Improved strong magnetic field performance of low angle grain boundaries of calcium and oxygen overdoped YBa2Cu3Ox

Daniels, G.; Gurevich, A.; Larbalestier, D. C.

doi:10.1063/1.1322053

Cited by 74 publications

(73 citation statements)

References 18 publications

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“…1). The percolative motion of AJ vortices along GBs gives rise to a linear region in the V − I characteristic of HTS polycrystals [6,8,9,10,11]. However no present experimental techniques can probe the cores of GB vortices, because the lack of the normal core makes AJ vortices "invisible" under STM, while neither the Lorentz microscopy nor magneto-optics have sufficient spatial resolution to distinguish A and AJ vortices.…”

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confidence: 99%

“…Transitions from a single to a multiple row vortex motion [9,11] result in a sharp upturn of the R F (B, 77K) curve at H 1 ≃ 4T in Fig. 4.…”

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confidence: 99%

“…Bridges 25 µm wide were patterned by Ar ion beam etching on a cooled sample mount to produce a four-point measurement geometry, as described in Ref. [9]. The voltage probes were 100µm apart, on either sides of the GB.…”

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Flux Flow of Abrikosov-Josephson Vortices along Grain Boundaries in High-Temperature Superconductors

et al. 2002

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We show that low-angle grain boundaries (GB) in high-temperature superconductors exhibit intermediate Abrikosov vortices with Josephson cores, whose length l along GB is smaller that the London penetration depth, but larger than the coherence length. We found an exact solution for a periodic vortex structure moving along GB in a magnetic field H and calculated the flux flow resistivity RF (H), and the nonlinear voltage-current characteristics. The predicted RF (H) dependence describes well our experimental data on 7 • unirradiated and irradiated Y Ba2Cu3O7 bicrystals, from which the core size l(T ), and the intrinsic depairing density J b (T ) on nanoscales of few GB dislocations were measured for the first time. The observed temperature dependence of J b (T ) = J b0 (1 − T /Tc) 2 indicates a significant order parameter suppression in current channels between GB dislocation cores.PACS numbers: PACS numbers: 74.20. De, 74.20.Hi, Mechanisms of current transport through grain boundaries (GB) in high-temperature superconductors (HTS) have attracted much attention, because a GB is a convenient tool to probe the pairing symmetry of HTS by varying the misorientation angle ϑ between the neighboring crystallites [1,2]. As ϑ increases, the spacing between the GB dislocations decreases, becoming comparable to the coherence length ξ(T ) at the angle ϑ 0 ≃ 4 − 6 • . The exponential decrease of the GB critical current density, makes GBs one of the principal factors limiting critical currents of HTS [3]. Atomic structure of GBs revealed by high-resolution electron microscopy have been used to determine local underdoped states of GB, defect-induced suppression of superconducting properties at the nanoscale and controlled increase of J b by overdoping of GB [2,4]. Much progress has been made in understanding the microscopic factors controlling J b (ϑ) at zero magnetic field, but the behavior of vortices on GBs is known to much lesser extent.The extreme sensitivity of J b (ϑ) to the misorientation angle makes GB a unique tool to trace the fundamental transition between Abrikosov (A) and Josephson (J) vortices[5] in a magnetic field H above the lower critical field H c1 . For ϑ ≪ ϑ 0 , vortices on a GB are A vortices with normal cores pinned by GB dislocations [6]. For ϑ > ϑ 0 , the maximum vortex current density circulating across the GB is limited to its intrinsic J b (ϑ), much smaller then the bulk depairing current density J d . Because vortex currents must cross the GB which can only sustain J b ≪ J d , the normal core of an A vortex turns into a J core, whose length l ≃ ξJ d /J b along the GB is greater then ξ, but smaller then the London penetration The AJ structures have two length scales: the core size l > ξ and the intervortex spacing a = (φ 0 /B) 1/2 . The larger core of AJ vortices leads to their weaker pinning along a GB, which thus becomes a channel for motion of AJ vortices between pinned A vortices in the grains [5,7] (Fig. 1). The percolative motion of AJ vortices along GBs gives rise to a linear region in the V −...

