductivity, and dielectric response), emphasizing reproducible results from fully oxygenated YBa 2 Cu 3 O 7 crystals (T c congruent 93 K) and films, is presented. The extrapolated values of σ 1 (ω) at low frequency are roughly consistent with the measured temperature-dependent dc resistivity. Although not well understood, this infrared conductivity can be interpreted in terms of a frequency-dependent scattering rate of ∼kT+ℎω, with a low-frequency mass enhancement of roughly 2 to 4 associated with a carrier-spin related interaction. Infrared measurements polarized along the c axis suggest a conductivity anisotropy of roughly 40:1 near T c in the normal state. In the superconducting state an energy scale of 2Δ c congruent 3kT c is suggested by c-axis polarized measurements, while a much larger characteristic energy of 2Δ a-b congruent 8kT c is evident in the (a-b)-plane conductivity. From the area missing from the conductivity up to this very large gap, a reasonable estimate (congruent 1700 A) for the (a-b)-plane penetration depth is obtained. Evidence for non-BCS temperature dependence, strong pair breaking scattering, and possible fluctuation effects is discussed. A comparison to infrared data from Bi 2 Sr 2 CaCu 2 O 8-y shows a similarly large energy scale, 2Δ a-b congruent 8kT c ; for the cubic Ba 0.6 K 0.4 BiO 3 superconductor a more conventional energy scale, 2Δ congruent 4kT c is observed

  15. Concepts for using trapped-flux bulk high-temperature superconductor in motors and generators

    International Nuclear Information System (INIS)

    Hull, John R; Strasik, Michael

    2010-01-01

    We review previous concepts for using bulk high-temperature superconductors (HTSs) in motors and generators and discuss methods for using trapped-flux (TF) HTSs in motors and generators that have been recently investigated in our laboratory. We examine the expected performance of a brushless motor/generator that uses TF bulk HTSs to provide magnetomotive force, where the stator windings are used to create the TF. A key feature is the use of dysprosium for the stator and rotor cores.

  16. Clean bulk YBaCuO superconductors doped by paramagnetic ions of Sm and Yb

    Czech Academy of Sciences Publication Activity Database

    Jirsa, Miloš; Volochová, D.; Kováč, J.; Diko, P.

    2017-01-01

    Roč. 131, č. 4 (2017), s. 1027-1029 ISSN 0587-4246 Institutional support: RVO:68378271 Keywords : YBaCuO * bulk superconductors * paramagnetic ions * microstructure * vortex pinning Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 0.469, year: 2016

  17. The effect of Sm addition on the microstructure and superconducting properties of YBCO bulk superconductors

    Czech Academy of Sciences Publication Activity Database

    Volochová, D.; Diko, P.; Piovarči, S.; Antal, V.; Kováč, J.; Jirsa, Miloš

    2017-01-01

    Roč. 131, č. 4 (2017), s. 1009-1011 ISSN 0587-4246 Institutional support: RVO:68378271 Keywords : YBaCuO * bulk superconductors * paramagnetic ions * microstructure * vortex pinning Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 0.469, year: 2016

  18. Bulk viscosity of spin-one color superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Sa' d, Basil A.

    2009-08-27

    The bulk viscosity of several quark matter phases is calculated. It is found that the effect of color superconductivity is not trivial, it may suppress, or enhance the bulk viscosity depending on the critical temperature and the temperature at which the bulk viscosity is calculated. Also, is it found that the effect of neutrino-emitting Urca processes cannot be neglected in the consideration of the bulk viscosity of strange quark matter. The results for the bulk viscosity of strange quark matter are used to calculate the r-mode instability window of quark stars with several possible phases. It is shown that each possible phase has a different structure for the r-mode instability window. (orig.)

  19. Bulk viscosity of spin-one color superconductors

    International Nuclear Information System (INIS)

    Sa'd, Basil A.

    2009-01-01

    The bulk viscosity of several quark matter phases is calculated. It is found that the effect of color superconductivity is not trivial, it may suppress, or enhance the bulk viscosity depending on the critical temperature and the temperature at which the bulk viscosity is calculated. Also, is it found that the effect of neutrino-emitting Urca processes cannot be neglected in the consideration of the bulk viscosity of strange quark matter. The results for the bulk viscosity of strange quark matter are used to calculate the r-mode instability window of quark stars with several possible phases. It is shown that each possible phase has a different structure for the r-mode instability window. (orig.)

  20. A superconducting conveyer system using multiple bulk Y-Ba-Cu-O superconductors and permanent magnets

    Science.gov (United States)

    Kinoshita, T.; Koshizuka, N.; Nagashima, K.; Murakami, M.

    Developments of non-contact superconducting devices like superconducting magnetic levitation transfer and superconducting flywheel energy storage system have been performed based on the interactions between bulk Y-Ba-Cu-O superconductors and permanent magnets, in that the superconductors can stably be levitated without any active control. The performances of noncontact superconducting devices are dependent on the interaction forces like attractive forces and stiffness. In the present study, we constructed a non-contact conveyer for which the guide rails were prepared by attaching many Fe-Nd-B magnets onto an iron base plate. Along the translational direction, all the magnets were arranged as to face the same pole, and furthermore their inter-distance was made as small as possible. The guide rail has three magnet rows, for which the magnets were glued on the iron plate such that adjacent magnet rows have opposite poles like NSN. At the center row, the magnetic field at zero gap reached 0.61T, while the field strengths of two rows on the side edges were only 0.48T due to magnetic interactions among permanent magnets. We then prepared a cryogenic box made with FRP that can store several bulk Y-Ba-Cu-O superconductors 25 mm in diameter cooled by liquid nitrogen. It was found that the levitation forces and stiffness increased with increasing the number of bulk superconductors installed in the box, although the levitation force per unit bulk were almost the same. We also confirmed that these forces are dependent on the configuration of bulk superconductors.

  1. New method for introducing nanometer flux pinning centers into single domain YBCO bulk superconductors

    International Nuclear Information System (INIS)

    Yang, W.M.; Wang, Miao

    2013-01-01

    Highlights: • Single domain YBCO bulks with Bi 2 O 3 additions fabricated by TSIG process. • Nanoscale Y 2 Ba 4 CuBiOx(YBi2411) particles introduced by Bi 2 O 3 additions. • The YBi2411 particles are about 150 nm, can act as effective flux pinning centers. • The optimal addition of Bi 2 O 3 is 0.7wt% to achieve higher levitation force. • The result is helpful to improve the quality of REBCO bulk superconductors. -- Abstract: Single domain YBCO superconductors with different additions of Bi 2 O 3 have been fabricated by top seeded infiltration and growth process (TSIG). The effect of Bi 2 O 3 additions on the growth morphology, microstructure and levitation force of the YBCO bulk superconductor has been investigated. The results indicate that single domain YBCO superconductors can be fabricated with the additions of Bi 2 O 3 less than 2 wt%; Bi 2 O 3 can be reacted with Y 2 BaCuO 5 and liquid phase and finally form Y 2 Ba 4 CuBiO x (YBi2411) nanoscale particles; the size of the YBi2411 particles is about 100 nm, which can act as effective flux pinning centers. It is also found that the levitation force of single domain YBCO bulks is increasing from 13 N to 34 N and decreasing to 11 N with the increasing of Bi 2 O 3 addition from 0.1 wt% to 0.7 wt% and 2 wt%. This result is helpful for us to improve the physical properties of REBCO bulk superconductors

  2. Gap-related trapped magnetic flux dependence between single and combined bulk superconductors

    Science.gov (United States)

    Deng, Z.; Miki, M.; Felder, B.; Tsuzuki, K.; Shinohara, N.; Uetake, T.; Izumi, M.

    2011-05-01

    Aiming at examining the trapped-flux dependence between single and combined bulk superconductors for field-pole applications, three rectangular Y 1.65Ba 2Cu 3O 7-x (YBCO) bulks with a possibly compact combination were employed to investigate the trapped-flux characteristics of single and combined bulks with a field-cooling magnetization (FCM) method. A gap-related dependence was found between them. At lower gaps of 1 mm and 5 mm, the peak trapped fields and total magnetic flux of combined bulks are both smaller than the additive values of each single bulk, which can be ascribed to the demagnetization influences of the field around the bulk generated by the adjacent ones. While, at larger gaps like 10 mm, the situation becomes reversed. The combined bulks can attain bigger peak trapped fields as well as total magnetic flux, which indicates that the magnetic field by the bulk combination can reach higher gaps, thanks to the bigger magnetic energy compared with the single bulk. The presented results show that, on one hand, it is possible to estimate the total trapped magnetic flux of combined bulks by an approximate additive method of each single bulk while considering a demagnetization factor; on the other hand, it also means that the performance of combined bulks will be superior to the addition of each single bulk at larger gaps, thus preferable for large-scaled magnet applications.

  3. Transport current anisotropy in oriented grained bulk YBa2Cu3O(x) superconductor

    International Nuclear Information System (INIS)

    Selvamanickam, V.; Salama, K.

    1990-01-01

    The anisotropy in transport current density has been studied on bulk YBa2Cu3O(x) superconductor. The transport current density measurements were performed on oriented grained YBa2Cu3O(x) superconductor with the current aligned at different angles to the a-b plane. The angular dependence of Jc shows a rapid drop when the transport current is misaligned from the a-b plane at small angles and then a slow decrease at higher angles. An anisotropy ratio of about 25 is observed at 77 K and zero field between the Jc along a-b plane and that perpendicular to the plane. 15 refs

  4. Transport current anisotropy in oriented grained bulk YBa2Cu3Ox superconductor

    International Nuclear Information System (INIS)

    Selvamanickam, V.; Salama, K.

    1990-01-01

    The anisotropy in transport current density has been studied on bulk YBa 2 Cu 3 O x superconductor. The transport current density measurements were performed on oriented grained YBa 2 Cu 3 O x superconductor with the current aligned at different angles to the a endash b plane. The angular dependence of J c shows a rapid drop when the transport current is misaligned from the a endash b plane at small angles and then a slow decrease at higher angles. An anisotropy ratio of about 25 is observed at 77 K and zero field between the J c along a endash b plane and that perpendicular to the plane

  5. Bulk electronic state of high-Tc cuprate La2-xSrxCuO4 observed by high-energy angle integrated and resolved photoemission spectroscopy

    International Nuclear Information System (INIS)

    Kasai, S.; Sekiyama, A.; Tsunekawa, M.; Ernst, P.T.; Shigemoto, A.; Yamasaki, A.; Irizawa, A.; Imada, S.; Sing, M.; Muro, T.; Sasagawa, T.; Takagi, H.; Suga, S.

    2005-01-01

    The high-energy core-level photoemission spectroscopy (PES) and angle-resolved photoemission spectroscopy (ARPES) measurements have been performed for La 2-x Sr x CuO 4 (LSCO). Polar-angle dependence of the Cu 2p core-level PES has revealed a discrepancy between bulk and surface. We have observed by the high-energy ARPES that the Fermi surface of LSCO with x=0.16 is electron-like, in contrast to previous low-energy ARPES results

  6. Motion stability of the magnetic levitation and suspension with YBa2Cu3O7-x high-Tc superconducting bulks and NdFeB magnets

    Science.gov (United States)

    Li, Jipeng; Zheng, Jun; Huang, Huan; Li, Yanxing; Li, Haitao; Deng, Zigang

    2017-10-01

    The flux pinning effect of YBa2Cu3O7-x high temperature superconducting (HTS) bulk can achieve self-stable levitation over a permanent magnet or magnet array. Devices based on this phenomenon have been widely developed. However, the self-stable flux pinning effect is not unconditional, under disturbances, for example. To disclose the roots of this amazing self-stable levitation phenomenon in theory, mathematical and mechanical calculations using Lyapunov's stability theorem and the Hurwitz criterion were performed under the conditions of magnetic levitation and suspension of HTS bulk near permanent magnets in Halbach array. It is found that the whole dynamical system, in the case of levitation, has only one equilibrium solution, and the singular point is a stable focus. In the general case of suspension, the system has two singular points: one is a stable focus, and the other is an unstable saddle. With the variation of suspension force, the two first-order singular points mentioned earlier will get closer and closer, and finally degenerate to a high-order singular point, which means the stable region gets smaller and smaller, and finally vanishes. According to the center manifold theorem, the high-order singular point is unstable. With the interaction force varying, the HTS suspension dynamical system undergoes a saddle-node bifurcation. Moreover, a deficient damping can also decrease the stable region. These findings, together with existing experiments, could enlighten the improvement of HTS devices with strong anti-interference ability.

  7. Transport properties of high-temperature superconductors: Surface vs bulk effect

    International Nuclear Information System (INIS)

    Burlachkov, L.; Koshelev, A.E.; Vinokur, V.M.

    1996-01-01

    We investigate surface-related transport properties of high-temperature superconductors. We find the mean vortex velocity under applied transport current determined by the activation energies for vortex penetration and exit through the Bean-Livingston barrier. We determine the current distribution between the surfaces of superconductor and the field and current dependencies of the transport activation energies. For a three-dimensional superconductor the transport activation energy, U s 3D , is found to decrease with the external field, H, and transport current, J, as U s 3D ∝H -1/2 and U s 3D ∝J -1/2 , respectively. In the quasi-two-dimensional compounds, U s 2D decays logarithmically with field and current. The interplay between the surface and the bulk contributions to the transport properties, such as current-voltage characteristics, is discussed. copyright 1996 The American Physical Society

  8. Dielectric response in high Tc superconductors

    International Nuclear Information System (INIS)

    Lopez-Aguilar, F.; Costa-Quintana, J.; Febrero, F.; Aurell, M.T.; Sanchez, A.; Munoz, J.S.; Balle, S.

    1989-01-01

    The random phase approximation integral equation is solved for obtaining the dynamically screened interaction between d electrons (W d (ω)), p electrons (W p (ω)) and p/d electrons (W pd (ω)). Some characteristic divergences of this last interaction correspond to the plasmon frequencies which one can relate with the effective masses of the p and d electrons close to E F by means of the relation ω p1 /ω p2 = (m 2 /m 1 ) 1/2 . Another feature of this W pd (ω) interaction is the attractive character for low frequencies. The lowest frequency for which ε pd = O decreases when the localization of states close to E F arising from the x 2 - y 2 symmetry increases

  9. Dielectric response in high Tc superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Lopez-Aguilar, F.; Costa-Quintana, J.; Febrero, F.; Aurell, M.T.; Sanchez, A.; Munoz, J.S. (Dept. de Fisica, Grupo de Electromagnetismo, Univ. Autonoma de Barcelona (Spain)); Balle, S. (Dept. de Fisica, Univ. de les Illes Balears, Palma de Mallorca (Spain))

    1989-12-01

    The random phase approximation integral equation is solved for obtaining the dynamically screened interaction between d electrons (W{sub d}({omega})), p electrons (W{sub p}({omega})) and p/d electrons (W{sub pd}({omega})). Some characteristic divergences of this last interaction correspond to the plasmon frequencies which one can relate with the effective masses of the p and d electrons close to E{sub F} by means of the relation {omega}{sub p1}/{omega}{sub p2} = (m{sub 2}/m{sub 1}){sup 1/2}. Another feature of this W{sub pd}({omega}) interaction is the attractive character for low frequencies. The lowest frequency for which {epsilon}{sub pd} = 0 decreases when the localization of states close to E{sub F} arising from the x{sup 2}-y{sup 2} symmetry increases. (orig.).

  10. High Tc superconductor-gallate crystal structures

    International Nuclear Information System (INIS)

    Gallagher, W.J.; Giess, E.A.; Gupta, A.; Laibowitz, R.B.; O'Sullivan, E.J.; Sandstrom, R.L.

    1990-01-01

    This patent describes a superconductive combination. It comprises a crystalline gallate layer, including a rare earth element or another element selected from the group consisting of Y, La, Bi, and Sc, or combinations of a rare earth element and at least one of the another elements. A superconductive layer thereon, the superconductive layer having a transition temperature in excess of 77 degrees K. and being an oxide material having Cu-O planes whose Cu and O atoms align with Ga and O atoms in the gallate layer

  11. Slip processing of high Tc superconductors

    International Nuclear Information System (INIS)

    Sinha, R.K.; Sinha, R.K.

    1991-01-01

    Slip-processing technique has been used to fabricate tapes and alumina-supported films of superconducting YBa 2 Cu 3 Osub(7-x). Good densification and connectivity are revealed by scanning electron microscopy. Both the tape and film show superconductivity well above the liquid nitrogen temperature with a transition range of 3deg and 5degK respectively. (author). 10 refs., 4 figs

  12. Electrochemistry of high-tc superconductors

    International Nuclear Information System (INIS)

    Petrij, O.A.; Tsirlina, G.A.

    1993-01-01

    The review deals with the problems of formation of a new section in modern electrochemistry related to various electrochemical aspects of high-temperature superconductivity. Specific properties of multicomponent oxides as electrode materials are pointed out. The data of experimental works on the study of degradation of superconducting ceramics, electroanalysis of complex oxide systems, electric deposition of metals and polymer films upon them are described. Special attention is paid to electrochemical approaches to electrosynthesis of films, possessing high-temperature superconductivity

  13. Anisotropic flux pinning in high Tc superconductors

    International Nuclear Information System (INIS)

    Kolesnik, S.; Igalson, J.; Skoskiewicz, T.; Szymczak, R.; Baran, M.; Pytel, K.; Pytel, B.

    1995-01-01

    In this paper we present a comparison of the results of FC magnetization measurements on several Pb-Sr-(Y,Ca)-Cu-O crystals representing various levels of flux pinning. The pinning centers in our crystals have been set up during the crystal growth process or introduced by neutron irradiation. Some possible explanations of the observed effects, including surface barrier, flux-center distribution and sample-shape effects, are discussed. ((orig.))

  14. Gap-related trapped magnetic flux dependence between single and combined bulk superconductors

    International Nuclear Information System (INIS)

    Deng, Z.; Miki, M.; Felder, B.; Tsuzuki, K.; Shinohara, N.; Uetake, T.; Izumi, M.

    2011-01-01

    Highlights: → Rectangular YBCO bulks to realize a compact combination. → The gap effect was added to consider in the trapped flux density mapping. → The trapped-flux dependence between single and combined bulks is gap related. → It is possible to estimate the total magnetic flux of bulk combinations. - Abstract: Aiming at examining the trapped-flux dependence between single and combined bulk superconductors for field-pole applications, three rectangular Y 1.65 Ba 2 Cu 3 O 7-x (YBCO) bulks with a possibly compact combination were employed to investigate the trapped-flux characteristics of single and combined bulks with a field-cooling magnetization (FCM) method. A gap-related dependence was found between them. At lower gaps of 1 mm and 5 mm, the peak trapped fields and total magnetic flux of combined bulks are both smaller than the additive values of each single bulk, which can be ascribed to the demagnetization influences of the field around the bulk generated by the adjacent ones. While, at larger gaps like 10 mm, the situation becomes reversed. The combined bulks can attain bigger peak trapped fields as well as total magnetic flux, which indicates that the magnetic field by the bulk combination can reach higher gaps, thanks to the bigger magnetic energy compared with the single bulk. The presented results show that, on one hand, it is possible to estimate the total trapped magnetic flux of combined bulks by an approximate additive method of each single bulk while considering a demagnetization factor; on the other hand, it also means that the performance of combined bulks will be superior to the addition of each single bulk at larger gaps, thus preferable for large-scaled magnet applications.

  15. Gap-related trapped magnetic flux dependence between single and combined bulk superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Z., E-mail: zgdeng@gmail.co [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, Tokyo 135-8533 (Japan); Miki, M.; Felder, B.; Tsuzuki, K.; Shinohara, N.; Uetake, T.; Izumi, M. [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, Tokyo 135-8533 (Japan)

    2011-05-15

    Highlights: {yields} Rectangular YBCO bulks to realize a compact combination. {yields} The gap effect was added to consider in the trapped flux density mapping. {yields} The trapped-flux dependence between single and combined bulks is gap related. {yields} It is possible to estimate the total magnetic flux of bulk combinations. - Abstract: Aiming at examining the trapped-flux dependence between single and combined bulk superconductors for field-pole applications, three rectangular Y{sub 1.65}Ba{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) bulks with a possibly compact combination were employed to investigate the trapped-flux characteristics of single and combined bulks with a field-cooling magnetization (FCM) method. A gap-related dependence was found between them. At lower gaps of 1 mm and 5 mm, the peak trapped fields and total magnetic flux of combined bulks are both smaller than the additive values of each single bulk, which can be ascribed to the demagnetization influences of the field around the bulk generated by the adjacent ones. While, at larger gaps like 10 mm, the situation becomes reversed. The combined bulks can attain bigger peak trapped fields as well as total magnetic flux, which indicates that the magnetic field by the bulk combination can reach higher gaps, thanks to the bigger magnetic energy compared with the single bulk. The presented results show that, on one hand, it is possible to estimate the total trapped magnetic flux of combined bulks by an approximate additive method of each single bulk while considering a demagnetization factor; on the other hand, it also means that the performance of combined bulks will be superior to the addition of each single bulk at larger gaps, thus preferable for large-scaled magnet applications.

  16. An overview of rotating machine systems with high-temperature bulk superconductors

    Science.gov (United States)

    Zhou, Difan; Izumi, Mitsuru; Miki, Motohiro; Felder, Brice; Ida, Tetsuya; Kitano, Masahiro

    2012-10-01

    The paper contains a review of recent advancements in rotating machines with bulk high-temperature superconductors (HTS). The high critical current density of bulk HTS enables us to design rotating machines with a compact configuration in a practical scheme. The development of an axial-gap-type trapped flux synchronous rotating machine together with the systematic research works at the Tokyo University of Marine Science and Technology since 2001 are briefly introduced. Developments in bulk HTS rotating machines in other research groups are also summarized. The key issues of bulk HTS machines, including material progress of bulk HTS, in situ magnetization, and cooling together with AC loss at low-temperature operation are discussed.

  17. Oxygenation and cracking in melt-textured YBCO bulk superconductors

    International Nuclear Information System (INIS)

    Kracunovska, S; Diko, P; Litzkendorf, D; Habisreuther, T; Bierlich, J; Gawalek, W

    2005-01-01

    Microstructural changes during the oxygenation of YBCO bulks were studied. It was shown that a lower temperature of oxygenation leads to the formation of a denser structure of a/b- and c-macrocracks and causes faster and more homogeneous oxygenation of the sample. The opening of created macrocracks is the way in which the macroscopic stresses induced by macroscopic 211 particle concentration inhomogeneity are released. This is very important, because it prevents the formation of fatal c-macrocracks, which divide the sample into more domains, during cooling from oxygenation temperature or during sample performance. Oxygenation with a multistage programme causes the oxygen concentration difference between the oxygenated layer and the tetragonal matrix to be smaller, and consequently fewer macrocracks are formed. This leads to the prolongation of oxygenation times for full oxygenation and to the insufficient release of macroscopic stresses. 211 low concentration regions and pores also enhance the oxygenation rate of YBCO bulks

  18. Temperature profile evolution in quenching high-Tc ...

    Indian Academy of Sciences (India)

    Abstract. Irreversible normal zones leading to quench is an important aspect of high-temperature superconductors (HTS) in all practical applications. As a consequence of quench, transport current gets diverted to the matrix stabilizer material of the high-Tc composite and causes Joule heating till the original conditions are ...

  19. Interior seeding for the fabrication of single-grain REBCO bulk superconductors

    International Nuclear Information System (INIS)

    Kim, C-J; Park, S-D; Jun, B-H; Park, H-W

    2016-01-01

    This study presents a new seeding technique, named ‘interior seeding’ which allows the growth of a single REBCO (RE: rare-earth elements) grain in the interior of REBCO compacts. The key techniques of interior seeding are to provide appropriate open space for seeds in the interior of REBCO powder compacts to supply air or oxygen to the seeds, and to minimize the contact area between the seeds and liquid. The advantages of interior seeding are as follows: (1) simultaneous growth from the seed to the top and bottom of the REBCO compacts is possible, (2) fractions of the a-b growth sector and the a-c growth sector on the top surface can be controlled and (3) the top surfaces of the single-grain REBCO bulk superconductors are free from samarium or neodymium contamination from the used seeds. The very large single-grain Y 1.5 Ba 2 Cu 3 O 7−y (Y1.5) bulk superconductors (42 mm) were successfully fabricated using a melt growth (MG) process combined with interior seeding. Also, large-grain Y1.5 bulk superconductors (41 mm) with 〈110〉/〈110〉 and 〈100〉/〈100〉 grain junctions were fabricated using multiple interior seeding. In this paper, the detailed process of interior seeding, the development of top surface patterns and the properties of single-grain Y123 bulk superconductors fabricated using interior seeding were reported. (paper)

  20. Maximum repulsed magnetization of a bulk superconductor with low pulsed field

    International Nuclear Information System (INIS)

    Tsuchimoto, M.; Kamijo, H.; Fujimoto, H.

    2005-01-01

    Pulsed field magnetization of a bulk high-T c superconductor (HTS) is important technique especially for practical applications of a bulk superconducting magnet. Full magnetization is not obtained for low pulsed field and trapped field is decreased by reversed current in the HTS. The trapped field distribution by repulsed magnetization was previously reported in experiments with temperature control. In this study, repulsed magnetization technique with the low pulsed field is numerically analyzed under assumption of variable shielding current by the temperature control. The shielding current densities are discussed to obtain maximum trapped field by two times of low pulsed field magnetizations

  1. Melt-growth bulk superconductors and application to an axial-gap-type rotating machine

    International Nuclear Information System (INIS)

    Zhang, Yufeng; Zhou, Difan; Ida, Tetsuya; Miki, Motohiro; Izumi, Mitsuru

    2016-01-01

    The present manuscript addresses key issues in the course of our study of materials processing of bulk high-temperature superconductors, trapped flux and its application to a prototype axial-gap-type rotating machine. The TUMSAT group has conducted a series of studies since 2003 on the growth of GdBa 2 Cu 3 O 7−δ bulk material and its application in a compact low-speed high-torque rotating machine. In the stage of material growth, gaining the advantage of a large motive torque density requires large integrated flux in the motor/generators. A large grain surface might be required with sophisticated techniques for the melt-growth texture in the bulk with optimal flux pinning. In the second stage, the in situ magnetization procedure for bulk superconductors in the applied machine is a crucial part of the technology. Pulsed current excitation by using an armature copper winding has magnetized field pole bulks on the rotor. The axial-gap flux synchronous machine studied in the past decade is a condensed technology and indicates that further scientific development is required for a future compact machine to be superior to conventional ones in accordance with the cryogenic periphery and flux stabilization. (paper)

  2. Pulsed-Field Magnetization Properties of Bulk Superconductors by Employment of Vortex-Type Coils

    Science.gov (United States)

    Deng, Z.; Shinohara, N.; Miki, M.; Felder, B.; Tsuzuki, K.; Watasaki, M.; Kawabe, S.; Taguchi, R.; Izumi, M.

    Vortex-type magnetizing coils are gaining more and more attention to activate bulk superconductors in pulsed-field magnetization (PFM) studies, compared with solenoid-type ones. Following existing reports, we present experimental results of the different penetration patterns of magnetic flux between the two kinds of coils. It was found that the magnetic flux will primarily penetrate inside the bulk from the upper and lower surfaces by using vortex coils, rather than from the periphery in the case of solenoid coils. Moreover, the bulk submitted to a small pulsed-field excitation exhibits a similar field profile as the excitation field (convex or concave shape); a phenomenon named field memory effect. The use of vortex- or solenoid-type coils in PFM will pose an influence on the initial flux penetration patterns during the flux trapping processes, but both coils can finally excite the best conical trapped field shape of the bulk.

