ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
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
    Properties of niobium–titanium superconducting wires with Nb artificial pinning centers (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1640-1646 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Artificial pinning center (APC) Nb 47 wt % Ti composite wires containing 24 vol % Nb pins were characterized as the wire diameter was reduced. As the nominal pin diameter dp was reduced from 165 to 15 nm, the nominally round pins transformed into ribbons with a relatively wide distribution in thickness, as compared to the α-Ti ribbons in optimized, conventionally processed Nb 47 wt % Ti. The maximum in the bulk flux pinning force Fp of 25 GN/m3 (4.2 K, 2.5 T) occurred at dp=40 nm, for which the measured Nb ribbon thickness ranged from 1 to 16 nm. This Fp value was about one third higher than that found in the best conventional Nb 47 wt % Ti. The upper critical magnetic field Hc2, measured by magnetization, decreased from 10.3 to 9 T as the Nb pins became proximity-effect coupled to the matrix. To better compare APC and conventional wires, we measured the properties of the best APC wire at a reduced temperature so that its Hc2 was the same as Hc2(4.2 K) for Nb 47 wt % Ti. The peak value of Fp was then 36 GN/m3 at 3 T, almost twice the maximum value yet reported for conventional Nb–Ti (∼19 GN/m3 at 5 T). In spite of the pinning force curve remaining sharply peaked at lower fields, the equalized 5 T critical current density was 4600 A/mm2, some 25% higher than the best values of conventional Nb–Ti. These properties demonstrate the strong potential of APC composites. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362979
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    The effect of anisotropic flux pinning microstructure on the sample length dependence of the magnetization critical current density in niobium–titanium superconductors (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1647-1651 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization measurements of the critical current density Jc in Nb 47 wt % Ti with Nb artificial pinning centers revealed that the shape and magnitude of the field dependent magnetization hysteresis ΔM(H) was a strong function of the sample length and that ΔM(H) for short wire samples was up to six times smaller than for long wires. This is caused by the strong anisotropy of the critical current density Jc. The magnitude of Jc flowing perpendicular to the wire axis J⊥ was deduced to be 50–175 times smaller than the longitudinal current density J(parallel). The source of the anisotropy lies in the anisotropic flux pinning microstructure of the wires. When the magnetization current crosses perpendicular to the filament axis at each end of the wire, the Lorentz force is parallel to the pinning center axis. The pinning force is weak in this direction and J⊥ is correspondingly small. The technologically important critical current density is the longitudinal current density J(parallel). It can be extracted from magnetization measurements only in the case of large length to diameter filaments, as is quantitatively analyzed here. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362963
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Evolution of the transport critical current density and irreversibility field as a function of heat treatment and pressing pressure during processing of Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox tapes (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 2296-2301 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Extended electric field-current density characteristics taken on the bare cores of monofilament (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes at 77 K have been used to measure the irreversibility field, H*, and the critical current density, Jc, at different stages of tape processing. The number of heat treatments and the uniaxial pressing pressure were the experimental variables. Both H* and Jc increased substantially with heat treatment and with deformation pressure. The data are consistent with an improvement in Jc from two factors, one being an increase in the 2223 phase fraction with increasing heat treatment, the second, independent cause being an increase in the flux pinning properties of the composite. The experiments show that improving Jc involves control of at least three factors: enhancing the volume fraction of 2223 phase; increasing flux pinning; and enhancement of the connectivity of the grain boundaries that lie within the current path. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364233
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Dependence of critical current density on microstructure in the SnMo6S8 Chevrel phase superconductor (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6377-6387 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Microstructure and superconducting properties of hot isostatic pressed SnMo6S8 were systematically studied. Magnetization was measured in fields up to 30 T at 4.2–14 K. SnMo6S8 exhibits critical current densities limited by flux pinning, not by granularity. Samples exhibited Birr(T)∼Bc2(T), indicative of strong flux pinning. Pinning force curves contained two distinct peaks, indicating that at least two pinning mechanisms are active. The microstructure contained two types of defects which could pin flux: grain boundaries and planar intragranular defects. Lower-field pinning (B/Bc2≤0.3) was directly correlated to the grain boundary density. Higher-field pinning (B/Bc2≥0.5) appeared to be controlled by the intragranular pins. Compared to Nb3Sn, the grain sizes are large and the contribution from grain boundary pinning is small. Inhibiting grain growth through lower-temperature processing and increasing the density of intragranular defects both appear feasible means of further increasing Jc. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359110
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Experiments concerning the connective nature of superconductivity in YBa2Cu3O7 (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 3308-3313 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Samples of YBa2Cu3O7 have been prepared with rather sharp inductive transitions having in the best cases breadths of 7 K and midpoint Tc values of 88 K. The resistive Tc midpoints are 92–95 K with transition widths of ±1–2 K. Flux shielding at 4.2 K is normally 100% and flux expulsion at 4.2 K reaches 95%. However, even small fields of order 1 mT decouple some 15%–20% of the volume, allowing flux to enter the samples. Resistive Hc2 measurements suggest that Hc2(0) varies from 〈1 to 〉300 T, depending on the criterion chosen. ac susceptibility measurements suggest that Hc2(0) is ∼60 T. Magnetization current densities are relatively high (150–200 A/mm2 at 1–10 T at 4.2 K) but measured transport current densities are small (≤1 A/mm2). Magnetization current densities at 77 K are about two orders of magnitude lower. The samples were seen to be heavily twinned by light microscopy (scale of 1–5 μm) and by transmission electron microscopy (scale of ∼250 nm). It is concluded that these measurements are consistent with a model of superconducting regions of reduced dimensionality coupled by tunneling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339339
