Coated conductors containing grains with big aspect ratios

Leitenmeier, S.; Bielefeldt, H.; Hammerl, G.; Schmehl, A.; Schneider, Claudia; Mannhart, J.

doi:10.1002/1521-3889(200208)11:7<497::aid-andp497>3.0.co;2-0

Cited by 5 publications

(5 citation statements)

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“…This is associated both with the increased cross-sectional area of these meandered boundaries and the suppression of the vortex channelling, it is impossible for a vortex to lie wholly within a meandered boundary meaning some sections are more strongly pinned, increasing the observed critical current. As an alternative to meandered grain boundaries, the use of grains with large aspect ratios was been proposed as a potential route to enhance the cross-sectional area of the grain boundary [89][90][91]. That such grains do provide enhanced properties has been demonstrated by Eickemeyer et al [16].…”

Section: Single Grain Boundaries Isolated Within Coated Conductorsmentioning

confidence: 99%

Importance of low-angle grain boundaries in YBa₂Cu₃O_7−δcoated conductors

Durrell¹,

Rutter²

2008

Supercond. Sci. Technol.

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Abstract. Over the past ten years the perception of grain boundaries in YBa 2 Cu 3 O 7−δ conductors has changed greatly. They are no longer a problem to be eliminated but an inevitable and potentially favourable part of the material. This change has arisen as a consequence of new manufacturing techniques which result in excellent grain alignment, reducing the spread of grain boundary misorientation angles. At the same time there is considerable recent evidence which indicates that the variation of properties of grain boundaries with mismatch angle is more complex than a simple exponential decrease in critical current. This is due to the fact that low-angle grain boundaries represent a qualitatively different system to high angle boundaries. The time is therefore right for a targetted review of research into low-angle YBa 2 Cu 3 O 7−δ grain boundaries. This article does not purport to be a comprehensive review of the physics of grain boundaries as found in YBa 2 Cu 3 O 7−δ in general; for a broader overview we would recommend that the reader consult the comprehensive review of Hilgenkamp and Mannhart (Rev. Mod. Phys., 74, 485, 2002). The purpose of this article is to review the origin and properties of the low-angle grain boundaries found in YBa 2 Cu 3 O 7−δ coated conductors both individually and as a collective system.

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Section: Single Grain Boundaries Isolated Within Coated Conductorsmentioning

confidence: 99%

Importance of low-angle grain boundaries in YBa₂Cu₃O_7−δcoated conductors

Durrell¹,

Rutter²

2008

Supercond. Sci. Technol.

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“…In contrast to the powder-in-tube technology where large grain boundary areas and grain alignment are used to enhance J c [7-9], today's coated conductor technologies [10][11][12] focus on grain alignment only. As we have shown, however, simple ways exist to also preferentially dope the grain boundaries [5] and engineer large effective grain boundary areas [13,14] to further enhance the performance of coated conductors.As pointed out in 1987, large effective grain boundary areas can be realized by engineering the microstructure of the superconductor to obtain grains with big aspect ratios, for example by stacking in a brickwall-type manner platelet-like grains on top of each other [6,7]. The enhancement of the critical currents hereby gained is responsible for the large J c of the Bi-based high-T c superconductors fabricated with the powder-in-tube technology [6-9].…”

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confidence: 99%

“…In contrast to the powder-in-tube technology where large grain boundary areas and grain alignment are used to enhance J c [7][8][9], today's coated conductor technologies [10][11][12] focus on grain alignment only. As we have shown, however, simple ways exist to also preferentially dope the grain boundaries [5] and engineer large effective grain boundary areas [13,14] to further enhance the performance of coated conductors.…”

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confidence: 99%

“…This algorithm was used to assess possible approaches for the optimization of coated conductors at 77 K. For the present calculations, the intragrain J c was taken to be 5 • 10 6 A/cm 2 , and the grain orientations and lengths were chosen using Gaussian distributions with parameterized widths (see also Ref. 13). To determine the effects of doping on I c the J c (θ)-dependence in the simulation was modified based on the experimental data [5], which show that at least in the range of 24 • < θ < 36 • the critical current density can be doubled by doping.…”

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confidence: 99%

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Possible solution of the grain-boundary problem for applications of high-Tc superconductors

Hammerl

Herrnberger

Schmehl

et al. 2002

Applied Physics Letters

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It is shown that the critical current density of high-Tc wires can be greatly enhanced by using a threefold approach, which consists of grain alignment, doping, and optimization of the grain architecture. According to model calculations, current densities of 4 · 10 6 A/cm 2 can be achieved for an average grain alignment of 10• at 77 K. Based on this approach, a road to competitive high-Tc cables is proposed.Vital for large scale applications of high-T c superconductors [1,2] is the solution of the grain boundary problem, which manifests itself by the exponential decrease of the grain boundary critical current density J c of the high-T c cuprates as a function of the grain boundary angle [3,4].We propose to solve this problem using a threefold approach: through 1) grain alignment [3], 2) grain boundary doping [5], and 3) optimization of the microstructure to maximize the effective grain boundary area [6]. In contrast to the powder-in-tube technology where large grain boundary areas and grain alignment are used to enhance J c [7-9], today's coated conductor technologies [10][11][12] focus on grain alignment only. As we have shown, however, simple ways exist to also preferentially dope the grain boundaries [5] and engineer large effective grain boundary areas [13,14] to further enhance the performance of coated conductors.As pointed out in 1987, large effective grain boundary areas can be realized by engineering the microstructure of the superconductor to obtain grains with big aspect ratios, for example by stacking in a brickwall-type manner platelet-like grains on top of each other [6,7]. The enhancement of the critical currents hereby gained is responsible for the large J c of the Bi-based high-T c superconductors fabricated with the powder-in-tube technology [6-9]. Recently we found ways to use large effective grain boundary areas to enhance J c of coated conductors that consist of two-or three dimensional grain boundary networks, as illustrated in Fig. 1. Although it is clear that each one of the three techniques described substantially enhances J c , the increase that can be gained by utilizing all three, for example as shown by Fig. 2, is unknown.Therefore we have calculated the performance, which can be achieved by combining grain orientation, doping, and large effective grain boundary areas. Based on these calculations, optimized sets of parameters for the fabrication of coated conductors are derived. The calculation of current percolation through disordered networks of weak links, some of which may be Josephson junctions, is a complex problem [6]; and several algorithms have been developed for its solution (see, e. g. Ref. 6,(15)(16)(17)(18)(19). As the fast algorithms are limited to two-dimensional networks, for the present work a new one had to be devised. Like in several of the existing algorithms, to achieve the required speed, phase effects and self fields were neglected. FIG. 2.Simplified sketch of a tape, fabricated by the rolling assisted biaxially textured substrate (RABiTS) technology, with a m...

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“…Each datapoint reflects an average of at least 20 calculations. The black lines are guidesto the eye (after[17]).…”

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confidence: 99%