  3. Measurement of electromagnetic force between multiple bulk superconductors; Fukusu no barukutai chodendotai to eikyujishakukairo niokeru denjiryoku sokutei

    Energy Technology Data Exchange (ETDEWEB)

    Otani, T.; Murakami, M. [Superconductivity Research Laboratory, Tokyo (Japan); Nagashima, K. [Railway Technical Research Institute, Tokyo (Japan); Murayama, M. [Shikoku Ekectric Power Co., Inc., Kagawa (Japan)

    1999-11-25

    The electromagnetic force (EMF) that is exhibited by the interaction between bulk superconductors and permanent magnets is used for magnetic levitation devices. To facilitate such applications, it is necessary to enhance the EMF. We measured the EMF for Y-Ba-Cu-O superconductors with different shapes and dimensions by varying the structure of disk magnets such as their thickness and the number of poles. The EMF is strongly dependent on the magnet structure as long as permanent magnets and good quality bulk superconductors are used. Thus, for the design of practical devices, it is important to optimize the magnet structure. (author)

  4. Maglev performance of a double-layer bulk high temperature superconductor above a permanent magnet guideway

    International Nuclear Information System (INIS)

    Deng, Z; Wang, J; Zheng, J; Lin, Q; Zhang, Y; Wang, S

    2009-01-01

    In order to improve the performance of the present high temperature superconducting (HTS) maglev vehicle system, the maglev performance of single- and double-layer bulk high temperature superconductors (HTSC) was investigated above a permanent magnet guideway (PMG). It is found that the maglev performance of a double-layer bulk HTSC is not a simple addition of each layer's levitation and guidance force. Moreover, the applied magnetic field at the position of the upper layer bulk HTSC is not completely shielded by the lower layer bulk HTSC either. 53.5% of the levitation force and 27.5% of the guidance force of the upper layer bulk HTSC are excited in the double-layer bulk HTSC arrangement in the applied field-cooling condition and working gap, bringing a corresponding improvement of 16.9% and 8.8% to the conventional single-layer bulk HTSC. The present research implies that the cost performance of upper layer bulk HTSC is a little low for the whole HTS maglev system.

  5. Maglev performance of a double-layer bulk high temperature superconductor above a permanent magnet guideway

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Z; Wang, J; Zheng, J; Lin, Q; Zhang, Y; Wang, S [Applied Superconductivity Laboratory, Southwest Jiaotong University, Chengdu, 610031 (China)], E-mail: asclab@asclab.cn

    2009-05-15

    In order to improve the performance of the present high temperature superconducting (HTS) maglev vehicle system, the maglev performance of single- and double-layer bulk high temperature superconductors (HTSC) was investigated above a permanent magnet guideway (PMG). It is found that the maglev performance of a double-layer bulk HTSC is not a simple addition of each layer's levitation and guidance force. Moreover, the applied magnetic field at the position of the upper layer bulk HTSC is not completely shielded by the lower layer bulk HTSC either. 53.5% of the levitation force and 27.5% of the guidance force of the upper layer bulk HTSC are excited in the double-layer bulk HTSC arrangement in the applied field-cooling condition and working gap, bringing a corresponding improvement of 16.9% and 8.8% to the conventional single-layer bulk HTSC. The present research implies that the cost performance of upper layer bulk HTSC is a little low for the whole HTS maglev system.

  6. Influence of grain boundary connectivity on the trapped magnetic flux of multi-seeded bulk superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Z., E-mail: zgdeng@gmail.com [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, Tokyo 135-8533 (Japan); Miki, M.; Felder, B.; Tsuzuki, K.; Shinohara, N.; Hara, S.; Uetake, T.; Izumi, M. [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, Tokyo 135-8533 (Japan)

    2011-09-15

    Four different performance multi-seeded YBCO bulks as representatives. A coupling ratio to reflect the coupling quality of GBs inside multi-seeded bulks. An averaged trapped magnetic flux density parameter was introduced. The top-seeded melt-growth process with multi-seeding technique provides a promising way to fabricate large-sized bulk superconductors in an economical way. To understand the essential characteristics of the multi-seeded bulks, the paper reports the influence of the grain boundary (GB) coupling or connectivity on the total trapped magnetic flux. The coupling ratio, the lowest trapped flux density in the GB area to the averaged top value of the two neighboring peak trapped fields, is introduced to reflect the coupling quality of GBs inside a multi-seeded bulk. By the trapped flux density measurement of four different performance multi-seeded YBCO bulk samples as representatives, it was found that the GB coupling plays an important role for the improvement of the total trapped magnetic flux; moreover, somewhat more significant than the widely used parameter of the peak trapped fields to evaluate the physical performance of bulk samples. This characteristic is different with the case of the well-grown single-grain bulks.

  7. High current density in bulk YBa2Cu3O/sub x/ superconductor

    International Nuclear Information System (INIS)

    Salama, K.; Selvamanickam, V.; Gao, L.; Sun, K.

    1989-01-01

    A liquid phase processing method for the fabrication of bulk YBa 2 Cu 3 O/sub x/ superconductors with large current carrying capacity has been developed. Slow cooling through the peritectic transformation (1030--980 degree C) has been shown to control the microstructure of these superconductors. A cooling rate of 1 degree C/h in this temperature range has yielded a microstructure with long plate type, thick grains oriented over a wide area. Current density up to 18 500 A/cm 2 has been obtained by continuous direct current measurements and in excess of 62 000 A/cm 2 with pulse current of 10 ms duration and 75 000 A/cm 2 using 1 ms pulse. The strong magnetic field dependence observed in sintered bulk 1-2-3 superconductors is also minimized to a large extent where a current density in excess of 37 000 A/cm 2 is obtained in a field of 6000 G

  8. Doping-Induced Isotopic Mg11B2 Bulk Superconductor for Fusion Application

    Directory of Open Access Journals (Sweden)

    Qi Cai

    2017-03-01

    Full Text Available Superconducting wires are widely used for fabricating magnetic coils in fusion reactors. Superconducting magnet system represents a key determinant of the thermal efficiency and the construction/operating costs of such a reactor. In consideration of the stability of 11B against fast neutron irradiation and its lower induced radioactivation properties, MgB2 superconductor with 11B serving as the boron source is an alternative candidate for use in fusion reactors with a severe high neutron flux environment. In the present work, the glycine-doped Mg11B2 bulk superconductor was synthesized from isotopic 11B powder to enhance the high field properties. The critical current density was enhanced (103 A·cm−2 at 20 K and 5 T over the entire field in contrast with the sample prepared from natural boron.

  9. Surface flux density distribution characteristics of bulk high-T{sub c} superconductor in external magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Torii, S.; Yuasa, K

    2004-10-01

    Various magnetic levitation systems using oxide superconductors are developed as strong pinning forces are obtained in melt-processed bulk. However, the trapped flux of superconductor is moved by flux creep and fluctuating magnetic field. Therefore, to examine the internal condition of superconductor, the authors measure the dynamic surface flux density distribution of YBCO bulk. Flux density measurement system has a structure with the air-core coil and the Hall sensors. Ten Hall sensors are arranged in series. The YBCO bulk, which has 25 mm diameter and 13 mm thickness, is field cooled by liquid nitrogen. After that, magnetic field is changed by the air-core coil. This paper describes about the measured results of flux density distribution of YBCO bulk in the various frequencies of air-core coils currents.

  10. Magnetic levitation and its application for education devices based on YBCO bulk superconductors

    International Nuclear Information System (INIS)

    Yang, W.M.; Chao, X.X.; Guo, F.X.; Li, J.W.; Chen, S.L.

    2013-01-01

    Highlights: • A small superconducting maglev propeller system has been designed and constructed based on YBCO bulk superconductors. • Several small maglev vehicle models have been designed and constructed based on YBCO bulk superconductors. • The models can be used as experimental or demonstration devices for the magnetic levitation applications. -- Abstract: A small superconducting maglev propeller system, a small spacecraft model suspending and moving around a terrestrial globe, several small maglev vehicle models and a magnetic circuit converter have been designed and constructed. The track was paved by NdFeB magnets, the arrangement of the magnets made us easy to get a uniform distribution of magnetic field along the length direction of the track and a high magnetic field gradient in the lateral direction. When the YBCO bulks mounted inside the vehicle models or spacecraft model was field cooled to LN 2 temperature at a certain distance away from the track, they could be automatically floating over and moving along the track without any obvious friction. The models can be used as experimental or demonstration devices for the magnetic levitation applications

  11. Enhancement of magnetic coupling between permanent magnets and bulk superconductors through iron embedding

    International Nuclear Information System (INIS)

    Seki, H.; Kurabayashi, H.; Suzuki, A.; Ikeda, M.; Akiyama, S.; Murakami, M.

    2009-01-01

    Magnetic torque can be transferred without contact through the coupling of permanent magnets (PM) and bulk superconductors (BSC). For this purpose, permanent magnets should have multiple pole configuration like NSNS. The magnitude of the transferable torque depends on the field strength and the gap between PM and BSC. It was found that the torque decays quickly with the gap. In order to enhance the strength of transferable magnetic torque, we prepared bulk Y-Ba-Cu-O superconductors for which Fe bars are embedded. Holes about 1 mm in diameter were mechanically drilled into bulk Y-Ba-Cu-O, and Fe bars about 0.9 mm in diameter were inserted followed by impregnation of Bi-Pb-Sn alloys with low melting points. The composite of Y-Ba-Cu-O and Fe bars attract magnetic fields generated from permanent magnet before cooling, and thereby magnetic coupling will be improved. We have found that the magnetic torque force can be greatly enhanced through iron embedding.

  12. Magnetic levitation and its application for education devices based on YBCO bulk superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Yang, W.M., E-mail: yangwm@snnu.edu.cn; Chao, X.X.; Guo, F.X.; Li, J.W.; Chen, S.L.

    2013-10-15

    Highlights: • A small superconducting maglev propeller system has been designed and constructed based on YBCO bulk superconductors. • Several small maglev vehicle models have been designed and constructed based on YBCO bulk superconductors. • The models can be used as experimental or demonstration devices for the magnetic levitation applications. -- Abstract: A small superconducting maglev propeller system, a small spacecraft model suspending and moving around a terrestrial globe, several small maglev vehicle models and a magnetic circuit converter have been designed and constructed. The track was paved by NdFeB magnets, the arrangement of the magnets made us easy to get a uniform distribution of magnetic field along the length direction of the track and a high magnetic field gradient in the lateral direction. When the YBCO bulks mounted inside the vehicle models or spacecraft model was field cooled to LN{sub 2} temperature at a certain distance away from the track, they could be automatically floating over and moving along the track without any obvious friction. The models can be used as experimental or demonstration devices for the magnetic levitation applications.

  13. Single domain YBCO/Ag bulk superconductors fabricated by seeded infiltration and growth

    International Nuclear Information System (INIS)

    Iida, K; Babu, N H; Shi, Y; Cardwell, D A; Miyazaki, T; Murakami, M; Sakai, N

    2008-01-01

    We have applied the seeded infiltration and growth (IG) technique to the processing of samples containing Ag in an attempt to fabricate Ag-doped Y-Ba-Cu-O (YBCO) bulk superconductors with enhanced mechanical properties. The IG technique has been used successfully to grow bulk Ag-doped YBCO superconductors of up to 25 mm in diameter in the form of single grains. The distribution of Ag in the parent Y-123 matrix fabricated by the IG technique is observed to be at least as uniform as that in samples grown by conventional top seeded melt growth (TSMG). Fine Y-211 particles were observed to be embedded within the Y-123 matrix for the IG processed samples, leading to a high critical current density, J c , of over 70 kA/cm 2 at 77.3 K in self-field. The distribution of Y-211 in the IG sample microstructure, however, is inhomogeneous, which leads to a variation in the spatial distribution of J c throughout the bulk matrix. A maximum-trapped field of around 0.43 T at 1.2 mm above the sample surface (i.e. including 0.7 mm for the sensor mould thickness) is observed at liquid nitrogen temperature, despite the relatively small grain size of the sample (20 mm diameter x 7 mm thickness)

  14. Evaluation of mechanical properties of Dy123 bulk superconductors by 3-point bending tests

    International Nuclear Information System (INIS)

    Katagiri, K.; Hatakeyama, Y.; Sato, T.; Kasaba, K.; Shoji, Y.; Murakami, A.; Teshima, H.; Hirano, H.

    2006-01-01

    In order to evaluate the mechanical properties, such as Young's modulus and strength, of Dy123 bulk superconductors and those with 10 wt.% Ag 2 O, we performed 3-point bending tests at room (RT) and liquid nitrogen temperatures (LNT) using specimens cut from the bulks. The Young's modulus and the bending strength increased with decrease in temperature. In the tests loading in the direction of c-axis and ones perpendicular to it, Young's moduli were almost comparable at both RT and LNT. Although the strengths for both orientations were also comparable at LNT, those at RT were different. Young's moduli loaded in the direction of c-axis for Ag 2 O added bulk specimens, 127 GPa in average at RT, were almost comparable to those without Ag 2 O, and 134 GPa at LNT, were slightly lower than those without Ag 2 O. On the other hand, the strengths at both RT and LNT were enhanced by 20% by the Ag addition. The mechanical properties of Dy123 bulks without Ag 2 O were compared with those of Y123 bulks obtained previously. The Young's modulus for loading in the direction of c-axis was slightly lower, and the strength was comparable to those in Y123 bulks, respectively

  15. Influence of grain boundary connectivity on the trapped magnetic flux of multi-seeded bulk superconductors

    Science.gov (United States)

    Deng, Z.; Miki, M.; Felder, B.; Tsuzuki, K.; Shinohara, N.; Hara, S.; Uetake, T.; Izumi, M.

    2011-09-01

    The top-seeded melt-growth process with multi-seeding technique provides a promising way to fabricate large-sized bulk superconductors in an economical way. To understand the essential characteristics of the multi-seeded bulks, the paper reports the influence of the grain boundary (GB) coupling or connectivity on the total trapped magnetic flux. The coupling ratio, the lowest trapped flux density in the GB area to the averaged top value of the two neighboring peak trapped fields, is introduced to reflect the coupling quality of GBs inside a multi-seeded bulk. By the trapped flux density measurement of four different performance multi-seeded YBCO bulk samples as representatives, it was found that the GB coupling plays an important role for the improvement of the total trapped magnetic flux; moreover, somewhat more significant than the widely used parameter of the peak trapped fields to evaluate the physical performance of bulk samples. This characteristic is different with the case of the well-grown single-grain bulks.

  16. Levitation properties of superconducting magnetic bearings using superconducting coils and bulk superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Arai, Yuuki; Seino, Hiroshi; Nagashima, Ken [Railway Technical Research Institute, 2-8-38 Hikari-cho, Kokubunji-shi, Tokyo 185-8540 (Japan)

    2010-11-15

    We have been developing a flywheel energy storage system (FESS) with 36 MJ energy capacity for a railway system with superconducting magnetic bearings (SMBs). We prepared two kinds of models using superconducting coils and bulk superconductors (SCs). One model demonstrated SMB load capacity of 20 kN and the other model proved non-contact stable levitation and non-contact rotation with SMBs. Combining these results, the feasibility of a 36 MJ energy capacity FESS with SMBs completely inside a cryostat has been confirmed. In this paper, we report the levitation properties of SMBs in these models.

  17. On the pinning performance analysis in bulk RE-123 twin-free superconductors

    Czech Academy of Sciences Publication Activity Database

    Jirsa, Miloš; Petrenko, Pavlo; Yao, X.; Muralidhar, M.

    463-465, - (2007), s. 353-356 ISSN 0921-4534. [International Symposium on Superconductivity /19./. Nagoya, 01.10.2006-03.10.2006] R&D Projects: GA MŠk 1P05ME728 Grant - others:MOST(CN) 2006CB601003; SSTC(CN) 055207077 Institutional research plan: CEZ:AV0Z10100520 Keywords : Penk effect * bulk RE-123 superconductors * pinning force scaling * pinning classification Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.079, year: 2007

  18. Levitation properties of superconducting magnetic bearings using superconducting coils and bulk superconductors

    International Nuclear Information System (INIS)

    Arai, Yuuki; Seino, Hiroshi; Nagashima, Ken

    2010-01-01

    We have been developing a flywheel energy storage system (FESS) with 36 MJ energy capacity for a railway system with superconducting magnetic bearings (SMBs). We prepared two kinds of models using superconducting coils and bulk superconductors (SCs). One model demonstrated SMB load capacity of 20 kN and the other model proved non-contact stable levitation and non-contact rotation with SMBs. Combining these results, the feasibility of a 36 MJ energy capacity FESS with SMBs completely inside a cryostat has been confirmed. In this paper, we report the levitation properties of SMBs in these models.

  19. Development of superconductor application technology

    Energy Technology Data Exchange (ETDEWEB)

    Hong, G W; Kim, C J; Lee, H G; Lee, H J; Kim, K B; Won, D Y; Jang, K I; Kwon, S C; Kim, W J; Ji, Y A; Yang, S W; Kim, W K; Park, S D; Lee, M H; Lee, D M; Park, H W; Yu, J K; Lee, I S; Kim, J J; Choi, H S; Chu, Y; Kim, Y S; Kim, D H

    1997-09-01

    Fabrication of high Tc bulk superconductor and its application, fabrication of superconducting wire for electric power device and analysis for cryogenic system were carried out for developing superconductor application technologies for electric power system. High quality YBaCuO bulk superconductor was fabricated by controlling initial powder preparation process and prototype flywheel energy storage device was designed basically. The superconducting levitation force measuring device was made to examine the property of prepared superconductor specimen. Systematic studies onthe method of starting powder preparation, mechanical fabrication process, heat treatment condition and analysis of plastic deformation were carried out to increase the stability and reproducibility of superconducting wire. A starting power with good reactivity and fine particle size was obtained by mechanical grinding, control of phase assemblage, and emulsion drying method. Ag/BSCCO tape with good cross sectional shape and Jc of 20,000 A/cm{sup 2} was fabricated by applying CIP packing procedure. Multifilamentary wire with Jc of 10,000 A/cm{sup 2} was fabricated by rolling method using square billet as starting shape. The joining of the multifilamentary wire was done by etching and pressing process and showed 50% of joining efficiency. Analysis on the heat loss in cryostat for high Tc superconducting device was carried out for optimum design of the future cryogenic system. (author). 66 refs., 104 figs.

  20. Development of superconductor application technology

    International Nuclear Information System (INIS)

    Hong, G. W.; Kim, C. J.; Lee, H. G.; Lee, H. J.; Kim, K. B.; Won, D. Y.; Jang, K. I.; Kwon, S. C.; Kim, W. J.; Ji, Y. A.; Yang, S. W.; Kim, W. K.; Park, S. D.; Lee, M. H.; Lee, D. M.; Park, H. W.; Yu, J. K.; Lee, I. S.; Kim, J. J.; Choi, H. S.; Chu, Y.; Kim, Y. S.; Kim, D. H.

    1997-09-01

    Fabrication of high Tc bulk superconductor and its application, fabrication of superconducting wire for electric power device and analysis for cryogenic system were carried out for developing superconductor application technologies for electric power system. High quality YBaCuO bulk superconductor was fabricated by controlling initial powder preparation process and prototype flywheel energy storage device was designed basically. The superconducting levitation force measuring device was made to examine the property of prepared superconductor specimen. Systematic studies onthe method of starting powder preparation, mechanical fabrication process, heat treatment condition and analysis of plastic deformation were carried out to increase the stability and reproducibility of superconducting wire. A starting power with good reactivity and fine particle size was obtained by mechanical grinding, control of phase assemblage, and emulsion drying method. Ag/BSCCO tape with good cross sectional shape and Jc of 20,000 A/cm 2 was fabricated by applying CIP packing procedure. Multifilamentary wire with Jc of 10,000 A/cm 2 was fabricated by rolling method using square billet as starting shape. The joining of the multifilamentary wire was done by etching and pressing process and showed 50% of joining efficiency. Analysis on the heat loss in cryostat for high Tc superconducting device was carried out for optimum design of the future cryogenic system. (author). 66 refs., 104 figs

  1. Mechanisms of conventional and high Tc superconductivity

    International Nuclear Information System (INIS)

    Kresin, V.L.; Morawitz, H.; Wolf, S.A.

    1993-01-01

    This book gives a careful and objective review of theories of superconductivity in traditional superconductors, organics, and high Tc cuprates. Of course, the authors do still present their own theories of cuprate superconductivity, but only in the final chapter after other possibilities have been discussed. The book should be especially useful for researchers entering the field of high Tc superconductivity. The reviews of photon mediated pairing and strong coupling theory are very welcome, since much of this material has not been reviewed since the classic 1969 volume edited by Parks. In particular the authors dispel the various myths that phonon mediated pairing leads to upper bounds on Tc. In addition to phonon mediated pairing the book discussed in detail pairing due to exchange of acoustic (demon) plasmons, excitons, or magnetic fluctuations. There have been so many diverse mechanisms based on strong correlation and large U Hubbard models that a book like this can only discuss a limited selection of the main contenders. In particular here the emphasis on Fermi liquid based models no doubt reflects the authors' own point of view. A whole chapter discusses the concepts of induced superconductivity, in the proximity effect, and its application to materials with several different electronic subsystems

  2. Development of superconducting magnetic bearing using superconducting coil and bulk superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Seino, H; Nagashima, K; Arai, Y [Railway Technical Research Institute, Hikari-cho 2-8-38, Kokubunji-shi, Tokyo (Japan)], E-mail: seino@rtri.or.jp

    2008-02-01

    The authors conducted a study on superconducting magnetic bearing, which consists of superconducting rotor and stator to apply the flywheel energy-storage system for railways. In this study, high temperature bulk superconductor (HTS bulk) was combined with superconducting coils to increase the load capacity of the bearing. In the first step of the study, the thrust rolling bearing was selected for application by using liquid nitrogen cooled HTS bulk. 60mm-diameter HTS bulks and superconducting coil which generated a high gradient of magnetic field by cusp field were adopted as a rotor and a stator for superconducting magnetic bearing, respectively. The results of the static load test and the rotation test, creep of the electromagnetic forces caused by static flux penetration and AC loss due to eccentric rotation were decreased to the level without any problems in substantial use by using two HTS bulks. In the result of verification of static load capacity, levitation force (thrust load) of 8900N or more was supportable, and stable static load capacity was obtainable when weight of 460kg was levitated.

  3. Development of superconducting magnetic bearing using superconducting coil and bulk superconductor

    International Nuclear Information System (INIS)

    Seino, H; Nagashima, K; Arai, Y

    2008-01-01

    The authors conducted a study on superconducting magnetic bearing, which consists of superconducting rotor and stator to apply the flywheel energy-storage system for railways. In this study, high temperature bulk superconductor (HTS bulk) was combined with superconducting coils to increase the load capacity of the bearing. In the first step of the study, the thrust rolling bearing was selected for application by using liquid nitrogen cooled HTS bulk. 60mm-diameter HTS bulks and superconducting coil which generated a high gradient of magnetic field by cusp field were adopted as a rotor and a stator for superconducting magnetic bearing, respectively. The results of the static load test and the rotation test, creep of the electromagnetic forces caused by static flux penetration and AC loss due to eccentric rotation were decreased to the level without any problems in substantial use by using two HTS bulks. In the result of verification of static load capacity, levitation force (thrust load) of 8900N or more was supportable, and stable static load capacity was obtainable when weight of 460kg was levitated

  4. Comparison of simulation and experiment on levitation force between GdBCO bulk superconductor and superconducting magnet

    Energy Technology Data Exchange (ETDEWEB)

    Araki, S., E-mail: satoshi@sum.sd.keio.ac.j [Department of System Design Engineering, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan); Nagashima, K.; Seino, H. [Railway Technical Research Institute, 2-8-38 Hikari-cho, Kokubunji, Tokyo 185-8540 (Japan); Murakami, T.; Sawa, K. [Department of System Design Engineering, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan)

    2009-10-15

    High temperature bulk superconductors have significant potential for various engineering applications such as a flywheel energy storage system. This system is expected to decrease the energy loss by using bulk superconductors for the bearing. Recently, the authors have developed a new superconducting magnet to realize large levitation force. In this system, the axial component of magnetic field is canceled each other but the radial component of magnetic field expects to be enhanced. Thus, it was expected that the large levitation force can be realized and its time relaxation will be decreased. And in the previous paper, the levitation force and its time relaxation were measured under the various conditions by using this new magnet. But it is difficult to consider what phenomenon has happened in the bulk from only experimental results. In addition the quantitative evaluation cannot be done only by the experimental results, for example, the influence of the magnetic field penetration and magnetic distribution around a bulk superconductor on the maximum force and so on. Thus, in this paper, the authors simulated the levitation force of bulk superconductor by using ELF/MAGIC, which is a three-dimensional electromagnetic analytical software. In the simulation the bulk was considered as a rigid body and the simulation was executed under the same conditions and model with the experiment. The distribution of magnetic field and the levitation force were obtained and discussed.

  5. Comparison of simulation and experiment on levitation force between GdBCO bulk superconductor and superconducting magnet

    International Nuclear Information System (INIS)

    Araki, S.; Nagashima, K.; Seino, H.; Murakami, T.; Sawa, K.

    2009-01-01

    High temperature bulk superconductors have significant potential for various engineering applications such as a flywheel energy storage system. This system is expected to decrease the energy loss by using bulk superconductors for the bearing. Recently, the authors have developed a new superconducting magnet to realize large levitation force. In this system, the axial component of magnetic field is canceled each other but the radial component of magnetic field expects to be enhanced. Thus, it was expected that the large levitation force can be realized and its time relaxation will be decreased. And in the previous paper, the levitation force and its time relaxation were measured under the various conditions by using this new magnet. But it is difficult to consider what phenomenon has happened in the bulk from only experimental results. In addition the quantitative evaluation cannot be done only by the experimental results, for example, the influence of the magnetic field penetration and magnetic distribution around a bulk superconductor on the maximum force and so on. Thus, in this paper, the authors simulated the levitation force of bulk superconductor by using ELF/MAGIC, which is a three-dimensional electromagnetic analytical software. In the simulation the bulk was considered as a rigid body and the simulation was executed under the same conditions and model with the experiment. The distribution of magnetic field and the levitation force were obtained and discussed.

  6. Models of high-Tc superconductivity and applications to electric generators and motors

    DEFF Research Database (Denmark)

    Sørensen, Mads Peter

    We present the Ginzburg Landau model for mesoscopic high-Tc superconductors of complex geometry. It is shown that giant vortices can form at boundary defects. The relation between total magnetic flux penetration through the superconductor and the externally applied field is established. This is i...

  7. Trapped field recovery of bulk superconductor magnets by static field magnetization

    Science.gov (United States)

    Deng, Z.; Tsuzuki, K.; Miki, M.; Felder, B.; Hara, S.; Izumi, M.