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Quantitative description of a high Jc Nb-Ti superconductor during its final optimization strain. I. Microstructure, Tc, Hc2, and resistivity (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 5962-5970 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A most important step in the critical current density (Jc) optimization of Nb-Ti is the large final drawing strain, in which α-Ti precipitates, initially approximately equiaxed and 100–200 nm in diameter, are drawn into ribbons, whose thickness (1–2 nm) is less than the superconducting coherence length [ξ (4.2 K)∼5 nm]. Using transmission electron microscopy, the precipitate thickness, spacing, cross-sectional area, and circumference were measured over the whole final drawing strain range. Each of these parameters was found to have a simple power dependence on the wire diameter. Tc, Hc2, and the resistivity (ρn) were also change considerably during the refinement of the precipitates. Directly after precipitation, Tc increased, and (dHc2/dT)Tc and ρn were reduced from the single-phase values. Drawing the wire returned these parameters to their single-phase values, as the precipitate thickness was reduced to less than ξ. This observation explains a long-standing peculiarity in this system, namely that the optimum Hc2 of high Jc conductors occurs for a composition close to Nb 46 wt.% Ti, even when the precipitation of 18 vol % of α-Ti shifts the matrix composition to a Nb-rich composition of theoretically lower Hc2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343624
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Quantitative description of a very high critical current density Nb-Ti superconductor during its final optimization strain. II. Flux pinning mechanisms (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 5971-5983 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Flux pinning by α-Ti precipitates has been studied in a carefully made Nb 48 wt. % Ti composite having very high critical current density and a macroscopically rather uniform precipitate array. The pinning was studied as a function of field (0–15 T) and temperature (2.3 K—Tc) for a ratio of the precipitate thickness (tppt) and the coherence length (ξ) which was varied between 10 and 0.1 by a large drawing strain. Surprisingly, the maximum bulk pinning force (Fp) occurred for tppt/2ξ(approximately-equal-to)0.1 and a precipitate spacing about one-eighth the fluxon spacing, suggesting that the flux pinning occurs at clusters of precipitates. In contrast to earlier studies, strict temperature scaling of Fp was not observed; the peak of the pinning force shifted to lower reduced fields as the temperature increased. The effect was largest for the finest scale microstructure. This nonscaling is interpreted in terms of two pinning mechanisms having different field and temperature dependencies. At low reduced fields, and at temperatures close to Tc, the core interaction (δHc) dominates. At higher reduced fields and low reduced temperatures, pinning due to variations in κ also contributes to Fp. Clusters of very fine α-Ti ribbon precipitates give rise to these variations in Hc and κ. A comparison of the specific pinning force with the core interaction model was made close to Tc, where the δHc pinning mechanism dominates. Good agreement was obtained for all precipitate thicknesses, indicating that the pinning can be quantitatively described by the core interaction and the direct summation models. No significant proximity effect suppression of the pinning force at fine precipitate dimensions was observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343625
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Poor intergrain connectivity of PbMo6S8 in sintered Mo-sheathed wires and the beneficial effect of hot-isostatic-pressing treatments on the transport critical current density (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 1606-1613 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructure of Mo-sheathed Chevrel-phase superconducting wires was investigated by high-resolution scanning electron microscopy (SEM). Excess Pb forms small nodules (10–30 nm) on the Chevrel-phase grains or wetting layers between the Chevrel grains. The critical current density Jc is strongly reduced when wetting layers are present. However, second-phase Mo exists as islands as large as 2–10 μm and has little harmful effect on Jc. Although some Mo-sheathed wires sintered at 700 °C show relatively high Jc ( ≥ 2 × 108 A/m2 at 8 T), the Chevrel phase in these wires has a very porous microstructure, and the Jc values measured with a magnetic field parallel to the current, Jc((parallel)), were only about 10% higher than the Jc values measured with a field perpendicular to the current, Jc(⊥). This clearly suggests that the transport current flows percolatively in these wires. Much denser microstructures were obtained by hot-isostatic-pressing (HIP) treatments at 1200 °C, and very high Jc values, (approximately-greater-than) 5 × 108 A/m2 at 8 T and 9.3 × 107 A/m2 at 23 T, which are of the order of the highest Jc values so far reported, were observed. High-resolution SEM observations of HIP'ed wires demonstrate that the interconnectivity between the Chevrel grains was much improved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349525
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Resistive transitions and the origin of the n value in superconductors with a Gaussian critical-current distribution (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3312-3315 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The resistive transition of a superconductor with a Gaussian distribution of critical currents is analyzed and exact relations for the voltage-current characteristic and the resistive transition index (n value) in such a superconductor are developed. Excellent fits are found to the experimental transitions in two very different types of superconductor; a Nb-Ti monofilament and a Bi2Sr2Ca2Cu3O10 tape.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354554
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Suppression of magnetic granularity by transport current in (Bi,Pb)2Sr2Ca2Cu3Ox tapes (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2720-2722 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using the magneto-optical technique, transport current flow in (Bi,Pb)2Sr2Ca2Cu3Ox (BSCCO) Ag-sheathed tapes has been imaged. For zero transport current, I, the magnetization currents display a pronounced macroscopic magnetic granularity (on a scale larger than the actual grain size) characterized by a percolative distribution of current loops. By applying I≈0.8Ic this granular behavior was largely replaced by a more uniform current flow. Due to the significant dependence of Ic on E in BSCCO, the extent to which the magnetic granularity is observed strongly depends on the magnetic prehistory and on the electric field E, whose characteristic values are very different for magnetization and transport measurements. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114304
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...