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“…Transitions from a single to a multiple row vortex motion [9,11] result in a sharp upturn of the R F (B, 77K) curve at H 1 ≃ 4T in Fig. 4.…”

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confidence: 99%

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Flux Flow of Abrikosov-Josephson Vortices along Grain Boundaries in High-Temperature Superconductors

et al. 2002

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“…One is to improve the local texture of the substrate, while a second is to engineer the threshold angle to greater values, an approach suggested possible by the results of Heinig et al 10 and by recent studies of Ca doping of YBa 2 Cu 3 O x thin films. 16,17 An important goal of the much present scale-up is to achieve J c Ͼ2 MA/cm 2 in 1-2 m-thick films. 18,19 A recent analysis of flux flow in bicrystals suggests that the J c of coated conductors will always be dominated by weak, multiply connected channels such as the flux-penetration network imaged here.…”

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confidence: 99%

Influence of nickel substrate grain structure on YBa2Cu3O7−x supercurrent connectivity in deformation-textured coated conductors

Reeves

Polyanskii

Kozlowski

et al. 2000

Applied Physics Letters

109

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Coupled magneto-optical imaging and local misorientation angle mapping have been used to demonstrate the percolative nature of supercurrent flow in YBa 2 Cu 3 O 7Ϫx ͑YBCO͒ coated conductors grown on deformation-textured Ni substrates. Barriers to current flow occur at many YBCO grain boundaries ͑GBs͒ which have propagated through the buffer layers from the underlying Ni substrate, and all Ni GBs with misorientation angles Ͼ4°initiate percolative current flow. This type of current barrier is characteristic of the conductor form and has been found to exist in samples with J c (0 T,77 K) values Ͼ2 MA/cm 2 . Sharpening of the local substrate texture or improving in low-angle GB properties should lead to higher J c values. © 2000 American Institute of Physics. ͓S0003-6951͑00͒00341-7͔High critical current density (J c ) conductors capable of operating in fields of several tesla at liquid-nitrogen temperature are critical to large-scale applications of hightemperature superconductors. Coated conductors ͑CCs͒ with biaxially textured YBa 2 Cu 3 O x ͑YBCO͒ respond to this need. [1][2][3] One widely employed approach today uses deformation texturing of a metal substrate, generally pure Ni, on which buffer layers and YBCO are grown. 1,2 Such architectures permit J c (0 T,77 K) values 1,2 Ͼ1 MA/cm 2 , but many samples have lower values. Here we couple magneto-optical imaging and local misorientation angle mapping to show that many such barriers to current flow occur at YBCO grain boundaries ͑GBs͒ which have propagated through the buffer layers from the Ni GBs in the underlying substrate. All Ni GBs with misorientation angles Ͼ4°were found to initiate percolative current flow. Since typical deformation-textured substrates have many GBs misoriented in the range of 5°-10°, this study shows that it will be very valuable for CC technology to further enhance substrate texture and/or to improve low-angle GB properties.Magneto-optical ͑MO͒ imaging, light microscopy, and backscattered electron Kikuchi pattern ͑BEKP͒ analysis of the local texture were conducted on a series of four CC samples grown on deformation-textured Ni substratres with in-plane and out-of-plane full width at half maxima of 6.6°-7.4°and 5.8°-8.7°, respectively, as measured by x-ray pole figures. The buffer and YBCO layers were deposited by pulsed-laser deposition ͑PLD͒ with architecture YBCO/CeO 2 /yttria-stabilized zirconia ͑YSZ͒/CeO 2 /Ni and thickness of 300-1200/100/500/100 nm for the respective oxide layers. The thickness of the YBCO layer varied from sample to sample without obvious differences in the properties measured by MO imaging and ac susceptibility. A 0.6-m-thick YBCO sample had a high transport J c (0 T,77 K) of 1.2 MA/cm 2 . The remaining samples were taken directly to other characterizations.A representative MO image of the granular fluxpenetration network obtained using standard imaging procedures 4,5 is shown in Fig. 1. This network is common to CCs with varying constructions from multiple sources. Among the variations are deformation-textured s...

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“…Both are made from similar 250 nm thick epitaxial YBCO films grown on a single crystal substrate for which MO investigations [11], [12] show that the current flow on scales of a few was uniform. The films were deposited on by pulsed laser deposition at 310 mTorr oxygen pressure and 820 , and then annealed in oxygen at 830 Torr and 520 for 30 min.…”

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confidence: 99%

Imaging Local Dissipation and Magnetic Field in YBCO Films With Artificial Defects

Abraimov

Polyanskii

Gurevich

et al. 2005

IEEE Trans. Appl. Supercond.

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Improved strong magnetic field performance of low angle grain boundaries of calcium and oxygen overdoped YBa2Cu3Ox

Cited by 74 publications

References 18 publications

Flux Flow of Abrikosov-Josephson Vortices along Grain Boundaries in High-Temperature Superconductors

Flux Flow of Abrikosov-Josephson Vortices along Grain Boundaries in High-Temperature Superconductors

Influence of nickel substrate grain structure on YBa2Cu3O7−x supercurrent connectivity in deformation-textured coated conductors

Imaging Local Dissipation and Magnetic Field in YBCO Films With Artificial Defects

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