    2011-11-01

    Thanks to the trapped field of bulk high-temperature superconductors, they can be used as field-pole magnets in the high temperature superconducting (HTS) rotating machines. For example, an output power of 10 kW at 720 rpm was realized by an average trapped field of 0.56 T of eight melt-textured GdBa2Cu3Oy (Gd-123) bulks at liquid nitrogen temperature in TUMSAT in 2004. Similarly to the HTS machines involving 1G or 2G wires, the trapped field of the bulk is possibly sensitive and even can be attenuated by the AC component field during the operation. Hence, it is necessary to recover the trapped field once being decreased to some extent in the practical application. From this point, we have investigated the trapped field recovery of HTS bulk magnets by static field magnetization in the paper. A series of different initial trapped fields after zero-field-cooling or field-cooling magnetization are used to simulate the attenuated trapped field. By comparing the trapped field peak and its distribution, the trapped field was found to be able to recover by the static field magnetization method with a stronger excitation field and the initial trapped flux inside the bulk also has an influence on the recovery process. The optimum recovery field was found to be about 2.5 times the saturated trapped field of the bulk at liquid nitrogen temperature, by which the bulk can regain the former best trapped field performance.

  8. Trapped field recovery of bulk superconductor magnets by static field magnetization

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Z., E-mail: zigang@kaiyodai.ac.jp [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, Tokyo 135-8533 (Japan); Tsuzuki, K.; Miki, M.; Felder, B.; Hara, S.; Izumi, M. [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, Tokyo 135-8533 (Japan)

    2011-11-15

    A series of initial trapped fields after ZFC or FC magnetization are used to simulate the attenuated trapped field. It is possible and easy to recover the lost trapped field and regain the best trapped field performance as before. In the re-magnetization process, the initial magnetic flux inside the bulk magnets will help to recover the trapped field. The optimum recovery field is recommended to be 2.5 times the saturation field of the bulk at LN2 temperature. Thanks to the trapped field of bulk high-temperature superconductors, they can be used as field-pole magnets in the high temperature superconducting (HTS) rotating machines. For example, an output power of 10 kW at 720 rpm was realized by an average trapped field of 0.56 T of eight melt-textured GdBa{sub 2}Cu{sub 3}O{sub y} (Gd-123) bulks at liquid nitrogen temperature in TUMSAT in 2004. Similarly to the HTS machines involving 1G or 2G wires, the trapped field of the bulk is possibly sensitive and even can be attenuated by the AC component field during the operation. Hence, it is necessary to recover the trapped field once being decreased to some extent in the practical application. From this point, we have investigated the trapped field recovery of HTS bulk magnets by static field magnetization in the paper. A series of different initial trapped fields after zero-field-cooling or field-cooling magnetization are used to simulate the attenuated trapped field. By comparing the trapped field peak and its distribution, the trapped field was found to be able to recover by the static field magnetization method with a stronger excitation field and the initial trapped flux inside the bulk also has an influence on the recovery process. The optimum recovery field was found to be about 2.5 times the saturated trapped field of the bulk at liquid nitrogen temperature, by which the bulk can regain the former best trapped field performance.

  9. Anisotropy and intergrain current density in oriented grained bulk YBa2Cu3Ox superconductor

    International Nuclear Information System (INIS)

    Selvamanickam, V.; Salama, K.

    1990-01-01

    The intergrain transport current density and its anisotropy have been studied in oriented grained bulk YBa 2 Cu 3 O x superconductors fabricated by the liquid phase processing method. Current density measurements were performed on oriented grained samples with the transport current aligned at different angles to the a-b plane. In these measurements, the transport current passed through several oriented grain boundaries. The results indicate that the critical current density drops rapidly when the transport current flows at small angles to the a-b plane and then decreases slowly at larger angles. At 77 K and zero magnetic field, an anisotropy ratio of about 25 is observed between J c along a-b plane and that perpendicular to the plane. Further, the critical current density in these samples is found to depend weakly on magnetic field even though the current crosses grain boundaries. These results support the notion that grain boundaries of these superconductors are different in nature from those of solid-state sintered samples.

  10. Alternating-current transport losses of melt-cast processed Bi-2212 bulk superconductor bars

    International Nuclear Information System (INIS)

    Tsukamoto, T; Inada, R; Inagaki, N; Andoh, H; Sugiura, T; Oota, A

    2003-01-01

    Using a melt-casting method, we have fabricated two pieces of Bi-2212 bulk superconductor bar with square and rectangular cross-sections, and we have investigated the alternating-current (ac) transport self-field losses at 77 K. Despite the main contribution of hysteresis loss of the superconductor, there is some difference in the loss behaviour between these two samples. To elucidate the origin, we make numerical calculations on the ac transport self-field losses as a function of current amplitude I 0 below the critical current I c . At a fixed I 0 , the calculated values using the uniform J c distribution and the actual cross-sectional geometry are much higher than the experimental data for the sample with a square cross-section 7.5 x 7.5 mm 2 , while there is good agreement between the calculation and the experiment for the sample with a rectangular cross-section 4.5 x 13.6 mm 2 . The discrepancy appearing in the sample with a square cross-section is ascribed to the actual J c distribution, which is confirmed by critical current measurements when scraping off the sample. The local J c value decreases significantly in going from the surface to the interior of the sample. This suppresses the extension of the flux-penetration region to the interior under ac current transmission and lowers the loss generation compared with the calculated results obtained by the uniform J c distribution

  11. Upper critical and irreversibility fields in Ni- and Co-doped pnictide bulk superconductors

    Science.gov (United States)

    Nikolo, Martin; Singleton, John; Solenov, Dmitry; Jiang, Jianyi; Weiss, Jeremy; Hellstrom, Eric

    2018-05-01

    A comprehensive study of upper critical and irreversibility magnetic fields in Ba(Fe0.95Ni0.05)2As2 (large grain and small grain samples), Ba(Fe0.94Ni0.06)2As2, Ba(Fe0.92Co0.08)2As2, and Ba(Fe0.92Co0.09)2As2 polycrystalline bulk pnictide superconductors was made in pulsed fields of up to 65 T. The full magnetic field-temperature (H-T) phase diagrams, starting at 1.5 K, were measured. The higher temperature, upper critical field Hc2 data are well described by the one-band Werthamer, Helfand, and Hohenberg (WHH) model. At low temperatures, the experimental data depart from the fitted WHH curves, suggesting an emergence of a new phase that could be attributed to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The large values of the Maki fitting parameter α indicate that the Zeeman pair breaking dominates over the orbital pair breaking and spin-paramagnetic pair-breaking effect is significant in these materials. Possible multi-band structure of these materials is lumped into effective parameters of the single-band model. Table of measured physical parameters allows us to compare these pnictide superconductors for different Co- and Ni- doping levels and granularity.

  12. Flux motion in Y-Ba-Cu-O bulk superconductors during pulse field magnetization

    International Nuclear Information System (INIS)

    Yoshizawa, K; Nariki, S; Sakai, N; Murakami, M; Hirabayasi, I; Takizawa, T

    2004-01-01

    We have studied the relationship between the magnetization and temperature change in Y-Ba-Cu-O bulk superconductor during pulse field magnetization (PFM). The flux motion was monitored using both Hall sensors and pick-up coils that are placed on a surface of a Y-Ba-Cu-O disc having dimensions of 15 mm in diameter and 0.95 mm in thickness. The peak value of the field was varied from 0.2 to 0.8 T. The effect of the static bias field was also studied in the range of 0-3 T. The temperature of the sample surface was measured using a resistance temperature sensor. The temperature increased with the magnitude of the applied pulsed magnetic field, and the amount of temperature rise decreased with increasing static bias field

  13. Coasting characteristic of the flywheel system under anisotropy effect of bulk high temperature superconductors

    Science.gov (United States)

    Wu, J. F.; Li, Y.

    2014-10-01

    High-temperature superconductors (HTSCs) array with aligned growth section boundary (GSB) pattern (AGSBP) exhibits larger levitation force and suppression of levitation force decay above a permanent magnet guideway (PMG) compared with misaligned GSB pattern (MGSBP) has been studied in maglev train application (Zheng et al., 2013). This result maybe helpful and support a new way for the HTS bearing design for flywheel systems. So, in this paper, we further examine this growth anisotropy effect on the maglev performance of flywheel system. Levitation force and coasting time were investigated from the point-view of HTS flywheel applications. The GS/GSB alignment of AGSBP bulk HTSCs produces larger levitation force than that of MGSBP, but the coasting time is shorter than that of MGSBP, that is to say, the electric magnetic drag force with AGSBP is larger than that of MGSBP. This result may also exist in the maglev guideline when the maglev train stops freely.

  14. Crack propagation and acoustic emission behavior of silver-added Dy123 bulk superconductor

    International Nuclear Information System (INIS)

    Yoneda, K.; Ye, J.

    2006-01-01

    The relationship between the crack propagation process and acoustic emission (AE) signals was investigated in 3-point bending tests in which stress loading was applied parallel to the c-axis of U-notched specimens cut from Dy123 bulk superconductors with and without the addition of silver (Ag). The average bending stress of the specimens containing 10 mass% of Ag was approximately 20% higher than that of the specimens without the addition of Ag; the total AE energy of the former specimens was approximately fourfold greater than that of the latter specimens. However, cracks initiated in all of the specimens at a bending stress level of around 25 MPa, regardless of the presence or absence of Ag. An analysis of the amplitude distribution revealed that the failure mode was matrix failure in both types of specimens. Cracks in the low-strength specimens without Ag propagated between gas holes or along cleavage planes, and the AE event count and total AE energy were low. By contrast, the high-strength Ag-added specimens had fewer gas holes and cleavage cracks on account of their improved microstructure. In these samples, crack propagation orthogonal to the cleavage planes caused Ag particles to separate from the matrix and induced cleavage cracks. The addition of Ag presumably had the effect of inhibiting crack propagation, with the result that the AE event count and AE energy increased. The results of this study indicate that failure phenomena can be interpreted by evaluating the amplitude distribution, AE event count and total AE energy. This suggests that the AE method is also applicable to evaluations of bulk superconductors

  15. Improving magnetic properties of MgB{sub 2} bulk superconductors by synthetic engine oil treatment

    Energy Technology Data Exchange (ETDEWEB)

    Taylan Koparan, E., E-mail: etaylan20@gmail.com [Department of Science Education, Eregli Faculty of Education, Bulent Ecevit University, TR-67300, Zonguldak (Turkey); Savaskan, B. [Energy Systems Engineering, Faculty of Technology, Karadeniz Technical University, 61830, Of, Trabzon (Turkey); Yanmaz, E. [Department of Mechatronics, Faculty of Engineering and Architecture, İstanbul Gelişim University, İstanbul (Turkey)

    2016-08-15

    Highlights: • The effects of synthetic engine oil treatment on magnetic properties of bulk MgB{sub 2} superconductors has been first time investigated and reported. • Synthetic engine oil used as a product which is cheap and a rich carbon source obviously has improved the superconducting magnetic properties of MgB{sub 2}. • The critical current density of all of MgB{sub 2} samples immersed at different standby time in engine oil in whole field range has been better than that of the pure MgB{sub 2} sample. • The MgB{sub 2} sample immersed at 300 min standby time in synthetic engine oil has the best performance compared to other samples. - Abstract: The present study focuses on the effects of standby time of the MgB{sub 2} samples immersed in synthetic engine oil on the critical current density ( J{sub c}(H)), magnetic field dependence of the pinning force density f{sub p}(b) and T{sub c} performances of MgB{sub 2} bulk superconductors. Synthetic engine oil was used as a product which is cheap and a rich carbon source. Manufactured MgB{sub 2} pellet samples were immersed at different standby time of 30 min, 120 min, 300 min and 1440 min in synthetic engine oil after the first heating process. Finally, MgB{sub 2} samples immersed in synthetic engine oil were sintered at 1000 °C and kept for 15 min in Ar atmosphere. The critical current density of all of MgB{sub 2} samples immersed at different standby time in engine oil in whole field range was better than that of the pure MgB{sub 2} sample because of the number of the pinning centers. The MgB{sub 2} sample immersed at 300 min standby time in synthetic engine oil has the best performance compared to other samples. The J{sub c} value for the pure sample is 2.0 × 10{sup 3} A/cm{sup 2}, whereas for the MgB{sub 2} sample immersed at 300 min standby time in engine oil the J{sub c} is enhanced to 4.8 × 10{sup 3} A/cm{sup 2} at 5 K and 3 T. The superconducting transition temperature (T{sub c}) did not change

  16. Improving magnetic properties of MgB_2 bulk superconductors by synthetic engine oil treatment

    International Nuclear Information System (INIS)

    Taylan Koparan, E.; Savaskan, B.; Yanmaz, E.

    2016-01-01

    Highlights: • The effects of synthetic engine oil treatment on magnetic properties of bulk MgB_2 superconductors has been first time investigated and reported. • Synthetic engine oil used as a product which is cheap and a rich carbon source obviously has improved the superconducting magnetic properties of MgB_2. • The critical current density of all of MgB_2 samples immersed at different standby time in engine oil in whole field range has been better than that of the pure MgB_2 sample. • The MgB_2 sample immersed at 300 min standby time in synthetic engine oil has the best performance compared to other samples. - Abstract: The present study focuses on the effects of standby time of the MgB_2 samples immersed in synthetic engine oil on the critical current density ( J_c(H)), magnetic field dependence of the pinning force density f_p(b) and T_c performances of MgB_2 bulk superconductors. Synthetic engine oil was used as a product which is cheap and a rich carbon source. Manufactured MgB_2 pellet samples were immersed at different standby time of 30 min, 120 min, 300 min and 1440 min in synthetic engine oil after the first heating process. Finally, MgB_2 samples immersed in synthetic engine oil were sintered at 1000 °C and kept for 15 min in Ar atmosphere. The critical current density of all of MgB_2 samples immersed at different standby time in engine oil in whole field range was better than that of the pure MgB_2 sample because of the number of the pinning centers. The MgB_2 sample immersed at 300 min standby time in synthetic engine oil has the best performance compared to other samples. The J_c value for the pure sample is 2.0 × 10"3 A/cm"2, whereas for the MgB_2 sample immersed at 300 min standby time in engine oil the J_c is enhanced to 4.8 × 10"3 A/cm"2 at 5 K and 3 T. The superconducting transition temperature (T_c) did not change with the increasing standby time of the samples in synthetic engine oil at all. The best diamagnetic property was

  17. Superconductors

    International Nuclear Information System (INIS)

    1988-01-01

    The chapter 6.3 p. 143 to 153 of this book deals with superconductors 19 items are briefly presented with address of manufacturer or laboratory to contact, mainly in the USA or Japan. In particular magnets, films, high temperature superconductors and various applications are presented [fr

  18. Metallorganic precursors route for high Tc superconducting materials and related phases

    International Nuclear Information System (INIS)

    Beltran-porter, D.; Gonzalez, A.; Sanchis, M.J.; Beltran-porter, A.; Ibanez, R.; Sapina, F.

    1991-01-01

    The adequacy of the precursors approach for high Tc superconducting materials is validated by means of three examples of a new synthesis of mixed oxides which are directly related to the high Tc superconductors. The synthesis temperature is lowered significantly, and the need for extending the classic 'building block' approach is shown. The hypothesis that topochemical reactions from molecular to extended solids are posssible is proven. 28 refs

  19. Design study of SMES system using high temperature superconductors

    International Nuclear Information System (INIS)

    Yoshihara, T.; Masuda, M.; Shintomi, T.; Hasegawa, J.

    1988-01-01

    Various studies of high Tc superconductors are being energetically pursued all over the world, since IBM Zurich Research Laboratory reported on the superconducting oxide. A new design using a high Tc superconductor is under study for 5000 MWh, on the assumption that it is available like conventional superconductors. Problems related to the Tc SMES system, mainly thermal insulation, refrigeration system, stability of superconductors, etc., are considered. Some design examples of high Tc SMES system are proposed

  20. Modelling and comparison of trapped fields in (RE)BCO bulk superconductors for activation using pulsed field magnetization

    Science.gov (United States)

    Ainslie, M. D.; Fujishiro, H.; Ujiie, T.; Zou, J.; Dennis, A. R.; Shi, Y.-H.; Cardwell, D. A.

    2014-06-01

    The ability to generate a permanent, stable magnetic field unsupported by an electromotive force is fundamental to a variety of engineering applications. Bulk high temperature superconducting (HTS) materials can trap magnetic fields of magnitude over ten times higher than the maximum field produced by conventional magnets, which is limited practically to rather less than 2 T. In this paper, two large c-axis oriented, single-grain YBCO and GdBCO bulk superconductors are magnetized by the pulsed field magnetization (PFM) technique at temperatures of 40 and 65 K and the characteristics of the resulting trapped field profile are investigated with a view of magnetizing such samples as trapped field magnets (TFMs) in situ inside a trapped flux-type superconducting electric machine. A comparison is made between the temperatures at which the pulsed magnetic field is applied and the results have strong implications for the optimum operating temperature for TFMs in trapped flux-type superconducting electric machines. The effects of inhomogeneities, which occur during the growth process of single-grain bulk superconductors, on the trapped field and maximum temperature rise in the sample are modelled numerically using a 3D finite-element model based on the H-formulation and implemented in Comsol Multiphysics 4.3a. The results agree qualitatively with the observed experimental results, in that inhomogeneities act to distort the trapped field profile and reduce the magnitude of the trapped field due to localized heating within the sample and preferential movement and pinning of flux lines around the growth section regions (GSRs) and growth sector boundaries (GSBs), respectively. The modelling framework will allow further investigation of various inhomogeneities that arise during the processing of (RE)BCO bulk superconductors, including inhomogeneous Jc distributions and the presence of current-limiting grain boundaries and cracks, and it can be used to assist optimization of

  1. Superconductors

    CERN Document Server

    Narlikar, A V

    2014-01-01

    Superconductors is neither about basic aspects of superconductivity nor about its applications, but its mainstay is superconducting materials. Unusual and unconventional features of a large variety of novel superconductors are presented and their technological potential as practical superconductors assessed. The book begins with an introduction to basic aspects of superconductivity. The presentation is readily accessible to readers from a diverse range of scientific and technical disciplines, such as metallurgy, materials science, materials engineering, electronic and device engineering, and chemistry. The derivation of mathematical formulas and equations has been kept to a minimum and, wherever necessary, short appendices with essential mathematics have been added at the end of the text. The book is not meant to serve as an encyclopaedia, describing each and every superconductor that exists, but focuses on important milestones in their exciting development.

  2. High Tc superconducting energy storage systems

    Energy Technology Data Exchange (ETDEWEB)

    Werfel, Frank [Adelwitz Technologiezentrum GmbH (ATZ), Arzberg-Adelwitz (Germany)

    2012-07-01

    Electric energy is basic to heat and light our homes, to power our businesses and to transport people and goods. Powerful storage techniques like SMES, Flywheel, Super Capacitor, and Redox - Flow batteries are needed to increase the overall efficiency, stability and quality of electrical grids. High-Tc superconductors (HTS) possess superior physical and technical properties and can contribute in reducing the dissipation and losses in electric machines as motors and generators, in electric grids and transportation. The renewable energy sources as solar, wind energy and biomass will require energy storage systems even more as a key technology. We survey the physics and the technology status of superconducting flywheel energy storage (FESS) and magnetic energy storage systems (SMES) for their potential of large-scale commercialization. We report about a 10 kWh / 250 kW flywheel with magnetic stabilization of the rotor. The progress of HTS conductor science and technological engineering are basic for larger SMES developments. The performance of superconducting storage systems is reviewed and compared. We conclude that a broad range of intensive research and development in energy storage is urgently needed to produce technological options that can allow both climate stabilization and economic development.

  3. Growth anisotropy effect of bulk high temperature superconductors on the levitation performance in the applied magnetic field

    Science.gov (United States)

    Zheng, J.; Liao, X. L.; Jing, H. L.; Deng, Z. G.; Yen, F.; Wang, S. Y.; Wang, J. S.

    2013-10-01

    Growth anisotropies of bulk high temperature superconductors (HTSCs) fabricated by a top-seeded melt texture growth process, that is, different pinning effect in the growth sectors (GSs) and growth sector boundaries (GSBs), possess effect on the macro flux trapping and levitation performance of bulk HTSCs. Previous work (Physics Procedia, 36 (2012) 1043) has found that the bulk HTSC array with aligned GSB pattern (AGSBP) exhibits better capability for levitation and suppression of levitation force decay above a permanent magnet guideway (PMG) compared with misaligned GSB pattern (MGSBP). In this paper, we further examine this growth anisotropy effect on the maglev performance of a double-layer bulk HTSC. In contrast to reported trapped flux cases (Supercond. Sci. Technol. 19 (2006) S466), the two superposed bulk HTSCs with same AGSBP with PMG are found to show better maglev performance. These series of results are helpful and support a new way for the performance optimization of present HTS maglev systems.

  4. Development of a generic seed crystal for the fabrication of large grain (RE)-Ba-Cu-O bulk superconductors

    International Nuclear Information System (INIS)

    Shi, Y; Babu, N Hari; Cardwell, D A

    2005-01-01

    The critical current density, J c , irreversibility field, B irr , and magnetic field trapping ability of (LRE)-Ba-Cu-O bulk superconductors, where LRE is a light rare earth element such as Nd, Sm, Eu and Gd, are generally superior to those of the more common melt-processed Y-Ba-Cu-O (YBCO). The lack of availability of a suitable seed crystal to grow large, single grain (LRE)-Ba-Cu-O superconductors with controlled orientation, however, has hindered severely the development of these materials for engineering applications over the past ten years. In this communication we report for the first time the development of a generic seed crystal that can be used to fabricate any rare earth (RE) based (RE)-Ba-Cu-O ((RE)BCO) superconductor in the form of a large single grain with controlled orientation. The new seed crystal will potentially enable large grain (LRE)-Ba-Cu-O bulk superconductors to be fabricated routinely, as is the case for YBCO. This will enable the field trapping and current-carrying characteristics of these materials to be explored in more detail than has been possible to date. (rapid communication)

  5. Effects of seed geometry on the crystal growth and the magnetic properties of single grain REBCO bulk superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hwi Joo; Lee, Hee Gyoun [Korea Polytechnic University, Siheung (Korea, Republic of); Park, Soon Dong; Jun, Bung Hyack; Kim, Chan Joong [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2017-09-15

    This study presents that the orientation and the geometry of seed affect on the growth behavior of melt processed single grain REBCO bulk superconductor and its magnetic properties. The effects of seed geometry have been investigated for thin 30mm x 30mm rectangular powder compacts. Single grain REBCO bulk superconductors have been grown successfully by a top seed melt growth method for 8-mm thick vertical thin REBCO slab. Asymmetric structures have been developed at the front surface and at the rear surface of the specimen. Higher magnetic properties have been obtained for the specimen that c-axis is normal to the specimen surface. The relationships between microstructure, grain growth and magnetic properties have been discussed.

  6. Improvement of the field-trapping capabilities of bulk Nd Ba Cu O superconductors using Ba Cu O substrates

    Science.gov (United States)

    Matsui, Motohide; Nariki, Shinya; Sakai, Naomichi; Iwafuchi, Kengo; Murakami, Masato

    2006-07-01

    We used Ba-Cu-O substrates to fabricate bulk Nd-Ba-Cu-O superconductors using a top-seeded melt-growth method. There were several advantages for the use of Ba-Cu-O substrate compared to conventional substrate materials such as MgO, ZrO2, Al2O3, RE123 and RE211 (RE = rare earth). The Ba-Cu-O did not react with the precursor and minimized liquid loss. Accordingly, the introduction of large-sized cracks was suppressed. We also found that Tc values were high at the bottom regions, which was ascribed to the beneficial effect of Ba-Cu-O in suppressing Nd/Ba substitution. As a result, we obtained bulk Nd-Ba-Cu-O superconductors that exhibited fairly good field-trapping capabilities, even at the bottom surfaces.

  7. Coasting characteristic of the flywheel system under anisotropy effect of bulk high temperature superconductors

    International Nuclear Information System (INIS)

    Wu, J.F.; Li, Y.

    2014-01-01

    Highlights: • Coasting time was investigated from the point-view of HTS flywheel applications. • The coasting time of aligned growth section boundary pattern (AGSBP) is shorter than that of MGSBP. • The electric magnetic drag force with AGSBP is larger than that of MGSBP. • This result may also exist in the maglev guideline when the maglev train stops freely. - Abstract: High-temperature superconductors (HTSCs) array with aligned growth section boundary (GSB) pattern (AGSBP) exhibits larger levitation force and suppression of levitation force decay above a permanent magnet guideway (PMG) compared with misaligned GSB pattern (MGSBP) has been studied in maglev train application (Zheng et al., 2013). This result maybe helpful and support a new way for the HTS bearing design for flywheel systems. So, in this paper, we further examine this growth anisotropy effect on the maglev performance of flywheel system. Levitation force and coasting time were investigated from the point-view of HTS flywheel applications. The GS/GSB alignment of AGSBP bulk HTSCs produces larger levitation force than that of MGSBP, but the coasting time is shorter than that of MGSBP, that is to say, the electric magnetic drag force with AGSBP is larger than that of MGSBP. This result may also exist in the maglev guideline when the maglev train stops freely

  8. Effects of seed orientation on the growth behavior of single grain REBCO bulk superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hee Gyoun [Korea Polytechnic University, Siheung (Korea, Republic of)

    2017-06-15

    This study presents a simple method to control the seed orientation which leads to the various growth characteristics of a single grain REBCO (RE: rare-earth elements) bulk superconductors. Seed orientation was varied systematically from c-axis to a-axis with every 30 degree rotation around b-axis. Orientations of a REBCO single grain was successfully controlled by placing the seed with various angles on the prismatic indent prepared on the surface of REBCO powder compacts. Growth pattern was changed from cubic to rectangular when the seed orientation normal to compact surface was varied from c-axis to a-axis. Macroscopic shape change has been explained by the variation of the wetting angle of un-reacted melt depending on the interface energy between YBa2Cu3O7-y (Y123) grain and melt. Higher magnetic levitation force was obtained for the specimen prepared using tilted seed with an angle of 30 degree rotation around b-axis.

  9. Coasting characteristic of the flywheel system under anisotropy effect of bulk high temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Wu, J.F., E-mail: wujf@ciomp.ac.cn; Li, Y.

    2014-10-15

    Highlights: • Coasting time was investigated from the point-view of HTS flywheel applications. • The coasting time of aligned growth section boundary pattern (AGSBP) is shorter than that of MGSBP. • The electric magnetic drag force with AGSBP is larger than that of MGSBP. • This result may also exist in the maglev guideline when the maglev train stops freely. - Abstract: High-temperature superconductors (HTSCs) array with aligned growth section boundary (GSB) pattern (AGSBP) exhibits larger levitation force and suppression of levitation force decay above a permanent magnet guideway (PMG) compared with misaligned GSB pattern (MGSBP) has been studied in maglev train application (Zheng et al., 2013). This result maybe helpful and support a new way for the HTS bearing design for flywheel systems. So, in this paper, we further examine this growth anisotropy effect on the maglev performance of flywheel system. Levitation force and coasting time were investigated from the point-view of HTS flywheel applications. The GS/GSB alignment of AGSBP bulk HTSCs produces larger levitation force than that of MGSBP, but the coasting time is shorter than that of MGSBP, that is to say, the electric magnetic drag force with AGSBP is larger than that of MGSBP. This result may also exist in the maglev guideline when the maglev train stops freely.

