Development of high critical current density in multifilamentary round-wire Bi2Sr2CaCu2O8+δ by strong overdoping

Shen, Tengming; Jiang, J.; Yamamoto, Akiyasu; Trociewitz, U.P.; Schwartz, J.; Hellstrom, E. E.; Larbalestier, D. C.

doi:10.1063/1.3242339

Cited by 40 publications

(43 citation statements)

References 27 publications

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“…Figure 8 shows this using FIBed transverse cross-sectional images at four different locations in the same filament from a 27-FP wire. Figure 8(a) shows an almost 100% dense microstructure, meaning that the I c of this section is dependent principally on the grain boundary properties, which can be significantly ameliorated by overdoping [12]. However, the three other images reveal porous structures inside the filament, the worst case being shown in figure 8(d) where the filament is a hollow shell, greatly suppressing connectivity by reduction of physical grain-to-grain connections.…”

Section: Discussionmentioning

confidence: 97%

“…It appears that the superconducting connectivity was also enhanced because J c increased significantly. Varying the cooling rate did not vary the flux pinning and thus had no effect on J c , since the irreversibility field H irr , evaluated by the extrapolated Kramer field H K , was the same for all samples after they received a full, final oxygenation that put the 2212 grains into a reproducible, overdoped state [12].…”

Section: Introductionmentioning

confidence: 99%

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Bubble formation within filaments of melt-processed Bi2212 wires and its strongly negative effect on the critical current density

Kametani

Shen

Jiang

et al. 2011

Supercond. Sci. Technol.

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(Bi2212) show that the critical current density J c is limited by the connectivity of the filaments, but what determines the connectivity is still elusive. Here we report on the role played by filament porosity in limiting J c . By a microstructural investigation of wires quenched from the melt state, we find that porosity in the unreacted wire agglomerates into bubbles that segment the Bi2212 melt within the filaments into discrete sections.These bubbles do not disappear during subsequent processing because they are only partially filled by Bi2212 grains as the Bi2212 forms on cooling. Correlating the microstructure of quenched wires to their final, fully processed J c values shows an inverse relation between J c and bubble density. Bubbles are variable between conductors and perhaps from sample to sample, but they occur frequently and almost completely fill the filament diameter, so they exert a strongly variable but always negative effect on J c . Bubbles reduce the continuous Bi2212 path within each filament and force supercurrent to flow through Bi2212 grains that span the bubbles or through a thin Bi2212 layer at the interface between the bubble and the Ag matrix. Eliminating bubbles appears to be a promising new path to raise the J c of Bi2212 round wires. Published in Superconductor Science and TechnologyGeneva, Switzerland CERN-ATS 2011-010May 2011 (Bi2212) show that the critical current density J c is limited by the connectivity of the filaments, but what determines the connectivity is still elusive. Here we report on the role played by filament porosity in limiting J c . By a microstructural investigation of wires quenched from the melt state, we find that porosity in the unreacted wire agglomerates into bubbles that segment the Bi2212 melt within the filaments into discrete sections. These bubbles do not disappear during subsequent processing because they are only partially filled by Bi2212 grains as the Bi2212 forms on cooling. Correlating the microstructure of quenched wires to their final, fully processed J c values shows an inverse relation between J c and bubble density. Bubbles are variable between conductors and perhaps from sample to sample, but they occur frequently and almost completely fill the filament diameter, so they exert a strongly variable but always negative effect on J c . Bubbles reduce the continuous Bi2212 path within each filament and force supercurrent to flow through Bi2212 grains that span the bubbles or through a thin Bi2212 layer at the interface between the bubble and the Ag matrix. Eliminating bubbles appears to be a promising new path to raise the J c of Bi2212 round wires.

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Section: Discussionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Bubble formation within filaments of melt-processed Bi2212 wires and its strongly negative effect on the critical current density

Kametani

Shen

Jiang

et al. 2011

Supercond. Sci. Technol.

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“…The upper limit to the critical current density (J c ), normally defined by I c /A sc (I c is the critical current and A sc is the superconducting cross-sectional area) is always determined by vortex pinning, but the meaning of J c defined in this way is only very uncertainly connected to the vortex-pinning limit if A sc varies locally. Extensive recent analysis of J c of Bi-2212 wires concludes that vortex pinning is optimized by a final low-temperature heat treatment (HT) in pure O 2 that overdopes the Bi-2212, raises the irreversibility field (H irr ), and reduces the electronic anisotropy [5]. The J c of typical wires is also enhanced by slow cooling through the resolidification step that follows melting of the Bi-2212 filament bundles [6].…”

Section: Introductionmentioning

confidence: 99%

Void and phase evolution during the processing of Bi-2212 superconducting wires monitored by combined fast synchrotron micro-tomography and x-ray diffraction

Scheuerlein

Michiel

Scheel

et al. 2011

Supercond. Sci. Technol.

