Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2686-2691 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The laser irradiation process is a promising method for the fabrication of metastable Al5–Nb3Al(Ge,Si) compounds. Thereby Nb-sheathed Nb-25 at. % Al(Ge,Si) microcomposite tapes are prepared by a conventional powder metallurgical method and heat treated by a high-intensity CO2-laser beam. The parameters selected during laser beam irradiation of the composite determine the relative amounts of molten, heat-affected or unreacted material. In order to obtain large overall superconducting currents, it is favorable to melt a large fraction of the microcomposite without melting the surrounding Nb sheath. The cooling rate after laser beam irradiation determines the structure and the formation of metastable phases in the resolidifying material. The sequences of the process are simulated by heat flow calculations, which consider laser power, beam diameter, tape velocity, thickness, and microstructure, as well as heat transfer coefficients. From these calculations we could deduce optimum conditions for the laser treatment, leading to Jc values of 105 A cm−2 at 10 T and 104 A cm−2 at 16 T.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 4440-4442 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: (Bi,Pb)2Sr2Ca2Cu3Ox Ag-sheathed tapes were fabricated by the standard "powder in tube'' technique. Because of the platelike growth of the Bi HTc-phase, it is possible to texture the wires by a rolling process, which improves the mechanical density. This implies an increase of the critical current density not only in zero magnetic field, but also in all external magnetic fields. By measuring ρ(T,B) curves, we have estimated the activation energy for thermically activated flux creep, U0, to vary between 200 and 20 meV in magnetic fields between 0.005 and 10 T. These low U0 values are approximately ten times smaller than in Y1Ba2Cu3O7−δ. For the Bi 2223 tapes, a power law U0∼B−α with α=0.277±0.030 was obtained.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 269-274 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure of pseudobinary Co-Zr and Cu-Zr metallic glasses, where Co and Cu were substituted by Fe, was studied by means of 57Fe-Mössbauer spectroscopy. The resulting spectra can be divided into two different classes: (1) For Zr concentrations larger than 67 at. %, the structure of the glass, as derived from Mössbauer spectroscopy, is nearly independent from a substitution, leading to only small changes of the average isomer shifts and quadrupole splittings. These small variations of hyperfine parameters can be ascribed to charge transfer effects. (2) For lower Zr contents, pronounced systematic changes of hyperfine parameters occur upon Co or Cu substitution. Beyond changes of the average hyperfine values, the corresponding quadrupole-splitting distributions become dependent on the degree of substitution, i.e., there is a concentration dependent splitting into two peaks. For the amorphous binary Zr-Fe system, these two peaks have been connected to two amorphous phases with concentrations near Zr2Fe and ZrFe2. At least for the Fe-doped Cu-Zr metallic glasses it could be demonstrated that Fe does not substitute the Cu sites but rather creates preferred environments.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 3775-3778 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic flux density and current density distributions of YBa2Cu3O7 films in soft magnetic environments are investigated by magneto-optics. Next to the magnets flux penetration is strongly modified. Current density distributions obtained by an inversion of the law of Biot–Savart show overcritical current densities in the current domains next to the magnets. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 5545-5548 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Y1Ba2Cu3O7−δ films with a thickness between 0.5 and 5 μm were grown on Si covered with an amorphous SiO2 layer, on Zr foils, and on a single-crystalline MgO substrates by KrF laser ablation. The influence of film thickness and substrate temperature on the structure, texture, and microstructure of the as-grown films was investigated by x-ray diffraction and scanning electron microscopy. At an appropriate, substrate-dependent temperature, on all three substrate materials, the films grow c-axis oriented up to a thickness of about 2 μm (critical thickness), followed by a sharp transition to a-axis-oriented growth occurring within about 100 nm. Similar changes could be observed by lowering the substrate temperature by 120 °C. Therefore, the hypothesis was propounded that the thickness dependence of the growth orientation of the film is due to a decrease of the surface temperature. To prove this the influence of raising the substrate temperature during the growth process was investigated. It could be shown that a linear increase of the substrate temperature leads to completely c-axis-oriented films up to thicknesses of 5 μm. A change of the thermal emissivity of the film surface as a possible cooling mechanism is discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 317-319 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Differently prepared samples with the nominal composition Y1.2Ba0.8CuOy are examined via microscopy, energy dispersive x-ray analysis, x-ray diffraction, and measurements of resistivity and susceptibility. Various phases are identified directly. Essentially these are Y2BaCuO5, which forms a matrix with semiconducting and antiferromagnetic properties and YBa2Cu3O7−x, which is present in a dendritic morphology. The dendritic appearance indicates that YBa2Cu3O7−x is formed by nucleation and growth during sintering. Despite the particular growth mechanism of sintered materials a strong analogy exists with dendritic growth during solid-state transformations in metallic alloys.