  10. Fabrication and characterizations of the BSCCO-2212/SrSO4 bulk superconductors

    International Nuclear Information System (INIS)

    Kim, Kyu Tae; Jang, Seok Hern; Park, Eui Cheol; Hwang, Sumin; Joo, Jin Hoo; Hong, Gye Won; Kim, Chan Joong; Kim, Hye Rim; Hyun, Ok Bae

    2006-01-01

    We fabricated Bi-2212/SrSO 4 bulk superconductors by the casting process and evaluated the effects of the powder mixing method and annealing temperature on the texture, microstructure, and critical current. In the process, the Bi-2212 powders were mixed with SrSO 4 by hand-mixing(HM) and planetary ball milling(PBM) method and then the powder mixtures were melted at 1100 - 1200 degrees C, solidified, and annealed. We observed that the rod made by the PBM had a more homogeneous microstructure and smaller SrSO 4 and second phases than that of the rod made by the HM, resulting in increased I c . The I c of the rod also depended on the annealing temperature and the highest I c was obtained to be 200 A when prepared by HM at 1200 degrees C and annealed at 810 degrees C which is probably due to the moderate density and 2212 texture and the smaller and less second phase compared to that at higher temperature. The possible causes of the variations of I c with the powder mixing method and annealing temperature were related to the microstructural evolution based on the SEM, EPMA, and DTA analyses.

  11. Effect of silver addition on the mechanical and field trapping properties of Gd-Ba-Cu-O bulk superconductors

    CERN Document Server

    Nariki, S; Matsui, M; Murakami, M

    2002-01-01

    The effect of Ag addition on the microstructure and the mechanical and field trapping properties of Gd-Ba-Cu-O bulk superconductor has been investigated. The single grain Gd-Ba-Cu-O bulk superconductors 32 mm in diameter were fabricated with 0-30 mass%Ag/sub 2/O additions by the melt growth method under controlled oxygen partial pressure of 1.0%. From microscopic observations, it was found that the macro- cracks in the a-b plane decreased with Ag addition. The three-point bending test showed that the average strength of Ag-free bulk was 69 MPa at room temperature, while the strength was dramatically improved to 110-115 MPa with 10-30 mass%Ag/sub 2/O additions. The trapped magnetic field of Ag-free bulk sample was 1.3 T at 77 K. The trapped field of bulk Gd-Ba-Cu-O samples with 10-20 mass%Ag/sub 2/O exhibited high values of 1.8-2.0 T at 77 K. However, the trapped field of the sample with 30 mass%Ag/sub 2/O addition was lowered to 1.1 T with decreasing the critical current density. The trapped field of Ag- adde...

  12. Observation of an hexatic vortex glass in flux lattices of the high Tc superconductor Bi2.1Sr1.9Ca0.9Cu2O8+δ

    International Nuclear Information System (INIS)

    Bishop, D.J.; Gammel, P.L.; Murray, C.A.; Mitzi, D.B.; Kapitulnik, A.

    1990-01-01

    We report observation of hexatic order in Abrikosov flux lattices in very clean crystals of the high T c superconductor Bi 2.1 Sr 1.9 Ca 0.9 Cu 2 O 8+δ (BSCCO). Our experiments consist of in situ magnetic decoration of the flux lattice at 4.2 K. Analysis of the decoration images shows that the positional order decays exponentially with a correlation length of a few lattice constants while the orientational order persists for hundreds of lattice constants and decays algebraically with an exponent η 6 =0.06±0.01. Our results confirm recent theoretical speculation that the positional order should be far more sensitive to disorder than the orientational order and that the low temperature ordered phase of the flux lines in these systems might be an hexatic glass

  13. Observation of a hexatic vortex glass in flux lattices of the high-Tc superconductor Bi2.1Sr1.9Ca0.9Cu2O8+δ

    International Nuclear Information System (INIS)

    Murray, C.A.; Gammel, P.L.; Bishop, D.J.; Mitzi, D.B.; Kapitulnik, A.

    1990-01-01

    We report observation of hexatic order in Abrikosov flux lattices in very clean crystals of the high-T c superconductor Bi 2.1 Sr 1.9 Ca 0.9 Cu 2 O 8+δ . Our experiments consist of in situ magnetic decoration of the flux lattice at 4.2 K. Analysis of the decoration images shows that the positional order decays exponentially with a correlation length of a few lattice constants while the orientational order persists for hundreds of lattice constants and decays algebraically with an exponent η 6 =0.06±0.01. Our results confirm recent theoretical speculation that the positional order should be far more sensitive to disorder than the orientational order and that the low-temperature ordered phase of the flux lines in these systems might be a hexatic glass

  14. Structure, resistivity, critical field, specific-heat jump at Tc, Meissner effect, a.c. and d.c. susceptibility of the high-Tc superconductor YBa2Cu3O7

    International Nuclear Information System (INIS)

    Junod, A.; Bezinge, A.; Graf, T.

    1987-01-01

    YBa 2 Cu 3 O 7 superconductors with inductive transitions as narrows as 0.45 K above 90 K were synthetized. Samples were characterized by thermogravimetry, differential thermal analysis, X-ray and neutron diffraction. The structure is characterized by a two-dimensional Cu-O network with square-pyramidal and square-planar coordinated Cu atoms. Results show a clear metallic behaviour of the resistivity. An orbital critical field as high as 300 T is extrapolated. Meissner flux expulsion up to 40% is observed. Small amounts of magnetic Cu 2+ ions are correlated with the presence of the impurity phase BaCuO 2 . The Pauli susceptibility and the specific-heat jump at T c are consistent with γ ≅ 2mJ/(K 2 gat) (9mJ/(K 2 mole-Cu)), neglecting all renormalizations

  15. Growth anisotropy effect of bulk high temperature superconductors on the levitation performance in the applied magnetic field

    International Nuclear Information System (INIS)

    Zheng, J.; Liao, X.L.; Jing, H.L.; Deng, Z.G.; Yen, F.; Wang, S.Y.; Wang, J.S.

    2013-01-01

    Highlights: • The single-layer bulk HTSC with AGSBP obtains better levitation performance than that of MGSBP. • The double-layer bulk with AGSBP obtains better levitation performance than that of MGSBP too. • The double-layer bulk finding is contrast to MGSBP if pursuing high trapped field. • The optimization is highlighted by simple and easy operation, thus economical in the practice. -- Abstract: Growth anisotropies of bulk high temperature superconductors (HTSCs) fabricated by a top-seeded melt texture growth process, that is, different pinning effect in the growth sectors (GSs) and growth sector boundaries (GSBs), possess effect on the macro flux trapping and levitation performance of bulk HTSCs. Previous work (Physics Procedia, 36 (2012) 1043) has found that the bulk HTSC array with aligned GSB pattern (AGSBP) exhibits better capability for levitation and suppression of levitation force decay above a permanent magnet guideway (PMG) compared with misaligned GSB pattern (MGSBP). In this paper, we further examine this growth anisotropy effect on the maglev performance of a double-layer bulk HTSC. In contrast to reported trapped flux cases (Supercond. Sci. Technol. 19 (2006) S466), the two superposed bulk HTSCs with same AGSBP with PMG are found to show better maglev performance. These series of results are helpful and support a new way for the performance optimization of present HTS maglev systems

  16. Growth anisotropy effect of bulk high temperature superconductors on the levitation performance in the applied magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, J., E-mail: jzheng@swjtu.edu.cn; Liao, X.L.; Jing, H.L.; Deng, Z.G.; Yen, F.; Wang, S.Y.; Wang, J.S.

    2013-10-15

    Highlights: • The single-layer bulk HTSC with AGSBP obtains better levitation performance than that of MGSBP. • The double-layer bulk with AGSBP obtains better levitation performance than that of MGSBP too. • The double-layer bulk finding is contrast to MGSBP if pursuing high trapped field. • The optimization is highlighted by simple and easy operation, thus economical in the practice. -- Abstract: Growth anisotropies of bulk high temperature superconductors (HTSCs) fabricated by a top-seeded melt texture growth process, that is, different pinning effect in the growth sectors (GSs) and growth sector boundaries (GSBs), possess effect on the macro flux trapping and levitation performance of bulk HTSCs. Previous work (Physics Procedia, 36 (2012) 1043) has found that the bulk HTSC array with aligned GSB pattern (AGSBP) exhibits better capability for levitation and suppression of levitation force decay above a permanent magnet guideway (PMG) compared with misaligned GSB pattern (MGSBP). In this paper, we further examine this growth anisotropy effect on the maglev performance of a double-layer bulk HTSC. In contrast to reported trapped flux cases (Supercond. Sci. Technol. 19 (2006) S466), the two superposed bulk HTSCs with same AGSBP with PMG are found to show better maglev performance. These series of results are helpful and support a new way for the performance optimization of present HTS maglev systems.

  17. High output power reluctance electric motors with bulk high-temperature superconductor elements

    Energy Technology Data Exchange (ETDEWEB)

    Kovalev, L.K. [Moscow State Aviation Institute (Technical University) (MAI), Moscow (Russian Federation)]. E-mail: kovalev@mail.sitek.net; Ilushin, K.V.; Penkin, V.T. [Moscow State Aviation Institute (Technical University) (MAI), Moscow (RU)] [and others

    2002-05-01

    We present new types of electric machines with the rotors containing bulk high-temperature superconductor (HTS)-YBCO and Bi-Ag-elements. We discuss different schematics of hysteresis, reluctance, 'trapped field' and composed synchronous HTS machines. The two-dimensional mathematical models describing the processes in such types of HTS machines were developed on the basis of the theoretical analysis of the electrodynamic and hysteresis processes in the single-domain and polycrystal YBCO ceramic samples and plate shape Bi-Ag elements. We give the test results of the series of hysteresis, reluctance, 'trapped field' and composed with permanent magnets HTS motors with an output power rating of 0.1-18 kW and current frequencies 50 Hz and 400 Hz. These results show that in the media of liquid nitrogen the specific output power per one unit weight of the HTS motor is four to seven times better than for conventional electric machines. A comparison of the theoretical and experimental characteristics of the developed HTS motors show that they are in good agreement. We discuss the test results for a liquid nitrogen cryogenic pump system with a hysteresis 500 W HTS motor. We describe several designs of new HTS motors operating in the media of liquid nitrogen with an output power 125 kW (and more) and a power factor of more than 0.8. We discuss future applications of new types of HTS motors for aerospace technology, on-land industry and transport systems. (author)

  18. Influence of crossed fields in structures combining large grain, bulk (RE)BCO superconductors and soft ferromagnetic discs

    International Nuclear Information System (INIS)

    Philippe, M P; Fagnard, J F; Wéra, L; Vanderheyden, B; Vanderbemden, P; Morita, M; Nariki, S; Teshima, H; Caps, H

    2016-01-01

    Bulk (RE)BCO superconductors are able to trap record magnetic fields and can be used as powerful permanent magnets in various engineering applications such as rotating machines and magnetic bearings. When such superconducting (SC) “trapped field magnets” are combined to a ferromagnetic (FM) disc, the total magnetic moment is increased with respect to that of the superconductor alone. In the present work, we study experimentally the magnetic behaviour of such hybrid FM/SC structures when they are subjected to cycles of applied field that are orthogonal to their permanent magnetization, i.e. a “crossed-field” configuration. Experimental results show that the usual “crossed-field demagnetization” caused by the cycles of transverse field is strongly reduced in the presence of the ferromagnet. (paper)

  19. The effect of magnet size on the levitation force and attractive force of single-domain YBCO bulk superconductors

    International Nuclear Information System (INIS)

    Yang, W M; Chao, X X; Bian, X B; Liu, P; Feng, Y; Zhang, P X; Zhou, L

    2003-01-01

    The levitation forces between a single-domain YBCO bulk and several magnets of different sizes have been measured at 77 K to investigate the effect of the magnet size on the levitation force. It is found that the levitation force reaches a largest (peak) value when the size of the magnet approaches that of the superconductor when the other conditions are fixed. The absolute maximum attractive force (in the field-cooled state) increases with the increasing of the magnet size, and is saturated when the magnet size approaches that of the superconductor. The maximum attractive force in the field-cooled (FC) state is much higher than that of the maximum attractive force in the zero field-cooled (ZFC) state. The results indicate that the effects of magnetic field distribution on the levitation force have to be considered during the designing and manufacturing of superconducting devices

  20. Materials process and applications of single grain (RE)-Ba-Cu-O bulk high-temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Li Beizhan; Zhou Difan; Xu Kun; Hara, Shogo; Tsuzuki, Keita; Miki, Motohiro; Felder, Brice; Deng Zigang [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology (TUMSAT), 2-1-6, Etchu-jima, Koto-ku, Tokyo 135-8533 (Japan); Izumi, Mitsuru, E-mail: izumi@kaiyodai.ac.jp [Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology (TUMSAT), 2-1-6, Etchu-jima, Koto-ku, Tokyo 135-8533 (Japan)

    2012-11-20

    This paper reviews recent advances in the melt process of (RE)-Ba-Cu-O [(RE)BCO, where RE represents a rare earth element] single grain high-temperature superconductors (HTSs), bulks and its applications. The efforts on the improvement of the magnetic flux pinning with employing the top-seeded melt-growth process technique and using a seeded infiltration and growth process are discussed. Which including various chemical doping strategies and controlled pushing effect based on the peritectic reaction of (RE)BCO. The typical experiment results, such as the largest single domain bulk, the clear TEM observations and the significant critical current density, are summarized together with the magnetization techniques. Finally, we highlight the recent prominent progress of HTS bulk applications, including Maglev, flywheel, power device, magnetic drug delivery system and magnetic resonance devices.

  1. Materials process and applications of single grain (RE)-Ba-Cu-O bulk high-temperature superconductors

    Science.gov (United States)

    Li, Beizhan; Zhou, Difan; Xu, Kun; Hara, Shogo; Tsuzuki, Keita; Miki, Motohiro; Felder, Brice; Deng, Zigang; Izumi, Mitsuru

    2012-11-01

    This paper reviews recent advances in the melt process of (RE)-Ba-Cu-O [(RE)BCO, where RE represents a rare earth element] single grain high-temperature superconductors (HTSs), bulks and its applications. The efforts on the improvement of the magnetic flux pinning with employing the top-seeded melt-growth process technique and using a seeded infiltration and growth process are discussed. Which including various chemical doping strategies and controlled pushing effect based on the peritectic reaction of (RE)BCO. The typical experiment results, such as the largest single domain bulk, the clear TEM observations and the significant critical current density, are summarized together with the magnetization techniques. Finally, we highlight the recent prominent progress of HTS bulk applications, including Maglev, flywheel, power device, magnetic drug delivery system and magnetic resonance devices.

  2. Pure and Y-substituted BaZrO3 ceramics. A possible support material for fabrication of YBa2Cu3O7-x high-Tc superconductors

    International Nuclear Information System (INIS)

    Wang Xiandong.

    1993-01-01

    This thesis concerns the preparation and characterization of cuprate based high-T c superconductors (Y-123 and Bi-2223) and especially development and testing of BaZrO 3 based materials. The formation of YBa 2 Cu 3 O y (Y-123) by a CO 2 -free route involving reaction sintering of stoichiometric mixtures of chemically prepared fine powders of Y 2 BaCuO 5 , BaCuO 2 and CuO have been studied by thermal and XRD analysis. The synthesis and sintering of BaZrO 3 powders prepared by the hydroxide-alkoxide-methanol sol-gel route have been studied. The phase relations in the system BaO-Y 2 O 3 -ZrO 2 have been studied to determine the solid solubility limits for the perovskite phase Ba X Y Y Zr Z O N (X+X+Z=3) at 1500 deg. C. In the binary system Y 2 O 3 -BaZrO 3 the solubility limit was found to be ≅19 mol% Y 2 O 3 , i.e. Ba 0.81 Y 0. 4 2 Zr 0.81 O 3 . along the joint BaYO 2.5 -Ba the boundary was determined to be at BaY 0.21 Zr 0 . 79 O 2.895 . evidence for a new solid solution series between Ba 3 Y 4 O 9 and ZrO 2 are given, and a partial 1500 deg. C phase diagram for the ternary system BaO-Y 2 O 3 -ZrO 2 is presented. The growth of BaZrO 3 single crystals have been attempted both by a laser zone floating technique and flux methods. The compatibility between YBa 2 Cu 3 O 7 -X and BaZrO 3 , Ba X Y Y Zr Z O 3-δ as well as BaHfO 3 have been studied at 950 deg. and 1050 deg. C. The results show the four most promising candidates as support materials for fabrication of YBa 2 Cu 3 O y to be BaHfO 3 , BaY 0.05 Zr 0.95 O 2.975 , , BaZrO 3 and BaY 0.1 Zr 0.9 O 2.95 . (EG)

  3. Superconductors

    International Nuclear Information System (INIS)

    Ekin, J.W.

    1983-01-01

    This chapter attempts to provide an introductory guide to interpreting handbook data on practical, high-current, superconducting materials, principally for magnet applications. An overview is given of the properties and operational limits of superconductive materials, as well as techniques used to fabricate practical superconducting wires. Topics considered include critical temperature, critical magnetic field, Type I and Type II superconductors, upper critical field values for practical materials, the temperature dependence of critical field and upper critical field, critical current, critical current density values for practical materials, the measurement of critical current, composite fabrication, stability, ac losses, eddy current loss, hysteretic loss, mechanical properties, critical current degradation, and superconducting materals selection and composite design

  4. Materials processing, pulsed field magnetization and field-pole application to propulsion motors on Gd123 bulk superconductors

    International Nuclear Information System (INIS)

    Izumi, M; Xu, C; Xu, Y; Morita, E; Kimura, Y; Hu, A; Ichihara, M; Murakami, M; Sakai, N; Hirabayashi, I; Sugimoto, H; Miki, M

    2008-01-01

    Gd123 bulk superconductor is one of the promising magnet materials. We studied the materials processing to grow high performance magnet with a doping of nano-sized metal oxides such as ZrO 2 as a candidature of pinning centre. The enhancement of the critical current density was obtained. Growth of nano-sized particles of Gd211 in addition to BaZrO 3 were observed by TEM. The formation of nano-sized particles appears a key to improve the integrated flux trapped inside the bulks and the TEM reveals an intriguing effect of the addition to the microstructure of bulk materials. Magnetization process is crucial especially for an extended machinery. Pulsed field magnetization was applied to the field-pole bulk on the rotor disk of the tested synchronous motor. The trapped flux density of 1.3 T for Gd123 bulk sample and of 60 mm diameter was reached in the limited dimension of the tested motor by a step cooling method down to 38 K with a closed-cycle condensed neon. The pulsed magnetic field was applied with a new type of split-armature coil. A large bulk of 140 mm diameter has also shown a potential flux trapping superior to other smaller specimens. The bulk magnet provides a strong magnetic field around the bulk body itself with high current density relative to a coil winding. A comparative drawing of a 'torque density' of a variety of motors which is defined as the torque divided by the volume of the motor indicates a potential advantage of bulk motor as a super permanent magnet motor

  5. Preparation of Bi-Pb-Sr-Ca-Cu-O high Tc thick films on Ag or MgO substrate with superconductor paste; Bi kei ko Tc chodendo paste ni yoru Ag, MgO kibanjo eno atsumaku sakusei

    Energy Technology Data Exchange (ETDEWEB)

    Takabatake, N. [Ishikawa Technical High School, Ishikawa (Japan); Tsubota, T.; Ishikawa, T.; Ohashi, K. [Kanazawa Institute of Technology, Ishikawa (Japan)

    1995-07-15

    The following were reported on making Bi series superconducting thick films by a wet method. A paste was made by adding PSO (or ethanol solution of ethylenegrycol) of Yushiro Chemical Industry Co., Ltd. as a binder to a Bi series 2223 single-phase powder sample (blending composition Bi:Pb:Sr:Ca:Cu=1.8:0.4:2:2:3.2); the sample was then coated on an Ag (or MgO) substrate with a brush; after being dried at 105{degree}C for one hour, it was thermally decomposed at 700{degree}C for one hour; then, the process of prissurized forming (at pressure 2 to 5 ton f/cm{sup 2}) and of sintering at 845{degree}C for 20 hours or more were performed on the sample to form a thick film sample. A critical temperature Tc, critical current density Jc, etc., were measured on such thick film sample. As a result, nearly same values were obtained as Tc (93K) and Jc (84A/cm{sup 2}) which were those of a bulk sample made by using the same powder sample, pressurizing at 2 ton f/cm{sup 2} for pelletizing, and sintering at 845{degree}C for 20 hours. 6 refs., 7 figs., 1 tab.

  6. Thickness dependence of the levitation performance of double-layer high-temperature superconductor bulks above a magnetic rail

    International Nuclear Information System (INIS)

    Sun, R.X.; Zheng, J.; Liao, X.L.; Che, T.; Gou, Y.F.; He, D.B.; Deng, Z.G.

    2014-01-01

    Highlights: • Thickness optimization of double-layer bulk HTSC arrangement is studied. • The new bulk HTSC arrangement makes better use of the flux distribution of the magnetic rails. • Levitation performance can be enhanced with the optimization. • The optimization can meet large levitation force requirements for HTS Maglev system. - Abstract: A double-layer high-temperature superconductor (HTSC) arrangement was proposed and proved to be able to bring improvements to both levitation force and guidance force compared with present single-layer HTSC arrangement. To fully exploit the applied magnetic field by a magnetic rail, the thickness dependence of a double-layer HTSC arrangement on the levitation performance was further investigated in the paper. In this study, the lower-layer bulk was polished step by step to different thicknesses, and the upper-layer bulk with constant thickness was directly superimposed on the lower-layer one. The levitation force and the force relaxation of the double-layer HTSC arrangement were measured above a Halbach magnetic rail. Experimental result shows that a bigger levitation force and a less levitation force decay could be achieved by optimizing the thickness of the lower-layer bulk HTSC. This thickness optimization method could be applied together with former reported double-layer HTSC arrangement method with aligned growth sector boundaries pattern. This series of study on the optimized combination method do bring a significant improvement on the levitation performance of present HTS maglev systems

  7. Thickness dependence of the levitation performance of double-layer high-temperature superconductor bulks above a magnetic rail

    Energy Technology Data Exchange (ETDEWEB)

    Sun, R.X.; Zheng, J.; Liao, X.L.; Che, T.; Gou, Y.F.; He, D.B.; Deng, Z.G., E-mail: zgdeng@gmail.com

    2014-10-15

    Highlights: • Thickness optimization of double-layer bulk HTSC arrangement is studied. • The new bulk HTSC arrangement makes better use of the flux distribution of the magnetic rails. • Levitation performance can be enhanced with the optimization. • The optimization can meet large levitation force requirements for HTS Maglev system. - Abstract: A double-layer high-temperature superconductor (HTSC) arrangement was proposed and proved to be able to bring improvements to both levitation force and guidance force compared with present single-layer HTSC arrangement. To fully exploit the applied magnetic field by a magnetic rail, the thickness dependence of a double-layer HTSC arrangement on the levitation performance was further investigated in the paper. In this study, the lower-layer bulk was polished step by step to different thicknesses, and the upper-layer bulk with constant thickness was directly superimposed on the lower-layer one. The levitation force and the force relaxation of the double-layer HTSC arrangement were measured above a Halbach magnetic rail. Experimental result shows that a bigger levitation force and a less levitation force decay could be achieved by optimizing the thickness of the lower-layer bulk HTSC. This thickness optimization method could be applied together with former reported double-layer HTSC arrangement method with aligned growth sector boundaries pattern. This series of study on the optimized combination method do bring a significant improvement on the levitation performance of present HTS maglev systems.

  8. Advanced nuclear materials development -Development of superconductor application technology-

    International Nuclear Information System (INIS)

    Hong, Kye Won; Lee, Heui Kyoon; Lee, Hoh Jin; Kim, Chan Joong; Jang, Kun Ik; Kim, Kee Baek; Kwon, Sun Chil; Park, Hae Woong; Yoo, Jae Keun; Kim, Jong Jin; Jang, Joong Chul; Yang, Suk Woo

    1995-07-01

    Fabrication of high Tc bulk superconductor and its application, fabrication of superconducting wire for electric power device and analysis for cryogenic system were carried out for developing superconductor application technologies for electric power system. High quality YBaCuO bulk superconductor was fabricated by controlling initial powder preparation process and prototype fly wheel energy storage device was designed basically. The superconducting levitation force measuring device was made to examine the property of prepared superconductor specimen. Systematic studies on the method of starting powder preparation, mechanical fabrication process, heat treatment condition and analysis of plastic deformation were carried out to increase the stability and reproducibility of superconducting wire. A starting powder with good reactivity and fine particle size was obtained by emulsion drying method. Ag/BSCCO tape with good cross sectional shape and Tc of 16,000 A/cm 2 was fabricated by applying CIP packing procedure. Multifilamentary wire with the Jc of approx. 10000 A/cm 2 was fabricated by rolling method using square billet as starting shape. The joining of the multifilament wire was done by etching and pressing process and showed 50% of joining efficiency. Analysis on the heat loss in cryostat for high Tc superconducting device was carried out for optimum design of the future cryogenic system. 126 figs, 14 tabs, 214 refs. (Author)

  9. Advanced nuclear materials development -Development of superconductor application technology-

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Kye Won; Lee, Heui Kyoon; Lee, Hoh Jin; Kim, Chan Joong; Jang, Kun Ik; Kim, Kee Baek; Kwon, Sun Chil; Park, Hae Woong; Yoo, Jae Keun; Kim, Jong Jin; Jang, Joong Chul; Yang, Suk Woo [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1995-07-01

    Fabrication of high Tc bulk superconductor and its application, fabrication of superconducting wire for electric power device and analysis for cryogenic system were carried out for developing superconductor application technologies for electric power system. High quality YBaCuO bulk superconductor was fabricated by controlling initial powder preparation process and prototype fly wheel energy storage device was designed basically. The superconducting levitation force measuring device was made to examine the property of prepared superconductor specimen. Systematic studies on the method of starting powder preparation, mechanical fabrication process, heat treatment condition and analysis of plastic deformation were carried out to increase the stability and reproducibility of superconducting wire. A starting powder with good reactivity and fine particle size was obtained by emulsion drying method. Ag/BSCCO tape with good cross sectional shape and Tc of 16,000 A/cm{sup 2} was fabricated by applying CIP packing procedure. Multifilamentary wire with the Jc of approx. 10000 A/cm{sup 2} was fabricated by rolling method using square billet as starting shape. The joining of the multifilament wire was done by etching and pressing process and showed 50% of joining efficiency. Analysis on the heat loss in cryostat for high Tc superconducting device was carried out for optimum design of the future cryogenic system. 126 figs, 14 tabs, 214 refs. (Author).

  10. Superconductors

    International Nuclear Information System (INIS)

    Newkirk, L.R.; Valencia, F.A.

    1977-01-01

    The structural quality of niobium germanide as a high-transition-temperature superconducting material is substantially improved by the presence of about 5 at. percent oxygen. Niobium germanide having this oxygen content may readily be prepared as a bulk coating bonded to a metallic substrate by chemical vapor deposition techniques. 2 figures, 1 table

  11. Superconductors

    Science.gov (United States)

    Newkirk, Lawrence R.; Valencia, Flavio A.

    1977-02-01

    The structural quality of niobium germanide as a high-transition-temperature superconducting material is substantially improved by the presence of about 5 at. % oxygen. Niobium germanide having this oxygen content may readily be prepared as a bulk coating bonded to a metallic substrate by chemical vapor deposition techniques.

  12. Spectroscopy of metal "superatom" nanoclusters and high-Tc superconducting pairing

    Science.gov (United States)

    Halder, Avik; Kresin, Vitaly V.