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Recent study of the current-limiting mechanisms in Bi-2212 round wires has suggested that agglomeration of the residual Bi-2212 powder porosity into bubbles of filament-diameter size occurs on melting the Bi-2212 filaments.These pores introduce a major obstacle to current flow, which greatly reduces the critical current density (J c ). Here we present an in situ non-destructive tomographic and diffraction study of the changes occurring during the heat treatment of wires and starting powder, as well as a room temperature study of ex situ processed wires. The in situ through-process study shows that the agglomeration of residual porosity is more complex than previously seen.Filament changes start with coalescence of the quasi-uniform and finely divided powder porosity into lens-shaped defects at about 850 0 C when the Bi-2201 impurity phase decomposes before the Bi-2212 starts to melt. These lens-shaped voids grow to bubbles of a filament diameter on melting of the Bi-2212 and continue to lengthen and then to agglomerate across multiple filaments while the filaments are in the liquid state. The experiment makes clear why melt processing is vital to developing high J c and also shows how rearrangement of the residual filament porosity on melting imposes a strong longitudinal inhomogeneity in each filament. Reducing the bubble density is clearly an important path to reaching much higher J c values in Bi-2212 round wires. Synchrotron micro-tomography is an exceptionally powerful technique for studying the spatial extent of the porosity on a scale of about 2 m and larger.Published in Superconductor Science and Technology (2011) Geneva, Switzerland CERN-ATS-2011-243December 2011 AbstractRecent study of the current-limiting mechanisms in Bi-2212 round wires has suggested that agglomeration of the residual Bi-2212 powder porosity into bubbles of filament-diameter size occurs on melting the Bi-2212 filaments. These pores introduce a major obstacle to current flow, which greatly reduces the critical current density (J c ). Here we present an in situ non-destructive tomographic and diffraction study of the changes occurring during the heat treatment of wires and starting powder, as well as a room temperature study of ex situ processed wires. The in situ through-process study shows that the agglomeration of residual porosity is more complex than previously seen. Filament changes start with coalescence of the quasi-uniform and finely divided powder porosity into lens-shaped defects at about 850 • C when the Bi-2201 impurity phase decomposes before the Bi-2212 starts to melt. These lens-shaped voids grow to bubbles of a filament diameter on melting of the Bi-2212 and continue to lengthen and then to agglomerate across multiple filaments while the filaments are in the liquid state. The experiment makes clear why melt processing is vital to developing high J c and also shows how rearrangement of the residual filament porosity on melting imposes a strong longitudinal inhomogeneity in each filament. Reducing the bubble density i...

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“…Considering the weakened intergrain connections after sintering, the increasing critical current density should be attributed to the doping effect on Bi-2212 phase. It is reported that the fabrication of overdoping Bi-2212 superconductors with oxygenation treatments could enhance the current capacity [35]. Thus, in this study, hole doping Li and K both can tune superconductors into overdoping region, thus lead to the enhancement of current capacity.…”

Section: Resultsmentioning

confidence: 68%

Doping effects on Bi-2212 high temperature superconducting thick films

Zhang

Hao

et al. 2015

J Mater Sci: Mater Electron

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Superconducting thick films of Bi 2 Sr 2 Ca 0.95 M 0.05 Cu 2.0 O 8?d (Bi-2212) with M = K, Li, and Al were fabricated by a dip coating process. The influences of different doping elements on the lattice structure, electrical transport properties and related superconducting properties were systematically investigated. XRD analyses confirmed that all the doping ions have successfully entered into the Bi-2212 matrix, and led to a systematical change of lattice parameters. Due to the change of thermodynamic properties with doping, the phase evolution process changed during the sintering process. Thus both the content of secondary phases and the size of Bi-2212 crystals changed, which influenced the intergrain connections. The carrier concentrations of thick films were also influenced by doping, which contributed to the changes of critical temperature. It can be deduced that the hole doping with either K ? or Li ? can tune the samples into overdoping region, thus led to the increase of critical current at 77 K with the maximum critical current density of *5300 A/cm 2 .

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Development of high critical current density in multifilamentary round-wire Bi2Sr2CaCu2O8+δ by strong overdoping

Cited by 40 publications

References 27 publications

Bubble formation within filaments of melt-processed Bi2212 wires and its strongly negative effect on the critical current density

Bubble formation within filaments of melt-processed Bi2212 wires and its strongly negative effect on the critical current density

Void and phase evolution during the processing of Bi-2212 superconducting wires monitored by combined fast synchrotron micro-tomography and x-ray diffraction

Doping effects on Bi-2212 high temperature superconducting thick films

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