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 2681-2688 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe a formalism for studying a superconducting disk shielding an arbitrary magnetic field. The theory is developed for problems with rotational symmetry, and the results are applied to investigating various experimental situations. In particular, we have considered a cylindrical permanent magnet which is brought over an ideal superconductor. The levitation force, F, and the induced supercurrent density, j, have been calculated and the results put into closed forms. Both magnitudes are analyzed in terms of suitable dimensionless parameters related to the relevant length scales: the distance between the magnet and the superconductor, the disk radius and the magnet transversal dimensions. We demonstrate that both F and j provide a very precise description in the whole range of parameters by means of simple expressions which strictly correspond to the limits. In the specific range of magnetic force microscopy, we show how to approximate F to the desired accuracy in terms of the reduced penetration depth λ/a, a being the distance between the given magnetic tip and the superconductor. Finally, the theory is used to obtain a simple criterion which determines whether effective medium theories are suitable or not for highly textured granular superconductors. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1648-1651 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of Fe substituted for Cu in YBa2Cu3O7−δ on the microstructure and the critical properties has been studied. In the concentration regime 0≤x≤0.05, the microstructure changes drastically from a twin structure for x≤0.01 to a microdomain structure for x≥0.02. The average spacing of the twin or domain boundaries varies from ∼90 nm for x=0 to ∼5 nm for x≥0.02, thus providing an ideal system to test the role of boundary pinning. Large intragranular pinning forces are observed for x≤0.01 followed by a sudden drop to values ∼20 times smaller for x≥0.02. However, although d/a0 (twin-spacing/flux-line lattice parameter) changes drastically from d/a0〉1 for x=0 to d/a0〈1 for x≥0.02, the same field dependence of Fp is observed for all Fe concentrations, i.e., Fp∼B2c2b(1−b)2. It is, therefore, concluded that the twin boundaries are not significantly contributing to the flux pinning and that the decrease in Fp for 0.01≤x≤0.02 is related to the decrease of the upper critical field Bc2, which is caused by a strong reduction of the electron density of states at the Fermi surface.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3975-3979 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Substitution of 3d elements Fe and Ni in the YBa2Cu3O7−δ superconductor was studied with the aim of understanding the role of substitution on the twin structure of the superconductor and the resultant microstructure on the pinning properties and Tc variation. The results of transmission electron microscopy (TEM), electron diffraction, and high-resolution electron microscopic studies (HREM) on the substituted samples of YBa2(Cu1−x,Mx)3O7−δ with M=Fe,Ni are reported here. TEM studies showed that the twin width decreases as x increases up to 0.015 for Fe substitution and is replaced by a 5-nm-size twin domain structure in the regime 0.015≤x≤0.05. This domain structure vanishes by x=0.12. HREM studies showed that these domains retain the orthorhombic structure of the unsubstituted sample contrary to the x-ray diffraction reports. In the case of Ni-substituted samples for x=0.05 the orthorhombic structure and the twin lamellas of the unsubstituted sample remain unaltered. The cooperative Jahn–Teller effect, limited in extent by the presence of Fe on the Cu(1) site, is proposed to be responsible for the formation of twin domains.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 1937-1942 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: CuNb3Sn microcomposite wires with Ti additions have been produced by the hot-powder-metallurgical preparation method. The influence of the Nb3Sn filament diameter, heat treatment, and Ti addition on the superconducting properties are discussed on the basis of critical current densities (up to fields of 22 T), critical temperatures, as well as x-ray microprobe analyses. Critical current measurements of Nb3Sn multifilamentary tapes indicate that filament/matrix interfaces are dominant flux pinning centers in these composites. When Ti is incorporated into the A15 phase, the upper critical field is enhanced by about 2 T with respect to unalloyed superconductors. A drastic improvement of the superconducting properties can be achieved by the utilization of larger Nb powder particles. In microcomposites prepared from larger Nb powder (100–300 μm), Bc2 is enhanced by about 3–4 T with respect to finer Nb powder (20–45 μm). Critical fields up to 21.4 T and critical current values of 1.2×104 A/cm2 at a magnetic field of 16 T and 4.5×103 A/cm2 at 18 T are obtained for microcomposites prepared from coarser Nb powder with an addition of 2 wt. % Ti.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...