    2015-12-01

    A unique property of metal nanoclusters is the "superatom" shell structure of their delocalized electrons. The electronic shell levels are highly degenerate and therefore represent sharp peaks in the density of states. This can enable exceptionally strong electron pairing in certain clusters composed of tens to hundreds of atoms. In a finite system, such as a free nanocluster or a nucleus, pairing is observed most clearly via its effect on the energy spectrum of the constituent fermions. Accordingly, we performed a photoionization spectroscopy study of size-resolved aluminum nanoclusters and observed a rapid rise in the near-threshold density of states of several clusters (A l37 ,44 ,66 ,68 ) with decreasing temperature. The characteristics of this behavior are consistent with compression of the density of states by a pairing transition into a high-temperature superconducting state with Tc≳100 K. This value exceeds that of bulk aluminum by two orders of magnitude. These results highlight the potential of novel pairing effects in size-quantized systems and the possibility to attain even higher critical temperatures by optimizing the particles' size and composition. As a new class of high-temperature superconductors, such metal nanocluster particles are promising building blocks for high-Tc materials, devices, and networks.

  13. Bec Model of HIGH-Tc Superconductivity in Layered Cuprates

    Science.gov (United States)

    Lomnitz, M.; Villarreal, C.; de Llano, M.

    2013-11-01

    High-Tc superconductivity in layered cuprates is described in a BCS-BEC formalism with linearly-dispersive s- and d-wave Cooper pairs moving in quasi-2D finite-width layers around the CuO2 planes. This yields a closed formula for Tc involving the layer width, the Debye frequency, the pairing energy and the in-plane penetration depth. The new formula has no free parameters and reasonably reproduces empirical values of superconducting Tcs for 11 different layered superconductors over a wide doping regime including YBCO itself as well as other compounds like LSCO, BSCCO and TBCCO. In agreement with the London formalism, the formula also yields a fair description of the Tc dependence of the lower critical magnetic field in highly underdoped YBCO.

  14. High-Tc superconducting antenna-coupled microbolometer on silicon

    Science.gov (United States)

    Rice, Joseph P.; Grossman, Erich N.; Borcherdt, L. J.; Rudman, D. A.

    1994-05-01

    A process is described for fabricating antenna-coupled resistive-edge microbolometers based on the high-Tc superconductor YBa2Cu3O7 (YBCO) on silicon. The YBCO and a buffer layer of yttria-stabilized zirconia (YSZ) were grown epitaxially on silicon to minimize excess electrical noise. A silicon-micromachined YBCO/YSZ air-bridge was incorporated to minimize the thermal conductance and the heat capacity. The thermal conductance of the air-bridge was measured to be 3 X 10-6 W/K at a temperature of 100 K. At an operating temperature of 89 K, the detector is estimated to have a response time of 2 microsecond(s) , a responsivity of the 1000 V/W range, and a noise-equivalent power in the 10-12 W/Hz1/2 range at 1000 Hz.

  15. High-{Tc} superconducting antenna-coupled microbolometer on silicon

    Energy Technology Data Exchange (ETDEWEB)

    Rice, J.P.; Grossman, E.N.; Borcherdt, L.J.; Rudman, D.A. [National Inst. of Standards and Technology, Boulder, CO (United States). Cryoelectronic Metrology Group

    1994-12-31

    A process is described for fabricating antenna-coupled resistive-edge microbolometers based on the high-{Tc} superconductor YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO) on silicon. The YBCO and a buffer layer of yttria-stabilized zirconia (YSZ) were grown epitaxially on silicon to minimize excess electrical noise. A silicon-micromachined YBCO/YSZ air-bridge was incorporated to minimize the thermal conductance and the heat capacity. The thermal conductance of the air-bridge was measured to be 3 {times} 10{sup {minus}6} W/K at a temperature of 100 K. At an operating temperature of 89 K, the detector is estimated to have a response time of 2 {micro}s, a responsivity in the 1,000 V/W range, and a noise-equivalent power (NEP) in the 10{sup {minus}12} W/Hz{sup 1/2} range at 1,000 Hz.

  16. Measurement method of moving vehicle in the magnetic levitation and propulsion system using high-Tc superconducting bulks; Koon chodendo barukutai wo riyoshita fujo suishin shisutemu no suishin tokusei keisoku shuho

    Energy Technology Data Exchange (ETDEWEB)

    Fuwa, Y.; Mizuma, T.

    1999-06-07

    The transportation system using simple magnetic levitation system got in the combination of high-temperature superconductivity bulk body and permanent magnet, which caught a quantum magnetic flux, is devised in great numbers, and the model equipment has also been manufactured. In the meantime, a grasp of levitation and guide characteristics is necessary for the case in which this levitation system is applied to the simple individual transportation system, and the measurement of the levitation characteristics is indispensable for the reason. In the conventional research, the measurement of the levitation characteristics has not been very much made. There was due to be no technique which measured kinetic characteristics of noncontacting surfacing and running travel body. In this study, measuring method for measuring these levitation characteristics was devised, and it was applied to actual measurement by the production of the model test equipment. Through this measurement, the purpose of this study is to show with that it is applicable for the real test equipment as this measuring method judges possibility of application to simple transportation system. (NEDO)

  17. Dissipation measurement in high Tc superconductors with electromagnetic probes

    International Nuclear Information System (INIS)

    Telschow, K.L.; O'Brien, T.K.; Idaho State Univ., Pocatello, ID

    1989-01-01

    The new ceramic superconducting materials, which have transition temperatures above that of liquid nitrogen, have great potential. However, most fabrication schemes produce consolidated forms with relatively low critical currents; successful application of these materials requires a means of measuring their critical parameters (such as critical current) that can be used to monitor and control fabrication processes. This paper describes a technique for measuring the onset of dissipation in a superconducting coating in a local and noncontacting manner. This work begins the process of developing noncontacting techniques for the measurement of critical currents on a local scale with the capability of providing spatial information. 6 refs., 6 figs

  18. Positron annihilation at defects in sintered high Tc perovskite superconductors

    International Nuclear Information System (INIS)

    Corbel, C.; Bernede, P.; Pascard, H.; Rullier-Albenque, F.; Kormann, R.; Marucco, J.F.

    1988-01-01

    We report positron lifetime measurements in sintered superconducting YBa 2 Cu 3 O 7-x and GdBa 2 Cu 3 O 7-x oxides. It is shown that the thermal behaviour of the positron lifetime spectra strongly depends on the preparation of the ceramics. A lifetime of 190±3 ps is attributed to oxygen deficient regions. Two lifetimes of 251±7 ps and 225±5 ps are attributed to a cation vacancy presenting a temperature dependent atomic arrangement. The lifetime transition (251 → 225 ps) occurs during decreases in temperature across the resistivity superconducting transition. This lifetime change indicates that the volume of the cation vacancy decreases in the superconducting state

  19. Simple-decoupling treatment of high-Tc superconductors

    International Nuclear Information System (INIS)

    Misawa, S.

    1992-01-01

    The t-J model is examined within the framework of the Hubbard-I-type decoupling method of the Green's functions and by using the Fukuyama's expression for Hall coefficient R H . The superconducting transition temperature T c and the normal-state R H at finite temperature are calculated as functions of doping-fraction δ. The obtained results are symmetrical with respect to hole- and electron-doping. In the small hole-doping case, the extended s-wave state is favorable, and the behaviors of T c and R H as functions of δ are qualitatively in agreement with the experimental results. (orig.)

  20. Evidence for intrinsic critical current density in high Tc superconductors

    International Nuclear Information System (INIS)

    Freltoft, T.; Minnhagen, P.; Jeldtoft Jensen, H.

    1991-01-01

    We present measurements of the voltage-current characteristics of high quality epitaxial YBaCuO films in zero magnetic field. According to the predictions of a current induced vortex pair breaking picture the voltage should follow the functional form V∝I(I-I c ) a-1 . An analysis designed to test this functional behavior is carried out. Consistency is found. (orig.)

  1. The 9th symposium of high Tc superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Hojou, Kiichi; Okayasu, Satoru; Sasase, Masato [eds.

    1998-03-01

    This workshop was carried out on December 11 and 12, 1997, at JAERI, Tokai in a series of modification of material by irradiation in `the multi core project II of the high temperature superconducting material research` organized by Science and Technology Agency. The following is the abstract of presentations concerning basic theories, various experimental results and material improvement of the superconductivity by high energy ion irradiation. The 26 papers are indexed individually. (J.P.N.)

  2. Selected problems in power applications of high Tc superconductors

    DEFF Research Database (Denmark)

    Tønnesen, Ole; Pedersen, Niels Falsig

    2001-01-01

    Two important problems connected with power applications of BSCCO tapes are discussed: (i) the problem of developing prototypes when the tape properties are changing, and (ii) the problem of flux pinning in intrinsic BSCCO. An overview of the different projects on superconducting power cables is ...

  3. Flux lattice melting in high-Tc superconductors

    International Nuclear Information System (INIS)

    Houghton, A.; Pelcovits, R.A.; Sudbo, A.

    1989-01-01

    We derive the wave-vector-dependent elastic moduli for a flux line lattice in compounds with underlying tetragonal crystalline symmetry. We find that it is essential to retain wave-vector dependence of the moduli when dealing with compounds where κ is large, as it is in the high-T c materials. We use our results to establish a Lindemann criterion for flux lattice melting, which we then compare with experimental data on two materials, and find excellent agreement. The melting curves are suppressed well below the mean-field superconducting-normal transition line and are linear in temperature over a wide range of magnetic fields. The point H=0, T=T c is approached as 1-T/T c ∼H 1/2 . The degree of suppression of the melting curves among the different compounds is accounted for in the main by differences in mass anisotropy

  4. Studying the kinetics of magnetization in high Tc superconductors

    Science.gov (United States)

    Turchinskaya, Marina

    1993-01-01

    The first microscopic maps of magnetic induction in YBa2Cu3O(7-x) crystals which directly show the dependence of flux flow on twin density and polytwin block and twin boundary orientation are reported. These maps were obtained by means of a recently-improved magneto-optical imaging technique. Pinning was lowest in untwinned regions and increased with increasing twin density. An isotropy in twin boundary pinning, defined as the ratio of the magnetic induction gradient across twin boundaries to that along twin boundaries, was 10 at 17 K; this ratio increased with increasing temperature. In polycrystals, twin boundaries also had a strongly anisotropic effect on flux flow into a grain from a grain boundary.

  5. Carbon-based superconductors towards high-Tc superconductivity

    CERN Document Server

    Haruyama, Junji

    2014-01-01

    Introduction of Condensed Matter Physics; Spin-state Crossover; Li Ion Battery; Huge Thermoelectric Power; Room-temperature Ferromagnetism; Partially Disordered Antiferromagnetic Transition; Superconductivity; Transport Properties Combined with Charge, Spin, and Orbital; Magnetoresistance and Spin Blocade; Intrinsic Inhomogeneity; Move/diffuse and Charge/discharge Effect.

  6. Pinning by oxygen vacancies in high-Tc superconductors

    International Nuclear Information System (INIS)

    Chudnovsky, E.M.

    1990-01-01

    It is shown that recent data of Murray et al. on spatial correlations in flux lattices of Bi-Sr-Ca-Cu-O (BSCCO) may be explained if one assumes that 1% of oxygen atoms in CuO 2 layers are missing. This estimate, being in remarkable agreement with that deduced by Kes and van der Beek from ac-susceptibility measurements, provides strong confidence that oxygen vacancies are the major source of pinning in BSCCO

  7. Thin film production of ceramic high-Tc-superconductors (targets)

    International Nuclear Information System (INIS)

    1992-01-01

    Presently high-quality thin superconducting films having high T c 's may prepared by the sputtering technique. However, a large-area coating is required for an industrial application. One requirement is the availability of sputter targets with controlled and reproducible properties. By means of basic experiments with respect to powder processing, shaping and the densification process superconducting targets up to 200 mm in diameter were prepared in the Y-Ba-Cu-O- system. Additionally, targets from other systems with different geometries (e.g. ring targets) were prepared. These targets were submitted to the project partners as well as to other institutes and companies. During the course of this project the foundations for an industrial-type coating of large-area substrates were elaborated. (orig.). 9 refs., 5 tabs., 15 figs [de

  8. Anisotropic properties of single crystals of high Tc superconductors

    International Nuclear Information System (INIS)

    Tholence, J.L.; Saint-Paul, M.; Laborde, O.; Monceau, P.; Guillot, M.; Niel, H.; Levet, J.C.; Potel, M.; Padiou, J.; Gougeon, P.

    1990-01-01

    In this article the authors make a review of some of the anisotropic properties of high T c compounds, essentially RE Ba 2 Cu 3 O 7 , Bi-SR-Ca-Cu-O and Tl-Ca-Ba-Cu-O systems. In section 2 a short description of the crystal growth is reported. Section 3 deals with the anisotropic elastic properties measured by ultrasonic techniques. In section 4 the authors discuss the anisotropy in magnetization measurements and consequently on the critical currents. Section 5 concerns the magnetoresistance measurements, and the determination of the superconducting critical magnetic field H c2 . Finally in section 6, in conclusion of result described in sections 4 and 5, the authors discuss on the pinning force and on the controversial Lorentz force for explaining the broadening of the superconducting transition under magnetic field. The authors apologize for not having quoted all the works published on these different topics, which is in fact practically impossible

  9. Superconductivity and charge transfer excitations in high Tc superconductors

    International Nuclear Information System (INIS)

    Balseiro, C.A.; Alascio, B.; Gagliano, E.; Rojo, A.

    1988-01-01

    We present some numerical results to show that in a simple model which includes Cu 3d and O 2p orbitals together with inter and intra atomic correlations pairing between holes can occur due to charge transfer excitations. We present also a simple approximation to derive an effective Hamiltonian containing an interaction between particles which is attractive for some values of the different microscopic parameters

  10. c-axis ac susceptibility in high-Tc superconductors

    International Nuclear Information System (INIS)

    Waldmann, O.; Lichtschlag, G.; Talalaevskii, A.; Kleiner, R.; Mueller, P.; Steinmeyer, F.; Gerhaeuser, W.

    1996-01-01

    We have investigated the angle and magnetic field dependence of the ac susceptibility in Bi 2 Sr 2 CaCu 2 O 8 and YBa 2 Cu 3 O 7 single crystals at low external fields. The ac field was applied perpendicular to the CuO 2 planes. The first and third harmonics of the ac susceptibility exhibit remarkably sharp features when the dc field component perpendicular to the CuO 2 planes passes a threshold field H th . H th is strongly temperature dependent, but is independent of the parallel field component. We propose a simple model which excellently explains the data. Within this model the peak structures are related to the irreversibility line. We discuss the implications of the model for the interpretation of the ac susceptibility. copyright 1996 The American Physical Society

  11. Electronic structure and chemical bond of high Tc superconductors

    International Nuclear Information System (INIS)

    Gupta, R.P.

    1988-01-01

    Results of the band structure calculations for the compound Bi 2 Sr 2 CaCu 2 O 8 are discussed and compared to those obtained for YBa 2 Cu 3 O 7 . An analysis of the contribution of the densities of states at the different atomic sites shows that the states at the Fermi energy. E F , have a strong bidimensional character due to the CuO 2 planes. Moreover, for the bismuth compound, the contribution of the Bi-O planes at E F is substantial. The elements Y and Ba in YBa 2 Cu 3 O 7 , Ca and Sr in Bi 2 Sr 2 CaCu 2 O 8 act essentially as electron donors, the corresponding densities of states at E F are very small. An analysis of the electronic charge at the different atomic sites is presented. The respective roles of the CuO 2 planes. Cu-O chains and Bi-O planes on the electronic properties at the Fermi level are discussed [fr

  12. Terahertz Responses of Intrinsic Josephson Junctions in High TC Superconductors

    International Nuclear Information System (INIS)

    Wang, H. B.; Wu, P. H.; Yamashita, T.

    2001-01-01

    High frequency responses of intrinsic Josephson junctions up to 2.5THz, including the observation of Shapiro steps under various conditions, are reported and discussed in this Letter. The sample was an array of intrinsic Josephson junctions singled out from inside a high T C superconducting Bi 2 Sr 2 CaCu 2 O 8+x single crystal, with a bow-tie antenna integrated to it. The number of junctions in the array was controllable, the junctions were homogeneous, the distribution of applied irradiation among the junctions was even, and the junctions could synchronously respond to high frequency irradiation

  13. Fluctuations of order parameters in the high Tc superconductors

    International Nuclear Information System (INIS)

    Das, M.P.; Saif, A.G.

    1987-07-01

    Recently we have proposed a phenomenological approach in terms of two coexisting macroscopic order parameters corresponding to the superconducting and insulating states and have discussed the electrodynamical responses of the superconducting ceramics. In this paper we discuss the fluctuations of the order parameters both in the static and in the dynamical situations in the mean field approach and obtain results for the electrical conductivity which possesses anomalies as in granular materials. (author). 22 refs

  14. Modification of High Tc Superconductors by Ion Implantation

    National Research Council Canada - National Science Library

    Geballe, T

    1997-01-01

    The transport properties of La-Ca manganites with the perovskite structure have been investigated over a wide range of temperatures above room temperature, and over the whole La-Ca concentration range...

  15. Localization effects in rare earth high Tc superconductors

    International Nuclear Information System (INIS)

    Badera, Nitu; Godbole, Bhavana; Srivastava, S.B.; Rathore, M.K.; Ganesa, V.

    2006-01-01

    The Y 1-x Gd x Ba 2 Cu 3 O 7-δ samples have been prepared for different concentration of Gd . We employ thermoelectric power technique, which is sensitive to changes at the Fermi surface to study these materials. Metallic diffusion model and two band model are used to evaluate the normal state properties of these materials. At concentrations above 5% clear wide linear regions have been observed suggesting good evidence for localized states. (author)

  16. Five-fold way to new high Tc superconductors

    Indian Academy of Sciences (India)

    shook the foundation of phonon-mediated pairing mechanism. In fact, certain in- ...... of superconducting Tc in doped cuprates below optimal doping. ...... ductor transition, the following are the minimal requirements for superconductivity:.

  17. Theoretical aspects of electronic structure of high Tc superconductors

    International Nuclear Information System (INIS)

    Gupta, R.P.

    1990-01-01

    Although the mechanism responsible for the high T c superconductivity is still unknown, it is nevertheless clear that superconductivity in hole doped materials depends sensitively on the number of holes, C h , per CuO 2 plane. A correlation between C h and T c has been established. In this paper we present several examples of the critical dependence of the charge transfer and thus the value of C h on the cristallographic characteristics. For example, our electronic structure investigations of YBa 2 Cu 3 O 6.5 using several configurations of the oxygen atoms on the chains show that the order-disorder phenomena of the oxygen atoms play a crucial role on the value of C h and T c . We have also studied the variation of the charge transfer and C h as a function of hydrostatic pressure for several cuprates: La 1.85 Sr 0.15 CuO 4 (ΔT c /Δp ∼ 0.3 - 0.4 K/kbar); YBa 2 Cu 4 O 8 (ΔT c /Δp ∼ 5.5 K/kbar). We show that the values of C h increase under pressure [fr

  18. Nonlinear phonons in high-Tc superconductors mixed crystals

    International Nuclear Information System (INIS)

    Gadzhiev, B.R.; Dzhavadov, N.A.

    1998-01-01

    The integrodifferential kinetic equation which is a generalization of the Landau-Ginzburg formalism is introduced. The peculiarities of nonlinear kinetics are investigated by entering the nonlocal function, which is a quantitative measure of time dispersion. The classification nonlocal function is made by its Hausdorff dimensionality d c . It is shown that in the case d c c =1, the relaxation equation is the equation of damping harmonic oscillator. In the case d c >1, the relaxation equation contains the time derivation arbitrary high order. After linearization of the corresponding dynamic equations near the corresponding nonlinear static equations the dispersion and then after spatial averaging, temperature and frequency dependency of corresponding dynamic susceptibility have been determined. It is shown that in the cases d c c >1 the temperature evolution system alongside with the soft mode is accompanied by the modes which depend nonlinearly on the temperature. The physical nature of quasiscattering in the incommensurate phases of layered crystals is studied. The obtained theoretical results are applied to the layered HTSC crystals. (author)

  19. Kosterlitz-Thouless transition in high-Tc superconductor films

    International Nuclear Information System (INIS)

    Davis, L.C.; Beasley, M.R.; Scalapino, D.J.

    1990-01-01

    Dynamical theory for the polarization of bound vortex-antivortex pairs near the Kosterlitz-Thouless transition (T KT =88.4 K) has been applied to thin films of YBa 2 Cu 3 O 7 . Calculations show that the correct order of magnitude is predicted for the loss function ωG/c 2 at T KT , but the temperature dependence below the transition is wrong. The theoretical value drops much more rapidly with decreasing temperature than observed experimentally. Similar disagreement is found for the penetration depth λ(T). Estimates of the loss function at microwave frequencies show rather large effects near the critical temperature, but these become negligible by 80 K. The performance of microwave devices operating at liquid-N 2 temperature should not be degraded by vortex-antivortex pairs

  20. The 9th symposium of high Tc superconductors

    International Nuclear Information System (INIS)

    Hojou, Kiichi; Okayasu, Satoru; Sasase, Masato

    1998-03-01

    This workshop was carried out on December 11 and 12, 1997, at JAERI, Tokai in a series of modification of material by irradiation in 'the multi core project II of the high temperature superconducting material research' organized by Science and Technology Agency. The following is the abstract of presentations concerning basic theories, various experimental results and material improvement of the superconductivity by high energy ion irradiation. The 26 papers are indexed individually. (J.P.N.)

  1. Positron Annihilation Studies of High-Tc Superconductors

    Science.gov (United States)

    Peter, M.; Manuel, A. A.

    1989-01-01

    First we present the principles involved in the study of the two-photon momentum distribution: The method requires deconvolution of the positron wavefunction and the estimation of matrix elements effects. Single crystal samples must be of sufficient quality to avoid positron trapping (tested by positron lifetime measurements). In ordinary metals (alkalis, transition- and rare earth metals and compounds) two-photon momentum distribution studies have given results in close agreement with relevant band structure calculations. Discrepancies have been successfully described as enhancement effects due to correlations. In the superconducting oxides, measurements are more difficult because there are fewer conduction electrons and more trapping. Correlation effects of a different nature are expected to be important and might render the band picture inappropriate. Two-photon momentum distribution measurements have now been made by several groups, but have been interpreted in different ways. We relate the current state of affairs, and our present interpretation, to the latest available results.

  2. The 11th symposium of high Tc superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Hojou, Kiichi; Okayasu, Satoru; Sasase, Masato [eds.] [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    2000-03-01

    This workshop was carried out on December 16 and 17, 1999, at JAERI, Tokai in a series of modification material by irradiation in 'the multi-core project II of the high temperature superconducting material research' organized by Science and Technology Agency. The following is the abstract of presentations concerning basic theories, various experimental results and material improvement of the superconductivity by high energy ion irradiation. (author)

  3. Magnetism and electron pairing in high-Tc superconductors

    Science.gov (United States)

    Tsang, T.

    1990-01-01

    Correlated wave functions are used for YBa2Cu3O(7-y) where epsilon(d)-epsilon(p) is about 0 for Cu3d- and 02p-electrons. The electrons are delocalized (metallic) for y less than 0.5 with weak and temperature-independent paramagnetism. In contrast, the systems are conventional antiferromagnetic insulators for y greater than 0.6 with a narrow y between 0.5 and 0.6 transition region. These results are in agreement with magnetic and neutron diffraction data.

  4. Vortex dynamics and correlated disorder in high-{Tc} superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Vinokur, V.M.

    1993-08-01

    We develop a theory for the vortex motion in the presence of correlated disorder in the form of the twin boundaries and columnar defects. Mapping vortex trajectories onto boson world lines enables us to establish the duality of the vortex transport in the systems with correlated disorder and hopping conductivity of charged particles in 2D systems. A glassy-like dynamics of the vortex lines with zero linear-resistivity and strongly nonlinear current-voltage behavior as V {proportional_to} exp[{minus} const/J{sup {mu}}] in a Bose glass state is predicted.

  5. The 11th symposium of high Tc superconductors

    International Nuclear Information System (INIS)

    Hojou, Kiichi; Okayasu, Satoru; Sasase, Masato

    2000-03-01

    This workshop was carried out on December 16 and 17, 1999, at JAERI, Tokai in a series of modification material by irradiation in 'the multi-core project II of the high temperature superconducting material research' organized by Science and Technology Agency. The following is the abstract of presentations concerning basic theories, various experimental results and material improvement of the superconductivity by high energy ion irradiation. (author)

  6. Grain alignment in bulk YBa2Cu3Ox superconductor by a low temperature phase transformation method

    International Nuclear Information System (INIS)

    Selvamanickam, V.; Goyal, A.; Kroeger, D.M.

    1994-01-01

    A quench and directional phase transformation process has been developed to achieve grain alignment in bulk YBa 2 Cu 3 O x superconductors at temperatures about 100 degree C below the peritectic temperature. Isothermal phase transformation of quenched precursors at 890 degree C for 3 min is found to result in the formation of more than 75% of YBa 2 Cu 3 O x phase without any formation of Y 2 BaCuO 5 . Phase transformation at higher temperatures leads to rapid formation of Y 2 BaCuO 5 in addition to YBa 2 Cu 3 O x . A well-aligned microstructure is achieved by directional phase transformation of the quenched compacts as a rate of 10 mm/h. The magnetic field dependence of the critical current density at 77 K of the directionally phase transformed material compares well with that of melt-textured YBCO and is superior to that of magnetically aligned and sintered YBCO

  7. Levitation force and magnetization in bulk and thin film high T{sub c} superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Riise, A.B

    1998-04-01

    The authors present high-resolution measurements of the repulsive vertical force and its associated stiffness between a Nd-B-Fe magnet and a YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} superconductor in cylindrical geometry. The results are compared with theoretical predictions. The calculations are based on a model in which the superconductor is assumed to be either a sintered granular material or consisting of grains embedded in a nonactive matrix so that only intragranular currents are important. The critical state model is applied to each grain individually and closed form expressions for both vertical force F{sub z} and stiffness are obtained in a configuration with cylindrical symmetry. The model explains all features of the experimental results in a consistent way. A good quantitative agreement has been obtained using only three adjustable parameters. Several central aspects of the phenomenon of magnetic levitation with high-T{sub c} superconductors are presented. High-resolution measurements are made of the repulsive vertical force and its associated stiffness as well as the horizontal stabilizing force and the stiffness governing lateral vibrations. The results obtained at 77 K using a granular YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} sample and Nd-Fe-B magnet in a rectangular levitation configuration are compared with theoretical predictions. The calculations, which are based on the critical state model with the assumption that it applies to the grins individually, give closed-form expressions for all the measured quantities. It is concluded that the present model explains all features of the observations in a consistent way. Using only three adjustable parameters a good agreement exists also at a quantitative level. Experimental studies and theoretical modelling of the levitation force on a permanent magnet placed above a superconducting thin film are offered. It is shown that measurements of the levitation force is a simple and precise method to determine the

  8. AC susceptibility response of bulk YBCO superconductors in the presence of a temperature gradient

    International Nuclear Information System (INIS)

    Bodi, A.C.; Kirschner, I.

