Disordered Nanocrystalline Superconducting<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow><mml:mi mathvariant="normal">P</mml:mi><mml:mi mathvariant="normal">b</mml:mi><mml:mi mathvariant="normal">M</mml:mi><mml:mi mathvariant="normal">o</mml:mi></mml:mrow><mml:mn>6</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">S</mml:mi><mml:mn>8</mml:mn></mml:msub></mml:math>with a Very Large Upper Critical Field

Niu, Hong‐Ying; Hampshire, D.P.

doi:10.1103/physrevlett.91.027002

Cited by 31 publications

(21 citation statements)

References 25 publications

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“…loss filamentary conductors made with YBCO. A number of improvements are possible in high density nanocrystalline YBCO materials: Flux pinning is expected to be very strong in high density, nanocrystalline samples prepared by ball milling [11][12][13]; The grain boundaries may be very clean due to the improved diffusion under high pressure; The densification of the material can improve the connectivity between grains thereby increasing J C [15,16], and the upper critical field (B C2 ) in the nano-structured superconductors may be increased by shortening the electron mean-freepath as has been found in the conventional superconductors such as Chevrel phase [11], elemental [17] and A15 compounds [18]. Improving B C2 of YBCO is particularly important for high magnetic field applications operating at liquid nitrogen temperatures.…”

Section: Introductionmentioning

confidence: 99%

Bulk nanocrystalline superconducting YBa₂Cu₃O_7-x

Xiang

Fleck

Hampshire

2008

J. Phys.: Conf. Ser.

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Section: Introductionmentioning

confidence: 99%

Bulk nanocrystalline superconducting YBa₂Cu₃O_7-x

Xiang

Fleck

Hampshire

2008

J. Phys.: Conf. Ser.

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“…Hence, the maximum observed enhancement is 2-3 T at 4.2 K. 3 In this Letter, we report that greater improvements in µ 0 H c2 (0) can be realized by introducing disorder instead of by alloying. Niu and Hampshire showed recently that highenergy ball milling of PbMo 6 S 8 superconductors, followed by controlled annealing in a hot isostatic press, resulted in a tripling of H c2 ′ at the expense of a modest reduction of T c from 15 to 12 K. 4 The µ 0 H c2 (0) values estimated by the WHH formula increased from 45 to 110 T. Based on this result, we explored whether a similar behavior could be induced in Nb 3 Sn.Past experiments have shown that the superconducting properties of Nb 3 Sn are optimized for compositions found at the tin-rich (stoichiometric) edge of the phase field. 5 Even for the stoichiometric composition, the superconducting properties are very sensitive to atomic site disorder introduced by irradiation or strain, 6 suggesting that the decrease in T c due to disorder might more than offset the benefit from the increase of H c2 ′.…”

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confidence: 99%

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confidence: 99%

Enhancement of the upper critical field of Nb3Sn utilizing disorder introduced by ball milling the elements

Cooley

Moodenbaugh

2006

Applied Physics Letters

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Nb 3 Sn was prepared by milling Nb and Sn powder mixtures followed by limited reactions to restrict disorder recovery. Although disorder reduced the superconducting critical temperature T c , the concomitant electron scattering increased the upper critical field µ 0 H c2 to as high as 35 T at 0 K, as determined by the Werthamer-Helfand-Hohenberg equation. H c2 was higher for longer milling times and lower annealing temperatures. Substitution of 2% Ti for Nb did not appreciably enhance H c2 , suggesting that alloying mitigates the benefits of disorder. Since alloyed Nb 3 Sn wires  have µ 0 H c2 (0) ≈ 29 T, wires based on heavily milled powders could extend the field range for applications if they can be made with high current density.Practically all high-field superconducting magnets operating above ~8 T at 4.2 K use Nb 3 Sn wires. This includes laboratory solenoids, large solenoids for fusion, dipoles and quadrupoles for particle accelerators, and very high field magnets for nuclear magnetic resonance. The operating envelope for Nb 3 Sn, presently ~8 < µ 0 H < ~21 T at 4.2 K (up to ~23 T at 2.0 K), is determined by the temperature dependence of the upper critical field H c2 (T) and the field H and temperature T dependence of the critical current density J c . While J c depends strongly on the development of a homogeneous fine-grained microstructure through control of the Nb 3 Sn formation reaction, H c2 is determined by the physics of the superconducting state itself.Very recently, Godeke et al. examined the factors that affect the H c2 (T) curve in a range of commercial and experimental Nb 3 Sn composite wires. 1 Generally, their results fall into two classes: 1) pure Nb 3 Sn wires which exhibit T c ≈ 18.0 K, µ 0 H c2 ′ ≡ µ 0 dH c2 /dT| Tc of about -2.0 T K -1 , and an extrapolated µ 0 H c2 (0) ≈ 26 T; and 2) alloyed wires with 1 to 2% Ti or Ta substituted for Nb which exhibit T c ≈17.5 K, µ 0 H c2 ′ ≈ -2.3 T K -1 , and µ 0 H c2 (0) ≈ 29 T. These wires' behaviors were described very well by theoretical descriptions developed during the 1960s, in particular the Werthamer, Helfand, and Hohenberg (WHH) 2 equationSince H c2 ′ is directly proportional to the normal-state electrical resistivity ρ N , alloying the Nb 3 Sn phase with Ti and/or Ta adds electron scattering and improves H c2 at low temperatures. Alloying also changes the electronic density of states and the electron-phonon coupling, since adding more than about 2% of Ti or Ta results in a drop of T c that more than counteracts the increase in H c2 ′. Hence, the maximum observed enhancement is 2-3 T at 4.2 K. 3 In this Letter, we report that greater improvements in µ 0 H c2 (0) can be realized by introducing disorder instead of by alloying. Niu and Hampshire showed recently that highenergy ball milling of PbMo 6 S 8 superconductors, followed by controlled annealing in a hot isostatic press, resulted in a tripling of H c2 ′ at the expense of a modest reduction of T c from 15 to 12 K. 4 The µ 0 H c2 (0) values estimated by the WHH formula increased from 45 ...

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“…Nevertheless, the developments in powder-in-tube technology means that long-length multifilamentary Nb 3 (Al 1-x Ge x ) wires may now be possible. According to BCS theory, B C2 (0) for a superconductor at zero temperature is given by [11]:…”

Section: Introductionmentioning

confidence: 99%