    1997-01-01

    Low-frequency AC susceptibility measurements on ceramic YBCO superconductors carried out at the presence of a quasi-one-dimensional temperature gradient are compared with those made without the temperature gradient. The values of the different characteristic temperatures measured on samples without and with a temperature gradient are identical but in the second case its characteristic temperature is a medium value. When the temperature gradient is constant on the sample the arithmetic medium value of the local temperatures is the effective characteristic temperature different phenomena. (orig.)

  9. Performance prediction of high Tc superconducting small antennas using a two-fluid-moment method model

    Science.gov (United States)

    Cook, G. G.; Khamas, S. K.; Kingsley, S. P.; Woods, R. C.

    1992-01-01

    The radar cross section and Q factors of electrically small dipole and loop antennas made with a YBCO high Tc superconductor are predicted using a two-fluid-moment method model, in order to determine the effects of finite conductivity on the performances of such antennas. The results compare the useful operating bandwidths of YBCO antennas exhibiting varying degrees of impurity with their copper counterparts at 77 K, showing a linear relationship between bandwidth and impurity level.

  10. Impurity scattering effect on charge transport in high-Tc cuprate junctions

    International Nuclear Information System (INIS)

    Tanaka, Y.; Asano, Y.; Kashiwaya, S.

    2004-01-01

    It is known that the zero-bias conductance peak (ZBCP) is expected in tunneling spectra of normal-metal/high-Tc cuprate junctions because of the formation of the midgap Andreev resonant states (MARS) at junction interfaces. In the present review, we report the recent theoretical study of impurity scattering effects on the tunneling spectroscopy. In the former part of the present paper, we discuss impurity effects in normal metal. We calculate tunneling conductance for diffusive normal metal (DN)/high Tc cuprate junctions based on the Keldysh Green's function technique. Besides the ZBCP due to the MARS, we can expect ZBCP caused by the different origin, i.e., the coherent Andreev reflection (CAR) assisted by the proximity effect in DN. Their relative importance depends on the angle a between the interface normal and the crystal axis of high-Tc superconductors. At α = 0, we find the ZBCP by the CAR for low transparent junctions with small Thouless energies in DN; this is similar to the case of diffusive normal metal/insulator/s-wave superconductor junctions. Under increase of α from zero to π/4, the contribution of MARS to ZBCP becomes more prominent and the effect of the CAR is gradually suppressed. Such complex spectral features would be observable in conductance spectra of high-Tc junctions at very low temperatures. In the latter part of our paper, we study impurity effects in superconductors. We consider impurities near the junction interface on the superconductor side. The conductance is calculated from the Andreev and the normal reflection coefficients which are estimated by using the single-site approximation in an analytic calculation and by the recursive Green function method in a numerical simulation. We find splitting of the ZBCP in the presence of the time reversal symmetry. Thus the zero-field splitting of ZBCP in the experiment does not perfectly prove an existence of broken time reversal symmetry state

  11. Processing of Mixed Oxide Superconductors

    Science.gov (United States)

    1990-07-01

    rapid changes world wide a major research centre on high Tc superconductors was awarded to Cambridge which involved moving the work and people to a...reports and paper is in the appendices. Separation Ceramic superconductors tend to be mixtures of phases, especially when first discovered. It would...properties of the superconducting state will in principle allow superconducting material to be levitated from the non superconductor and several designs

  12. The enhancement of critical current density on the bulk of BPSCCO-system superconductor with silver additions

    International Nuclear Information System (INIS)

    Engkir Sukirman; Wisnu Ari Adi; Puji Sulisworo dan W Prasuad

    1999-01-01

    The influence of silver additions on the critical current density (Jc) of BPSCCO-bulk superconductor was investigated, with the aim of getting an increase of its Jc and trying to find out a correlation of Jc and structures of BPSCCO-silver composites. The BPSCCO-system superconductors with nominal composition Bi 1.84 Pb 0.34 Sr 2.00 Ca 2.03 Cu 3.06 O x (2223-phase) were synthesized by using solid state reaction method. The silver added was in the powder-AgO form varied from 0 to 30 wt % AgO. The critical current density, crystal structure, and micro-structure of BPSCCO-silver composites were characterized by means of four-point probe, x-ray diffractometer, and scanning electron microscope that is equipped with a link system energy dispersive spectrometer. It was found that silver additions to BPSCCO cause a reasonable improvement in Jc from 120 to 215 A/cm 2 , and a slight increase in Tc from 92 to 108 K, and lattice parameters of the 2223-phase from a 3.811(3) to 3.820(2) A, and from c = 37.08(3) to 37.15(2) A, with the optimum value occurs at 20 wt % AgO. The AgO powders added to the BPSCCO specimens were converted to Ag 2 O and metallic Ag during the annealing process at 827degC for 96 h in air. The addition of AgO to BPSCCO system does not necessarily lead to decomposition of the 2223-phase. The AgO reacts with and suppresses the 2201-phase. (author)

  13. Remagnetization of bulk high-temperature superconductors subjected to crossed and rotating magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Vanderbemden, P [SUPRATECS and Department of Electrical Engineering and Computer Science B28, Sart-Tilman, B-4000 Liege (Belgium); Hong, Z [Centre for Advanced Photonics and Electronics, Engineering Department, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA (United Kingdom); Coombs, T A [Centre for Advanced Photonics and Electronics, Engineering Department, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA (United Kingdom); Ausloos, M [SUPRATECS and Department of Physics B5, Sart-Tilman, B-4000 Liege (Belgium); Babu, N Hari [IRC in Superconductivity, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Cardwell, D A [IRC in Superconductivity, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Campbell, A M [IRC in Superconductivity, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom)

    2007-09-15

    Bulk melt-processed Y-Ba-Cu-O (YBCO) has significant potential for a variety of high-field permanent-magnet-like applications, such as the rotor of a brushless motor. When used in rotating devices of this kind, however, the YBCO can be subjected to both transient and alternating magnetic fields that are not parallel to the direction of magnetization and which have a detrimental effect on the trapped field. These effects may lead to long-term decay of the magnetization of the bulk sample. In the present work, we analyze both experimentally and numerically the remagnetization process of a melt-processed YBCO single domain that has been partially demagnetized by a magnetic field applied orthogonal to the initial direction of trapped flux. Magnetic torque measurements are used as a tool to probe changes in the remanent magnetization during various sequences of applied field. The application of a small magnetic field between the transverse cycles parallel to the direction of original magnetization results in partial remagnetization of the sample. Rotating the applied field, however, is found to be much more efficient at remagnetizing the bulk material than applying a magnetizing field pulse of the same amplitude. The principal features of the experimental data can be reproduced qualitatively using a two-dimensional finite-element numerical model based on an E-J power law. Finally, the remagnetization process is shown to result from the complex modification of current distribution within the cross-section of the bulk sample.

  14. Remagnetization of bulk high-temperature superconductors subjected to crossed and rotating magnetic fields

    International Nuclear Information System (INIS)

    Vanderbemden, P; Hong, Z; Coombs, T A; Ausloos, M; Babu, N Hari; Cardwell, D A; Campbell, A M

    2007-01-01

    Bulk melt-processed Y-Ba-Cu-O (YBCO) has significant potential for a variety of high-field permanent-magnet-like applications, such as the rotor of a brushless motor. When used in rotating devices of this kind, however, the YBCO can be subjected to both transient and alternating magnetic fields that are not parallel to the direction of magnetization and which have a detrimental effect on the trapped field. These effects may lead to long-term decay of the magnetization of the bulk sample. In the present work, we analyze both experimentally and numerically the remagnetization process of a melt-processed YBCO single domain that has been partially demagnetized by a magnetic field applied orthogonal to the initial direction of trapped flux. Magnetic torque measurements are used as a tool to probe changes in the remanent magnetization during various sequences of applied field. The application of a small magnetic field between the transverse cycles parallel to the direction of original magnetization results in partial remagnetization of the sample. Rotating the applied field, however, is found to be much more efficient at remagnetizing the bulk material than applying a magnetizing field pulse of the same amplitude. The principal features of the experimental data can be reproduced qualitatively using a two-dimensional finite-element numerical model based on an E-J power law. Finally, the remagnetization process is shown to result from the complex modification of current distribution within the cross-section of the bulk sample

  15. Temperature dependence of the mechanical properties of melt-processed Dy-Ba-Cu-O bulk superconductors evaluated by three point bending tests

    International Nuclear Information System (INIS)

    Katagiri, K; Nyilas, A; Sato, T; Hatakeyama, Y; Hokari, T; Teshima, H; Iwamoto, A; Mito, T

    2006-01-01

    Dy-Ba-Cu-O bulk superconductor has an excellent capability of trapping magnetic flux and lower heat conductivity at cryogenic temperatures as compared with Y-Ba-Cu-O bulk superconductor. The Young's modulus and the bending strength in the range from room temperature to 7 K were measured by the three-point bending tests using specimens cut from a melt-processed Dy-Ba-Cu-O bulk superconductor. They were tested in a helium gas flow type cryostat at Forschungszentrum Karlsruhe and in a liquid nitrogen bath at Iwate University. The Young's modulus was calculated by either the slope of stress-strain curve or that of the load-deflection curve of the specimen. Although the bending strength measured in the two institutes coincided well, there was a significant discrepancy in the Young's modulus. The Young's modulus and bending strength increased with decrease of temperature down to 7 K. The amount of increase in the Young's modulus and the bending strength were about 32% and 36% of those at room temperature, respectively. The scatter of data for each run was significant and did not depend on temperature. The temperature dependence of the Young's modulus coincided with that in Y-Ba-Cu-O obtained by ultrasonic velocity. The temperature dependence of the Young's modulus and the bending strength was discussed from the view point of interatomic distance of the bulk crystal

  16. Feasibility of introducing ferromagnetic materials to onboard bulk high-T{sub c} superconductors to enhance the performance of present maglev systems

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Zigang, E-mail: zgdeng@gmail.com [Applied Superconductivity Laboratory (ASCLab), Southwest Jiaotong University (SWJTU), Chengdu, Sichuan 610031 (China); State Key Laboratory of Traction Power (TPL), Southwest Jiaotong University (SWJTU), Chengdu, Sichuan 610031 (China); Wang, Jiasu [Applied Superconductivity Laboratory (ASCLab), Southwest Jiaotong University (SWJTU), Chengdu, Sichuan 610031 (China); Zheng, Jun; Zhang, Ya [Applied Superconductivity Laboratory (ASCLab), Southwest Jiaotong University (SWJTU), Chengdu, Sichuan 610031 (China); State Key Laboratory of Traction Power (TPL), Southwest Jiaotong University (SWJTU), Chengdu, Sichuan 610031 (China); Wang, Suyu [Applied Superconductivity Laboratory (ASCLab), Southwest Jiaotong University (SWJTU), Chengdu, Sichuan 610031 (China)

    2013-02-14

    Highlights: ► Ferromagnetic materials guide the flux distribution of the PMG to bulk positions. ► With ferromagnetic materials, guidance performance can be enhanced greatly. ► A new HTS Maglev system with onboard ferromagnetic materials is designed. ► The design can meet large guidance force requirements for practical applications. -- Abstract: Performance improvement is a long-term research task for the promotion of practical application of promising high-temperature superconducting (HTS) magnetic levitation (maglev) vehicle technologies. We studied the feasibility to enhance the performance of present HTS Maglev systems by introducing ferromagnetic materials to onboard bulk superconductors. The principle here is to make use of the high magnetic permeability of ferromagnetic materials to alter the flux distribution of the permanent magnet guideway for the enhancement of magnetic field density at the position of the bulk superconductors. Ferromagnetic iron plates were added to the upper surface of bulk superconductors and their geometric and positioning effects on the maglev performance were investigated experimentally. Results show that the guidance performance (stability) was enhanced greatly for a particular setup when compared to the present maglev system which is helpful in the application where large guidance forces are needed such as maglev tracks with high degrees of curves.

  17. Influence of soft ferromagnetic sections on the magnetic flux density profile of a large grain, bulk Y–Ba–Cu–O superconductor

    International Nuclear Information System (INIS)

    Philippe, M P; Wéra, L; Fagnard, J-F; Vanderheyden, B; Vanderbemden, P; Ainslie, M D; Dennis, A R; Shi, Y-H; Cardwell, D A

    2015-01-01

    Bulk, high temperature superconductors have significant potential for use as powerful permanent magnets in a variety of practical applications due to their ability to trap record magnetic fields. In this paper, soft ferromagnetic sections are combined with a bulk, large grain Y–Ba–Cu–O high temperature superconductor to form superconductor/ferromagnet hybrid structures. We study how the ferromagnetic sections influence the shape of the profile of the trapped magnetic induction at the surface of each structure and report the surface magnetic flux density measured by Hall probe mapping. These configurations have been modelled using a 2D axisymmetric finite element method based on the H-formulation and the results show excellent qualitative and quantitative agreement with the experimental measurements. The model has also been used to study the magnetic flux distribution and predict the behaviour for other constitutive laws and geometries. The results show that the ferromagnetic material acts as a magnetic shield, but the flux density and its gradient are enhanced on the face opposite to the ferromagnet. The thickness and saturation magnetization of the ferromagnetic material are important and a characteristic ferromagnet thickness d* is derived: below d*, saturation of the ferromagnet occurs, and above d*, a weak thickness-dependence is observed. The influence of the ferromagnet is observed even if its saturation magnetization is lower than the trapped flux density of the superconductor. Conversely, thin ferromagnetic discs can be driven to full saturation even though the outer magnetic field is much smaller than their saturation magnetization. (paper)

  18. Characteristic of the flux pinning at intergrain boundaries in bulk Bi-Pb-Sr-Ca-Cu-O superconductors

    International Nuclear Information System (INIS)

    Wang Yugui; Yang Yu; Xiong Xiaozhong; Yuan Songliu; Wang Shunxi

    1991-02-01

    The magnetization measurement shows that there are two kinds of different intergrain boundaries in the sintered Bi 1.8 Pb 0.34 Sr 1.86 Ca 2 Cu 3 O y superconductors. One has nearly no pinning force for flux line, the other can trap some flux line in the low field range where a pinning current may be sustained. When the applied field is removed, most of the remanent magnetization comes from the intergrain boundaries. The area of hysteresis loop at low field and the remanent magnetization for the cold-pressed bulk samples are significantly increased. Cold pressing results in aligning the grain orientation and raising the packing density, both of which enhanced intergrain coupling. The J c value of 1040 A/cm 2 at H = 0 and 150 A/cm 2 at H = 1 k Oe are obtained. The flux creep along the intergrain boundaries and the pinning potential energy U 0 for the coldpressed samples are also discussed

  19. Influence of lateral displacement on the levitation performance of a magnetized bulk high-T{sub c} superconductor magnet

    Energy Technology Data Exchange (ETDEWEB)

    Liu, W., E-mail: tonny-violet@163.com [College of Nuclear Technology and Automation Engineering, Chengdu University of Technology, Chengdu 610059 (China) and Applied Superconductivity Laboratory, Southwest Jiaotong University, Chengdu 610031 (China); Wang, J.S.; Ma, G.T.; Zheng, J. [Applied Superconductivity Laboratory, Southwest Jiaotong University, Chengdu 610031 (China); State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031 (China); National Laboratory of Rail Transit, Chengdu, 610031 (China); Tuo, X.G.; Li, L.L. [College of Nuclear Technology and Automation Engineering, Chengdu University of Technology, Chengdu 610059 (China); Ye, C.Q.; Liao, X.L. [Applied Superconductivity Laboratory, Southwest Jiaotong University, Chengdu 610031 (China); National Laboratory of Rail Transit, Chengdu, 610031 (China); Wang, S.Y. [Applied Superconductivity Laboratory, Southwest Jiaotong University, Chengdu 610031 (China); State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031 (China); National Laboratory of Rail Transit, Chengdu, 610031 (China)

    2012-03-15

    Compared with the permanent magnet, the magnetized bulk high-T{sub c} superconductor magnet (MBSCM) can trap higher magnetic field due to its strong flux pinning ability, so it is a good candidate to improve the levitation performance of high-T{sub c} superconductive (HTS) maglev system. The trapped magnetic flux of a MBSCM is sustained by the inductive superconducting current produced by the magnetizing process and is susceptible to the current intensity as well as configuration. In the HTS maglev system, the lateral displacement is an important process to change the superconducting current within a MBSCM and then affects its levitation performance, which is essential for the traffic ability in curve-way, the loading capacity of lateral impact and so on. The research about influence of lateral displacement on the levitation performance of MBSCM is necessary when MBSCM is applied on the HTS maglev vehicle. The experimental investigations about the influence of lateral displacement on the levitation performance of a MBSCM with different trapped fluxes and applied fields are processed in this article. The analyses and conclusions of this article are useful for the practical application of MBSCM in HTS maglev system.

  20. Electronic structure and superconductivity of FeSe-related superconductors.

    Science.gov (United States)

    Liu, Xu; Zhao, Lin; He, Shaolong; He, Junfeng; Liu, Defa; Mou, Daixiang; Shen, Bing; Hu, Yong; Huang, Jianwei; Zhou, X J

    2015-05-13

    FeSe superconductors and their related systems have attracted much attention in the study of iron-based superconductors owing to their simple crystal structure and peculiar electronic and physical properties. The bulk FeSe superconductor has a superconducting transition temperature (Tc) of ~8 K and it can be dramatically enhanced to 37 K at high pressure. On the other hand, its cousin system, FeTe, possesses a unique antiferromagnetic ground state but is non-superconducting. Substitution of Se with Te in the FeSe superconductor results in an enhancement of Tc up to 14.5 K and superconductivity can persist over a large composition range in the Fe(Se,Te) system. Intercalation of the FeSe superconductor leads to the discovery of the AxFe2-ySe2 (A = K, Cs and Tl) system that exhibits a Tc higher than 30 K and a unique electronic structure of the superconducting phase. A recent report of possible high temperature superconductivity in single-layer FeSe/SrTiO3 films with a Tc above 65 K has generated much excitement in the community. This pioneering work opens a door for interface superconductivity to explore for high Tc superconductors. The distinct electronic structure and superconducting gap, layer-dependent behavior and insulator-superconductor transition of the FeSe/SrTiO3 films provide critical information in understanding the superconductivity mechanism of iron-based superconductors. In this paper, we present a brief review of the investigation of the electronic structure and superconductivity of the FeSe superconductor and related systems, with a particular focus on the FeSe films.

  1. Magnetic levitation and its application for education devices based on YBCO bulk superconductors

    Science.gov (United States)

    Yang, W. M.; Chao, X. X.; Guo, F. X.; Li, J. W.; Chen, S. L.

    2013-10-01

    A small superconducting maglev propeller system, a small spacecraft model suspending and moving around a terrestrial globe, several small maglev vehicle models and a magnetic circuit converter have been designed and constructed. The track was paved by NdFeB magnets, the arrangement of the magnets made us easy to get a uniform distribution of magnetic field along the length direction of the track and a high magnetic field gradient in the lateral direction. When the YBCO bulks mounted inside the vehicle models or spacecraft model was field cooled to LN2 temperature at a certain distance away from the track, they could be automatically floating over and moving along the track without any obvious friction. The models can be used as experimental or demonstration devices for the magnetic levitation applications.

  2. Dynamic characteristics and finite element analysis of a magnetic levitation system using a YBCO bulk superconductor

    International Nuclear Information System (INIS)

    Ueda, H; Ishiyama, A

    2004-01-01

    We have been developing a magnetic levitating device with two-dimensional movement, namely a 'levitating X-Y transporter'. For the real design of a levitating X-Y transporter, it is necessary to clarify the levitation characteristics, such as the lift, the levitation height and the stability against mechanical disturbances. Furthermore various kinds of force may be applied to the levitating part and cause mechanical oscillation. Therefore the characteristics of oscillation are also important factors in the dynamic stability of such a levitation system. In this paper, we examine experimentally the lift and the restoring force and develop a new simulation code based on the three-dimensional hybrid finite and boundary element method to analyse the dynamic electromagnetic behaviour of the HTS bulk. We have investigated a suitable permanent-magnet arrangement to enhance the levitation characteristics through experiment and numerical simulation. We can then determine the suitable conditions for stable levitation from those results

  3. New superconductors from granular to high T$_{c}$

    CERN Document Server

    Deutscher, Guy

    2018-01-01

    How new are the high Tc superconductors, as compared to the conventional low Tc ones? In what sense are these oxides different from regular metals in their normal state? How different is the mechanism for high Tc superconductivity from the well-known electron-phonon interaction that explains so well superconductivity in metals and alloys? What are the implications of the new features of the high Tc oxides for their practical applications? This interesting book aims to provide some answers to those questions, drawing particularly on similarities between the high Tc oxides and granular superconductors, which also present a short coherence length, a small superfluid density and an inhomogeneous structure.

  4. New superconductors from granular to high T$_{c}$

    CERN Document Server

    Deutscher, Guy

    2006-01-01

    How new are the high Tc superconductors, as compared to the conventional low Tc ones? In what sense are these oxides different from regular metals in their normal state? How different is the mechanism for high Tc superconductivity from the well-known electron-phonon interaction that explains so well superconductivity in metals and alloys? What are the implications of the new features of the high Tc oxides for their practical applications? This book aims to give some answers to those questions, drawing particularly on similarities between the high Tc oxides and granular superconductors, which also present a maximum of their critical temperature near the metal-insulator transition.

  5. Enhancement of critical currents in bulk and Ag-sheathed Bi(Pb)-2223 superconductors

    International Nuclear Information System (INIS)

    Brauer, D.J.; Eujen, R.; Hudepohl, J.

    1991-01-01

    This paper reports on the superconducting properties of the Bi(Pb)-2223 phase that have been optimized. Prolonged annealing of coarse powder raised j c in bulk samples to as high as 1100 Acm -2 at 77 K. the temperature dependence was studied between 96 and 4.2 K whereby j c rose gradually from 120 to 2100 Acm -2 . T c dropped from 107 K to 64 K in magnetic fields up to 4 T but decreased by only 1 K/T in higher fields. A tape prepared by rolling and subsequent annealing of Ag tubes containing Bi(Pb)-2223 powder exhibited a j c of 1700 Acm -2 at 77 K and 11000 Acm -2 at 4.2 K. The latter j c dropped to 3000 Acm -2 in a magnetic field of 0.25 t, but it was still 1200 Acm -2 in a 10 T field. A tape fabricated by pressing a drawn and annealed wire proved to be less sensitive to low magnetic fields

  6. High-Tc superconducting microbolometer for terahertz applications

    Science.gov (United States)

    Ulysse, C.; Gaugue, A.; Adam, A.; Kreisler, A. J.; Villégier, J.-C.; Thomassin, J.-L.

    2002-05-01

    Superconducting hot electron bolometer mixers are now a competitive alternative to Schottky diode mixers in the terahertz frequency range because of their ultra wideband (from millimeter waves to visible light), high conversion gain, and low intrinsic noise level. High Tc superconductor materials can be used to make hot electron bolometers and present some advantage in term of operating temperature and cooling. In this paper, we present first a model for the study of superconducting hot electron bolometers responsivity in direct detection mode, in order to establish a firm basis for the design of future THz mixers. Secondly, an original process to realize YBaCuO hot electron bolometer mixers will be described. Submicron YBaCuO superconducting structures are expitaxially sputter deposited on MgO substrates and patterned by using electron beam lithography in combination with optical lithography. Metal masks achieved by electron beam lithography are insuring a good bridge definition and protection during ion etching. Finally, detection experiments are being performed with a laser at 850 nm wavelength, in homodyne mode in order to prove the feasibility and potential performances of these devices.

  7. Critical currents and superconductivity ferromagnetism coexistence in high-Tc oxides

    CERN Document Server

    Khene, Samir

    2016-01-01

    The book comprises six chapters which deal with the critical currents and the ferromagnetism-superconductivity coexistence in high-Tc oxides. It begins by gathering key data for superconducting state and the fundamental properties of the conventional superconductors, followed by a recap of the basic theories of superconductivity. It then discusses the differences introduced by the structural anisotropy on the Ginzburg-Landau approach and the Lawrence-Doniach model before addressing the dynamics of vortices and the ferromagnetism-superconductivity coexistence in high-Tc oxides, and provides an outline of the pinning phenomena of vortices in these materials, in particular the pinning of vortices by the spins. It elucidates the methods to improve the properties of superconducting materials for industrial applications. This optimization aims at obtaining critical temperatures and densities of critical currents at the maximum level possible. Whereas the primary objective is the basic mechanisms pushing the superco...

  8. Cryogenic milling for the fabrication of high J{sub c} MgB{sub 2} bulk superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kim, D. N.; Kang, M. O.; Park, H. W. [Korea University of Technology and Education, Cheonan (Korea, Republic of); Jun, B. H.; Kim, C. J. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2017-06-15

    Cryogenic milling which is a combined process of low-temperature treatment and mechanical milling was applied to fabricate high critical current density (J{sub c}) MgB{sub 2} bulk superconductors. Liquid nitrogen was used as a coolant, and no solvent or lubricant was used. Spherical Mg (6-12 μm, 99.9 % purity) and plate-like B powder (⁓ 1 μm, 97 % purity) were milled simultaneously for various time periods (0, 2, 4, 6 h) at a rotating speed of 500 rpm using ZrO{sub 2} balls. The (Mg{sup +2B}) powders milled were pressed into pellets and heat-treated at 700°C for 1 h in flowing argon. The use of cryomilled powders as raw materials promoted the formation reaction of superconducting MgB{sub 2}, reduced the grain size of MgB{sub 2}, and suppressed the formation of impurity MgO. The superconducting critical temperature (T{sub c}) of MgB{sub 2} was not influenced as the milling time (t) increased up to 6 h. Meanwhile, the critical current density (J{sub c}) of MgB{sub 2} increased significantly when t increased to 4 h. When t increased further to 6 h, however, Jc decreased. The J{sub c} enhancement of MgB{sub 2} by cryogenic milling is attributed to the formation of the fine grain MgB{sub 2} and a suppression of the MgO formation.

  9. Comparative Review on Thin Film Growth of Iron-Based Superconductors

    Directory of Open Access Journals (Sweden)

    Yoshinori Imai

    2017-07-01

    Full Text Available Since the discovery of the novel iron-based superconductors, both theoretical and experimental studies have been performed intensively. Because iron-based superconductors have a smaller anisotropy than high-Tc cuprates and a high superconducting transition temperature, there have been a lot of researchers working on the film fabrication of iron-based superconductors and their application. Accordingly, many novel features have been reported in the films of iron-based superconductors, for example, the fabrication of the epitaxial film with a higher Tc than bulk samples, the extraction of the metastable phase which cannot be obtained by the conventional solid state reaction, and so on. In this paper, we review the progress of research on thin film fabrications of iron-based superconductors, especially the four categories: LnFeAs(O,F (Ln = Lanthanide, AEFe2As2 (AE = Alkaline-earth metal, FeCh (Ch = Chalcogen, and FeSe monolayer. Furthermore, we focus on two important topics in thin films of iron-based superconductors; one is the substrate material for thin film growth on the iron-based superconductors, and the other is the whole phase diagram in FeSe1-xTex which can be obtained only by using film-fabrication technique.

  10. Superconductivity and ceramic superconductors II; Proceedings of the Symposium, Orlando, FL, Nov. 12-15, 1990. Ceramic transactions. Vol. 18

    International Nuclear Information System (INIS)

    Nair, K.M.; Balachandran, U.; Chiang, Y.-M.; Bhalla, A.S.

    1991-01-01

    The present symposium on superconductivity and ceramic superconductors discusses fundamentals and general principles, powder processing and properties, fabrication and properties, and device reliability and applications. Attention is given to phase formation in the Tl-Ca-Ba-Cu-O system, comparative defect studies in La2CuO4 and La2NiO4, solid solution and defect behavior in high Tc oxides, oxygen ion transport and disorder in cuprates, and Sr-free Bi-Ln-Ca-Cu-O superconductors. Topics addressed include the preparation of superconductor Y-Ba-Cu-O powder by single-step calcining in air, low-temperature synthesis of YBa2Cu3O(7-x), synthesis of high-phase purity ceramic oxide superconductors by the xerogel method, and the preparation and characterization of the BYa2Cu4O8 superconductor. Also discussed are optical studies of humidity-based corrosion effects on thin film and bulk ceramic YBa2Cu3O(7-delta), thermomechanical processing of YBa2Cu3O(x)/Ag sheathed wires, and the expansion of high-Tc superconducting ceramics

  11. Controlled levitation of Y-Ba-Cu-O bulk superconductors and energy minimum analysis; Y-Ba-Cu-O baruku chodendotai no fujo to enerugi kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Magashima, K. [Railway Technical Research Institute, Tokyo (Japan); Iwasa, Y. [Francis Bitter Magnet Laboratory, Canbridge (United States); Sawa, K. [keio University, Tokyo (Japan); Murakami, M. [Superconductivity research Laboratory, Tokyo (Japan)

    1999-11-25

    The levitation of bulk Y-Ba-Cu-O superconductors can be controlled using a Bi-Sr-Ca-Cu-O (Bi2223) superconducting electromagnet. It was found that stable levitation without tilting could be obtained only when the sample trapped a certain amount of fields, the minimum of which depended on the external field and sample dimensions. We employed a novel analysis method for levitation based on the total energy balance, which is much simpler than the force method and could be applied to understanding general levitation behavior. Numerical analyses thus developed showed that stable levitation of superconductors with large dimensions cen only be achieved when the induced currents can flow with three-dimensional freedom. (author)

  12. A study on the development of high Tc superconducting materials

    International Nuclear Information System (INIS)

    Won, D. Y.; Hong, G. Y.; Lee, H. G.; Lee, H. J.; Kim, C. J.; Kwon, S. C.; Kim, K. B.; Kang, Y. H.; Chang, I. S.; Choi, M. J.

    1992-01-01

    The major work of this project aims to develop the frictionless superconducting bearing with a high speed. The high magnetization YBaCuO bulk superconductor was prepared by Quasi-melt process. The frictionless superconducting magnetic bearing standed a rotating bar with a speed of 75,000 rpm, which were operated by an electric controller. The low temperature chemical vapor deposition technique was developed. YBaCuO superconducting film showing a superconductivity above 77K was successfully prepared at 650 deg C. Effect of oxygen partial pressure, substrate, deposition temperature on the film properties were also investigated. (Author)

  13. Magnetization and flux pinning in high-Tc cuprates: Irradiated and oxygen deficient materials

    International Nuclear Information System (INIS)

    Thompson, J.R.; Civale, L.; Marwick, A.D.; Holtzberg, F.

    1992-11-01

    This work surveys recent studies of the intragrain current density J and vortex pinning in high Tc superconductors. Materials include Y 1 Ba 2 Cu 3 O 7-δ and Bi 2 Sr 2 Ca 1 Cu 2 O 8 single crystals and aligned polycrystals. To probe the flux pinning, we modified the strength, number, and morphology of defects. Varying the oxygen content (7-δ) in YBa 2 Cu 3 O 7-δ or irradiating the materials with ions, having either light or heavy masses, gives systematic changes in the character of the all-important defects

  14. A high Tc superconducting liquid nitrogen level sensor

    International Nuclear Information System (INIS)

    Jin, J. X.; Liu, H. K.; Dou, S. X.; Grantham, C.; Beer, J.

    1996-01-01

    Full text: The dramatic resistance change in the superconducting-normal transition temperature range enables a high T c superconductor to be considered for designing a liquid nitrogen level sensor. A (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10+x Ag clad superconducting wire is selected and tested as a continuous liquid nitrogen level sensor to investigate the possibility for this application. The (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10+x Ag clad superconducting wire has approximately 110 K critical temperature, with more flexible and stable properties compared with bulk shape ceramic high T c superconductors. The voltage drops across the sensor are tested with different immersion lengths in liquid nitrogen. The accuracy of the HTS sensor is analysed with its dR/dT in the superconducting-normal transition range. The voltage signal is sensitive to liquid nitrogen level change, and this signal can be optimized by controlling the transport current. The problems of the Ag clad superconductor are that the Ag sheath thermal conductivity is very high, and the sensor normal resistance is low. These are the main disadvantages for using such a wire as a continuous level sensor. However, a satisfactory accuracy can be achieved by control of the transport current. A different configuration of the wire sensor is also designed to avoid this thermal influence

  15. High-Tc superconducting electric motors

    International Nuclear Information System (INIS)

    Schiferl, R.; Stein, J.

    1992-01-01

    In this paper, the advantages and limitations of using superconductors in motors are discussed. A synchronous motor with a high temperature superconducting field winding for pump and fan drive applications is described and some of its unique design features are identified. A 10,000 horsepower superconducting motor design is presented. The critical field and current density requirements for high temperature superconducting wire in motors is discussed. Finally, recent progress in superconducting wire performance is presented

  16. An efficient and economical way to enhance the performance of present HTS Maglev systems by utilizing the anisotropy property of bulk superconductors

    International Nuclear Information System (INIS)

    Deng Zigang; Wang Jiasu; Zheng Jun; Zhang Ya; Wang Suyu

    2013-01-01

    We report a simple, efficient and economical way to enhance the levitation or guidance performance of present high-temperature superconducting (HTS) Maglev systems by exploring the anisotropic properties of the critical current density in the a–b plane and along the c-axis of bulk superconductors. In the method, the bulk laying mode with different c-axis directions is designed to match with the magnetic field configuration of the applied permanent magnet guideway (PMG). Experimental results indicate that more than a factor of two improvement in the levitation force or guidance force is achieved when changing the laying mode of bulk superconductors from the traditional fashion of keeping the c-axis vertical to the PMG surface to the studied one of keeping the c-axis parallel to the PMG surface, at the maximum horizontal and vertical magnetic field positions of the PMG, respectively. These phenomena resulted from the physical nature of the generated levitation force and guidance force (electromagnetic forces) and the fact that there are different critical current densities in the a–b plane and along the c axis. Based on the experimental results, new HTS Maglev systems can be designed to meet the requirements of practical heavy-load or curved-route applications. (paper)

  17. An efficient and economical way to enhance the performance of present HTS Maglev systems by utilizing the anisotropy property of bulk superconductors

    Science.gov (United States)

    Deng, Zigang; Wang, Jiasu; Zheng, Jun; Zhang, Ya; Wang, Suyu

    2013-02-01

    We report a simple, efficient and economical way to enhance the levitation or guidance performance of present high-temperature superconducting (HTS) Maglev systems by exploring the anisotropic properties of the critical current density in the a-b plane and along the c-axis of bulk superconductors. In the method, the bulk laying mode with different c-axis directions is designed to match with the magnetic field configuration of the applied permanent magnet guideway (PMG). Experimental results indicate that more than a factor of two improvement in the levitation force or guidance force is achieved when changing the laying mode of bulk superconductors from the traditional fashion of keeping the c-axis vertical to the PMG surface to the studied one of keeping the c-axis parallel to the PMG surface, at the maximum horizontal and vertical magnetic field positions of the PMG, respectively. These phenomena resulted from the physical nature of the generated levitation force and guidance force (electromagnetic forces) and the fact that there are different critical current densities in the a-b plane and along the c axis. Based on the experimental results, new HTS Maglev systems can be designed to meet the requirements of practical heavy-load or curved-route applications.

  18. Effects of artificial holes in very large single-grain Y_1_._5Ba_2Cu_3O_7_-_y bulk superconductors

    International Nuclear Information System (INIS)

    Park, S. D.; Jun, B. H.; Kim, C. J.; Park, H. W.

    2017-01-01

    The effects of artificial holes on the trapped magnetic fields and magnetic levitation forces of very large single-grain Y_1_._5Ba_2Cu_3O_7_-_y (Y1.5) bulk superconductors were studied. Artificial holes were made for Y1.5 powder compacts by die pressing using cylindrical dies with a diameter of 30 mm or 40 m, or rectangular dies with a side length of 50 mm. The single grain Y1.5 bulk superconductors (25 mm, 33 mm in diameter and 42 mm in side length) with artificial holes were fabricated using a top-seeded melt growth (TSMG) process for the die-pressed Y1.5 powder compacts. The magnetic levitation forces at 77 K of the 25 mm single grain Y1.5 samples with one (diameters of 4.2 mm) or six artificial holes (diameters of 2.5 mm) were 10-17% higher than that of the Y1.5 sample without artificial holes. The trapped magnetic fields at 77 K of the Y1.5 samples with artificial holes were also 9.6-18% higher than that of the Y1.5 sample without artificial holes. The 33 mm and 42 mm single grain Y1.5 samples with artificial holes (2.5 mm and 4.2 mm in diameter) also showed trapped magnetic fields 10-13% higher than that of the Y1.5 samples without artificial holes in spite of the reduced superconducting volume fraction due to the presence of artificial holes. The property enhancement in the large single grain Y1.5 bulk superconductors appears to be attributed to the formation of the pore-free regions near the artificial holes and the homogeneous oxygen distribution in the large Y123 grains

  19. Control of Y-211 content in bulk YBCO superconductors fabricated by a buffer-aided, top seeded infiltration and growth melt process

    International Nuclear Information System (INIS)

    Namburi, Devendra K; Shi, Yunhua; Palmer, Kysen G; Dennis, Anthony R; Durrell, John H; Cardwell, David A

    2016-01-01

    Bulk (RE)–Ba–Cu–O ((RE)BCO, where RE stands for rare-earth), single grain superconductors can trap magnetic fields of several tesla at low temperatures and therefore can function potentially as high field magnets. Although top seeded melt growth (TSMG) is an established process for fabricating relatively high quality single grains of (RE)BCO for high field applications, this technique suffers from inherent problems such as sample shrinkage, a large intrinsic porosity and the presence of (RE) 2 BaCuO 5 (RE-211)-free regions in the single grain microstructure. Seeded infiltration and growth (SIG), therefore, has emerged as a practical alternative to TSMG that overcomes many of these problems. Until now, however, the superconducting properties of bulk materials processed by SIG have been inferior to those fabricated using the TSMG technique. In this study, we identify that the inferior properties of SIG processed bulk superconductors are related to the presence of a relatively large Y-211 content (∼41.8%) in the single grain microstructure. Controlling the RE-211 content in SIG bulk samples is particularly challenging because it is difficult to regulate the entry of the liquid phase into the solid RE-211 preform during the infiltration process. In an attempt to solve this issue, we have investigated the effect of careful control of both the infiltration temperature and the quantity of liquid phase powder present in the sample preforms prior to processing. We conclude that careful control of the infiltration temperature is the most promising of these two process variables. Using this knowledge, we have fabricated successfully a YBCO bulk single grain using the SIG process of diameter 25 mm that exhibits a trapped field of 0.69 T at 77 K, which is the largest value reported to date for a sample fabricated by the SIG technique. (paper)

  20. Early high-Tc commercial activity

    International Nuclear Information System (INIS)

    Anon.

    1988-01-01

    The high temperature superconductors have already begun to generate the first stirrings of commercial activity. Companies that supply instruments and chemicals to researchers have enjoyed increased business. At least one company has begun to supply educational materials. Venture capital firms have invested about $15 million in startups to capitalize on developments in high-field applications, superconducting electronics, and magnetic shielding. Consulting firms are gathering and selling market research information. And the federal government is studying the question of how to cooperate with American companies to commercialize the research taking place in the national laboratories. This article discusses these issues

  1. Conductus makes high-Tc integrated circuit

    International Nuclear Information System (INIS)

    Anon.

    1991-01-01

    This paper reports that researchers at Conductus have successfully demonstrated what the company says is the world's first integrated circuit containing active devices made from high-temperature superconductors. The circuit is a SQUID magnetometer made from seven layers of material: three layers of yttrium-barium-copper oxide, two layers of insulating material, a seed layer to create grain boundaries for the Josephson junctions, and a layer of silver for making electrical contact to the device. The chip also contains vias, or pathways that make a superconducting contact between the superconducting layers otherwise separated by insulators. Conductus had previously announced the development of a SQUID magnetometer that featured a SQUID sensor and a flux transformer manufactured on separate chips. What makes this achievement important is that the company was able to put both components on the same chip, thus creating a simple integrated circuit on a single chip. This is still a long way from conventional semiconductor technology, with as many as a million components per chip, or even the sophisticated low-Tc superconducting chips made by the Japanese, but the SQUID magnetometer demonstrates all the elements and techniques necessary to build more complex high-temperature superconductor integrated circuits, making this an important first step

  2. 16O DIGME of high Tc materials

    International Nuclear Information System (INIS)

    Vickridge, I.C.; Tallon, J.; Presland, M.

    1995-01-01

    Measurements have been performed of the repeatability of the yield of the 871 keV gamma ray from the 16 O(d, p) 17 O * reaction induced by a 1.8 MeV deuterium beam incident on Y 1 Ba 2 Cu 3 O 7-δ . It is shown that the yield is stable to 0.2% (±1σ) for deuteron fluences up to 298 μC/mm 2 , and that current integration contributes less than 0.3% random error to the yield measurements. The contribution to current integration of molecular hydrogen contamination of the deuteron beam is shown to be less than 0.15%. Yields from different points on the same sample show variations which suggest that this material is not sufficiently stable in the long term to be used as a reference material for the precision DIGME method of oxygen determination in high T c superconductors. (orig.)

  3. Gauge Model of High-Tc Superconductivity

    International Nuclear Information System (INIS)

    Ng, Sze Kui

    2012-01-01

    A simple gauge model of superconductivity is presented. The seagull vertex term of this gauge model gives an attractive potential between electrons for the forming of Cooper pairs of superconductivity. This gauge model gives a unified description of superconductivity and magnetism including antiferromagnetism, pseudogap phenomenon, stripes phenomenon, paramagnetic Meissner effect, Type I and Type II supeconductivity and high-T c superconductivity. The doping mechanism of superconductivity is found. It is shown that the critical temperature T c is related to the ionization energies of elements and can be computed by a formula of T c . For the high-T c superconductors such as La 2-x Sr x CuO 4 , Y Ba 2 Cu 3 O 7 , and MgB 2 , the computational results of T c agree with the experimental results.

  4. A novel propulsion method for high- Tc superconducting maglev vehicle

    Science.gov (United States)

    Ma, Guangtong; Wang, Jiasu; Wang, Suyu; Liu, Minxian; Jing, Hua; Lu, Yiyun; Lin, Qunxu

    2008-01-01

    High-Tc superconducting (HTS) maglev is considered as a perfect transportation type because of its unique inherent stability. A direct current (DC) linear motor using the permanent magnet guideway (PMG) as the stator and the on-board coil as the rotor instead of the present inductive or synchronous alternate current (AC) linear motor which has an economic disadvantage due to the necessity to lay primary coil along the guideway is proposed in this paper. In order to modulate the magnetic field under the PMG, an inverse E shape ferromagnetic device (IESFD) core is designed. The possible winding method for the on-board coil is listed, and the analytical result shows that a considerable net ampere force and thus the propulsion force can be generated by this special structure. The influence of the concentrated effect of the IESFD on the maglev performance of HTS bulk is studied by a numerical program, and the results show that the levitation force with the IESFD is 90% of that without. It is also indicated that the load capability and lateral performance of the maglev vehicle combined this propulsion method can be improved thanks to the attractive effect between the IESFD and PMG. The cost of the HTS maglev vehicle will be remarkably reduced and then shorten the distance to practical application with this propulsion method.

  5. The new superconductors. Les nouveaux supraconducteurs

    Energy Technology Data Exchange (ETDEWEB)

    Gervais, F

    1991-01-01

    The first half of the book is a scanning of superconductivity from 1911 to our days, with Bardeen-Cooper-Schrieffer theory in 1957, with the concept of phonons and the importance of the Brillouin zone, with the discovery of high-tc superconductors oxides by Bednortz and Mueller in 1986. The second part is dealing with physical investigation means for trying to explain this high-tc superconductivity.

  6. Rotational loss of a ring-shaped flywheel supported by high Tc superconducting levitation

    International Nuclear Information System (INIS)

    Teshima, Hidekazu; Tawara, Taichi; Shimada, Ryuichi.

    1997-01-01

    This paper describes the experimental results for the rotational loss of a ring-shaped flywheel supported by high T c superconducting levitation. Superconducting levitation is appropriate for rotating a ring-shaped flywheel which has neither shaft nor hub because it is a non-contact and automatically stable levitation without any control systems. The rotational loss has been investigated using a small-scaled experimental machine consisting of 16 bulk superconductors 46 mm in diameter and a ring-shaped flywheel about 300 mm in diameter. The rotational loss decreased as the levitation gap height increased. In low-speed rotational regions, the rotational loss was in proportion to the rotation speed and depended more on the levitation gap. In high-speed rotational regions, the rotational loss was in proportion to the third power of the rotation speed and depended less on the levitation gap. The cubic rotational loss in He was reduced to one-fifth of that in air. The magnetic field pinned in bulk superconductors induces a loss in the materials composing the ring-shaped flywheel. The rotational loss of a ring-shaped flywheel supported by superconducting levitation can be reduced by improving the uniformity of the magnetic fields along the ring, enlargement of the bulk superconductor(s), and densely arranging the bulk superconductors. (author)

  7. Superatom representation of high-TC superconductivity

    International Nuclear Information System (INIS)

    Panas, Itai

    2012-01-01

    A “super-atom” conceptual interface between chemistry and physics is proposed in order to assist in the search for higher T C superconductors. The plaquettes generating the checkerboard superstructure in the cuprates, the C 60 molecules in K 3 C 60 , and the Mo 6 S 8 2- clusters in Chevrel phase materials offer such candidate super-atoms. Thus, in the present study high-T C superconductivity HTSC is articulated as the entanglement of two disjoint electronic manifolds in the vicinity of a common Fermi energy. The resulting HTSC ground state couples near-degenerate protected local super-atom states to virtual magnons in an antiferromagnetic AFM embedding. The composite Cooper pairs emerge as the interaction particles for virtual magnons mediated “self-coherent entanglement” of super-atom states. A Hückel type resonating valence bond RVB formalism is employed in order to illustrate the real-space Cooper pairs as well as their delocalization and Bose Einstein condensation BEC on a ring of super-atoms. The chemical potential μ BEC for Cooper pairs joining the condensate is formulated in terms of the super-exchange interaction, and consequently the T C in terms of the Neél temperature. A rationale for the robustness of the HTSC ground state is proposed: achieving local maximum “electron correlation entropy” at the expense of non-local phase rigidity.

  8. Influence of Sm2O3 microalloying and Yb contamination on Y211 particles coarsening and superconducting properties of IG YBCO bulk superconductors

    Science.gov (United States)

    Vojtkova, L.; Diko, P.; Kovac, J.; Vojtko, M.

    2018-06-01

    Single grain YBa2Cu3O7‑x (YBCO or Y123) bulk superconductors were produced by an infiltration growth process. The solid phase precursor was prepared by solid state synthesis from Y2O3 + BaCuO2 powders. The influence of the addition of Sm2O3 and YB contamination from the substrate on the microstructure and superconducting properties was analyzed. The dependences of Yb concentration on the distance from the bottom of the samples measured by energy dispersive spectroscopy microanalysis used in conjunction with scanning electron microscopy confirmed the contamination of the samples during the melting stage of the sample preparation. It is shown that the addition of Sm in low concentration and its combination with Yb from the substrate modify the coarsening of the Y211 particles as well as lead to the appearance of a secondary peak effect in the field dependences of the critical current density.

  9. Evaluating superconductors for microwave applications

    International Nuclear Information System (INIS)

    Hammond, B.; Bybokas, J.

    1989-01-01

    It is becoming increasingly obvious that some of the earliest applications for high Tc superconductors will be in the microwave market. While this is a major opportunity for the superconductor community, it also represents a significant challenge. At DC or low frequencies a superconductor can be easily characterized by simple measurements of resistivity and magnetic susceptibility versus temperature. These parameters are fundamental to superconductor characterization and various methods exist for measuring them. The only valid way to determine the microwave characteristics of a superconductor is to measure it at microwave frequencies. It is for this reason that measuring microwave surface resistance has emerged as one of the most demanding and telling tests for materials intended for high frequency applications. In this article, the theory of microwave surface resistance is discussed. Methods for characterizing surface resistance theoretically and by practical implementation are described

  10. The influence of slow cooling on Y211 size and content in single-grain YBCO bulk superconductor through the infiltration-growth process

    Energy Technology Data Exchange (ETDEWEB)

    Ouerghi, A [Systems and Applied Mechanics Laboratory LASMAP, Polytechnic School of Tunisia, Rue El Kawarezmi La Marsa 743, Université de Carthage Tunis (Tunisia); Moutalbi, N., E-mail: nahed.moutalbi@yahoo.fr [Systems and Applied Mechanics Laboratory LASMAP, Polytechnic School of Tunisia, Rue El Kawarezmi La Marsa 743, Université de Carthage Tunis (Tunisia); Noudem, J.G. [CRISMAT-ENSICAEN (UMR-CNRS 6508), Université de Caen-Basse-Normandie, F-14050 Caen (France); LUSAC, Université de Caen-Basse-Normandie F-50130 Cherbourg-Octeville (France); M' chirgui, A. [Systems and Applied Mechanics Laboratory LASMAP, Polytechnic School of Tunisia, Rue El Kawarezmi La Marsa 743, Université de Carthage Tunis (Tunisia)

    2017-03-15

    Highlights: • YBCO bulk superconductors are produced by optimized Seeded Infiltration and Growth process. • The slow cooling time, in a fixed slow cooling temperature window, affects considerably the surface morphology and the bulk’s microstructure. • The Y211 particle’s size and content depend on the slow cooling time and its distribution behavior changes from one position to another. • There is an optimum slow cooling time, estimated to 88h, over which the shrinkage for both the liquid phase and the Y211 pellet is maximal, without any improvement of the crystal grain growth. • The magnetic trapped flux distribution for a given sample brings out the single grain characteristic. - Abstract: Highly textured YBa{sub 2}Cu{sub 3}O{sub 7-δ} (Y123) superconductors were produced using modified Textured Top Seeded Infiltration Growth (TSIG) process. The liquid source is made of only Y123 powder whereas the solid source is composed of Y{sub 2}BaCuO{sub 5} (Y211) powder. We aim to control the amount of liquid that infiltrates the solid pellet, which in turn controls the final amount of Y{sub 2}BaCuO{sub 5} particles in Y123 matrix. The effect of the slow cooling kinetics on sample morphology, on grain growth and on final microstructure was too investigated. It is shown that appropriate slow cooling time may also contribute to the control of the amount of Y211 inclusions in the final structure of Y123 bulk. We report herein the Y211 particle size and density distribution in the whole Y123 matrix. The present work proves that finest Y211 particles locate under the seed and that their size and density increase with distance from the seed.

  11. Strong correlations and the search for high-Tc superconductivity in chromium pnictides and chalcogenides

    Science.gov (United States)

    Pizarro, J. M.; Calderón, M. J.; Liu, J.; Muñoz, M. C.; Bascones, E.

    2017-02-01

    Undoped iron superconductors accommodate n =6 electrons in five d orbitals. Experimental and theoretical evidence shows that the strength of correlations increases with hole doping, as the electronic filling approaches half filling with n =5 electrons. This evidence delineates a scenario in which the parent compound of iron superconductors is the half-filled system, in analogy to cuprate superconductors. In cuprates the superconductivity can be induced upon electron or hole doping. In this work we propose to search for high-Tc superconductivity and strong correlations in chromium pnictides and chalcogenides with n slave-spin and multiorbital random-phase-approximation calculations we analyze the strength of the correlations and the superconducting and magnetic instabilities in these systems with the main focus on LaCrAsO. We find that electron-doped LaCrAsO is a strongly correlated system with competing magnetic interactions, with (π ,π ) antiferromagnetism and nodal d -wave pairing being the most plausible magnetic and superconducting instabilities, respectively.

  12. Some experimental and theoretical aspects of the surface impedance in bulk high-temperature superconductors at 10 GHz

    Energy Technology Data Exchange (ETDEWEB)

    Deville, A.; Fawaz, H.; Gaillard, B. (Lab. d' Electronique des Milieux Condenses, Univ. de Provence, Centre Saint-Jerome, 13 - Marseille (France)); Noel, H.; Potel, M. (Lab. de Chimie Minerale, Univ. de Rennes, 35 (France)); Monnereau, O. (Lab. de Chimie des Materiaux, Univ. de Provence, Centre Saint-Charles, 13 - Marseille (France))

    1992-07-15

    After a presentation of the theoretical framework, and a short review of existing r.f. results in high-temperature superconductors, we present our own 10 GHz measurements on YBa[sub 2]Cu[sub 3]O[sub 7] single crystals and sintered samples. We use an electron spin resonance (ESR) heterodyne spectrometer and measurements of the reflection coefficient and resonant frequency of a cavity to get information not only on the surface resistance, R[sub S], as generally done, but also on the surface reactance, X[sub S]. The theoretical analysis of the frequency shift is made by adapting Slater's perturbation method to the present problem. In order to explain both the R[sub s] and X[sub S] results, and previous ESR observations, while keeping theoretical simplicity, we are led to suggest that in the normal state these materials show an unconventional skin effect, where the phenomenon is governed not by the d.c. conductivity, but by an effective (lower) conductivity, the other characteristics being unchanged. We briefly discuss the superconductor results and the validity of the two-fluid model. (orig.).

  13. Structure and properties of YBa2Cu3O7-δ superconductor doped with bulk cadmium oxide

    Directory of Open Access Journals (Sweden)

    A Echresh

    2010-09-01

    Full Text Available In this paper, the Y1-xCdxBa2Cu3O7-δ superconductor with x=0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5 are prepared using the solid state method and the structure, electrical resistance, critical current density and critical temperature of it, have been studied. The results show that these doping do not affect so much on the structure and lattice parameters. The electrical resistance of samples increased with doping. A little amount of doping cadmium improve critical current density such that the sample x=0.1 has a maximum critical current density among the samples. The critical temperature with doping cadmium up to x=0.2 has little fluctuation and its variation can be ignored, but by increasing up to x=0.5 the critical temperature decreases gradually.

  14. Epitaxial effects in thin films of high-Tc cuprates with the K2NiF4 structure

    Science.gov (United States)

    Naito, Michio; Sato, Hisashi; Tsukada, Akio; Yamamoto, Hideki

    2018-03-01

    La2-xSrxCuO4 (LSCO) and La2-xBaxCuO4 (LBCO) have been recognized as the archetype materials of "hole-doped" high-Tc superconductors. Their crystal structures are relatively simple with a small number of constituent cation elements. In addition, the doping level can be varied by the chemical substitution over a wide range enough to obtain the full spectrum of doping-dependent electronic and magnetic properties. These attractive features have dedicated many researchers to thin-film growth of LSCO and LBCO. The critical temperature (Tc) of LSCO and LBCO is sensitive to strain as manifested by a positive pressure coefficient of Tc in bulk samples. In general, films are strained if they are grown on lattice-mismatched substrates (epitaxial strain). Early attempts (before 1997) at the growth of LSCO and LBCO films resulted in depressed Tc below 30 K as they were grown on a commonly used SrTiO3 substrate (in-plane lattice parameter asub = 3.905 Å): the in-plane lattice parameters of LSCO and LBCO are ≤3.80 Å, and hence tensile epitaxial strain is introduced. The situation was changed by the use of LaSrAlO4 substrates with a slightly shorter in-plane lattice constant (asub = 3.756 Å). On LaSrAlO4 substrates, the Tc reaches 45 K in La1.85Sr0.15CuO4, 47 K in La1.85Ba0.15CuO4, and 56 K in ozone-oxidized La2CuO4+δ films, substantially higher than the Tc's of the bulk compounds. The Tc increase in La1.85Sr0.15CuO4 films on LaSrAlO4 and decrease on SrTiO3 are semi-quantitatively in accord with the phenomenological estimations based on the anisotropic strain coefficients of Tc (dTc/dεi). In this review article, we describe the growth and properties of films of cuprates having the K2NiF4 structure, mainly focusing on the increase/decrease of Tc by epitaxial strain and quasi-stable phase formation by epitaxial stabilization. We further extract the structural and/or physical parameters controlling Tc toward microscopic understanding of the variation of Tc by epitaxial strain.

  15. Process parameters, orientation, and functional properties of melt-processed bulk Y-Ba-Cu-O superconductors

    International Nuclear Information System (INIS)

    Zakharchenko, I.V.; Terryll, K.M.; Rao, K.V.; Balachandran, U.

    1995-03-01

    This study compared the microstructure, texturing, and functional properties (critical currents) of YBa 2 Cu 3 O 7-x -based bulk pellets that were prepared by the quench-melt-growth-process (QMGP), melt-textured growth (MTG), and conventional solid-state reaction (SSR) approaches. Using two X-ray diffraction (XRD) methods, θ-2θ, and rocking curves, the authors found that the individual grains of two melt-processed pellets exhibited remarkable preferred orientational alignment (best rocking curve width = 3.2 degree). However, the direction of the preferred orientation among the grains was random. Among the three types of bulk materials studied, the QMGP sample was found to have the best J c values, ∼ 4,500 A/cm 2 at 77 K in a field of 2 kG, as determined from SQUID magnetic data

  16. Experimental Observation of Non-'S-Wave' Superconducting Behavior in Bulk Superconducting Tunneling Junctions of Yba2Cu3O7-δ

    Directory of Open Access Journals (Sweden)

    Leandro Jose Guerra

    1998-06-01

    Full Text Available Evidence of non-s-wave superconductivity from normal tunneling experiments in bulk tunneling junctions of YBa2Cu3O7-δ is presented. The I-V and dI/dV characteristics of bulk superconducting tunneling junctions of YBa2Cu3O7-δ have been measured at 77.0K and clear deviation from s-wave superconducting behavior has been observed. The result agrees with d-wave symmetry, and interpreting the data in this way, the magnitude of the superconducting energy gap, 2Δ, is found to be (0.038 ± 0.002 eV. Comparing this energy gap with Tc (2Δ/kB Tc = 5.735, indicates that these high-Tc superconductors are strongly correlated materials, which in contrast with BCS-superconductors are believed to be weakly correlated.

  17. Oxygen stoichiometry and the high Tc superconducting oxides

    International Nuclear Information System (INIS)

    Tarascon, J.M.; Bagley, B.G.

    1989-01-01

    Methods for determining the oxygen content in high Tc materials, such as thermogravimetric analysis and chemical analysis, are discussed. Consideration is given to La-based cuprates, Y-based cuprates, and Bi-based cuprates. Superconducting transition temperatures are analyzed as a function of the Cu(1)-O(4) bond lengths for several different compositions in the Y-based system. 28 references

  18. Critical current of high Tc superconducting Bi223/Ag tapes

    NARCIS (Netherlands)

    Huang, Y.; ten Haken, Bernard; ten Kate, Herman H.J.

    1998-01-01

    The magnetic field dependence of the critical current of various high Tc superconducting Bi2223/Ag tapes indicates that the transport current is carried through two paths: one is through weakly-linked grain boundaries (Josephson junctions); another is through well-connected grains. The critical

  19. Modification of the trapped field in bulk high-temperature superconductors as a result of the drilling of a pattern of artificial columnar holes

    International Nuclear Information System (INIS)

    Lousberg, Gregory P; Vanderbemden, Ph; Vanderheyden, B; Fagnard, J-F; Ausloos, M

    2010-01-01

    The trapped magnetic field is examined in bulk high-temperature superconductors that are artificially drilled along their c-axis. The influence of the hole pattern on the magnetization is studied and compared by means of numerical models and Hall probe mapping techniques. To this aim, we consider two bulk YBCO samples with a rectangular cross-section that are drilled each by six holes arranged either on a rectangular lattice (sample I) or on a centered rectangular lattice (sample II). For the numerical analysis, three different models are considered for calculating the trapped flux: (i), a two-dimensional (2D) Bean model neglecting demagnetizing effects and flux creep, (ii), a 2D finite-element model neglecting demagnetizing effects but incorporating magnetic relaxation in the form of an E - J power law, and, (iii), a 3D finite element analysis that takes into account both the finite height of the sample and flux creep effects. For the experimental analysis, the trapped magnetic flux density is measured above the sample surface by Hall probe mapping performed before and after the drilling process. The maximum trapped flux density in the drilled samples is found to be smaller than that in the plain samples. The smallest magnetization drop is found for sample II, with the centered rectangular lattice. This result is confirmed by the numerical models. In each sample, the relative drops that are calculated independently with the three different models are in good agreement. As observed experimentally, the magnetization drop calculated in the sample II is the smallest one and its relative value is comparable to the measured one. By contrast, the measured magnetization drop in sample (1) is much larger than that predicted by the simulations, most likely because of a change of the microstructure during the drilling process.

  20. Recent development in crystal growth of large-diameter Y-QMG (reg sign) bulk superconductors; Y kei ogata QMG (reg sign) baruku koonchodendotai no kaihatsu jokyo

    Energy Technology Data Exchange (ETDEWEB)

    Fujimoto, T.; Morita, M. [Nippon Steel Corporation, Tokyo (Japan); Masahashi, N. [Tohoku University, Miyagi (Japan). Institute for Materials Research

    1999-11-25

    The current status of large-diameter Y-Ba-Cu-O OMG(reg sign) bulk superconductors is described. 75 mm-diameter QMG(reg sign) samples with fairly concentric trapped-magnetic-flux-density distributions have been successfully grown. In addition, a record-high value of the magnetic levitation force, 171 kgf, measured at 77 K using a 90 mm-diameter Nd-Fe-B magnet has been obtained for a 100 mm-diameter sample. The crystal orientation of subgrains in the sample was determined using Electron Back-Scattering Diffraction as well as using a conventional optical apparatus including a He-Ne-laser. For the sample grown under normal process conditions, the maximum value of the [001]-axis misorientation angles at the subgrain-boundaries we obtained in the c-substructure region is 2.9 degree. However, in the a/b-substructure regions, the misorientation angles are larger, and the maximum value obtained is 6.6 degree, exceeding the critical angle at which a significant reduction of the critical current density occurs in Y123 thin films due to the weak-link problem. (author)

  1. Effects of Bi-2212 addition on the levitation force properties of bulk MgB2 superconductors

    International Nuclear Information System (INIS)

    Taylan Koparan, E.; Savaskan, B.; Guner, S.B.; Celik, S.

    2016-01-01

    We present a detailed investigation of the effects of Bi 2 Sr 2 Ca 1 Cu 2 O 8+κ (Bi-2212) adding on the levitation force and magnetic properties of bulk MgB 2 obtained by hot press method. The amount of Bi-2212 was varied between 0 and 10 wt% (0, 2, 4, 6, 10 wt%) of the total MgB 2 . Moreover, we present MgB 2 bulk samples fabricated by using different production methods including hot pressing method to our knowledge. All samples were prepared by using elemental magnesium (Mg) powder, amorphous nano-boron (B) powder and Bi-2212 powder which are produced by hot press method. As a result of hot press process, compact pellet samples were manufactured. The vertical and lateral levitation force measurements were executed at the temperatures of 20, 24 and 28 K under zero-field-cooled (ZFC) and field-cooled (FC) regimes for samples with various adding levels. At 24 K and 28 K under ZFC regime, the 2 wt% Bi-2212 added sample exhibits a higher vertical levitation force than the pure sample. Bi-2212 added MgB 2 samples compared to the pure sample have lower attractive force values in FC regime. The magnetic field dependence of the critical current density J c was calculated from the M-H loops for Bi-2212 added MgB 2 samples. The 2 wt% Bi-2212 added sample has the best levitation and critical current density performance compared to other samples. The critical temperature (T c ) has slightly dropped from 37.8 K for the pure MgB 2 sample to 36.7 K for the 10 wt% of Bi-2212 added sample. The transition temperature slightly decreases when Bi-2212 adding level is increased. (orig.)

  2. Flux Pinning in Superconductors

    CERN Document Server

    Matsushita, Teruo

    2007-01-01

    The book covers the flux pinning mechanisms and properties and the electromagnetic phenomena caused by the flux pinning common for metallic, high-Tc and MgB2 superconductors. The condensation energy interaction known for normal precipitates or grain boundaries and the kinetic energy interaction proposed for artificial Nb pins in Nb-Ti, etc., are introduced for the pinning mechanism. Summation theories to derive the critical current density are discussed in detail. Irreversible magnetization and AC loss caused by the flux pinning are also discussed. The loss originally stems from the ohmic dissipation of normal electrons in the normal core driven by the electric field induced by the flux motion. The readers will learn why the resultant loss is of hysteresis type in spite of such mechanism. The influence of the flux pinning on the vortex phase diagram in high Tc superconductors is discussed, and the dependencies of the irreversibility field are also described on other quantities such as anisotropy of supercondu...

  3. Phenomenological Theory for Pseudogap States in High Tc Cuprate

    Directory of Open Access Journals (Sweden)

    Zhang Fuchun

    2012-03-01

    Full Text Available Pseudogap phase in the underdoped region of high-Tc cuprate is one of the challenging issues in condensed matter physics. In this talk, I will describe a phenomenological theory for this phase, based on analogies to the approach to Mott localization at weak coupling in lower dimensional systems. I will make comparisons of the theory to a series of the experiments, including angle resolved photoemission spectroscope, scanning tunneling microscope.

  4. Co-current Doping Effect of Nanoscale Carbon and Aluminum Nitride on Critical Current Density and Flux Pinning Properties of Bulk MgB2 Superconductors

    Science.gov (United States)

    Tripathi, D.; Dey, T. K.

    2018-05-01

    The effect of nanoscale aluminum nitride (n-AlN) and carbon (n-C) co-doping on superconducting properties of polycrystalline bulk MgB2 superconductor has been investigated. Polycrystalline pellets of MgB2, MgB2 + 0.5 wt% AlN (nano), MgB_{1.99}C_{0.01} and MgB_{1.99}C_{0.01} + 0.5 wt% AlN (nano) have been synthesized by a solid reaction process under inert atmosphere. The transition temperature (TC) estimated from resistivity measurement indicates only a small decrease for C (nano) and co-doped MgB2 samples. The magnetic field response of investigated samples has been measured at 4, 10, and 20 K in the field range ± 6 T. MgB2 pellets co-doped with 0.5 wt% n-AlN and 1 wt% n-C display appreciable enhancement in critical current density (J_C) of MgB2 in both low (≥ 3 times), as well as, high-field region (≥ 15 times). J_C versus H behavior of both pristine and doped MgB2 pellets is well explained in the light of the collective pinning model. Further, the normalized pinning force density f_p(= F_p/F_{pmax}) displays a fair correspondence with the scaling procedure proposed by Eisterer et al. Moreover, the scaled data of the pinning force density (i.e., f_p{-}h data) of the investigated pellets at different temperature are well interpreted by a modified Dew-Hughes expression reported by Sandu and Chee.

  5. Second international Israeli conference on High Tc Superconductivity

    International Nuclear Information System (INIS)

    1993-01-01

    The superconductivity fields covered in this conference are: theory, applications, devices, flux properties high frequencies, Josephson junctions, magnetism, material sciences and physical properties of superconductors, spectroscopy and resonances and thin films

  6. Studies of nonlinear electrodynamics of high-temperature superconductors

    International Nuclear Information System (INIS)

    Lam, Q.H.

    1991-01-01

    Nonlinear electrodynamics of high-Tc superconductors are studied theoretically and experimentally. For powdered samples, a novel model is presented in which the metallographically observed superconducting grains in the powder are modeled as superconducting current loops of various areas with weak links. Surprising harmonic generation behavior in an ac field, H 1 cos(ωt), is predicted by the model; the power at high harmonics show sharp dips almost periodic in a super-posing dc magnetic field, revealing flux quantization in the prototype loops in the model. Such oscillation of the harmonic power in dc magnetic field, P nf (H dc ), is experimentally observed in powdered YBa 2 Cu 3 O 7 . For bulk sintered cylindrical samples, a generalized critical state model is presented. The nonlinear electrodynamics are due to flux-pinning. Experiments in ac and dc magnetic fields on a sintered cylindrical rod of YBa 2 Cu 3 O 7 yield unambiguous evidence of independent inter- and intragranular contributions to the complex harmonic permeability μ n = μ' n - iμ double-prime n . These data, together with P nf (H dc ), are explained quantitatively by the generalized critical state model, yielding a dependence on magnetic field of J c (H) ∼ H 02 local for the intergranular component, a steeper field dependence than for conventional type-II superconductors. Temperature-dependence measurements reveal that, while the intragranular supercurrents disappear at T c ≥ 91.2 K, the intergranular supercurrents disappear at T ≥ 86.6 K

  7. High Tc superconducting magnetic multivibrators for fluxgate magnetic-field sensors

    International Nuclear Information System (INIS)

    Mohri, K.; Uchiyama, T.; Ozeki, A.

    1989-01-01

    Sensitive and quick-response nonlinear inductance characteristics are found for high Tc superconducting (YBa 2 Cu 3 O 7-chi ) disk cores at 77K in which soft magnetic BH hysteresis loops are observed. Various quick response magnetic devices such as modulators, amplifiers and sensors are built using these cores. The magnetizing frequency can be set to more than 20 MHz, which is difficult for conventional ferromagnetic bulk materials such as Permalloy amorphous alloys and ferrite. New quick-response fluxgate type magnetic-field sensors are made using ac and dc voltage sources. The former is used for second-harmonic type sensors, while the latter is for voltage-output multivibrator type sensors. Stable and quick-response sensor characteristics were obtained for two-core type multivibrators

  8. The exponential critical state of high-Tc ceramics

    International Nuclear Information System (INIS)

    Castro, H.; Rinderer, L.

    1994-01-01

    The critical current in high-Tc materials is strongly reduced by a magnetic field. We studied this dependency for tubular YBCO samples. We find an exponential drop as the field is increased from zero up to some tens of oersted. This behavior was already observed by others, however little work has been done in this direction. We define what we call the ''exponential critical state'' of HTSC and compare the prediction for the magnetization with experimental data. Furthermore, the ''Kim critical state'' is obtained as the small field limit. (orig.)

  9. Effects of artificial holes in very large single-grain Y{sub 1.5}Ba{sub 2}Cu{sub 3}O{sub 7-y} bulk superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Park, S. D.; Jun, B. H.; Kim, C. J. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Park, H. W. [Korea University of Technology and Education, Cheonan (Korea, Republic of)

    2017-09-15

    The effects of artificial holes on the trapped magnetic fields and magnetic levitation forces of very large single-grain Y{sub 1.5}Ba{sub 2}Cu{sub 3}O{sub 7-y} (Y1.5) bulk superconductors were studied. Artificial holes were made for Y1.5 powder compacts by die pressing using cylindrical dies with a diameter of 30 mm or 40 m, or rectangular dies with a side length of 50 mm. The single grain Y1.5 bulk superconductors (25 mm, 33 mm in diameter and 42 mm in side length) with artificial holes were fabricated using a top-seeded melt growth (TSMG) process for the die-pressed Y1.5 powder compacts. The magnetic levitation forces at 77 K of the 25 mm single grain Y1.5 samples with one (diameters of 4.2 mm) or six artificial holes (diameters of 2.5 mm) were 10-17% higher than that of the Y1.5 sample without artificial holes. The trapped magnetic fields at 77 K of the Y1.5 samples with artificial holes were also 9.6-18% higher than that of the Y1.5 sample without artificial holes. The 33 mm and 42 mm single grain Y1.5 samples with artificial holes (2.5 mm and 4.2 mm in diameter) also showed trapped magnetic fields 10-13% higher than that of the Y1.5 samples without artificial holes in spite of the reduced superconducting volume fraction due to the presence of artificial holes. The property enhancement in the large single grain Y1.5 bulk superconductors appears to be attributed to the formation of the pore-free regions near the artificial holes and the homogeneous oxygen distribution in the large Y123 grains.

  10. A universal order underlying the pseudogap regime of the underdoped high Tc cuprates

    Science.gov (United States)

    Harrison, Neil

    2014-03-01

    A major achievement in condensed matter physics in the last quarter century has been a step towards the understanding of the unconventional d-wave superconducting state in the copper-oxide materials. Surprisingly, the normal state out of which the superconducting state emerges remains a mystery at low charge carrier densities, i.e., in the underdoped regime. This regime is of particular interest because it is characterised by an unusual momentum dependent energy pseudogap in the excitation spectrum that has defied explanation and is key to a full understanding of the unconventional d-wave superconducting state. I will present new quantum oscillation experimental results within the pseudogap regime of the high Tc superconductors YBa2Cu3O6+x and YBa2Cu4O8 which now extend up to the optimally-doped regime. These data reveal the evolution of the Fermi surface approaching the putative quantum critical point under the superconducting dome. A comprehensive angle-resolved study of the Fermi surface enables us to unambiguously identify a specific form of order that accounts for the observed quantum oscillations as well as other spectroscopic, transport and thermodynamic probes within the pseudogap regime. The author would like to thank B. Ramshaw, S. Sebastian, F. Balakirev, C. Mielke, M. Altarawneh, P. Goddard, S. Sabok, B. Babrowski, D. Bonn, W. Hardy, R. Liang and G. Lonzarich. This work was supported by the DOE BES ``Science of 100 tesla'' project and by the NSF and Florida State.

  11. High-Tc dc-SQUID gradiometers in flip-chip configuration

    Science.gov (United States)

    Peiselt, K.; Schmidl, F.; Linzen, S.; Anton, A. S.; Hübner, U.; Seidel, P.

    2003-12-01

    We describe a new design of a gradiometric flip-chip antenna, which is inductively coupled to a dc-SQUID gradiometer. Both components are patterned out of thin films of the high-Tc superconductor YBa2Cu3O7-x (YBCO). For the flip-chip antenna, a 40 mm × 10 mm SrTiO3 single crystalline substrate is used, while the gradiometer sensors are prepared on 10 mm × 10 mm SrTiO3 bicrystal substrates. Special attention is paid to the inductive coupling between the flip-chip antenna and the read-out gradiometer antenna. We investigate different designs of coupling loops in order to optimize the coupling inductance between both components of the sensor. With optimized coupling the sensor achieves a field-gradient resolution of 12 fT cm-1 Hz-1/2 in the white noise region and of 310 fT cm-1 Hz-1/2 at 1 Hz in the unshielded laboratory environment.

  12. Pressure and high-Tc superconductivity in sulfur hydrides.

    Science.gov (United States)

    Gor'kov, Lev P; Kresin, Vladimir Z

    2016-05-11

    The paper discusses fundamentals of record-TC superconductivity discovered under high pressure in sulfur hydride. The rapid increase of TC with pressure in the vicinity of Pcr ≈ 123GPa is interpreted as the fingerprint of a first-order structural transition. Based on the cubic symmetry of the high-TC phase, it is argued that the lower-TC phase has a different periodicity, possibly related to an instability with a commensurate structural vector. In addition to the acoustic branches, the phonon spectrum of H3S contains hydrogen modes with much higher frequencies. Because of the complex spectrum, usual methods of calculating TC are here inapplicable. A modified approach is formulated and shown to provide realistic values for TC and to determine the relative contributions of optical and acoustic branches. The isotope effect (change of TC upon Deuterium for Hydrogen substitution) originates from high frequency phonons and differs in the two phases. The decrease of TC following its maximum in the high-TC phase is a sign of intermixing with pairing at hole-like pockets which arise in the energy spectrum of the cubic phase at the structural transition. On-pockets pairing leads to the appearance of a second gap and is remarkable for its non-adiabatic regime: hydrogen mode frequencies are comparable to the Fermi energy.

  13. Experience in determination of the composition and texture of Y-Ba high-Tc superconductors

    International Nuclear Information System (INIS)

    Shamraj, V.F.; Efimov, Yu.V.; Babarehko, A.A.; Myasnikova, E.A.; Bolokhova, T.A.; Shul'gin, A.I.

    1990-01-01

    A method for the determination of phase composition and texture of powder and strip samples of Y-Ba HTSC has been developed. Phase analysis was conducted by comparing X-ray patterns of analyzed and model patterns of various phases in the system Y-Ba-Cu-O using literature data on crystal structures of the phases. The texture of rolled strips was studied by the method of plotting direct polar figures using an automate diffractometer. It is shown that combination of standard method of micro X-ray diffraction analysis with the study of oxygen content in HTSC, usign ultralong wave spectroprobe, provides for the determination of the important component and permits to reveal microheterogeneity of the samples

  14. Identification of ACAP components in thallium series high-Tc superconductors

    International Nuclear Information System (INIS)

    Adonkin, V.T.; Dyakin, V.V.; Yefanov, V.S.; Tanatar, M.A.; Akimov, A.I.; Chernyakova, A.P.

    1992-01-01

    Angle correlation of annihilation photons (ACAP) curves have been studied in thallium series compounds with general formula Tl m Ba 2 Ca n-1 Cu n O x (m =1, n =3; m =2, n = 1,2,3). The dispersions of two Gaussian components established have been shown to change in a systematic way with T due to changes in both stoichiometry and the number of Cu-O and Tl-O layers in the formula unit. The narrow component has been assumed to be due to free electrons. The broad component has been shown to be due to Tl-O layers and has been assumed to be due either to Tl-O electron pockets or thallium vacancies in the layers

  15. Experimental evidence for flux-lattice melting. [in high-Tc superconductors

    Science.gov (United States)

    Farrell, D. E.; Rice, J. P.; Ginsberg, D. M.

    1991-01-01

    A low-frequency torsional oscillator has been used to search for flux-lattice melting in an untwinned single crystal of YBa2Cu3O(7-delta). The damping of the oscillator was measured as a function of temperature, for applied magnetic fields in the range H = 0.1-2.3 T. A remarkably sharp damping peak has been located. It is suggested that the temperature of the peak corresponds to the melting point of the Abrikosov flux lattice.

  16. Higher critical current density achieved in Bi-2223 High-Tc superconductors

    Directory of Open Access Journals (Sweden)

    M.S. Shalaby

    2016-07-01

    Full Text Available Bi2Sr2Ca2Cu3Ox (Bi-2223 were prepared using a solid state reaction method at different sintering times and temperatures. Structural phase identifications have been done using X-Ray analysis and refinement by Reitveld method which proves the coexistence of Bi-2223 and Bi-2212 phases. The critical transition temperature Tc and critical current density Jc values were measured using superconducting quantum interference device magnetometer (SQUID and by the magneto-optics technique. A remarkable rapid decrease to the diamagnetic signal in the magnetization versus temperature M(T at 110 K and Jc around 1.2 × 107 A/m2 at 5 K are confirmed for the Bi-2223 compound.

  17. Role of oxygen and structural defects in properties of high-Tc superconductors

    International Nuclear Information System (INIS)

    Raveau, B.; Michel, C.; Hervieu, M.; Deslandes, F.; Maignan, A.

    1989-01-01

    Almost two years have passed since the discovery of superconductivity in mixed-valence copper oxides. A number of papers have now been published in this field. In spite of these numerous results, the mechanisms which govern superconductivity in those oxides are so far not understood. The authors discuss how the study of the crystal chemistry of these oxides suggests that two points are of capital importance for the appearance of superconductivity in those compounds: the low dimensionality of the structure and the mixed-valence of copper

  18. Sample size effect on the determination of the irreversibility line of high-Tc superconductors

    International Nuclear Information System (INIS)

    Li, Q.; Suenaga, M.; Li, Q.; Freltoft, T.

    1994-01-01

    The irreversibility lines of a high-J c superconducting Bi 2 Sr 2 Ca 2 Cu 3 O x /Ag tape were systematically measured upon a sequence of subdivisions of the sample. The irreversibility field H r (T) (parallel to the c axis) was found to change approximately as L 0.13 , where L is the effective dimension of the superconducting tape. Furthermore, it was found that the irreversibility line for a grain-aligned Bi 2 Sr 2 Ca 2 Cu 3 O x specimen can be approximately reproduced by the extrapolation of this relation down to a grain size of a few tens of micrometers. The observed size effect could significantly obscure the real physical meaning of the irreversibility lines. In addition, this finding surprisingly indicated that the Bi 2 Sr 2 Ca 2 Cu 2 O x /Ag tape and grain-aligned specimen may have similar flux line pinning strength

  19. Electron-positron momentium distribution measurements of high-Tc superconductors and related systems

    International Nuclear Information System (INIS)

    Wachs, A.L.; Turchi, P.E.A.; Howell, R.H.; Jean, Y.C.; Fluss, M.J.; West, R.N.; Kaiser, J.H.; Rayner, S.; Haghighi, H.; Merkle, K.L.; Revcolevshi, A.; Wang, Z.Z.

    1989-01-01

    The authors discuss measurements of the 2D-angular correlation of positron annihilation radiation (ACAR) in La 2 CuO 4 , YBa 2 Cu 3 O 7 (YBCO), and NiO. The measurements for NiO are the first such 2D-ACAR measurements; the YBCO results are of a higher statistical quality than previously reported. The data are compared with complementary theoretical calculations and with each other. The authors discuss the implication of this analysis for ACAR studies of similar and related systems

  20. Effect of post-sintering treatment on properties of Bi-based high Tc superconductors

    International Nuclear Information System (INIS)

    Nagai, Masayuki; Kozuka, Akira; Morishita, Ken; Nishino, Tadashi; Hattori, Takeo; Takata, Masasuke

    1989-01-01

    A new method to obtain the pure 110K phase in the system Bi-Sr-Ca-Cu-O was examined employing post-sintering treatment. The mixture of Bi 2 O 3 , SrCO 3 , CaCO 3 and CuO with the basic composition of Bi/Sr/Ca/Cu=2/2/1/2 was calcined. The resulting powder was soaked in ethanol containing copper acetate and calcium acetate, the amounts of which were determined to give the composition of Bi/Sr/Ca/Cu=2/2/2/3 after sintering. The resistivity was measured by the d.c. four probe method in a cryostat. The current level was maintained at 50 mA and the voltage drop was determined by averaging the values in the forward and reverse directions. The zero T c ranged from 65 to 69K for the samples after sintering, while that ranged from 69 to 71K for those with post-sintering treatment. The effect of the treatment was not drastic but significant. Modified post-sintering treatment is being examined and the results are reported in the symposium